1991 ACURA NSX Service Repair Manual

Electronic Control System

Electronic Control System

The electronic control system consists of the Transmission Control module (TCM), sensors, a linear solenoid and 4

solenoid valves. Shifting and lock-up are electronically controlled for comfortable driving under and conditions.

The TCM is located on the insulator center bulkhead, behind the driver's seat.

Shift control

Shifting is related to engine torque through the linear solenoid used to operate throttle valve B which is controlled by the

TCM.

Getting a signal from each sensor, the TCM detects the appropriate gear shifting and activates shift control solenoid

valves A and/or B.

The combination of driving signals to shift control solenoid valves A and B is shown in the table below.

Lock-up control

From sensor input signals, the TCM detects whether to turn the lock-up ON or OFF and activates lock-up control solenoid

valve A and/or B accordingly.

The combination of driving signals to lock-up control solenoid valves A and B is shown in the table below.

(cont'd)ProCarManuals.com

Description
Electronic Control System (cont'd)
TRANSMISSION CONTROL MODULE (TCM)

ENGINE
CONTROL
MODULE
(ECM) Shift Control

Lock-up

Control

TCS Control Unit
EPS Control Unit Engine RPM
Air Conditioning Signal Brake Switch Signal
Vehicle Speed Sensor Signal
Mainshaft Speed Sensor Signal
Countershaft Speed Sensor Signal

Self-Diagnosis
Function

Self-Diagnosis Indicator

INTERLOCK
CONTROL UNIT
Lock-up Control Solenoid
Valve B
Lock-up Control Solenoid
Valve A Shift Control Solenoid

Valve B

Shift Control Solenoid
Valve A

Linear Solenoid
Throttle Position
Sensor Signal
Engine Coolant

Temperature
Sensor Signal
Accet Pedal

Angle Signal

Service Check
Connector
ProCarManuals.com

Description

Hydraulic Control

The valve bodies include the main valve body, regulator valve body, lock-up valve body, secondary valve body, servo

body, throttle valve body and 2nd accumulator body.

The oil pump is driven by splines on the left end of the torque converter which is attached to the engine. Oil flows through

the regulator valve to maintain specified pressure through the main valve body to the manual valve, and the servo body,

directing pressure to each of the clutches.

Vehicle Speed Signal

2ND ACCUMULATOR BODY

REGULATOR VALVE BODY

LOCK-UP VALVE BODY

SERVO BODY

THROTTLE VALVE BODY

LINEAR SOLENOID
SECONDARY VALVE BODY
MAIN VALVE BODYProCarManuals.com

Throttle Valve Body

The throttle valve body is mounted on the servo valve body with the throttle valve built in.

LINEAR

SOLENOID
THROTTLE VALVE B

THROTTLE VALVE

BODY

Throttle Valve B, Linear Solenoid

Throttle valve B converts changes in the throttle opening to changes in transmission hydraulic pressure, to determine

transmission shift quality and lock-up operation. The throttle valve B also operates on accumulator back pressure to

make smooth changes from one gear to another.

The end of the valve contacts the linear solenoid which is controlled by the TCM.

The throttle pedal load has been reduced by eliminating the cable.

(cont'd)
LINEAR SOLENOIDProCarManuals.com

Description

Hydraulic Control (cont'd)

Regulator Valve Body

The regulator valve body is mounted on the main valve body with the regulator valve, lock-up control valve and cooler

relief valve built in. The stator shaft arm contacts the end of the regulator valve.

The hydraulic pressure (line pressure) is controlled by the regulator valve.

COOLER RELIEF VALVE

REGULATOR VALVE

LOCK-UP CONTROL

VALVE

STATOR SHAFT ARM
REGULATOR VALVE

BODYProCarManuals.com

Regulator Valve

The regulator valve maintains a constant hydraulic pressure sent from the oil pump to the hydraulic control system, while

also furnishing oil to the lubricating system and torque converter.

Oil flows through B and B'. The oil which enters through B flows through the valve orifice to A pushing the regula* 01

valve to the right. According to the level of hydraulic pressure through B, the position of the valve changes, and the

amount of the oil through B' from D also changes. This operation is continued, maintaining line pressure.

(ENGINE NOT RUNNING) (ENGINE RUNNING)

To TORQUE CONVERTER

Stator Reaction Hydraulic Pressure Control

Hydraulic pressure increase according to torque is performed by the regulator valve using stator torque reaction. The

stator shaft is splined in the stator and its arm end contacts the regulator spring cap. When the car is accelerating or

climbing (Torque Converter Range), stator torque reaction acts on the stator shaft and the stator arm pushes the regula-

tor spring cap in this direction in proportion to the reaction. The spring compresses and the valve moves to increase

the regulated control pressure or line pressure. Line pressure is maximum when the stator reaction is maximum.
To RELIEF VALVE
From OIL PUMP

STATOR SHAFT

(cont'd)

REGULATOR SPRING CAP
REGULATOR VALVEProCarManuals.com

Description

Hydraulic Control (cont'd)

Main Valve Body

The main valve body is located on the torque converter housing. The oil pump gear, torque converter check valve, manu-

al valve, 1 —2, 2—3, 3—4 shift valves, relief valve and one-way relief valve are all built into the main valve body.

The primary function of this valve body is switching on and off oil passages and controlling the hydraulic pressure going

to the hydraulic control system.

TORQUE COVERTER

CHECK VALVE
OIL PUMP DRIVEN GEAR

OIL PUMP DRIVE GEAR

MANUAL VALVE

DETENT SPRING

MAIN VALVE BODY

2-3 SHIFT VALVE

1-2 SHIFT VALVE
MANUAL VALVE
3-4 SHIFT

VALVE
ONE-WAY RELIEF

VALVE
RELIEF VALVEProCarManuals.com

Oil Pump

The external tooth gear type oil pump consists of a housing together with the main valve body, a pump drive gear, a

pump driven gear, and a pump shaft. The oil pump is installed on the torque converter housing. The pump's driving force

is transmitted by the torque converter pump (directly connected to the engine) to the pump shaft. The gears are provided

in the housing. The intake and exhaust lines and the torque converter line are provided in the housing.

One way Relief Valve

The one-way relief valve is used at times of high speed or high temperature to send relief oil to the oil cooler so that

cooling of ATF will be effective.

(cont'd)ProCarManuals.com