1997 ACURA NSX Service Repair Manual

Position

The flow of fluid through the torque converter circuit is the same as in the position. Fluid (1) from the ATF pump flows

through the manual valve and becomes line pressure (3). It then flows through the 1-2 shift valve to the servo valve (3),

moving the shift fork shaft to the reverse position.

Under this condition, shift control solenoid valve A is turned ON and valve B is turned OFF as in 3rd gear. As a result, the

1-2 shift valve moves to the left side. Fluid (3') flows through the servo valve and the manual valve to the 4th clutch, and

power is transmitted through the 4th clutch.

Reverse Inhibitor Control

When the position is selected while the vehicle is moving forward at a speed over 6 mph (10 km/h), the TCM out-

puts 1st signal (A: OFF, B: ON), and the 1-2 shift valve is moved to the right side. Line pressure (3) is intercepted by

the 1-2 shift valve, and power is not transmitted since the 4th clutch and the servo valve are not operating.

NOTE: When used, "left" or "right" indicates direction on the hydraulic circuit.
Hydraulic Flow (cont'd)
DescriptionProCarManuals.com

Position

The flow of fluid through the torque converter circuit is the same as in position.

Line pressure (1) becomes line pressure (3) as it passes through the manual valve. Line pressure (3) flows through the 1-2

shift valve, to the servo valve, and to the servo control valve, moving the shift fork to the reverse position as in the

position.

Hydraulic pressure is not supplied to the clutches, and power is not transmitted.

NOTE: When used, "left" or "right" indicates direction on the hydraulic circuit.ProCarManuals.com

Lock-up System
Description

Lock-up Clutch

1. Operation (clutch on)

With the lock-up clutch on, fluid in the chamber between the converter cover and lock-up piston is discharged, and the

converter fluid exerts pressure through the piston against the converter cover. As a result, the converter turbine is locked

on the converter cover firmly. This bypasses the converter, placing the vehicle in direct drive.

2. Operation (clutch off)

With the lock-up clutch off, fluid flows in the reverse of CLUTCH ON. As a result, the lock-up piston moves away from the

converter cover, and the torque converter lock-up is released.ProCarManuals.com

In position and position (2nd, 3rd, and 4th gear), pressurized fluid is drained from the back of the torque converter

through a passage, causing the lock-up piston to be held against the torque converter cover. As this takes place, the main-

shaft rotates at the same speed as the engine crankshaft. Together with hydraulic control, the TCM optimizes the timing of

the lock-up system. Under certain conditions, the lock-up operation is applied during deceleration, in position in (2nd,

3rd, and 4th gear), and in position (3rd and 4th gears).

The lock-up shift valve controls the range of lock-up according to lock-up control solenoid valves A and B, and throttle

valve B. When lock-up control solenoid valves A and B activate, modulator pressure changes. Lock-up control solenoid

valves A and B are mounted on the torque converter housing, and are controlled by the TCM.ProCarManuals.com

No Lock-up

Pressurized fluid regulated by the modulator works on both ends of the lock-up shift valve and on the left side of the lock-

up control valve. Under this condition, the pressure on both ends of the lock-up shift valve are equal, and the shift valve is

moved to the right side by valve spring tension. Fluid from the ATF pump flows through the left side of the lock-up clutch

to the torque converter; the lock up clutch is OFF.

NOTE: When used, "left" or "right" indicates direction on the hydraulic circuit.
Lock-up System (cont'd)
DescriptionProCarManuals.com

Partial Lock-up

Lock-up Control Solenoid Valve A: ON Lock-up Control Solenoid Valve B: OFF

The TCM switches solenoid valve A ON to release modulator pressure in the left cavity of the lock-up shift valve.

Modulator pressure in the right cavity of the lock-up shift valve overcomes the spring force, and the lock-up shift valve is

moved to the left side.

The torque converter pressure is separated into two passages:

Torque Converter Inner Pressure: enters into right side to engage lock-up clutch

Torque Converter Back Pressure: enters into left side to disengage lock-up clutch

Back pressure (F2) is regulated by the lock-up control valve, and the position of the lock-up timing valve B is determined

by throttle B pressure, tension of the valve spring, and pressure regulated by the modulator. Also, the position of the lock-

up control valve is determined by throttle valve B pressure, back pressure of the lock-up control valve, and torque converter

pressure regulated by the check valve. In low speed range, throttle B pressure working on the right side of the lock-up con-

trol valve is low, causing the valve to be moved to the right side. With the lock-up control solenoid valve B kept OFF, mod-

ulator pressure is maintained in the left end of the lock-up control valve; the lock-up control valve is moved slightly to the

left side. This slight movement of the lock-up control valve causes the back pressure to be lowered slightly, resulting in

partial lock-up.

NOTE: When used, "left" or "right" indicates direction on the hydraulic circuit.ProCarManuals.com

Half Lock-up

Lock-up Control Solenoid Valve A: ON Lock-up Control Solenoid Valve B: ON

Modulator pressure is released by solenoid valve B, causing modulator pressure in the left cavity of the lock-up control

valve to lower.

Also, modulator pressure in the left cavity of the lock-up timing valve B is low. Throttle B pressure is still low at this time,

so, lock-up timing valve B is kept on the right side by spring force.

With lock-up control solenoid valve B turned ON, the lock-up control valve is moved somewhat to the right side, causing

back pressure (F2) to lower. This allows move fluid (F1) to work on the lock-up clutch to engage the clutch. Back pressure

(F2), which still exists, prevents the clutch from engaging fully.

NOTE: When used, "left" or "right" indicates direction on the hydraulic circuit.
Lock-up System (cont'd)
DescriptionProCarManuals.com

Full Lock-up

Lock-up Control Solenoid Valve A: ON Lock-up Control Solenoid Valve B: ON

When the vehicle speed further increases, the throttle B pressure is increased in accordance with the throttle opening.

The lock-up timing valve B overcomes the spring force and moves to the left side. Also this valve closes the fluid port

leading to the torque converter check valve.

Under this condition, the throttle B pressure working on the right end of the lock-up control valve becomes greater than

that on the left end (modulator pressure in the left end has already been released by the solenoid valve B); i. e., the lock-

up control valve is moved to the left side. As this happens, the torque converter back pressure is released fully, causing

the lock-up clutch to be engaged fully.

NOTE: When used, "left" or "right" indicates direction on the hydraulic circuit.ProCarManuals.com