Engine Compression Retarders
The engine compression retarder uses the engine's compression stroke to absorb energy from the vehicle's motion. Normally the piston compresses the cylinder air for the next power stroke, and this compression of the cylinder air takes energy. That energy is normally provided by another cylinder which is in its power stroke.
The engine compression retarder uses up vehicle motion energy during the compression stroke of each piston because the other cylinders are not producing power during their power stroke time interval. No (or insignificant) engine power is generated, because the throttle must be at the idle position for the retarder to operate.
During the retarder mode of operation, when the piston approaches the top of the compression stroke, the retarder system opens the exhaust valves for that piston, which vents the energy which was absorbed from the vehicle's motion. The retarder works by absorbing energy during the compression stroke, and throwing away this energy through the exhaust valves as the piston completes its compression stroke.
The most popular engine compression retarder is the Jake Brake. This retarder system is manufactured by the Jacobs Manufacturing Company, and their product is available for Caterpillar, Cummins, Detroit Diesel, and Mack engines, just to name a few.
The electric signal activates the solenoid valve. The active solenoid valve applies engine oil pressure to the control valve. The engine oil presure force moves the ported piston of the control valve up until the piston port aligns with the high pressure oil passage to the slave piston. The check ball in the control valve allows the engine oil pressure to fill the slave piston and the master piston voids via the high pressure oil passage. As the cylinder completes its compression stroke, the cylinder injector pushrod rises and lifts the master piston. This forces the oil out from above the master piston into the slave piston. Remember, the check ball in the control valve prevents the high oil pressure from bleeding back into the lower pressure engine oil supply.
As the injector pushrod moves upwards, the slave piston pushes down on the exhaust crosshead which opens the exhaust valves. This releases the compressed air which provided the retarder braking action. When the retarder is deactivated, the solenoid valve vents the engine oil pressure, which allows the control valve spring to lower it's ported piston, which seals off the high pressure oil passage.
To activate the Jake Brake, four requirements must be met, as shown in the diagram above. The dash switch must be on, the clutch must be engaged, the throttle must be at idle, and the driver and/or cruise control must have activated the retarder. Engine RPM must be kept high for the most retarder effect.