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 find a vehicle load level which will match the engine power output specified 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 difficult 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.
Min/Max Governor with Speed Control
The Min/Max Governor with Speed Control offers the best combination of the Full Range Governor and the Min/Max Governor. It provides smooth shifting with automatic/automated transmissions while driving, and precise engine speed control when the vehicle is parked.
Available:
All electronically controlled on-highway engines covered in this handbook (Note: Excludes C-10, C-12, C-15, C-16 PM OCT01)
Range:
Advantages:
The Governor Type parameter allows the operator to customize engine speed control by specifying the appropriate governor for the selected transmission type. When the Governor Type is properly set as recommended below, optimum engine speed control is achieved.
Disadvantages:
None
Recommendations:
The Full Range Governor is recommended for vehicles with manual transmissions.
The Min/Max Governor is recommended for vehicles with automatic/automated transmissions.
The Min/Max Governor with Speed Control is recommended for all automatic/automated transmission-equipped vehicles with that require precise engine speed control when parked.