Engine retard operation scheduling and management in a hybrid vehicle
A hybrid vehicle includes a powertrain having a retarded diesel engine, an electric machine and energy storage system. The engine and motor are operatively coupled through one or more planetary gearsets and selective coupling paths in accordance with application and release of various torque transfer devices to a drivetrain via an output. Regenerative and retarded engine braking are coordinated to provide priority to energy return to an energy storage system in accordance with predetermined power flow limits.
1. Method for controlling retarded engine operation to effect a desired powertrain brake torque in a hybrid powertrain including an unthrottled engine having an engine retard mechanism and an electrically variable transmission having at least one motor operative in a regenerative mode to provide a regenerative brake torque contribution and an energy storage system, comprising:
providing a desired engine brake torque contribution;
requesting retarded engine operation based on energy storage system power flow and charge power limit; and
enabling retarded engine operation when the desired engine brake torque contribution exceeds by a predetermined amount the brake torque available from simple motoring of the engine, and non-engine related powertrain constraints do not limit engine brake torque beyond a predetermined amount.
2. The method as claimed in claim 1 wherein retarded engine operation is requested when power flow into the energy storage system exceeds a predetermined limit.
3. The method as claimed in claim 1 wherein retarded engine operation is not requested when the energy storage system power capacity exceeds the power being dissipated by retarded engine operation.
4. The method as claimed in claim 1 further comprising providing a desired retarded engine speed and requesting retarded engine operation based on desired retarded engine speed and a desired retarded engine speed limit.
5. The method as claimed in claim 1 further comprising providing a desired retarded engine speed and requesting retarded engine operation based on desired retarded engine speed and a desired retarded engine speed limit.
6. Method for scheduling retarded engine operation to effect a desired powertrain brake torque in a hybrid powertrain including an engine including an engine retard mechanism and an electrically variable transmission having at least one motor operative in a regenerative mode to provide a regenerative brake torque contribution and an energy storage system, comprising:
providing a desired engine braking torque;
determining whether engine retard operation is enabled based on available simple engine motoring torque, available retarded engine braking torque and desired engine braking torque;
determining whether engine retard operation is inhibited based on transmission constraints which affect feasible braking torque;
determining whether engine retard operation is requested based art energy storage system power flow and charge power limit; and
scheduling engine retard operation based on the enablement of, inhibition of and request for engine retard operation.
7. The method as claimed in claim 6 further comprising freezing the scheduled engine retard operation while a transmission shift is in progress.
8. The method as claimed in claim 6 further comprising overriding engine retard operation based on a high priority condition selected from the group consisting of throttle depression, auxiliary brake request and anti-lock brake active.