Multistage supercharging system control apparatus

A multistage supercharging system control apparatus for controlling a multistage supercharging system which comprises:

• a high-pressure turbo charger including a high-pressure turbine which is rotated and driven by exhaust gas, and a high-pressure compressor which is rotated and driven by the high-pressure turbine so as to pressurize supply gas;
• a low-pressure turbo charger including a low-pressure turbine which is rotated and driven by exhaust gas at a location downstream of the high-pressure turbine with respect to an exhaust gas flow direction, and a low-pressure compressor which is rotated and driven by the low-pressure turbine so as to pressurize supply gas at a location upstream of the high-pressure compressor with respect to an supply gas flow direction;
• and
• an intake-exhaust passage configured such that a supercharging mode can be switched between a twin supercharging mode in which exhaust gas is supplied to the low-pressure turbine via the high-pressure turbine, whereby supercharging is performed by the low-pressure compressor and the high-pressure compressor, and a single supercharging mode in which exhaust gas is supplied to the low-pressure turbine while being caused to bypass the high-pressure turbine, whereby supercharging is performed by the low-pressure compressor,
• the multistage supercharging system control apparatus comprising:
• low-pressure-side supercharging pressure acquisition means for acquiring a low-pressure-side supercharging pressure acquired value corresponding to the pressure of supply gas at an outlet of the low-pressure compressor operated in the twin supercharging mode;
• supercharging mode changeover means for prohibiting changeover from the twin supercharging mode to the single supercharging mode when the low-pressure-side supercharging pressure acquired value is less than a target supercharging pressure in the single supercharging mode, and permitting the changeover from the twin supercharging mode to the single supercharging mode when the low-pressure-side supercharging pressure acquired value is equal to or greater than the target supercharging pressure;
• and
• low-pressure-side supercharging pressure increasing means configured such that, when the low-pressure-side supercharging pressure acquired value is less than the target supercharging pressure in the single supercharging mode, the low-pressure-side supercharging pressure increasing means increases the pressure of supply gas at the outlet of the low-pressure compressor, while maintaining constant the supercharging pressure generated by the entire multistage supercharging system, wherein
• the high-pressure turbo charger is a viable-geometry-type turbo charger having a variable nozzle provided at an exhaust gas inlet of the high-pressure turbine;
• the low-pressure-side supercharging pressure increasing means is configured such that, when the low-pressure-side supercharging pressure acquired value is less than the target supercharging pressure in the single supercharging mode, the low-pressure-side supercharging pressure increasing means controls the variable nozzle to the closing side, while increasing the ratio of exhaust gas which bypasses the high-pressure turbine;
• and
• the low-pressure-side supercharging pressure increasing means is configured to control the variable nozzle on the open side with respect to an opening at which the efficiency of the high-pressure turbine becomes the highest.

A multistage supercharging system control apparatus for controlling a multistage supercharging system which comprises:

• a high-pressure turbo charger including a high-pressure turbine which is rotated and driven by exhaust gas, and a high-pressure compressor which pressurizes intake air which is rotated and driven by the high-pressure turbine so as to pressurize supply gas;
• a low-pressure turbo charger including a low-pressure turbine which is rotated and driven by exhaust gas at a location downstream of the high-pressure turbine with respect to an exhaust gas flow direction, and a low-pressure compressor which is rotated and driven by the low-pressure turbine so as to pressurize supply gas at a location upstream of the high-pressure compressor with respect to a supply gas flow direction;
• and
• an intake-exhaust passage configured such that a supercharging mode can be switched between a twin supercharging mode in which exhaust gas is supplied to the low-pressure turbine via the high-pressure turbine, whereby supercharging is performed by the low-pressure compressor and the high-pressure compressor, and a single supercharging mode in which exhaust gas is supplied to the low-pressure turbine while being caused to bypass the high-pressure turbine, whereby supercharging is performed by the low-pressure compressor,
• the multistage supercharging system control apparatus comprising:
• single-mode supercharging pressure acquisition means for acquiring a single-mode supercharging pressure acquired value corresponding to a supercharging pressure generated by the entire multistage supercharging system operated in the single supercharging mode;
• and
• supercharging mode changeover means for prohibiting changeover from the single supercharging mode to the twin supercharging mode when the single-mode supercharging pressure acquired value is less than a target value of the pressure of supply gas at the outlet of the low-pressure compressor in the twin supercharging mode, and permitting the changeover from the single supercharging mode to the twin supercharging mode when the single-mode supercharging pressure acquired value is equal to or greater than the target value.