PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620 - LESSON 2/TASK 2
9.
Engine Retarder System
a. Purpose. Engine retarder systems are used on many larger vehicles
equipped with diesel engines. They are designed to provide additional
stopping ability to a vehicle in motion. These systems also relieve the
service brakes of excessive heat buildup and wear due to prolonged
application. An auxiliary means of power absorption is used to accomplish
the additional braking process. Basically, three different engine retarder
systems are currently in use.
b. Compression Brake. The compression brake operates by restricting
the exhaust gas flowing from the engine. The system basically consists of a
butterfly valve fitted into the exhaust pipe between the exhaust manifold
and muffler. The system is activated by a switch mounted in the cab. The
valve is controlled by an air or vacuum switch mounted on the accelerator
pedal. The system operates by restricting the exhaust gases, causing a
pressure rise in the exhaust manifold. This pressure increase can vary from
30 to 40 psi. The compression brake causes a pressure buildup in the
cylinder during the exhaust stroke. The engine then becomes a lowpressure
pump driven by the wheels. This, in turn, slows down or retards the
vehicle.
c. Hydraulic Retarder. The hydraulic retarder is a pedaloperated unit
mounted in the transmission. This system assists the service brakes in
controlling the vehicle's speed during long downhill braking or when slowing
down in stop and go traffic. The system consists of a retarder cavity
located between the converter and transmission housing. The cavity contains
a rotor that is connected to the turbine output shaft. Stationary reaction
vanes are mounted on both sides of the rotor. When the transmission fluid
fills the cavity, it churns against the reaction vanes and slows down the
rotor. The retarding efforts are then transmitted to the drive line to slow
down the vehicle.
The retarder will continue to operate as long as the retarder pedal is
depressed. The rotational energy is transformed into heat energy and
absorbed by the transmission fluid. If the retarder is operated
continuously, however, the fluid temperature can rise faster than it can be
cooled.
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