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 TM 9-8000
housing. The cavity contains a rotor that is connected to
the turbine output shaft. Stationary reaction vanes are
5-40. Jacobs Engine Brake.
The Jacobs engine
mounted on both sides of the rotor.
When the
brake (Fig. 5-31) consists of a slave piston mounted
transmission fluid fills the cavity, it churns against the
over the exhaust valve.
The system operates by
reaction vanes and slows down the rotor. The retarding
opening the exhaust valve near the top of the
efforts then are transmitted to the drive line to slow down
compression stroke.
This releases the compressed
the vehicle. The retarder will continue to operate as
cylinder charge into the exhaust system. This blowdown
long as the retarder pedal is depressed. The rotational
of compressed air into the exhaust system prevents the
energy is transformed into heat energy and absorbed by
return of energy from the piston on the expansion stroke.
the transmission fluid.
If the retarder is operated
The result is an energy loss because the work done in
continuously, the fluid temperature can rise faster than it
compressing the charge is not returned to the usable
can be cooled.
Once this happens and the fluid
energy.
The system Is operated by a three position
temperature approaches a predetermined level, a
switch that allows the driver to select the degree of
warning light on the instrument panel indicates that the
braking required.
The three-position switch is set to
retarder operation should be discontinued until the fluid
allow braking on two, four, or all cylinders. This enables
cools down and the warning light goes out. When the
the driver to predetermine how much braking will be
retarder pedal is released, the retarder valve closes and
needed to properly slowdown the vehicle.
the fluid in the cavity automatically discharges and
permits the rotor to turn without drag.
Figure 5-31. Jacobs Engine Break
TA233467
5-40
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