Methods and systems are provided for operating a split exhaust engine system that provides blowthrough air and exhaust gas recirculation to an intake passage via a first exhaust manifold and exhaust gas to an exhaust passage via a second exhaust manifold. In one example, an air-fuel control method for the engine system may include flowing air from the intake manifold through a plurality of engine cylinders to a junction of the exhaust passage and a bypass passage in response to a condition, the junction positioned along the exhaust passage between first and second emission control devices. The method may further include flowing exhaust gas to the first emission control device while flowing the air to the junction.

A control device for an engine is provided, which includes a combustion chamber formed by a cylinder and a piston, an intake air amount adjuster that adjusts an intake air amount supplied to the combustion chamber, a controller switchable of a combustion mode between a fuel-lean first combustion mode and a stoichiometric second combustion mode based on an engine operating state, and an intake air cooler that cools the intake air supplied to the combustion chamber. The controller controls the intake air cooler to start intake air cooling in response to a request for switching the combustion modes, and after the intake air cooling is started, controls the intake air amount adjuster to start the switching of the combustion modes, and then controls the intake air cooler and the intake air amount adjuster so that the switching of the combustion modes ends after the intake air cooling is finished.

Methods and systems are provided for extending a duration of engine idle-stop while reducing a frequency of engine restart from idle-stop. In one example, in response to engine restart conditions where combustion torque is not necessary, an engine can be rotated electrically, without fuel delivery, via an electric motor. The unfueled engine spinning via the motor drives an FEAD which in turns drives an actuator coupled to the FEAD, such as an AC compressor or an automatic transmission oil pump.

A method for controlling the air-fuel ratio of a vehicle includes: calculating the air amount charged in a cylinder of an engine by using a fresh air amount, a residual air amount remaining inside the cylinder of the engine, and a backflow gas amount flowing back into the cylinder upon the valve overlap of an intake vale and an exhaust valve of the engine, correcting it with the purge gas flow rate supplied to an intake manifold of the engine when the active purge system is operated, calculating the final fuel amount by correcting the fuel amount injected by a fuel injection device with the amount of the fuel component contained in the purge gas when the active purge system is operated, and controlling the air-fuel ratio based on the final air amount and the final fuel amount.

A compression-release brake system for operating an exhaust valve of an engine during an engine braking operation. The compression-release brake system comprises a self-contained compression brake control module (CBCM) operatively coupled to the exhaust valve for controlling a lift and a phase angle thereof. The CBCM includes a casing defining an actuator cavity, a actuation piston disposed outside the casing so as to define an actuation piston cavity between the casing and the actuation piston, and a check valve provided between the actuation piston cavity and a compression brake actuator disposed in the actuator cavity. The actuation piston reciprocates relative to the casing. The compression brake actuator includes an actuator element and a biasing spring. The actuator element selectively engages the check valve when deactivated so as to unlock the actuation piston cavity and disengages from the check valve when activated so as to lock the actuation piston cavity.

A method for operating a reciprocating piston internal combustion engine in an engine braking mode includes moving an outlet valve of a first cylinder for a first time into a closed position, subsequently for a first time into an open position, subsequently in a direction of the closed position, and subsequently for a second time into the open position. The outlet valve is held open during the moving in the direction of the closed position for such a long time that the first cylinder is filled with gas which flows via an outlet duct out of a second cylinder. The outlet valve is moved, during the moving in the direction of the closed position, into an intermediate position which lies between the open position and the closed position, where from the intermediate position the outlet valve is moved for the second time into the open position.

Systems and methods for opening and closing exhaust poppet valves of an engine are disclosed. In one example, the exhaust poppet valves may be opened and closed twice during a cycle of an engine via two serially arranged cam lobes that are coupled to a crankshaft so that hydrocarbons may be retained in a cylinder.

A variable control method of exhaust temperature increase includes, when a cam phaser, which is connected to a double cam shaft having a coaxial arrangement structure of an outer shaft and an inner shaft, is operated and when a cam angle is determined as being varied by a controller, a cam phaser position change control is performed of decreasing a flow rate of an internal exhaust gas recirculation (EGR) supplied to a cylinder of an engine with a cam advance angle, increasing the flow rate of the EGR with a cam retard angle, or blocking the flow rate of the EGR with a maximal cam advance angle.

Methods and systems are provided for operating a split exhaust engine system that provides blowthrough air and exhaust gas recirculation to an intake passage via a first exhaust manifold and exhaust gas to an exhaust passage via a second exhaust manifold. In one example, the engine system may be installed in a hybrid vehicle, and, in response to a request to restart the engine while the vehicle is being propelled via motor torque only, the engine may be rotated unfueled via the motor torque at less than cranking speed while at least partially opening a valve disposed in a passage coupled between the first exhaust manifold and the intake passage. In another example, in response to the request to restart the engine, all exhaust valves of a second set of exhaust valves coupled to the second exhaust manifold may be deactivated.

Methods and systems are provided for extending a duration of engine idle-stop while reducing a frequency of engine restart from idle-stop. In one example, in response to engine restart conditions where combustion torque is not necessary, an engine can be rotated electrically, without fuel delivery, via an electric motor. The unfueled engine spinning via the motor drives an FEAD which in turns drives an actuator coupled to the FEAD, such as an AC compressor or an automatic transmission oil pump.