Crescent CS7010 - Steering System; Functional Description; Steering Limit Switches

86Service Manual – CS7010™
22 - Steering System
Functional Description
The steering system utilizes steer-by-wire technology, which
means there is no mechanical connection between the operator’s
steering wheel and the drive wheel steering mechanism. The
steering mechanism at the drive wheel uses a large ring gear to
rotate the entire drive wheel and motor assembly. A smaller spur
gear is attached to the steering motor, to provide a signicant
gear reduction and control of the larger ring gear of the drive
assembly.
The steering motor is controlled by a dedicated steering
controller, which monitors the performance and position of the
steering motor, as well as receiving steering position commands
from the operator’s steering wheel.
The operator’s steering wheel is connected to a rotary position
sensor with integral TFD (Tactile Feedback Device a.k.a. Torque
Feedback Device). (“Tactile” is the more correct term, but
“Torque” is more intuitive to the function.). The TFD provides
resistance to turning the wheel (i.e. it opposes torque) to give the
operator the feel of a mechanical steering wheel control.
Steering Limit Switches
To ensure the steering controller doesn’t command the drive
wheel to turn past its design limits, proximity sensors are
mounted below the ring gear to notify the controller that
it has reached its intended steering limits. As a redundant
measure, there is also a mechanical stop beyond the positions
of the proximity sensors that the wheel cannot rotate past.
The limit switches are ferrous metal sensing reed switches,
that contain a small but strong rare earth magnet that
deects the reed contact inside the switch in the presence of
iron-based metals.
Function
When the steering controller is rst energized, it doesn’t
know the locations of the limit switches until it senses
them. When the steering controller is commanded to turn
the wheel far enough to reach a limit switch, the switch
closes when the sensor ag passes in front of the sensor. The
steering controller then backs off on the steering angle so
the ag clears the sensor position. As a result, the sensors
close only momentarily when they are activated, because the
wheel immediately moves back away.
Steering
Sensor
Steering
Actuator
Steering
Controller
Reed
Switch
Sensor
Flag
Limit
Switches