1991 ACURA NSX change time

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

Brake Booste r
Tests
Functiona l Tes t
1. Wit h th e engin e stopped , depres s th e brak e peda l
severa l time s t o deplet e th e vacuu m reservoir , the n
depres s th e peda l har d an d hol d i t fo r 1 5 seconds .
I f th e peda l sinks , eithe r th e maste r cylinde r i s
bypassin g internally , o r th e brak e syste m (maste r
cylinder , lines , modulator , proportionin g valve , o r
calipers ) ar e leaking .
2 . Star t th e engin e wit h th e peda l depressed . I f th e pe -
da l sink s slightly , th e vacuu m booste r i s operatin g
normally , i f th e peda l heigh t doe s no t vary , th e
booste r o r chec k valv e i s faulty .
3 . Wit h th e engin e running , depres s th e brak e peda l
lightly . Appl y jus t enoug h pressur e t o hol d bac k au -
tomati c transmissio n creep . I f th e brak e peda l sink s
mor e tha n 2 5 m m (1. 0 in. ) i n thre e minutes , th e
maste r cylinde r i s faulty . A sligh t chang e i n peda l
heigh t whe n th e A/ C compresso r cycle s o n an d of f
i f normal . (Th e A/ C compresso r loa d change s th e
vacuu m availabl e t o th e booster. )
Leak Tes t
1. Depres s th e brak e peda l wit h th e engin e running ,
the n sto p th e engine . I f th e peda l heigh t doe s no t
var y whil e depresse d fo r 3 0 seconds , th e vacuu m
booste r i s OK . I f th e peda l rises , th e booste r i s faulty .
2 . Wit h th e engin e stopped , depres s th e brak e peda l
severa l time s usin g norma l pressure . Whe n th e pe -
da l i s firs t depressed , i t shoul d b e low . O n consecu -
tiv e applications , th e peda l heigh t shoul d graduall y
rise . I f th e peda l positio n doe s no t vary , chec k th e
booste r chec k valve .
Booste r Chec k Valv e Tes t
1. Disconnec t th e brak e booste r vacuu m hos e a t th e
booste r o r a t th e booste r sid e o f th e valve .
2 . Star t th e engin e an d le t i t idle . Ther e shoul d b e vacu -
um . I f n o vacuu m is available , th e chec k valv e is no t
workin g properly . Replac e th e chec k valv e an d
retest .
ProCarManuals.com

In general, it would be ideal if the high rpm performance of a racing engine and the low rpm performance of a standard
passenger car engine could be combined in a single engine. This would result in a maximum performance engine with a
wide power band. Two of the major differences between racing engines and standard engines are the timing of the in-
take/exhaust valves
and the
degree
of
valve
lift.
Racing engines have longer intake/exhaust
timing
and a
higher valve
lift

than standard engines. The Honda Variable Valve Timing and Valve Lift Electronic Control System takes this into ac-
count.
When
valve
actuation
is set for low rpm
timing
and
lift,
low rpm
torque
is
better
than
in a
standard
engine.
When
valve actuation is then switched for high rpm timing and lift, output improves to the level given by a racing engine. Untilnow, few variable valve timing systems have been commercialized. In those that have, only the time that both valves are
open (intake/exhaust overlap) could be changed. Honda's system is the first in the world in which both the valve timing
and the degree of valve lift can be changed as needed, making it the most advanced valve train mechanism available.
Valve Timing
(exhaust/intake) Valve Lift Racing Engine

Exhaust Intake
VTEC Engine

Low High Low
Exhaust Intake
Standard Engine

Exhaust Intake

Max. Power

Low rpm Torque
Idling Stability

TDC = Top Dead Center

Low rpm

High rpm
VTEC engine
RPM switch over

point
Standard engine

rpm

BDC = Bottom Dead Center
O = Optimum Characteristic

The engine is equipped with two valve timing and valve lift settings which change according to driving conditions.ProCarManuals.com

System Description

Power Unit

The power unit consists of a driving circuit, current sensor, field effect transistor (FET) bridge circuit, and two relays.
It receives control signals from the 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 modulation (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
(Motor rotational speed fast)
ONE CYCLE

AVERAGE

VOLTAGE (60%)

VOLTAGE APPLIED RATIO

IN ONE CYCLE: 60%

CURRENT

SENSOR

POWER

RELAY

FROM

BATTERY

RELAY

CONTROL

SIGNALS

VOLTAGE APPLIED RATIO

IN ONE CYCLE: 40%

AVERAGE

VOLTAGE (40%)

(Motor rotational speed slow)

DIGITAL VOLTAGE
ONE CYCLE

CURRENT
FEED BACK

DRIVE

SIGNAL

< Rotational Direction Control >
Normal Mode Control:
The table below shows the normal control mode to con-
trol the flow of current from the battery:
("PWM" in the table indicates PWM control based on
torque sensor data). Return Control Mode:
Return control mode improves the steering return charac-
teristics. ("PWM" in the table denotes PWM control based on torque sensor data while "PWM-r" PWM con-
trol based on rotation sensor).
POWER UNIT

FET DRIVE

CIRCUIT
GROND


FAIL SAFE

RELAY

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 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 power unit. The current sensor detects motor driving

current and transmits data to the EPS control unit. If there is a problem in the system, a cut-off signal is sent from the EPS
control unit to relay, then the relay cuts off motor current to switch to manual steering operation. (V) is called the duty ratio
of motor is slow. As the duty ratio increases, the rotational speed increases to increase the torque. When the duty ratio is low, the rotational speed
Its relationship is expressed by V = E x
Steering
condition Steering to
rightStraight

ahead

Steering to
left

OFFOFF
ON

FET

(1)
FET

(2)
FET

(3)
FET

(4)

OFF

OFF

OFF

ON
OFF

PWM

OFF
OFF

PWM
Motor operation
Stops
Operates in direction
steering to the left Operates in direction
steering to the right
Steering condition
Return from right steering
to straight ahead
Return from left steering
to straight ahead
FET (1)

PWM-r

OFF
FET (2)

OFF

PWM-r
FET (3)

OFF

PWM
OFF

PWM

FET (4)

MOTORProCarManuals.com

Caster

Loosen the pivot adjuster mounting nuts under

the compliance pivot and adjust the cam posi-

tion so that the right and left graduations on the

adjusting cam are in contact with the groove

walls.

Graduation in contact

with groove wall
GROOVE WALL

Loosen

the nuts

65 N·m

(6.5 kg-m, 47 Ib-ft)
Graduation in

contact with

groove wall

4. Measure and record the readings for the camber

and toe according to the alignment equipment

manufacturer's instructions.
5. Adjust the camber and toe at the same time on one

side of the car. Repeat for the other side of the car.

NOTE:

One graduation on the camber adjusting cam

equals approximately 10 minutes of camber

change.

One full turn of the tie rod equals approximately

8 mm.

6. Measure the caster according to the alignment

equipment manufacturer's instructions.

7. Adjust the caster.

NOTE: One graduation on the caster adjusting

cam equals approximately 10 minutes of caster

change.

8. Measure the readings for camber and toe.

9. Readjust the camber and toe to the specifications

shown.

Front Specifications

Toe-out: 3.5 1.0 mm

Camber:
-0°20
30

Caster: 8° 00 45ProCarManuals.com