TM 5-3810-300-24&P-3
14.3.4
LIMITING SPEED MEC
(Fast Idle Cylinder)
The limiting speed governor equipped with a fast idle air
cylinder is used on vehicle engines where the engine
powers both the vehicle and auxiliary equipment.
The fast idle system consists of a fast idle air cylinder
installed in place of the buffer screw and a throttle
locking air cylinder mounted on a bracket fastened to the
governor cover (Fig. 1). An engine shutdown air
cylinder, if used, is also mounted on the governor cover.
Fig. 2 - Fast Idle Air Cylinder
The fast idle air cylinder and the throttle locking air
cylinder are actuated at the same time by air from a
common air line. The engine shutdown air cylinder is
Operation
connected to a separate air line.
During highway operation, the governor functions as a
The air supply for the fast idle air cylinder is usually
limiting speed governor.
controlled by an air valve actuated by an electric
solenoid. The fast idle system should be installed so that
For operation of auxiliary equipment, the vehicle is
it will function only when the parking brake system is in
stopped and the parking brake set. Then, with the
operation to make it tamper-proof.
engine running, the low-speed switch is placed in the ON
position. When the fast idle air cylinder is actuated, the
The vehicle accelerator-to-governor throttle linkage is
force of the dual idle spring (Fig. 2) is added to the force
connected to a yield link so the operator cannot
of the governor low-speed spring, thus increasing the
overcome the force of the air cylinder holding the speed
engine idle speed.
control lever in the idle position while the engine is
operating at the single fixed high idle speed.
The governor now functions as a constant speed
governor at the high idle speed setting, maintaining a
near constant engine speed regardless of the load within
the capacity of the engine. The fast idle system provides
a single fixed high idle speed that is not
Fig. 3 - Throttle Locking Air Cylinder
Fig. 1 - Governor with Fast Idle Cylinder
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