Verification of CEVT Steering System Specification1323010/FULLTEXT01.pdfcovered in this report....

Verification of CEVT Steering System

Specification

Adam Lundström

Mechanical Engineering, master's level

2019

Luleå University of Technology

Department of Engineering Sciences and Mathematics

Preface

This thesis was performed for China Euro Vehicle technology AB, CEVT, inGothenburg and is the final stage of my master’s degree in mechanical engineer-ing. During my work I have learned a lot about product development and planning,but also strategies for product testing and evaluation. I have gathered many usefulexperiences that I believe will be of great benefit for my future career.I would like to sincerely thank my supervisor Magnus Karlberg at Lulea Univer-sity of Technology for his commitment and sharing his knowledge. I would alsolike to thank my mentor Angelica Wingfors at CEVT for her support during thisproject.

i

ii PREFACE

Sammanfattning

Detta examensarbete behandlar upprattandet av en kravspecifikation for styrkolon-nen, mellan-axeln, styrleder och styrvaxeln pa fordon utvecklade av CEVT. Daflera komponentkrav har arvts fran tidigare projekt och saknar motivering var enverifiering av kravspecifikationen nodvandig. For att sakerstalla att inga krav varoverflodiga, olampliga eller saknades upprattades en ny kravspecifikation och ver-ifieringen genomfordes i form av en jamforelse mellan den befintliga och nyaspecifikationen.Identifierade kundkrav samlades in pa komplett-bil niva och klassificerades medavseende pa kundens tillfredstallelse kontra implementering enligt Kano mod-ellen. De subjektiva kundkraven oversattes till objektiva, kvantifierbara metrikerpa komplett-bil niva for att sedan brytas ned till komponentniva. Kundkrav ochmetriker korrelerades sedan mot varandra samt graderades och visualiserades genomen House of Quality matris. Numeriska mal for metrikerna baserades pa dess in-verkan pa kundens tillfredsstallelse.Detta resulterade i 50 identifierade metriker kopplade till styrkolonnen och ytterli-gare 58 stycken kopplade till styrvaxeln. Jamforelsen resulterade i 22 avvikelsermellan den befintliga och nya specifikation varav 8 metriker identifierades forfortsatt undersokning. Fortsatt arbete bestar av att undersoka malen for dessa 8metriker samt relatera malen till konkurrenters prestanda.

iii

iv SAMMANFATTNING

Abstract

This thesis covers the development of a component specification for the steeringsystem of vehicles engineered by CEVT. This includes the components steeringcolumn, intermediate shaft, steering gear and tie rods. Due to the reuse of require-ments on the component specification from previous projects it now lacks connec-tion to customer needs. A verification of the component specification is necessaryto ensure that no redundant or unnecessary requirements are present. The verifica-tion was performed through a comparison between a newly established specifica-tion and the current one.Identified customer needs were gathered on complete vehicle level and classifiedaccording to customer satisfaction with respect to implementation according tothe Kano model. The subjective customer needs were translated into objective,quantifiable metrics on complete vehicle level that was then decomposed ontocomponent level. Customer needs and metrics were then correlated against eachother and visualized through the House of Quality matrix. Numeric targets for themetrics were based on its impact on customer satisfaction.This resulted in 50 identified metrics connected to the steering column and 58metrics connected to the steering gear. The comparison resulted in 22 deviationsbetween the new and current specification where 8 metrics was identified for fur-ther investigation. Further development would include investigation of these 8identified metrics and relate targets to competitors’ performance.

v

vi ABSTRACT

Contents

Preface i

Sammanfattning iii

Abstract v

List of Figures viii

1 Introduction 11.1 Company presentation . . . . . . . . . . . . . . . . . . . . . . . 11.2 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.3 Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.4 Aim . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.5 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Steering system 52.1 Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.2 Power assisted steering . . . . . . . . . . . . . . . . . . . . . . . 8

3 Theory 113.1 Product development process . . . . . . . . . . . . . . . . . . . . 113.2 Quality function deployment . . . . . . . . . . . . . . . . . . . . 12

3.2.1 The house of quality . . . . . . . . . . . . . . . . . . . . 123.3 Kano model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143.4 Non-uniformity . . . . . . . . . . . . . . . . . . . . . . . . . . . 163.5 Steering feel & Road feel . . . . . . . . . . . . . . . . . . . . . . 173.6 Material strength & fatigue . . . . . . . . . . . . . . . . . . . . . 19

vii

viii CONTENTS

4 Method 214.1 Customer needs . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4.1.1 Kano classification . . . . . . . . . . . . . . . . . . . . . 224.2 Metrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234.3 House of Quality . . . . . . . . . . . . . . . . . . . . . . . . . . 27

4.3.1 Customer need and metric relationship . . . . . . . . . . . 294.3.2 Metric correlation . . . . . . . . . . . . . . . . . . . . . . 294.3.3 Impact . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

4.4 Benchmarking . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304.5 Target setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

4.5.1 Vehicle dynamics attributes . . . . . . . . . . . . . . . . 314.5.2 Noise, vibration & harshness attributes . . . . . . . . . . 324.5.3 Weight attribute . . . . . . . . . . . . . . . . . . . . . . . 334.5.4 Durability & Strength attributes . . . . . . . . . . . . . . 334.5.5 Ergonomic attributes . . . . . . . . . . . . . . . . . . . . 35

4.6 Specification comparison . . . . . . . . . . . . . . . . . . . . . . 35

5 Results 375.1 Customer needs . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

5.1.1 Kano classification . . . . . . . . . . . . . . . . . . . . . 395.2 Metrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395.3 House of Quality . . . . . . . . . . . . . . . . . . . . . . . . . . 43

5.3.1 Steering column . . . . . . . . . . . . . . . . . . . . . . 435.3.2 Steering gear . . . . . . . . . . . . . . . . . . . . . . . . 48

5.4 Steering system specification . . . . . . . . . . . . . . . . . . . . 525.5 Specification comparison . . . . . . . . . . . . . . . . . . . . . . 55

6 Discussion and Conclusions 57

Bibliography 61

Appendix A Whole vehicle metrics 63

Appendix B Metric correlation 67

List of Figures

1.1 Steering system components . . . . . . . . . . . . . . . . . . . . 3

2.1 Steering system with surrounding components . . . . . . . . . . . 62.2 Steering column . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.3 Steering gear rack and pinion setup . . . . . . . . . . . . . . . . . 72.4 Cross section of steering gear with dual pinion EPAS . . . . . . . 82.5 Cross section of steering gear with belt drive EPAS . . . . . . . . 9

3.1 Stage gate product development process . . . . . . . . . . . . . . 113.2 Illustration of House of Quality . . . . . . . . . . . . . . . . . . 133.3 Illustration of Kano-model . . . . . . . . . . . . . . . . . . . . . 153.4 Steering shaft components . . . . . . . . . . . . . . . . . . . . . 163.5 Angular velocity variation with respect to operating angle β . . . 173.6 Stress-strain curve . . . . . . . . . . . . . . . . . . . . . . . . . 193.7 SN-curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

4.1 List of metrics . . . . . . . . . . . . . . . . . . . . . . . . . . . 254.2 Needs-metrics matrix . . . . . . . . . . . . . . . . . . . . . . . . 264.3 House of Quality template . . . . . . . . . . . . . . . . . . . . . 274.4 Signs used for House of Quality . . . . . . . . . . . . . . . . . . 284.5 Visual presentation of ergonomic measurements [15] . . . . . . . 35

5.1 House of Quality for steering column filtered on vehicle dynamicsattribute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

5.2 House of Quality for steering column filtered on noise, vibrationand harshness attribute . . . . . . . . . . . . . . . . . . . . . . . 45

5.3 House of Quality for steering column filtered on strength, durabil-ity and solidity attribute . . . . . . . . . . . . . . . . . . . . . . . 46

ix

x LIST OF FIGURES

5.4 House of Quality for steering column filtered on ergonomics, costand regulations . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

5.5 House of Quality for steering gear filtered on vehicle dynamicsattribute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

5.6 House of Quality for steering gear filtered on strength, durabilityand solidity attribute . . . . . . . . . . . . . . . . . . . . . . . . 49

5.7 House of Quality for steering gear filtered to EPAS functions . . . 505.8 House of Quality for steering gear filtered on weight, cost and

regulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515.9 Component specification for the steering column . . . . . . . . . 535.10 Component specification for the steering gear . . . . . . . . . . . 545.11 New and current specification comparison for the steering column 555.12 New and current specification comparison for the steering gear . . 56

A.1 Needs-metrics matrix for whole vehicle metrics . . . . . . . . . . 66

B.1 Correlation of metrics for steering column . . . . . . . . . . . . . 68B.2 Correlation of metrics for steering gear . . . . . . . . . . . . . . . 69

CHAPTER 1

Introduction

1.1 Company presentationChina Euro Vehicle Technology AB, hereby referred to as CEVT, is an innovationcentre for the Geely Group. Geely Group is a Chinese owned, global automotivegroup. CEVT was founded in 2013 in Gothenburg and has grown rapidly to cur-rently employ over 2000 people. The company was founded with the purpose ofcreating a common platform for Geely, Lync & Co and Volvo. This meant creat-ing a modular architecture that is scalable, prepared for front or all-wheel driveand combustion engine or hybrid propulsion. The platform was named CompactModular Architecture (CMA) and debuted 2017 in the Volvo XC40 and the Lync& Co 01.No production is conducted at CEVT since they are an innovation centre. CEVT’smain objective is to develop automotive technology for future demands. Au-tonomous drive, in car deliveries and connectivity are some areas that CEVT iscurrently developing.

1.2 BackgroundIn product development the customer needs and component specifications are es-sential for the final product. The customer needs are interpreted opinions aboutthe product and how the product should look, feel and perform according to thecustomer. All these subjective opinions are then translated into objective require-ments that ultimately ends up on the product specification. Product requirementsare further decomposed into component level i.e. a component specification.In this long chain and through many iterations it’s likely to lose connection be-

1

2 CHAPTER 1. INTRODUCTION

tween the component requirements and the customer needs. The optimal workingmethod would be to gather up to date customer needs and formulate a new prod-uct specification for each new product. Time, cost and other project constraintsoften doesn’t allow for this and component specifications may be reused. Thismay result in that the product no longer is something that the customer requested.It is also possible to end up with requirements that doesn’t add value to the prod-uct and this may result in the product being overengineered, more complex andmore expensive than necessary. The same thing is true for the opposite, if someimportant aspect is missing from the component specification the customer willmost likely not be satisfied with the product.To be competitive within the automotive market it is critical to assure that all re-quirements originate from customer needs and brings value to the product for theend customer. The product should perform according to the customers desire.

1.3 PurposeThis master thesis is completed for CEVT. CEVT wants to be leading in technol-ogy development within the automotive industry. To design competitive productsand solutions it is important to formulate a correct product specification. If therequirements stated on the product specification does not align with the customerneeds it will probably not be successful. The component specifications for steer-ing system have gone through many iterations and some requirements are lackingconnection to customer needs. Therefore, a verification of the current componentspecification is required to ensure that it is correctly formulated and includes nec-essary conditions to design successful products.

1.4 AimThe goal of this project is to verify the component specification set for steeringgear, steering column and steering shaft. These components are outlined in Figure1.1. Requirements on the component specification shall have a clear connectionto their respective customer needs. This shall result in easy rule of thumb forengineers at CEVT how variables affect the perceived steering performance for theend-customer. Requirements that are redundant or in any other way not necessaryshall be removed from the component specifications. Requirements that doesn’tbring value for the end customer shall be either reformulated appropriately orremoved. Where applicable requirements shall be formulated with a margin valueand a setpoint value.

1.5. LIMITATIONS 3

1.5 LimitationsThis project is limited to the following components: steering column, steeringgear and intermediate shaft. Components such as floor seal and heat shield willnot be examined in this report. Components of the steering system are outlined inFigure 1.1.

Figure 1.1: Steering system components

Since the aim of this project is to verify the component specification for thecomponents mentioned earlier, sub functions from other departments will not becovered in this report. These includes requirements regarding active and passivesafety such as crash characteristics, steering assist functions and collapse of thesteering column. Requirements that are generated shall be independent of func-tion which means that functional requirements will not be regarded in this report.Functional requirements are formed after concept generation and selection whichis out of scope for this project.

4 CHAPTER 1. INTRODUCTION

CHAPTER 2

Steering system

The steering system of an automobile controls the trajectory of the vehicle. Sincethe steering system is a part of the chassis all forces except aerodynamic are trans-mitted via the chassis. They are often divided into lateral, longitudinal and verticalof which the steering together with wheels and suspension are functions of lateralmomentum. For safety reasons it is important that the vehicle accurately followsthe course dictated by the driver. A confident feeling that the steering respondspredictably and reliably must be obtained. [1]The general outline and surrounding parts of the steering system is presented inFigure 2.1. The steering wheel attaches to the steering columns which is attachedto the cross car beam of the vehicle. The rotational motion of the steering wheelis transferred through the steering column, through the steering shaft and into thesteering gear. The steering gear is attached onto the subframe of the vehicle andconverts rotational motion into linear motion onto the tie rod that is connected tothe suspension assembly and the linear motion creates torque around the wheelsvertical axis which makes the wheel turn in the desired direction.

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6 CHAPTER 2. STEERING SYSTEM

Figure 2.1: Steering system with surrounding components

2.1 ComponentsA generic representation of the steering column is presented in Figure 2.2. Itsmain attributes are transferring rotational motion to steering shaft and to aid duringcrash by collapsing. The collapse of the steering column absorbs forces acting onthe driver. Steering column also integrates features such as the steering lock thatprohibits unauthorized use of the steering. Since the steering wheel is attachedto the steering column it must be ergonomically designed. The steering columnis therefore commonly adjustable either 2-way, vertically up and down, or 4-way,axial and vertical. The locking mechanism for adjustment can be either manual,electrical or electrically clamped. The main differences between these three arethe level of interaction needed by the driver. For a manual system, it is commonlydesigned with a lever that operates the locking mechanism. To adjust the positionof the steering wheel, the lever is released and the driver can manually movethe steering wheel to a suitable position and then lock it in place by pulling thelever. For an electrically clamped system the locking mechanism consists of anelectric motor that operates the locking mechanism. In this case the driver pushesa button to either release or clamp the current position. For an electrical locking

2.1. COMPONENTS 7

mechanism, the movement of the steering column is dictated by an electric motorthat the driver controls via buttons or knobs.

Figure 2.2: Steering column

The steering gear is commonly constructed as a rack and pinion drive althoughother technologies exist such as belt drive and recirculating ball. The pinion con-sists of a helix tooth that meshes with the rack and are commonly power assisted.The setup is presented in Figure 2.3.

Figure 2.3: Steering gear rack and pinion setup

The gearing between pinion and rack will determine the speed of the steering,referring to distance covered by the steering gear per degree of rotation by the


steering wheel. The rack-travel is another important parameter that determinesthe distance covered by the steering rack from straight ahead position to end lock.The steering shaft is the link between the steering column and the steering gear,transmitting the rotational motion from the column to the steering gear. It is usu-ally designed with two universal joints and absorbs axial motion between the bodyand chassis. During a crash the steering shaft works as a buffer zone, the shaftslides inside itself and absorbs some of the force.

2.2 Power assisted steeringChrysler introduced a power assisted steering system in 1951 to reduce steering ef-fort. The power assisted steering was hydraulically powered and would become anindustry standard for coming 50 years. Hydraulic power assisted steering (HPAS)is now rarely used in modern automobiles, instead electric power assisted steering(EPAS) is more common. This is due to several reasons such as EPAS is moreenergy efficient partly because it is only active when needed and partly to fewerlosses. A more energy efficient system results in better fuel economy. EPASalso allows for more flexible packaging since it eliminates the need of a hydraulicpump, hydraulic lines, valves and so on [1].Some variants of EPAS include single pinion assist, which integrates the electricassist to the primary steering gear pinion shaft. Single pinion EPAS can also beintegrated into the steering column by placing the electro-mechanical power uniton the upper steering column. Dual pinion EPAS, presented in Figure 2.4, trans-fers torque via a second drive pinion on the steering gear. This design can handlehigher rack loads than the single pinion. In belt driven EPAS, presented in Figure

Figure 2.4: Cross section of steering gear with dual pinion EPAS

2.2. POWER ASSISTED STEERING 9

2.5, the torque is transferred through a recirculating ball screw which moves therack. The belt drive can cope with higher loads than the other variants but is alsomore expensive.

Figure 2.5: Cross section of steering gear with belt drive EPAS

The basic structure of an EPAS-system consists of a torque sensor, steeringwheel angle sensor, geared electric motor and ECU. The torque sensor as well assteering wheel angle sensor sends information to the ECU which will calculatea suitable torque that shall be applied by the electric motor. Torque could alsobe applied based on input from other sources such as an ECU responsible forautonomous drive, corrective steering assist or automated parking.

CHAPTER 3

Theory

3.1 Product development processA product development process is a sequence of steps or activities that is employedto design a product. A generic product development process consists of 6 phasesillustrated in Figure 3.1 which is a stage-gate process. The stage-gate process is aproject management technique that is often used within product development andis suitable for efficient management of internal resources. The innovation processis split into several different phases which has a determined output. Between eachphase is a gate that determines if the input reached appropriate quality. Develop-ment may not continue past a gate before appropriate results has been obtainedthat fulfills the gate. [2] [3]

Figure 3.1: Stage gate product development process 1

1Based on K. T. Ulrich and S. D. Eppinger, Product Design and Development, Exhibit 2-2

11

12 CHAPTER 3. THEORY

The planning phase, often referred to as the ”phase zero”, consists of opportu-nity identification. The planning phase dictates project approval and launch of theproduct development. The output of the planning phase is the mission statementthat specifies market, business goals and constraints. In the concept developmentphase customer needs are gathered, product specification established, conceptsgenerated and evaluated. The product specification is the precise description ofwhat the product should endure, do, and provide. A specification consists of ametric and a value that could be a specific number, range or an inequality. Theunit of these values should be clearly labeled. [2]

3.2 Quality function deploymentQuality Function Deployment (QFD) was founded 1966 in Japan by Yoji Akaowith the purpose to integrate the voice of the customer into engineering character-istics. QFD includes planning and communication routines that focuses resourcesto design, manufacture and market goods that is attractive to the customer. Thefoundation of QFD is that products shall reflect customer desires. [4] [5]

3.2.1 The house of qualityThe house of quality is a design tool implemented in QFD for inter-functionalplanning. Since the adoption of the House of Quality within Toyota Auto Body,start-up and preproduction costs were reduced by more than 60%. Additionally, acomparison between a Japanese vehicle manufacturer with QFD and an Americanvehicle manufacturer without QFD showed that the Japanese vehicle manufacturermade fewer design changes and 90% of them before product launch. [6]

The house of quality starts with customer requests called customer attributes. Cus-tomer attributes are often referred to as the ”what” in the House of Quality and arebased on the customers own words on how the product should perform. It is com-mon to encounter contradicting attributes that potentially could be solved with acreative solution but a trade-off between the two is commonly required. To easethe process of deciding where the trade-off should take place the house of qualitymeasures relative importance between customer attributes. Relative importance isoften collected through statistical techniques based on customer interviews.The customer attributes are correlated to measurable engineering attributes, re-ferred to as the ”how”. These are preferably quantifiable which allows for anobjective measurement how the component or product performs. The relationshipbetween Customer attributes and engineering attributes are then defined with aspecific grading system for verification that customer attribute is met. Correlation

3.2. QUALITY FUNCTION DEPLOYMENT 13

between engineering attributes are typically added to highlight positive or nega-tive correlation between metrics.A benchmark to competitors products based on customer attributes is also inte-grated into the House of Quality. This is performed to evaluate the products abilityto fulfil customer attributes relative to competitors. Preferably, this evaluation isbased on interviews or surveys of customers. Target values are then assigned foreach engineering attribute and a specific importance rating is calculated. The im-portance rating is based on multiplication of relative importance of customer needand its relation to respective engineering attribute. An illustration of the House ofQuality is presented in Figure 3.2.

Figure 3.2: Illustration of House of Quality 2

2Based on Li-En Wang, Hesitant fuzzy integrated MCDM approach for quality function de-ployment: a case study in electric vehicle, ResearchGate 2006


The House of Quality can be extended through several different ways. Onecommon extension is to add a rating for technical difficulty to achieve target val-ues. This highlights where resources are spent most efficiently to maximize cus-tomer satisfaction. Another extension is to add a correlation between customerattributes which highlight positive or negative relationship between requirements.

3.3 Kano modelThe Kano model is a product development theory developed in the 1980s by Nori-aki Kano. The development was performed as a scientific study regarding qualitydefinitions. Two definite aspects of quality were identified: objective and subjec-tive, and a correlation between the two. This resulted in five different classifica-tions of quality definitions. [7]

Attractive Quality Elements: Elements that are not crucial for the customer butprovide satisfaction when its fulfilled.One-Dimensional Quality Elements: Elements that result in customer satisfactionwhen fulfilled and dissatisfaction when they are not.Must-Be Quality Elements: Elements that are expected and brings dissatisfactionwhen they are not fulfilled.Indifferent Quality Elements: Elements that no matter the resources results in nei-ther satisfaction or dissatisfaction.Reverse Quality Elements: Elements that result in satisfaction when not fulfilledand dissatisfaction when fulfilled.

The first 3 classifications, Attractive, One-Dimensional and Must-Be was muchmore common than the other two, Indifferent and Reverse. [7]All classifications were then plotted onto a 2-dimensional diagram with the ver-tical axis representing customer satisfaction and the horizontal axis representingdegree of implementation. This diagram is known as the Kano-model, presentedin Figure 3.3.

3.3. KANO MODEL 15

Figure 3.3: Illustration of Kano-model 3

The ”Must-Be” elements or basic attributes are conditions or qualities thatthe product or service is expected to fulfil by the customer. Implementation ofthis element may not return customer satisfaction by itself, although not includingit will result in customer dissatisfaction. A general example of this would beimplementation of a steering wheel on an automobile.For one-dimensional elements or performance elements, satisfaction is dependenton its performance. If the performance is good, the customer becomes satisfied.If the performance is poor, the customer becomes dissatisfied. A general exampleof this would be acceleration of an automobile where more is better.Attractive elements or ”delighters” will, if they are present, result in customersatisfaction even with low functionality. They don’t cause dissatisfaction if theyare not present but when they are included they often creates a strong selling pointfor the product. [8]This is generally something the customer have not experienced before, but as timepass and the feature becomes an industry standard, the attribute becomes a Must-Be element. An example of this would be touch-screens or autonomous driving.

3Based on Chandra Munagavalasa, Excite and Delight Your Cus-tomers by Using the Kano, https://www.agileconnection.com/article/

excite-and-delight-your-customers-using-kano-model

https://www.agileconnection.com/article/excite-and-delight-your-customers-using-kano-model

https://www.agileconnection.com/article/excite-and-delight-your-customers-using-kano-model


3.4 Non-uniformityDue to packaging constrains it is not possible to design a perfectly symmetricsteering system. In Figure 2.3 the interface between rack and pinon is off cen-tre. The EPAS systems shown in Figure 2.4 and 2.5 have connecting interfacesthat are off centre as well. Additionally, the shaft connecting steering column tosteering gear must accommodate angles in two planes due to the location of theseinterfaces. The angle that the steering column and steering wheel is mounted canalso be changed by the driver, resulting in a range of possible angles. The shaft isalso carefully designed to collapse in the correct way in case of a crash. The shaftis commonly designed with universal joints to obtain desired range of angles. Ageneric steering shaft is illustrated in Figure 3.4. It consists of the ”upper shaft”,which is part of the steering column, pinion extension or ”lower shaft” whichconnects to the steering gear and the intermediate shaft that is the connection be-tween upper and lower shaft. The steering shaft is connected to the other shaftsvia universal joints.

Figure 3.4: Steering shaft components

A characteristic of universal joints is the non-uniformity of motion throughthe joint. Angular-velocity varies with 2 cycles per revolution between the inputand output shaft, illustrated in Figure 3.5.

This results in fluctuations that is accompanied by corresponding angular ac-celerations dependent on operating angle. Output torque is also affected accordingto the product of input torque and angular velocity ratio. The angular accelerationgives rise to an inertia torque as well as vibrations [9].

3.5. STEERING FEEL & ROAD FEEL 17

Figure 3.5: Angular velocity variation with respect to operating angle β 4

The non-uniformity motion can be eliminated with two opposite phased universaljoints in series. In this case the fluctuations are cancelled out and the velocity ratiobecomes 1:1 between input and output shaft [9]. Due to packaging, passive-safetydesign and the fact that the steering wheel position is adjustable which changesthe geometry, it is not possible to design the shaft in this way. The design ofthe shaft often results in a compromise between these criteria where the velocityfluctuations are minimized to the greatest extent possible.

3.5 Steering feel & Road feelTwo main sources of feedback to the driver can be identified, visual feedback inform of traffic lights, position of the vehicle and such, the other is haptic feed-back. Haptic feedback can be classified as feel of forces, vibrations and torqueacting on the vehicle and the steering wheel itself. This feedback is the main at-tribute referred to when talking about ”steering feel” or ”road feel”. Steering feelis commonly expressed in subjective terms such as ”precise”, ”slow” or ”loose”.A well-tuned steering system allows the driver to the greatest amount of accuracyposition the vehicle with the least amount of effort. Steering feel depends on therelationship between steering wheel torque and steering wheel angle. Importantparameters that are often considered when tuning a steering system to achievea subjectively good steering feel includes start torque, steering wheel damping,torque build-up and valley feel [10].Start torque is the amount of torque required to turn the steering wheel centre po-sition to a small angle. The start torque is connected to several parameters and areoften depending on vehicle velocity as it is dependent on the power steering assist.

4Based on http://www.sdp-si.com/catalogs/D757-Couplings-Universal-Joints3.php Retrieved 2019-03-06

http://www.sdp-si.com/catalogs/D757-Couplings-Universal-Joints3.php

http://www.sdp-si.com/catalogs/D757-Couplings-Universal-Joints3.php


The torque build-up refers to the increase in steering wheel torque as the steeringwheel angle increases. This relationship is not linear as it is highly dependent onmany different factors such as vehicle speed, steering wheel angle, yaw responseetc. Steering wheel damping is an artificial characteristic that is tuned through theEPAS-system. Its main objective is to limit extreme steering inputs, especially athigh vehicle speed. Steering wheel input speed should not be high enough to upsetthe balance of the vehicle. It also contributes to obtain a relaxed feeling throughelimination of subjective tendencies such as ”twitchy” and ”nervous” behaviour ofthe vehicle. The valley feel is a part of the torque build up. In a graph of steeringwheel angle with respect to steering wheel torque a valley around centre position,steering wheel angle equal to zero, should be obtained. This partly ensures thatthe steering wheel returns to centre position and through descending torque com-municate the centre position of the steering wheel to the driver.

Road feel which is the ability of the steering system to provide the driver withinformation about the surface the vehicle is driven on. Road feel should give anindication of how much grip is available at a given moment as well as bumps andother irregularities on the surface. Road feel is categorized as the relationship be-tween steering wheel torque and lateral acceleration [10] [11].Some important parameters that governs road feel includes torque build-up, hys-teresis and yaw response. These parameters are mostly determined by the chassisand the geometry of the front suspension. Two broad classification are commonlyreferred to when the steering system is evaluated, on-centre steering and off-centresteering. On-centre steering refers to small steering angles and negligible lateralacceleration. A technical study regarding on-centre steering was conducted byK.D. Norman, Objective Evaluation Method for On-centre Handling Performance[12]. The key parameters that was identified were:

T0g [Nm]: Steering wheel torque at 0g - an indication of friction in the steeringsystem.G0g [Nm/g]: Steering torque gradient at 0g - change in torque vs change in lateralacceleration, related to ”road feel” and directional sense.T0.1g [Nm]: Steering wheel torque at 0.1g - a measure of steering effort.G0.1g [Nm/g]: Steering gradient at 0.1g - related to road feel just off the straightahead directionay,0Nm [g]: Lateral acceleration at 0 Nm - an indication of returnability.hst [-]: Steering hysteresis - related to the time delay between steer input and yawrate.

3.6. MATERIAL STRENGTH & FATIGUE 19

Off-centre steering refers to large steering angle with considerable lateral ac-celeration. Parameters that define steering feel and road feel during off-centresteering situations are heavily dependent on vehicle dynamics influenced by chas-sis, tires and suspension geometry. It is difficult to isolate the steering system andresearch are therefore focused on steady state cornering [13].

3.6 Material strength & fatigueMaterial strength is a measurement how a material behaves during stresses andstrains. Yield strength and tensile strength are employed methods to predict aresponse of a solid object. The yield point in a stress-strain curve indicates theelastic limit and marks the beginning of plastic deformation of a material. Tensilestrength is the ability to withstand loads tending to elongate the material. Themaximum stress a material can withstand without fracture is called ultimate tensilestrength, often referred to as the material’s ultimate strength [14]. A representationof the stress-strain curve with yield strength and ultimate tensile strength markedis presented in Figure 3.6.

Figure 3.6: Stress-strain curve 5

To predict fatigue of a material SN-curves are commonly used. The SN-diagram is generated by inducing cyclic stress on the material and notes how manycycles it can endure before failure occur. Test is then repeated for several differentstress amplitudes to end up with a diagram. The vertical axis of the diagram cor-responds to the stress amplitude and the horizontal axis to number of cycles untilfailure. The SN-curve have logarithmic scales and thus creates a straight line with3 different regions called low cycle fatigue, high cycle fatigue and infinite life.

5Based on: https://www.chegg.com/homework-help/definitions/

stress-strain-curve-5 Retrieved 2019-03-25

https://www.chegg.com/homework-help/definitions/stress-strain-curve-5

https://www.chegg.com/homework-help/definitions/stress-strain-curve-5


Low cycle fatigue is defined by the plastic deformation region with stresses abovethe yield stress of the material. High cycle fatigue is defined in the elastic regionwith stresses below the yield stress of the material. The third region, infinite life,is targeted at ferrous materials like steel that become asymptotic after 106 cycleswhen stresses are below a certain level [14].A representation of an SN-curve is presented in Figure 3.7.

Figure 3.7: SN-curve 6

The slope of the SN-curve is defined by the K-factor. The K-factor relatesstress and number of cycles to failure of the material. [14] As a material is sub-jected to cyclic stress it will accumulate damage. The amount of damage dependson the stress amplitude and how many cycles it has been exposed to. For a givenload and number of cycles an accumulated amount of damage can be calculated.This number is hard to relate to and equivalent force amplitude for a given numberof cycles is often used instead. The equivalent force amplitude, Fa,eq, is presentedin Equation 3.1 where Dtot represents the accumulated damage and ncycles repre-sents the set number of cycles.

Fa,eq =( Dtot

ncycles)

1K

2(3.1)

6Based on: https://community.plm.automation.siemens.com/t5/

Testing-Knowledge-Base/What-is-a-SN-Curve/ta-p/355935 Retrieved 2019-03-25

https://community.plm.automation.siemens.com/t5/Testing-Knowledge-Base/What-is-a-SN-Curve/ta-p/355935

https://community.plm.automation.siemens.com/t5/Testing-Knowledge-Base/What-is-a-SN-Curve/ta-p/355935

CHAPTER 4

Method

A project plan with sub-targets and deadlines were established during the firstweek. The approach chosen for this project was to create new component specifi-cations. The existing component specifications are not regarded during the projectand the verification will be performed through a comparison between the newand existing component specifications. Deviations between the two will be high-lighted and examined.This project will follow a stage gate process by Ulrich & Eppinger [2]. It is limitedto the concept development phase and product specification will be the deliveryof this project. The planning phase will not be regarded in this thesis.

4.1 Customer needsCustomer needs that CEVT has gathered on whole vehicle performance was ex-amined. These involve all functions and aspects of the vehicle that the customerfind important. Since the customer needs and their relative importance can shiftdepending on which vehicle is examined a specific Lynk & Co model is chosenfor this project.The customer needs are linked to areas such as performance, handling, ride com-fort, durability, safety, ergonomics etc. These customer needs were filtered withrespect to their connection with the steering system.Legal requirements related to the steering system were then examined. Legalrequirements should be treated as customer needs according to [5]. Legal require-ments regarding the steering system of automobiles includes United Nations Eco-nomic Commission for Europe, UNECE 79-03, Regulation number 12, 116-00and 94-03. Many countries have their own regulations and they often overlap each

21

22 CHAPTER 4. METHOD

other. The general strategy in this case is to identify the ”toughest” regulation, re-ferred to as a dimensioning regulation, and apply that one only. Requirementswere also filtered according to project scope in which passive safety was elimi-nated. All customer needs were then organized into groups of different areas.The relative importance of customer needs was also provided from CEVT’s mar-ket division. Tools such as relative importance matrix are sometimes used to de-termine the relative importance, the provided values however are obtained withstatistical data. Since a lot of effort already has been placed in this area thesevalues were used as a base for this work. The relative importance was graded ona scale of 3, which was changed into a scale of 5 to obtain greater diversificationbetween the individual customer needs. Grading ranged between 1, 3 and 5 andthrough discussions with system managers at steering department grades of 2 and4 could be identified.Every customer need was numbered with the configuration of one number cor-responding to the specific area and one unique number representing the specificcustomer need. This will aid the traceability of requirements to customer needs.

4.1.1 Kano classificationAdopting the Kano-model into the product development process has several ben-efits. The main one being the visual representation of where resources are bestspent to improve the product from the customers aspect. A Kano classification ispreferably established through interviews or surveys with end-customers, askingfunctional and dysfunctional questions. Such information is not available for thisproject and instead New Car Buyers Survey, NCBS will be used. NCBS includesquestions such as main reason for buying a specific make and model, good pointsabout the vehicle, bad points about the vehicle, reliability, quality and many more.The frequency of which a specific customer need is mentioned were not presentwithin the survey and therefore no conclusions could be made based on this. Clas-sifications were instead based on the top 10 noted customer needs within each area.This data was filtered on vehicle size and class according to the project scope. Itwas also organized between the specific model used for this project and competi-tors in the same size and price range. This resulted in 83 482 unique answers outof which 508 of them were related to owners of the Lynk & Co model that is usedin this project. Data is then compared between these two to point out deviations.This was performed manually when the data was sorted. Results from the NCBSmay not be distributed by CEVT and are therefore excluded from this report.If a customer need is ranked high on ”reason for buying” and/or on ”good points”and not among the top within competitors, the customer need is classified as anattractive element. The customer need may not be present among complaints for

4.2. METRICS 23

competitors nor the current model to receive this classification. Satisfying this cus-tomer need creates a selling point for the product but it’s not generally requestedaligns with the definition of attractive elements.Customer needs that are present on both ”good points” and ”bad points” can gen-erally be classified as performance element. The only two elements that crossesthe horizontal axis of the Kano model, meaning that they are present in first or sec-ond quadrant and third or fourth quadrant are performance and reverse elements.Since performance elements are much more common than reverse elements anassumption is made that they belong to performance element.Customer needs that are not mentioned among good points and consistently presentamong complaints, such as ”bad points” or ”experienced problems” are classifiedas basic needs. When the same customer need is not mentioned in the ”good” cat-egory and only in the ”bad”, customer satisfaction is never received in this area. Ifthis customer need is not met or not implemented well enough the customer willcomplain about the performance in this regard. This aligns with the definition ofbasic need elements.The indifferent elements are hard to capture using this data. Due to the lack of dys-functional questions an indifferent response is not presented in this data. Whendata is showing the top good/bad things about the product, the indifferent needswill not be shown. The indifferent elements were also much uncommon than theattractive, performance and basic need elements. Because of this, no indifferentclassifications were made.Customer need areas were classified according to previous mentioned approach.If a trend could be identified for specific needs that belonged to the same area, thatarea was classified accordingly. Individual customer needs that did not follow thistrend was classified separately to the appropriate element. Customer needs thatoriginates from regulation were all classified as basic need elements.

4.2 MetricsSince the customer needs are vague and subjective a translation into objective met-rics are necessary to accurately measure performance within a certain area. Ac-cording to [2], the most useful metrics are those that reflect as directly as possiblethe degree to which the product satisfies the customer needs. This specificationonly generates solution independent requirements and because of this some con-straints were necessary to define. Two subsystems were identified that would notchange for a foreseeable future, these were the steering column and the steeringgear. The subsystems constrain the function but not the design and thus createsdesign space.The customer needs were translated into metrics on first level that affects the


whole vehicle performance in the specific area. Then the metrics were sortedaccording to project scope and then decomposed in several levels to end up onsubsystem level. The subsystems were split between steering gear, steering col-umn and steering shaft. Electronic hardware and software requirements were cat-egorized separately. This methodology is commonly used for complex systemsand reduces the risk of disregarding an important metric. The metrics should beobjective and measurable but some results in subjective metrics as well. Sincesome desired characteristics are hard to define they must be graded subjectively.An example of this would be sound quality, where intensity and frequency bandcould be defined objectively, however the customer might pick up on noise suchas ”clonk” or ”rattle”. These types of noises are generally considered undesiredand hard to objectively define. Therefore a subjective metric is required in this sit-uation. Another example would be steering wheel vibration which to some degreeis undesirable, although a completely vibration free steering wheel would greatlydeteriorate the feedback to the driver. The important part in these scenarios arethat grading is well defined and repeatable, in this way performance can be mea-sured accurately.The metrics identified at this stage should be independent of function. This meansthat metrics at system level shall not be dependent of the solution as this shall bedefined later in the product development process. The primary purpose of this isnot limiting design space during concept development. The component specifi-cation should be continuously updated during the product development process.This is performed later in the concept development phase as the metrics in thisstage are defined by their function. This project is limited to function independentrequirements as the concept generation is out of scope.The metrics were structured into a list according to Figure 4.1, where each metricwas given a unique number and the corresponding customer need is documented.Units of the metrics were listed and documented according to the figure. The im-pact, which refers to the importance of the specific metric, is skipped in this step.The reason for this is that the importance of each metric will be calculated throughHouse of Quality.

4.2. METRICS 25

Figure 4.1: List of metrics 7

To further visualize the relationship between metrics and customer needs a”needs-metrics matrix” was conducted. The matrix consists of rows that corre-sponds to customer needs and columns that corresponds to metrics. a cell thatis marked in the matrix visualizes a relationship between the specific customerneed and the specific metric. A representation of the matrix is presented in Figure4.2. This matrix visualizes potential gaps within the customer need and metricsrelationship and ensures complete coverage.



Figure 4.2: Needs-metrics matrix 8


4.3. HOUSE OF QUALITY 27

4.3 House of QualityA House of Quality was created in Excel using a template provided by GeorgiaInstitute of Technology9shown in Figure 4.3.

Figure 4.3: House of Quality template

This template has 16 slots each for metrics and customer needs. Since thisproject involves greater numbers of metrics and customer needs the template hadto be expanded. After the expansion the number of slots for metrics was 60 andnumber of slots for customer needs was 35. The Kano classification was inte-grated into the House of Quality through a column next to the customer needs

9Georgia Institute of Technology: House of Quality Template (Excel) - corrected version,http://2110.me.gatech.edu/resources, Retrieved 2019-02-25

http://2110.me.gatech.edu/resources


with text and colour representing the specific classification.Since the metrics already was decomposed onto subsystem level it made senseto construct the House of Quality on subsystem level as well. The subsystemswere split into steering gear and steering column, the steering shaft was coupledwith the steering column and electronic requirements were coupled with the steer-ing gear. Previously documented customer needs and metrics were imported intorespective House of Quality. Relative importance was applied into the Houseof Quality and calculated into percentages. A direction of improvement for themetrics was visualized through signs. An up-arrow indicating an improvementif the specific metric is increased above target, a down-arrow indicating a benefitif achieved below target and a 45-degree tilted square indicating no benefit froman increase or decrease. A correlation of the metrics was examined and gradedaccording to the scale: strong positive represented by two ”+” signs, positive rep-resented by one ”+” sign, negative represented by one ”-” sign, strong negativerepresented by two ”-” sings or no correlation represented by no sign. The rela-tionship between customer needs and metrics was also graded according to thescale of: strong relationship represented by a black dot, moderate relationship rep-resented by a circle and weak relationship represented by a triangle. All signs formetric correlation, direction of improvement and relationship between customerneed and metric are presented in Figure 4.4.

Figure 4.4: Signs used for House of Quality

A strong relationship corresponds to a score of 9, a moderate to 3 and a weakto 1. This score is then multiplied with the relative customer need importance toend up with a technical importance rating. This number will be used as base for


the impact parameter shown in Figure 4.1.To identify weak relationships a cell is set to identify maximum relationship foreach customer need. If the relationship is less than 3, meaning that either the rela-tionship is weak or non-existing, this cell will be coloured red. The same methodis applied to the metrics, if a specific metric only has weak or non-existing relation-ship with customer need it will be coloured red. Based on this information metricsand customer needs are revaluated accordingly to eliminate metrics and customerneeds that are redundant, non-applicable or does not fit within the project scopeand prerequisites.

4.3.1 Customer need and metric relationshipTo determine correct relationship-score discussions with both system managersand attribute owners was performed. Based on their experience, some definite re-lationships could be identified and graded. Additionally, data from rig tests andcomplete vehicle tests were gathered to conclude further relationships. Completevehicle tests from vehicle dynamics as well as noise, vibration and harshness de-partment provided objective and subjective data. From this data a direction ofimprovement could be identified for several metrics.The grading between strong, moderate and weak relationship was decided subjec-tively. CEVT’s internal subjective grading system was used in subjective evalu-ations from the complete vehicle tests. This scale is relative to core competitorsand customer satisfaction. Based on the complete vehicle targets on this scale forthe specific area and gain or reduction in score from previous mentioned tests, aconclusion of the relationship rating could be established. For metrics that lackeddata the relationship rating was instead decided based on experience from attributeand system managers.

4.3.2 Metric correlationA correlation of metrics was performed placed at the top of the House of Quality.The correlation indicates how metrics affect each other if one of them are altered.A positive correlation indicates that if one metric is increased, the other increaseas well. Negative correlation indicates that if one metric is increased the other oneis decreased.Since several metrics are based on physics they can be correlated through math-ematics. A mathematical correlation will provide a definite direction of the cor-relation. A classification between moderate and strong is also required and areusually conducted through calculation of a correlation coefficient. A correlationcoefficient ranges between -1 and +1 and are usually considered strong if above


0,7 or below -0,7. This method requires lots of statistical data to draw such conclu-sions. Since such material was not available the classifications was instead basedon previous gathered information.

4.3.3 ImpactAll metrics was linked to a separate sheet in the excel document to visualize asummary of metrics and their priority. All metrics and their respective identifica-tion number was linked as well as the absolute and relative technical importancerating. The impact parameter ranges between 1 and 3 and is calculated based onthe absolute technical importance rating. Absolute technical importance ratingthat was equal to or below 15th percentile was classified as impact of 1. Absolutetechnical importance rating that was equal to or above 85th percentile was clas-sified as an impact of 3. Metrics that achieved an absolute technical importancerating between 16th and 84th percentile were all classified as an impact of 2. Theimpact number is correlated to competitor targets which is used for target settingof the metrics.

4.4 BenchmarkingBenchmarking is a comparison of the product to competitors products based onmetrics. This phase is linked closely to the mission statement and market identifi-cation of where the product should be placed in the market based on performanceand price. A benchmark is usually conducted by gathering competitor’s productand study them in detail. This covers a complete disassembling to objectively mea-sure performance of each component. Such information is not available at CEVT,benchmark is instead conducted on whole vehicle performance. Each attributeoften has their own benchmark criteria that is conducted on competitor vehicles.This has several reasons, for instance handling performance is heavily dependenton which type of front suspension and tires that are used. A specific property ormetric that is compared between two different front suspension designs may leadto completely different outcome regarding handling performance. Evaluation thatis performed on whole vehicle performance is much more comparable betweendifferent vehicles with different designs.

4.5 Target settingThe results from target setting of identified metrics are the numerical values thatis presented on the component specification. These values are what objectively

4.5. TARGET SETTING 31

defines the products performance. A benchmark is usually the foundation for thetarget setting where competitors solutions are examined carefully. Depending onwhich market segment the product is aimed at, target is set as a reference to theperformance of the competitor. Since no such detailed data is available a differentapproach is necessary.System managers for steering gear and steering column were interviewed to sortout which attributes are affected by which components. Representatives for eachattribute were then interviewed to establish reasonable marginal targets based ontheir experience and available test results. For applicable metrics a setpoint valuewas defined to aid selection of future concept. Applicable metrics were those thatshowed improvement with altered target but was technically difficult to achieve.

4.5.1 Vehicle dynamics attributesVehicle dynamics are primarily targeted at handling, steering feel and road feelperformance. These properties are affected by many different factors of whichthe steering system is one part. Benchmarks of competitor vehicles has been per-formed with regards to their handling performance. Parameters that are measuredand logged during several driving scenarios includes steering wheel torque, steer-ing wheel angle and lateral acceleration among others. These parameters are re-lated to road feel and steering feel and are tuned by vehicle dynamics department.This project will focus on parameters that are affected by components of the steer-ing system.”Friction feel” is measured objectively through steering wheel torque at 0g lateralacceleration, T0g. This provides an indication of amount of friction that is presentin the steering system according to [12]. T0g is measured and benchmarked byvehicle dynamics department and is dimensioning factor for frictional force in thesteering gear. Based on competitor’s performance an acceptable range for T0g isdefined and through this data an acceptable frictional force in the steering gearcan be obtained.Torsional stiffness of the steering system is another parameter that is linked tosteering feel. Tests have been performed with a less stiff steering shaft with im-paired performance consequently. Target for torsional stiffness for the whole sys-tem, meaning steering column, steering shaft and input of the steering gear, arebased on the current setup. A functional requirement is also necessary to restrictlash in the system. Lash can occur in the joints of the steering shaft and has anegative impact on steering feel. This also is objectively defined as the amount ofsteering wheel angle at a specific applied torque.Hysteresis of the steering is also measured through steering wheel torque versussteering wheel angle both on-centre and off-centre. On-centre hysteresis catego-rized as part of the torque deadband and off-centre hysteresis is measured while


cornering at a specific lateral acceleration. Target for hysteresis is defined by a han-dling profile which dictates desired handling characteristics of the vehicle. Basedon these measurements hysteresis requirements are defined for steering gear andsteering column.

4.5.2 Noise, vibration & harshness attributesNoise, vibration & harshness, NVH, attributes are heavily focused on flexiblemodes and eigenfrequencies of components. There are several sources of vibra-tion in a vehicle, the combustion engine being one of them. The natural frequen-cies of the components should be avoided in the frequency range of vibrationscaused by the combustion engine running at idle and low RPM. This is especiallytrue for components that are placed in the interior, such as the steering column.The natural frequency of the steering column should also be placed above the nat-ural frequency of the cross-car beam. This is due to the connection between thecross-car beam and the steering column is not a perfectly rigid system. To ensurethat the component does not end up in resonance an applicable headroom is cho-sen.Another contributor of vibration are road imperfections. Vibrations that originatesfrom wheels and suspension are primarily targeted at the steering gear. The lowfrequencies classified as rumble are focused to reduce transmission from steeringgear to steering wheel. Flexible modes of the steering gear and the EPAS are alsorestricted in this frequency range. Filters are integrated in the EPAS-system toreduce the impact of road induced vibrations.A subjective relative target for interior noise and vibration is broken down to theEPAS-system. A maximum sound pressure at driver position and front passen-ger position for different orders are defined. Maximum vibration levels at theattachment points for the subframe are also defined as dimensioning criteria forthe EPAS-system. In case of electrically operated steering wheel adjustment thesame criteria are used, defining maximum noise levels.The noise quality is judged subjectively with regards to clonk, squeak and rattle.None of these are allowed from either the steering gear nor the steering columnduring static or driving conditions. In case of manual steering wheel adjustment,operating lever and adjustment forces are judged subjectively in terms of smoothand linear motion. Subjective grading targets are set for these parameters accord-ing to CEVT’s relative scale.

4.5. TARGET SETTING 33

4.5.3 Weight attributeWeight has a relation to acceleration, deceleration, fuel economy and handlingperformance among others. Fuel economy has a correlation to emissions whichhighly regulated. Weight is thereby an important parameter for all componentsof the car. Weight attribute department was interviewed to examine the reasoningbehind the weight targets. The process of defining the weight target starts withthe complete car specification. This is a product specification set for whole carperformance including the kerb weight of the vehicle. The kerb weight is decidedbased on previous mentioned factors with respect to the performance targets. Kerbweight and performance targets of the vehicle are compared to competitors. Kerbweight is then decomposed to each subsystem stating a maximum allowed weight.Subsystem weight are also benchmarked to competitors to assure the product iscompetitive. Weight targets are ultimately decomposed into component level andends up on the component specification.

4.5.4 Durability & Strength attributesThe durability & strength attributes are targeted at forces, torques, strength andfatigue of components and structures within the vehicle. Components and theirattachments are modelled through finite element method as well as kinematicallyanalysed. These analyses ensure that critical components don’t break or deformduring normal to hard use. Analyses are also verified using rig-tests.The dimensioning criteria are based on events that are likely to occur during thelifetime of the vehicle and exert large forces to the vehicle. These events in-clude many different scenarios such as braking in pothole or driving over a curb.Forces are measured during these scenarios at the tie rod’s attachment point to theknuckle. The axial force will travel through the ball joints to the steering gear andits attachment points at the subframe.The event that exerted the largest axial force at the tie rod’s attachment point wasexamined. The peak amount of force at the event was noted and set as the foun-dation for the strength requirements. Yield strength and ultimate tensile strengthof the components are derived from this data. An applicable safety factor wasapplied to achieve suitable headroom over the measured forces.As of fatigue life of components the provided data for accumulated damage wereused. This is also based on certain scenarios that exert large forces but are likelyto occur more often than those used for strength dimensioning. These scenariosinclude for example maximum braking and accelerating, corrugated surfaces andpotholes. Each scenario is repeated a certain number of times to end up with anaccumulated damage of the component. The event that contributed to the largestamount of damage was noted and its equivalent force amplitude for 50000 cycles


was compared. The number of cycles is chosen for comparison reasons as it isa standard value at CEVT. Based on this data, objective as well as functional re-quirements with regards to fatigue life could be defined for tie rods and steeringgear. Failure of components such as ball joints or housing of the steering gear isdefined by regulations and local laws. Appropriate safety factors are chosen abovelegal regulations for these criteria.Strength requirements that is targeted to the steering column are influenced by pas-sive safety requirements. Since this project will not include passive safety charac-teristics only the solidity, torsional strength and fatigue aspects were inspected forthis attribute. For solidity aspects a minimum stiffness is defined for a relativelysmall amount of force applied in various directions on the steering wheel. Thisis complemented with a maximum displacement requirement for a large force. Itis defined in this way since stiffness is non-linear between these two forces. Stiff-ness requirements are valid in its nominal position as well as all extreme positionsof the steering wheel. Endurance of the adjustment mechanism are defined as afunctional requirement where it is unlocked, adjusted and locked for a number ofcycles that represents the lifetime of the vehicle.Torsional strength of steering column and steering shaft are defined in terms ofyield strength and ultimate strength. Yield strength and ultimate strength are de-cided with an appropriate safety factor. Torsional fatigue of the steering columnand steering shaft is a functional requirement. It is defined as a range of torquesat a certain frequency that components are subjected to a given number of cyclesthat represents the lifetime of the vehicle.Temperature ranges in which the steering system should operate normally arebased on complete vehicle cold climate and hot climate testing. Minimum andmaximum operating temperatures are defined based on this data. Corrosion andsealing of components are based as functional requirements through testing. Chem-ical resistance is based on ISO 16750-5: Road vehicles – Environmental condi-tions and testing for electrical and electronic equipment – Part 5: Chemical loads.This standard dictate what types of chemicals, application method and duration ofexposure that the component is subjected to.

4.6. SPECIFICATION COMPARISON 35

4.5.5 Ergonomic attributesThe ergonomic attributes that is involved with the steering includes areas such assteering wheel adjustment range, adjustment forces, adjustment locking mecha-nism and the nominal position of the steering wheel. The position is referred toas the ”A-point”. The optimal position for the A-point has been researched andthe SAE standard: Driver Preference for Fore-Aft Steering Wheel Location [15],is used for this purpose.The heel and hip of the driver are used as reference and the position of the A-pointis measured vertically and horizontally from the drivers heel. Measurements arepresented in Figure 4.5 outlined H17 and L11 respectively.

Figure 4.5: Visual presentation of ergonomic measurements [15]

These measurements are the deciding factor where the A-point and therebythe steering wheel should be placed.

4.6 Specification comparisonA comparison between the newly created component specification and the cur-rently used specification was concluded as part of the verification. Metrics wasfirst compared to indicate if some aspect were either lacking or redundant. Sev-eral requirements in the currently used specification were solution dependent andtherefore difficult to compare. Other aspects such as subcontractor specific re-quirements e.g. manufacturing related, was not regarded as this also is dependenton the design of the component.


3 different colours were used for highlighting deviations between the new andcurrent specification. The colours that was used were green, yellow and red. Agreen colour indicates no difference, a yellow indicates either updated target orthat further investigation regarding the target is necessary. A red cell indicatesthat the metric is not present on the current specification.First, the metrics on the specifications was compared. The metrics that was solu-tion dependent on the current specification and targeted at the same characteristicas the new specification were assumed to be correct. Deviations of the metricsbetween new and current specification were marked with a red colour. Targets foreach metric were then compared between the new and currently used specifica-tion. Targets that deviated were marked with a yellow colour and a proposal for aupdated target was documented. If the specific metric did not have enough data toassign a target the target was coloured yellow. If no deviations on either metric ortarget could be identified the target was coloured green.

CHAPTER 5

Results

5.1 Customer needsThe identified customer need areas are presented in Table 5.1. The left columnrepresents the area number which all individual customer needs are referencing.

Table 5.1: Area number declaration

Area No Customer need area1 Handling & Performance2 Sustainable3 Driver Assistance4 Quality5 Comfort & Convenience6 Legal Regualtion7 Economy

Individual customer needs are presented in Table 5.2 and are numbered in theformat of X.X. The first number is referencing which area the customer need iscategorized as and the second number represents the individual customer need.The relative importance of the customer needs is presented in the third columnand are graded from 1 to 5. 5 being the most important and 1 being the leastimportant. The total number of identified customer needs is 35.

37

38 CHAPTER 5. RESULTS

Table 5.2: Customer needs and their relative importance

ID Customer need Relativeimportance

1.1 The car can travel straight without turning the wheel 31.3 The car has good control and stability during lane change 31.4 The car has good control and stability during parking and low speed driving 31.6 Steering is precise and gives confidence when steering straight ahead 31.7 Steering is precise and gives confidence when cornering mid to high speed 31.9 Steering does not transmit road disturbances to steering wheel 41.11 Low interior noise and vibration 51.13 High quality operational sounds 41.14 Fast acceleration / deceleration 32.1 Sustainable materials 24.1 Ability to withstand misuse and overload 44.2 Ability to withstand repeated loads from normal to hard use 34.3 Good corrosion resistance 44.4 Steering system is dependable 44.8 Steering operates normally when driving in harsh conditions 34.18 No unexpected noise during driving situations 54.19 High overall quality impression when grabbing and pulling 55.1 Comfortable placement of steering wheel 36.2 Steering angle is not limited by the steering transmission 16.3 Effectiveness of the steering equipment is not affected by magnetic or electrical fields 16.4 After adjustment for steering geometry a positive connection is obtained between

components1

6.5 If part of the steering gear fail there shall be no immediate change in steering angle 36.6 Steering ensures easy and safe handling of the vehicle up to its maximum designed

speed3

6.7 Wheels at half lock, constant speed of 10 km/h, turning circle remains or becomelarger if steering wheel is released

1

6.8 Device to prevent unauthorized use shall be designed so it is necessary to put out oforder to use the steering

1

6.9 Steering lock shall be designed so it cannot rapidly and discrete by common hand toolsrendered ineffective

1

6.10 Steering lock shall be fitted in such way that in blocked position it cannot be removedwithout special tools.

1

6.11 Device to prevent unauthorized use excludes any risk of accidental operation whileengine is running

3

6.12 A device to prevent unauthorized use acting on the steering shall render the steeringinoperative

1

6.13 When the device to prevent unauthorized use is set to act it shall not be possible toprevent the device from functioning

1

6.14 Full functionality of the steering lock after 2500 locking cycles 16.15 Test procedure for steering lock using a torque limiting device 16.16 Steering lock shall withstand continuously or intermittently, a torque of at least 100Nm. 17.1 Good fuel economy 37.2 Low purchasing cost & service cost 4

5.2. METRICS 39

5.1.1 Kano classificationThe Kano classification of customer need areas is presented in Table 5.3. Cus-tomer need with area number 2, Sustainable, and area number 3, Driver assis-tance, are not classified. 4 customer need areas were classified with respectiveKano quality element. Additional classification not shown in the Table includescustomer needs related to noise, which were classified into Must-be elements. Theindividual customer need classifications are presented in section 5.3.1 and 5.3.2.

Table 5.3: Kano classification of customer need areas

Area No Customer Need Kano classification1 Handling & Performance Attractive2 Sustainable Not classified3 Driver Assistance Not classified4 Quality Performance5 Comfort & Convenience Must-be6 Legal Regulation Must-be7 Economy Performance

5.2 MetricsMetrics that were decomposed to subsystem level and connected to the steeringcolumn are presented in Table 5.4. The metrics on whole vehicle performanceare presented in Appendix A, Table A.1. Each metric is defined with an applica-ble unit and those that are non-dimensional are marked ”-” and the abbreviations”Func” and ”subj” corresponds to functional and subjective requirement respec-tively. The total number of identified metrics within the defined area acting on thesteering column resulted in 50.

Metrics that were decomposed to subsystem level and connected to the steer-ing gear are presented in Table 5.5. The total number of metrics identified actingon the steering gear resulted in 46.


Table 5.4: Metrics identified for steering column

Need Nos. Metric No. Subsystem Metric Unit1.1, 1.4, 6.7 1 Average torque to rotate Nm

1.1, 6.7 2 Torsional force variation %1.2, 1.3, 1.7 3 On-center lash Func1.2, 1.3, 1.7 4 Hysteresis -

1.3 5 Joint lash Func1.4, 1.7 6 Non-uniformity P-P angle velocity %1.1, 1.6 7 Off-center stiffness Nm/◦

1.1, 1.6 8 On-center stiffness Nm/◦

1.2, 1.7, 4.1 9 Vertical stiffness N/mm1.2, 1.7, 4.1 10 Lateral stiffness N/mm1.2, 1.7, 4.1 11 Torsional stiffness Nm/◦

1.9, 4.18 12 Steering transmitted vibration L/dB1.13 13 Steering wheel adjustment noise subj1.13 14 Noise limit dB

4.1, 4.19 15 Max deflection at specific force mm2.1 16 Material standard -4.1 17 Torsional strength Nm4.1 18 Axial strength Func4.3 19 Corrosion resistance Func

4.2, 4.4 20 Endurance stroke Func4.2 21 Adjustment mechanism endurance Func4.2 22 Lock endurance cycles

4.2, 4.4 23 Torsional endurance cycles4.2, 4.4 24 Vibration endurance Func

4.1, 4.2, 4.4 25 Entry/exit durability Func4.1, 4.2 26 Adjustment lever strength Func4.2, 4.8 27 Heat aging Func

4.1, 4.4, 4.8 28 Chemical resistance Func4.8 29 Minimum temperature ◦C4.8 30 Maximum temperature ◦C

4.19 31 SW adjustment force vertical N4.19 32 SW adjustment force axial N

4.18, 1.11 33 Lateral eigenfrequency Hz4.18, 1.11 34 Vertical eigenfrequency Hz ◦C4.19, 1.13 35 SW adjustment up/down P2P force variation N4.19, 1.13 36 SW adjustment in/out P2P force variation N7.1, 1.14 37 Weight kg7.1, 7.2 38 Cost SEK

5.1 39 SW adjustment range axial mm5.1 40 SW adjustment range vertical mm6.3 41 Electric field tolerance Func6.3 42 Magnetic field tolerance Func4.1 43 Axial strength adjustment mechanism N4.1 44 Vertical strength adjustment mechanism kN6.9 45 Time to disable steering lock s

6.16 46 Minimum torque R116 Annex 4 Nm6.16, 6.8 47 Torque to rotate steering lock engaged Nm

6.10 48 Ability to disassemble steering lock Binary6.11 49 Ability to engage steering lock while driving Binary6.13 50 Ability to prevent activation of steering lock Binary

5.2. METRICS 41

Table 5.5: Metrics identified for steering gear

Need Nos. Metric No. Subsystem Metric Unit1.1, 6.7 1 Rack pull friction N1.1, 6.7 2 Breakaway toque / Stick-slip N

1.2, 1.3, 1.7 3 C-factor mm/rev1.2, 1.3, 1.7 4 Rotor stiffness Nm/◦

1.2, 1.3, 1.7 5 Hysteresis Nm1.2, 1.3, 1.7 6 Input shaft lateral stiffness N/mm

1.6 7 Resistance against motion Tie rod Nm1.4 8 Torque to rotate Nm1.4 9 Dynamic Assist torque Nm1.4 1o Torque ripple Nm

1.4, 1.7 11 Rack travel mm1.4, 1.7 12 Torque balance Nm

1.2, 1.7, 4.1 13 Compliance input shaft Nm/◦

1.2, 1.7, 4.1 14 Lateral stiffness N/mm1.2, 1.7, 4.1 15 Axial stiffness N/mm

1.9, 4.18, 1.11 16 Vibration transfer Nm/kN4.18, 1.11 17 Running noise limit L/dB1.11, 4.18 18 Sound quality Clonk & rattle subj.

2.1 19 Material-standard -4.1, 4,4 20 Minimum Buckling load kN4.4, 7.2 21 Maximum buckling load kN

4.1 22 Static torsional strength Nm4.1 23 Quasi static strength kN4.1 24 Mechanical shock endurance Func4.2 25 Torsional fatigue Func4.2 26 Vibration fatigue Func4.2 27 Boot fatigue Func4.3 28 Corrosion resistance Func4.4 29 Service life Func4.4 30 EPAS functional voltage V4.4 31 Fixation of rack %4.2 32 Ozone resistance Func4.8 33 Static air leakage cc/min4.8 34 Water ingress Binary4.8 35 Chemical resistance Func

4.8, 4.4 36 Minimum temperature ◦C4.8, 4.4 37 Maximum temperature ◦C4.2, 4.4 38 Joint endurance Func4.1, 4.4 39 Joint pull/press out force N

4.8 40 Thermal aging Func1.11 41 EPAS Flexible modes @ rumble Func

1.14, 7.1 42 Weight kg6.5 43 Failure test Binary

7.1, 7.2 44 Cost SEK6.3 45 Magnetic field resistance Func6.3 46 Electric field resistance Func


Metrics identified for software functions of the EPAS is presented in Table 5.6.The ”Function” column refers to CEVT’s internal naming of software functionwithin EPAS electronics. These functions are tuned and a range for the variablesgoverning these functions are defined, hence no unit is defined. These functionsare treated as metrics connected to the subsystem steering gear and the numberingtherefore continues from the previous table.The need metric matrix is presented in Appendix A, Figure A.1.

Table 5.6: Metrics identified for software functions

Need Nos. Function Metric No.1.1 Active return 47

1.3, 1.6 Steering wheel damping 481.4, 4.18 Software end stops 491.4, 4.18 Extended software end stops 50

4.1 Power ramp down at block 511.4 Friction compensation 52

1.3, 1.4, 1.7, 6.6 Vehicle speed dependent assist 531.1 Pull/drift compensation 54

1.6, 1.7 Enhanced driver feedback 551.1 Torque steer compensation 561.4 Inertia compensation 571.9 Active nibble control 58


5.3 House of QualityResults from House of Quality are presented in this section. The House of Qual-ity is divided onto subsystem-level, results from steering column is presented insection 5.3.1 and from steering gear in section 5.3.2.

5.3.1 Steering columnThe House of Quality for the steering column are presented in Figure 5.1, 5.2, 5.3and 5.4. In the far-left column the numbering of the customer needs is presented.Column number 2 displays the Kano quality element for the specific need. Col-umn number 3 and 4 displays the relative importance and absolute importancerespectively, of the customer needs. In column number 5 the maximum relation-ship score of all metrics is displayed. Column number 6 represents the area andindividual number of the customer need. The customer needs are presented incolumn number 7.Top and second row visualizes the metric number and direction of improvementrespectively. In row number 3 the metrics are presented, and the relationship ma-trix is located below. The rows below customer needs and relationship matrix arethe targets and overall priorities area. The row marked target is used to visual-ize target number for each metric, this information is classified and are excludedfrom the report. The row below target marked max relationship visualizes themaximum relationship score of the metric to all customer needs. In the 2 rowsbelow the absolute and relative technical importance rating score are visualizedfor each metric.In Figure 5.1 customer needs and metrics are filtered to their relationship to ve-hicle dynamics attribute. In Figure 5.2 customer needs and metrics are filteredto their relationship to noise, vibration and harshness attribute. In Figure 5.3 cus-tomer needs and metrics are filtered to their relationship to strength, durabilityand solidity attribute. In Figure 5.4 metrics and customer needs connected to er-gonomics, cost and regulations are presented.

The correlation between metrics are presented Figure B.1.


Figure 5.1: House of Quality for steering column filtered on vehicle dynamicsattribute


Figure 5.2: House of Quality for steering column filtered on noise, vibration andharshness attribute


Figure 5.3: House of Quality for steering column filtered on strength, durabilityand solidity attribute


Figure 5.4: House of Quality for steering column filtered on ergonomics, cost andregulations


5.3.2 Steering gearHouse of quality for the steering gear follows the same set-up as the House ofQuality for steering column in section 5.3.1. In Figure 5.5 House of Quality forsteering gear is presented where customer needs and metrics is filtered on vehicledynamics attribute.

Figure 5.5: House of Quality for steering gear filtered on vehicle dynamics at-tribute


In Figure 5.6 customer needs and metrics are filtered on strength, durabilityand solidity attribute.

Figure 5.6: House of Quality for steering gear filtered on strength, durability andsolidity attribute


In Figure 5.7 customer needs and metrics are filtered on EPAS functions.

Figure 5.7: House of Quality for steering gear filtered to EPAS functions


In Figure 5.8 metrics and customer needs are filtered on performance, cost andregulations.

Figure 5.8: House of Quality for steering gear filtered on weight, cost and regula-tions

The metrics correlation is presented in Figure B.2.


5.4 Steering system specificationThe complete specification for the steering column is presented in Figure 5.9 andfor the steering gear in Figure 5.10. Metrics and a corresponding explanationare located in columns marked ”Metrics” and ”Comment”. Technical importancerating is presented under the name weight, both in absolute and relative score.The impact, which is calculated based on the weight number, is located next tothe relative weight. Setpoint target and marginal target are confidential and there-fore excluded from this report. In the far-right column the units of the metricsare presented. The abbreviation ”Func.” corresponds to functional and impliesa functional requirement without unit. The abbreviation ”Subj.” corresponds tosubjective and implies a subjective target for that metric.

5.4. STEERING SYSTEM SPECIFICATION 53

Figure 5.9: Component specification for the steering column


Figure 5.10: Component specification for the steering gear

5.5. SPECIFICATION COMPARISON 55

5.5 Specification comparisonThe new and current specification was compared and deviations highlighted throughcolours. Targets on the current specification were not split between setpoint andmarginal and all targets were therefore treated as the marginal values. A greencoloured cell indicates that metric, target and testing method match. A yellowcoloured cell indicates that target has been updated or lack of enough data to as-sign a target. A red cell indicates that metric differ or is not present on the currentspecification.A total of 17 deviations was identified for marginal values and another 5 setpointvalues was proposed. Figure 5.11 presents results from comparison between newand current specification for the steering column. Figure 5.12 presents resultsfrom comparison between new and current specification for the steering gear.

Figure 5.11: New and current specification comparison for the steering column


Figure 5.12: New and current specification comparison for the steering gear

CHAPTER 6

Discussion and Conclusions

The first goal of this thesis was to ensure all requirements within project scopehas a clear connection to customer needs. This has with reasonable certainty beenachieved using the House of Quality. The House of Quality provides a graphicalrepresentation of the relationship between metrics and customer needs. It also vi-sualizes the degree of strength for the relationship according to the scale of weak,moderate and strong. All identified metrics has been assigned relationship to itscorresponding customer need. This data visualizes the connection between metricand customer need.Some uncertainties are present connected to the House of Quality. The classifi-cation of weak, moderate and strong connection between metrics and customerneeds were decided mostly based on experience from engineers at CEVT. This in-troduces a risk of subjective opinions to be present during the classification. Therisk is reduced through involving numerous individuals and reaching a consensus,however the classification could be improved with the use of correlation analysis.

The second goal were to provide easy rule of thumb for CEVT how variables affectthe customer satisfaction. This goal has been achieved through Kano-classificationof customer needs categories that provides information of which areas customersatisfaction can be achieved. Together with the relationship matrix, individualmetrics can be identified that affect one or several specific customer needs. Addi-tionally, the metric correlation provides information how parameters affect othermetrics if they are altered.Kano classification of customer needs were performed based on survey data fromNCBS. NCBS does not include functional and dysfunctional questions which isthe preferred format for Kano classification. Since the survey lack functional anddysfunctional questions indifferent and reverse elements could not be identified.

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58 CHAPTER 6. DISCUSSION AND CONCLUSIONS

It is possible that such elements are present and to ensure sufficient certainty hasbeen reached of the classifications additional data and questions formulated ac-cording to previous mentioned format should be added. Since the questions in theNCBS are general and does not go into detail the customer need areas were classi-fied. There is a possibility that individual customer needs within one area deviatesand belongs to a different classification which needs to be examined. Legal cus-tomer needs were classified as Must-be elements without data. The reason for thiswas that the legal requirements are mandatory to fulfil in order to sell the product.The metric correlations are created in the same way as the metric and customerneed relationship matrix. Because of this it may also be influenced by subjectiveopinions since it is based on experience from several individuals. Subjective opin-ions are reduced by involving several individuals but cannot be negligible. Toachieve the most accurate results a correlation survey between metrics should beperformed.

The third goal was to clear redundant, not necessary or requirements that doesnot add value from the specification. This goal is partially met through the com-parison of new and current specification. The technical importance rating fromHouse of Quality provides an indication of impact on customer satisfaction foreach metric.Due to the lack of benchmark data the target set for each metric has been basedon simulations and test results. All targets are therefore not related to competitors’performance and its value has some uncertainty. Product performance with refer-ence to market segmentation is difficult to assure without data on the performanceof competitors’ products. To confirm the performance of the product matches themarket segment for which the product is aimed at a benchmark of competitor com-ponents should be performed.The two subsystems that was identified, steering gear and steering column, arereferred to as components. These subsystems were agreed to be the main parts ofthe steering system and would not be changed in a foreseeable future. Because ofthis the project focused on these subsystems but remained solution independent.The applied constraints were that it should consist of these two subsystems andthey should be mechanically connected. Since the requirements does not constrainthe design of the components it allows for a flexible design space.Due to the strategy of this thesis where only solution independent requirementswhere investigated there are requirements that is not investigated. Solution depen-dent requirements on the current specification did not have anything to compareagainst and are therefore not regarded. These requirements can be investigatedduring future work as all requirements become solution dependent later in theproduct development process. All requirements that could be compared has withreasonable certainty been cleared from redundant and not necessary requirements.

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Further work is however necessary to achieve complete results in this regard.

The fourth goal was to formulate margin and setpoint values for applicable targets.This goal is achieved in the new specification where setpoint targets were added.Setpoint values were only added for metrics that showed improvement when tar-get was altered but was technically difficult to achieve. This strategy was chosendue to contradicting arguments. A single metric can involve several attributes andaffect them differently. For example, vehicle dynamics department want to obtaina rigid system with high stiffness to achieve good steering feel and road feel. Thiswould however also affect noise, vibration and harshness department as a rigid,stiff system could transmit more vibrations and cause noise. The marginal valuein this regard is a balance between the two attributes and a setpoint value could bedefined in either direction. Therefore setpoint values were only defined for someof the metrics.

60 CHAPTER 6. DISCUSSION AND CONCLUSIONS

Bibliography

[1] M. Harrer and P. Pfeffer, Steering Handbook. Springer, 2017, ISBN: 978-3-319-05449-0.

[2] K. T. Ulrich and S. D. Eppinger, Product Design and Development, 5th ed.McGraw-Hill, 2012, ISBN: 978-0-07-340477-6.

[3] R. G. Cooper, “Stage-gate systems: A new tool for managing new prod-ucts”, pp. 44–54, 1990.

[4] K. Ishihara, QFD, the Customer-driven Approach to Quality Planning andDeployment. Asian Productivity Organization, 1994, ISBN: 978-9-2833-1121-8.

[5] D. Clausing and J. R. Hauser, “The house of quality”, Harvard BusinessReview, 1988.

[6] L. P. Sullivan, Quality Function Deployment. American Society for QualityControl, 1986.

[7] L. B. Coleman, The Customer-Driven Organization: Employing the KanoModel. Taylor & Francis Group, 2014, ISBN: 978-1-4822-1710-0.

[8] L. Weber and M. Wallace, Quality Control for Dummies. Wiley Publishing,Inc., 2007, ISBN: 978-0-470-06909-7.

[9] T. Karyser, Power Transmission and Bearing Handbook. Penton PublishingCo., 1975.

[10] V. Chevatco, Exploration of steering feel. Thesis, KTH Royal Institute ofTechnology, 2015.

[11] S. Grunder, A. Gaedke, H. Hsu, and M. Harrer, The new EPSapa in thePorsche 911 - innovative control concept for a sports car typical steeringfeel. Internationales Munchner Fahrwerk-Symposium, 2012.

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62 BIBLIOGRAPHY

[12] K. D. Norman, Objective evaluation of on-center handling performance.SAE Technical Paper 840069, 1984.

[13] P. Pfeffer and M. Harrer, On-centre steering wheel torque characteristicsduring steady state cornering. SAE Technical Paper 2008-01-0502, 2008.

[14] V. B. Bhandari, Design of Machine Elements, 3rd ed. New Delhi: Tata McGraw Hill Education Private Limited, 2010, ISBN: 978-0-07-068179-8.

[15] M. P. Reed, Driver Preference for Fore-Aft Steering Wheel Location. SAETechnical Paper 2013-01-0453, 2013.

APPENDIX A

Whole vehicle metrics

Metrics identified for whole vehicle performance in regard to handling capabilityare presented in table A.1. Metrics number 1 - 6 originates from on-center andoff-center steering evaluation. Metric number 7, 11, 15, 16 and 17 impacts thematerial selection and the general design of the components. Metric number 8, 9,10 and 21 are noise, vibration and hardness (NVH) related. Metric number 12,13 and 14 are driver assistance related and are a part of big functions. Becauseof this they lack a quantifiable unit and are set as a function (”Func.”). To assuredurability which is part of the quality area, tests are implemented for metric num-ber 18, 20, 28 and 29. The unit of these metrics are binary (”Bin.”) which meansthat the component either pass or fail the test. Some metrics translated from legalcustomer needs, area code 6, are already targeted on subsystem level, examplemetric number 28 that is aimed at steering gear.

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64 APPENDIX A. WHOLE VEHICLE METRICS

Table A.1: Metric list for whole vehicle performance

Num Need Nos. Metric Unit1 1.1, 1.6 Returnability Nm2 1.2, 1.3, 1.7 Steering torque gradient @0 g Nm/g3 1.3 Steering torque gradient @0.1 g Nm/g4 1.4 Steering wheel torque @0.1 g Nm5 1.4, 1.7 Steering wheel torque @0 g Nm6 1.1, 1.6 Lateral acceleration @0 Nm g7 1.2, 1.7 Material stiffness Nm/deg8 1.9, 4.14 Steering transmitted vibration m/s2

9 4.14 1.11 Steering transmitted noise dB10 1.13 Sound quality jury subj.11 2.1 Sustainable materials Func.12 3.3 Corrective steering assist Func.13 3.4 Automated parking Func.14 3.5 Autonomous drive Func.15 4.1, 6.15 Material strength MPa16 4.2 Material fatigue cycles17 4.3 Corrosion protection -18 4.4, 6.14 Long term testing Bin19 4.8, 4.9 Sealing capability kPa20 4.9 Climate testing Bin21 4.18 System eigenfrequency Hz22 4.19, 4.20 Quality jury Subj.23 5.1 Packaging -24 5.1 Adjustable SW pos. mm25 6.2 Steering stop Func.26 6.3 Electric/magnetic field tol.27 6.4 SW adjustment locking force N28 6.5 Failure test of steering gear Bin29 6.6 High speed test Bin30 6.8, 6.9, 6.12, 6.13 Steering lock Func.31 6.9 Time to break steering lock s32 6.10 Special fitting steering lock Bin33 6.11 SL engagement while driving Bin

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The need-metrics matrix is presented in Figure A.1. The left column representcustomer needs and top row represent metrics. The metrics are linked to whole ve-hicle performance. A marked dot in the matrix symbolizes a relationship betweenthe corresponding need and metric. A total of 37 customer needs and 33 metricswere identified. The total number of relationships found was 60.

66 APPENDIX A. WHOLE VEHICLE METRICS

Figure A.1: Needs-metrics matrix for whole vehicle metrics

APPENDIX B

Metric correlation

Correlation between metrics identified for the steering column is presented in Fig-ure B.1 and for the steering gear in Figure B.2. Correlation is executed via diag-onal squares where each references a specific metric. When two diagonal linesmeet a series of symbols classifies the correlation, symbols used are defined inFigure 4.4.

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68 APPENDIX B. METRIC CORRELATION

Figure B.1: Correlation of metrics for steering column

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Figure B.2: Correlation of metrics for steering gear

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