Hydrostatic positive displacement machine

Abstract

A hydrostatic positive displacement machine has a cam ring for adjusting the displacement volume thereof. This cam ring is guided in translation by approximately diametrically arranged outer circumferential surface segments on associated inner surface segments of a housing of the positive displacement machine.

Claims

1. A hydrostatic positive displacement machine, comprising: a housing; a rotor mounted in the housing so as to be rotatable about an axis of rotation, said rotor being fitted with radially movable space dividers; and a cam ring having an inner circumferential surface on which the space dividers are supported, wherein an annular space is formed between the rotor and the cam ring, said annular space being subdivided by the space dividers into hydrostatic working spaces configured to revolve with the rotor and be brought alternately into pressure medium connection with a high pressure and a low pressure, wherein the cam ring has approximately diametrically arranged outer circumferential surface segments configured to guide the cam ring in a straight line translation transversely to the axis of rotation on associated inner surface segments of the housing, wherein at least one of the outer circumferential surface segments has a first surface portion directly opposite a second surface portion of an associated inner surface segment which does not mirror the second surface portion in a load-free mode of the positive displacement machine, wherein the first surface portion is non-planar and the second surface portion is planar.

2. The positive displacement machine according to claim 1, wherein a contact area of the second l surface portion with the first surface portion is approximately equal to the second surface portion in a loaded mode.

3. The positive displacement machine according to claim 1, wherein a surface pressure between the at least one of the outer circumferential surface segments and the inner surface segment is distributed in a spatially uniform manner in a loaded mode.

4. The positive displacement machine according to claim 1, wherein the first surface portion is produced by one of erosion and 3-D milling such that a surface pressure is distributed in a spatially uniform manner.

5. The positive displacement machine according to claim 1, further comprising: a low-pressure duct fixed in relation to the housing; and a high-pressure duct fixed in relation to the housing, wherein the low-pressure duct and the high-pressure duct open into said annular space, and wherein the at least one of the outer circumferential surface segment is arranged adjacent to a mouth of the high-pressure duct and remote from a mouth of the low-pressure duct.

6. The positive displacement machine according to claim 1, wherein cross sections of the at least one of the outer circumferential surface segment are one of cambered and convex transversely to the axis of rotation in a load-free mode.

7. The positive displacement machine according to claim 1, wherein longitudinal sections of the at least one of the outer circumferential surface segment are hollow or concave along the axis of rotation in a load-free mode.

8. The positive displacement machine according to claim 1, wherein a length of the at least one of the outer circumferential surface segment in a translatory direction is approximately equal to or greater than a length of a projection of the inner circumferential surface in a plane defined by the translatory direction.

9. The positive displacement machine according to claim 1, wherein a hydrostatic relief field is provided between the at least one of the outer circumferential surface segment and the inner surface segment.

10. The positive displacement machine according to claim 1, wherein a length of the at least one of the outer circumferential surface segment in a translatory direction is approximately equal to or greater than a length of a projection of the inner circumferential surface in a plane defined by the translatory direction.

11. A hydrostatic positive displacement machine, comprising: a housing; a rotor mounted in the housing so as to be rotatable about an axis of rotation, said rotor fitted with radially movable space dividers; and a cam ring having an inner circumferential surface on which the space dividers are supported, wherein an annular space is formed between the rotor and the cam ring, said annular space subdivided by the space dividers into hydrostatic working spaces configured to revolve with the rotor and be brought alternately into pressure medium connection with a high pressure and a low pressure, wherein the cam ring has approximately diametrically arranged outer circumferential surface segments configured to guide the cam ring in translation transversely to the axis of rotation on associated inner surface segments of the housing, wherein at least one of the outer circumferential surface segments has a non-planar surface directly opposite the associated inner surface segment in a load-free mode of the positive displacement machine, wherein longitudinal sections of the at least one of the outer circumferential surface segment are hollow or concave along the axis of rotation in a load-free mode, wherein the at least one of the outer circumferential surface segments has a first surface portion directly opposite a second surface portion of the associated inner surface segment which does not mirror the second surface portion of the associated inner surface segment in a load-free mode of the positive displacement machine, and wherein a contact area of the second surface portion with the first surface portion is approximately equal to the second surface portion in a loaded mode.

12. The hydrostatic positive displacement machine of claim 11, wherein the outer circumferential surface segments are configured to guide the cam ring in a straight line translation transversely to the axis of rotation on associated inner surface segments of the housing.

13. The positive displacement machine according to claim 11, wherein a surface pressure between the at least one of the outer circumferential surface segments and the inner surface segment is distributed in a spatially uniform manner in a loaded mode.

14. The positive displacement machine according to claim 11, wherein the at least one of the outer circumferential surface segments is produced by one of erosion and 3-D milling such that a surface pressure is distributed in a spatially uniform manner.

15. The positive displacement machine according to claim 11, further comprising: a low-pressure duct fixed in relation to the housing; and a high-pressure duct fixed in relation to the housing, wherein the low-pressure duct and the high-pressure duct open into the annular space, and wherein the at least one of the outer circumferential surface segment is arranged adjacent to a mouth of the high-pressure duct and remote from a mouth of the low-pressure duct.

16. The positive displacement machine according to claim 11, wherein cross sections of the at least one of the outer circumferential surface segment are one of cambered and convex transversely to the axis of rotation in a load-free mode.

17. The positive displacement machine according to claim 11, wherein a hydrostatic relief field is provided between the at least one of the outer circumferential surface segment and the inner surface segment.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) A number of illustrative embodiments of a hydrostatic positive displacement machine according to the disclosure are shown in the drawings. The disclosure will now be explained in greater detail by means of the figures of said drawings, wherein:

(2) FIG. 1 shows a first illustrative embodiment in a cross section,

(3) FIG. 2 shows a topology of a cam ring of a conventional positive displacement machine in an unloaded mode and the deformation thereof in the loaded mode, in a cross section,

(4) FIG. 3 shows a topology of a first illustrative embodiment of a cam ring of the positive displacement machine from FIG. 1 in the unloaded mode, in a cross section,

(5) FIG. 4 shows a topology of a second illustrative embodiment of a cam ring in the unloaded mode, in a longitudinal section,

(6) FIG. 5 shows a topology of a third illustrative embodiment of a cam ring in the unloaded mode, in a longitudinal section, and

(7) FIG. 6 shows a topology of a fourth illustrative embodiment of a cam ring in the unloaded mode, in a cross section.

DETAILED DESCRIPTION

(8) It may be assumed that components or structural parts which remain the same throughout the figures and illustrative embodiments are provided with the same reference signs.

(9) According to FIG. 1, a positive displacement machine 1 is configured as a vane pump. The vane pump 1 has a housing 2, in which a drive shaft 4 is accommodated in a rotatably mounted manner. Connected for conjoint rotation to the drive shaft 4 is a rotor 6, which has circumferentially uniformly distributed radial recesses 8, each of which is fitted with a space divider 10 configured as a vane. In this arrangement, the vanes 10 are accommodated in a sliding manner in the radial recesses 8 and preloaded radially outwards.

(10) The rotor 6 is surrounded radially by a cam ring 12 having a substantially circular-cylindrical inner circumferential surface, with the result that an annular space 14 is formed between said cam ring and the rotor 6. The vanes 10 are supported radially on the outside on an inner circumferential surface 34 of the cam ring 12. In this way, the annular space 14 is subdivided into hydrostatic working spaces 18 by the vanes 10. In pressure medium connection with the annular space 14 there is a low-pressure duct 20 of a low-pressure connection 22 of the positive displacement machine 1 and a high-pressure duct 24 of a high-pressure connection 26 of the positive displacement machine 1. Here, mouths 28, 30 of the pressure medium ducts 20, 24 extend approximately in a kidney shape on both sides of an axis of rotation 32 of the drive shaft 4.

(11) The cam ring 12 is mounted for translation transversely to the axis of rotation 32 in the housing 2. In this way, the displacement volume of the positive displacement machine 1 can be adjusted since the eccentricity of the inner circumferential surface 34, on the which the vanes 10 are supported, with respect to the axis of rotation 32 can be varied by moving the cam ring 12.

(12) Radially on the outside, the cam ring 12 has a predominantly circular-cylindrical outer circumferential surface 38, which has two diametrically arranged, flattened outer circumferential surface segments 40 and 42. Both outer circumferential surface segments 40, 42 extend substantially parallel to sliding axis 44 of the cam ring 12. By means of the outer circumferential surface segments 40, 42, the cam ring 12 is guided in a sliding manner on corresponding inner surface segments 46, 48 of the housing 2.

(13) To illustrate the problems solved by the positive displacement machine 1 according to the disclosure, FIG. 2 shows a partial section through a conventional positive displacement machine 1 having a conventional cam ring 12. FIG. 2 shows the housing 2 and the conventional cam ring 12 in the region of its outer circumferential surface segment 42 and the inner surface segment 48 in the loaded operating state, in which the high-pressure kidney-shaped port 30 is supplied with high pressure present at the high-pressure connection 26. Accordingly, the high pressure is present in those working spaces which are in pressure medium connection with the high-pressure kidney-shaped port and acts on the inner circumferential surface of the cam ring 12.

(14) It should be noted that, to illustrate the disclosure, the following topologies or deformations which deviate from a plane are shown on an exaggerated scale.

(15) Starting from its topology 42 which is planar or flat in the unloaded mode, the outer circumferential surface segment 42 shown in FIG. 2 is deformed radially inwards with a maximum deformation s when the inner circumferential surface is subjected to pressure, whereby the cam ring 12 is then in contact with the inner surface segment 48 only with its end regions 50as viewed in the direction of the sliding axis. For force transmission from the conventional cam ring 12 to the housing 2, there is thus only a relatively small proportion of the planar topology 42 still available. For this reason, a surface pressure between the resulting outer circumferential surface segment 42 and the inner surface segment 48 is increased, leading to increased wear.

(16) FIG. 3 shows the cam ring 12 according to the disclosure of the positive displacement machine 1 from FIG. 1 in a cross section transversely to the axis of rotation 32. The topology of the outer circumferential surface segment 42 according to the disclosure is made cambered, oppositely to the above-described deformation s, at +s. Here, the outer circumferential surface segment 42 has been provided with a radius r by means of external circular grinding. If the inner circumferential surface 34 is then subjected to the force symbolized by the arrow, there is in principle an approximately concave deformation of the kind already known from the conventional outer circumferential surface segment 42 shown in FIG. 2. Owing to the cambered or convex embodiment of the outer circumferential surface segment 42, however, a substantially planar shape of the outer circumferential surface segment 42 is obtained according to the disclosure in the case of load, corresponding approximately to the planar topology 42 shown in FIG. 3.

(17) FIG. 4 shows a longitudinal section, taken along the axis of rotation 32, of a second illustrative embodiment of a cam ring 112 according to the disclosure. The sliding direction (y) of the cam ring 112 is consequently aligned perpendicularly to the plane of view. Like the cam ring 12 shown in FIG. 3, the cam ring 112 shown in FIG. 4 shows the cross-sectional camber discussed. Since the force illustrated as an arrow in FIG. 4 and acting on the inner circumferential surface 34 would lead, starting from an imagined planar outer circumferential surface segment, to convex longitudinal sections and, as a consequence, to a reduced contact stress between the outer circumferential surface segment 142 and the inner surface segment 48, projections of cam ring 112 are arranged in the edge regions in this development. When subjected to load, outer circumferential surface segment 142 then deforms again in the direction of the planar topology 42.

(18) FIG. 5 shows a third illustrative embodiment of an outer circumferential surface segment 242 according to the disclosure of optimized topology, the cross sections of which, as already described, are of cambered design, and the longitudinal sections of which, as shown in FIG. 5 (along the axis of rotation 32) have a relief configured to a specific operating point of the positive displacement machine. Reliefs of this kind can be produced by means of 3-D milling or profile grinding, for example.

(19) FIG. 6 shows a fourth illustrative embodiment of a cam ring 312 having an outer circumferential surface segment 342 according to the disclosure of optimized topology. Outer circumferential surface segment 342 is also ground with the aid of the abovementioned 3-D milling or profile grinding to a topology optimized for one operating point. Moreover, a length L of outer circumferential surface segment 342, measured in a translatory direction (y), is greater than a length l of a projection of the inner circumferential surface 34 onto a plane defined by the translatory direction (y), transversely to the axis of rotation 32. In this way, the force acting on the inner circumferential surface 34, which is symbolized as an arrow, can be transferred via the relatively large outer circumferential surface segment 342 to the inner surface segment 48, thereby further reducing the contact stress.

(20) A disclosure is made of a hydrostatic positive displacement machine, which is preferably configured on the vane or roller-cell principle. Here, a rotor fitted with vanes or rollers is mounted so as to be rotatable about an axis of rotation in a housing of the positive displacement machine. The vanes or rollers acting as space dividers are supported on an inner circumferential surface of a cam ring, wherein an annular space is formed between the rotor and the cam ring, said annular space being subdivided by the space dividers into hydrostatic working spaces. For translatory guidance of the cam ring transversely to the axis of rotation, said ring has outer circumferential surface segments, via which it is supported movably on associated inner surface segments of the housing. According to the disclosure, at least one of the outer circumferential surface segments has a topology which deviates from that of a plane in a load-free mode of the positive displacement machine.

LIST OF REFERENCE SIGNS

(21) 1 hydrostatic positive displacement machine 1 conventional hydrostatic positive displacement machine 2 housing 4 drive shaft 6 rotor 8 radial recess 10 space divider 11 cam ring 12 conventional cam ring 14 annular space 18 working space 20 low-pressure duct 22 low-pressure connection 24 high-pressure duct 26 high-pressure connection 28 low-pressure kidney-shaped port 30 high-pressure kidney-shaped port 32 axis of rotation 34 inner circumferential surface 36 adjusting device 38 outer circumferential surface 40, 42 outer circumferential surface segment 42 conventional, loaded outer circumferential surface segment 42 planar topology of outer circumferential surface segment 44 sliding axis 46, 48 inner surface segment r radius of camber l length of projection L length of outer circumferential segment