Single-stage and multi-stage roots pump

Abstract

 In the single-stage roots pump, in order to increase the compression ratio, three or more rotors (8,9,10) among 1st to n-th rotors forming one set, at least one of the air suction port (2b,2e) defined by the (n-2)th and (n-1)th rotors and the air suction port defined by the (n-1)th and n-th rotors being opened, the air discharging port (2d) defined by the (n-2)th and (n-1)th rotors being communicated with the air suction port (2e) defined by the (n-1)th and n-th rotors at the same side of an imaginary surface (FF) including the plurality of shafts, and the air discharging port defined by the (n-1)th and n-th rotors being opened.
In the multi-stage roots pump, in order to communicate the discharging port of the preceding stage pumping chamber and the air suction port of the succeeding stage pumping chamber, three or more rotors among the 1st to n-th rotors forming one set in the same set, in the pumping chamber of a frontmost stage, at least one of air suction port defined by the (n-2)th and (n-1)th rotors, and the air suction port defined by the (n-1) and n-th rotors being opened, and the air discharging port defined by the (n-1)th and n-th rotors being communicated with the air suction port defined by the (n-2)th and (n-1)th rotors of the pumping chamber of a succeeding step at the same side of an imaginary surface including the plurality of shafts, in the pumping chamber of each stage except for the frontmost stage and the rearmost stage, the air discharging port defined by the (n-2)th and (n-1)th rotors being communicated with the air suction port defined by the (n-1)th and n-th rotors at the same side of the imaginary surface, and in the pumping chamber of the rearmost stage the air discharging port defined by the (n-1)th and n-th rotors being opened.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] This invention relates to a single-stage roots pump driven by a rotary driving device such as motors and performing pumping operation by a single-stage pumping chamber; a single-stage pumping apparatus in which the single-stage roots pump and the rotary driving device are made integral; a multi-stage roots pump driven by a rotary driving device and performing a pumping operation in each stage sequentially; and a multi-stage pumping apparatus in which the multi-stage roots pump and the rotary driving device are made integral.

Related Background Art

[0002] In an conventional single-stage pumping apparatus, a single-stage roots pump and a motor are made integral. The single-stage roots pump has one pumping chamber provided with an air suction port and an air discharging port formed in a casing in which a pair of rotors mounted on two shafts are disposed in parallel to mesh with each other for rotation. In the casing, both of the air suction port and the air discharging port of the pumping chamber are opened. One of the shafts of the single-stage roots pump is connected with a driving shaft protruded from a main body of the motor. At a tip end of one shaft connected with the driving shaft of the motor, a driving gear is fixed to mesh with a driven gear fixed at a tip end of the other shaft of the single-stage roots pump for transmitting rotation.

[0003] In order to vacuum a chamber by using the above single-stage pumping apparatus for reducing pressure therein, the air suction port of single-stage roots pump is opened to the chamber and the air discharging port thereof is opened to an atmosphere. And the single-stage roots pump is driven by the motor. As a result, each of the rotors is meshed and rotated in the pumping chamber of the single-stage roots pump to perform the pumping operation, so that the air in the chamber is discharged to the atmosphere to realize reduced-pressure state of the chamber.

[0004] Meanwhile, in an conventional multi-stage pumping apparatus, a multi-stage roots pump and a motor are made integral. In the multi-stage roots pump, a plurality of pumping chamber each having an air suction port and an air discharging port in a casing thereof are formed in parallel. In each pumping chamber, a pair of (two) rotors are mounted on two parallel shafts to mesh with each other for rotation. The air suction port of the frontmost stage pumping chamber is opened in the casing. A partitioning wall relatively long in an axial direction is formed between the preceding (former) stage pumping chamber and the succeeding (next) stage pumping chamber, so the air discharging port of the preceding stage pumping chamber extends around the portitioning wall by about 180 degree to be sequentially communicated with the air suction port of the succeeding stage pumping chamber. The air discharging port of the rearmost stage pumping chamber is opened. On one the shafts of multi-stage roots pump, a driving shaft protruded from a main body of the motor for transmitting rotation is connected. At a tip end of one shaft connected with the driving shaft of the motor, a driving gear is fixed to mesh with a driven gear fixed at a tip end of another shaft of the multi-stage roots pump for transmitting rotation.

[0005] In order to vacuum a chamber by using the above multi-stage pumping apparatus for reducing pressure therein, the air suction port of the frontmost stage pumping chamber of the multi-stage roots pump is opened to the chamber, while the air discharging port of the rearmost stage pumping chamber thereof is opened to the atmosphere, and the multi-stage roots pump is driven by the motor. As a result, each of rotors are meshed and rotated in the pumping chamber of the multi-stage roots pump to perform the pumping operation, so that the air in the chamber is discharged to the atmosphere to realize reduced-pressure state of the chamber. However, in the above conventional single-stage roots pump or single-stage pumping apparatus, the pressurized air for the pumping operation is supplied by the single-stage roots pump but the paired rotors are disposed in one pumping chamber, which results in that the compression ratio of sufficiently high or large is hardly obtained. Thus, the vacuuming state can not be realized even by using the single stage roots pump or the single stage pumping apparatus.

[0006] On the other hand, in the above conventional multi-stage roots pump or multi-stage pumping apparatus, relatively large compression ratio can be obtained since the multi-stage roots pump has a plurality of pumping chambers to perform almost vacuuming state.

[0007] However, in the above conventional multi-stage roots pump or multi-stage pumping apparatus, for sequentially communicating the air discharging port of the preceding stage pumping chamber and the air suction port of succeeding stage pumping chamber, a communicating passage surrounding the pump or apparatus by about 180 degree is formed in a partitioning wall provided between the pumping chamber of the preceding stage and the pumping chamber of the succeeding stage. For this reason, the partitioning wall becomes longer in the axial direction, which makes axial length of the multi-stage roots pump or multi-stage pumping apparatus longer, so that a setting area (foot space) of the pump or apparatus is enlarged to make setting difficult.

[0008] It is of course possible in the multi-stage roots pump to sequentially communicate the air discharging port of the preceding stage and the air suction port of the succeeding stage by an added or extra pipe, as disclosed in the Japanese Patent Laid-open No.4-8891. However, arranging such pipe is troublesome to cause increase of the manufacturing cost.

Summary of the Invention

[0009] In view of the above, that first purpose of the present invention is to provided the single-stage roots pump or single-stage pumping apparatus in which large compression ratio can be obtained.

[0010] For achieving the above purpose, the single-stage roots pump according to the present invention comprises a casing forming one pumping chamber having air suction ports and air discharging ports; a plurality of motors mounted on a plurality of parallel shafts respectively to mesh with each other for rotation in the pumping chamber; three or more of said rotors among the 1st rotor to n-th rotor sequentially meshed with each other forming one set; at least one of the air suction port defined by the (n-2)th rotor and the (n-1)th rotor and the air suction port defined by the (n-1)th rotor and the n-th rotor being opened; the air discharging port defined by the (n-2)th rotor and the (n-1)th rotor being communicated with the air suction port defined by the (n-1)th rotor and the n-th rotor at the same side of an imaginary surface including the plurality of shafts for supporting the plurality of rotors; and the air discharging port defined by the (n-1)th rotor and the n-th rotor being opened.

[0011] In the above single-stage roots pump, the pumping operation is performed by supplying the pressurized air which is same as the conventional pump, but one set of the rotors (rotor means) comprised of three rotors is adopted different from the conventional pump. Provided that the sequentially meshed rotors are named as the 1st rotor, 2nd rotor ···(n-1)th rotor and n-th rotor, one pumping chamber has two or more air suction ports and two or more air suction ports. These air suction ports and air discharging ports are located, in the pumping chamber, so that one or more air suction port(s) and one or more air discharging port(s) are located at both of one side and other side of imaginary surface defined by a plurality of shafts for supporting the rotors. In addition, in this pumping chamber, both of the air suction port and the air discharging port are adjacently presented at the same side of the imaginary surface.

[0012] In connection with the above, at least one of the air suction port defined by the (n-2)th rotor and the (n-1)the rotor and the air suction port defined by the (n-1)th rotor and the n-th rotor is opened. Also, the air discharging port defined by the 1st rotor and the second rotor can be communicated with the air suction port defined by the 2nd rotor and the 3rd rotor at the same side of the imaginary surface. Likewisely, the air discharging port defined by the (n-2)the rotor and the (n-1)th rotor can be communicated with the air suction port defined by the (n-1)th rotor and the n-th rotor at the same side of the imaginary surface. And the air discharging port defined by the (n-1)th rotor and the n-th rotor is opened.

[0013] Thus, a plurality of pumping operations can be performed in one pumping chamber in this single-stage roots pump, so that the compression ratio can be set larger to increase the pumping operation for vacuuming.

[0014] When two or more air suction ports including the air suction port defined by the (n-2)th rotor and the (n-1)th rotor and the air suction port defined by the (n-1)th rotor and the n-th rotor are opened in the single-stage roots pump, the number of the initial air suction ports is increased to raise the pumping operation such as the vacuuming.

[0015] When one set of the rotors is comprised of three or more rotors, if the rotors of even number constitute one set, one of the number of the air suction port or the air discharging port become large than the other of them by one in one pumping chamber at the same side of the imaginary surface defined by the plurality of shafts. Here, the paired air suction port and the air discharging port can be communicated with each other at the same side of the imaginary surface, but the first air suction port and the last air discharging port are located at the opposite side relative to the imaginary surface. In order to avoid such location, it is necessary to provide the communicating path surrounding the pump or apparatus by about 180 degrees or to attach the pipe.

[0016] On the other hand, when the rotors of odd number constitute the one set, the air suction port and the air discharging port of the same number are presented in the pumping chamber at the same side of the imaginary surface. Here, the first air suction port and the last air discharging port are located at the same side of the imaginary surface, so that the surrounding communicating path or the pipe attachment need not be provided, which results in good appearance of the apparatus.

[0017] In communicating the air discharging port defined by the (n-2)th rotor and the (n-1)the rotor and the air suction port defined by the (n-1)th rotor and the n-th rotor at the same side of the imaginary surface including a plural shafts, it is possible to communicate them sequentially by the attached pipe. However, communicating the air discharging port and the air suction port by a communicating groove formed on the casing is preferable to omit the pipe attachment.

[0018] The single-stage pumping apparatus is comprised of said single-stage roots pump and a rotary driving device having a driving main body and a driving shaft protruded from the driving main body. Here, a timing gear train comprised of a driving gear fixed to the driving shaft of said rotary driving device and driven gears fixed to each of the shafts for supporting the rotors of said single-stage roots pump to be driven by the driving gear is interposed between said single-stage roots pump and said rotary driving device.

[0019] In the single stage pumping apparatus in which the single stage roots pump and the rotary driving device such as the motor are made integral. So, a driving force transmitted from a driving shaft of the rotary driving unit is converted to rotation of each rotor via the a timing gear train comprised of a driving gear and driven gears, and each of the shafts. Consequently, any slipping occurred in driving the pump by the belt will not occur, and influence of the shaft torsion in the single-stage roots pump is small, so that the driving force of the rotary driving device can be easily converted to rotation of all rotors in each pumping chamber. Thus, the pumping operation can be performed smoothly in the pumping chambers.

[0020] Another purpose of the present invention is provide the multi-stage roots pump or multi-stage pumping apparatus which can reduced the manufacturing cost and can make setting thereof easier.

[0021] The first type multi-stage roots pump according to the present invention comprises a casing forming a plurality of parallel pumping chambers each having air suction ports and air discharging ports, and plurality of rotors mounted on a plurality of parallel shafts to be meshed with each other for rotation in each of said pumping chambers. The pump is characterized by that three or more rotors among the 1st rotor to n-th rotor sequentially meshed form one set in the same set; in the pumping chamber of a frontmost stage, at least one of air suction port defined by the (n-2)th rotor and the (n-1)th rotor, and the air suction port defined by the (n-1) the rotor and the n-th rotor is opened, and the air discharging port defined by the (n-1)th rotor and the n-th rotor is communicated with the air suction port defined by the (n-2)th rotor and the (n-1)th rotor of the pumping chamber of a succeeding step at the same side of an imaginary surface including the plurality of shafts; in the pumping chamber of each stage except for the frontmost stage and the rearmost stage, the air discharging ports defined by the (n-2)th rotor and the (n-1)th rotor is communicated with the air suction port defined by the (n-1)th rotor and the n-th rotor at the same side of the imaginary surface; and in the pumping chamber of the rearmost stage the air discharging port defined by the (n-1)th rotor and the n-th rotor is opened.

[0022] When the multi-stage roots pump adopts one or more set(s) of rotors each of which is comprised of three or more rotors, two or more air suction ports and two or more air discharging ports are presented in the pumping chamber of each (same) stage. Among these air suction ports and air discharging ports, one or more air suction ports and one or more air discharging port are located in the pumping chamber of same stage, at both of one side and the other side of the imaginary surface, and are necessarily located adjacent to each other at the same side of the imaginary surface.

[0023] For this reason, in the frontmost stage pumping chamber, at least one of the air suction port defined by the (n-2)th rotor and the (n-1)th rotor, and the air suction port defined by the (n-1)therotor and the n-th rotor is opened; and the air discharging port defined by the (n-1)th rotor and the n-th rotor can be communicated with the an suction port defined by the (n-2)the rotor and the (n-1)the rotor in the pumping chamber of the succeeding stage at the same side of the imaginary surface. Here "succeeding stage" includes next stage and stage(s) succeeding thereto.

[0024] Also, in the pumping chamber of the each stage except for the frontmost stage and the rearmost stage, the air discharging port defined by the 1st rotor and the 2nd rotor can be communicated with the air suction port defined by the 2nd rotor and the 3rd rotor at the same side of the imaginary surface. Sequentially, the air discharging port defined by the (n-2)the rotor and the (n-1)the rotor can be communicated with the air suction port defined by the (n-1)th rotor and n-th rotor at the same side of the imaginary surface.

[0025] In the rearmost stage pumping chamber, the air discharging port defined by the (n-1)th rotor and the n-th rotor is opened.

[0026] Thus, there is no need to provide the communicating path surrounding the pump or apparatus by 180 degrees to extend between the preceding stage pumping chamber and the succeeding stage pumping chamber for communication therebetween, or the long partitioning wall containing the communicating path, different from the conventional art. Alternately, it is enough for the pump to form the partitioning wall between the pumping chamber of the preceding stage and the pumping chamber of the succeeding stage as the mere partition. As a result, on account of shortened axial length of the pump, the foot space can be minimized and setting of the pump or apparatus can be made easier.

[0027] In communicating the air discharging port of the preceding stage with the air suction port of the succeeding stage sequentially at the same side of the imaginary surface, it is of course possible to use the attached pipes. Even in such case, since the pipes are located at the same side of the imaginary surface, the pipe arrangement becomes easier to reduce the manufacturing cost. Thus, according to the first type multi-stage roots pump, setting of the pump or apparatus becomes easier on account of the minimized foot space.

[0028] In the multi-stage roots pump, when two or more air suction ports among the air suction port defined by the (n-2)th rotor and the (n-1)th rotor and the air suction port defined by the (n-1)th rotor and the n-th rotor are opened, the number of the initial air suction ports is increased so that the pumping effect such as the vacuuming can be improved.

[0029] The second type multi-stage roots pump according to the present invention comprises a casing forming a plurality of parallel pumping chambers each having air suction ports and air discharging ports, and plurality of rotors mounted on a plurality of parallel shafts to be meshed with each other for rotation in each of said pumping chambers. The pump is characterized by that three or more rotors among a 1st rotor to n-th rotor sequentially meshed from one set in the same set; in the pumping chambers of each stage except for the rearmost stage forming a continuous stage, at least two of suction port defined by the (n-2)th rotor and the (n-1)th rotor and the air suction port defined by the (n-1) the rotor and the n-th rotor are opened, and the air discharging port defined by the (n-2)th rotor and the (n-1)th rotor and the air discharging port defined by the (n-1)th rotor and the n-th rotor are respectively communicated with the air suction port defined by the (n-2)th rotor and the (n-1)th rotor of the pumping chamber of a succeeding step at the same side of an imaginary surface including the plurality of shafts; in the pumping chamber of each stage except for the frontmost stage and the rearmost stage, the air discharging port defined by the (n-2)th rotor and the (n-1)th rotor is communicated with the air suction port defined by the (n-1)th rotor and the n-th rotor at the same side of the imaginary surface; and in the pumping chamber of the rearmost stage, the air discharging port defined by the (n-1)th rotor and the n-th rotor is opened.

[0030] In the second type multi-stage roots pump, in the pumping chamber of the same stage constituting the continuous stages including the frontmost stage but excepting the rearmost stage, at least two air suction ports, one of which is defined by the (n-2)th rotor and the (n-1)th rotor and other of which is defined by the (n-1)th rotor and the n-th rotor, are opened. Also in that same stage pumping chamber, the air discharging port defined by the (n-2)th rotor and the (n-1)th rotor and the air discharging port defined by the (n-1)th rotor and the n-th rotor can be respectively communicated with the air suction port defined by the (n-2)th rotor and the (n-1)th rotor of the succeeding stage pumping chamber, at the same side of the imaginary surface. Here "succeeding stage" includes the next stage and the stage(s) succeeding thereto.

[0031] In the pumping chamber of the same stage except for the frontmost stage and the rearmost stage, the air discharging port defined by the (n-2)th rotor and the (n-1)th rotor can be communicated with the air suction port defined by the (n-1)th rotor and the n-th rotor at the same side of the imaginary surface. In the rearmost stage pumping chamber, the air discharging port defined by the (n-1)th rotor and the n-th rotor is opened.

[0032] Thus, the increased number of the initial air suction ports in the multi-stage roots pump can improve the pumping effect such as the vacuuming.

[0033] When one set of the rotors is comprised of three or more rotors, if the rotors of even number constitute one set, one of the number of the air suction port or the air discharging port become large than the other of them by one in the pumping chamber of the same stage at the same side of the imaginary surface defined by the plurality of shafts. Here, the paired air suction port and the air discharging port can be communicated with each other at the same side of the imaginary surface, but the first air suction port and the last air discharging port are located at the opposite side relative to the imaginary surface. For this reason, it is necessary to provide the communicating path surrounding the pump or apparatus by about 180 degrees or to attach the pipe.

[0034] On the other hand, when the rotors of odd number constitute the one set, the air suction port and the air discharging port of the same number are presented in the pumping chamber of the same stage at the same side of the imaginary surface. Here, the first air suction port and the last air discharging port are located at the same side of the imaginary surface, so that the surrounding communicating path or the pipe attachment need not be provided, which results in good appearance of the apparatus.

[0035] In communicating the air discharging port defined by the (n-2)th rotor and the (n-1)the rotor and the air suction port defined by the (n-1)th rotor and the n-th rotor at the same side of the imaginary surface including a plural shafts, it is possible to communicate them sequentially by the attached pipe. However, communicating the air discharging port and the air suction port by a communicating groove formed on the casing is preferable to omit the pipe attachment.

[0036] In any way, both of the first and second type multi-stage roots pump has common feature that in the pumping chamber of each stage except for the frontmost stage and the rearmost stage, the air discharging port defined by the (n-2)th rotor and the (n-1)th rotor is communicated with the air suction port defined by the (n-1)th rotor and the n-th rotor at the same side of the imaginary surface.

[0037] The third type multi-stage roots pump according to the present invention comprises a casing forming a plurality of parallel pumping chambers each having air suction ports and air discharging ports, and a plurality of rotors mounted on the plurality of shafts respectively to mesh with each other in the pumping chamber. The pump is characterized by that three or more rotors forming one set; the air suction port of the frontmost stage pumping chamber being opened; the air discharging port of the preceding stage pumping chamber is sequentially communicated with the air suction port of the succeeding stage pumping chamber at the same side of an imaginary surface including the plurality of shafts; and the air discharging port of the rearmost stage pumping chamber being opened, in the casing.

[0038] When the multi-stage roots pump adopts one or more set(s) of rotors each of which is comprised of three or more rotors, two or more air suction ports and two or more air discharging ports are presented in the pumping chamber of each (same) stage. Among these air suction ports and air discharging ports, one or more air suction ports and one or more air discharging port are located in the pumping chamber of same stage, at both of one side and the other side of the imaginary surface, and are necessarily located adjacent to each other at the same side of the imaginary surface.

[0039] Thus, in both of the pumping chambers of the preceding stage and the pumping chamber of the succeeding stage, one or more air suction port(s) and one or more air discharging port(s) are necessarily presented at the same side of the imaginary surface, so that the air discharging port of the preceding stage pumping chamber and the air suction port of the succeeding stage pumping chamber can be sequentially communicated at the same side of the imaginary surface.

[0040] Thus, there is no need to provide the communicating path surrounding the pump or apparatus by 180 degrees between the preceding stage pumping chamber and the succeeding stage pumping chamber, or the long partitioning wall containing the communicating path. Alternately, it is enough for the apparatus to form the partitioning wall between the pumping chamber of the preceding stage and the pumping chamber of the succeeding stage as the mere partition. As a result, on account of shortened axial length of the pump, the foot space can be minimized and setting of the pump or apparatus can be made easier.

[0041] Even when the pipe is used in communicating the air discharging port of the preceding stage with the air suction port of the succeeding stage sequentially at the same side of the imaginary surface, since the pipes are located at the same side of the imaginary surface, the pipe arrangement becomes easier to reduce the manufacturing cost.

[0042] Thus, according to the third type multi-stage roots pump, setting of the pump or apparatus becomes easier on account of the minimized foot space.

[0043] When one set of the rotors is comprised of three or more rotors, if the rotors of even number constitute one set, one of the number of the air suction port or the air discharging port become large than the other of them by one in the pumping chamber of the same stage at the same side of the imaginary surface. Here, the paired air suction port and the air discharging port can be communicated with each other at the same side of the imaginary surface, but the first air suction port and the last air discharging port are located at the opposite side relative to the imaginary surface.

[0044] On the other hand, when the rotors of odd number constitute the one set, the air suction port and the air discharging port of the same number are presented in the pumping chamber of the same stage at the same side of the imaginary surface. Here, the first air suction port and the last air discharging port are located at the same side of the imaginary surface, so that the surrounding communicating path or the pipe attachment need not be provided, which results in good appearance of the apparatus.

[0045] In communicating the air discharging port defined by the (n-2)th rotor and the (n-1)the rotor and the air suction port defined by the (n-1)th rotor and the n-th rotor at the same side of the imaginary surface including a plural shafts. So, it is possible and preferable to form communicating groove on the casing to omit the pipe attachment.

[0046] In the multi-stage pumping apparatus which a is comprised of the 1st to 3rd type multi-stage roots pump and the driving device such as the motor, the air suction port of the frontmost stage pumping chamber and the air discharging port of the rearmost stage pumping chamber are separated away to large extent, which means the air suction port of the frontmost stage pumping chamber or the air discharging port of the rearmost stage pumping chamber is located at the position closest to the timing gear train. With respect to this, the air discharging port of the rearmost stage pumping chamber is preferably opened at the point closest to the timing gear train.

[0047] According to such location or arrangement, the air suction port of the frontmost stage pumping chamber is opened at the position most remote from the timing gear training, so that the oil attached to the timing gear train will not scatter in the chamber where the air suction port is opened. Thus, pressure of the chamber can be reduced with maintaining environment therein.

Brief Explanation of the Drawings

[0048] 

Fig. 1 is a front cross-sectional view of a single-stage pumping apparatus according to a first embodiment;

Fig. 2 is a cross-sectional view along line 2-2 of Fig. 1;

Fig. 3 is a plan view of the first embodiment;

Fig. 4 is a plan view of a lower plate used in the first embodiment;

Fig. 5 is a schematic view for explaining an air-flow in the first embodiment;

Fig. 6 is a schematic view for explaining an air-flow in a single-stage pumping apparatus according to a second embodiment;

Fig. 7 is a front cross-sectional view of a multi-stage pumping apparatus according to a third embodiment;

Fig. 8 is a cross-sectional view along line 8-8 of Fig. 7;

Fig. 9 is a plan view of the third embodiment;

Fig. 10 is a plan view of a lower plate used in the third embodiment;

Fig. 11 is a schematic view for explaining an air-flow in the third embodiment;

Fig. 12 is a front cross-sectional view of a multi-stage pumping apparatus according to a fourth embodiment;

Fig. 13 is a plan view of the fourth embodiment;

Fig. 14 is a plan view of a lower plate used in the fourth embodiment;

Fig. 15 is a schematic view for explaining an air-flow in the fourth embodiment;

Fig. 16 is a front cross-sectional view of a multi-stage pumping apparatus according to a fifth embodiment;

Fig. 17 is a cross-sectional view along line 17-17 of Fig. 16;

Fig. 18 is a plan view of the fifth embodiment;

Fig. 19 is a plan view of a lower plate used in the fifth embodiment;

Fig. 20 is a schematic view for explaining an air-flow in the fifth embodiment; and

Fig. 21 is a cross-sectional view showing deformation of Figs. 2, 8 and 17.

Detailed Explanation of the Preferred Embodiments

〈First Embodiment〉

[0049] In a single-stage pumping apparatus shown in Figs. 1 and 2, a single-stage roots pump P is combined with a motor M integrally. In the single-stage roots pump P as shown in Fig. 1, a front housing 1, a first and second cylinder blocks 2 and 3, and a rear housing 4 are accumulated or stacked via sealing member (not shown), and are connected to each other by bolts (not shown) to form a part of a casing.

[0050] Through the front housing 1, first and second cylinder blocks 2 and 3, and rear housing 4, three axial holes are formed in parallel and horizontally. A first, second and third shafts 5, 6 and 7 are inserted into each axial hole so that axes thereof form a flat plane-like imaginary surface F-F. In circular axial holes formed in the front housing 1, bearings 1a to 1c for supporting the first to third shafts 5 to 7 are provided.

[0051] As shown in Fig. 2 in the front cylinder block 2, a pumping chamber 2a comprised of three circular chamber sections centers of which are located on one line so that adjacent parts are overlapped partially with each other is formed at the rear side. A groove (not shown) is formed on an inner surface of the pumping chamber 2a to receive the O-ring. In a right, center and left sections of the pump chamber 2a, a first rotor 8 mounted on the first shaft 5, second rotor 9 mounted on the second shaft 6, and third rotor 10 mounted on the third shaft 7 are respectively provided. Each of the rotors 8, 9 and 10 has four-leaves shape to be meshed with each other for rotation and form one set. At a portion of an upper wall located between the section for a first rotor 8 and a section for the second rotor 9, an air suction port 2b is formed, and at a portion of the upper wall located between the section for the second rotor 9 and a section for the third rotor 10, an air discharging port 2c is formed respectively, in a vertical direction. On a lower wall of the pump chamber 2a, an air discharging port 2d and an air suction port 2e are formed at portion located between a section for the first and second rotors 8 and 9, and a portion located between the second and third rotors 9 and 10, respectively.

[0052] As shown in Fig. 1, in the second cylinder block 3, a gear chamber 3a having similar shape to the above gear chamber 2a is formed at a rear side, around which a groove for receiving the O-ring is provided. In the gear chamber 3a, on the second shaft 6 positioned in the center section a drive gear 11 is mounted, and on the first and third shafts 5 and 7 positioned in the right and left sections driven gears 12 and 13 are mounted respectively to mesh with the drive gear 11 and forming a timing gear train.

[0053] In each of axial holes of the rear housing 4, bearings 4a to 4c for supporting the first to third shafts 5 to 7 are provided. To the rear housing 4, a drive main body 14 of the motor M is fixed by bolts (not shown) from which a driving shaft 6 is protruded to be connected with the second shaft 6 by a coupling (not shown).

[0054] As shown in Figs. 2 and 3, on an upper surfaces of the front housing 1, first and second cylinder blocks 2 and 3, and rear housing 4, an upper plate 16 is mounted via a gasket 15 and connected with them by bolts (not shown). As shown in Figs. 2 and 4, on a lower surfaces of the front housing 1, first and second cylinder blocks 2 and 3, and rear housing 4, a lower plate 18 is mounted via a gasket 17 and connected with them by bolts (not shown).Thus, the upper and lower plates 16 and 18 form a remaining part of the casing.

[0055] As shown in Figs. 2 and 3, through the upper plate 16, an air suction port 16a communicating with the suction port 2b of the first cylinder block 2, and an air discharging port 16b communicating with the discharging port 2c of the first cylinder block 2 are respectively formed vertically. As shown in Figs. 2 and 4, on a surface of the lower plate 18, a communicating groove 18a for communicating the discharging port 2d and the suction port 2e of the first cylinder block 2 is formed orthogonal to the shafts 5 to 7.

[0056] Thus, the single-stage pumping apparatus including the single-stage roots pump which adopts the first to third rotors 8 to 10 forming one set of the rotors to have the smallest diameter is realized.

[0057] When this single-stage pumping apparatus is used to vacuum a chamber for reducing pressure therein, the air sucking chamber 16a on the upper plate 16 is communicated with the chamber via a hose and the like, while the air discharging port 16b on the upper plate 16 is opened to the atmosphere via a hose and the like, as shown in Fig. 5, and the single-stage roots pump P is driven by the motor M. As a result, the rotor 8, 9 and 10 rotate in the pumping chamber 2a of the single-stage roots pump P with meshing with each other to perform pumping operation sequentially therein, so that air in the chamber is discharged to the atmosphere to realize the pressure-reduced condition thereof.

[0058] Here, in this single-stage pumping apparatus, since one set of rotor (rotor means) comprised of three (odd number of) rotors 8 to 10 is adopted, two air suction ports 2b, 2e and two air discharging ports 2d, 2c are provided for the pumping chamber 2a. Especially, above the imaginary surface F-F defined by axes of the first to third shafts 5 to 7, one suction port 2b and one discharging port 2c are necessarily presented in an adjacent relation, while below the imaginary surface one suction port 2e and one discharging port 2d are necessarily presented in the adjacent relation. Therefore, a linear short communicating groove 18a provided on a surface of the lower plate 18 can easily communicate the air discharging port 2d and air suction port 2e of the pumping chamber 2a with each other below the imaginary surface F-F without using any pipe attachment and the like.

[0059] As mentioned above, in this single-stage pumping apparatus, plural pumping operations performed in one pumping chamber 2a can increase the compression ratio to perform effective vacuuming. In addition, the air suction port 2b and air discharging port 2c of this single-stage pumping apparatus formed by penetrating through the upper plate 16 can render good appearance.

[0060] Also, in this single-stage pumping apparatus, the driving force from the driving shaft of motor M is transmitted and converted through a timing gear train comprised of a driving gear 11 and driven gears 12 and 13, and the first to third shafts, finally to the first to third rotors 5 to 7. Accordingly, not only any slipping occurring in belt driving system will not occur, but the first to third shafts will not be twisted on account of short distance between supported portion at both ends and the center portion where the gear is mounted. Consequently, driving force of the motor M can easily converted to rotation of the first to third rotors 5 to 7 in the pumping chamber 2a to perform the pumping operation smoothly.

〈2nd Embodiment〉

[0061] In the single-stage pumping apparatus, as shown in Fig. 6, one set of rotors is comprised of four (first to fourth) rotors (not shown).

[0062] As a result, in this pumping chamber 2a, two air suction ports 2f and 2j, and one air discharging ports 2i are presented above the imaginary surface F-F, while one air suction port 2h, and two air discharging ports 2g and 2k are presented below the imaginary surface F-F. Here, paired air suction port 2j and the air discharging port 2i, and paired air suction port 2h and air discharging port 2g are located at same side of the imaginary surface F-F, so that they can be communicated with each other at the each side of the imaginary surface. However, the first air suction port 2f and the last air discharging port 2k are positioned at opposite side of the imaginary surface F-F. In order to avoid such positioning, some communicating passage surrounding the pumping apparatus by about 180 degree, or same pipe attachment becomes necessary.

〈3rd Embodiment〉

[0063] A multi-stage pumping apparatus is shown in Figs. 7 to 11. As shown in Figs. 7 and 8, a multi-stage roots pump P is combined with a motor M integrally. In the multi-stage roots pump P as shown in Fig. 7, a front housing 21, a first, second, third, fourth and fifth cylinder blocks 22, 23, 24, 25 and 26, and a rear housing 27 are accumulated via sealing member (not shown), and are connected to each other by bolts (not shown) to form a part of a casing.

[0064] Through the front housing 21, first to fifth cylinder blocks 22 to 26 and rear housing 27, three axial holes are formed in parallel and horizontally. A first, second and third shafts 28, 29 and 30 are inserted into each axial hole so that axes thereof form a flat plane-like imaginary surface F-F. In circular axial holes formed in the front housing 21, bearings 21a to 21c for supporting the first to third shafts 28 to 30 are provided.

[0065] In the first to fourth cylinder block 22 to 25, as shown in Fig. 8 for the third cylinder block 24, a pumping chamber 24a having the same shape as that of the first embodiment is formed at the rear side, and a groove (not shown) is formed on an inner surface thereof to receive the O-ring. In a right, center and left sections of the pump chamber 24a, a first rotor 31 mounted on the first shaft 28, second rotor 32 mounted on the second shaft 29, and third rotor 33 mounted on the third shaft 30 are respectively provided. These rotors 31, 32 and 33 have four-leaves shape to be meshed with each other for rotation and form one set. At a portion of an upper wall located between the section for a first rotor 31 and a section for the second rotor 32, an air suction port 24b is formed, and at a portion of the upper wall located between the section for the second rotor 32 and a section for the third rotor 33, an air discharging port 24c is formed respectively, in a vertical direction. On a lower wall of the pump chamber 24a, an air discharging port 24d and an air suction port 24e are formed at portion located between a section for the first and second rotors 31 and 32, and a portion located between the second and third rotors 32 and 33, respectively.

[0066] For the first, second and fourth cylinder blocks 22, 23 and 25, pumping chambers 22a, 23a and 25a of three partially overlapped circles shape are formed at rear side thereof, on an upper wall and a lower wall of which air suction ports 22b, 22e; 23b, 23e; 25b and 25e, and air discharging ports 22c, 22d; 23c, 23d; 25c, 25d are formed vertically, as shown in Figs. 8, 9 and 11. Thus, in the pumping chambers 22a, 23a, 24a and 25a of each stage, two air suction ports 22b, 22e; 23b, 23e; 24b, 24e and 25b, 25e, and two air discharging ports 22d, 22c; 23d, 23c; 24d, 24c; and 25d, 25c are necessarily presented. In the pumping chamber 22a, 23a and 25a, first to third rotors 34 to 36, 37 to 39 and 39 to 42 are disposed. Here, the frontmost stage pumping chamber 22a of the first cylinder block 22 is longest, the pumping chamber 23a and 24a of the second and third cylinder blocks 23 are 24 secondary and thirdly longest respectively, and the rearmost-stage pumping chamber 25a of the fourth cylinder block 25 in shortest. Corresponding to axial length of the pumping chambers 22a, 23a, 24a and 25a, axial lengths of the first to third rotors 31 to 33, 34 to 36, 37 to 39 and 40 to 42 are different from each other.

[0067] As shown in Fig. 8, in the fifth cylinder block 26, a gear chamber 26a having similar shape to the above pumping chamber 22a is formed at a rear side, around which a groove for receiving the O-ring is provided. In the gear chamber 36a, on the second shaft 29 positioned in the center section a drive gear 43 is mounted, and on the first and third shafts 28 and 30 positioned in the right and left sections driven gears 44 and 45 are mounted respectively to mesh with the drive gear 43 and forming a timing gear train.

[0068] In each of axial holes of the rear housing 27, bearings 27a to 27c for supporting the first to third shafts 28 to 30 are provided. To the rear housing 27, a drive main body 46 of the motor M is fixed by bolts (not shown) from which a driving shaft is protruded to be connected with the second shaft 29 by a coupling (not shown).

[0069] As shown in Figs. 8 and 9, on an upper surfaces of the front housing 21, first to fifth cylinder blocks 22 to 26 and rear housing 27, an upper plate 48 is mounted via a gasket 47 and connected with them by bolts (not shown). As shown in Figs. 8 and 10, on a lower surfaces of the front housing 21, first to fifth cylinder blocks 22 and 26 and rear housing 27, a lower plate 50 is mounted via a gasket 49 and connected with them by bolts (not shown). Thus, the upper and lower plates 48 and 50 form a remaining part of the casing.

[0070] As shown in Fig. 9, through the upper plate 48, an air suction port 48a communicating with the suction port 22b of the first cylinder block 22, and an air discharging port 48b communicating with the air discharging port 25c of the first cylinder block 25 are respectively formed vertically. Also, on a rear surface of the upper plate 48, an oblique communicating groove 48c for communicating the air discharging port 22c of the first cylinder block 22 and the suction port 23b of the second cylinder block 23, an oblique communicating groove 48d for communicating the air discharging port 23c of the second cylinder block 23 and the air suction port 24b of the third cylinder block 24, and an oblique communicating groove 48e for communicating the discharging port 24c of the third cylinder block 24 and the suction port 25b of the fourth cylinder block 25 are formed, respectively.

[0071] Likewisely, as shown in Fig. 10 , on a front surface of the lower plate 50, an oblique communicating groove 50a for communicating the air discharging port 22d and the suction port 22e of the first cylinder block 22, an oblique communicating groove 50b for communicating the air discharging port 23d and the air suction port 23e of the second cylinder block 23, and an oblique communicating groove 50c for communicating the discharging port 24d and the suction port 24e of the third cylinder block 24, and an oblique communicating groove 50d for communicating the discharging port 25d and the suction port 25e of the fourth cylinder block 25 are respectively provided. Here, all of the communicating grooves 50a to 50d are orthogonal to the shafts 28 to 30.

[0072] Thus, the multi-stage pumping apparatus including the multi-stage roots pump which adopts the first to third rotors 31 to 33, 34 to 36, 37 to 39 and 40 to 42 each forming one set of the rotors to have the smallest diameter is realized.

[0073] When this multi-stage pumping apparatus is used to vacuum a chamber to reduce pressure therein, the air sucking chamber 48a on the upper plate 48 is communicated with the chamber via a hose and the like, while the air discharging port 48b on the upper plate 48 is opened to the atmosphere via a hose and the like, as shown in Fig. 11, and the multi-stage roots pump P is driven by the motor M. As a result, the rotor 31 to 42 rotate in each of the pumping chambers 22a, 23a, 24a and 25a of the multi-stage roots pump P with meshing with each other to perform pumping operation sequentially, so that air in the chamber is discharged to the atmosphere to realize the pressure-reduced condition thereof.

[0074] Here, in this multi-stage pumping apparatus, four sets of rotor (rotor means) each of which is comprised of three (odd number of) rotors 31 to 33, 34 to 36, 37 to 39 and 40 to 42 are adopted. As a result, the air suction ports 22b, 22e; 23b, 23e; 24b, 24e; and 25b, 25e, and the air discharging ports 22d, 22c; 23d, 23c; 24d, 24c; and 25d, 25c are arranged so that at both of above and below sides of the imaginary surface including the shafts 28 to 30, one air suction port and one air discharging port are necessarily presented in the pumping chambers 22a, 23a, 24a and 25s of each stage. In addition, in the pumping chambers 22a, 23a, 24a and 25a of each stage, the air suction ports 22b, 22e, 23b, 23e, 24b, 24e, 25b and 25e are necessarily positioned adjacent to the air discharging ports 22d, 22c, 23d, 23c, 24d, 24c, 25d and 25d, respectively.

[0075] Therefore, communicating grooves 48c, 48d and 48e formed on a rear surface of the upper plate 48 can communicate the discharging ports 22c, 23c and 24c of the preceding-stage pumping chambers 22a, 23a and 24a with the suction ports 23b, 24b and 25b of the succeeding-stage pumping chambers 23a, 24a and 25a sequentially above the imaginary surface F-F easily without using the pipe attachment. Likewisely, communicating grooves 50a, 50b and 50c formed on a front surface of the lower plate 50 can communicate the discharging ports 22d, 23d, 24d and 25d with the air suction ports 22e, 23e, 24e and 25e sequentially in each of the stages below the imaginary surface F-F easily without using the pipe attachment.

[0076] Accordingly, there is no need to form relatively long partitioning walls disposed between the pumping chambers 22a, 23a and 24a of the preceding stage and the pumping chambers 23a, 24a and 25a of the succeeding stage and having the communicating passage surrounding the pumping apparatus by about 180 degrees, which is absolutely necessary in the conventional art. Alternatively, as shown in Fig. 8, it is enough to form the partitioning walls 23f, 24f and 25f between the preceding pumping chambers 22a, 23a and 24a and the succeeding pumping chambers 23a, 24a and 25a, as the mere partitions, which can make axial length of the multi-stage roots pump shorter. As a result, foot space can be minimized to make setting of the multi-stage pumping apparatus easier and to reduce the manufacturing cost thereof.

[0077] Also, in this multi-stage pumping apparatus, the driving force from the driving shaft of the motor M is transmitted and converted through the timing gear train comprised of a driving gear 43 and driven gears 44 and 45, and the first to third shafts 28 to 30, to four sets of the first to third rotors 31 to 42. Accordingly, not only any slipping occurring in belt driving system will not occur, but the first to third shafts 28 to 30 will not be twisted on account of short distance between the both end portions supported by the bearings and the center portion where the gears 43 to 45 are mounted. Consequently, driving force of the motor M can easily converted to rotation of the first to third rotors 31 to 42 in each of the pumping chambers 22a to 25a 2a to perform the pumping operation smoothly.

[0078] Further, in this multi-stage pumping apparatus, the suction port 48a is opened at position furthest from the timing gear train while the discharging port 48b is opened at position nearest thereto, which means they are spaced to the maximum, so that lubricating oil on the timing gear train is prevented from scattering in the chamber to which the suction port 48a is opened. Thus, pressure in the chamber can be reduced with maintaining good environment condition.

〈4th Embodiment〉

[0079] The multi-stage pumping apparatus of this embodiment differs from that of the third embodiment, in construction of the front housing 51, upper and lower plates 52 and 53, as shown in Figs. 12 to 15.

[0080] In detail, as shown in Fig. 12, through a front housing 51 an air suction port 51a is formed vertically. Also, as shown in Fig. 13, at a front end and a rear surface of an upper plate 52, an air suction port 52a communicating with an air suction port 51a of the front housing 51, and an axial communicating groove 52b for communicating the suction ports 51a, 52a and an air suction port 22b of the first cylinder block 22 are formed, respectively. Further, as shown in Fig. 14 on a front surface of the lower plate 53, an axial communicating groove 53a for communicating the air suction ports 51a, 52a with an air suction port 22e of the first cylinder block 22, and a branched communicating groove 53b (two passages are joined to each other at position of 53b) for communicating an air discharging port 22d of the first cylinder block 22 and an air discharging port 23d of the second cylinder block 23 with an air suction port 23e of the second cylinder block 23 are formed respectively.

[0081] In this multi-stage pumping apparatus, the suction port 22b defined by the first and second rotors 34 and 35, and the suction port 22e defined by the second and third rotors 35 and 36 are opened in the frontmost stage pumping chamber 22a. In addition, the discharging port 22d of the frontmost stage pumping chamber 22a defined by the first and second rotors 34 and 35 is communicated with the suction port 23e of the next stage pumping chamber 23a defined by the second and third rotors 38 and 39, below the imaging surface F-F. Further, the discharging port 22c of the frontmost stage pumping chamber 22a defined by the second and third rotors 35 and 36 is communicated with the suction port 23b of the next stage pumping chamber 23a defined by the first and third rotors 37 and 38, above the imaginary surface F-F. Thus, in this multi-stage pumping apparatus, the increased numbers of the suction ports 22b and 22e opened to the first pumping chamber 22a compared with that of the third embodiment can increase the vacuuming operation.

〈5th Embodiment〉

[0082] The fifth embodiment disclosed in Figs. 16 to 20 differs from the third embodiment shown in Figs. 7 to 11 in the following points. That is, an air suction port 61d is formed on a front housing 61 while an air discharging port 67d is formed on a rear housing 67; the air sucking and the air discharging operations are performed in two roots in each of the stages; and an air discharging port in the preceding stage and the air discharging port of succeeding stage are located at the same side of the imaginary surface F-F. Hereinafter, the portions or elements corresponding to that of the third embodiments are shown by the reference numerals to which sixty (60) is added compared to that of the third embodiment, add different portions or elements are explained mainly.

[0083] As shown in Fig. 16, an air suction port 61d is formed on a front housing 61 vertically, and an air discharging port 67d is formed on a rear housing 67 vertically, respectively. As shown in Fig. 18, at a front end and a rear end of the upper plate 91, an air suction port 91a communicated with the air suction port 61d and an air discharging port 91b communicated with an air discharging port 67c of the rear housing 67 are vertically formed respectively. On a rear surface of the upper plate 91, an axial communicating groove 91c for communicating the suction port 91a, 61d with an air suction port 62b of the first cylinder 62, an oblique communicating groove 91d for communicating an air discharging port 62c of the first cylinder 62 with an air suction port 63b of the second cylinder block 63, an oblique communicating groove 91e for communicating an air discharging port 63c of the second cylinder block 63 with an air suction port 64b of the third cylinder block 64, an oblique communicating groove 91f for communicating an air discharging port 64c of the third cylinder block 64 with an air suction port 65b of the four cylinder block 65, and an axial communicating groove 91g for communicating an air discharging port 65c of the fourth cylinder block 65 with an air discharging port 91b, 67c are formed respectively.

[0084] In addition, as shown in Fig. 19 on a front surface of the lower plate 89, an axial communicating groove 89a for communicating the suction port 91a, 61d with an air suction port 62e of the first cylinder 62, an oblique communicating groove 89b for communicating an air discharging port 62d of the first cylinder 62 with an air suction port 63e of the second cylinder block 63, an oblique communicating groove 89c for communicating an air discharging port 63d of the second cylinder block 63 with an air suction port 64e of the third cylinder block 64, an oblique communicating groove 89d for communicating an air discharging port 64d of the third cylinder block 64 with an air suction port 65e of the four cylinder block 65, and an axial communicating groove 89e for communicating an air discharging port 65d of the fourth cylinder block 65 with an air discharging port 91b, 67c are formed respectively.

[0085] Thus, the multi-stage pumping apparatus including the multi-stage roots pump which adopts four sets of the first to third rotors 71 to 73, 74 to 76, 77 to 79 and 80 to 82 each forming one set of the rotors to have the smallest diameter is realized.

[0086] When this multi-stage pumping apparatus is used to vacuum a chamber to reduce pressure therein, the air suction port 91a of the front housing 61 is communicated with the chamber via a hose and the like, while the air discharging port 91b of the front housing 61 is opened to the atmosphere via a hose and the like, as shown in Fig. 20, and the multi-stage roots pump P is driven by the motor M. As a result, the rotor 71 to 82 rotate in each of the pumping chambers 62a, 63a, 64a and 65a of the multi-stage roots pump P with meshing with each other to perform pumping operation sequentially, so that air in the chamber is discharged to the atmosphere to realize the pressure-reduced condition thereof.

[0087] Here, in this multi-stage pumping apparatus, four sets of rotors each of which is comprised of three (odd number of) rotors 71 to 73, 74 to 76, 77 to 79 and 80 to 82 are adopted. As a result, in the pumping chambers 62a, 63a, 64a and 65a of each stage, one air suction ports 62b, 63b 64b and 65b, and one air discharging ports 62c, 63c, 64c and 65c are presented above the imaginary surface F-F including the first to third shafts 68 to 70, while one air suction ports 62e, 63e, 64e and 65e, and one air discharging ports 62d, 63d, 64d and 65d are presented below the imaginary surface F-F. In other words, in both of the preceding stage pumping chambers 62a, 63a and 64a and in the succeeding stage pumping chambers 63a, 64a and 65a, one air suction ports 63b, 64b and 64b, and one air discharging ports 62c, 63c and 64c are presented above the imaginary surface F-F, one air suction ports 62e and 63e, 64e and one air discharging ports 62d, 63d and 64d are presented below the imaginary surface F-F.

[0088] Therefore, communicating grooves 91d, 91e and 91f formed on a rear surface of the upper plate 91 can communicate the air discharging ports 62c, 63c and 64c of the preceding stage pumping chambers 62a, 63a and 64a with the air suction ports 63b, 64b and 65b of the succeeding stage pumping chambers 63a, 64a and 65a sequentially above the imaginary surface F-F easily without using the pipe attachment. Likewisely, communicating grooves 89b, 89c and 89d formed on a front surface of the lower plate 89 can communicate the air discharging ports 63d, 64d and 65d of the preceding stages 62a, 63a and 64a with the air suction ports 63e, 64e and 65e of the succeeding stages 63a, 64a and 65a sequentially in each of the stages below the imaginary surface F-F easily without using the pipe attachment.

[0089] Accordingly, there is no need to form relatively long partitioning walls disposed between the pumping chambers of the preceding stage and the pumping chambers of the succeeding stage and having the communicating passage surrounding the pumping apparatus by about 180 degrees. Alternatively, as shown in Fig. 16, it is enough to form the partitioning walls between the preceding stage pumping chambers 62a, 63a and 64a, and the succeeding stage pumping chambers 63a, 64a and 65a as the mere partitions, which can make axial length of the multi-stage roots pump shorter. As a result, foot space can be minimized to make setting of the multi-stage pumping apparatus easier and to reduce the manufacturing cost thereof.

[0090] Also, the driving force from the driving shaft of the motor M is transmitted and converted through a timing gear train comprised of a driving gear 83 and driven gears 84 and 85, and the first to third shafts 68 to 70, to the first to third rotors 71 to 82. Accordingly, not only any slipping will not occur, but the first to third shafts 68 to 70 will not be twisted. Consequently, driving force of the motor M can easily converted to rotation of the first to third rotors 71 to 82 in each of the pumping chambers 62a to 65a to perform the pumping operation smoothly.

[0091] Further, the air suction port 91a is opened at position furthest from the timing gear train while the air discharging port 91b is opened at position nearest thereto, so that lubricating oil on the timing gear train is prevented from scattering in the chamber to which the suction port 91a is opened. Thus, pressure in the chamber can be reduced with maintaining good environment condition.

〈Deformation〉

[0092] As show in Fig. 21, it is possible in the first to fifth embodiments to arrange the first to third shaft 95 to 97 for supporting the first to third rotors 98 to 100 so that the imaginary surface F1-F2-F3 is comprised of the first section F1-F2 connecting the second and third shafts 96 and 97, and the second section F2-F3 connecting the first and second shafts 95 and 96 to be crossed at the second shaft 96 by a predetermined angle.

[0093] Such arrangement of the rotors 98 to 100 also can communicate the air suction ports and the air discharging ports with each other sequentially above and below the imaginary surface F1-F2-F3. Especially, at the lower side of the imaginary surface F1-F2-F3, it is enough to provide the communicating passage relatively short in the circumferential direction, although relatively long communicating passage is necessary in the upper side of the imaginary surface F1-F2-F3.

[0094] In the single-stage roots pump, in order to increase the compression ratio, three or more rotors among 1st to n-th rotors forming one set, at least one of the air suction port defined by the (n-2)th and (n-1)th rotors and the air suction port defined by the (n-1)th and n-th rotors being opened, the air discharging port defined by the (n-2)th and (n-1)th rotors being communicated with the air suction port defined by the (n-1)th and n-th rotors at the same side of an imaginary surface including the plurality of shafts, and the air discharging port defined by the (n-1)th and n-th rotors being opened.

[0095] In the multi-stage roots pump, in order to communicate the discharging port of the preceding stage pumping chamber and the air suction port of the succeeding stage pumping chamber, three or more rotors among the 1st to n-th rotors forming one set in the same set, in the pumping chamber of a frontmost stage, at least one of air suction port defined by the (n-2)th and (n-1)th rotors, and the air suction port defined by the (n-1) and n-th rotors being opened, and the air discharging port defined by the (n-1)th and n-th rotors being communicated with the air suction port defined by the (n-2)th and (n-1)th rotors of the pumping chamber of a succeeding step at the same side of an imaginary surface including the plurality of shafts, in the pumping chamber of each stage except for the frontmost stage and the rearmost stage, the air discharging port defined by the (n-2)th and (n-1)th rotors being communicated with the air suction port defined by the (n-1)th and n-th rotors at the same side of the imaginary surface, and in the pumping chamber of the rearmost stage the air discharging port defined by the (n-1)th and n-th rotors being opened.

Claims

1. A single-stage roots pump (P) including a casing (2) forming one pumping chamber (2a) having air suction ports (2b, 2e) and air discharging ports (2d, 2c), a plurality of rotors (8 to 10) mounted on a plurality of parallel shafts (5 to 7) respectively to mesh with each other for rotation in the pumping chamber,

characterized by that three or more of said rotors among the 1st rotor to n-th rotor sequentially meshed with each other form one set;

at least one of the air suction port (2b) defined by the (n-2)th rotor and the (n-1)th rotor and the air suction port (2e) defined by the (n-1)th rotor and the n-th rotor is opened;

the air discharging port (2d) defined by the (n-2)th rotor and the (n-1)th rotor is communicated with the air suction port (2e) defined by the (n-1)th rotor and the n-th rotor, at the same side of an imaginary surface (F-F) including the plurality of shafts for supporting the plurality of rotors; and

the air discharging port (2c) defined by the (n-1)th rotor and the n-th rotor is opened.

2. A single-stage roots pump according to claim 1, wherein odd numbers of said rotors form one set.

3. A single-stage roots pump according to claim 2, wherein the odd number is three.

4. A single-stage roots pump according to claim 1, 2 or 3, wherein the air discharging port defined by the (n-2)th rotor and the (n-1)th rotor, and the air suction port defined by the (n-1)th rotor and the n-th rotor are communicated with each other by a communicating groove formed in said casing.

5. A single-stage roots pump according to claim 1, further comprising the air discharging port defined by the 1st rotor and the 2nd rotor is communicated with the air suction port defined by the 2nd rotor and the 3rd rotor at the same side of the imaginary surface, and sequentially, the air discharging port defined by the (n-2)th rotor and the (n-1)th rotor is communicated with the air suction port defined by the (n-1)the rotor and the n-th rotor at the same side of the imaginary surface.

6. A single-stage roots pump according to claim 1, wherein the imaginary surface is comprised a fist section including the first shaft and the second shaft and a second section including the second shaft and the third shaft, both of which are crossed at the second shaft.

7. A single-stage pumping apparatus comprised of said single-stage roots pump (P) according to one of the claims 1 to 6, and a rotary driving device (M) having a driving main body and a driving shaft protruded from the driving main body,

wherein a timing gear train (11 to 13) comprised of a driving gear (11) fixed to the driving shaft (6) of said rotary driving device and driven gears (12, 13) fixed to each of the shafts (5, 7) for supporting the rotors of said single-stage roots pump to be driven by the driving gear is interposed between said single-stage roots pump and said rotary driving device.

8. A multi-stage roots pump comprising a casing forming a plurality of parallel pumping chambers each having air suction ports and air discharging ports, and plurality of rotors mounted on a plurality of parallel shafts to be meshed with each other for rotation in each of said pumping chambers,

characterized by that three or more rotors among the 1st rotor to n-th rotor sequentially meshed form one set in the same set;

in the pumping chamber of each stage except for a frontmost stage and a rearmost stage, the air discharging ports defined by the (n-2)th rotor and the (n-1)th rotor is communicated with the air suction port defined by the (n-1)th rotor and the n-th rotor at the same side of am imaginary surface (F-F9 including the plurality of shafts for supporting the plurality of the shafts;

in the pumping chamber (22a) of a frontmost stage, at least an air suction port (22b) defined by the (n-2)th rotor and the (n-1)th rotor is opened, and the air discharging port (22c) defined by the (n-1)th rotor and the n-th rotor is communicated with the air suction port (23b) defined by the (n-2)th rotor and the (n-1)th rotor of the pumping chamber of a succeeding step at the same side of the imaginary surface (F-F); and

in the pumping chamber (25a) of the rearmost stage the air discharging port (25c) defined by the (n-1)th rotor and the n-th rotor is opened.

9. A multi-stage roots pump (P) comprising a casing forming a plurality of parallel pumping chambers (22a, 23a, 24a, 25a) each having air suction ports (22b, 22e, 23b, 23e, 24b, 24e, 25b, 25e) and air discharging ports (22c, 22d, 23c, 23d, 24c, 24d, 25c, 25d), and plurality of rotors (31 to 42) mounted on a plurality of parallel shafts (28 to 30) to be meshed with each other for rotation in each of said pumping chambers,

characterized by that three or more rotors among the 1st rotor to n-th rotor sequentially meshed form one set in the same set;

in the pumping chamber (22a) of a frontmost stage, at least one of air suction port (22b) defined by the (n-2)th rotor and the (n-1)th rotor, and the air suction port (22e) defined by the (n-1) the rotor and the n-th rotor is opened, and the air discharging port (22c) defined by the (n-1)th rotor and the n-th rotor is communicated with the air suction port (23b) defined by the (n-2)th rotor and the (n-1)th rotor of the pumping chamber of a succeeding step at the same side of an imaginary surface (F-F)including the plurality of shafts for supporting the plurality of the shafts;

in the pumping chamber of each stage except for the frontmost stage and the rearmost stage, the air discharging ports (23c, 24c) defined by the (n-2)th rotor and the (n-1)th rotor is communicated with the air suction port (24b, 25b) defined by the (n-1)th rotor and the n-th rotor at the same side of the imaginary surface; and

in the pumping chamber (25a) of the rearmost stage the air discharging port (25c) defined by the (n-1)th rotor and the n-th rotor is opened.

10. A multi-stage roots pump according to claim 9 , wherein odd numbers of said rotors form one set.

11. A multi-stage roots pump according to claim 10, wherein the odd number is three.

12. A multi-stage roots pump according to claim 9, 10 or 11, wherein in the pumping chamber of each stage, the air discharging port defined by the (n-2)th rotor and the (n-1)th rotor, and the air suction port defined by the (n-1)th rotor and the n-th rotor are communicated with each other by a communicating groove formed in said casing.

13. A multi-stage roots pump according to claim 9, further comprising in the pumping chamber of each stage except for the frontmost stage and the rearmost stage, the air discharging port defined by the 1st rotor and the 2nd rotor is communicated with the air suction port defined by the 2nd rotor and the 3rd rotor at the same side of the imaginary surface, and sequentially the air discharging port defined by the (n-2)th rotor and the (n-1)th rotor is communicated with the air suction port defined by the (n-1)the rotor and the n-th rotor at the same side of the imaginary surface.

14. A multi-stage roots pump according to claim 9, wherein the imaginary surface is comprised a fist section including the first and second shafts and a second section including the second and third shafts, both of which are crossed at the second shaft.

15. A multi-stage pumping apparatus comprised of said multi-stage roots pump (P) according to one of the claims 9 to 14 and a rotary driving device (M) having a driving main body and a driving shaft protruded from the driving main body,

wherein a timing gear train (43 to 45) comprised of a driving gear (43) fixed to the driving shaft (29) of said rotary driving device and driven gears (44, 45) fixed to each of the shafts (28, 30) for supporting the rotors of said multi-stage roots pump to be driven by the driving gear is interposed between said multi-stage roots pump and said rotary driving device.

16. A multi-stage pumping apparatus according to claim 15, wherein the air suction port of the frontmost stage is opened at a position remotest from the timing gear train, and the air discharging port of the rearmost stage is opened at a position closest to the timing gear train.

17. A multi-stage roots pump (P) comprising a casing forming a plurality of parallel pumping chambers (22a, 23a, 24a, 25a) each having air suction ports (22b, 22e, 23b, 23e, 24b, 24e, 25b, 25e) and air discharging ports (22c, 22d, 23c, 23d, 24c, 24d, 25c, 25d) , and plurality of rotors (71 to 82) mounted on a plurality of parallel shafts (68 to 70) to be meshed with each other for rotation in each of said pumping chambers,

characterized by that three or more rotors among a 1st rotor to n-th rotor sequentially meshed form one set in the same set;

in the pumping chambers (22a to 24a) of each stage except for the rearmost stage forming a continuous stage, at least two of suction port (22b, 22e, 23b, 23e, 24b, 24e) defined by the (n-2)th rotor and the (n-1)th rotor and the air suction port (22c, 22d, 23c, 23d, 24c, 24d) defined by the (n-1) the rotor and the n-th rotor are opened, and the air discharging port (22c, 23c, 24c) defined by the (n-2)th rotor and the (n-1)th rotor and the air suction port (23b, 24b, 25b) defined by the (n-1)th rotor and the n-th rotor are respectively communicated with the air suction port defined by the (n-2)th rotor and the (n-1)th rotor of the pumping chamber of a succeeding step at the same side of an imaginary surface (F-F) including the plurality of shafts for supporting the plurality of the shafts;

in the pumping chamber (23a, 24a) of each stage except for the frontmost stage and the rearmost stage, the air discharging port (23c, 24c) defined by the (n-2)th rotor and the (n-1)th rotor is communicated with the air suction port (24b, 25b) defined by the (n-1)th rotor and the n-th rotor at the same side of the imaginary surface; and

in the pumping chamber (25a) of the rearmost stage, the air discharging port (25c) defined by the (n-1)th rotor and the n-th rotor is opened.

18. A multi-stage roots pump according to claim 17, wherein odd numbers of said rotors form one set.

19. A multi-stage roots pump according to claim 18, wherein the odd number is three.

20. A multi-stage roots pump according to claim 17, 18 or 19, wherein in the pumping chamber of each stage, the air discharging port defined by the (n-2)th rotor and the (n-1)th rotor and the air suction port defined by the (n-1)th rotor and the n-th rotor are communicated with each other by a communicating groove formed in said casing.

21. A multi-stage roots pump according to claim 17, further comprising in the pumping chamber of each stage except for the frontmost stage and the rearmost stage, the air discharging port defined by the 1st rotor and the 2nd rotor is communicated with the air suction port defined by the 2nd rotor and the 3rd rotor at the same side of the imaginary surface, and sequentially the air discharging port defined by the (n-2)th rotor and the (n-1)th rotor is communicated with the air suction port defined by the (n-1)the rotor and the n-th rotor at the same side of the imaginary surface.

22. A multi-stage roots pump according to claim 17, wherein the imaginary surface is comprised a fist section including the first and second shafts and a second section including the second and third shafts, both of which are crossed at the second shaft.

23. A multi-stage pumping apparatus comprised of said multi-stage roots pump (P) according to one of the claims 17 to 22 and a rotary driving device (M) having a driving body and a driving shaft protruded from the driving body,

wherein a timing gear train (43 to 45) comprised of a driving gear (43) fixed to the driving shaft (29) of said rotary driving device and driven gears (44, 45) fixed to each of the shafts (28, 30) for supporting the plurality of rotors of said multi-stage roots pump to be driven by the driving gear is interposed between said multi-stage roots pump and said rotary driving device.

24. A multi-stage pumping apparatus according to claim 23, wherein the air suction port of the frontmost stage is opened at a position remotest from the timing gear train, and the air discharging port of the rearmost stage is opened at a position closest to the timing gear train.

25. A multi-stage roots pump (P) comprising a casing (61, 67) forming a plurality of parallel pumping chambers (62a, 63a, 64a, 65a) each having air suction ports (63b, 62d, 63b, 63d, 64b, 64d, 65b, 65d) and air discharging ports (62a, 62c, 63a, 63c, 64a, 64c, 65a, 65c), and a plurality of rotors (71 to 73) mounted on the plurality of shafts (68 to 70) respectively to mesh with each other in the pumping chamber,

characterized by that three or more rotors form one set;

the air suction port (91a) of the frontmost stage pumping chamber (62a) is opened, the air discharging ports (62c, 63c, 64c) of the preceding stage pumping chamber (62a, 63a, 64a) is sequentially communicated with the air suction port (63b, 64b, 65b)of the succeeding stage pumping (63a, 64a, 65a) chamber at the same side of an imaginary surface including the plurality of shafts, and the air discharging port (65c) of the rearmost stage pumping chamber (65a) is opened, in said casing.

26. A multi-stage roots pump according to claim 25, wherein odd numbers of said rotors form one set.

27. A multi-stage roots pump according to claim 26, wherein the odd number is three.

28. A multi-stage roots pump according to claim 25, 26 or 27, wherein the air discharging port of the preceding stage pumping chamber is communicated with the air suction port of the succeeding stage pumping chamber by a communicating groove formed in said casing.

29. A multi-stage roots pump according to claim 25, wherein the imaginary surface is comprised a fist section including the first a and second shafts and a second section including the second and third shafts, both of which are crossed at the second shaft.

30. A multi-stage pumping apparatus comprised of said multi-stage roots pump (P) according to one of the claims 25 to 29, and a rotary driving device (M) having a driving main body and a driving shaft protruded from the driving main body,

wherein a timing gear train (83 to 85) comprised of a driving gear (83) fixed to the driving shaft (69) of said rotary driving device and driven gears (84,85) fixed to each of the shafts (68, 70) for supporting the plurality of rotors of said multi-stage roots pump to be driven by the driving gear is interposed between said multi-stage roots pump and said rotary driving device.

31. A multi-stage pumping apparatus according to claim 30, wherein the air suction port of the frontmost stage is opened at a position remotest from the timing gear train, and the air discharging port of the rearmost stage is opened at a position closest to the timing gear train.

Drawing