U.S. patent number 3,680,312 [Application Number 05/079,532] was granted by the patent office on 1972-08-01 for hydrostatic machine.
This patent grant is currently assigned to Linde Aktiengesellschaft. Invention is credited to Franz Forster.
United States Patent |
3,680,312 |
Forster |
August 1, 1972 |
HYDROSTATIC MACHINE
Abstract
A hydrostatic machine, e.g. a hydrostatic pump or hydrostatic
motor operating in a closed fluid circuit and having a housing into
which leakage of the hydraulic medium can occur, is provided with
check valves communicating between the housing and the main ports
to enable leakage fluid to pass directly into the main hydraulic
circuit.
Inventors: |
Forster; Franz (Haibach,
DT) |
Assignee: |
Linde Aktiengesellschaft
(Weisbaden, DT)
|
Family
ID: |
5747900 |
Appl.
No.: |
05/079,532 |
Filed: |
October 9, 1970 |
Foreign Application Priority Data
|
|
|
|
|
Oct 10, 1969 [DT] |
|
|
P 19 51 234.6 |
|
Current U.S.
Class: |
60/455; 60/489;
60/912 |
Current CPC
Class: |
F04B
1/2064 (20130101); F16H 39/14 (20130101); F16H
61/40 (20130101); Y10S 60/912 (20130101) |
Current International
Class: |
F04B
1/20 (20060101); F16H 39/14 (20060101); F16H
39/00 (20060101); F16H 61/40 (20060101); F16h
039/02 (); F16h 039/10 () |
Field of
Search: |
;60/53A,52US,DIG.5,53R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Geoghegan; Edgar W.
Claims
I claim:
1. A hydraulic system comprising a hydrostatic pump and a
hydrostatic motor constituting hydrostatic machines; means
connecting said machines in a closed fluid-circulating path and
including a high-pressure passage and a low-pressure passage; a
pressure-retentive housing surrounding at least one of said
machines and forming a chamber maintainable at an elevated pressure
corresponding substantially to that of said low-pressure passage;
and a duct wholly within said housing constituting the sole
leakage-fluid path therefrom and connecting said low-pressure
passage with said chamber, and a check valve in said duct for
unidirectional flow of fluid between said chamber and said
low-pressure passage and blocking reverse flow of fluid through
said duct between said low-pressure passage and said chamber.
2. The hydraulic system defined in claim 1 wherein a respective
duct connects each of said passages with said chamber and is
provided with a respective check valve permitting unidirectional
flow of fluid from the chamber into said passages.
3. The hydraulic system defined in claim 1, further comprising
distributing valve means for selectively connecting said duct with
one of said passages.
4. The hydraulic system defined in claim 1, further comprising a
feed pump connected with said chamber for circulating fluid
therethrough.
5. The hydraulic system defined in claim 4, further comprising a
heat-dissipating cooler in a hydraulic circuit with said feed
pump.
6. The hydraulic system defined in claim 1 wherein both said
machines are provided within said housing.
7. The hydraulic system defined in claim 1, further comprising a
hydropneumatic accumulator connected to said chamber for
maintaining a predetermined pressure level therein.
8. The hydraulic system defined in claim 1, further comprising
means for maintaining the pressure within said chamber at a level
of substantially 6 to 8 atmospheres gauge.
9. The hydraulic system defined in claim 1 wherein said housing
encloses a pair of hydrostatic pumps, coupled together in a
double-pump aggregate.
Description
FIELD OF THE INVENTION
My present invention relates to hydraulic machines and, more
particularly, to hydrostatic machines operating in a closed fluid
circuit.
BACKGROUND OF THE INVENTION
Hydrostatic machines, e.g. hydrostatic pumps and motors, generally
are provided with a closed circuit and a pair of main ports
connected with a hydraulic load and serving as discharge or intake
ports, depending upon the sense of operation of the machine. Among
the important hydrostatic machines of this class are the so-called
axial-piston pumps and axial-piston motors which serve,
respectively, to displace the hydrostatic fluid under the drive of
a power source, e.g. an internal-combustion engine or an electric
motor and/or may be driven by hydraulic fluid pressure to operate,
in turn, a mechanical member such as the output shaft. Axial-piston
devices and the principles involved therein are described in FLUID
POWER, U.S. Government Printing Office, 1966, at pages 109-112 and
pages 199 and following, respectively.
For the most part, an axial-piston pump may comprise a rotary
cylinder barrel provided with a plurality of angularly equispaced
cylinder bores successively communicating with a pair of
kidney-shaped fluid-distribution apertures on a fluid-distribution
surface against which the cylinder barrel is held under axial
pressure. The pistons within the cylinders are reciprocated by
virtue of rotation of the barrel and the fact that the pistons bear
upon a control surface which is inclined to the axes of rotation of
the barrel so that during about half of each rotation the pistons
are urged inwardly while the pistons are able to move outwardly
during the remainder of each rotation.
Inward displacement of the pistons, of course, corresponds to a
reduction in the volume of the chamber behind the piston to expel
fluid in the form of a hydraulic medium through one kidney-shaped
aperture while outward movement of the piston expands the chamber
to draw the hydraulic medium into the cylinder bore from the other
kidney-shaped aperture. The kidney-shaped apertures, of course, are
connected to the discharge and intake ports of the hydraulic
machine, respectively, depending upon the angle and direction of
tilt of the control surface, the displacement of the pump and the
function of the main port (as high-pressure or low-pressure port)
can be established. The pump shaft may be connected to the control
surface to drive the latter and may also be coupled with the barrel
via means as described, for example, in the commonly assigned
copending application Ser. No. 68,254 filed Aug. 31, 70 by Walter
HEYL. A hydrostatic motor operating in accordance with the same
principles, will generally comprise a cylinder barrel having a
surface perpendicular to its axis of rotation abuting a
fluid-distribution surface whose arcuate apertures communicate with
the individual cylinder bores opening at this surface. The pistons
may bear against an inclined control surface and are coupled with
an output shaft via the latter so that fluid entering through one
of the apertures forces the piston successively outwardly to drive
the barrel and, consequently, rotate the shaft. Inclination of the
control surface in this case, determines the speed of the shaft and
the torque delivered to any load which may be coupled
therewith.
It is not uncommon to interconnect the discharge port of the pump
with the intake side of the motor and the outlet side of the motor
with the intake side of the pump by suitable conduits and thereby
create a hydrostatic drive or transmission in which the
transmission ratio between the input shaft of the pump and the
output shaft of the motor is established by the inclination of the
barrel axes of the hydrostatic machines to the axis of the
respective shaft. Such transmissions may be wholly contained in a
common housing or may be mounted remote from one another so that
they can be connected by relatively long lines. One advantage of
the hydrostatic transmission is precisely the possibility of
providing the hydrostatic pump in the vicinity of a prime mover or
other energy source, while the hydrostatic motors are mounted
directly adjacent the load driven thereby. Transmissions of this
nature have been found to be particularly suitable in vehicular
applications wherein the prime mover is an internal-combustion
engine and the load is the vehicle wheel. Of course, a number of
hydrostatic motors can be connected to a single pump or a number of
pumps may be provided to service a single hydrostatic motor. In
general, however, it is found to be advantageous to provide each
hydrostatic pump with a hydrostatic motor in a closed fluid
path.
It should be understood that the term "closed fluid path" is
intended herein to refer to a system in which the pump is connected
directly to the load, i.e. each of the conduits communicating with
the ports of the pump run to the corresponding ports of the motor.
While one of the conduits may be operated as a high-pressure
transmission line while the other conduit is at low pressure, the
hydrostatic machines are generally reversible to interchange the
functions of these lines. Furthermore, both machines may be
provided in a closed housing so that the entire transmission
network and fluid supply is contained within this housing from
which only the input and output shafts emerge. In closed
circulating paths of the character described, it is necessary to
hold the low-pressure side at a predetermined pressure level and an
auxiliary pump and/or a pressure-regulating valve may be used to
this end.
It will be appreciated that effective operation of the axial-piston
pump or axial-piston motor is accompanied and in fact may require
some leakage of the hydraulic medium from the system, e.g. at the
fluid-distribution surfaces of a valve plate and the rotating
cylinder drum, respectively. When a closed circulating path was
required, it has been necessary in some prior-art devices to
provide a further conduit between the pump and load to convey the
leakage fluid from one hydrostatic machine to the other. This is,
of course, a significant disadvantage when the pump is greatly
removed from the motor and when complex mechanisms are interposed
between them. In an excavating machine, for example, the
hydrostatic pump may be mounted upon a chassis carrying a turntable
which, in turn, is provided with the excavating scoops and like
devices. When the turntable is used, it rotates relatively to the
chassis. Hence hydrostatic motors carried by the turntable must be
connected through a rotating seal with the hydrostatic pump and the
need for an additional conduit between the hydrostatic motor and
the hydrostatic pump complicates such systems to a further extent.
It will be appreciated that conduits for the indicated purposes
must be capable of withstanding pressure and the use of an
additional conduit involves increasing complexities because of the
associated seals.
In open hydraulic circuits, moreover, i.e. those using a collecting
reservoir into which fluid flows in a pressureless state, it is
common to connect the leakage-fluid conduit to the reservoir so
that the fluid returns to the power cycle, the leakage path being
pressureless. It is also known to provide, in such systems (open
fluid-circulating path), pumps which are disposed directly in the
reservoir and leakage can occur directly into the reservoir. These
systems make use of a relatively large housing for the pump and
possible pressurization of the fluid therein to prevent cavitation
at the inlet side of the pump. In all cases, however, techniques
which have been found to be satisfactory for handling the leakage
fluid of the open hydraulic circuit, i.e. those using fluid
reservoirs, have not been found to be practical or satisfactory in
closed fluid circuits while the need for added leakage-fluid
conduits renders earlier closed systems expensive and complex.
OBJECTS OF THE INVENTION
It is the principal object of the present invention to provide an
improved hydrostatic machine arrangement of the closed-circulation
type wherein the aforementioned disadvantages are obviated.
Another object of my invention is to provide an improved
hydrostatic machine, e.g. axial-piston pump or axial-piston motor,
in which the handling of leakage fluids is simplified, which is of
lower cost and simpler operation than earlier systems, and which
can be used for arrangements such as excavators in which two
hydraulic machines are interconnected but separated by means
creating sealing difficulties.
SUMMARY OF THE INVENTION
The above and other objects of the invention, which will become
apparent hereinafter, are attained in a hydraulic machine which
comprises a housing, preferably closely surrounding the
axial-piston barrel which is connected directly with the
low-pressure port of the machine, i.e. the intake port of a
hydrostatic pump or the discharge port of a hydrostatic motor, via
a check valve designed to permit unidirectional flow of the
hydraulic medium from the housing surrounding the barrel into the
low-pressure port. The housing sealingly closes the hydrostatic
machine and, when the ports of the machine are functionally
interchangeable, both of them may be connected with the housing
chamber by respective check valves, only the check valve
communicating with the low-pressure port being open to permit the
pressure differential thereacross to feed the leakage fluid into
the low-pressure side. The high-pressure side, of course, maintains
its check valve closed when the ports are functionally
interchanged; again the pressure differential favors flow of
leakage fluid from the sealed housing to the low-pressure side.
Consequently, the present invention provides a housing which may be
sustained at elevated pressure and, at any rate, a pressure equal
to or in excess of that of the low-pressure side of the hydrostatic
machine, a check valve connecting the interior of the housing with
the low-pressure duct, conduit or port, and a hydrostatic machine
disposed within this housing and having a leakage path opening from
the machine into the housing whereby the leakage medium can
traverse the check valve into the low-pressure ducts. A separate
leakage-fluid collector is thereby eliminated, the system does not
require a separate line between the pump and motor for conducting
the leakage fluid and compensating for leakage losses, and only two
ducts need bridge the hydrostatic pump and motor. Furthermore, the
cooling of the hydrostatic machine is improved by virtue of the
fact that there is a continuous circulation of the leakage medium
from the machine into the space surrounding the machine and
enclosed by the housing, and from the housing into the low-pressure
side of the machine.
The present invention is applicable to hydrostatic pumps and
motors, the intake of the former being the low-pressure side
whereas the discharge of the latter is at low pressure. However
invention can also apply to more than one hydrostatic machine in a
single housing, i.e. a double-pump assembly in which two
hydrostatic pumps are provided within a single housing, two
hydrostatic drives including a pump and one or more motors, the
housing in each case being generally closed. However, it has been
found that increasing the size of the housing to accommodate more
than one hydrostatic machine opens the door to difficulties with
respect to maintaining the seal of the housing and it is therefore
preferred to provide a housing for each machine which closely
surrounds the axial-piston drum thereof. It should be noted that
one not only achieves a saving in the cost of a leakage-fluid duct
when the present invention is used, but also reduces the
complexities of the pump and motor structures themselves since
fittings, ports, chambers and like structure associated with the
leakage ducts are eliminated as well. It is possible by such
simplification of the overall structure to eliminate the tendency
of the machine to leak and thereby reduce maintenance and
surveillance.
The reduction of the leakage losses from the main closed hydraulic
circuit into the housing surrounding the hydrostatic machine is a
consequence in part of the high back pressure maintained in the
sealed housing and, therefore, prevalent at the outlet side of the
leakage path. As a result, no feed pump need be used to compensate
for leakage loss in a great many cases and, wherever a feed pump is
required in a system under the present invention, it may be
dimensioned to have a smaller capacity and energy consumption than
the feed pumps which have been used heretofore with similar
hydraulic machines operating, for example, in closed circuits with
pressureless housings or the like.
When no feed pump is required, I have found it to be advantageous
to provide, at one or more locations along the closed hydraulic
path, equalization reservoirs or hydropneumatic accumulators
adapted to deliver, while maintaining the pressure in the housing,
fluid to the latter to compensate for the leakage losses from the
main hydraulic circuit. Such accumulators may be of the type
described at pages 86 - 89 of FLUID POWER, cited earlier. The
accumulator, which is maintained at the predetermined pressure
within the sealed housing, compensates for changes in the volume of
fluid available in the main circulating path as a result of thermal
expansion and contraction of the fluid and the conduits containing
same, elastic yieldability of the conduit walls, etc.
When a hydropneumatic accumulator is employed, I have found it
advantageous after a period determined by experience, e.g. a
thousand operating hours, to charge the accumulator and restore the
pressure therein. Of course, the accumulator should only be
provided at the low-pressure side of the closed circulation path
and, when the hydraulic machine is reversible so that the ports
alternate in function between high-pressure and low-pressure ports,
reversing-valve means is used in accordance with the invention to
connect the low-pressure side with the accumulator at all times.
Two such accumulators may, of course, be provided and connected
with the sides of the hydraulic network by cutoff valve means so
that the accumulator currently at the high-pressure side is blocked
while the other accumulator is rendered effective. Furthermore,
when a pair of interconnected hydrostatic machines are employed,
the accumulator can communicate directly with the interior of one
of the machine housings or the common housing of both machines to
maintain the pressure in the low-pressure side of the network
substantially constant indirectly.
When a feed pump is provided, i.e. when the hydrostatic machine is
provided with a pump designed to deliver the hydraulic medium to
the closed fluid path to compensate for leakage losses, a secondary
circulation is established between the housing chamber of one
machine preferably the motor and the low-pressure line thereof. A
cooling system can be provided in the latter case at the discharge
side of the feed pump. The cooler may be a conventional radiator
built onto the housing of the apparatus or other conventional
heat-dissipating device. Hence the interior of the housing is
constantly rinsed with fresh cool hydraulic medium and the machine
is able to operate with increasing efficiency.
According to still another feature of this invention, the
hydrostatic machine forms part of a hydraulic transmission driven
by an internal-combustion engine and the working fluid of the
hydrostatic drive is also the lubricant for the internal combustion
engine. The feed pump and cooling pump can thereby constitute the
means for maintaining the predetermined pressure within the
housing, the means for cooling the latter, and the means for
lubricating the engine.
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 an embodiment of a
hydrostatic machine according to the invention;
FIG. 2 is a side-elevational view, partly in axial section and
partly in diagrammatic form, illustrating another embodiment of the
invention wherein the hydrostatic machine employs a feed pump;
FIG. 3 is a view similar to FIG. 2 of a hydrostatic transmission
according to the invention;
FIG. 4 is a view similar to FIG. 1 illustrating how the invention
is applied to a double-pump assembly; and
FIG. 5 is an elevational view diagrammatically illustrating the
application of the invention to another hydrostatic transmission
having a single housing.
SPECIFIC DESCRIPTION
In FIG. 1 I have shown a hydrostatic machine having a shaft 1 which
may serve as the input shaft of the hydrostatic pump and which is
journaled in a pair of axially spaced bearings 5 and 6 of a housing
3, 4 interconnected at 3a. The shaft 1 carries a cylinder drum 2
provided with a plurality of angularly equispaced axially extending
cylinder bores 7, each slidably receiving a piston 8 shiftable into
and out of the cylinder bore 7 parallel to its own axis and the
axis of the shaft 1. Each of the pistons 8 is provided with a
swivel head or ball 8a which is received swivelably within a shoe
plate 9 of annular configuration, slidably bearing against a
control disk 10 whose surface 10a is inclined at the angle .alpha.
to the axis A of the shaft. Spring means (not shown) may be
provided to ensure that the pistons 8 and the shoe 9 seats firmly
against the control surface 10a at all operating speeds of the
rotary machine.
The housing 3, 4 comprises a bell-shaped member 3 having a neck 3b
in which the bearing 5 is received and which is formed with a
lip-type seal capable of maintaining a subatmospheric pressure in a
chamber 16 surrounding the cylinder barrel 2. The latter is
provided with apertures 7a which open at a valve surface 2a bearing
against the opposing surface of a valve or distributing plate 15
composed of low-friction material, e.g. bronze, seated against the
plate 4. The plate 15 is provided with a pair of arcuate apertures
15a and 15b, respectively registering with several of the apertures
7a as the barrel 2 rotates relative to the plate 15. Such arcuate
apertures are disclosed in the aforementioned publication. Each of
the apertures 15a and 15b registers, in turn, with a respective
connecting passage 13 or 14 communicating, in turn, with the ports
11 and 12 to which suitable conduit means may be connected for
joining the hydrostatic machine of FIG. 1 in a closed hydraulic
circuit. A typical circuit is that illustrated in FIG. 3. When port
11 forms the high-pressure side of the machine, port 12 represents
the low-pressure side and vice versa. The pressure at the
low-pressure side may be maintained constant by a feed pump or
pressure-regulation valve interconnecting the high and low-pressure
sides. The low-pressure side preferably is held at about 6 to 8
atmospheres gauge. The same pressure is maintained by seal 23
within the housing. When the system is a hydrostatic motor, the
discharge is at this pressure while, when the machine is a
hydrostatic pump, the supply or intake is at this pressure.
The interior 16 of the housing communicates via respective bores 17
and 18, formed directly in plate 4, with respective check valves 20
and compartments 19 and 21 operating, respectively, into the
passages 13 and 14 mentioned earlier. The check valves 20 are
poled, oriented and constructed to permit unidirectional flow of
fluid from the housing into the low-pressure conduit or branch when
a pressure differential in favor of such flow is established and to
block reverse flow of fluid under any circumstances. Since reverse
flow is blocked when the pressure differential favors an outflow
from the network into the chamber 16, whenever the operating high
pressure is maintained in one of the networks, the corresponding
check valve blocks flow therethrough and only the other check valve
can operate, this only when the pressure within the housing exceeds
the pressure within the low-pressure side as indicated.
The shaft 1 may be coupled to a prime mover, e.g. an electric motor
or an internal combustion engine for use of the machine as a pump,
or may be connected to a load such as the driving wheels of an
automotive vehicle having a hydrostatic transmission. In the mode
of operation of the machine as a pump, the barrel 2 is rotatably
entrained by the shaft 1 while the pistons 8 ride with the shoe 9
along the control surface 10a which is inclined to the axis of
rotation of the barrel as noted earlier. As the pistons 8 are
shifted between their fully extended position and a fully retracted
position, they vary the size of the chamber 7 behind the piston and
thereby draw fluid through one port and force it out through the
other in a repetitive intake/discharge cycle. When the machine is
operated as a motor, hydraulic fluid is delivered by a hydrostatic
pump at one port to drive the pistons outwardly as the barrel
swings into registry with that port, the fluid then passing at low
pressure into the discharge side for return to the pump. In either
case, one of the ports 11 or 12 will be a high-pressure port while
the other is the low-pressure port.
When port 11 is under high pressure and port 12 is under low
pressure, the fluid in line 13 is likewise at an elevated pressure
to bias the check valve 19 into a closed position. Fluid from the
chamber 16 cannot enter the closed hydraulic network via line 17.
However, the normal pressure in the housing chamber 16 is 6 to 8
atmospheres (gauge) and suffices, when the pressure drops at the
low-pressure duct 14 and port 12, to bleed the leakage fluid from
the chamber 16 into the hydraulic line 14 for return to the main
circulating path. The fluid within the chamber 16 in part derives
from leakage at the control surfaces 2a. When the control surface
10a is adjusted to vary the functions of the ports or the sense of
rotation is altered, only the check valve associated with the
low-pressure side will be operative. The high-pressure check valve
will invariably be closed.
In FIG. 2, I show a hydrostatic machine according to the invention
which is constituted as a pump and embodies many of the features
already described in connection with FIG. 1. In this embodiment,
the shaft 101, extending out of the housing portion 103 is
connected with a drive means such as an inlet combustion engine or
electric motor. The shaft 101 is provided with an extension 25
beyond the bearing 106 running to a feed pump 26, the latter being
bolted onto the housing portion 104 forming the fluid-distribution
ports 111 and 112 as well as ducts 113 and 114 as previously
described.
The intake line 27 of the pump 26 is fed from a reservoir 28 while
the pressure side of the pump 26 is connected via line 29 to the
using compartment 116 through the wall 103 thereof, preferably at
the bottom of the wall. A return line 31 communicates with the
compartment 116 at the upper side thereof via a fitting which is
provided with a check valve 32 allowing unidirectional flowing from
the housing to the reservoir 28. Valve 32 is provided with a strong
spring 32a so that it simultaneously constitutes a
pressure-regulating valve maintaining an adjustable pressure in the
compartment 116 at about 6 to 8 atmospheres. In this case, the
reservoir 28 can be open to the atmosphere and can constitute a
heat exchanger or heat-dissipating cooler directly. As an
alternative, the reservoir 28 may be closed to maintain a given
pressure within the system and the cooler may be provided as a
separate heat exchanger or radiator in a fluid circuit with the
pump 26. The pump 26, consequently, circulates fresh fluid through
the interior of the housing constantly with the advantages already
set forth. In general, the machine of FIG. 2 operates in the manner
previously described in FIG. 1 when the barrel 102 is rotated by
shaft 101 to shift the pistons 107 in the cylinder bores 108 of the
closed hydraulic circuit and permit the check valve 120 or 122
associated with the low-pressure side to connect the respective
passage 113 or 114 with the interior of the housing.
The hydrostatic drive illustrated in FIG. 3 comprises, in
accordance with the usual practice, a hydrostatic pump whose shaft
201 is connected with an internal combustion engine and whose
hydrostatic motor has its shaft 301 connected with a load. The
shafts 201 and 301 are rotatably connected with the cylinder
barrels 202, 302 whose pistons 208, 308 are axially shiftable, via
inclined control surfaces not shown, within the cylinder bores 207,
307 to displace hydrostatic fluid along a closed path
inter-connecting the ports 211 and 311 via a line 33 and the ports
212, 312 via a line 34. It will be appreciated that the lines 33
and 34 may be relatively long when the pump and the motor are to be
separated by some distance or can be eliminated when a single
support block is provided in place of the separate fluid
distribution plates 204, 304. The remainder of the system,
including the fluid-distribution antifriction plates 215, 315 the
ports 217 and 317 connected to the low-pressure side of the network
and the check valves 220, 320 and 222, 322 is, of course, identical
with the corresponding parts of the system of FIG. 1. In addition,
a pressure-equalization reservoir 36, in which a compressed gas is
maintained in the compartment 36a to form a yieldable cushion for
the membrane 36b connected with line 35 and the chamber 216. A
valve 36c serves to permit recharging of the accumulator. With
expansion of the fluid within the transmission as a result of
heating, there is a volume increase which is taken up by the
accumulator 36 with compression of the gas cushion therein. Should
there be a leak from the housing or an elastic yielding of the
ducts from a housing and portions thereof, additional fluid is
delivered by the accumulator. No separate feed pump is
necessary.
In FIG. 4, I show a system wherein a housing 403, 404 is common to
a pair of cylinder drums 402, with respective shafts 401 driven via
gears 401a from a gear 401b on the crankshaft 401c of an automotive
vehicle or like installation using a double pump aggregate. Since
separate closed hydraulic networks may be provided with the
low-pressure ports 412 at the same pressure and the high-pressure
ports 411 at respective elevated pressures, a check valve 420 is
provided to connect both ports 412 with the interior 416 of the
housing. The other check valves 422 for the high-pressure side are
provided as previously described.
FIG. 5 shows a system wherein the cylinder drums 502 and 602 of the
hydrostatic pump and hydrostatic motor are mounted in a common
housing 503 and have input and output shafts 501 and 601
respectively connected to a source of rotary movement and a load.
The control member 510 is here shown to be pivotal via lever 510'
to adjust the displacement of the pump and a similar means may be
provided for tilting the control plate 610. A single valve block
504 is here used with the intake side of the duct 514 connected
with the check valve 520. Pressure within the system may be
controlled by a regulating valve 650 connecting the high and low
pressure lines or by a feed pump 526 driven by gearing 561 from the
pump shaft 501. The major distinction between the system of FIG. 5
and that of FIG. 4 is the single housing for the barrels of both
the pump and motor of this latter system.
In FIG. 5, I also show a distributing valve 520a by which the check
valve 520 and the duct associated therewith may be switched between
the current low-pressure line 514 and the high-pressure line 513
when the hydraulic machines are reversed as described earlier. In
this case only a single check valve need be used. The valve 520a
may be coupled as represented by the dot-dash line 520b with lever
510' to effect automatically the change-over.
* * * * *