Idle speed control

A control method for an internal combustion engine having an intake manifold and a throttling device connected thereto for regulating airflow inducted therein, comprising the steps of:

• detecting an operator actuated engine idle speed command;
• detecting engine speed and calculating engine acceleration;
• calculating a ratio of said engine acceleration to a speed variable related to said detected engine speed;
• decelerating the engine to a preselected engine speed in response to said idle speed command detection by adjusting the throttling device to concurrently force both said detected engine speed and said calculated engine acceleration within a predetermined acceleration and speed range by decreasing the inducted airflow when said ratio is less than a first preselected value and increasing said inducted airflow when said ratio is greater than a second preselected value so that both said calculated engine deceleration and said detected engine speed occur within said range;
• and
• regulating engine speed after said preselected engine speed is detected to maintain said detected engine speed at a desired idle speed by adjusting said throttling device in response to a difference between said detected engine speed and said desired engine speed to drive said difference towards zero.

A control system for an internal combustion engine having an intake manifold and a throttling device connected thereto for regulating airflow inducted therein, comprising:

• detecting means for detecting an operator actuated engine idle speed command;
• an engine speed sensor coupled to the engine for detecting engine speed;
• calculating means for calculating engine acceleration and for calculating a ratio of said engine acceleration to a difference between said detected engine speed and a predetermined engine speed which is less than said preselected engine speed;
• adjustment means for adjusting the throttling device in response to said idle speed command detection to decelerate the engine to a preselected engine speed, said adjusting step forcing both said detected engine speed and said detected engine acceleration within a predetermined acceleration and speed range by decreasing the inducted airflow when said ratio is less than a first preselected value and increasing said inducted airflow when said ratio is greater than a second preselected value;
• and
• said adjustment means also adjusting said throttling device after said preselected engine speed is detected to maintain said detected engine speed at a desired idle speed, said adjustment means being responsive to a difference between said detected engine speed and said desired engine speed to force said difference towards zero.