IMU Based Velocity Estimation Impact on Stopping Distance for Heavy-Duty Class 8 Truck Air Brake Systems with ABS

An accurate estimate of vehicle speed is essential for optimal anti-lock braking system (ABS) calculations. Currently, most vehicles including heavy-duty class 8 trucks mainly rely on wheel speed sensors (WSS) to estimate velocity. However, as soon as braking is applied, WSS become inaccurate for determining the velocity due to the longitudinal slip developed in the tires. Using the inertial measurement unit (IMU) to estimate vehicle speed allows for its use in conjunction with the WSS to accurately calculate the slip ratio at each tire. These slip ratio values can then be used as the main control variable in the ABS algorithm to utilize the grip available more fully at each tire, to improve stopping distance and controllability. A steady state braking analysis model is developed and validated against Federal Motor Vehicle Safety Standards (FMVSS) 121 60-0 mph stopping distance data for a loaded class 8 tractor semi-trailer combination. Once the model is validated to show good correlation to measured deceleration data, it is used to estimate the theoretical peak steady state deceleration with the ideal slip ratio at each tire. Then a semi-empirical approach is used to consider current air brake system and ABS algorithm capabilities in the analysis. Lastly, the initial transient phase of 60-0 mph stop is accounted for to get a realistic stopping distance improvement estimate for a loaded heavy-duty truck.