Hybrid powertrain architectures comprise torque-generative devices, including internal combustion engines and electric machines, which transmit torque through a transmission device to a vehicle driveline. A hybrid powertrain architecture reduces fuel consumption through the engine by shutting off the engine at opportune moments during ongoing vehicle operation, including events such as the vehicle stopped at a light or in traffic, or when the vehicle is operating on a downhill portion of a highway. A powertrain architecture includes, e.g., an engine and transmission system controlled and mechanized to shut off the engine, and restart it using a belt drive through an alternator, often referred to as a belt-alternator-starter (BAS) device. Other powertrain architectures include engine and transmission systems wherein one or more electrical motors generate motive torque which is transmitted to the vehicle driveline directly or through the transmission.
One such transmission includes a two-mode, compound-split, electro-mechanical transmission which utilizes an input member for receiving motive torque from a prime mover power source, typically an internal combustion engine, and an output member for delivering motive torque from the transmission to the vehicle driveline. Electrical machines, operatively connected to an electrical energy storage device, comprise motor/generators operable to generate motive torque for input to the transmission, independently of torque input from the internal combustion engine. The electrical machines are further operable to transform vehicle kinetic energy, transmitted through the vehicle driveline, to electrical energy potential that is storable in the electrical energy storage device. A control system monitors various inputs from the vehicle and the operator and provides operational control of the powertrain system, including controlling transmission gear shifting, controlling the torque-generative devices, and regulating the electrical power interchange between the electrical energy storage device and the electrical machines.
The exemplary electro-mechanical transmissions are selectively operative in fixed gear modes and continuously variable modes through actuation of the torque-transfer clutches, typically employing a hydraulic circuit to effect clutch actuation, including fixed gear modes and continuously variable modes. Engineers implementing powertrain systems having electro-mechanical transmissions are tasked with implementing control schemes to monitor system states and control operation of various systems and actuators to effectively control powertrain operation.
Operation of the powertrain system includes selectively starting and stopping operation of the internal combustion engine. Engine stopping can be operator-initiated, wherein the vehicle operator stops the engine operation by way of a key-off crank action. Engine stopping further comprises automatic engine stop events during ongoing vehicle operation, wherein the engine is automatically stopped by the control system. This typically occurs in response to a control system determination of an opportunity to stop the engine and referred to as a quiescent auto-stop event. The control system selectively stops operation of the internal combustion engine to optimize energy efficiency, and for other reasons.
During an engine stop event, compression torque pulses are generated in unfired engine cylinders and transmitted to a transmission torque damper and the engine block, which may result in objectionable vibrations reaching the vehicle operator, especially at resonant frequencies for the powertrain and various driveline components.
There is a need for a control scheme which effectively stops operation of an internal combustion engine and accommodates pressure pulses and vibrations including during ongoing vehicle operation. Such a system is described hereinafter.