Hummer H1 Service Manual page 207

5-8 Transmission/Transfer Case
TORQUE CONVERTER CLUTCH PULSE WIDTH
MODULATED SOLENOID
The torque converter clutch (TCC) solenoid is located on the
transmission valve body and is energized by the PCM. The
TCC solenoid acts on the TCC apply valve to control torque
converter clutch application.
The TCC solenoid is pulse width modulated by the PCM. This
means that the PCM pulses the solenoid so that the hydraulic
pressure against the torque converter clutch modulates. This
modulated pressure allows the TCC to slip slightly thus keep-
ing the TCC balanced just at the point of engagement.
In operation, energizing the solenoid allows converter clutch
signal fluid and 2-3 drive fluid, to act on the ball and plunger
(Figure 5-11).
CORE
COIL
FRAME
SIGNAL
FLUID
EXHAUST
PORT
PLUNGER
CONNECTOR
Figure 5-11: Converter Clutch Solenoid Cross
PRESSURE CONTROL SOLENOID VALVE
The solenoid (Figure 5-12) uses filtered actuator fluid to regu-
late torque signal fluid pressure. The solenoid is controlled by
the PCM and is located on the valve body.
Torque signal fluid increases line pressure when required.
Fluid is directed by the control solenoid against the reverse/
boost valve (Figure 5-13). Pressure on the boost valve forces it
against the pressure regulator valve adding to regulator valve
spring pressure. This action moves the pressure regulator valve
upward allowing greater flow into the line pressure feed pas-
sage.
The PCM energizes the control solenoid when throttle opening
decreases. Torque signal fluid pressure then falls off and the
regulator valve returns to normal position. Line pressures are
boosted at high throttle openings and during reverse gear oper-
ation only. A failure in the transmission electrical circuit will
also cause higher line pressures. This is a protective feature de-
signed to prevent clutch slip.
METERING
BALL O-RINGS
CONVERTER
CLUTCH SIGNAL
FLUID INLET
FILTERED
2-3 DRIVE
FLUID
Section
______________________________________________
Torque signal fluid from the solenoid, also affects the torque
signal compensator valve in the accumulator, and the accumu-
lator valve in the valve body.
At low throttle openings, the PCM applies a maximum of 1.1
amps current to the solenoid. This keeps the motor armature
and coil energized holding the plunger away from the valve.
The valve is moved inward by torque signal fluid pressure
blocking the filtered actuator feed port and exposing the ex-
haust port. Torque signal fluid then exits through the exhaust
port and returns to the system. Pressure on the reverse boost
valve is minimal or at zero.
At higher throttle openings, PCM current flow to the solenoid
decreases to zero. At this point, the solenoid armature and coil
are de-energized (Figure 5-12). The plunger and valve are
moved outward by spring force closing the exhaust port. Once
the exhaust port is closed, torque signal fluid is directed to the
boost valve. The combination of torque signal fluid and regula-
tor valve spring pressure, then moves the pressure regulator
valve to a higher pressure setting.
The solenoid replaces the vacuum modulator used on previous
transmissions. Torque signal fluid acts much like throttle pres-
sure fluid in prior transmissions.
FILTERED
ACTUATOR
FEED FLUID
VALVE
TORQUE
SIGNAL
FLUID
Figure 5-12: Pressure Control Solenoid In Energized
ARMATURE
EXHAUST
PORT
PLUNGER
ASSEMBLY
DAMPER
SPRING
(Closed) State
®
SPRING
COIL