Most cars on the road today are FWD based and send power to the rear when front wheel spin occurs. The control of how much power sent to the rear is usually done by either viscous coupler or an electromagnetic clutch in the rear differential. The Mazda’s use an electromagnetic clutch that operates on pulse width modulation (PWM) from the car's computer. When the front wheels spin, a PWM 12v signal is sent to the electromagnetic clutch, thus spinning the rear wheels when needed. The PWM duty cycle is dependent on how much power is needed in the rear when front wheel spin occurs. The computer knows when the front wheels spin from the ABS sensors or wheel speed sensors at each wheel. The plan is to use a Raspberry Pi B+ and reconfigure the electromagnetic clutch operation to be customized when racing. The inputs would be ABS sensor from each wheel (analog voltage converted to speed in mph) and accelerator pedal position (0 to 100% pedal position). The output would be the 12V PWM signal to the electromagnetic clutch. A library is currently being created with friends to run through all the different scenarios of the factory traction control system. Next steps are to hook up an oscilloscope to each ABS sensor and the PWM output, then record data while driving the car around. Solid state relay cannot cycle fast enough, so circuit design from converting Raspberry Pi B+ PWM signal to 12V PWM is still being explored.
Figure 1: Electromagnetic clutch found in Mazdaspeed6; pulled out for testing.
Levon Markossian - 2021