U.S. patent number 3,868,889 [Application Number 05/309,649] was granted by the patent office on 1975-03-04 for fluid device having means for aligning a cylinder barrel.
This patent grant is currently assigned to The Oilgear Company. Invention is credited to Wilfred S. Bobier.
United States Patent |
3,868,889 |
Bobier |
March 4, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
FLUID DEVICE HAVING MEANS FOR ALIGNING A CYLINDER BARREL
Abstract
A fluid device of the axial piston type having high and low
pressure operating passages, one of which may be an inlet and the
other an outlet depending upon the pumping or motoring function of
the device. The fluid device which may be of the fixed or variable
displacement type has a rotatable cylinder barrel with each end of
a plurality of pistons disposed for reciprocation within cylinder
bores in the cylinder barrel, and cylinder ports successively
communicating each of the cylinder bores with arcuate inlet and
outlet passages formed in a valving face disposed at one end of the
cylinder barrel. The other ends of the pistons are drivingly
engaged by an inclined thrust plate assembly disposed to impart a
reciprocal stroking movement to the pistons within the cylinder
bores as the cylinder barrel is rotated. In one example of the
invention, the thrust plate assembly, the cylinder barrel and other
rotating components of the fluid device are constructed of a
sintered material enclosed in a plastic housing which is preloaded
by a predetermined amount that is a function of the expansion
forces exerted on the housing by the fluid pressure acting against
the pistons within the cylinder bores. In a second example of the
invention, a variable displacement fluid device is disclosed as
having several means for varying the inclination of the thrust
plate assembly with respect to the longitudinal axis of the shaft
on which the rotating cylinder barrel is carried.
Inventors: |
Bobier; Wilfred S. (Bloomfield
Hills, MI) |
Assignee: |
The Oilgear Company (Milwaukee,
WI)
|
Family
ID: |
26739819 |
Appl.
No.: |
05/309,649 |
Filed: |
November 27, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
60333 |
Aug 3, 1970 |
3739691 |
|
|
|
Current U.S.
Class: |
91/506 |
Current CPC
Class: |
F04B
1/324 (20130101); F04B 1/2035 (20130101); F04B
1/20 (20130101) |
Current International
Class: |
F04B
1/20 (20060101); F04B 1/32 (20060101); F04B
1/12 (20060101); F01b 013/04 (); F04b 049/00 () |
Field of
Search: |
;91/504-507
;417/222 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Freeh; William L.
Attorney, Agent or Firm: Basile and Weintraub
Parent Case Text
This is a division of co-pending U.S. Pat. Application Ser. No.
60,333 filed Aug. 3, 1970, now U.S. Pat. No. 3,739,691.
Claims
What is claimed is as follows:
1. A fluid pressure energy translating device of the axial piston
type, comprising: a housing; a cylinder barrel rotatably mounted
within said housing, said cylinder barrel having a plurality of
arcuately spaced cylinder bores and cylinder ports communicating
each of said cylinder bores with one end of said cylinder barrel; a
plurality of pistons with inner ends disposed for reciprocal
stroking movement within said cylinder bores; a valve face having
arcuate passages; said valve face and said one end of said cylinder
barrel being disposed for relative rotary movement with said
cylinder ports communicating successively with said arcuate
passages in said valve face; thrust plate means comprising a yoke
support fixedly mounted in said housing and a yoke movably
supported by said yoke support, said yoke being in a driving
relationship with the other ends of said pistons for imparting said
reciprocal stroking movement to said pistons within said cylinder
barrel bores as said cylinder barrel rotates; bearing means having
an outer race carried within said housing, an inner race carried
around a portion of the peripheral surfaces of said cylinder
barrel, said bearing means providing radial support for said
cylinder barrel, said bearing means being in contact with said yoke
support at a plurality of circumferentially spaced locations for
properly locating said cylinder barrel with respect to said yoke;
said outer race being carried by said housing concentric with said
housing bore; said means for varying the inclination of said yoke
comprising a pair of sleeve members each disposed along an axis
paralleling the axis of said shaft and radially outwardly spaced
from the peripheral surface of said cylinder barrel, each of said
sleeve members having one end of a piston member reciprocably
mounted therein, the other ends of said piston members adapted to
abut a portion of said yoke to pivot said yoke, said sleeve members
being radially spaced a distance from the centerline of said shaft
axis to abut the outer race of said bearing means at locations
which are between said cylinder barrel and said sleeve members to
maintain said bearing races in abutment with said yoke support,
said piston members carried within said sleeves being so spaced
from said longitudinal axis of said shaft to freely reciprocate in
a spaced relationship from the outer periphery of said outer
race.
2. The fluid pressure energy translating device defined in claim 1
further comprising a plurality of roller bearings disposed between
said inner and outer races, the yoke facing ends of said roller
bearings and said inner race being substantially flush; a portion
of said inner race extending beyond said other end of said cylinder
barrel and having an annular inclined inner surface flared upwardly
from said other cylinder barrel end and toward said yoke facing end
of said inner race.
3. A fluid pressure energy translating device of the axial piston
type, comprising: a housing having a longitudinal bore; first
bearing means mounted in said bore; a shaft rotatably supported by
said bearing means; a cylinder barrel drivingly connected to and
rotatable with said shaft, said cylinder barrel having a plurality
of arcuately spaced cylinder bores and cylinder ports communicating
each of said cylinder bores with one end of said cylinder barrel; a
plurality of pistons with inner ends disposed for reciprocal
stroking movement within said cylinder bores; a valve face having
arcuate passages; said valve face and said one end of said cylinder
barrel being disposed for relative rotary movement with said
cylinder ports communicating successively with said arcuate
passages in said valve face, said first bearing means being spaced
from said cylinder barrel a fixed distance; thrust plate means
comprising a U-shaped yoke support journalled on said first bearing
means and in abutment with said housing, said yoke support having
longitudinally extending and laterally spaced legs defining concave
bearings therein between and corners at the extended ends of said
yoke support legs, a movable yoke having correspondingly shaped
bearing surfaces mating with said yoke support bearing surfaces,
such that said yoke is movably supported by said yoke support; said
yoke being in a driving relationship with the other ends of said
pistons for imparting said reciprocal stroking movement to said
pistons within said cylinder barrel bores as said cylinder barrel
rotates; second bearing means having an outer race carried around a
portion of the peripheral surfaces of said cylinder barrel, said
second bearing means providing radial support for said cylinder
barrel, the four corners of the yoke support defined by said
extended ends providing abutments to support said second bearing
means at circumferentially spaced locations on said second bearing
means for properly locating said cylinder barrel with respect to
said yoke.
4. The fluid pressure energy translating device defined in claim 3
further comprising a plurality of roller bearings disposed between
said inner and outer races, the yoke facing end of said roller
bearings and said inner race being substantially flush, a portion
of said inner race extending beyond the other end of said cylinder
barrel and having an annularly inclined inner surface flared
upwardly from said other cylinder barrel end and toward said yoke
facing end of said inner race.
5. The fluid pressure energy translating device defined in claim 3,
further comprising: means for varying the inclination of said yoke
with respect to the longitudinal axis of said shaft for selectively
varying the amount of reciprocal stroking movement imparted to said
pistons within said cylinder barrel bores.
6. A fluid pressure energy translating device of the axial piston
type comprising:
a housing;
a cylinder barrel rotatably mounted within said housing, said
cylinder barrel having a plurality of arcuately spaced cylinder
bores and cylinder ports communicating each of said cylinder bores
with one end of said cylinder barrel;
a plurality of pistons with inner ends disposed for reciprocal
stroking movement within said cylinder bores;
a valve face having arcuate passages, said valve face and said one
end of said cylinder barrel being disposed for relative rotary
movement, with said cylinder ports communicating successively with
said arcuate passages in said valve face;
an inclined thrust plate comprising a yoke support fixedly mounted
in said housing and a yoke movably supported by said yoke support,
said yoke being in a driving relationship with the other end of
said piston for imparting a reciprocal stroking movement to said
pistons within said cylinder barrel as said cylinder barrel
rotates;
means for varying the inclination of said yoke with respect to the
longitudinal axis of rotation of said cylinder barrel for
selectively varying the amount of reciprocal stroking movement
imparted to said pistons as said cylinder barrel rotates;
bearing means having an outer race carried by said housing
concentric with said housing bore;
an inner race carried around a portion of the peripheral surface of
said cylinder barrel;
a plurality of roller bearings disposed between said inner and
outer races;
said means for varying the inclination of said yoke comprising a
pair of spaced sleeve members, each disposed along an axis parallel
to the axis of rotation of said cylinder barrel and radially
outwardly spaced from the peripheral surface of said cylinder
barrel, each of said sleeve members having one end of a piston
reciprocably mounted therein, the other end of said pistons adapted
to abut a portion of said yoke to pivot said yoke about an axis
transversely disposed with respect to the axis of rotation of said
cylinder barrel, said sleeves being radially spaced a distance from
the axis of rotation of said cylinder barrel to abut the outer race
of said bearing means at locations which are between said cylinder
barrel and said sleeve members to maintain said outer race in
contact with said yoke support at a plurality of circumferentially
spaced locations for properly locating said cylinder barrel with
respect to said yoke, said piston members being carried within said
sleeves and so spaced from said axis of rotation of said cylinder
barrel as to freely reciprocate in a spaced relationship with
respect to the outer periphery of said outer race.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to fluid devices and particularly to
those of the axial piston type which may function either as a fluid
pump or as a fluid motor.
2. Description of the Prior Art
Heretofore, fluid pumping or motoring devices of the axial piston
type have been constructed of a metallic housing having a revolving
cylinder barrel with a plurality of parallel cylinder bores herein,
within which pistons are reciprocated by means of a thrust plate
assembly or the like. A rotary valve mechanism in the form of
cylinder ports at one end of the cylinder barrel alternately
connects each cylinder bore with an inlet and an outlet passage of
the device as the cylinder barrel is rotated.
The thrust plate assembly in fluid devices of the variable
displacement type normally takes the form of a yoke having
transversely extending pintles rotatably carried in bearings
suitably mounted to the wall of the housing such that the entire
force exerted against the thrust plate assembly due to the fluid
pressure acting against the piston within the cylinder barrel bores
is taken by the housing, thus necessitating a strong metal housing.
Such metal housings are expensive in that they must be cast molded
and subsequently require a machining operation to provide the
necessary precision that is needed in such constructions. It would
be desirable to provide a housing for such axial piston fluid
devices, constructed of a plastic material which would eliminate
the subsequent machining operations and the resulting expenses
normally incurred in using such metal housings. For example,
housings constructed for fluid devices having the same displacement
capacity would cost approximately $2.00 for a metal housing as
compared to $.60 for a housing constructed of a plastic material.
The equipment needed to manufacture a metal housing costs
approximately $750,000.00 as compared to $3,500.00 for an injection
mold which would be used in constructing a housing of a plastic
material.
Further, heretofore fluid devices of the variable displacement type
have used a thrust plate assembly which is normally of a metal
construction such as cast iron or steel which, in addition to
requiring substantial machining, adds to the overall weight of the
device. It would be desirable to replace such cast iron and/or
steel thrust plate assemblies with one constructed of a sintered
material which, heretofore, has not been possible because of the
high loads and complicated shape that such thrust plate assemblies
require.
In addition to the high loads transmitted to the thrust plate
assembly, suitable means must be provided which permit an easy
movement of the thrust plate assembly with respect to the
longitudinal axis of the drive shaft on which the cylinder barrel
is rotated so as to vary the amount of reciprocal stroking movement
imparted to the pistons within the cylinder bores to thereby permit
a selected variation in the displacement of such axial piston fluid
devices.
In such previously constructed axial piston fluid devices, the
displacement control mechanism used to control the inclination of
the thrust plate assembly with respect to the longitudinal axis of
the drive shaft has necessitated a different design for both the
fixed displacement device and the variable displacement pump as the
displacement control mechanism is normally constructed as part of
the housing in such variable displacement devices, thus requiring a
larger housing for the variable displacement device. Heretofore, if
the same housing were used for both variable and fixed displacement
units, a larger housing would have been required since portions
thereof would be used to mount the displacement control mechanism.
The use of such a variable displacement housing in a fixed
displacement unit results in an unduly large unit in proportion to
its displacement. It would therefore be desirable to provide a
housing which is constructed for both variable displacement and
fixed displacement devices without requiring a larger housing for
the variable displacement design.
It is also a conventional practice that such previously used
devices have been normally constructed to use only one type of
displacement varying control mechanism, whereas it may be desirable
to have a fluid device having a housing construction which is
adaptable for use with manual controls, pressure compensated
controls and the like, thus eliminating the necessity of having
several different housing designs for the same capacity unit so as
to accommodate different displacement control applications.
Fluid devices of the axial piston type normally are characterized
by having a valving face formed by a flat surface on which the
cylinder barrel normally runs in abutment and in a fluid sealing
relationship. The abutting face of the cylinder barrel on which the
cylinder ports are disposed normally has been provided with
arcuately spaced elevated pressure pads disposed radially outwardly
from the cylinder ports providing a bearing surface on which the
cylinder barrel rides in a manner which avoids excessive wear. Such
bearing pads are more commonly referred to as "Kingsbury Pads" and
have functioned in an acceptable manner in the past to compensate
for wear and variations in oil viscosity due to changing
temperatures and different fluids. In devices of this type
operating at high speeds and high pressures, considerable
difficulty may be experienced in providing a satisfactory running
surface between the cylinder barrel and the valving face due to a
lack of oil flow across the face of the cylinder barrel from the
cylinder ports to the Kingsbury pads.
It would therefore be desirable to provide a new and improved
Kingsbury pad for such axial piston fluid devices.
As speed and pressure is increased in such previously used fluid
devices, there is always an accompanying increase in noise. This
general increase in noise with increased speed and pressure may be
attributed to a number of factors in devices of the axial piston
type. First, the sound frequencies generated by the device increase
with speed as the components of the device are subjected to
increased alternating impact forces; second, the intensity of speed
related sounds increases as the impact forces between components of
the device increase; and third, the excitation spectrum of the
significant piston harmonics also broadens, thus increasing the
number of resonant responses.
It would therefore be desirable to provide a fluid device wherein
the attendant noise and vibration levels are significantly
reduced.
SUMMARY OF THE INVENTION
The present invention, which will be described subsequently in
greater detail, comprises a fluid pumping or motoring device of the
axial piston type having construction which permits the adaptation
of an outer plastic housing with a substantially large percentage
of the rotating parts thereof constructed of a sintered material,
providing an axial piston fliud device adapted for use over a wide
range of applications.
It is therefore an object of the present invention to provide a
rotary fluid device of the axial piston type having an improved
construction which is readily adapted to low cost
manufacturing.
It is also an object of the present invention to provide a rotary
fluid device of the axial piston type having an improved cylinder
barrel construction resulting in a reduction in surface wear and
galling between the cylinder barrel and the valving face.
It is also an object of the present invention to provide a rotary
fluid device of the axial piston type having an improved thrust
plate assembly resulting in greater reliability and long life while
operating at high pressures and temperatures, proportioned and
simplified so that it can be made inexpensively from sintered
materials.
It is also an object of the present invention to provide a rotary
fluid device of the axial piston type having a construction which
contributes to the reduction in the general noise radiated by such
a device.
It is also an object of the present invention to provide a rotary
fluid device of the axial piston type having means for varying the
displacement thereof, and a housing construction adaptable to
accommodate a variety of displacement varying mechanisms.
Other objects, advantages, and applications of the present
invention will become apparent to those skilled in the art of such
fluid devices when the accompanying description is read in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The description herein makes reference to the accompanying drawings
wherein like reference numerals refer to like parts throughout the
several views, and in which:
FIG. 1 is a longitudinal cross sectional view of a fluid device
incorporating a feature of the present invention;
FIG. 2 is a longitudinal cross sectional view of the fluid device
illustrated in FIG. 1 and taken generally on line 2--2 thereof;
FIG. 3 is a fragmentary transverse cross sectional view of the
fluid device of FIG. 1 and illustrating a component thereof and
taken generally on line 3--3 of FIG. 2;
FIG. 4 is a side view of the component illustrated in FIG. 3;
FIG. 5 is a fragmentary, exploded view of the fluid device
illustrated in FIG. 1;
FIG. 6 is a fragmentary cross sectional view of a fluid device
incorporating another feature of the present invention;
FIG. 7 is a fragmentary, transverse, cross-sectional view of the
fluid device illustrated in FIG. 6 and taken on lines 7--7 thereof;
and
FIGS. 8 through 11 are fragmentary views of several modifications
of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings, and particularly FIGS. 1 and 2, there is
illustrated a fluid device in the form of an axial piston pump 10
comprising a housing 12 having a body section 14 constructed of a
plastic material and a longitudinally disposed bore 18 enclosed by
a cap 20 secured to the body section 14 by bolts 22 extending
axially through the cap 20 and the body section 14 and threadedly
engaging clamps 15. An O-ring 24 insures a fluid tight seal between
the juncture of the body section 14 and the cap 20. The body
section 14 includes a pilot portion 26 forming a mounting flange 28
having mounting holes 30 extending therethrough to permit the
mounting of the pump 10 at a desired location. The housing bore 18
provides a chamber 32 in which a rotating group 33 is positioned.
The rotating group 33 includes a cylinder barrel 34 which is
provided with a plurality of arcuately spaced cylinder bores 36,
each having one end of a piston 38 axially slidable therein. A
plurality of cylinder ports 40 axially aligned with each cylinder
bore 36 communicate each of the cylinder bores 36 with a front face
42 of the cylinder barrel 34. Each of the pistons 38 have spherical
ends 44 on which are swaged socketed shoes 46. The cylinder barrel
34 is positioned axially between a valving face 48 formed on the
inner face of the cap 20 and an inclined thrust plate assembly 50.
The valving face 48 serves in a well known manner to provide a
properly phased connection between the cylinder ports 40 and a pair
of arcuate ports 52 and 54 such that the cylinder ports 40
communicate successively with the arcuate ports 52 and 54 as the
cylinder barrel 34 rotates. The arcuate ports 52 and 54 are,
respectively, connected to the external inlet and outlet connection
ports 53 and 55 of the pump 10.
The piston shoes 46 have outwardly extending flanges 56 which are
contacted by an annular cage 58 with holes corresponding to each
piston 38. The annular cage 58 has a centrally disposed conical
bore 62 adapted to contact a spherical outer surface 64 of a collar
66 which is, in turn, carried on a drive shaft 68 that extends
longitudinally through the housing bore 18. A spring 70 disposed
between the piston end of the cylinder barrel 34 and the collar 66
exerts a force urging the face 42 of the cylinder barrel 34 into
engagement with the valving face 48, while at the same time biases
the shoes 46 by means of the collar 66 and the annular cage 58 into
engagement with the thrust plate assembly 50. The drive shaft 68 is
supported between bearings 72 and 74. The bearing 72 is carried in
a bore 75 of a decreased diameter at the thrust plate assembly end
of the housing 12 while the bearing 74 (shown only in FIG. 1) is
carried in a centrally disposed bore 76 within the cap 20. The
drive shaft 68 is effective to transmit torque from a prime mover
(not shown) to the cylinder barrel 34 through a splined driving
connection 78 in a conventional manner. A conventional shaft seal
80 is provided in the decreased diameter bore 75 and retained in
position by a snap ring 82.
The cylinder barrel 34 is provided with a skirt portion 84 snuggly
fitted in a recessed portion 86 at the piston end of the cylinder
barrel 34 to form an inner race 88 for roller bearings 90; the
outer race 92 of which is carried by the body section 14 in
abutment with the thrust plate assembly in a manner which will be
described in greater detail hereinafter. The skirted portion 84 has
an annular inclined inner surface 96 extending upwardly from the
cylinder barrel 34 and terminating in such a manner that the thrust
plate assembly end 98 of the inner race 88 is flush with the thrust
plate assembly end 100 of the roller bearings 90. Heretofore, fluid
devices have been constructed with the inner race of the bearing
extending beyond the roller bearings the same distance as the outer
race. By having the end 98 of the inner race 88 flush with the end
100 of the roller bearings 90, a greater diameter of thrust plate
assembly 50 with respect to the longitudinal axis is provided which
may increase the displacement capacity of the pump 10 by as much as
15% as compared to fluid devices heretofore constructed by allowing
the pistons to operate on a larger piston bore circle. The piston
bore circle is a circle defined by the longitudinal axes of the
pistons 38 as the same rotate about the longitudinal axis of the
shaft 68. As the diameter of the piston bore circle is increased,
the diameter of each piston bore 36 may likewise be increased, thus
the displacement of the pump 10 may be increased without increasing
the overall size thereof.
The face 42 of the cylinder barrel 34 which is substantially
identical to the configuration illustrated in FIG. 7, comprises a
plurality of bearing pads 102, separated from one another by radial
grooves 104 and separated from the balancing lands 106 of the
cylinder ports 40 by an annular groove 108. The bearing pads 102
are generally referred to as "Kingsbury pads" and function in a
manner well known in the art. The bearing pads 102 are further
provided with a concave contour on the inner wall 110 facing the
cylinder ports 40 to provide a large oil pool to aid in lubricating
the bearing pads 102 as the cylinder barrel 34 rotates. The oil
pools decrease excessive wear during high temperature and high
speed operations, thereby increasing the life of the face 42 of the
cylinder block 34.
As can best be seen in FIG. 7, the cylinder ports 40 are arranged
in a circle, having a radius equal to the radius of the arcuate
ports 52 and 54 (shown in phantom lines in FIG. 7) so that
communication will be maintained throughout the full length of the
arcuate ports 52 and 54. This communication will be interrupted
whenever a cylinder port 40 moves across a cut-off portion or space
separating the arcuate ports 52 and 54.
With reference to FIGS. 1 and 2, as the cylinder barrel 34 rotates,
a reciprocating stroking motion is imparted to the pistons 38 due
to the inclination of the thrust plate assembly 50, thus a relative
reciprocating motion between the cylinder barrel 34 and the pistons
38 results as the cylinder barrel 34 rotates wherein the cylinder
bores 36 are alternately compressed and expanded, resulting in
fluid being drawn into and expelled from the cylinder bores 36
through the cylinder ports 40.
From the foregoing it can be seen that when a rotary movement is
imparted to the outer end 112 of the drive shaft 68, the cylinder
barrel 34 will be revolved to alternately register the cylinder
bores 36 with the arcuate ports 52 and 54 of the valving face 48 by
means of the cylinder ports 40.
Referring to FIGS. 1-5 for an understanding of the accompanying
description of the thrust plate assembly 50 which comprises a
movable yoke 55 and a fixed yoke support 57. The fixed yoke support
57 has a U-shaped configuration, the bottom wall 59 of which has an
bore 61 through which the drive shaft 68 extends. The bore 61 has
an end enlarged portion 63 having an inner diameter closely fitting
the outer diameter of the drive shaft support bearing 72, and thus
as can best be seen in FIG. 1 the yoke support 57 is axially
aligned with respect to the drive shaft 68 when positioned on the
outer periphery of the bearing 72.
The yoke support 57 includes a pair of axially projecting sidewalls
65, each of which has arcuately shaped bearing surface 67
supporting the movable yoke 55 on which the piston shoes 46
slidably engage as the cylinder barrel 34 is rotated so as to
impart a reciprocal stroking movement to the pistons 38. The yoke
55 has a pair of transversely extending aligned support pins 69 and
71 each of which has arcuately shaped bearing surfaces 73 contoured
to meet with the arcuately shaped bearing surfaces 67 of the
projecting sidewalls 65 such that the yoke 55 is adapted to pivot
within the side wall bearing surfaces 67 about a axis 75 defined by
the radius of the transversely extending support pins 69 and 71 in
a manner which will be described in greater detail hereinafter.
The yoke support pin 71 includes a L-shaped arm 77 integrally
formed therewith and projecting rearwardly away from the support
pin 71. The projecting leg of the arm 77 carries a member 79 (FIGS.
1 and 2) having a slot 81 in which a connecting pin 83 is disposed.
The connecting pin 83 extends through an opening 85 formed in a
sidewall of the body section 14 and is adapted to be coupled to any
one of several displacement varying mechanisms such as the types
disclosed in the aforementioned patent application. The opening 85
is so sized as to permit the member 79 to be positioned
therethrough onto the arm 77 during assembly with the connecting
pin 83 extending through the housing body section 14 and adapted to
pivot about the axis 75 defined by the radius of the support pins
69 and 71 without interference with the sidewall of the housing
bore 85 14. As can best be seen in FIG. 2, the preferred axis of
rotation for the connecting pin 83 and for purposes of description
the longitudinal axis of the support pins 69 and 71, is the axis 75
passing through the center point about which each of the arcuate
bearing surfaces 73 is formed. The axis 75 should intersect the
plane at which the centers of the spherical piston ends 44 lie and
may also intersect the longitudinal axis of the drive shaft 68.
However, the axis 75 may be vertically offset from the drive shaft
axis, in a well known manner, depending upon the desired
results.
The arcuately shaped bearing surfaces 67 formed on the sidewalls of
the yoke support 57 are in the form of a plastic bearing 87, such
as a teflon-lead bearing or the like, which provides the necessary
support to withstand the load transmitted through the pistons 38
and the movable yoke 55, while at the same time offering the least
amount of frictional resistance to the pivotal movement of the yoke
55 therewithin. The plastic bearings 87 have a central aperture 89
(FIG. 5) adapted to receive a boss 91 formed in each sidewall 65 to
securely retain the bearing 87 on its associated sidewall 65.
The yoke 55 has a circular thrust bearing face 93 with which the
shoes 46 cooperate and a hemispherical cross section 95 (FIS. 5)
with an elliptical, centrally disposed bore 97 through which the
drive shaft 68 extends. The elliptical shape of the bore 97 permits
the yoke 55 to rotate about the shaft 68 without interference
therewith. Since the yoke 55 and the yoke support 57 are both
constructed of a sintered material, the radial thickness 99 (FIG.
5) of support pins 69 and 71, as measured from the bearing face 93
to the bottom of the support pin bearing surface 73 must be at
least 40% of the total thickness or longitudinal 101 of the yoke 55
as measured from the bearing face 93 to the bottom thereof to
assure that the yoke 55 will withstand the loads to which it is
subjected, while the L-shaped arm 77 extending from the support pin
71 should have a length which is at least equal to the yoke
thickness 101 in order to provide good fill characteristics when
the same is manufactured.
The amount of friction between the bearing surfaces of the yoke 55
and the yoke support 57 will be directly proportional to the load
exerted thereon, while the frictional torque is in direct
proportion to the radius of the arcuate bearing surfaces or 73. In
the present design the radius of the bearing surfaces is kept to a
minimum, and thus the frictional torque minimized. It should also
be noted that present construction of the yoke 55 and the yoke
support 57 results in the length 103 and the thickness 101 of the
yoke 55 being respectively shorter and greater than comparable
components of presently used devices. The shorter length and
increased thickness of the yoke 55 reduces unit vibrations and
results in an extremely quiet pump compared to such presently used
designs.
Since the periphery of the yoke support 57 is rectangular and the
periphery of the yoke 55 is circular, each corner 117 of the yoke
support 57 will project radially outwardly beyond the yoke 55 as
illustrated in FIG. 3 in phantom lines. As can best be seen in FIG.
2, the bearing 90 is axially positioned with respect to the center
of each piston ball 44 by the abutment of the thrust plate facing
side 94 of outer race 92 against the corners 117 of the yoke
support 57. This arrangement provides a simple construction which
insures proper axial alignment, which is essential for a smooth,
efficient and accurate operation of the pump 10.
Referring now to FIGS. 6 and 7 wherein there is illustrated a
modification of the present invention in the form of a variable
displacement axial piston pump 120 comprising a housing 122 having
an internal bore 124 enclosed by a cap 126 by means of screws (not
shown) extending through the cap 126 and into threaded bores within
the housing 122, the pump 120 is similar to the pump 10 disclosed
in FIGS. 1 and 2 in that it is provided with a drive shaft 68 on
which a cylinder barrel 34 is rotatably mounted and having a
plurality of parallel cylinder bores 36 and cylinder ports 40
through which fluid communication to arcuate passageways 52 and 54
(FIG. 7) in the valving face 48 formed on the inner face of the cap
126 for directing fluid from an inlet port (not shown) to an outlet
port (not shown). Radial support for the cylinder barrel 34 is
provided by roller bearings 90 in the same manner as described
hereinbefore. Each of the cylinder bores 36 has a piston 38
reciprocably mounted therein with the pistons 38, in turn, having
rounded ends 44 on which piston shoes 46 are positioned against a
thrust plate assembly 50 by means of the contact cage 58, the
collar 66 and spring 70 in a manner substantially identical as
hereinbefore described.
The thrust plate assembly 50 comprises the fixed yoke support 57
carried on the inner wall of the housing 122 by bearing 75 and
includes a pair of axially projecting sidewalls 65, each of which
has an arcuately shaped bearing surface 67 supporting a movable
yoke 136 on which the piston shoes 46 slidably engage as the
cylinder barrel 34 is rotated so as to impart a reciprocal stroking
movement to the pistons 38. The yoke 136 has a pair of transversely
extending, aligned support pins 138, each having arcuately shaped
bearing surfaces 140 contoured to mate with the arcuately shaped
bearing surfaces 67 of the projecting sidewalls 65, such that the
yoke 136 is adapted to pivot within the sidewall bearing surfaces
67 about the axes 75 of the transversely extending support pins 138
(only one of which is shown in FIG. 6). The yoke 136 includes a
pair of transverse arms 142 and 144 which project in a plane
perpendicular to the support pins 138 and have rounded bearing
surfaces 146 and 147 at their projecting ends which respectively
cooperate with a pair of pistons 148 and 150 to rotate the yoke 136
within the bearing surface 67 in a manner which will be described
in greater detail hereinafter.
The pistons 148 and 150 are slidably mounted for reciprocal
movement, respectively, within sleeve members 152 and 154 which, in
turn, are carried within stepped bores 156 in the cap 126. Each
sleeve member 152 and 154 has an enlarged end portion 158 which
abuts a step 160 within bores 156, and is secured to the cap 126 by
screws 162 extending through cover plates 164 and 166 into threaded
bores 168 within the cap 126. The inner ends of each sleeve member
152 and 154 abuts one side of the outer race 92 of the roller
bearings 90 to maintain the opposite side 94 of the outer race 92
in abutment with the corner 117 formed on the yoke support 57 in
the same manner hereinbefore described with respect to the pump 10.
As can best be seen in FIGS. 6 and 7, the sleeve members 152 and
154 have a sufficient radial thickness such that the pistons 148
and 150 will traverse the outer surface of the outer race 92
without interference therewith.
The sleeve member 152 has a spring 170 in compression between the
cover plate 164 and the piston 148 biasing the piston 148 to engage
the round bearing surface 146 of the arm 142 and rotate the yoke
136 so as to stroke the yoke 136 to a full displacement position,
that is, the yoke is at an angle with respect to the longitudinal
axis of the drive shaft 68 that permits the greatest degree of
relative reciprocal stroking movement between the pistons 38 and
the cylinder bores 36.
The interior 153 of the sleeve member 154 is adapted to be
communicated to a source of pressure through a pressure compensated
valve 172 or the like, which selectively controls the pressure
admitted to the interior of the sleeve member 154 to move the
piston 150 against the bearing surface 147 of the arm 144 to
selectively position the yoke for controlling the inclination of
the thrust plate with respect to the longitudinal axis of the drive
shaft 68. Thus, the displacement of the pump 10 may be varied to
provide any desired output from a minimum output to a maximum
output.
The cylinder barrel 34, the piston shoes 46, the yoke 136 and the
yoke support 57 are all constructed of a sintered metal which, in
addition to reducing the weight of the pump 120, increases the
lubricating characteristics of the rotating components and results
in a fluid device which is substantially less expensive to
manufacture than fluid devices previously used.
The plastic housing illustrated in FIG. 2 has an outer annular
recessed portion 270 at the drive shaft end thereof on which the
elongated metal clamps 15 are carried. By tightening the bolts 22
within threaded bore 280 in the clamps 15, the plastic body section
14 may be precompressed to a predetermined amount, which is a
function of the pressure at which the pump 10 will operate. During
operation of the pump 10, the pressure within each cylinder bore 36
generates a force against each piston 38 which acts in a direction
normal to the face of the cylinder barrel 34. This force can be
resolved in an axial component force and a radial component force
acting at the center of the spherical piston ends 44. These forces
tend to exert a load on the plastic body section 14 of the housing
12 which tends to longitudinally expand the same. By precompressing
the plastic body section 14 by a predetermined amount, the effect
of the expansion loads exerted on the plastic body section 14 by
internal forces of the rotating group 33 will be cancelled.
Thus, it can be seen that the present invention has provided a
rugged, compact and low cost fluid device of the axial piston type
that can function as a motor or a pump and which has an improved
means for mounting the cylinder barrel and for varying the
displacement thereof.
While the forms of the embodiments of the invention as disclosed
herewithin constitute a preferred form, it is to be understood that
other forms might be adopted, all coming within the spirit of the
invention and the scope of the appended claims.
* * * * *