198 Auto Suspension and Steering
Front main steering
angle sensor
Control
module
Rear wheel
sensor
Rear main steering
angle sensor
Rear steering
actuator
Rear sub steering
angle sensor
Rear wheel
sensor
Front sub steering angle sensor
Speed sensor
Figure 9-64. Typical electromechanical four-wheel steering system. The control module receives electrical inputs from the vehicle
speed sensors and the steering angle sensors. (Honda)
Electromechanical Four-Wheel Steering
Electromechanical four-wheel steering uses a control
module to operate the rear wheel steering mechanism. The
control module depends on sensor inputs to determine the
output commands to the rear-wheel steering mechanism.
Electrical input to a stepper motor operates the steering
mechanism. A stepper motor is an electric motor that
moves in small amounts. Figures 9-64 and 9-65 illustrate
the system components and layout.
As shown in Figure 9-66, the stepper motor is
connected to the steering linkage through a worm
gear-and-ball nut assembly that resembles those used on
conventional steering gears. The worm gear-and-ball nut
assembly is installed on one side of the motor. The steering
linkage is attached directly to the gears on one side and
passes through the motor winding to connect with the
other side.
The control module receives inputs from the vehicle
speed sensor and steering angle sensors installed on the
front and rear steering mechanisms. Based on these inputs,
the module energizes the motor to move the rear wheels. If
the system develops a defect, centering springs return the
unit to the straight ahead position and a dashboard
mounted light warns the driver.
The electromechanical system installed on a few older
Asian cars uses a metal rod called a steering angle transfer
shaft. This shaft extends from the front steering gear
assembly to a steering gear mounted on the rear axle. The
rear steering gear uses the shaft movement as an input sen-
sor to control an electromechanical rear steering system.
The rear steering system consists of an electric stepper
motor and internal gears. The gears operate external steer-
ing linkage to turn the rear wheels.