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
Stormer, Russell D. (Department: 3617)
Wheel substitutes for land vehicles
With means for tensioning track by moving at least one endwheel
Having hydraulic adjusting means
C305S143000
Reexamination Certificate
active
06305762
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to a drive track chain of a work machine, and more particularly to a valve assembly for controlling actuation of an actuator of a track tensioning system.
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.
DISCOURSE OF THE INVENTION
In accordance with a first embodiment of the present invention, there is provided a valve assembly for controlling actuation of an actuator of a track tensioning system for adjusting tension on a drive track chain. The valve assembly includes a valve housing defining (i) a master chamber, (ii) a slave chamber, (iii) a fluid passage which fluidly couples the master chamber to the slave chamber, and (iv) a fluid outlet which fluidly couples the slave chamber to the actuator. The valve assembly also includes a master valve member positioned within the master chamber. The master valve member (i) isolates the master chamber from the slave chamber when the master valve member is positioned in a first master position, and (ii) places the master chamber in fluid communication with the slave chamber when the master valve member is positioned in a second master position. The valve assembly further includes a slave piston positioned within the slave chamber, the slave piston (i) isolates the fluid outlet from the slave chamber when the slave piston is positioned in a first slave position, and (ii) places the fluid outlet in fluid communication with the slave chamber when the slave piston is positioned in a second slave position. Movement of the master valve member 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. Movement of the slave piston from the first slave position to the second slave position causes actuation of the actuator, whereby tension on the drive track chain is adjusted by the actuator.
In accordance with a second embodiment of the present invention, there is provided an undercarriage assembly of a work machine. The undercarriage assembly includes a pressurized hydraulic fluid source, a drive track chain, and an actuator mechanically coupled to the drive track chain so as to adjust tension on the drive track chain. The undercarriage also includes a valve assembly for controlling actuation of the actuator. The valve assembly has (i) a valve housing defining (a) a fluid chamber, (b) a chamber inlet, and (c) a chamber outlet, (ii) a piston positioned within the fluid chamber so as to divide the fluid chamber into a spring chamber portion and a high-pressure chamber portion, and (iii) a biasing spring positioned in the spring chamber portion so as to exert a spring bias on an outer surface of the piston. The chamber inlet fluidly couples the hydraulic fluid source to the spring chamber portion. The chamber outlet fluidly couples the high-pressure chamber portion to the actuator. The piston has a first fluid contact surface which is positioned in the spring chamber portion. The piston further has a second fluid contact surface which is positioned in the high-pressure chamber portion. The first fluid contact surface has a first diameter, (vi) the second fluid contact surface has a second diameter. The first diameter is greater than the second diameter.
In accordance with a third embodiment of the present invention, there is provided an undercarriage assembly of a work machine. The undercarriage assembly includes a first frame member and a second frame member which is movable relative to the first frame member. The undercarriage assembly includes an actuator mechanically coupled to the second frame member so as to move the second frame member relative to the first frame member. The undercarriage assembly also includes an idler wheel rotatably secured to the second frame member. The undercarriage assembly further includes a drive track chain which is advanced around the idler wheel. Moreover, the undercarriage assembly includes a pressurized hydraulic fluid source. The undercarriage assembly also includes a valve assembly for controlling actuation of the actuator. The valve assembly has (i) a valve housing defining (a) a fluid chamber, (b) a chamber inlet, and (c) a chamber outlet, (ii) a p
Addison Bradford G.
Caterpillar Inc.
Stormer Russell D.
LandOfFree
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