Copyright by Goodheart-Willcox Co., Inc.
Chapter 9 Automatic Transmission Control Components 197
Output shaft
Governor
body
Primary valve
Outer
weight
Attaching bolts
Oil
collector
body
Counterweight
Primary
weight
Valve
Secondary
weights
Spring
Ex
Governor
Drive gear
B
A
Governor
shaft
Primary weight
Primary spring
Secondary
check ball
Fluid leaks
out here
at low rpm
Governor
drive gear
Output
shaft
At higher rpm,
weight moves out,
pulls check ball
in or closed
Governor
pressure
Orifice
Line
pressure
Governor
driven gear
Secondary
spring
Primary check ball
Secondary weight
Speedometer
drive gear
Figure 9-15. This illustration shows two kinds of gover nors that
control governor pressure by permitting restricted
flow through the governor valve. A—Output shaft-
mounted governor. B—Case-mounted, gear-driven governor.
(Ford, General Motors)
Figure 9-16. The governor drive gear on the output shaft drives
the governor. Transmission fluid leaks out past the check balls
at low rpm. At higher rpm, the weights are thrown outward,
against spring tension. The check balls are pulled inward, block-
ing the passageway and causing governor pressure to increase.
When pressure is great enough to overcome the throttle pres-
sure acting on the other end of the shift valve, upshift occurs.
(General Motors)
builds up rapidly with increasing vehicle speed until about
20 mph (32 km/h). At higher speeds, pressure increases
more gradually to prevent it from becoming too high in the
high vehicle-speed ranges. Shaft-mounted and gear-driven
versions of this type of governor are shown in Figure 9-15.
Note that a variation of this valve does not have sepa-
rate weights; the weight is an integral part of the valve itself.
The motion of the governor, aided by the weight, causes the
valve to move outward and open.
Another kind of governor has two openings, or ports,
that are served by check balls. Oil pressure pushes the balls
away from the openings, and oil flows out. Weights are
thrown outward as the governor rotates. This action moves
the check balls to close the openings, causing the pressure in
the circuit to rise. See Figure 9-16. Line pressure is fed to this
governor through an orifice, which limits the amount of fluid
that can flow in the governor circuit. At low speeds, the balls
are positioned so transmission fluid leaks out through the
openings. The governor pressure is zero. As the vehicle
speeds up, the weights begin to move the check balls inward,
allowing governor pressure to build. At maximum governor
pressure, the ports are completely closed off.
Detent Valve
The detent valve, also called the kickdown valve, is
used on some transmissions to aid downshifting.
Downshifting is often needed when a vehicle that is already
in a higher gear attempts to climb a hill or accelerate to
pass. When the accelerator is pushed all the way to the
floor, the valve provides a forced downshift, increasing
torque to the drive wheels. The vehicle, in this circum-
stance, is said to be in passing gear.
The detent valve may be operated through a kickdown
linkage connected to the engine throttle or by an electric
solenoid. In operation, the valve increases pressure on the
throttle side of the shift valves. The extra pressure forces the
shift valves to the downshifted position, putting the trans-
mission in a lower gear.