Hydraulic piston machines

A housing for a hydraulic piston machine comprising two shells of part-cylindrical form, the shells connectable together along a parting plane in which the rotating axis of the drive-shaft lies to contain within internal working elements of the machine. Either or both housing shells may be provided with a opening connecting the interior to the exterior of the shell(s) to provide means for fluid distribution of the machine. A non-deformable liner-element located within one or more of said openings for isolating pressurized fluid passing through the machine from coming into direct contact with the housing shells.

FIELD OF THE INVENTION 
This invention relates to hydrostatic rotary hydraulic piston machines of 
the positive displacement pressure-fluid type, and is particularly 
directed at further improvements to machines having a housing structure 
formed by two interconnecting shells, for example, of the type shown and 
described in our pending International Application No. PCT/GB-93/01051. 
In the case of a radial piston type of hydraulic machine, a cylinder-barrel 
is mounted for rotation on a ported pintle-valve, and is provided with a 
number of generally radial cylinder-bores. Each cylinder-bore contains a 
piston and each piston is operatively engaged to a surrounding annular 
track-ring. Arcuate-ports provided in the pintle-valve are arranged to 
communicate with fluid inlet and outlet conduits attached to the exterior 
of the machine, and thus rotary movement of the cylinder-barrel is 
accompanied by radial displacement of the pistons and corresponding 
displacement of fluid through these fluid conduits. A control-system may 
be included which acts in determining the degree of eccentricity required 
between the track-ring and pintle-valve, and therefore regulates the 
supply of hydraulic fluid output from the hydrostatic machine to meet the 
varying fluid demand of the hydraulic circuit. 
In the case of an axial piston machine type of hydraulic machine, a 
cylinder-barrel is mounted for rotation on a drive-shaft, and is provided 
with a number of generally axially aligned cylinder-bores. Each 
cylinder-bore contains a piston and each piston is operatively engaged to 
a swash-plate member. Arcuate-shaped ports in a valve-plate are arranged 
to be in fluid communication with fluid inlet and outlet conduits attached 
to the exterior of the machine, and thus rotary movement of the 
cylinder-barrel is accompanied by axial displacement of the pistons and 
corresponding displacement of fluid through these fluid conduits. 
In machines of either type described above, pressurized fluid passing 
through the passages or openings provided in the housing shells can cause 
a number of problems such as fluid leakage through the material of the 
walls surrounding such passages or openings. If surface crack defects, or 
porosity in the material exist within such walls, an unacceptable high 
amount of fluid can escape to the outer environment of the machine. This 
is especially a problem when the housing shells are manufactured as 
aluminium pressure die-castings, because pressurized fluid has been known 
to seep through such castings if exposed in direct contact. 
Furthermore, a solution shown in British Patent Application No. 9224046.4 
(one of the priority applications in our co-pending PCT/GB93/01051) has 
attempted to overcome this problem by preventing pressurized fluid from 
coming into direct contact with the walls of the shells. In this solution, 
a hollow coupling-sleeve is used in combination with a deformable 
seal-ring. The action of tightening the hollow coupling-sleeve in the 
housing shell causes the seal-ring to become deformed at each of its ends 
against corresponding seats, such that once fully deformed against such 
seats, high-pressure fluid passing through both the hollow coupling-sleeve 
and ring-seal during operation of the hydrostatic machine is consequently 
prevented from directly contacting the surrounding walls of the housing 
shells. 
However, this prior solution has been found to have a number of serious 
drawbacks, for instance: 
The usual small dimensional imperfections found in manufacturing of all the 
inter-connecting components, in particular, when the longitudinal axes of 
the respective seats are not concentric with one another or become 
mis-aligned during machine assembly, will require a greater effort being 
used to sufficiently deform the ring-seal against the seats. Unless a 
leak-free seal is obtained, an unacceptably high fluid leakage results at 
these seats during machine operation, thereby preventing the machine from 
performing at the desired level of operating efficiency. 
However, such greater effort when applied to sufficiently deform the 
ring-seal against the seats, can result in severe damage to the housing 
shell. For instance, by having to excessively tighten the hollow 
coupling-sleeve, the engagement threads provided in the shell become torn, 
and/or the resulting strain in the housing material causes cracks to 
appear in the relatively thin-walls of the shell. In either case, such 
damage may not be noticed during machine assembly, and may then only 
appear when the hydrostatic machine is operational and fluid loss to the 
environment is apparent. Subsequent repair to the machine may either be 
impossible or extremely costly to perform. 
What is therefore required is an effective and reliable solution which 
overcomes all the prior difficulties and drawbacks described above. 
It is therefore an object of the invention to provide the machine in which 
the pressurized fluid is prevented from direct exposure with the openings 
provided in the housing shells, that does not require high dimensional or 
positional accuracy between the joining parts, is economic to perform 
without relying on the deformation of any of the parts towards obtaining a 
leak-free seal, and does not impose undue loads in the housing shell 
structure that could result in cracking or other failure. 
SUMMARY OF THE INVENTION 
From one aspect the invention consists in a housing for a hydraulic piston 
hydrostatic machine having a drive-shaft, comprising two shells 
connectable together along a parting plane on which the rotating axis of 
the drive-shaft lies and wherein each said shell is provided with at least 
one opening, said openings arranged perpendicular to said parting plane 
and connecting the interior and exterior in each of said shells together. 
A non-deformable liner-element is postioned within at least one of said 
openings to connect the internally disposed pintle-valve valve with an 
external fluid conduit in the case of a radial piston machine, or to 
connect the internally disposed valve-plate with an external fluid conduit 
in the case of an axial piston machine. Thus the non-deformable 
liner-element effectively lines the opening that already exist in the 
shell. In the case of a uni-flow directional machine, only one 
liner-element is fitted, whereas in the case of a reversible-flow machine, 
two such liner-elements may be used. The non-deformable liner-elements in 
effect, contain within the high pressure fluid entering or leaving the 
machine, and thereby prevents the high pressure fluid from directly 
contacting the opening provided in the housing shell. 
As a further feature of the invention, a pair of flange-elements may be 
included, each attachable to an exterior surface provided on the shells 
and containing within a main fluid passageway that accepts a fluid conduit 
so that the machine may be attached to and used to service a hydraulic 
circuit. The flange-elements, although separable from their respective 
shell surfaces initially, become fastened to the respective shell surfaces 
when the machine is in the fully assembled condition. Furthermore, by such 
means, the flange-elements act as a clamp to aid in retaining the two 
shells together, and where an auxiliary fluid passageway may be included 
in one of the flange-elements to communicate with the control-system of 
the machine. 
As a still further feature of the invention, the non-deformable 
liner-element transfers fluid from the internal working elements of the 
machine to the main fluid passageway provided in the flange-element. 
A still further feature of the invention discloses the use of primary and 
secondary mounting-flanges on the exterior surface of the housing shells. 
The primary mounting-flange is used to attach the machine to a 
complementary surface that is provided for instance, on a prime-mover, 
whereas the secondary mounting-flange allows a second hydraulic machine to 
be attached to primary machine. In the radial piston type of machine, a 
self-aligning bearing may be located near the outer end of the 
pintle-valve in the primary machine for applications demanding a high 
degree of side-load at the protruding driving end of the drive-shaft, for 
instance when when a gear or pulley is used to transfer power from a 
prime-mover to the machine. 
A still further feature of the invention concerns improved means for the 
retaining the pistons and slippers together in such machines. In this 
invention, the usual end float found in prior art machines has been 
eliminated by means of including a resilient washer which imparts a slight 
pre-load between the piston and slipper components. As a result, noise and 
vibration typically found in prior art machines is reduced. 
These and other features and objects of the invention will become more 
apparent from the description of the invention with reference to the 
accompanying drawings.

BRIEF DESCRIPTION OF THE FIRST EMBODIMENT OF THE INVENTION 
In the first embodiment of the invention shown in FIGS. 1-4, the machine 1 
comprises an outer housing structure which surrounds the internal working 
piston elements. The housing structure is formed by two shells 3, 4 of 
part-cylindrical form which interconnect with each other on a common 
parting-plane 5 along which the axes of the drive-shaft 6 and pintle-valve 
7 will lie. Each shell 3, 4 is provided with an opening 69, 70 
respectively, the openings intercommunicating the interior and exterior 
surfaces of each shell together. 
Shell 3 is provided with one large semi-circular pocket 8 and a number of 
smaller semi-circular recesses such as those shown as 9, 11. Similarly 
shell 4 is also provided with an equal number of such pockets and 
recesses, shown for example, as pocket 16 and recesses 12, 17. 
Attachment points are provided in both shells, for instance, holes 20a, 
21a, 22a in shell 3 to correspond with a similar number of holes in shell 
4, shown for example as hole 22a in FIG. 3 and hole 22b in FIG. 4. 
The exterior of each shells 3, 4 is provided with a flat mounting face 18, 
19 onto which respective flange-element 38, 39 are attached. 
Once all the internal elements of the machine 1 have been positioned in 
place in the interior of shell 3, for instance, in such pockets and 
recesses shown as 8, 9, 11, anaerobic-sealant is applied, for instance, by 
the well known process called "silk-screening", to the upper exposed 
surface of shell 3 as shown in FIG. 1 along which lies the parting-plane 
5. Shell 4 is then lowered onto shell 3 along parting-plane 5, and a 
number of self-threading screws 25 are attached, as shown for example in 
FIG. 4, for holes 22a, 22b. Flange-elements 38, 39, preferably 
manufactured in iron or steel, are then attached to their respective 
mounting faces 18, 19 provided on an exterior surface of the shells 3, 4, 
and bolts 44 inserted through holes 21b, 21a, 45 to engage with nuts 46. A 
further bolt 47 is also used as shown in FIG. 3. Once all the 
self-threading screws 25 and bolts 44, 47 have been tightened, shells 3, 4 
are thus locked together to form the housing structure for the machine 1. 
Thus when shells 3, 4 are together, respective recesses in each shell 
combine to form complete apertures, for instance, recesses 8, 16 combining 
as an aperture which forms the internal-chamber 26 of the machine. 
Likewise, recesses 9, 17 combine to form an aperture which surrounds the 
pintle-valve 7. After the anaerobic sealant has cured, the resulting 
internal-chamber 26 is sealed from the outer surrounding environment. 
Further recesses are formed in each respective shell 3, 4 and are used to 
support other internal elements of the machine, for instance, recess 10 in 
shell 3 combines with a corresponding recess (not visible) in shell 4 
creating an aperture that provides a support surface for the pivot-pin 27. 
Similarly, recesses 11, 12 combine together to provide an internal 
sub-chamber 28 for the various internal elements that comprise the 
displacement control-system mechanism for the machine 1. 
In order to provide a mounting surface for the purpose of attaching the 
hydraulic machine to a remote and separate structure, each shell 3, 4 is 
provided with outwardly extending arms (only arm 50 visible in FIG. 2), 
which once the shells 3, 4 are together, provide a first mounting-flange 
member 51. 
To allow a further hydrostatic machine to be attached to the first 
hydrostatic machine 1, a second mounting-flange member 52 is included at 
the rear end of machine 1. In this case, each shell combines with the 
other shell to form the outwardly extending arms 53, 54 as shown in FIG. 
1. As shown, the outwardly extending arms 53, 54 of the second 
mounting-flange member 52 may be arranged to be perpendicular to those 
outwardly extending arms 50 of the first mounting-flange member 51. 
Register 55 is provided on the first mounting-flange member 51 and 
similarly, a register 13 is provided on the second mounting flange-member 
52. 
DESCRIPTION OF THE INTERNAL ELEMENTS 
A shaft-seal 30 is positioned between shells 3, 4 to surround the 
drive-shaft 6 in order to prevent any fluid escaping from the 
internal-chamber 26. 
Respective shells 3, 4 combine to form an internal cylindrical location 
pocket for a bearing, such as ball-bearing 33 which provides support for 
drive-shaft 6. 
For applications where two or more hydrostatic machines need to be driven 
from the same drive-shaft, drive-shaft 6 may be waisted in diameter in the 
region shown as 62 thereby allowing it to extended through the interior 
(hollow passage 43) of the pintle-valve 7 to protrude at 89 from the rear 
side of the machine 1 for coupling to a drive-shaft of a second 
hydrostatic machine (not shown). A self-aligning bearing 63 is located 
within a pocket 64 provided in the pintle-valve 7 so to provide further 
support for drive-shaft 6. 
As shown in FIG. 2, a tongue 35 is provided on drive-shaft 6 which fits 
into a corresponding slot 36 provided in an "oldham" type misalignment 
coupling 37. The coupling 37 fits into a slot 40 provided on the end face 
41 of the cylinder-barrel 42, and acts to compensate for any inaccuracy 
that may exist between the respective axes of the drive-shaft 6 and 
pintle-valve 7. 
As shown in FIG. 3, two pintle-ports 56, 57 are provided in pintle-valve 7, 
and where pintle-port 56 is connected by an internal longitudinal bore 58 
to arcuate-port 61. Pintle-port 57 is connected by an internal 
longitudinal bore 60 to arcuate-port 59. 
Flange-element 39 has a low-pressure fluid admittance passageway 65 which 
interfaces with opening 70 provided in shell 4. Opening 70 is so 
positioned in shell 4 to be linked or joined with pintle-port 56 in the 
pintle-valve 7. The longitudinal axes of both passageway 65 and opening 70 
are substantially coincident, and thereby arranged to be perpendicular to 
the parting-plane 5 of the machine 1. Passageway 65 is threaded 66 in 
order to accept a suitable external fluid-conduit (such as a pipe) which 
thereby can connect the machine 1 to a hydraulic circuit. Similarly, 
flange-element 38 has a high-pressure fluid discharge passageway 75 which 
is threaded 72 in order to accept a suitable external fluid-conduit. 
Opening 69 provided in shell 3 is so positioned to be able to join with 
both passageway 75 and pintle-port 57. Location recesses 73, 74 are 
provided in both the pintle-valve 7 and flange-element 38 as shown in FIG. 
3 for the non-deformable liner-element 81. Non-deformable liner-element 81 
extends through opening 69 and acts to fluidly couple pintle-port 57 to 
passageway 75, thereby effectively lining opening 69 to prevent the 
surrounding wall 84 of shell 3 from being subjected to high pressure 
fluid. 
In the event of any small amount of pressurized fluid contained within 
non-deformable liner-element 81 escaping, for instance, should the 
non-deformable liner-element 81 rupture during machine operation, a 
drainage groove 86 is provided that connects the annular cavity 82 
surrounding the non-deformable liner-element 81 to the internal chamber 26 
of the machine 1. Thus any leakage of pressurized fluid is caused to 
become de-pressurised immediately on entering annular cavity 82. As a 
result, there is no likelihood of the housing structure failing, as 
pressurized fluid is prevented from gaining access to the parting-plane 5 
between the shells 3, 4, which could otherwise cause the shells 3, 4 to 
become prized apart and separated. 
The cylinder-barrel 42 is supported for rotation on the pintle-valve 7 and 
includes a number of cylinder-bores 90 each connected through a respective 
"necked" cylinder-port 91 to allow fluid distribution between each of the 
cylinder-bores 90 and a respective pair of elongate arcuate-ports 59, 61 
formed on the periphery of the pintle-valve 7. 
Each cylinder-bore 90 contains a piston 93 which is attached to a 
respective slipper 95 by means of a rivet 94. The longitudinal or shank 
portion of the rivet 94 is a relatively close fit inside an axial 
longitudinal hole provided in the piston 93, so allowing the required 
amount of pressurized fluid from cylinder-bore 90 to reach the 
bearing-face of the slipper 95 for the creation of a hydrostatic bearing 
in a manner well know in the art. Pistons 93 and slippers 95 mate together 
on a part-spherical socket 98 to allow articulation of the slipper 95 on 
the piston 93. 
The rivet 94 has a head 87 at one end which is allowed to articulate in a 
female pocket 83 provided in the interior of the slipper 95. The rivet 94 
may be provided with a groove 113 at a location on the shank portion just 
proud from the base of the piston 93 as shown in FIG. 1, and where a 
resilient retaining-ring 114 engages into groove 113 to hold the piston 93 
and slipper 95 together in their assembled state. Alternatively, the 
resilient retaining-ring may be of the Starlock type, which can be placed 
over the shank portion of the rivet without the aid of a groove. 
Guidance-rings 100, 101 are provided and serve to keep the slippers 95 in 
close proximity with the annular surface 104 of the track-ring 105. This 
feature combined with the centrifugal force on the piston/slipper serves 
to enhance the suction characteristics of this type of hydrostatic 
machine. 
The track-ring 105 is provided with a hole 120 into which pivot-pin 27 is 
located, pivot-pin 27 being extended at either end 121, 122 to protrude 
from hole 120 to be supported directly in shells 3, 4. Thereby the 
track-ring 105 is supported within the machine and allowed limited 
articulated movement about the pivot-pin 27. Although not shown, hollow 
cylindrical-collars may be fitted over the protruding ends 121, 122 of 
pivot-pin 27, to reduce the pressure loading imposed on the shell 
material. 
A boss 92 is provided on one end face 96 of the track-ring 105 into which a 
threaded hole 97 is provided. A control-pin comprising a bolt 99 and 
collar 102 is included, and where the bolt 99 locates into the threaded 
hole 97 to hold the collar 102 against the end face of boss 92. The collar 
102 projects into a cavity 129 provided in the interior of a 
manifold-block 130, and where the collar 102 is engaged on opposite sides 
by actuating servo-rams 135, 136 as shown in FIG. 4. 
The manifold-block 130 comprises the main component of the displacement 
control system for the machine 1, shown positioned between shells 3, 4 and 
attached to respective flange-elements 38, 39 by means of a hollow-sleeve 
107 and the body portion 108 of the pressure relief-valve 183. 
Servo-ram 135 is purposely designed to be larger in diameter than servo-ram 
136, each being fitted into a respective cylinder 137, 138 in the 
manifold-block 130. Coil-spring 133 is located behind servo-ram 135 in 
cylinder 137 so that during periods when the machine 1 operates at 
low-pressure, the spring 133 biases track-ring 105 to its maximum 
eccentric position. Plug 143 is used to close off cylinder 137 in 
manifold-block 130. 
In flange-element 38, channels 110, 111 are provided which communicate 
fluid from the discharge passageway 75 by way of hollow-sleeve 107 to 
manifold-block 130. Also a channel 112 and chamber 113 are provided in 
flange-element 39 allowing fluid to be communicated from the 
manifold-block 130 to the admittance passageway 65 for reasons as will be 
explained below. 
In manifold-block 130, five channels 170, 171, 172, 173, 174 are provided, 
and where plugs (only plug 176 visible for conduit 172) are used to close 
the ends of the channels 170, 172, 174. 
The fluid from the discharge side of the machine 1 on entering hollow 
sleeve 107, flows into channels 170, 171, and where channel 171 leads to a 
cylinder 138 which contains the small servo-ram 136, and thereby, cylinder 
138 is always maintained at the same pressure level as in the 
high-pressure discharge passageway 75. 
Fluid can also pass from channel 171 into an intersecting channel 172 in 
which is contained the body portion 180 of a fluid throttling orifice 115. 
Any fluid passing through orifice 115 enters channel 173, from where it 
can act against the poppet-head 182 of pressure relief-valve 183. Channel 
174 intersects with channel 173 so that fluid can also gain access into 
the cylinder 137 containing the large servo-ram 135. 
During periods when the relief-valve 183 remains "closed", fluid in 
channels 173, 174 is maintained at the same pressure level as the fluid 
contained in channels 171, 172 up-stream of the orifice 115. Because 
servo-ram 135 is larger in area than servo-ram 136, the resulting force 
produced by servo-ram 135 is greater than the resulting force produced by 
servo-ram 136, and as a consequence, servo-ram 135 is predominant in 
determining the degree of eccentricity of the track-ring 105. 
During periods when the fluid discharge pressure level from the machine 1 
is sufficiently high that the pressurized fluid within channel 173 causes 
poppet-head 182 to lift off its seat 184 (compressing coil-spring 185), 
the relief-valve 183 is "opened". Fluid in channels 173, 174 can then flow 
through chamber 113 and channel 112 to be returned to low-pressure fluid 
admittance passageway 65 of the machine 1. 
As the pressure level in channels 173, 174 falls in value below that still 
experienced in channels 170, 171, 172 up-stream of the orifice 115, the 
pressure level acting behind the large area servo-ram 135 is now lower in 
magnitude than the pressure level acting behind the smaller area servo-ram 
136. 
Thereby the resulting force produced by the small area servo-ram 136 is now 
greater than the resulting force produced by large area servo-ram 135, and 
this causes the small area servo-ram 136 to slide in a a direction towards 
the open end of its cylinder 138 to move the collar 102, thereby causing 
the track-ring 105 to partially rotate about the pivot-pin 27 so reducing 
eccentricity of the track-ring 105 relative to the pintle-valve 7. 
Therefore, during this condition, the small area servo-ram 136 becomes 
predominant in determining the degree of eccentricity of the track-ring 
105. 
By such movement, the servo-rams 135, 136 respond to pressure levels in the 
hydraulic circuit to cause alterations in the degree of eccentricity of 
track-ring 105 and corresponding alteration in the fluid discharge output 
from the machine 1. 
For the displacement control system of the machine 1 to operate 
successfully, the level of pressure of the fluid in channels 173, 174 is 
dependent on both the "cracking" pressure setting of the relief-valve 183 
and the amount of induced pressured-drop across the orifice 115, and these 
act to determine the amount of pressure differential between cylinders 
137, 138. 
The orifice 115 also prevents a large amount of pressurized fluid passing 
between channels 170, 173, so that only a small amount of hydraulic energy 
is lost from high-pressure discharge passageway 75. As a result, even 
during periods when the relief-valve 183 is "open", the overall volumetric 
efficiency performance of the machine still remains high. 
In order to maintain the track-ring 105 is close relationship with the 
manifold-block 130, clearance-adjusting means comprising two bent-spring 
wire-clips 200, 201 are used, which act against a pad 205 to bias 
track-ring 105 against the adjacent face of the manifold-block 130. The 
recesses 206, 207 provided in respective shells 3, 4 are purposely angled 
in order to allow the spring-clips 200, 201 to curl-up on themselves to 
provide tensioning means as soon as the shells 3, 4 are locked together 
during assembly. As a result, any clearance that may exist between the 
track-ring 105 and manifold-block 130 is removed, thereby preventing these 
components from unduly vibrating during the operation of the machine 1. 
Operation of the Machine 
The operation of the machine 1 is as follows: Rotation of the drive-shaft 6 
causes the cylinder-barrel 42 to rotate. If track-ring 105 is set in an 
eccentric relationship to the pintle-valve 7, outward sliding movement of 
the pistons 93 in their respective cylinder-bores 90 is obtained, such 
that fluid from some external source, such as a hydraulic reservoir, is 
drawn in via the low-pressure fluid admittance passageway 65 to 
pintle-port 56, longitudinal bore 58, arcuate-port 61 to the interior of 
cylinder-bore 90 via "necked" cylinder-port 91. When the piston 93 returns 
inwards in its cylinder-bore 90, the fluid is expelled from the interior 
of cylinder-bore 90 via "necked" cylinder-port 91 into the opposite 
arcuate-port 59 from where it in directed along longitudinal bore 60 to 
reach pintle-port 57. The fluid then passes through non-deformable 
liner-element 81 to reach the high-pressure fluid discharge passageway 75 
for coupling by a conduit to service a hydraulic circuit, such as a 
hydraulic motor. During periods when the poppet-head 182 of relief-valve 
183 remains loaded against its seat 184 by coil-spring 185, fluid delivery 
pressure from the high-pressure fluid discharge passageway 75 of the 
machine 1 is received by both servo-rams 135, 136 acting against the 
collar 102. As the large servo-ram 135 (down-stream of the throttle-valve 
180) is larger in area than the small servo-ram 136, the resultant force 
from the large servo-ram 135 on the collar 102 is sufficient to keep the 
track-ring 105 in an eccentric relationship to the pintle-valve 7. 
However, when the force generated by fluid pressure on the poppet-head 182 
is greater than the tension of the coil-spring 185, the poppet-head 182 is 
lifted from its seat 184 to "open" the relief-valve 183 and release fluid 
to the low-pressure fluid admittance circuit of the machine 1. As a 
consequence, the pressure level acting behind the large servo-ram 135 
falls in value such that it is no-longer sufficient to hold the track-ring 
105 in its initial position. Thus the force of the small servo-ram 136 is 
now greater than the force acting behind the large servo-ram 135, so that 
small servo-ram 136 now becomes the effective controller of the machine 1, 
and the eccentricity of the track-ring 105 relative to the pintle-valve 7 
is reduced from the initial position. As the small servo-ram 136 remains 
at delivery pressure whereas the level of pressure acting on the large 
servo-ram 135 is governed by the magnitude of the pressure drop across 
orifice 115, the opposing forces on the projecting collar 102 of the 
track-ring 105 are sufficient to keep the vibration of the track-ring 105 
to a very low levels. When the track-ring 105 is moved into a concentric 
relationship with the pintle-valve 7, the pistons 93 no-longer reciprocate 
in their respective cylinder-bores 90, and fluid is no-longer displaced 
through the machine 1. 
By this simple and inexpensive means, the pump displacement is controlled 
with a high degree of stability and accuracy. In order to change the 
operating characteristics of the machine 1, the tension of coil-spring 185 
can be adjusted by means of screw 190. 
BRIEF DESCRIPTION OF THE SECOND EMBODIMENT OF THE INVENTION 
In the second embodiment of the invention shown in FIGS. 5 & 6, the 
hydrostatic machine 220 is of the axial piston type and comprises two 
shells 221, 222 of part-cylindrical form which connect together on 
parting-plane 224 along which the axis of the drive-shaft 225 lies. As for 
the first embodiment, all the working elements of the hydrostatic machine 
are contained within the surrounding housing shells when in their 
assembled condition. 
The drive-shaft 225 is supported by bearings 227, 228 and carries a 
cylinder-barrel 230 near its mid-point. The cylinder-barrel 230 is rigidly 
connected to the drive-shaft 225 and therefore rotates at equal speed. 
The cylinder-barrel 230 is provided with a plurality of axially arranged 
cylinders 231, each cylinder 231 communicating through a port 232 provided 
at one end of the cylinder-barrel 230 to become fluidly coupled to a pair 
of timing-slots 236, 237 formed in a stationary valve-plate 240. The ports 
232 and timing-slots 236, 237 thereby can transfer liquid flowing between 
the valve-plate 240 and the rotating cylinder-barrel 230. Within each 
cylinder 231, a piston 242 is disposed, each piston 242 has at one end a 
spherical-head 244 which is mounted into a complementary-shaped socket 245 
formed in the slipper 246. 
The swash-plate 250 substantially is semi-cylindrically-shaped 251 on one 
side and has a flat surface 252 on the other side to which the slippers 
246 are in operational engagement. 
The semi-cylindrically-shaped surface 251 of the swash-plate 250 is engaged 
in an arcuate surface 255 provided in an end support-member 256 that is 
fixedly held in place between the two shells 221, 222 of the machine 220. 
The inclination of the swash-plate 250 can be varied by turning the 
adjustment-shaft 259 which carries at its inner end a lever 260 having a 
tongue 261 that fits into a slot 262 provided in the swash-plate 250. As 
the tongue 261 moves in slot 262, the action causes partial rotation of 
the swash-plate 250 about arcuate surface 255 in the end support-member 
256 and thereby the inclination angle of swash-plate 250 is changed with 
respect to the longitidinal reciprocating axis of the pistons 242. 
Each of the two timing-slots 236, 237 in the valve-plate 240 connect with 
respective holes 262, 263, the ends of each of the holes 262, 263 being 
provided with a screw-thread 265, 266. 
Preferably, two non-deformable liner-elements 270, 271 are used is this 
machine 220, and they are broadly cylindrical in shape and have a hollow 
interior 272, 273, and where at least at one end, they are preferably 
threaded 275, 276. 
Non-deformable liner-element 270 is thereby inserted through opening 283 
provided in shell 221 to protrude into internal chamber 290, and by means 
of having a thread 275 at its inner most end, it is connected to a 
complementary threaded hole 265 provided in the valve-plate 240. 
Similarly, non-deformable liner-element 271 is inserted through opening 
284 in shell 222 to connect, by means of its threaded end 276, the 
complementary threaded hole 266 provided in the valve-plate 240. With the 
application of a thread lock and seal compound such as manufactured by the 
Loctite company, these connections are leak-free, and high-pressure fluid 
is prevented from escaping from holes 262, 263 inside the valve-plate 240. 
Where the outer cylindrical form 280, 281 of each non-deformable 
liner-element 270, 271 is surrounded by the respective openings 283, 284, 
sealing compound may be applied at this interface to prevent liquid 
leaking out of internal chamber 290. Alternatively, a sealing device such 
as an `O` ring may be used at this interface. 
That end of the non-deformable liner-element 270 which protrudes out from 
shell 221 may be provided with a threaded-end 292 for connection to an 
external fluid conduit (such as a pipe) linking the machine 220 to a 
hydraulic circuit. Likewise, that end of non-deformable liner-element 271 
may also be provided with a threaded-end 293 to connect with a fluid 
conduit. 
The action of the non-deformable liner-elements 270, 271 once installed in 
the machine 220 also provides location for the valve-plate 240 by means of 
the threaded connection between all three components. As a result, the 
liquid interface between the valve-plate and external fluid conduits is 
performed without the risk of the high-pressure liquid coming into direct 
contact with the housing shells 221, 222 of the machine 220. 
Rotation of the drive-shaft 225 causes the cylinder-barrel 230 to rotate. 
When the swash-plate 250 is inclined with respect to the rotational axis 
of the machine 220, the pistons 242 reciprocate within their cylinders 
231, and liquid is displaced through the machine 220. For instance, when 
piston 242 moves in a direction away from the valve-plate 240, a partial 
vacuum is created in its cylinder 231 and this causes fluid to be drawn 
into the machine 220 through non-deformable liner-element 270 from 
external fluid conduit (not shown). The liquid passing through the hollow 
interior 272 of non-deformable liner-element 270 to pass into hole 262 and 
timing-slot 236 in the stationary valve-plate 240 and into port 232 
leading to the cylinder 231 of the moving piston 242. 
During the later part of the cycle as the piston 242 moves in a direction 
towards the valve-plate 240, and the liquid within the cylinder 232 is 
expelled via port 232 into the opposite timing-slot 237 in valve-plate 
240. From here the fluid flows into hole 263 and through the hollow 
interior 263 of non-deformable liner-element 271 to a connecting 
fluid-conduit (not shown) that may be attached to the threaded end 293. 
BRIEF DESCRIPTION OF THE THIRD EMBODIMENT OF THE INVENTION 
The third embodiment of the invention shown in FIGS. 7 & 8 discloses an 
axial piston machine 300 of the same general type as already described in 
the second embodiment, but where in this case, both non-deformable 
liner-elements 301, 302 have now been re-positioned so as to be coincident 
with parting-plane 305 between the two housing shells 306, 307. 
To ease explaination, the top housing shell 306 has been removed in FIG. 7 
in order to show the internal components of the machine 300. 
As shown in FIG. 8, two semi-circular recesses 307, 308 are provided in 
shell 306, and similarly, two semi-circular recesses 309, 310 are provided 
in shell 307. 
Once the shells 306, 307 are assembled together, respective pairs of 
semi-circular recesses 307, 309 and 308, 310 form complete pockets shown 
as 311 and 312 respectively. 
Pocket 311 is arranged to completely surround the outer cylindrical form 
315 of non-deformable liner-element 301, whereas pocket 312 surrounds the 
outer cylindrical form 316 of non-deformable liner-element 302. 
The nature of each of the non-deformable liner-element 301, 302 used in 
this embodiment are identical to those already described for the second 
embodiment. Essentially both non-deformable liner-elements 301, 302 have 
hollow interiors 317, 318, and are threaded at each end shown respectively 
as threads 320, 321 and 322, 323. 
Likewise, both non-deformable liner-element 301, 302 operate in similar 
manner by connecting external fluid conduits (not shown) to internal 
threaded holes 325, 326 provided in an internally disposed valve-plate 
327. 
Sealing compound may be applied to the interface between respective pockets 
311, 312 and cylindrical forms 315, 316 and once cured, creates a 
leak-free boundary such that liquid inside internal chamber 330 is 
prevented from seeping out at this interface. 
A plurality of bolts, such as bolt 333 shown in FIG. 8, are inserted 
through holes, such as holes 334, 335 to hold shells 306, 307 together in 
the assembled condition. 
Accordingly, all three embodiments described in this invention exhibit the 
same general improvement in that high-pressure liquid is contained within 
the non-deformable liner-elements such that the high-pressure liquid 
passing into and out of the machine is thereby unable to come into direct 
contact with the openings provided in the housing shells. As a result, the 
housing shells may be economically manufactured in aluminium by the 
pressure die-casting process without any risk from the high-pressure 
liquid causing problems, for instance, either by the forces exerted by the 
pressurized liquid creating cracks in the relatively thin walls of the 
shells, or through the occurance of leakage should the walls of the shells 
be slightly porous.