Patent ID: 8204664

Claim:
Method for controlling braking in a vehicle including a friction braking system and a powertrain system including a torque machine operative to react tractive torque input from a wheel of the vehicle, a microprocessor performs the following steps: monitoring operation of the powertrain system; determining a driver intended total brake torque; determining a regenerative braking capacity based upon the operation of the powertrain system; determining a regenerative braking request based upon a time-rate change in the regenerative braking capacity comprising determining the regenerative braking request based upon the regenerative braking capacity modified using a first slope regulating function when the time-rate change in the regenerative braking capacity exceeds a threshold and determining the regenerative braking request based upon the regenerative braking capacity modified using a second slope regulating function when the time-rate change in the regenerative braking capacity is within the threshold; and determining a motor torque command for the torque machine based upon the regenerative braking request; wherein determining the regenerative braking request based upon the regenerative braking capacity modified using the first slope regulating function when the time-rate change in the regenerative braking capacity exceeds the threshold comprises applying a three-term Weibull function in a forward-fitting large curve fit operation to maximize the regenerative braking request based upon the regenerative braking capacity; and wherein determining the regenerative braking request based upon the regenerative braking capacity modified using the second slope regulating function when the time-rate change in the regenerative braking capacity is within the threshold comprises applying a three-term Weibull function in a forward fitting small curve fit operation to maximize the regenerative braking request based upon the regenerative braking capacity.