Suzuki 2009 LT-A500XP, Service Manual

Page: 530 / 624

6C-4 Power Assisted Steering System:
Control System
In the EPS control unit, the steering assist control determines the basic power assist force and the convergence
control improves the steering operation feeling. The controller determines the target motor current by the calculation of
these controls and the maximum current limiting control and it also regulates the motor current so that the target motor
current and the actual current are matched.
Power steering control input / output flow chart
EPS motor
Steering assist
control
Convergence
control
Vehicle speed
signal
Motor angular
speed (estimated)
Torque sensor
Motor current
(actual)
EPS unit
Target current
calculation Maximum corrent
control
I931H1630004-05
Control Description
Steering assist control
This control determines the steering assist current on the basis of steering torque as
detected by the torque sensor and of speed signal supplied from the speed sensor.
This is the fundamental control necessary for the P/S system.
Convergence control
This control prevents convergence from deteriorating at a high speed by making
current (compensating current) flow in the direction to keep the steering from
turning, thereby improving vehicle maneuvering stability.
Maximum current control
If the steering input is sustained at a standstill, the motor continues to draw the
maximum current for full-assist and the motor and EPS control unit may get
overheated. To prevent this condition from occurring, this control limits and
gradually reduces the maximum current flowing through the motor.
Failsafe control
In the EPS control unit, a failsafe function is integrated in the motor circuit for the
purpose of safety. With the failsafe circuit in normal condition, the system is ON for
the motor to draw current. If an abnormal condition is detected in the P/S system by
the self-diagnostic function, the system turns OFF the circuit to interrupt the current
supply to the motor so that the system can stop operation. Refer to “Fail-safe
Function Description (Page 6C-5)”.