Note: Descriptions are shown in the official language in which they were submitted.
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VARIABLE DISPLACEMENT PUMP HAVING A ROTATING CAM RING
Background of the Invention
[0001] The present invention relates to a pump, and more specifically to a
high-
speed vane pump that finds particular use in fuel pumps, metering, and control
for jet
engines.
[0002] Current vane pumps use one or more stationary, or non-rotating, cam
rings. Outer radial tips of the vanes slide along the cam rings. The rings are
not,
however, free to rotate relative to the housing. The stationary cam rings are
rigidly fixed
to a pump housing in a fixed displacement pump, or the cam ring moves or
pivots to
provide variable displacement capability. Thus, as will be appreciated by one
skilled in
the art, these types of positive displacement pumps include a stator or
housing having
inlet and outlet ports, typically at locations diametrically offset relative
to an axis of
rotation of a rotor received in a pump chamber. Plural, circumferentially
spaced and
radially extending guides or vanes extend outwardly from the rotor. Since the
rotor axis
is offset and parallel to an axis of the housing chamber, the offset
relationship of the axes
causes the vanes to move radially inward and outward relative to the rotor
during
rotation.
[0003] Outer tips of the vanes contact the cam ring and the contact forces of
the
individual vanes, usually numbering from six to twelve, impose frictional drag
forces on
the cam ring. These drag forces convert directly into mechanical losses that
reduce the
overall efficiency of the pump. In many applications, these mechanical drag
losses far
exceed the theoretical power to pump the fluid.
[0004] When used in the jet engine environment, for example, vane pumps use
materials that are of generally high durability and wear resistance due to the
high velocity
and loading factors encountered by these vane pumps. Parts manufactured from
these
materials generally cost more to produce and suffer from high brittleness. For
example,
tungsten carbide is widely used as a preferred material for vane pump
components used in
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jet engines. Tungsten carbide is a very hard material that finds particular
application in
the vane, cam ring, and side plates. However, tungsten carbide is
approximately two and
one-half (2%) times the cost of steel, for example, and any flaw or overstress
can result in
cracking and associated problems. In addition, the ratio of the weight of
tungsten carbide
relative to steel is approximately 1.86 so that weight becomes an importnat
consideration
for these types of applications. Thus, although the generally high durability
and wear
resistance make tungsten carbide suitable for the high velocity and loading
factors in vane
pumps, the weight, cost, and high brittleness associated therewith results in
a substantial
increase in overall cost.
[0005] Even using special materials such as tungsten carbide, current vane
pumps
are somewhat limited in turning speed. The limit relates to the high vane tip
sliding
velocity relative to the cam ring. Even with tungsten carbide widely used in
the vane
pump, high speed pump operation over 12,000 RPM is extremely difficult.
[0006] Improved efficiencies in the pump are extremely desirable, and
increased
efficiencies in conjunction with increased reliability and the ability to use
a vane-type
pump for other applications are desired.
Summary of the Invention
[0007] An improved gas turbine fuel pump exhibiting increased efficiency and
reliability is provided by the present invention.
[0008] More particularly, the gas turbine fuel pump includes a housing having
a
pump chamber and an inlet and outlet in fluid communication with the chamber.
A rotor
is received in the pump chamber and a cam member surrounds the rotor and is
freely
rotatable relative to the housing.
[0009] A journal bearing is interposed between the cam member and the housing
for reducing mechanical losses during operation of the pump.
[0010] The journal bearing is a continuous annular passage defined between the
cam member and the housing.
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The rotor includes circumferentially spaced vanes having outer radial tips in
contact with the cam member.
The pump further includes a cam sleeve pivotally secured within the housing to
selectively vary the eccentricity between the cam member and the rotor.
The gas turbine fuel pump exhibits dramatically improved efficiencies over
conventional vane pumps that do not employ the freely rotating cam member.
The fuel pump also exhibits improved reliability at a reduced cost since
selected
components can be formed of a reasonably durable, less expensive material.
The improved efficiencies also permit the pump to be smaller and more compact
which is particularly useful for selected applications where size is a
critical
feature.
In accordance with an aspect the present invention provides a variable
displacement gas turbine fuel pump comprising:
a housing having a pump chamber, and an inlet and outlet in
fluid communication with the pump chamber;
a rotor received in the pump chamber;
a cam member surrounding the rotor and freely rotating relative to
the housing;
a cam sleeve radially interposed between the cam member and
the housing;
means for altering a position of the cam sleeve in the housing to
selectively vary pump output;
a spacer ring radially interposed between the cam sleeve and
the housing wherein the spacer ring includes a generally planar cam sleeve
rolling surface that allows a centerpoint of the cam sleeve to linearly
translate;
and
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a journal bearing interposed between the cam member and the cam
sleeve for reducing mechanical losses during operation of the pump.
In accordance with another aspect the present invention provides
a variable displacement gas turbine fuel pump for supplying jet fuel from a
supply to a set of downstream nozzles, the gas turbine fuel pump
comprising:
a housing having a fuel inlet and a fuel outlet in operative
communication with a pump chamber;
a rotor received in the pump chamber, the rotor having plural vanes
that segregate the pump chamber into individual pump chamber portions;
a cam ring received around the rotor having radially inner and outer
surfaces, the inner surface slidingly engaging the vanes;
a cam sleeve radially interposed between the cam ring and the
housing;
a spacer ring radially interposed between the cam sleeve and the
housing, the cam sleeve being secured to the spacer ring to selectively vary
eccentricity between the cam ring and the rotor;
means for altering a position of the cam sleeve in the housing to
selectively vary pump output; and
a cam journal bearing surrounding the cam ring in communication
with the fuel inlet whereby jet fuel serves as the fluid film in the journal
bearing for
the cam ring, wherein the journal bearing is a continuous annular passage
between the cam ring and the cam sleeve.
In accordance with a further aspect the present invention provides a
method of operating a gas turbine fuel pump that includes a housing having a
pump chamber that receives a rotor therein and a cam member surrounding the
rotor, a cam sleeve surrounding the cam member and a spacer ring disposed
between the cam sleeve and the housing, a generally planar surface along an
inner surface thereof adjacent an anti-rotation pin interconnecting the spacer
ring
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and the cam sleeve, and upon which the cam sleeve rolls in response to
actuation
of the altering means, the method comprising the steps of:
supporting the cam member via a journal bearing disposed between the cam
member and the cam sleeve in the housing;
allowing the rotor to rotate freely relative to the cam member; and
linearly translating a centerpoint of the cam sleeve to limit pressure
pulsations in seal zones of the assembly.
In accordance with a further additional aspect the present invention provides
a fuel
pump comprising:
a housing having a pump chamber, and an inlet and outlet in fluid
communication with the pump chamber;
a rotor received in the pump chamber;
a cam sleeve received in the housing; and
an actuator operatively associated with the cam sleeve that allows a
centerpoint of the cam sleeve to linearly translate to selectively vary pump
output.
Still other benefits and advantages of the invention will become apparent to
one skilled in
the art upon reading the following detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded perspective view of a preferred embodiment of the fluid
pump.
FIG. 2 is a cross-sectional view through the assembled pump of FIG. 1.
FIG. 3 is a longitudinal cross-sectional view through the assembled pump.
FIG. 4 is a cross-sectional vieew similar to FIG. 2 illustrating a variable
displacement pump
with the support ring located in a second position.
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As shown in the Figures, a pump assembly 10 includes a housing 12 having a
pump
chamber 14 defined therein. Rotatably received in the chamber is a rotor 20
secured to a
shaft 22 for rotating the rotor within the chamber. Peripherally or
circumferentially spaced
about the rotor are a series of radially extending grooves 24 that operatively
receive blades
or vanes 26 having outer radial tips that extend from the
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periphery of the rotor. The vanes may vary in number, for example, nine (9)
vanes are
shown in the embodiment of Figure 2, although a different number of vanes can
be used
without departing from the scope and intent of the present invention. As is
perhaps best
illustrated in Figure 2, the rotational axis of the shaft 22 and rotor 20 is
referenced by
numeral 30. Selected vanes (right-hand vanes shown in Figure 2) do not extend
outwardly from the periphery of the rotor to as great an extent as the
remaining vanes
(left-hand vanes in Figure 2) as the rotor rotates within the housing chamber.
Pumping
chambers are defined between each of the vanes as the vanes rotate in the pump
chamber
with the rotor and provide positive displacement of the fluid.
[0022] With continued reference to Figure 2, a spacer ring 40 is rigidly
secured in
the housing and received around the rotor at a location spaced adjacent the
inner wall of
the housing chamber. The spacer ring has a flat or planar cam rolling surface
42 and
receives an anti-rotation pin 44. The pin pivotally receives a cam sleeve 50
that is non-
rotatably received around the rotor. First and second lobes or actuating
surfaces 52, 54
are provided on the sleeve, typically at a location opposite the anti-rotation
pin. The
lobes cooperate with first and second actuator assemblies 56, 58 to define
means for
altering a position of the cam sleeve 50. The altering means selectively alter
the stroke or
displacement of the pump in a manner well known in the art. For example, each
actuator
assembly includes a piston 60, biasing means such as spring 62, and a closure
member 64
so that in response to pressure applied to a rear face of the pistons,
actuating lobes of the
cam sleeve are selectively moved. This selective actuation results in rolling
movement of
the cam sleeve along a generally planar or flat surface 66 located along an
inner surface
of the spacer ring adjacent on the pin 44. It is desirable that the cam sleeve
undergo a
linear translation of the centerpoint, rather than arcuate movement, to limit
pressure
pulsations that may otherwise arise in seal zones of the assembly. In this
manner, the
center of the cam sleeve is selectively offset from the rotational axis 30 of
the shaft and
rotor when one of the actuator assemblies is actuated and moves the cam sleeve
(Figure
2). Other details of the cam sleeve, actuating surface, and actuating
assemblies are
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generally well known to those skilled in the art so that further discussion
herein is
deemed unnecessary.
[00231 Received within the cam sleeve is a rotating cam member or ring 70
having a smooth, inner peripheral wall 72 that is contacted by the outer tips
of the
individual vanes 26 extending from the rotor. An outer, smooth peripheral wall
74 of the
cam ring is configured for free rotation within the cam sleeve 50. More
particularly, a
journal bearing 80 supports the rotating cam ring 70 within the sleeve. The
journal
bearing is filled with the pump fluid, here jet fuel, and defines a
hydrostatic or
hydrodynamic, or a hybrid hydrostatic/hydrodynamic bearing. The frictional
forces
developed between the outer tips of the vanes and the rotating cam ring 70
result in a cam
ring that rotates at approximately the same speed as the rotor, although the
cam ring is
free to rotate relative to the rotor since there is no structural component
interlocking the
cam ring for rotation with the rotor. It will be appreciated that the ring
rotates slightly
less than the speed of the rotor, or even slightly greater than the speed of
the rotor, but
due to the support/operation in the fluid film bearing, the cam ring possesses
a much
lower magnitude viscous drag. The low viscous drag of the cam ring substitutes
for the
high mechanical losses exhibited by known vane pumps that result from the vane
frictional losses contacting the surrounding stationary ring. The drag forces
resulting
from contact of the vanes with the cam ring are converted directly into
mechanical losses
that reduce the pumps overall efficiency. The cam ring is supported solely by
the journal
bearing 80 within the cam sleeve. The journal bearing is a continuous passage.
That is,
there is no interconnecting structural component such as roller bearings,
pins, or the like
that would adversely impact on the benefits obtained by the low viscous drag
of the cam
ring. For example, flooded ball bearings would not exhibit the improved
efficiencies
offered by the journal bearing, particularly a journal bearing that
advantageously uses the
pump fluid as the fluid bearing.
[00241 In prior applications these mechanical drag losses can far exceed the
mechanical power to pump the fluid in many operating regimes of the jet engine
fuel
pump. As a result, there was a required use of materials having higher
durability and
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wear resistance because of the high velocity and load factors in these vane
pumps. The
material weight and manufacturing costs were substantially greater, and the
materials also
suffer from high brittleness. The turning speed of those pumps was also
limited due to
the high vane sliding velocities relative to the cam ring. Even when using
special
materials such as tungsten carbide, high speed pump operation, e.g., over
12,000 RPM,
was extremely difficult.
[00251 These mechanical losses resulting from friction between the vane and
cam
ring are replaced in the present invention with much lower magnitude viscous
drag losses.
This results from the ability of the cam ring to rotate with the rotor vanes.
A relatively
low sliding velocity between the cam ring and vanes results, and allows the
manufacturer
to use less expensive, less brittle materials in the pump. This provides for
increased
reliability and permits the pump to be operated at much higher speeds without
the
concern for exceeding tip velocity limits. In turn, higher operating speeds
result in
smaller displacements required for achieving a given flow. In other words, a
smaller,
more compact pump can provide similar flow results as a prior larger pump. The
pump
will also have an extended range of application for various vane pump
mechanisms.
[00261 Figure 3 more particularly illustrates inlet and outlet porting about
the
rotor for providing an inlet and outlet to the pump chamber. First and second
plates 90,
92 have openings 94, 96, respectively. Energy is imparted to the fluid by the
rotating
vanes. Jet fuel, for example, is pumped to a desired downstream use at an
elevated
pressure.
[00271 As shown in Figure 4, neither of the actuating assemblies is
pressurized so
that the cam sleeve is not pivoted to vary the stroke of the vane pump. That
is, this no
flow position of Figure 4 can be compared to Figure 2 where the cam sleeve 50
is pivoted
about the pin 44 so that a close clearance is defined between the cam sleeve
and the
spacer ring 40 along the left-hand quadrants of the pump as illustrated in the
Figure. This
provides for variable displacement capabilities in a manner achieved by
altering the
position of the cam sleeve.
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[0028] In the preferred arrangement, the vanes are still manufactured from a
durable, hard material such as tungsten carbide. The cam ring and side plates,
though, are
alternately formed of a low cost, durable material such as steel to reduce the
weight and
manufacturing costs, and allow greater reliability. Of course, it will be
realized that if
desired, all of the components can still be formed of more expensive durable
materials
such as tungsten carbide and still achieve substantial efficiency benefits
over prior
arrangements. By using the jet fuel as the fluid that forms the journal
bearing, the
benefits of tungsten carbide for selected components and steel for other
components of
the pump assembly are used to advantage. This is to be contrasted with using
oil or
similar hydraulic fluids as the journal bearing fluid where it would be
necessary for all of
the jet fuel components to be formed from steel, thus eliminating the
opportunity to
obtain the benefits offered by using tungsten carbide.
[00291 The invention has been described with reference to the preferred
embodiments. Obviously, modifications and alterations will occur to others
upon reading
and understanding the preceding detailed description. It is intended that the
invention be
construed as including all such modifications and alterations in so far as
they come within
the scope of the appended claims or the equivalents thereof.
