Management of

Transmission/Powertrain

Division

Baja SAE USB 2010-2011

By: Reinaldo Wiener (head of

division)

• The main goal of Baja SAE Competitions

is to design and build an All Terrain

prototype which is submitted by a series of

challenging test.

• The Powertrain System design has a lot of

influence in the prototype performance

because equilibrium between high torque

and top speed must be achieved.

• The first task as head of the division was

to recollect the information about common

problems in past competition:

– CVT overheating

– Time loss during assembly and disassembly

– Failure of transmission shaft

– Impacts at the bottom of the gearbox during

bumps

– Oil leakage in the gearbox

• After recovering the most influencing problems,

as team, we set the objectives for

powertrain/transmission team the general

objectives were:

– Improve the prototype’s dynamical response (improve

position in acceleration, and hill climb)

– Reduce car weight without sacrificing reliability

(strength-weight ratio)

– Improve the shaft resistance

– Prevent parts overheating

– Prevent oil leak

– Make all possible with a very low budget

• Characterize the CVT behavior:

– A Continuous Variable Transmission is a type of

transmission that acts like an automatic gearbox.

There are some parameters than can be modified in

order to obtain a better performance.

– Measure velocity, acceleration and time in a distance

of 150ft using telemetry equipment, using different

configurations of the CVT in previous prototypes

– Data clean up and interpretation

Dynamic Response

Vehicle Dynamics

• Characterize the aerodynamics load

curve: – This was the first time that the load curve was

measure. The trial consist in pulling the car with a

load cell attached and measure the load and velocity

(no wind tunnel available).

• Characterize the engine curve:

– A low cost prototype with an air cooled disk brake

was design and build (dyno). It was also the first time

that the actual engine curve was obtained.

– Measure of engine torque and engine speed using a

competition engine.

Dynamic Response

RESUMEN TRANSMISION 2009-2010

Load Curve (Aerodynamics)

RESUMEN TRANSMISION 2009-2010

Dyno Tests

• Simulation of dynamic response using the

data recovered

– It is assumed that load curve from previous

prototypes are very similar to the new one

– Select the final gear reduction which is a key

parameter for the gearbox design

Dynamic Response

RESUMEN TRANSMISION 2009-2010

Estimated Curves

• Gear box conceptual design was developed

taking into account that the final gear must be

reduced in order to avoid shock during bumps.

• Minimize all components weight, running Finite

elements analysis to check stress and strain.

• Introduction of cover design to reduce oil

leakage

• Develop of a system to open the gearbox faster

for maintenance.

Minimize Weight

Conceptual design

of the Gearbox

Stress Analysis

(FEA)

Stress Analysis

(FEA)

• The output shaft connect the gearbox to the wheels. In

order to avoid output shat failure, a series of test were

performed on a shaft used by commercial ATVs.

– The first test recollected the superficial hardness of the shaft

– The second recollected the hardness in the transversal section

for different radii. This second test suggested that a thermal

treatment were performed on the shaft (probably a quenching

treatment)

– The final test were performed to study the chemical composition

of the shaft in order to study if it was a special alloy material or a

common steel. It was discovered that the material was an AISI

1040.

• This study suggest that after machining, the piece must

pass trough thermal treatment to harden the surface and

avoid break due torsional stresses.

Output shaft

CVT Overheating

• To prevent CVT overheating holes were added

in strategic position in the CVT cover in order to

let air flow in and out.

• CFD Simulations help to obtain temperature

distribution and inlet velocity for different

configurations.

• The simulated cover model were manufactured

and CFD model were validated. Temperature

improvement was achieved and Conf3 were

selected.

CVT Overheating

CVT Modeling and

CDF Simulation

The Result

The Result

• First experimental load and engine curves

were obtained

• Improvement of dynamics behavior

• No CVT damage due the high

temperatures

• No failure of output shafts in tests

• No leak in the gearbox

• No impacts on the gearbox during bumps

The Result

• Development of a degree final project which

purpose was to describe the dynamic behavior

of a CVT (Continuously Variable Transmission)

applied to the ATV prototype.

• This give a more accurate approach to the

dynamic behavior of the vehicle.

• This project was to opt for mechanical

engineering degree, earning an honorable

distinction for it.