Excavating – Road grader-type – Condition responsive
Reexamination Certificate
1999-12-16
2001-06-26
Novosad, Christopher J. (Department: 3671)
Excavating
Road grader-type
Condition responsive
C037S195000, C180S009100, C305S144000, C305S145000, C305S149000
Reexamination Certificate
active
06249994
ABSTRACT:
CROSS REFERENCE
Cross reference is made to copending U.S. patent application Ser. No. 09/464,964, entitled “Apparatus and Method for Adjusting Tension of a Drive Track Chain of a Work Machine Which Utilizes a Sensor for Sensing Position of an Undercarriage Component” by Thomas E. Oertley; Ser. No. 09/464,963, entitled “Valve Assembly For Controlling Actuation of an Actuator of a Track Tensioning System” by Thomas E. Oertley; Ser. No. 09/464,965, entitled “Apparatus and Method for Operating a Hydraulic Excavator Which Has a Position Sensor for Sensing Position of an Idler Wheel” by Thomas E. Oertley; Ser. No. 09/464,966, entitled “Track Tensioning Assembly for Adjusting Tension on a Drive Track Chain of a Work Machine Having an Actuator Which Includes a Pair of Concentrically Arranged Pistons” by Thomas E. Oertley; and Ser. No. 09/464,967, entitled “Track Tensioning Assembly for Adjusting Tension on a Drive Track Chain of a Work Machine Having a Slack Adjuster Device Associated Therewith” by Clifford E. Miller, each of which is assigned to the same assignee as the present invention, and each of which is filed concurrently herewith.
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 track tensioning assembly of a hydraulic excavator.
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 hydraulic drive system for driving a drive track chain, (ii) a track tensioning assembly for adjusting tension on the drive track chain, (iii) a hydraulic work implement for performing a work function, and (iv) a fluid supply circuit for providing pressurized hydraulic fluid to both the hydraulic drive system and the hydraulic work implement. The method includes the step of advancing the pressurized hydraulic fluid from the fluid supply circuit to the work implement when the work machine is being operated in a work mode of operation. The method also includes the step of diverting the pressurized hydraulic fluid from the work implement to the drive system when the work machine is being operated in a travel mode of operation. The method further includes the step of detecting a fluid pressure increase within the drive system in response to diversion of the pressurized hydraulic fluid from the work implement to the drive system. Moreover, the method includes the step of operating the track tensioning assembly so as to decrease tension on the track chain in response to detection of the fluid pressure increase.
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 a hydraulic drive system for driving the drive track chain. The work machine also includes an actuator mechanically coupled to the drive track chain so as to adjust tension on the drive track chain. Moreover, the work machine includes a hydraulic work implement for performing a work function. Yet further, the work machine includes a fluid supply circuit for providing pressurized hydraulic fluid to both the drive system and the work implement. The work machine also includes a tensioning valve fluidly coupled to both the drive system and the accumulator. Pressurized hydraulic fluid is advanced to the drive system from the fluid supply circuit so as to advance the work machine when the work machine is being operated in a travel mode of operation. Pressurized hydraulic fluid is communicated to the tensioning valve from the drive system so as to position the tensioning valve in a decrease-tension valve position when the work machine is being operated in the travel mode of operation. The actuator is configured to decrease tension on the drive track chain when the tensioning valve is positioned in the decrease-tension valve position.
In accordance with a third embodiment of the present invention, there is provided a hydraulic excavator. The hydraulic excavator includes a hydraulic implement assembly having a boom assembly with a bucket secured thereto. The hydraulic excavator includes a dri
Caterpillar Inc.
Maginot Addison & Moore
Novosad Christopher J.
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