Managing engine retarding torque during coast mode

摘要

When a vehicle is in coast mode (zero engine fuelling) and an engine compression brake operation is enabled, the currently engaged gear ratio or vehicle speed is determined. To prevent overloading of the drive train components, in particular the axle assembly, due to the engine retarding torque, the retarding torque is maintained below the known coast mode torque capacity of the drive train taking account of the gear ratio or vehicle speed. The retarding torque may be reduced by altering turbocharger boost (wastegate settings), deactivating engine accessories such as the cooling fan or air-conditioning unit, or changing the engine braking settings (number of engine exhaust valves controlled). Coast mode can be detected by the accelerator pedal position, or fuelling rate when cruise control is in operation. Engine retarding torque may be determined from boost pressure and compression brake setting, or from engine or vehicle deceleration and road inclination measurements.