Abstract: A spark plug for an internal combustion engine includes a housing, an insulator, a center electrode, a ground electrode, and a plug cover. The housing has a cylindrical shape. The insulator is held on an inner side of the housing. The insulator has a cylindrical shape. The center electrode is held on an inner side of the insulator. The ground electrode forms a discharge gap with the center electrode. The plug cover, together with the housing, configures an auxiliary combustion chamber in which the discharge gap is arranged. The plug cover includes a spray hole that communicates between the inside and outside of the plug cover. The ground electrode is connected to a plurality of locations on an auxiliary-chamber inner wall surface that includes surfaces of the housing and the plug cover that are exposed to the auxiliary combustion chamber.

Abstract: A spark plug for an internal combustion engine includes a housing, an insulator, a center electrode, a ground electrode, and a plug cover. The housing has a cylindrical shape. The insulator is held on an inner side of the housing. The insulator has a cylindrical shape. The center electrode is held on an inner side of the insulator. The ground electrode forms a discharge gap with the center electrode. The plug cover, together with the housing, configures an auxiliary combustion chamber in which the discharge gap is arranged. The plug cover includes a spray hole that communicates between the inside and outside of the plug cover. The ground electrode is connected to a plurality of locations on an auxiliary-chamber inner wall surface that includes surfaces of the housing and the plug cover that are exposed to the auxiliary combustion chamber.

Abstract: When a driving region of an engine is in a specified self-ignited combustion region, a valve timing is controlled in such a manner as to establish a negative valve overlap period in which an exhaust valve and an intake valve are closed. During the negative valve overlap period, a direct injection is performed to reform a fuel. After the direct injection, a port injection is performed to control an output. Thereby, a self-ignited combustion control is performed. During the self-ignited combustion control, a fuel reform degree of the fuel injected by the direct fuel injection is detected, and a self-ignited combustion condition in a present combustion cycle is estimated based on the fuel reform degree detected in the present combustion cycle. A fuel injection quantity of the intake port fuel injection is corrected according to the estimated self-ignited combustion condition in order to stabilize the self-ignited combustion condition.

Abstract: An ON-ignition signal is outputted from an ignition control portion in a period from a posterior time point of the power stroke to an valve opening timing of an exhaust valve so that a capacitor is charged. Then, when it is determined that the maximum value of an ion-output value detected during a negative valve overlap period becomes greater than or equal to a threshold, it is determined that the applied voltage between an center electrode and a ground electrode of a spark plug is dropped. The ON-ignition signal is outputted again to charge the capacitor before the intake valve is opened.

Abstract: When an engine is driven in a compression self-ignited combustion region, a fuel injector injects a fuel into a cylinder in a negative-valve-overlap period where an exhaust valve and an intake valve are both closed. Then, the fuel is injected into the cylinder in an intake stroke. The injected fuel is compressed in a compression stroke to be self-ignited. When it is determined that a steep combustion occurs and a fuel injection quantity in the negative-valve-overlap period is greater than a lower determination threshold, the fuel injection quantity in the negative-valve-overlap period is reduced. When the fuel injection quantity is not greater than the lower determination threshold, an oxygen quantity in the cylinder is reduced.

Abstract: A controller performs compression self-ignition combustion control for combusting a mixture gas by injecting fuel into a cylinder in a negative valve overlapping period (NVO period), in which both of an exhaust valve and an intake valve are closed, and by causing self-ignition of the mixture gas using compression in a compression stroke. If knocking is detected during the above control, the controller performs knock suppression control for correcting a fuel injection quantity in the NVO period to suppress the knocking. If a pressure increase rate of cylinder pressure during the combustion is lower than a threshold value, the controller performs increase correction of the fuel injection quantity in the NVO period. If the pressure increase rate is equal to or higher than the threshold value, the controller performs decrease correction of the fuel injection quantity in the NVO period.

Abstract: An ON-ignition signal is outputted from an ignition control portion in a period from a posterior time point of the power stroke to an valve opening timing of an exhaust valve so that a capacitor is charged. Then, when it is determined that the maximum value of an ion-output value detected during a negative valve overlap period becomes greater than or equal to a threshold, it is determined that the applied voltage between an center electrode and a ground electrode of a spark plug is dropped. The ON-ignition signal is outputted again to charge the capacitor before the intake valve is opened.

Abstract: When a driving region of an engine is in a specified self-ignited combustion region, a valve timing is controlled in such a manner as to establish a negative valve overlap period in which an exhaust valve and an intake valve are closed. During the negative valve overlap period, a direct injection is performed to reform a fuel. After the direct injection, a port injection is performed to control an output. Thereby, a self-ignited combustion control is performed. During the self-ignited combustion control, a fuel reform degree of the fuel injected by the direct fuel injection is detected, and a self-ignited combustion condition in a present combustion cycle is estimated based on the fuel reform degree detected in the present combustion cycle. A fuel injection quantity of the intake port fuel injection is corrected according to the estimated self-ignited combustion condition in order to stabilize the self-ignited combustion condition.