Methods and systems include determining a cylinder air-fuel ratio imbalance in a multi-cylinder engine. In one example, the method may include sequentially firing an engine cylinder to provide an expected air-fuel deviation and learning cylinder air-fuel ratio imbalance based on an error between an actual air-fuel ratio deviation from a maximum lean air-fuel ratio relative to an expected air-fuel deviation during a deceleration fuel shut-off event.

Methods and systems are provided for learning fuel injector error for cylinder groups during a deceleration fuel shut-off (DFSO), where all cylinders of an engine are deactivated, sequentially firing each cylinder of a cylinder group, each cylinder fueled via consecutive first and second fuel pulses of differing fuel pulse width from an injector. Based on a lambda deviation between the first and second pulses, a fuel error for the injector and an air-fuel ratio imbalance for each cylinder is learned. Alternatively or additionally, a difference in crankshaft acceleration between the first and second pulses relative to the expected deviation may be used to learn torque error, and adjust fuel injector error and air-ratio imbalance for each cylinder.

Methods and systems are provided to determine air-fuel imbalance of cylinders in a variable displacement engine. In one example, the method may include during a cylinder deactivation event, sequentially deactivating each cylinder of a cylinder group including two or more cylinders and estimating a lambda deviation for each cylinder following the sequential deactivation of each cylinder of the cylinder group; and learning an air error for each cylinder based on the estimated lambda deviation.

In one aspect, a method is described. An operational engine torque is calculated. The engine is operated in a skip fire manner to deliver the operational engine torque. A reference engine torque is calculated using a torque model. The torque model involves estimating torque at a working chamber level. The reference engine torque is compared to the calculated operational engine torque to assess the accuracy of the operational engine torque calculation. Various embodiments of the present invention involve software, devices, systems and engine controllers that are related to one or more of the above operations.

Systems are provided for detecting a change in performance of an engine component. In one example, a system includes a first pressure sensor of a first exhaust manifold coupled to a first subset of cylinders of an engine, a second pressure sensor of a second exhaust manifold coupled to a second subset of cylinders of the engine, a passage coupling the first exhaust manifold to an intake manifold, and a controller configured to detect a change in performance of any cylinder of the engine based on frequency content from the first pressure sensor and from the second pressure sensor during both a first mode where no exhaust gas from the first exhaust manifold is provided to the intake manifold, and during a second mode where all exhaust gas from the first exhaust manifold is provided to the intake manifold, and adjust an operating parameter responsive to the change in performance.

An electronic control unit provided in an internal combustion engine detects a degree of inter-cylinder variation of the amount of fuel that is injected from a port injector, and a degree of inter-cylinder variation of the amount of fuel that is injected from an in-cylinder injector. In a case where the inter-cylinder variation of one of the port injector and the in-cylinder injector is equal to or greater than a predefined value, a process is executed of limiting, so as not to exceed an upper limit value, an injection proportion of the injector for which the inter-cylinder variation is equal to or greater than the predefined value. This upper limit value is set to be smaller as the degree of inter-cylinder variation of the injector, for which the inter-cylinder variation is equal to or greater than a predefined value, increases.

An individual cylinder air-fuel ratio estimation of estimating an air-fuel ratio of an individual cylinder is performed on a sensed value of an air-fuel ratio sensor set in an exhaust gas collection part of an engine, and an individual cylinder air-fuel ratio control of controlling the air-fuel ratio of the individual cylinder is performed in such a way that a variation in the air-fuel ratio between the cylinders becomes small on the basis of an estimated air-fuel ratio of the individual cylinder. Further, it is determined whether or not a misfire of the engine is caused and when it is determined that the misfire of the engine is caused, the individual cylinder air-fuel ratio estimation and the individual cylinder air-fuel ratio control are stopped and an individual cylinder correction value by the individual cylinder air-fuel ratio control is reset. In this way, it is possible to avoid the individual cylinder air-fuel ratio control from being performed continuously as usual in a state where the air-fuel ratio of the individual cylinder cannot be controlled correctly due to the effect of the misfire.

Systems and methods are for controlling internal combustion engines having a plurality of piston-cylinders that cause rotation of a crankshaft. A crankshaft sensor is configured to sense rotational speed of the crankshaft. A controller is configured to calculate an an engine speed increase for each piston-cylinder based upon the rotational speed of the crankshaft and then balance the engine speed increases of the respective piston-cylinders by modifying a combustion input to one or more of the piston-cylinders in order to reduce engine vibration.

A fuel injection amount control apparatus comprises an air-fuel ratio sensor disposed between an exhaust gas merging portion and an upstream catalyst. The control apparatus performs a feedback correction on an amount of fuel to be injected by the fuel injection valve so that an air-fuel ratio represented by the output value of the upstream air-fuel ratio sensor becomes equal to a target air-fuel ratio set at stoichiometric air-fuel ratio. The control apparatus obtains an air-fuel ratio imbalance indicating value, which becomes larger as a difference in air-fuel ratio of each of the mixtures supplied to each of the combustion chambers among the cylinders becomes larger, and performs an increasing correction to the instructed fuel injection amount in such a manner that an air-fuel ratio determined by the instructed fuel injection amount becomes richer than the stoichiometric air-fuel ratio as the obtained air-fuel ratio imbalance indicating value increases.

A method, a combustion engine controller, and a combustion engine incorporating the controller to implement the method are provided. The method includes determining a first dedicated exhaust gas recirculation (D-EGR) cylinder parameter value of a first D-EGR cylinder parameter associated with a first D-EGR cylinder of the combustion engine; and regenerating the first D-EGR cylinder responsive to the first D-EGR cylinder parameter value satisfying a threshold indicative of a carbon build-up level.