People

Christopher R. Carlson

Description

Accurate estimation of tire force-slip characteristis requires measurement of vehicle acceleration, velocity and wheelspeeds. Until recently it has been difficult to measure absolute vehicle velocity, estimation schemes relied on some sort of state observers and intertial sensors. Recent work here at Stanford uses GPS velocity to directly measure absolute velocity accurate to 2 [cm/s].

Several research groups propose that tire longitudinal stiffness at low values of slip may indicate the tire to road friction coefficient and thus the peak value of the force slip curve. Our work here shows that longitudinal stiffness estimates exhibit considerable sensitivity to tire inflation pressure, normal loading, tread depth and temperature. This suggests that any analysis which seeks to identify these properties must carefully account for at least these test conditions.

Talks

• Nonlinear Least Squares Estimation of Longitudinal Slip and Effective Radius

• Introduction to Total Least Squares Parameter Estimation

• AVEC2002 Talk on estimating inflation pressure, wheel slip and tire properties.

• Most recent results as of December 2002, includes a more complete test matrix, including inflation pressure, tire type, road surface and normal loading. Publication to appear, ACC 2003.

Publications

• Calculating Longitudinal Wheel Slip and Tire Parameters Using GPS Velocity, ACC 2001

• Identifying Tire Pressure Variation by Nonlinear Estimation of Longitudinal Stiffness and Effective Radius, AVEC 2002

• Nonlinear Estimation of Longitudinal Tire Slip Under Several Driving Conditions, ACC 2003

Links

• NHTSA tire pressure monitoring systems report