Accuracy of EDR During Rotation on Low Friction Surfaces

The accuracy of the Powertrain Control Module Event Data Recorder was tested during vehicle yaw and rotation on a flooded skid pad at the Michigan State Police training facility in Lansing, MI. The low friction of the skid pad allowed longer, slower rotations that allowed more detailed study of the behavior. The vehicle was deliberately put into rotation and allowed to rotate to rest under three different conditions: heavy throttle applied initially, heavy braking applied and held, and light to no throttle applied. Six runs were made under each condition. Data was collected from the PCM EDR and compared to a VBOX III (with IMU) 100 Hz differential GPS speed and yaw rate measurement system from which slip angle could be calculated. Graphs of PCM speed/brake/accel pedal data versus time showing VBOX speed and the cosine of the slip angle (where 1 = moving straight ahead and 0 = moving sideways) are presented. Under heavy throttle the tires break loose and spin up resulting in the PCM over-reporting ground speed regardless of slip angle. During braking the PCM under reports ground speed consistently, and as the rotation approaches 90 degrees and the wheels are scrubbing sideways and not rolling, the reported speed drops to or near zero. With light to no throttle the speed reported shows partial correlation to the slip angle cosine. In some cases as the vehicle rotation continues past 90 to 180 or 270 to 360 degrees, the tires begin rolling again and the EDR reported speed recovers to the near the actual speed.