1. Field of the Invention
The present invention relates to method and apparatus for controlling an internal combustion engine using an overtemperature preventing (OTP) fuel incremental correction.
2. Description of the Related Art
In an internal combustion engine, when the load of the engine such as the intake air amount is increased, thus increasing the temperature of the exhaust gas, a catalyst converter, an exhaust pipe and the like may become overheated and damaged. To avoid such overheating, a so-called OTP fuel incremental correction is carried out.
On the other hand, when knocking is generated and an extremely high temperature and pressure occur in the engine, the engine may become overheated and damaged. Accordingly, a knocking control system (KCS) has been suggested in which the ignition timing is retarded to eliminate the knocking. Also, when the coolant temperature of the engine is extremely high, for example, higher than 100.degree. C., heavy knocking may be generated and the torque of the engine reduced. Accordingly, a correction system has been suggested in which the ignition timing is retarded to reduce knocking and the temperature of the coolant temperature THW. But, when the corrections by retarding the ignition timing due to the knocking control system, and by retarding the ignition timing due to the high engine temperature, are carried out, the temperature of the exhaust gas is further increased. Accordingly, a fuel incremental correction made necessary by the retarding of the ignition timing is carried out in addition to the above-mentioned OTP fuel incremental correction. In the prior art, the above-mentioned fuel incremental correction due to the retarding of the ignition timing is carried out approximately in accordance with the sum of the retarded crank angle (AKCS) of the ignition timing brought about by the knocking control and the retarded crank angle (AHOT) of the ignition timing brought about by the high engine temperature control, or in accordance with a one-dimensional function using each parameter (see: Japanese Unexamination Utility Model Publication (Kokai) No. 59-141171).
When, however, the above-mentioned fuel incremental correction brought about by the ignition timing control is carried out in accordance with the sum of two parameters AKCS and AHOT, or the one-dimensional function defined by each parameter, it is impossible to maintain the temperature of the exhaust gas at a definite value, as will be explained later, and in addition, an excessive amount of incremental fuel is supplied to the engine, thus degrading the emission characteristics, the fuel consumption characteristics, the engine output characteristics, and the like.