Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to hydraulic pumps and motors of
the kind in which a rotary cylinder barrel containing a
plurality of pistons has a ported face bearing against a
stationary surface containing the inlet and delivery ports.
The invention particularly relates to the port faces, which
are usually flat, but may be of part spherical or of conical
form.
The port faces are usually substantially
hydro-statically balanced and are spring loaded together, so
that there is intimate contact and negligible leakages from
the high pressure portings. Usually the face of the cylinder
barrel is in the form of an annular ring pierced by openings
into the cylinders, so that the openings are bounded by
narrow annular sealing lands.
Because of the intimate sealing contact at the narrow
annular sealing lands, if there is zero leakage, the surfaces
run very hot and it is necessary to employ proved bearing
materials, such as one hard surface and one having a lower
melting point.
The major limitation to the service lives of these forms
of pumps and motors is port face leakages resulting from
deformation, or from wear at the mating port faces. The
purpose of the invention is to provide means for reducing
this limitation to service life.
The closed inside edge of each of the two confronting
annular sealing lands is well cooled by the flow of liquid to
and from the portings. The outer edges of the outer sealing
lands are also well cooled, in this case by the liquid in the
pump housing, but the inner edges of the inner sealing lands
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are in contact with a very small volume of substantially
static liquid surrounding the axis of the cylinder barrel.
Because of this, the confronting inner sealing lands run at a
considerably higher temperature than the outer lands and this
results in thermal deformation, causing the two opposing
surfaces to become slightly convex. This results in
increased leakages at the outer sealing land, which is
further cooled by this flow while the increased surface
loading at the inner lands, with zero leakage, results in a
further increase in temperature.
An -object of the invention is to provide an adequate
cooling flow to the inside of the inner sealing land, thereby
promoting substantially uniform temperatures across the whole
surface of the port face and minimising thermal deformations.
The main cause of abrasive wear between the port faces
is small solid particles in the liquid being forced into the
interface, where they become imbedded in the soft surface and
produce abrasive wear at the hard counterface. The flow of
liquid through the portings serves to flush abrasive
particles away from the adjacent inside edges of the sealing
lands and solid particles are centrifuged away from the outer
edges of the outer sealing lands. However, ~olid particles
are centrifuged into the interface at the inner edges of the
~inner sealing lands and this results in a high rate of
abrasive wear.
A secondary object of preferred embodiments of the
invention is to so direct a cooling flow to the inner edges
of the inner sealing lands that it purges solid particles
from this zone, thereby substantially eliminating a major
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cause of abrasive wear.
The need to employ one surface having a low melting
point results in other causes of failure, such as cavitation
erosion of the soft surfaces, or when leakage begins at a small
radial scratch, it rapidly increases due to erosion from the
flow of high pressure liquid. Ideally, both surfaces should be
of hard abrasive resistant materials, but this is possible only
if the surfaces are continually cooled over the whole of their
areas.
A further object of preferred embodiments of the inven-
tion is to permit the use of two hard materials running together
for the port faces.
An aspect of the invention is as follows:
A hydraulic pump or motor of the type having a rotary
cylinder barrel rotatable within a body chamber adapted to be
filled with fluid, said barrel containing a plurality of cir-
cumferentially spaced pistons and having a cylinder port face
containing a like plurality of circumferentially spaced
cylinder ports, said cylinder port face bearing against a
stationary port surface on a port block containing circumfe-
rentially spaced inlet and delivery ports, characterised in
that at least one passage is provided in each of said barrel
and port block, each passage extend~ng substantially radially
from said chamber to a region radially inside said cylinder
port face such that rotation of the barrel centrifugally
causes fluid to flow continuously from the said chambex to
and from said region through said passages, at least said
passage in said barrel communicating with said region closely
adjacent the radially inner most edge of said cylinder port
face.
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Preferred embodiments of the invention will now be
described, by way of example only, with reference to the
accompanying drawings in which:
Figure 1 is a sectional side-elevation illustrating a
fixed displacement pump or motor according to the invention;
Figure 2 is an enlarged view of part of the cylinder
barrel and port block interface region of the barrel shown in
Figure 1;
Figure 3 is a view of the cylinder barrel port faces
taken on line 3-3 of Figure 2;
Figure 4 is an enlarged view similar to Figure 2 but
illustrating another embodiment of the invention.
Figure 5 is a view similar to Figure 3 but showing a
different arrangement of the cylinder barrel port faces; and
Figure 6 is a view of the stationary port block surface
complimentary to the moving surface shown in Figure 5.
Referring to the drawings, the pump or motor illustrated
in Figures 1 and 2 includes a stationary port block 10
aga1nst which a cylinder barrel 11 rotates. The cylinder
barrel is urged against~the port block by a spring 12 and as
it rotates, a plurality of cyIinder ports 13 are successively
brought into communication with an inlet port 8 and an outlet
port 9 provided in the stationary port block. The basic
structure and operation of these hydraulic pumps or motors is
well known and need not be described further.
In a preferred embodiment of the invention, radial holes
15 are drilled between each cylinder of the cylinder barrel
11 and axial drillings 16 are provided to these radial
drillings. Preferably the axial drillings should cut
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slightly into the inner edge 17 of the inner sealing land 18,
so that they collect all abrasive matter centrifuged to that
zone. One or more drillings or passages 19 are also provided
in the stationary port block 10, providing a connection from
the liquid in the body cavity 20 to a region 21 inside the
inner sealing lands 18. The drillings 19 may, for example,
be arranged at an angle to the mating port surfaces as shown
in Figures 1 and 2 or parallel as shown in Figure 4.
Because of the rotation of the liquid in the housing,
there is a centrifugal pressure gradient in this liquid
during operation. -This causes a flow to the inside of the
inner sealing lands 18, which is then centrifuged through the
rotor drillings 15, providing a continuous cooling flow
circulation and purging solid particles from the region 21
inside of the inner sealing lands. This preferred
arrangement thereby meets the first two objectives-stated
above.
In a further preferred embodiment, the inner and outer
rotating sealing lands 22 and 23 respectively are of a
radially wavy form as shown in Figure 5, so that there is no
continuous circumferential line of contact between the
counterfaces during rotation. In this way, all areas of the
eotating sealing faces are continuously cooled by passing
over freshly wetted areas of the stationary,surface.
When applied to the preferred radially wavy sealing
lands, the previously described axial drillings 16, leading
to the radial drillings 15 in the rotor 11 are preferably
drilled to the outermost radius of the inside wavy edge 24
where solid particles would otherwise accumulate.
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Preferably, the stationary surface should be shot
peened, as shown in Figure 6, or minute pockets 25 should be
formed by other means, so that these small pockets of liquid
enter the interface. Any rise of temperature causes the
liquid in these pockets to expand, or to vaporise thereby
forcing the surfaces very slightly apart and avoiding the
formation of metal junctions.
Preferably one or both the sealing faces should be
surfaced with a very hard material of high melting point,
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~ such as tungc~an carbide.
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Although the invention has been described with reference
to specific examples, it will be appreciated by those skilled
in the art that the invention may be embodied in many other
forms.
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