Roots pump

Abstract

Roots pump (10) with: a rotary shaft (16) rotated by a drive source (22); a drive rotor (20) driven by the rotary shaft (16); a driven rotor (21) which is driven in cooperation with the drive rotor (20); a housing unit (11) comprising: a rotor housing (14) accommodating the drive rotor (20) and the driven rotor (21), the rotor housing (14) having an end wall (14a) through which the rotary shaft (16) extends, and a peripheral wall (14b) extending from an outer periphery of the end wall (14a); and a cover element (15) which closes an opening of the rotor housing (14); and a sealing element (50) arranged between the rotor housing (14) and the cover element (15), wherein the peripheral wall (14b) has a mating surface facing the cover element (15), the cover element (15) has a mating surface facing the peripheral wall (14b), at least one of the mating surfaces has an annular first groove (60), the first groove (60) has a side surface (61) on a radially inner side and a side surface (62) on a radially outer side, the side surfaces (61, 62) facing each other, the sealing element (50) is accommodated in the first groove (60), the rotor housing (14) has a bulging portion (47) which is a part of the peripheral wall (14b) which bulges radially inward at a position between the drive rotor (20) and the driven rotor (21), the bulging section (47) has the following: a mating surface facing the cover element (15); and a second groove (66) connected to the side surface (61) on the radially inner side of the first groove (60), the sealing element (50) comprises: a ring-like sealing body (51); first projections (52) projecting from the seal body (51) toward either the side surface (61) on the radially inner side or the side surface (62) on the radially outer side of the first groove (60), the first projections (52) being arranged at intervals in a circumferential direction of the seal body (51); and a second projection (55) which projects further radially inward from the sealing body (51) than the first projections (52), each first projection (52) has a distal end (52e) which is in contact with either the side surface (61) on the radially inner side or the side surface (62) on the radially outer side of the first groove (60), and the second projection (55) is arranged in the second groove (66) so as to determine a position of the sealing body (51) in the first groove (60).

Description

Background1. Field of InterestThe present invention relates to a Roots pump.2. Description of the Related Art.For example, Japanese Patent Application Laid-Open JP 2006-283664 A discloses a Roots pump including a rotary shaft rotated by a drive source, a drive rotor driven by the rotary shaft, and a driven rotor driven in association with the drive rotor. The Roots pump also includes a housing unit having a rotor housing and a cover member. The rotor housing includes an end wall through which the rotary shaft extends and a peripheral wall extending from the outer periphery of the end wall. The cover member closes an opening of the rotor housing. The rotor housing accommodates the drive rotor and the driven rotor. The peripheral wall and the cover member have mating surfaces that abut each other. At least one of the mating surfaces has a loop-shaped (loop-shaped) first groove. In the first groove, a sealing member is accommodated, which seals the inside of the housing unit from the outside of the housing unit.For example, when a vehicle equipped with the root pump is traveling in the vicinity of a coast, the housing unit may be exposed to salt water. In such a case, the sealing member prevents salt water from entering the housing unit through the clearance between the peripheral wall and the cover member. However, when the clearance between the radially outer side surface of the first groove and the sealing member is large, salt water is likely to accumulate in the clearance. As the salt concentration of the salt water accumulated in the clearance increases, the salt water may corrode the portions of the housing unit that are in contact with the salt water or those portions of the sealing member that are in contact with the salt water.A fuel cell vehicle has a fuel cell system that supplies oxygen and hydrogen to a fuel cell to generate power. For example, the Roots pump disclosed in the above-described laid-open specification is used as a pump that supplies hydrogen to the fuel cell. The Roots pump draws in hydrogen that has not reacted with the oxygen in the fuel cell. The hydrogen contains water generated during power generation in the fuel cell. The sealing member prevents leakage of the hydrogen containing the generated water to the outside of the housing unit from the inside of the housing unit through the clearance between the circumferential wall and the cover member. However, when the clearance between the radially inner side surface of the first groove and the sealing member is large, the hydrogen containing the generated water is likely to accumulate in the clearance. The generated water contained in the hydrogen accumulated in the space may corrode portions of the housing unit that are in contact with the generated water or portions of the sealing member that are in contact with the generated water.In some cases, the shape of the first groove is not an accurate circular loop but an elliptical loop or a rectangular loop, and the sealing member accommodated in the first groove is shaped to have a shape of an elliptical loop or a rectangular loop corresponding to the shape of the first groove. In this case, when the sealing member is accommodated such that its position in the circumferential direction is offset with respect to the first groove, clearances can be generated between the side surfaces of the first groove and the sealing member. The salt water or the generated water explained above may accumulate in such a space, which deteriorates the corrosion resistance of the housing unit or the sealing member. In addition, since there is a great demand for size reduction in Roots pumps, it is desirable to increase corrosion resistance without increasing size.DE 10 2019,100 404 A1 discloses a motor-driven Roots pump with a gear housing element which has bearing receiving recesses. The bearing receiving recesses have seal receiving recesses for annular sealing members, respectively, for sealing a transmission chamber and a motor chamber from each other.DE 20 511 36 A discloses a rotary piston compressor having a cylindrical conveying rotor and a cylindrical sealing rotor in a housing which rolls off on the conveying rotor, of which the conveying rotor is provided on its circumference with teeth which are spaced apart in the circumferential direction and which engage sealingly in recesses of the sealing rotor during the rotation of the rotors, and having a gas inlet opening which leads into the conveying space at the level of the intersecting edges of the conveying and sealing rotor bore of the housing, and a gas outlet opening which is formed in the housing part enclosing the sealing rotor on the side of the housing opposite the gas inlet opening in the vicinity of the intersecting edges.It is an object of the present invention to provide a Roots pump which can improve corrosion resistance without increasing the size.SummaryThis Summary sets forth a introduction to a selection of concepts in a simplified form that are described in more detail in the Detailed Description below. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be taken as an aid in determining the scope of the claimed subject matter.A Roots pump (Roots pump) according to an aspect of the present invention includes a rotating shaft rotated by a driving source, a driving rotor driven by the rotating shaft, a driven rotor driven in cooperation with the driving rotor, and a housing unit. The housing unit includes a rotor housing accommodating the driving rotor and the driven rotor, and a cover member closing an opening of the rotor housing. The rotor housing has an end wall through which the rotation shaft extends and a circumferential wall extending from an outer periphery of the end wall. The Roots pump also has a sealing member disposed between the rotor housing and the cover member. The peripheral wall includes a fitting surface (mating surface) facing the cover member, and the cover member has a fitting surface (mating surface) facing the peripheral wall. At least one of the mating surfaces has an annular first groove. The first groove has a side surface on a radially inner side and a side surface on a radially outer side, and the side surfaces face each other. The sealing member is accommodated in the first groove. The rotor housing has a bulging portion that is a part of the circumferential wall bulging radially inward at a position between the driving rotor and the driven rotor. The bulge portion has a fitting surface (mating surface) facing the cover member and a second groove connected to the side surface on the radially inner side of the first groove. The sealing member has an annular sealing body, first protrusions protruding from the sealing body to either the side surface on the radially inner side or the side surface on the radially outer side of the first groove, the first protrusions being arranged at intervals in a circumferential direction of the sealing body, and a second protrusion protruding from the sealing body further radially inward than the first protrusions. Each first protrusion has a distal end that is in contact with either the side surface on the radially inner side or the side surface on the radially outer side of the first groove. The second protrusion is disposed in the second groove to determine a position of the sealing body in the first groove.Further features and aspects will become apparent from the description, the drawings and the claims detailed below.Brief Description of the DrawingsFIG. 1 shows a cross-sectional view of a Roots pump according to an embodiment. FIG. 2 is a cross-sectional view taken along line 2- 2 of FIG. 1. FIG. 3 is a cross-sectional view taken along line 3- 3 of FIG. 1. FIG. 4 is a cross-sectional view taken along line 4- 4 of FIG. 3. FIG. 5 is a front view of a sealing member. FIG. 6 is a cross-sectional view taken along line 6- 6 of FIG. 5. FIG. 7 is a cross-sectional view taken along line 7- 7 of FIG. 5. FIG. 8 is a cross-sectional view taken along line 8- 8 of FIG. 5. FIG. 9 is an enlarged cross-sectional view of a part of the Roots pump FIG. 3 shows a positioning projection and a positioning groove. FIG. 10 is a cross-sectional view taken along line 10- 10 of FIG. 9. FIG. 11 is an enlarged cross-sectional view of a portion of the sealing member of FIG. 5. FIG. 12 is an enlarged front view of an open end of the rotor housing. FIG. 13 is a cross-sectional view taken along line 13--13 of FIG. 3. FIG. 14 is an enlarged cross-sectional view of a Roots pump according to another embodiment, showing a portion having a positioning protrusion.Throughout the drawings and the detailed description, like reference numerals refer to the same elements. The drawings need not be to scale, and the relative size, proportions, and mapping of elements in the drawings may be exaggerated for clarity, illustration, and simplicity.Detailed DescriptionThe present description is intended to provide a thorough understanding of the methods, apparatus, and / or systems that are described. Modifications and equivalents of the described methods, apparatus, and / or systems will be apparent to those skilled in the art. Sequences of operations are exemplary and may be changed according to what is apparent to a person skilled in the art, except for operations necessarily occurring in a particular order. Descriptions of functions and constructions known to those skilled in the art may be omitted.The embodiments may take various forms and are not limited to the examples described. However, the examples described are thorough and complete, and will convey the full scope of disclosure to those skilled in the art.A Roots pump 10 according to an embodiment will be described below with reference to FIGS. 1 to 10. The Roots pump 10 (a Roots pump) of the present embodiment is mounted on a fuel cell vehicle. The fuel cell vehicle has a fuel cell system that supplies oxygen and hydrogen to a fuel cell to generate power. The Roots pump 10 is used as a hydrogen pump for the fuel cell vehicle. More specifically, the Roots pump 10 circulates hydrogen (hydrogen off-gas) which is a fluid discharged from the fuel cell back to the fuel cell.As shown in FIG. 1, the Roots pump 10 has a housing unit 11 including a motor housing 12, a gear housing 13, a rotor housing 14, and a cover member 15. The motor housing 12 has a plate-shaped end wall 12 aand a peripheral wall 12 bextending from the outer periphery of the end wall 12 a. The gear case 13 has a plate-shaped end wall 13a and a peripheral wall 13b extending from the outer periphery of the end wall 13a. The peripheral walls 12b, 13b are tubular. The term "tubular" used in the present specification refers not only to a structure having a circular cross section, but may also refer to a structure having a non-circular cross section such as an elliptical cross section and a rectangular cross section.The gear housing 13 is coupled to an open end of the circumferential wall 12 bof the motor housing 12. An outer surface 13 cof the end wall 13 aof the gear housing 13 abuts an opening end surface 12 cof the circumferential wall 12 bof the motor housing 12. The end wall 13 aof the gear housing 13 closes the opening of the circumferential wall 12 bof the motor housing 12.The rotor housing 14 has a plate-shaped end wall 14a and a peripheral wall 14b extending from the outer periphery of the end wall 14a. The circumferential wall 14 bof the rotor housing 14 of the present invention is tubular, and more specifically, has an elliptical cross section. The rotor housing 14 is coupled to an open end of the circumferential wall 13 bof the gear housing 13. An outer surface 14 cof the end wall 14 aof the rotor housing 14 abuts an opening end surface 13 dof the circumferential wall 13 bof the gear housing 13. The end wall 14 aof the rotor housing 14 closes the opening of the circumferential wall 13 bof the gear housing 13.The cover member 15 is plate-shaped. The cover member 15 of the present embodiment is elliptic in plan view. The cover member 15 is coupled to an open end of the circumferential wall 14 bof the rotor housing 14. An end surface (end side) 15 aof the cover member 15 abuts an opening end surface 14 dof the circumferential wall 14 bof the rotor housing 14. The cover member 15 is coupled to the rotor housing 14 while the opening of the circumferential wall 14 bof the rotor housing 14 is closed.The Roots pump 10 has a drive shaft 16 and a driven shaft 17 rotatably supported by the housing unit 11 while being arranged in parallel with each other. A rotation axis r 1 of the drive shaft 16 and a rotation axis r 2 of the driven shaft 17 extend in the axial direction of the circumferential walls 12 b, 13 band 14 b. A disk-shaped (plate-shaped) drive gear 18 is fixed to the drive shaft 16. A disk-shaped (plate-shaped) driven gear 19 meshing with the drive gear 18 is fixed to the driven shaft 17. The drive shaft 16 is provided with a drive rotor 20. The driven shaft 17 is provided with a driven rotor 21 which is engaged with the drive rotor 20.The Roots pump 10 includes an electric motor 22 that rotates the drive shaft 16. The drive shaft 16 is thus a rotary shaft that is rotated by the electric motor 22, which is a drive source. The electric motor 22 is accommodated in a motor chamber 23 formed in the housing unit 11. The motor chamber 23 is defined by the end wall 12 aof the motor housing 12, the peripheral wall 12 bof the motor housing 12, and the end wall 13 aof the gear housing 13. The electric motor 22 includes a motor rotor 22 aand a stator 22 b. The motor rotor 22 ais fixed to the drive shaft 16 so as to rotate integrally with the drive shaft 16. The stator 22 bis fixed to the inner circumferential surface of the circumferential wall 12 bof the motor housing 12 and surrounds the motor rotor 22 a. The motor rotor 22 aand the stator 22 bare tubular and more specifically have circular cross sections. The stator 22 bincludes a coil (winding) 22 ccoiled around teeth (not shown). When power is supplied to the coil (winding) 22c, the electric motor 22 is operated (operated) so that the motor rotor 22a rotates integrally with the drive shaft 16.The housing unit 11 has a gear chamber (gear chamber) 24 accommodating the drive gear 18 and the driven gear 19. The gear chamber 24 is defined by the end wall 13 aof the gear case 13, the peripheral wall 13 bof the gear case 13, and the end wall 14 aof the rotor case 14. The drive gear 18 and the driven gear 19 are accommodated in the gear chamber 24 while being meshed with each other. Oil is sealed in the transmission chamber 24. The oil contributes to lubricating the drive gear 18 and the driven gear 19 and to preventing temperature rise. The drive gear 18 and the driven gear 19 rotate while being set in the oil so as to allow high-speed rotation without seizure or wear.The housing unit 11 has a rotor chamber 25 in which the driving rotor 20 and the driven rotor 21 are accommodated, which are engaged with each other. The rotor chamber 25 is defined by the end wall 14 aof the rotor housing 14, the peripheral wall 14 bof the rotor housing 14, and the cover member 15. The rotor housing 14 thus accommodates the driving rotor 20 and the driven rotor 21. The drive rotor 20 and the driven rotor 21 are accommodated in the rotor chamber 25 while being engaged with each other. In the present embodiment, the motor chamber 23, the gear chamber 24, and the rotor chamber 25 are arranged in this order in a direction along the rotation axis r 1 of the drive shaft 16.The end wall 13 aof the gear housing 13 separates the gear chamber 24 and the motor chamber 23 from each other in the direction along the rotation axis r 1 of the drive shaft 16. the end wall 14 aof the rotor housing 14 separates the gear chamber 24 and the rotor chamber 25 from each other in the direction along the rotation axis r 1 of the drive shaft 16. the cover member 15 separates the rotor chamber 25 from the outside in the direction along the rotation axis r 1 of the drive shaft 16.The drive shaft 16 extends through the end wall 13 aof the gear case 13 and the end wall 14 aof the rotor case 14. the driven shaft 17 extends through the end wall 14 aof the rotor case 14. an inner surface 13 eof the end wall 13 aof the gear case 13 forms a first wall surface of the gear chamber 25. the outer surface 14 cof the end wall 14 aof the rotor case 14 forms a second wall surface of the gear chamber 24 that faces the first wall surface. The first wall surface is closer to the motor chamber 23 than the second wall surface in a direction along the rotation axis r 1 of the drive shaft 16 or the rotation axis r 2 of the driven shaft 17.A first bearing accommodation recess 27 is formed in the inner surface 13 eof the end wall 13 aof the transmission case 13. The first bearing accommodation recess 27 is formed in a circular hole shape and accommodates a first bearing 26. The drive shaft 16 extends through the first bearing housing recess 27 and is rotatably supported by the first bearing 26. A first seal accommodation recess 29 is formed on a bottom surface 27 aof the first bearing accommodation recess 27. The first seal accommodation recess 29 is formed in a circular hole shape and accommodates a first sealing member 28. The drive shaft 16 extends through the first seal accommodation recess 29. the first sealing member 28 separates the transmission chamber 24 and the motor chamber 23 from each other. The first seal accommodation recess 29 is continuous with the first bearing accommodation recess 27. A ring-like first spacer 30 is disposed between the first bearing 26 and the bottom surface 27 aof the first bearing accommodation recess 27 in the direction along the rotation axis r 1 of the drive shaft 16.The term "ring-like" used in the present specification may refer to any structure that forms a loop that is a continuous shape without ends. Such "ring-like" shapes include, but are not limited to, a circular shape, an elliptical shape, and a polygonal shape with sharp or rounded corners.A second bearing accommodation recess 32 is formed on (in) the outer surface 14 cof the end wall 14 aof the rotor housing 14. The second bearing accommodation recess 32 is formed in a circular hole shape and accommodates a second bearing 31. The drive shaft 16 extends through the second bearing housing recess 32 and is rotatably supported by the second bearing 31. The drive shaft 16 thus extends through the end wall 14 aof the rotor housing 14, and a second seal accommodation recess 34 is formed in (at) a bottom surface 32 aof the second bearing accommodation recess 32. The second bearing accommodation recess 32 is formed in a circular hole shape and accommodates a ring-like second sealing member 33. The drive shaft 16 extends through the second seal accommodation recess 34. the second sealing member 33 separates the transmission chamber 24 and the rotor chamber 25 from each other. The second seal accommodation recess 34 is continuous with the second bearing accommodation recess 32. A ring-like second spacer 35 is disposed between the second bearing 31 and the bottom surface 32 aof the second bearing accommodation recess 32 in the direction along the rotation axis r 1 of the drive shaft 16.In addition, a third bearing accommodation recess 37 is formed on (in) the outer surface 14 cof the end wall 14 aof the rotor housing 14. The third bearing accommodation recess 37 is formed in a circular hole shape and accommodates a third bearing 36. The driven shaft 17 extends through the third bearing housing recess 37 and is rotatably supported by the third bearing 36. A third seal accommodation recess 39 is formed in (on) a bottom surface 37 aof the third bearing accommodation recess 37. The third seal accommodation recess 39 is formed in a circular hole shape and accommodates a ring-like third sealing member 38. The driven shaft 17 extends through the third seal accommodation recess 39. the third sealing member 38 separates the transmission chamber 24 and the rotor chamber 25 from each other. The third seal accommodation recess 39 is continuous with the third bearing accommodation recess 37. A ring-like third spacer 40 is disposed between the third bearing 36 and the bottom surface 37 aof the third bearing accommodation recess 37 in the direction along the rotation axis r 2 of the driven shaft 17.A fourth bearing accommodation recess 42 is formed on (in) the inner surface 13 eof the end wall 13 aof the transmission case 13. The fourth bearing accommodation recess 42 is formed in a circular hole shape and accommodates a fourth bearing 41. The driven shaft 17 has a first end disposed in the fourth bearing housing recess 42 and rotatably supported by the fourth bearing 41. The driven shaft 17 extends through the third bearing accommodation recess 37 and the third seal accommodation recess 39. the driven shaft 17 has a second end protruding into the rotor chamber 25. The driven rotor 21 is mounted on the second end of the driven shaft 17. The second end of the driven shaft 17 is a free end. The driven shaft 17 is thus supported in a cantilevered manner by the housing unit 11.A bearing portion 44 is formed on (in) an inner surface 12 eof the end wall 12 aof the motor housing 12. The bearing portion 44 accommodates a fifth bearing 43. The bearing portion 44 is tubular and has a circular cross section. The drive shaft 16 has a first end disposed in the bearing portion 44 and rotatably supported by the fifth bearing 43. The drive shaft 16 extends through the first seal accommodation recess 29, the first bearing accommodation recess 27, the transmission chamber 24, the second bearing accommodation recess 32, and the second seal accommodation recess 34. The drive rotor 20 is mounted to the second end of the drive shaft 16. The second end of the drive shaft 16 is a free end. The drive shaft 16 is thus supported in a cantilevered manner by the housing unit 11.As shown in FIGS. 2 and 3, the driving rotor and the driven rotor 21 are arranged so as to be adjacent to each other in the longitudinal direction of the circumferential wall 14 bof the motor housing 14 as viewed in the axial direction of the circumferential wall 14 b. The rotation axis r 1 of the drive shaft 16 and the rotation axis r 2 of the driven shaft 17 are on a straight line extending in the horizontal direction as viewed in the axial direction of the circumferential wall 14 bof the rotor housing 14.The driving rotor 20 and the driven rotor 21 are each formed such that the width at a central portion is smaller than the widths at the opposite end portions in a cross section perpendicular to the rotation axis r 1 of the drive shaft 16 and the rotation axis r 2 of the driven shaft 17. the driving rotor 20 has two vanes 20 aand two recesses 20 bbetween the two vanes 20 a. The driven rotor 21 has two vanes 21a and two recesses 21b between the two vanes 21a.The drive rotor 20 and the driven rotor 21 can rotate in the rotor chamber 25 while repeating an engagement between the vanes 20 aof the drive rotor 20 and the recesses 21 bof the driven rotor 21 and an engagement between the recesses 20 bof the drive rotor 20 and the vanes 21 aof the driven rotor 21. The drive rotor 20 rotates in a direction of an arrow R 1 in FIGS. 2 and 3, and the driven rotor 21 rotates in a direction of an arrow R 2 in FIGS. 2 and 3.The rotor housing 14 has a suction port 45 through which hydrogen is sucked into the rotor chamber 25 and a discharge port 46 through which hydrogen in the rotor chamber 25 is discharged. The suction port 45 and the discharge port 46 are formed in the circumferential wall 14 bof the rotor housing 14, and are disposed at positions opposing to each other across the rotor chamber 25 (they are opposed to each other). The suction port 45 and the discharge port 46 connect the rotor chamber 25 to the outside.A direction Z 1 along a straight line connecting the suction port 45 and the discharge port 46 is perpendicular to the rotation axis r 1 of the drive shaft 16 and the rotation axis r 2 of the driven shaft 17. the Roots pump 10 of the present embodiment is mounted on the fuel cell vehicle such that the suction port 45 is open vertically downward with respect to the outside of the Roots pump 10 and that the discharge port 46 is open vertically upward with respect to the outside of the Roots pump 10. Accordingly, the suction port 45 is disposed below the rotor chamber 25 in the vertical direction. The discharge port 46 is disposed above the rotor chamber 25 in the vertical direction. The direction Z 1 in FIGS. 2 and 3 coincides with the vertical direction, which is the direction of gravity.The inner circumferential surface of the circumferential wall 14 bof the rotor housing 14 includes a first guide surface 141 b, a second guide surface 142 b, and two connection surfaces 143 b. The first guide surface 141 bextends in a semi-circular manner about the rotation axis of the drive rotor 20 and guides the drive rotor 20. The rotational axis of the drive rotor 20 coincides with the rotational axis r 1 of the drive shaft 16. The second guide surface 142 bextends in a semi-circular manner around the rotation axis of the driven rotor 21 and guides the driven rotor 21, and the second guide surface 142 bextends along an imaginary circle C 2 along which an outermost portion 21 eof each blade 21 aof the driven rotor 21 moves as the driven rotor 21 rotates. The rotation axis of the driven rotor 21 coincides with the rotation axis r2 of the driven shaft 17. The two connecting surfaces 143 bconnect the first guide surface 141 band the second guide surface 142 bto each other, and are disposed at positions opposing each other across the rotor chamber 25.One of the two connecting surfaces 143 bincludes a first curved (arc-like) surface 47 aand a second curved (arc-like) surface 47 b. The first curved surface 47 ais continuous to the first guide surface 141 bto extend around the rotation axis of the drive rotor 20, and guides the drive rotor 20. The first curved surface 47 aand the first guide surface 141 bare arranged on a concentric circle. The second curved surface 47 bis continuous to the second guide surface 142 bto extend curvedly (arc-like) about the rotation axis of the driven rotor 21, and is connected to the first curved surface 47 a. The second curved surface 47 bguides the driven rotor 21, and the second curved surface 47 bextends along the imaginary circle C 2 along which the outermost portion 21 eof each blade 21 aof the driven rotor 21 moves. The second curved surface 47 band the second guide surface 142 bare arranged on a concentric circle. A part of the circumferential wall 14 bof the rotor housing 14 forms a bulge portion 47 including the first curved surface 47 aand the second curved surface 47 b. The rotor housing 14 thus has the bulging portion 47, which is a part of the circumferential wall 14 bthat bulges radially inward at a position between the drive rotor 20 and the driven rotor 21. The bulge portion 47 is defined by the first curved surface 47 aand the second curved surface 47 band bulges further radially inward than the remaining portions of the circumferential wall 14 b.The bulge portion 47 is disposed at an upper portion of the circumferential wall 14 bof the rotor housing 14 in the vertical direction. One of the two connecting surfaces 143 bopposing the bulge portion 47 via the rotor chamber 25 is a smooth surface 48 that does not bulge toward the bulge portion 47. In the present embodiment, the smooth surface 48 is a flat surface extending in the horizontal direction. The suction port 45 extends through the circumferential wall 14 bof the rotor housing 14 and is open in the smooth surface 48. The discharge port 46 extends through the bulge portion 47. the discharge port 46 is open in the connection surface 143 bto be located above the boundary between the first curved surface 47 aand the second curved surface 47 b.When the drive shaft 16 is rotated by the electric motor 22, the driven shaft 17 rotates in a direction opposite to the rotational direction of the drive shaft 16 by the action of the drive gear 18 and the driven gear 19 which mesh with each other. This causes the drive rotor 20 and the driven rotor 21 to rotate in opposite directions while being engaged with each other. By the rotations of the drive rotor 20 and the driven rotor 21, the Roots pump 10 draws hydrogen into the rotor chamber 25 through the suction port 45 and discharges hydrogen from the rotor chamber 25 through the discharge port 46. The drive rotor 20 is driven by the drive shaft 16, and the driven rotor 21 works in cooperation with the drive rotor 20.As shown in FIG. 1, a sealing member 50 is disposed between the opening end surface 12 cof the motor housing 12 and the outer surface 13 cof the end wall 13 aof the gear housing 13, and serves as a seal between the opening end surface 12 cand the outer surface 13 c. Another sealing member 50 is disposed between the opening end surface 13d of the gear case 13 and the outer surface 14c of the end wall 14a of the rotor case 14, and serves as a seal between the opening end surface 13d and the outer surface 14c. Further, another sealing member 50 is disposed between the opening end surface 14 dof the rotor housing 14 and the end surface (end side) 15 aof the cover member 15, and serves as a seal between the opening end surface 14 dand the end surface 15 a. The respective sealing members 50 separate the inside of the housing unit 11 from the outside. The sealing members 50 are elastic bodies. The sealing members 50 are made of rubber.In the following description, the structure of the sealing member 50 provided between the opening end surface 14 dof the rotor housing 14 and the end surface 15 aof the cover member 15 will be described. The remaining two sealing elements 50 have substantially the same structure. The detailed description of them is thus omitted.As shown in FIG. 4, the opening end surface 14 dof the rotor housing 14 has a seal accommodation groove 60 that is an annular first groove. The sealing member 50 is accommodated in the seal accommodation groove 60. The opening of the seal accommodation groove 60 is closed by the end surface 15 aof the cover member 15. The opening end surface 14 dof the rotor housing 14 is a first forming surface that forms a mating surface (mating surface, fitting surface) facing the cover member 15. The end surface 15 aof the cover member 15 is a second forming surface that forms a mating surface (mating surface, mating surface) facing the rotor housing 14. In the present embodiment, the seal accommodation groove 60 is formed in the first formation surface, and the opening of the seal accommodation groove 60 is closed by the second formation surface. The seal accommodation groove 60 is formed in either the mating surface of the circumferential wall 14 bof the rotor housing 14 or the mating surface of the cover member 15. That is, the seal accommodation groove 60 is formed in either the first formation surface of the rotor housing 14 or the second formation surface of the cover member 15. The bulge portion 47 includes a mating surface (mating surface, mating surface) that faces the cover member 15.The seal accommodation groove 60 has an inner side annular circumferential surface 61 disposed on the inner side of the housing unit 11 and an outer side annular circumferential surface 62 disposed on the outer side in the housing unit 11. The inner side circumferential surface 61 is a side surface on the radially inner side of the seal accommodation groove 60. the outer side circumferential surface 62 is a side surface on the radially outer side of the seal accommodation groove 60. the seal accommodation groove 60 also has a bottom surface 63 that connects the bottom side edge of the inner side circumferential surface 61 and the bottom side edge of the outer side circumferential surface 62. The seal accommodation groove 60 thus has the bottom surface 63 and two side surfaces connected to the bottom surface 63 which are the groove inner side circumferential surface 61 and the groove outer side circumferential surface 62.The inner side peripheral surface 61 is disposed on the side closer to the inner peripheral surface of the peripheral wall 14 bwith respect to the bottom surface 63. The outer side peripheral surface 62 is disposed on the side closer to the outer peripheral surface of the peripheral wall 14 bwith respect to the bottom surface 63. Therefore, one of the two side surfaces of the seal accommodation groove 60 is disposed on the side closer to the inner circumferential surface of the circumferential wall 14 bwith respect to the bottom surface 63, and the other side surface is disposed on the side closer to the outer circumferential surface of the circumferential wall 14 bwith respect to the bottom surface 63. The inner side circumferential surface 61 and the outer side circumferential surface 62 extend in parallel to the axial direction of the circumferential wall 14 b. The bottom surface 63 extends in a direction perpendicular to the axial direction of the peripheral wall 14 b. The bottom surface 63 extends parallel to the opening end surface 14 dof the rotor housing 14.The seal accommodation groove 60 has an annular inner side chamfered portion 64 formed between the opening side edge of the inner side circumferential surface 61 and the opening end surface 14 dof the rotor housing 14. The seal accommodation groove 60 also has an outer side annular chamfer portion 65 formed between the opening side edge of the outer side circumferential surface 62 and the opening end surface 14 dof the rotor housing 14. The inner side chamfer portion 64 and the outer side chamfer portion 65 are chamfered (chamfered) surfaces that extend in a straight manner and are inclined with respect to the opening end surface 14 dof the rotor housing 14. The inner side chamfer portion 64 and the outer side chamfer portion 65 of the seal accommodation groove 60 facilitate the installation of the seal member 50 to the seal accommodation groove 60.As shown in FIG. 3, the seal accommodation groove 60 formed in the open end surface 14 dof the rotor housing 14 has an elliptical ring shape extending along the circumferential wall 14 bof the rotor housing 14. The seal member 50 accommodated in the seal accommodation groove 60 is formed to have an elliptical ring-like shape according to the shape of the seal accommodation groove 60.As shown in FIG. 5, the sealing member (sealing member) 50 has an elliptical ring-like sealing body 51 and pressing protrusions 52. The pressing protrusions 52, which are first protrusions, are arranged at equal intervals (intervals) in the circumferential direction of the seal body 51. In the following description, the direction extending through the seal body 51 is referred to as an axial direction of the seal body 51. An arbitrary direction perpendicular to the axis of the seal body 51 and extending from the axis is referred to as a radial direction of the seal body 51.The pressing protrusions 52 are arranged at equal intervals in the circumferential direction of the seal body 51. The pressing protrusions 52 are thin and plate-like shaped and protrude from the inner circumferential surface 51 aof the seal body 51. The thickness direction of each pressing protrusion 52 coincides with the axial direction of the seal body 51. Each pressing protrusion 52 has parallel flat surfaces on opposite sides in the thickness direction. Each pressing protrusion 52 has a curved surface continuous to and bulging from the inner circumferential surface 51 aof the seal body 51.As shown in FIG. 6, the seal body 51 has an annular first contact portion 531 and an annular second contact portion 532. The first contact portion 531 and the second contact portion 532 are spaced apart from each other in the radial direction of the seal body 51 and extend over the entire circumference of the seal body 51.The first contact portion 531 is disposed on the radially inner side of the first groove 53 a. The second contact portion 532 is disposed on the radially outer side of the first groove 53 a. The first contact portion 531 is continuous to the inner circumferential surface 51 aof the seal body 51. The second contact portion 532 is continuous to an outer circumferential surface 51 bof the seal body 51. The first contact portion 531 and the second contact portion 532 are adjacent to each other in the radial direction of the seal body 51. The outer surface of the first contact portion 531 and the outer surface of the second contact portion 532 overlap each other as viewed in the radial direction of the seal body 51. in other words, the outer surface of the first contact portion 531 and the outer surface of the second contact portion 532 are disposed at the same position in the axial direction of the seal body 51. The outer surface of the first contact portion 531 and the outer surface of the second contact portion 532 are connected to each other by the inner surface of the first groove 53 a. The inner surface of the first groove 53 ais curved to be curved (arc-like).A width H 1 of the first contact portion 531 in the radial direction of the seal body 51 is uniform (equal width) in the circumferential direction of the seal body 51. A width H 2 of the second contact portion 532 in the radial direction of the seal body 51 is uniform (equal width) in the circumferential direction of the seal body 51. The width H 1 of the first contact portion 531 and the width H 2 of the second contact portion 532 are equal to each other.The seal body 51 has an annular third contact portion 541 and an annular fourth contact portion 542. The third contact portion 541 and the fourth contact portion 542 are spaced apart from each other in the radial direction of the seal body 51 and extend over the entire circumference of the seal body 51.The third contact portion 541 is disposed on the radially inner side of the second groove 54 a. The fourth contact portion 542 is disposed on the radially outer side of the second groove 54 a. The third contact portion 541 is continuous to the inner circumferential surface 51 aof the seal body 51. The fourth contact portion 542 is continuous to the outer circumferential surface 51 bof the seal body 51. The third contact portion 541 and the fourth contact portion 542 are adjacent to each other in the radial direction of the seal body 51. The outer surface of the third contact portion 541 and the outer surface of the fourth contact portion 542 overlap with each other as viewed in the radial direction of the seal body 51. in other words, the outer surface of the third contact portion 541 and the outer surface of the fourth contact portion 542 are disposed at the same position in the axial direction of the seal body 51. The outer surface of the third contact portion 541 and the outer surface of the fourth contact portion 542 are connected to each other by the inner surface of the second groove 54 a. The inner surface of the second groove 54 ais curved to be curved (arc-like).A width H 3 of the third contact portion 541 in the radial direction of the seal body 51 is uniform (equal width) in the circumferential direction of the seal body 51. A width H 4 of the fourth contact portion 542 in the radial direction of the seal body 51 is uniform (equal width) in the circumferential direction of the seal body 51. The width H 3 of the third contact portion 541 and the width H 4 of the fourth contact portion 542 are equal to each other. The width H 1 of the first contact portion 531, the width H 2 of the second contact portion 532, the width H 3 of the third contact portion 541, and the width H 4 of the fourth contact portion 542 are equal to each other.In FIG. 6, the distance L 1 is the distance between the inner circumferential surface 51 aand the outer circumferential surface 51 bof the seal body 51 in the radial direction of the seal body 51. a distance L 2 is the distance between the outer surface of the first contact portion 531 and the outer surface of the third contact portion 541 in the axial direction of the seal body 51. the distance L 2 is also the distance between the outer surface of the second contact portion 532 and the outer surface of the fourth contact portion 542 in the axial direction of the seal body 51. the distance L 1 is smaller than the distance L 2. A deepest portion 531 aof the first groove 53 aand a deepest portion 541 aof the second groove 54 aare disposed at overlapping positions as viewed in the axial direction of the seal body 51. In other words, the deepest portion 531 aof the first groove 53 aand the deepest portion 541 aof the second groove 54 aare disposed at the same position in the radial calculation of the seal body 51. Thus, a straight line S 1 connecting the deepest portion 531 aof the first groove 53 aand the deepest portion 541 aof the second groove 54 aextends in the axial direction of the seal body 51. a length L 3 of the straight line S 1 is uniform (equal) in the circumferential direction of the seal body 51. The depths of the first groove 53 aand the second groove 54 aare equal (uniform) in the circumferential direction of the seal body 51. The depth of the first groove 53a is equal to the depth of the second groove 54a.As shown in FIG. 7, each pressing protrusion 52 is disposed at the center of the inner circumferential surface 51 aof the seal body 51 with respect to the axial direction of the seal body 51 before the seal member 50 is accommodated in the seal accommodation groove 60. Before the seal member 50 is accommodated in the seal accommodation groove 60, a dimension (or thickness) L 4 of the pressing protrusion 52 in the axial direction of the seal body 51 is less than the length L 3 of the straight line S 1 connecting the deepest portion 531 aof the first groove 53 aand the deepest portion 541 aof the second groove 54 ato each other. A distance L 5 is the distance in the radial direction of the seal body 51 from the outer circumferential surface 51 bof the seal body 51 to a distal end 52 eof the pressing protrusion 52. Before the seal member 50 is accommodated in the seal accommodation groove 60, the distance L 5 is less than a distance L 6 that is the distance in the radial direction of the seal accommodation groove 60 between the inner side circumferential surface 61 and the outer side circumferential surface 62 (see FIG. 4 ). Further, a depth L 7 of the seal accommodation groove 60 (see FIG. 4 ) is larger than the length L 3 of the straight line S 1 connecting the deepest portion 531 aof the first groove 53 aand the deepest portion 541 aof the second groove 54 ato each other. Therefore, the depth L 7 of the seal accommodation groove 60 is larger than the dimension L 4 of the pressing protrusion 52 in the axial direction of the seal body 51.As shown in FIG. 4, the first contact portion 531 and the second contact portion 532 are in contact with the bottom surface 63 of the seal accommodation groove 60. The outer surface of the first contact portion 531 and the outer surface of the second contact portion 532 are thus pressed against the rotor housing 14. Over the entire circumference of its ring-like structure, the first groove 53 ais recessed with respect to the outer surface of the first contact portion 531 and the outer surface of the second contact portion 532. The first groove 53 ais not in contact with the rotor housing 14. The first contact portion 531 and the second contact portion 532 are in contact with the rotor housing 14 in a mating direction (mating direction, fitting direction) of the opening end surface 14 dof the rotor housing 14 and the end surface 15 aof the cover member 15 (indicated by an arrow X 1 in FIG. 4 ). The mating direction may be referred to as a facing direction.The third contact portion 541 and the fourth contact portion 542 are in contact with the end surface 15 aof the cover member 15. The outer surface of the third contact portion 541 and the outer surface of the fourth contact portion 542 are thus pressed against the cover member 15. Over the entire circumference of its ring-like structure, the second groove 54 ais recessed with respect to the outer surface of the third contact portion 541 and the outer surface of the fourth contact portion 542. The second groove 54 ais not in contact with the cover member 15. The third contact portion 541 and the fourth contact portion 542 are in contact with the cover member 15 in a mating direction of the opening end surface 14 dof the rotor housing 14 and the end surface 15 aof the cover member 15. The mating direction of the opening end surface 14 dof the rotor housing 14 and the end surface 15 aof the cover member 15 coincides with the axial direction of the circumferential wall 14 bof the rotor housing 14. The seal member 50 is accommodated in the seal accommodation groove 60 so as to be pressed against the rotor housing 14 and the cover member 15. The first groove 53 aand the second groove 54 aare recessed away from each other in the mating direction of the circumferential wall 14 bof the rotor housing 14 and the cover member 15.The pressing protrusions 52 protrude from the inner circumferential surface 51 aof the seal body 51 toward the inner side circumferential surface 61 of the seal accommodation groove 60. The distal ends 52 eof the pressing protrusions 52 contact and press the inner side peripheral surface 61. The seal body 51 receives, from the inner side circumferential surface 61, a reaction force to the pressing force acting on the inner side circumferential surface 61 through the pressing protrusions 52, so that the seal body 51 is in contact with and pressed against the outer side circumferential surface 62. Accordingly, the seal body 51 is pressed between the inner side circumferential surface 61 and the outer side circumferential surface 62 by the actions of the pressing protrusions 52. Therefore, the pressing protrusions 52 press the seal body 51 against the outer periphery of the seal accommodation groove 60.The outer surface of the first contact portion 531, the outer surface of the second contact portion 532, and the outer circumferential surface 51 bof the seal body 51 form a first seal portion (seal portion) 53 that is pressed against the rotor housing 14 and has a first seal length. On the other hand, the outer surface of the third contact portion 541 and the outer surface of the fourth contact portion 542 form a second seal portion (seal portion) 54 that is pressed against the cover member 15 and has a seal length different from the first seal length.The seal body 51 thus includes the first seal portion 53 pressed against the rotor housing 14 and the second seal portion 54 pressed against the cover member 15. The first sealing portion 53 includes the first contact portion 531 and the second contact portion 532. The second sealing portion 54 includes the third contact portion 541 and the fourth contact portion 542.As shown in FIGS. 8 and 9, the seal member 50 has a positioning protrusion 55, which is a second protrusion protruding from the inner circumferential surface 51 aof the seal body 51. The positioning protrusion 55 is in a thin plate shape. The thickness direction of the positioning protrusion 55 coincides with the axial direction of the seal body 51. The positioning protrusion 55 has parallel flat surfaces on the opposite sides in the thickness direction. The width direction of the positioning protrusion 55 coincides with the circumferential direction of the seal body 51. The positioning protrusion 55 has parallel flat surfaces on the opposite sides in the width direction, and the flat surfaces are continuous to the inner circumferential surface 51 aof the seal body 51. The positioning protrusion 55 has a protrusion distal end 55 athat has a curved surface protruding away from the inner circumferential surface 51 aof the seal body 51. The positioning protrusion 55 connects the surfaces on the opposite sides in the thickness direction of the positioning protrusion 55 to each other and connects the surfaces on the opposite sides in the width direction of the positioning protrusion 55. the positioning protrusion 55 has the protrusion distal end 55 eand a connection portion 55 athat connects the seal body 51 to the protrusion distal end 55 e.As shown in FIG. 8, the positioning protrusion 55 is disposed at the center of the inner circumferential surface 51 aof the seal body 51 with respect to the axial direction of the seal body 51. A dimension (or thickness) L 8 of the positioning protrusion 55 in the axial direction of the seal body 51 is equal to the dimension (or thickness) L 4 of the pressing protrusion 52 before the seal member 50 is accommodated in the seal accommodation groove 60. In addition, in the radial direction of the seal body 51, a distance L 9 from the outer circumferential surface 51 bof the seal body 51 to the protrusion distal end 55 eof the positioning protrusion 55 is larger than the distance L 5 from the outer circumferential surface 51 bof the seal body 51 to the distal end 52 eof the pressing protrusion 52 before the seal member 50 is accommodated in the seal accommodation groove 60. Accordingly, the positioning protrusion 55 protrudes further radially inward from the seal body 51 than the pressing protrusion 52.As shown in FIGS. 9 and 10, the seal accommodation groove 60 includes a positioning groove 66 in the inner side circumferential surface 61, and the positioning groove 66 is a second groove into which the positioning protrusion 55 is inserted. Thus, the positioning groove 66 is formed in the inner side circumferential surface 61 that is located on the inner side of the bottom surface 63 with respect to the radial direction of the circumferential wall 14 bof the rotor housing 14. The positioning groove 66 is formed in a portion of the inner side peripheral surface 61 corresponding to the removal bulging portion 47. Therefore, the positioning groove 66 is provided in the bulge portion 47 and is continuous to the inner side circumferential surface 61 of the seal accommodation groove 60. The opening of the positioning groove 66 is continuous to the opening end surface 14 dof the circumferential wall 14 bof the rotor housing 14. The opening of the positioning groove 66 is closed by the end surface 15 aof the cover member 15.The positioning groove 66 includes a positioning bottom surface 66 a, two positioning side surfaces 66 b, and a positioning connection surface 66 c. The positioning bottom surface 66 ais continuous to the bottom surface 63 of the seal accommodation groove 60, and is disposed on the same plane as the bottom surface 63. The positioning side surfaces 66 bare continuous to the inner side circumferential surface 61 of the seal accommodation groove 60, and are connected to the positioning bottom surface 66 a. The positioning side surfaces 66 bextend parallel to the axial direction of the circumferential wall 14 bof the rotor housing 14 and are continuous to the opening end surface 14 dof the circumferential wall 14 bof the rotor housing 14, respectively. The positioning joint surface 66 cis connected to the positioning bottom surface 66 aand the positioning side surfaces 66 b. The positioning joint surface 66 cis a curved surface recessed away from the seal accommodation groove 60. The positioning joint surface 66 cis continuous to the opening end surface 14 dof the circumferential wall 14 bof the rotor housing 14.A distance L 10 is the distance from the outer side circumferential surface 62 to a deepest portion 66 eof the positioning groove 66 in the radial direction of the circumferential wall 14 bof the rotor housing 14. the distance L 10 is larger than the distance L 9 from the outer circumferential surface 51 bof the seal body 51 to the distal protrusion end 55 eof the positioning protrusion 55. as shown in FIG. 9, a dimension (or a width) L 11 of the positioning protrusion 55 in the circumferential direction of the seal body 51 is smaller than a dimension (or a width) L 12 of the positioning groove 66. as shown in FIG. 10, a depth (L 13 of the positioning groove 66 is equal to the depth L 7 of the seal accommodation groove 60; therefore, the depth L 13 of the positioning groove 66 is larger than the dimension (or thickness) L 8 of the positioning protrusion 55 in the axial direction of the seal body 51.The positioning protrusion 55 is inserted into the positioning groove 66 without being pressed (pressed) against the positioning bottom surface 66 aor the positioning side surfaces 66 b. Thus, the positioning protrusion 55 is inserted into the positioning groove 66 without at least the portions except the protrusion distal end 55 eare pressed against the inner surface of the positioning groove 66. The positioning protrusion 55 is inserted into the positioning groove 66 so that the protrusion distal end 55 eis spaced apart from the positioning joint surface 66 c. Therefore, the distal protrusion end 55 eof the positioning protrusion 55 is spaced apart from the inner surface of the positioning groove 66. In this manner, the distal protrusion end 55 eof the positioning protrusion 55 is not in contact with the inner surface of the positioning groove 66, so that there is a clearance between the distal protrusion end 55 eof the positioning protrusion 55 and the inner surface of the positioning groove 66.FIG. 4 is a cross-sectional view of the seal member 50 taken along the axial direction of the seal body 51; in particular, FIG. 4 is a cross-sectional view showing the distal end 52 eof the pressing protrusion 52. The seal member 50 is configured to have, before being elastically deformed in the seal accommodation groove 60, over 100% of a fill factor (fill factor) with respect to the seal accommodation groove 60 in the cross section shown in FIG. 4.As shown in FIG. 11, the seal body 51 has through holes 56. The through holes 56 are arranged at intervals in the circumferential direction of the seal body 51. Each through hole 56 is disposed in a region between two of the pressing protrusions 52 that are adjacent to each other in the circumferential direction of the seal body 51. Each through hole 56 is disposed at a position equally spaced from two of the pressing protrusions 52 that are adjacent to each other in the circumferential direction of the seal body 51.As shown in FIG. 6, each through hole 56 connects the first groove 53 aand the second groove 54 ato each other. Thus, the seal body 51 has portions in which the first groove 53 aand the second groove 54 aare connected to each other through the through holes 56. The axial direction of each through hole 56 coincides with the axial direction of the seal body 51. Each through hole 56 thus extends straight in the axial direction of the seal body 51. The opening edge (open edge) of the first opening is connected to the outer surface of the first contact portion 531 and the outer surface of the second contact portion 532 by a part of the inner surface of the first groove 53 a. Each through hole 56 has a second opening that is open in the second groove 54 a. The opening edge of the second opening is connected to the outer surface of the third contact portion 541 and the outer surface of the fourth contact portion 542 by a part of the inner surface of the second groove 54 a.In FIG. 12, reference numerals "56e" denote lowermost portions 56e of one or more of the through holes 56 disposed at the lowermost positions in the vertical direction. Of the first contact portion 531 and the second contact portion 532, the first contact portion 531 is disposed on the radially inner side of the first groove 53 a. The lowermost portions 56 eof one or more of the through holes 56 disposed at the lowermost positions are disposed below a lowermost portion 53 aof the first contact portion 531 in the vertical direction. Of the third contact portion 541 and the fourth contact portion 542 that are adjacent to each other, the third contact portion 541 is disposed on the radially inner side of the second groove 54 a. The lowermost portions 56 eof one or more of the through holes 56 disposed at the lowermost positions are disposed below a lowermost portion 54 eof the third contact portion 541 in the vertical direction.The operation of the present embodiment will be described below.The seal member 50 is installed in the seal accommodation groove 60 by inserting the positioning protrusion 55 into the positioning groove 66 and then inserting the seal body 51 into the seal accommodation groove 60. The positioning protrusion 55 is disposed in the positioning groove 66 so as to determine the position of the seal body 51 in the seal accommodation groove 60. This limits displacement (displacement) in the circumferential direction of the seal member 50 with respect to the seal accommodation groove 60, so that a clearance is unlikely to be generated between the outer side circumferential surface 62 of the seal accommodation groove 60 and the seal member 50.The seal member 50 is elastically deformed when housed in the seal housing groove 60. The seal member 50 is configured to have, before being accommodated in the seal accommodation groove 60, a fill factor (fill factor) of over 100% with respect to the seal accommodation groove 60 in the cross section including the distal end 52 eof the pressing protrusion 52 along the axial direction of the seal body 51. Thus, when the cover member 15 is attached to the rotor housing 14, the seal member 50 is pressed (crushed) in the mating direction of the opening end surface 14 dof the rotor housing 14 and the end surface 15 aof the cover member 15 in a state in which the first contact portion 531 and the second contact portion 532 are in contact with the bottom surface 63 of the seal accommodation groove 60 and the third contact portion 541 and the fourth contact portion 542 are in contact with the end surface 15 aof the cover member 15. The seal member 50 is elastically deformed by being pushed in in the mating direction of the opening end surface 14 dof the rotor housing 14 and the end surface 15 aof the cover member 15. This causes the pressing protrusions 52 to come into contact with and press the inner side peripheral surface 61.When the pressing protrusions 52 press the inner side peripheral surface 61, the pressing protrusions 52 are pressed by receiving, from the inner side peripheral surface 61, a reaction force to the pressing force applied to the inner side peripheral surface 61 through the pressing protrusions 52. Accordingly, the seal body 51 receives an elastically deforming force (elastic deforming force) directed from the pressing protrusions 52 toward the opposite sides in the circumferential direction of the seal body 51. At this time, the first contact portion 531 and the second contact portion 532 are in contact with the bottom surface 63 of the seal accommodation groove 60, and the third contact portion 541 and the fourth contact portion 542 are in contact with the end surface 15 aof the cover member 15. This allows the seal body 51 to be elastically deformed toward the outer side circumferential surface 62. As a result, the seal body 51 is elastically deformed so as to cause the outer circumferential surface 51 bof the seal body 51 to come into contact with and press the outer side circumferential surface 62.For example, when the fuel cell vehicle travels in the vicinity of a coast (marine coast), the housing unit 11 may be exposed to salt water. In such a case, the seal member 50 prevents salt water from entering the inside of the housing unit 11 from the outside of the housing unit 11 through the clearance between the opening end surface 14 dof the rotor housing 14 and the end surface 15 aof the cover member 15.For example, the salt water flowing through the clearance between the opening end surface 14 dof the rotor housing 14 and the end surface 15 aof the cover member 15 may flow through the clearance between the outer circumferential surface 51 bof the seal body 51 and the outer side circumferential surface 62, and through the clearance between the second contact portion 532 and the bottom surface 63. In this case, since the salt water spreads in the first groove 53a disposed on the radially inner side of the second contact portion 532, the straightness (straightness) of the flow of the salt water will be lost. Accordingly, the salt water is unlikely to pass through the sealing member 50, and is unlikely to enter the housing unit 11.For example, the salt water flowing through the clearance between the opening end surface 14 dof the rotor housing 14 and the end surface 15 aof the cover member 15 may flow through the clearance between the fourth contact portion 542 and the end surface 15 aof the cover member 15. In this case, since the salt water spreads in the second groove 54a disposed on the radially inner side of the fourth contact portion 542, the straightness of the flow of the salt water will be lost. Accordingly, the salt water is unlikely to pass through the sealing member 50, and is unlikely to enter the housing unit 11.The seal body 51 receives, from the inner side circumferential surface 61, a reaction force to the pressing force acting on the inner side circumferential surface 61 through the pressing protrusions 52, so that the seal body 51 comes into contact with and presses the outer side circumferential surface 62. Thereby, the clearance between the outer side peripheral surface 62 and the seal member 50 is reduced (reduced). Thus, salt water is unlikely to be accumulated in the clearance between the outer side circumferential surface 62 of the seal accommodation groove 60 and the sealing member 50.As shown in FIG. 13, the first seal length of the first seal portion 53 is the length of a part (portion) of the path from the outside of the housing unit 11 to the inside of the housing unit 11 through the boundary between the rotor housing 14 and the first seal portion 53. The first seal length is the total of the outer surface of the first contact portion 531, the outer surface of the second contact portion 532, and the outer circumferential surface 51 bof the seal body 51. A second seal length of the second seal portion 54 is the length of a part (portion) of the path from the outside of the housing unit 11 to the inside of the housing unit 11 through the boundary between the cover member 15 and the first seal portion (seal portion) 53. The second seal length is the total of the outer surface of the third contact portion 541 and the outer surface of the fourth contact portion 542. Therefore, the progress of corrosion of the rotor housing 14, the cover member 15, and the seal member 50 varies between a case where corrosion is caused by salt water existing between the rotor housing 14 and the seal member 50 and a case where corrosion is caused by salt water existing between the cover member 15 and the seal member 50.For example, when the material and the surface roughness of the rotor housing 14 and the cover member 15 are similar, the progress of corrosion in a region between the cover member 15 having a shorter sealing length and the second sealing portion (sealing portion) 54 is more dominant (more protruding) than in a region between the rotor housing 14 and the first sealing portion 53. however, since a certain part of the salt water accumulated in the second groove 54 aflows to the first groove 53 athrough the through holes 56, it is possible to retard the progress of corrosion in the region between the cover member 15 and the second sealing portion 54.In addition, when the surface roughness of the rotor housing 14 is larger than the surface roughness of the cover member 15, leakage of salt water is less likely to occur in the region between the cover member 15 and the second sealing portion 54 than in the region between the rotor housing 14 and the first sealing portion 53. Accordingly, even when the first sealing length of the first sealing portion 53 is larger than the second sealing length of the second sealing portion 54, progress of corrosion in the region between the rotor housing 14 and the first sealing portion 53 may be more dominant than in the region between the cover member 15 and the second sealing portion 54. However, since a certain part of the salt water accumulated in the first groove 53 aflows to the second groove 54 athrough the through holes 56, it is possible to allow corrosion to occur, delaying the progress of corrosion in the region between the rotor housing 14 and the first seal portion 53.As described above, salt water can flow back and forth between the inside of the first groove 53 aand the inside of the second groove 54 athrough the through holes 56. Thus, despite the difference in seal length, the difference in progress of corrosion between the region between the rotor housing 14 and the seal member 50 and the region between the cover member 15 and the seal member 50 is likely to be reduced.The above-described embodiment has the following advantages. (1) Since the seal body 51 is pressed between the inner side peripheral surface 61 and the outer side peripheral surface 62 by the actions of the pressing protrusions 52, the clearance between the outer side peripheral surface 62 and the seal member 50 is reduced. Thus, salt water is unlikely to accumulate in the clearance between the outer side peripheral surface 62 and the sealing member 50. This improves the corrosion resistance of the housing unit 11 and the sealing member 50.The seal accommodation groove 60 may have a shape that is not a completely exact circular shape as in the present embodiment, but is, for example, an elliptical loop or a rectangular loop. In such cases, the seal member (seal member) 50 accommodated in the seal accommodation groove 60 is shaped to have a shape of an elliptical loop or a rectangular loop according to the shape of the seal accommodation groove 60. When the seal member 50 is accommodated such that its circumferential position is offset (displaced) with respect to the seal accommodation groove 60, clearances can be generated between the outer side circumferential surface 62 of the seal accommodation groove 60 and the seal member 50.In this regard, the root pump 10 of the present embodiment has the positioning groove 66 connected to the inner side circumferential surface 61 of the seal accommodation groove 60 in the bulge portion 47. the positioning protrusion 55 protruding from the seal body 51 is disposed in the positioning groove 66 to determine the position of the seal body 51 in the seal accommodation groove 60. This limits the displacement (displacement) in the circumferential direction of the seal member 50 with respect to the seal accommodation groove 60, so that a clearance is unlikely to be generated between the outer side circumferential surface 62 of the seal accommodation groove 60 and the seal member 50. As a result, salt water is unlikely to accumulate in the clearance between the outer side peripheral surface 62 and the sealing member 50. Thereby, the corrosion resistance of the housing unit 11 and the sealing member 50 is improved.The bulging portion 47 is a part of the peripheral wall 14 bof the rotor housing 14 that bulges inward at a position between the drive rotor 20 and the driven rotor 21. Thus, even when the rotor housing 14 has the bulge portion 47, the bulge portion 47 adversely affects neither the rotation of the drive rotor 20 and the driven rotor 21, nor increases the size of the Roots pump 10. Accordingly, corrosion resistance is improved without increasing the size of the Roots pump 10.(2) The distal protrusion end 55 eof the positioning protrusion 55 is not in contact with the inner surface of the positioning groove 66, so that there is a clearance between the distal protrusion end 55 eof the positioning protrusion 55 and the inner surface of the positioning groove 66. This structure allows a fluid to flow into the clearance between the protrusion distal end 55 eof the positioning protrusion 55 and the inner surface of the positioning groove 66. Accordingly, the seal body 51 is pressed between the inner side circumferential surface 61 and the outer side circumferential surface 62 of the seal accommodation groove 60 not only by the actions of the pressing protrusions 52 but also by the pressure of the fluid.More specifically, the discharge port 46 extends through the bulge portion 47 in the present embodiment. The area around the bulge portion 47 in the rotor chamber 25 is therefore exposed to the discharge pressure. The positioning groove 66 is formed in the inner side circumferential surface 61 that is disposed on the inner side of the bottom surface 63 with respect to the radial direction of the circumferential wall 14 bof the rotor housing 14. In addition, the positioning groove 66 is formed in a portion of the inner side peripheral surface 61 corresponding to the bulge portion 47. This structure causes hydrogen around the bulge portion 47 to flow into the clearance between the positioning protrusion 55 and the inner surface of the positioning groove 66 through the clearance between the opening end surface 14 dof the rotor housing 14 and the end surface 15 aof the cover member 15. Accordingly, the seal member 50 is pressed between the inner side circumferential surface 61 and the outer side circumferential surface 62 by the pressure of the hydrogen.This is likely to further reduce the clearance between the outer side peripheral surface 62 and the seal member 50. Therefore, salt water is more unlikely to accumulate in the clearance between the outer side peripheral surface 62 and the sealing member 50. As a result, the corrosion resistance of the housing unit 11 and the sealing member 50 is improved even more.(3) The bulging portion 47 is defined by the first bulging surface 47 aand the second bulging surface 47 band bulges more inward than the remaining portions of the circumferential wall 14 bof the rotor housing 14. This structure is advantageous because even if the rotor housing 14 has the recess portion 47, the bulge portion 47 does not adversely affect the rotation of the drive rotor 20 and the driven rotor 21, nor increases the size of the Roots pump 10.(4) Hydrogen sucked into the rotor chamber 25 through the suction port 45 may contain water, for example. In such a case, when the bulge portion 47 is disposed at a lower portion of the circumferential wall 14 bof the rotor housing 14 in the vertical direction, water present in the rotor chamber 25 is likely to flow to the suction port 45 extending through the bulge portion 47, and water is likely to accumulate in the rotor chamber 25. In this regard, the bulge portion 47 is disposed in the upper portion of the circumferential wall 14 bof the rotor housing 14 in the vertical direction in the present embodiment. Further, one of the two connecting surfaces 143 bopposing the bulge portion 47 via the rotor chamber 25 is a smooth surface 48 that does not bulge toward the bulge portion 47. Accordingly, even if water is present in the rotor chamber 25, water on the smooth surface 48 will easily drain out of the rotor chamber 25 through the suction port 45 due to its own weight. As a result, for example, ice formed when the water in the rotor chamber 25 is frozen is prevented from fixing the driving rotor and the driven rotor 21 to the inner circumferential surface of the circumferential wall 14 bof the rotor housing 14. That is, the driving rotor 20 and the driven rotor 21 are not prevented from being smoothly rotated by the ice.(5) The positioning protrusion 55 is inserted into the positioning groove 66 without pressing at least portions except the protrusion distal end 55 eon the inner surface of the positioning groove 66. When portions of the positioning protrusion 55 except at least the protrusion distal end 55 eare pressed against the inner surface of the positioning groove 66, the pressing operation of the pressing protrusions 52 becomes insufficient. The present embodiment avoids such a problem. Thus, even when the positioning protrusion 55 is inserted into the positioning groove 66, the seal body 51 is pressed between the inner side circumferential surface 61 and the outer side circumferential surface 62 in an advantageous and favorable manner by the actions of the pressing protrusions 52. Accordingly, a clearance is unlikely to be generated between the outer side circumferential surface 62 of the seal accommodation groove 60 and the seal member 50. Therefore, salt water is unlikely to accumulate in the clearance between the outer side circumferential surface 62 of the seal accommodation groove 60 and the seal member 50. Thereby, the corrosion resistance of the housing unit 11 and the sealing member 50 is improved.(6) The distal protrusion end 55 eof the positioning protrusion 55 is spaced apart from the inner surface of the positioning groove 66. Thus, when the seal member 50 is installed in the seal accommodation groove 60, the seal body 51 is not pressed between the inner side circumferential surface 61 and the outer side circumferential surface 62 by the actions of the positioning protrusions 55. This facilitates the installation of the seal member 50 into the seal accommodation groove 60.(7) The seal member 50 has portions in which the first groove 53 aand the second groove 54 aare connected to each other through the through holes 56. This allows salt water to flow back and forth between the inside of the first groove 53 aand the inside of the second groove 54 athrough the passage surface 56. This reduces a difference in progress of corrosion between the region between the rotor housing 14 and the seal member 50 and the region between the cover member 15 and the seal member 50.(8) In the seal body 51, each through hole 56 is disposed in a region between two of the pressing protrusions 52 that are adjacent to each other in the circumferential direction of the seal body 51. When each through hole 56 is disposed in a portion corresponding to the pressing protrusion 52 in the seal body 51, the through hole 56 is highly likely to disappear when the pressing protrusion 52 is pressed so that the seal body 51 is deformed. The present embodiment reduces the probability of occurrence of such a case.(9) The lowermost portions 56 eof one or more of the through holes 56 disposed at the lowermost positions in the vertical direction are disposed below the lowermost portion 53 eof the first contact portion 531 and the lowermost portion 54 eof the third contact portion 541 in the vertical direction. This structure allows salt water accumulated in the first groove 53 ato flow into the through holes 56 before reaching the first contact portion 531 disposed on the radially inner side of the first groove 53 a. Thus, salt water accumulated in the first groove 53 ais prevented from accumulating in the space between the first contact portion 531 and the rotor housing 14. In addition, for example, the salt water accumulated in the second groove 54 aflows into the through holes 56 before reaching the third contact portion 541 disposed on the radially inner side of the second groove 54 a. Thus, salt water accumulated in the second groove 54 ais prevented from accumulating in the space between the third contact portion 541 and the cover member 15. This is likely to suppress (restrain) corrosion in the region between the rotor housing 14 and the seal member 50 and in the region between the cover member 15 and the seal member 50. As a result, the corrosion resistance of the housing unit 11 and the sealing member 50 is improved.(10) The seal body 51 has the through holes 56 arranged at intervals (at intervals) in the circumferential direction of the seal body 51. This ensures rigidity of the seal body 51 and limits a decrease in the sealing performance of the seal member 50.(11) Each through hole 56 has a first opening that is open in the first groove 53 a. The opening edge of the first opening is connected to the outer surface of the first contact portion 531 and the outer surface of the second contact portion 532 by a part of the inner surface of the first groove 53 a. Each through hole 56 has a second opening that is open in the second groove 54 a.The opening side edge of the second opening is connected to the outer surface of the third contact portion 541 and the outer surface of the fourth contact portion 542 by a part of the inner surface of the second groove 54 a. This structure allows, for example, salt water accumulated in the first groove 53 ato be easily guided to the first opening of each through hole 56 through a part of the inner surface of the first groove 53 a. This structure also allows salt water collected in the second groove 54 a, for example, to be easily guided to the second opening of each through hole 56 through a part of the inner surface of the second groove 54 a. This allows the salt water to easily flow back and forth between the inside of the first groove 53 aand the inside of the second groove 54 athrough the through holes 56.(12) Salt water flowing through the clearance between the opening end surface 14 dof the rotor housing 14 and the end surface 15 aof the cover member 15 is distributed inside the first groove 53 aand the second groove 54 a. Accordingly, the straightness of the flow of the salt water is lost, so that the salt water is unlikely to pass through the seal member 50. Thereby, the sealing performance of the seal member 50 is improved.(13) The distance L 1 is the distance between the inner peripheral surface 51 aand the outer peripheral surface 51 bof the seal body 51 in the radial direction of the seal body 51. the distance L 2 is the distance between the outer surface of the first contact portion 531 and the outer surface of the third contact portion 541 in the axial direction of the seal body 51. the distance L 2 is also the distance between the outer surface of the second contact portion 532 and the outer surface of the fourth contact portion 542 in the axial direction of the seal body 51. the distance L 1 is smaller than the distance L 2. Even in this case, when the cover member 15 is attached to the rotor housing 14, the seal member 50 is prevented from being collapsed (collapsed) or twisted because the pressing protrusions 52 are in contact with the inner side circumferential surface 61.(14) The dimension L 4 of the pressing protrusion 52 in the axial direction of the seal body 51 is less than the length L 3 of the straight line S 1 connecting the deepest portion 531 aof the first groove 53 aand the deepest portion 541 aof the second groove 54 ato each other. The depth L 7 of the seal accommodation groove 60 is larger than the dimension L 4 of the pressing protrusion 52, thereby preventing the pressing protrusions 52 from coming into contact with the bottom surface 63 of the seal accommodation groove 60 and the end surface 15 aof the cover member 15. Thus, the seal body 51 receives, from the inner side circumferential surface 61, a reaction force to the pressing force applied to the inner side circumferential surface 61 by the pressing protrusions 52, so that the seal body 51 is elastically deformed to easily press the outer side circumferential surface 62. Thereby, a reduction in the clearance between the outer side circumferential surface 62 of the seal accommodation groove 60 and the seal member 50 is ensured.(15) Before the seal member 50 is accommodated in the seal accommodation groove 60, the distance L 5 in the radial direction of the seal body 51 between the outer circumferential surface 51 bof the seal body 51 and the distal end 52 eof each pressing protrusion 52 is less than the distance L 6 in the radial direction of the seal accommodation groove 60 between the inner side circumferential surface 61 and the outer side circumferential surface 62. This allows the seal member 50 to be easily accommodated in the seal accommodation groove 60, facilitating the installation of the seal member 50 in the seal accommodation groove 60.(16) The depth L 7 of the seal accommodation groove 60 is larger than the length L 3 of the straight line S 1 connecting the deepest portion 531 aof the first groove 53 aand the deepest portion 541 aof the second groove 54 ato each other. Thus, when the seal member 50 is elastically deformed by being deformed in the mating direction of the opening end surface 14 dof the rotor housing 14 and the end surface 15 aof the cover member 15, the first groove 53 aand the second groove 54 ado not disappear. In addition, when the seal body 51 is elastically deformed by receiving, from the inner side circumferential surface 61, a reaction force to the pressing force applied to the inner side circumferential surface 61 through the pressing protrusions 52, the first groove 53 aand the second groove 54 ado not disappear.(17) The pressing protrusions 52 are arranged at equal intervals (equal intervals) in the circumferential direction of the seal body 51. With this configuration, when the pressing protrusions 52 are pressed, the seal body 51 is likely to be elastically deformed toward the opposite sides in the circumferential direction of the seal body 51 from the pressing protrusions 52. This prevents the seal body 51 from being elastically deformed in a manner of pushing away the cover member 15. Accordingly, the sealing performance is maintained between the opening end surface 14 dof the rotor housing 14 and the end surface 15 aof the cover member 15.The above-described embodiment may be modified as follows. The above-described embodiment and the following modifications may be combined as long as the combined modifications remain technically consistent with each other.As shown in FIG. 14, at least the protrusion distal end 55 eof the positioning protrusion 55 may be in contact with the inner surface of the positioning groove 66. With this configuration, the seal body 51 is pressed between the inner side peripheral surface 61 and the outer side peripheral surface 62 by the operations of the positioning protrusion 55 in addition to the operations of the pressing protrusions 52. This allows the clearance between the outer side peripheral surface 62 and the sealing member 50 to be easily reduced (reduced). Therefore, salt water is more unlikely to accumulate in the clearance between the outer side peripheral surface 62 and the sealing member 50. Thereby, the corrosion resistance performance of the housing unit 11 and the sealing member 50 is more improved.In the embodiment, the seal accommodation groove 60 may have a true circular loop shape (accurate loop shape), and the seal member 50 accommodated in the seal accommodation groove 60 may have a true circular loop shape (accurate loop shape) corresponding to the shape of the seal accommodation groove 60. Also in this structure, the displacement (sliding) in the circumferential direction of the seal member 50 with respect to the seal accommodation groove 60 is restricted by inserting the positioning protrusion 55 into the positioning groove 66. This allows the sealing member 50 to be accommodated in the seal accommodation groove 60 such that the lowermost parts 56 eof one or more of the through holes 56 are arranged among the lowermost parts 53 bof the first contact portion 531 and the lowermost parts 54 eof the third contact portion 541 in the vertical direction.In the embodiment, the seal accommodation groove 60 may be formed in the end surface 15 aof the cover member 15, not in the opening end surface 14 dof the rotor housing 14, and the opening of the seal accommodation groove 60 may be closed by the opening end surface 14 dof the rotor housing 14.In the embodiment, a seal accommodation groove 60 may be formed in the end surface 15 aof the cover member 15 in addition to the opening end surface 14 dof the rotor housing 14, and the seal accommodation grooves 60 may be aligned with each other as viewed in the mating direction of the opening end surface 14 dof the rotor housing 14 and the end surface 15 aof the cover member 15. In other words, it is sufficient that the seal accommodation groove 60 is formed in either the first formation surface of the rotor housing 14 or the second formation surface of the cover member 15. When the peripheral wall 14 band the cover member 15 each have the seal accommodation groove 60, the third contact portion 541 and the fourth contact portion 542 contact the bottom surface 63 of the seal accommodation groove 60 formed in the end surface 15 aof the cover member 15. The pressing protrusions 52 press the inner side circumferential surface 61 of each seal accommodation groove 60 at the boundary between the circumferential wall 14 band the cover member 15. Thereby, the difference between the sealing length between the cover member 15 and the sealing member 50 and the sealing length between the rotor housing 14 and the sealing member 50 is reduced (decreased). As a result, the sealing performance of the sealing member 50 is improved.In the embodiment, the pressing protrusions 52 may protrude from the outer circumferential surface 51 bof the seal body 51. In addition, the seal member 50 may be accommodated in the seal accommodation groove 60 in a state where the pressing protrusions 52 are in contact with the outer side circumferential surface 62. In this case, the inner circumferential surface 51 aof the seal body 51 receives, from the outer side circumferential surface 62, a reaction force to the pressing force applied to the outer side circumferential surface 62 by the pressing protrusions 52, so that the inner circumferential surface 51 aof the seal body 51 is in contact with and presses against the inner side circumferential surface 61. For example, hydrogen sucked into the rotor chamber 25 contains water generated during power generation in the fuel cell. The seal member 50 limits the leakage of hydrogen containing the generated water to the outside of the housing unit 11 from the inside of the rotor chamber 25 through the clearance between the opening end surface 14 dof the rotor housing 14 and the end surface 15 aof the cover member 15. Thus, hydrogen containing generated water is unlikely to accumulate in the clearance between the seal accommodation groove outer side circumferential surface 62 and the seal member 50. Thereby, the corrosion resistance of the housing unit 11 and the sealing member 50 is improved.In the embodiment, the bulge portion 47 may be disposed at a lower (lower) portion of the circumferential wall 14 bof the rotor housing 14 in the vertical direction.In the exemplary embodiment, the two connecting surfaces 143 bmay each comprise a first curved (arc-like) surface 47 aand a second curved (arc-like) surface 47 b. That is, it is sufficient that at least one of the two connection surfaces 143 bincludes a first curved surface 47 aand a second curved surface 47 b. In this case, the peripheral wall 14 bof the rotor housing 14 has a bulge portion 47 at each of the two positions opposing each other across the rotor chamber 25.In the embodiment, the discharge port 46 may extend through the circumferential wall 14 bof the rotor housing 14 and be open at the smooth surface 48, and the suction port 45 may extend through the bulge portion 47. That is, the suction port 45 may be disposed above the rotor chamber 25 in the vertical direction, and the discharge port 46 may be disposed below the rotor chamber 25 in the vertical direction.In the embodiment, the smooth surface 48 may be a curved surface that does not bulge toward the bulge portion 47. That is, it is sufficient that the connection surfaces 143 bopposing the bulge portion 47 via the rotor chamber 25 is the smooth surface 48 that does not bulge toward the bulge portion 47.In the embodiment, the positioning protrusion 55 may be disposed in the positioning groove 66 in a state where at least portions except the protrusion distal end 55 eare pressed (pressed) against the positioning groove 66.In the embodiment, the lowermost parts (lowermost portions) 56 eof one or more of the through holes 56 disposed at the lowermost positions in the vertical direction may be disposed in the same plane in the horizontal direction as the lowermost portion 53 eof the first contact portion 531 and the lowermost portion 54 eof the third contact portion 541.In the embodiment, the lowermost parts (lowermost portions) 56 eof one or more of the through holes 56 disposed at the lowermost positions in the vertical direction may be disposed above (above) the lowermost portion 53 eof the first contact portion 531 and the lowermost portion 54 eof the third contact portion 541 in the vertical direction.In the embodiment, each through hole 56 may be disposed at a position closer to one of the two pressing protrusions 52 that are adjacent to each other in the circumferential direction of the seal body 51. That is, each through hole 56 may be disposed at a position that is at different distances from two of the pressing protrusions 52 that are adjacent to each other in the circumferential direction of the seal body 51.In the embodiment, each through hole 56 may be disposed at a position in the seal body 51 corresponding to one of the pressing protrusions 52 in the circumferential direction of the seal body 51.In the embodiment, the number of the through holes 56 is not specifically limited, but may be changed.In the embodiment, the through holes 56 may be replaced with a ring-like hole extending over the entire circumference of the seal body 51.In the embodiment, the shape of the through hole 56 is not limited to a circular shape, but may be, for example, a rectangular shape. That is, the shape of the through hole 56 is not specifically limited as long as the through hole 56 connects the first groove 53 aand the second groove 54 ato each other.In the embodiment, the seal body 51 does not necessarily have the through holes 56.In the embodiment, the sealing member 50 does not necessarily have to have the first groove 53 a. In this case, the seal member 50 has a groove-free end surface at the first end in the axial direction of the seal body 51, and the entire groove-free end surface can be in contact with the rotor housing 14 in the mating direction of the opening end surface 14 dof the rotor housing 14 and the end surface 15 aof the cover member 15. This ensures a long seal length between the rotor housing 14 and the seal member 50.In the exemplary embodiment, the sealing element 50 does not necessarily have to have the second groove 54 a. In this case, the seal member 50 has a groove-free end surface at the second end in the axial direction of the seal body 51, and the entire groove-free end surface may be in contact with the cover member 15 in the mating direction of the opening end surface 14 dof the rotor housing 14 and the end surface 15 aof the cover member 15. This ensures a long seal length between the cover member 15 and the seal member 50.In the embodiment, the sealing member 50 may include two or more first grooves 53 aformed in the sealing body 51.In the exemplary embodiment, the sealing element 50 can have two or more second grooves 54 aformed in the sealing body 51.In the exemplary embodiment, the sum of the width H 3 of the third contact portion 541 and the width H 4 of the fourth contact portion 542 may be greater than the sum of the width H 1 of the first contact portion 531 and the width H 2 of the second contact portion 532.In the embodiment, the distance L 1 in the radial direction of the seal body 51 between the inner circumferential surface 51 aand the outer circumferential surface 51 bof the seal body 51 may be larger than the distance L 2 in the axial direction of the seal body 51 between the outer surface of the first contact portion 531 and the outer surface of the third contact portion 541, and may be larger than the distance L 2 in the axial direction of the seal body 51 between the outer surface of the second contact portion 532 and the outer surface of the fourth contact portion 542.In the embodiment, the dimension L 4 of the pressing protrusion 52 in the axial direction of the seal body 51 may be equal to the length L 3 of the straight line S 1 connecting the deepest portion 531 aof the first groove 53 aand the deepest portion 541 aof the second groove 54 ato each other.In the embodiment, the dimension L 4 of the pressing protrusion 52 in the axial direction of the seal body 51 may be larger than the length L 3 of the straight line S 1 connecting the deepest portion 531 aof the first groove 35 aand the deepest portion 541 aof the second groove 54 aas long as the dimension L 4 is smaller than the distance L 2 in the axial direction of the seal body 51 between the outer surfaces of the first and second contact portions 531, 532 and the outer surfaces of the third and fourth contact portions 541, 542.In the embodiment, the number of the pressing protrusions 52 may be changed to any number larger than one.In the embodiment, the inner side circumferential surface 61 and the outer side circumferential surface 62 do not necessarily have to extend parallel to the axial direction of the circumferential wall 14 bof the rotor housing 14, but may extend obliquely relative to the axial direction of the circumferential wall 14 bof the rotor housing 14, and may not be parallel to each other.In the embodiment, the material of the sealing member 50 is not limited to rubber as long as it is an elastic material.In the embodiment, the driving rotor 20 and the driven rotor 21 may have a three-blade shape or a four-blade shape in a cross section perpendicular to the rotation axis r 1 of the driving shaft 16 or the rotation axis r 2 of the driven shaft 17.In the embodiment, the driving rotor 20 and the driven rotor 21 may have helical (spiral) shapes.In the embodiment, the Roots pump 10 may be driven by, for example, an internal combustion engine functioning as a drive source.In the embodiment, the Roots pump 10 need not necessarily be applied as a hydrogen pump for a fuel cell vehicle that supplies hydrogen to a fuel cell, but may be applied for other purposes.Various changes in form and details may be made in the examples discussed above without departing from the scope of the claims and their equivalents. The distances are for the purpose of description only and are not for the purpose of limitation. The description of features in each example is to be considered applicable to similar features or aspects in other examples. Suitable results may be achieved when sequences are performed in a different order and / or when components of a described system, architecture, device, or circuit are combined differently and / or replaced or supplemented by other components or their equivalents. The scope of the present invention is defined not by the detailed description, but by the claims and their equivalents. All variations within the scope of the claims and their equivalents are included in the disclosure.The housing of a Roots pump includes a rotor housing having a circumferential wall and a cover member closing an opening of the rotor housing. At least one of a mating surface of the peripheral wall or a mating surface of the cover member has an annular first groove accommodating a seal member. The rotor housing has a bulge portion having a second groove. The sealing member has first protrusions protruding from a ring-like sealing body and a second protrusion protruding radially inward from the sealing body further than the first protrusions. Each first protrusion has a distal end that is in contact with a side surface on a radially inner side or on a radially outer side of the first groove. The second protrusion is disposed in the second groove to determine the position of the seal body in the first groove.

Claims

A Roots pump (10) comprising: a rotary shaft (16) rotated by a drive source (22); a drive rotor (20) driven by the rotary shaft (16); a driven rotor (21) driven in cooperation with the drive rotor (20); a housing unit (11) comprising: a rotor housing (14) accommodating the drive rotor (20) and the driven rotor (21), the rotor housing (14) having an end wall (14a) through which the rotary shaft (16) extends and a peripheral wall (14b) extending from an outer periphery of the end wall (14a); and a cover member (15) closing an opening of the rotor housing (14); and a sealing member (50) disposed between the rotor housing (14) and the cover member (15), wherein the peripheral wall (14b) has a mating surface facing the cover member (15), the cover member (15) has a mating surface facing the peripheral wall (14b), at least one of the mating surfaces has an annular first groove (60), the first groove (60) has a side surface (61) on a radially inner side and a side surface (62) on a radially outer side, the side surfaces (61, 62) facing each other, the sealing member (50) is accommodated in the first groove (60), the rotor housing (14) has a bulge portion (47) which is a part of the peripheral wall (14b) bulging radially inward at a position between the drive rotor (20) and the driven rotor (21), the bulge portion (47) has a mating surface, facing the cover member (15); and a second groove (66) connected to the side surface (61) on the radially inner side of the first groove (60), the sealing member (50) comprising: an annular sealing body (51); first protrusions (52) protruding from the sealing body (51) toward either the side surface (61) on the radially inner side or the side surface (62) on the radially outer side of the first groove (60), the first protrusions (52) being arranged at intervals in a circumferential direction of the sealing body (51); and a second protrusion (55) protruding radially inward from the seal body (51) more than the first protrusions (52), each first protrusion (52) having a distal end (52e) in contact with one of the side surface (61) on the radially inner side and the side surface (62) on the radially outer side of the first groove (60), and the second protrusion (55) being disposed in the second groove (66) so as to determine a position of the seal body (51) in the first groove (60).The Roots pump (10) according to claim 1, wherein the second protrusion (55) includes: a protrusion distal end (55e); and a connection portion (55a) connecting at least the protrusion distal end (55e) to the seal body (51), and at least the protrusion distal end (55e) is in contact with an inner surface of the second groove (66).The Roots pump (10) according to claim 1, wherein the second protrusion (55) includes: a protrusion distal end (55e); and a connecting portion (55a) connecting the protrusion distal end (55e) to the seal body (51), and the protrusion distal end (55e) is separated from an inner surface of the second groove (66) so as to create a clearance between the protrusion distal end (55e) and the inner surface of the second groove (66).The Roots pump (10) according to any one of claims 1 to 3, wherein an inner circumferential surface of the circumferential wall (14b) includes: a first guide surface (141b) extending semi-circularly around a rotation axis of the driving rotor (20); a second guide surface (142b) extending semi-circularly around a rotation axis of the driven rotor (21); a first curved surface (47a) continuous from the first guide surface (141b) so as to extend arc-like around the rotation axis of the driving rotor (20); and a second curved surface (47b) continuous to the second guide surface (142b) so as to extend in an arc shape about the rotation axis of the driven rotor (21), the second curved surface (47b) being connected to the first curved surface (47a), and the bulging portion (47) being defined by the first curved surface (47a) and the second curved surface (47b) and bulging further radially inward than remaining portions of the peripheral wall (14b).The Roots pump (10) according to any one of claims 1 to 4, wherein the rotor housing (14) has a discharge port (46) connecting a rotor chamber (25) in the rotor housing (14) to an outside of the housing unit (11), and the discharge port (46) extends through the bulge portion (47).The root pump (10) according to claim 5, wherein the bulge portion (47) is disposed in an upper portion of the peripheral wall (14b) in a vertical direction.The Roots pump (10) according to any one of claims 1 to 6, wherein the seal body (51) includes: an annular first contact portion (531) and an annular second contact portion (532) that are in contact with the circumferential wall (14b); and an annular third contact portion (541) and an annular fourth contact portion (542) that are in contact with the cover member (15), the first contact portion (531) and the second contact portion (532) are spaced apart from each other in a radial direction of the seal body (51), and the third contact portion (541) and the fourth contact portion (542) are spaced apart from each other in the radial direction of the seal body (51).The Roots pump (10) according to claim 7, wherein the seal body (51) comprises: an annular first groove (53a) formed between the first contact portion (531) and the second contact portion (532); and an annular second groove (54a) formed between the third contact portion (541) and the fourth contact portion (542).The Roots pump (10) according to claim 8, wherein the seal body (51) has through holes (56) connecting the first groove (53a) and the second groove (54a) to each other, and the through holes (56) are arranged at intervals in the circumferential direction of the seal body (51).The Roots pump (10) according to claim 9, wherein each of the through holes (56) is disposed in a region between two of the first protrusions (52) that are adjacent to each other in the circumferential direction of the seal body (51).

Images