ACURA NSX 1991 Service Repair Manual
Manufacturer: ACURA, Model Year: 1991, Model line: NSX, Model: ACURA NSX 1991Pages: 1640, PDF Size: 60.48 MB
Page 1321 of 1640
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
Page 1322 of 1640
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
Page 1323 of 1640
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
Page 1324 of 1640
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
Page 1325 of 1640
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
Page 1326 of 1640
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
Page 1327 of 1640
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
Page 1328 of 1640
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
Page 1329 of 1640
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'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
Page 1330 of 1640
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