Building Better TractorsJune 1, 2007 By: Melanie Martella, Sensors Sensors
If you haven't spent much time around agricultural equipment, you may not know that modern tractors are very large, very powerful, and increasingly sophisticated to handle the rough terrain and other conditions they deal with every day. To improve the fuel efficiency and reliability while decreasing manufacturing costs, the Challenger track tractor went through a major redesign from the ground up. An integral design change was to switch from a hydraulic
CHALLENGE: To convert a tractor to steer-by-wire
steering system to a steer-by-wire (electronic) one. This change would eliminate the many mechanical parts involved in a hydraulic system, thus reducing the overall weight of the vehicle and increasing its fuel efficiency. In addition, the move would reduce the number of parts potentially subject to failure. The company decided to work with BEI Duncan Electronics to develop the steer-by-wire system.
The first challenge was to adjust how the steering felt. By removing the hydraulics from the steering system, an operator turning the wheel no longer felt the torque imparted by the hydraulics, losing his sense of control. An electronic steering system has no intrinsic torque—sensors detect how much the wheel is turned and send an output signal to the CPU to turn the wheels or tracks to the appropriate angle. Duncan therefore built a mechanical package with precise spring and stop mechanism adjustments, within the sensor enclosure, to recreate the feel of hydraulic steering for the operator.
The second challenge was to develop a gear train reduction in the steering system. Steering wheels can move over 360° while sensors cannot. The goal was to map a longer mechanical movement to a shorter electrical angle. Duncan eliminated the mechanical backlash by designing a mechanical enclosure around the sensors that minimized movement to 1° while still providing instantaneous absolute position feedback for motion control.
Finally, to ensure safe operation, Duncan incorporated a triple-redundant sensor pack. If one sensor should fail, a fault code alerts the operator, while the remaining sensors keep the vehicle operating until it can be serviced.
Duncan's individual sensors and triple-redundant sensor assembly steer-by-wire system has been incorporated into AGCO's current Challenger MT700B Series of track tractors.
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