POSITIVE-DISPLACEMENT MACHINE

Abstract

A hydraulic positive-displacement machine includes at least two radially or axially spaced-apart groups of cylinder-piston units. The cylinders of the primary group can be made to communicate fluidically with cylinders of the secondary group via intermediate valves. At least two intermediate valves can be switched independently of one another.

Description

BACKGROUND OF THE INVENTION

The invention relates to a hydraulic positive-displacement machine.

In conventional hydrostatic positive-displacement machines, which can be embodied as radial or axial piston machines, for instance, the control of the inflow and outflow of the individual cylinder-piston units revolving along an orbit is done mechanically. In the case of an axial piston pump, for example, two pressure crescents are used, by way of which the connections with the high-pressure side and the low-pressure side open during a certain range of the orbit and thus during a certain stroke segment of the cylinder-piston units.

In radial piston pumps, one high-pressure valve and one low-pressure valve per cylinder-piston unit are provided, and the valves are, mechanically controlled. The high-pressure valve of each unit for instance always opens if a certain built-up pressure in the applicable cylinder of the unit is exceeded, so that the pressure fluid with elevated pressure can flow off to the high-pressure side of the pump.

A disadvantage of such hydrostatic positive-displacement machines is that all the cylinder-piston units are always active, or in other words that the volume flow of the machine is always defined by the displacement of all the units.

International Patent Disclosure WO 2008/012558 A2 discloses valve-controlled positive-displacement machines, known as digital displacement units (DDUs), in which each cylinder-piston unit is assigned one electrically actuated low-pressure valve and one electrically actuated high-pressure valve.

Thus the units are triggerable via the two valves separately in the pump mode, motor mode and a so-called idle mode. In the idle mode, individual units can be deactivated by permanently opening the low-pressure valves and closing the high-pressure valve, or in other words they can be switched to be forceless by suitable actuation of both valves. It is thus possible to reduce the volume flow or the rotary speed of the positive-displacement machines.

A disadvantage of such valve-controlled positive-displacement machines is that the cylinder-piston units switched to be forceless in the idle mode also have pressure fluid flowing through them, resulting in a friction loss.

Published International Patent Disclosure WO 2006/109079 discloses a valve-controlled positive-displacement machine (DUO), in which each cylinder-piston unit of a primary radial plane, via an intermediate valve, is assigned a further secondary cylinder-piston unit of a secondary radial plane. The secondary plane, along an axis of rotation, is spaced apart from the first plane. The intermediate valves can be opened or closed via a common coil and a common magnet armature. As a result, the volumetric flow or torque of the machine can be changed, and a “shutoff” of the second plane is effected via a closure of the intermediate valves, so that no volumetric flow involving friction arises in conjunction with the second plane.

A disadvantage of such positive-displacement machines is that the cylinder-piston units of the second radial plane can be switched on or off only in common.

SUMMARY OF THE INVENTION

By comparison, it is the object of the invention to create a positive-displacement machine whose volumetric flow or torque can be adjusted more flexibly.

The hydraulic positive-displacement machine according to the invention has at least two groups, spaced apart radially or axially from one another, of cylinder-piston units, in which cylinders of the primary group can be made to communicate fluidically with cylinders of the secondary group via intermediate valves. According to the invention, at least two intermediate valves are switchable independently of one another. As a result, the flexibility of the volumetric flow (in the case of a pump) or torque (In the case of a motor) is increased.

In an especially preferred refinement, the number of cylinder-piston units is equivalent to the number of secondary cylinder-piston units. Cylinder heads are secured in pairs on one another and can be made to communicate fluidically via an intermediate valve, and wherein all the intermediate valves are switchable independently of one another. As a result of this 1-1-1 relation between the primary cylinder, intermediate valve and secondary cylinder, the flexibility of the secondary cylinder-piston units is maximized.

In an especially preferred exemplary embodiment of the positive-displacement machine of the invention, each primary cylinder-piston unit can be activated or deactivated via an electrically or electrohydraulically actuated high-pressure valve and via an electrically or electrohydraulically actuated low-pressure valve. As a result, individual cylinder-piston units can be switched to be forceless, and the volumetric or rpm of the positive-displacement machine can thus be adjusted. As a result of this digital displacement unit (DUO), the flexibility of the primary cylinder-piston units and thus of the entire positive-displacement machine is also maximized.

In a preferred variant, the positive-displacement machine is a radial piston machine, and the primary cylinder-piston units are located in a primary radial plane, and the secondary cylinder-piston units are located in a secondary radial plane, and the planes are located spaced apart from one another along an axis of rotation of a shaft.

For designing the intermediate valves (and in particular their bores), it is advantageous if the cylinder heads are each located in pairs one after the other in the axial direction of the shaft.

In a variant of the invention, the positive-displacement machine is an axial piston machine, and the primary cylinder-piston units are located on an inner circular cylinder, and the secondary cylinder-piston units are located on an outer circular cylinder.

In a preferred refinement of the positive-displacement machine of the invention, the intermediate valves are unlockable check valves embodied as seat valves, whose closing direction in each case is oriented from the primary cylinder to the secondary cylinder. These valves offer what in apparatus terms is simple and thus tight locking off of the secondary cylinders.

If the positive-displacement machine is a motor, it is preferred if a closing body of each check valve, in a currentless basic position, blocks off a respective connecting conduit between the cylinder heads, and in a position activated by a lifting magnet, it uncovers the respective connecting conduit. Thus as the motor is being run up to operating speed, the secondary units can be switched on by the supply of current to the lifting magnets, to increase the absorption volume and torque of the motor. In continuous operation of the motor, the secondary units are blocked off by shutoff of the current for the lifting magnets.

Each check valve can have a valve body, whose reciprocation direction is located approximately parallel to the shaft, and wherein the closing body is located on one end portion of the valve body, and a magnet armature of the lifting magnet is disposed on another end portion of the valve body.

Each lifting magnet can be located on the side of the secondary cylinder head remote from the primary cylinder head, and wherein each valve body has an intermediate portion, which penetrates a work chamber of the respective secondary cylinder head.

In the exemplary embodiment of a DUO as a motor, for cost reasons the intermediate valves can be embodied as switching more slowly than the high-pressure valves and the low-pressure valves, if the intermediate valves are active only during the running up of the motor to operating speed and are shut off at higher rpm levels.

In an alternative refinement of the positive-displacement machine of the invention, the intermediate valves are proportional valves. Thus suction throttling can be achieved, as a result of which the secondary cylinders that are switched on are not completely filled. As a result, the volumetric flow or rpm stages that result from the stroke volumes of the secondary cylinder-piston units in a characteristic curve of the machine are smoothed.

If the cylinders of the secondary group are larger than the cylinders of the primary group, an increase in volumetric flow or torque results with secondary units switched on, which makes for more than a doubling. This can be advantageous, depending on the usage demands made of the machine.

In a preferred refinement of the positive-displacement machine of the invention, the secondary cylinder-piston units have a larger idle volume than the primary cylinder-piston units. Thus the “relative expansion” of the pressure fluid in the shut-off state of the secondary cylinder-piston units upon the outward motion of their pistons is reduced, thus reducing the lost energy of the machine in that operating state.

BRIEF DESCRIPTION OF THE DRAWINGS

One exemplary embodiment of the invention will be described in detail below in conjunction with the drawings.

FIG. 1 shows one exemplary embodiment of a valve-controlled radial piston machine of the invention, in a longitudinal section; and

FIG. 2 is a detail of the exemplary embodiment of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an exemplary embodiment of a valve-controlled radial piston machine of the invention in section. It has a primary radial plane 1 and a secondary radial plane 2, and each plane 1, 2 has six cylinder-piston units, which are arranged in a star pattern around a shaft 4. Of the six units in each plane, only two units 6a, 6b and 8a, 8b, facing one another, are shown in FIG. 1. Each of the cylinder-piston units 6a, 6b, 8a, 8b has a work chamber 10a, 10b, 12a, 12b and a piston 14a, 14b, 16a, 16b; the pistons 14a, 14b, 16a, 16b are braced on an eccentric element 18 of the shaft 4.

The shaft 4, which depending on the mode of operation of the radial piston machine shown is a drive shaft or a power takeoff shaft, is supported rotatably, together with the eccentric element 18 secured to it, in the radial piston machine via two roller bearings 20, 22. FIG. 1 shows a rotary position of the eccentric element 18 in which a circumferential portion of comparatively large radius (in FIG. 1) is located above the shaft 4, while a circumferential portion with a comparatively small radius of the eccentric element 18 is located below the shaft 4. Thus the upper pistons (in FIG. 1) 14a, 16a are at top dead center—with respect to their work stroke—while the two facing pistons 14b, 16b—with respect to their work stroke—are shown at bottom dead center.

The primary cylinder-piston units 6a, 6b are embodied as Digital Displacement Units (DDUs), and each has one electrically actuated high-pressure valve (not shown) and one electrically actuated low-pressure valve 24a, 24b. As a result, each primary cylinder-piston unit 6a, 6b can be operated in either the motor or pump mode or in the idle mode. In the idle mode, the corresponding primary work chamber 10a, 10b is permanently in communication via the low-pressure valve 24a, 24b with a low-pressure connection of the machine and is disconnected from a high-pressure connection (neither of these connections is shown) and is thus switched to be forceless or in other words inactive. For example, three of the total of six primary cylinder-piston units 6a, 6b can be deactivated by the idle mode. As a result, a delivery volume (in the case of a pump) or a power takeoff rpm of the shaft 4 (in the case of a motor) is reduced.

FIG. 2 shows a detail of the radial piston machine of FIG. 1. Here only one of the total of six pairs of cylinder-piston units, each comprising a primary unit 6a and an associated secondary unit 8a, is shown. The cylinders 26a, 28a are received pivotably in a cylinder head 30a, 32a, so that the piston 14a, 16a guided in the cylinder 26a, 28a can also rest uniformly on the oblique transitional regions (not shown) of the eccentric element 18. The pistons 14a, 16a are each prestressed against the eccentric element 18 by a respective compression spring 34a, 36a braced on the cylinder 26a, 28a.

Each low-pressure valve 24a is inserted into the cylinder head 30a of the primary unit 6a. It has a coil, which serves as a lifting magnet, by way of which a valve body 40 can be moved, so that the valve body controls the communication of the work chamber 10a with the low-pressure connection. On the high-pressure side, FIG. 2 shows only a portion of a high-pressure conduit 42, which discharges laterally into the work chamber 10a, and whose communication with high pressure is controlled via a high-pressure valve (not shown).

In the associated secondary cylinder head 32a, a closure 44 is inserted in sealing fashion; its size is approximately equivalent to that of the low-pressure valve 24a.

According to the invention, all the primary work chambers 10a communicate via a respective connecting conduit 46, 48 with a respective secondary work chamber 12a. Each connecting conduit 46, 48 extends approximately parallel to the shaft 4 and discharges into the respective cylinder head 30a, 32a. Between the connecting conduit portion 46 on the primary side and the connecting conduit portion 48 on the secondary side, an unlockable check valve 50 is located, whose approximately spherical closing body 51, in the closed state of the valve as shown, rests sealingly on a valve seat.

A rod 52 of the valve body connects the closing body 51 to a magnet armature 54. The rod 52 extends from the closing body 51 through the connecting conduit portion 48 on the secondary side, through the portion of the work portion 12a surrounded by the cylinder head 32a, and, still in sealing fashion, through the cylinder head 32a, until it is connected on its outside to the magnet armature 54. The magnet armature 54 is embraced by a coil 56, which forms a lifting magnet.

According to the invention, each connecting conduit 46, 48 and each check valve 50 is assigned a separate lifting magnet 54, 56, so that each individual secondary cylinder-piston unit 8a can be connected to the primary unit 6a, or disconnected from it.

By means of the coil 56, shown in currentless form in FIG. 2, the closing body 51 rests on the valve seat, where it is held either by the pressure in the work chamber 10a or by an additional spring (not shown). When current is supplied to the coil 56, the closing body 51 is shifted to the right (in FIG. 2) by the magnet armature 54 via the rod 52, so that the connecting conduit 46, 48 is opened. Thus the primary work chamber 10a is enlarged by the volume of the secondary work chamber 12a, and the two pistons 14a, 16a execute synchronous work strokes. Thus in the case of a motor, for instance, its absorption volume and its torque are increased. This operating state of the motor is advantageous for instance on starting or running up of the motor, while at a higher rpm (such as rated rpm), the secondary units 8a are disconnected again from the primary units 6a.

Because of the possibility of blocking off the secondary cylinder-piston units, in the idle mode the flow of pressure fluid into and out of work chambers, which is largely ineffective but involves friction, is reduced. Because of the intermediate valves that can be switched individually in accordance with the invention, the flexibility of the machine is increased, in particular by means of finely graduated possibilities for changing the operating state.

In a departure from the exemplary embodiment shown, each lifting magnet can be located on the side of the primary cylinder head remote from the secondary cylinder head, and each valve body has an intermediate portion that penetrates a work chamber of the respective primary cylinder head. This exemplary embodiment has the advantage that the lifting magnet is not in the pressure fluid, but instead is in a dry area.

What is disclosed is a hydraulic positive-displacement machine having at least two radially or axially spaced-apart groups of cylinder-piston units; cylinders of the primary group can be made to communicate fluidically with cylinders of the secondary group via intermediate valves. At least two intermediate valves can be switched independently of one another.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in a positive-displacement machine, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.

Claims

1. A hydraulic positive-displacement machine, comprising:

at least two groups (1, 2) of cylinder-piston units (6a, 6b, 8a, 8b) spaced apart radially or axially from one another, wherein cylinders (26a) of a primary group (1) of said at least two groups of cylinder-piston units are configured to communicate fluidically with cylinders (28a) of a secondary group (2) of said at least two groups of cylinder-piston units via intermediate valves (50), wherein at least of said two intermediate valves (50) are switchable independently of one another.

2. The positive-displacement machine as defined by claim 1, wherein a number of cylinder-piston units (6a, 6b) in said primary group (1) is equivalent to a number of cylinder-piston units (8a, 8b) in said secondary group (2), and wherein cylinder heads (30a, 32a) are secured in pairs on one another and are configured to communicate fluidically via an intermediate valve (50), and wherein all the intermediate valves (50) are switchable independently of one another.

3. The positive-displacement machine as defined by claim 1, wherein each cylinder-piston unit (6a, 6b) of said primary group (1) is activatable or deactivatable via an electrically or electrohydraulically actuated high-pressure valve and via an electrically or electrohydraulically actuated low-pressure valve (24a, 24b).

4. The positive-displacement machine as defined by claim 1, wherein said machine is a radial piston machine, wherein the cylinder-piston units (6a, 6b) of the primary group (1) are located in a primary radial plane (1), and the cylinder-piston units (8a, 8b) of the secondary group (2) are located in a secondary radial plane (2), and wherein the primary radial plane (1) and secondary radial plane(2) are spaced apart from one another along an axis of rotation of a shaft (4).

5. The positive-displacement machine as defined by claim 2, wherein the cylinder heads (30a, 32a) are each located in pairs one after the other in an axial direction of the shaft (4).

6. The positive-displacement machine as defined by claim 1, wherein said machine is an axial piston machine, wherein the cylinder-piston units of the primary group (1) are located on an inner circular cylinder, and the cylinder-piston units of the secondary group (2) are located on an outer circular cylinder.

7. The positive-displacement machine as defined by claim 1, wherein the intermediate valves are unlockable check valves (50) embodied as seat valves, wherein a closing direction of each of said check valves is oriented from a cylinder (26a) of said primary group (1) to a cylinder (28a) of said secondary group (2).

8. The positive-displacement machine as defined by claim 7, wherein said machine is a hydraulic motor, wherein a closing body (51) of each of said check valves (50), in a currentless basic position, blocks off a respective connecting conduit (46, 48) between cylinder heads (30a, 32a), and in a position activated by a lifting magnet (54, 56), said closing body (51) of each of said check valves (50) uncovers a respective connecting conduit (46, 48).

9. The positive-displacement machine as defined by claim 8, wherein each of said check valves (50) has a valve body (51, 52, 54), wherein a reciprocation direction of each said valve body is located approximately parallel to a shaft (4), and wherein the closing body (51) is located on one end portion of the valve body (51, 52, 54), and a magnet armature (54) of the lifting magnet (54, 56) is disposed on another end portion of the valve body (51, 52, 54).

10. The positive-displacement machine as defined by claim 9, wherein each lifting magnet (54, 56) is located on a side of a secondary cylinder head (32a) remote from a primary cylinder head (30a), and wherein each valve body (51, 52, 54) has an intermediate portion, wherein said intermediate portion penetrates a work chamber of a respective secondary cylinder head.

11. The positive-displacement machine as defined by claim 3, wherein the intermediate valves (50) are configured to switch more slowly than the high-pressure valves and the low-pressure valves (24a, 24b).

12. The positive-displacement machine as defined by claim 1, wherein the intermediate valves are proportional valves.

13. The positive-displacement machine as defined by claim 7, wherein the cylinders (28a) of the secondary group (2) are larger than the cylinders (26a) of the primary group (1).

14. The positive-displacement machine as defined by claim 1, wherein the cylinder-piston units (8a, 8b) of the secondary group (2) have a larger idle volume than the cylinder-piston units (6a, 6b) of the primary group (1).