Honda NSX-T 1998 Manual page 903

Main Menu
System Description
Function and Operation (cont'd)
The power module in the EPS 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 modulation (PWM) method on receipt of an input of driving signals from the CPU.
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
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 steering rotation speed data).
Damper Control Mode:
The damper mode control, which improves the convergence of steering, is performed with damper mode signals from the
CPU.
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
Its relationship is expressed by When the duty ratio is low, the rotational