A control apparatus for an internal combustion engine performs a first acquisition process for acquiring a first index value corresponding to an integrated amount of intake air during a performance of the fuel cutoff process, and a cancellation process for cancelling the fuel cutoff process when the first index value becomes equal to or larger than a first predetermined value during the performance of the fuel cutoff process. Besides, the control apparatus performs a second acquisition process for acquiring a second index value corresponding to an elapsed time from the end of the fuel cutoff process to the subsequent start of the fuel cutoff process, and a change process for making the first predetermined value smaller when the second index value is small in starting the fuel cutoff process than when the second index value is large in starting the fuel cutoff process.

Engine systems which are safer and have reduced risk of fire are desirable in a wide range of equipment markets. The present engine systems utilize sensors and control systems which reduce the probability of fire or spark exiting the exhaust system. The sensors may monitor a wide range of conditions within the exhaust system to alter the operating parameters of the engine to prevent ignition of objects adjacent the engine system during use. By altering operation of the engine, conditions such as exhaust temperature or unburned fuel can be controlled to minimize risk of undesired ignition.

Methods and systems are provided for maintaining efficiency of a catalyst that is positioned in an exhaust system downstream of an internal combustion engine. In one example, the catalyst may be heated via supplying fuel to a cylinder that does not combust the fuel. The fuel may be oxidized at the catalyst via excess oxygen in the exhaust system.

Systems and methods are provided for diagnosing cylinders in an engine. In one example, the method may include while receiving first feedback from a vibration sensor coupled to a first cylinder of the engine, perturbing the first cylinder during engine operation. Responsive to the first feedback indicating a first vibration level difference greater than or equal to a first threshold difference, a first indication of a first degradation condition of the first cylinder may be set, and thereafter the engine may be operated based on whether or not the first indication was set.

Systems and methods are provided for cooling an overheated engine using a combination of variable displacement engine (VDE) technology and direct injection technology. In one example, a method may include deactivating a subset of engine cylinders based on an engine temperature and directly injecting liquid fuel into the deactivated cylinders. In this way, an increased thermal conductivity of the liquid fuel compared to air decreases the engine temperature at a faster rate than when air-based engine cooling methods are used, thereby preventing overheating-related engine degradation.

An internal combustion engine with a plurality of cylinders is a drive device in which the drive torque available can be reduced. The ignition timing which is set at the internal combustion engine is adjusted in the retarded direction starting from an initial ignition timing until the ignition timing corresponds to a threshold ignition timing. To reduce the drive torque further, at least one cylinder, among the plurality of cylinders, is deactivated by suspending fuel injection into the cylinder, and the remaining cylinder(s) continue to be operated with fuel injection using the ignition timing. The remaining cylinders of the internal combustion engine which continue to be operated are supplied with a quantity of fuel which is larger in comparison with an initial quantity of fuel present before the cylinder deactivation, to set a substoichiometric fuel/oxygen ratio.

A diagnostic system and method that (a) that uses models indicative of both successful firing and skips to determine if cylinders of a skip fire controlled internal combustion engine have successfully fired or successfully skipped and (b) uses filtered exhaust gas pressure readings for detecting faults associated with EGR systems and/or turbocharger systems.

Engine controllers and control schemes are provided for managing engine state transitions requiring increased compressor pressure ratios in turbocharged engines. In some circumstances, turbo lag can be mitigated by initially transitioning the engine to an intermediate engine state that directly or indirectly increases airflow through the engine and turbocharger relative to what would be possible if the engine were immediately commanded to operate at the target engine state. After reaching a point where the desired torque is actually generated at the intermediate engine state, the operational settings are gradually reduced to the target effective firing density while increasing the operational compressor pressure ratio to the target compressor ratio.

A CPU determines that misfires are occurring in a cylinder subject to determination of whether misfires are occurring when a value obtained by subtracting a rotation fluctuation amount ΔT30[n−2] from a rotation fluctuation amount ΔT30[n] is greater than or equal to a determination threshold. The rotation fluctuation amount ΔT30[n] is subject to the misfire determination. The rotation fluctuation amount ΔT30[n−2] is 360° CA earlier than the rotation fluctuation amount ΔT30[n]. When stopping fuel supply to a cylinder #1 and determining whether misfires are occurring in cylinder #4, the CPU determines whether misfires are occurring after executing a correcting process that corrects the determination threshold to a second determination threshold Δth2, which is less than a first determination threshold Δth1.

Methods and systems are provided for providing secondary air to an exhaust system during catalyst warm-up. In one example, a method may include, during a cold start condition, operating an engine with a first number of cylinders unfired and a remaining number of cylinders fired during an engine cycle, opening an intake valve of an unfired cylinder of the first number of cylinders during an expansion stroke of the unfired cylinder, and opening an exhaust valve of the unfired cylinder during a compression stroke of the unfired cylinder. In this way, the unfired cylinders may provide the secondary air to the exhaust system during a stroke that increases mixing of the secondary air with burned exhaust gas from fired cylinders, thus increasing exotherm production in the exhaust system to increase a temperature of the catalyst.