roots pump

Abstract

A Roots pump capable of reducing damage due to biting of foreign matter and capable of suppressing reduction in pump performance is provided. A tip end portion (22a) of a rotor (22) has a pair of rotor peripheral surfaces (23) and a tip end portion peripheral surface (24). The pair of rotor peripheral surfaces each faces a rotor chamber peripheral surface (27) via a first radial gap (CL1). The pair of rotor peripheral surfaces each has a predetermined width in a rotation direction (R) of the rotor. The tip end portion peripheral surface is provided between the pair of rotor peripheral surfaces in the rotation direction. The tip end portion peripheral surface faces the rotor chamber peripheral surface via a second radial gap (CL2) that is larger than the first radial gap. The tip end portion peripheral surface captures foreign matter (D) in a rotor chamber (25) at the time of rotation of the rotor. In the rotation direction, a width (W2) at which the rotor chamber peripheral surface faces the tip end portion peripheral surface is wider than a sum of a pair of the predetermined widths (W1) at which the rotor chamber peripheral surface faces the rotor peripheral surfaces.

Description

TECHNICAL FIELD

[0001] The present application relates to a Roots pump. BACKGROUND

[0002] For example, a gas pump as a Roots pump is disclosed in Patent Literature 1. In the gas pump, a pair of rotors are each disposed in a cylindrical space as a rotor chamber. An inner peripheral surface of the cylindrical space forms a housing inner peripheral surface as a rotor chamber peripheral surface. Each rotor has a large circular arc surface on an outer peripheral surface of a tip end portion. The large circular arc surface is formed to have a curvature radius equivalent to that of the housing inner peripheral surface.

[0003] In such a Roots pump, a predetermined radial gap is sealed between the housing inner peripheral surface and the tip end portion of the rotor. The radial gap is set to a value that suppresses leakage of fluid from a high pressure side to a low pressure side via the radial gap.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent Application Laid-Open No. 6-264879 SUMMARY

[0007] PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] Foreign matter sometimes enters the rotor chamber of the Roots pump. When the foreign matter is larger than the radial gap, the foreign matter bites between the housing inner peripheral surface and the tip end portion of the rotor. When the rotor rotates in a state where the foreign matter bites between the housing inner peripheral surface and the tip end portion of the rotor, the tip end portion of the rotor and the housing inner peripheral surface are damaged by the foreign matter. In order to suppress such damage, it is conceivable to make the radial gap larger than the foreign matter. However, when the radial gap is made larger than the foreign matter, the amount of leakage of fluid from the high pressure side to the low pressure side through the radial gap increases, and thus the pump performance decreases, which is undesirable.

[0009] MEANS FOR SOLVING THE PROBLEMS

[0010] The gist of the Roots pump for solving the above-described problems is that the Roots pump has: a housing; a rotor chamber delimited by the housing and having a suction hole that sucks fluid and a discharge hole that discharges fluid; a pair of rotary shafts rotatably supported to the housing; and a pair of cocoon-shaped rotors mounted to the pair of rotary shafts and rotating in the rotor chamber, the rotor chamber having a rotor chamber peripheral surface composed of a pair of circular arc surfaces connecting the suction hole and the discharge hole in the radial direction of the rotors and facing the tip end portions of the rotors via a predetermined radial gap, the fluid sucked from the suction hole being guided by the circular arc surfaces of the rotor chamber peripheral surface to be discharged from the discharge hole by rotation of the pair of rotors, the tip end portions of the rotors having: a pair of rotor peripheral surfaces facing the rotor chamber peripheral surface having a pair of predetermined widths in the direction of rotation of the rotors via a first radial gap; and a tip end portion peripheral surface provided between the pair of rotor peripheral surfaces in the direction of rotation, facing the rotor chamber peripheral surface via a second radial gap larger than the first radial gap, and capturing foreign matter in the rotor chamber when the rotors rotate, the width of the rotor chamber peripheral surface facing the tip end portion peripheral surface being larger than the sum of the pair of predetermined widths of the rotor chamber peripheral surface facing the pair of rotor peripheral surfaces in the direction of rotation.

[0011] Thus, the second radial gap is larger than the first radial gap in both the direction of rotation of the rotors and the radial direction. Therefore, even if foreign matter enters between the preceding rotor peripheral surface and the facing rotor chamber peripheral surface when the rotors rotate, the foreign matter can be released to between the tip end portion peripheral surface and the rotor chamber peripheral surface by rotation of the rotors. Thereafter, even if the rotors rotate, the foreign matter is positioned between the tip end portion peripheral surface and the rotor chamber peripheral surface, so that the foreign matter can be inhibited from entering between the following rotor peripheral surface and the facing rotor chamber peripheral surface. That is, the foreign matter is captured between the tip end portion peripheral surface and the facing rotor chamber peripheral surface. Also, since the second radial gap between the tip end portion peripheral surface and the rotor chamber peripheral surface is as large as to capture the foreign matter, the foreign matter can be inhibited from being kept biting between the tip end portion of the rotors and the rotor chamber peripheral surface.

[0012] In order to capture the foreign matter, the tip end portion peripheral surface is provided at the tip end portion of the rotors, but the radial gap at the tip end portion of the rotors is not only the second radial gap formed by the tip end portion peripheral surface. That is, by providing the rotor peripheral surface at the tip end portion of the rotors, the first radial gap smaller than the second radial gap is provided as the radial gap at the tip end portion of the rotors.

[0013] Further, by the labyrinth effect generated by the size relationship between the first radial gap and the second radial gap, the sealing property of the tip end portion can be ensured. Therefore, even if the tip end portion peripheral surface is provided at the tip end portion, the amount of leakage of the fluid from the high pressure side to the low pressure side between the tip end portion of the rotor and the rotor chamber peripheral surface can be suppressed. Therefore, damage due to the intrusion of the foreign matter can be reduced, and the decrease in the pump performance can be suppressed.

[0014] With respect to the Roots pump, it can also be that the rotor peripheral surface and the tip end portion peripheral surface are circular arc surfaces, the circular arc radius of the circular arc surface of the tip end portion peripheral surface is larger than the circular arc radius of the circular arc surface of the rotor peripheral surface, and is larger than the circular arc radius of the circular arc surface of the rotor chamber peripheral surface.

[0015] Thus, the rotor in which the second radial gap is larger than the first radial gap can be easily manufactured.

[0016] With respect to the Roots pump, it can also be that the tip end portion peripheral surface is a flat surface provided between the pair of rotor peripheral surfaces.

[0017] Thus, the tip end portion peripheral surface can be easily manufactured.

[0018] With respect to the Roots pump, it can also be that the tip end portion peripheral surface is a curved surface that is recessed in a circular arc shape as it goes from the tip end portion of the rotor toward the axis center of the rotary shaft along a straight line connecting the tip end portion of the rotor and the center point of the rotary shaft.

[0019] Thus, the second radial gap can be enlarged, and thus the foreign matter can be easily captured.

[0020] With respect to the Roots pump, it can also be that the rotor has a narrowed portion provided between the pair of tip end portions and narrowing and fixing the rotary shaft, the narrowed portion having a narrowed peripheral surface, the narrowed peripheral surface having a circular arc surface composed of a circular arc radius smaller than the circular arc radius of the circular arc surface of the tip end portion peripheral surface.

[0021] Thus, a gap is demarcated between the tip end portion peripheral surface and the narrowed peripheral surface of the narrowed portion. Further, the foreign matter that has entered between the rotors can be released to the gap.

[0022] With respect to the Roots pump, it can also be that a groove recessed toward the rotary shaft compared to the tip end portion peripheral surface is provided at the tip end portion of the rotor, the groove being provided extending in the axial direction of the rotary shaft.

[0023] Thus, when the foreign matter that has entered the second radial gap enters the groove, the state of the foreign matter being captured can be easily maintained.

[0024] Effects of Invention

[0025] According to the present application, damage due to the intrusion of the foreign matter can be reduced, and the decrease in the pump performance can be suppressed. Attached Figure Description

[0026] Figure 1 This is a cross-sectional view showing the Roots pump of the first embodiment.

[0027] Figure 2 This is a cross-sectional view showing the Roots pump of the first embodiment.

[0028] Figure 3 It is an enlarged sectional view showing the circumferential surface of the rotor and the circumferential surface of the top end.

[0029] Figure 4 This is an enlarged cross-sectional view showing the rotor of the comparative example.

[0030] Figure 5 It is an enlarged cross-sectional view showing the narrowed section and the periphery of the top section.

[0031] Figure 6 This is an enlarged cross-sectional view showing the rotor of the Roots pump according to the second embodiment.

[0032] Figure 7 This is an enlarged cross-sectional view showing the rotor of the Roots pump according to the third embodiment.

[0033] Figure 8 This is an enlarged cross-sectional view of the rotor of a Roots pump, showing another example.

[0034] Explanation of reference numerals in the attached figures

[0035] CL1…first radial clearance, CL2…second radial clearance, R…direction of rotation, r1, r2, r3, r4…radii of arc, T…straight line, W1, W2…width, 10…Roots pump, 11…casing, 16…rotor shaft, 22…rotor, 22a…top end, 22b…narrowing section, 23…rotor circumferential surface, 24…top end circumferential surface, 24a…groove, 25…rotor chamber, 27…rotor chamber circumferential surface, 27a…arc surface, 45…suction port, 46…discharge port, 221…narrowing circumferential surface. Detailed Implementation

[0036] [First Implementation]

[0037] The following is based on Figures 1-5 The first embodiment that embodies the Roots pump will be described.

[0038] <The Roots Pump Overview>

[0039] Roots pumps are used as hydrogen pumps in fuel cell vehicles. These vehicles are equipped with a fuel cell system that supplies oxygen and hydrogen to generate electricity. The Roots pump resupply the fuel cell with hydrogen discharged from it. Therefore, the Roots pump draws in and discharges hydrogen as a fluid.

[0040] <case>

[0041] As shown in Figure 1 FIG. 1, the Roots pump 10 has a cylindrical case 11. The case 11 has a motor case 12, a gear case 13, a rotor case 14, and a cover member 15.

[0042] The motor case 12 is joined to the gear case 13. In addition, the rotor case 14 is joined to the gear case 13. The cover member 15 is joined to the rotor case 14.

[0043] The motor case 12 has a bottom wall 12a that is plate-shaped and a peripheral wall 12b that extends in a cylindrical shape from an outer peripheral portion of the bottom wall 12a. The gear case 13 has a bottom wall 13a that is plate-shaped and a peripheral wall 13b that extends in a cylindrical shape from an outer peripheral portion of the bottom wall 13a. The rotor case 14 has a bottom wall 14a that is plate-shaped and a peripheral wall 14b that extends in a cylindrical shape from an outer peripheral portion of the bottom wall 14a.

[0044] The bottom wall 13a of the gear case 13 is butted against the peripheral wall 12b of the motor case 12. The bottom wall 14a of the rotor case 14 is butted against the peripheral wall 13b of the gear case 13. The cover member 15 is plate-shaped. The cover member 15 is butted against the peripheral wall 14b of the rotor case 14.

[0045] A gear chamber 13c is demarcated in the case 11. The gear chamber 13c is demarcated by the bottom wall 13a of the gear case 13, the peripheral wall 13b of the gear case 13, and the bottom wall 14a of the rotor case 14.

[0046] <rotor chamber>

[0047] The Roots pump 10 has a rotor chamber 25 that is demarcated by the case 11. The rotor chamber 25 is demarcated by the bottom wall 14a of the rotor case 14, the peripheral wall 14b of the rotor case 14, and the cover member 15.

[0048] The case 11 has a pair of rotor chamber end faces 26 and a rotor chamber peripheral face 27. One of the pair of rotor chamber end faces 26 is formed by an inner wall face 14c of the bottom wall 14a of the rotor case 14, and the other of the pair of rotor chamber end faces 26 is formed by an inner wall face 15a of the cover member 15. The pair of rotor chamber end faces 26 are located on opposite sides of each other with the rotor chamber 25 interposed therebetween. The rotor chamber peripheral face 27 is formed by an inner peripheral face 14d of the peripheral wall 14b. The rotor chamber peripheral face 27 is constituted by a pair of circular arc faces 27a.

[0049] <rotation shaft>

[0050] The Roots pump 10 has a driving shaft 16a and a driven shaft 16b as a pair of rotary shafts 16. The driving shaft 16a is arranged in parallel with the driven shaft 16b. Hereinafter, the driving shaft 16a and the driven shaft 16b will be collectively referred to as the pair of rotary shafts 16. The extending direction of the shaft center L of the rotary shaft 16 is set as the axial direction. The driving shaft 16a penetrates the bottom wall 13a of the gear housing 13 and the bottom wall 14a of the rotor housing 14. The driven shaft 16b penetrates the bottom wall 14a of the rotor housing 14.

[0051] The first driving bearing 31a is arranged on the bottom wall 13a of the gear housing 13. The second driving bearing 31b is arranged on the bottom wall 14a of the rotor housing 14. The third driving bearing 31c is arranged on the bottom wall 12a of the motor housing 12. The driving shaft 16a is rotatably supported to the housing 11 via the first driving bearing 31a, the second driving bearing 31b, and the third driving bearing 31c.

[0052] The first driven bearing 41a is arranged on the bottom wall 13a of the gear housing 13. The second driven bearing 41b is arranged on the bottom wall 14a of the rotor housing 14. The driven shaft 16b is rotatably supported to the housing 11 via the first driven bearing 41a and the second driven bearing 41b. Thus, the pair of rotary shafts 16 is rotatably supported to the housing 11.

[0053] The first sealing member 32a is provided on the bottom wall 13a of the gear housing 13. The first sealing member 32a seals between the driving shaft 16a and the bottom wall 13a of the gear housing 13. The second sealing member 32b is provided on the bottom wall 14a of the rotor housing 14. The second sealing member 32b seals between the driving shaft 16a and the bottom wall 14a. The third sealing member 32c is provided on the bottom wall 14a of the rotor housing 14. The third sealing member 32c seals between the driven shaft 16b and the bottom wall 14a.

[0054] <Electric motor>

[0055] The Roots pump 10 has an electric motor 50 that rotates the driving shaft 16a. The electric motor 50 is housed in a motor chamber 12c defined by the housing 11. The motor chamber 12c is defined by the bottom wall 12a of the motor housing 12, the peripheral wall 12b of the motor housing 12, and the bottom wall 13a of the gear housing 13. The electric motor 50 rotates the driving shaft 16a.

[0056] The Roots pump 10 has a circular plate-shaped driving gear 18 fixed to the driving shaft 16a, and a circular plate-shaped driven gear 19 fixed to the driven shaft 16b. The driving gear 18 and the driven gear 19 are housed in a gear chamber 13c. The driven gear 19 is rotated in engagement with the driving gear 18. The driven gear 19 is rotated in the direction opposite to the direction of rotation of the driving shaft 16a by the driving gear 18 and the driven gear 19.

[0057] <Intake port and exhaust port>

[0058] The rotor chamber 25 has an intake port 45 for drawing hydrogen into the rotor chamber 25 and an exhaust port 46 for discharging hydrogen from the rotor chamber 25. The intake port 45 and the exhaust port 46 are formed on the peripheral wall 14b of the rotor housing 14. The intake port 45 and the exhaust port 46 face each other across the rotor chamber 25. The intake port 45 and the exhaust port 46 communicate with the outside of the rotor chamber 25. A pair of arcuate surfaces 27a on the peripheral surface 27 of the rotor chamber connect the intake port 45 and the exhaust port 46.

[0059] <Drive rotor and driven rotor>

[0060] like Figure 1 and Figure 2 As shown, the Roots pump 10 has a driving rotor 20 and a driven rotor 21, which are a pair of double-lobe cocoon-shaped rotors 22. Hereinafter, the driving rotor 20 and the driven rotor 21 will be referred to as a pair of rotors 22. In the Roots pump 10, hydrogen gas drawn in from the suction port 45 is guided by the arcuate surface 27a of the rotor chamber 25 through the rotation of the pair of rotors 22. The hydrogen gas guided by the arcuate surface 27a is discharged from the Roots pump 10 through the discharge port 46. In the Roots pump 10, the less leakage of fluid from the high-pressure side to the low-pressure side through the radial clearance between the rotor 22 and the circumferential surface 27 of the rotor chamber, the higher the pump performance.

[0061] The drive rotor 20 is a rotor that rotates via the drive gear 18. The driven rotor 21 is a rotor that rotates via the driven gear 19. A pair of rotors 22 are housed in the rotor chamber 25. The drive rotor 20 is mounted on the drive shaft 16a. The driven rotor 21 is mounted on the driven shaft 16b. The driven rotor 21 rotates together with the drive rotor 20. Therefore, it can be said that the drive rotor 20 and the driven rotor 21 are cocoon-shaped rotors 22 rotating in opposite directions within the rotor chamber 25.

[0062] A pair of rotor chamber end faces 26 face each other axially across a pair of rotors 22 on a pair of rotating shafts 16. A rotor chamber peripheral surface 27 surrounds the radial outer peripheral region of the pair of rotors 22. Furthermore, the radial direction of the drive rotor 20 coincides with the radial direction of the drive shaft 16a, and the radial direction of the driven rotor 21 coincides with the radial direction of the driven shaft 16b.

[0063] Each of the pair of rotors 22 has a pair of top ends 22a and a narrowing portion 22b disposed between the pair of top ends 22a. The straight line connecting the pair of top ends 22a of the rotor 22 and the axis L of the rotation shaft 16 is defined as "T".

[0064] Each tip portion 22a has a pair of rotor peripheral surfaces 23, a tip portion peripheral surface 24 between the pair of rotor peripheral surfaces 23, and a curved surface 222 connected to each rotor peripheral surface 23. The rotor peripheral surfaces 23 and the tip portion peripheral surface 24 are circular arc surfaces. The curved surface 222 is a curved surface based on an involute curve.

[0065] As shown in Figure 3 each of the pair of rotor peripheral surfaces 23 faces the rotor chamber peripheral surface 27 via a first radial gap CL1. Therefore, it can be said that the rotor chamber peripheral surface 27 faces the tip portion 22a of the rotor 22 in the radial direction of the rotor 22 via the predetermined first radial gap CL1. In addition, each of the pair of rotor peripheral surfaces 23 has a predetermined width in the rotation direction R of the rotor 22. In the rotor chamber peripheral surface 27, the width facing each rotor peripheral surface 23 is set as "W1". The circular arc surface of each rotor peripheral surface 23 is a circular arc surface having a circular arc radius r1 with the axis L as a center point.

[0066] Here, the circular arc surface 27a of the rotor chamber peripheral surface 27 is a circular arc surface having a circular arc radius r2 with the axis L as a center point. The circular arc radius r1 of the rotor peripheral surface 23 is slightly smaller than the circular arc radius r2 of the circular arc surface 27a. The first radial gap CL1 described above is formed between the rotor peripheral surface 23 and the circular arc surface 27a. The first radial gap CL1 is set in a predetermined range in a manner capable of suppressing leakage of hydrogen from the high-pressure side to the low-pressure side through the first radial gap CL1.

[0067] The tip portion peripheral surface 24 is provided between the pair of rotor peripheral surfaces 23 in the rotation direction R. The width in which the rotor chamber peripheral surface 27 faces the tip portion peripheral surface 24 in the rotation direction R is set as "W2". This width W2 is wider than the sum of the pair of widths W1 in which the rotor chamber peripheral surface 27 faces the rotor peripheral surfaces 23. Therefore, the following equation holds.

[0068] W2 > W1 + W1 … Equation

[0069] Therefore, the size of the tip portion peripheral surface 24 in the rotation direction R is larger than the size of each rotor peripheral surface 23 in the rotation direction R.

[0070] The top peripheral surface 24 faces the rotor chamber peripheral surface 27 via a second radial clearance CL2, which is larger than the first radial clearance CL1. The top peripheral surface 24 is an arc surface with an arc radius r3 centered on the shaft center L. The arc radius r3 of the top peripheral surface 24 is larger than the arc radius r1 of the rotor peripheral surface 23, and larger than the arc radius r2 of the arc surface 27a of the rotor chamber peripheral surface 27. Therefore, the second radial clearance CL2 gradually increases along the rotational direction R as it moves from one rotor peripheral surface 23 toward the other. Furthermore, the second radial clearance CL2 reaches its maximum at the midpoint of the pair of rotor peripheral surfaces 23 in the rotational direction R. The second radial clearance CL2 gradually decreases along the rotational direction R as it moves from the midpoint of the pair of rotor peripheral surfaces 23 toward the other.

[0071] As described above, the Roots pump 10 resupplyes the hydrogen discharged from the fuel cell to the fuel cell. Therefore, foreign matter D discharged from the fuel cell may sometimes mix into the rotor chamber 25. Additionally, foreign matter D generated within the rotor chamber 25 due to contact or other reasons may sometimes mix into the rotor chamber 25. The first radial clearance CL1 is smaller than the maximum size of the foreign matter D.

[0072] The second radial clearance CL2 is larger than the maximum size of the foreign object D. The second radial clearance CL2 is larger than the first radial clearance CL1. Specifically, the maximum value of the second radial clearance CL2 is about 5 times larger than the maximum value of the first radial clearance CL1. The top peripheral surface 24 of this second radial clearance CL2 traps the foreign object D in the rotor chamber 25 when the rotor 22 rotates.

[0073] like Figure 2 As shown, the narrowing portion 22b is the part that fixes the rotating shaft 16. The narrowing portion 22b is provided between a pair of top portions 22a and narrows. The narrowing portion 22b has a pair of narrowed circumferential surfaces 221. The pair of narrowed circumferential surfaces 221 clamp the rotating shaft 16 in the radial direction.

[0074] like Figure 5 As shown, the narrowed circumferential surface 221 is an arc surface with an arc radius of r4. The arc radius r4 of the narrowed circumferential surface 221 is smaller than the arc radius r3 of the top circumferential surface 24. Therefore, at the point in time when the pair of rotor circumferential surfaces 23 and the top circumferential surface 24 are facing the narrowed circumferential surface 221, a gap K is formed between the top circumferential surface 24 and the narrowed circumferential surface 221.

[0075] The clearance K gradually increases from one rotor circumferential surface 23 toward the other rotor circumferential surface 23. Furthermore, the radial clearance K is largest at the midpoint between the two rotor circumferential surfaces 23 in the rotational direction R. The radial clearance K is larger than the maximum size of the foreign object D. The clearance K gradually decreases from the midpoint between the two rotor circumferential surfaces 23 toward the other rotor circumferential surface 23.

[0076] In the Roots pump 10, hydrogen gas drawn in through the suction port 45 is sealed by the top end 22a of the rotor 22. The sealed hydrogen gas is then pressurized towards the discharge port 46. The sealed hydrogen gas is discharged from the discharge port 46. The region from when the hydrogen gas is sealed through the suction port 45 to when it is discharged through the discharge port 46 is designated as the "pressurization region." In this pressurization region, the hydrogen gas drawn in through the suction port 45 is sealed and pressurized by the top end 22a of the rotor 22. The pressurization region is the area from the beginning of the sealing position of the rotor 22 to the end of the sealing position.

[0077] [The Role of the Implementation Method]

[0078] Next, the function of this embodiment will be explained.

[0079] Drive shaft 16a rotates via electric motor 50. Driven shaft 16b rotates in the opposite direction to drive shaft 16a via gears 18 and 19. Consequently, a pair of rotors 22 rotate in opposite directions. The Roots pump 10, through the rotation of the rotors 22, draws hydrogen into rotor chamber 25 via suction port 45 and discharges hydrogen from rotor chamber 25 via discharge port 46.

[0080] Hydrogen gas drawn in through the suction port 45 is sealed and compressed by the top end 22a of the rotor 22. In the Roots pump 10, when the rotor 22 is in the closed final position, the top end 22a of one of the rotors 22 is closest to the discharge port 46. At this time, internal compression of the hydrogen gas occurs in the space enclosed by the pair of rotors 22. The space enclosed by the pair of rotors 22 is sealed by the top end 22a of each rotor 22. The seal achieved by the top end 22a is performed by the rotor circumferential surface 23 and the top end circumferential surface 24.

[0081] A first radial gap CL1 exists between the rotor circumferential surface 23 and the rotor chamber circumferential surface 27. Additionally, a second radial gap CL2, larger than the first radial gap CL1, exists between the top peripheral circumferential surface 24 and the rotor chamber circumferential surface 27. Therefore, high-pressure hydrogen gas leakage to the low-pressure side is suppressed by the labyrinth effect based on the first radial gap CL1 and the second radial gap CL2.

[0082] Figure 4A rotor 90 of a comparative example is shown. The tip end portion 91 of the rotor 90 has a circular-arc peripheral surface 92. The circular-arc peripheral surface 92 is a circular-arc surface of the same circular-arc radius r1 as the rotor peripheral surface 23 of the embodiment. Therefore, the circular-arc peripheral surface 92 is opposed to the rotor chamber peripheral surface 27 via the 1st radial gap CL1. The tip end portion 91 of the rotor 90 of the comparative example is opposed to the rotor chamber peripheral surface 27 via the 1st radial gap CL1 throughout the entire length of the circular-arc peripheral surface 92 along the rotation direction R.

[0083] In the Roots pump having the rotor 90 of the comparative example, since the 1st radial gap CL1 is smaller than the maximum size of the foreign matter D, in the case where the foreign matter D is mixed into the rotor chamber 25, the foreign matter D enters between the rotor peripheral surface 23 and the rotor chamber peripheral surface 27. Thereafter, during rotation of the rotor 90 in the rotation direction R, the foreign matter D continues to exist between the circular-arc peripheral surface 92 and the rotor chamber peripheral surface 27. That is, the foreign matter D continues to bite between the circular-arc peripheral surface 92 and the rotor chamber peripheral surface 27.

[0084] On the contrary, in the present embodiment, the foreign matter D first enters between the rotation-direction-leading-side rotor peripheral surface 23 of the pair of rotor peripheral surfaces 23 and the rotor chamber peripheral surface 27. Thereafter, accompanying rotation of the rotor 22 in the rotation direction R, the foreign matter D goes toward the tip end peripheral surface 24 on the rotation-direction-lagging-side of the rotor peripheral surface 23.

[0085] Here, as described above, the relation of W2 > W1 + W1 holds. In addition, the 2nd radial gap CL2 is larger than the 1st radial gap CL1. Therefore, even if the foreign matter D enters between the rotation-direction-leading-side rotor peripheral surface 23 and the opposed rotor chamber peripheral surface 27 at the time of rotation of the rotor 22, the foreign matter D is released to between the tip end peripheral surface 24 and the rotor chamber peripheral surface 27 by rotation of the rotor 22.

[0086] And, the 2nd radial gap CL2 is larger than the maximum size of the foreign matter D. Therefore, the foreign matter D is positioned between the tip end peripheral surface 24 and the rotor chamber peripheral surface 27, but does not bite between the tip end peripheral surface 24 and the rotor chamber peripheral surface 27.

[0087] Thereafter, even if the rotor 22 rotates, the foreign matter D is positioned between the tip end peripheral surface 24 and the rotor chamber peripheral surface 27, so it is possible to suppress the foreign matter D from entering between the rotation-direction-lagging-side rotor peripheral surface 23 and the opposed rotor chamber peripheral surface 27. That is, the foreign matter D becomes in a state of being held captured between the tip end peripheral surface 24 and the opposed rotor chamber peripheral surface 27.

[0088] The foreign matter D is sent toward the discharge hole 46 with rotation of the rotor 22. Thereafter, when the tip end peripheral surface 24 and the discharge hole 46 are opposed, the foreign matter D is discharged from the discharge hole 46 to the outside of the rotor chamber 25.

[0089] As Figure 5As shown, the tip portion 22a sometimes opposes the narrowed portion 22b as the pair of rotors 22 rotates. At this time, a gap K is defined between the tip portion peripheral surface 24 and the narrowed peripheral surface 221. When the foreign matter D enters between the pair of rotors 22, the foreign matter D can be released to the gap K.

[0090] [Effects of the 1st Embodiment]

[0091] According to the above-described embodiment, the following effects can be obtained.

[0092] (1-1) The pair of rotor peripheral surfaces 23 and the tip portion peripheral surface 24 are provided at the tip portion 22a of the rotor 22. Also, the 2nd radial gap CL2 is larger than the 1st radial gap CL1 in both the radial direction and the rotational direction R. Therefore, even when the foreign matter D enters between the preceding-side rotor peripheral surface 23 and the opposing rotor chamber peripheral surface 27 as the rotor 22 rotates, the foreign matter D can be captured between the tip portion peripheral surface 24 and the rotor chamber peripheral surface 27 by the rotation of the rotor 22. Thereafter, even if the rotor 22 rotates, the foreign matter D is positioned between the tip portion peripheral surface 24 and the rotor chamber peripheral surface 27, so the foreign matter D can be inhibited from entering between the following-side rotor peripheral surface 23 and the opposing rotor chamber peripheral surface 27. Therefore, the foreign matter D can be inhibited from becoming in a state of biting between the tip portion 22a of the rotor 22 and the rotor chamber peripheral surface 27. As a result, the tip portion 22a and the rotor chamber peripheral surface 27 can be inhibited from being damaged or the foreign matter can be inhibited from being generated due to the biting of the foreign matter D.

[0093] In order to capture the foreign matter D, the tip portion peripheral surface 24 is provided at the tip portion 22a of the rotor 22, but the rotor peripheral surface 23 is also provided at the tip portion 22a of the rotor 22. Therefore, the 1st radial gap CL1 that is smaller than the 2nd radial gap CL2 formed by the tip portion peripheral surface 24 is provided at the tip portion 22a.

[0094] Also, the sealability of the tip portion 22a can be ensured by the labyrinth effect that occurs from the size relationship between the 1st radial gap CL1 and the 2nd radial gap CL2. Therefore, even if the tip portion peripheral surface 24 is provided at the tip portion 22a, the amount of leakage of hydrogen gas from the high-pressure side to the low-pressure side through between the tip portion 22a and the rotor chamber peripheral surface 27 can be inhibited. Therefore, the damage due to the biting of the foreign matter D can be reduced, and the decrease in pump performance can be inhibited.

[0095] (1-2) The radius of curvature r3 of the arc surface of the tip portion peripheral surface 24 is larger than the radius of curvature r1 of the arc surface of the rotor peripheral surface 23, and is also larger than the radius of curvature r2 of the arc surface 27a of the rotor chamber peripheral surface 27. Therefore, the rotor 22 that makes the 2nd radial gap CL2 larger than the 1st radial gap CL1 can be easily manufactured.

[0096] (1-3) The radius of curvature r4 of the tapered circumferential surface 221 of the tapered portion 22b is smaller than the radius of curvature r3 of the circular arc surface of the tip portion circumferential surface 24. Therefore, when the tip portion 22a and the tapered portion 22b face each other, a gap K can be demarcated between the tip portion circumferential surface 24 and the tapered circumferential surface 221. Also, foreign matter D that has entered between the rotors 22 can be released to the gap K.

[0097] [2nd Embodiment]

[0098] Next, according to the 2nd embodiment, the shape of the tip portion 22a of the rotor 22 is changed. Figure 6 The 2nd embodiment is a structure in which the shape of the tip portion 22a of the rotor 22 in the 1st embodiment is changed, and thus detailed description of the same parts is omitted.

[0099] As shown in FIG. 6, in the tip portion 22a of the rotor 22, the tip portion circumferential surface 24 is a flat surface provided between the rotor circumferential surfaces 23. The tip portion circumferential surface 24 is a flat surface that connects the pair of rotor circumferential surfaces 23 in a straight line shape to each other. The 1st radial gap CL1 is the same as that of the 1st embodiment, but the 2nd radial gap CL2 is larger than that of the 1st embodiment. Figure 6 [Effects of the 2nd Embodiment]

[0100] Therefore, according to the 2nd embodiment, in addition to the effects of (1-1) described in the 1st embodiment, the following effects can be obtained.

[0101] (2-1) Since the tip portion circumferential surface 24 is flat, the tip portion circumferential surface 24 can be easily manufactured in the rotor 22.

[0102] [3rd Embodiment]

[0103] Next, according to the 3rd embodiment, the shape of the tip portion 22a of the rotor 22 is changed.

[0104] Figure 7 As shown in FIG. 7, the tip portion circumferential surface 24 is a curved surface that is recessed in a circular arc shape as it goes from the tip portion 22a of the rotor 22 toward the axis L of the rotation shaft 16 along the straight line T. The tip portion circumferential surface 24 connects the pair of rotor circumferential surfaces 23 in a circular arc shape to each other. The 1st radial gap CL1 is the same as that of the 1st embodiment, but the 2nd radial gap CL2 is larger than that of the 1st embodiment.

[0105] [Effects of the 3rd Embodiment] Figure 7

[0106] [Effects of the 3rd Embodiment]

[0107] ​​Thus, according to the third embodiment, the following effects can be obtained in addition to the effects of (1-1) described in the first embodiment.

[0108] (3-1) Since the tip portion peripheral surface 24 is a circular arc surface that is recessed toward the axis L, the second radial gap CL2 can be enlarged. As a result, the foreign matter D is easily captured in the tip portion peripheral surface 24.

[0109] The present embodiment can be implemented as follows. The present embodiment and the following modified examples can be implemented in combination with each other within a range that is not technically contradictory.

[0110] In each of the embodiments, as shown in FIG. 1, a groove 24a that is recessed toward the rotation shaft 16 compared to the tip portion peripheral surface 24 can be provided in the tip portion 22a of the rotor 22. Figure 8

[0111] In the rotor 22 of the first embodiment, a plurality of grooves 24a are preferably provided in the tip portion peripheral surface 24. The grooves 24a are provided so as to extend in the entire length of the tip portion peripheral surface 24 in the axial direction of the rotation shaft 16. The opening width of the groove 24a in the rotation direction R and the depth of the groove 24a in the radial direction are preferably the size that can accommodate the entire foreign matter D. However, even if the foreign matter D that has entered the groove 24a protrudes from the tip portion peripheral surface 24, the depth of the groove 24a can be appropriately changed as long as the size of the second radial gap CL2 is such that the foreign matter D does not come into contact with the rotor chamber peripheral surface 27.

[0112] The groove 24a can be formed in the tip portion peripheral surface 24 of the second embodiment, and the groove 24a can be formed in the tip portion peripheral surface 24 of the third embodiment. The groove 24a can be formed in the rotor chamber peripheral surface 27.

[0113] In the constricted portion 22b of the rotor 22, the circular arc radius r4 of the constricted peripheral surface 221 can be the same as the circular arc radius r3 of the tip portion peripheral surface 24, or can be larger than the circular arc radius r3 of the tip portion peripheral surface 24.

[0114] The rotor 22 can be, for example, three-lobed or four-lobed when viewed in a cross section orthogonal to the axial direction of the rotation shaft 16.

[0115] The Roots pump 10 can be, for example, a pump that uses an engine as a driving source. In this case, the driving shaft 16a penetrates the bottom wall 13a of the gear housing 13 in order to be coupled to the engine as a driving source provided outside the gear chamber 13c.

[0116] The Roots pump 10 can not be a hydrogen pump for a fuel cell that supplies hydrogen gas to a fuel cell, but can be a pump used in other applications. In any case, the fluid that is sucked into the rotor chamber 25 is not limited to hydrogen gas.​

Claims

1. A Roots pump, comprising: case; The rotor chamber is defined by the housing and has an intake port for drawing in fluid and an outlet port for discharging fluid. A pair of rotating shafts, the pair of rotating shafts being rotatably supported by the housing; as well as A cocoon-shaped pair of rotors, each mounted on a pair of rotating shafts and rotating within the rotor chamber. The rotor chamber has a rotor chamber peripheral surface, which is formed in the radial direction of the rotor by a pair of arcuate surfaces connecting the intake port and the discharge port, and faces the top end of the rotor via a predetermined radial gap. As the pair of rotors rotate, the fluid drawn in from the suction port is guided by the arcuate surface of the rotor chamber circumference and discharged from the discharge port. Its features are, The top end of the rotor has: A pair of rotor circumferential surfaces, the pair of rotor circumferential surfaces facing the rotor chamber circumferential surface having a pair of predetermined widths in the direction of rotation of the rotor via a first radial clearance; as well as The top peripheral surface is positioned between a pair of rotor peripheral surfaces in the rotational direction, facing the rotor chamber peripheral surface via a second radial gap larger than the first radial gap, and traps foreign objects inside the rotor chamber when the rotor rotates. In the direction of rotation, the width of the rotor chamber peripheral surface facing the top end peripheral surface is wider than the sum of the predetermined widths of the rotor chamber peripheral surface facing the pair of rotor peripheral surfaces. The rotor's circumferential surface and the top end's circumferential surface are arc surfaces. The radius of the arc surface of the top end is larger than the radius of the arc surface of the rotor, and also larger than the radius of the arc surface of the rotor chamber.

2. The Roots pump according to claim 1, characterized in that, The rotor has a narrowed portion disposed between the pair of top portions, which narrows and fixes the rotating shaft. The narrowing portion has a narrowing circumferential surface, which is an arc surface composed of an arc radius smaller than the arc radius of the arc surface of the top portion circumferential surface.

3. The Roots pump according to claim 1 or 2, characterized in that, A groove is provided at the top end of the rotor, which is recessed toward the rotation axis compared to the circumferential surface of the top end, and the groove extends axially along the rotation axis.

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