Vehicle engine torque control with engine drag control mode

Abstract

A vehicle powertrain torque control provides an engine drag control mode of operation during periods of undesired engine drag induced wheel slip by modifying the torque of the vehicle engine in closed loop control to maintain a driven wheel speed at a predetermined target velocity lower than the vehicle speed by a target velocity difference providing as much engine braking as is consistent with a desired degree of lateral traction. The control derives a velocity error as the difference between the driven wheel speed and the target velocity and derives and delivers to the powertrain a torque command for reducing the velocity error. The torque control determines the engine drag control mode in response to the wheel speed sensors, preferably causing entry of the engine drag control mode when the driven wheel speed that is closest to the vehicle speed falls below the target velocity while powertrain delivered torque and throttle position are below predetermined values indicative of deceleration. The target velocity difference is preferably determined as a weighted difference between vehicle speed and vehicle turn curvature, the difference being reduced by the latter for quicker response in vehicle turns.