The Baja SAE Series is an annual competition organized by the Society of Automotive Engineers and has the objective to encourage undergraduate students to design, manufacture and test and All-Terrain vehicle prototype. There are almost 100 participants and it was a good opportunity to put in practice the knowledge acquired in class. In 2010 we achieved the 1st place in design, it has been the highest achievement in the whole team’s history, and it was of course a consequence of our hard work. As Powertrain head I led several tests in order to characterize the dynamical behavior of the vehicle, these developments settles a good base for future generations.

1. Management of
Transmission/Powertrain
Division
Baja SAE USB 2010-2011
By: Reinaldo Wiener (head of
division)

2. • 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.

3. • 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

4. • 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

5. • 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

6. Vehicle Dynamics

7. • 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

8. RESUMEN TRANSMISION 2009-2010
Load Curve (Aerodynamics)

9. RESUMEN TRANSMISION 2009-2010
Dyno Tests

10. • 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

11. RESUMEN TRANSMISION 2009-2010
Estimated Curves

12. • 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

13. Conceptual design
of the Gearbox

14. Stress Analysis
(FEA)

15. Stress Analysis
(FEA)

16. • 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

17. 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.

18. CVT Overheating

19. CVT Modeling and
CDF Simulation

20. The Result

21. 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

22. 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.