Vacuum pump

Abstract

 Passage structure for a vacuum pump has a flange, a muffler, a valve hole forming body, a guide pipe and an exhaust pipe. The flange is coupled to the muffler. The muffler is detachably fitted into the valve hole forming body. The valve hole forming body is detachably fitted into the guide pipe. The exhaust pipe is coupled to the guide pipe via the valve hole forming body. Each flange of the muffler, the valve hole forming body and the guide pipe is screw-on all together. A backflow preventing means is constituted of the guide pipe, the valve hole forming body, a valve body and a return spring. The guide pipe accommodates the valve body and the return spring therein. The valve body opens and closes a valve hole formed at the valve hole forming body. A separation preventing means is engaged with an inner circumferential surface of the guide pipe.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates to passage structure for a vacuum pump that drives a gas transferring assembly based on rotation of a rotary shaft, generates vacuum action by transferring gas due to motion of the gas transferring assembly, and a backflow preventing means is interposed in a gas passage.

[0002] Japanese Unexamined Patent Publication No. 2-157490 and No. 8-14172 disclose a roots pump, a kind of vacuum pump, having a pair of coadjacent rotors. The rotors are engaged with each other and relatively rotate. Rotation motion of a pair of the rotors rotating in mesh with each other transfers gas as compresses the gas. A first rotary shaft is driven by a motor, and a second rotary shaft is driven by the first rotary shaft through gear mechanism. The gas discharged from a main body of the pump is led to an exhaust gas control device via a gas passage outside the main body of the pump. Japanese Unexamined Patent Publication No. 2-157490 discloses a device that has a muffler interposed in the gas passage outside the main body of the pump. In the vacuum pump, pulsation arises in the gas passage outside the main body of the pump, which causes to produce noise. A muffler is provided for restraining such noise, and a check valve is employed as the muffler. A valve body constituting the check valve opens and closes a valve hole. The valve body closes the valve hole when the amount of the gas exhausted from the pump is zero. The check valve restrains the above-mentioned pulsation.

[0003] Some kind of exhaust [e.g. Perfluorocarbon (PFC), etc.] is solidified when temperature becomes lower or pressure becomes higher. If such solidified exhaust is caught into a gap between the valve body and its guide portion, the valve body cannot smoothly open and close the valve hole. Accordingly, the check valve may not function as a device that prevents the pulsation. Therefore, disassembling the check valve is regularly needed in order to remove the solidified exhaust remaining in the check valve. However, when the check valve is disassembled, the valve body falls out thereof due to force of an internal spring. Assembling the check valve is needed to be careful about the valve body not falling out thereof, so that assembling the check valve is awkward.

SUMMARY OF THE INVENTION

[0004] The present invention contemplates to alleviate the above-mentioned inconveniences. Accordingly, it is an object of the present invention to improve a backflow preventing means interposed in a gas passage of exhaust so as to assemble and disassemble the means easily.
   To achieve this object, a vacuum pump has a rotary shaft, a gas transferring assembly and a backflow preventing means. The gas transferring assembly is driven based on rotation of the rotary shaft. Vacuum action is generated by transferring gas due to motion of the gas transferring assembly. The backflow preventing means is interposed in a gas passage. According to the present invention, the backflow preventing means is constituted of a guide pipe, a valve body, a valve hole forming body and an urging means. The guide pipe forms a part of the gas passage. The valve body is slidably guided in an axial direction of the guide pipe therein. The valve hole forming body forms a valve hole which is opened and closed by the valve body. The urging means urges the valve body in a direction to close the valve hole. The guide pipe and the valve hole forming body are formed separately so that they can be assembled and disassembled. A separation preventing means is fitted to the guide pipe. Thereby, the valve body is prevented from falling out of the guide pipe while the guide pipe and the valve hole forming body are separated from each other, and the valve body is urged by the urging means.
   Accordingly, the separation preventing means can prevent the valve body from falling out of the guide pipe while the guide pipe and the valve hole forming body are separated from each other, and the urging means urges the valve body toward the valve hole forming body.

[0005] Furthermore, according to the present invention, the valve body is at a position where the separation preventing means does not affect the valve body while the valve body is urged by the urging means, and the guide pipe and the valve hole forming body are assembled.
   Accordingly, the valve body is not affected by the separation preventing means while the guide pipe and the valve hole forming body are assembled, and the valve hole is closed by the valve body. Thereby, the separation preventing means may not prevent the valve body from opening and closing the valve hole.

[0006] The present invention has such a feature that a circular clip is employed as the separation preventing means, and the circular clip is engaged with an inner circumferential surface of the guide pipe.
   Accordingly, the separation preventing means can simply be constructed by using the circular clip.

[0007] The present invention includes a feature as follows. The valve body is provided with a shutter closing the valve hole, an annular circumferential wall and a plurality of slide contact portions disposed on the circumferential wall. The slide contact portions are guided so as to keep in slide contact with the inner circumferential surface of the guide pipe. Meeting a plurality of the slide contact portions, the separation preventing means can prevent the valve body from falling out of the guide pipe.

[0008] A plurality of the slide contact portions seen in a direction in which the valve body moves, a slide contact range where the guide pipe and the slide contact portions is a part of entire circumference of the guide pipe. Such structure can restrain solidified exhaust from being caught into the gaps between the slide contact portions and the valve body. Also, the slide contact portions of the valve body urged toward the valve hole forming body by the urging means meet the separation preventing means while the guide pipe and the valve hole forming body are separated from each other. Thereby, the valve body can be prevented from falling out of the guide pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The features of the present invention that are believed to be novel are set forth with particularity in the appended claims. The invention together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

Fig. 1 is a cross-sectional plan view illustrating a whole multi-stage roots pump according to a first embodiment of the present invention;

Fig. 2a is a cross-sectional view, taken along the line I-I in Fig. 1;

Fig. 2b is a cross-sectional view, taken along the line II-II in Fig. 1;

Fig. 3a is a cross-sectional view, taken along the line III-III in Fig. 1;

Fig. 3b is a cross-sectional view, taken along the line IV-IV in Fig. 1;

Fig. 4a is an essential cross-sectional plan view illustrating the first embodiment of the present invention;

Fig. 4b is a cross-sectional view, taken along the line V-V in Fig. 4a;

Fig. 4c is an essential cross-sectional plan view illustrating a state that a guide pipe is detached from a valve hole forming body;

Fig. 5 is an essential cross-sectional plan view illustrating a second embodiment of the present invention; and

Fig. 6 is an essential cross-sectional plan view illustrating a third embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] A first embodiment of the present invention will now be described with reference to Figs. 1 through 4. The present invention is applied to a multi-stage roots pump in the first embodiment.
   As shown in Fig. 1, a multi-stage roots pump 11 has a rotor housing 12, a front housing 13, an end plate 36, a rear housing 14, a cylinder block 15 and a plurality of partition walls 16. The front housing 13 is coupled to the front end of the rotor housing 12. The end plate 36 is coupled to the front housing 13. The rear housing 14 is coupled to the rear end of the rotor housing 12. The rotor housing 12 is constituted of the cylinder block 15 and a plurality of the partition walls 16. As shown in Fig. 2b, the cylinder block 15 is constituted of a pair of block pieces 17, 18, and the partition walls 16 are constituted of a pair of wall pieces 161, 162. As shown in Fig. 1, a space between the front housing 13 and a frontmost partition wall 16, spaces between the partition walls 16 and a space between the rear housing 14 and a rearmost partition wall 16 are defined as pump chambers 51, 52, 53, 54, 55, respectively.
   A rotary shaft 19 is rotatably supported by the front housing 13 and the rear housing 14 via radial bearings 21, 37. Also, a rotary shaft 20 is rotatably supported by the front housing 13 and the rear housing 14 via radial bearings 22, 38. Both the rotary shafts 19, 20 are disposed in parallel with each other in a horizontal direction. The rotary shafts 19, 20 extend through the partition walls 16.
   A plurality of rotors 23, 24, 25, 26, 27 is integrally formed with the rotary shaft 19 as gas transferring assemblies. Also, the same number of rotors 28, 29, 30, 31, 32 as the rotary shaft 19 is integrally formed with the rotary shaft 20. The rotors 23 through 32 are congruously formed as seen in a direction of axes 191, 201 of the rotary shafts 19, 20. Thickness of the rotors 23, 24, 25, 26, 27 becomes thinner in this order. Also, thickness of the rotors 28, 29, 30, 31, 32 becomes thinner in this order. A pair of the rotors 23, 28 is accommodated in the pump chamber 54 so as to engage with each other with a small gap. Also, a pair of the rotors 24, 29 is accommodated in the pump chamber 55 so as to engage with each other. Likewise, a pair of the rotors 25, 30, a pair of the rotors 26, 31 and a pair of the rotors 27, 32 are accommodated in the pump chambers 56, 57, 58, respectively.

[0011] A gear housing 33 is coupled to the rear housing 14. The rotary shafts 19, 20 extend through the rear housing 14 and protrude their rear ends into the gear housing 33. A pair of gears 34, 35 secured to the respective rear ends of the rotary shafts 19, 20 is engaged with each other. An electric motor M is installed to the gear housing 33. Driving force of the electric motor M is transmitted to the rotary shaft 19 through a coupling 10, and the rotary shaft 19 is rotated by the electric motor M in a direction of an arrow R1 in Figs. 2a, 2b, 3a, 3b. The rotary shaft 20 is driven by the electric motor M through a pair of the gears 34, 35, and the rotary shaft 20 is rotated in a direction of an arrow R2 (a counter direction relative to the direction which the rotary shaft 19 rotates) as shown in Figs. 2a, 2b, 3a, 3b.
   As shown in Figs. 1 and 2b, passages 163 are defined within the partition walls 16. As shown in Fig. 2b, inlets 164 and outlets 165 of the passages 163 are formed at the partition walls 16. The coadjacent pump chambers 54, 55, 56, 57, 58 are intercommunicated via the passages 163, respectively.
   As shown in Fig. 2a, an intake port 171 is formed through the block piece 17 so as to communicate with the pump chamber 54. As shown in Fig. 3b, an exhaust port 181 is formed through the block piece 18 so as to communicate with the pump chamber 58. Gas introduced into the pump chamber 54 via the intake port 171 is transferred to the pump chamber 55 via the frontmost inlet 164, the frontmost passage 163 and the frontmost outlet 165 by rotation of the rotors 23, 28. Likewise, the gas is transferred in order of reducing volume, that is, in order of the pump chambers 55, 56, 57, 58. The gas transferred into the pump chamber 58 is exhausted outside via the exhaust port 181. Besides, the rotors 23 through 32 are the gas transferring assemblies in order to transfer the gas.
   As shown in Fig. 3b, a flange 39 is coupled to the exhaust port 181. As shown in Fig. 4a, a muffler 40 is coupled to the flange 39, and a cylindrical valve hole forming body 48 is detachably fitted into the muffler 40. Also, a cylindrical guide pipe 41 is detachably fitted into the valve hole forming body 48. An exhaust pipe 42 is coupled to the guide pipe 41. Flanges 401, 481, 411 are formed on the muffler 40, the valve hole forming body 48 and the guide pipe 41, respectively. Each flange 401, 481, 411 is screw-on all together by a bolt 49. The exhaust pipe 42 is welded to the guide pipe 41, and is coupled to an exhaust gas control device (not shown). The flange 39, the muffler 40, the guide pipe 41 and the exhaust pipe 42 constitute passage structure for transferring exhaust which is discharged from the multi-stage roots pump 11 to the exhaust gas control device.
   A valve body 43 and a return spring 44 are accommodated in the guide pipe 41. A tapered valve hole 482 is formed in the valve hole forming body 48, and the valve body 43 opens and closes the valve hole 482 in accordance with a reciprocation thereof. The valve body 43 is constituted of a shutter 45 closing the valve hole 482, a cylindrical circumferential wall 46, a plurality of slide contact portions 47 (four in the present embodiment) disposed on an outer circumferential surface of the circumferential wall 46, and a seal ring 50 secured to an outer periphery of the shutter 45. The valve hole forming body 48, the guide pipe 41, the valve body 43 and the return spring 44 constitute a backflow preventing means. The return spring 44 is an urging means for urging the valve body 43 in a direction to close the valve hole 482.
   A plurality of the slide contact portions 47 is disposed on the outer circumferential surface of the circumferential wall 46 of the valve body 43 in equiangular positions so as to be distributed around the circumferential wall 46. The seal ring 50 contacts with and separates from a tapered surface of the valve hole 482. When the seal ring 50 is in contact with the tapered surface of the valve hole 482, the valve hole 482 is closed by the valve body 43. Passage holes 461 are bored through the circumferential wall 46 between the coadjacent slide contact portions 47. Each shape of the slide contact portions 47 is long in a direction in which the valve body 43 moves. As shown in Fig. 4b, protrusion ends 471 of the slide contact portions 47 keep in slide contact with an inner circumferential surface 412 of the guide pipe 41.
   As shown in Figs. 4a and 4b, a circular clip 51 is engaged with the inner circumferential surface of 412 of the guide pipe 41. While the muffler 40, the valve hole forming body 48 and the guide pipe 41 are assembled by screwing, the valve body 43 cannot meet the circular clip 51.
   The exhaust gas is discharged from the smallest pump chamber 58 to the flange 39 via the exhaust port 181, and reaches the valve hole 482 via the muffler 40. When force acting on the shutter 45 of the valve body 43 based on pressure in the muffler 40 is higher than force acting on the shutter 45 based on resultant force of pressure in the guide pipe 41 and urging force of the return spring 44, the valve body 43 opens the valve hole 482. The exhaust gas passed through the valve hole 482 passes by the circumferential wall 46 of the valve body 43, passes through the passage holes 461, and flows into the exhaust pipe 42.

[0012] The following advantageous effect can be obtained in the first embodiment.

[0013] (1-1) When the guide pipe 41 and the valve hole forming body 48 are separated from each other by unbolting, the slide contact portions 47 of the valve body 43 urged by the return spring 44 meet the circular clip 51 as shown in Fig. 4c. Accordingly, while the guide pipe 41 and the valve hole forming body 48 are separated from each other, the valve body 43 remains in the guide pipe 41. Therefore, structure for continuously keeping the valve body 43 in the guide pipe 41 improves the backflow preventing means so as to assemble and disassemble easily.

[0014] (1-2) As shown in Fig. 4a, the valve body 43 does not meet the circular clip 51 while the guide pipe 41 and the valve hole forming body 48 are assembled, and the valve body 43 is situated at a position where the valve body 43 closes the valve hole 482. In other words, a separation preventing action of the circular clip 51 does not affect the valve body 43 while the guide pipe 41 and the valve hole forming body 48 are in a state as shown in Fig. 4a. Also, the circular clip 51 does not block the valve body 43 from opening and closing the valve hole 482.

[0015] (1-3) The circular clip 51 can easily be engaged with the inner circumferential surface 412 of the guide pipe 41. Besides, an extra space for fitting the circular clip 51 is small. Accordingly, the separation preventing means can simply be constructed by using the circular clip 51.

[0016] (1-4) The valve body 43 is guided by the inner circumferential surface 412 of the guide pipe 41 so as to open and close the valve hole 482. However, the guide pipe 41 and the valve body 43 keep in slide contact with each other via a plurality of the slide contact portions 47 disposed on the outer circumferential surface of the circumferential wall 46 of the valve body 43 so as to be distributed around the circumferential wall 46. The slide contact portions 47 keep in slide contact with a part of entire circumference of the inner circumferential surface 412 of the guide pipe 41 as seen in a direction in which the valve body 43 moves. That is, a slide contact range where the guide pipe 41 and a plurality of the slide contact portions 47 keep in slide contact with each other is a part of entire circumference of the guide pipe 41. Such structure that the valve body 43 keeps in slide contact with a part of entire circumference of the guide pipe 41 can restrain the solidified exhaust from being caught into the gaps between the inner circumferential surface 412 and the valve body 43. Accordingly, smooth motion of the valve body 43 is not deteriorated, and an operational failure of the backflow preventing means can be restrained from occurring.
   The slide contact portions 47 obtaining such an advantageous effect are disposed in the vicinity of the inner circumferential surface 412 at appropriate positions so as to meet the circular clip 51. Accordingly, the slide contact portions 47 are appropriate meeting means as for the circular clip 51 when the guide pipe 41 and the valve hole forming body 48 are separated from each other.

[0017] A second embodiment of the present invention will now be described with reference to Fig. 5. The same reference numerals denote the same components in Fig. 5 as compared with the first embodiment.
   A ring screw 52, which is the separation preventing means, is threaded into the inner circumferential surface 412 of the guide pipe 41. The slide contact portions 47 of the valve body 43 urged by the return spring 44 meet the ring screw 52 while the guide pipe 41 and the valve hole forming body 48 are separated from each other. Accordingly, the valve body 43 remains in the guide pipe 41 while the guide pipe 41 and the valve hole forming body 48 are separated from each other.

[0018] A third embodiment of the present invention will now be described with reference to Fig. 6. The same reference numerals denote the same components in Fig. 6 as compared with the first embodiment.

[0019] A separation preventing ring 53 made of synthetic resins is fitted into the guide pipe 41. The separation preventing ring 53 as the separation preventing means is provided with a plurality of hooked pieces 531, and end hooks 532 of the hooked pieces 531 are hooked on recesses 413 of the inner circumferential surface 412. The slide contact portions 47 of the valve body 43 urged by the return spring 44 meet ends of the hooked pieces 531 while the guide pipe 41 and the valve hole forming body 48 are separated from each other. Accordingly, the valve body 43 remains in the guide pipe 41 while the guide pipe 41 and the valve hole forming body 48 are separated from each other.

[0020] The present invention is not limited to the embodiments described above, but may be modified into examples as follows.

(1) The guide pipe 41 and the valve hole forming body 48 are disposed in a vertical direction, and the guide pipe 41 is disposed above the valve hole forming body 48 so as to urge the valve body 43 by its deadweight.

(2) The present invention may be applied to a backflow preventing means which is disposed in a suction pipe coupling to a main body of a vacuum pump.

(3) The present invention may be applied to a vacuum pump except a roots pump.

(4) The present invention may be applied to passage structure of a vacuum pump such as follows. The vacuum pump includes a plurality of drive shafts, rotors, and a plurality of pump chambers or a single pump chamber. The drive shafts are disposed in parallel with one another. The rotors are secured to each drive shaft. The coadjacent rotors are engaged with each other. A set of rotors engaged with each other is accommodated in a plurality of pump chambers or a single pump chamber.

[0021] According to the present invention as described above, the guide pipe and the valve hole forming body are formed separately so that they can be assembled and disassembled. The valve body is prevented from falling out of the guide pipe while the guide pipe and the valve hole forming body are separated from each other, and the valve body is urged by the urging means. Such the separation preventing means is fitted to the guide pipe that the backflow preventing means interposed in the gas passage of the exhaust gas can easily be assembled and disassembled. Also, such advantageous effect can be performed.

[0022] Therefore the present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein but may be modified within the scope of the appended claims.

[0023] Passage structure for a vacuum pump has a flange, a muffler, a valve hole forming body, a guide pipe and an exhaust pipe. The flange is coupled to the muffler. The muffler is detachably fitted into the valve hole forming body. The valve hole forming body is detachably fitted into the guide pipe. The exhaust pipe is coupled to the guide pipe via the valve hole forming body. Each flange of the muffler, the valve hole forming body and the guide pipe is screw-on all together. A backflow preventing means is constituted of the guide pipe, the valve hole forming body, a valve body and a return spring. The guide pipe accommodates the valve body and the return spring therein. The valve body opens and closes a valve hole formed at the valve hole forming body. A separation preventing means is engaged with an inner circumferential surface of the guide pipe.

Claims

1. Passage structure for a vacuum pump comprising:

a rotary shaft;

a gas transferring assembly driven based on rotation of the rotary shaft;

wherein vacuum action is generated by transferring gas due to motion of the gas transferring assembly;

a backflow preventing means interposed in a gas passage;

wherein said backflow preventing means comprises a guide pipe forming as a part of the gas passage, a valve body slidably guided in an axial direction of the guide pipe therein, a valve hole forming body forming a valve hole being opened and closed by the valve body and an urging means for urging the valve body in a direction to close the valve hole;

wherein the guide pipe and the valve hole forming body are attachably and detachably formed separately;

a separation preventing means being installed to the guide pipe; and

   whereby said separation preventing means prevents the valve body from falling out of the guide pipe while the guide pipe and the valve hole forming body are detached, and the urging means urges the valve body.

2. Passage structure for a vacuum pump according to claim 1, wherein the valve body is at a position where said separation preventing means does not act on the valve body, while the valve body is urged by said urging means, and while the guide pipe and the valve hole forming body are assembled.

3. Passage structure for a vacuum pump according to claim 1, wherein said separation preventing means is a circular clip engaged with an inner circumferential surface of the guide pipe.

4. Passage structure for a vacuum pump according to claim 1,
   wherein said valve body has a shutter closing the valve hole, an annular circumferential wall and a plurality of slide contact portions disposed on the circumferential wall so as to be distributed around the circumferential wall,
   wherein the slide contact portions are guided so as to keep in slide contact with an inner circumferential surface of said guide pipe, and
   wherein said separation preventing means is engaged with the slide contact portions so as to prevent the valve body from falling out of the guide pipe.

5. Passage structure for a vacuum pump according to claim 1, wherein said separation preventing means is a ring screw engaged with an inner circumferential surface of the guide pipe.

6. Passage structure for a vacuum pump according to claim 1, wherein said separation preventing means is a separation preventing ring engaged with an inner circumferential surface of the guide pipe.

7. Passage structure for a vacuum pump according to claim 6, wherein said separation preventing ring is made of synthetic resin.

Drawing