Gear fitting structure

Abstract

To establish compatibility between an improvement in assemblability and an improvement in operability, in a shaft-gear fitting structure.SOLUTION: A fitting structure 1 comprises a shaft hole 20 which is provided in a gear 2 and opened at both ends in an axial direction and into which a shaft 3 is to be inserted, and an insertion part 40 which is provided in the shaft 3 and positioned within the shaft hole 20. A difference of an inside diameter R2 of the shaft hole 20 in the same position in the axial direction with respect to an outside diameter R3 of the insertion part 40 is a clearance δ. A first clearance δa of a one-end side opening 21 in the axial direction of the shaft hole 20 is larger than a second clearance δb in a predetermined position on the other side in the axial direction with respect to the one-end side opening 21.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a fitting structure between a shaft and a gear. [Background technology]

[0002] Patent Document 1 discloses a screw compressor driven by a motor. In order to transmit the driving force generated by the motor to the rotor shaft of the screw rotor, a pinion attached to the end of the rotor shaft is meshed with a pull gear attached to the motor output shaft. The rotor shaft is inserted into a shaft hole formed in the center of the pinion. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-040294 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the above example, both the outer diameter (diameter of the outer peripheral surface) of the rotor shaft and the inner diameter (diameter of the inner peripheral surface of the shaft hole) of the pinion are constant in the axial direction. When an interference fit is applied to the fit between the two, assembly is less easy than when a clearance fit is applied, and when a clearance fit is applied, operability is less easy than when an interference fit is applied.

[0005] An object of the present invention is to achieve both improved assembly and improved operability in a fitting structure between a shaft and a gear. [Means for solving the problem]

[0006] One aspect of the present invention provides a gear fitting structure that rotates integrally with a shaft, the gear comprising: a shaft hole that is provided on the gear and opens at both axial ends, through which the shaft is inserted; and an insertion portion that is provided on the shaft and positioned inside the shaft hole, wherein when the difference between the inner diameter of the shaft hole and the outer diameter of the insertion portion at the same position in the axial direction is defined as clearance, a first clearance at one end opening of the shaft hole in the axial direction is larger than a second clearance at a predetermined position on the other side of the one end opening in the axial direction.

[0007] Here, the term "clearance" is defined as the difference between the inner diameter of the shaft hole and the outer diameter of the insertion part, and is obtained by subtracting the outer diameter of the insertion part of the shaft from the inner diameter of the shaft hole. The clearance is an example of an index that quantitatively indicates the degree of tightness of the fit. The larger the clearance, the looser the fit. Before the shaft is inserted into the shaft hole, the "clearance" can take not only positive values ​​but also negative values. In other words, the "clearance" includes not only the term "gap" that is generally used when the inner diameter of the shaft hole is larger than the outer diameter of the shaft, but also the term "tightening" that is generally used when the outer diameter of the shaft is larger than the inner diameter of the shaft hole. The numerical value of the tightening is generally a positive value or an absolute value, whereas the "clearance" is specified with negative values ​​allowed. Also, "the same position in the axial direction" means the same position in the axial direction when the shaft has been inserted, that is, when the fitting structure is completed.

[0008] According to the above configuration, the clearance at the one end opening is the first clearance. The clearance at a predetermined position on the other axial side of the one end opening is the second clearance. The second clearance is smaller than the first clearance. When the shaft is inserted into the shaft hole through the one end opening, the shaft is easily inserted into the shaft hole. When the shaft is inserted after reaching the predetermined position, the clearance is smaller, so a larger force is required for insertion. However, compared to a case where the degree of fit is uniformly tight over the entire axial direction, labor saving in assembly is realized. At the one axial end side, the shaft may be eccentric with respect to the gear as a trade-off for ensuring assembly. However, since the clearance is smaller in the latter half of the insertion operation, eccentricity that may occur in the first half of the insertion operation is eliminated. The gear and the insertion part can be aligned over the entire axial direction, improving operability after assembly.

[0009] The clearance may be constant at the first clearance from the one end opening toward the predetermined position, and may switch from the first clearance to the second clearance at the predetermined position.

[0010] According to the above configuration, a fitting structure having different clearances in the axial direction can be easily manufactured.

[0011] The clearance may gradually decrease from the first clearance to the second clearance from the one end opening toward the predetermined position.

[0012] According to the above-mentioned configuration, as the shaft is inserted, the centre of the shaft coincides with the centre of the shaft hole of the gear, further improving the ease of assembly.

[0013] The clearance may be constant at the second clearance from the predetermined position toward an opening on the other axial end side of the shaft hole.

[0014] According to the above configuration, a fitting structure having different clearances in the axial direction can be easily manufactured.

[0015] The outer diameter of the insertion portion may be constant in the axial direction, and the clearance may vary in accordance with changes in the inner diameter of the shaft hole.

[0016] According to the above configuration, a fitting structure in which the clearance varies in the axial direction can be easily realized.

[0017] The fitting structure of the gear may include a first fitting portion formed by the shaft hole and the insertion portion at one end side in the axial direction, and a second fitting portion formed by the shaft hole and the insertion portion at the other end side in the axial direction further than the first fitting portion, wherein the first fitting portion is a clearance fit, and the second fitting portion is an intermediate fit or an interference fit.

[0018] Here, "clearance fit" is defined in JIS B 0401 and is a fitting method when, for example, the minimum allowable dimension of the outer diameter of the shaft is smaller than the maximum allowable dimension of the inner diameter of the shaft hole. "Interference fit" is defined in JIS B 0401 and is a fitting method when, for example, the maximum allowable dimension of the outer diameter of the shaft is larger than the minimum allowable dimension of the inner diameter of the shaft hole. "Intermediate fit" is defined in JIS B 0401 and is a fitting method in which, when fitted together, there is either a gap or interference between the shaft hole and the shaft.

[0019] According to the above configuration, by inserting the shaft into the shaft hole from one end side, the assemblability is improved at the first fitting portion. Although the assemblability is somewhat reduced at the second fitting portion, the reduction in assemblability is mitigated compared to when the entire fitting structure is an interference fit. Furthermore, it is possible to solve the problem that can arise when the entire fitting structure is a clearance fit, i.e., the reduction in operability.

[0020] The shaft may be a rotor shaft of a screw compressor, and the gear may be a pinion that rotates integrally with the rotor shaft of the screw compressor.

[0021] According to the above configuration, it is possible to provide a screw compressor that is easy to assemble and has good operability. Effect of the Invention

[0022] According to the present invention, in a fitting structure between a shaft and a gear, it is possible to improve both assembly ease and operability. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a cross-sectional view showing an oil-free screw compressor as an application example of a fitting structure according to an embodiment. [Diagram 2] FIG. 2 is a cross-sectional view showing the fitting structure according to the first embodiment in an assembled state. [Diagram 3] FIG. 2 is an exploded cross-sectional view showing the fitting structure according to the first embodiment. [Figure 4] 4 is a cross-sectional view showing an example of a first half stage of a shaft insertion operation in the fitting structure according to the first embodiment. FIG. [Diagram 5] 5 is a cross-sectional view showing an example of a latter stage of a shaft insertion operation in the fitting structure according to the first embodiment. FIG. [Figure 6] FIG. 11 is a cross-sectional view showing a fitting structure according to a second embodiment in an exploded state. [Figure 7] FIG. 11 is a cross-sectional view showing the fitting structure according to the second embodiment in an assembled state. [Figure 8] FIG. 11 is a cross-sectional view showing a fitting structure according to a third embodiment in an exploded state. [Figure 9] 13 is a cross-sectional view showing an example of a first half stage of a shaft insertion operation in the fitting structure according to the third embodiment. FIG. [Figure 10] 13 is a cross-sectional view showing an example of a latter stage of a shaft insertion operation in the fitting structure according to the third embodiment. FIG. [Figure 11] FIG. 13 is a cross-sectional view showing the fitting structure according to the fourth embodiment in an assembled state. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereinafter, an embodiment will be described with reference to the drawings. Note that the same or corresponding elements are designated by the same reference numerals throughout the drawings, and detailed description thereof will be omitted.

[0025] (First embodiment) FIG. 1 shows a compressor 80 to which a fitting structure 1 according to a first embodiment is applied. The compressor 80 is, as an example, an oil-free screw compressor. The compressor 80 includes a compressor body 81 and a gear box 82. The compressor body 81 has a rotor pair consisting of a male rotor 83 and a female rotor (not shown) that are meshed with each other. In FIG. 1, the axis of a screw rotor shaft 84 is represented by axis A.

[0026] The compressor body 81 has a casing 81A, a casing 81B, and a cover 81C, which are connected in this order from the other axial side (the right side of the paper in FIG. 1). The casing 81A is connected to a gear casing 82A on the other axial side. The casing 81A forms a rotor chamber 86 that houses the rotor pair. The casing 81B holds a bearing 87 that supports the screw rotor shaft 84, and a shaft seal portion 88 that is arranged between the rotor chamber 86 and the bearing 87.

[0027] One end of the screw rotor shaft 84 protrudes from the casing 81B and is covered with a cover 81C. A drive timing gear 90 is fixed to this end (i.e., the suction side shaft end of the screw rotor shaft 84). A driven timing gear that meshes with the drive timing gear 90 is fixed to the end of the screw rotor shaft of the female rotor (not shown).

[0028] When a motor (not shown) is operated, the screw rotor shaft 84 of the male rotor 83 is rotated. The rotation of the screw rotor shaft 84 is transmitted to the screw rotor shaft of the female rotor via a drive timing gear 90 and a driven timing gear. The screw rotor shaft of the female rotor rotates in synchronization with the screw rotor shaft 84 of the male rotor 83, and the rotor pair rotates in a meshed state. Gas is sucked in through the suction port 89a of the compressor body 81, compressed in the rotor chamber 86, and discharged from the discharge port 89b of the compressor body 81.

[0029] The fitting structure 1 according to this embodiment can be applied to the screw rotor shaft 84 of the male rotor 83 and the drive timing gear 90. Although detailed illustration is omitted, it can also be applied to the screw rotor shaft of the female rotor and the driven timing gear. Furthermore, although detailed illustration is omitted, it can also be applied to the screw rotor shaft 84 of the male rotor 83 and the pinion gear provided on the discharge side shaft end of the screw rotor shaft 84 of the male rotor 83.

[0030] The drive timing gear 90 is, for example, a pinion, and has a disk-shaped base 11 and a boss portion 12 protruding from an end face of the base 11. Teeth 13 are cut on the outer periphery of the base 11. The drive timing gear 90 has a shaft hole 20 through which the screw rotor shaft 84 is inserted. The base 11 and the boss portion 12 are arranged coaxially. The shaft hole 20 is provided in the center of the drive timing gear 90. The shaft hole 20 passes through the base 11 and the boss portion 12 and is open on both axial sides.

[0031] The screw rotor shaft 84 has a protruding end portion that protrudes from the cover 81C. The protruding end portion has a journal portion 31, an insertion portion 40, and a male thread portion 32, which are arranged in this order from the other axial side toward the one axial side. The journal portion 31 is positioned inside the ball bearing 38. The insertion portion 40 is positioned inside the shaft hole 20. A nut 39 is screwed into the male thread portion 32. The drive timing gear 90 is clamped in the axial direction between the end face of the ball bearing 38 and the nut 39. However, the protruding end portion does not have to have the male thread portion 32.

[0032] Hereinafter, the fitting structure 1 of the gear 2 will be described with reference to Fig. 2 and subsequent figures. The fitting structure 1 is composed of the gear 2 and a shaft 3 which rotate together. The pinion serving as the drive timing gear 90 described above is one suitable example of the gear 2. The screw rotor shaft 84 described above is one suitable example of the shaft 3 inserted into the gear 2.

[0033] 2 and 3, as described above, the gear 2 has a base portion 11, a boss portion 12, teeth 13, and a shaft hole 20. The boss portion 12 is provided on one axial side of the base portion 11. An opening 21 on one end side of the shaft hole 20 is formed in an end face of the boss portion 12, and an opening 22 on the other end side of the shaft hole 20 is formed in an end face of the base portion 11.

[0034] As described above, the shaft 3 has the insertion portion 40. The insertion portion 40 is positioned inside the shaft hole 20. The axial distance from the one end opening 21 to the other end opening 22 is the length L20 of the shaft hole 20. The axial length L40 of the insertion portion 40 is equal to the length L20 of the shaft hole 20. The axis A2 of the gear 2 and the axis A3 of the shaft 3 are coaxial with each other and thereby form a common axis A.

[0035] A clearance fit is applied to one axial side of the shaft hole 20 and the insertion portion 40. An intermediate fit or an interference fit is applied to the other axial side of the shaft hole 20 and the insertion portion 40.

[0036] Here, for convenience of illustration in this disclosure, the "inner diameter R2" of the shaft hole 20 refers to the radius, not the diameter, of the inner peripheral surface 23 of the shaft hole 20 of the gear 2. Similarly, the "outer diameter R3" of the insertion portion 40 refers to the radius of the outer peripheral surface 41 of the insertion portion 40 of the shaft 3. "Clearance δ" refers to the difference between the inner diameter R2 of the shaft hole 20 and the outer diameter R3 of the insertion portion 40 at the same position in the axial direction (δ=R2-R3), and can be positive or negative.

[0037] In this embodiment, the term "loose fit" refers to a fitting method in which the minimum allowable dimension of the outer diameter R3 of the insertion portion 40 is smaller than the maximum allowable dimension of the inner diameter R2 of the shaft hole 20. In this embodiment, the term "interference fit" refers to a fitting method in which the maximum allowable dimension of the outer diameter R3 of the insertion portion 40 is larger than the minimum allowable dimension of the inner diameter R2 of the shaft hole 20. In this embodiment, the term "intermediate fit" refers to a fitting method in which the relationship between the inner diameter R2 of the shaft hole 20 and the outer diameter R3 of the insertion portion 40 can be either a clearance fit or an interference fit. When the fitting method is an intermediate fit, the clearance δ can be either a positive value or a negative value.

[0038] The clearance δ at the one end opening 21 of the shaft hole 20 is a first clearance δa. The first clearance δa is a positive value, and the inner diameter R2 of the shaft hole 20 is larger than the outer diameter R3 of the insertion portion 40. More specifically, the maximum allowable dimension of the inner diameter R2 is smaller than the minimum allowable dimension of the outer diameter R3. The fitting method at the one end opening 21 is a clearance fit.

[0039] On the other hand, the clearance changes at a predetermined position 20a on the other axial side of the one end opening 21 of the shaft hole 20. The clearance δ on the other axial side of the predetermined position 20a is a second clearance δb. The second clearance δb is a negative value. Since it is difficult to represent the length of a negative value on a two-dimensional plane, for convenience of illustration, the second clearance δb is illustrated as an absolute value (|δb|). The fitting method at the predetermined position 20a on the other axial side of the one end opening 21 of the shaft hole 20 is an interference fit.

[0040] In this embodiment, the clearance δ is constant at a first clearance δa from the one end opening 21 toward the predetermined position 20a. The clearance δ switches from the first clearance δa to a second clearance δb at the predetermined position 20a. The clearance δ is constant at a second clearance δb from the predetermined position 20a toward the other end opening 22.

[0041] The outer diameter R3 of the shaft 3 is constant throughout the entire axial direction at least in the insertion portion 40 and in a portion on the other axial side of the insertion portion 40. In contrast, the inner diameter R2 of the shaft hole 20 varies in the axial direction. The clearance δ varies in the axial direction according to the variation in the inner diameter R2 of the shaft hole 20.

[0042] In this embodiment, the center line of the shaft hole 20 is coaxial with the axis A2 of the gear 2. The shaft hole 20 has a constant first inner diameter R2a in the section from the one end opening 21 to the predetermined position 20a. The shaft hole 20 has a constant second inner diameter R2b in the section from the predetermined position 20a to the other end opening 22. The second inner diameter R2b is smaller than the first inner diameter R2a.

[0043] The inner peripheral surface of the shaft hole 20 includes a one-end side inner peripheral surface 23a having a first inner diameter R2a, an other-end side inner peripheral surface 23b having a second inner diameter R2b, and a step surface 23c connecting the one-end side inner peripheral surface 23a and the other-end side inner peripheral surface 23b. Both the one-end side inner peripheral surface 23a and the other-end side inner peripheral surface 23b have a uniform circular cross section in the axial direction.

[0044] The other side edge of the one end side inner circumferential surface 23a is continuous with one side edge of the other end side inner circumferential surface 23b at the predetermined position 20a via a step surface 23c that is annular when viewed in the axial direction. The step surface 23c faces one axial side. The inner diameter of the step surface 23c corresponds to the second inner diameter R2b, and the outer diameter of the step surface 23c corresponds to the first inner diameter R2a. Note that, to improve workability, a relief groove may be provided on the inner circumferential surface of the shaft hole 20 at the predetermined position 20a. If a relief groove is provided on the inner circumferential surface of the shaft hole 20 at the predetermined position 20a, there is no step surface 23c.

[0045] The predetermined position 20a may be exactly in the center between the one end opening 21 and the other end opening 22. That is, the axial length L20a from the one end opening to the predetermined position may be equal to the axial length L20b from the predetermined position to the other end opening. The predetermined position 20a may be located on one axial side from the center position. The predetermined position 20a may be located on the other axial side from the center position. The predetermined position 20a may be located at a position corresponding to the boss portion 12 of the shaft hole 20, or may be located at a position corresponding to the base portion 11 of the shaft hole 20.

[0046] In the fitting structure 1 configured in this manner, first, as shown in Fig. 4, the shaft 3 is inserted into the shaft hole 20 via the one-end opening 21. The tip of the shaft 3, i.e., the portion on the other axial side of the insertion portion 40, is inserted. This portion has the same diameter as or a smaller diameter than the insertion portion 40. Therefore, this portion can enter the shaft hole 20 without any particular resistance.

[0047] As the insertion of the shaft 3 progresses, a portion expected to function as the insertion portion 40 (hereinafter, simply referred to as the insertion portion 40) passes through the one-end opening 21. The outer diameter R3 of the insertion portion 40 is smaller than the first inner diameter R2a. Therefore, in the first half of the insertion of the insertion portion 40 into the shaft hole 20, the insertion of the shaft 3 progresses in a manner of clearance fit. That is, a positive clearance δ is set between the inner peripheral surface 23 (the one-end inner peripheral surface 23a) of the shaft hole 20 and the outer peripheral surface 41 of the insertion portion 40. As shown in FIG. 4, within the range of this clearance δ, the axis A3 is allowed to be eccentric or inclined with respect to the axis A2. Therefore, the shaft 3 smoothly advances to the other axial side without causing scratches (so-called galling) on ​​the inner peripheral surface 23 of the shaft hole 20. When the tip of the shaft 3 reaches the predetermined position 20a, the tip of the shaft 3 abuts against the step surface 23c.

[0048] As shown in Fig. 5, in order to proceed with the insertion of the shaft 3, the shaft 3 is required to be press-fitted into a portion having a second inner diameter R2b smaller than the outer diameter R3 of the shaft 3. That is, in the latter half of the insertion of the insertion part 40 into the shaft hole 20, the insertion of the shaft 3 proceeds in a manner of interference fit. The interference fit aligns the shaft 3 with the gear 2. This eliminates the eccentricity or inclination of the axis A3 with respect to the axis A2 that occurred in the first half of the insertion.

[0049] Returning to Fig. 2, when the insertion portion 40 is positioned inside the shaft hole 20 and the insertion of the shaft 3 into the shaft hole 20 is completed, the shaft hole 20 and the insertion portion 40 form a first fitting portion 1A at one axial end. The shaft hole 20 and the insertion portion 40 form a second fitting portion 1B at the other axial end. The fitting structure 1 according to this embodiment has these two types of fitting portions.

[0050] The first fitting portion 1A is located on one axial side of the predetermined position 20a and is a clearance fit. The first fitting portion 1A is composed of an inner peripheral surface 23a on one end side and an outer peripheral surface 41. The first inner diameter R2a is larger than the outer diameter R3, and the first clearance δa is a positive value.

[0051] In contrast, the second fitting portion 1B is located on the other axial side of the predetermined position 20a, and is an interference fit. The second fitting portion 1B is composed of the other end side inner peripheral surface 23b and the outer peripheral surface 41. When the insertion is completed, the other end side inner peripheral surface 23b and the outer peripheral surface 41 are in close contact with each other, and the inner diameter R2 of the shaft hole 20 appears to be equal to the outer diameter of the insertion portion 40. However, before the insertion starts, the second inner diameter R2b is smaller than the outer diameter R3, and the second clearance δb is a negative value (the absolute value is shown in the drawing).

[0052] According to the fitting structure 1 of this embodiment, in the first half of the assembly, the shaft 3 is inserted into the shaft hole 20 in a manner of clearance fit, so that the assembly is easy. When the shaft 3 is inserted after reaching the predetermined position 20a, the clearance δ is reduced, so that a larger thrust is required for insertion. However, compared to the case where a tight fit is applied over the entire axial direction, the assembly can be labor-saving. In addition, the shaft 3 may be eccentric or inclined with respect to the gear 2 at one axial end side in exchange for improved assembly. In the second half of the assembly, the shaft 3 is inserted into the shaft hole 20 in a manner of tight fit, so that the eccentricity or inclination can be eliminated. Therefore, the vibration of the gear 2 during operation can be suppressed. The backlash of the gear 2 is eliminated, so that the risk of seizure during operation can be reduced.

[0053] In this way, the fitting structure 1 for the gear 2 according to this embodiment can improve both ease of assembly and operability. In particular, when the fitting structure 1 is applied to the screw rotor shaft 84 of the compressor 80 and the drive timing gear 90 fixed thereto (see FIG. 1), the synchronization of the rotor pair is improved by eliminating backlash.

[0054] In addition, the outer diameter of the insertion portion 40 is constant. In order to make the clearance δ different between one axial side and the other axial side, the inner diameter R2 of the shaft hole 20 is different between a first inner diameter R2a on one axial side and a second inner diameter R2b on the other axial side. The first inner diameter R2a is set on the one end side inner circumferential surface 23a from the one end side opening 21 to the predetermined position 20a, but is constant. The second inner diameter R2b is also set on the other end side inner circumferential surface 23b from the other end side opening 22 to the predetermined position 20a, but is constant. Therefore, the one end side inner circumferential surface 23a and the other end side inner circumferential surface 23b can be easily formed.

[0055] Second embodiment Next, a fitting structure according to a second embodiment will be described with reference to Figs. 6 and 7, focusing on the differences from the above embodiment.

[0056] In the above embodiment, the one-end side inner circumferential surface 23a has a constant inner diameter, but in this embodiment, the one-end side inner circumferential surface 23a forms a conical surface, and the first inner diameter R2a decreases from the one-end side opening 21 toward the predetermined position 20a. The first inner diameter R2a is maximum at the one-end side opening 21 and minimum at the predetermined position 20a. In this embodiment, the first inner diameter R2a has the same value as the second inner diameter R2b at the predetermined position 20a, and the one-end side inner circumferential surface 23a is continuous with the other-end side inner circumferential surface 23b without a step. However, this is just an example, and even when the one-end side inner circumferential surface 23a is a conical surface, the one-end side inner circumferential surface 23a may be continuous with the other-end side inner circumferential surface 23b via a step.

[0057] In this way, the clearance δ gradually decreases from the first clearance δa to the second clearance δb from the one end opening 21 toward the predetermined position 20a. In this case, as in the above embodiment, both the ease of assembly and the ease of operation can be improved. In particular, in this embodiment, the outer diameter R3 of the shaft 3 is equal to the first inner diameter R2a at the second predetermined position 20b on one axial side of the predetermined position 20a. Therefore, as the insertion of the shaft 3 progresses, the axis A3 of the shaft 3 can be gradually aligned with the axis A2 of the gear 2, and the shaft 3 can be easily press-fitted into the gear 2 after the shaft 3 reaches the predetermined position 20a.

[0058] Third embodiment Next, a fitting structure according to a third embodiment will be described with a focus on differences from the first embodiment with reference to Figures 8 to 10. Note that in Figures 8 to 10, one axial side is shown on the right side of the paper, unlike Figures 2 to 9 showing the above embodiment.

[0059] In the first embodiment, in order to vary the clearance δ depending on the axial position, the inner diameter R2 of the shaft hole 20 varies depending on the axial position, while the outer diameter R3 of the insertion portion 40 is constant. In contrast to this, in the present embodiment, the inner diameter R2 of the shaft hole 20 is constant from the one end opening 21 to the other end opening 22. The insertion portion 40 is stepped, and the outer circumferential surface 41 of the insertion portion 40 has a one end outer circumferential surface 41a on one axial side and an other end outer circumferential surface 41b on the other axial side.

[0060] The first outer diameter R3a of the one-end outer peripheral surface 41a is smaller than the second outer diameter R3b of the other-end outer peripheral surface 41b. The one-end outer peripheral surface 41a is continuous with the other-end outer peripheral surface 41b at a predetermined position 40a via a step surface 41c. The first outer diameter R3a is constant in the axial direction at the one-end outer peripheral surface 41a. The second outer diameter R3b is constant in the axial direction at the other-end outer peripheral surface 41b.

[0061] The first outer diameter R3a is smaller than the inner diameter R2, and the second outer diameter R3b is equal to or slightly larger than the inner diameter R2.

[0062] 8, the length L40a from one end of the insertion portion 40 to the predetermined position 40a (i.e., the axial length of the one-end outer peripheral surface 41a) is shorter than the length L40b from the other end of the insertion portion 40 to the predetermined position 40a (i.e., the axial length of the other-end outer peripheral surface 41b). This is merely an example, and the relationship between the lengths L40a and L40b is not particularly limited. If the length L40b is shorter, it is beneficial in that friction during insertion is reduced.

[0063] During assembly, one end of the shaft 3 is inserted into the shaft hole 20 via the other end opening 22. One axial side of the insertion portion 40 has a relatively small diameter, so the shaft 3 smoothly advances axially inside the shaft hole 20. As the insertion progresses, the step surface 41c of the insertion portion 40 abuts against the other end face of the gear 2 (the peripheral edge of the other end opening). Thereafter, the shaft 3 is press-fitted into the shaft hole 20.

[0064] As a result, when the insertion portion 40 is positioned inside the shaft hole 20 and insertion of the shaft 3 into the shaft hole 20 is completed, the shaft hole 20 and the insertion portion 40 form a first fitting portion 1A at one axial end. The shaft hole 20 and the insertion portion 40 form a second fitting portion 1B at the other axial end. The fitting structure 1 according to this embodiment also has two types of fitting portions.

[0065] The first fitting portion 1A is located on one axial side of the predetermined position 40a and is a clearance fit. The first fitting portion 1A is composed of an inner peripheral surface 23 and a one-end outer peripheral surface 41a. The inner diameter R2 is larger than the first outer diameter R3a, and the first clearance δa is a positive value.

[0066] In contrast, the second fitting portion 1B is located on the other axial side of the predetermined position 40a, and is an intermediate fit. The second fitting portion 1B is composed of an inner peripheral surface 23 and an outer peripheral surface 41b on the other end side. Before the start of insertion, the inner diameter R2 is smaller than the second outer diameter R3b, and the second clearance δb is a negative value (the absolute value is shown in the drawing). In this embodiment, as in the above embodiment, it is possible to achieve both improved assembly and improved operability.

[0067] (Fourth embodiment) Next, with reference to FIG. 11, a fitting structure according to a fourth embodiment will be described, focusing on the differences from the first embodiment.

[0068] In this embodiment, the inner diameter R2 of the shaft hole 20 varies depending on the axial position. The gear 2 has a one-end inner peripheral surface 23a that defines one axial side of the shaft hole 20, and an other-end inner peripheral surface 23b that defines the other axial side. Furthermore, the gear 2 has a flange portion 24 that protrudes radially inward from both the one-end inner peripheral surface 23a and the other-end inner peripheral surface 23b at a predetermined axial position of the shaft hole 20. In FIG. 11, the flange portion 24 is provided at a predetermined position closer to the other-end opening 22 than the one-end opening 21, but the position at which the flange portion 24 is provided can be appropriately determined depending on the ease of assembly, the length of the shaft 3, the use of the fitting structure 1, and the like. The flange portion 24 has a flange inner peripheral surface 23d as a part of the inner peripheral surface 23 of the shaft hole 20. The flange inner peripheral surface 23d is continuous with the one-end inner peripheral surface 23a via an end face 23c1 on one side of the flange portion 24. Furthermore, the flange inner peripheral surface 23d is continuous with the other end side inner peripheral surface 23b via the other end surface 23c2 of the flange portion 24.

[0069] The inner diameter R2 of the shaft hole 20 includes a first inner diameter R2a of the one-end inner circumferential surface 23a, a second inner diameter R2b of the other-end inner circumferential surface 23b, and a third inner diameter R2c of the flange inner circumferential surface 23d. The first inner diameter R2a and the second inner diameter R2b are larger than the third inner diameter R2c. In the example shown in Fig. 11, the second inner diameter R2b is larger than the first inner diameter R2a, but the magnitude relationship between the first inner diameter R2a and the second inner diameter R2b is not particularly limited.

[0070] In contrast, the insertion portion 40 has a constant outer diameter R3 over the entire axial direction. The outer diameter R3 is smaller than both the first inner diameter R2a and the second inner diameter R2b. The outer diameter R3 is equal to or larger than the third inner diameter R2c.

[0071] During assembly, the shaft 3 may be inserted into the shaft hole 20 via the one-end opening 21 or the other-end opening 22. In either case, the shaft 3 can be inserted into the shaft hole 20 by a clearance fit. After the shaft 3 reaches the flange portion, the shaft 3 is press-fit into the shaft hole 20 so as to pass through the inner peripheral surface of the flange. The axial length of the flange portion 24 is shorter than the one-end inner peripheral surface and the other-end inner peripheral surface. Therefore, resistance generated by the press-fitting is small, and deterioration of the ease of assembly in the latter half of the insertion operation can be suppressed.

[0072] As a result, when the insertion portion 40 is positioned inside the shaft hole 20 and the insertion of the shaft 3 into the shaft hole 20 is completed, the shaft hole 20 and the insertion portion 40 form a first fitting portion 1A at one axial end, a second fitting portion 1B at the center in the axial direction, and a third fitting portion 1C at the other axial end.

[0073] The first fitting portion 1A is a clearance fit. The second fitting portion 1B is an intermediate fit or an interference fit. The third fitting portion 1C is a clearance fit, like the first fitting portion 1A. The second fitting portion 1B, to which an intermediate fit or a wet fit is applied, does not necessarily need to be formed up to the opening on the other end side. In this embodiment, as in the above embodiment, both improved assembly and improved operability can be achieved.

[0074] (Modification) Although the embodiment has been described above, the above configurations can be appropriately changed or deleted within the scope of the present invention.

[0075] In the above embodiment, the diameter of one of the shaft hole 20 and the insertion portion 40 varies depending on the axial position, while the diameter of the other is constant throughout the axial direction. This is merely an example, and both diameters may vary. When the outer diameter R3 of the shaft 3 is changed, the one-end outer peripheral surface 41a may be a conical surface, as in the second embodiment.

[0076] The fitting structure 1 is useful when applied to an oil-free screw compressor because it can improve both the production efficiency and the operating performance of the compressor. However, the fitting structure may be applied to power transmission other than that of a compressor.

[0077] In the fourth embodiment, a fitting member (not shown) separate from the gear 2 and the shaft 3 may be provided in the third fitting portion 1C to realize a fitting structure between the gear 2 and the shaft 3. That is, in the third fitting portion 1C, the inner peripheral surface 23b at the other end side of the shaft hole 20 of the gear 2 and the outer peripheral surface 41 of the shaft 3 do not realize a fitting structure, but the gear 2 and the shaft 3 are fitted together via a fitting member (not shown). Therefore, the difference between the inner peripheral surface 23b at the other end side of the shaft hole 20 of the gear 2 and the outer peripheral surface 41 of the shaft 3 is large enough to allow the fitting member to be provided. Note that, as in the fourth embodiment, the first fitting portion 1A is a clearance fit, and the second fitting portion 1B is an intermediate fit or an interference fit.

[0078] The present disclosure may include the following aspects. (Aspect 1) A gear engagement structure that rotates integrally with a shaft, a shaft hole provided in the gear, the shaft hole being open at both ends in an axial direction and through which the shaft is inserted; an insert provided on the shaft and positioned within the shaft hole; Equipped with When the difference between the inner diameter of the shaft hole and the outer diameter of the insertion portion at the same position in the axial direction is defined as a clearance, a first clearance at an opening on one end side in the axial direction of the shaft hole is larger than a second clearance at a predetermined position on the other side in the axial direction from the opening on the one end side; Gear fitting structure. (Aspect 2) the clearance is constant at the first clearance from the one end opening toward the predetermined position, and switches from the first clearance to the second clearance at the predetermined position; 2. The gear fitting structure according to claim 1. (Aspect 3) The clearance gradually decreases from the first clearance to the second clearance from the one end opening toward the predetermined position. 2. The gear fitting structure according to claim 1. (Aspect 4) the clearance is constant at the second clearance from the predetermined position toward the other axial end opening of the shaft hole, A gear fitting structure according to any one of aspects 1 to 3. (Aspect 5) The outer diameter of the insertion portion is constant in the axial direction, and the clearance changes according to a change in the inner diameter of the shaft hole. A gear fitting structure according to any one of aspects 1 to 4. (Aspect 6) a first fitting portion formed by the shaft hole and the insertion portion at one end side of the axial direction; a second fitting portion formed by the shaft hole and the insertion portion at the other end side in the axial direction of the first fitting portion; Equipped with The first fitting portion is a clearance fit, and the second fitting portion is an intermediate fit or an interference fit. A gear fitting structure according to any one of the first to fifth aspects. (Aspect 7) The shaft is a screw rotor shaft of a screw compressor, and the gear is a pinion that rotates integrally with the screw rotor shaft in the screw compressor. A gear fitting structure according to any one of the first to sixth aspects. [Explanation of symbols]

[0079] 1. Fitting structure 1A First fitting part 1B Second fitting part 1C 3rd fitting part 2. Gears 3-axis 11 Base 12 Boss section 13 Teeth 20 Shaft hole 20a Predetermined position 21 One end opening 22 Other end opening 23 Inner surface 23a Inner peripheral surface on one end side 23b Inner peripheral surface on other end side 23c Step surface 23c1,23c2 End face 23d Flange inner surface 24 Flange 31 Journal Section 32 Male thread 40 Insertion section 40a in place 41 Outer surface 41a One end side outer peripheral surface 41b Other end side outer peripheral surface 41c Step surface 80 Compressor 81 Compressor body 81A, 81B Casing 81C Cover 82 Gearbox 82A Gear casing 83 Male Rotor 84 Screw rotor shaft 86 Rotor Room 87 Bearing 88 Shaft seal 89a Intake port 89b Discharge port 90 Drive timing gear A axis A2 axis A3 axis L20 Shaft hole length L20a: Length from one end opening to a specified position L20b Length from a given position to the opening on the other end L40 Length of insertion tube L40a Length from one end of the insertion part to the specified position L40b Length from the specified position to the other end of the insertion part R2 Inner diameter R2a First inner diameter R2b 2nd inner diameter R2c 3rd inner diameter R3 outer diameter R3a 1st outer diameter R3b 2nd outer diameter δ Clearance δa First clearance δb Second clearance

Claims

1. A gear engagement structure that rotates integrally with a shaft, a shaft hole provided in the gear, the shaft hole being open at both ends in an axial direction and through which the shaft is inserted; an insert provided on the shaft and positioned within the shaft hole; Equipped with When the difference between the inner diameter of the shaft hole and the outer diameter of the insertion portion at the same position in the axial direction is defined as a clearance, a first clearance at an opening on one end side in the axial direction of the shaft hole is larger than a second clearance at a predetermined position on the other side in the axial direction from the opening on the one end side; Gear fitting structure.

2. the clearance is constant at the first clearance from the one end opening toward the predetermined position, and switches from the first clearance to the second clearance at the predetermined position; The gear fitting structure according to claim 1.

3. the clearance gradually decreases from the first clearance to the second clearance from the one end opening toward the predetermined position; The gear fitting structure according to claim 1.

4. the clearance is constant at the second clearance from the predetermined position toward the other end opening of the shaft hole in the axial direction; The gear fitting structure according to any one of claims 1 to 3.

5. The outer diameter of the insertion portion is constant in the axial direction, and the clearance changes according to a change in the inner diameter of the shaft hole. The gear fitting structure according to any one of claims 1 to 3.

6. a first fitting portion formed by the shaft hole and the insertion portion at one end side of the axial direction; a second fitting portion configured by the shaft hole and the insertion portion at the other end side in the axial direction relative to the first fitting portion; Equipped with The first fitting portion is a clearance fit, and the second fitting portion is an intermediate fit or an interference fit. The gear fitting structure according to any one of claims 1 to 3.

7. The shaft is a rotor shaft of a screw compressor, and the gear is a pinion that rotates integrally with the rotor shaft in the screw compressor. The gear fitting structure according to any one of claims 1 to 3.

Images