Acura NSX 1991 Manual page 414

Main Menu
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.
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 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.
Table of Contents
(Motor rotational speed slow)
AVERAGE /
VOLTAGE APPLIED RATIO
VOLTAGE (40%)
IN ONE CYCLE: 40%
(Motor rotational speed fast)
ONE CYCLE
RELAY
CONTROL
SIGNALS
CURRENT
FEED BACK
DRIVE
SIGNAL
FET DRIVE
CIRCUIT
ONE CYCLE
VOLTAGE APPLIED RATIO
IN ONE CYCLE: 60%
FROM POWER CURRENT
BATTERY
RELAY
SENSOR
GROUND
AVERAGE
VOLTAGE (60%)
CONTROL UNIT
FAIL SAFE
RELAY