1. Field of the Invention
The present invention relates to a control device for controlling the operation of a mechanically driven supercharger in an internal combustion engine.
2. Description of the Related Art
It is well known to equip an internal combustion engine with a mechanically driven supercharger which is driven by and mechanically connected to a crankshaft of the engine via an electromagnetic clutch (c.f., for example, Japanese Unexamined Patent Publication No. 56-167817). By selectively engaging or disengaging the electromagnetic clutch in response to the engine revolutions (rpm) and load, it is possible to reduce the driving loss of the engine by releasing the clutch when the engine rpm and load is low and to attain a high engine power due to the supercharging by engaging the clutch when the engine rpm and load are high. It is also possible to obtain a very rapid response during engine acceleration, as the electromagnetic clutch can be instantaneously turned on.
It is also known to increase the amount of fuel in the air/fuel ratio (i.e., enrich the A/F mixture) when the engine is cold. A problem arises in that if the engine is raced (i.e., wide-open throttle) when the engine is still cold, the engine rpm is abruptly increased when the engine is raced and the subsequent closure of the throttle causes a large vacuum to occur just downstream of the throttle valve, resulting in a phenomena wherein a part of the air introduced past the throttle valve is made to pulsate and return toward the throttle valve. The injected fuel also flows back toward the throttle valve together with the back-flow of air. This back-flowing fuel tends to be deposited on the internal wall of the air intake pipe, due to the cold condition of the engine. If the supercharger is operating, a larger amount of the air is introduced into the engine, which causes an accompanying increase in the amount of fuel introduced therein. Thus the proportion of back-flowing fuel becomes large. If the engine is accelerated (e.g., upon vehicle move-off) under such circumstances, the deposited fuel is instantaneously introduced into the engine together with the newly injected fuel. Thus an excessive amount of fuel is introduced into the engine; flooding the combustion chambers and making the spark plugs wet.
This can be avoided by stopping the operation of the supercharger, when the engine is cold. However, such a stoppage will bring a deterioration in the engine performance while the vehicle is running. The above-explained fuel back-flowing tendency becomes more remarkable if the throttle valve is arranged upstream of the supercharger, so that the volumetric area between the throttle valve and an intake valve becomes larger.