ACURA NSX 1991 Service Repair Manual

Description

Hydraulic Flow (cont'd)

The line pressure (1) becomes the line pressure (4), (18), (25) as it passes through the manual valve. Also, the line pressure (1) goes to the modulator valve through the filter and becomes the modulator pressure (6). The modulator pressure (6)
is supplied to the 1-2 shift valve and 2-3 shift valve. The 1 -2 shift and 2-3 shift valves are moved to the left side because the shift control solenoid valve A is turned ON and B

is OFF by the
TCM.
The line pressure (18) is supplied to the 3-4 shift valve, and it is moved to the left side. The line pressure (4) is the 1st
clutch pressure (10), then the 1st clutch is engaged.
The line pressure (4) becomes the 1st-hold clutch pressure (16) via the 1-2 shift valve, 2-3 shift valve, 3-4 shift valve
and manual valve, then the 1st-hold clutch is engaged.

NOTE:
When used,
"left"
or
"right" indicates
direction
on the
flowchart.
PositionProCarManuals.com

The line pressure (1) becomes the line pressure (4), (25) as it passes through the manual valve.

The line pressure (1) goes to the modulator valve and becomes the modulator pressure (6). The modulator pressure (6)

is supplied to the 1-2 shift valve and 3-4 shift valve. The 1-2 shift and 3-4 shift valves are moved to the left side and

the 2-3 shift valve is moved to the right side because the shift control solenoid valve A and B are turned OFF by the

TCM.

The line pressure (4) goes through the 2nd clutch pressure (20) to the 2nd clutch, then the 2nd clutch is engaged.

The line pressure (4) passing through the orifice becomes the 1st clutch pressure (10) and flows to the 1st clutch.

However no power is transmitted by means of the one-way clutch.

NOTE: When used,
"left"
or
"right"
indicates direction
on the
flowchart.

(cont'd)
PositionProCarManuals.com

Description

Hydraulic Flow (cont'd)

The line pressure (1) becomes the modulator pressure (6) as it passes the modulator valve.

Also, the modulator pressure (6) is supplied to the 1 -2 shift valve and 2-3 shift valve, and they are moved to the left side

because the shift control solenoid A is turned ON and B is OFF by the TCM.

The line pressure (4) becomes the clutch pressure control (5) and the 3rd clutch pressure (31).

Then it goes to the 3rd clutch. The 3rd clutch is engaged.

The line pressure (4) passing through the orifice becomes the 1st clutch pressure (10) and flows to the 1st clutch.

However no power is transmitted by means of the one-way clutch as in 2nd speed.

NOTE:
When used,
"left"
or
"right"
indicates direction
on the
flowchart.
PositionProCarManuals.com

1st speed

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

The line pressure (1) becomes the line pressure (4) and it becomes the 1st clutch pressure (10).

The 1st clutch pressure is applied to the 1st clutch and 1st accumulator, consequently the vehicle will move as the

engine power is transmitted.

The line pressure (1) becomes the modulator pressure (6) by the modulator valve and travels to each shift valve.

The 1-2 shift valve is moved to the right side because the shift control solenoid valve A is turned OFF and B is ON by

the
TCM.

The line pressure (1) also flows to the throttle valve.

NOTE: When used,
"left"
or
"right"
indicates direction
on the
flowchart.

(cont'd)
PositionProCarManuals.com

Description

Hydraulic Flow (cont'd)

2nd.speed

The flow of fluid up to the 1-2 and 2-3 shift valves is the same as in the 1st speed range. As the speed of the car

reaches the prescribed value, the solenoid valve A is turned ON by means of the TCM. As a result, the 1 -2 shift valve

is moved to the left side and uncovers the port leading to the 2nd clutch; the 2nd clutch is engaged.

Fluid flows by way of:

Line Pressure (4)

2-3 Shift Valve
CPC Valve
Clutch Pressure Control (4')
1 -2 Shift Valve

Clutch Pressure Control (5)

2nd Clutch Pressure (21)
Orifice

2nd Clutch Pressure (20)
2nd Clutch

The hydraulic pressure also flows to the 1 st clutch. However no power is transmitted by means of the one-way

clutch.

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

3. 3rd Speed

The flow of fluid up to the 1-2, 2-3 and 3-4 shift valves is the same as in the 2nd speed. As the speed of the car

reaches the prescribed value, the shift control solenoid valve B is turned OFF (Shift control solenoid valve A remains

ON). The 2-3 shift valve is then moved to the left side, uncovering the oil port leading to the 3rd clutch. Since the

3-4 shift valve is moved to the right side to cover the oil port to the 4th clutch, the 3rd clutch is engaged.

Fluid flows by way of:

(cont'd)
Line Pressure (4)
CPC Valve
Clutch Pressure Control (4')
1-2 Shift Valve
Clutch Pressure Control

(5)
2-3 Shift Valve
Clutch Pressure Control (5)
3-4 Shift Valve
3rd Clutch Pressure (31)
3rd Clutch

The hydraulic pressure also flows to the 1st clutch. However no power is transmitted by means of the one-way

clutch as in the 2nd speed.

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

Description

Hydraulic Flow (cont'd)

4. 4th Speed

The flow of fluid up to the 1-2, 2-3 and 3-4 shift valves is the same as in the 3rd speed. When the speed of the

car reaches the prescribed value, the shift control solenoid valve A is turned OFF (Shift control solenoid valve B remains

OFF). As this takes place, the 3-4 shift valve is moved to the left side and uncovers the oil port leading to the 4th

clutch. Since the 1-2 and 2-3 shift valves are kept on the left side, the fluid flows through the 4th clutch; the power

is transmitted through the 4th clutch.

Fluid flows by way of:

Line Pressure (4)
CPC Valve
Clutch Pressure Control (4')
1 -2 Shift Valve

Clutch Pressure Control

(5)
2-3 Shift Valve
Clutch Pressure Control (5)
3-4 Shift Valve
4th Clutch Pressure (41)

Manual

Valve
4th Clutch Pressure (40)
4th Clutch

The hydraulic pressure also flows to the 1st clutch. However no power is transmitted by means of the one-way

clutch as in 2nd and 3rd speed.

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

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

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

valve (3), causing the shift fork shaft to be moved in to the reverse position.

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

result, the 1 -2 shift valve is also moved to the left side. The fluid (3') will flow through the servo valve and manual valve

to the 4th clutch; 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), the 1-2 shift valve is moved to the right side. The line pressure (3) is intercepted by

the 1 -2 shift valve, consequently the power is not transmitted as the 4th clutch and servo valve are not operated.

NOTE:
When used,
"left"
or
"right"
indicates direction
on the
flowchart.

(cont'd)
PositionProCarManuals.com

Description

Hydraulic Flow (cont'd)

Position

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

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

through the 1 -2 shift valve to the servo valve and the servo control valve, causing the shift fork to be moved to the

reverse position as in the position.

However, the hydraulic pressure is not supplied to the clutches. The power is not transmitted.

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

Lock-up System
In position and position in 2nd, 3rd and 4th, pressurized fluid is drained from the back of the torque converter
through an oil passage, causing the lock-up piston to be held against the torque converter cover. As this takes place, themainshaft 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 3rd and 4th speed.
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 solenoidvalves A and B are mounted on the torque converter housing, and are controlled by the TCM.
(cont'd)ProCarManuals.com