Patent Application
20220074396
This application claims priority under 35 U.S.C. ยง 119 to application no. DE 10 2020 211 284.3, filed on Sep. 9, 2020 in Germany, the disclosure of which is incorporated herein by reference in its entirety.
The disclosure relates to a hydrostatic axial piston machine, in particular an axial piston pump, of swash plate construction. The axial piston machine has a housing, a drive shaft rotatably mounted in the housing, a cylinder drum connected to the drive shaft in a rotationally secure manner and having displacement pistons, a swash plate, which is mounted in the housing and has a face on which the displacement pistons are supported and the angular position of which with respect to the axis of rotation of the drive shaft and of the cylinder drum can be varied in order to adjust the swept volume by pivoting the swash plate about a pivot axis. For pivoting the swash plate, there is an adjusting device having an adjusting cylinder, which extends longitudinally substantially in the direction of the axis of rotation of the drive shaft and is located on one side of the drive shaft and of the cylinder drum, and having a double-acting adjusting piston, which can be moved longitudinally in the adjusting cylinder and which comprises a piston and a piston rod, which is connected in a fixed manner to the piston, is guided in a guide bore adjoining the adjusting cylinder and is articulated to the swash plate.
DE 10 2014 211 965 A1 discloses an axial piston pump in which use is made of two single-acting adjusting pistons to adjust the swash plate to a larger swivel angle and to a smaller swivel angle, of which adjusting pistons a first, larger adjusting piston adjoins an actuating chamber for which the inflow and the outflow of pressure fluid is controlled by means of a control valve, and of which adjusting pistons a smaller adjusting piston, also referred to as an opposing piston, adjoins a second actuating chamber, which is permanently connected to the high-pressure side of the axial piston pump, in which therefore high pressure is constantly present during operation. In this case, the longitudinal axes of the two adjusting pistons run parallel to the axis of the drive shaft of the axial piston pump. The adjusting pistons rest by means of a bearing surface against a respective sliding shoe, which is mounted on a ball journal inserted into the swash plate so as to be pivotable in all directions. A movement in a plane perpendicular to the axis of the drive shaft is possible between the bearing surface of an adjusting piston and the associated sliding shoe when the swash plate is adjusted.
In a hydrostatic axial piston pump known from DE 103 51 473 A1, the swash plate can be pivoted about a pivot axis which is at a distance from the axis of rotation of the drive shaft and of the cylinder drum. The swash plate can be pivoted in one direction by a single-acting adjusting piston and in the opposite direction by the drive mechanism forces and a helical compression spring. Although the axial piston pump has an adjusting device of low complexity here, it has disadvantages with regard to some functionalities, such as a limited force level for adjustment and limited pivotability of the swash plate through a zero position.
DE 1 908 234 A discloses a hydrostatic axial piston pump of swash plate construction in which, in order to adjust the swept volume, the swash plate is pivoted with the aid of a double-acting adjusting piston. The adjusting piston adjoins a first actuating chamber, for which the inflow and the outflow of pressure fluid is controlled by means of a control valve, and adjoins an annular actuating chamber of smaller cross section, in which a high pressure is constantly present. The piston of the adjusting piston can be moved only in a straight line and cannot be tilted and is motionally coupled in a complicated manner to the swash plate by means of a coupling rod, which is connected to the piston via a first swivel joint and to the swash plate via a second swivel joint.
DE 37 14 888 C2 discloses a hydrostatic axial piston machine of swash plate construction which has a double-acting annular adjusting piston which surrounds the cylinder drum and which comprises a circular cylindrical bushing that is guided at both ends in the direction of the axis of rotation of the drive shaft and carries on the outside a ring which divides an annular space between the housing and the bushing into two actuating chambers. The bushing of the adjusting piston is motionally coupled to the swash plate via a ball joint and a sliding joint. The sliding joint is formed between a driver pin on the swash plate and a spherical bushing, which is movable on the driver pin in the axial direction thereof. The ball joint is formed between the spherical bushing and an internally spherically formed retaining ring, which is inserted into the adjusting piston bushing and receives the spherical bushing. Here, therefore, surface contact between the spherical bushing and the retaining ring and thus the adjusting piston is sought.
The object underlying the disclosure is that of developing a hydrostatic axial piston machine of the type described at the outset in such a way that the adjusting device is of simple and inexpensive construction and requires little installation space.
This object is achieved for a hydrostatic axial piston machine of the type specified at the outset in that the joint between the adjusting piston and the swash plate is a movable swivel joint, which comprises a joint body receptacle on one part and a joint body on the other part of the two parts comprising the adjusting piston and the swash plate, and in that the joint body is closely guided in the joint body receptacle in the direction of movement of the adjusting piston, can be rotated about an axis of rotation running parallel to the pivot axis and can be moved with a directional component perpendicular to the direction of movement of the adjusting piston and perpendicular to the axis of rotation. According to the disclosure, only linear contact is provided between the joint body and the joint body receptacle. There is no component with a cylindrically or spherically curved inner surface against which the joint body would rest over an extended area. As a result, the articulated connection between the adjusting piston and the swash plate is of simple configuration and can be produced inexpensively. Moreover, assembly is simple because, with the adjusting piston already inserted, the joint body can easily be pushed into the joint body receptacle when the swash plate is inserted.
A hydrostatic axial piston machine according to the disclosure can be further developed in an advantageous manner.
The joint body receptacle is preferably located in the adjusting piston and the joint body is preferably located on the swash plate. An adjusting piston provided with a joint body receptacle, i.e. with a recess, can easily be inserted into the adjusting cylinder. Thereafter, there is no longer need for manipulations of the adjusting piston. The swash plate, on the other hand, can easily be assembled with a projecting joint body.
Even if the adjusting cylinder and the adjusting piston are arranged in such a way that the adjusting piston is movable not parallel but slightly obliquely to the axis of rotation of the drive shaft, it is preferred that the joint body receptacle located in the adjusting piston extends perpendicularly to the direction of movement of the adjusting piston, thus enabling the joint body to be moved in the joint body receptacle perpendicularly to the direction of movement of the adjusting piston. The force which is necessary for adjusting the swash plate thus acts on the adjusting piston in the longitudinal direction thereof.
It is conceivable for the joint body to be a roller which extends into an elongate joint body receptacle. However, the joint body preferably has a spherical surface. The joint body receptacle is a receiving hole whose diameter, in accordance with a clearance fit, is slightly larger than the diameter of the spherical surface and into which the joint body enters by means of the spherical surface.
The joint body can be a ball journal, which is fastened, in particular, to the swash plate, in particular being pressed in or screwed in. Alternatively, it is also possible for a ball to be machined directly on the swash plate.
The joint body can also be a spherical cap bearing, i.e. a bushing with a spherical outer surface, which is held on a journal, in particular of the swash plate.
The receiving hole for a spherical joint body is preferably designed as a blind hole, thus ensuring that the adjusting piston still has sufficient stability in the region of the receiving hole. To ensure that no excess pressure or reduced pressure builds up between the joint body having the spherical surface and the bottom of the receiving hole during a movement of the joint body, the region of the receiving hole located in front of the joint body is fluidically connected to the interior of the housing.
In particular, a relief hole, the diameter of which is substantially smaller than the diameter of the receiving hole, leads outwards through material of the adjusting piston from the region of the receiving hole located in front of the joint body. Thus, there is no need for a groove in the surface of the joint body to relieve said region.
The receiving hole is preferably located in an axial plane which passes through the longitudinal axis of the adjusting piston, i.e. the axis of the receiving hole intersects the longitudinal axis of the adjusting piston. The spherical surface of the joint body is then advantageously arranged at such a distance from the pivot axis of the swash plate that the longitudinal axis of the adjusting piston extends at a distance outside the circular arc on which the center of the spherical surface of the joint body moves when the swash plate pivots. This can also be ensured, in the case of an adjusting piston arranged obliquely with respect to the axis of rotation of the drive shaft, if the joint body is arranged on the swash plate in such a way that, when the swash plate is pivoted from a first extreme position into a second extreme position, the distance between the center of the spherical surface of the joint body and the central axis of the adjusting piston initially decreases and then increases again.
The piston rod is not guided in every position over its entire length by the guide bore since the outlay for producing a straight guide bore increases with the length of the guide bore. The guide bore is preferably only long enough that the piston rod still projects beyond the guide bore when it is completely retracted, thus ensuring that the length of guidance of the piston rod in the guide bore is independent of the position of the adjusting piston. However, it is advantageous if the length of guidance of the piston rod in the guide bore is greater on the side remote from the cylinder drum than on the side close to the cylinder drum. At its end remote from the adjusting cylinder, the guide bore therefore ends at different distances from the adjusting cylinder. As a result, a tilting moment acting on the adjusting piston is well absorbed. This is based on the consideration that the pressure acting in a fluid chamber on the piston section of the adjusting piston decreases to the housing pressure via the gap between the guide bore and the piston rod. The longer the gap, the greater the force generated by the pressure in the gap. By means of a different length of guidance and thus gap length, it is therefore possible to generate a resultant transverse force acting on the adjusting piston.
The piston of the adjusting piston can have on the outside an annular groove in which there is a piston ring resting against the wall of the adjusting cylinder. The guidance for the adjusting piston is thus provided solely by the piston rod on a single diameter, and therefore no stiffness is to be expected.
If an axial piston machine according to the disclosure is (also) operated as an axial piston pump, then preferably at least one return spring designed as a helical compression spring is present, which is arranged in front of the piston rod in a receptacle of the housing and is clamped between the housing and the piston rod of the adjusting piston and the axis of which coincides with the axis of the adjusting piston. The return spring is thus loaded in a purely linear manner. Its two ends are supported on mutually parallel surfaces. The return spring ensures that the swash plate assumes a preferred position, preferably a fully pivoted-out position, when the axial piston machine is out of operation. At the beginning of operation, the axial piston machine delivers immediately, thus enabling a pressure build-up.
Two exemplary embodiments of an axial piston machine according to the disclosure of swash plate construction are illustrated in the drawings. The disclosure is now explained in greater detail with reference to the figures of these drawings.
In the drawings:
First of all, the embodiment shown in
The hydrostatic axial piston machine according to
The axial piston machine has a drive shaft 15, which is mounted rotatably about an axis of rotation 18 by means of a first taper roller bearing 16, which is inserted into the bottom 17 of the housing pot 11, and a second taper roller bearing (not shown), which is accommodated by the connection plate 12. A cylinder drum 19 is connected to the drive shaft 15 in a rotationally secure but axially movable manner and has an odd number, for example nine, of piston bores 20, which are arranged at equal angular spacings on a pitch circle and are aligned parallel to the axis of rotation 18 and are open with their entire cross section towards the end of the cylinder drum 19 remote from the connection plate 12 while, at the end of the cylinder drum facing the connection plate 12, they open into arcuate orifice slots 21 lying on the same pitch circle.
Arranged between the cylinder drum 19 and the connection plate 12 is a distributor plate 25, which is held non-rotatably with respect to the connection plate 12 and which has two kidney-shaped control apertures in the form of circular arcs, which are not visible in the section according to
A displacement piston 26 is accommodated in each piston bore 20 and carries a sliding shoe 27, which is movable in all directions, on a piston head located outside the piston bore 20. Via its sliding shoe, each displacement piston 26 rests against a face 34 of a swash plate 35, which is mounted pivotably about a pivot axis 36 in two bearing shells inserted into the housing pot 11. The pivot axis 36 intersects the axis of rotation 18 of the drive shaft 15 at a right angle and extends perpendicularly to the plane of the drawing of
To ensure that, after a displacement stroke during which they are pushed into the piston bores 20, the displacement pistons 26 remain securely on the face 34 of the swash plate 35 and move out of the piston bores in the suction stroke, a retraction plate 40 rests on a shoulder of the sliding shoes 27 and bears with a central rim hole 41 against a retraction ball 42, which is constructed in the manner of a spherical layer and is coupled in a rotationally secure but axially movable manner to the drive shaft 15. A helical compression spring, which is omitted in
To change the angular position of the swash plate 35, the axial piston machine has an adjusting device 45, which comprises a double-acting adjusting piston 46, which is designed as a differential piston with two effective surfaces of different sizes, the larger of which is referred to as the actuating surface 47 and the smaller one as the counter surface 48. The adjusting piston 46 has a piston section 49 on which the effective surfaces are formed, and a piston rod 50, which projects away from the piston section 49 on one side. The piston section 49 and the piston rod 50 of the adjusting piston 46 can be moved rectilinearly in the longitudinal direction in a stepped housing bore 51 extending slightly obliquely to the axis of rotation 18 of the drive shaft 15, the piston section 49 being located in the bore section 52 of the housing bore 51 which has the larger diameter and forms an adjusting cylinder, while the piston rod 50 is guided in a longitudinally movable manner in the bore section 53 with the smaller diameter. The central axis 54 of the housing bore 51 and of the adjusting piston 46 is drawn as a dashed line in
Bore section 53 has a length such that, even when the piston rod 50 is completely retracted, it still projects by a certain distance beyond bore section 53 and projects into a section 55 of the housing bore 51 in which the diameter is slightly larger than in bore section 53. The piston rod 50 is thus always guided over the same length, irrespective of the position of the adjusting piston.
The piston section 49 of the adjusting piston 46 divides bore section 52 of the housing bore 51 into an actuating chamber 56, the cross section of which corresponds to bore section 52 and the actuating surface 47 of the adjusting piston 46, and into a counter chamber 57, which has an annular cross section, the outside diameter of which is equal to the diameter of bore section 52 and the inside diameter of which is equal to the outside diameter of the piston rod 50 and which corresponds to the counter surface 48 of the adjusting piston 46. The actuating surface 47 is approximately three times as large as the counter surface 48. The counter chamber 57 is permanently fluidically connected to the pressure connection of the axial piston machine. Thus, it is the high pressure which prevails in the counter chamber 57. This pressure generates a force on the annular counter surface 48 of the adjusting piston 46 which acts in the direction of retraction of the piston rod 50. A piston ring 58 is inserted into a circumferential annular groove of the piston section 49 in order to seal the actuating chamber 56 and the counter chamber 57 from one another.
The length of guidance and thus also the gap length between bore section 53 and the piston rod 50 are greater on the outside of bore section 53 than on the inside located toward the interior of the housing 10. Accordingly, the gap length over which the pressure acting in the counter chamber 57 decreases to the housing pressure is also greater on the outside than on the inside. In
The housing bore 51 is closed off from the outside by a screw plug 60.
The actuating chamber 56 can be controlled by a single or by a plurality of control valves, which connect the actuating chamber to a pressure fluid source or to a tank, or shut off the actuating chamber both from the pressure fluid source, which can also be formed by the pressure connection of the machine, and from the tank. When the actuating chamber 56 is connected to a pressure fluid source, pressure fluid flows to the actuating chamber and the piston rod 50 is extended. When the actuating chamber 53 is connected to the tank, pressure fluid can be displaced out of the actuating chamber and the piston rod 50 is retracted. When the actuating chamber 56 is shut off, the piston rod remains at rest.
A blind hole 65 extending perpendicularly to the central axis 54 is introduced into the piston rod 50 of the adjusting piston 46 close to the free end and extends perpendicularly to the central axis 54, from which hole a smaller hole 66 leads outwards into the section 55 of the housing bore 51.
A journal 67 is formed integrally on the swash plate 35, onto which journal a spherical bushing 68 is pushed as far as a shoulder and is held on the shoulder by a retaining ring. The diameter of the spherical surface of the spherical bushing 68 is equal to the diameter of the blind hole 65. The journal 67, together with the spherical bushing 68, passes through an opening 69 of the section 55, which opening is elongate in the direction of the central axis 54 of the adjusting piston 46 and of the housing bore 51, into the blind hole 65 of the adjusting piston 46. If the play necessary for the mobility of the spherical bushing in the blind hole is disregarded, the line of contact between the spherical bushing 68 and the wall of the blind hole, that is to say the adjusting piston 46, is a circle.
If the adjusting piston 46 now moves, the spherical bushing 68 is taken along in both directions of movement and the swash plate 35 is thereby pivoted. In this case, the depth to which the spherical bushing 68 penetrates into the blind hole 65 and the position of the contact line between the spherical bushing and the adjusting piston along the blind hole also change. At the same time, the spherical cap 68 rotates with respect to the adjusting piston 46 about an axis of rotation which runs parallel to the pivot axis 36 and moves with the depth of penetration. The joint between the adjusting piston 46 and the swash plate 35 is thus a movable swivel joint, in particular a movable ball joint with the spherical bushing 68 held on the swash plate 35 as the joint body and the blind hole 65 on the adjusting piston 46 as the joint body receptacle.
In the case of a position of the swash plate 35 between the zero position and one maximally pivoted position, the axial piston machine operates as a pump. In the case of a position of the swash plate 35 between the zero position and the other maximum pivoted position, the axial piston machine operates as a motor with the same direction of rotation and without a change between the pressure connection and the tank connection.
The adjusting device 45 further comprises two actuating springs 75 and 76, which are arranged concentrically with one another, are designed as helical compression springs and are clamped between the bottom of the housing bore 51 and the adjusting piston. The actuating springs are thus loaded in the direction of their longitudinal axis and act in the direction of retraction of the adjusting piston 46. The swash plate 35 thus assumes the position shown in
Of the exemplary embodiment shown in
In contrast to the first exemplary embodiment, in the second exemplary embodiment a ball journal 80 is pressed into a hole 79 in the swash plate 35, which ball journal penetrates with its ball head 81 into the blind hole 65 of the adjusting piston 46 and by means of which the adjusting piston 46 is able to pivot the swash plate 35.
In contrast to the first exemplary embodiment, the bore section 53 in which the piston rod 50 of the adjusting piston 46 is guided reaches as far as the bottom of the housing bore 51, thus ensuring that, irrespective of the position of the adjusting piston 46, the piston rod is always guided over its length located outside bore section 52 and, apart from the region of the opening 69 between the housing bore 51 and the interior of the housing 10, and the gap length between the piston rod 50 and bore section 53 depends on the position of the adjusting piston 46.
In the second exemplary embodiment, a relief hole 66 for the blind hole 65 leads in the axial direction of the adjusting piston 46 into the blind hole 65 because, owing to the narrow gap radially outside the piston rod 50, radially no pressure equalization, or at least no rapid pressure equalization, is possible.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2020 211 284.3 | Sep 2020 | DE | national |
