A combustion control system for an engine mounted on an automobile is provided, which includes an ignition plug, intake and exhaust passages, an EGR passage, an EGR valve, and a control device having a processor which controls the ignition plug and the EGR valve according to an engine operating state and reduces deposit being accumulated inside a combustion chamber. The control device performs a control in which an accumulating amount of the deposit is estimated, and a control in which the deposit is removed when the estimated accumulating amount becomes more than a given setting value. In the deposit removal control, a control of the ignition plug in which a mixture gas is caused to combust by igniting the mixture gas, and a control of the EGR valve in which an amount of exhaust gas introduced into the combustion chamber is decreased, are performed.

In a method for controlling an engine, based on a control map of an engine speed N and a fuel injection amount Q of a common-rail fuel injection unit, a controller calculating the fuel injection amount Q depending on the engine speed N, calculating an injection amount deviation Qn as a fuel injection amount increase, and determining that an engine is in a transient state if the injection amount deviation Qn exceeds a reference transient injection amount deviation A2 or if a transient injection amount deviation count Xq is larger than or equal to a reference transient injection amount deviation count X2. If it is determined that the engine is in the transient state, the controller controls an EGR unit and a boost controller according to an excess air ratio that is an indicator indicating the state of the engine.

An exhaust purification system comprises a catalyst 20, an upstream side air-fuel ratio sensor 40, a downstream side air-fuel ratio sensor 41, and an air-fuel ratio control device. The air-fuel ratio control device alternately switches a target air-fuel ratio between a rich set air-fuel ratio and a lean set air-fuel ratio, calculates an oxygen storage amount and an oxygen discharge amount, updates a learning value, and corrects an air-fuel ratio-related parameter based on the learning value. The air-fuel ratio control device changes a condition for switching the target air-fuel, stores the learning value at the time when the operating state of the internal combustion engine changes from the first state to the second state as a first state value, and updates the learning value to the first state value when the operating state of the internal combustion engine returns from the second state to the first state.

Methods and systems are provided for on-board diagnostics of an exhaust gas recirculation (EGR) system of an engine coupled to a hybrid vehicle. In one example, a method may include, upon receiving an engine shut-down request, prior to engine spin-down, rotating the engine at an idling speed via an electric motor and carrying out diagnostics of the EGR system. EGR diagnostics may include estimating a ratio of accumulated difference between a measured EGR flow and an EGR limit to accumulated intake air flow, over a duration of time, and indicating EGR system degradation in response to the ratio being higher than a threshold.

A method of implementing start-stop in an internal combustion engine, the engine having exhaust gas recirculation (EGR) from at least one dedicated EGR (D-EGR) cylinder. For stopping the engine, the camshaft is locked, and a hydraulic cam phaser is used to cushion the engine inertia. The engine is stopped such that one of the D-EGR cylinders is in top-dead center position. For starting the engine, that D-EGR cylinder is fuel-injected, and exhaust bleed-off performed if necessary.

A method for monitoring leakage of an exhaust gas recirculation system for an engine of a vehicle includes: determining, by a controller, whether the engine is in an idle state in which the exhaust gas recirculation system is not operated; determining, by the controller, whether small flow leakage of the exhaust gas recirculation system occurs based on a predicted pressure of gas sucked into an intake manifold connected to the engine and a measured pressure of gas sucked into the intake manifold when the engine is in the idle state; and determining, by the controller, that leakage of the exhaust gas recirculation system occurs when the measured pressure is greater than the predicted pressure.

A compression ignition gasoline engine includes a fuel injection valve for injecting fuel containing gasoline as a main component into a cylinder; an EGR device operative to perform high-temperature EGR of introducing burnt gas generated in the cylinder into the cylinder at a high temperature; an octane number determination unit for determining whether fuel injected from the fuel injection valve has a prescribed octane number; and a combustion control unit for controlling the fuel injection valve and the EGR device in such a way that HCCI combustion occurs within the cylinder. The combustion control unit controls the EGR device, in at least a partial load operating range in which HCCI combustion is performed, in such a way that the EGR rate increases, as compared with a case where fuel is determined to have a prescribed octane number, when fuel is determined not to have a prescribed octane number.

Methods and systems are provided for on-board diagnostics of an exhaust gas recirculation (EGR) system of an engine coupled to a hybrid vehicle. In one example, a method may include, upon receiving an engine shut-down request, prior to engine spin-down, rotating the engine at an idling speed via an electric motor and carrying out diagnostics of the EGR system. EGR diagnostics may include estimating a ratio of accumulated difference between a measured EGR flow and an EGR limit to accumulated intake air flow, over a duration of time, and indicating EGR system degradation in response to the ratio being higher than a threshold.

A controller according to the present disclosure, in each combustion cycle that composes a change cycle, calculates the average .sub.n of a control amounts from the first combustion cycle to the nth (1<=n<=N) combustion cycle and calculates the error .sub.n.sub.o of the average .sub.n with respect to the average .sub.o of a reference normal population. Also, the controller sets both a positive threshold Z.sub./2*.sub.o/n.sup.1/2 and a negative threshold Z.sub./2*.sub.o/n.sup.1/2 based on the standard error .sub.o/n.sup.1/2 of the reference normal population in the case where the number of data is n. Then, the controller changes the operation amount to make the error .sub.n.sub.o approach the positive threshold Z.sub./2*.sub.o/n.sup.1/2 or the negative threshold Z.sub./2*.sub.o/n.sup.1/2 when the error .sub.n.sub.o exceeds neither the positive threshold Z.sub./2*.sub.o/n.sup.1/2 nor the negative threshold Z.sub./2*.sub.o/n.sup.1/2 at any combustion cycle.

An internal combustion engine includes an intake passage of the internal combustion engine, an exhaust passage of the internal combustion engine, and an EGR passage connecting the intake passage and the exhaust passage. The internal combustion engine further includes a throttle valve provided downstream of a connected part to the EGR passage in the intake passage, and configured to control an intake air quantity toward a downstream side of the connected part, and an intake throttle valve provided upstream of the connected part to the EGR passage in the intake passage. In a control device of the internal combustion engine, an opening degree of the intake throttle valve is determined on the basis of an opening degree of the throttle valve.