Methods and system for skip-firing of an engine

A method for an engine, comprising:

• determining when to initiate a skip-fire mode based on engine operating conditions including one or more of engine speed, commanded fuel injection amount, engine load, fuel rail pressure, or fuel injector pulse-width;
• initiating the skip-fire mode in response to the engine operating conditions decreasing below a threshold;
• closing intake valves of non-firing cylinders during power or exhaust strokes of the non-firing cylinders;
• and
• determining a number of cylinders to skip during the skip-fire mode based on one or more of engine speed, fuel demand, exhaust gas temperature, or exhaust gas oxygen concentration, and further comprising determining which cylinders to skip based on the number of cylinders to be skipped and a pre-set pattern for controlling engine vibration, power, and speed stability.

A method for an engine, comprising:

• determining when to initiate a skip-fire mode based on engine operating conditions including one or more of engine speed, commanded fuel injection amount, engine load, fuel rail pressure, or fuel injector pulse-width;
• initiating the skip-fire mode in response to the engine operating conditions decreasing below a threshold;
• closing intake valves of non-firing cylinders during power or exhaust strokes of the non-firing cylinders;
• determining a number of cylinders to skip during the skip-fire mode based on one or more of engine speed, fuel demand, exhaust gas temperature, or exhaust gas oxygen concentration, and further comprising determining which cylinders to skip based on the number of cylinders to be skipped and a pre-set pattern for controlling engine vibration, power, and speed stability;
• and
• determining a firing frequency for each firing cylinder over an upcoming threshold number of engine cycles based on the number of cylinders to be skipped during each engine cycle and a desired firing pattern for each engine cycle.

A method for an engine, comprising:

• determining when to initiate a skip-fire mode based on engine operating conditions including one or more of engine speed, commanded fuel injection amount, engine load, fuel rail pressure, or fuel injector pulse-width;
• initiating the skip-fire mode in response to the engine operating conditions decreasing below a threshold;
• closing intake valves of non-firing cylinders during power or exhaust strokes of the non-firing cylinders;
• and
• initiating the skip-fire mode in response to a determination that one or more fuel injectors or cylinders of the engine is degraded and, in response to initiating the skip-fire mode in response to the determination that one or more fuel injectors or cylinders of the engine is degraded, calling for a service interruption to implement a corrective action to service the degraded fuel injector or cylinder.

A system for an engine, comprising:

• a plurality of engine cylinders, each cylinder including:
• a first intake valve actuator mechanically driven by a crankshaft;
• and
• a second intake valve actuator not driven by the crankshaft;
• and
• a controller with computer readable instructions stored in non-transitory memory for:
• not injecting fuel into all of the plurality of engine cylinders when fueling demands decrease below a threshold;
• adjusting intake valves of firing cylinders via the first intake valve actuator;
• adjusting intake valves of non-firing cylinders via the second intake valve actuator;
• and
• wherein the controller is electrically coupled to each second intake valve actuator for adjusting the position of the intake valves independently of the crankshaft by adjusting command signals sent to each second intake valve actuator and wherein the computer readable instructions further include instructions for maintaining the intake valves of non-firing cylinders open after the intake valves of firing cylinders are closed by the first intake valve actuator.