Current TRL: 7 (4/27/22)

“The drivetrain design is complete and fully assembled, including safety features such as chain guard and half shafts. To get to TRL 48 we need to complete the assembly of motor controller, cooling system, and drivetrain on chassis to do a physical load test to test the torque on the drivetrain.

Drivetrain System

 Full Drivetrain Assembly


Current Drivetrain Design

Exploded view of drivetrain enclosure(Assembly_Simulation)

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 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 23 kW and can transmit around 400 N-m of maximum torque to the rear wheels, providing quick acceleration and the ability to adapt to longer endurance-type races.

Main Documents

  • Complete Drivetrain parts list (Drivetrain-BOM ) (Last Updated: 5/12/2021)
  • Complete Drivetrain Inventor File (Full Inventor file) (Last Updated: 2020)
  • Drivetrain Rule requirement for the Formula Hybrid Competition (doc)(Last Updated: 10/9/2021)
  • Full Literature Review (Last Updated: 10/9/2021)
  • FEA Analysis for Drivetrain(file)(Last Updated: 11/30/2021)
  • Mid-year budget update(doc) (Last Updated: 12/9/2021)
  • Drivetrain Derivation (pdf) (Last Updated: 12/10/21)
  • Matlab Code for Gear ratio(MatlabGR)(Last Updated: 12/9/2021)
  • Matlab analysis for 0-60 MPH/Top Speed/G-force (MatlabMPH)(Last Updated: 12/12/2021)
  • Drivetrain Midyear Poster(FSAE Drivetrain 2022 Poster)(Last Updated: 12/12/2021)
  • Midyear ProgressReport (Link here)(Last Updated: 12/17/2021)
  • Club Handoff Checklist and Instructions (link)(Last Updated: 3/12/2022)

Achievements(Last Updated: 12/17/2021)

Developed a physics-based model in MATLAB to analyze car performance. We find the effective 0-60 acceleration time, max velocity, effective gear ratio in different scenarios, and maximum torque to the wheel. FEA analysis was completed on Ansys to analyze the stress in the drivetrain sprockets and housing under max forces and normal forces in case of failure. Chainguard manufacturing, general finish parts order, and manufacturing of drivetrain. Manual proof of concept run test.

  • FEA Analysis for Drivetrain(file)(Last Updated: 11/30/2021)
  • Mid-year budget update(doc) (Last Updated: 12/9/2021)
  • Drivetrain Derivation (pdf) (Last Updated: 12/10/21)
  • Matlab Code for Gear ratio(MatlabGR)(Last Updated: 12/9/2021)
  • Matlab analysis for 0-60 MPH/Top Speed/G-force (MatlabMPH)(Last Updated: 12/12/2021)

Future Plan(Last Updated: 12/17/2021)

For Current Design:

  • Update model to predict the max acceleration and speed on a 15-degree incline.
  • Find the Torque lost due to internal friction and the moment of inertia for all moving parts to improve the current model.
  • Take power-torque curves and acceleration data with the car running to verify the model.
  • Arrange a straight-line test and see the 0-60 mph acceleration time and top speed to validate the model prediction.
  • Figure out the max torque the housing can withstand to see if power needs to be limited.

For Future Design:

  • Design, test, and analyze a CVT (Continuously Variable Transmission) to aim for a 0-60 MPH time under 10 sec.
  • Reduce the weight of the drivetrain.
  • Develop a continuously adjustable chain tensioner for easy adjustment.

For Testing:

  • A test on an eddy-current chassis for the drivetrain system would provide useful data to analyze the model’s physical characteristics such as torque lost and rotational inertia.
  • Going to an off-campus testing facility can also help the team to validate the system model and deliver the test and analysis tools for the future team to evaluate and optimization their future drivetrain design.

Literature Review

The 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 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 the 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 10 sec and maintain top speed around the track.

Full Literature Review

Progress Report 

  • Stakeholders: Our stakeholders would probably be the Lafayette Motor Sports Club team.  We want to engage with them by understanding their needs and goals for the race car design and communicating with them through slack and weekly club meetings.
  • User (or Stakeholder) Needs: The drivetrain must be Lightweight, rigid, efficient, and low cost.
  • Updated Schedule: (Link Here)
  • Updated Budget: (Link Here)
  • Midyear ProgressReport (Link here)

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 electric vehicles have a shorter range than internal combustion vehicles due to battery capacity. With the electric power testing system, we hope that we can help engineers to test their power units 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 measure 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). We hope that a test on an eddy-current chassis for the drivetrain system would provide useful data to analyze the model’s physical characteristics such as torque loss due to internal system friction and rotational inertia as well as help the team to validate and improve the system model so that we can deliver the test and analysis tools for the future team to evaluate and optimization their drivetrain designs.

Drivetrain Poster 2022

Problem Statement: The world is moving towards all-electric vehicles. However, most EVs have a shorter range than internal combustion vehicles due to battery capacity. The purpose of this study is to increase the drivetrain efficiency and thus increase the range by developing a physics-based model to simulate the drivetrain performance on track for the current design and formulate solutions to improve upon for future designs.

FSAE Drivetrain 2022 Poster

Metrics, Constraints, and Objectives:

Metrics:

  • The drivetrain should reach 0-60 mph in under 10 seconds.
  • The drivetrain needs to be able to provide enough torque to get up a 15-degree incline.
  • The drivetrain should have the most efficient gear ratio to be able to achieve a minimum top speed of around 60 mph.
  • The drivetrain housing needs to withstand a torque of 140 Nm from the motor.

Constraints:

  • The motor for this year’s car must be the Emrax 208 liquid-cooled motor. 
  • The overall weight of the car is estimated to be 1000lbs.
  • The drivetrain housing must be able to fit behind the driver seat in between the rear wheels on the chassis with the cooling systems and the motor controller.
  • All the moving parts inside of the drivetrain housing must be structurally sound to withstand the impulse forces from the motor.

Objectives:

  • The drivetrain housing must be lightweight, rigid, and efficient.
  • The drivetrain should provide enough angular velocity to reach a reasonable top speed while providing enough torque to achieve a relatively steep incline.
  • The drivetrain gear ratio should remain efficient while maintaining desirable top speed around the track.
  • The gear ratio and the chain tensioner for the drivetrain should be easily adjustable.

Codes and Standards:

  • The standard for Verification and Validation in Computational Solid Mechanics (Link here)

The codes and standards linked above are based on verification and validation of solid mechanics, this can be applied in the testing of the drivetrain design.

  • The codes for Measurement of Shaft Power (Link here)

The codes and standards linked above detail the correct way to measure shaft power.

  • The standard for Fatigue Testing Power Transmission Roller Chain (Link here)

The codes and standards linked above detail the fatigue standards for the powertrain chain.

Concept Generation

This system’s design problem involves accurately modeling the drivetrain system with theoretical calculations regarding the maximum top speed and estimating 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 torque and speed to support the car on track due to the past team never successfully testing 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 the previous team had not tested the drivetrain system instead they only did a test on a different motor which is set up in the dyno room. The Major differences between the motor in the dyno room and the drivetrain system are 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 the drivetrain can help the team to model the system on Matlab and solve the physical characteristic of the model to predict the performance of the race car. Furthermore, there have been discussions in designing a multi-speed transmission system for the 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 wants to take on the challenge is that multiple articles show the increased efficiency and performance that can be reached when the multi-speed transmission is implemented. The drivetrain team wants to set up the CVT(Continuously Variable Transmission) design and Matlab simulation 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 with the 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 affect the output of the system. It is important to have a model developed for the drivetrain team to find the most efficient single gear ratio and to achieve the best performance possible (maximum top speed while maintaining 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 characteristics such as friction and rotational inertia. The drivetrain team has to develop a test plan outside of the dyno room to test the overall output of the drivetrain when installed on the chassis instead of the motor itself. Some possible dynamometer testing idea includes testing the racecar on an eddy-current chassis testing facility off-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. 

FEA Analysis for Drivetrain Components

Related Documents:

  • FEA Analysis for Drivetrain(file)(Last Updated: 11/30/2020)

Drivetrain Derivation for Physics-based Model

Model Dynamics

                                                                  Side View

                                                               FBD for One Wheel 

Related Documents:

  • Drivetrain Derivation (pdf) (Last Updated: 12/10/21)
  • Matlab Code for Gear ratio Plot (MatlabGR)(Last Updated: 12/9/2020)
  • Matlab analysis for 0-60 MPH/Top Speed/G-force (MatlabMPH)(Last Updated: 12/12/2020)

Motor torque vs speed curve (from manufacture data) 

Due to we didn’t collect any motor data from the motor itself, I used the manufacturing data to plot the maximum motor torque over the maximum motor speed curve in terms of our estimated maximum power from the battery pack with 90 percent efficiency between the battery pack and the motor. More motor details can be found in the document below. 

Motor Gear Ratio Analysis 

The red-colored line in the figure above shows the velocity vs. time plot for a 1000 lb car with a gear ratio of 2:1. Compared to the yellow and purple line, it shows that a gear ratio of 2:1 takes the longest amount of time to get to the maximum velocity, however, all three lines reach the same maximum speed. The yellow and purple line reaches the maximum speed at a similar time, however, a gear ratio of 4:1 requires a much larger rear sprocket to accommodate the increased amount of teeth which increases weight and most likely costs more time and money to manufacture. We validate that a 1000 lb car with a gear ratio of 3:1 is the ideal solution. This is the gear ratio that the previous team chose for the drivetrain design, this ratio combines fast acceleration without compromising speed on the top end. 

Predicted Performance of current gear ratio 3:1 from Matlab

       Top speed graph

(reaches top speed around 76 MPH around 40 secs under max acceleration)

0-60MPH graph

(time to reach 0-60MPH is around 13 secs)

Maximum Torque at the wheel graph

(Provides a maximum torque of 400 N-m to the wheels without slipping)

Maximum Acceleration graph

(The maximum acceleration is around 0.32 g)

Components:

Emrax 208 Motor

 

Related Documents:

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 04/02/21
7 Full integration motor controller, cooling system, and drivetrain on chassis to do a physical load test to test the torque on the drivetrain 03/05/22
6 Develop a better system model with real data on a testing bench for the torque output of the motor with increasing load. Completed
5 The drivetrain is fully fitted with a motor controller, cooling, and the necessary electronics to collect data without load for the output torque in a controlled environment. Completed
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 the drivetrain connected to the wheels. Completed
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. Completed
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

Meet the Team

KaiYuan Ma:

In charge of developing a physics-based model to simulate the 0-60 Max acceleration/ TopSpeed/Maximum G-force as well as doing Finite Element analysis on the drivetrain components which includes both sprockets, drivetrain housing, bolts, and plate spacers. Moreover, in charge of Matlab code to perform analysis for drivetrain efficiency and plot appropriate data for easy interpretation and presentation, update the website and keep the sub-team to beat the deadlines, and do research for future improvement. Last but not least,  also participate in taking measurements in the lab as well as manufacturing and assembly.

Kyle Flanagan:

In charge of assembly, manufacturing, editing the website, writing Reports for various testing plans, calculating budget as well as handling manufacturing of the CAD files for final assembly. And also in charge of order missing parts needed for final assembly and as well as keeping the club updated. Last but not least,  also participate in FE analysis on drivetrain components and research future improvement.

Additional  Documentation

  • Drivetrain Poster (Drivetrain Poster) (Last Updated: 2021)
  • Initial Tech Readiness Report (Report) (Last Updated: 9/22/21)
  • General overview from Past Team (file) (Last Updated: 2021)