Roots pump

Abstract

To improve the performance of a root pump.SOLUTION: An end part on a first bearing 23 side on a hole forming surface 64 becomes a press-in part 65 in which a rotary shaft 25 is pressed. Therefore, a distance between a press-in portion of an inner ring 51 of the first bearing 23 and the rotary shaft 25 and the press-in part 65 of the hole forming surface 64 is minimized, an area where a rotor 40 thermally expands in an axial direction of the rotary shaft 25 is decreased depending on thermal expansion in the axial direction in the rotary shaft 25. An end part on a second bearing 24 side in the hole forming surface 64 becomes a clearance fitting part 66 in which the rotary shaft 25 is clearance-fitted. Therefore, a clearance between the end part of the second bearing 24 side on the hole forming surface 64 and the rotary shaft 25 is minimized. Consequently, even if the pressure of hydrogen gas is applied to the rotor 40, bending inward in a diametrical direction of the rotary shaft 25 in the rotor 40 based on the press-in part 65 becomes smaller.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a Roots pump.

Background Art

[0002] A Roots pump includes a housing, a rotor chamber, a rotating shaft, and a rotor. The housing has a suction hole and a discharge hole. The suction hole sucks in fluid. The discharge hole discharges fluid. The rotor chamber is defined in the housing. The rotor chamber communicates with the suction hole and the discharge hole. The rotating shaft is disposed inside the housing. The rotor has an insertion hole through which the rotating shaft is inserted. The rotor rotates integrally with the rotating shaft in the rotor chamber by the rotating shaft being press-fitted onto a hole forming surface that defines the insertion hole. Therefore, the hole forming surface has a press-fit portion into which the rotating shaft is press-fitted. When the rotor rotates, fluid is sucked into the rotor chamber from the suction hole, and the fluid in the rotor chamber is discharged from the discharge hole.

[0003] Incidentally, as disclosed in, for example, Patent Document 1, a Roots pump that includes a first bearing and a second bearing that respectively rotatably support, relative to the housing, portions of the rotating shaft located on opposite sides of the rotor has been conventionally known. The first bearing and the second bearing each include an inner ring, an outer ring, and rolling elements. The outer ring surrounds the inner ring and is supported by the housing. The rolling elements are disposed between the inner ring and the outer ring. For example, the rotating shaft is press-fitted into the inner ring of the first bearing and is clearance-fitted onto the inner ring of the second bearing.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0005] In such a Roots pump, when the pump is driven, the housing, rotor, and rotating shaft are affected by heat. The housing expands axially with respect to the rotating shaft, with the press-fit portion between the inner ring of the first bearing and the rotating shaft as the starting point. At this time, because the rotating shaft is clearance-fitted to the inner ring of the second bearing, the axial thermal expansion of the rotating shaft in the housing is not constrained between the second bearing and the rotating shaft. As a result, even if axial thermal expansion of the rotating shaft occurs in the housing, the load on the second bearing is avoided.

[0006] Here, the amount of displacement in the rotor due to axial thermal expansion of the rotating shaft depends on the axial thermal expansion of the rotating shaft because the rotating shaft is press-fitted into the hole-forming surface. The longer the distance between the press-fit portion of the inner ring of the first bearing and the rotating shaft and the press-fit portion of the hole-forming surface, the larger the region in which the rotor expands axially relative to the rotating shaft, depending on the axial thermal expansion of the rotating shaft.

[0007] For example, consider the case where the coefficient of thermal expansion of the housing material and the rotor material are greater than the coefficient of thermal expansion of the rotating shaft material. In this case, the difference between the displacement due to axial thermal expansion of the rotating shaft in the housing and the displacement due to axial thermal expansion of the rotating shaft in the rotor becomes large. Therefore, there is a risk that the clearance between the rotor and the housing will become too wide, or that the rotor and housing will come into contact.

[0008] If the clearance between the rotor and housing becomes too large, the performance of the Roots pump deteriorates. On the other hand, it is also necessary to have a large clearance between the rotor and housing from the start to prevent contact between the rotor and housing. However, increasing the clearance between the rotor and housing from the start degrades the performance of the Roots pump, which is undesirable. Therefore, improving the performance of the Roots pump is desirable. [Means for solving the problem]

[0009] A Roots pump that solves the above problems comprises a housing having an intake port for drawing in fluid and an outlet port for discharging fluid; a rotor chamber defined in the housing and communicating with the intake port and the outlet port; a rotating shaft disposed inside the housing; a rotor having an insertion hole through which the rotating shaft is inserted and through which the rotating shaft is pressed into a hole-forming surface forming the insertion hole, thereby rotating integrally with the rotating shaft within the rotor chamber; and a first bearing and a second bearing that rotatably support the portions of the rotating shaft located on both sides of the rotor relative to the housing, wherein the first bearing and the second bearing each have an inner ring and an outer ring surrounding the inner ring and supported by the housing, and A Roots pump having rolling elements provided between an inner ring and an outer ring, wherein the rotating shaft is press-fitted into the inner ring of the first bearing and clearance-fitted into the inner ring of the second bearing, the coefficient of linear expansion of the housing material and the coefficient of linear expansion of the rotor material are greater than the coefficient of linear expansion of the rotating shaft material, and as the rotor rotates, fluid is drawn into the rotor chamber from the intake hole and the fluid in the rotor chamber is discharged from the discharge hole, wherein the end of the hole-forming surface on the first bearing side is a press-fit portion into which the rotating shaft is press-fitted, and at least the end of the hole-forming surface on the second bearing side is a clearance-fit portion into which the rotating shaft is clearance-fitted.

[0010] According to this, the distance between the press-fit portion of the inner ring of the first bearing and the rotating shaft and the press-fit portion of the hole-forming surface is minimized, thereby reducing the region in which the rotor expands axially relative to the rotating shaft, depending on the axial thermal expansion of the rotating shaft. As a result, the difference between the displacement of the housing due to the axial thermal expansion of the rotating shaft and the displacement of the rotor due to the axial thermal expansion of the rotating shaft can be reduced. Therefore, it becomes easier to avoid the clearance between the rotor and the housing becoming too wide, or the rotor and housing coming into contact.

[0011] Here, for example, if the end of the hole-forming surface on the first bearing side is a press-fit portion into which the rotating shaft is press-fitted, the pressure of the fluid acting on the rotor may cause the rotor to bend radially inward relative to the rotating shaft, with the press-fit portion as the pivot point. If the rotor bends radially inward relative to the rotating shaft with the press-fit portion as the pivot point, the clearance between the rotor and the housing becomes too wide, which degrades the performance of the Roots pump.

[0012] Therefore, at least the end on the second bearing side of the hole-forming surface is a gap-fitting portion into which the rotating shaft is gap-fitted. This makes it possible to minimize the clearance between the end on the second bearing side of the hole-forming surface and the rotating shaft. As a result, even when fluid pressure acts on the rotor, the radial inward deflection of the rotating shaft in the rotor, with the press-fitting portion as the base point, can be reduced. Thus, it is avoided that the clearance between the rotor and the housing becomes too wide. In this way, the performance of the Roots pump can be improved.

[0013] In the above-described Roots pump, only the end of the hole-forming surface on the second bearing side is the gap-fitting portion, and the clearance between the gap-fitting portion and the rotating shaft is preferably smaller than the clearance between the portion of the hole-forming surface between the press-fitting portion and the gap-fitting portion and the rotating shaft.

[0014] According to this design, since only the end on the second bearing side of the hole-forming surface is a gap-fitting portion, it becomes easier to manage the clearance between the end on the second bearing side of the hole-forming surface and the rotating shaft. Therefore, it becomes easier to minimize the clearance between the end on the second bearing side of the hole-forming surface and the rotating shaft. As a result, even when fluid pressure acts on the rotor, it becomes easier to reduce the radial inward deflection of the rotating shaft in the rotor, with the press-fit portion as the starting point.

[0015] In the above-described Roots pump, it is preferable that the hole-forming surface has a gap-fitting portion in all parts except the press-fit portion. The configuration in which the parts of the hole-forming surface other than the press-fit portion are gap-fitting portions facilitates the machining of the hole-forming surface or the outer surface of the rotating shaft. Therefore, the configuration of the Roots pump can be simplified.

[0016] In the above-described Roots pump, it is preferable that the entire rotor has a solid structure. This increases the overall rigidity of the rotor, making it easier to avoid rotor deformation. Therefore, by press-fitting the rotating shaft into the press-fit section, it becomes easier to avoid problems such as the rotor deforming radially outward relative to the rotating shaft and interfering with the housing.

[0017] In the above-described Roots pump, it is preferable that the rotor has a solid structure only in the portion that overlaps with the press-fit portion in the radial direction of the rotating shaft. According to this, the portion of the rotor that overlaps with the press-fit portion in the radial direction of the rotation axis becomes less prone to deformation. As a result, when the rotation axis is press-fitted into the press-fit portion, the rotor deforms radially outward relative to the rotation axis, making it easier to avoid problems such as the rotor interfering with the housing.

[0018] In the above-described Roots pump, the rotor has a through hole that penetrates the rotor on the radially outer side of the rotating shaft relative to the insertion hole, and it is preferable that ribs are provided in the portion of the through hole that overlaps with the press-fit portion in the radial direction of the rotating shaft.

[0019] According to this, the portion of the rotor that overlaps with the press-fit portion in the radial direction of the rotation axis becomes less prone to deformation. As a result, when the rotation axis is press-fitted into the press-fit portion, the rotor deforms radially outward relative to the rotation axis, making it easier to avoid problems such as the rotor interfering with the housing.

[0020] In the roots pump described above, the housing preferably comprises 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 suction hole and the discharge hole are formed in the second housing component, the first bearing is held by the first housing component, and the second bearing is held by the second housing component.

[0021] Since the suction hole and the discharge hole are formed in the second housing component, the temperature of the second housing component is more likely to become higher than that of the first housing component under the influence of fluid suction and discharge. Accordingly, the second housing component is more prone to thermal expansion than the first housing component. Here, the first bearing is held by the first housing component. The inner ring of the first bearing needs to be set with an interference allowance that takes into account the amount of displacement caused by thermal expansion of the first housing component. Since the amount of displacement caused by thermal expansion of the first housing component is smaller than that of the second housing component, the interference allowance for the inner ring of the first bearing can be easily ensured. Therefore, the configuration in which the first bearing is held by the first housing component and the second bearing is held by the second housing component can facilitate the design of the roots pump.

Effects of the Invention

[0022] According to the present invention, the performance of a roots pump can be improved.

Brief Description of Drawings

[0023] [Figure 1] It is a cross-sectional view showing a roots pump according to an embodiment. [Figure 2] It is a cross-sectional view taken along line 2-2 in FIG. 1. [Figure 3] It is an enlarged cross-sectional view showing a part of the roots pump. [Figure 4] It is an enlarged cross-sectional view showing a part of a roots pump according to another embodiment. [Figure 5] It is an enlarged cross-sectional view showing a part of a roots pump according to another embodiment. [Figure 6] This is a cross-sectional view of a Roots pump in another embodiment. [Modes for carrying out the invention]

[0024] The following describes one embodiment of the Roots pump with reference to Figures 1 to 3. The Roots pump of this embodiment is a hydrogen pump for fuel cells used in fuel cell systems. The Roots pump is installed in vehicles such as fuel cell vehicles. The Roots pump inhales and discharges hydrogen gas as a fluid.

[0025] <Overall configuration of Roots Pump 10> As shown in Figure 1, the Roots pump 10 includes a housing 11. The housing 11 is cylindrical. The housing 11 is made of a metal material. For example, the housing 11 is made of aluminum.

[0026] The housing 11 comprises a first housing member 12, a second housing member 13, a third housing member 14, a fourth housing member 15, and a fifth housing member 16. The housing 11 is formed by integrally assembling the first housing member 12, the second housing member 13, the third housing member 14, the fourth housing member 15, and the fifth housing member 16.

[0027] The first housing member 12 has a first end wall 12a and a first circumferential wall 12b. The first end wall 12a is plate-shaped. The first circumferential wall 12b extends cylindrically from the outer circumference of the first end wall 12a. The first housing member 12 has a first bearing retaining portion 12c. The first bearing retaining portion 12c is cylindrical. The first bearing retaining portion 12c protrudes into the first housing member 12 from the center of the inner surface of the first end wall 12a.

[0028] The second housing member 13 has a second end wall 13a and a second circumferential wall 13b. The second end wall 13a is plate-shaped. The second circumferential wall 13b extends cylindrically from the outer circumference of the second end wall 13a. The second housing member 13 is connected to the first housing member 12. The second end wall 13a closes the opening of the first circumferential wall 12b of the first housing member 12. The second housing member 13 has a pair of second bearing retaining portions 13c. The pair of second bearing retaining portions 13c are provided on the second end wall 13a. One of the pair of second bearing retaining portions 13c is a hole that penetrates the second end wall 13a in the thickness direction. The other of the pair of second bearing retaining portions 13c is a recess formed on the inner surface of the second end wall 13a.

[0029] The third housing member 14 has a third end wall 14a and a third circumferential wall 14b. The third end wall 14a is plate-shaped. The third circumferential wall 14b extends cylindrically from the outer circumference of the third end wall 14a. The third housing member 14 is connected to the second housing member 13. The third end wall 14a closes the opening in the second circumferential wall 13b of the second housing member 13. The third housing member 14 has a pair of third bearing retaining portions 14c. The pair of third bearing retaining portions 14c are provided on the third end wall 14a. The pair of third bearing retaining portions 14c are holes that penetrate the third end wall 14a in the thickness direction.

[0030] The fourth housing member 15 has a fourth end wall 15a, a boss portion 15b, and a pair of fourth bearing retaining portions 15c. The fourth end wall 15a is plate-shaped. The fourth housing member 15 is connected to the third housing member 14. The fourth end wall 15a closes the opening in the third circumferential wall 14b of the third housing member 14. The boss portion 15b is cylindrical. The boss portion 15b protrudes from the fourth end wall 15a. The pair of fourth bearing retaining portions 15c are provided on the boss portion 15b.

[0031] The fifth housing member 16 is plate-shaped. The fifth housing member 16 is connected to the fourth housing member 15. The fifth housing member 16 closes the opening of the boss portion 15b.

[0032] The Roots pump 10 comprises a motor chamber 17, a gear chamber 18, a rotor chamber 19, and a pair of bearing housing chambers 20. The motor chamber 17, gear chamber 18, rotor chamber 19, and the pair of bearing housing chambers 20 are defined in the housing 11. The motor chamber 17 is defined by a first end wall 12a, a first circumferential wall 12b, and a second end wall 13a. The gear chamber 18 is defined by a second end wall 13a, a second circumferential wall 13b, and a third end wall 14a. Each of the pair of second bearing retainers 13c opens into the gear chamber 18.

[0033] The Roots pump 10 includes a bearing 21, which is held in a first bearing retainer 12c. The Roots pump 10 also includes a pair of bearings 22, each of which is held in a second bearing retainer 13c. Each of the pair of bearings 22 is located between the motor chamber 17 and the gear chamber 18.

[0034] The rotor chamber 19 is defined by a third end wall 14a, a third circumferential wall 14b, and a fourth end wall 15a. Therefore, the rotor chamber 19 is defined by a third housing member 14 and a fourth housing member 15. The third housing member 14 is the first housing component. The fourth housing member 15 is the second housing component. Therefore, the housing 11 has the first housing component and the second housing component. Each of the pair of third bearing retainers 14c opens into the rotor chamber 19 and the gear chamber 18. Each of the pair of third bearing retainers 14c is located between the gear chamber 18 and the rotor chamber 19.

[0035] The Roots pump 10 comprises a pair of first bearings 23 and a pair of second bearings 24. Each of the pair of first bearings 23 is held in a third bearing retaining portion 14c. Thus, the pair of first bearings 23 are held in the third housing member 14, which is the first housing structure.

[0036] Each of the pair of bearing housing chambers 20 is defined by a boss portion 15b and a fifth housing member 16. Each of the pair of second bearings 24 is held in a fourth bearing retaining portion 15c. Thus, the pair of second bearings 24 are held in the fourth housing member 15, which is a second housing component.

[0037] The Roots pump 10 is equipped with a rotating shaft 25. The rotating shaft 25 is located inside the housing 11. The rotating shaft 25 consists of a drive shaft 26 and a driven shaft 27. In the following description, "drive shaft 26 and driven shaft 27" may sometimes be simply referred to as "rotating shaft 25".

[0038] The drive shaft 26 and the driven shaft 27 are made of metal. For example, the drive shaft 26 and the driven shaft 27 are made of stainless steel. Therefore, the coefficient of thermal expansion of the housing 11 is greater than the coefficient of thermal expansion of the rotating shaft 25.

[0039] The drive shaft 26 and the driven shaft 27 are arranged parallel to each other. The direction in which the central axis L1 of the drive shaft 26 and the central axis L2 of the driven shaft 27 extend is the axial direction of the rotation shaft 25. The drive shaft 26 passes through the second end wall 13a, the third end wall 14a, and the fourth end wall 15a. The driven shaft 27 passes through the third end wall 14a and the fourth end wall 15a. The drive shaft 26 is rotatably supported in the housing 11 via bearings 21, 22, 1, and 24. The driven shaft 27 is rotatably supported in the housing 11 via bearings 22, 1 and 24.

[0040] The Roots pump 10 includes a first sealing member 28, a pair of second sealing members 29, and a pair of third sealing members 30. The first sealing member 28 is provided on the second end wall 13a. The first sealing member 28 seals the space between the drive shaft 26 and the second end wall 13a. The pair of second sealing members 29 are provided on the third end wall 14a. One of the pair of second sealing members 29 seals the space between the drive shaft 26 and the third end wall 14a. The other of the pair of second sealing members 29 seals the space between the driven shaft 27 and the third end wall 14a. The pair of third sealing members 30 are provided on the fourth end wall 15a. One of the pair of third sealing members 30 seals the space between the drive shaft 26 and the fourth end wall 15a. The other of the pair of third sealing members 30 seals the space between the driven shaft 27 and the fourth end wall 15a.

[0041] The Roots pump 10 is equipped with a motor 31. The motor 31 is housed in a motor chamber 17. Therefore, the motor chamber 17 houses the motor 31. The motor 31 is connected to a drive shaft 26. The motor 31 rotates the drive shaft 26.

[0042] The Roots pump 10 includes a drive gear 32 and a driven gear 33. The drive gear 32 and the driven gear 33 are housed in a gear chamber 18. Therefore, 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 driven shaft 27. The driven gear 33 rotates in mesh with the drive gear 32. The driven shaft 27 rotates in the opposite direction to the drive shaft 26 by the drive gear 32 and the driven gear 33.

[0043] As shown in Figures 1 and 2, the housing 11 has an intake port 34 and a discharge port 35. The intake port 34 and the discharge port 35 penetrate the fourth housing member 15 and the fifth housing member 16. Therefore, the intake port 34 and the discharge port 35 are formed in the fourth housing member 15, which is the second housing component. The rotor chamber 19 communicates with the intake port 34 and the discharge port 35. The intake port 34 draws hydrogen gas into the rotor chamber 19. The discharge port 35 discharges the hydrogen gas from the rotor chamber 19.

[0044] The Roots pump 10 is equipped with a rotor 40. The rotor 40 consists of a drive rotor 41 and a driven rotor 42. In the following description, the "drive rotor 41 and driven rotor 42" may sometimes be simply referred to as "rotor 40". The drive rotor 41 and driven rotor 42 are made of metal. For example, the drive rotor 41 and driven rotor 42 are made of aluminum. Therefore, the coefficient of thermal expansion of the housing 11 material and the coefficient of thermal expansion of the rotor 40 material are the same. Consequently, the coefficient of thermal expansion of the housing 11 material and the coefficient of thermal expansion of the rotor 40 material are greater than the coefficient of thermal expansion of the rotating shaft 25 material.

[0045] As shown 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 of the roots type, with a cross-sectional view perpendicular to the axial directions of the drive shaft 26 and the driven shaft 27 formed in a bifoliate (gourd-shaped) form. The drive rotor 41 and the driven rotor 42 each have a pair of teeth 43 and a pivot portion 44 located between the pair of teeth 43.

[0046] The shaft support 44 has an insertion hole 45. Therefore, the rotor 40 has an insertion hole 45. The insertion hole 45 penetrates the shaft support 44. The diameter of the insertion hole 45 is constant. 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. Therefore, the rotating shaft 25 is inserted through the insertion hole 45.

[0047] The outer circumferential surfaces of the pair of teeth 43 form the peaks of the rotor 40. The outer circumferential surface of the pivot portion 44 forms the valleys of the rotor 40. The teeth 43 of the drive rotor 41 and the pivot portion 44 of the driven rotor 42 can mesh. The pivot portion 44 of the drive rotor 41 and the teeth 43 of the driven rotor 42 can mesh. The pair of teeth 43 have a solid structure. The rotor 40 has a solid structure in its entirety, except for the through hole 45. Therefore, in this embodiment, the rotor 40 has a solid structure as a whole. The drive rotor 41 and the driven rotor 42 are configured to mesh with each other. The drive rotor 41 is attached to the drive shaft 26. The drive rotor 41 rotates integrally with the drive shaft 26 within the rotor chamber 19. The driven rotor 42 is attached to the driven shaft 27. The driven rotor 42 rotates integrally with the driven shaft 27 within the rotor chamber 19. The driven rotor 42 rotates together with the drive rotor 41. The drive rotor 41 rotates in the direction of arrow R1 shown in Figure 2, while the driven rotor 42 rotates in the direction of arrow R2 shown in Figure 2.

[0048] The intake port 34 is connected to the hydrogen outlet 48a of the fuel cell 48 via the first connecting pipe 46. The discharge port 35 is connected to the hydrogen supply port 48b of the fuel cell 48 via the second connecting pipe 47.

[0049] When the drive shaft 26 rotates due to the drive of the motor 31, the drive gear 32 and driven gear 33, which are meshed with each other, rotate synchronously. As the drive gear 32 and driven gear 33 rotate synchronously, the driven shaft 27 rotates in the opposite direction to the drive shaft 26. As a result, the drive rotor 41 and driven rotor 42 rotate in opposite directions while remaining meshed with each other. In the Roots pump 10, hydrogen gas that did not react with oxygen in the fuel cell 48 is drawn into the rotor chamber 19 through the hydrogen outlet 48a, the first connecting pipe 46, and the intake port 34. The hydrogen gas drawn into the rotor chamber 19 is discharged from the discharge port 35 and supplied to the fuel cell 48 through the second connecting pipe 47 and the hydrogen supply port 48b. Therefore, the Roots pump 10 supplies hydrogen gas to the fuel cell 48 by the rotation of the drive rotor 41 and the driven rotor 42. In this way, in the Roots pump 10, hydrogen gas is drawn into the rotor chamber 19 from the suction port 34 as the drive rotor 41 and driven rotor 42 rotate, and the hydrogen gas in the rotor chamber 19 is discharged from the discharge port 35.

[0050] As shown in Figure 3, the pair of first bearings 23 and the pair of second bearings 24 each have an inner ring 51, an outer ring 52, and rolling elements 53. The outer ring 52 surrounds the inner ring 51 and is supported by the housing 11. The rolling elements 53 are provided between the inner ring 51 and the outer ring 52. The first bearings 23 and second bearings 24 in this embodiment are ball bearings configured by providing a plurality of balls, which are rolling elements 53, between the inner ring 51 and the outer ring 52. Note that the first bearings 23 and second bearings 24 may also be roller bearings in which rollers are used as rolling elements 53.

[0051] Each first bearing 23 and each second bearing 24 rotatably supports the portions of the drive shaft 26 and driven shaft 27 located on either side of the drive rotor 41 and driven rotor 42 relative to the housing 11. The drive shaft 26 and driven shaft 27 are press-fitted into the inner ring 51 of each first bearing 23 and clearance-fitted into the inner ring 51 of each second bearing 24.

[0052] The outer ring 52 of each first bearing 23 is held in place by interference fit in each third bearing retaining portion 14c. The inner ring 51 of each first bearing 23 rotates integrally with the rotating shaft 25. The outer ring 52 of each second bearing 24 is held in place by interference fit in each fourth bearing retaining portion 15c. An O-ring 54 is fitted to the portion of the rotating shaft 25 that is located inside the inner ring 51 of each second bearing 24. The inner ring 51 of each second bearing 24 then rotates integrally with the rotating shaft 25 via the O-ring 54.

[0053] <Relationship between rotor 40 and rotating shaft 25> The relationship between the rotor 40 and the rotating shaft 25 will be explained below. Note that the relationship between the drive rotor 41 and the drive shaft 26 is almost the same as the relationship between the driven rotor 42 and the driven shaft 27, so it will simply be explained as "the relationship between the rotor 40 and the rotating shaft 25".

[0054] The rotating shaft 25 has a large-diameter portion 61, a small-diameter portion 62, and a medium-diameter portion 63. The large-diameter portion 61, the small-diameter portion 62, and the medium-diameter portion 63 are located inside the insertion hole 45 of the rotating shaft 25. The outer diameter of the large-diameter portion 61 is larger than the outer diameter of the small-diameter portion 62 and the outer diameter of the medium-diameter portion 63. The outer diameter of the medium-diameter portion 63 is larger than the outer diameter of the small-diameter portion 62. The large-diameter portion 61 is located closer to the first bearing 23 than the small-diameter portion 62 and the medium-diameter portion 63. The large-diameter portion 61 is press-fitted into the end of the hole-forming surface 64 that forms the insertion hole 45, on the side of the first bearing 23. Therefore, the end of the hole-forming surface 64 on the side of the first bearing 23 becomes a press-fit portion 65 into which the rotating shaft 25 is press-fitted. The rotor 40 then rotates integrally with the rotating shaft 25 within the rotor chamber 19 by press-fitting the rotating shaft 25 into the hole-forming surface 64.

[0055] The medium-diameter portion 63 is continuous with the end of the large-diameter portion 61 opposite to the first bearing 23. The small-diameter portion 62 is continuous with the end of the medium-diameter portion 63 opposite to the large-diameter portion 61. The medium-diameter portion 63 is located closer to the second bearing 24 than the large-diameter portion 61 and the small-diameter portion 62. The medium-diameter portion 63 is fitted into the hole-forming surface 64 at the end on the second bearing 24 side. Therefore, the end of the hole-forming surface 64 on the second bearing 24 side becomes a gap-fitting portion 66 into which the rotating shaft 25 is fitted. In this embodiment of the Roots pump 10, only the end of the hole-forming surface 64 on the second bearing 24 side is a gap-fitting portion 66. The clearance between the gap-fitting portion 66 and the medium-diameter portion 63 of the rotating shaft 25 is smaller than the clearance between the area between the press-fit portion 65 and the gap-fitting portion 66 on the hole-forming surface 64 and the small-diameter portion 62 of the rotating shaft 25. Furthermore, the clearance between the gap fitting portion 66 and the rotating shaft 25 is pre-set so that there is no interference between the hole forming surface 64 and the middle diameter portion 63 of the rotating shaft 25, even if both the rotor 40 and the rotating shaft 25 undergo thermal expansion.

[0056] [Effect of the Embodiment] Next, the operation of this embodiment will be described. Incidentally, when the Roots pump 10 is driven, the housing 11, rotor 40, and rotating shaft 25 are affected by heat. For example, the third housing member 14 expands axially with respect to the rotating shaft 25, with the press-fit portion between the inner ring 51 of the first bearing 23 and the rotating shaft 25 as the starting point. Furthermore, the fourth housing member 15 also expands axially with respect to the rotating shaft 25, following the axial thermal expansion of the rotating shaft 25 in the third housing member 14. At this time, since the rotating shaft 25 is clearance-fitted to the inner ring 51 of the second bearing 24, the axial thermal expansion of the rotating shaft 25 in the fourth housing member 15 is not constrained between the second bearing 24 and the rotating shaft 25. As a result, even if axial thermal expansion of the rotating shaft 25 occurs in the fourth housing member 15, the load on the second bearing 24 is avoided.

[0057] Here, the amount of displacement in the rotor 40 due to the axial thermal expansion of the rotating shaft 25 depends on the axial thermal expansion of the rotating shaft 25, as the rotating shaft 25 is press-fitted into the hole-forming surface 64. The longer the distance between the press-fit portion of the inner ring 51 of the first bearing 23 and the rotating shaft 25 and the press-fit portion 65 of the hole-forming surface 64, the larger the region in which the rotor 40 expands axially relative to the rotating shaft 25, depending on the axial thermal expansion of the rotating shaft 25.

[0058] Therefore, the end of the hole-forming surface 64 on the first bearing 23 side is a press-fit portion 65. As a result, the distance between the press-fit portion between the inner ring 51 of the first bearing 23 and the rotating shaft 25 and the press-fit portion 65 of the hole-forming surface 64 is minimized, so that the region in which the rotor 40 expands axially relative to the rotating shaft 25, depending on the axial thermal expansion of the rotating shaft 25, becomes smaller. As a result, the difference between the displacement amount in the third housing member 14 due to the axial thermal expansion of the rotating shaft 25 and the displacement amount in the rotor 40 due to the axial thermal expansion of the rotating shaft 25 becomes smaller. Consequently, it becomes easier to avoid the clearance between the rotor 40 and the fourth housing member 15 becoming too wide, or the rotor 40 coming into contact with the third end wall 14a of the third housing member 14.

[0059] Here, for example, if the end of the hole-forming surface 64 on the first bearing 23 side is a press-fit portion 65 into which the rotating shaft 25 is press-fitted, the pressure of hydrogen gas acting on the rotor 40 may cause the rotor 40 to deflect radially inward relative to the rotating shaft 25, with the press-fit portion 65 as the pivot point. Therefore, the end of the hole-forming surface 64 on the second bearing 24 side is a gap-fit ​​portion 66 into which the rotating shaft 25 is gap-fitted. Thus, the clearance between the end of the hole-forming surface 64 on the second bearing 24 side and the rotating shaft 25 is kept to a minimum. As a result, even if the pressure of hydrogen gas acts on the rotor 40, the radial inward deflection of the rotating shaft 25 in the rotor 40 with the press-fit portion 65 as the pivot point is reduced. Thus, the clearance between the rotor 40 and the third circumferential wall 14b of the third housing member 14 is avoided from becoming too wide.

[0060] [Effects of the Embodiment] The above embodiment can be achieved to obtain the following effects. (1) The end of the hole-forming surface 64 on the first bearing 23 side is a press-fit portion 65 into which the rotating shaft 25 is press-fitted. This makes the distance between the press-fit portion between the inner ring 51 of the first bearing 23 and the rotating shaft 25 and the press-fit portion 65 of the hole-forming surface 64 as short as possible, so that the region in which the rotor 40 expands axially with respect to the axial thermal expansion of the rotating shaft 25 can be reduced. As a result, the difference between the displacement amount in the housing 11 due to the axial thermal expansion of the rotating shaft 25 and the displacement amount in the rotor 40 due to the axial thermal expansion of the rotating shaft 25 can be reduced. Therefore, it is easier to avoid the clearance between the rotor 40 and the housing 11 becoming too wide, or the rotor 40 and the housing 11 coming into contact.

[0061] Here, for example, if the end of the hole-forming surface 64 on the first bearing 23 side is a press-fit portion 65 into which the rotating shaft 25 is press-fitted, the pressure of hydrogen gas acting on the rotor 40 may cause the rotor 40 to bend radially inward relative to the rotating shaft 25, with the press-fit portion 65 as the pivot point. If the rotor 40 bends radially inward relative to the rotating shaft 25 with the press-fit portion 65 as the pivot point, the clearance between the rotor 40 and the housing 11 will become too wide, degrading the performance of the Roots pump 10.

[0062] Therefore, the end of the hole-forming surface 64 on the second bearing 24 side is a gap-fitting portion 66 into which the rotating shaft 25 is gap-fitted. This makes it possible to minimize the clearance between the end of the hole-forming surface 64 on the second bearing 24 side and the rotating shaft 25. As a result, even when hydrogen gas pressure acts on the rotor 40, the radial inward deflection of the rotating shaft 25 in the rotor 40 with the press-fitting portion 65 as the starting point can be reduced. Thus, it is avoided that the clearance between the rotor 40 and the housing 11 becomes too wide. As a result, the performance of the Roots pump 10 can be improved.

[0063] (2) Since only the end of the hole-forming surface 64 on the second bearing 24 side is a gap-fitting portion 66, it becomes easier to manage the clearance between the end of the hole-forming surface 64 on the second bearing 24 side and the rotating shaft 25. Therefore, it is possible to minimize the clearance between the end of the hole-forming surface 64 on the second bearing 24 side and the rotating shaft 25. As a result, even when hydrogen gas pressure acts on the rotor 40, it is possible to minimize the radial inward deflection of the rotating shaft 25 in the rotor 40 with the press-fit portion 65 as the starting point.

[0064] (3) The entire rotor 40 has a solid structure. This increases the overall rigidity of the rotor 40, making it easier to avoid deformation of the rotor 40. Therefore, when the rotating shaft 25 is press-fitted into the press-fit portion 65, it becomes easier to avoid problems such as the rotor 40 deforming radially outward relative to the rotating shaft 25 and interfering with the housing 11.

[0065] (4) Because the fourth housing member 15 has an intake hole 34 and a discharge hole 35 formed therein, it is more susceptible to the effects of hydrogen gas intake and discharge, and its temperature tends to rise higher than that of the third housing member 14. Therefore, the fourth housing member 15 is more susceptible to thermal expansion than the third housing member 14. Here, the first bearing 23 is held in the third housing member 14. The inner ring 51 of the first bearing 23 needs to be set to a press-fit allowance that takes into account the displacement due to the thermal expansion of the third housing member 14. Since the displacement due to thermal expansion of the third housing member 14 is smaller than that of the fourth housing member 15, it is easier to secure the press-fit allowance for the inner ring 51 of the first bearing 23. Therefore, the configuration in which the first bearing 23 is held in the third housing member 14 and the second bearing 24 is held in the fourth housing member 15 makes the design of the Roots pump 10 easier.

[0066] [Example of changes] The above embodiment can be implemented with the following modifications. The above embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0067] ○ As shown in Figure 4, the hole-forming surface 64 may have a gap-fitting portion 66 in areas other than the press-fitting portion 65. In short, it is sufficient that at least the end of the hole-forming surface 64 on the second bearing 24 side is a gap-fitting portion 66 into which the rotating shaft 25 is gap-fitted. A configuration in which the area of ​​the hole-forming surface 64 other than the press-fitting portion 65 is a gap-fitting portion 66 makes it easy to process the hole-forming surface 64 or the outer surface of the rotating shaft 25. Therefore, the configuration of the Roots pump 10 can be simplified.

[0068] ○ As shown in Figure 5, the rotor 40 may have a solid structure only in the portion that overlaps with the press-fit portion 65 in the radial direction of the rotating shaft 25. The rotor 40 has a recess 70. The recess 70 is formed in each of the pair of teeth 43. The recess 70 opens to the end face of the rotor 40 on the fourth housing member 15 side. The recess 70 is formed in the portion that overlaps with the medium diameter portion 63 and the small diameter portion 62 of the rotating shaft 25 in the radial direction of the rotating shaft 25. The portion of the rotor 40 that overlaps with the press-fit portion 65 in the radial direction of the rotating shaft 25 has a solid structure. This makes it difficult for the portion of the rotor 40 that overlaps with the press-fit portion 65 in the radial direction of the rotating shaft 25 to deform. Therefore, when the rotating shaft 25 is press-fitted into the press-fit portion 65, the rotor 40 deforms radially outward of the rotating shaft 25, making it easier to avoid problems such as the rotor 40 interfering with the housing 11. Furthermore, compared to a rotor 40 with a solid structure, the rotor 40 can be made lighter. As a result, the inertia of the rotor 40 can be reduced.

[0069] ○ As shown in Figure 6, the rotor 40 may have a through hole 71 that penetrates the rotor 40 on the radially outer side of the rotating shaft 25 relative to the insertion hole 45. A rib 72 may be provided in the portion of the rotating shaft 25 that overlaps with the press-fit portion 65 in the radial direction within the through hole 71. The through hole 71 is formed in each of the pair of teeth 43. This makes it difficult for the portion of the rotor 40 that overlaps with the press-fit portion 65 in the radial direction of the rotating shaft 25 to deform. Therefore, it is easier to avoid problems such as the rotor 40 deforming radially outward of the rotating shaft 25 when the rotating shaft 25 is press-fitted into the press-fit portion 65, causing the rotor 40 to interfere with the housing 11. In addition, since the through hole 71 penetrates the rotor 40, it is easier to suppress the accumulation of foreign matter in the rotor chamber 19 in the through hole 71. Therefore, it is possible to suppress an increase in the weight of the rotor 40. As a result, the inertia of the rotor 40 can be reduced.

[0070] ○ In this embodiment, the outer diameter of the portion of the rotating shaft 25 located inside the insertion hole 45 may be constant. The portion of the insertion hole 45 closer to the first bearing 23 may be made into a smaller diameter hole, while the portion of the insertion hole 45 closer to the second bearing 24 may be made into a larger diameter hole. As a result, the end of the hole-forming surface 64 on the first bearing 23 side may be made into a press-fit portion 65, while the end of the hole-forming surface 64 on the second bearing 24 side may be made into a gap-fit ​​portion 66.

[0071] ○ In this embodiment, the first bearing 23 may be held in the fourth housing member 15 and the second bearing 24 may be held in the third housing member 14. ○ In this embodiment, the intake port 34 and the discharge port 35 may be formed, for example, in the third peripheral wall 14b of the third housing member 14.

[0072] ○ In this embodiment, the drive rotor 41 and the driven rotor 42 may be of the roots type, for example, having a three-lobed cross-section perpendicular to the axial direction of the drive shaft 26 and the driven shaft 27.

[0073] ○ In this embodiment, the Roots pump 10 does not have to be mounted on a fuel cell vehicle. In short, the Roots pump 10 is not limited to being mounted on a vehicle. ○ In this embodiment, the Roots pump 10 does not have to be a hydrogen pump for fuel cells used in a fuel cell system; it can be any pump that sucks in and discharges fluid.

[0074] The above embodiment includes the configuration described in the following appendix. <Note 1> A housing having an intake port for drawing in fluid and an outlet port for discharging fluid, A rotor chamber defined in the housing and communicating with the intake port and the discharge port, A rotating shaft located inside the housing, A rotor having an insertion hole through which the rotating shaft is inserted, and the rotating shaft is press-fitted into the hole-forming surface that forms the insertion hole, thereby rotating integrally with the rotating shaft within the rotor chamber, The rotating shaft comprises a first bearing and a second bearing that rotatably support the portions located on both sides of the rotor relative to the housing, respectively. The first bearing and the second bearing are Insider, An outer ring that surrounds the inner ring and is supported by the housing, Each of the following has rolling elements provided between the inner ring and the outer ring, The rotating shaft is press-fitted into the inner ring of the first bearing and clearance-fitted into the inner ring of the second bearing. The coefficient of thermal expansion of the housing material and the coefficient of thermal expansion of the rotor material are greater than the coefficient of thermal expansion of the rotating shaft material. A Roots pump in which, as the rotor rotates, fluid is drawn into the rotor chamber from the intake port and the fluid in the rotor chamber is discharged from the discharge port, The end of the hole-forming surface on the first bearing side is a press-fit portion into which the rotating shaft is press-fitted. A Roots pump characterized in that at least the end of the hole-forming surface on the second bearing side is a gap-fitting portion into which the rotating shaft is gap-fitted.

[0075] <Note 2> Only the end portion on the second bearing side of the hole-forming surface constitutes the gap-fitting portion. The Roots pump according to Appendix 1, characterized in that the clearance between the gap fitting portion and the rotating shaft is smaller than the clearance between the portion between the press-fit portion and the gap fitting portion on the hole-forming surface and the rotating shaft.

[0076] <Note 3> The Roots pump according to <Note 1>, characterized in that the hole-forming surface has a gap-fitting portion in all parts except the press-fit portion.

[0077] <Note 4> A Roots pump according to any one of <Appendix 1> to <Appendix 3>, characterized in that the entire rotor has a solid structure.

[0078] <Note 5> The Roots pump according to any one of <Appendix 1> to <Appendix 3>, characterized in that the rotor has a solid structure only in the portion that overlaps with the press-fit portion in the radial direction of the rotation shaft.

[0079] <Note 6> The rotor has a through hole that penetrates the rotor on the radially outer side of the rotation axis relative to the insertion hole, A Roots pump according to any one of <Appendix 1> to <Appendix 3>, characterized in that a rib is provided in the portion of the rotating shaft within the through hole that overlaps with the press-fit portion in the radial direction.

[0080] <Note 7> The housing comprises 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 structure has the intake port and the discharge port formed therein. The first bearing is held in the first housing structure, The Roots pump according to any one of <Appendix 1> to <Appendix 6>, characterized in that the second bearing is held in the second housing structure. [Explanation of Symbols]

[0081] 10...Roots pump, 11...Housing, 14...Third housing member which is a component of the first housing, 15...Fourth housing member which is a component of the second housing, 19...Rotor chamber, 23...First bearing, 24...Second bearing, 25...Rotating shaft, 34...Intake port, 35...Discharge port, 40...Rotor, 45...Through hole, 51...Inner ring, 52...Outer ring, 53...Rolling element, 64...Hole forming surface, 65...Press-fit part, 66...Clearance fitting part, 71...Through hole, 72...Rib.

Claims

1. A housing having an intake port for drawing in fluid and an outlet port for discharging fluid, A rotor chamber defined in the housing and communicating with the intake port and the discharge port, A rotating shaft located inside the housing, A rotor having an insertion hole through which the rotating shaft is inserted, and the rotating shaft is press-fitted into the hole-forming surface that forms the insertion hole, thereby rotating integrally with the rotating shaft within the rotor chamber, The rotating shaft comprises a first bearing and a second bearing that rotatably support the portions located on both sides of the rotor with respect to the housing, respectively. The first bearing and the second bearing are Insider, An outer ring that surrounds the inner ring and is supported by the housing, Each of the following has rolling elements provided between the inner ring and the outer ring, The rotating shaft is press-fitted into the inner ring of the first bearing and clearance-fitted into the inner ring of the second bearing. The coefficient of thermal expansion of the housing material and the coefficient of thermal expansion of the rotor material are greater than the coefficient of thermal expansion of the rotating shaft material. A Roots pump in which, as the rotor rotates, fluid is drawn into the rotor chamber from the intake port and the fluid in the rotor chamber is discharged from the discharge port, Only the portion of the hole-forming surface including the end on the first bearing side is a press-fit portion into which the rotating shaft is press-fitted. The portion of the hole-forming surface other than the press-fit portion, including the end on the second bearing side, is a gap-fit ​​portion into which the rotating shaft is gap-fitted. A Roots pump characterized in that the axial length of the press-fit portion in the hole-forming surface is shorter than the axial length of the gap-fit ​​portion.

2. The Roots pump according to claim 1, characterized in that the entire rotor has a solid structure.

3. A housing having an intake port for drawing in fluid and an outlet port for discharging fluid, A rotor chamber defined in the housing and communicating with the intake port and the discharge port, A rotating shaft located inside the housing, A rotor having an insertion hole through which the rotating shaft is inserted, and the rotating shaft is press-fitted into the hole-forming surface that forms the insertion hole, thereby rotating integrally with the rotating shaft within the rotor chamber, The rotating shaft comprises a first bearing and a second bearing that rotatably support the portions located on both sides of the rotor with respect to the housing, respectively. The first bearing and the second bearing are Insider, An outer ring that surrounds the inner ring and is supported by the housing, Each of the following has rolling elements provided between the inner ring and the outer ring, The rotating shaft is press-fitted into the inner ring of the first bearing and clearance-fitted into the inner ring of the second bearing. The coefficient of thermal expansion of the housing material and the coefficient of thermal expansion of the rotor material are greater than the coefficient of thermal expansion of the rotating shaft material. A Roots pump in which, as the rotor rotates, fluid is drawn into the rotor chamber from the intake port and the fluid in the rotor chamber is discharged from the discharge port, The end of the hole-forming surface on the first bearing side is a press-fit portion into which the rotating shaft is press-fitted. At least the end of the hole-forming surface on the second bearing side is a gap-fitting portion into which the rotating shaft is gap-fitted. The Roots pump is characterized in that the rotor has a solid structure only in the portion that overlaps with the press-fit portion in the radial direction of the rotating shaft.

4. A housing having an intake port for drawing in fluid and an outlet port for discharging fluid, A rotor chamber defined in the housing and communicating with the intake port and the discharge port, A rotating shaft located inside the housing, A rotor having an insertion hole through which the rotating shaft is inserted, and the rotating shaft is press-fitted into the hole-forming surface that forms the insertion hole, thereby rotating integrally with the rotating shaft within the rotor chamber, The rotating shaft comprises a first bearing and a second bearing that rotatably support the portions located on both sides of the rotor with respect to the housing, respectively. The first bearing and the second bearing are Insider, An outer ring that surrounds the inner ring and is supported by the housing, Each of the following has rolling elements provided between the inner ring and the outer ring, The rotating shaft is press-fitted into the inner ring of the first bearing and clearance-fitted into the inner ring of the second bearing. The coefficient of thermal expansion of the housing material and the coefficient of thermal expansion of the rotor material are greater than the coefficient of thermal expansion of the rotating shaft material. A Roots pump in which, as the rotor rotates, fluid is drawn into the rotor chamber from the intake port and the fluid in the rotor chamber is discharged from the discharge port, The end of the hole-forming surface on the first bearing side is a press-fit portion into which the rotating shaft is press-fitted. At least the end of the hole-forming surface on the second bearing side is a gap-fitting portion into which the rotating shaft is gap-fitted. The rotor has a through hole that penetrates the rotor on the radially outer side of the rotation axis relative to the insertion hole, A Roots pump characterized in that a rib is provided in the portion of the through hole in which the rotation shaft overlaps with the press-fit portion in the radial direction.

5. The housing comprises 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 structure has the intake port and the discharge port formed therein. The first bearing is held in the first housing structure, The Roots pump according to claim 1, characterized in that the second bearing is held in the second housing structure.

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