Nissan Silvia. Manual — part 7
TCM FUNCTION
=NMAT0013S03
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
NMAT0013S04
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 revolu-
tion sensor (installed on transmission) malfunctions.
Overdrive control switch
A/T mode switch
Sends a signal, which prohibits a shift to “D
4
” (overdrive) position, to the
TCM.
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 or POWER indicator lamp
Shows TCM faults, when A/T control components malfunction.
Control Mechanism
NMAT0180
LINE PRESSURE CONTROL
NMAT0180S01
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.
GI
MA
EM
LC
EC
FE
CL
MT
PD
AX
SU
BR
ST
RS
BT
HA
SC
EL
IDX
OVERALL SYSTEM
Control System (Cont’d)
AT-25
SAT003J
Normal Control
NMAT0180S0101
The line pressure to throttle opening characteristics is set for suit-
able clutch operation.
SAT004J
Back-up Control (Engine brake)
NMAT0180S0102
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
NMAT0180S0103
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
NMAT0180S0104
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.
OVERALL SYSTEM
Control Mechanism (Cont’d)
AT-26
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
NMAT0180S02
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
NMAT0180S0201
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
NMAT0180S0202
SAT047J
GI
MA
EM
LC
EC
FE
CL
MT
PD
AX
SU
BR
ST
RS
BT
HA
SC
EL
IDX
OVERALL SYSTEM
Control Mechanism (Cont’d)
AT-27
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
NMAT0180S03
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
NMAT0180S0301
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
ON
OFF
Selector lever
“D” position
Gear position
D
4
D
3
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
NMAT0180S0302
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
OVERALL SYSTEM
Control Mechanism (Cont’d)
AT-28
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