Supercharging pressure control system for supercharged internal combustion engines

In a supercharging pressure control system for a supercharged internal combustion engine including an intake passage for guiding intake air to said engine, and a supercharger arranged in said intake passage for supercharging said engine with said intake air, said supercharging pressure control system comprising supercharging pressure-detecting means arranged in said intake passage at a location downstream of said supercharger for detecting an actual value of supercharging pressure of said intake air located downstream of said supercharger and caused by said supercharger, a bypass passage connected to said intake passage such that said bypass passage bypasses said supercharger, a supercharging pressure control valve arranged in said bypass passage for controlling said supercharging pressure of said intake air, driving means connected to said supercharging pressure control valve for driving said supercharging pressure control valve, and control means connected to said driving means for controlling said driving means,

• the improvement wherein said control means includes:
• desired supercharging pressure value-setting means for setting a desired value of said supercharging pressure of said intake air;
• valve opening-determining means for determining an actual value of degree of opening of said supercharging pressure control valve;
• desired opening value-setting means for setting a desired value of said degree of opening of said supercharging pressure control valve depending on operating conditions of said engine;
• and
• control mode-selecting means for selecting a feedback control mode on the one hand in which said degree of opening of said supercharging pressure control valve is controlled so as to make said actual value of said supercharging pressure of said intake air detected by said supercharging pressure-detecting means equal to said desired value of said supercharging pressure of said intake air set by said desired supercharging pressure value-setting means, when said actual value of said supercharging pressure of said intake air detected by said supercharging pressure-detecting means has reached said desired value of said supercharging pressure of said intake air set by said desired supercharging pressure value-setting means, and for selecting an open-loop control mode on the other hand in which said degree of opening of said supercharging pressure control valve is controlled to said desired value of said degree of opening of said supercharging pressure control valve when said actual value of said degree of opening of said supercharging pressure control valve determined by said valve opening-determining means during said feedback control becomes smaller than said desired value of said degree of opening of said supercharging pressure control valve.