Wheel substitutes for land vehicles – With means for tensioning track by moving at least one endwheel – Having hydraulic adjusting means
Reexamination Certificate
1999-12-16
2001-10-23
Morano, S. Joseph (Department: 3617)
Wheel substitutes for land vehicles
With means for tensioning track by moving at least one endwheel
Having hydraulic adjusting means
C305S144000
Reexamination Certificate
active
06305763
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to a drive track chain of a work machine, and more particularly to an apparatus and method for operating a hydraulic excavator which has a position sensor for sensing position of an idler wheel.
BACKGROUND OF THE INVENTION
A work machine, such as a track-type tractor or excavator, is typically supported and propelled by a pair of undercarriage assemblies, each one of which includes an endless drive track chain having a plurality of interconnected articulating components or links. The undercarriage assembly typically also includes a drive sprocket and one or more idler wheels, around each of which the drive track chain is advanced.
During operation of the work machine, it is necessary to maintain tension on the drive track chain in order to keep the chain from derailing from the drive sprocket and/or the idler rollers. In order to maintain tension on the drive track chain, a tension adjustment mechanism such as a hydraulic cylinder or coiled spring is often included in heretofore designed undercarriages. In particular, the cylinder or coiled spring urges the front idler roller in a direction away from the rear idler roller (or rear drive sprocket in the case of an excavator) thereby creating tension on the track chain.
Over a period of time, a number of the components associated with the undercarriage assembly, such as the links and bushings of the drive track chain and even the idler rollers themselves, begin to wear thereby creating slack in the drive track chain. In order to remove the slack from the drive track chain, it is necessary to increase the tension of the track chain. Such an increase in the tension is generally accomplished by manually injecting or otherwise inserting a material, such as grease, into the tension adjustment mechanism associated with the undercarriage assembly.
The use of such tension adjustment mechanisms has a number of drawbacks associated therewith. For example, manual injection of grease into the slack adjustment mechanism is a labor intensive task which can often lead to a decrease in the efficiency associated with operation of the work machine. Moreover, the drive track chain may inadvertently be operated for a period of time with excessive slack therein. This is true since the drive track chain may be operated with excessive slack from the point in time in which slack is first introduced into the track chain until the point in time in which the tension is manually increased. Such excessive slack may cause irregular wear of a number of the components associated with the undercarriage assembly. Moreover, such excessive slack may also cause the drive track chain to derail during movement of the work machine thereby reducing the efficiency of the work machine due to the delays caused by repair of the undercarriage assembly.
In order to avoid the problems associated with excessive slack in the drive track chain, heretofore designed undercarriage assemblies have been operated with relatively large amounts of tension on the drive track chain. However, operation of the undercarriage assembly with a relatively taut track chain during advancement of the work machine increases the rate at which components associated with the undercarriage assembly wear thereby potentially reducing the useful life of the undercarriage assembly.
Moreover, with particular regard to excavators, it is generally desirable to have the drive track chain relatively taut during performance of a digging or other type of work function in order to prevent the excavator from rolling back and forth within the interior of the drive track chain as a result of recoil forces generated during performance of the digging operation. Hence, a relatively high tension level is typically maintained on the drive track chains of excavators at all times even though it is known that use of such a high tension level increases the rate at which components associated with the undercarriage assembly wear during advancement of the excavator.
What is needed therefore is a track tensioning assembly which overcomes one or more of the above-mentioned drawbacks.
DISCLOSURE OF THE INVENTION
In accordance with a first embodiment of the present invention, there is provided a method of operating a work machine having (i) a drive motor for driving a drive track chain, (ii) a track tensioning assembly for adjusting tension on the drive track chain, and (iii) a work implement for performing a work function. The method includes the step of idling the drive motor so as to cease advancement of the work machine during a first period of time. The method further includes the step of operating the work implement so as to perform the work function during the first period of time. The method also includes the step of operating the track tensioning assembly so as to increase tension on the drive track chain during the first period of time. The method yet further includes the step of actuating the drive motor so as to advance the work machine during a second period of time. Moreover, the method includes the step of operating the track tensioning assembly so as to decrease tension on the drive track chain during the second period of time.
In accordance with a second embodiment of the present invention, there is provided a work machine. The work machine includes a drive track chain and an idler wheel for providing tension to the drive track chain. The work machine also includes an actuator mechanically coupled to the idler wheel so as to selectively move the idler wheel between a number of wheel positions. The work machine further includes a first sensor for sensing position of the idler wheel. The work machine yet further includes a second sensor for determining if the work machine is being operated in a drive mode of operation or a work mode of operation. Yet further, the work machine includes a processing unit electrically coupled to both the first sensor and the second sensor. The work machine also includes a memory device electrically coupled to the processing unit. The memory device has stored therein a plurality of instructions which, when executed by the processing unit, causes the processing unit to (i) monitor output from the second sensor so as to determine if the work machine is being operated in the work mode of operation, (ii) generate an increase-tension control signal if the work machine is being operated in the work mode of operation, (iii) actuate the actuator in response to generation of the increase-tension control signal so as to advance the idler wheel in a first direction which causes tension on the drive track chain to be increased, and (iv) monitor output from the first sensor so as to determine position of the idler wheel during advancement of the idler wheel in the first direction.
In accordance with a third embodiment of the present invention, there is provided a hydraulic excavator. The excavator includes a hydraulic implement assembly having a boom assembly with a bucket secured thereto. The excavator also includes a drive track chain and a track tensioning assembly for tensioning the drive track chain. The excavator further includes a sensor configured to detect operation of the implement assembly by an operator of the excavator. Yet further, the excavator includes a controller electrically coupled to the sensor. The controller is configured to operate the track tensioning assembly so as to increase tension of the drive track chain when the sensor detects operation of the implement assembly by the operator of the work machine.
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patent: 485
Caterpillar Inc.
Maginot Addison & Moore
Morano S. Joseph
Nguyen Long Bao
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