Variable displacement piston apparatus

Abstract

Disclosed is a variable displacement piston apparatus capable of absorbing a deviation in the pitch of a pair of spherical holes in which a pair of balls supporting the swash plate are disposed and improving the wear resistance of the balls and the swash plate. The configuration of the variable displacement piston apparatus according to the present invention includes: a cylinder barrel 110 rotatably supported within a housing together with a shaft; a plurality of pistons 112 axially slidably inserted into the cylinder barrel; a swash plate 120 that changes the stroke of the pistons; two support balls 130 that rotatably support the swash plate; two cylindrical holes 122 formed at positions in the swash plate facing the two support balls; and two ball guides 140 accommodated in the cylindrical holes and supporting the support balls; wherein each of the ball guides has a cylindrical outer peripheral surface 142 and a concave spherical surface 144 that supports the support ball, and both or one of the ball guides are characterized in that the concave spherical surface is eccentric with respect to the outer peripheral surface and is rotatable within the cylindrical hole of the swash plate.

Description

TECHNICAL FIELD

[0001] The present invention relates to a variable displacement piston apparatus used in construction machinery, industrial equipment, and related applications.BACKGROUND ART

[0002] Variable displacement piston apparatuses are sometimes used in construction and industrial machinery. In particular, specific examples include variable displacement piston pumps and variable displacement piston motors. A swash plate variable displacement piston pump, which is a type of variable displacement piston pump, is capable of varying the pump displacement by tilting a swash plate.

[0003] For example, Patent Document 1 discloses a variable displacement pump including "a cylinder barrel, which is rotatably supported within a housing together with a shaft and a swash plate, which is slidable against a plurality of piston heads slidably inserted into the cylinder barrel in an axial direction and is non-rotatably supported within the housing relative to rotation of the shaft". In the variable displacement pump of Patent Document 1, a tilt angle of the swash plate is varied as the swash plate is pressed by a drive unit provided in the housing and is tilted about two balls or cylindrical bodies that define an axis orthogonal to the rotation axis of the shaft.

[0004] Patent Document 2 discloses a swash plate type hydraulic pump characterized to include: "a housing; a drive shaft supported by a bearing provided in the housing; a cylinder block having a plurality of cylinder rooms and pistons and being rotated by the drive shaft; a swash plate disposed facing the cylinder block; and a pair of spherical shafts disposed in a diametrical direction of the swash plate to support the swash plate, in which each spherical shaft is configured to have a hemispherical head that engages with a hemispherical concave bearing formed in the swash plate and a stem fitted into a receiving hole of the housing, and a thin film of diamond-like carbon is coated on a surface of either each spherical shaft head or the concave bearing of the swash plate."PRIOR ART DOCUMENTSPATENT DOCUMENTS

[0005] Patent Document 1: JP 2915559 B Patent Document 2: JP 2004-044467 A SUMMARY OF THE INVENTIONPROBLEMS TO BE SOLVED BY THE INVENTION

[0006] In the swash plate variable displacement piston pump, a ball supporting the swash plate or the spherical shaft as disclosed in Patent Document 2 is disposed in a concave spherical hole formed in the swash plate. The spherical hole is formed using a machining tool such as a machining center; however, in mass production scenarios, variations in machining accuracy may lead to deviation in the pitch between the pair of spherical holes (i.e., an interval between the two spherical holes).

[0007] In the configuration of Patent Document 2, since there is no clearance such as between the hemispherical head and stem that constitute the spherical shaft and the hemispherical concave bearing formed in the swash plate, nor between the concave bearing and the swash plate, any deviation that may occur in the pitch between the pair of spherical holes cannot be absorbed. As a result, the contact between the spherical shaft, particularly the head, and the concave bearing, becomes misaligned, thereby reducing the contact area. Consequently, the spherical shaft (or ball) that supports the swash plate and the concave spherical hole are likely to wear, which may lead to abnormal variations in performance (displacement) due to changes in the support angle of the swash plate caused by wear or even damage due to excessive wear.

[0008] In view of such problems, the present invention aims to provide a variable displacement piston apparatus capable of improving the wear resistance of the tilt support portion of the swash plate.MEANS FOR SOLVING THE PROBLEMS

[0009] To solve the above problems, a representative configuration of the variable displacement piston apparatus according to the present invention is characterized by including: a cylinder barrel rotatably supported within a housing together with a shaft; a plurality of pistons slidably inserted into the cylinder barrel in an axial direction; a swash plate varying a piston stroke; two support balls rotatably supporting the swash plate; two cylindrical holes formed in the swash plate at positions facing the two support balls; and two ball guides accommodated in the cylindrical holes to support the support balls, wherein the respective ball guide has a cylindrical outer peripheral surface and a concave spherical surface that supports the support ball, wherein both or one of the ball guides have the concave spherical surface eccentrically offset with respect to the outer peripheral surface, and wherein the respective ball guide is rotatable within the cylindrical hole of the swash plate.

[0010] To solve the above problems, another configuration of the variable displacement piston apparatus according to the present invention is characterized by including: a cylinder barrel rotatably supported within a housing together with a shaft; a plurality of pistons slidably inserted into the cylinder barrel in an axial direction; a swash plate changing a piston stroke; two support balls rotatably supporting the swash plate; two cylindrical holes formed in the housing at positions facing the two support balls; and two ball guides accommodated in the cylindrical holes to support the support balls, wherein the respective ball guide has a cylindrical outer peripheral surface and a concave spherical surface that supports the support ball, wherein both or one of the ball guides have the concave spherical surface eccentrically offset with respect to the outer peripheral surface, and wherein the respective ball guide is rotatable within the cylindrical hole of the swash plate.EFFECTS OF THE INVENTION

[0011] According to the present invention, it is possible to provide a variable displacement piston apparatus capable of improving wear resistance at the tilting support portion of the swash plate by absorbing deviations in the pitch of a pair of concave spherical holes that serve as the tilting support portion of the swash plate.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1is a diagram illustrating a variable displacement piston pump as a variable displacement piston apparatus according to the present embodiment. FIG. 2is a diagram illustrating details of a swash plate and support balls. FIG. 3is a diagram illustrating a pitch of a pair of cylindrical holes. FIG. 4is a diagram illustrating other embodiments of the variable displacement piston pump. MODE FOR CARRYING OUT THE INVENTION

[0013] Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Dimensions, materials, and other specific numerical values shown in the embodiments are merely examples to facilitate understanding of the invention and do not limit the present invention unless otherwise specified. In addition, in this specification and drawings, elements having substantially the same functions and configurations are given the same reference numerals to omit redundant explanation, and elements not directly related to the present invention are omitted from illustration or description.

[0014] FIG. 1 is a diagram illustrating a variable displacement piston pump (hereinafter referred to as a piston pump 100) as a variable displacement piston apparatus according to the present embodiment. FIG. 1(a) is a diagram illustrating an internal structure of the piston pump 100. FIG. 1(b) is a sectional view taken along line A-A of FIG. 1(a). Here, although the present embodiment illustrates the variable displacement piston pump as the variable displacement piston apparatus, the present invention can also be applied to a variable displacement piston motor.

[0015] The piston pump 100 of the present embodiment is an apparatus that supplies a fluid such as hydraulic oil to a construction machine or an industrial machine (not shown) through a discharge port (not shown). As shown in FIG. 1(a), the piston pump 100 according to the present embodiment includes a housing 102. Disposed within the housing 102 is a cylinder barrel 110 that is rotatably supported together with a shaft 104 (axis).

[0016] A plurality of pistons 112, slidable in an axial direction D1 of the shaft 104, are inserted into the cylinder barrel 110. The plurality of pistons 112 are arranged in a circumferential direction of the cylinder barrel 110 and reciprocate when the cylinder barrel 110 rotates, thereby discharging hydraulic oil from the discharge port. Further, a head 112a of each piston is attached to a piston shoe 114 which slides in contact with a swash plate 120.

[0017] The swash plate 120 is supported within the housing 102 so as not to rotate relative to the rotation of the shaft 104 and changes the stroke length of the pistons 112 by tilting. As shown in FIG. 1(b), the swash plate 120 has an insertion hole 120a through which the shaft 104 is inserted.

[0018] Further, as shown in FIG. 1(b), the swash plate 120 is rotatably supported by two support balls 130. Furthermore, as shown in FIG. 1(a), the piston pump 100 is provided with a spring unit 190 that presses the swash plate 120. The spring unit 190 includes a spring 192 and a spring holder 194.

[0019] The spring unit 190 is provided to generate a moment in a direction opposite (i.e., counterclockwise) to a clockwise moment generated on the swash plate 120 about the support balls 130 as fulcrums due to hydraulic pressure from the plurality of pistons 112. With this structure, when the clockwise moment due to hydraulic pressure exceeds the counterclockwise moment generated by the load of the spring unit 190, the swash plate 120 tilts clockwise about the support balls 130 as fulcrums.

[0020] FIGS. 2(a) and (b) are diagrams illustrating details of the swash plate 120 and the support ball 130. FIG. 2(a) is a diagram showing the state in which the swash plate 120 is supported by the support ball 130. FIG. 2(b) is a front view and a cross-sectional view of the ball guides 140. FIG. 2(c) is a diagram showing a state in which the support ball 130 is removed from the swash plate 120.

[0021] As illustrated in FIG. 1(b) and FIG. 2(a), the housing 102 is formed with a hemispherical hole 102a at a position corresponding to each of the two support balls 130, and each support ball 130 is retained within the respective hemispherical hole. Furthermore, in the swash plate 120, two cylindrical holes 122 are formed at positions respectively facing the two support balls 130. The two ball guides 140, which support the support balls 130, are accommodated in the two cylindrical holes 122. Thus, the swash plate 120 is supported on the housing 102 via the support balls 130. It should be noted that the term "hemispherical hole" is not limited to a shape that is strictly a bisected sphere but also encompasses other shapes capable of rotatably supporting a portion of the support ball 130 in a manner that prevents displacement from the support structure.

[0022] As shown in FIG. 2(b), each of the two ball guides 140 has a cylindrical outer peripheral surface 142 and a concave spherical surface 144 for supporting the support ball 130. As a characteristic of the piston pump 100 of the present embodiment, with respect to the ball guide 140, a center C2 of the concave spherical surface 144 is eccentrically offset relative to a center C1 of the outer peripheral surface 142. This amount of eccentricity is defined as t. In addition, the ball guide 140 is rotatable within the cylindrical hole 122 of the swash plate 120.

[0023] FIG. 3 is a diagram illustrating the pitch of the pair of cylindrical holes 122. FIGS. 3(a) to 3(e) illustrate examples of states in which the ball guides 140 are not accommodated in the pair of cylindrical holes 122. FIGS. 3(f) to 3(j) illustrate examples of states in which the ball guides 140 supporting the support balls 130 are accommodated in the pair of cylindrical holes 122.

[0024] In the swash plate 120 of FIG. 3(c), an interval between the pair of cylindrical holes 122 is equal to the predetermined interval L. That is, the swash plate 120 of FIG. 3(c) has no deviation in the pitch between the pair of cylindrical holes 122. In contrast, the swash plate 120 of FIG. 3(a) has a deviation of "-2t" from the predetermined interval L, and the swash plate 120 of FIG. 3(b) has a deviation of "-t" from the predetermined interval L.

[0025] In addition, the swash plate 120 of FIG. 3(d) has a deviation of "+t" from the prescribed interval L, and the swash plate 120 of FIG. 3(e) has a deviation of "+2t" from the prescribed interval L. The intervals between the pair of cylindrical holes 122 in FIGS. 3(f) to 3(j) correspond respectively to FIGS. 3(a) to 3(e).

[0026] In the case where there is no deviation in the pitch between the pair of cylindrical holes 122, as in the swash plate 120 shown in FIG. 3(c), the center-to-center interval between the support balls 130 supported by the ball guides 140 also becomes L, as shown in FIG. 3(h). In this case, the rotation angle of each ball guides 140 within the cylindrical holes 122 is 0 degree, and the center-to-center interval between the concave spherical surfaces 144 is also L.

[0027] In contrast, when there is a deviation in the pitch between the pair of cylindrical holes 122, as shown in FIGS. 3(f), 3(g), 3(i), and 3(j), the ball guides 140 accommodated in the pair of cylindrical holes 122 are pressed against the support balls 130 via the swash plate 120 by the hydraulic pressure from the plurality of pistons 112 and the load of the spring unit 190 and rotate within the cylindrical holes 122 following (being pushed by) the support balls 130.

[0028] As specific examples, in FIGS. 3(g) and 3(i), although the interval between the cylindrical holes 122 is L ± t, the center-to-center interval between the concave spherical surfaces 144 becomes L by rotation of the ball guides 140 by ±30 degrees. Similarly, in FIGS. 3(f) and 3(j), although the interval between the cylindrical holes 122 is L ± 2t, the center-to-center interval between the concave spherical surfaces 144 becomes L by rotation of the ball guides 140 by ±90 degrees. In this manner, deviations in the pitch between the pair of cylindrical holes 122, that is, deviations in the pitch between the pair of spherical holes, are absorbed. Accordingly, the support balls 130 and the concave spherical surfaces 144 are able to slide across the entire surface, thereby improving the wear resistance of the support balls 130 and the swash plate 120 and preventing abnormal changes in performance (displacement) caused by variations in the support angle of the swash plate due to wear or damage due to excessive wear.

[0029] It should be noted that, in the present embodiment, an example is illustrated in which both of the two ball guides 140, accommodated in the two cylindrical holes 122 formed in the swash plate 120 to support the support balls 130, have the concave spherical surfaces that are eccentrically offset with respect to the outer peripheral surfaces; however, the invention is not limited to this configuration. For example, the present invention can also be applied to a configuration in which only one of the two ball guides 140 has the concave spherical surface that is eccentrically offset with respect to the outer peripheral surface. Furthermore, the present invention can also be applied to two ball guides that are accommodated in two cylindrical holes formed in the housing 102 to support the support balls. As shown in FIG. 4, the swash plate 120 is formed with a hemispherical hole at a position corresponding to each of the two support balls 130, and each support ball 130 is retained within the respective hemispherical hole. It should be noted that the term "hemispherical hole" is not limited to a shape that is strictly a bisected sphere but also encompasses other shapes capable of rotatably supporting a portion of the support ball 130 in a manner that prevents displacement from the support structure.

[0030] As described above, preferred embodiments of the present invention have been described with reference to the accompanying drawings, but it goes without saying that the present invention is not limited to such examples. It is apparent that a person skilled in the art can conceive of various modifications or variations within the scope described in the claims, and such modifications or variations are naturally understood to fall within the technical scope of the present invention.INDUSTRIAL APPLICABILITY

[0031] This invention pertains to a variable displacement piston apparatus employed in construction machinery, industrial equipment, and related applications.LIST OF REFERENCE NUMERALS

[0032] D1axial direction 100piston pump 102housing 102ahemispherical hole 104shaft 110cylinder barrel 112piston 112ahead of piston 114piston shoe 120swash plate 120ainsertion hole 122cylindrical hole 130support ball 140ball guide 142outer peripheral surface 144concave spherical surface 190spring unit 192spring 194spring holder

Claims

1. A variable displacement piston apparatus (100) comprising: a cylinder barrel (110) rotatably supported within a housing together with a shaft (104); a plurality of pistons (112) slidably inserted into the cylinder barrel (110) in an axial direction; a swash plate (120) varying a piston stroke; two support balls (130) rotatably supporting the swash plate (120); two cylindrical holes (122) formed in the swash plate (120) at positions facing the two support balls (130); and two ball guides (140) accommodated in the cylindrical holes (122) to support the support balls (130), wherein the respective ball guide (140) has a cylindrical outer peripheral surface and a concave spherical surface that supports the support ball (130), wherein both or one of the ball guides (140) have the concave spherical surface eccentrically offset with respect to the outer peripheral surface, and wherein the respective ball guide (140) is rotatable within the cylindrical hole (122) of the swash plate (120).

2. A variable displacement piston apparatus (100) comprising: a cylinder barrel (110) rotatably supported within a housing together with a shaft (104); a plurality of pistons (112) slidably inserted into the cylinder barrel (110) in an axial direction; a swash plate (120) changing a piston stroke; two support balls (130) rotatably supporting the swash plate (120); two cylindrical holes (122) formed in the housing at positions facing the two support balls (130); and two ball guides (140) accommodated in the cylindrical holes (122) to support the support balls (130), wherein the respective ball guide (140) has a cylindrical outer peripheral surface and a concave spherical surface that supports the support ball (130), wherein both or one of the ball guides (140) have the concave spherical surface eccentrically offset with respect to the outer peripheral surface, and wherein the respective ball guide (140) is rotatable within the cylindrical hole (122) of the housing.

3. The variable displacement piston apparatus (100) according to Claim 1, wherein the housing is formed with a concave spherical surface capable of rotatably supporting a portion of the support ball (130) at a position corresponding to the ball guide (140).

4. The variable displacement piston apparatus (100) according to Claim 2, wherein the swash plate (120) is formed with a concave spherical surface capable of rotatably supporting a portion of the support ball (130) at a position corresponding to the ball guide (140).

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