Power plants – Pressure fluid source and motor – Servo-motor having externally operated control valve sets...
Reexamination Certificate
2002-12-27
2004-02-24
Look, Edward K. (Department: 3745)
Power plants
Pressure fluid source and motor
Servo-motor having externally operated control valve sets...
C060S488000, C417S269000, C417S206000
Reexamination Certificate
active
06694729
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to hydraulic pumps, although other uses will be apparent from the teachings disclosed herein. In particular, the present invention relates to Bantam Duty Pumps (BDP) which can be combined with motors and other remotely-located units. When used in this manner, these BDP units provide an infinitely variable flow rate between zero and maximum in both forward and reverse modes of operation.
Pumps discussed herein are of the axial piston design which utilize spherical-nosed pistons, although variations within the spirit of this invention will be apparent to those with skill in the art and the invention should not be read as being limited to such pumps. One such prior art pump is shown in FIG.
1
. The pump is a variable displacement pump
10
designed for vehicle applications. A compression spring
12
located inside each piston
14
holds the nose
16
of the piston
14
against a thrust-bearing
18
. A plurality of such pistons positioned about the center of the cylinder
20
forms a cylinder block kit
22
. The variable displacement pump
10
features a cradle mounted swashplate
24
with direct-proportional displacement control. Tilt of swashplate
24
causes oil to flow from pump
10
; reversing the direction of tilt of the swashplate
24
reverses the flow of oil from the pump
10
. The pump is fluidly connected with a motor to form a pump-motor circuit having a high pressure side and a low pressure side through which the oil flows. See generally FIG.
4
C. Controlling the oil flow direction, i.e. changing the high and low pressure sides, controls the motor output rotation. Tilt of the swashplate
24
is controlled through operation of a swashplate control shaft
26
(also referred to herein as trunnion arm). The trunnion arm is connected to a slide which connects with the swashplate. Generally, movement of the trunnion arm
26
produces a proportional swashplate movement and change in pump flow and/or direction. This direct-proportional displacement control (DPC) provides a simple method of control. For example, when the operator operates a control shaft, e.g., a foot pedal, that control shaft is mechanically linked to the swashplate
24
resulting in direct control. This direct control is to be contrasted with powered control specifically indirect proportional control to move the swashplate
24
. Such indirect control is often provide through the use of hydraulic and electro-mechanical devices (and combinations thereof).
A fixed displacement gerotor charge pump
28
is generally provided in BDP units. Oil from an external reservoir (such as reservoir
200
in
FIG. 4C
) and filter is pumped into the low pressure side by the charge pump
28
. Fluid not required to replenish the closed loop flows either into the pump housing
30
through a cooling orifice or back to the charge pump
28
inlet through the charge pressure relief valve. Charge check valves
32
are included in the pump
10
and end cap
34
(cap
34
) to control the makeup of oil flow of the system. A screw type bypass valve
36
is utilized in the pump
10
to permit movement of the machine (tractor, vehicle, etc.) and allow the machine to be pushed or towed. Opening a passage way between fluid ports with the bypass valve
36
allows oil to flow, thereby opening the pump-motor circuit, which then allows the motor to turn with little resistance because the vehicle wheels will not back drive the pump
10
.
While such pumps are useful, they have the disadvantage of having a preferred alignment direction. More particularly, the housing
30
has a preferred alignment with the end cap. This preferred alignment direction is created by the hose coupling, or connections, between the motor
38
and the pump end cap
34
(see FIGS.
2
and
3
). The placement of the system ports
40
determines the preferred alignment of the housing
30
. This is particularly troublesome when one desires to control a hydraulically powered vehicle with pumps positioned on either side of the vehicle and where the control arms for the individual pumps also must be mounted to the outer sides thereof. A control arm for the left pump
10
L (FIG.
2
), for instance, can be conveniently connected to the trunnion arm
26
to provide control of the swashplate from the left. However, to connect a control arm to the right pump
10
R, for instance, the pump must be rotated to place the trunnion arm
26
nearer to the right side of the vehicle. Costly hose fittings are then required to connect the hoses
44
to the pump
10
R. Alternatively a cumbersome and costly U-shaped control linkage
46
may be connected to the trunnion arm
26
while maintaining the pump end cap in its preferred orientation, as shown in FIG.
3
.
An improvement on the earlier pumps having preferred alignment is shown in
FIG. 4C
; the corresponding end cap
156
is shown in FIG.
14
A.
FIGS. 4C and 14A
disclose a prior art pump wherein the end cap
156
may be connected to the housing in one of two orientations. Specifically, end cap
156
is rotatable 180° with respect to the housing. This permits the trunnion arm
26
to be placed on opposing sides. This improved “symmetric pump” has shortcomings, however, which the present invention overcomes. The advantages of a symmetric pump according to the present invention over the prior art “symmetric pump” will be apparent to those with skill in the art from the teachings herein.
SUMMARY OF THE INVENTION
The present invention overcomes these and other problems by providing a pump which does not have a preferred mounting alignment. One object of the present invention is to provide a new and improved pump. A further object is to provide a symmetric pump having a symmetric housing and a symmetric end cap.
Another object of the present invention is to provide an improved hydrostatic vehicle.
Another object of the present invention is to provide means for utilizing a hydraulic pump in multiple directions without the cost of expensive fittings and accessories.
Accordingly, the present invention includes a hydrostatic powered vehicle comprising a vehicle frame and first and second hydrostatic pumps connected to the frame in first and second user selected orientations. The first pump comprises a housing having a control arm and being mounted such that the control arm extends in a first user selected direction. An end cap is connected to the housing and has a pair of case drains opening parallel to the first user selected direction. Based upon a desire hose layout, for example, a user selects one of the case drains to be plugged. The second pump similarly comprises a housing having a control arm and being mounted such that the control arm extends in a second user selected direction. An end cap is connected to the housing and has a pair of case drains opening parallel to the second user selected direction. Similar to the first end cap, a user selects one of the case drains to be plugged. Thusly, the hydraulic hose and pump control layouts may be user selected and optimized for minimum complexity.
In one embodiment of the hydrostatic powered vehicle, first and second wheels are respectively connected to first and second motors. And first and second hydrostatic pumps are respectively fluidly connected to the first and second motors. The first hydrostatic pump comprises a housing having a control arm extending in a first direction. An end cap is connected to the housing and has a pair of case drains opening parallel with the first direction and opposite each other. One of the pair of case drains is plugged based upon user criteria. The second hydrostatic pump comprises a housing having a control arm extruding in a second direction. An end cap is likewise connected to the second pump housing. The end cap has a pair of case drains opening parallel with the second direction and opposite each. One of the pair of case drains is plugged base upon user criteria. The fluid hose layout may thus be optimized for the vehicle.
The hydrostatic powered vehicle may, for some applications, comprise a ve
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