Wheel substitutes for land vehicles – With means for tensioning track by moving at least one endwheel – Condition responsive
Reexamination Certificate
1999-12-16
2001-08-28
Morano, S. Joseph (Department: 3617)
Wheel substitutes for land vehicles
With means for tensioning track by moving at least one endwheel
Condition responsive
Reexamination Certificate
active
06280010
ABSTRACT:
CROSS REFERENCE
Cross reference is made to copending U.S. patent applications 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. 09/465,467, entitled “Apparatus and Method for operating a Track Tensioning Assembly of a Hydraulic Excavator” by Thomas E. Oertley; and Ser. No. 09/464,966, 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 a 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.
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 track tensioning assembly for adjusting tension on a drive track chain of a work machine. The track tensioning assembly includes a main housing defining a main chamber. The track tensioning assembly also includes a recoil piston positioned within the main chamber. The recoil piston has a recoil central passage defined therein. The track tensioning assembly further includes a master piston secured within the recoil central passage. The master piston (i) increases fluid pressure in the main chamber when the master piston is positioned in a first master position, and (ii) decreases fluid pressure within the main chamber when the master piston is positioned in a second master position. The track tensioning assembly also includes a slave piston having a first end positioned within the main chamber and a second end extending out of the main housing so as to be mechanically coupled to the drive track chain. The slave piston (i) increases tension on the drive track chain when the slave piston is positioned in a first slave position, and (ii) decreases tension on the drive track chain when the slave piston is positioned in a second slave position. Movement of the master piston from the first master position to the second master position causes movement of the slave piston from the first slave position to the second slave position.
In accordance with a second embodiment of the present invention, there is provided an undercarriage assembly of a work machine. The undercarriage assembly includes an idler wheel and a drive track chain which is advanced around the idler wheel. The undercarriage assembly also includes a track tensioning assembly for adjusting tension on the drive track chain. The track tensioning assembly has (i) a main housing defining a main chamber, (ii) a recoil piston positioned within the main chamber, the recoil piston having a recoil central passage defined therein, (iii) a master piston positioned within the recoil central passage, the master piston (a) increases fluid pressure in the main chamber when the master piston is positioned in a first master position, and (b) decreases fluid pressure within the main chamber when the master piston is positioned in a second master position, and (iv) a slave piston having a first end positioned within the main chamber and a second end extending out of the main housing so as to be mechanically coupled to the idler wheel, the slave piston (a) urges the idler wheel in a first direction so as to increase tension on the drive track chain when the slave piston is positioned in a first slave position, and (b) urges the idler wheel in a second direction so as to decrease tension on the drive track chain when the slave piston is positi
Caterpillar Inc.
Maginot, Addison & Moor
Morano S. Joseph
Nguyen Long Bao
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