The ME engine concept of a servo-hydraulic system for activation of the fuel oil injection and the exhaust valves. The actuators are electronically controlled by a number of control units forming the Engine Control System (ECS). Fuel injection is accomplished by pressure boosters. The fuel plunger on the ME engine is driven by a piston actuated with pressurized control oil from an electronically controlled proportional valve as the power source. The exhaust valve is opened hydraulically, and closed by an air spring (as on the MC engine). Similar to the fuel injection pressure booster, the electronically controlled exhaust valve actuator is driven by the pressurized control oi which, for the exhaust valve, is fed through an on/off type control valve or a proportional type control valve. In the hydraulic loop, lubricating oil is used as the medium. It is filtered through a fine filter and pressurized by a hydraulic power supply (HPS) unit mounted on the engine.