Abstract: A system for controlling the supercharge pressure in an internal combustion engine having a mechanical supercharger which is connected to the crankshaft of an engine and includes a variable compressing construction capable of varying the internal compression ratio. The system comprises a supercharge pressure varying assembly for varying the supercharge pressure, a detector for detecting the operational condition of the supercharge pressure varying assembly, and a control device for operating the supercharge pressure varying assembly into a supercharge pressure reducing position in response to the detection, by the detector, of the fact that the supercharge pressure varying assembly is in a low level compressing state in an operational condition of the engine in which the mechanical supercharger should be brought into a high level compressing state. Thus, even if an abnormality occurs in the variable compressing assembly, an increase in the temperature of the intake gas in the engine is prevented.

Abstract: A method for controlling the supercharge pressure in an internal combustion engine having a mechanical supercharger which is connected to the crankshaft in the engine and in which the internal compression ratio of the supercharger can be varied. In the method, the internal compression ratio of the mechanical supercharge is varied on the basis of at least a preset supercharge pressure and an engine revolution rate. This ensures that the supercharge pressure can be matched with the internal compression ratio to prevent a pulsing, thereby preventing noise from being generated.