Multistage dry vacuum pump

Abstract

A multistage dry vacuum pump includes a housing, pump chambers formed in the housing, each having an inlet and an outlet, a rotor provided in each pump chamber, a shaft connected to each rotor, a rotation driving device connected to the shaft, an intermediate exhaust conduit, one end thereof connected to the outlet of the pump chamber other than the most downstream and the other end thereof opened to outside, and a first fluid flow control device provided in the intermediate exhaust conduit for closing the same when fluid pressure in the outlet side of the pump chamber connected to the intermediate exhaust conduit is lower than that outside the other end of the intermediate exhaust conduit, and for opening the same when fluid pressure is equal to or higher than that outside the same.

Description

FIELD OF THE INVENTION

This invention generally relates to a vacuum pump. More particularly, this invention generally relates to a multistage dry vacuum pump with low electricity consumption and large exhaust rate in wide range of degree of vacuum.

BACKGROUND

Conventionally, a multistage dry vacuum pump having a pair of shafts supporting plurality of rotors provided in a housing is known. The multistage dry vacuum pump includes a plurality of pump chambers each accommodating a pair of rotors. There are slight clearance between the pair of rotors in each pump chambers and between the rotor and an inner wall of the housing. The pair of rotors are rotated in opposite direction at high speed to compress fluid sucked from a main inlet of the housing and transport from an earlier pump chamber to a later pump chamber serially and exhaust the fluid from the main inlet of the housing to atmosphere.

This kind of the multistage dry vacuum pump compresses and exhausts fluid sucked from the inlet of the pump chamber against pressure applied from downstream. A compressing work is defined as the amount of work to exhaust the fluid to downstream from the outlet against the pressure. Particularly, the amount of compressing work in proportion to pressure and a scavenging volume becomes maximum at the last pump chamber because pressure of an outlet of the last pump chamber is the same as atmospheric pressure. In this case, because compressing work is in proportion with the scavenging volume of the pump chamber as described above, the smaller the scavenging volume of the last pump chamber becomes, the smaller the compressing work becomes. Accordingly, by reducing the scavenging volume of the pump chamber of downstream side, the compressing work can be reduced. Therefore, electricity consumption can also be reduced.

In order to reduce the scavenging volume of a downstream pump chamber, a known pump is structured that a thickness of each rotors supported by each of a pair of shafts and accommodated in each pumps becomes thinner in the downstream pump chamber to reduce its scavenging volume of the downstream pump chamber. Further, JP2002-364569A describes that the number of blades of the rotor for the Roots pump becomes larger in a later pump chamber to reduce the scavenging volume thereof. Further, JP2003-155988A describes a multistage dry vacuum pump with an assistant pump connected to an outlet of a later pump chamber of the multistage dry vacuum pump to make combination of two exhaust systems.

In the multistage Roots vacuum pump according to JP2002-364569A, thickness of the rotors for the Roots pump are reduced and the number of the blades of the rotors for the Roots pump is increased in the later pump chamber to reduce electricity consumption, for example, by making the scavenging volume of the last pump chamber provided at the main outlet side about 25% of the scavenging volume of the first pump chamber provided at the main inlet side, or the like. In case that the scavenging volume becomes smaller in the later pump chamber as mentioned above, when sucking pressure is such high as equal to or higher than 10000 Pa, the sucking pressure of the later pump chamber can exceed pressure of the outside of the multistage dry vacuum pump (atmospheric pressure, or the like). On the other hand, pressure of the outlet of the last pump is constant and the same as pressure of the outside of the multistage dry vacuum pump (atmospheric pressure). Therefore, these pump chambers become resistance for fluid flow. These causes increase in electricity consumption and rapid decrease in exhaust rate.

In addition, the pump described in JP2003-155988A includes the assistant pump with a small scavenging volume provided at the pump body and an exhaust conduit having a one-way valve letting fluid flow to atmosphere provided in parallel with the assistant pump. Therefore, decrease in exhaust rate and increase in electricity consumption at the high sucking pressure area described in JP 2002-364569A can be solved in some degree. However, the pump has two exhaust systems, which causes more complicated structure, lower reliability, and high manufacturing cost of the pump caused by increase of the number of parts for the pump including piping system, and causes lower efficiency and larger installation space of the pump caused by combination of pumps.

A need thus exists for a multistage dry vacuum pump having high exhaust rate and low electricity consumption at wide vacuum range from high pressure to low pressure of sucking pressure of exhausted fluid and good operationality and simple structure to make it compact at lower manufacturing cost.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, a multistage dry vacuum pump includes a housing having a main inlet and a main outlet, a plurality of pump chambers formed in the housing in series and spatially connecting the main inlet with the main outlet, each pump chamber having an inlet connected to upstream and an outlet connected to downstream, a plurality of rotors each rotatably provided in the each pump chamber for transporting fluid in a scavenging space defined in the pump chamber through the outlet of the pump chamber to the downstream by rotating, a shaft connected to each rotor provided in the each pump chamber for rotating the each rotor synchronously, a rotation driving means connected to the shaft, an intermediate exhaust conduit, one end thereof being connected to the outlet of the pump chamber located at other than the most downstream side and the other end thereof being opened to outside, and a first fluid flow control means provided in the intermediate exhaust conduit for closing the intermediate exhaust conduit when the fluid pressure in the one end of the intermediate exhaust conduit is lower than that in the other end of the intermediate exhaust conduit and for opening the intermediate exhaust conduit when the fluid pressure in the one end of the intermediate exhaust conduit is equal to or higher than that in the other end of the intermediate exhaust conduit.

According to another aspect of the present invention, a multistage dry vacuum pump includes a housing having a main inlet and a main outlet, a plurality of pump chambers formed in the housing in series and spatially connecting the main inlet with the main outlet, each pump chamber having an inlet connected to upstream side and an outlet connected to downstream side, drive and dependent rotors provided rotatably in the each pump chamber, the drive rotor and the dependent rotor transporting fluid in a scavenging space defined in the pump chamber through the outlet of the pump chamber to the downstream by synchronously rotating, a drive shaft connected to each drive rotor provided in the each pump chamber for synchronously rotating the each drive rotor, a dependent shaft connected to each dependent rotor provided in the each pump chamber for synchronously rotating the each dependent rotor, a rotation driving means connected to the drive shaft, a transmitting means for transmitting rotation of the drive shaft to the dependent shaft, an intermediate exhaust conduit, one end thereof being connected to the outlet of the pump chamber located at other than the most downstream side and the other end thereof being opened to outside, and a first fluid flow control means provided in the intermediate exhaust conduit for closing the intermediate exhaust conduit when the fluid pressure in the one end of the intermediate exhaust conduit is lower than that in the other end of the intermediate exhaust conduit and for opening the intermediate exhaust conduit when the fluid pressure in the one end of the intermediate exhaust conduit is equal to or higher than that in the other end of the intermediate exhaust conduit.

According to another aspect of the present invention, a multistage dry vacuum pump includes a housing having a main inlet and a main outlet, a plurality of pump chambers formed in the housing in series and spatially connecting the main inlet with the main outlet, each pump chamber having an inlet connected to upstream side and an outlet connected to downstream side, a plurality of rotors each rotatably provided in the each pump chamber for transporting fluid in a scavenging space defined in the pump chamber from the outlet of the pump chamber to the downstream by rotating, a shaft connected to each rotor provided in the each pump chamber for rotating the each rotor synchronously, a rotation driving means connected to the shaft, and a pressure adjusting means for adjusting the fluid pressure in the outlet side of the pump chamber to be equal to or lower than atmospheric pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and additional features and characteristics of the present invention will become more apparent from the following detailed description considered with reference to the accompanying drawings, wherein:

FIG. 1 shows a vertical cross-sectional view of a multistage dry vacuum pump according to a first embodiment of the present invention.

FIG. 2 shows a transverse cross-sectional view taken on line II-II of FIG. 1 according to the first embodiment of the present invention.

FIG. 3 shows a vertical cross-sectional view of the multistage dry vacuum pump according to a second embodiment of the present invention.

DETAILED DESCRIPTION

Embodiments of the present invention will be explained with reference to the illustrations of the drawing figures as follows.

A first embodiment of the present invention will be explained with reference to the illustrations of the drawing figures as follows. FIG. 1 shows a vertical cross-sectional view of a multistage dry vacuum pump according to the first embodiment of the present invention.

FIG. 2 shows a transverse cross-sectional view taken on line II-II of FIG. 1. Generally, a multistage dry vacuum pump has 4-6 compression steps. In the following example, a multistage dry vacuum pump having four compression steps will be explained.

As shown in the figures, the multistage dry vacuum pump includes a housing 2, a plurality of rotors (first rotors 12a and 12b, second rotors 13a and 13b, third rotors 14a and 14b, and fourth rotors 15a and 15b), each pair provided in each pump chamber 8, 9, 10, 11 formed in the housing 2, a pair of shaft (a first shaft 16a and a second shaft 16b) rotatably supported in the housing 2 having the four-steps pump chambers 8, 9, 10, 11, and a shaft driving means 20 serving as a rotation driving means connected to the shaft 16a.

As shown in FIG. 1, the housing 2 is made of metallic material such as iron, aluminum in cylindrical shape. The housing 2 includes a main inlet 3 and a main outlet 4. The housing 2 further includes the plurality of pump chambers 8, 9, 10, 11 (in following example, four-steps) at the inside thereof as described above. These four pump chambers are divided by walls 5, 6, 7 each other. These four pump chambers, that is, a first pump chamber 8, a second pump chamber 9, a third pump chamber 10, a fourth pump chamber 11 are connected in series and in this order from the main inlet 3 to the main outlet 4. An inlet of the first pump chamber 8 is serving as the main inlet 3. An outlet 29 of the fourth pump chamber 10 is connected to the main outlet 4 via a main exhaust conduit 31.

As shown in FIG. 1, a width (thickness) of the each pump chamber is set to become smaller in order of the pump chambers 8, 9, 10, 11. In other words, as shown in FIG. 1, the each pump chamber is formed to fill a relation T1>T2>T3>T4, where T1 is a width of the first pump chamber 8, T2 is a width of the second pump chamber 9, T3 is a width of the third pump chamber 10, and T4 is a width of the fourth pump chamber 11. Further, the each pump chamber 8, 9, 10, 11 accommodates the each pair of the rotor. Because the each pump chamber fulfills the relation as described above, a thickness of the each pair of rotor 12a and 12b, 13a and 13b, 14a and 14b, 15a and 15b is also determined by the width of the each pump chamber described above.

As representatively shown in FIG. 2, the pair of cocoon-shaped second rotor 13a and 13b is rotatably provided in the second pump chamber 9. Similarly, the pair of cocoon-shaped first rotor 12a and 12b (third rotor 14a and 14b, fourth rotor 15a and 15b) is rotatably provided in the first pump chamber 8 (the third pump chamber 10, the fourth pump chamber 11).

Further, the pair of the shaft 16a and 16b is penetrating the pump chambers and rotatably supported in the housing 2. One of the pair of first rotor 12a, one of the pair of the second rotor 13a, one of the pair of the third rotor 14a, one of the pair of the fourth rotor 15a are serially connected to the same first shaft 16a. The other of the first rotor 12b, the other of the second rotor 13b, the other of the third rotor 14b, the other of the fourth rotor 15b are serially connected to the same second shaft 16b. Accordingly, the one of the first rotor 12a, the one of the second rotor 13a, the one of the third rotor 14a, the one of the fourth rotor 15a are synchronously rotated in accordance with a rotation of the first shaft 16a. Similarly, the other of the first rotor 12b, the other of the second rotor 13b, the other of the third rotor 14b, the other of the fourth rotor 15b are synchronously rotated in accordance with rotation of the second shaft 16b.

The pump chambers 8 and 9 being adjacent each other provided in the housing 2 are connected by a first fluid transport conduit 17. Similarly, the pump chambers 9 and 10 being adjacent each other provided in the housing 2 are connected by a second fluid transport conduit 18. The pump chambers 10 and 11 being adjacent each other provided in the housing 2 are connected by a third fluid transport conduit 19. The main inlet 3 and the main outlet 4 are spatially connected via these pump chambers and these fluid transport conduits to compress fluid sucked from the main inlet 3 in the four pump chambers and to transport it through the fluid transport conduits serially and to exhaust it from the main outlet 4 to atmosphere.

Further, the main exhaust conduit 31 is provided in the housing 2. One end of the main exhaust conduit 31 is connected to the outlet 29 of the fourth pump chamber 11. The other end of the main exhaust conduit 31 is connected to the main outlet 4 via a confluent chamber 40 of the exhaust conduits. Further, an intermediate exhaust conduit 30 is provided in parallel with the main exhaust conduit 31. One end of the intermediate exhaust conduit 30 is connected to an outlet 28 of the third pump chamber 10. The other end of the intermediate exhaust conduit 30 is connected to the main outlet 4 via the confluent chamber 40 of the exhaust conduits. Accordingly, the other end of the main exhaust conduit 31 and the other end of the intermediate exhaust conduit 30 are connected to the main outlet 4 via the confluent chamber 40 of the exhaust conduits, in other words, the other ends of the both conduits 31, 30 are connected to the outside (atmosphere) through the main outlet 4.

A one-way valve 32 letting fluid flow to the outside (atmosphere) serving as a first fluid flow control means is provided in the intermediate exhaust conduit 30. The one-way valve 32 includes a valve seat 32b, a sphere 32c, and a spring 32d in a valve chest 32a. The sphere 32c contacts with the valve seat 32b to close the intermediate exhaust conduit 30 by biasing force of the spring 32d.

As shown in FIG. 1, biasing force of the spring 32d is applied from the outside (atmosphere). When the fluid pressure in the outlet 28 side of the third pump chamber 10 is lower than that of the outside (atmosphere), the pressure difference therebetween is applied to the spring 32d in the same direction as biasing force thereof. Therefore, the sphere 32c contacts with the valve seat 32d to close the intermediate exhaust conduit 30 more firmly.

On the other hand, when the fluid pressure of the outlet 28 side of the third pump chamber 10 is higher than that of the outside (atmosphere), force generated from the pressure difference therebetween is applied to the spring 32d against the biasing force thereof. When the force is larger than the biasing force of the spring 32d, the sphere 32c is separated from the valve seat 32d to open the intermediate exhaust conduit 30. Accordingly, When the fluid pressure of the fluid sucked from the main inlet 3 is high and sucking pressure of the forth pump chamber 11 (exhaust pressure of the third pump chamber 10) is higher than atmospheric pressure, part of the sucked fluid is exhausted from the outlet 28 connected to the fluid transport conduit 19 and the inlet of the fourth pump chamber 11 via the intermediate exhaust conduit 30 and the one-way valve 32 to atmosphere. Here, it is preferable that the biasing force of the spring 32d is as small as possible for energy saving.

Here, it is needless to say that when the sucking pressure of the fourth pump chamber 11, in other words, the exhaust pressure of the third pump chamber 10, is lower than the atmospheric pressure, atmospheric air does not flow back from the one-way valve 32 letting fluid flow to atmosphere into the multistage dry vacuum pump 1 via the intermediate exhaust conduit 30.

The main inlet 3 side of the housing 2 is integral with a side cover 22 of the main inlet 3 side. The main outlet 4 side of the housing 2 is integral with a side cover 23 of the main outlet 4 side. Two bearings 24a and 24b of the main inlet 3 side is provided at the side cover 22 of the main inlet 3 side. Two bearings 25a and 25b of the main outlet 4 side is provided at the side cover 23 of the main outlet 4 side. The bearings 24a and 25a rotatably support the first shaft 16a. The bearings 24b and 25b rotatably support the second shaft 16b.

As shown in FIG. 1, timing gears 21a and 21b are engaged to one ends of the shafts 16a and 16b respectively to rotate the pair of shaft 16a and 16b synchronously and in opposite direction each other. A motor 20 serving as the rotation driving means is connected to the other end of the first shaft 16a, the other end not engaged to the timing gear 21a. Accordingly, the shaft 16a is serving as a drive shaft, and the shaft 16b is serving as a driven shaft. Further, the rotors 12a, 13a, 14a and 15a connected to the shaft 16a are serving as drive rotors, and the rotors 12b, 13b, 14b and 15b connected to the shaft 16b are serving as driven rotors.

A gear cover 26 is provided around the timing gears 21a and 21b. As shown in FIG. 1, the gear cover 26 is attached to opposing side of the side cover 23 of the main outlet 3 side to the housing 2. The gear cover 26 accommodates the timing gears 21a, 21b and oil 27 for lubricating the timing gears 21a, 21b and the bearings 25a, 25b. Meanwhile, the bearing 24a and 24b are lubricated by grease.

The pair of the rotor 13a and 13b are rotated by the timing gears 21a and 21b engaged with the shafts 16a and 16b with a phase difference and in opposite direction each other indicated by arrows shown in FIG. 2 to suck the fluid from upper part and to exhaust fluid to lower part of the pump chamber 9 accommodating the rotors 13a and 13b as shown in the FIG. 1. Similarly, the pair of the rotor 12a and 12b engaged with the shafts 16a and 16b respectively are rotated in opposite direction each other to suck and exhaust the fluid in the pump chamber 8 accommodating the rotors 12a and 12b. Similarly, the pair of the rotor 14a and 14b engaged with the shafts 16a and 16b respectively are rotated in opposite direction each other to suck and exhaust the fluid in the pump chamber 10 accommodating the rotors 14a and 14b. Further, the pair of the rotor 15a and 15b engaged with the shafts 16a and 16b respectively are rotated in opposite direction each other to suck and exhaust the fluid at the pump chamber 11 accommodating the rotors 15a and 15b.

As shown in FIG. 2, there is slight clearance between the pair of the rotor 13a and 13b. The rotors 13a and 13b are provided not to contact with each other by the timing gears 21a and 21b. Further, there is slight clearance between an outer surface of the rotors 13a, 13b and an inner surface of the second pump chamber 9 not to contact with each other. The other pair of the rotor 12a and 12b, the pair of the rotor 14a and 14b, the pair of the rotor 15a and 15b are similarly structured.

As shown in FIG. 2, a space S surrounded by the rotors 13a, 13b and the inner surface of the second pump chamber 9 is a scavenging space. A cross-sectional shape of the each pump chamber and a cross-sectional shape of each rotors accommodated in the each pump chamber are identical with that shown in FIG. 2. On the other hand, as shown in FIG. 1, the width of the each pump chamber is designed to be smaller from the pump chamber provided at upstream side to the pump chamber provided at downstream side. Accordingly, a scavenging volume of the each pump chamber is designed to become smaller from the pump chamber provided at the upstream side to the pump chamber provided at the downstream side.

An operation of the multistage dry vacuum pump will be explained as follows.

At first, the motor 20 serving as the rotation driving means drives and the first shaft 16a connected to the motor 20 is driven. The rotors 12a, 13a, 14a and 15a connected to the shaft 16a rotates in the each pump chamber with the rotation of the first shaft 16a. Meanwhile, the first shaft 16a is connected to the second shaft 16b by the timing gears 21a and 21b. Therefore, the rotation of the motor 20 is transmitted to the second shaft 16b to be inversely rotated. Accordingly, the rotors 12b, 13b, 14b and 15b connected to the second shaft 16b are rotated synchronously and at the same speed with the rotors 12a, 13a, 14a and 15a and in inverse direction with the rotation of the rotors 12a, 13a, 14a and 15a.

By the rotation of the each rotor, the fluid sucked from the main inlet 3 is at first compressed in the first pump chamber 8 and transported to the second pump chamber 9 via the first fluid transport conduit 17. Further, the fluid compressed in the second pump chamber 9 is transported to the third pump chamber 10 via the second fluid transport conduit 18. Further, the fluid compressed in the third pump chamber 10 is transported to the fourth pump chamber 11 via the third fluid transport conduit 19. Thus the fluid sucked from the main inlet 3 is compressed in and transported to the each pump chamber provided in a descending order of the scavenging volume of the pump chambers.

The outlet 28 of the third pump chamber 10 is connected to the intermediate exhaust conduit 30 connected to the main outlet 4 via the one-way valve 32 letting fluid flow to atmosphere and the confluent chamber 40 of the exhaust conduits. Further, the outlet 29 of the fourth pump chamber 11 is connected to the main exhaust conduit 31 connected to the main outlet 4 via the confluent chamber 40 of the exhaust conduits. Therefore, the transported fluid sucked from the main inlet 3 and compressed in each pump chamber 8, 9, 10 and 11 is transported through the intermediate exhaust conduit 30 or the main exhaust conduit 31 and finally exhausted through the main outlet 4 to the outside (atmosphere) via the confluent chamber 40 of the exhaust conduits.

In other words, when pressure of the fluid sucked from the main inlet 3 is relatively low, for example, equal to or lower than a certain 100 Pa, because a mass flow rate of the fluid is small, exhaust pressure of the each pump chamber from the first pump chamber 8 to the third pump chamber 10 does not become equal to or higher than atmospheric pressure. Accordingly, the sucked fluid is not exhausted to atmosphere via the intermediate exhaust conduit 30 connecting the fluid transport conduit 19 with the main outlet 4 and having the one-way valve 32 letting fluid flow to atmosphere. The fluid sucked from the main inlet 3 is exhausted to the outside (atmosphere) through the outlet 29 of the fourth pump chamber 11 via the main exhaust conduit 31 and through the main outlet 4.

On the other hand, when pressure of the fluid sucked from the main inlet 3 is relatively high, for example, equal to or higher than 10000 Pa, exhaust pressure of the outlet 28 of the third pump chamber 10, that is, sucking pressure of the fourth pump chamber 11 connected via the third fluid transport conduit 19 may be higher than the atmospheric pressure (It depends on a volume of each pump chamber). In this case, part of the sucked fluid is exhausted to atmosphere via the intermediate exhaust conduit 30 having the one-way valve 32 letting fluid flow to atmosphere. Therefore, the sucking pressure of the fourth pump chamber 11 may not be higher than the atmospheric pressure. Thus, the fourth pump chamber 11 may not be resistance for exhaust performance of the each pump chamber provided before the fourth pump chamber 11.

As explained above, the multistage dry vacuum pump 1 includes the intermediate exhaust conduit 30, the one end thereof connected to the outlet (the outlet 28 in this embodiment) of the pump chamber other than the fourth pump chamber 11 provided at the most downstream (the third pump chamber 10 in this embodiment), the other end thereof being opened to outside, and the one-way valve 32 provided in the intermediate exhaust conduit 30 for closing the intermediate exhaust conduit 30 when the fluid pressure in the one end of the intermediate exhaust conduit 30 (pressure in the outlet 28 side of the third pump chamber 10) is lower than that of the other end thereof (atmospheric pressure) and for opening the intermediate exhaust conduit 30 when the fluid pressure in one end of the intermediate exhaust conduit 30 (pressure in the outlet 28 of the third pump chamber 10) is equal to or higher than pressure in the other end of the intermediate exhaust conduit 30 (atmospheric pressure). Accordingly, when the pressure of the fluid sucked from the main inlet 3 is relatively low, the sucked fluid is exhausted through the outlet 29 of the fourth pump chamber 11 and the main exhaust conduit 31, and finally exhausted through the main outlet 4 to the outside (atmosphere). On the other hand, when sucking pressure of the fluid sucked from the main inlet 3 is relatively high, for example, exhaust pressure of the third pump chamber 10 is higher than the atmospheric pressure, part of the sucked fluid is exhausted to atmosphere via the intermediate exhaust conduit 30 connected with the main outlet 4 having the one-way valve 32 letting fluid flow to atmosphere. Therefore, the sucking pressure of the fourth pump chamber 11 may not be higher than the atmospheric pressure.

Therefore, an exhaust rate of the multistage dry vacuum pump having the pump chambers becoming serially smaller from the main inlet 3 to the main outlet 4 for reducing electricity consumption is not decreased even when the multistage dry vacuum pump sucks and exhausts the fluid at relatively high sucking pressure. In addition, not like a conventional exhaust system for reducing low electric consumption without reducing an exhaust rate including an assistant pump having a small scavenging volume connected to the multistage dry vacuum pump and an exhaust conduit with a one-way valve letting fluid flow to atmosphere in parallel with the assist pump, the multistage dry vacuum pump according to the embodiment of the present invention does not have problems such as complex structure and lowering of reliability caused by increase of the number of parts of the pump including piping system, increase in manufacturing cost, efficiency lowering caused by combination of the pumps, and increase in installing space.

In the embodiment, the multistage dry vacuum pump includes the intermediate exhaust conduit 30 having the one-way valve 32 letting fluid flow to atmosphere and provided at the outlet 28 of the third pump chamber 10 and connected to the main outlet 4. However, the multistage dry vacuum pump may include an intermediate exhaust conduit connected to the main outlet 4 with a one-way valve letting fluid flow to atmosphere provided at the outlet of the other plurality of the pump chambers such as the second pump chamber 9 and the third pump chamber 10. In addition, the multistage dry vacuum pump may include an opening/closing member such as a shutter and a pressure sensor for detecting pressure of the one end and the other end of the intermediate exhaust conduit 30 for opening/closing the shutter based on a detection result of the pressure sensor.

A second embodiment of the present invention will be explained with reference to FIG. 3 as follows. FIG. 3 shows a multistage dry vacuum pump according to this embodiment.

Pump chambers 8, 9 being adjacent each other in length direction of shafts 16a and 16b are connected by a first fluid transport conduit 17 in a housing 2. Similarly, pump chambers 9, 10 adjacent each other in length direction of the shafts 16a and 16b is connected by a second fluid transport conduit 18. Similarly, pump chambers 10, 11 being adjacent each other in length direction of the shafts 16a and 16b are connected by a third fluid transport conduit 19. Thus, fluid sucked from a main inlet 3 of the multistage dry vacuum pump 1 is compressed by four steps and exhausted from a main outlet 4 of the multistage dry vacuum pump 1 to atmosphere.

A main exhaust conduit 31 connecting an outlet 29 of the fourth pump chamber 11 with the main outlet 4 and an intermediate exhaust conduit 30 connecting an outlet 28 of the third pump chamber 10 with the main outlet 4 in parallel with the main exhaust conduit 31 are provided in the housing 2. A one-way valve 33 letting fluid flow to atmosphere serving as a second fluid flow control means is provided in the main exhaust conduit 31. The fluid sucked from the main inlet 3 is exhausted to atmosphere via the outlet 29 and the one-way valve 33 letting fluid flow to atmosphere and the main exhaust conduit 31. According to this structure, it can prevent that atmospheric air flows back through the one-way valve 33 from the main outlet 4 via the main exhaust conduit and atmospheric air flows into the vacuum processing chamber even when the multistage dry vacuum pump 1 is stopped.

Further, a one-way valve 32 letting fluid flow to atmosphere is provided in the intermediate exhaust conduit 30 connecting the outlet 30 of the third pump chamber 10 with the main outlet 4 to exhaust the sucked fluid to atmosphere when the pressure of the sucked fluid from the main inlet 3 is high and sucking pressure of the fourth pump chamber 11 becomes higher than atmospheric pressure. Here, the atmospheric air does not flow back into the third pump chamber 10 via the intermediate exhaust conduit 30 because of the one-way valve 32 letting fluid flow to atmosphere when the sucking pressure of the fourth pump chamber 11, in other words, exhaust pressure of the third pump chamber 10, is lower than the atmospheric pressure.

Further, each other end of the intermediate exhaust conduit 30 and the main exhaust conduit 31 is connected to the main outlet 4 via a confluent chamber 40 of the exhaust conduits.

A detailed structure of the multistage dry vacuum pump will not be repeated because the structure thereof is the same as that of the multistage dry vacuum pump according to the first embodiment already explained above. Operation of the multistage dry vacuum pump structured as described above will be explained as follows.

With rotation of each rotor, the fluid sucked from the main inlet 3 is compressed in the first pump chamber 8 at first and transported into the second pump chamber 9 via the first fluid transport conduit 17. Next, the fluid compressed in the second pump chamber 9 is transported into the third pump chamber 10 via the second fluid transport conduit 18. Then, the fluid compressed in the third pump chamber 10 is transported into the fourth pump chamber 11 via the third fluid transport conduit 19. Thus, the fluid sucked from the main inlet 3 is compressed in each pump chamber 8, 9, 10 and 11 provided in series and having a scavenging volume of the each pump chamber becoming smaller in this order.

Here, the intermediate exhaust conduit 30 having the one-way valve 32 letting fluid flow to atmosphere connected to the main outlet 4 is connected to the outlet 28 of the third pump chamber 10. Further, the main exhaust conduit 31 having the one-way valve 33 letting fluid flow to atmosphere connected to the main outlet 4 is connected to the outlet 29 of the fourth pump chamber 11. Accordingly, the fluid sucked from the main inlet 3 and serially compressed in the each pump chamber in series are exhausted from the outlet 28 or the outlet 29 and finally exhausted from the main outlet 4 to the outside (atmosphere).

In other words, when the pressure of the fluid sucked from the main inlet 3 is relatively low, for example, when exhausting fluid at the pressure equal to or lower than several 100 Pa, exhaust pressure of the pump chambers from the first pump chamber 8 to the third pump chamber 10 does not become the atmospheric pressure normally because a mass flow rate of the fluid is small. Accordingly, part of the sucked fluid is not exhausted via the intermediate exhaust conduit 30 having the one-way valve 32 letting fluid flow to atmosphere and the main outlet 4. The fluid sucked from the main inlet 3 is transported to the outlet 29 of the fourth pump chamber 11 and the main exhaust conduit 31 and exhausted from the main outlet 4 to the outside (atmosphere).

On the other hand, when the pressure of fluid sucked from the main inlet 3 is relatively high, for example equal to or higher than 10000 Pa, exhaust pressure of the third pump chamber 10, in other words, sucking pressure of the fourth pump chamber 11 connected with the third fluid transport conduit 19 sometimes can be higher than the atmospheric pressure (It depends on the pump chambers). In this case, part of the sucked fluid is transported via the intermediate exhaust conduit 30 connecting the outlet 28 with the main outlet 4 and having the one-way valve 32 letting fluid flow to atmosphere to the outside (atmosphere). Therefore, the sucking pressure of the fourth pump chamber 11 does not become higher than the atmospheric pressure, and the fourth pump chamber 11 does not become resistance for exhaust performance of the pump chambers before the fourth pump chamber 11.

Further, the intermediate exhaust conduit 30 connecting the outlet 28 of the third pump chamber 10 with the main outlet 4 and the main exhaust conduit 31 connecting the outlet 29 of the fourth pump chamber 11 with the main outlet 4 have the one-way valves 32 and 33 letting fluid flow to atmosphere respectively. Therefore, the atmospheric air does not flow back from the main outlet 4 via the exhaust conduits 30 and 31 even when the multistage dry vacuum pump 1 stops operation when the vacuum processing chamber connected to the multistage dry vacuum pump and the multistage dry vacuum pump via the main inlet 3 is in vacuo or decompressed. Accordingly, rapid worsening of degree of vacuum of the vacuum processing chamber and the multistage dry vacuum pump can be prevented. Further, contamination of the vacuum processing chamber and the multistage dry vacuum pump caused by flowing back of contaminated atmospheric air can be prevented. In addition, noise generated by the multistage dry vacuum pump when the fluid is compressed can partially be reduced by the one-way valves 32 and 33.

Further, each outlet of the multistage dry vacuum pump to the outside (atmosphere) is gathered together to single main outlet 4 via the confluent chamber 40 of the exhaust conduits. Therefore, all of the sucked fluid is exhausted from the main outlet 4. Accordingly, when connecting the outlet of the multistage dry vacuum pump with an exhaust duct or an exhausting device for exhaust fluid, the number of the required joints and pipes can be reduced and the installation of the multistage dry vacuum pump becomes easy.

According to an aspect of the present invention, the fluid sucked from the inlet is compressed in and transported into the each pump chamber connected in series from the upstream to the downstream by rotating the shaft connected with the plurality of the rotors at high speed and exhausted to the outside via the most downstream pump chamber and the main outlet. In this case, vacuum about from 1 to 100 Pa is generally required for pressure of the sucking. Therefore, the number of compressing steps (pumps connected in series) is usually 4-6 steps. As described above, in order to reduce compressing work, the scavenge volume of the each pump chamber is reduced in accordance with compression of the sucked fluid from the upstream to the downstream. However, when the sucking pressure of the first pump chamber (most upstream pump chamber) is relatively high, for example, at the pressure range exceeding 10000 Pa, the sucking pressure of the last pump chamber or the pump chamber before the last pump chamber, or the like, exceeds pressure of the outside (atmospheric pressure). Therefore, these pump chambers become just resistance for the fluid flow. As a result, the exhaust rate becomes low rapidly and electricity consumption becomes high.

On the other hand, according to the embodiments of the present invention, the multistage dry vacuum pump has the intermediate exhaust conduit, one end thereof connected with one or the plurality of pump chambers other than the last pump chamber (the pump chamber provided at the most downstream) and the fluid flow control means provided in the intermediate exhaust conduit for closing the intermediate exhaust conduit when the exhaust pressure of the multistage dry vacuum pump side is lower than pressure of the outside and for opening the intermediate exhaust conduit when the exhaust pressure of the multistage dry vacuum pump side is higher than pressure of the outside. Therefore, when the sucking pressure of the fluid of the first pump chamber (the pump chamber provided at the most upstream) is such high as equal to or higher than 10000 Pa and the sucking pressure of the later pump chamber exceeds pressure of the outside (atmospheric pressure), the sucked fluid is exhausted via the fluid flow control means. Therefore, the later pump chamber does not become resistance for the fluid flow. Accordingly, decrease of the exhaust rate becomes small and electricity consumption can be low.

In addition, the fluid flow control means described above can generally be a one-way valve letting fluid flow to atmosphere. The fluid flow control means can be an open/close valve opened and closed mechanically based on detected pressure.

According to another aspect of the present invention, flowing back of surrounding air (atmospheric air) through the exhaust conduit into the multistage dry vacuum pump and the vacuum processing chamber connected with the multistage dry vacuum pump can be prevented when the multistage dry vacuum pump is stopped. Therefore, vacuum break and contamination of the vacuum processing chamber can be prevented. Further, noise generated in the multistage dry vacuum pump by compressing the fluid can be shut and noise thereof can be reduced.

According to another aspect of the present invention, the multistage dry vacuum pump has one outlet to the outside thereof (atmosphere). Therefore, the number of joints and pipes used for connecting the outlet of the multistage dry vacuum pump with the exhaust duct can be reduced, which is advantageous for installing the multistage dry vacuum pump.

The principles, preferred embodiment and mode of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the sprit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.

Claims

1. A multistage dry vacuum pump, comprising: a housing having a main inlet and a main outlet; a plurality of pump chambers formed in the housing in series and spatially connecting the main inlet with the main outlet; each pump chamber having an inlet connected to upstream and an outlet connected to downstream; a plurality of rotors each rotatably provided in the each pump chamber for transporting fluid in a scavenging space defined in the pump chamber through the outlet of the pump chamber to the downstream by rotating; a shaft connected to each rotor provided in the each pump chamber for rotating the each rotor synchronously; a rotation driving means connected to the shaft; an intermediate exhaust conduit, one end thereof being connected to the outlet of the pump chamber located at other than the most downstream side and the other end thereof being opened to outside; and a first fluid flow control means provided in the intermediate exhaust conduit for closing the intermediate exhaust conduit when the fluid pressure in the one end of the intermediate exhaust conduit is lower than that in the other end of the intermediate exhaust conduit and for opening the intermediate exhaust conduit when the fluid pressure in the one end of the intermediate exhaust conduit is equal to or higher than that in the other end of the intermediate exhaust conduit.

2. The multistage dry vacuum pump according to claim 1, wherein a volume of the scavenging space defined in the each pump chamber becomes smaller sequentially from the pump chamber provided at the upstream side to the pump chamber provided at the downstream side.

3. The multistage dry vacuum pump according to claim 1, further comprising: a main exhaust conduit, one end thereof connected to the outlet of the pump chamber provided at the most downstream side, the other end thereof connected to the main outlet; and a second fluid flow control means provided in the main exhaust conduit for closing the main exhaust conduit when the fluid pressure in the one end of the main exhaust conduit is lower than that in the other end of the main exhaust conduit and for opening the main exhaust conduit when the fluid pressure in the one end of the main exhaust conduit is equal to or higher than that in the other end of the main exhaust conduit.

4. The multistage dry vacuum pump according to claim 2, further comprising: a main exhaust conduit, one end thereof connected to the outlet of the pump chamber provided at the most downstream side, the other end thereof connected to the main outlet; and a second fluid flow control means provided in the main exhaust conduit for closing the main exhaust conduit when the fluid pressure in the one end of the main exhaust conduit is lower than that in the other end of the main exhaust conduit and for opening the main exhaust conduit when the fluid pressure in the one end of the main exhaust conduit is equal to or higher than that in the other end of the main exhaust conduit.

5. The multistage dry vacuum pump according to claim 3, wherein the other end of the intermediate exhaust conduit is connected to the other end of the main exhaust conduit.

6. The multistage dry vacuum pump according to claim 4, wherein the other end of the intermediate exhaust conduit is connected to the other end of the main exhaust conduit.

7. A multistage dry vacuum pump comprising: a housing having a main inlet and a main outlet; a plurality of pump chambers formed in the housing in series and spatially connecting the main inlet with the main outlet, each pump chamber having an inlet connected to upstream side and an outlet connected to downstream side; drive and driven rotors provided rotatably in the each pump chamber, the drive rotor and the driven rotor transporting fluid in a scavenging space defined in the pump chamber through the outlet of the pump chamber to the downstream by synchronously rotating; a drive shaft connected to each drive rotor provided in the each pump chamber for synchronously rotating the each drive rotor; a driven shaft connected to each dependent rotor provided in the each pump chamber for synchronously rotating the each dependent rotor; a rotation driving means connected to the drive shaft; a transmitting means for transmitting rotation of the drive shaft to the driven shaft; an intermediate exhaust conduit, one end thereof being connected to the outlet of the pump chamber located at other than the most downstream side and the other end thereof being opened to outside; and a first fluid flow control means provided in the intermediate exhaust conduit for closing the intermediate exhaust conduit when the fluid pressure in the one end of the intermediate exhaust conduit is lower than that in the other end of the intermediate exhaust conduit and for opening the intermediate exhaust conduit when the fluid pressure in the one end of the intermediate exhaust conduit is equal to or higher than that in the other end of the intermediate exhaust conduit.

8. The multistage dry vacuum pump according to claim 7, wherein a volume of the scavenging space defined in the each pump chamber becomes smaller sequentially from the pump chamber provided at the upstream side to the pump chamber provided at the downstream side.

9. The multistage dry vacuum pump according to claim 7, further comprising: a main exhaust conduit, one end thereof connected to the outlet of the pump chamber provided at the most downstream side, the other end thereof connected to the main outlet; and a second fluid flow control means provided in the main exhaust conduit for closing the main exhaust conduit when the fluid pressure in the one end of the main exhaust conduit is lower than that in the other end of the main exhaust conduit and for opening the main exhaust conduit when the fluid pressure in the one end of the main exhaust conduit is equal to or higher than that in the other end of the main exhaust conduit.

10. The multistage dry vacuum pump according to claim 8, further comprising: a main exhaust conduit, one end thereof connected to the outlet of the pump chamber provided at the most downstream side, the other end thereof connected to the main outlet; and a second fluid flow control means provided in the main exhaust conduit for closing the main exhaust conduit when the fluid pressure in the one end of the main exhaust conduit is lower than that in the other end of the main exhaust conduit and for opening the main exhaust conduit when the fluid pressure in the one end of the main exhaust conduit is equal to or higher than that in the other end of the main exhaust conduit.

11. The multistage dry vacuum pump according to claim 9, wherein the other end of the intermediate exhaust conduit is connected to the other end of the main exhaust conduit.

12. The multistage dry vacuum pump according to claim 10, wherein the other end of the intermediate exhaust conduit is connected to the other end of the main exhaust conduit.

13. A multistage dry vacuum pump comprising: a housing having a main inlet and a main outlet; a plurality of pump chambers formed in the housing in series and spatially connecting the main inlet with the main outlet, each pump chamber having an inlet connected to upstream side and an outlet connected to downstream side; a plurality of rotors each rotatably provided in the each pump chamber for transporting fluid in a scavenging space defined in the pump chamber from the outlet of the pump chamber to the downstream by rotating; a shaft connected to each rotor provided in the each pump chamber for rotating the each rotor synchronously; a rotation driving means connected to the shaft; and a pressure adjusting means for adjusting the fluid pressure in the outlet side of the pump chamber to be equal to or lower than atmospheric pressure.

14. The multistage dry vacuum pump according to claim 13, wherein the pressure adjusting means adjusts the fluid pressure in the outlet side of the pump chamber equal to or lower than the atmospheric pressure by opening the outlet side of the pump chamber when the fluid pressure in the outlet side of the pump chamber is higher than the atmospheric pressure.

15. The multistage dry vacuum pump according to claim 14, wherein the pressure adjusting means includes an intermediate exhaust conduit, one end thereof being connected to the outlet of the pump chamber located at other than the most downstream side and the other end thereof being opened to outside; and a first fluid flow control means provided in the intermediate exhaust conduit for closing the intermediate exhaust conduit when the fluid pressure in the one end of the intermediate exhaust conduit is lower than that in the other end of the intermediate exhaust conduit and for opening the intermediate exhaust conduit when the fluid pressure in the one end of the intermediate exhaust conduit is equal to or higher than that in the other end of the intermediate exhaust conduit.

16. The multistage dry vacuum pump according to claim 13, wherein a volume of the scavenging space defined in the each pump chamber becomes smaller sequentially from the pump chamber provided at the upstream side to the pump chamber provided at the downstream side.

17. The multistage dry vacuum pump according to claim 15, further comprising: a main exhaust conduit, one end thereof connected to the outlet of the pump chamber provided at the most downstream side, the other end thereof connected to the main outlet; and a second fluid flow control means provided in the main exhaust conduit for closing the main exhaust conduit when the fluid pressure in the one end of the main exhaust conduit is lower than that in the other end of the main exhaust conduit and for opening the main exhaust conduit when the fluid pressure in the one end of the main exhaust conduit is equal to or higher than that in the other end of the main exhaust conduit.

18. The multistage dry vacuum pump according to claim 16, further comprising: a main exhaust conduit, one end thereof connected to the outlet of the pump chamber provided at the most downstream side, the other end thereof connected to the main outlet; and a second fluid flow control means provided in the main exhaust conduit for closing the main exhaust conduit when the fluid pressure in the one end of the main exhaust conduit is lower than that in the other end of the main exhaust conduit and for opening the main exhaust conduit when the fluid pressure in the one end of the main exhaust conduit is equal to or higher than that in the other end of the main exhaust conduit.

19. The multistage dry vacuum pump according to claim 15, wherein the other end of the intermediate exhaust conduit is connected to the other end of the main exhaust conduit.

20. The multistage dry vacuum pump according to claim 16, wherein the other end of the intermediate exhaust conduit is connected to the other end of the main exhaust conduit.