Hummer H1 (2002+). Manual - part 52

 

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 Transmission/Transfer Case  5-7

  

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05745159

 

SHIFT SOLENOIDS

 

Two solenoids are used to control upshifts and downshifts in
the forward gear ranges. Solenoid A controls the 1-2 shift
valve while Solenoid B controls the 2-3 shift valve. Both sole-
noids are mounted on the valve body and operated by the
PCM.

The solenoids are energized or de-energized separately and in
combination to control shifts. The following chart outlines so-
lenoid activities in the various gear ranges.

The solenoids are de-energized when the PCM completes the
solenoid ground circuit. Incoming fluid passes around the
check ball and exits through the exhaust port (Figure 5-9). En-
ergizing the solenoid causes the coil to extend the plunger
blocking off the exhaust port. Incoming fluid is then routed
back to the 1-2 or 2-3 shift valve, overcomes spring pressure,
and moves the valve to required shift position.

An example of solenoid actuation is provided in Figure 5-10
which illustrates third gear flow. Solenoid A is de-energized
(off) causing signal A fluid to exhaust through the outlet port.
The 1-2 shift valve remains in position through normal valve
spring pressure. Energizing solenoid B, blocks the exhaust port
causing signal B and actuator feed pressure to act against the 2-
3 valve and spring. The two fluid pressures overcome spring
pressure moving the 2-3 valve into Upshift position. However,
in manual 1 and 2 ranges D21 fluid pressure prevents the 2-3
valve from moving to upshift position despite solenoid B ener-
gized state.

 

Figure 5-9:   Shift Solenoid Cross Section

Figure 5-10:   Shift Solenoid Actuation (Third Gear 

Shown)

 

Gear Range

1-2 Solenoid A

2-3 Solenoid B

 

Park, Reverse, 
Neutral

ON

OFF

First

ON

OFF

Second

OFF

OFF

Third

OFF

ON

Fourth

ON

ON

CONNECTOR

COIL

FRAME

PLUNGER

METERING

BALL

O-RING

SIGNAL

FLUID

INLET
PORT

EXHAUST

PORT

 

5-8

Transmission/Transfer Case

 

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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).

 

Figure 5-11:   Converter Clutch Solenoid Cross 

Section

 

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.

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.

 

Figure 5-12:   Pressure Control Solenoid In Energized 

(Closed) State

FRAME

COIL

CORE

METERING

BALL

O-RINGS

SIGNAL

FLUID

EXHAUST

PORT

CONNECTOR

PLUNGER

FILTERED

2-3 DRIVE

FLUID

CONVERTER

CLUTCH SIGNAL

FLUID INLET

VALVE

EXHAUST

PORT

ARMATURE

SPRING

COIL

ASSEMBLY

PLUNGER

FILTERED

ACTUATOR

FEED FLUID

DAMPER

SPRING

TORQUE

SIGNAL

FLUID

 

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 Transmission/Transfer Case  5-9

  

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05745159

 

Figure 5-13:   Pressure Control Solenoid Boost 

Schematics

 

ENGINE SENSOR INPUTS

 

The electronic accelerator pedal, coolant temperature sensor,
A/C switch, brake switch, and crankshaft position sensor, all
affect transmission operation.

The electronic accelerator pedal input signals inform the PCM
of throttle position. This input affects pressure control solenoid
operation and transmission line pressure. The solenoid in-
creases line pressure at higher throttle openings.

The coolant temperature sensor input affects transmission
shifting. The sensor signal can prevent shifts into overdrive
fourth gear when coolant temperatures are low or extremely
high.

Crankshaft position sensor inputs are used by the PCM to ad-
just shift points and fluid pressures.

A signal from the A/C switch informs the PCM when the A/C
switch and compressor are engaged. This signal affects trans-
mission shift points to compensate for increased engine load
and idle rpm.

The brake switch signal is used by the PCM to control down-
shift points and torque converter release. Brake application
completes the switch circuit to the PCM which then downshifts
the transmission as needed.

 

TORQUE CONVERTER

 

The torque converter consists of a cover, clutch pressure plate
and damper, turbine, stator, and pump (Figure 5-14).

A roller clutch in the stator hub prevents stator freewheeling
until coupling speed is reached. The clutch maintains torque
multiplication until this point.

The converter clutch, located between the cover/impeller and
the stator, eliminates normal internal slippage at cruise speeds.
The clutch pressure plate has friction material bonded to it that
engages the cover/impeller when applied. Clutch applied at
normal cruise speeds improves fuel economy and reduces fluid
temperature.

The converter is not a repairable part. It is serviced only by re-
placement.

EXHAUST

PORT

REVERSE/

BOOST

VALVE

PRESSURE

REGULATOR

VALVE

 

5-10

Transmission/Transfer Case

 

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Figure 5-14:   Torque Converter Components

STATOR

HUB

TURBINE

SHAFT

ROLLER

CLUTCH

STATOR SHAFT

(PART OF OIL

PUMP COVER)

CONVERTER

PUMP

TURBINE

CONVERTER

COVER/

IMPELLER

CLUTCH PRESSURE

PLATE AND DAMPER