PROBLEM TO BE SOLVED: To precisely estimate a surface friction coefficient in a short time.;SOLUTION: A reference yaw angle acceleration arithmetic part 5 calculates a reference yaw angle acceleration on the basis of steering angle δ, yaw rate γand lateral acceleration Gy supplied from a filter 4. The yaw rate γ supplied from the filter 4 is differentiated to calculate actual yaw angle acceleration. A computing element 7 subtracts the reference yaw angle acceleration from the actual yaw angle acceleration to calculate residual error err. A minimum square method arithmetic part 8 calculates the inclination a of the lateral acceleration Gy to the residual error err. A μ estimation part 9 estimates surface friction coefficient μ, when it is judged that the inclination a exceeds a prescribed threshold TH, on the basis of the lateral acceleration Gy at that time.;COPYRIGHT: (C)2003,JPO
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