Multi-stroke variable displacement engine

#Some vehicles include engines that may be partially deactivated to increase the fuel efficiency by reducing the effective displacement of the engine during select operating conditions. As such, some engines may be referred to as having a variable displacement capability, whereby combustion in one or more cylinders of the engine may be temporarily deactivated or discontinued while other cylinders of the engine continue to carry out combustion. Where increased engine output is requested by the vehicle operator, the deactivated cylinders may be activated by once again performing combustion to thereby increase the effective engine displacement and provide the requested engine output to the vehicle operator.

#The inventors of the present disclosure have recognized a disadvantage with the above approach. As one example, the inventors have recognized that during some conditions the above approach may result in frequent transitions from a deactivated state of the cylinders to an activated state where combustion is performed. These transitions may increase noise, vibration, and harshness (NVH) of the engine that may be perceived by the vehicle operator. Additionally, fuel efficiency may be reduced where frequent transitions between active and deactivated states are performed by the engine. As such, engines having this variable displacement capability may exhibit only limited fuel efficiency improvements while perceived drivability of the vehicle from an operator's perspective may be reduced.

#As a non-limiting example, at least some of the above issues may be addressed by a method of operating a vehicle propulsion system, comprising: operating an engine to produce an engine output; transferring the engine output to one or more drive wheels via a transmission; responsive to a first condition, varying torque supplied to the drive wheels by adjusting a relative number of combusting cylinders and deactivated cylinders of the engine; and responsive to a second condition, varying the torque supplied to the drive wheels by adjusting a number of strokes performed by the combusting cylinders per combustion cycle while shifting the transmission between different gear ratios.

#FIG. 1 illustrates an example multi-stroke variable displacement internal combustion engine arranged in a vehicle propulsion system.

#FIG. 2 illustrates a flow chart depicting an example process flow that may be used to control the engine of FIG. 1.

#FIG. 3 depicts an example map that may be used by the control system to control the engine of FIG. 1 in accordance with the process flow of FIG. 2.

#FIG. 1 illustrates a multi-stroke variable displacement internal combustion engine 100. Engine 100 may include one or more combustion chambers or cylinders 110, a non-limiting example of which is depicted schematically in FIG. 6. In some embodiments, engine 100 may be configured as a component of a vehicle propulsion system. For example, engine 100 may be operatively coupled with one or more drive wheels indicated schematically at 130 via a transmission 140. In other embodiments, engine 100 may be configured as a component of a power generation system, and may be optionally coupled with an electrical generation device such an electric machine.

#Transmission 140 may include a plurality of selectable gear ratios. As will be described in the context of FIGS. 7 and 8, the transmission may be transitioned between two or more of these gear ratios responsive to the particular operating mode of the engine. For example, at least some of the engine cylinders may include multi-stroke cylinders, which are configured to selectively carry out a multi-stroke operation. A multi-stroke operation may include adjusting a number of strokes performed by the multi-stroke cylinder per cycle. As a non-limiting example, a multi-stroke cylinder may be operated in a four stroke cycle under some conditions and may be operated in a two stroke cycle under other conditions.

#At least some of the engine cylinders may include variable displacement cylinders, which are configured to selectively carry out a deactivation operation. A deactivation operation may include discontinuing combustion of air and fuel within the deactivated variable displacement cylinder for one or more cycles. While the variable displacement cylinders are in a deactivated state, other cylinders of the engine, such as the multi-stroke cylinders may continue to carry out combustion, thereby enabling the engine to be operated with a reduced effective displacement.