Interdisciplinary Challenges
The powertrain combines challenges from mechanical and electrical engineering. To implement wheel-hub motors, the electrical motors and the gearbox must be tightly packaged and the design must be well-coordinated. Adding to the interdisciplinary character of the assembly, cooling and control systems needed to be designed from scratch as well.
About our Powertrain
The powertrain pushes our car forward and has a great impact on the overall car performance. For the first time in the history of KaRaT we use a 4WD concept for the 2021 season. This enables us to develop much more precise power delivery in all situations. This search for optimal performance goes hand in hand with the control units inside the drivetrain and provides exciting new challenges.
Technical highlights
Take a look at the key components of our powertrain and our supporters!
Motors
Powerhouse directly at the wheel-hub
For the first tim in KaRaT-history, we are implementing wheel-hub motors. By having a motor per wheel, we are able to fully control the vehicles behaviour and maximize traction.
- 4 synchronous motors with up to 35kW each
- up to 29.1Nm of torque per motor (without gearbox)
- lightweight aluminum rotor shafts
- up to 20.000 rpm
Gearbox
Design based on vi-suspensionGen
The 35kW and 20.000rpm of the motor need to be delivered to the road. For this purpose, as a first-year design, we use a 1,5-step planetary gearbox with a total gear ratio of about 11:1.
The output shaft of the motor serves as the sun of the gearbox. Having a stationary ring gear mounted to the upright, the carrier of our planetary pins transfers the rotational movement to the wheel.
Power Electronics
Getting the power from the accumulator to the motor
We use two twin-inverters from Lenze which are optimised for mobile applications. To ensure a 50:50 weight balance, one is placed at the rear of the car while the other one is located beneath the knees of the driver.
But, performance does not only come with powerful components alone. They need to work together across a variety of situations and thereby ensure maximum power delivery at any moment. Control algorithms need to be programmed and optimised to reach that goal.
Wheel Hubs
HIghly Integrated Design
Our wheel hubs also serve as the output shaft of our gearbox. Therefore, they have to withstand heavy loads and are heavily constrained regarding the geometry to allow for the gearbox to fit inside. For this reason, they are also made out of two parts.
To fasten our wheels, we use a single nut as a centerlock. Hard anodizing ensures a surface which can withstand the forces acting on the threading of this centerlock.
Cooling
Custom Watercooling to ensure maximum performance
Having more and more powerfull compoents than in previous seasons, we also need to stack up our cooling. Two separate circuits cool each one inverter with two motors by using a radiator located on top of the diffusor at the rear of the car.
Fluid simulation was used to design a cooling structure at the motors with maximum efficiency.