Apparatus for controlling the speed of an engine

An apparatus for controlling the speed of an engine, wherein airflow supplied to the engine through an air intake passage is controlled by adjusting a throttle valve located in the air intake passage, and wherein the throttle valve is substantially closed to restrict the airflow to the engine when the engine is idling, said apparatus comprising:

• an idle passage communicating with the intake passage, said idle passage having two ends respectively connected downstream and upstream of the throttle valve;
• an actuated control valve located in the idle passage, said control valve being arranged to control the airflow to the engine when the engine is idling;
• detecting means for detecting an engine condition and;
• determining means for determining increase of a load in accordance with a detected load;
• mapping means for providing an attenuation factor based on a change rate of the engine speed;
• first computing means for computing a duty factor for the control valve based the engine condition;
• and
• control means for digitally controlling the control valve with the computed duty factor, said control means being arranged to increase the airflow amount through the control valve to a predetermined amount based on the increase of the load to the engine which is determined by the determining means, said increased airflow amount being subsequently decreased to a predetermined magnitude at a dropping rate determined by the attenuation factor.

An apparatus for controlling the speed of an engine, wherein airflow supplied to the engine through an air intake passage is controlled by adjusting a throttle valve located in the air intake passage, and wherein the throttle valve is substantially closed to restrict the airflow to the engine when the engine is idling, said apparatus comprising:

• an idle passage communicating with the intake passage, said idle passage having two ends respectively connected downstream and upstream of the throttle valve;
• an idle speed control valve located in the idle passage, said control valve being subject to a duty control to control the airflow to the engine when the engine is idling;
• detecting means for detecting an engine condition;
• determining means for determining an increase of a load to the engine in accordance with a detected load;
• first computing means for computing a duty factor for the control valve based on the engine condition;
• second computing means for computing a target airflow amount of the control valve based on the detected engine condition;
• mapping means for storing an attenuation rate based on a change rate of the engine speed;
• and
• control means for controlling the control valve with the computed duty factor, said control means being arranged to change the duty factor so as to increase the airflow amount through the control valve to a predetermined amount based on the increase of the load to the engine, said increased duty factor being attenuated with the attenuation rate, and wherein said duty factor is converged to a duty factor corresponding to the idling state of the engine when it is substantially free of load, at which time said control means controls the airflow amount through the control valve to achieve the target airflow amount computed by the second computing means.

A method for controlling an idling speed of an engine, wherein a digitally controlled idle valve controls airflow in an idle passage connected to an air intake passage, the idle passage being arranged to bypass a throttle valve located in the air intake passage, said method comprising steps of:

• detecting an engine condition and an increase of load to the engine by sensor means;
• computing a duty factor for the control valve based the engine condition and the increase of the load;
• and
• digitally controlling the control valve with the duty factor, wherein the airflow amount through the control valve is increased to a predetermined amount when the load applied to the engine, said increased airflow amount being corrected by a attenuation rate factor chosen based on a change rate of the engine speed.