The referenced U.S. Pat. No. 4,425,888, Engel, et al., assigned to the asignee of the present application describes a speed control or governing system for an automotive-type internal combustion engine, especially a self-ignited internal combustion engine, that is, for example of the diesel engine type. In accordance with the disclosure of the reference, the command value of speed is raised by a proportional-integrating acting controller when the actual speed has reached a predetermined relationship with respect to the command speed. In such a speed control system, commanded speed is changed when the difference between actual speed and commanded speed reaches a predetermined level or value. The difference between actual speed and commanded speed is maintained constant.
As the speed drops, particularly when the speed drops below a lower threshold level, a different control function becomes effective. The drop in commanded speed is then matched, at least roughly, to the actual speed drop, as determined by operating characteristics of the engine when it has normal operating temperature.
If the engine is cold, the actual speed drop may be more rapid than the speed drop when the engine is warm. Consequently, it is possible that the controller will not follow rapidly enough the actual changes in speed of the engine and a predetermined minimum idle speed may actually be passed, by the engine when it is still cold and the engine will stall. The control system, as described, while functioning well with an engine which is warm may not prevent stalling of the engine due to the excessively rapid speed drop when the engine is still cold.