SWEDEN PUMPS

Abstract

Roots pump (10) with: a housing (11) with a suction opening (34) through which a fluid is introduced and an outlet opening (35) through which the fluid is discharged; a rotor chamber (19) formed in the housing (11) and connected to the suction opening (34) and the outlet opening (35); a rotating shaft (25, 26, 27) which is arranged in the housing (11); a rotor (40, 44, 42) with an insertion hole (45) through which the rotating shaft (25, 26, 27) is inserted, and a hole-forming surface (64) that forms the insertion hole (45), wherein the rotor (40, 44, 42) is arranged to rotate in the rotor chamber (19) together with the rotating shaft (25, 26, 27) which is press-fitted in the hole-forming surface (64); and a first bearing (23) and a second bearing (24) which support the rotating shaft (25, 26, 27) on opposite sides of the rotor (40, 44, 42) so that the rotating shaft (25, 26, 27) is rotatable relative to the housing (11), each bearing having: an inner ring (51); an outer ring (52) that surrounds the inner ring (51) and is supported by the housing (11); and a rolling element (53) arranged between the inner ring (51) and the outer ring (52), wherein: the rotating shaft (25, 26, 27) is press-fitted into the inner ring (51) of the first bearing (23) and into the inner ring (51) of the second bearing (24) with a distance between the rotating shaft (25, 26, 27) and the inner ring (51) of the second bearing (24), a linear expansion coefficient of a housing material (11) and a linear expansion coefficient of a rotor material (40, 44, 42) are greater than a linear expansion coefficient of a rotating shaft material (25, 26, 27), and A rotation of the rotor (40, 44, 42) causes the fluid to be introduced into the rotor chamber (19) through the suction opening (34) and discharged from the rotor chamber (19) through the outlet opening (35), characterized in that an edge section of the hole formation surface (64) adjacent to the first bearing (23) serves as an interference fit section (65) in which the rotating shaft (25, 26, 27) is interference fitted, and at least one edge section of the hole formation surface (64) adjacent to the second bearing (24) serves as a spacer fit section (66) in which the rotating shaft (25, 26, 27) is fitted with a distance between the rotating shaft (25, 26, 27) and the spacer fit section (66).

Description

Background of the inventionTechnical field

[0001] The present invention relates to a Roots pump (or Roots pump). State of the art

[0002] A Roots pump includes a housing, a rotor chamber, a rotary shaft, and a rotor. The housing has a suction port and a discharge port. Fluid is introduced through the suction port. The fluid is discharged through the discharge port. The rotor chamber is formed in the housing. The rotor chamber is connected to the suction port and the discharge port. The rotary shaft is disposed in the housing. The rotor has an insertion hole through which the rotary shaft is inserted, and a hole forming surface forming the insertion hole. The rotor rotates in the rotor chamber, together with the rotary shaft press-fitted into the hole forming surface. That is, the hole forming surface has a press-fit portion into which the rotary shaft is press-fitted. The rotation of the rotor causes fluid to be introduced into the rotor chamber through the suction port and discharged from the rotor chamber through the discharge port.

[0003] Japanese Utility Model Application JP S59-165987 U discloses a known Roots pump comprising a first bearing and a second bearing supporting the rotating shaft on opposite sides of the rotor, respectively, so that the rotating shaft is rotatable relative to the housing. The first bearing and the second bearing each include an inner ring, an outer ring, and a rolling element. The outer ring surrounds the inner ring and is supported by the housing. The rolling element is disposed between the inner ring and the outer ring. The rotating shaft is, for example, press-fitted into the inner ring of the first bearing and fitted into the inner ring of the second bearing with a clearance between the rotating shaft and the inner ring of the second bearing.

[0004] During the rotation of such a Roots pump, the housing, rotor, and rotating shaft are affected by heat. The housing may thermally expand in the axial direction of the rotating shaft from the press-fit area of ​​the inner ring of the first bearing, into which the rotating shaft is press-fitted. Since the rotating shaft is fitted in the inner ring of the second bearing with a clearance between the rotating shaft and the inner ring, thermal expansion of the housing in the axial direction of the rotating shaft is unobstructed at a position between the second bearing and the rotating shaft. This prevents a load from being applied to the second bearing when the housing thermally expands in the axial direction of the rotating shaft.

[0005] The rotor and the rotating shaft thermally expand in the axial direction of the rotating shaft, causing the rotor to be displaced / offset in the axial direction of the rotating shaft. Since the rotating shaft is press-fitted in the hole formation surface, the amount of displacement of the rotor due to thermal expansion depends on the thermal expansion of the rotating shaft in the axial direction of the rotating shaft. A range in which the rotor thermally expands in the axial direction of the rotating shaft depending on the thermal expansion of the rotating shaft expands with an increase in the distance between the press-fit portion of the inner ring of the first bearing, into which the rotating shaft is press-fitted, and the press-fit portion of the hole formation surface, into which the rotating shaft is press-fitted.

[0006] For example, the linear expansion coefficient of the housing material and the linear expansion coefficient of the rotor material may be larger than the linear expansion coefficient of the rotating shaft material. This increases the difference between the offset amount of the housing and the offset amount of the rotor in the axial direction of the rotating shaft due to thermal expansion. This may therefore cause an excessive increase in the clearance between the rotor and the housing or contact between the rotor and the housing.

[0007] To prevent the rotor from coming into contact with the casing, it is necessary to increase the clearance between the rotor and the casing. However, excessively increasing the clearance between the rotor and the casing reduces the performance of the Roots pump. Accordingly, it is desirable to increase the performance of the Roots pump.

[0008] Patent specification DE 10 2020 108 266 A1 of the present applicant discloses a shaft component coupling structure comprising a shaft component and a press-fit component with a press-fit hole. The shaft component has a first cylindrical portion, a second cylindrical portion, a third cylindrical portion, and a fourth cylindrical portion. The press-fit hole has a first inner diameter portion, a second inner diameter portion, and a third inner diameter portion. A length A from an end portion to an end portion is greater than a length B from an end portion to an end portion. A length C from the end portion to an end portion is greater than a length D from the end portion to an end portion. The lengths A, B, C, and D satisfy a relationship of (AB) < (CD).

[0009] Patent DE 10 2022 104 412 A1 discloses a geared motor comprising a motor and a speed reducer. The geared motor comprises a first detector arrangement section for arranging a first rotation detector that detects rotation of a rotor shaft, a second detector arrangement section for arranging a second rotation detector that detects rotation of an output element of the speed reducer, and a third detector arrangement section for arranging a torque detector. The geared motor is operable when the first rotation detector is arranged in the first detector arrangement section, the second rotation detector is arranged in the second detector arrangement section, and the torque detector is arranged in the third detector arrangement section, and is operable even when a part of it is arranged.

[0010] The present invention, which has been made in view of the above-mentioned problem, is directed to providing a Roots pump having an increased performance. Summary of the invention

[0011] The above-mentioned technical problem is solved with a Roots pump according to claim 1. According to one aspect of the present invention, a Roots pump (or Roots lobe pump) is provided, comprising: a housing; a rotor chamber; a rotary shaft; a rotor; and a first bearing and a second bearing. The housing has a suction port through which a fluid is introduced and a discharge port through which the fluid is discharged. The rotor chamber is formed in the housing and connected to the suction port and the discharge port. The rotary shaft is arranged in the housing. The rotor has an insertion hole through which the rotary shaft is inserted, and a hole forming surface forming the insertion hole. The rotor is configured to rotate in the rotor chamber together with the rotary shaft press-fitted into the hole forming surface.The first bearing and the second bearing support the rotating shaft on opposite sides of the rotor, respectively, so that the rotating shaft is rotatable relative to the housing. Each of the first bearing and the second bearing includes an inner ring, an outer ring surrounding the inner ring and supported by the housing, and a rolling element disposed between the inner ring and the outer ring. The rotating shaft is press-fitted into the inner ring of the first bearing and fitted into the inner ring of the second bearing with a clearance (or clearance fit) between the rotating shaft and the inner ring of the second bearing. A linear expansion coefficient of a material of the housing and a linear expansion coefficient of a material of the rotor are larger than a linear expansion coefficient of a material of the rotating shaft.Rotation of the rotor causes the fluid to be introduced into the rotor chamber through the suction port and discharged from the rotor chamber through the discharge port. An edge portion of the hole-forming surface adjacent to the first bearing serves as a press-fit portion into which the rotary shaft is press-fitted. At least one edge portion of the hole-forming surface adjacent to the second bearing serves as a clearance-fit portion into which the rotary shaft is fitted, with a clearance (or clearance fit) between the rotary shaft and the clearance-fit portion.

[0012] Further aspects and advantages of the invention will become apparent from the following description taken in conjunction with the accompanying drawings, which illustrate by way of example the principles of the invention. Short description of the characters

[0013] The invention, together with objects and advantages thereof, will best be understood by reference to the following description of the embodiments together with the accompanying drawings in which: Fig. 1 is a cross-sectional view of a Roots pump according to one embodiment; Fig. 2 a cross-sectional view through the Roots pump along the line II-II in Fig. 1 is; Fig. Figure 3 is a partially enlarged cross-sectional view of the Roots pump; Fig. 4 is a partially enlarged cross-sectional view of a Roots pump according to another embodiment; Fig. 5 is a partially enlarged cross-sectional view of a Roots pump according to another embodiment; and Fig. 6 is a cross-sectional view of a Roots pump according to another embodiment. Detailed description of the embodiments

[0014] In the following, an embodiment of a Roots pump is described with reference to the attached Fig. 1 to 3. The Roots pump of the present embodiment is a hydrogen pump for a fuel cell used in a fuel cell system. The Roots pump is mounted on a vehicle, such as a fuel cell vehicle. The Roots pump introduces and discharges hydrogen gas as a fluid. <Gesamtkonfiguration von Rootspumpe 10>

[0015] As in Fig. As illustrated in Figure 1, a Roots pump 10 includes a housing 11. The housing 11 has a cylindrical shape. The housing 11 is made of a metallic material. For example, the housing 11 is made of aluminum.

[0016] The housing 11 comprises a first housing part 12, a second housing part 13, a third housing part 14, a fourth housing part 15, and a fifth housing part 16. The first housing part 12, the second housing part 13, the third housing part 14, the fourth housing part 15, and the fifth housing part 16 are joined together in one piece to form the housing 11.

[0017] The first housing part 12 has a first end wall 12a and a first peripheral wall 12b. The first end wall 12a has a plate shape. The first peripheral wall 12b has a cylindrical shape and extends from the outer peripheral portion of the first end wall 12a. The first housing part 12 has a first bearing holding portion 12c. The first bearing holding portion 12c has a cylindrical shape. The first bearing holding portion 12c protrudes into the first housing part 12 from the central portion of the inner surface of the first end wall 12a.

[0018] The second housing 13 has a second end wall 13a and a second peripheral wall 13b. The second end wall 13a has a plate shape. The second peripheral wall 13b has a cylindrical shape and extends from the outer peripheral portion of the second end wall 13a. The second housing 13 is connected to the first housing 12. The opening of the first peripheral wall 12b of the first housing 12 is closed by the second end wall 13a. The second housing 13 has a pair of second bearing holding portions 13c. The pair of second bearing holding portions 13c are formed in the second end wall 13a. One of the second bearing holding portions 13c is a hole formed through the second end wall 13a in the thickness direction of the second end wall 13a. The other of the second bearing holding portions 13c is a recess formed in the inner surface of the second end wall 13a.

[0019] The third housing 14 has a third end wall 14a and a third peripheral wall 14b. The third end wall 14a has a plate shape. The third peripheral wall 14b has a cylindrical shape and extends from the outer peripheral portion of the third end wall 14a. The third housing 14 is connected to the second housing 13. The opening of the second peripheral wall 13b of the second housing 13 is closed by the third end wall 14a. The third housing 14 has a pair of third bearing holding portions 14c. The pair of third bearing holding portions 14c are formed in the third end wall 14a. The pair of third bearing holding portions 14c are holes formed through the third end wall 14a in the thickness direction of the third end wall 14a.

[0020] The fourth housing part 15 has a fourth end wall 15a, a hub 15b, and a pair of fourth bearing holding portions 15c. The fourth end wall 15a has a plate shape. The fourth housing part 15 is connected to the third housing part 14. The opening of the third peripheral wall 14b of the third housing part 14 is closed by the fourth end wall 15a. The hub 15b has a cylindrical shape. The hub 15b protrudes from the fourth end wall 15a. The pair of fourth bearing holding portions 15c are formed in the hub 15b.

[0021] The fifth housing part 16 has a plate shape. The fifth housing part 16 is connected to the fourth housing part 15. The opening of the hub 15b is closed by the fifth housing part 16.

[0022] The Roots pump 10 includes a motor chamber 17, a gear chamber 18, a rotor chamber 19, and a pair of bearing-receiving chambers 20. The motor chamber 17, the gear chamber 18, the rotor chamber 19, and the pair of bearing-receiving chambers 20 are formed in the housing 11. The motor chamber 17 is defined by the first end wall 12a, the first peripheral wall 12b, and the second end wall 13a. The gear chamber 18 is defined by the second end wall 13a, the second peripheral wall 13b, and the third end wall 14a. Each of the second bearing-receiving portions 13c opens to the gear chamber 18.

[0023] The Roots pump 10 includes a bearing 21. The bearing 21 is held by the first bearing holding portion 12c. The Roots pump 10 includes a pair of bearings 22. Each of the bearings 22 is held by the corresponding second bearing holding portion 13c. The pair of bearings 22 is located between the motor chamber 17 and the transmission chamber 18.

[0024] The rotor chamber 19 is defined by the third end wall 14a, the third peripheral wall 14b, and the fourth end wall 15a. That is, the rotor chamber 19 is defined by the third housing part 14 and the fourth housing part 15. The third housing part 14 serves as the first housing component of the present invention. The fourth housing part 15 serves as the second housing component of the present invention. That is, the housing 11 includes the first housing component and the second housing component. Each of the third bearing holding portions 14c opens to the gear chamber 18 and the rotor chamber 19. The pair of third bearing holding portions 14c is located between the gear chamber 18 and the rotor chamber 19.

[0025] The Roots pump 10 includes a pair of first bearings 23 and a pair of second bearings 24. Each of the first bearings 23 is held by the corresponding third bearing holding portion 14c. That is, the pair of first bearings 23 is held by the third housing part 14 serving as the first housing component.

[0026] The pair of bearing receiving chambers 20 are defined / bounded by the hub 15b and the fifth housing part 16. Each of the second bearings 24 is held by the corresponding fourth bearing holding portion 15c. That is, the pair of second bearings 24 is held by the fourth housing part 15 serving as the second housing component.

[0027] The Roots pump 10 has a rotating shaft 25. The rotating shaft 25 is arranged in the housing 11. The rotating shaft 25 has a drive shaft 26 and an output shaft 27 (or driven shaft 27). In the following description, the drive shaft 26 and the output shaft 27 may be referred to simply as the rotating shaft 25.

[0028] The drive shaft 26 and the output shaft 27 are made of a metallic material. The drive shaft 26 and the output shaft 27 are made of stainless steel, for example. Accordingly, the linear expansion coefficient of the material of the housing 11 is greater than the linear expansion coefficient of the material of the rotary shaft 25.

[0029] The input shaft 26 and the output shaft 27 are arranged parallel to each other. A direction in which an axis L1 of the input shaft 26 and an axis L2 of the output shaft 27 extend serves as the axial direction of the rotary shaft 25. The input shaft 26 penetrates the second end wall 13a, the third end wall 14a, and the fourth end wall 15a. The output shaft 27 penetrates the third end wall 14a and the fourth end wall 15a. The input shaft 26 is rotatably supported by the housing 11 via the bearing 21, the bearing 22, the first bearing 23, and the second bearing 24. The output shaft 27 is rotatably supported by the housing 11 via the bearing 22, the first bearing 23, and the second bearing 24.

[0030] The Roots pump 10 has a first sealing element 28, a pair of second sealing elements 29, and a pair of third sealing elements 30. The first sealing element 28 is arranged in the second end wall 13a. The first sealing element 28 seals a gap between the drive shaft 26 and the second end wall 13a. The pair of second sealing elements 29 is arranged in the third end wall 14a. One of the second sealing elements 29 seals a gap between the drive shaft 26 and the third end wall 14a. The other of the second sealing elements 29 seals a gap between the output shaft 27 and the third end wall 14a. The pair of third sealing elements 30 is arranged in the fourth end wall 15a. One of the third sealing elements 30 seals a gap between the drive shaft 26 and the fourth end wall 15a. The other of the third sealing elements 30 seals a gap between the output shaft 27 and the fourth end wall 15a.

[0031] The Roots pump 10 has a motor 31. The motor 31 is housed in the motor chamber 17. That is, the motor chamber 17 houses the motor 31. The motor 31 is connected to the drive shaft 26. The motor 31 drives the drive shaft 26.

[0032] The Roots pump 10 has a drive gear 32 and a driven gear 33. The drive gear 32 and the driven gear 33 are housed in the gear chamber 18. The gear chamber 18 houses the drive gear 32 and the driven gear 33. The drive gear 32 is fixed to the drive shaft 26. The driven gear 33 is fixed to the output shaft 27. The output gear 33 meshes with the drive gear 32 and rotates together with it. The output shaft 27 is rotated by the drive gear 32 and the driven gear 33 in the opposite direction of the rotation of the drive shaft 26.

[0033] As in Fig. 1 and Fig. 2, the housing 11 has a suction port 34 and an exhaust port 35. The suction port 34 and the exhaust port 35 are formed by the fourth housing part 15 and the fifth housing part 16. That is, the fourth housing part 15, which serves as the second housing component, has the suction port 34 and the exhaust port 35. The rotor chamber 19 is connected to the suction port 34 and the exhaust port 35. Hydrogen gas is introduced into the rotor chamber 19 through the suction port 34. The hydrogen gas is exhausted from the rotor chamber 19 through the exhaust port 35.

[0034] The Roots pump 10 includes a rotor 40. The rotor 40 includes a drive rotor 41 and an output rotor 42. In the following description, the drive rotor 41 and the output rotor 42 may be simply referred to as the rotor 40. The drive rotor 41 and the output rotor 42 are made of a metallic material. For example, the drive rotor 41 and the output rotor 42 are made of aluminum. Accordingly, the linear expansion coefficient of the material of the rotor 40 is equal to the linear expansion coefficient of the material of the housing 11. Therefore, the linear expansion coefficient of the material of the housing 11 and the linear expansion coefficient of the material of the rotor 40 are greater than the linear expansion coefficient of the material of the rotating shaft 25.

[0035] As in Fig. As illustrated in Figure 2, the drive rotor 41 and the driven rotor 42 are housed in the rotor chamber 19. The drive rotor 41 and the driven rotor 42 are two-blade rotors, each having two blades in a cross-section perpendicular to the axial direction of the drive shaft 26 and the output shaft 27. The drive rotor 41 and the driven rotor 42 each have a pair of toothed portions 43 and a shaft support portion 44 located between the toothed portions 43.

[0036] The shaft support portion 44 has an insertion hole 45 and a hole forming surface 64 that forms the insertion hole 45. That is, (both) the drive rotor 41 and (respectively) the driven rotor 42 as the rotor 40 (i.e., the rotor of the present invention) each have the insertion hole 45 (i.e., the insertion hole of the present invention). The insertion hole 45 is formed through the shaft support portion 44. The insertion hole 45 has a constant hole diameter. The drive shaft 26 is inserted through the insertion hole 45 of the drive rotor 41. The driven shaft 27 is inserted through the insertion hole 45 of the driven rotor 42. That is, the rotary shaft 25 is inserted through the insertion hole 45.

[0037] The outer peripheral surfaces of the tooth portions 43 form the projections of the rotor 40. The outer peripheral surfaces of the shaft support portions 44 form the recesses of the rotor 40. The tooth portions 43 of the drive rotor 41 and the shaft support portions 44 of the driven rotor 42 are configured to mesh with each other. The shaft support portions 44 of the drive rotor 41 and the tooth portions 43 of the driven rotor 42 are configured to mesh with each other. The pair of tooth portions 43 has a solid structure. The rotor 40 has a solid structure as a whole except for the insertion holes 45. That is, the rotor 40 of the present embodiment has a solid structure as a whole. The drive rotor 41 and the driven rotor 42 are configured so that the drive rotor 41 and the driven rotor 42 mesh with each other. The drive rotor 41 is attached to the drive shaft 26.The drive rotor 41 rotates together with the drive shaft 26 in the rotor chamber 19. The output rotor 42 is attached to the output shaft 27. The output rotor 42 rotates together with the output shaft 27 in the rotor chamber 19. The output rotor 42 rotates together with the drive rotor 41. The drive rotor 41 rotates in the direction indicated by an arrow R1 in . Fig. 2, and the output rotor 42 rotates in the direction indicated by an arrow R2 in Fig. 2 indicated direction.

[0038] The suction opening 34 is connected to a hydrogen outlet 48a of a fuel cell 48 via a first connecting line 46. The outlet opening 35 is connected to a hydrogen inlet 48b of the fuel cell 48 via a second connecting line 47.

[0039] When the drive shaft 26 is rotated by the activated motor 31, the drive gear 32 and the driven gear 33, which mesh with each other, rotate synchronously. As the drive gear 32 and the driven gear 33 rotate synchronously, the drive shaft 26 and the driven shaft 27 rotate in opposite directions. Accordingly, the drive rotor 41 and the driven rotor 42, which mesh with each other, rotate in opposite directions. This causes hydrogen gas that has not reacted with oxygen in the fuel cell 48 to be introduced into the rotor chamber 19 through the hydrogen outlet 48a, the first connecting pipe 46, and the suction port 34 in the Roots pump 10. The hydrogen gas introduced into / to the rotor chamber 19 is / is discharged through the outlet opening 35 and supplied to the fuel cell 48 through the second connecting line 47 and the hydrogen inlet 48b.Accordingly, the Roots pump 10 supplies the hydrogen gas to the fuel cell 48 through the rotation of the drive rotor 41 and the driven rotor 42. Thus, in the Roots pump 10, with the rotation of the drive rotor 41 and the driven rotor 42, the hydrogen gas is introduced into the rotor chamber 19 through the suction port 34 and discharged from the rotor chamber 19 through the discharge port 35.

[0040] As in Fig. 3, each of the first bearings 23 and the second bearings 24 includes an inner ring 51, an outer ring 52, and a rolling element 53. The outer ring 52 surrounds the inner ring 51 and is supported by the housing 11. The rolling element 53 is disposed between the inner ring 51 and the outer ring 52. The first bearing 23 and the second bearing 24 of the present embodiment are ball bearings including balls, which, in this embodiment, are the rolling element 53 between the inner ring 51 and the outer ring 52. The first bearing 23 and the second bearing 24 may be roller bearings with rollers serving as the rolling element 53.

[0041] One of the first bearings 23 and one of the second bearings 24 support the input shaft 26, respectively, on opposite sides of the input rotor 41, so that the input shaft 26 is rotatable relative to the housing 11. The other of the first bearings 23 and the other of the second bearings 24 support the output shaft 27, respectively, on opposite sides of the output rotor 42, so that the output shaft 27 is rotatable relative to the housing 11. The input shaft 26 is press-fitted into the inner ring 51 of one of the first bearings 23 and into the inner ring 51 of one of the second bearings 24, with a clearance (or clearance fit) between the input shaft 26 and the inner ring 51 of one of the second bearings 24. The output shaft 27 is press-fitted into the inner ring 51 of the other of the first bearings 23, and into the inner ring 51 of the other of the second bearings 24 with a clearance (ora clearance fit) between the output shaft 27 and the inner ring 51 of the other of the second bearings 24.

[0042] The outer ring 52 of each first bearing 23 is tightly fitted into the corresponding third bearing holding portion 14c. The inner rings 51 of the first bearing 23 rotate together with the rotating shaft 25. The outer ring 52 of each second bearing 24 is tightly fitted into the corresponding fourth bearing holding portion 15c. O-rings 54 are attached to a portion of the rotating shaft 25 located inside the inner rings 51 of the second bearing 24. The inner rings 51 of the second bearing 24 rotate together with the rotating shaft 25 via the O-rings 54. <Verhältnis zwischen dem Rotor 40 und der Drehwelle 25>

[0043] The following describes the relationship between the rotor 40 and the rotating shaft 25. The relationship between the drive rotor 41 and the drive shaft 26 is almost the same as the relationship between the output rotor 42 and the output shaft 27 and will be referred to and described simply as the relationship between the rotor 40 and the rotating shaft 25.

[0044] The input shaft 26 and the output shaft 27 (ie, the rotary shaft 25) each have a large diameter portion 61, a small diameter portion 62, and a middle diameter portion 63. The large diameter portions 61, the small diameter portions 62, and the middle diameter portions 63 of the input shaft 26 and the output shaft 27 are a portion located within the corresponding insertion holes 45. The outer diameter of each large-diameter section 61 is larger than the outer diameter of the small-diameter section 62 and the outer diameter of the middle-diameter section 63. The outer diameter of the middle-diameter section 63 is larger than the outer diameter of the small-diameter section 62. The large-diameter section 61 is located closer to the first bearing 23 than the small-diameter section 62 and the middle-diameter section 63 are to the first bearing 23.The insertion hole 45 is formed through the hole-forming surface 64, and the large-diameter portion 61 is press-fitted into an edge portion of the hole-forming surface 64 adjacent to the first bearing 23. Accordingly, the edge portion of the hole-forming surface 64 adjacent to the first bearing 23 serves as a press-fit portion 65 into which the rotating shaft 25 is press-fitted. The rotor 40 rotates in the rotor chamber 19 together with the rotating shaft 25 press-fitted into the hole-forming surface 64.

[0045] Each intermediate diameter portion 63 is continuous with an end of the large diameter portion 61 remote from the first bearing 23. Each small diameter portion 62 is continuous with an end of the intermediate diameter portion 63 remote from the large diameter portion 61. The intermediate diameter portion 63 is closer to the second bearing 24 than the large diameter portion 61 and the small diameter portion 62 are to the second bearing 24. The intermediate diameter portion 63 is fitted in an edge portion of the hole formation surface 64 adjacent to the second bearing 24 with a clearance (or clearance fit) between the intermediate diameter portion 63 of the rotary shaft 25 and the hole formation surface 64. Accordingly, the edge portion of the hole forming surface 64 adjacent to the second bearing 24 serves as a clearance fitting portion 66 in which the rotary shaft 25 is fitted with a clearance (ora clearance fit) between the rotary shaft 25 and the clearance fit portion 66. In the Roots pump 10 of the present embodiment, only the edge portion of the hole formation surface 64 adjacent to the second bearing 24 serves as the pitch fitting portion 66. The distance (or pitch fit) between the medium diameter portion 63 of the rotary shaft 25 and the pitch fitting portion 66 is smaller than a distance (or pitch fit) between the small diameter portion 62 of the rotary shaft 25 and a part of the hole formation surface 64 between the press-fitting portion 65 and the pitch fitting portion 66. The distance between the pitch fitting portion 66 and the rotary shaft 25 is determined to prevent interference between the medium diameter portion 63 of the rotary shaft 25 and the hole formation surface 64 when both the rotor 40 and the rotary shaft 25 thermally expand. [Operation]

[0046] The operation of the Roots pump according to the present embodiment will be described below.

[0047] While the Roots pump 10 is driven, the housing 11, the rotor 40, and the rotating shaft 25 are affected by heat. For example, the third housing part 14 thermally expands in the axial direction of the rotating shaft 25 from a press-fit area of ​​the inner ring 51 of the first bearing 23 into which the rotating shaft 25 is press-fitted. The fourth housing part 15 also thermally expands in the axial direction of the rotating shaft 25 following the thermal expansion of the third housing part 14. The thermal expansion of the fourth housing part 15 in the axial direction of the rotary shaft 25 is not hindered at a position between the second bearing 24 and the rotary shaft 25 because the rotary shaft 25 is fitted into the inner ring 51 of the second bearing 24 with a clearance (or clearance fit) between the rotary shaft 25 and the inner ring 51 of the second bearing 24.This prevents a load from being applied to the second bearing 24 when the fourth housing part 15 thermally expands in the axial direction of the rotary shaft 25.

[0048] The rotor 40 and the rotating shaft 25 thermally expand in the axial direction of the rotating shaft 25, so that the rotor 40 is displaced in the axial direction of the rotating shaft 25. Since the rotating shaft 25 is press-fitted into the hole-forming surface 64, the amount of displacement of the rotor 40 due to thermal expansion depends on the thermal expansion of the rotating shaft 25 in the axial direction of the rotating shaft 25. A range in which the rotor 40 thermally expands in the axial direction of the rotating shaft 25 depending on the thermal expansion of the rotating shaft 25 expands with an increase in the distance between the press-fit portion of the inner ring 51 of the first bearing 23, into which the rotating shaft 25 is press-fitted, and the press-fit portion 65 of the hole-forming surface 64.

[0049] The edge portion of the hole formation surface 64 adjacent to the first bearing 23 serves as the press-fit portion 65. This configuration can minimize the distance between the press-fit portion of the inner ring 51 of the first bearing 23, into which the rotating shaft 25 is press-fitted, and the press-fit portion 65 of the hole formation surface 64, thereby reducing the area in the axial direction where the rotor 40 thermally expands in the axial direction of the rotating shaft 25 due to the thermal expansion of the rotating shaft 25. This configuration therefore reduces the difference between the displacement amount of the third housing part 14 and the displacement amount of the rotor 40 in the axial direction of the rotating shaft 25 due to the thermal expansion. This configuration is therefore suitable for preventing an excessive increase in the clearance (orthe clearance fit) between the rotor 40 and the fourth housing part 15 or to prevent contact of the rotor 40 with the third end wall 14a of the third housing part 14.

[0050] According to the present embodiment, the edge portion of the hole-forming surface 64 adjacent to the first bearing 23 serves as the press-fit portion 65 into which the rotating shaft 25 is press-fitted. This configuration can cause hydrogen gas pressure to act on the rotor 40, thereby causing deformation of the rotor 40 in the radially inward direction of the rotating shaft 25 from the press-fit portion 65. However, the edge portion of the hole-forming surface 64 adjacent to the second bearing 24 serves as the clearance-fit portion 66 into which the rotating shaft 25 is fitted with a clearance (or clearance fit) between the rotating shaft 25 and the clearance-fit portion 66. This configuration minimizes the distance between the rotating shaft 25 and the edge portion of the hole-forming surface 64 adjacent to the second bearing 24.This configuration therefore reduces the deformation of the rotor 40 in the radially inward direction of the rotary shaft 25 from the press-fit portion 65, even when a pressure of the hydrogen gas acts on the rotor 40. This configuration is therefore suitable for preventing an excessive increase in the clearance (or clearance fit) between the rotor 40 and the third peripheral wall 14b of the third housing part 14. [Beneficial effects]

[0051] The above embodiment offers the following advantageous effects. (1) The edge portion of the hole formation surface 64 23 adjacent to the first bearing serves as the press-fitting portion 65 into which the rotating shaft 25 is press-fitted. This configuration can minimize the clearance between the press-fitting portion of the inner ring 51 of the first bearing 23, into which the rotating shaft 25 is press-fitted, and the press-fitting portion 65 of the hole formation surface 64, thereby reducing the range in the axial direction where the rotor 40 thermally expands in the axial direction of the rotating shaft 25 due to the thermal expansion of the rotating shaft 25. This configuration therefore reduces the difference between the displacement amount of the housing 11 and the displacement amount of the rotor 40 in the axial direction of the rotating shaft 25 due to the thermal expansion. This configuration is therefore suitable for preventing an excessive increase in the clearance (or the clearance).the clearance fit) between the rotor 40 and the housing 11 or to prevent contact of the rotor 40 with the housing 11.

[0052] According to the present embodiment, the edge portion of the hole formation surface 64 adjacent to the first bearing 23 serves as the press-fit portion 65 into which the rotating shaft 25 is press-fitted. This configuration may cause pressure of the hydrogen gas to act on the rotor 40, thereby causing deformation of the rotor 40 in the radially inward direction of the rotating shaft 25 from / to the press-fit portion 65. When the rotor 40 deforms in the radially inward direction of the rotating shaft 25 from / to the press-fit portion 65, the clearance between the rotor 40 and the housing 11 may excessively increase, and the performance of the Roots pump 10 may therefore decrease.

[0053] However, the edge portion of the hole-forming surface 64 adjacent to the second bearing 24 serves as the clearance-fitting portion 66 into which the rotating shaft 25 is fitted, with a clearance between the rotating shaft 25 and the clearance-fitting portion 66. This configuration can minimize the clearance between the rotating shaft 25 and the edge portion of the hole-forming surface 64 adjacent to the second bearing 24. This configuration can therefore reduce the deformation of the rotor 40 in the radially inward direction of the rotating shaft 25 from / to the press-fitting portion 65, even when a pressure of the hydrogen gas acts on the rotor 40. This configuration therefore prevents an excessive increase in the clearance (or clearance fit) between the rotor 40 and the housing 11. Accordingly, this configuration increases the performance of the Roots pump 10. (2) According to the present embodiment, only the edge portion of the hole formation surface 64 adjacent to the second bearing 24 serves as the pitch fitting portion 66. This configuration facilitates control of the distance between the rotating shaft 25 and the edge portion of the hole formation surface 64 adjacent to the second bearing 24. This configuration thus enables minimization of the distance between the rotating shaft 25 and the edge portion of the hole formation surface 64 adjacent to the second bearing 24. This configuration therefore allows reduction of the deformation of the rotor 40 in the radially inward direction of the rotating shaft 25 from / from the press fitting portion 65 even when a pressure of the hydrogen gas acts on the rotor 40. (3) The rotor 40 has a solid structure as a whole. This configuration increases the overall rigidity of the rotor 40 and is therefore suitable for preventing deformation of the rotor 40. This configuration is suitable for preventing interference between the rotor 40 and the housing 11 due to deformation of the rotor 40 in the radially outward direction of the rotating shaft 25, which may be caused by the interference fit of the rotating shaft 25 in the interference fit portion 65. (4) The fourth housing 15 has the suction port 34 and the exhaust port 35, so the temperature of the fourth housing 15 is likely to be higher than the temperature of the third housing 14 due to the introduction and discharge of the hydrogen gas. Accordingly, the fourth housing 15 is more likely to thermally expand than the third housing 14. According to the present embodiment, the first bearing 23 is held by the third housing 14. The inner ring 51 of the first bearing 23 needs to have an interference fit clearance in consideration of the displacement amount of the third housing 14 due to thermal expansion. The displacement amount of the third housing 14 due to thermal expansion is smaller than the displacement amount of the fourth housing 15 due to thermal expansion. This allows an interference fit clearance for the inner ring 51 of the first bearing 23 to be easily ensured.Accordingly, the configuration of the Roots pump 10 in which the first bearing 23 and the second bearing 24 are respectively held by the third housing part 14 (i.e., the first housing component) and the fourth housing part 15 (i.e., the second housing component) facilitates a design of the Roots pump 10. [Modification]

[0054] The above embodiment may be modified as follows. The embodiment and the following modifications may be combined with each other to a technically consistent extent. ◯ As in Fig. As shown in Figure 4, the hole-forming surface 64, except for the edge portion of the hole-forming surface 64 serving as the press-fit portion 65, can serve as the clearance-fitting portion 66. That is, at least the edge portion of the hole-forming surface 64 adjacent to the second bearing 24 serves as the clearance-fitting portion 66, in which the rotating shaft 25 is fitted with a clearance (or clearance fit) between the rotating shaft 25 and the clearance-fitting portion 66. The configuration in which the hole-forming surface 64, except for the edge portion of the hole-forming surface 64 serving as the press-fit portion 65, serves as the clearance-fitting portion 66 facilitates machining of the hole-forming surface 64 or the outer peripheral surface of the rotating shaft 25. This thus enables simplification of the configuration of the Roots pump 10. ◯ As in Fig. 5, the rotor 40 may have a solid structure only in a portion of the rotor 40 that overlaps the press-fit portion 65 in the radial direction of the rotary shaft 25. According to this modification, the rotor 40 has a recess 70. The recess 70 is formed in each of the tooth portions 43. The recess 70 opens at the end face of the rotor 40 adjacent to the fourth housing part 15. The recess 70 is formed in a part of the tooth portion 43 that overlaps the medium-diameter portion 63 and the small-diameter portion 62 of the rotary shaft 25 in the radial direction of the rotary shaft 25. The rotor 40 has a solid structure in the portion of the rotor 40 that overlaps the press-fit portion 65 in the radial direction of the rotary shaft 25. This configuration is therefore suitable for suppressing the deformation of the portion of the rotor 40 that overlaps the press-fit portion 65 in the radial direction of the rotary shaft 25.This configuration is therefore suitable for preventing interference between the rotor 40 and the housing 11 due to deformation of the rotor 40 in the radially outward direction of the rotating shaft 25, which may be caused by the press fit of the rotating shaft 25 in the press fit portion 65. In addition, this configuration reduces the weight of the rotor 40 compared to a configuration of the rotor 40 with a solid structure as a whole. This configuration therefore reduces the inertia of the rotor 40. ◯ As in Fig.6, the rotor 40 may have a through-hole 71 formed through the rotor 40 and located outside the insertion hole 45 in the radial direction of the rotary shaft 25. The rotor 40 may have a rib 72 in the through-hole 71 at a position overlapping the press-fitting portion 65 in the radial direction of the rotary shaft 25. The through-hole 71 is formed in each of the tooth portions 43. This configuration suppresses deformation of the portion of the rotor 40 that overlaps the press-fitting portion 65 in the radial direction of the rotary shaft 25. This configuration is therefore suitable for preventing interference between the rotor 40 and the housing 11 due to deformation of the rotor 40 in the radially outward direction of the rotary shaft 25, which may be caused by the press-fitting of the rotary shaft 25 in the press-fitting portion 65. The through hole 71 is formed through the rotor 40.This configuration suppresses the accumulation of foreign matter in the rotor chamber 19 in the through-hole 71. Accordingly, this configuration suppresses an increase in the weight of the rotor 40. This configuration also reduces the inertia of the rotor 40. ◯ In the above embodiment, the portion of the rotary shaft 25 located within the insertion hole 45 may have a constant diameter. In this configuration, the insertion hole 45 may have a small diameter near the first bearing 23 and a large diameter near the second bearing 24. Accordingly, the edge portion of the hole-forming surface 64 adjacent to the first bearing 23 may serve as the press-fit portion 65, and the edge portion of the hole-forming surface 64 adjacent to the second bearing 24 may serve as the pitch-fit portion 66. ◯ In the above-mentioned embodiment, the first bearing 23 can be held by the fourth housing part 15 and the second bearing 24 by the third housing part 14. ◯ In the above embodiment, the suction opening 34 and the outlet opening 35 can be formed, for example, in the third peripheral wall 14b of the third housing part 14. ◯ In the above embodiment, the drive rotor 41 and the output rotor 42 may be, for example, three-blade rotors each having three blades in the cross section perpendicular to the axial direction of the drive shaft 26 and the output shaft 27. ◯ In the above embodiment, the Roots pump 10 may not be mounted on the fuel cell vehicle. That is, the Roots pump 10 is not limited to vehicle-mounted Roots pumps. ◯ In the above embodiment, the Roots pump 10 requires a configuration that introduces and discharges a fluid, but cannot be a hydrogen pump for a fuel cell used in the fuel cell system.

[0055] The above embodiment includes configurations described in the following notes. <Anmerkung 1>

[0056] A roots pump with: a housing having a suction opening through which a fluid is introduced and an outlet opening through which the fluid is discharged; a rotor chamber formed in the housing and connected to the suction port and the discharge port; a rotating shaft arranged in the housing; a rotor having an insertion hole through which the rotary shaft is inserted and a hole-forming surface forming the insertion hole, the rotor being adapted to rotate in the rotor chamber together with the rotary shaft press-fitted in the hole-forming surface; and a first bearing and a second bearing supporting the rotary shaft on opposite sides of the rotor, respectively, so that the rotary shaft is rotatable relative to the housing, each of the first bearing and the second bearing comprising: an inner ring; an outer ring surrounding the inner ring and supported by the housing; and a rolling element arranged between the inner ring and the outer ring, wherein: the rotary shaft is press-fitted into the inner ring of the first bearing and into the inner ring of the second bearing with a clearance between the rotary shaft and the inner ring of the second bearing, a linear expansion coefficient of a material of the housing and a linear expansion coefficient of a material of the rotor are greater than a linear expansion coefficient of a material of the rotary shaft, and rotation of the rotor causes the fluid to be introduced into the rotor chamber through the suction opening and discharged from the rotor chamber through the outlet opening, whereby an edge portion of the hole forming surface adjacent to the first bearing serves as a press-fitting portion in which the rotary shaft is press-fitted, and at least one edge portion of the hole forming surface adjacent to the second bearing serves as a space fitting portion in which the rotary shaft is fitted with a space between the rotary shaft and the space fitting portion. <Anmerkung 2>

[0057] The Roots pump according to note 1, where only the edge portion of the hole formation surface adjacent to the second bearing serves as a clearance fit portion, and the distance between the rotary shaft and the spacer fitting portion is smaller than a distance between the rotary shaft and a part of the hole forming surface between the press fitting portion and the spacer fitting portion. <Anmerkung 3>

[0058] The Roots pump according to note 1, wherein the hole forming surface, except for the edge portion of the hole forming surface serving as the press-fitting portion, serves as the pitch-fitting portion. <Anmerkung 4>

[0059] The Roots pump according to any one of notes 1 to 3, wherein the rotor as a whole has a solid structure. <Anmerkung 5>

[0060] The Roots pump according to any one of notes 1 to 3, wherein the rotor has a solid structure only in a portion of the rotor overlapping the press-fitting portion in a radial direction of the rotary shaft. <Anmerkung 6>

[0061] The Roots pump according to one of the notes 1 to 3, where the rotor has: a through hole formed through the rotor and located outside the insertion hole in a radial direction of the rotary shaft; and a rib in the through hole at a position overlapping the press-fitting portion in the radial direction of the rotary shaft. <Anmerkung 7>

[0062] The Roots pump according to one of the notes 1 to 6, where the housing has a first housing component and a second housing component, the rotor chamber is defined by the first housing component and the second housing component, the second housing component has the suction opening and the outlet opening, the first bearing is held by the first housing component, and the second bearing is held by the second housing component.

Claims

[1] Roots pump (10) with: a housing (11) having a suction opening (34) through which a fluid is introduced and an outlet opening (35) through which the fluid is discharged; a rotor chamber (19) formed in the housing (11) and connected to the suction opening (34) and the outlet opening (35); a rotary shaft (25, 26, 27) arranged in the housing (11); a rotor (40, 44, 42) having an insertion hole (45) through which the rotary shaft (25, 26, 27) is inserted, and a hole-forming surface (64) forming the insertion hole (45), wherein the rotor (40, 44, 42) is adapted to rotate in the rotor chamber (19) together with the rotary shaft (25, 26, 27) press-fitted in the hole-forming surface (64); and a first bearing (23) and a second bearing (24) which support the rotary shaft (25, 26, 27) on opposite sides of the rotor (40, 44, 42), respectively, so that the rotary shaft (25, 26, 27) is rotatable relative to the housing (11), each of the first bearing (23) and the second bearing (24) comprising: an inner ring (51); an outer ring (52) surrounding the inner ring (51) and supported by the housing (11); and a rolling element (53) arranged between the inner ring (51) and the outer ring (52), wherein: the rotary shaft (25, 26, 27) is press-fitted into the inner ring (51) of the first bearing (23) and into the inner ring (51) of the second bearing (24) with a distance between the rotary shaft (25, 26, 27) and the inner ring (51) of the second bearing (24), a linear expansion coefficient of a material of the housing (11) and a linear expansion coefficient of a material of the rotor (40, 44, 42) are greater than a linear expansion coefficient of a material of the rotary shaft (25, 26, 27), and rotation of the rotor (40, 44, 42) causes the fluid to be introduced into the rotor chamber (19) through the suction opening (34) and discharged from the rotor chamber (19) through the outlet opening (35), characterized by , that an edge portion of the hole-forming surface (64) adjacent to the first bearing (23) serves as a press-fitting portion (65) in which the rotary shaft (25, 26, 27) is press-fitted, and at least one edge portion of the hole forming surface (64) adjacent to the second bearing (24) serves as a spaced fitting portion (66) in which the rotary shaft (25, 26, 27) is fitted with a space between the rotary shaft (25, 26, 27) and the spaced fitting portion (66). [2] Roots pump (10) according to claim 1, characterized by , that only the edge portion of the hole-forming surface (64) adjacent to the second bearing (24) serves as a distance fitting portion (66), and the distance between the rotary shaft (25, 26, 27) and the spacer fitting portion (66) is smaller than a distance between the rotary shaft (25, 26, 27) and a part of the hole forming surface (64) between the press fitting portion (65) and the spacer fitting portion (66). [3] Roots pump (10) according to claim 1, characterized by that the hole forming surface (64), except for the edge portion of the hole forming surface (64) serving as the press-fitting portion (65), serves as the spacer fitting portion (66). [4] Roots pump (10) according to one of claims 1 to 3, characterized by that the rotor (40, 44, 42) as a whole has a solid structure. [5] Roots pump (10) according to one of claims 1 to 3, characterized bythat the rotor (40, 44, 42) has a solid structure only in a portion of the rotor (40, 44, 42) overlapping the press-fitting portion (65) in a radial direction of the rotary shaft (25, 26, 27). [6] Roots pump (10) according to one of claims 1 to 3, characterized by that the rotor (40, 44, 42) has: a through hole (71) formed through the rotor (40, 44, 42) and located outside the insertion hole (45) in a radial direction of the rotary shaft (25, 26, 27); and a rib (72) in the through hole (71) at a position overlapping the press-fitting portion (65) in the radial direction of the rotary shaft (25, 26, 27). [7] Roots pump (10) according to one of claims 1 to 6, characterized by , that the housing (11) has a first housing component (14) and a second housing component (15), the rotor chamber (19) is defined by the first housing component (14) and the second housing component (15), the second housing component (15) has the suction opening (34) and the outlet opening (35), the first bearing (23) is held by the first housing component (14), and the second bearing (24) is held by the second housing component (15).

Images