Vacuum pump apparatus

Abstract: A vacuum pump has a pump casing (3) accommodating pump rotor (5) and stator (4), a motor housing (10a) connected to an end of the pump casing and accommodating a driving motor (8) having a driving shaft (8a) drivingly connected to the pump rotor. An oil pump (12) is disposed outside the pump casing and the motor housing and operative to suck lubricant oil from an oil reservoir (11) and feed the thus sucked lubricant oil to bearings (7) supporting the driving shaft. The motor housing has an exhaust port (18) connected by an exhaust line (18a) to an oil mist filter (13) of a high oil-collection efficiency. The oil mist filter has a drain line (17) connected to a suction port of the oil pump (12) so that mist of lubricant contained in gas exhausted from the motor housing (10a) is collected by the oil mist filter and sucked by the oil pump and returned thereby to the bearings, whereby the cycle of supply of fresh or additional lubricant oil to the oil reservoir can be prolonged to extend the maintenance-free period for the pump.

Description: The invention relates to a vacuum pump apparatus comprising a pump mechnism section including a pump casing having suction and discharge ports formed therein, and pump rotor and stator both accommodated in said pump casing; a pump-driving section including a motor housing connected to an end of said pump casing and a driving motor accommodated in said motor housing, said driving motor having a driving shaft extending from said motor housing through said end of said pump casing into said pump casing and drivingly connected to said pump rotor so that said pump rotor is rotated by said driving motor to suck a gas through said suction port into said pump casing and discharge the thus sucked gas from said pump casing through said discharge port; bearing means rotatably supporting said driving shaft on said end of said pump casing; means for introducing purge gas into said pump casing and said motor housing and providing a seal between said pump casing and said motor housing; said motor housing defining a reservoir for lubricatant oil to be fed to said bearing means; said motor housing having formed therein an exhaust port through which a part of the purge gas and mist of the lubricant oil which has lubricated said bearing means can be discharged out of said motor housing; an exhaust line having an upstream end connected to said exhaust port; and oil mist filter means disposed in said exhaust line to separate said part of the purge gas from the lubricant oil discharged from said motor housing to thereby collect the thus separated lubricant oil, said oil mist filter means having a gas-outlet for said part of the purge gas separated from the lubricant oil discharged from said motor housing, said oil mist filter means further having a drain line for the thus collected lubricant oil. The vacuum pump of the generic kind is disclosed in JP-A-1-130093 and is structured such that lubricant oil exhausted through an exhaust port of a pump-driving section is collected by an oil mist filter and is returned from the filter directly into an oil reservoir provided in the pump-driving section. Fig. 5 is a diagrammatic illustration of the vacuum pump of the JP-A-1-130093 showing the fluid flows in the vacuum pump. The vacuum pump of Fig. 5 comprises a pump mechanism section 9 which is isolated from a pump-driving section 10 by menas of a shaft seal section 6. The pump mechanism section 9 is operated in a vacuumed condition, while the pump-driving section 10 is under the atmospheric pressure. The shaft seal section 6 is supplied with purge gas and divides the flow 15 of the purge gas into two brunches 19 and 20 which respectively enter the pump mechanism section 9 and the pump-driving section 10. The pump-driving section 10 incorporates ball bearings (not shown) which are supplied with lubricant oil by an oil pump 12 disposed outside the vacuum pump. The purge gas introduced into the pump mechanism section is discharged therefrom through a discharge port 2, while the purge gas introduced into the pump-driving section 10 is discharged therefrom through an exhaust port 18. An oil mist filter 21 is provided in an exhaust line 21a connected to and extending from the exhaust port 18. The oil mist filter 21 has a drain lilne 17 which is connected to an oil reservoir (not shown) provided in the pump-driving section 10 so that the lubricant oil exhausted from the pump-driving section is collected by the filter and returned to the pump. In order to avoid an undue pressure rise in the pump-driving section 10 as well as to prevent the collected lubricant oil from blowing out of the drain line 17 of the oil mist filter, the oil mist filter was required to be of a structure providing an extremely low pressure loss. For this reason, the lubricant oil exhausted from the pump-driving section together with the purge gas also exhausted therefrom could be collected only to limited percentages, with resultant disadvantages that the amount of the lubricant oil exhausted and released from the oil mist filter into the atmosphere was increased and that the oil reservoir had to be supplied with fresh lubricant oil at a short interval or cycle. Moreover, in the case where the vacuum pump is used with a semiconductor producing apparatus or the like which must be operated in a cleaned room, the pump is to be also installed in the cleaned room. In such case, therefore, a difficulty is involved that the gas exhausted from the pump-driving section of the vacuum pump must be processed so as not to contaminate the cleaned room. Thus, the pump had to be equipped with two different discharge lines, one being a line connected to the discharge port of the pump mechanism section and the other being an exhaust line for the purge gas and mist of lubricant oil exhausted from the pump-driving section. US-A-4 231 307 shows a centrifugal refrigerant compressor which comprises a compressing section in a housing, an intermediate gear and bearing section in a housing, and a motor section in a housing. The compressor is provided with an oil separation and return system including an oil and refrigerant gas line extending from the gear and bearing housing to a filter housing and a refrigerant gas return line extending from the filter housing to a suction space in the compressing section housing. The filter housing has an oil outlet to which is connected an oil return line. The compressor is further provided with an oil pump which is provided inside the gear and bearing housing and has a discharge port from which an oil supply line extends to a second oil pump which is in the form of a jet pump to which the oil return line from the oil filter housing is connected. The jet pump is operative to suck oil from the oil outlet of the filter housing so that the oil from the oil outlet of the filter housing is combined with or added to the oil from the oil pump and the mixed oil is fed to bearings and gears in the gear and bearing housing. The oil separation and return system shown in US-A-4 213 307 necessitates the jet pump so as to suck the oil from the oil filter housing. This is because the oil outlet of the filter housing is connected to the oil supply line extending from the discharge port of the first oil pump. It is an object of the present invention to reliably collect the lubricant oil discharged from the pump-driving section of a vacuum pump apparatus and remarkably reduce the amount of lubricant oil exhausted out of the pump to thereby extend the interval of supply of fresh lubricant oil into the oil reservoir, using only a single pump discharge line. This object is achieved with the vacuum pump of the generic kind in that an oil pump is disposed outside said pump casing and said motor housing and is operative to suck the lubricant oil from said reservoir and feed the thus sucked lubricant oil to said bearing means, and said drain line has a downstream end communicated with a suction port of said oil pump so that the lubricant oil collected by said oil mist filter means is sucked by said oil pump and flows through said drain line to said oil pump so as to be mixed with or added to the lubricant oil sucked by said oil pump from said reservoir. As will be seen from the structure of the vacuum pump of the present invention pointed out above, the drain line of the oil mist filter has its downstream end communicated with the suction port of the oil pump. Accordingly, because the oil mist filter is subjected to vacuum created by the oil pump, the oil mist filter does not exert any resistance to the discharge of the purge gas and mist of lubricant oil from the pump-driving section of the vacuum pump. Accordingly, the oil mist filter can be of a high oil-collection efficiency that is capable of collect substantially all parts of the lubricant oil exhausted from the pump-driving section of the vacuum pump. Moreover, an oil mist filter having such a high oil-collection efficiency is operative to reduce the amount of gas flowing, together with the oil thus collected lubricant oil, from the filter through the drain line into and through the oil pump. Thus, the use of an oil mist filter of such a high oil-collection efficiency can avoid the occurrence of reduction in the performance of the oil pump which otherwise would be caused by the use of such oil mist filter. It would be possible also in the prior art to provide an oil mist filter of a high oil-collection efficiency. However, because high oil-collection efficiency involves a high pressure loss, an oil mist filter of such a high oil-collection efficiency if simply provided in an exhaust line in the prior art vacuum pump apparatus will exert a resistance to the flow of gas-oil mixture exhausted from the pump-driving section of the pump apparatus, so that the pressure in the pump-driving section is increased to pressurize the lubricant oil in the oil reservoir and thus forcibly cause the lubricant oil to blow out of the drain line of the oil mist filter. In a preferred embodiment of the vacuum pump apparatus according to the present invention, the drain line of the oil mist filter is provided with means for increasing a resistance of the drain line to the fluid flow therethrough. The resistance increasing means may preferably comprise at least one restriction orifice provided in the drain line. The restriction orifice will increase the resistance of the drain line to the fluid flow therethrough and thus reduce the amount of gas sucked into the oil pump for thereby avoiding the occurrence of reduction in the oil-pumping performance of the oil pump which would otherwise be caused if a large amount of gas is sucked into the oil pump. The provision of the oil mist filter of a high oil-collection efficiency is effective to assure that the amount of the lubricant oil exhausted from the oil mist filter through the gas-outlet thereof can be greatly reduced. As a result, an exhaust line connected to and extending from the gas-outlet of the oil mist filter can be connected to or merged into a pump discharge line extending from the discharge port of the pump mechanism section of the vacuum pump to greatly simplify the overall structure of the pump. As will be apparent from the foregoing description, the present invention provides many advantageous merits which can be summarized as follows: The amount of lubricant oil exhausted from the pump-driving section of the vacuum pump into the atmosphere can be extremely reduced to prolong the interval of supply of fresh oil to the oil reservoir; Because the exhausted lubricant oil can be separated from the exhausted gas and collected at a high rat, the thus separated gas can be released into the atmosphere with reduced effect on oil-contamination of the environment and, in addition, necessitates reduced care for the exhaust line; The improvement by the invention can be achieved by adding simple component parts to the conventional vacuum pump and provides remarkable advantageous results; and The collection of exhausted lubricant oil at a high rate permits the exhaust line to be connected to the pump discharge line and, thus, makes it possible to unite the pump discharge line and the gas exhaust line into a single line. The drain line extending from the oil mist filter means has its downstream end communicated with the suction port of the oil pump. Accordingly, the oil separation and return system of the applicant's vacuum pump apparatus does not require any pump to be provided in addition to the oil pump. The invention will become more apparent from the following description made with reference to the accompanying drawings in which Fig. 1 is a partly axial sectional and partly diagrammatic illustration of an embodiment of the vacuum pump apparatus according to the present invention; Fig. 2 is an enlarged elevational view of an embodiment of the drain line of the vacuum pump apparatus shown in Fig. 1; Fig. 3 is a graph showing the relationship between the length of a pipe forming a part of the drain line and the rate of the flow through the pipe into the oil pump; and Fig. 4 is a diagrammatic illustration of a second embodiment of the invention. Referring to Fig. 1, a pump machanism section 9 includes a pump casing 3 having formed therein suction and discharge ports 1 and 2 and pump stator and rotor 4 and 5 both accommodated in the pump casing 3 and disposed in opposed relationship. A pump-driving section 10 includes a motor housing 10a fixedly connected to an end of the pump casing 3 and a motor 8 disposed in the motor housing 10a and having a driving shaft 8a which is drivingly connected to the pump rotor 5. When the pump rotor 5 is driven by the motor 8, the pump mechanism section 9 operates to suck a gas into the pump casing 3 through the suction port 1, as indicated by an arrow A in Fig. 1, and discharges the thus sucked gas from the pump casing 3 through the discharge port 2, as indicated by another arrow B also shown in Fig. 1. In the end wall of the pump casing 3 to which the motor casing 10a is connected, a passage 15 is formed to introduce purge gas, as indicated by a further arrow C, to shaft seals 6 operative to distribute the purge gas to the pump casing 3 and the motor housing 10a so that the pump mechanism section 9 and the pump-driving section 10 are kept at predetermined pressures, respectively. The driving shaft 8a is rotatably supported by upper and lower bearings 7. The upper bearing 7 is mounted on the end of the pump casing 3 to which the motor housing 10a is connected. The other or lower bearing 7 is mounted in the motor housing 10a. The motor housing 10a has a lower part which defines therein an oil reservoir 11 for storing an amount of lubricant oil therein. An oil pump 12 is disposed outside the pump casing 3 and the motor housing 10a to suck the lubricant oil from the oil reservoir 11 and through an oil suction line 12a and positively circulate or feed the thus sucked oil through an oil feeding line 12b to the bearings 7. The motor housing 10a has formed therein an exhaust port 18 connected with an exhaust line 18a in which is disposed an oil mist filter 13 of a high oil-collection efficiency. The oil mist filter 13 has a gas-outlet 14 forming a part of the exhaust line 18a and a drain port connected with a drain line 17 having a downstream end connected to the oil suction line 12a so that the oil mist filter 13 is subjected to a vacuum force created in the oil pump 12. An embodiment of the structural details of the drain line 17 will be described hereunder with reference to Fig. 2. The drain line includes a box 23 for collecting fine particles of foreign matter. The particle collection box 23 has an inlet formed in the top wall thereof and connected to the drain port of the oil mist filter 13 by a short conduit 22. The top wall of the box 23 has also formed therein an outlet connected with an end of a pipe line 24 having a small inner diameter. The other end of the pipe line 24 is connected to the oil suction line 12a of the oil pump 12. A plurality of restriction orifices 25 are provided in the pipe line 24 to increase the resistance of the pipe line 24 to the fluid flow therethrough. Fig. 3 graphically illustrates the results of tests on the relationship between the length 1 of the pipe line 24 and the rate G of the fluid flow therethrough. The solid line in Fig. 3 shows the result of the test in which the pipe line 24 was not provided with any restriction orifice 25, while the broken line shows the result of the test in which the pipe line 24 was provided with restriction orifices 25. It will be seen from the test results shown in Fig. 3 that the rate Q of the flow of a gas-oil mixture through the pipe line 24 can be adjusted by varying the number of restriction orifices 25 to be installed in the pipe line 24 and by varying the length 1 of the pipe line 24. Accordingly, the flow rate Q can be adjusted to fall within the range which is allowable for the oil pump 12 to avoid the occurrence of gas flow into the pump at such an unduly high level that will deteriorate the oil-pumping performance of the oil pump 12. For the reasons pointed out above, the oil mist filter 13 disposed in the exhaust line 18a can be of a high oil-collection efficiency, so that the interval or cycle with which the oil reservoir in the motor housing 10a is supplied with fresh or additional lubricant oil can be extended to assure a prolonged maintenance-free period of the pump. In addition, the amount of lubricant oil released into the atmosphere through the gas-outlet 14 of the oil mist filter 13 can be reduced to minimize the problem of contamination of a room in which the vacuum pump is installed. Moreover, the particle collection box 23 provided in the drain line 17 just downstream of the oil mist filter 13 is operative to collect and trap therein any fine particles of a foreign matter which would fall from the filter 13 and, thus, guard the pipe line 24 downstream of the particle collecting box 23. Fig. 4 shows another embodiment of the invention which is based on the preceding embodiment described with reference to Figs. 1 - 3. In the embodiment shown in Fig. 4, the exhaust line connected to the exhaust port 18 of the pump-driving section 10 includes a filter-exhaust line 18b connected at one end to the gas-outlet 14 of the oil mist filter 13. The other or downstream end of the filter-exhaust line 18b is connected to a pump discharge line 26 connected to and extending from the discharge port 2 of the pump mechanism section 9 of the vacuum pump. This design advantageously reduces the number of pipe lines to be extended from the vacuum pump to a point remote therefrom and, thus, simplifies the arrangement of pipes and assures a simplified maintenance of the vacuum pump apparatus. It will be noted that these advantageous results can be obtained from the fact that substantially all parts of the lubricant oil exhausted from the pump-driving section 10 can be removed from the exhausted gas by the oil mist filter 13.

Claims: A vacuum pump apparatus comprising: a pump mechanism section (9) including a pump casing (3) having suction and discharge ports (1, 2) formed therein, and pump rotor (5) and stator (4) both accommodated in said pump casing; a pump-driving section (10) including a motor housing (10a) connected to an end of said pump casing (3) and a driving motor (8) accommodated in said motor housing, said driving motor having a driving shaft (8a) extending from said motor housing through said end of said pump casing (3) into said pump casing (3) and drivingly connected to said pump rotor so that said pump rotor is rotated by said driving motor to suck a gas through said suction port into said pump casing and discharge the thus sucked gas from said pump casing through said discharge port (2); bearing means (7) rotatably supporting said driving shaft on said end of said pump casing; means (15, 6) for introducing purge gas into said pump casing and said motor housing and providing a seal between said pump casing and said motor housing; said motor housing defining a reservoir (11) for lubricatant oil to be fed to said bearing means; said motor housing having formed therein an exhaust port (18) through which a part of the purge gas and mist of the lubricant oil which has lubricated said bearing means can be discharged out of said motor housing; an exhaust line (18a, 18b) having an upstream end connected to said exhaust port; and oil mist filter means (13) disposed in said exhaust line to separate said part of the purge gas from the lubricant oil discharged from said motor housing to thereby collect the thus separated lubricant oil, said oil mist filter means having a gas-outlet (14) for said part of the purge gas separated from the lubricant oil discharged from said motor housing, said oil mist filter means further having a drain line (17) for the thus collected lubricant oil, CHARACTERIZED IN THAT an oil pump (12) is disposed outside said pump casing and said motor housing and is operative to suck the lubricant oil from said reservoir (11) and feed the thus sucked lubricant oil to said bearing means, and said drain line has a downstream end communicated with a suction port of said oil pump (12) so that the lubricant oil collected by said oil mist filter means is sucked by said oil pump and flows through said drain line to said oil pump so as to be mixed with or added to the lubricant oil sucked by said oil pump from said reservoir (11). A vacuum pump apparatus according to Claim 1, further including means (25) for increasing a resistance of said drain line (17) to the fluid flow through said drain line, said resistance increasing means being disposed in said drain line between said oil mist filter means (13) and said oil pump (12). A vacuum pump apparatus according to Claim 2, wherein said resistance increasing means comprise at least one restriction orifice means (25) provided in said drain line. A vacuum pump apparatus according to Claim 2, further including means (23) disposed in said drain line for collecting fine particles of foreign matter flowing through said drain line. A vacuum pump apparatus according to Claim 1, further including a pump discharge line (26) extending from said discharge port (2) of said pump casing (3), said exhaust line (18a, 18b) having a downstream potion (18b) extending from said gas-outlet (14) of said oil mist filter means (13) to said pump discharge line (26). A vacuum pump apparatus according to Claim 2, further including a pump discharge line (26) extending from said discharge port (2) of said pump casing (3), said exhaust line (18a, 18b) having a downstream potion (18b) extending between said gas-outlet (14) of said oil mist filter means (13) and said pump discharge line (26). A vacuum pump apparatus according to Claim 4, further including a pump discharge line (26) extending from said discharge port (2) of said pump casing (3), said exhaust line (18a, 18b) having a downstream portion (18b) extending between said gas-outlet (14) of said oil mist filter means (13) to said pump discharge line (26).

Inventors: MURATA KATSUHIKO, NAKAMORI KAZUAKI, TANIYAMA MINORU, MURATA, KATSUHIKO, NAKAMORI, KAZUAKI, TANIYAMA, MINORU
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1993
Main classification: F04D29
IPC codes: F04D29, F04D19