Jeep cherokee 2000 Service Manual page 1022

21 - 114 AUTOMATIC TRANSMISSION—30RH
DESCRIPTION AND OPERATION (Continued)
The higher engine speed and line pressure would
open the vent too far and reduce line pressure too
much. Throttle pressure, which increases with engine
speed (throttle opening), is used to oppose the move-
ment of the pressure valve to help control the meter-
ing passage at the vent. The throttle pressure is
combined with spring pressure to reduce the force of
the throttle pressure plug on the pressure valve. The
larger spring at the right closes the regulator valve
passage and maintains or increases line pressure.
The increased line pressure works against the reac-
tion area of the line pressure plug and the reaction
area left of land #3 simultaneously moves the regu-
lator valve train to the right and controls the meter-
ing passage.
The kickdown valve, along with the throttle valve,
serve to delay upshifts until the correct vehicle and
engine speed have been reached. It also controls
downshifts upon driver demand, or increased engine
load. If these valves were not in place, the shift
points would be at the same speed for all throttle
positions. The kickdown valve is actuated by a cam
connected to the throttle. This is accomplished
through either a linkage or a cable. The cam forces
the kickdown valve toward the throttle valve com-
pressing the spring between them and moving the
throttle valve. As the throttle valve land starts to
uncover its port, line pressure is "metered" out into
the circuits and viewed as throttle pressure. This
increased throttle pressure is metered out into the
circuits it is applied to: the 1–2 and 2–3 shift valves.
When the throttle pressure is high enough, a 3–2
downshift will occur. If the vehicle speed is low
enough, a 2–1 downshift will occur.
SWITCH VALVE
When the transmission is in Drive Second just
before the TCC application occurs (Fig. 33), the pres-
sure regulator valve is supplying torque converter
pressure to the switch valve. The switch valve directs
this pressure through the transmission input shaft,
into the converter, through the converter, back out
between the input shaft and the reaction shaft, and
back up to the switch valve. From the switch valve,
the fluid pressure is directed to the transmission
cooler, and lubrication pressure returns from the
cooler to lubricate different portions of the transmis-
sion.
Once the TCC control valve has moved to the left
(Fig. 34), line pressure is directed to the fail–safe
valve, and then to the tip of the switch valve, forcing
the valve downward. The switch valve now vents oil
from the front of the piston in the torque converter,
and supplies line pressure to the (rear) apply side of
the torque converter piston. This pressure differen-
tial causes the piston to apply against the friction
material, cutting off any further flow of line pressure
oil. After the switch valve is shuttled downward
allowing line pressure to engage the TCC, torque
converter pressure is directed past the switch valve
into the transmission cooler and lubrication circuits.
CONVERTER CLUTCH CONTROL VALVE
The torque converter clutch (TCC) control valve
controls the back (ON) side of the torque converter
clutch. When the PCM energizes the TCC solenoid to
engage the converter clutch piston, pressure is
applied to the TCC control valve which moves to the
left and applies pressure to the fail–safe valve.
FAIL-SAFE VALVE
The pressure coming from the TCC control valve
dead–ends at the fail–safe valve until governor pres-
sure on the right side of the valve increases. The
pressure must be high enough to overcome the throt-
tle and spring pressure on the left side of the valve
and push the valve to the left. The pressure will then
flow to the switch valve.
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