Infiniti QX4 (R50). Manual — part 7
Control System
=NBAT0013
OUTLINE
NBAT0013S01
The automatic transmission senses vehicle operating conditions through various sensors. It always controls
the optimum shift position and reduces shifting and lock-up shocks.
SENSORS
E
TCM
E
ACTUATORS
PNP switch
Throttle position sensor
Closed throttle position switch
Wide open throttle position switch
Engine speed signal
A/T fluid temperature sensor
Revolution sensor
Vehicle speed sensor
Overdrive control switch
ASCD control unit
Stop lamp switch
Turbine revolution sensor
Shift control
Line pressure control
Lock-up control
Overrun clutch control
Timing control
Fail-safe control
Self-diagnosis
CONSULT-II communication
line
Duet-EU control
Shift solenoid valve A
Shift solenoid valve B
Overrun clutch solenoid valve
Torque converter clutch sole-
noid valve
Line pressure solenoid valve
O/D OFF indicator lamp
T/F control unit
CONTROL SYSTEM
NBAT0013S02
SAT125K
GI
MA
EM
LC
EC
FE
TF
PD
AX
SU
BR
ST
RS
BT
HA
SC
EL
IDX
OVERALL SYSTEM
Control System
AT-25
TCM FUNCTION
=NBAT0013S03
The function of the TCM is to:
I
Receive input signals sent from various switches and sensors.
I
Determine required line pressure, shifting point, lock-up operation, and engine brake operation.
I
Send required output signals to the respective solenoids.
INPUT/OUTPUT SIGNAL OF TCM
NBAT0013S04
Sensors and solenoid valves
Function
Input
PNP switch
Detects select lever position and sends a signal to TCM.
Throttle position sensor
Detects throttle valve position and sends a signal to TCM.
Closed throttle position switch
Detects throttle valve’s fully-closed position and sends a signal to TCM.
Wide open throttle position switch
Detects a throttle valve position of greater than 1/2 of full throttle and sends
a signal to TCM.
Engine speed signal
From ECM.
A/T fluid temperature sensor
Detects transmission fluid temperature and sends a signal to TCM.
Revolution sensor
Detects output shaft rpm and sends a signal to TCM.
Vehicle speed sensor
Used as an auxiliary vehicle speed sensor. Sends a signal when revolution
sensor (installed on transmission) malfunctions.
Overdrive control switch
Sends a signal, which prohibits a shift to “D
4
” (overdrive) position, to the
TCM.
ASCD control unit
Sends the cruise signal and “D
4
” (overdrive) cancellation signal from ASCD
control unit to TCM.
Turbine revolution sensor
Sends an input shaft revolution signal.
Stop lamp switch
Sends the lock-up release signal to the TCM at time of D
4
(lock-up).
Output
Shift solenoid valve A/B
Selects shifting point suited to driving conditions in relation to a signal sent
from TCM.
Line pressure solenoid valve
Regulates (or decreases) line pressure suited to driving conditions in rela-
tion to a signal sent from TCM.
Torque converter clutch solenoid
valve
Regulates (or decreases) lock-up pressure suited to driving conditions in
relation to a signal sent from TCM.
Overrun clutch solenoid valve
Controls an “engine brake” effect suited to driving conditions in relation to a
signal sent from TCM.
O/D OFF indicator lamp
Shows TCM faults, when A/T control components malfunction.
Control Mechanism
NBAT0180
LINE PRESSURE CONTROL
NBAT0180S01
TCM has the various line pressure control characteristics to meet
the driving conditions.
An ON-OFF duty signal is sent to the line pressure solenoid valve
based on TCM characteristics.
Hydraulic pressure on the clutch and brake is electronically con-
trolled through the line pressure solenoid valve to accommodate
engine torque. This results in smooth shift operation.
OVERALL SYSTEM
Control System (Cont’d)
AT-26
SAT003J
Normal Control
NBAT0180S0101
The line pressure to throttle opening characteristics is set for suit-
able clutch operation.
SAT004J
Back-up Control (Engine brake)
NBAT0180S0102
If the selector lever is shifted to “2” position while driving in D
4
(OD)
or D
3
, great driving force is applied to the clutch inside the trans-
mission. Clutch operating pressure (line pressure) must be
increased to deal with this driving force.
SAT005J
During Shift Change
NBAT0180S0103
The line pressure is temporarily reduced corresponding to a
change in engine torque when shifting gears (that is, when the shift
solenoid valve is switched for clutch operation) to reduce shifting
shock.
At Low Fluid Temperature
NBAT0180S0104
I
Fluid viscosity and frictional characteristics of the clutch facing
change with fluid temperature. Clutch engaging or band-con-
tacting pressure is compensated for, according to fluid
temperature, to stabilize shifting quality.
SAT006J
I
The line pressure is reduced below 60°C (140°F) to prevent
shifting shock due to low viscosity of automatic transmission
fluid when temperature is low.
GI
MA
EM
LC
EC
FE
TF
PD
AX
SU
BR
ST
RS
BT
HA
SC
EL
IDX
OVERALL SYSTEM
Control Mechanism (Cont’d)
AT-27
SAT007J
I
Line pressure is increased to a maximum irrespective of the
throttle opening when fluid temperature drops to −10°C (14°F).
This pressure rise is adopted to prevent a delay in clutch and
brake operation due to extreme drop of fluid viscosity at low
temperature.
SHIFT CONTROL
NBAT0180S02
The shift is regulated entirely by electronic control to accommodate
vehicle speed and varying engine operations. This is accomplished
by electrical signals transmitted by the revolution sensor and
throttle position sensor. This results in improved acceleration per-
formance and fuel economy.
SAT008J
Control of Shift Solenoid Valves A and B
NBAT0180S0201
The TCM activates shift solenoid valves A and B according to sig-
nals from the throttle position sensor and revolution sensor to
select the optimum gear position on the basis of the shift schedule
memorized in the TCM.
The shift solenoid valve performs simple ON-OFF operation. When
set to “ON”, the drain circuit closes and pilot pressure is applied to
the shift valve.
[Relation between shift solenoid valves A and B and gear positions]
Shift solenoid valve
Gear position
D
1
, 2
1
, 1
1
D
2
, 2
2
, 1
2
D
3
D
4
(OD)
N-P
A
ON (Closed)
OFF (Open)
OFF (Open)
ON (Closed)
ON (Closed)
B
ON (Closed)
ON (Closed)
OFF (Open)
OFF (Open)
ON (Closed)
Control of Shift Valves A and B
NBAT0180S0202
SAT047J
OVERALL SYSTEM
Control Mechanism (Cont’d)
AT-28
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