An engine brake, an Jake brake, and an exhaust brake, etc. have been used in commercial vehicles as an auxiliary brake to assist a foot brake with more secured braking force by reducing power transmitted to a crank shaft.
The engine brake among the above listed brakes, decelerates a vehicle by preventing driving force generation to forcibly open an exhaust valve at a compression top dead center and discharging a compressed air to atmosphere to prevent piston movement by the compressed air when an acceleration pedal is released during a four cycle (an intake stroke→a compression stroke→an explosion stroke→an exhaust stroke).
The engine brake uses negative pressure resistance acting on a piston during the intake stroke, compression resistance during the compression stroke, compression resistance during the exhaust stroke, and a mechanical friction force generated during engine rotation, as a braking force.
Such an engine brake is mounted at an upper portion of an engine and connected to an exhaust cam, an exhaust rocker arm, intake/exhaust valves, and an engine oil circulation structure of a cylinder head.
However, the engine brake can only be mounted in the engine at which an exhaust cam having a protrusion is applicable since movement of the exhaust rocker arm pressing down the exhaust valve before reaching the compression top dead center is directly connected with the exhaust cam having the protrusion.
Accordingly, an improved variable intake/exhaust valve system capable of satisfying the fuel efficiency has been applied to the engine brake connected with the engine cam having the protrusion.
However, the compression top dead center of the exhaust cam having the protrusion in the variable intake/exhaust valve system cannot be determined.