A control device for an internal combustion engine includes an electronic control unit configured to switch a control algorithms for a calculation of a command value of the actuator between a first control algorithm and a second control algorithm. The electronic control unit is configured to calculate a value obtained by adding a value of a term of the second control algorithm changing in accordance with the deviation calculated in a present control cycle to the command value calculated in a previous control cycle in accordance with the first control algorithm as a value of the command value calculated in the present control cycle in a first control cycle after switching from the first control algorithm to the second control algorithm. The value of the term changing in accordance with the deviation includes an update amount of an I term of the I control calculated in the present control cycle.

An anomaly determination apparatus determines an anomaly of a current control apparatus which supplies a control current to a control target and includes a current anomaly determination section. The current anomaly determination section is configured to compare a normal numerical range within which a state quantity changing with the control current falls in a particular state with a particular state quantity which is the state quantity corresponding to the control current generated by the control current generation section in the particular state, and determine that at least one of the reference resistor, the reference current generation section, and the control current generation section is in an anomalous state in the case where the particular state quantity has deviated from the normal numerical range. By using the current anomaly determination section, the anomaly determination apparatus can determine an anomaly of the current control apparatus.

A method for monitoring the operation of a sensor is provided. The method comprises the step of representing the operation of the sensor by: i) storing a plurality of data values, each data value corresponding to the sensor output signal, wherein said step is performed during a time period such that said data values are distributed over a range of possible data values, ii) defining a plurality of discrete intervals within said range of possible data values; and iii) calculating the frequency of the data values within each interval thus forming a sensor representation. The method further comprises the steps of receiving at least one reference sensor representation; and comparing said sensor representation with said at least one reference sensor representation.

A control system for an internal combustion engine includes a temperature sensor and an engine controller. The sensor measures the temperature of exhaust gas passing through an exhaust manifold of the engine during each cycle. The controller selectively operates the engine in a first state and a second state. In the first, normal state, a quantity of fuel based on an open loop fuel mass command value is injected into the engine each cycle. In the second state, the controller determines a temperature of the exhaust gas during a normal cycle, injects the quantity and additional fuel into the engine during a second cycle, determines the temperature of the exhaust gas during the second cycle, compares the temperatures, and adjusts the command value for fuel to be injected each cycle when operating the engine in the first state.

A control device for an internal combustion engine, equipped with: an exhaust purification catalyst provided in the exhaust passage of the internal combustion engine and capable of absorbing oxygen; a downstream air-fuel ratio sensor provided downstream from the exhaust purification catalyst in the direction of the exhaust flow; and an engine control device that controls the internal combustion engine in response to the output from the downstream air-fuel ratio sensor. The downstream air-fuel ratio sensor is configured such that the applied voltage for which the output current is zero changes in response to the exhaust air-fuel ratio, and such that when the exhaust air-fuel ratio equals the theoretical air-fuel ratio and the applied voltage in the downstream air-fuel ratio sensor is increased, the output current increases in conjunction therewith. When the air-fuel ratio of the exhaust gas is detected by the downstream air-fuel ratio sensor, the applied voltage in the downstream air-fuel ratio sensor is fixed at a constant voltage, with this constant voltage being a voltage for which the output current is zero when the exhaust air-fuel ratio is a predetermined air-fuel ratio that is leaner than the theoretical air-fuel ratio.

Invention suppresses deterioration of emission if there is air-fuel ratio imbalance among cylinders. Apparatus (100) controlling an engine including first and second air-fuel ratio sensors respectively disposed on upstream and downstream of catalyst, has: first determining device determining first F/B controlled variable according to deviation between output value and target value of first air-fuel ratio sensor; second determining device determining second F/B controlled variable according to deviation between output value and target value of second air-fuel ratio sensor; controlling device controlling fuel injection amount based on first and second F/B controlled variables; detecting device detecting air-fuel ratio imbalance among cylinders; and correcting device correcting second F/B controlled variable in direction in which there is hardly change of fuel injection amount to lean air-fuel ratio side, according to output deviation between first and second air-fuel ratio sensors, if air-fuel ratio imbalance is detected.

Methods are disclosed for determining an oxidation state of a catalyst using RF signals. The method may include introducing radio-frequency signals into a resonant chamber including a catalyst, modulating an air-fuel ratio of an engine upstream of the catalyst to generate a sequence of uniform pulses and at least one altered pulse that differs from the uniform pulses, and comparing a frequency response of two or more resonant modes of the radio-frequency signals during the sequence to determine an oxidation state of the catalyst. The method may further include adjusting the air-fuel ratio based on the comparing step. Two or more altered pulses may be inserted into the air-fuel ratio sequence. The altered pulse may have a pulse width and/or amplitude that differs from the uniform pulses. The methods may be used to adjust an air-fuel ratio to correct or impart a bias.

The purpose of the present invention is to detect deterioration of dead time characteristics of an air-fuel ratio sensor with high accuracy without causing running performance and exhaust performance to worsen. The present invention provides a control device for an engine, characterized by being equipped with: a means for detecting an air-fuel ratio; a means for changing the air-fuel ratio in a predetermined cycle; and a means for sending a notification of an abnormality in the air-fuel ratio detection means or causing at least a portion of the engine control to run in a fail-safe mode when the amplitude of an output signal of the air-fuel ratio detection means at a predetermined frequency is within a predetermined range and the required time or required angle to arrive at a predetermined value of the output signal of the air-fuel ratio detection means from a reference position or reference time point of an engine-related parameter is equal to a predetermined value or higher.

Methods and systems are provided for detecting an air-fuel imbalance based on output from multiple degradation monitors. In one example, a method comprises, during feedback engine air-fuel ratio control responsive to output of an exhaust gas sensor positioned downstream of a catalyst, indicating a cylinder imbalance responsive to a catalyst transfer function determined only within a specified frequency range based on the exhaust gas sensor output after determining that the catalyst is nominal, and adjusting an actuator in response to the indicated cylinder imbalance. In this way, air-fuel ratio imbalances may be accurately identified and mitigated, thereby reducing emissions.

The objective of the present invention is to provide an exhaust purification system that is capable of purifying exhaust gas during both lean and stoichiometric driving. The exhaust purification system is equipped with: a feedback-use identifier, which identifies parameter values such that the error between the output value from a LAF sensor and the estimated value for the LAF sensor output as obtained from a model equation is minimized; and a stoichiometric driving mode controller. The controller performs feedback control and thereby determines the fuel injection amount such that in the stoichiometric driving mode the equivalence ratio value as calculated from the parameters reaches a target value which is set such that a three-way purification reaction occurs in an under-engine catalyst. The identifier identifies the model parameters before feedback control is initiated by the controller.