The present application claims priority to German Utility Model Application No. 20 2022 106 185.8, entitled “PISTON ASSEMBLY”, and filed on Nov. 3, 2022. The entire contents of the above-listed application is hereby incorporated by reference for all purposes.
The present disclosure relates to a piston assembly and to a variable displacement hydraulic unit including the piston assembly. The variable displacement hydraulic unit may include a variable displacement hydraulic pump or a variable displacement hydraulic motor, for example.
Hydraulic piston assemblies including a cylinder and a piston movably disposed within the cylinder are widely used in the art of hydraulic devices. In some cases, the cylinder may be open at one end and is closed or sealed off at its open end by a cap assembly. For example, during assembly the cylinder may be kept open for some time and may close its open end by putting on the cap assembly only at a later stage.
Known piston assemblies of this sort typically require additional seals such as sealing rings to seal the cap assembly. These seals are usually mounted on the cylinder. For example, a cylinder wall enclosing the cylinder may include an annular groove or indentation, and a sealing ring may be disposed or received in the groove or indentation formed in the cylinder wall. However, producing a piston assembly including seals of the aforementioned type is often complex and expensive.
Thus, there is demand for a piston assembly including a cylinder and a cap assembly closing the cylinder at an axial end thereof which can be produced simply and at low cost.
This demand is met by a piston assembly including the features described herein and by a variable displacement hydraulic unit including said piston assembly.
The presently proposed piston assembly comprises at least:
As the cap assembly includes an insertion portion which is received in the cylinder, one or more seals may be mounted on the insertion portion. For instance, a cylinder wall enclosing the cylinder may then not need to include additional machined portions such as grooves or indentations for mounting the seals on the cylinder wall. The fact that the piston is partially or at least partially received in the insertion portion of the cap assembly may render the cap assembly stable.
The piston assembly may comprise a housing. The cylinder may be formed in the housing. The cap assembly may then be fixed or axially fixed to the housing.
The piston assembly may comprise a hydraulic chamber formed axially in between the cap assembly and the piston, wherein a hydraulic pressure in the hydraulic chamber is configured to bias the piston in a first direction along the axis.
A cylinder wall enclosing the cylinder may have a cylindrical shape and may include no machined portion or portions in or on the cylinder wall.
The cap assembly may comprise an outer sealing member disposed radially in between the insertion portion of the cap assembly and a cylinder wall enclosing the cylinder. The outer sealing member may be mounted on the insertion portion of the cap assembly. For example, a radially outer surface of the insertion portion of the cap assembly may comprise an outer annular indentation. The outer sealing member may then be received in the outer annular indentation.
The cap assembly may comprise an inner sealing member disposed radially in between the insertion portion of the cap assembly and the piston. The inner sealing member may be mounted on the insertion portion of the cap assembly. For example, a radially inner surface of the insertion portion of the cap assembly may comprise an inner annular indentation. The inner sealing member may be received in the inner annular indentation.
The piston assembly may comprise a first biasing member for biasing the piston in a first direction along the axis. The piston assembly may comprise an axially displaceable zeroing member limiting axial movement of the first biasing member. The first biasing member may be axially supported on the cap assembly. The piston assembly may further comprise a second biasing member for biasing the piston in a second direction along the axis, opposite to the first direction. For example, the zeroing member may be configured to limit axial movement of the first biasing member in a first direction along the axis and to limit axial movement of the second biasing member in a second direction along the axis, opposite to the first direction.
The piston may comprise a body portion and a protrusion extending from the body portion in a lateral direction perpendicular to the axis. The first biasing member may be configured to be axially supported on the protrusion and to bias the piston in the first axial direction when at least a portion of the protrusion extends beyond the zeroing member in the second axial direction. Additionally or alternatively, the second biasing member may be configured to be axially supported on the protrusion and to bias the piston in the second axial direction when at least a portion of the protrusion extends beyond the zeroing member in the first axial direction. An axial extension of the protrusion may be equal to an axial extension of the zeroing member.
The piston assembly may comprise a first thrust ring axially disposed in between the zeroing member and the first biasing member and in between the protrusion and the first biasing member. The first biasing member may be configured to be supported on the protrusion via the first thrust ring and to move the piston in the first direction until the first thrust ring hits the zeroing member. Additionally or alternatively, the piston assembly may comprise a second thrust ring axially disposed in between the zeroing member and the second biasing member and in between the protrusion and the second biasing member. The second biasing member may be configured to be supported on the protrusion via the second thrust ring and to move the piston in the second direction until the second thrust ring hits the zeroing member.
The first biasing member and/or the second biasing member may at least partially enclose the piston.
The piston assembly may comprise a rotatable gudgeon including an eccentric pin engaged with the zeroing member so that the zeroing member is displaceable along the axis by rotating the rotatable gudgeon.
The piston assembly may comprise a worm screw or leadscrew engaged with the zeroing member so that the zeroing member is displaceable along the axis by rotating the worm screw or leadscrew.
The presently proposed variable displacement hydraulic unit comprises a swashplate, and the above-described piston assembly, wherein the piston is coupled to the swashplate for rotating the swashplate.
Embodiments of the presently proposed subject matter are illustrated in the accompanying drawing and are described in the following detailed description.
The hydraulic unit 100 includes a casing 1, a rotatable shaft 2 such as pump shaft or motor shaft at least partially disposed in the casing 1, a cylinder block 3 (see
The hydraulic unit 100 further includes a piston assembly 101. More detailed views of the piston assembly 101 are depicted in
In the embodiment depicted here, movement of the piston 7 along the axis 8 is controllable via hydraulic forces. When no net hydraulic force acts on the piston 7 along the axis 8, the biasing members 9a, 9b move the piston 7 back to a zero position. Ideally, in the zero position of the piston 7 the swashplate 5 is arranged perpendicular to the rotation axis 2a of the shaft 2 so that a stroke of the pistons 4 vanishes. Or in other words, when the piston 7 is in the zero position, the hydraulic unit 100 should be in a neutral configuration in which it does not displace fluid upon rotation of the shaft 2. However, due to manufacturing tolerances and/or mechanical wear the zero position of the piston 7 may not always exactly correspond to the neutral configuration of the hydraulic unit 100. Therefore, in order to make sure that the hydraulic unit 100 is in the neutral configuration when the piston 7 is in the zero position, the zero position of the piston 7 can be set or adjusted by displacing the zeroing member 110 along the axis 8, as will be explained in further detail below.
Along the axis 8, the first axial direction 8a points from the first axial end 12a of the cylinder 12 to the second axial end 12b of the cylinder 12, and the second axial direction 8b points from the second axial end 12b of the cylinder 12 to the first axial end 12a of the cylinder 12. The piston 7 is disposed within the cylinder 12. A cylinder axis of the cylinder 12 coincides with the axis 8. The piston 7 is movable relative to the housing 11. Along the axis 8 the piston 7 extends from a first axial end 7a to a second axial end 7b. The piston 7 includes a cylindrical or at least partially cylindrical body portion 7c extending along the axis 8 and a protrusion 7d extending from the body portion 7c in a lateral direction perpendicular to the axis 8. Here, at least a section of the protrusion 7d has an annular shape. The protrusion 7d runs around the body portion 7c. In the embodiment depicted here, the body portion 7c and the protrusion 7d are formed in one piece. The piston 7 may be forced or moved in the first axial direction 8a by a hydraulic pressure in a first hydraulic chamber 25a, and the piston 7 may be forced or moved in the second axial direction 8b by a hydraulic pressure in a second hydraulic chamber 25b. The hydraulic chambers 25a, 25b are formed within the cylinder 12.
The piston assembly 101 further includes a first cap assembly 13a which closes or seals off the cylinder 12 at its first axial end 12a. The first cap assembly 13a includes an insertion portion 14a extending along the axis 8, and a cap portion 15a extending perpendicular to the axis 8. Here, the insertion portion 14a and the cap portion 15a are formed in one piece. The first cap assembly 13a is fixed to the housing 11, for example by a plurality of screws 16a (see
Here, the insertion portion 14a has the shape of a hollow cylinder. An outer radius of the insertion portion 14a is equal to or just slightly smaller than a radius of the cylinder 12. The piston assembly 101 further includes at least one first outer sealing member 17a such as a rubber or metal sealing ring. The first outer sealing member 17a is disposed radially in between the insertion portion 14a and the cylinder wall 18 enclosing the cylinder 12. The first outer sealing member 17a is mounted on the insertion portion 14a. More specifically, the first outer sealing member 17a is received in an outer indentation 19a formed in a radially outer surface of the insertion portion 14a of the first cap assembly 13a. The first outer sealing member 17a prevents fluid such as oil from leaking out of the cylinder 12.
The piston 7 or, more specifically, the body portion 7c of the piston 7 is partially received in the hollow cylindrical insertion portion 14a of the first cap assembly 13a. An inner radius of the hollow cylindrical insertion portion 14a is equal to or just slightly larger than a radius of the body portion 7c of the piston 7. The piston assembly 101 further includes at least one first inner sealing member 20a such as a rubber or metal sealing ring. The first inner sealing member 20a is disposed radially in between the hollow cylindrical insertion portion 14a and the body portion 7c of the piston 7. The first inner sealing member 20a is mounted on the insertion portion 14a. More specifically, the first inner sealing member 20a is received in an inner indentation 21a formed in a radially inner surface of the hollow cylindrical insertion portion 14a of the first cap assembly 13a. The first inner sealing member 20a prevents fluid such as oil from leaking into a hollow 22a formed axially in between the piston 7 and the cap portion 15a of the first cap assembly 13a.
The piston assembly 101 further includes a second cap assembly 13b which closes or seals off the cylinder 12 at its second axial end 12b. The second cap assembly 13b includes an insertion portion 14b extending along the axis 8, and a cap portion 15b extending perpendicular to the axis 8. Here, the insertion portion 14b and the cap portion 15b are formed in one piece. The second cap assembly 13b is fixed to the housing 11, for example by a plurality of screws which may extend parallel to the axis 8 and fix the cap portion 15b to the housing 11 (not shown). The insertion portion 14b of the second cap assembly 13b is received in the cylinder 12. The second cap assembly 13b, more specifically the insertion portion 14b of the second cap assembly 13b, delimits the second hydraulic chamber 25b in the first axial direction 8a.
Here, the insertion portion 14b has the shape of a hollow cylinder. An outer radius of the insertion portion 14b is equal to or just slightly smaller than a radius of the cylinder 12. The piston assembly 101 further includes at least one second outer sealing member 17b such as a rubber or metal sealing ring. The second outer sealing member 17b is disposed radially in between the insertion portion 14b and a cylinder wall 18 enclosing the cylinder 12. The second outer sealing member 17b is mounted on the insertion portion 14b. More specifically, the second outer sealing member 17b is received in an outer indentation 19b formed in a radially outer surface of the insertion portion 14b of the second cap assembly 13b. The second outer sealing member 17b prevents fluid such as oil from leaking out of the cylinder 12.
The piston 7 or, more specifically, the body portion 7c of the piston 7 is partially received in the hollow cylindrical insertion portion 14b of the second cap assembly 13b. An inner radius of the hollow cylindrical insertion portion 14b is equal to or just slightly larger than the radius of the body portion 7c of the piston 7. The piston assembly 101 further includes at least one second inner sealing member 20b such as a rubber or metal sealing ring. The second inner sealing member 20b is disposed radially in between a radially inner wall of the hollow cylindrical insertion portion 14b and the body portion 7c of the piston 7. The second inner sealing member 20b is mounted on the insertion portion 14b. More specifically, the second inner sealing member 20b is received in an inner indentation 21b formed in a radially inner surface of the hollow cylindrical insertion portion 14b of the second cap assembly 13b. The second inner sealing member 20b prevents fluid such as oil from leaking into a hollow 22b formed axially in between the piston 7 and the cap portion 15b of the second cap assembly 13b.
The zeroing member 110 is partially received in a recess 23 formed in the housing 11. Portions 11a, 11b of the housing 11 enclosing the recess 23 limit movement of the zeroing member 110 along the axis 8. More specifically, the portion 11a limits movement of the zeroing member 110 in the second axial direction 8b, and the portion 11b limits movement of the zeroing member 110 in the first axial direction 8a. The zeroing member 110 protrudes partially into the cylinder 12. Here, a length or extension of the recess 23 along the axis 8 and a length or extension of the zeroing member 110 along the axis 8 are such that a maximum stroke of the zeroing member 110 along the axis 8 within the recess 23 is at most 20 percent or at most ten percent of the axial length or of the axial extension of the recess 23. As can be seen in
In the embodiment depicted in
The first biasing member 9a biases or is configured to bias the piston 7 in the first axial direction 8a along the axis 8. In the embodiment depicted here, the first biasing member 9a is received on and encloses or at least partially encloses the piston 7. More specifically, the first biasing member 9a is received on and encloses or at least partially encloses the body portion 7c of the piston 7. Along the axis 8, the first biasing member 9a is supported on the first cap assembly 13a. Further, along the axis 8 the first biasing member 9a is supported on either the zeroing member 110 or the protrusion 7d of the piston 7 at all times. Or in other words, the first biasing member 9a is preloaded or at least partially compressed in between the first cap assembly 13a and either the zeroing member 110 or the protrusion 7d of the piston 7 at all times. More specifically, along axis 8 the first biasing member 9a is supported on the insertion portion 14a of the first cap assembly 13a. Or in other words, along the axis 8 the first biasing member 9a is supported on the housing 11 via the first cap assembly 13a.
Along the axis 8, the first biasing member 9a is disposed in between the first cap assembly 13a and the protrusion 7d of the piston 7. More specifically, along the axis 8 the first biasing member 9a is disposed in between the insertion portion 14a of the first cap assembly 13a and the protrusion 7d of the piston 7. Along the axis 8 the first biasing member 9a is disposed in between the first cap assembly 13a and the zeroing member 110. More specifically, along the axis 8 the first biasing member 9a is disposed in between the insertion portion 14a of the first cap assembly 13a and the zeroing member 110.
The piston assembly 101 further includes a first thrust ring 24a. Along the axis 8 the first thrust ring 24a is disposed in between the first biasing member 9a and the zeroing member 110 and in between the first biasing member 9a and the protrusion 7d of the piston 7. The first thrust ring 24a is received on the piston 7, more specifically on the body portion 7c of the piston 7. In the radial direction perpendicular to the axis 8, the first thrust ring 24a at least partially overlaps with the zeroing member 110. Or in other words, with respect to the axis 8 a maximum radius of the first thrust ring 24a determined perpendicular to the axis 8 is larger than a minimum radius of the zeroing member 110 determined perpendicular to the axis 8. Further, in the radial direction the first thrust ring 24a at least partially overlaps with the protrusion 7d of the piston 7. Or in other words, with respect to the axis 8 a minimum radius of the first thrust ring 24a determined perpendicular to the axis 8 is smaller than a maximum radius of the protrusion 7d determined perpendicular to the axis 8.
Thus, along the axis 8 the first biasing member 9a is configured to be supported on the protrusion 7d via the first thrust ring 24a and to move the piston 7d in the first axial direction 8a when or as long as the protrusion 7d extends or at least partially extends beyond the zeroing member 110 in the second axial direction 8d until the first thrust ring 24a hits or strikes against the zeroing member 110. A biasing force the first biasing member 9a exerts on the zeroing member 110 and a frictional force between the rotatable gudgeon 111 and the housing 11 are such that the first biasing member 9a may not move the zeroing member 110 along the axis 8 against the frictional force between the rotatable gudgeon 111 and the housing 11. In this way, the zeroing member 110 limits movement of the first biasing member 9a in the first axial direction 8a.
The second biasing member 9b biases or is configured to bias the piston 7 in the second axial direction 8b along the axis 8. In the embodiment depicted here, the second biasing member 9b is received on and encloses or at least partially encloses the piston 7. More specifically, the second biasing member 9b is received on and encloses or at least partially encloses the body portion 7c of the piston 7. Along the axis 8, the second biasing member 9b is supported on the second cap assembly 13b. Further, along the axis 8 the second biasing member 9b is supported on either the zeroing member 110 or the protrusion 7d of the piston 7 at all times. Or in other words, the second biasing member 9b is preloaded or at least partially compressed in between the second cap assembly 13b and either the zeroing member 110 or the protrusion 7d of the piston 7 at all times. More specifically, along axis 8 the second biasing member 9b is supported on the insertion portion 14b of the second cap assembly 13b. Or in other words, along the axis 8 the second biasing member 9b is supported on the housing 11 via the second cap assembly 13b.
Along the axis 8 the second biasing member 9b is disposed in between the second cap assembly 13b and the protrusion 7d of the piston 7. More specifically, along the axis 8 the second biasing member 9b is disposed in between the insertion portion 14b of the second cap assembly 13b and the protrusion 7d of the piston 7. Along the axis 8, the second biasing member 9b is disposed in between the second cap assembly 13b and the zeroing member 110. More specifically, along the axis 8 the second biasing member 9b is disposed in between the insertion portion 14b of the second cap assembly 13b and the zeroing member 110.
The piston assembly 101 further includes a second thrust ring 24b. Along the axis 8, the second thrust ring 24b is disposed in between the second biasing member 9b and the zeroing member 110 and in between the second biasing member 9b and the protrusion 7d of the piston 7. The second thrust ring 24b is received on the piston 7, more specifically on the body portion 7c of the piston 7. In the radial direction perpendicular to the axis 8, the second thrust ring 24b at least partially overlaps with the zeroing member 110. Or in other words, with respect to the axis 8 a maximum radius of the second thrust ring 24b determined perpendicular to the axis 8 is larger than a minimum radius of the zeroing member 110 determined perpendicular to the axis 8. Further, in the radial direction the second thrust ring 24b at least partially overlaps with the protrusion 7d of the piston 7. Or in other words, with respect to the axis 8 a minimum radius of the second thrust ring 24b determined perpendicular to the axis 8 is smaller than a maximum radius of the protrusion 7d determined perpendicular to the axis 8.
Thus, along the axis 8 the second biasing member 9b is configured to be supported on the protrusion 7d via the second thrust ring 24b and to move the piston 7d in the second axial direction 8b when or as long as the protrusion 7d extends or at least partially extends beyond the zeroing member 110 in the first axial direction 8a until the second thrust ring 24b hits or strikes against the zeroing member 110. A biasing force the second biasing member 9b exerts on the zeroing member 110 and a frictional force between the rotatable gudgeon 111 and the housing 11 are such that the second biasing member 9b may not move the zeroing member 110 along the axis 8 against the frictional force between the rotatable gudgeon 111 and the housing 11. In this way, the zeroing member 110 limits movement of the second biasing member 9b in the second axial direction 8b.
In
As, starting from the situation illustrated in
The resulting situation is depicted in
In
Similar to the situations shown in
Like the hydraulic unit 100 of
For the sake of brevity and simplicity, in the following only those features of the hydraulic unit 200 of
In contrast to the piston assembly 101 of the hydraulic unit 100 of
The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure
Number | Date | Country | Kind |
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20 2022 106 185.8 | Nov 2022 | DE | national |