To provide reliable ignition and complete combustion by connecting an electrically controllable valve to a hydraulically controllable valve.
A servomechanism 47 has a hydraulically controllable three-port two-position directional control valve 61 and an electrically controllable three- port two-position directional control valve 91 connected to the three-port two- position directional control valve 61. The casing 62 of the three-port two-position directional control valve 61 has a first passage 63 joined to an inlet port 46, a second passage 64 joined to an outlet port 56, and a third passage 66 communicating with the connection 48 of a high pressure pump 41. A control valve element 67 disposed in the casing 62 connects the first passage 63 to the third passage 66 at a second switching position 86 to supply fuel to a piston 51 and connects the third passage 66 to the second passage 64 for returning fuel to a fuel tank 15 at a first switching position 84.
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