Title of Invention

AN IMPROVED TANDEM PUMP ASSEMBLY

Abstract A tandem pump assembly of the type including a housing (H) defining a fluid inlet port (37) and a fluid outlet port (35), a first pump (11) disposed in the housing (H) and driven by an input shaft (19). The first pump (11) comprises a variable displacement, over-center pump, including first fluid pressure responsive means (31) for varying the displacement of the first pump (11) in response to the porting of a control pressure (47). The first pump has an inlet (67) in fluid communication with the fluid inlet port (37), and an outlet (65) in fluid communication with the fluid outlet port (35). A second pump (33) is disposed in the housing (H) and driven by the input shaft (19), said second pump having an inlet in fluid communication with the fluid inlet port (37), and an outlet in fluid communication with the fluid outlet port (35). The assembly is characterized by the tandem pump assembly including pressure override valve means (71,73) associated with only the first pump (11), and operable, in response to a fluid pressure at the fluid outlet port (35) in excess of a pressure override setting (79), to communicate pressurized fluid to the first fluid pressure responsive means (31), in a manner tending to decrease the displacement of the first pump (11) without effecting the displacement of the second pump (33), until said fluid pressure is substantially equal to the pressure override setting (79), even if it is necessary for the first pump (11) to go over-center from its initial displacement.
Full Text TITLE OF INVENTION
[0001] Pump Control Override For Tandem Pumps.
BACKGROUND OF THE DISCLOSURE
[0002] The present invention relates to variable displacement hydrostatic
pumps and displacement varying controls therefor, and more particularly, to
such pumps which are of the "tandem" pump type.
[0003] Although the present invention may be utilized with variable
displacement hydrostatic pumps of different types (i.e., wherein the actual
pumping element or "rotating group" can be any one of several different types),
the present invention is especially adapted for use with axial piston pumps of
the "swashplate" type (or the swash and cradle type), and will be described in
connection therewith.
[0004] A typical variable displacement axial piston pump, especially of the
type used in mobile applications, includes some sort of operator-controlled input
device, such as a joy stick or manually operable handle. By means of such an
input, the operator can change the tilt angle of the swashplate, thus varying the
displacement of the pump (i.e., the volume of fluid pumped per revolution of the
input shaft). Typically, the actual movement of the swashplate on such a pump
is accomplished by a fluid pressure responsive device, such as a servo-piston,
or a pair of servo-cylinders. In either case, when the operator moves the input
control, the result is that control pressure (normally the outlet pressure from the
charge pump) is communicated to the fluid pressure operated device to either
increase or decrease the tilt angle of the swashplate, depending upon the
direction of movement of the input control.
[0005] Within the mobile hydraulics industry, there is a certain range of sizes
(pump displacements) for axial piston pumps which has become the standard
within the industry. For example, there are the relatively smaller axial piston
pumps having displacements in the range of about 2.0 to about 3.0 cubic inches
per revolution, and there are the relatively larger axial piston pumps having
displacements in the range of about 7.0 to about 9.0 cubic inches per
revolution. Therefore, each manufacturer of axial piston pumps provides a
pump model corresponding to the relatively smaller displacement noted above,
a pump model corresponding to the relatively larger displacement noted above,
and a number of models in between the two displacement extremes, as
described above. The various axial piston pump models offered by each
manufacturer satisfy the vast majority of the mobile application requirements for
such pumps. However, there are occasionally vehicle applications which
require a pump having a substantially larger displacement than the largest size
normally available for mobile hydraulic uses.
[0006] In order to meet the occasional, relatively lower volume applications
which require much larger pump displacements, those skilled in the art have
developed "tandem" pumps in which a single pump assembly houses two
separate (but typically identical) axial piston rotating groups, both driven by a
single, common input shaft (which also drives the charge pump, as is well
known to those skilled in the art).
[0007] Although such tandem pumps can be plumbed in several different
ways, and the present invention could be utilized in connection with practically
any type of tandem pump, it is especially suited for use in connection with a
tandem pump in which the output flows of the two rotating groups are combined,
and communicated to a single load (e.g., a hydraulic motor), as opposed to the
situation in which the output flow of each rotating group is utilized by a different
load. Therefore, the present invention will be described in connection with, and
is preferably used with, a tandem pump having both rotating groups
communicated to a common pump outlet port.
[0008] It has been common practice in the tandem pumps sold commercially,
prior to the present invention, to include with each of the pumping elements (the
"rotating groups") all of the various pump control features required for operation
of the pump. For example, if the tandem pump requires, as is normally the
case, a high pressure relief valve and check valve assembly, it has been
common practice to include such an assembly in the end cap of each of the
axial piston rotating groups, such that the overall tandem pump assembly
actually is provided with two sets of high pressure relief valves and check
valves. Among the pump controls commonly required for tandem pumps is
some sort of internal pressure override (IPOR) control, by means of which an
excessive load pressure will result in a reduction in the pump displacement (i.e.,
a reduction in the tilt angle of the swashplate).
[0009] Although there is generally no functional disadvantage in providing a
tandem pump assembly with redundant pump controls, such redundancy does
add substantially to the overall cost of the tandem pump and in most cases may
also be undesirable in terms of packaging, weight, and the overall size of the
tandem pump assembly.
BRIEF SUMMARY OF THE INVENTION
[0010] Accordingly, it is an object of the present invention to provide an
improved tandem pump assembly which overcomes the above-described
shortcomings of the prior art.
[0011] It is a more specific object of the present invention to provide such an
improved tandem pump assembly which has the various pump displacement
controls required for satisfactory performance, but at a substantially reduced
cost, and with improved packaging and reduced weight for the overall tandem
pump assembly.
[0012] The above and other objects of the invention are accomplished by the
provision of a tandem pump assembly of the type including a housing defining a
fluid inlet port and a fluid outlet port. A first pump is disposed in the housing
and driven by an input shaft, the first pump comprising a variable displacement,
over-center pump, including first fluid pressure responsive means for varying the
displacement of the first pump in response to the porting of a control pressure.
The first pump has an inlet in fluid communication with the fluid inlet port, and
an outlet in fluid communication with the fluid outlet port. A second pump is
disposed in the housing and is driven by the input shaft. The second pump has
an inlet in fluid communication with the fluid inlet port and an outlet in fluid
communication with the fluid outlet port.
[0013] The improved tandem pump assembly is characterized by the
assembly including pressure override valve means associated with only the first
pump, and operable, in response to a fluid pressure at the fluid outlet port in
excess of a pressure override setting, to communicate pressurized fluid to the
first fluid pressure responsive means, in a manner tending to decrease the
displacement of the first pump, without effecting the displacement of the second
pump, until the fluid pressure at the fluid outlet port is substantially equal to the
pressure override setting.
[0014] In response to a more limited aspect of the present invention, the
displacement of the first pump may be decreased until the first pump reaches a
neutral (zero) displacement condition and, if the fluid pressure at said fluid outlet
port is still in excess of the pressure override setting, the displacement of the
first pump may go over-center (thus reversing direction of flow from the first
pump) until the fluid pressure at the fluid outlet port is brought down to the level
of the pressure override setting.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is an illustration, partly in schematic and partly in cross-section,
of a system including a tandem pump assembly made in accordance with the
present invention.
[0016] FIG. 2 is a fragmentary, axial cross-section of the pressure override
valve means which comprises one aspect of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0017] Referring now to the drawings, which are not intended to limit the
invention, FIG. 1 illustrates a tandem pump assembly made in accordance with
the present invention. The tandem pump assembly of FIG. 1 includes a first
variable displacement axial piston pump, of the over-center type, generally
designated 11, hydraulically coupled to a fixed displacement motor 13 (or to any
other hydraulic load) partly by means of a pair of fluid conduits 15 and 17. The
axial piston pump 11 may be of a well-known type, including an input shaft 19,
which provides the input drive to a rotating group, generally designated 21, as
well as to a charge pump 23. As is well known to those skilled in the art, the
output of the charge pump 23 is the primary source for make-up fluid either to
conduit 15, through a relief and check valve assembly 25, or to conduit 17,
through a relief and check valve assembly 27. As is also well known to those
skilled in the art, the output of the charge pump 23 is communicated to
whichever of the conduits 15 or 17 is at the lower fluid pressure.
[0018] The pump 11 further includes a swashplate 29 which is tiltable to vary
the displacement of the pump, by means of a servo-piston assembly, generally
designated 31, as is now well known in the art, including a moveable servo
piston 31 P. It should be noted that, in FIG. 1, the swashplate 29 and servo-
piston assembly 31 are illustrated both inside the pump 11, and separately
therefrom (above the pump 11 in FIG. 1), for ease of illustration. Although the
servo-piston assembly 31 is illustrated herein as a single piston within a cylinder
(having pressure chambers 31a and 31b at either end thereof, as shown in
FIG. 2), it is also well known to those skilled in the art to vary the displacement
of the swashplate 29 by means of a pair of separate stroking cylinders, one
disposed to tilt the swashplate in one direction (corresponding to forward in a
propel application) and the other stroking cylinder being disposed to tilt the
swashplate in the opposite direction (corresponding to reverse). References
hereinafter, and in the appended claims, to "fluid pressure responsive means"
for varying the displacement of a pump will be understood to mean and include
either of the arrangements described hereinabove, or any similar, functionally
equivalent arrangement for varying the displacement of the swashplate 29 in
response to a fluid pressure ("control" or "servo" pressure).
[0019] Referring still primarily to FIG. 1, the tandem pump assembly, in the
subject embodiment, also includes a second variable displacement axial piston
pump 33 which is connected, hydraulically, in parallel with the pump 11, such
that when the inlet of the pump 11 is in fluid communication with the fluid
conduit 17, the inlet of the pump 33 is also in fluid communication with the fluid
conduit 17. Similarly, when the outlet of the pump 11 is in fluid communication
with the fluid conduit 15, the outlet of the pump 33 is also in fluid communication
with the fluid conduit 15. As was noted previously, and for purposes of
subsequent description, the rotating groups of both of the pumps 11 and 33 are
being driven by the input shaft 19 such that the fluid conduit 15 is the high
pressure conduit, and is connected to a fluid outlet port of the tandem pump, as
represented schematically in FIG. 1 by a conduit 35. The tandem pump
assembly also includes a fluid inlet port, as represented schematically by a
conduit 37.
[0020] Although not an essential feature of the present invention, typically,
the second pump 33 would be substantially identical to the pump 11 in terms of
including a rotating group (not shown in the schematic of the pump 33), just like
the rotating group 21 of the pump 11, with the displacement of the pump 33
being controlled by the tilt angle of a swashplate 39. Normally, in commercially
available tandem pump assemblies, the two pumps (11 and 33) are of not only
the same general construction, but also, the same displacement (flow volume
per revolution of input shaft 19). Also, it is typical to enclose both of the pump
assemblies, i.e., both the pump 11 and the pump 33 within a common housing
structure or assembly, designated herein as "H" in both of FIGS. 1 and 2.
[0021] Typically, although not essential, the second pump 33 would also
include the same general type of "pressure responsive means" for varying the
displacement of the pump, i.e., the tilt angle of the swashplate 39. Therefore, in
FIG. 1 there is illustrated schematically a pair of stroking cylinders 41 and 43,
corresponding to the pressure chambers 31a and 31b at the opposite ends of
the servo-piston assembly 31. As was noted previously, the details of the
construction of either the servo-piston assembly or the stroking cylinders are not
essential features of the invention.
[0022] As is well known to those skilled in the art, the fluid pressure
communicated to the servo-piston assembly 31, and therefore, the
displacement of the swashplate 29, may be determined by a manually operated
main control valve, generally designated 45. In the subject embodiment, and by
way of example only, the main control valve 45 is made in accordance with the
teachings of U.S. Patent No. 4,050,247, assigned to the assignee of the present
invention and incorporated herein by reference. Control fluid pressure from the
charge pump 23 is communicated by a conduit 47 to the control valve 45, which
then directs control pressure to either the upper pressure chamber 31a of the
servo-piston assembly 31, by means of a conduit 49, or to the lower pressure
chamber 31b, by means of a conduit 51, all of which is now well known to those
skilled in the art.
[0023] In a similar manner, the fluid pressure in the stroking cylinders 41 and
43 and therefore, the displacement of the swashplate 39 is determined by a
manually operated main control valve, generally designated 55, which is also
preferably made in accordance with the teachings of the above-incorporated
U.S. 4,050,247, and preferably, would be substantially identical to the control
valve 45. Control pressure from the charge pump 23 is communicated by a
conduit 57 through the control valve 55 and from there to either the stroking
cylinder 41 by means of a conduit 59 or to the stroking cylinder 43 by means of
a conduit 61.
[0024] Those skilled in the art of tandem pumps will understand that each of
the control valves 45 and 55 may have its own separate manual input handle,
but with the two handles "ganged" together for movement in unison, such that
the operator is required to move only one of the handles, but with the result that
both move together. Alternatively, there may be provided a single, separate
manual input, to be controlled by the operator, with appropriate linkage to each
of the control valves 45 and 55. It should be understood by those skilled in the
art that the present invention is not limited to any particular arrangement for
providing the input control movement to vary the displacement of the two pumps
(11 and 33) of the tandem pump assembly.
[0025] Referring now to FIG. 2, in conjunction with FIG. 1, one important
aspect of the tandem pump assembly of the present invention will be described.
As is shown somewhat schematically and fragmentarily in FIG. 2, the first pump
11 includes an end cap 63, which may be configured in the manner of the
pumps sold commercially by the assignee of the present invention. The end
cap 63 defines an outlet 65 and an inlet 67 which are in communication with the
fluid outlet port 35 and the fluid inlet port 37, respectively, of the tandem pump
assembly. Typically, the fluid ports 35 and 37 would both be defined by the
common housing assembly H, although the construction details of such are not
shown herein.
[0026] Referring now primarily to FIG. 2, the pump 11 is provided with a pair
of internal pressure override (IPOR) valves 71 and 73. In the subject
embodiment, and by way of example only, the IPOR valves 71 and 73 are
physically disposed within the end cap 63 (although shown as being separate
therefrom schematically, for ease of illustration). Also, the IPOR valves 71 and
73 are preferably identical to each other, thus being readily interchangeable,
during the assembly of the pump. For purposes of the subsequent description,
only the IPOR valve 71 and its function will be described, recognizing that the
IPOR valve 73 would operate in the same manner, if the direction of rotation of
the input shaft 19 were reversed.
[0027] The endcap 63 includes a fluid passage 75, in open fluid
communication with the outlet 65, such that, with the input shaft 19 rotating in its
normal, "forward" direction, high pressure fluid is communicated by the rotating
group 21 to the outlet 65, and from there, by means of the fluid conduit 15 to the
fluid outlet port 35, as was described previously. Therefore, high pressure (or
"system" pressure) is present in the fluid passage 75 under normal operating
conditions.
[0028] The endcap 63 also has a fluid passage 77 in open communication
with the upper pressure chamber 31a of the servo piston assembly 31. The
IPOR valve 71 includes a biasing spring 79 which biases a valve member 81
toward its closed position as shown in FIG. 2. Typically, the biasing force of the
spring 79 may be set or adjusted to exert a closing force on the valve member
81 corresponding to a predetermined, desired pressure override setting. For
example, the spring 79 could be set such that, as long as the pump outlet
pressure (i.e., the pressure in the outlet 65 and in the fluid passage 75) is below
6000 psi, the valve member 81 remains in its closed position of FIG. 2, and the
pump operates in the normal manner.
[0029] Assume now, for purposes of further explanation, that an input has
been provided to both of the main control valves 45 and 55, such that the
swashplates 29 and 39 are both displaced to the nearly maximum displacement
position (for example, about 15 to about 18 degrees) as is shown for the
swashplate 29 in FIG. 2. In accordance with an important aspect of the present
invention, if the pressure at the fluid outlet port 35 of the tandem pump
assembly begins to increase beyond the 6000 psi pressure override setting of
the IPOR valve 71, the valve member 81 will unseat, in opposition to the biasing
force of the spring 79, permitting a small amount of pressurized fluid to flow
from the fluid passage 75 past the valve member 81 and then through the fluid
passage 77 to the upper pressure chamber 31a of the servo piston assembly
31.
[0030] In accordance with another important aspect of the invention, it
should be noted that, although the second pump 33 may be nearly identical to
the first pump 11, one difference (for purposes of the invention) is that the
second pump 33 does not include any IPOR valves. Therefore, in the operating
scenario described in the preceding paragraph, as the pressurized fluid is
communicated from the outlet 65 through the IPOR valve 71, to the upper
pressure chamber 31a, the result is that the piston 31P within the servo piston
assembly 31 is forced somewhat downward, in FIG. 2, which, as may be seen in
FIG. 1, will have the result of changing the tilt of the swashplate 29 from its
displacement, as shown in FIGS. 1 and 2, toward a "decreased" displacement.
In many operating situations, just a slight decrease (perhaps two or three fewer
degrees of tilt angle of the swashplate 29) would be enough to reduce the
pressure in the outlet 65, conduit 15 and outlet port 35 to a level at least
somewhat below the 6000 psi pressure override setting.
[0031] It should be understood by those skilled in the art, based upon a
reading and understanding of this specification, that while the decrease in the tilt
angle of swashplate 29 is occurring, as described, no change in the tilt angle of
the swashplate 39 is occurring (assuming that no change in the manual input to
the tandem pump assembly is occurring). Thus, although in general, the
manual input to both of the pumps 11 and 33 is the same, and the displacement
of the pumps is initially and normally the same, in the "pressure override"
scenario described above, the displacement of the first pump 11 decreases to a
displacement less than that of the second pump 33. The above-described
decrease in the displacement of the pump 11, with no corresponding decrease
in the displacement of the pump 33, is one important aspect of the present
invention.
[0032] Assuming now, for purposes of further explanation of the present
invention, that the vehicle operator is attempting to move a load which would
require a fluid pressure at the fluid outlet port 35 well above the pressure
override setting, the operation of the invention will be as follows: As the
pressure in the outlet 65 rises above the 6000 psi pressure override setting,
thus opening the valve member 81 as was described previously, pressurized
fluid is communicated into the upper pressure chamber 31a, as was described
previously. However, because of the excessive load imposed on the motor 13,
moving the servo piston 31P down somewhat in FIG. 2 to decrease the tilt angle
of the swashplate 29 does not immediately reduce the pressure in the outlet 65
below the pressure override setting. In that situation, the IPOR valve 71
remains open, continuing to communicate pressurized fluid into the upper
pressure chamber 31a, and continuing to "decrease" the tilt angle of the
swashplate 29 toward its neutral condition (i.e., in which the swashplate is
vertical or perpendicular to the axis of the input shaft 19).
[0033] If the load on the motor 13 is such that, even when the swashplate 29
reaches its neutral condition, the pressure at the fluid outlet port 35 is still in
excess of the 6000 psi pressure override setting, the IPOR valve 71 will
continue to operate, and the tilt angle of the swashplate 29 will continue to
"decrease". Therefore, it will be understood by those skilled in the art, based
upon the present specification, that references herein, and in the appended
claims, to the swashplate 29 of the first pump "decreasing" will be understood to
mean and possibly include both (a) decreasing from some predetermined
displacement toward a neutral condition; and (b) continuing to move in the same
rotational direction, from the neutral condition, toward an increasing
displacement, but at the opposite tilt angle.
[0034] Therefore, if necessary, in order to reduce the tandem pump outlet
pressure below the pressure override setting, the swashplate 29 of the first
pump 11 will decrease from the position shown in FIG. 2 to a neutral condition
(moving clockwise in FIG. 2) and then will continue to pivot clockwise beyond
neutral, such that the outlet 65 will now serve as the pump inlet, and the inlet 67
will now serve as the pump outlet. When this condition occurs, the first pump
11 is actually "absorbing" energy by receiving (at what is now its inlet), the
pressure output of the second pump 33, flowing through the fluid conduit 15.
Thus, the tilt angle of the swashplate 29 will continue to "decrease", as that term
was defined above, until the pressure at the fluid outlet port 35 of the tandem
pump assembly stabilizes at a pressure below the pressure override setting.
[0035] In accordance with another aspect of the invention, and referring
again primarily to FIG. 1, it may be seen that the relief and check valve
assemblies 25 and 27, mentioned previously, are provided in conjunction with
only the first pump 11. Typically, the relief and check valve assemblies 25 and
27 would also be disposed within the endcap 63, as are the IPOR valves 71 and
73. Therefore, in the case of the second pump 33, which would normally also
include an endcap similar to the endcap 63, the endcap for the second pump 33
could be made simpler and less expensive, because there would now be no
need to core and machine various passages, and ports, etc. to accommodate
either IPOR valve assemblies or relief and check valve assemblies. In addition,
and even more importantly, the manufacturing cost (or purchased part cost) of
two IPOR valves and two relief and check valve assemblies would be
eliminated.
[0036] It should be apparent to those skilled in the art, from a reading and
understanding of the present specification, that, because of the parallel
hydraulic connection of the first and second pumps (11 and 33) within the
common housing assembly H of the tandem pump assembly, the relief and
check valve assemblies 25 and 27 in the endcap 63 of the first pump 11 will
provide all of the necessary circuit protection functions. Therefore, if for any
reason, the high pressure (system pressure) conduit (i.e., conduit 15 in the
previous example) contains fluid pressure in excess of the relief setting, that
excess pressure will be cross-ported to the low pressure conduit (conduit 17 in
the example). Or, if the fluid pressure in the low pressure conduit drops below
charge pressure (typically about 200-400 psi) from the charge pump 23, charge
pressure will be communicated from the pump 23 past the associated relief and
check valve assembly into the low pressure conduit, as is well known to those
skilled in the art.
[0037] It will be appreciated by those skilled in the art of hydraulic pumps that
there is great commercial desirability in the ability to provide a tandem pump
assembly, which effectively doubles the pump output capability of either of the
pumps (11 or 33) individually, but wherein the various pump displacement
controls (i.e., those of the "cross-port" type) are provided at essentially the same
total cost as would be required for just one pump individually.
[0038] The invention has been described in great detail in the foregoing
specification, and it is believed that various alterations and modifications of the
invention will become apparent to those skilled in the art from a reading and
understanding of the specification. It is intended that all such alterations and
modifications are included in the invention, insofar as they come within the
scope of the appended claims.
WE CLAIM
1. A tandem pump assembly of the type including a housing (H) defining a
fluid inlet port (37) and a fluid outlet port (35); a first pump (11) disposed
in said housing (H) and driven by an input shaft (19), said first pump (11)
comprising a variable displacement, over-center pump, including first fluid
pressure responsive means (31) for varying the displacement of said first
pump (11) in response to the porting of a control pressure (47), said first
pump having an inlet (67) in fluid communication with said fluid inlet port
(37), and an outlet (65) in fluid communication with said fluid outlet port
(35); a second pump (33) disposed in said housing (H) and driven by said
input shaft (19), said second pump having an inlet in fluid communication
with said fluid inlet port (37), and an outlet in fluid communication with
said fluid outlet port (35); characterized by:
(a) said tandem pump assembly including pressure override valve
means (71,73) associated with only said first pump (11), and
operable, in response to a fluid pressure at said fluid outlet port
(35) in excess of a pressure override setting (79), to communicate
pressurized fluid to said first fluid pressure responsive means (31),
in a manner tending to decrease the displacement of said first
pump (11) without effecting the displacement of said second pump
(33), until said fluid pressure is substantially equal to said pressure
override setting (79).
2. A tandem pump assembly as claimed in claim 1, characterized by said
first pump (11) comprises an axial piston pump having a tillable
swashplate (29), and said first fluid pressure responsive means (31) is
operable to vary the tilt angle of said swashplate (29) in response to
variations in said control pressure (47).
3. A tandem pump assembly as claimed in claim 1, characterized by said
first fluid pressure responsive means comprising a servo control cylinder
(31) including a piston (31P) biased by said control pressure (47,51)
toward a position corresponding to increased displacement of said first
pump (11).
4. A tandem pump assembly as claimed in claim 3, characterized by said
pressure override valve means including one IPOR valve (71) having its
inlet (75) in fluid communication with said outlet (65) of said first pump
(11), said IPOR valve (71) having its outlet (77) in fluid communication
with said servo control cylinder (31) to communicate said pressurized
fluid thereto to bias said piston in a direction opposite the direction in
which said piston is biased by said control pressure (47,51).
5. A tandem pump assembly as claimed in claim 1, characterized by a
single relief valve assembly (25,27) having a relief setting, said relief
valve assembly being operable, in response to a fluid pressure at said
fluid outlet port (35) in excess of said relief setting, to communicate
pressurized fluid from said fluid outlet port (35) to said fluid inlet port (37),
until said fluid pressure is substantially equal to said relief setting.
6. A tandem pump assembly as claimed in claim 1, characterized by said
second pump (33) comprising a variable displacement pump including
second fluid pressure responsive means (41,43) for varying the
displacement of said second pump (33) in response to the porting of said
control pressure (57).


A tandem pump assembly of the type including a housing (H) defining a
fluid inlet port (37) and a fluid outlet port (35), a first pump (11) disposed in the
housing (H) and driven by an input shaft (19). The first pump (11) comprises a
variable displacement, over-center pump, including first fluid pressure
responsive means (31) for varying the displacement of the first pump (11) in
response to the porting of a control pressure (47). The first pump has an inlet
(67) in fluid communication with the fluid inlet port (37), and an outlet (65) in
fluid communication with the fluid outlet port (35). A second pump (33) is
disposed in the housing (H) and driven by the input shaft (19), said second
pump having an inlet in fluid communication with the fluid inlet port (37), and an
outlet in fluid communication with the fluid outlet port (35). The assembly is
characterized by the tandem pump assembly including pressure override valve
means (71,73) associated with only the first pump (11), and operable, in
response to a fluid pressure at the fluid outlet port (35) in excess of a pressure
override setting (79), to communicate pressurized fluid to the first fluid pressure
responsive means (31), in a manner tending to decrease the displacement of
the first pump (11) without effecting the displacement of the second pump (33),
until said fluid pressure is substantially equal to the pressure override setting
(79), even if it is necessary for the first pump (11) to go over-center from its
initial displacement.

Documents:

352-kol-2004-abstract-1.1.pdf

352-kol-2004-abstract.pdf

352-kol-2004-amanded claims.pdf

352-kol-2004-amanded pages of specification.pdf

352-kol-2004-claims.pdf

352-KOL-2004-CORRESPONDENCE-1.1.pdf

352-KOL-2004-CORRESPONDENCE.1.3.pdf

352-kol-2004-correspondence.pdf

352-kol-2004-description (complete)-1.1.pdf

352-kol-2004-description (complete).pdf

352-kol-2004-drawings-1.1.pdf

352-kol-2004-drawings.pdf

352-kol-2004-examination report reply recieved.pdf

352-KOL-2004-EXAMINATION REPORT.1.3.pdf

352-kol-2004-form 1-1.1.pdf

352-kol-2004-form 1.pdf

352-KOL-2004-FORM 18.1.3.pdf

352-kol-2004-form 18.pdf

352-kol-2004-form 2-1.1.pdf

352-kol-2004-form 2.pdf

352-kol-2004-form 3-1.1.pdf

352-KOL-2004-FORM 3.1.3.pdf

352-kol-2004-form 3.pdf

352-KOL-2004-FORM 5.1.3.pdf

352-kol-2004-form 5.pdf

352-KOL-2004-GPA.1.3.pdf

352-kol-2004-gpa.pdf

352-KOL-2004-GRANTED-ABSTRACT.pdf

352-KOL-2004-GRANTED-CLAIMS.pdf

352-KOL-2004-GRANTED-DESCRIPTION (COMPLETE).pdf

352-KOL-2004-GRANTED-DRAWINGS.pdf

352-KOL-2004-GRANTED-FORM 1.pdf

352-KOL-2004-GRANTED-FORM 2.pdf

352-KOL-2004-GRANTED-LETTER PATENT.pdf

352-KOL-2004-GRANTED-SPECIFICATION.pdf

352-kol-2004-others-1.1.pdf

352-KOL-2004-OTHERS.1.3.pdf

352-kol-2004-petition under rule 137.pdf

352-KOL-2004-REPLY TO EXAMINATION REPORT.1.3.pdf

352-kol-2004-specification.pdf

352-KOL-2004-TRANSLATED COPY OF PRIORITY DOCUMENT.1.3.pdf

352-kol-2004-translated copy of priority document.pdf


Patent Number 248984
Indian Patent Application Number 352/KOL/2004
PG Journal Number 38/2011
Publication Date 23-Sep-2011
Grant Date 19-Sep-2011
Date of Filing 24-Jun-2004
Name of Patentee EATON CORPORATION
Applicant Address EATON CENTER, 1111 SUPERIOR AVENUE, CLEVELAND, OHIO
Inventors:
# Inventor's Name Inventor's Address
1 STEVEN JOHN ZUMBUSCH 9700 MEADOWLARK LANE, CHANHASSEN, MINNESOTA
PCT International Classification Number F16D 31/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 10/618,417 2003-07-11 U.S.A.