Fig. 16PG-Clutch Apply -Servo Release Circuit
Fig. 17PG-Throttle Valve Operation
driven by the input shaft, and the other is a part of the clutch
assembly, the planetary is driven at a 1:1 ratio when the two
are locked together.
At the same time the clutch is being applied, the high
clutch apply pressure acts on the downshift timing valve,
unseating the ball and entering the low servo release circuit.
The servo release pressure equals the servo apply pressure
acting on the other side of the piston. This pressure balance
allows the servo springs to release the band. Thus, with the
band released, and the high clutch applied, the transmission
makes the shift from low to high.
NOTE: Since a common passage supplies pressure to the
clutch and servo release, the shift to high is fast and
Throttle Valve Circuits
opening and closing of the mainline port regulates TV pressure
at a given plunger position.
Release of the accelerator reduces the plunger spring force
and the hydraulic pressure on the right end of the valve moves
the valve to the left opening the TV pressure to exhaust. Thus,
TV pressure increases or decreases in direct proportion to
throttle valve spring force.
Minimum Throttle Upshifts occur when TV pressure is
regulated at a minimum. The TV pressure is delivered to the
right side of the regulator valve, causing the regulator to move
left and contact the stem of the shift valve. With the regulator
valve moved to the left, a by-pass port is opened which applies
TV pressure to the spring side of the large diameter shift valve
spool (fig. 18PG).
In drive range, throttle valve pressure is used to provide a
wide range of automatic shift points to match the transmission
ratio to varying driving conditions. In the paragraph describing
the automatic upshift, we mentioned that throttle valve pres
sure aided spring pressure to oppose governor pressure acting
on the shift valve (fig. 17PG). If there was no throttle pressure
acting on the low-drive shift valve, the upshift would always
occur at the same speed, when governor pressure overcomes
spring pressure on the shift valve.
Since the throttle and detent valves are connected by link
age to the accelerator, the effect of different accelerator posi
tions directly controls TV and detent pressure. Depressing the
accelerator pedal causes the throttle valve plunger to increase
the spring force on the valve moving it to the right. This opens
mainline pressure to the area between the spools. At this
point, the pressure enters the TV pressure passage and also
passes through a small hole drilled in the valve and fills the
blind cavity at the right end of the valve.
The pressure in the TV passage is delivered to the detent
valve and the low-drive shift valve. As the hydraulic force
builds in the TV circuit, the pressure acting on the right end of
the valve equals or overcomes spring pressure, the throttle
valve moves to the left closing the mainline pressure port. The
NOTE: TV pressure in this area balances the pressure on
the right of the regulator valve. This balanced condition
allows the regulator valve to be moved by the shift valve
without offering additional resistance.
Fig. 18PG-Minimum Throttle Upshift