It may be desirable for a vehicle to decelerate at a predetermined rate during select vehicle operating conditions. For example, if a driver fully releases an accelerator pedal, it may be desirable for the vehicle to decelerate at a predetermined rate until the vehicle reaches a creep speed. The vehicle braking may be provided via an engine providing a negative torque to the vehicle driveline. The negative driveline torque is applied to the vehicle's wheels to decelerate the vehicle. One way to apply a negative torque to the driveline via the engine is to enter a deceleration fuel shut off mode (DFSO) or deceleration fuel cut off mode. In DFSO mode, fuel supplied to one or more engine cylinders ceases or is shut off so that combustion ceases in cylinders with fuel shut off, thereby deactivating the cylinders. Deactivated cylinders may induct air from the engine's intake manifold and expel the air to the engine's exhaust system without the air participating in combustion. Pumping air through the engine provides a negative torque to the driveline via the engine and it converts the vehicle's kinetic energy into heat and torque to keep the engine spinning. However, the vehicle's kinetic energy is not recoverable or reusable when it is transformed into heat and torque to rotate the engine.
The inventors herein have recognized the above-mentioned issues and have developed a powertrain operating method, comprising: providing a negative input torque to a transmission via a motor in response to the motor being available to supply the negative input torque and driver demand torque less than a threshold; and providing the negative input torque to the transmission via an engine operating in a deceleration fuel cut off mode in response to the motor being unavailable to supply the negative input torque and the driver demand torque less than the threshold.
By providing negative driveline torque via a motor when the motor is available to provide the negative driveline torque, a vehicle's kinetic energy can be stored as electrical energy to conserve power. However, during conditions where the motor is not available to convert the vehicle's kinetic energy to electrical energy, the vehicle's engine may provide the requested driveline braking so that the vehicle may decelerate at a desired rate. Further, a torque converter clutch unlocking schedule based on whether or not the motor is available to provide a negative torque to the driveline schedules torque converter unlocking according to a first torque converter clutch unlocking schedule when the motor is available to provide a desired braking torque to the driveline. Torque converter unlocking is scheduled according to a second torque converter clutch unlocking schedule when the motor is not available to provide a desired braking torque to the driveline.
The present description may provide several advantages. For example, the approach may improve utilization of a vehicle's kinetic energy. Further, the approach may reduce driveline torque disturbances. In addition, the approach may provide improved torque converter clutch control.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.