1991 ACURA NSX torque

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 direc-

tion 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 the steering signals to the EPS control unit. A phase compensating

circuit 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

Function and Operation

EPS Control Unit

The control unit receives input signals from the car's speed sensors, torque sensor and rotation sensor. It performs a mul-

titude of control functions, including a circuit which can detect troubles in each functional part of the system and the con-

trol 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 operational if the engine stalls with the ignition switch in ON (II) 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 rotation 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 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

torque 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.

Rotation sensor
Torque sensor

Steering rotation duty

Unloader duty

(Reduces over-current flow

at full-lock position)

Output duty
Torque duty

Mode changeover

• Normal mode

• Return mode

• Damper mode
Motor control

signal output
Base duty
Car speed sensorsProCarManuals.com

System Description

Function and Operation

The control unit consists of a driving circuit, current sensor, field effect transistor (FET) bridge circuit, and two relays. It

receives control signals from the central processing unit (CPU) and controls the driving current of the motor. The driving

circuit controls the rotational direction and speed of the motor by driving the FET bridge circuit with a pulse width modu-

lation (PWM) method on receipt of an input of driving signals from the EPS control unit.

Rotational Speed Control

The PWM driving signal is a digital signal repeating the process of voltage ON/OFF at a constant frequency, which

changes the ratio of ON time per one cycle of this signal. The ratio is called the duty ratio. When there is a change in duty

ratio, the average voltage changes as smoothly as an analog type. The ratio of digital signal voltage (E) and the average

voltage (V) is called the duty ratio (8). Its relationship is expressed by V = E x 8. When the duty ratio is low, the rotational

speed of motor is slow. As the duty ratio increases, the rotational speed increases to increase the torque.

(Motor rotational speed slow)

ONE CYCLE
(Motor rotational speed fast)

ONE CYCLE

AVERAGE /

VOLTAGE (40%)
VOLTAGE APPLIED RATIO

IN ONE CYCLE: 40%

RELAY

CONTROL

SIGNALS
VOLTAGE APPLIED RATIO

IN ONE CYCLE: 60%
AVERAGE

VOLTAGE (60%)

FROM

BATTERY
POWER

RELAY
CURRENT

SENSOR

Rotational Direction Control

Normal Mode Control:

The table below shows the normal control mode to con-

trol the flow of current from the battery:

CURRENT

FEED BACK

DRIVE

SIGNAL

FET DRIVE

CIRCUIT
GROUND

FAIL SAFE

RELAY

("PWM" in the table indicates PWM control based on

torque sensor data).

Return Control Mode:

Return control mode improves the steering return char-

acteristics. ("PWM" in the table denotes PWM control

based on torque sensor data while "PWM-r" PWM con-

trol based on rotation sensor).

Damper Control Mode:

The damper mode control, which improves the convergence of steering, is performed with damper mode signals from the

control unit. In this mode, a short current circuit is formed on the motor side by turning off FET (1) and (2), and turning on

FET (3) and (4), which suppresses the returning speed of the steering.

Motor Driving Current Control

A current sensor, power relay and fail-safe relay are built into the control unit. The current sensor detects motor driving

current. If there is a problem in the system, a cut-off signal is sent from the CPU to relay, then the relay cuts off motor cur-

rent to switch to manual steering operation.
CONTROL UNITProCarManuals.com

Steering Colum n
Installatio n
SRS component s ar e locate d i n thi s area . Revie w th e
SR S componen t locations , precautions , an d procedure s
i n th e SR S sectio n 24 befor e performin g repair s o r ser -
vice .
1 . Sli p th e lowe r en d o f th e steerin g join t ont o th e pin -
io n shaft .
2 . Repositio n th e colum n assembl y o n th e hange r
bracket , an d loosel y tighte n wit h 8 m m flang e nuts .
COLUM N ASSEMBL Y
8 m m FLANG E NUT S16 N- m(1.6 kg-m , 1 2 Ib-ft )
3. Tighte n t o th e steerin g join t bolts .
NOTE :
• B e sur e tha t th e lowe r bol t i s securel y i n th e
groov e in th e steerin g gearbo x pinio n shaft .
• B e sur e th e pinio n shaf t an d th e steerin g colum n
shaf t ar e aligned ; th e join t shoul d sli p o n freely .
I f no t repositio n th e steerin g rac k t o correc t th e
misalignment .
STEERING JOIN T
Sli p th e uppe r en d o f th e steerin g join t ont o th e steerin g
shaf t (lin e u p th e bol t hol e wit h th e groov e aroun d th e
shaft ) an d loosel y instal l th e uppe r bolt .
STEERIN G COLUM NSHAFTPull dow n whil e
tightenin g bolt .
Bol t mus t lin e u p wit h fla t
on shaft .
STEERIN G GEARBO XPINION SHAF T
TOOTHE D LOC KWASHER S
STEERING JOIN T BOLT S22 N- m (2. 2 kg-m , 1 6 Ib-ft )
4. Instal l th e colum n holde r wit h th e 8 m m bolts .
COLUM NHOLDER8 m m BOLT S22 N- m(2.2 kg-m , 1 6 Ib-ft )
5. Tighte n th e 8 m m flang e nut s t o th e specifie d
torque .
6 . Instal l th e steerin g join t cove r wit h th e clamp s an d
clips .
CLIP
CLAMP S
STEERIN G JOIN T COVE R
ProCarManuals.com

Front Suspension

Torque Specifications

CAUTION:

• Replace the self-locking nuts after removal.

• Replace the self-locking bolts if you can easily thread a non-self-locking nut past their nylon locking inserts. (It should

require 1 N-m (0.1 kg-m, 0.7 Ib-ft) of torque to turn the test nut on the bolt).

• The vehicle should be on the ground before any bolts or nuts connected to rubber mounts or bushings are tightened.

• Torque the castle nut to the lower torque specification, then tighten it only far enough to align the slot with the pin

hole. Do not align the nut by loosening.

NOTE: Wipe off any dirt, oil or grease from the threads before tightening the fasteners.

: Corrosion resistant bolt/nut.

FLANGE BOLT

10 x
1.25
mm

60 N-m (6.0 kg-m, 43 Ib-ft)

CASTLE NUT

12 x
1.25
mm

55-65
N-m
(5.5-6.5
kg-m,
40-47
Ib-ft)

SELF-LOCKING NUTS

12 x
1.25
mm

Replace.

95 N-m (9.5 kg-m. 69 Ib-ft)
SELF-LOCKING NUT

10 x
1.25
mm

Replace.

44 N-m (4.4 kg-m, 32 Ib-ft)

SELF-LOCKING NUT

12 x
1.25
mm

Replace.

125 N-m (12.5 kg-m, 90 Ib-ft)

CASTLE NUT

12 x
1.25
mm

55-65
N-m
(5.5-6.5
kg-m,
40-47
Ib-ft)

SELF-LOCKING NUT

12 x
1.25
mm

Replace.

95 N-m (9.5 kg-m. 69 Ib-ft)

FLANGE BOLT

10 x
1.25
mm

60 N-m (6.0 kg-m, 43 Ib-ft)

FLANGE BOLT

12 x
1.25
mm

95 N-m (9.5 kg-m, 69 Ib-ft)

SELF-LOCKING NUT

12 x
1.25
mm

Replace.

85 N-m (8.5 kg-m, 61 Ib-ft)
CASTLE NUT

10 x
1.25
mm

40-48
N-m

(4.0-4.8
kg-m,

29-35
Ib-ft)

CASTLE NUT

12 x
1.25
mm

55-65
N-m
(5.5-6.5
kg-m,
40-47
Ib-ft)

FLANGE BOLT

12 x
1.25
mm

95 N-m (9.5 kg-m, 69 Ib-ft)
CALIPER BRACKET

MOUNTING BOLT

110 N-m

(11 kg-m, 80 Ib-ft)
CASTLE NUT

12 x
1.25
mm

55-65
N-m
(5.5-6.5
kg-m,

40-47
Ib-ft)
SELF-LOCKING NUTS

12 x
1.25
mm

Replace.

85 N-m (8.5 kg-m. 61 Ib-ft)ProCarManuals.com

7. Tighten the new spindle nut to specified torque,

then stake the spindle nut shoulder against the

spindle.

335 N-m

(33.5 kg-m, 242 Ib-ft)

Stake

After tightening, use a

drift to stake spindle

nut shoulder against

the spindle.ProCarManuals.com

31. Remove the compliance pivot assembly by remov-

ing the bolts and nuts shown.

32. Remove the upper control arm assembly by remov-

ing the flange bolt shown.

SELF-LOCKING

NUTS

12 x
1.25
mm

Replace.

95 N-m

(9.5 kg-m, 69 Ib-ft)

FLANGE BOLT

10 x
1.25
mm

60 N-m

(6.0 kg-m, 43 Ib-ft)
FLANGE BOLTS

10 x
1.25
mm

60 N-m

(6.0 kg-m, 43 Ib-ft)

Corrosion resistant bolt/nut
NOTE:

• Install the upper control arm on the frame before

installing the compliance pivot assembly.

• Install the compliance pivot bolts and nuts. Tor-

que them to the specified torque in the order.

1. Loosely tighten the flange bolt

2. Insert the stud bolts into the frame.

3. Install the three flange bolts and tighten to the

specified torque.

4. Install the two flange bolts and tighten to the

specified torque.

5. Tighten the flange bolt

6. Install the 12 mm self-locking nuts and tighten

to the specified torque.

STUD BOLT

FLANGE BOLTS

10 x
1.25
mm

60 N-m

(6.0 kg-m, 43 Ib-ft)

FLANGE BOLTS

12 x
1.25
mm

95 N-m

(9.5 kg-m, 69 Ib-ft)
SELF-LOCKING

NUTS

12 x
1.25
mm

Replace.

95 N-m

(9.5 kg-m, 69 Ib-ft)

UPPER CONTROL

ARM

FLANGE BOLT

12 x
1.25
mm

95 N-m

(9.5 kg-m, 69 Ib-ft)

Corrosion resistant

bolt/nut
COMPLIANCE

PIVOT ASSEMBLYProCarManuals.com

Rear Suspension

Torque Specifications

CAUTION:

• Replace the self-locking nuts after removal.

• Replace the self-locking bolts if you can easily thread a non-self-locking nut past their nylon locking inserts. (It should

require 1 N-m (0.1 kg-m, 0.7 Ib-ft) of torque to turn the test nut on the bolt).

• The vehicle should be on the ground before any bolts or nuts connected to rubber mounts or bushings are tightened.

• Torque the castle nut to the lower torque specification, then tighten it only far enough to align the slot with the pin

hole. Do not align the nut by loosening.

NOTE: Wipe off the dirt, oil or grease on the threads before tightening the fasteners.

Corrosion resistant bolt/nut

SELF-LOCKING NUT

10 x
1.25
mm

Replace

54 N-m (5.4 kg-m, 39 Ib-ft)
FLANGE BOLT

12 x
1.25
mm

95 N-m
(9.5
kg-m,

69 Ib-ft)

SELF-LOCKING NUT

12 x
1.25
mm

Replace.

85 N-m

(8.5 kg-m, 61 Ib-ft)

SELF-LOCKING NUT

14 x 1.5 mm

Replace.

125 N-m

(12.5 kg-m, 90 Ib-ft)

FLANGE BOLTS

10 x
1.25
mm

60 N-m

(6.0 kg-m, 43 Ib-ft)
CASTLE NUT

10 x
1.25
mm

40-48
N-m
(4.0-4.8
kg-m,

29-35
lb-ft)

CASTLE NUT

12 x
1.25
mm

55-65
N-m

(5.5-6.5
kg-m,
40-47
Ib-ft)

SPINDLE NUT

26 x 1.5 mm

Replace.

335 N-m (33.5 kg-m, 242 Ib-ft)

NOTE: After tighten-

ing, use a drift to

stake the spindle nut

shoulder against the

driveshaft.

SELF-LOCKING NUT

14 x 1.5 mm

Replace.

125 N-m

(12.5 kg-m, 90 Ib-ft)
CASTLE NUT

12 x
1.25
mm

55-65 N-m

(5.5-6.5
kg-m,
40-47
Ib-ft)
DAMPER MOUNTING NUT

12 x
1.25
mm

Replace.

95 N-m (9.5 kg-m, 69 Ib-ft)

CALIPER BRACKET

MOUNTING BOLT

110 N-m

(11 kg-m, 80 Ib-ft)ProCarManuals.com