COIL AS 3843893 - Caterpillar

The Cat Compression Brake is designed to maintain a constant exhaust valve lift throughout the engine cycle by holding the exhaust valves open. Having the exhaust valve open before the piston reaches top dead center on the compression stroke produce an amount of negative torque. The negative torque aides in slowing down the engine.
Illustration 1 g02549058Braking is achieved is by using oil to move actuator (1) that holds exhaust valves (2) open. The movement of the exhaust valve is still initiated by the camshaft. The exhaust valves would normally close completely under normal operation. The Cat Compression Brake will prevent the valve from fully closing when braking is desired.
Illustration 2 g02549059Each Cat Compression Brake Actuator contains a piston (4) that is responsible for contacting the valve bridge and preventing the exhaust valves from closing completely. The engine oil return line (4) contains check valve (3). The check valve will prevent engine oil from returning to the supply rail when the exhaust valves are forced to remain open. The valves will remain open during the intake, compression, and power strokes of the cylinder.