ACURA NSX 1991 Service Repair Manual

Manual Steering
Overhaul (Cont'd)
25. Install the lock nut on the rack guide screw, and en the locknut while holding the rack guide screw

with a wrench.

LOCKNUT
68 N·
m (6.8 kg-m, 49 Ib-ft)
CROW FOOT
26. Screw each rack end into the rack while holding the lock washer so its tabs are in the slots in therack end.
NOTE: Install the stopper washer with the cham-
fered side facing out.

Installation

direction.

LOCK WASHER

RACK END
STOPPER WASHER
27. Tighten the rack end securely, then bend the lock
washer back against the flat on the flange as shown.
NOTE: Coat the stopper
washer with grease suffi

ciently.

RACK END
55 N .
m

(5.5 kg-m, 40 Ib-ft)

28. Install the boots on the rack end with the tube
clamps.
NOTE:
TUBE CLAMP
BOOT

STEERING GREASE
(Honda P/N 08733-B070E)

Coat the inside of the boot.
SILICONE GREASE
Coat the sliding surface of the rack
end.

Coat the rack end and inside of the boot with the

grease.
Before installing the boot, be sure that the pres-
sure inside of the boot is the atmospheric
pressure.

Install the boot band with the rack in the straight

ahead condition (i.e. right and left tie-rods are

equal in length).

WRENCH,ProCarManuals.com

29. Install the new boot bands on the boot and bend both
sets of locking tabs.
30. Lightly tap on the doubled portions to reduce their
height.

NOTE: After assembling, slide the rack right and left
to be certain that the boots are not deformed or
twisted.
31. If the tie-rod ends were removed, install the tie- rods on the right and left rack ends and screw them

in until the threaded section is 11 mm (0.4 in) in

length.
BOOT BAND

11 mm
(0.4
in)

TIE-ROD END

LOCKNUT

Hand tighten.
32. Install the gearbox on the front crossbeam (see page 17-20).
33. Check the wheel alignment and adjust if necessary (see section 18).ProCarManuals.com

Manual Steering
Ball Joint Boot Replacement
1 . Remove the circlip and the boot. CAUTION: Do not contaminate the boot installation
section with grease.
2. Pack the interior of the boot and lip with grease.

LIP

BOOT INSTALLATION SECTION

3. Wipe the grease off the sliding surface of the ball pin, then pack the lower area with fresh grease.
CAUTION:

BALL PIN TAPERED SECTION

BOOT INSTALLATION

SECTION

4. Install the boot in the groove of the boot installation section securely, then bleed air. 5. Insert the special tool into the threads in the ball pin

and align the end of the tool with the groove in the

boot.

Slide the set ring over the tool and into position.

BOOT

BALL JOINT

BOOT CLIP

GUIDE

07MAG-SL00100

Adjust the depth

by turning the tool.
CAUTION: After installing the boot, check the ball
pin tapered section for grease contamination andwipe it off if necessary.
SET RING

Keep grease off the boot installation section and
the tapered section of the ball pin. Do not allow dust, dirt, or other foreign materi-
als to enter the boot.ProCarManuals.com

System Description

Electrical Power Steering (EPS)

Outline

The NSX uses an electric motor-driven power steering, which possesses the characteristics best suited for a mid engine

automobile. This system is a power-assisted steering device, with a motor inside the steering gearbox driven by the EPS

control unit and power unit. Its distinctive features are described below:

ALTERNATOR

VEHICLE

SPEED SENSOR
STEERING WHEEL

EPS CONTROL UNIT

POWER UNIT

BATTERY

STEERING GEARBOX
STEERING

COLUMN
Minimized loss of engine horsepower and decreased fuel consumption.

A linear steering feel and the reduction of kickback.

The system is compact and lightweight because it requires no complicated hydraulic piping, etc.ProCarManuals.com

FUSE BOX
System Description

Major Components

The Electrical Power Steering system is composed of the following major components:

EPS CONTROL UNIT

COUNTERSHAFT

SPEED SENSOR

ALTERNATOR
SPEEDOMETER
EPS INDICATOR

LIGHT
STEERING

SENSOR
BATTERY
POWER UNIT

MOTOR

IGNITION

SWITCH
A steering gearbox that converts rotary operation of the steering wheel into transverse operation via a rack and pinion

mechanism. Steering sensors and an actuating motor are incorporated.

A control unit that computes the optimum amount of power assistance, taking into account steering torque, steering

speed, and vehicle speed. Selfdiagnosis functions are included.

A power unit that drives the motor according to the signals from the EPS control unit. A current sensor is built in to

give feedback information to the EPS control unit. Two relays shut off the power if a problem in the system occurs.

A speed sensor, the countershaft speed sensor, send vehicle speed signal to the EPS control unit. Also the

speedometer send vehicle speed signal to the EPS control unit. Two signals are used as a double-check.ProCarManuals.com

System Operation

Manual Steering Operation

Steering wheel input rotates the pinion of the gearbox through the universal joint. Due to the rack and pinion mechanism,

the rotation of pinion is converted into a transverse motion at the rack, which steers the front wheels throught the tie-

rods and knuckles the same as an ordinary rack and pinion system.

Assisting Operation

In addition to the manual steering operation, the steering sensor on the pinion shaft transmits a signal to the EPS control

unit when it receives a steering input. The EPS control unit calculates an adequate motor control with addition of speed

signals then transmits a control signal to the power unit. Based on the signal from the EPS control unit, the power unit

drives the motor inside the gearbox. The torque generated by the motor is transmitted to ball screw through gears and

converted into an assisting thrust in the axial direction of rack. The assisting thrust acts in the steering direction and

lessens the steering force required at the steering wheel.

POWER UNIT

RECIRCULATING

BALL SCREW

STEERING SENSOR

STEERING GEARBOX
MOTOR

STEERING WHEEL
RACK
EPS CONTROL UNITProCarManuals.com

System Description

Function and Operation

Steering Sensor

The steering sensor consists of a torque sensor, an in-

terface, and the rotation sensor.
INPUT

SHAFT
TORSION BAR

SPIRAL

GROOVE

GUIDE

PIN
INTERFACE

CIRCUIT
Torque Sensor

The torque sensor converts steering torque input and its

direction to voltage signals, in conjunction with the in-

terface.

A torsional force caused by steering operation is convert-

ed to an axial movement of a slider core. A variable

differential transformer is installed around the slider core.

Within the tranceformer are three coils, primary coil on

the inside, and two secondary coils, one for right turns

and one for left turns.

Alternating current is passed through the primary coil

when the system is energized. The amount of mutual in-

duction from the primary coil to the secondary coils

changes depending on the position of the slider coil.

The input shaft and the slider are one piece. Rotation of

the shaft moves the slider in a circular direction. The pin-

ion is turned via the torsion bar. The slider core is installed

on the pinion shaft on grooves, and turns with the pin-

ion shaft.

When there is little resistance, the input shaft tortion bar,

pinion shaft, and the slider core turn together to the same

angle. The slider core does not move up/down.

When there is resistance on the input shaft (hard to steer situation), and the slider pin is turned at an angle by the steering

wheel, the tortion bar is twisted due to the resistance. Accordingly, the pinion shaft turns at a smaller angle. The differ-

ence in the turning angles changes the position of the slider pin in the groove, forcing the slider core upward or down-

ward, depending on the direction of the direction of the turn.
TRANSFORMER

PINION GEAR

SLIDER

WING

PRIMARY COIL

UPPER SECONDARY COIL

LOWER SECONDARY COIL

SLIDER

DWG

No.

A

B

C
Steering condition

Steering to right

(load steering)

Advancing straight ahead

(no load steering)

Steering to left

(load steering)
Slider movement

Upward shift

Neutral

Downward shift
Induction voltage on secondary coil

Voltage on upper coil increases and that on the lower

decreases

Voltage on upper and lower coils are equal

Voltage on lower coil increases and that on the upper

decreasesProCarManuals.com

Rotation Sensor

The rotation sensor is housed inside the steering gearbox near the pinion. It converts the rotation speed and direction

of steering into voltage signals. The rotation of the steering wheel is transmitted to the pinion, which drives the sensor

by accelerating its speed through the three pieces of transmission the gears. Acting as a kind of direct current generator,

the sensor generates direct current voltage proportionately with the rotational speed of the pinion. When the steering

direction is reversed, the voltage is generated in the opposite direction. No power is generated when driving straight

ahead without turning the steering wheel.

Interface Circuit

The interface circuit is housed inside the steering gearbox near the pinion. It rectifies and amplifies the signals from the

torque sensor and the rotation sensor and transmits steering signals to the EPS control unit. A phase compensating cir-

cuit is also built in, which changes the output signals in accordance with the drive signals input from the EPS control unit.

TRANSMISSION GEARS

INTERFACE CIRCUIT

ROTATION SENSORProCarManuals.com

System Description

EPS Control Unit

The control unit receives input signals from the car's speed sensors, torque sensor and steering rotation sensor, and
outputs control signals to the power unit. It performs a multitude of control works including a circuit which diagnoses
troubles in each functional part of the system and the control unit itself. The control unit operates the system while the engine is in the process of starting, on receipt of voltage generated by the alternator. The system remains operationalif the engine stalls with the ignition switch in ON position.
< Basic Control >

(1) Travelling speeds are compiled into data, receiving input signals from the car&#39;s speed sensors.
(2) The magnitude and direction of torque are compiled into data, receiving input signals from the torque sensor.
(3) The rotational speed and direction of steering are compiled into data, receiving input signals from the steering rota- tion sensor.
(4) Determination of motor torque data from the prescribed assisting force map, based on the car speed data, steering rotational speed data and the steering torque data.
(5) Changeover of control modes and output of control signals to the power unit, based on data on car speed, direction of torque and rotational direction of steering.
Normal Control Mode:
The rotational direction of motor is determined after changing over to the left/right steering mode in accordance with tor-
que direction data. The mode is switched to the straight ahead mode when the output data is zero.
Return Control Mode:
According to torque direction data and steering rotational direction data, the mode is changed over to the return control
mode to improve the steering return characteristic.
Damper Control Mode:
According to car speed data, torque value data and steering rotational speed data, the mode is changed over to the damper
control mode to improve the convergence property of the steering.
Steering rotation sensor
Steering rotation duty Steering torque sensor
Unloader duty

(Reduces over-current flow
at full-lock position)
Output duty

Mode changeover
Normal mode

Return mode
Damper mode
Torque duty
Motor control
signal output To power unit
Base duty

Car speed sensorProCarManuals.com

Self-Diagnosis Function

The EPS control unit monitors the system inputs and outputs, and the driving current of the motor. If there is a problem

in the system, the control unit turns the system off by actuating the relay in the power unit. Power assist stops and

normal manual steering operation resumes. The control unit also turns the EPS indicator light on to alert the driver, and

memorizes the problem in the form of a code. Connecting the terminals of the service check connector with a jumper

wire enables the EPS indicator light to blink the problem code when the ignition switch is turned on.

Unloader Control

If the steering wheel is turned fully and held in the full-lock position, the steering torque reaches the maximum point,

and an over-current flows to the motor and the power unit. The control unit detects this and reduces the current flow

to the motor.

Average Moving Current Control

The electric current flow to the motor is estimated from the current values detected by the current sensor, and the aver-

age current is obtained at two second intervals. The motor driving current is suppressed when the average current value

exceeds a predetermined marginal value. The control unit regurates the motor current during continuous loading to sup-

press any excessive temperature rise in the power unit and the motor.

Over-Voltage Control

If there is an excessive increase in power source voltage due to a poor battery condition, an alternator voltage regulator

problem, etc., the motor assisting force increases, resulting in excessive control. To prevent this, the control unit signals

to the power unit are corrected to ensure that adequate assisting force is generated.ProCarManuals.com