Method of braking in hybrid vehicle

摘要

A method of operating a hybrid electric vehicle coordinates operation of an internal combustion engine, a motor, and friction brakes to mitigate a driveline lash crossing without delaying generation of negative torque. In response to a request to transition from positive torque to negative torque, the engine and motor are controlled to rapidly reduce powertrain torque to a small positive value, slowly reduce powertrain torque through the driveline lash zone, and then rapidly reduce powertrain torque to the target. To avoid delay, the friction brakes are applied in a coordinated manner to supply the negative torque during the transition.

主权项

1. A hybrid electric vehicle comprising:
a driveline configured to deliver a powertrain torque to vehicle wheels; friction brakes configured to deliver a braking torque to the vehicle wheels; an internal combustion engine configured to deliver positive torque to the driveline; an electric motor configured to alternately deliver positive and negative torque to the driveline; and a controller programmed to respond to a request to transition from positive wheel torque to negative wheel torque by
commanding the engine and electric motor to reduce the powertrain torque from an initial positive value to a positive threshold value at a first rate of change,commanding the brakes to exert a brake torque while commanding the engine and electric motor to reduce the powertrain torque from the positive threshold value to a negative threshold value at a second rate of change having a magnitude less than a magnitude of the first rate of change to mitigate a lash crossing disturbance, andcommanding the brakes to increase the brake torque to zero while commanding the electric motor to reduce the driveline torque from the negative threshold value to a target negative value at a third rate of change having a magnitude greater than the magnitude of the second rate of change.