Automotive Systems

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Detroit diesel engines use both mechanical and hydraulic governors on the engines of the following type:

  1. Mechanical limiting speed governor
  2. Variable mechanical speed governor
  3. Variable low-speed limiting speed mechanical governor
  4. Mechanical constant speed governor (earlier engines)
  5. Dual-range limiting speed mechanical governor
  6. Woodward SG hydraulic governor
  7. Woodward PSG hydraulic governor
  8. Woodward electric governor

On Detroit diesel engines the type of governor used is dependent on the particular engine application; therefore, setup can vary slightly between engines. All Detroit diesel mechanical governors are easily identifiable by a nameplate attached to the governor housing. The following letters are typical examples.

DWLS: double-weight limiting speed (mobile equipment)

SWLS: single-weight limiting speed (mobile equipment)

SWVS: single-weight variable speed (industrial and marine)

VLSLS: variable low-speed limiting speed (highway vehicles)

DWDRG: double-weight dual range governor (highway vehicles)

SG, PSG, SGX, UG8: Woodward

The functions of all these governors, whether mechanical or hydraulic, are to control engine speed and correct for any change in load applied or removed from the engine. They all work on the basic principle of weights against spring pressure; therefore, all governors are of the speed-sensing type.

Since the action of all these governors is the same,the two most common types found on a Detroit diesel engine—the limiting and variable speed governors.

The limiting speed type governor is found in both single- and double-weight version and can also be found on both in-line and V-type engines. Riveted on the side of the governor housing is an identification plate, which shows the following:

  1. Governor part number
  2. Date of manufacture
  3. Idle speed range
  4. Type, such as DWLS, meaning double-weight limiting speed
  5. Drive ratio

Regardless of whether the limiting speed governor is of the single- or double-weight variety, the action of the governor is the same. The purpose of the limiting speed governor is as follows:

  • Controls engine idle speed
  • Limits the maximum speed of the engine

The application of the engine determines whether a single- or double-weight governor will be used. The most prominent application for the limiting speed governor is highway truck engines, since the governor has no control in the intermediate engine speed range.

This allows the operator to have complete control of the injector rack movement through throttle action alone. his permits fast throttle response for engine acceleration or deceleration.

The variable speed mechanical governor is found extensively on industrial and marine applications, since it is designed for the following functions:

  1. Controls the engine idle speed
  2. Controls the maximum engine speed hydraulic-type governors (industrial and generator sets)
  3. Holds the engine speed at any position between idle and maximum as desired and set by the operator.

The response and reaction of the variable speed mechanical governor is similar to that of the limiting speed type with just a few exceptions. Since the variable speed mechanical governor controls speed through-out the total rpm range, there is no intermediate range as with the limiting speed governor. The variable speed governor uses only one set of weights and one spring.

In a variable speed mechanical governor, any given but with a difference only in purpose, we will discuss throttle setting or load from idle to maximum speed, a state of balance can exist. If, however, the load is increased or decreased, a corrective action will be initiated. The bell crank lever and pivoting differential lever will be moved by the action of the governor spring or weights to reestablish a state of balance.

Remember the governor can only react and change to the rpm of the engine.

The variable speed mechanical governor is readily identifiable from the limiting speed governor by the fact that it has only one lever on the top of the governor cover, which is the stop/run lever. The speed control lever is located vertically on the end of the governor spring housing. A large booster spring is attached between the speed control lever and a bracket on the cylinder head, used to assist the operator in overcoming governor resistance during throttle movement. The letters SWVS (single-weight variable speed) are stamped on the governor identification plate.


Before performing any adjustments or repairs to the governor, it is recommended that you consult the manufacturer’s service manual.

Published by SweetHaven Publishing Services
Based upon a text provided by the U.S. Navy

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