1997 ACURA NSX transmission

Description

The automatic transmission is a combination of a 3-element torque converter and a triple-shaft electronically controlled

automatic transmission which provides 4 speeds forward and 1 speed reverse. The entire unit is positioned in line with the

engine.

Torque Converter, Gears, and Clutches

The torque converter consists of a pump, turbine, and stator, assembled in a single unit.

They are connected to the engine crankshaft so they turn together as a unit as the engine turns.

Around the outside of the torque converter is a ring gear which meshes with the starter pinion when the engine is being

started. The entire torque converter assembly serves as a flywheel while transmitting power to the transmission main-

shaft. The transmission has three parallel shafts: the mainshaft, the countershaft, and the secondary shaft. The mainshaft

is in line with the engine crankshaft.

The mainshaft includes the 1st and 4th clutches, and gears for 3rd, 4th, reverse, and 1st (3rd gear is integral with the main-

shaft, while reverse gear is integral with 4th gear).

The countershaft includes the 1st-hold and 3rd clutches, and gears for 2nd, 3rd, 4th, reverse, 1st, and parking.

The secondary shaft includes the 2nd clutch and gears for 2nd and 3rd.

The 4th and reverse gears can be locked to the countershaft at its center, providing 4th gear or reverse, depending on

which way the selector is moved.

The gears on the mainshaft and secondary shaft are in constant mesh with those on the countershaft.

When certain combinations of gears in the transmission are engaged by clutches, power is transmitted from the mainshaft

to the countershaft to provide positions.

Electronic Control

The electronic control system consists of the Transmission Control Module (TCM), sensors, a linear solenoid, a shift switch,

and 4 solenoid valves. Shifting and lock-up are electronically controlled for comfortable driving under all conditions.

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

Hydraulic Control

The valve bodies include the main valve body, secondary valve body, servo body, regulator valve body, throttle valve

body, lock-up valve body, and the 2nd accumulator body.

They are bolted to the torque converter housing as an assembly.

The main valve body contains the manual valve, 1-2 shift valve, 2-3 shift valve, 3-4 shift valve, relief valve, one-way relief

valve, and oil pump gears.

The secondary valve body contains the 3-2 kick-down valve, clutch pressure control (CPC) valve, 2nd orifice control valve, 3rd

orifice control valve, modulator valve, 4th exhaust valve, servo control valve, 2nd exhaust valve, and 4-3 kick-down valve.

The servo body contains the accumulator pistons and servo valve. The throttle valve body includes the throttle valve B

which is bolted to the servo body.

The regulator valve body contains the pressure regulator valve, lock-up control valve, and cooler relief valve. Fluid from

the regulator passes through the manual valve to the various control valves.

The lock-up valve body contains the lock-up timing B valve and lock-up shift valve. The 2nd accumulator body contains

the accumulator pistons and limited slip differential relief valve.

The torque converter check valve is located in the torque converter housing, under the main valve body.

The 1st, 1st-hold, 3rd, and 4th clutches receive fluid from their respective feed pipes and the 2nd clutch receives fluid from

the internal hydraulic circuit.

Shift Control Mechanism

Input from various sensors located throughout the vehicle determines which shift control solenoid valve the TCM will acti-

vate. Activating a shift control solenoid valve changes modulator pressure, causing a shift valve to move. This pressurizes

a line to one of the clutches, engaging that clutch and its corresponding gear.

Lock-up Mechanism

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

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

mainshaft rotates at the same speed as the engine crankshaft. Together with hydraulic control, the TCM optimizes the tim-

ing of the lock-up mechanism.

The lock-up valves control 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. The lock-up control solenoid valves

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

(cont'd)ProCarManuals.com

(cont'd)
Description

Gear Selection

Starting is possible only in positions through use of a slide-type, neutral-safety switch.

Automatic Transaxle (A/T) Gear Position Indicator

The A/T gear position indicator in the instrument panel shows what gear has been selected without having to look down

at the console.

With the shift lever in the position, the indicator light next to the in the instrument panel will display the gear

selected.

ATF Cooler

With this mid-engine type vehicle, the radiator is mounted at the front of the vehicle, so the ATF cooler is installed directly

on the transmission housing.
Rear wheels locked; parking pawl engaged with parking gear on countershaft.

All clutches released.

Reverse; reverse selector engaged with countershaft reverse gear and 4th clutch locked.

All clutches released.

General driving; starts off in 1st, shifts automatically to 2nd, 3rd, then 4th, depending on

vehicle speed and throttle position. Downshifts through 3rd, 2nd, and 1st on deceleration

to stop.

The lock-up mechanism comes into operation in 2nd, 3rd, and 4th gear.

Manual Shifting Driving; starts off 1st or 2nd, shifts to 2nd, 3rd, and 4th with the shift

switch operation.

Although, this position has an automatic shifting area:

• 1-2 upshift

• 4-3 downshift, 3-1 downshift, 2-1 downshift

depending on vehicle speed.

When the vehicle decelerates to a stop, the transmission shifts to 1st gear automatically.

The transmission can shift to 2nd gear by pushing the shift switch up while the vehicle is

stopped.

The lock-up mechanism comes into operation in 2nd, 3rd, and 4th gear.

Driving in 2nd gear; stays in 2nd gear, does not shift up and down.

For engine braking or better traction starting off on loose or slippery surface.

Driving in 1st gear, stays in 1st gear, does not shift up.

For engine braking.ProCarManuals.com

Clutches
Description

The four-speed automatic transmission uses hydraulically-actuated clutches to engage or disengage the transmission

gears. When hydraulic pressure is introduced into the clutch drum, the clutch piston is applied. This presses the friction

discs and steel plates together, locking them so they don't slip. Power is then transmitted through the engaged clutch pack

to its hub-mounted gear.

When hydraulic pressure is bled from the clutch pack, the piston releases the friction discs and the steel plates, and they

are free to slide past each other. This allows the gear to spin independently of its shaft, transmitting no power.

1st Clutch

The 1st clutch engages/disengages 1st gear, and is located at the end of the mainshaft, just behind the left side cover.

The 1st clutch is supplied hydraulic pressure by its ATF feed pipe within the mainshaft.

1st-hold Clutch

The 1st-hold clutch engages/disengages 1st-hold or position, and is located at the end of the countershaft, just behind

the left side cover. The 1st-hold clutch is supplied hydraulic pressure by its ATF feed pipe within the countershaft.

2nd Clutch

The 2nd clutch engages/disengages 2nd gear, and is located on the secondary shaft. The 2nd clutch is supplied hydraulic

pressure through the secondary shaft by a circuit connected to the 2nd accumulator body.

3rd Clutch

The 3rd clutch engages/disengages 3rd gear, and is located at the end of the countershaft, opposite the left side cover.

The 3rd clutch is supplied hydraulic pressure by its ATF feed pipe within the countershaft.

4th Clutch

The 4th clutch engages/disengages 4th gear, as well as reverse gear, and is located at the center of the mainshaft. The 4th

clutch is supplied hydraulic pressure by its ATF feed pipe within the mainshaft.

One-way Clutch

The one-way clutch is positioned between the parking gear and 1st gear, with the parking gear splined to the countershaft.

The 1st gear provides the outer race surface, and the parking gear provides the inner race surface. The one-way clutch

locks up when power is transmitted from the mainshaft 1st gear to the countershaft 1st gear.

The 1st clutch and gears remain engaged in the 1st, 2nd, 3rd, and 4th gear ranges in the position.

However, the one-way clutch disengages when the 2nd, 3rd, or 4th clutches/gears are applied in the posi-

tion. This is because the increased rotational speed of the gears on the countershaft over-ride the locking "speed range"

of the one-way clutch. Thereafter, the one-way clutch freewheels with the 1st clutch still engaged.ProCarManuals.com

Description

Electronic Control System

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

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

located on the insulator center bulkhead, behind the driver's seat.ProCarManuals.com

Shift Control

Engine torque controls shifting through the linear solenoid. The linear solenoid is controlled by the TCM, and it is used to

operate the throttle valve.

The TCM instantly determines which gear to select by various signals sent from sensors, and actuates shift control

solenoid valves A and B to control shifting. Also, Sport Shifting mode has been adopted to shift gears up and down manu-

ally in position, while using the shift switch on the steering column's right pod.

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

Sport Shifting (Manual Shifting) mode

In position, the driver can use the shift switch on the steering column's right pod to shift gears up and down, much

like a manual transmission.

• Pushing up on the shift switch: Transmission upshifts to the next higher gear.

• Pushing down on the shift switch: Transmission downshifts.

The number of the selected gear is displayed in the shift indicator next to the indicator.ProCarManuals.com

Electronic Control System (cont'd)
Description

• Automatic shifting control in Sport Shifting mode

This position also has automatic shifting areas:

• 1-2 upshift

• 4-3 downshift, 3-1 downshift, 2-1 downshift

depending on vehicle speed. To prevent engine over-revving, the transmission has a 1-2 automatic upshift speed, and 4-3,

3-1, 2-1 downshift allowable speeds.

• When the vehicle reaches the 1-2 automatic upshift speed, the TCM outputs the 1-2 upshift signal to the transmis-

sion and the transmission upshifts to 2nd from 1st gear.

• When the vehicle is coasting over the 4-3 downshift allowable speed and 3-2 downshift allowable speed, the TCM

does not input the downshift signal from the shift switch, and the transmission does not downshift.

• When the vehicle is coasting over the 2-1 downshift allowable speed in 2nd gear, the TCM inputs the signal to wait

until it reaches the 2-1 downshift allowable speed, then the shift indicator blinks to indicate it is waiting to downshift

to
1st.

When the vehicle decelerates to a stop, the transmission shifts to 1st gear automatically.

The transmission can be shifted to 2nd gear by pushing the shift switch up while the vehicle is stopped. This allows the

vehicle to start off in 2nd gear.

Lock-up Control

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

solenoid valve A and/or B accordingly.

The lock-up control mechanism comes into operation in 2nd, 3rd, and 4th, in positions.

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

Hydraulic Control
Description

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

body, the servo body, the throttle valve body and the 2nd accumulator body.

The ATF pump is driven by splines on the left end of the torque converter which is attached to the engine. Fluid flows

through the regulator valve to maintain specified pressure through the main valve body to the manual valve directing

pressure to each of the clutches.

The shift control solenoid valve assembly, the lock-up control solenoid valve assembly and the linear solenoid are bolted

on the outside of the transmission.ProCarManuals.com

Throttle Valve Body

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

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.ProCarManuals.com