Current TRL: 3 (9/30/21)

“The drivetrain design is complete, however, it is not fully assembled. We are missing one half-shaft and crucial safety features such as chain guards and a scatter shield. To get to level 4, we need to complete the assembly with electronic components and test it in a controlled setting.”

Drivetrain

Drivetrain current state

Exploded view of drivetrain enclosure

The drivetrain package is comprised of an Emrax 208 liquid-cooled axial flux synchronous motor, eccentric rings for easy chain tensioning, motor shaft support bearings, a flex hub that allows for any angular misalignment of the motor shaft during load, and a limited-slip differential to maintain rear-wheel independence. A sleek 4 bolt mounting system allows the self-contained drivetrain assembly to easily be removed and installed on the chassis. The entire drivetrain assembly also maintains the ingress protection rating of IP65 in order to pass competition qualifying events. The Emrax 208 provides a nice coupling for a chain-driven system, with a single gear ratio, 3:1. The gear ratio was optimized for acceleration and endurance of the vehicle during testing. Overall the drivetrain was developed to provide max power of 32 kW and transmit 80 N-m of torque to the wheels, providing quick acceleration and the ability to adapt to longer endurance-type races.

Main Documents

Literature Review

Drivetrain system of the FSAE formula car is important because it ensures the ability to deliver the maximum power and efficiency from the motor to the car and remain as light and stiff as possible. The system is comprised of a drivetrain housing, Emrax 208 liquid cooled axial flux synchronous motor, emDriver 500 motor controller, a limited slip differential and a chain-driven system with a single gear ratio. Due to past drivetrain housing flexural issues in previous years, the new housing design which contains all these components has been manufactured but has not been tested for rigidity, while ensuring the maximum performance. A rigid housing was fundamental to ensure stiffness and reduce vibration isolation which would further limit the power output of the car. This year’s main design consideration is to test system’s rigidity in simulation and controlled environment and develop a better system to maximize the EV performance of the vehicle and range as such it can reach a maximum acceleration of 0-60 mph under 4 sec and increases top speed while maintaining efficiency at high speed.

Full Literature Review

Design Problem

This system’s design problem involves accurately modeling the drivetrain system with theoretical calculations regarding the maximum top speed and estimate the maximum range it can reach. The previous team had not done any system analysis for the single speed system to see if the gear ratio of 3:1 can sufficiently provide desired toque and speed to support the car on tract due to the past team never successfully tested the motor on the drivetrain. Another challenge would be that the drivetrain system doesn’t have a sufficient testing facility to record the power output for the drivetrain system. That is because previous team had not test the drivetrain system instead they only did test on a different motor which is set up in the dyno room. The Major differences of the motor in the dyno room and the drivetrain system is its gear ratio which changes the system output and the differences between air cooled and water cooled motor. It is important to be able to record the output of the drivetrain data, because the data collected from drivetrain can help the team to model the system on Matlab and solve the physical characteristic of the model in order to predict the performance the race car. Furthermore, there has being discussions in design a multi-speed transmission system for future team to improve the performance of the race car even though the industry standards are using single speed transmission for EV’s. The reason the drivetrain team want to take on the challenge is because multiple articles shows the increased efficiency and performance can be reached when the multi-speed transmission is implemented. The drivetrain team want to set up the test facility for the future team to test the theory and validate if the use of multi-speed transmission can improve efficiency in electric vehicles.

Conceptual Solution

First, we need to develop a system model in relationship to input voltage and output angular velocity to simulate the most efficient single gear ratio to power the race car in terms of known battery capacity and estimated weight of the car. With the system model developed, we can test different gear ratios and see how it can greatly effect the output of the system. It is important to have a model developed in order for the drivetrain team to find the most efficient single gear ratio and to achieve the best performance possible (maximum top speed while maintain sufficient torque to support the car to go uphill) for the race car. A test bench for the drivetrain system would provide useful data to analyze the model’s physical characteristic such as friction and rotational inertia. Drivetrain team have to develop a test facility outside of dyno room to test the overall output of the drivetrain when installed on chassis instead of the motor itself. A testing facility can help the team to validate the system model and deliver the test and analysis tools for future team to evaluate and optimization their future drivetrain design. Some possible dynamometer testing idea includes design and manufacture a fully functional eddy-current chassis testing facility on campus. Furthermore, the team has the idea of designing a CVT (Continuously Variable Transmission) for the future team to increase the efficiency and performance of the race car. 

Drivetrain Broader Impact

With the rising popularity of pure electric vehicles, the drivetrain team is set to develop an inexpensive test system to achieve maximum efficiency for our electric race car. Most of the electric vehicles have shorter range than internal combustion vehicles due to the battery capacity. With the electric power testing system, we hope that we can help engineers to test their power unit to increase the drivetrain efficiency and thus increase the range for the electric vehicles. The Electric Vehicles drivetrain system power testing is very different from traditional internal combustion engines, which typically measures speed, torque, and a few temperatures, pressures, and flows. Very precise control of speed and torque is typically not required in testing internal combustion engines, so dynamometers used for standard combustion engine testing (for example, water brake and eddy current) were never designed to handle the types of precision required by hybrid or electric powertrains, nor can they test the regenerative (motoring) modes of operation. So it is very useful to develop an inexpensive pure electric test system to provide all of the functionality of a traditional system, with the added ability to test high-power regenerative electrical drives, high voltage battery and charging systems, and communicating with any number of smart control modules (MCU’s). 

Metrics, Constraints and Objectives:

Metrics:

The drivetrain should reach 0-60 mph in under 4 seconds.

The drivetrain should be able to provide enough torque to get up a 15 degree incline.

The drivetrain should have the most efficient gear ratio to achieve a maximum speed of around 40 mph.

The drivetrain housing should withstand a torque of 200 N-m.

Constraints:

The motor for this years car must be the Emrax 208 liquid cooled motor. 

The drivetrain housing must fit behind the driver seat in between the rear wheels on the chassis.

The drivetrain housing must be structurally sound to withstand the forces from torque.

Objectives:

The drivetrain housing must be lightweight, rigid, and efficient.

The drivetrain should provide enough torque to achieve a fast acceleration.

The drivetrain gear ratio should achieve a steady maximum speed around the track.

 

Codes and Standards:

We were not able to find any relevant codes and standards. We scoured numerous resources online as well as in the drive.

 

 

Components:

Emrax 208 Motor

 

Related Documents:

  • Motor User Manual (PDF) (Last Updated: 10/1/2021)
  • Motor Characterization data from past(Motor-Characterization)
  • Old Results of Motor Characterization from 2020:

emDriver 500 Motor Controller

The Motor Controller consists of 3 main parts: an aluminum 6061 plate the body will lay on which would then be mounted on the chassis, an aluminum 3003 body with 3-panel cutouts, and an aluminum 3003 lid.

Related Documents:

Drexler 140 mm Limited Slip differential

 

Slip differential that maximizes efficiency with the preload adjustment.

Related Documents:

Drivetrain Housing 2021

The overall design for the drivetrain housing.

Related Documents:

Spline Half Shafts with Roller Bearings

The half shafts are the rods that connect the wheel hubs to the drivetrain.
The ends of the half shafts are splined to allow secure press-fit connections
with the roller bearings, which are fitted onto the ends of the half shafts. The
roller bearings are what slide into the housings on the wheel hub and the
drivetrain, allowing for movement with the wheels and the suspension
system.

Subsystem TRL Chart

TRL What does this look like? Expected Completion Date
9 The drivetrain has been used at the competition Race day
8  Full integration with the car and tested at Metzgar 04/01/21
7 Full integration motor controller, cooling system, and drivetrain on chassis in order to do a physical load test to test the torque on the drivetrain 03/01/21
6 Develop a better system model with real data on a testing bench for the torque output of the motor with increasing load and potentially develop efficiency calculations based on battery potential. 12/30/21
5 The drivetrain is fully fitted with a motor controller, cooling, and the necessary electronics in order to collect data without load for the output torque in a controlled environment. 12/15/21
4 Fit the drivetrain with chains on the chassis, test the rigidity of the tripod housing shafts, fill the differential with oil, and test differential with drivetrain connect to the wheels. 11/15/21
3   Parts are fabricated and purchased to pass safety standards and are ready for assembly and the model is proved to provide sufficient torque and power. 10/20/21
2 Inventor file and model prediction is developed to determine the gear ratio and drivetrain placement Completed
1 Drivetrain concept created and the appropriate motor and placement is chosen for the chassis Completed

 

Additional  Documentation