Four Wheel Steering
The Si 4WS model in the U. S and
the SR 4WS model in Canada are
equipped with an electronic Four
Wheel Steering system.
As inputs, the 4WS system uses a
vehicle speed sensor and a sensor to measure how far the front
wheels are turned.
The electronic control unit for 4WS system uses these inputs to deter-
mine which direction to steer the
rear wheels, and at what angle. Depending on vehicle speed and the
angle of the front wheels, the rear
wheels will be "countersteered"
(steered in the opposite direction of
the front wheels) or "same-steered"
(steered in the same direction as
the front wheels). The 4WS electronic control unit
drives an electric motor built into
the rear steering box. Sensors for
rear wheel angle and speed provide
feedback. The electronic control
unit uses this feedback to compare
the actual rear wheel angle to the
desired angle.
When the driver turns the front
wheels with the car traveling less
than 18 mph (30 km/h), the rear
wheels are countersteered. The angle of countersteer increases as
the angle of the front wheels in-
creases, to a maximum counter-
steer angle of six degrees. This
improves response when parallel
parking or making sharp turns.
Above 18 mph (30 km/h), the rear
wheels are same-steered as the driver begins to turn the steering
wheel. The rear wheel angle for
any given steering wheel angle is
not fixed; it increases as vehicle speed increases. This improves
response in lane-changing maneu-
vers.
As the driver continues to turn the
steering wheel, the rear wheels are
steered back to the straight-ahead
position and then to countersteer
mode. As with same steer, the
angle of countersteer varies with
vehicle speed; increasing and then decreasing as the speed rises. This
gives improved handling in low, medium, and high speed curves.
The 4WS system's electronic
control unit monitors the sensors
whenever the ignition is ON. If it detects a problem anywhere in the
system, it lights the 4WS indicator
on the instrument panel and turns
the system off. With the system off,
the rear wheels remain pointed
straight ahead. Your car will then
drive like a conventional car
without 4WS.
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