TO THROTTLE VALVE
FROM
MANUAL
SELECTOR
VALVE
BALL
LINKAGE
K.D. VALVE ROD
SPRING
TO SHIFT VALVE
ASf02071
Figure 2-71.--Kickdown valve (separate valve arrangement).
TO CLUTCH
TO APPLY
AREA OF
VENT
SERVO
FROM
GOVERNOR
THROTTLE
VALVE
SHIFT VALVE
LINKAGE
MANUAL
SELECTOR
ROD
VALVE
KICKDOWN VALVE
ASf02072
Figure 2-72.--Functional shift valve controls.
full throttle with kickdown operation. When the
valve is fully open (maximum throttle oil pressure). At
the same time, the governor pressure is high (higher
operator feels the resistance, he or she knows the
than the throttle pressure because the kickdown valve
accelerator is at full throttle. Further movement, called
is needed for downshift). Notice in the figure that the
"going through detent," causes kickdown.
kickdown oil pressure, while acting on both a small and
Operating Ranges
large surface area of the shift valve, will have a
resulting force that acts in direct opposition to the
The hydraulic control system will shift
governor oil pressure. What we have is kickdown oil
automatically depending on vehicle speed and load
pressure, throttle oil pressure, and the spring tension of
conditions, except for reverse operation. The operator
the throttle end of the shift valve acting against
is able to control the timing of transmission shifts and
governor oil pressure. The shift valve moves to
make a forced downshift when necessary. For reverse
uncover the servo port (downshift position) and at the
operation, another planetary gear unit is added. To
same time release the clutch. Reseating of the
operate the reverse planetary unit, another operating
kickdown ball, by releasing the accelerator pedal, will
unit (servo) is added. The different gear ratio changes
cause the transmission to again up shift.
discussed are D for direct drive, L for low range, N for
The kickdown valve is unseated normally just a
neutral, and R for reverse operation.
little beyond full throttle. There is usually a device
NEUTRAL RANGE.--The neutral position (N)
installed to indicate to the operator that the accelerator
is the no-power-flow position of the transmission. The
pedal has reached the point of kickdown. The device is
neutral position is selected by the operator by placing
generally a spring or hydraulically loaded plug, which
the manual selector lever or push button in N. Most
offers resistance to accelerator pedal movement after
vehicle engines will not start unless the N position has
reaching full throttle. This is a very desirable feature,
since the vehicle may at times have to be operated at
been selected.
2-55
