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Nissan Silvia. Manual - part 7

TCM FUNCTION

=NMAT0013S03

The function of the TCM is to:

Receive input signals sent from various switches and sensors.

Determine required line pressure, shifting point, lock-up operation, and engine brake operation.

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

” (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.

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

(OD)

or D

, 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

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

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

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

, 2

, 1

, 2

, 1

(OD)

N-P

ON (Closed)

OFF (Open)

ON (Closed)

OFF (Open)

ON (Closed)

Control of Shift Valves A and B

NMAT0180S0202

SAT047J

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

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

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

Content .. 5 6 7 8 ..