Root pump

Abstract

To provide a root pump capable of suppressing deterioration of pump performance while reducing damage caused by foreign matter being caught.SOLUTION: A tip part 22a of a rotor 22 has a pair of rotor peripheral surfaces 23 and a recessed peripheral surface 24. Each of the pair of rotor peripheral surfaces 23 faces a rotor chamber peripheral surface 27 across a first radial clearance CL1. Each of the pair of rotor peripheral surfaces 23 has a predetermined width in a rotation direction R of the rotor 22. The recessed peripheral surface 24 is recessed between the pair of rotor peripheral surfaces 23 in the rotation direction R. The recessed peripheral surface 24 faces the rotor chamber peripheral surface 27 across a second radial clearance CL2 that is larger than the first radial clearance CL1. The recessed peripheral surface 24 captures foreign matter D within a rotor chamber 25 when the rotor 22 rotates. A width W2 of the rotor chamber peripheral surface 27 facing the recessed peripheral surface 24 in the rotation direction R is wider than the sum of a pair of predetermined widths W1 of the rotor chamber peripheral surface 27 facing the rotor peripheral surface 23.SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] For example, Patent Document 1 discloses an air pump as a roots pump. In the air pump, each of a pair of rotors is disposed in a columnar space as a rotor chamber. The inner peripheral surface of the columnar space forms an inner peripheral surface of a housing as a rotor chamber peripheral surface. Each rotor has a large arc surface on the outer peripheral surface of the tip portion. The large arc surface is formed with a curvature radius equivalent to that of the inner peripheral surface of the housing.

[0003] In such a roots pump, between the inner peripheral surface of the housing and the tip portion of the rotor, it is sealed by a predetermined radial clearance. The radial clearance is set to a value that suppresses leakage of fluid from the high-pressure side to the low-pressure side through the radial clearance.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Foreign objects may enter the rotor chamber of a roots pump. If a foreign object is larger than the radial clearance, the foreign object will be caught between the inner peripheral surface of the housing and the tip of the rotor. If the rotor rotates with a foreign object caught between the inner peripheral surface of the housing and the tip of the rotor, the tip of the rotor and the inner peripheral surface of the housing will be damaged by the foreign object. To suppress such damage, it is conceivable to make the radial clearance larger than the foreign object. However, if the radial clearance is made larger than the foreign object, the amount of fluid leakage from the high-pressure side to the low-pressure side through the radial clearance increases, resulting in a decrease in pump performance, which is not preferable.

Means for Solving the Problems

[0006] A roots pump for solving the above problems includes a housing, a rotor chamber defined in the housing and having a suction hole for sucking fluid and a discharge hole for discharging fluid, a pair of rotary shafts rotatably supported by the housing, and a pair of may-shaped rotors respectively attached to the pair of rotary shafts and rotated in the rotor chamber. The rotor chamber is composed of a pair of arc surfaces connecting the suction hole and the discharge hole in the radial direction of the rotor, and has a rotor chamber peripheral surface facing the tip of the rotor with a predetermined radial clearance. When the pair of rotors rotate, the fluid sucked from the suction hole is guided to the arc surface of the rotor chamber peripheral surface and discharged from the discharge hole. The tip of the rotor faces the rotor chamber peripheral surface with a first radial clearance, and has a pair of rotor peripheral surfaces each having a predetermined width in the rotation direction of the rotor, and a recessed peripheral surface recessed between the pair of rotor peripheral surfaces in the rotation direction and facing the rotor chamber peripheral surface with a second radial clearance larger than the first radial clearance, and capturing foreign objects in the rotor chamber when the rotor rotates. The gist is that the width of the rotor chamber peripheral surface facing the recessed peripheral surface in the rotation direction is wider than the sum of the pair of predetermined widths of the rotor chamber peripheral surface facing the rotor peripheral surface.

[0007] According to this, the second radial clearance is larger than the first radial clearance in both the rotational direction and the radial direction of the rotor. Therefore, when the rotor rotates, even if a foreign object enters between the leading rotor peripheral surface and the opposing rotor chamber peripheral surface, the foreign object can be released between the recessed peripheral surface and the rotor chamber peripheral surface by the rotation of the rotor. After that, even when the rotor rotates, since the foreign object is located between the recessed peripheral surface and the rotor chamber peripheral surface, the entry of the foreign object between the trailing rotor peripheral surface and the opposing rotor chamber peripheral surface is suppressed. That is, the foreign object is captured between the recessed peripheral surface and the opposing rotor chamber peripheral surface. And since the second radial clearance between this recessed peripheral surface and the rotor chamber peripheral surface is of a size capable of capturing the foreign object, it is possible to suppress the foreign object from remaining bitten between the tip of the rotor and the rotor chamber peripheral surface.

[0008] For capturing foreign objects, a recessed peripheral surface is provided at the tip of the rotor, but the radial clearance at the tip of the rotor is not only the second radial clearance formed by the recessed peripheral surface. That is, by providing a rotor peripheral surface at the tip of the rotor, a first radial clearance smaller than the second radial clearance is provided as the radial clearance at the tip of the rotor.

[0009] And due to the labyrinth effect caused by the size relationship between the first radial clearance and the second radial clearance, the sealing performance at the tip can be ensured. Therefore, even if a recessed peripheral surface is provided at the tip, the amount of fluid leakage from the high-pressure side to the low-pressure side through between the tip of the rotor and the rotor chamber peripheral surface can be suppressed. Thus, it is possible to suppress a decrease in pump performance while reducing damage caused by foreign objects being bitten in.

[0010] Regarding the roots pump, the rotor peripheral surface and the recessed peripheral surface are arc surfaces, and the arc radius of the arc surface in the recessed peripheral surface may be larger than the arc radius of the arc surface of the rotor peripheral surface and also larger than the arc radius of the arc surface in the rotor chamber peripheral surface.

[0011] According to this, a rotor capable of making the second radial clearance larger than the first radial clearance can be easily manufactured. Regarding the Roots pump, the recessed circumferential surface may be a flat surface recessed with respect to the rotor circumferential surface.

[0012] According to this, the recessed circumferential surface can be easily manufactured. Regarding the Roots pump, the recessed circumferential surface may be an arcuate surface that is recessed in an arc shape from the tip of the rotor toward the axis of the rotary shaft along a straight line connecting the tip of the rotor and the center point of the rotary shaft.

[0013] According to this, since the second radial clearance can be widened, it becomes easier to capture foreign matter. Regarding the Roots pump, the rotor may have a constricted portion provided between the pair of the tip portions and to which the rotary shaft is fixed, and the constricted portion may have a constricted circumferential surface having an arc surface with a smaller arc radius than the recessed circumferential surface.

[0014] According to this, a gap is defined between the recessed circumferential surface and the constricted circumferential surface of the constricted portion. And foreign matter that has entered between the rotors can be allowed to escape into the gap. Regarding the Roots pump, a groove recessed toward the rotary shaft more than the recessed circumferential surface may be provided at the tip portion of the rotor, and the groove may extend in the axial direction of the rotary shaft.

[0015] According to this, when foreign matter that has entered the second radial clearance enters the groove, it becomes easier to maintain the state of capturing the foreign matter.

Advantages of the Invention

[0016] According to the present invention, it is possible to suppress a decrease in pump performance while reducing damage caused by biting of foreign matter.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0018] [First Embodiment] Hereinafter, a first embodiment in which a roots pump is embodied will be described with reference to FIGS. 1 to 5. <Overall Roots Pump> The roots pump is mounted on a fuel cell vehicle as a hydrogen pump. The fuel cell vehicle is equipped with a fuel cell system that supplies oxygen and hydrogen for power generation. The roots pump supplies the hydrogen gas discharged from the fuel cell back to the fuel cell. Therefore, the roots pump inhales and discharges hydrogen gas as a fluid.

[0019] <Housing> As shown in FIG. 1, the roots pump 10 has a cylindrical housing 11. The housing 11 includes a motor housing 12, a gear housing 13, a rotor housing 14, and a cover member 15.

[0020] The motor housing 12 is connected to the gear housing 13. Also, the rotor housing 14 is connected to the gear housing 13. The cover member 15 is connected to the rotor housing 14.

[0021] The motor housing 12 has a plate-shaped bottom wall 12a and a peripheral wall 12b that extends cylindrically from the outer peripheral portion of the bottom wall 12a. The gear housing 13 has a plate-shaped bottom wall 13a and a peripheral wall 13b that extends cylindrically from the outer peripheral portion of the bottom wall 13a. The rotor housing 14 has a plate-shaped bottom wall 14a and a peripheral wall 14b that extends cylindrically from the outer peripheral portion of the bottom wall 14a.

[0022] The bottom wall 13a of the gear housing 13 and the peripheral wall 12b of the motor housing 12 are butted against each other. The bottom wall 14a of the rotor housing 14 and the peripheral wall 13b of the gear housing 13 are butted against each other. The cover member 15 is plate-shaped. The cover member 15 is butted against the peripheral wall 14b of the rotor housing 14.

[0023] A gear chamber 13c is defined in the housing 11. The gear chamber 13c is defined by the bottom wall 13a of the gear housing 13, the peripheral wall 13b of the gear housing 13, and the bottom wall 14a of the rotor housing 14.

[0024] <Rotor chamber> The Roots pump 10 has a rotor chamber 25 defined in the housing 11. The rotor chamber 25 is defined by the bottom wall 14a of the rotor housing 14, the peripheral wall 14b of the rotor housing 14, and the cover member 15.

[0025] The housing 11 has a pair of rotor chamber end faces 26 and a rotor chamber peripheral surface 27. One of the pair of rotor chamber end faces 26 is formed by the inner wall surface 14c of the bottom wall 14a of the rotor housing 14, and the other of the pair of rotor chamber end faces 26 is formed by the inner wall surface 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 surface 27 is formed by the inner peripheral surface 14d of the peripheral wall 14b. The rotor chamber peripheral surface 27 consists of a pair of arcuate surfaces 27a.

[0026] <Rotating shaft> The roots pump 10 has a rotating shaft 16, which includes a drive shaft 16a and a driven shaft 16b. The drive shaft 16a and the driven shaft 16b are arranged in parallel. The direction in which the axis L of the rotating shaft 16 extends is defined as the axial direction. The drive 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.

[0027] 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 drive shaft 16a is rotatably supported by the housing 11 via the first driving bearing 31a, the second driving bearing 31b, and the third driving bearing 31c.

[0028] 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 by the housing 11 via the first driven bearing 41a and the second driven bearing 41b. Therefore, the pair of rotating shafts 16 are rotatably supported by the housing 11.

[0029] The first seal member 32a is provided on the bottom wall 13a of the gear housing 13. The first seal member 32a seals the space between the drive shaft 16a and the bottom wall 13a of the gear housing 13. The second seal member 32b is provided on the bottom wall 14a of the rotor housing 14. The second seal member 32b seals the space between the drive shaft 16a and the bottom wall 14a. The third seal member 32c is provided on the bottom wall 14a of the rotor housing 14. The third seal member 32c seals the space between the driven shaft 16b and the bottom wall 14a.

[0030] <Electric motor> The roots pump 10 has an electric motor 50 that rotates a drive shaft 16a. The electric motor 50 is housed in a motor chamber 12c defined in the housing 11. The motor chamber 12c is defined by a bottom wall 12a of the motor housing 12, a peripheral wall 12b of the motor housing 12, and a bottom wall 13a of the gear housing 13. The electric motor 50 rotates the drive shaft 16a.

[0031] The roots pump 10 has a disk-shaped drive gear 18 fixed to the drive shaft 16a and a disk-shaped driven gear 19 fixed to the driven shaft 16b. The drive gear 18 and the driven gear 19 are housed in a gear chamber 13c. The driven gear 19 meshes with the drive gear 18 and rotates. The driven gear 19 rotates in a direction opposite to that of the drive shaft 16a by the drive gear 18 and the driven gear 19.

[0032] <Suction hole and discharge hole> The rotor chamber 25 is provided with a suction hole 45 for sucking hydrogen gas into the rotor chamber 25 and a discharge hole 46 for discharging the hydrogen gas in the rotor chamber 25. The suction hole 45 and the discharge hole 46 are formed in the peripheral wall 14b of the rotor housing 14. The suction hole 45 and the discharge hole 46 face each other with the rotor chamber 25 interposed therebetween. The suction hole 45 and the discharge hole 46 communicate the rotor chamber 25 with the outside. A pair of arc surfaces 27a of the rotor chamber peripheral surface 27 connect the suction hole 45 and the discharge hole 46.

[0033] <Drive rotor and driven rotor> As shown in FIGS. 1 and 2, the roots pump 10 has a drive rotor 20 as a pair of two-lobed comma-shaped rotors 22 and a driven rotor 21. In the roots pump 10, when the pair of rotors 22 rotate, the hydrogen gas sucked from the suction hole 45 is guided to the arc surface 27a of the rotor chamber 25. The hydrogen gas guided to the arc surface 27a is discharged from the discharge hole 46 to the outside of the roots pump 10. In the roots pump 10, the smaller the amount of fluid leakage from the high-pressure side to the low-pressure side through the radial clearance between the rotor 22 and the rotor chamber peripheral surface 27, the higher the pump performance.

[0034] The drive rotor 20 is a rotor rotated by the drive gear 18. The driven rotor 21 is a rotor rotated by the driven gear 19. The pair of rotors 22 are housed in the rotor chamber 25. The drive rotor 20 is attached to the drive shaft 16a. The driven rotor 21 is attached to 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 may-shaped rotors 22 that rotate in opposite directions to each other within the rotor chamber 25.

[0035] The pair of rotor chamber end faces 26 face each other across the pair of rotors 22 in the axial direction of the pair of rotating shafts 16. The rotor chamber peripheral surface 27 surrounds the radially outer peripheral regions of the pair of rotors 22. Note that 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.

[0036] Each of the pair of rotors 22 has a pair of tip portions 22a and a constricted portion 22b provided between the pair of tip portions 22a. Let the straight line connecting the pair of tip portions 22a of the rotor 22 and the axis L of the rotating shaft 16 be "T".

[0037] Each tip portion 22a has a pair of rotor peripheral surfaces 23, a recessed peripheral surface 24 located between the pair of rotor peripheral surfaces 23, and a curved surface 222 connected to each rotor peripheral surface 23. The rotor peripheral surface 23 and the recessed peripheral surface 24 are arc surfaces. The curved surface 222 is a surface based on an involute curve.

[0038] As shown in FIG. 3, each of the pair of rotor peripheral surfaces 23 faces the rotor chamber peripheral surface 27 with a first radial clearance CL1. Therefore, it can be said that the rotor chamber peripheral surface 27 faces the tip portion 22a of the rotor 22 with a predetermined first radial clearance CL1 in the radial direction of the rotor 22. Also, each of the pair of rotor peripheral surfaces 23 has a predetermined width in the rotation direction R of the rotor 22. Let the width facing each rotor peripheral surface 23 on the rotor chamber peripheral surface 27 be "W1". The arc surface of each rotor peripheral surface 23 is an arc surface with an arc radius r1 centered on the axis L.

[0039] Here, the arc surface 27a of the rotor chamber peripheral surface 27 is an arc surface with an arc radius r2 centered on the axis L. The arc radius r1 of the rotor peripheral surface 23 is slightly smaller than the arc radius r2 of the arc surface 27a. A first radial clearance CL1 as described above is formed between the rotor peripheral surface 23 and the arc surface 27a. The first radial clearance CL1 is set within a predetermined range so as to suppress leakage of hydrogen gas from the high-pressure side to the low-pressure side through the first radial clearance CL1.

[0040] The recessed peripheral surface 24 is recessed between a pair of rotor peripheral surfaces 23 in the rotational direction R. The width at which the rotor chamber peripheral surface 27 faces the recessed peripheral surface 24 in the rotational direction R is "W2". This width W2 is wider than the sum of a pair of widths W1 at which the rotor chamber peripheral surface 27 faces the rotor peripheral surface 23. For this reason, the following equation holds.

[0041] W2>W1+W1… Equation Therefore, the dimension of the recessed peripheral surface 24 in the rotational direction R is larger than the dimension of each rotor peripheral surface 23 in the rotational direction R.

[0042] The recessed peripheral surface 24 faces the rotor chamber peripheral surface 27 with a second radial clearance CL2 that is larger than the first radial clearance CL1. The recessed peripheral surface 24 is an arc surface with an arc radius r3 centered on the axis L. The arc radius r3 of the arc surface in the recessed peripheral surface 24 is larger than the arc radius r1 of the arc surface of the rotor peripheral surface 23 and larger than the arc radius r2 of the arc surface 27a in the rotor chamber peripheral surface 27. For this reason, the second radial clearance CL2 gradually increases in the rotational direction R as it goes from one rotor peripheral surface 23 to the other rotor peripheral surface 23. And, among the second radial clearances CL2, at the position that is in the middle of a pair of rotor peripheral surfaces 23 in the rotational direction R, the second radial clearance CL2 is the largest. The second radial clearance CL2 gradually decreases in the rotational direction R as it goes from the position that is in the middle of a pair of rotor peripheral surfaces 23 toward the other rotor peripheral surface 23.

[0043] As described above, the roots pump 10 supplies the hydrogen gas discharged from the fuel cell back to the fuel cell. For this reason, foreign matter D discharged from the fuel cell may enter the rotor chamber 25. Further, foreign matter D generated by contact or the like within the rotor chamber 25 may enter the rotor chamber 25. The first radial clearance CL1 is smaller than the maximum dimension of the foreign matter D.

[0044] The second radial clearance CL2 is larger than the maximum dimension of the foreign matter 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 five times larger than the maximum value of the first radial clearance CL1. The recessed circumferential surface 24 that defines such a second radial clearance CL2 captures foreign matter D in the rotor chamber 25 when the rotor 22 rotates.

[0045] As shown in FIG. 2, the constricted portion 22b is a portion where the rotating shaft 16 is fixed. The constricted portion 22b is provided between a pair of tip portions 22a and is constricted. The constricted portion 22b has a pair of constricted circumferential surfaces 221. The pair of constricted circumferential surfaces 221 sandwich the rotating shaft 16 in the radial direction of the rotating shaft 16.

[0046] As shown in FIG. 5, the constricted circumferential surface 221 is an arcuate surface with an arc radius r4. The arc radius r4 of the constricted circumferential surface 221 is smaller than the arc radius r3 of the recessed circumferential surface 24. For this reason, when the pair of rotor circumferential surfaces 23 and the recessed circumferential surface 24 face the constricted circumferential surface 221, a gap K is formed between the recessed circumferential surface 24 and the constricted circumferential surface 221.

[0047] The gap K gradually increases as it goes from one rotor circumferential surface 23 to the other rotor circumferential surface 23. And, among the gaps K, at the position that is in the middle of the pair of rotor circumferential surfaces 23 in the rotation direction R, the dimension of the gap K in the radial direction is the largest. The dimension of the gap K in the radial direction is larger than the maximum dimension of the foreign matter D. The gap K gradually decreases as it goes from the position that is in the middle of the pair of rotor circumferential surfaces 23 to the other rotor circumferential surface 23.

[0048] In the roots pump 10, the hydrogen gas sucked in from the suction hole 45 is confined by the tip 22a of the rotor 22. The confined hydrogen gas is pumped toward the discharge hole 46 while being confined. The confined hydrogen gas is discharged from the discharge hole 46. The region from when the hydrogen gas is confined through the suction hole 45 until it is discharged through the discharge hole 46 is defined as the "pumping region". In this pumping region, the hydrogen gas sucked in from the suction hole 45 is confined and pumped by the tip 22a of the rotor 22. The pumping region is the region from the confinement start position to the confinement end position of the rotor 22.

[0049] [Operation of the Embodiment] Next, the operation of this embodiment will be described. The drive shaft 16a rotates by the drive of the electric motor 50. Then, the driven shaft 16b rotates in the reverse direction with respect to the drive shaft 16a via the gear connection of the drive gear 18 and the driven gear 19. As a result, the pair of rotors 22 rotate in opposite directions to each other. The roots pump 10 sucks hydrogen gas into the rotor chamber 25 through the suction hole 45 and discharges the hydrogen gas from the rotor chamber 25 through the discharge hole 46 by the rotation of the pair of rotors 22.

[0050] The hydrogen gas sucked in from the suction hole 45 is confined and pumped by the tip 22a of the rotor 22. In the roots pump 10, when the rotor 22 is at the confinement end position, one tip 22a of the rotor 22 is closest to the discharge hole 46. At this time, internal compression of the hydrogen gas occurs in the space confined by the pair of rotors 22. The space confined by the pair of rotors 22 is sealed by the tips 22a of the respective rotors 22. The sealing by the tip 22a is performed by the rotor peripheral surface 23 and the recessed peripheral surface 24.

[0051] There is a first radial clearance CL1 between the rotor circumferential surface 23 and the rotor chamber circumferential surface 27. Also, there is a second radial clearance CL2, which is larger than the first radial clearance CL1, between the recessed circumferential surface 24 and the rotor chamber circumferential surface 27. Therefore, leakage of high-pressure hydrogen gas to the low-pressure side is suppressed by the labyrinth effect due to the first radial clearance CL1 and the second radial clearance CL2.

[0052] Fig. 4 shows a rotor 90 of a comparative example. The tip 91 of the rotor 90 has an arc circumferential surface 92. The arc circumferential surface 92 is an arc surface with the same arc radius r1 as the rotor circumferential surface 23 of the embodiment. Therefore, the arc circumferential surface 92 faces the rotor chamber circumferential surface 27 with the first radial clearance CL1. The tip 91 of the rotor 90 of the comparative example faces the rotor chamber circumferential surface 27 with the first radial clearance CL1 over the entire length of the arc circumferential surface 92 along the rotation direction R.

[0053] In a roots pump having the rotor 90 of the comparative example, since the first radial clearance CL1 is smaller than the maximum dimension of the foreign matter D, if the foreign matter D has entered the rotor chamber 25, the foreign matter D enters between the rotor circumferential surface 23 and the rotor chamber circumferential surface 27. Thereafter, while the rotor 90 is rotating in the rotation direction R, the foreign matter D continues to exist between the arc circumferential surface 92 and the rotor chamber circumferential surface 27. That is, the foreign matter D remains in a state of being caught between the arc circumferential surface 92 and the rotor chamber circumferential surface 27.

[0054] In contrast, in the present embodiment, the foreign matter D first enters between the rotor circumferential surface 23 on the leading side in the rotation direction R of the pair of rotor circumferential surfaces 23 and the rotor chamber circumferential surface 27. Thereafter, as the rotor 22 rotates in the rotation direction R, the foreign matter D moves toward the recessed circumferential surface 24 on the trailing side in the rotation direction R from the rotor circumferential surface 23.

[0055] Here, as described above, the relationship W2 > W1 + W1 holds. Also, the second radial clearance CL2 is larger than the first radial clearance CL1. Therefore, when the rotor 22 rotates, even if a foreign object D enters between the leading rotor peripheral surface 23 and the opposing rotor chamber peripheral surface 27, due to the rotation of the rotor 22, the foreign object D escapes between the recessed peripheral surface 24 and the rotor chamber peripheral surface 27.

[0056] And the second radial clearance CL2 is larger than the maximum dimension of the foreign object D. Therefore, although the foreign object D is located between the recessed peripheral surface 24 and the rotor chamber peripheral surface 27, it will not be caught between the recessed peripheral surface 24 and the rotor chamber peripheral surface 27.

[0057] After that, even when the rotor 22 rotates, since the foreign object D is located between the recessed peripheral surface 24 and the rotor chamber peripheral surface 27, it is suppressed that the foreign object D enters between the trailing rotor peripheral surface 23 and the opposing rotor chamber peripheral surface 27. That is, the foreign object D remains captured between the recessed peripheral surface 24 and the opposing rotor chamber peripheral surface 27.

[0058] The foreign object D is sent toward the discharge hole 46 as the rotor 22 rotates. Then, when the recessed peripheral surface 24 faces the discharge hole 46, the foreign object D is discharged from the discharge hole 46 to the outside of the rotor chamber 25.

[0059] As shown in FIG. 5, as the pair of rotors 22 rotate, there are times when the tip 22a and the constricted portion 22b face each other. At this time, a gap K is defined between the recessed peripheral surface 24 and the constricted peripheral surface 221. When a foreign object D enters between the pair of rotors 22, the foreign object D can be allowed to escape into the gap K.

[0060] [Effects of the First Embodiment] According to the above embodiment, the following effects can be obtained. (1-1) On the tip 22a of the rotor 22, a pair of rotor circumferential surfaces 23 and a recessed circumferential surface 24 are provided. And the second radial clearance CL2 is larger than the first radial clearance CL1 in both the radial direction and the rotational direction R. For this reason, when the rotor 22 rotates, even if a foreign object D enters between the leading rotor circumferential surface 23 and the opposing rotor chamber circumferential surface 27, due to the rotation of the rotor 22, the foreign object D can be captured between the recessed circumferential surface 24 and the rotor chamber circumferential surface 27. After that, even when the rotor 22 rotates, since the foreign object D is located between the recessed circumferential surface 24 and the rotor chamber circumferential surface 27, the entry of the foreign object D between the trailing rotor circumferential surface 23 and the opposing rotor chamber circumferential surface 27 is suppressed. For this reason, it is possible to suppress the foreign object D from remaining caught between the tip 22a of the rotor 22 and the rotor chamber circumferential surface 27. As a result, it is possible to suppress damage to the tip 22a and the rotor chamber circumferential surface 27 due to the biting-in of the foreign object D, and the generation of foreign objects.

[0061] For capturing the foreign object D, a recessed circumferential surface 24 is provided at the tip 22a of the rotor 22, and a rotor circumferential surface 23 is also provided at the tip 22a of the rotor 22. For this reason, at the tip 22a, a first radial clearance CL1 that is smaller than the second radial clearance CL2 formed by the recessed circumferential surface 24 is provided.

[0062] And due to the labyrinth effect caused by the size relationship between the first radial clearance CL1 and the second radial clearance CL2, the sealing performance at the tip 22a can be ensured. Therefore, even if the recessed circumferential surface 24 is provided at the tip 22a, the leakage amount of hydrogen gas from the high-pressure side to the low-pressure side through between the tip 22a and the rotor chamber circumferential surface 27 can be suppressed. Accordingly, it is possible to suppress a decrease in pump performance while reducing damage due to the biting-in of the foreign object D.

[0063] (1-2) The arc radius r3 of the arc surface on the recessed circumferential surface 24 is larger than the arc radius r1 of the arc surface of the rotor circumferential surface 23 and larger than the arc radius r2 of the arc surface 27a on the rotor chamber circumferential surface 27. Therefore, the rotor 22 with the second radial clearance CL2 larger than the first radial clearance CL1 can be easily manufactured.

[0064] (1-3) The arc radius r4 of the constricted circumferential surface 221 of the constricted portion 22b is smaller than the arc radius r3 of the arc surface of the recessed circumferential surface 24. Therefore, when the tip portion 22a and the constricted portion 22b face each other, a gap K can be defined between the recessed circumferential surface 24 and the constricted circumferential surface 221. And foreign matter D that has entered between the rotors 22 can be discharged into the gap K.

[0065] [Second Embodiment] Next, a second embodiment in which the roots pump 10 is embodied will be described with reference to FIG. 6. Since the second embodiment has a configuration in which the shape of the tip portion 22a of the rotor 22 in the first embodiment is changed, detailed description of the same parts will be omitted.

[0066] As shown in FIG. 6, at the tip portion 22a of the rotor 22, the recessed circumferential surface 24 is a flat surface that is recessed with respect to the rotor circumferential surface 23. The recessed circumferential surface 24 is a flat surface that linearly connects the pair of rotor circumferential surfaces 23. The first radial clearance CL1 is the same as that in the first embodiment, but the second radial clearance CL2 is larger than that in the first embodiment.

[0067] [Effects of the Second Embodiment] Therefore, according to the second embodiment, in addition to the effect of (1-1) described in the first embodiment, the following effects can be obtained.

[0068] (2-1) Since the recessed circumferential surface 24 is planar, the recessed circumferential surface 24 can be easily manufactured on the rotor 22. [Third Embodiment] Next, a third embodiment in which the roots pump 10 is embodied will be described with reference to FIG. 7. Since the third embodiment has a configuration in which the shape of the tip portion 22a of the rotor 22 in the first embodiment is changed, detailed description of similar parts will be omitted.

[0069] As shown in FIG. 7, the recessed circumferential surface 24 is an arcuate surface that is recessed in an arc shape as it extends from the tip portion 22a of the rotor 22 along the straight line T toward the axis L of the rotary shaft 16. The recessed circumferential surface 24 is a curved surface that connects the pair of rotor circumferential surfaces 23 in an arc shape. The first radial clearance CL1 is the same as that in the first embodiment, but the second radial clearance CL2 is larger than that in the first embodiment.

[0070] [Effects of the Third Embodiment] Therefore, according to the third embodiment, in addition to the effects of (1-1) described in the first embodiment, the following effects can be obtained.

[0071] (3-1) Since the recessed circumferential surface 24 is in the shape of an arcuate surface that is recessed toward the axis L, the second radial clearance CL2 can be widened. As a result, it becomes easier to capture the foreign matter D on the recessed circumferential surface 24. This embodiment can be implemented with the following modifications. This embodiment and the following modification examples can be implemented in combination with each other within a technically non - conflicting range.

[0072] ○ In each embodiment, as shown in FIG. 8, a groove 24a that is recessed toward the rotary shaft 16 more than the recessed circumferential surface 24 may be provided at the tip portion 22a of the rotor 22. In the rotor 22 of the first embodiment, it is preferable that a plurality of grooves 24a are recessed in the recessed circumferential surface 24. The grooves 24a extend over the entire axial length of the rotary shaft 16 on the recessed circumferential surface 24. The opening width of the groove 24a in the rotational direction R and the depth of the groove 24a in the radial direction are preferably sized to accommodate the entire foreign object D. However, even if the foreign object D that has entered the groove 24a protrudes from the recessed circumferential surface 24, if the foreign object D does not contact the rotor chamber circumferential surface 27 by utilizing the size of the second radial clearance CL2, the depth of the groove 24a may be changed as appropriate.

[0073] Grooves 24a may be formed in the recessed circumferential surface 24 of the second embodiment, or grooves 24a may be formed in the recessed circumferential surface 24 of the third embodiment. Grooves 24a may be formed in the rotor chamber circumferential surface 27.

[0074] ○ In the constricted portion 22b of the rotor 22, the arc radius r4 of the constricted circumferential surface 221 may be the same as or larger than the arc radius r3 of the recessed circumferential surface 24. ○ In a cross-sectional view perpendicular to the axial direction of the rotary shaft 16, the rotor 22 may be, for example, three-lobed or four-lobed.

[0075] ○ The Roots pump 10 may use, for example, an engine as a drive source. In this case, since the drive shaft 16a is connected to the engine, which is a drive source provided outside the gear chamber 13c, it penetrates the bottom wall 13a of the gear housing 13.

[0076] ○ The Roots pump 10 does not have to be a hydrogen pump for a fuel cell that supplies hydrogen gas to the fuel cell, and may be used for other applications. In short, the fluid inhaled into the rotor chamber 25 is not limited to hydrogen gas.

Explanation of Reference Numerals

[0077] CL1... the first radial clearance, CL2... the second radial clearance, R... the rotation direction, r1, r2, r3, r4... the arc radii, T... the straight line, W1, W2... the widths, 10... the roots pump, 11... the housing, 16... the rotating shaft, 22... the rotor, 22a... the tip portion, 22b... the constricted portion, 23... the rotor peripheral surface, 24... the recessed peripheral surface, 24a... the groove, 25... the rotor chamber, 27... the rotor chamber peripheral surface, 27a... the arc surface, 45... the suction hole, 46... the discharge hole, 221... the constricted peripheral surface.

Claims

1. A housing, a rotor chamber defined in the housing and having a suction hole for sucking a fluid and a discharge hole for discharging the fluid, a pair of rotating shafts rotatably supported by the housing, and a pair of may-shaped rotors respectively attached to the pair of rotating shafts and rotated in the rotor chamber. The rotor chamber consists of a pair of arc surfaces connecting the suction hole and the discharge hole in the radial direction of the rotor, and has a rotor chamber peripheral surface facing the tip of the rotor with a predetermined radial clearance, wherein when the pair of rotors rotate, the fluid sucked from the suction hole is guided to the arc surface of the rotor chamber peripheral surface and discharged from the discharge hole, and it is a roots pump, The tip of the rotor faces the rotor chamber peripheral surface with a first radial clearance, and has a pair of rotor peripheral surfaces each having a predetermined width in the rotation direction of the rotor, is recessed between the pair of rotor peripheral surfaces in the rotation direction, faces the rotor chamber peripheral surface with a second radial clearance larger than the first radial clearance, and has a recessed peripheral surface for capturing foreign matter in the rotor chamber when the rotor rotates, the width in which the rotor chamber peripheral surface faces the recessed peripheral surface in the rotation direction is wider than the sum of the pair of predetermined widths in which the rotor chamber peripheral surface faces the rotor peripheral surface, the rotor peripheral surface and the recessed peripheral surface are arc surfaces, and the arc radius of the arc surface in the recessed peripheral surface is larger than the arc radius of the arc surface of the rotor peripheral surface and larger than the arc radius of the arc surface of the rotor chamber peripheral surface. A roots pump characterized by this.

2. The rotor has a constricted portion provided between the pair of tip portions and constricted, to which the rotating shaft is fixed, The constricted portion has a constricted peripheral surface having an arc surface with an arc radius smaller than that of the recessed peripheral surface. The roots pump according to claim 1, characterized by this.

3. A groove recessed toward the rotating shaft from the recessed peripheral surface is provided at the tip of the rotor, and the groove extends in the axial direction of the rotating shaft. The roots pump according to claim 1 or claim 2, characterized by this.

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