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Firma convenzione Politecnico di Milano e Veneranda Fabbrica

del Duomo di MilanoAula Magna – Rettorato

Mercoledì 27 maggio 2015

MeccPhD Evaluation

Alireza Izadi

Cycle XXVIII Dynamics and Vibration of Mechanical Systems and Vehicle

Thesis Title: Active roll control of an articulated heavy vehicle using

the existing air suspension

Supervisors: Prof. Edoardo Sabbioni/Prof. Federico CheliTutor: Prof. Massimiliano Gobbi

Alireza Izadi, MeccPhD, Three and a half year Evaluation 2/32

Contents

1. Introduction2. Methodological approach3. Vehicle Modeling4. Control Logics design5. Actuators Modeling6. Results

– Comparison of different control logics– Comparison of actuators– Active tractor and active trailer– Robustness

7. Conclusion8. Doctoral curriculum


Problem and solutions

The problem:• 35 % of fatal accidents caused by HVs• Rollover causes 38% of fatal accidents in HVs

and it is the most horrible accident.

Preventability of rollover accidents:• 50% are impossible to control even with

professional drivers.

Solution:• Active roll control is the most strong solution

for rollover accidents

Fig 1. Preventability of rollover accidents by driver.

Fig 2. Passive roll control vs. active anti‐roll control application.

3.3

38.4

49.7

8.6

0

10

20

30

40

50

60

Possible Maybe Impossible unknown

Problem and solutions

Aim of work, main features, and innovative aspects

Methodological approach Vehicle models Control logics Actuators Results Conclusion

(a) (b)


Aim of the work, main features and innovative aspects

Aim of the work:is to develope a rollover controller to tilt the vehicle toward the inside of turn to minimize lateral load transfer.

2. Main features: appropriate improvement with robust operation to different payloads and velocities, proper energy consumption, flow rate and bandwidth of actuators, low installation and operational costs

In comparison with the state of the art considering Control logics Actuators (active anti roll bars)

3. Innovative aspects: o Using the full potential of existing air springs for roll control design,o Designing the control logic based on:

o minimum measurements, o precise and low cost estimations and o an optimal load distribution on the axles.

Problem and solutions Aim of work, main features, and innovative aspects



Methodological approach

Fig 3. Methodological approach for active air suspension design.



1. Vehicle Modeling 2. Control Design 3. Actuator Modeling

A. Multibody VM

B. 9‐DoF VM

C. 5‐DoF roll‐plane VM

D. Logic 1

E. Logic 2

F. Logic 3

G. Active anti‐roll bars

H. Active air springs

A. Multibody VMActuatorsControl

Logic+‐ /x

4. System integration

Mod

eling

System

integration

5.The best compromise for rollover controllerResult


Active Roll control design process



7. Conclusion


1. Nonlinear multibody vehicle model

A complicated nonlinear vehicle modelincludes:

• 192 ordinary differential equations,• 76 bodies,• 30 multibody degrees of freedom• 73 multibody coordinates,• Nonlinearities Jounce and rebounds bump stops 5th wheel roll, pitch and yaw bumps Spring hysteresis Tire deflection



The multibody model is used for co‐simulating with Simulink to:1. validate the simplified linear vehicle models and 2. describe the response of the tractor semitrailer.

Fig 4. Visualization of nonlinear multibody vehicle model.


2. Linear models

‐ Simplified 9‐DoF vehicle model: ‐ Simplified 5‐DoF vehicle model:

9‐DoF tractor semitrailer model. ∅ ∅

∅ ∅ ∅

∅ ∅ ∅ ∅ ∅ ∅ ∅ ∅ ∅ ∅

Fig 5. 9‐DoF tractor semitrailer model and states is used in the full state and partial state feedback controllers.

Fig 6. 5‐DoF roll plane model and states is used in reduced order controller design.



This model is used for designing our full state feedback controller.

This model is applied for designing our minimum order controller.

Validated by Nonlinear Multibody Model

∅ ∅ ∅ ∅ ∅ ∅ ∅


Comparison of linear and nonlinear vehicle model

Fig 7. Trajectory of tractor semitrailer.

Fig 12. load transfer on wheels.

Fig 11. Suspension roll angle. Fig 8. Yaw angle of tractor semitrailer.

Fig 9. Yaw rate of tractor semitrailer. Fig 10. Lateral acceleration of tractor semitrailer.







7. Conclusion


Control logics

Control objective of all controllers:• Reducing the load transfer by tilting the vehicle towards the turn.

Control logics:Logic 1: Proportional lateral acceleration feedback controlLogic 2: Full-State feedback controlLogic 3: Optimal minimum order control

Selection criteria:• The controllers response in transient and steady state condition(reliability),• Robustness• Number of measurements • Estimation precision and costs• implementability




Logic 1: Proportional lateral acceleration feedback

PD Controller

PD Controller

ActuatorsActuators Multi‐body Vehicle

Multi‐body Vehicle

,

Fig 13. Proportional lateral acceleration feedback control logic.

LOGIC 1 (Specifications): 1. The simplest controller includes only a proportional gain.2. Minimum number of measurements.



Gain selection :The control law is:

.The proportional gain is tuned to have a proper suspension roll angle in oppositedirection of the roll moment caused by the lateral acceleration.


Logic 2: Full-state feedback controller (LQR)

LOGIC 2 (Specifications):1. It is a multivariable optimal controller with disturbance rejection properties.2. It needs the highest number of measurements among the controllers.



Linear Quadratic Regulator Actuation System

,

Control technique:To use the linear quadratic optimization to regulate the load transfer in the presence of steering disturbance.

∅ ∅ ∅ ∅ ∅

Fig 14. State feedback control logic algorithm.



Control gain matrix calculation :1. Considering the linear dynamic system:

2. Control problem:The control minimizes the quadratic performance index:

Q : the relative weighting of the performance output xR : the weighting matrix of control input u(t).

3. Optimal control law:

Where



, Eqn. 1

x x Eqn. 2

x δ Eqn. 3

S is the unique solution of algebraic Riccati formula.

Linear Quadratic Regulator Actuation System

,


Disadvantages of logic 2:1. It requires all the internal states of the system and all the disturbance

states available for feedback,2. difficult and expensive to measure states,3. the sensor output signals are corrupted by noise.




A practical proposition is:• to measure selected vehicle states• Estimate the unmeasured states• Filter measurement noise

1. An optimal controller with minimum measurements and proper estimations2. Reasonable estimation cost

Logic 3: An optimal minimum order controller


The minimum order controller consists 1. A state estimator 2. An optimal controller

Logic 3: Optimal minimum order controller

Fig 15. The designed minimum order controller.

ActuatorsForce control MB Vehicle

,,

State Estimator

LQR

, ∆∅ ∅ ∅ ∅ ∅ ∅ ∅ ∅ ∅ ∅



MeasurementsSpeed Steer angle Lateral acceleration Air springs elongation Air spring pressure

Table 1. Measurements of minimum order controller.

The estimations are in a very good agreement with measurements.√





7. Conclusion


Actuators

.

Fig 16. ARB system configuration (SATA). Fig 17. Air springs configuration.

1. Active anti-roll bars 2. Active air springs



Two actuator models were developed:1. Active anti‐roll bars with 4 Hz bandwidth2. Active air springs with 2 Hz bandwidth


Active air springs configuration

Axle Bandwidth L1 (mm) L2 (mm) Load reduction (%)

Steer

2 Hz‐ ‐ 20

Drive 500 500 50

Trailer 500 480 46



Steer axle Drive axle Trailer axles

Table 2: BPW 360K‐1 air springs with 360 mm diameter.

Fig 18. Air springs configuration on steer axle (a), drive axle (b) and trailer axle (c).

(a) (b) (c)

Fig 19. air spring installation on trailer axle.





7. Conclusion


Suspension response by using controllers - Ramp steering (steady state maneuver, 60 km/h)

1. The controllers have small and acceptable deviations, thus they have satisfactoryresponse for active air springs system.

2. Suspension tilts inward the turn to reach the maximum capacity of air springs andthen it tilts backward.

3. All in all, there is a considerable improvement in rollover threshold.

Fig 21. Normalized load transfer vs. lateral acceleration. Fig 22. Suspension roll angle vs. lateral acceleration.

Comparison of ControllersActive air springs

Actuators capability

Actuators comparison

Active combinations and 5th wheel study Robustness AnalysisRESULTS:RESULTS:


Suspension response by using controllers - Double lane change steering (Transient maneuver, 60 km/h)

• In DLC the optimal controllers are performing very good.• The response of optimal controllers are better than proportional lateral acceleration

feedback controller which causes higher improvement for them.

Fig 23. Normalized load transfer vs. lateral acceleration. Fig 24. Suspension roll angle vs. lateral acceleration.






Controller selection

The minimum order control logic is the most appropriate control logic for the roll control purpose.





Specifications of control logic 3• low number of measurements,• reasonable estimation cost,• very good response in steady state and transient condition,• with disturbance rejection properties.





7. Conclusion


Actuators comparison- Ramp steering (steady state maneuver, 60 km/h, )

Maximum Improvement Active anti‐roll bars Active air springs

Normalized load transfer (%) 16.81 9.81

Rollover threshold (%) 17.99 7.64





Table 4. Normalized load transfer and rollover threshold improvements.

Fig 25. Active and passive normalized load transfer for active anti‐roll bars (a) and active air springs (b).

Active anti‐roll bars Active air springs

Although active anti‐roll bars have higher capabilities, air springs have a considerable improvement within their potentials.

(a) (b)

Active anti‐roll bars Active air springs

17.99 7.64





7. Conclusion


• Active tractor has the worst maneuverability, even worse than passive vehicle,• Both combinations are worsening the rollover threshold and the active roll control is

recommended to use only for fully active vehicle.

Active combinations





Active combinations:1. Active tractor2. Active semitrailer

The comparison considers:1. Rollover threshold improvement in steady state maneuver2. Maximum speed for a severe DLC maneuver

Fully Active Active Tractor Active Semitrailer Passive

Rollover threshold Improvement (%) 7.64 ‐15.96 ‐4.59 0

Maximum speed in DLC (km/h) 112 90 102 98

Table 5. Rollover improvements in steady state maneuver and maximum speed in a severe transient maneuver for active combinations.

90

Active Tractor

112

Fully Active





7. Conclusion


Robustness to payload positionRamp steering (steady state maneuver, 60 km/h)

Payload position for three controllers

Standard X +15% X ‐15% X ‐25% Z +15% Z ‐15% X +15% Z +15%Improvement (%) 7.6 9.4 8.7 8.8 7.5 6.0 10.4





The robustness analysis was done for different positions of maximum payload• X is the distance of center of payload to hitch

• Z is the height of center of gravity of payload

Table 7. Robustness of active air springs to different payload positions and different controllers.

• All the three controllers are robust to payload positions and even the improvementin the worst condition is more than standard position

• The robustness of minimum order optimal controller is very good for our roll controlsystem.

• Minimum order control is confirmed for its robustness


Conclusion

Within the constraints and limitation of our system:1. The improvement is comparable with active anti-roll bars2. The energy consumption is low3. The costs are very low and easy to implement

Active air springs Active anti‐roll bars

Main features

Rollover preventability (%) 7.64 17.99

Robustness

Energy consumption of actuators [W] 1650 2118

Installation cost 0 high

Operational cost Very low high

All in all, considering the actuators, rollover threshold improvement, loadtrasnfer reduction, energy consumption and costs:Active air springs are the most proper compromise for this rollover controller.


I APPRECIATE YOUR CONSIDERATION.Alireza Izadi

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