Patent Grant
11619203
This application claims priority under 35 U.S.C. § 119 to application no. DE 10 2020 212 630.5, filed on Oct. 7, 2020 in Germany, the disclosure of which is incorporated herein by reference in its entirety.
The disclosure relates to a hydrostatic axial piston machine having a cylinder drum that rotates during operation and has a plurality of cylinder bores in which displacement pistons that carry out a stroke movement during operation are arranged and each of which, together with the walls of a cylinder bore and a connecting duct to an end face of the cylinder drum, delimits a displacement space with a displacement volume that is dependent on the position of the displacement piston. Each cylinder bore opens out in a control opening in one end face of the cylinder drum. The axial piston machine, which can be in the form of a bent axis machine or of a swash plate machine and can be designed with a fixed displacement volume or with a variable displacement volume, also comprises a control part against which the cylinder drum bears with the end face and on which a first kidney-shaped control port in the form of a circular arc and a second kidney-shaped control port in the form of a circular arc and, between the two kidney-shaped control ports, a first changeover web and a second changeover web are formed, within which the displacement pistons take up a dead center position and reverse their direction of movement. A compensating opening that is able to be overlapped by a control opening is located in each changeover web. The two compensating openings are connected together via a compensating fluid path. In the changeover webs, the pressure changeover between high pressure and low pressure takes place in the displacement spaces.
In hydrostatic axial piston machines, a pressure reducing fluid path without a valve is usually formed by what is known as a pilot groove, which has been introduced into that side of a control plate that faces the cylinder drum and which starts at a distance from a kidney-shaped control port in the control plate, undergoes an increase in cross section toward the kidney-shaped control port and ultimately opens into the kidney-shaped control port. A hydrostatic axial piston machine having such a pilot groove is known for example from DE 17 03 347 A. Specifically, respective pilot grooves are located at each end of each of the two kidney-shaped control ports, and so a total of four pilot grooves are present. A hydrostatic axial piston machine having pilot grooves at the kidney-shaped control ports is also known from DE 37 25 361.
In the case of such a conventional pressure changeover, each displacement space is thus connected, in the region of the dead center position of a displacement piston, to the respectively other pressure level via a notch or a bore as pilot control. Depending on the application, changeover systems with a negative or positive overlap exist. In the case of a positive overlap, there is briefly no connection of the displacement volume to be changed over to a kidney-shaped control port. In the case of a negative overlap, by contrast, there is briefly a connection to both kidney-shaped control ports. The purpose of the pressure changeover is to switch the pressure level in the displacement volume back and forth as gently as possible without abrupt, sudden changes between the two pressure levels of the kidney-shaped control ports. On account of the compressibility of the fluid, an additional amount of pressure fluid is required for compressing the pressure fluid in a closed capacity, while upon relaxation, this amount has to escape again. This has the effect that conventional pressure changeover systems always lose a part of the medium from the high-pressure side to the low-pressure side, this having a negative effect on the efficiency.
In principle, the notches and bores can always be designed optimally only for a narrow operating range. This form of the pressure changeover system has proven successful in the past. On account of the demand for increasing output, namely for higher pressure with a simultaneous increase in speed, the conventional changeover system reaches physical limits, however: The rate of pressure change increases during the changeover phase. In addition, the pressure change is no longer fully achieved during the overlapping phase of the displacement space and pilot control, and so the pressure level in the displacement space changes abruptly as the overlap with the kidney-shaped control ports of the control part continues. As a result, strong pressure shocks are sent into the line system, resulting in high pressure pulsing and volumetric flow (mass flow) pulsing in the low pressure and high pressure system. The pressure pulsing becomes all the greater, the narrower the ducts are dimensioned to be. In 4-quadrant-capable pumps and hydraulic motors that are operated in a closed hydraulic circuit, the flow ducts, for example the ducts in the control lens of a bent axis machine, have to be dimensioned in a narrow manner for strength reasons, this exacerbating the pulsing problem.
For example, the situation for a bent axis motor with a conventional notch changeover system at a high speed will be outlined. This motor is designed with a positive notch overlap, and so there is no connection of the displacement space to be changed over with high or low pressure when a displacement piston is located at top dead center, that is to say passes least far into the cylinder bore. A few rotation angle degrees later, the displacement volume is relaxed into the low-pressure kidney-shaped control port. At the end of the overlapping phase with the changeover notch in front of the low-pressure kidney-shaped control port, the pressure level has only dropped by for example 50%, however. The further relaxation takes place largely without constriction via the direct connection of the low-pressure kidney-shaped control port and the displacement space. As a result of the strong pressure-shock stimulation, the majority of the fluid on the low-pressure side is greatly accelerated by the cylinder drum, this then causing a hydraulic undersupply at the cylinder drum. During this phase, significant evaporation (cavitation) can occur on the low-pressure side, since the fluid, after the pressure-shock wave has leveled off, first of all has to be slowed down in order subsequently to refill the resultant cavities (cavitation bubbles). The starting acceleration toward the cylinder drum allows the steam zones to condense implosively, resulting in very high pressure spikes in the region of the low-pressure side. The implosion of such bubbles in the vicinity of fixed walls results in fatigue-like breakdown of the material structure, resulting in local pitting on the cylinder drum and on the control part.
DE 21 04 933 A1 discloses a hydrostatic axial piston machine in which respective compensating openings are located in the middle of the two changeover webs, and the two compensating openings are connected together by a compensating fluid path. In that case, the angular spacing between a compensating opening and a kidney-shaped control port is at least as large as the angular width of a control opening of a cylinder bore. DE 21 04 933 A1 discloses an axial piston machine with an even number of displacement pistons and an axial piston machine with an odd number of displacement pistons. In such an axial piston machine with an odd number of displacement pistons, the pressure compensation between displacement spaces that change from the low-pressure side to the high-pressure side and displacement spaces that change from the high-pressure side to the low-pressure side takes place in two stages. In that case, the compensating fluid path between the two compensating openings and thus the surrounding material is exposed to highly dynamic loading. This has a negative effect on the durability of the control part in which the compensating fluid path is formed and which is usually a separate control plate or control lens.
The object of the disclosure is to configure a hydrostatic axial piston machine, in particular a hydrostatic axial piston motor having the features mentioned at the beginning, such that, for both directions of rotation, cavitation that occurs in particular at high speeds is avoided and the noise behavior is good.
This object is achieved, in the case of a hydrostatic axial piston machine having the features mentioned at the beginning, in that the two compensating openings are arranged adjacent to the first kidney-shaped control port, in that a further compensating opening that is able to be overlapped by the control openings is located in each changeover web, said further compensating opening being arranged adjacent to the second kidney-shaped control port, in that the two further compensating openings are connected together via a second compensating fluid path, and in that the angular spacing between the two compensating openings arranged in the same changeover web is greater than the angular width of a control opening. In this case, the vertex of the abovementioned angles lies preferably on the axis of rotation of the cylinder drum.
In an axial piston machine according to the disclosure, the dynamic load pulses only between 50% high pressure and 100% high pressure in the compensating fluid path between the two high-pressure side compensating openings and only between 0 and 50% high pressure in the compensating fluid path between the two low-pressure side compensating openings. The dynamic loading of a control plate or control lens is therefore low, such that the machine exhibits good durability. Since the angular spacing between the two compensating openings in a changeover web is greater than the angular width of the control openings in the cylinder drum, this ensures that the high-pressure kidney-shaped control port and the low-pressure kidney-shaped control port are not connected together via three control openings and the two compensating fluid paths in a hydraulic short circuit. The function is in this case entirely independent of the direction in which the axial piston machine rotates and in which kidney-shaped control port the high pressure prevails and in which one the low pressure prevails.
A hydrostatic axial piston machine according to the disclosure can be developed further in an advantageous manner.
Preferably, the two compensating openings that are adjacent to a kidney-shaped control port and are connected together via a compensating fluid path have the same angular spacing from the kidney-shaped control port.
In this case, it is furthermore preferred that the two compensating openings that are adjacent to a kidney-shaped control port have the same angular spacing from this kidney-shaped control port as the two compensating openings that are adjacent to the other kidney-shaped control port have from the other kidney-shaped control port. If the two kidney-shaped control ports have the same arc length, this therefore results, in plan view of that side of the control part that faces the cylinder drum, in a symmetric arrangement of the kidney-shaped control ports and of the compensating openings with regard to a plane located centrally between the two kidney-shaped control ports. The ratios are then always the same regardless of which kidney-shaped control port is the high-pressure kidney-shaped control port and which one is the low-pressure kidney-shaped control port and in which direction the axial piston machine rotates.
It is favorable for the strength of the control part when the angular spacing of the compensating openings from the adjacent kidney-shaped control port is at least approximately the same as the angular width of the compensating openings.
The disclosure and its advantageous configurations can be employed with particular advantages in a hydrostatic axial piston machine in which the number of cylinder bores that are present and thus also the number of displacement pistons is odd.
Advantageously, at the start of a compensating flow between two control openings that overlap two compensating openings connected together by a compensating fluid path, there is still a small passage cross section between a control opening leaving a kidney-shaped control port and the kidney-shaped control port. In variable-displacement axial piston machines, the compensating fluid paths can be designed correctly for the capacities to be changed over only in respect of a speed, a delta-p and a displacement volume. However, the design should take into consideration the entire range of operating points with regard to pressure and speed, but also with regard to the variable displacement volume. Preferably, therefore, entirely closed-off capacities which are formed by the displacement spaces are avoided. The complete shutting off of a displacement space during the piston stroke has the result that, depending on the piston movement, extreme positive pressures (when reducing the displacement space capacity) or even negative pressures (when increasing the displacement space capacity) arise. Consequently, extreme pulsing should be expected both on the low-pressure side and on the high-pressure side. The intake behavior could also be impaired, this being problematic in particular in the case of a machine used in an open circuit.
It is likewise advantageous when, toward the end of a compensating flow between two control openings that overlap two compensating openings connected together by a compensating fluid path, the control opening that has left a kidney-shaped control port only comes out of overlap with the corresponding compensating opening when the other control opening is still overlapping the other compensating opening and there is already a small passage cross section between the other control opening and the kidney-shaped control port.
Since the outlined overlap is allowed, the angle over which the kidney-shaped control ports extend can be very large, and so extreme positive pressures when a displacement space is reduced in size or even negative pressures when a displacement space is increased in size and thus strong pulsing both on the low-pressure side and on the high-pressure side are avoided.
At the start and toward the end of a compensating flow, the inductance of the oil column in a compensating fluid path has a significant influence on the dynamics of the changeover. Since the compensating fluid paths, which are preferably formed by bored holes, i.e. by a plurality of individual bores, are relatively long and thin, some time is required before the oil column in a compensating fluid path is accelerated and before the direction of flow in a compensating fluid path changes under reversing pressure conditions and the pressure fluid flows counter to the original direction. In the case of a hydrostatic axial piston machine according to the disclosure, this operation takes place once for each individual compensating fluid path per changeover operation. These dynamics can be considered when determining the opening angle of the kidney-shaped control ports. It is advantageous for the kidney-shaped control ports to be embodied in a shorter manner in the specific application of an axial piston machine that tends to run slowly than in an axial piston machine that tends to run quickly, in order to reduce the opening area, or for the kidney-shaped control ports to be embodied in a longer manner in the specific application of axial piston machines that tend to run quickly than in axial piston machines that tend to run slowly, in order to increase the opening area.
If the displacement volume of the hydrostatic axial piston machine is variable, then preferably, at the minimum displacement volume, the volume of the compensating fluid path between two compensating openings is less than one tenth of the free volume of a displacement space at the inner dead center of the displacement piston. The inner dead center should be understood as being the dead center with the smallest cylinder volume. It is thus clear that a compensating fluid path does not represent a volume known from the prior art in the form of a precompression volume or decompression volume. A precompression volume is initially charged to high pressure and, during a drop in pressure, sends pressure fluid to a displacement space which is changing to the kidney-shaped control port subjected to high pressure and in which the pressure is rising. Then, the precompression volume is charged back up to high pressure from the high-pressure kidney-shaped control port via the control opening of the displacement space. In a decompression volume, low pressure initially prevails before pressure fluid flows to it during a pressure rise from a displacement space which is changing from the high-pressure kidney-shaped control port to the low-pressure kidney-shaped control port and in which the pressure is dropping. Then, via the control opening of the displacement space, the decompression volume is connected to the low-pressure kidney-shaped control port and the pressure in the decompression volume drops to low pressure again.
A hydrostatic axial piston machine usually has a control plate which is separate from a housing part with the working ports and in which the kidney-shaped control ports are located. In an axial piston machine of bent axis design with a variable displacement volume, during an adjustment, the control plate moves along with the cylinder drum and has a lens-like shape, for which reason it is also known as a control lens. Preferably, in addition to the kidney-shaped control ports and the compensating openings, the compensating fluid paths are also located between the compensating openings entirely in the separate control plate, in particular in the control lens that is moved with the cylinder drum during adjustment of the displacement volume.
The advantages of a hydrostatic axial piston machine according to the disclosure come to bear especially when the two kidney-shaped control ports are able to be subjected to high pressure and to low pressure, as is the case in particular when used in a closed hydraulic circuit.
An exemplary embodiment of a hydrostatic axial piston machine of bent axis design according to the disclosure and two variants of a control lens with compensating openings and compensating fluid paths are illustrated in the drawings. The disclosure will now be explained in more detail on the basis of the figures of these drawings, in which
The variable-displacement hydrostatic axial piston machine of bent axis design illustrated in
A drive shaft 15 having a drive flange 16 is mounted in a rotatable manner in the housing part 11 in an O arrangement by means of two tapered roller bearings.
The end plate 12 has, facing the interior 14, two axially spaced-apart circular-cylindrical, hollow bearing faces 17, on which a control plate 18 with corresponding bearing faces 19 bears and along which the control plate is displaceable by an adjusting device, of which only the adjusting pin 23 that dips into a central bore 22 in the control plate 18 is visible in
The control plate 18 has, from the control face 26 to the bearing faces 19, two apertures 30 and 31, which open, in the control face 26, into two kidney-shaped control ports 32 and 33 in the form of a circular arc that lie on a pitch circle. The aperture 30 opens out in one bearing face 19 as an elongate, rectangular slot 34, and the aperture 31 opens out in the other bearing face 19 as an elongate, rectangular slot 35. Located in each bearing face 17 of the end plate 12 is a slot (not apparent in the section according to
The axial piston machine furthermore comprises a cylinder drum 40, which is arranged between the drive flange 16 and the control plate 18. The cylinder drum 40 is supported on the control face 26 of the control plate 18 in a hydrostatically mounted manner with an appropriately adapted end face as bearing face 41. In the cylinder drum 40, for example seven or nine axially extending cylinder bores 42 that are distributed uniformly on a pitch circle are formed, which open out on the planar end face of the cylinder drum 40 that faces the drive flange 16. At the concave bearing face 41 of the cylinder drum 40, the cylinder bores 42 open out via opening ducts 43, extending obliquely toward a central axis of the cylinder drum, on the pitch circle on which the kidney-shaped control ports 32 and 33 of the control plate 18 also lie. The mouths of the opening ducts on the bearing face 41 form control openings 39 of the cylinder bores 42 and have a width which is equal to the width of the kidney-shaped control ports and are curved like the kidney-shaped control ports. Their length on the pitch circle is slightly smaller than the diameter of a cylinder bore. In the cylinder bores 42, pistons 44 are arranged so as to be movable back and forth. Their free ends that project out of the cylinder bores 42 are connected to the drive flange 16 so as to be able to be entrained in rotation via ball joints. Each ball joint consists of a ball head 45 formed at the free end of the associated piston 44 and of a hollow sphere portion which is formed in the drive flange 16 and in which the ball head 45 is received in a rotatable manner. A retaining plate 46 keeps the ball heads 45 within the hollow sphere portions.
Fitted in a central, stepped through-bore 47 in the cylinder drum 40 is a helical compression spring 48, which supports a central pin 49 on the drive flange 16, said central pin 49 likewise being mounted by means of a ball joint in the drive flange 16, projecting into the through-bore 47 and guiding the cylinder drum 40.
As is more clearly apparent from
The two compensating openings 55 and 57 adjacent to the kidney-shaped control port 32 are connected fluidically together by a first compensating fluid path 59 and the two compensating openings 56 and 58 adjacent to the kidney-shaped control port 33 are connected fluidically together by a second compensating fluid path 60. Both compensating fluid paths 59 and 60 are produced by bored holes within the control lens 18. Specifically, each compensating fluid path is made up of an oblique bore 61, which extends from the control face 26 and the mouth of which forms the compensating opening 55 or 56, respectively, an oblique bore 62, which likewise extends from the control face 26 and the mouth of which forms the compensating opening 57 or 58, respectively, and two further bores 63 and 64 that meet one another, intersect the oblique bores 61 and 62 and guide the respective compensating fluid path around the central bore 22 in the control lens 18. Toward the outside, the bores 63 and 64 are closed in a manner not illustrated in more detail by a stopper.
Overall, the control lens 18 is thus entirely symmetric with respect to a plane 65 in which the axis of the central bore 22 of the control lens lies and which extends centrally between the two kidney-shaped control ports 32 and 33 through the changeover webs 36 and 37. The bores 61, 62, 63 and 64 are clearly discernible in
The control lens 18 according to
In order to distinguish them better from one another, in
It is now assumed that the axial piston machine is operated as a hydraulic motor in a closed hydraulic circuit and pressure fluid delivered by a pump flows to the working port to which the kidney-shaped control port 32 is connected. In the kidney-shaped control port 32, high pressure thus prevails in the control lens 18 and low pressure at a level of for example 30 bar prevails in the kidney-shaped control port 33. The cylinder drum 40 rotates, in the plan view according to
In the rotational position of the cylinder drum 40 relative to the control lens 18 according to
Once the cylinder drum 40 has rotated five degrees further into the position shown in
Once the cylinder drum 40 has rotated five degrees further into the position shown in
Once the cylinder drum 40 has rotated five degrees further into the position shown in
In the rotational position, shown in
After a further rotation through five degrees, i.e. after a rotation of 25 degrees in total starting from the rotational position according to
While the cylinder drum 40 is on its way to the rotational position according to
During the rotation of the cylinder drum 40 through a further five degrees into the rotational position shown in
In the control lens 18 shown in
Such a control lens 18 is shown in
If pressure fluid delivered by a pump flows to the working port, connected to the kidney-shaped control port 33, of the axial piston machine, the cylinder drum 40 rotates clockwise relative to the control plate 18 in the views according to
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2020 212 630.5 | Oct 2020 | DE | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 3040672 | Foerster | Jun 1962 | A |
| 5593285 | Watts | Jan 1997 | A |
| Number | Date | Country |
|---|---|---|
| 1 703 347 | Jan 1972 | DE |
| 2 104 933 | Aug 1972 | DE |
| 37 25 361 | Feb 1989 | DE |
| Entry |
|---|
| Bosch, Axial Piston Machine with a Revolving Cylinder Drum—(“DE2104933A_MT”) Machine Translation (original1971) (Year: 1971). |
| Number | Date | Country | |
|---|---|---|---|
| 20220106945 A1 | Apr 2022 | US |
