ALTERNATOR 3218928 - Caterpillar

The compression brake helps the operator to slow the speed of the vehicle on grades, in curves, or for necessary speed reduction. The service brakes should not be used continuously on long descending grades. The compression brake gives the vehicle some braking power without using the service brakes. The engine crankshaft is turned by the rear wheels during downhill operation or during any slow down condition. The engine crankshaft is turned through the differential, through the drive shaft, through the transmission, and through the clutch. An application of a braking force can be made to the engine pistons in order to reduce the speed of the vehicle.When the compression brake is activated, braking power is accomplished by opening the engine's exhaust valves. The exhaust valves are opened near the top of the compression stroke in order to release the highly compressed air into the exhaust system. The compression brake can only be activated when the engine is in the no-fuel position. This conversion is made possible by a master piston to slave piston arrangement. Movement of the rocker arm from one exhaust valve is transferred hydraulically to the exhaust valve of another cylinder. This opens the exhaust valves of the cylinder with the compressed air. The valves are opened near the top of that cylinder's normal compression stroke cycle. The compressed cylinder charge is now released into the exhaust manifold. The compressed air pressure that is released to the atmosphere prevents the energy from returning to the engine piston on the power stroke. The result is a loss of energy since the work that is done by the compression of the cylinder charge is not returned by the expansion process. This loss of energy is taken from the rear wheels. The rear wheels provide the braking action for the vehicle.Components of the Compression Brake (Model 346D)
Illustration 1 g00534221
Installed Compression Brake (1) Rear housing (2) Front housing (3) Stud (4) Support bracketThe compression brake consists of two different housings. One housing is for the first three cylinders. The other housing is for the last three cylinders. The housings are mounted on support brackets (4) and on two studs (3) that are at the end of the rocker shaft brackets. Special exhaust rocker arm adjusting screws and exhaust valve bridges are necessary. Later engines have only one support bracket (4) for each housing.Note: Only the exhaust valve mechanisms are used in the operation of the compression brake. A spacer is used on top of the valve cover base to permit installation of the valve cover. The compression brake increases the height of the engine. The height increase is less than 50.8 mm (2.0 inch).Both the front and rear compression brake housings consist of the following parts:
three master pistons
three slave pistons
three control valves
one solenoid valveCompression Brake Operation (Model 346D)
Illustration 2 g00534226
Master-Slave Circuit Schematic (1) Solenoid valve (2) Spring (3) Control Valve (4) High pressure oil passage (5) Slave piston adjustment screw (6) Master piston (7) Rocker arm shaft oil passage (8) Engine oil