Motor vehicles – Steering by driving – Independently operable drive motors
Reexamination Certificate
1999-06-01
2001-09-04
Dickson, Paul N. (Department: 3618)
Motor vehicles
Steering by driving
Independently operable drive motors
C180S006640, C180S235000, C180S308000
Reexamination Certificate
active
06283237
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to a method and apparatus for steering an articulated machine and, more particularly, to a method and apparatus for utilizing independent variable speed devices to turn the articulated machine.
BACKGROUND ART
Various systems have been developed to steer a machine. One well known system is a rack and pinion system found in passenger vehicles. However, rack and pinion systems are not well suited for heavy machinery such as skidders, front loaders, scrapers, or articulated trucks. In these applications, the steered wheels may become ineffective in the soft earth. Articulated machines have been used as an alternative steering system.
Articulated machines have a front frame member, a rear frame member, and an articulation joint connecting the front and rear frame members. Typically, to steer an articulated machine, the front frame member must be rotated relative to the longitudinal axis of the rear frame member about the articulation joint while the machine is being propelled.
To rotate the front frame member, these machines commonly include articulation cylinders mounted between the frame members. The articulation cylinders are operated in opposite directions. That is, when one cylinder is extended forward, the other cylinder is retracted rearward and vice versa causing the front of the machine to face the intended turn.
Articulated machines are typically propelled by an internal combustion engine that drives the machine's wheels through a transmission, driveshaft, and differential. The machine is turned when the engine drives the wheels with the machine articulated by the hydraulic cylinders.
Prior alternatives have been developed to the prior articulated machine steering system described above. One such example is a machine utilizing skid steering. Skid steering machines are steered by driving the wheels on one side of the machine at a different rate of speed or direction than the wheels on the other side. For example, in such a steering system, the front wheels are not permitted to pivot relative to the rear wheels. As a result, several of the wheels are dragged, or “skidded,” as the machine makes its turn since all of the wheels are not rotating at the same speed. Because the wheels are dragged, skid steering is typically limited to machines having a short wheel base and/or light weight.
Thus, it is desirable to provide an improved steering system for an articulated machine that overcomes the shortcomings of the prior art. The present invention is directed to overcoming one or more of the problems as set forth above.
DISCLOSURE OF THE INVENTION
In one aspect of the present invention a steering system for turning a machine is provided. The system has a plurality of wheels that include a first and second wheel that share a first axis of rotation. The plurality of wheels also includes at least one tether wheel that has a second axis of rotation and may be pivoted relative to the first and second wheels. The first and second axes of rotation define a turning angle. A plurality of drive units include first and second drive units for independently rotating the first and second wheels respectively at variable speeds. A steering input device produces a steering input signal, and a controller receives the steering input signal and produces drive unit request signals to control the drive units. The drive unit request signals may command a turn by rotating the wheels at different speeds thereby altering the turning angle and turning the machine. In this manner, the present invention may steer the machine without articulation cylinders, a transmission, a drive shaft, or a differential.
In another aspect of the present invention a method for turning a machine is provided. The method includes producing a steering input signal from a steering input device representing a desired turning angle, and processing the turning angle in a controller. The method further includes producing a plurality of drive unit request signals from the controller to control a plurality of independent drive units for rotatingly driving a plurality of wheels, and rotatingly driving the plurality of wheels at different speeds with the plurality of drive units to steer the machine.
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Caterpillar Inc.
Dickson Paul N.
Howard & Howard
Lerner Avraham H.
Meyers Liza J.
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