To reduce wasteful compression work in the whole operating range to prevent loss of thermal efficiency by controlling the opening and closing of a relief valve to control the injection condition of injection gas according to the operating condition of an engine in response to a detection signal from a sensor.
In the case of gas injection into an engine, the pressure of compressed gas for injection in a compressed gas reservoir 4 is calculated using a pressure value detected by a cylinder internal pressure sensor 23 by a controller 9, and electronic control for opening and closing a relief valve 24 to reach the pressure is conducted. As the gas which is passed through the relief valve 24 is returned to a main gas reservoir 13, if the necessary injection gas pressure is lower, the extract gas quantity is decreased as a result so that the compression work of gas is minimized. The gas injection pressure, the gas injection period, the gas injection timing and the gas injection quantity ratio are controlled according to the operating condition. At this time, the optimum gas injection condition can be obtained by controlling the operation of an operating oil pump 21 by the controller 9 so that the minimum gas compression power is enough.
NAKAGAWA HIROSHI
ENDO HIROYUKI
