Honda Acura NSX 1991 Service Manual page 605

System Description
Control Unit
The control unit receives input signals from the car's speed sensors, torque sensor and steering rotation sensor, and
outputs control signals to the power unit. It performs a multitude of control works including a circuit which diagnoses
troubles in each functional part of the system and the control 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
< Basic Control >
(3) The rotational speed and direction of steering are compiled into data, receiving input signals from the steering rota-
tion 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 and output of control signals to the power unit, based on data on car speed, direction
of torque and rotational direction of steering.
Normal Control Mode:
The rotational direction of motor is determined afater 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.
Steering rotation duty
Mode changeover
N o r m a l m o d e
l
Return mode
l
Damper mode
l
switch in ON position.
Unloader duty
(Reduces over-current flow
at full-lock position)