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Engine/Gear Parameters
Governor Type
OEM
Description:
Caterpillar offers three governor options, selectable with
the Governor Type parameter. These three options are
the Full Range Governor, and two types of the Min/Max
Governor.
Full Range Governor
This governor type allows the engine to maintain engine
speed for a given throttle position. The Full Range
Governor is capable of injecting the maximum amount of
fuel for a given desired engine speed.
The Full Range Governor is very sensitive to
changes in engine speed, and is therefore not the
preferred governor type for vehicles using automatic
transmissions. For example, if the ECM wants to
maintain 1500 rpm, the governor will try to maintain
the desired speed. When an automatic transmission
performs an upshift, the actual engine speed will fall
below the desired engine speed of 1500 rpm. The Full
Range Governor would then inject a large amount of
fuel in an attempt to increase the engine speed back
up to the desired engine speed of 1500 rpm. This
causes undesirable, harsh shifting with an automatic
transmission.
Min/Max Governor
The Min/Max Governor, however, is well-suited for
vehicles with automatic transmissions. The Min/
Max governor will only control engine speed when
at the minimum (low idle) or maximum (top engine
limit) allowed engine speed. When in between these
two extremes, the engine will produce the power
proportional to the throttle position. This results
in smoother shifting with automatic/automated
transmissions.
The Min/Max Governor optimizes automatic
transmission shift quality and power modulation,
allowing the operator to adjust the engine power output
to match typical vehicle operating conditions. The
engine speed will vary to fi nd a vehicle load level which
will match the engine power output specifi ed by the
throttle. If the throttle is commanding more power than
the vehicle load will offer, the engine will accelerate
to the top engine limit. This makes it very diffi cult to
maintain a constant engine speed when the vehicle is
parked. Slightly depressing the throttle pedal with the
vehicle parked will cause the engine to go to the top
engine limit, which may be undesirable for applications
that require precise engine speed control while parked.
This problem can be solved by the third governor type.