Honda Acura NSX 1991, Service Manual

Page: 607 / 1420

System Description
Power Unit
The power unit consists of a driving circuit, current sensor, field effect transistor 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 method
on receipt of an input of driving signals from the 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
and the average voltage
is called the duty ratio Its relationship is expressed by V = E x 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) (Motor rotational speed fast)
RELAY
CONTROL
FROM POWER
CURRENT
S I G N A L S
B
A
T
T E R
Y /
R E L A Y
S E N S O R
<Rotational Direction Control
Normal Mode Control:
The table below shows the normal control mode to con-
trol the flow of current from the battery:
Steering FET FET FET FET
condition
Motor operation
to Operates in direction
to the rrght
Straight
ahead
OFF OFF OFF OFF Stops
to Operates in direction
to the left
in the table indicates PWM control based on
CURRENT
FEED BACK
I
I
G R O N D
F A I L S A F E
FET
,
. . . .
CIRCUIT
RELAY
torque sensor data).
Return Control Mode:
Return control mode improves the steering return
teristics. (“PWM” in the table denotes PWM control
Steering condition
FET FET FET FET
Return from right steering
to straight ahead
OFF PWM
based on torque sensor data while “PWM-r” PWM
trol based on rotation sensor).
Return from left steering
to straight ahead
OFF PWM-r PWM OFF
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
and and
on FET (3) and 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 control unit. If there is a problem in the system, a cut-off signal is sent from the control
unit to relay, then the relay cuts off motor current to switch to manual steering operation.
17-38