Infiniti QX4 (R50). Manual - part 8

Pilot pressure generated by the operation of shift solenoid valves
A and B is applied to the end face of shift valves A and B.
The drawing above shows the operation of shift valve B. When the
shift solenoid valve is “ON”, pilot pressure applied to the end face
of the shift valve overcomes spring force, moving the valve upward.

LOCK-UP CONTROL

NBAT0180S03

The torque converter clutch piston in the torque converter is locked
to eliminate torque converter slip to increase power transmission
efficiency. The solenoid valve is controlled by an ON-OFF duty
signal sent from the TCM. The signal is converted to oil pressure
signal which controls the torque converter clutch piston.

Conditions for Lock-up Operation

NBAT0180S0301

When vehicle is driven in 4th gear position, vehicle speed and
throttle opening are detected. If the detected values fall within the
lock-up zone memorized in the TCM, lock-up is performed.

Overdrive control switch

OFF

Selector lever

“D” position

Gear position

Vehicle speed sensor

More than set value

Throttle position sensor

Less than set opening

Closed throttle position switch

OFF

A/T fluid temperature sensor

More than 40°C (104°F)

SAT010J

Torque Converter Clutch Solenoid Valve Control

NBAT0180S0302

The torque converter clutch solenoid valve is controlled by the
TCM. The plunger closes the drain circuit during the “OFF” period,
and opens the circuit during the “ON” period. If the percentage of
OFF-time increases in one cycle, the pilot pressure drain time is
reduced and pilot pressure remains high.
The torque converter clutch piston is designed to slip to adjust the
ratio of ON-OFF, thereby reducing lock-up shock.

SAT011J

OFF-time INCREASING

Amount of drain DECREASING

Pilot pressure HIGH

Lock-up RELEASING

IDX

OVERALL SYSTEM

Control Mechanism (Cont’d)

AT-29

Torque Converter Clutch Control Valve Operation

NBAT0180S0303

SAT048J

Lock-up Released
The OFF-duration of the torque converter clutch solenoid valve is
long, and pilot pressure is high. The pilot pressure pushes the end
face of the torque converter clutch control valve in combination with
spring force to move the valve to the left. As a result, converter
pressure is applied to chamber A (torque converter clutch piston
release side). Accordingly, the torque converter clutch piston
remains unlocked.
Lock-up Applied
When the OFF-duration of the torque converter clutch solenoid
valve is short, pilot pressure drains and becomes low. Accordingly,
the control valve moves to the right by the pilot pressure of the
other circuit and converter pressure. As a result, converter pres-
sure is applied to chamber B, keeping the torque converter clutch
piston applied.
Also smooth lock-up is provided by transient application and
release of the lock-up.

OVERRUN CLUTCH CONTROL (ENGINE BRAKE
CONTROL)

NBAT0180S04

Forward one-way clutch is used to reduce shifting shocks in down-
shifting operations. This clutch transmits engine torque to the
wheels. However, drive force from the wheels is not transmitted to
the engine because the one-way clutch rotates idle. This means the
engine brake is not effective.
The overrun clutch operates when the engine brake is needed.

Overrun Clutch Operating Conditions

NBAT0180S0401

Gear position

Throttle opening

“D” position

, D

gear position

Less than 3/16

“2” position

, 2

gear position

“1” position

, 1

gear position

At any position

SAT014J

OVERALL SYSTEM

Control Mechanism (Cont’d)

AT-30

SAT015J

Overrun Clutch Solenoid Valve Control

NBAT0180S0402

The overrun clutch solenoid valve is operated by an ON-OFF sig-
nal transmitted by the TCM to provide overrun clutch control
(engine brake control).
When this solenoid valve is “ON”, the pilot pressure drain port
closes. When it is “OFF”, the drain port opens.
During the solenoid valve “ON” pilot pressure is applied to the end
face of the overrun clutch control valve.

SAT049J

Overrun Clutch Control Valve Operation

NBAT0180S0403

When the solenoid valve is “ON”, pilot pressure A is applied to the
overrun clutch control valve. This pushes up the overrun clutch
control valve. The line pressure is then shut off so that the clutch
does not engage.
When the solenoid valve is “OFF”, pilot pressure A is not gener-
ated. At this point, the overrun clutch control valve moves down-
ward by spring force. As a result, overrun clutch operation pressure
is provided by the overrun clutch reducing valve. This causes the
overrun clutch to engage.
In the “1” position, the overrun clutch control valve remains pushed
down so that the overrun clutch is engaged at all times.

Control Valve

NBAT0181

FUNCTION OF CONTROL VALVE

NBAT0181S01

Valve name

Function

Pressure regulator valve

Pressure regulator plug

Pressure regulator sleeve plug

Regulate oil discharged from the oil pump to provide optimum line pressure for all
driving conditions.

Pressure modifier valve

Used as a signal supplementary valve to the pressure regulator valve. Regulates
pressure-modifier pressure (signal pressure) which controls optimum line pressure for
all driving conditions.

Modifier accumulator piston

Smooths hydraulic pressure regulated by the pressure modifier valve to prevent pul-
sations.

Pilot valve

Regulates line pressure to maintain a constant pilot pressure level which controls
lock-up mechanism, overrun clutch, 3-2 timing required for shifting.

Accumulator control valve
Accumulator control sleeve

Regulate accumulator back-pressure to pressure suited to driving conditions.

Manual valve

Directs line pressure to oil circuits corresponding to select positions.
Hydraulic pressure drains when the shift lever is in Neutral.

IDX

OVERALL SYSTEM

Control Mechanism (Cont’d)

AT-31

Valve name

Function

Shift valve A

Simultaneously switches three oil circuits using output pressure of shift solenoid valve
A to meet driving conditions (vehicle speed, throttle opening, etc.).
Provides automatic downshifting and up-shifting (1st

2nd

3rd

4th gears/4th

3rd

2nd

1st gears) in combination with shift valve B.

Shift valve B

Simultaneously switches three oil circuits using output pressure of shift solenoid valve
B in relation to driving conditions (vehicle speed, throttle opening, etc.).
Provides automatic downshifting and up-shifting (1st

2nd

3rd

4th gears/4th

3rd

2nd

1st gears) in combination with shift valve A.

Shuttle shift valve S

Switches hydraulic circuits to provide 3-2 timing control and overrun clutch control in
relation to the throttle opening.
Inactivates the overrun clutch to prevent interlocking in 4th gear when the throttle is
wide open.

Overrun clutch control valve

Switches hydraulic circuits to prevent engagement of the overrun clutch simulta-
neously with application of the brake band in 4th gear. (Interlocking occurs if the
overrun clutch engages during D

gear operation.)

4-2 relay valve

Memorizes that the transmission is in 4th gear. Prevents the transmission from down-
shifting from 4th gear to 3rd and then to 2nd in combination with 4-2 sequence valve
and shift valves A and B when downshifting from 4th to 2nd gear.

4-2 sequence valve

Prevents band servo pressure from draining before high clutch operating pressure
and band servo releasing pressure drain (from the same circuit) during downshifting
from 4th to 2nd gear.

Servo charger valve

An accumulator and a one-way orifice are used in the 2nd gear band servo oil circuit
to dampen shifting shock when shifting from 1st to 2nd gear.
To maintain adequate flow rate when downshifting from 4th or 3rd gear to 2nd gear,
the servo charger valve directs 2nd gear band servo hydraulic pressure to the circuit
without going through the one-way orifice when downshifting from 3rd or a higher
gear.

3-2 timing valve

Prevents a late operation of the brake band when shifting selector lever from “D” to
“1” or “2” position while driving in D

“1” reducing valve

Reduces low & reverse brake pressure to dampen engine-brake shock when down-
shifting from the “1” position 2nd gear to 1st gear.

Overrun clutch reducing valve

Reduces oil pressure directed to the overrun clutch and prevents engine-brake shock.
In “1” and “2” positions, line pressure acts on the overrun clutch reducing valve to
increase the pressure-regulating point, with resultant engine brake capability.

Torque converter relief valve

Prevents an excessive rise in torque converter pressure.

Torque converter clutch control valve,
torque converter clutch control plug and
torque converter clutch control sleeve

Activate or inactivate the lock-up function.
Also provide smooth lock-up through transient application and release of the lock-up
system.

Shuttle shift valve D

Switches hydraulic circuits so that output pressure of the torque converter clutch sole-
noid valve acts on the lock-up valve in the “D” position of 2nd, 3rd and 4th gears. (In
the “D” position 1st gear, lock-up is inhibited.)

Lock-up control is not affected in “D” position 2nd, 3rd or 4th gears, unless output
pressure of the torque converter clutch solenoid valve is generated by a signal
from the control unit.

OVERALL SYSTEM

Control Valve (Cont’d)

AT-32

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