Patent ID: 8720200
Filing Date: 2014-05-13
Classification: F02B,F02D,Y02T

Abstract:
1. A multistage supercharging system comprising: a high-pressure turbocharger 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 air, the high-pressure turbocharger being a variable-geometry-type turbocharger having a variable nozzle provided at an exhaust gas inlet of the high-pressure turbine; a low-pressure turbocharger 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 air at a location upstream of the high-pressure compressor with respect to a supply air flow direction; passages, including an intake passage and an exhaust passage, configured such that a supercharging mode is switched between a twin supercharging mode, realized at, at least one of a first range of speed and a first range of load, 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, realized at, at least one of a second range of speed and a second range of load, the second range of speed being higher than the first range of speed, the second range of load being higher than the first range of load, the first and second range of speed not overlapping and the first and second range of load not overlapping, 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; a memory having instructions; and a central processing unit for executing the instructions, the central processing unit, when executing the instructions, performing the steps of: acquiring a low-pressure-side supercharging pressure acquired value corresponding to a pressure of supply air at an outlet of the low-pressure compressor operated in the twin supercharging mode; 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 when the low-pressure-side supercharging pressure acquired value is less than the target supercharging pressure in the single supercharging mode, increasing the pressure of supply air at the outlet of the low-pressure compressor, while maintaining constant the supercharging pressure generated by the entire multistage supercharging system, wherein when the low-pressure-side supercharging pressure acquired value is less than the target supercharging pressure in the single supercharging mode, controlling the variable nozzle to the closing side, while increasing the ratio of exhaust gas which bypasses the high-pressure turbine; and controlling the variable nozzle on the open side with respect to an opening position at which the efficiency of the high-pressure turbine becomes the highest.