U.S. patent number 3,906,841 [Application Number 05/386,012] was granted by the patent office on 1975-09-23 for axial-piston machine.
This patent grant is currently assigned to Linde Aktiengesellschaft. Invention is credited to Walter Heyl.
United States Patent |
3,906,841 |
Heyl |
September 23, 1975 |
Axial-piston machine
Abstract
An axial-piston machine having a cylinder drum which is urged
under pressure against a surface for distributing fluid thereto, is
provided with respective (pressurizing) pistons, each under the
pressure of a working cylinder, which react against a common body
to develop the force retaining the cylinder drum against the
control surface.
Inventors: |
Heyl; Walter (Oberafferbach,
DT) |
Assignee: |
Linde Aktiengesellschaft
(Wiesbaden, DT)
|
Family
ID: |
5852735 |
Appl.
No.: |
05/386,012 |
Filed: |
August 6, 1973 |
Foreign Application Priority Data
Current U.S.
Class: |
91/487 |
Current CPC
Class: |
F04B
1/2035 (20130101); F04B 1/2007 (20130101) |
Current International
Class: |
F04B
1/20 (20060101); F01B 001/00 () |
Field of
Search: |
;91/487,488,499,506,507 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Freeh; William L.
Assistant Examiner: LaPointe; G. P.
Attorney, Agent or Firm: Ross; Karl F. Dubno; Herbert
Claims
I claim:
1. In an axial piston machine having a shaft, a cylinder drum
coupled with said shaft for rotation therewith, a plurality of
working cylinders formed in said cylinder drum in an annular array,
respective working pistons received in said working cylinders and
axially shiftable therein while bearing upon an inclined surface at
one side of said cylinder drum, and a fluid-distribution surface
extending transverse to the axis of said cylinder drum at the other
side thereof and communicating with said working cylinders, the
improvement wherein said cylinder drum is formed with a plurality
of pressing cylinders within said array each communicating with at
least one of said working cylinders for pressurization thereby, a
pressing piston received within each of said pressing cylinders and
displaceable therein, and an annular abutment retained on said
shaft against axial displacement away from said fluid-distribution
surface and engaged by said pressing pistons whereby said cylinder
drum is urged in the direction of said fluid-distribution surface,
said abutment rotating with said shaft, each of said working
cylinders being connected to a respective pressing cylinder by a
respective connecting passage formed in said cylinder drum, each of
said working cylinders being formed with a guide bushing at said
side of said cylinder drum, each of said connecting passages
opening into the respective working cylinder behind the respective
guide bushing.
2. The improvement defined in claim 1 wherein each of said guide
bushings is formed with a circumferential relief groove and said
cylinder drum is formed with respective relief passages each
communicating with a respective one of said relief grooves.
3. The improvement defined in claim 2 wherein the relief passage
and the connecting passage of each working cylinder are aligned and
form parts of a bore extending into said drum and inclined to the
axis of the respective working cylinder.
Description
FIELD OF THE INVENTION
The present invention relates to axial-piston machines and, more
particularly, to an axial-piston hydrostatic pump or a motor having
a cylinder barrel or drum which is held under pressure against a
fluid-distribution surface at which a fluid pressure is
developed.
BACKGROUND OF THE INVENTION
An axial-piston machine, e.g., an axial-piston pump or motor, also
referred to as a hydrostatic pump or motor, may comprise a cylinder
drum or barrel which is provided with an array of angularly
equispaced cylinder bores (working cylinders), the pistons of which
are axially shiftable by mechanical action or hydraulic force,
depending upon whether the machine is operative as a pump or motor.
In an axial-piston pump, for example, the drum may be rotated with
respect to a fixed control plate, inclined about an axis
perpendicular to the axis of the drum, the control plate being at
an angle to the drum axis so that, as the drum is rotated, e.g., by
a shaft or the like, pistons are forced into the respective bores
at one side and are permitted to emerge from the respective bores
at the other side. As the drum is rotated, each piston
progressively is driven into the respective working cylinder and
drawn therefrom, thereby decreasing and increasing the volume of
the working chamber alternately during each rotation of the
cylinder drum. The latter is provided with ports opening into each
of the chambers at the base of the drum and slidably engages a
fluid-distribution surface provided with openings respectively
communicating with an intake fitting and a discharge fitting of the
machine. The intake fitting communicates with an opening which
registers with the cylinders as the volume of each working cylinder
increases through the region subtended by this opening, thereby
enabling the hydrostatic medium (hydraulic fluid) to be drawn into
the individual cylinders, whereas the discharge fitting
communicates with the cylinders via an opening in the region in
which the cylinder volumes contract so that hydraulic fluid is
displaced through this opening under pressure.
As axial-piston hydrostatic motor, similarly, may comprise a
cylinder drum rotatable about its axis and an array of axially
displaceable pistons cooperating with an inclined control member
which permits the stroke of the piston to increase as the drum
rotates toward one side, but reduces the extent to which the piston
can emerge from a working cylinder toward the other side of the
drum path. Consequently, when fluid is supplied under pressure over
part of the control surface, the tendency of the piston to increase
their extension in this region causes a rotation of the drum.
Machines of this type are collectively referred to as hydrostatic
axial-piston machines or as swash plate pumps and motors.
Axial-piston machines of the aforementioned type are employed with
rotatable or stationary shafts, with shafts coupled to the cylinder
drums or the inclined plate, or with various other means for
driving the cylinder drum or deriving torque from the rotation
thereof.
For example, in a driven-flange-type of hydrostatic machine, the
inclined flange or disk may be mounted upon a shaft which is
coupled with the cylinder drum while the latter rotates upon a
fixed shaft inclined to the first-mentioned driven shaft. In these
systems it is known to provide between the fixed shaft or stub
shaft upon which the cylinder drum is journaled, a hydraulic system
exerting fluid pressure on the drum so as to urge it axially in the
direction of the fluid-distribution surface. This is especially
desirable when the drum is mounted with limited axial
displaceability upon the stationary shaft. In general, the
hydraulic means may include surfaces on the drum and on the shaft
which define between them oppositely effective piston surfaces when
hydraulic fluid from one or some of the working cylinders is
delivered to the space between these surfaces. Arrangements have
been proposed in which two sets of surfaces are provided, one of
which is in constant communication with the low-pressure side of
the hyrostatic machine while the other set is in fluid
communication with the high pressure side thereof.
These hydraulic devices work substantially uniformly around the
entire periphery of the drum-support shaft and thus the axial force
applied to the cylinder drum resists uniformly the buildup of
pressure at the interface between the fluid-distribution surface
and the drum. Since the pressure on the high pressure side of this
surface will always be larger than the pressure on the other side
of the surface, the forces applied to the cylinder do not
necessarily balance and can exert a twisting action preventing
proper positioning of the cylinder drum or causing the latter to
bind against the shaft. Where bearings are provided between the
shaft and the drum, these bearings show excessive wear because of
the nonuniformity of force distribution.
In one system for providing a fluid-pressure bias to hold the
cylinder drum, which is mounted for rotation on a central shaft
rigid with the housing with axial play, against the
fluid-distribution surface, a sleeve is journaled upon the drum
shaft or axially seated thereagainst and defines with the drum a
pressurizable compartment chargeable with a fluid medium, e.g., the
working medium of the machine, to press the base of the cylinder
drum against this fluid-distribution surface.
It is also known to use such a sleeve (axially seated against the
shaft or axle) to define two pressurizable chambers or compartments
with the drum, the chambers being effective upon pressurization to
retain the drum against the fluid-distribution surface. To this
end, one of the chambers is in fluid communication with the
high-pressure passages of the machine (high-pressure side) while
the other chamber is in fluid communication with the low-pressure
passages or low-pressure side thereof.
A similarly functioning prior-art arrangement provides mutually
engageable abutments on the support shaft, which is mounted in the
housing with axial play, and upon the drum, the aforementioned
pressurizable compartment or chamber being formed between the shaft
and the housing so that, upon pressurization of the chamber, the
shaft draws the drum against the fluid-distribution surface.
In all of the aforedescribed systems, the working chambers are
designed to provide an axial force to the drum and it is a
precondition of effective operation of such systems that the drum
be mounted with no lateral or radial play. When such play is
present, e.g. as a result of manufacturing tolerances and wear of
the parts, the pressure at the high-pressure side of the
fluid-distribution surface urging the drum away from the latter is
substantially greater than the similarly directed pressure at the
low-pressure side. As a consequence, canting of the drum may occur
with all of the disadvantages which are generally associated with
misalignment of rotary members.
Furthermore, when the drum is mounted with some freedom of axial
displacement, the restoring force can be generated by a spring and
by overdimensioning slightly the surface in the cylinder head which
is effective in the direction opposite the pressure at the
fluid-distribution surface. The spring also provides force in the
absence of hydraulic pressure. These forces are relatively small
and thus it has been necessary to provide the sealing surface area
at the fluid-distribution surface with small dimensions so the
axial force on the drum, determined by the product of the
interfacial pressure and sealing surface area will be relatively
small. Since the surface is small, wear can be pronounced and large
quantities of the hydraulic medium may pass, at the worn sealing
surfaces, as leakage into the housing.
The term "fluid-distribution surface" as described above is
intended, in accordance with the present invention, to refer to the
surface at which the cylinder passages come into fluid
communication with the inlet and outlet ports and at which the
pressure is developed which urges the cylinder drum axially away
from this surface. The fluid-distributing surface may be formed
directly in the housing and may be juxtaposed directly with the
base of the drum or may be formed between the drum and a fixed
fluid-distribution or valve plate and the drum. When the
nonrotatable valve plate is axially shiftable, however, the
distribution surface will generally be that norotatable surface of
the housing which is juxtaposed with the plate and the latter will
be considered an axially movable part of the drum for the present
purposes. It should also be understood that the principles
described below are intended to be applicable to so-called
inclined-disk axial-piston machines in which the drum is rotatable
relatively to the inclined plate against which the pistons react,
and to a driven-flange machine in which this plate is rotated about
its axis inclined to the drum axis and the drum is entrained
therewith.
OBJECTS OF THE INVENTION
It is the principal object of the invention to provide an improved
axial-piston machine in which the aforedescribed disadvantages can
obviated.
Still another object of this invention is to provide a machine of
the character described with improved means for urging the cylinder
drum against the fluid-distribution surface to avoid the difficulty
mentioned earlier whereby the force at this surface against the
drum is unbalanced between the high-pressure side and the
low-pressure side.
Still another object of this invention is to provide a means for
urging the drum of an axial-piston machine against its
fluid-distribution surface whereby the sealing lands of the drum
can have an increased surface area by comparison to earlier
axial-piston machines.
SUMMARY OF THE INVENTION
These objects and others which will become apparent hereinafter are
attained, in accordance with the present invention, in an
axial-piston machine in which the cylinder drum is provided with a
plurality of pressing cylinder bores; each connected to one or more
working cylinders of the drum of the axial-piston machine or
connected in groups to respective working cylinders, the pressing
cylinders receiving respective pressing pistons bearing against the
axially fixed member, e.g., the shaft, for applying to the cylinder
drum a force balancing the force at the fluid-distribution surface
in the region of the associated working piston. In other words,
when the working cylinder bore communicates with the associated
port at the high-pressure side of the fluid-distribution surface
there is a greater force in the region of the high-pressure side
urging the corresponding side of the drum axially away from the
fluid-distribution surface and there is developed at the pressing
cylinder bore an elevated pressure which is applied to the
respective pressing piston and then to the axially fixed member to
counteract the increased pressure at the fluid-distribution
surface. Of course, the working cylinders should not be able to
communicate with one another through the pressing cylinders.
For each working cylinder or at least for each n working cylinders,
where n is an integer such 2, 3, etc., there is provided at least
one pressure or force-generating bore in the manner described. When
a large number of working cylinders are provided in the cylinder
drum, it may be advantageous to associate a pressurizing cylinder
with each second, third, etc., working cylinders. Normally,
however, each working cylinder will be associated with one pressing
cylinder. Of course, as noted earlier, a number of pressing
cylinders may be provided for each working cylinder. According to
an important feature of the present invention, the pressing
cylinders are disposed in an annular array inwardly of the working
cylinders and have pistons inclined in the direction of the axis of
rotation of the drum and bearing against a flange axially fixed to
the shaft.
Each pressurizing cylinder is preferably disposed in the cylinder
drum adjacent the respective working cylinder and communicates
therewith in the manner described in greater detail hereinafter. In
this manner, the half of the drum exposed to high pressure at the
fluid-distribution surface is urged with the greatest force (by the
pressing cylinders) in the counteracting direction and the half of
the drum exposed to the lowest pressure at the fluid-distribution
surface receives a correspondingly lower pressure from the
pressurizing cylinders on this side of the drum. Each of the
working cylinders and the associated pressing cylinder can be
connected by a transverse bore.
According to still another feature of the invention, each of the
working-cylinder bores is provided with a guide bushing for the
respective working piston, composed of a material which in contact
with the working piston offers frictional characteristics and wear
characteristics which are desirable (i.e., low-sliding friction and
minimum piston wear). In the present case, I dispose the connecting
bore so that the latter opens immediately ahead of the inner end of
the bushing into the working cylinder, i.e., with respect to the
cylinder head, prior to the guide bushing.
To prevent the working fluid from passing out of the cylinder bore
in a leakage path all around the guide bushing, the latter is
provided with a circumferential groove into which a vent passage in
the wall of the cylinder drum opens. The depressurizing and vent
passages are advantageously inclined with respect to the axes of
the working piston and the pressure cylinder and may be inclined as
with the connecting passage mentioned above so that the two
passages may be formed as a single linear bore in one machining
operation. Advantageously, the passages lie along a chord of the
cylinder drum and are inclined outwardly away from the
fluid-distribution surface.
The axes of the pressurizing cylinders can, of course, be parallel
to the cylinder-drum axis although it is preferred to have the
pressure cylinder axes inclined to this cylinder drum axis away
from the fluid-distribution surface. Each of the pressurizing
cylinders, therefore, may have an axis lying in a plane through the
cylinder drum axis and may be offset from a plane through the
cylinder drum axis and the axis of the working cylinder with which
the pressure cylinder communicates. The axis of each pressurizing
cylinder may include an acute angle with the cylinder drum axis,
the angle being selected so as to provide the desired axial force
component for a given pressure behind the piston in the
pressurizing cylinder and the desired moment when acting upon the
flange fixed to the shaft. It will be appreciated that
substantially all of the pressure generated in the pressurizing
cylinder will be transmitted directly to the shaft when the piston
therein is parallel to the shaft axis and this force may be
excessive. By selecting an acute angle in the manner described, the
moment of force contributed by each pressurizing piston may be
varied accordingly. When the axes of the pressurizing pistons lie
along a cone whose apex lies toward the fluid distribution surface
the moment attributed to the pressurizing pistons is reduced by
comparison to an arrangement in which the axes lie along a cylinder
centered on the axis of the cylinder drum and the pressurizing
pistons are parallel to the cylinder drum axis. When, however, the
conical surface defined by the axes of the pressurizing pistons has
its apex turned away from the fluid-distribution surface, the
moment is increased by comparison with that developed by
pressurizing pistons parallel to the axis of the cylinder drum.
According to still another feature of the invention, the cylinder
drum is held against the fluid-distribution surface even in the
absence of working fluid pressure by providing, in one or more of
the pressurizing-cylinder bores a coil spring which bears upon the
pressurizing piston and reacts against the cylinder. Preferably the
springs are disposed symmetrically with respect to the
cylinder-drum axis and are disposed in pressurizing cylinders
angularly equispaced about this axis. Each of the pressurizing
cylinders can, of course, receive one of the springs which may be
of the compression coil type.
Each of the pressurizing pistons may, moreover, be formed with an
extension at least partially filling the spring-receiving space so
as to decrease the fluid volume thereof and thereby reduce dead
space in the system.
The pressurizing pistons can bear against an abutment ring or crown
which, in turn, bears axially upon the shaft away from the
fluid-distribution surface. This crown can be formed with a
ball-shaped or conical cap-like configuration cooperating with a
complementary formation on a retaining ring holding the shoes of
the working pistons against the inclined control plate of the
machine. Of course, when the crown is rigid with the shaft, i.e.,
has no freedom of axial displacement relative thereto, a rigid
support is provided for the shoes and the retaining plate must
therefore be made so as to have some play between the shoes and the
crown and thus to enable thermal expansion and contraction to occur
without binding and to allow for assembly of the parts.
DESCRIPTION OF THE DRAWING
The above and other objects, features and advantages of the present
invention will become more readily apparent from the following
description, reference being made to the accompanying drawing in
which:
FIG. 1 is an axial cross-sectional view through a portion of a
cylinder drum embodying the present invention;
FIG. 2 is a cross-sectional view representing a detail of FIG. 1
and taken generally along the line II -- II of FIG. 3;
FIG. 3 is a cross-sectional view taken generally along the line III
-- III of FIG. 1 with the pistons and guide bushings removed;
FIG. 4 is a side-elevational view, partly broken away of an
axial-piston machine according to the invention; and
FIG. 5 is a detail view illustrating another embodiment of the
invention.
SPECIFIC DESCRIPTION
Referring first to FIG. 4, it will be apparent that the
axial-piston machine, operated as a pump in the embodiment
described, comprises a housing 20 which is broken away to reveal a
shaft 21 whose splines 30 may be connected with a driving source,
e.g., an electric or internal-combustion engine. The shaft 21
passes through an opening 31 in a control disk 22 which is mounted
via a lug 32, shown in dot-dash lines, for pivotal displacement in
a bearing 33 of the housing, likewise shown in dot-dash lines. The
pivotal movement, about an axis perpendicular to the plane of the
paper, can be effected by a servomechanism or manual means
adjustable externally of the housing 20.
The control plate 22 is formed with a surface 29 lying in a plane
transverse to the axis 35 of the shaft 21 and a cylinder drum 1 and
the angle .alpha. between the surface 29 and the axis 35 can
therefore be adjusted to vary the displacement of the pump.
A plurality of shoes 24 slidingly engage the surface 29 and are
held thereagainst by a retaining plate 36 having a ball-shaped or
conical hub 37 engaging a complementary portion 38 of a support
crown 12' functionally similar to the support crown 12 shown in
greater detail in FIG. 1 and axially bearing upon the shaft 21 in
the direction of arrow 39. The support crown 12' is keyed to the
shaft for rotation therewith.
Each of the shoes 24 has a ball-shaped socket receiving the
generally ball-shaped head 25 of respective working pistons 26
which are axially shiftable in respective cylinders 2 (FIG. 3)
angularly spaced about the axis 35 and formed in the cylinder drum
1. The latter is keyed to the shaft 21 as well and can be rotated
by this shaft. The auxiliary or pressurizing pistons 9 bear against
a flange 40 of the crown. The housing 20 is also provided with a
fluid-distribution surface (FIG. 1) and with a pair of fittings 27,
28, serving as the high-pressure and low-pressure ports
respectively.
When the shaft 21 is rotated, the drum 1 is entrained angularly
about the axis 35 so that the working pistons 26 are alternately
driven into the drum and drawn therefrom to displace the hydraulic
fluid and induce it to flow into the cylinder bores, respectively,
thereby effecting displacement at a rate determined by the pivotal
angle of the control plate 22. The pistons 9 bear upon the crown
12' and thus apply pressure on the shaft in the direction of arrow
39, the reaction pressure represented by arrow 41 serving to hold
the cylinder drum against the fluid-distribution surface.
In the embodiment illustrated in FIG. 1, the fluid-distribution
surface is provided by a stationary plate 42 which is formed with
kidney-shaped ports 43 and 44, respectively, communicating with the
ports 27 and 28, the rear end 45 of the cylinder drum 1 being
provided with a low-friction bearing disk 46 at which the cylinder
bores 2 open. The cylinder drum is also formed with a neck 47 whose
inwardly extending splines 48 engage in the flutes of a splined
portion 14 of the shaft for rotatable entrainment of the cylinder
drum with the shaft. The crown 12 of the embodiment shown in FIGS.
1 - 3 has a cylindrical portion 50 surrounding the neck 47 and
terminating in the transverse flange 40 against which the pressure
pistons 9 bear with rounded ends 49. The cylindrical portion 50, at
its upper end, is turned inwardly and has a fluted portion 51
engaging the spline shaft 14. The crown member 12, moreover, bears
axially against a sleeve 13 which abuts a shoulder 52 of the
shaft.
In accordance with the present invention, the cylinder drum is
provided with a plurality of annularly equispaced working cylinder
bores 2 whose axes are parallel to one another and to the axis 35
of the cylinder drum. Each of the working cylinders 2 receives a
guide sleeve 3 (shown in elevation in FIG. 2) through which the
respective working piston 26 passes and which is formed along its
outer circumference with a depressurizing roof 4.
Adjacent each working cylinder 2, the cylinder drum 1 is formed
with an auxiliary or pressurizing cylinder bore 5 which has an axis
55 defining an acute angle with the axis of the .beta. cylinder
drum such that all of the axes 55 lie along a conical surface whose
apex is turned toward the fluid-distribution surface. A linear bore
7 is inclined to the axis 55 (see FIG. 2) at an angle .gamma. so
that it may form a relief or vent portion 7a and a connecting
portion 7b as described previously. The connecting portion
communicates between the pressurizing cylinder 5, behind its piston
9, and the cylinder bore 2 behind the guide bushing 3 thereof. The
leading edge 8 of the guide bushing can thus be seen to be set back
to the left from the passage 7b. The guide bushing 3 has an
outwardly open circumferential relief group 4 which communicates
with the portion 7a of the bore 7 and opens at the periphery of the
drum as shown for one of the cylinder bores in FIG. 4.
Each of the pressurizing cylinders 5 receives a piston 9 having an
axial projection 10 partly filling the bore behind this piston and
surrounded by a spring 11 which biases the piston 9 to the left and
the cylinder drum 1 to the right. Each piston 9 bears against the
crown 12 which, in turn, is seated axially against the shaft 14.
Consequently, the pressure buildup in each of the working cylinders
2 is communicated to the respective cylinder bore 5 and drives its
piston 9 to the left to bias that side of the cylinder drum against
the fluid-distribution surface 42 and maintain a tight seal with
the fluid-distribution surface, limiting leakage therefrom.
In FIG. 5 it can be seen that a spring 60 may be provided around
one or more of the pistons 9 between the crown 12 and the cylinder
drum 1 to urge the latter in the direction of the
fluid-distribution surface. In this case, the springs 11 may be
omitted.
* * * * *