Power plants – Pressure fluid source and motor – Methods of operation
Reexamination Certificate
2002-05-07
2004-07-20
Lazo, Thomas E. (Department: 3745)
Power plants
Pressure fluid source and motor
Methods of operation
C091S275000
Reexamination Certificate
active
06763661
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to hydraulic systems for work vehicles, and more particularly to work vehicles having appendages such as boom assemblies with bucket portions or other movable elements.
BACKGROUND OF THE INVENTION
Various work vehicles such as construction work vehicles (e.g., loader-backhoes) include movable appendages such as boom assemblies that can be used to scoop up or otherwise move material such as soil, sand and gravel. Such boom assemblies often include multiple segments that are movable relative to one another, and the boom assemblies in particular typically include buckets or other movable elements at the far ends of the boom assemblies away from the vehicles. These end elements of the boom assemblies are typically the portions of the boom assemblies that come into direct contact with the material to be scooped up or moved.
In various circumstances, the material that is being scooped up or otherwise moved by the boom assembly of a work vehicle has a gummy or otherwise adherent consistency. Such materials can include various forms of clay, for example. In particular, the consistency of the material is such that, as the end element of the boom assembly encounters the material, a portion of the material tends to adhere to the end element. Further because of the material's consistency, the material does not tend to fall off or otherwise become dislodged from the portion of the boom assembly to which it is adhering. Consequently, some of the material can become attached to the boom assembly during a digging cycle or job and remain attached during the digging cycle/job, such that not all of the material in the boom assembly is dumped out after each digging cycle/job.
Continued adhering of the material to the end element can be undesirable for a variety of reasons. First, the adhering of material to the end element can reduce the volume within the end element and consequently reduce the amount of material that can be picked up and moved by the end element in a given amount of time. Also, because the material is attached to the end element, the work vehicle can appear to be unsightly and uncleanly. Further, in certain circumstances, it can be unsuitable to use the bucket or other end element of the work vehicle to move other materials as long as the first material is still adhering to the end element. Thus, it can become necessary to remove the adhering materials from the end element by way of a separate operation after usage of the work vehicle.
Another problem encountered by work vehicles with boom assemblies is that the end elements can have difficulty in initially plowing or otherwise moving through the material that is to be scooped up or otherwise moved. This is particularly true in the case of hard materials such as black-top or frozen or frosted dirt. It also is the case where the material has either a gummy or adherent consistency, or where the material has been compacted under pressure such that it is difficult to pierce.
It is possible to operate conventional construction work vehicles in such a manner as to address these problems. In a conventional construction work vehicle, the position of the bucket or other end element is typically controlled by one or more hydraulic cylinders that each have head and rod chambers. The provision of hydraulic fluid from a pump toward a cylinder, as well as the allowing of hydraulic fluid to exit the cylinder toward a tank, are in turn determined by a valve. An operator can rapidly switch the position of the valve so that, at certain times, hydraulic fluid pressure from the pump is directed toward the head chamber while hydraulic fluid is allowed to exit the rod chamber toward the tank and, at alternating times, hydraulic fluid pressure from the pump is directed toward the rod chamber while hydraulic fluid is allowed to exit the head chamber toward the tank.
By alternating the status of the valve and consequently the hydraulic fluid pressure exerted at the cylinder, the bucket or other end element experiences a changing force that can result in a vibrational movement of the end element. This vibrational movement can dislodge materials that are adhering to the end element. Also, the vibrational movement can facilitate plowing or other movement of the bucket or other end element through material that is difficult to pierce through, since the vibrational movement tends to cause the material to break apart.
Despite the effectiveness of this conventional operation for creating vibration of the bucket or other end element, this operation has certain disadvantages. First, to obtain this vibration in conventional construction work vehicles, the operator must repeatedly switch the position of the valve. More specifically, the operation typically requires repeated switching of the position or statuses of one or more valves associated with the hydraulic cylinder(s) so that, at certain times, the valve(s) couple the pump to the head chamber of the cylinder(s) and the tank to the rod chamber of the cylinder(s), and at alternating times, the valve(s) couple the pump to the rod chamber of the cylinder(s) and the tank to the head chamber of the cylinder(s). This manual switching operation can become arduous since, for example, it can require repeated moving of a lever on the part of the operator (in the case where spool valves are employed).
Second, in certain circumstances, the bucket or other end element will undesirably tend to have an overall movement in a particular direction as it is being vibrated, rather than maintain its original or nominal position. This can occur because the operator is unable to consistently vary the pressures applied back and forth to the bucket so that the bucket maintains its original position. That is, the operator in some situations will tend to apply pressure in one direction too long during vibration of the bucket, which can tend to move the bucket away from its original position.
This problem can be exacerbated when the bucket or other end element is carrying a load or is otherwise experiencing a force from an outside source, which can include a force provided by the material through which the end element is attempting to plow or move. In such circumstances, it can be difficult for the operator to vary the position of the valve in a way that counteracts the influence of these forces such that the original, nominal bucket position is maintained. Consequently, as the positions of the valve(s) are repeatedly switched, the end element may move downward under the force of gravity, move away from the material through which the end element is attempting to move, or otherwise move away from its original position.
Such movement of the bucket or other end element can be a problem in a number of situations. For example, when the bucket is being operated in close proximity to other machinery, such as a dump truck, it can be a nuisance for the operator to have to repeatedly align the bucket to its original position when vibration of the bucket moves the bucket away from that original position. Also, movement of the bucket or other end element away from the material through which the end element is attempting to move can be counterproductive in that it reduces the ability of the end element to cut through the material.
Additionally, while movement of the bucket or other end element away from its original position is undesirable in many circumstances, there are also circumstances in which it is desired that the element experience an overall movement in a particular direction as it is vibrating. For example, this can be the case when the bucket is being used to loosen or break through hard materials along the ground, such as black-top. In these circumstances, it can again be difficult for an operator to manually perform the vibration operation in the desired manner. However, in this case, the difficulty arises because it is difficult for the operator to manually vary the position of the valve in a manner whereby the resulting amount of movement of the bucket in one direction consis
Pfaff Joseph L.
Tabor Keith A.
Husco International Inc.
Lazo Thomas E.
Quarles & Brady LLP
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