Abstract: A control unit employed in a variable valve timing apparatus vibrates a control signal for controlling an oil-pressure control valve. If the vibration center of the duty value of the control signal for driving the oil-pressure control valve lies in a dead band, the vibration takes the duty value to the outside of the dead center temporarily. Thus, even if the center value of the control signal lies in the dead band, the valve timing of the oil-pressure control valve changes with variations in control signal. As a result, the width of the dead band appears small or to have a value of zero. Accordingly, the response characteristic of variations in valve timing to the variations in control signal is improved. The vibration of the control signal is also effective for detection of a width of the dead band.

Abstract: At a time point at which an ignition switch is made OFF and an engine is stopped, an output of a downstream gas sensor is read, thereafter, at a time point at which a predetermined time period has elapsed from stopping the engine, the output of the downstream gas sensor changed by flowing the atmosphere back into an exhaust pipe is read. Thereafter, a change in the output of the downstream gas sensor until the predetermined time period has elapsed from stopping the engine is calculated, the change in the output is compared with an abnormality determinant and when the change in the output is smaller than the abnormality determinant, response of the downstream gas sensor is determined to be abnormal.

Abstract: An emission control system has a catalyst and a sensor responding to a component of exhaust gas. In order to speed warming up the catalyst, the emission control system increases the amount of heat dissipated by exhaust gas. A diagnosis of the emission control system is carried out by determining whether the amount of heat dissipated by exhaust gas is sufficient or insufficient. The amount of heat dissipated by exhaust gas is represented by the length of time to an activated state of the sensor. In the diagnosis, the amount of heat generated by a heater provided in the sensor is taken into consideration.

Abstract: A valve timing control apparatus for an internal combustion engine is provided which is designed to ensure the drivability of the engine in the event of failure in operation of a variable valve timing control system made up of intake and exhaust side variable valve timing control mechanisms. If one of intake and exhaust side variable valve timing control mechanism has failed, the control apparatus actuates the other variable valve timing control mechanism to control the timing of opening and closing of a corresponding one of intake and exhaust valves so as to decrease an amount of overlap between the opening and closing of the intake and exhaust valves.

Abstract: A knock control apparatus for engine has a knock sensor for detecting vibrations of the engine. The knock control apparatus determines an occurrence of knock by using at least one of a statistical process, a waveform process and a FFT process. The knock control apparatus desirably uses at least two of the above-described process for improving the accuracy of knock determination. The knock control apparatus learns a corrective value during a stable condition of the engine. The learned value is used for determining an ignition timing when the engine is in a transitional condition. Therefore, it is possible to detect a knock accurately, and reduce a knock when the engine is in the transitional condition.

Abstract: At a time point at which an ignition switch is made OFF and an engine is stopped, an output of a downstream gas sensor is read, thereafter, at a time point at which a predetermined time period has elapsed from stopping the engine, the output of the downstream gas sensor changed by flowing the atmosphere back into an exhaust pipe is read. Thereafter, a change in the output of the downstream gas sensor until the predetermined time period has elapsed from stopping the engine is calculated, the change in the output is compared with an abnormality determinant and when the change in the output is smaller than the abnormality determinant, response of the downstream gas sensor is determined to be abnormal.

Abstract: A valve timing control apparatus for an internal combustion engine is provided which is designed to ensure the drivability of the engine in the event of failure in operation of a variable valve timing control system made up of intake and exhaust side variable valve timing control mechanisms. If one of intake and exhaust side variable valve timing control mechanism has failed, the control apparatus actuates the other variable valve timing control mechanism to control the timing of opening and closing of a corresponding one of intake and exhaust valves so as to decrease an amount of overlap between the opening and closing of the intake and exhaust valves.

Abstract: An emission control system has a catalyst and a sensor responding to a component of exhaust gas. In order to speed warming up the catalyst, the emission control system increases the amount of heat dissipated by exhaust gas. A diagnosis of the emission control system is carried out by determining whether the amount of heat dissipated by exhaust gas is sufficient or insufficient. The amount of heat dissipated by exhaust gas is represented by the length of time to an activated state of the sensor. In the diagnosis, the amount of heat generated by a heater provided in the sensor is taken into consideration. The diagnosis can also be carried out before and after the warming up the catalyst. The heater can also be deactivated. Detection of an abnormality of a secondary air control system can be based on a component of exhaust gas. If the amount of heat dissipated by exhaust gas is found insufficient, additional control can be executed.

Abstract: A control unit employed in a variable valve timing apparatus vibrates a control signal for controlling an oil-pressure control valve. If the vibration center of the duty value of the control signal for driving the oil-pressure control valve lies in a dead band, the vibration takes the duty value to the outside of the dead center temporarily. Thus, even if the center value of the control signal lies in the dead band, the valve timing of the oil-pressure control valve changes with variations in control signal. As a result, the width of the dead band appears small or to have a value of zero. Accordingly, the response characteristic of variations in valve timing to the variations in control signal is improved. The vibration of the control signal is also effective for detection of a width of the dead band.

Abstract: A knock control apparatus for engine has a knock sensor for detecting vibrations of the engine. The knock control apparatus determines an occurrence of knock by using at least one of a statistical process, a waveform process and a FFT process. The knock control apparatus desirably uses at least two of the above-described process for improving the accuracy of knock determination. The knock control apparatus learns a corrective value during a stable condition of the engine. The learned value is used for determining an ignition timing when the engine is in a transitional condition. Therefore, it is possible to detect a knock accurately, and reduce a knock when the engine is in the transitional condition.