WO2018215514A1

WO2018215514A1 - Hydrostatic relief and lubrication notches on valve segment running face

Info

Publication number: WO2018215514A1
Application number: PCT/EP2018/063457
Authority: WO
Inventors: Jens Bagusch
Original assignee: Danfoss Power Solutions Gmbh & Co Ohg
Priority date: 2017-05-23
Filing date: 2018-05-23
Publication date: 2018-11-29
Also published as: DE102017208755A1

Abstract

The invention relates to improved bearing and lubrication between cylinder blocks (3) and valve segments (2) of hydraulic axial piston units (1) and their rotating kits. In the valve segments first and a second kidney-shaped ports (11, 21) are formed rotationally symmetric with regard to a rotational axis of the cylinder block for providing a suction and a discharge port for charging and discharging hydraulic fluid to and from cylinder bores (8) in the cylinder block. At the radial outer edges of the kidney-shaped ports a plurality of concave formed hydrostatic bearing notches (50) are provided on a sliding surface (7) facing the cylinder block and intersecting with one of the kidney-shaped ports. Alternatively the bearing notches can be located on a bottom surface (9) of the cylinder block extending outwards from outer edges of openings (35) for charging and discharging hydraulic fluid to and from the cylinder bores.

Description

HYDROSTATIC RELIEF AND LUBRICATION NOTCHES ON VALVE SEGMENT RUNNING

FACE The present invention relates to a hydraulic axial piston unit of the swashplate or the bent axis construction type. Preferably, the axial piston unit according to the invention is of the variable displacement type; however, hydraulic axial piston units of the constant type are also covered by the invention. The present invention relates in particular to valve segments used in such hydraulic axial piston units mentioned before.

In hydraulic axial piston pumps and hydraulic axial piston motors, i.e. in hydraulic axial piston units reciprocally movable working pistons are arranged in general in axial direction of a rotation axis of a cylinder block. Here it can be differentiated between two generally different construction types, hydraulic axial piston units of the swashplate type and hydraulic axial piston pumps of the bent axis type. As these types of hydraulic axial piston units are well known to a person with skills in the relevant art, explanations with regard to the working principle of these hydraulic axial piston units can be omitted at this point. It should be noted that there are hydraulic axial piston units of the swashplate type with rotating or stationary swashplate and, accordingly, stationary or rotating cylinder block, respectively. There are as well as bent axis hydraulic axial piston units with a rotating cylinder block being pivotable for the adjustment of its displacement volume. The latter is nowadays the most common design for hydraulic axial piston pumps; however, the other type of hydraulic axial piston pump with rotating swashplate is also covered by the inventive idea. The bent axis construction type is used frequently in motor applications. In all kinds of hydraulic axis axial piston units hydraulic fluid is delivered/discharged via a non- rotating valve segment which faces the cylinder block bottom surface, which is the cylinder block side remote from the piston heads, which are being supported by the shaft or the swashplate, in particular by guiding shoes. In all cases the valve segment is rotationally fixed with respect to the casing of the hydraulic axial piston unit and comprises a kidney-shaped inlet port and a kid- ney-shaped outlet port for charging and discharging hydraulic fluid to the cylinder bores of the cylinder block. Both kidney-shaped ports are arranged on the valve segment in circumferential direction with regard to the rotational axis of the cylinder block and are forming respectively a kidney-shaped charge port and a kidney-shaped discharge port during the circular motion of the cylinder bores around the rotational axis. The radius and respectively the diameter of the central line of these kidney-shaped ports in the valve segment coincides with the reference circle of the centre points of the openings in the cylinder block bottom surface, which openings form the ends of fluid channels connecting the cylinder bores with the cylinder block bottom surface. These fluid channels can be parallel to the rotational axis of the cylinder block or can be inclined towards rotational axis of the cylinder block leading to a smaller diameter of the reference circle of the central lines of the kidney-shaped ports in the valve segment enabling thereby a reduced diameter of the valve segment. A reduced diameter of the valve segment allows a reduction of construction space;

In alternative embodiments the valve segment sliding surface contacting the cylinder block bottom surface can be formed planar leading to a disc-shaped valve segment or can be formed curved leading to a spherical-shaped valve segment sliding surface. In further embodiments in particular bearing plates made of bronze or a by a bimetal process can be rotationally fixed to the cylinder block bottom area forming the contact surface to the valve segment. In the other way round valve plates made of bronze or a by a bimetal process can be fix to the valve segment forming the valve segment sliding surface facing the cylinder block bottom surface. In both cases, i.e. using a rotating bearing plate or a still standing valve friction is reduced when these plates are made of bronze, or are bi-metal, or are of another material capable to reduce friction forces. In case of such a bearing plate fixed to the cylinder block bottom the bearing plate comprises passages connecting the cylinder bore openings with the kidney-shaped ports in the valve segment. In the other case, when a valve plate is used, the same have to show kidney- shaped passages in order to fluidly connect the openings in the bottom surface of the cylinder block bottom to the kidney-shaped ports in the valve segment.

In all cases, regardless if a disk-shaped valve segment or a spherical valve segment is used, in operation of the hydraulic axial piston unit the cylinder block rotates with respect to the stationary valve segment thereby causing different kinds of loads and stress to both important parts of a hydraulic axial piston unit, in particular to the valve segment and/or to the valve plate or the bearing plate. Furthermore, in operation of a hydraulic axial piston pump, one half of the number of cylinder bores is charged with high pressure and the other half is charged with low pressure, this provides on one hand for a tipping moment of the cylinder block leading to different friction conditions on either pressure side of the valve segment. On the other hand as the pressure pro- file in circumferential direction along the kidney-shaped ports is not constant, especially under high load conditions of the hydraulic axial piston unit, the valve segment can even be deformed in regions with pressure peaks. Seen in circumferential direction of the kidney-shaped ports, this leads to an uneven gap, i.e. to a non-constant distance between the cylinder block bottom surface and the valve segment sliding side. For a person with relevant skills in the art it is obvious that such varying conditions along the circumferential direction of the valve segment are not favourable for the operation of a hydraulic axial piston unit, as these conditions lead to losses in performance and robustness and lead to increased friction and wear on the sliding surfaces. CN 104 776 018 shows η-shaped grooves on the valve segment extending from the discharge port only towards the radial outer side, in order to provide fluid dynamic pressure lubrication to reduce leakage, vibration and noises between the valve segment and the cylinder block and to reduce the cylinder block tipping moment.

It is therefore an object of the invention to improve these non-constant gap conditions between the valve segment and the cylinder block, especially under high load conditions of the hydraulic axial piston unit, to improve the robustness and to reduce friction and wear of the involved parts of a hydraulic axial piston unit. Thereby, these improvements should be of simple design and effective for all type of hydraulic axial piston units. At the same time these improvements should be simple to be realized, to be implemented and cost effective. Furthermore, the inventive improvement should be capable to be applied in already existing hydraulic axis piston units. The object of the invention is solved by a valve segment of hydraulic axial piston units according to the general part of claim 1 , wherein the valve segment comprises a kidney-shaped first port and a kidney-shaped second port for providing in an alternating manner - depending on the rotational direction - a suction port and a discharge port for charging and discharging hydraulic fluid to and from cylinder bores of the cylinder block of the hydraulic axial piston unit. The valve seg- ment according to the invention is characterized in that the first port and the second port is formed rotationally symmetric with regard to a rotational axis of the cylinder block, and in that a plurality of concave formed hydrostatic bearing notches are extending at least from the radial outer edges of the first port and the second port on the sliding side of the valve segment which is facing the cylinder block. The inventive valve segment is further characterized in that each of the notches of the plurality of the hydrostatic bearing notches intersects with one of the first port or the second port.

Here, the sliding surface of the valve segment is sliding on the bottom surface of the cylinder block or on a bottom surface provided by a bearing plate fixed to the cylinder block bottom. In another embodiment a valve plate made of bronze or bi-metal or other friction reducing material can be fixed to the valve segment, wherein the sliding surface is formed on the valve plate side facing the cylinder block.

As the openings of the fluid channels which connect the kidney-shaped ports on the valve seg- ment with the cylinder bores in the cylinder block comprise the same radial width as the central line of the kidney-shaped ports, i.e. the radial outmost contour of these channels run on the out- er edge of the kidney-shaped ports, the hydrostatic bearing notches located at the radial outer side of the kidney-shaped ports provides for an improved hydrostatic relief and lubrication between the cylinder block bottom and the valve segment. According to the invention these hydrostatic bearing notches are located preferably in zones of the valve segment which are burden with the highest loads during operation of the hydraulic axial piston unit. These zones bearing the highest loads are usually located around half circumferential way of the kidney-shaped ports or half circumferential way between the outer dead point and the inner dead point of the reciprocating pistons in the cylinder bores. In a first embodiment of the invention at either port at least at the radial outer side one hydrostatic relief bearing notch is carried out at the mid portion of the circumferential length of each kidney-shaped port. In another embodiment more than one hydrostatic bearing notch is arranged, preferably an odd-numbered number of hydrostatic bearing notches equidistant to the one hydrostatic bearing notch located at the circumferential centre of a kidney-shaped port. In first trials of the inventive concept it has been found that 3 to 7 bearing notches arranged on the outer side of each kidney-shaped port provide with a reasonable result for reducing the frictional forces and wear between a bottom surface of the cylinder block and the sliding surface of a valve segment or of a valve plate. For a person with skills in the relevant art it is obvious that each number of hydrostatic bearing notches is applicable depending on the geometrical conditions and the performance conditions for which the hydraulic axial piston unit is designed for. Therefore it is also obvious that the hydrostatic bearing notches according to the invention can be arranged on either side of the kidney-shaped ports, i.e. also on the inner edge of these ports. As the biggest inventive effect of the hydrostatic bearing notches is achieved with the hydrostatic bearing notches arranged on the high pressure side kidney-shaped port it would not be sufficient for a hydraulic axial piston unit which is driven in only one rotational direction, to provide the inventive hydrostatic bearing notches on only the high pressure port of a valve segment, in order to achieve more steady load and friction conditions between the valve segment and the cylinder block. Therefore, for bi- directional driven hydraulic axial piston units the inventive introduction of hydrostatic bearing notches according to the invention should be carried out at both kidney-shaped ports of valve segment or the valve plate, as the suction port and the discharge port will change with the change of the rotational direction. A person with skills in the relevant art recognize easily that the opening size and the depth of the bearing notches depend on the scheduled use and performance of the hydraulic axial piston unit. One can imagine also using different sizes of bearing notches in one valve segment/valve plate at the same time, for instance having the biggest bearing notch at the circumferential central portion of the kidney-shaped port and decreasing the size of the bearing notches in the valve segment in direction to the regions corresponding to the dead points of the working piston motions.

Even though an odd number of bearing notches at the kidney-shaped ports of the valve segment or the valve plate is preferred a person with skills in the relevant art recognizes that also an even number of bearing notches is applicable in the sense of the invention. As the bearing notches according to the invention are located at the radial circumferential outer edge of the suction port and/or the discharge port, i.e. the high pressure port and/or the low pressure port, the opening(s) of the bearing notches facing towards the cylinder block are located in an area outside the fluid channel openings such that having a hydrostatic bearing effect on the involved parts, i.e. for the cylinder block/bearing plate bottom surface and the valve segment respectively the valve plate sliding surface. As mentioned before the cylinder block bottom surface can be formed by a bearing plate fixed to the cylinder block bottom surface. Thereby, the bearing plate rotates with the cylinder block. As mentioned before also, the hydrostatic bearing notches effectively provide a bearing effect of the cylinder block/bearing plate on the valve segment or on the valve plate, if such a valve plate is fixed to the valve segment, providing therewith an enhanced robustness of the valve segment and therewith for the whole hydraulic axial piston unit. At the same time friction forces and wear between the cylinder block and the valve segment are reduced, as hydrostatic bearings areas are formed between the valve segment sliding surface and the bottom surface of the cylinder block. Furthermore, the distance/the gap between the cylinder block and the valve segment seen in circumferential direction do not vary as much as between valve segments and cylinder blocks known from the state of the art.

Up to here the invention was detailed in general for the embodiment to introduce hydrostatic bearing notches in the sliding surface of the valve segment or the valve plate fixed to the valve segment in order to achieve a bearing and/or friction effect between the surfaces moving relatively to each other. The same bearing and lubrication effect to solve the underlying object of the invention is achieved too by - according to the embodiment of claim 1 1 - introducing the hydrostatic bearing notches to the bottom surface of the cylinder block. Here the hydrostatic bearing notches according to the invention extend radially outwards from the edges of the openings formed by the fluid channels in the cylinder block bottom surface. Here, each hydrostatic bearing notch intersects with one of the openings and is thereby fluidly connected to the fluid channels in the cylinder block for charging and discharging hydraulic fluid to and from the cylinder bores in the cylinder block. The hydrostatic bearing notches preferably extend radially outward with respect to the rotational axis of the cylinder block, however, preferably do not extend outside an outer sealing contour surrounding the opening in the bottom surface of the cylinder block. Thereby, as it is valid for the embodiment having the hydrostatic bearing notches on the sliding surface of the valve segment, the hydrostatic bearing notches can show a partial spherical, conical or tubular form having a rounded or chamfered radial outer end, wherein the depth of the hydrostatic bearing notches preferably decreases in the radial outer direction perpendicular to the rotational direction of the cylinder block. In an further embodiment according to the invention the hydrostatic bearing notches introduced to the cylinder block bottom surface or to the bearing plate bottom surface, neighbouring hydrostatic bearing notches can be fluidly connected to each other by means of a hydrostatic bearing groove running circumferentially on the corresponding surface connecting at least two hydrostatic bearing notches with each other.

Analogous to the aforementioned embodiment of fixing a friction reduction valve plate to the valve segment comprising the sliding surface, on the cylinder block bottom area a bearing plate, e.g. made of bronze or of a bi-metal material or any other friction reducing material, can be fixed to the cylinder block, which is turning with the cylinder block. If such a bearing plate is used the inventive hydrostatic bearing notches are introduced onto that surface facing the valve segment and thereby forms the bottom surface of the cylinder block. It is clear to a person with skills in the relevant art that this bottom surface can show a planar or spherical design depending on the general design of the hydraulic axial piston unit to which the invention is applied to. In general the invention can be applied to all kind of hydraulic axial piston units whether they are of the swashplate or the bent axis construction type. Thereby the inventive hydrostatic bearing notches can either be applied to the sliding surface of the valve segment respectively to a valve plate fixed to the valve segment, or to the bottom surface of the cylinder block respectively to a bearing plate fixed to the cylinder block. From this a person with skills in the relevant art derives easily that the invention can be applied also to spare parts for already existing hydraulic axial piston units or to rotating kits of such hydraulic axial piston units, in particular to those of the bent axis construction type.

In the following figures exemplary embodiments of hydraulic axial piston units having a valve segment or a cylinder block according to the invention are depicted in more detail, however, the invention is not limited to these embodiments. All features of the disclosed and illustrated em- bodiments may be combined in any desired combination with one another within the scope of invention. It is shown in:

Figure 1 a cross-sectional view of a hydraulic axial piston unit of the bent axis construction type;

Figure 2 a cross-sectional view of a hydraulic axial piston unit of the swashplate construction type; Figure 3 a plan view of a valve segment according to the state of the art;

Figure 4 a three dimensional view of a valve segment according to the invention,

Figure 5 a detailed view of the valve segment of Figure 4;

Figure 6 another embodiment of the valve segment of Figure 4 in a detailed view;

Figure 7 a plan view of a bottom surface of a cylinder block according to the invention; Figure 1 shows a hydraulic axial piston unit 1 of the bent axis construction type having a cylinder block 3 showing a rotational axis 5. In a plurality of cylinder bores 8 circumferentially arranged in parallel around the rotational axis 5 working pistons 4 can move reciprocally. Thereby, due to an angle between the rotational axis 5 and the axis of a shaft 6 each working piston 4 perform one (complete) stroke within its correspondent cylinder bore 8 (see also Figure 2). At the bottom of cylinder block 3, i.e. at the remote end of cylinder block 3 facing away from shaft 6 a valve segment 2 rotatable fixed with regard to the rotational axis 5 is located, which can be swiveled in conjunction with the cylinder block 3 to different displacement volumes of the hydraulic axial piston unit 1 . In the bent axis hydraulic axial piston unit 1 according to Figure 1 between valve segment 2 and cylinder block 3 a bearing plate 20 is fixed to the cylinder block 3 and rotates with cylinder block 3 such that friction forces occur in operation of the hydraulic piston unit 1 between valve segment 2 and bearing plate 20. As bearing plate 20 is commonly made of a bimetal material, like bronze, bearing plate 20 has a lower friction index and a better wear resistance as the commonly used steel or cast material of cylinder block 3. Here, bronze is used frequently as a preferred material for bearing plate 20 in order to avoid sticking problems be- tween the two surfaces which rub against each other. Needless to say that a valve plate 10 instead of bearing plate 20 fixed to the valve segment 2 constitutes an alternative embodiment for a friction reduced combination of valve segment 2 and cylinder block 3 for the bent axis hydraulic axial piston unit 1 according to Figure 1 .

In operation of the hydraulic axial piston unit 1 hydraulic fluid is supplied to and discharged from the cylinder bores 8 of cylinder block 3 via the valve segment 2. For this purpose valve segment 2 shows two kidney-shaped ports 1 1 , 21 extending in circumferential direction with respect to rotational axis 5 (see also Figures 4 to 6). As shown in more detail with the swashplate hydraulic axial piston unit 1 according to Figure 2, these kidney-shaped ports are in fluid connection with cylinder bores 8 of cylinder block 3 via fluid channels 35 in bearing plate 20.

Analogous to Figure 1 , Figure 2 shows a hydraulic axial piston unit 1 of the swashplate construction type having a cylinder block 3 with a rotational axis 5, which in this case is concentrically to the axis of shaft 6. Within the cylinder block 3 working pistons 4 are located in cylinder bores 8 and can move in direction of rotational axis 5 reciprocally. The reciprocal strokes of working pistons 4 are enabled by tilting of swashplate 30. On swashplate 30 the heads of the working pistons 4 are fixed in axial and radial direction with respect to rotational axis 5, however, rotationally free in circumferential direction. Such that each working pistons 4 fulfill one complete stroke in one complete revolution of the cylinder block 3 around rotational axis 5. Between the cylinder block 3 and an end plate 33 of casing 40 a valve segment 2 is located stationary with the casing 40 for guiding hydraulic fluid to and from the cylinder bores 8 in cylinder block 3 via fluid channels 36, which connect openings 35 in the bearing plate 20 with the cylinder bores 8 in cylinder block 3.

In an alternative embodiment bearing plate 20, which - according to the embodiment of Figure 2 - is fixed to cylinder block 3 can be replaced by a valve plate 20 being fixed to valve segment 2. In the latter embodiment sliding surface 7 would change to that side of valve plate 10 which faces the bottom surface 9 cylinder block 3, which is now the surfaces of the cylinder block 3, which faces the valve plate 10. In both embodiments the valve plate 10 as well as the bearing plate 20 preferably is made of a bi-metal or bronze in order to reduce friction between the sliding surface 7 and the bottom surface 9.

An example for such a valve segment 2 according to the prior art CN 104 776 018 and mentioned already before on page 3 is shown in Figure 3, showing a valve segment 2 for a hydraulic axial piston unit being drivable in only one rotational direction ω. The valve segment 2 according to the state of the art comprises kidney-shaped ports 1 1 , 21 wherein the kidney-shaped port 1 1 on the left side of Figure 3 builds an oil discharge outlet for discharging compressed oil out of the cylinder bores (not shown). On the other side, the right side, a non-symmetrical kidney- shaped inlet port 21 is shown with radially oriented straight control edges 15, 16 at the beginning and at the end of the inlet port 21 . η-shaped grooves are extending from discharge port 1 1 towards the radial outer side of the valve segment 2 to provide fluid dynamic pressure lubrication in order to reduce leakage between the valve segment 2 and the not shown cylinder block. With these single side η-shaped grooves hydrostatic relief is achieved on the high pressure side only, thereby augmenting the pressure load on the low pressure side, here the right side in Figure 3.

Figure 4 shows an embodiment of a valve segment 2 according to the invention showing two rotationally symmetric formed kidney-shaped ports 1 1 , 21 . The rotationally symmetric design allows the use of the inventive valve segment 2 in hydraulic axial piston units drivable in both rotational directions. On the respective outer sides of the kidney-shaped ports 1 1 , 21 hydrostatic bearing notches 50 are arranged for providing a hydrostatic relief of the bearing forces between a cylinder block 3 and the valve segment 2. Preferably the inventive arrangement of these hydrostatic bearing notches 50 on both kidney-shaped ports 1 1 and 21 provides for an effective compensation for the tipping moment of the cylinder block during operation of the hydraulic axial unit. In this embodiment shown in Figure 4 the hydrostatic bearing notches 50 are arranged in the circumferential mid portions of the kidney-shaped ports 1 1 and 21 , i.e. in zones of the highest pressure forces during operation of a hydraulic axial piston unit 1 . Figure 5 is a detailed view of the left kidney-shaped port 1 1 of Figure 4 showing in detail that the radial outer edges 52 of the hydrostatic bearing notches 50 do not extend radially outside the outer sealing contour 14 of valve segment 2. Thus, according to the invention it is possible to create a hydrostatic relief within the sealing contours of the outer sealing contour 14 and the inner sealing contour 13 in order to generate a pressure force balance between the suction side and the discharge side of the valve segment 2 of a hydrostatic axial piston unit 1 .

In Figure 6 another embodiment of the inventive hydrostatic bearing notches 50 is shown. Here, neighboring hydrostatic bearing notches 50 are fluidly connected to each other via hydrostatic bearing grooves 55 within the radial outer sealing contour 14 of the valve segment 2. Here, the hydraulic pressure is distributed evenly over all hydrostatic bearing notches 50 on the sliding surface 7 of the valve segment 2.

In particular from Figures 5 to 6 a person with skills in the relevant art can derive that the hydrostatic bearing notches 50 according to the invention can be distributed along the whole outer or inner edge 12 or 22 of the kidney-shaped ports 1 1 and 21 in order to improve the hydrostatic bearing conditions between the rotating cylinder block 3 and the stationary valve segment 2. A person with skills in the relevant art can derives further from this Figures that the hydrostatic bearing notches 50 can be of concave spherical or cylindrical or any other concave form porting within the sealing contours 13, 14 high and low pressurized hydraulic fluid to zones of the sliding surface 7 between the valve segment 2 and the cylinder block 3, which, in the state of the art, are not fed or supported by hydrostatic pressure.

Figure 7 shows a further embodiment according to the invention and, e.g. according to a hydraulic axial piston unit 1 shown in Figure 2. Shown is a bottom surface 9 of a cylinder block 3 comprising a plurality of cylinder bores 8, each of which are fluidly connected via fluid channels 36 to openings 35 at the bottom surface 9 of the cylinder block 3. A plurality of inventive hydrostatic bearing notches 50 is introduced to a bottom surface 9 of the cylinder block 3 or to a bearing plate 10 rotationally fixed to the cylinder block 3. Thereby the bottom surface 9 can be of a planar or spherical design. Each of the plurality of concave formed hydrostatic bearing notches 50 extends radially from the outer edge 37 of the openings 35 and intersects with one of the open- ings 35. Preferably the hydrostatic bearing notches 50 are formed within an outer sealing contour 14 surrounding the openings 35.

As mentioned above with the explanations given to Figure 4 - the embodiment comprising the inventive hydrostatic bearing notches in the sliding surface 7 of the valve segment 2 - the hydro- static bearing notches in the bottom surface 9 of cylinder block 3 can show also a partial spherical, conical or tubular form having a rounded or chamfered radial outer end 52. Thereby the depth of the hydrostatic bearing notches 50 can decrease in the radial outer direction perpendicular to the rotational direction 5. In Figure 7 it is shown - in an analogous way like in Figure 6 - that neighbouring hydrostatic bearing notches 50 can be connected fluidly to each other by means of a hydrostatic bearing groove 55.

Especially with the embodiments of Figures 4 and 7 a person with skills in the relevant art de- rives that the inventive hydrostatic bearing notches 50 can be introduced either to the bottom surface 9 of the cylinder block 3 or to the sliding surface 7 of valve segment 2. Same is valid if on the respective cylinder block 3 or the valve segment 2 a bearing plate 20 or a valve plate 10 is fixed thereto. A person with skills in the relevant art further derives, in particular from Figure 4 that the inventive hydrostatic bearing notches 50 can be applied a rotating kit 60 too, e.g. com- prising a valve segment 2, a bearing plate 10, a cylinder block 3 with working pistons 4 arranged therein, and a shaft 6. Such a person easily understands from these explanations that the inven- tion is also applicable to spare parts for valve segments 2, valve plate 10, cylinder blocks 3 and or bearing plates 20.

Finally, a person with skills in the relevant art easily understands from these explanations too that the invention is also applicable to spare parts for valve segments 2, valve plates 10, cylinder blocks 3 and/or bearing plates 20.

List of reference numbers

Hydraulic axial piston unit 30 Swashplate

Valve segment 32 Bottom area cylinder block

Cylinder block 33 Endplate

Working piston

Rotational axis 35 Openings

Shaft 36 Fluid channels

Sliding surface 37 Outer edge

Cylinder bore

Bottom surface 40 Casing

Valve plate

First kidney-shaped port 50 Hydrostatic bearing notch

Outer edge

Inner sealing contour 52 Radial outer end

Outer sealing contour

Initial control edge 55 Bearing groove

Closing control edge

Bearing plate 60 Rotating kit

Second kidney-shaped port

Inner edge 100 η-shaped Grooves

Claims

1 . Valve segment (2) for a hydraulic axial piston unit (1 ), comprising a kidney-shaped first port (1 1 ) and a kidney-shaped second port (21 ) formed in the valve segment (2) for providing a suction port and a discharge port for charging and discharging hydraulic fluid to and from openings (35) of fluid channels (36) in a cylinder block (3) of a hydraulic axial piston unit (1 ), characterized in that

the first port (1 1 ) and the second port (21 ) are formed rotationally symmetric with regard to a rotational axis (5) of the cylinder block (3),

a plurality of concave formed hydrostatic bearing notches (50) are extending radially outwards from the radial outer edges (12, 22) of the first port (1 1 ) and the second port (21 ) on a sliding surface (7) of the valve segment (2), and

each of the plurality of hydrostatic bearing notches (50) intersects with one of the first port (1 1 ) or the second port (21 ).

2. Valve segment (2) according to claim 1 , wherein the hydrostatic bearing notches (50) are formed within an outer sealing contour (14) surrounding the first port (1 1 ) and the second port (21 ).

3. Valve segment (2) according to claim 1 or 2, wherein the hydrostatic bearing notches (50) show a partial spherical, conical or tubular form having a rounded or chamfered radial outer end (52).

4. Valve segment (2) according to one of the preceding claims, wherein the depth of the hydrostatic bearing notches (50) decreases in a radial outer direction perpendicular to the rotational direction (5).

5. Valve segment (2) according to one of the preceding claims, wherein the sliding surface (7) is located on a valve plate (10) fixed to the valve segment (2).

6. Valve segment (2) according to one of the preceding claims, wherein neighbouring hydrostatic bearing notches (50) associated with either the first port (1 1 ) or the second port (21 ) are fluidly connected to each other by means of a hydrostatic bearing groove (55).

7. Valve segment (2) according to one of the preceding claims, wherein an odd-number of hydrostatic bearing notches (50) is associated with one of the first port (1 1 ) and the second port (21 ).

8. Valve segment (2) according to one of the preceding claims, wherein hydrostatic bearing notches (50) are located also on the inner edge of the first port (1 1 ) and/or the second port (21 ).

9. Valve segment (2) according to one of the preceding claims, wherein the valve segment (2) shows a planar or spherical design.

10. Hydraulic axial piston unit (1 ) comprising a valve segment (2) according to one of claims 1 to 9.

1 1 . Cylinder block (3) for a hydraulic axial piston unit (1 ), comprising a plurality of cylinder bores (8) arranged around a rotational axis (5) and fluidly connected via fluid channels (36) to openings (35) at a bottom surface (9) of the cylinder block (3), wherein the openings (35) are provided for charging and discharging hydraulic fluid to and from the cylinder bores (8),

characterized in that

on the bottom surface (9) a plurality of concave formed hydrostatic bearing notches (50) are extending radially outwards from outer edges (37) of the openings (35), and each of the plurality of hydrostatic bearing notches (50) intersects with one of the openings (35).

12. Cylinder block (3) according to claim 1 1 , wherein the hydrostatic bearing notches (50) are formed within an outer sealing contour (14) surrounding the openings (35).

13. Cylinder block (3) according to claim 1 1 or 12, wherein the hydrostatic bearing notches (50) show a partial spherical, conical or tubular form having a rounded or chamfered radial outer end (52).

14. Cylinder block (3) according to one of claims 1 1 to 13, wherein the depth of the hydrostatic bearing notches (50) decreases in the radial outer direction perpendicular to the rotational direction (5).

15. Cylinder block (3) according to one of claims 1 1 to 14, wherein neighbouring hydrostatic bearing notches (50) are fluidly connected to each other by means of a hydrostatic bearing groove (55).

16. Cylinder block (3) according to one of claims 1 1 to 15, wherein the bottom surface (9) is located on a bearing plate (20) rotationally fixed to the cylinder block (3).

17. Cylinder block (3) according to one of claims 1 1 to 15, wherein the bottom surface (9) shows a planar or spherical design.

18. Hydraulic axial piston unit (1 ) comprising a cylinder block (3) according to one of claims 1 1 to 17.

19. Rotating kit for a hydraulic axial piston unit (1 ) of the bent axis construction type, comprising a cylinder block (3) according to one of claims 1 1 to 17.