US2877947A - Vacuum pump - Google Patents

Description

March 17, 1959 K. vF. wEssLlNG ETAL l 2,877,947

VACUUM PUMP L Z lf2 March 17, 1959 K. F. wssLlNG ETAL 2,877,947

VACUUM PUMP Filed Nov. 29. 1956 8 Sheets-Sheet 3 .Emea l. www@ ew 'lsezzial BY Y March 17, 1959 K. F.VWESSLING ETAL VACUUM PUMP s sheets-sheet 4 v Filed Nov. 29, 195e March 17, 1959 K. F. wx-:ssLlNG ETAL. v 2:,877g947' VACUUM PUMP Filed Nov. 29, 1956 8i Sheets-Sheet' 5 mnei 17H/65532' if@ 56rd 117655671 Za Meg/4 March` 17, 1959 K. F. wEssLlNG ETA; 2,877,947

VACUUM PUMP l Filed Nov. 29, 1956 8 Sheets-Sheet 6 @fmII-4072*.:

March 17, 1:9539 1K.|=.wEssLn\1ca ETAL A2,877,947 y VACUUM PUMP v Filed Nov. 29, r195e s sheets-sheet 7 March 17, 1959 K. F. wEs'sLlNG ETAL 2,877,947

VACUUM PUMP Filed Nov. 29, 195e v s sheets-'sheet 8 United States :Office y '2,871,947 Patented Mar. 17, 1959 VACUUlVI PUMP Application November 29, 1956, Serial No. 625,161v 1 Claim. (Cl. 2311-153) Our invention relates to a vacuum pump, and more particularly, to a rotary, oil sealed, two-stage, series connected pump utilizing the internal vane principle.

, Copending application Serial No. 546,052, tiled November 10, 1955, by Victor C. Garrison, Edward M. Nakaji, and Kenneth F. Wessling, and assigned to the assignee of our application, discloses a pump of this character. Our invention relates to, but is not limited to, improvements of the pump described in said copending application, and for purposes of facilitating the understanding of our improvements, much of the disclosure of said application is included herein.

Much work has been done by people active in this art to provide a vacuum pump that will pump down or reach its ultimate (that is, provide the rated vacuum) in la minimum of time. Our studies have revealed that this can be done on the pump described in said copending application by providing for better and quicker evacuation of the internal spaces within the pump `and shortening the path that lubricating oil must travel through the pump. We have found that a substantial reduction in operating temperatures results when the principles of our invention are employed.

The principal objects of our invention are to improve the capability of the pump described in said copending application, as well as -other similar pumps, to reach its ultimate, to reduce the time required to provide the rated vacuum, and to reduce the operating temperatures of the pump.

Another object of the invention is to provide a vacuum pump that runs quieter at low operating pressures than conventional pumps.

Other objects, uses, and advantages will be obvious or become apparent from 'a consideration of the following specification taken in conjunction with the accompanying drawings.

In the drawings:

Figure l is a vertical cross sectional view of the pump illustrated in said copending application, as viewed along line 1--1 of Figure 2;

Figure 2 is a vertical cross sectional view `along line 2-2 of Figurel;

Figure 3 is a vertical cross sectional view along line 3-3 of Figure l, with parts broken away for clarity of illustration;

Figure 3a is a fragmental View of one of the pump ports shown in Figure 3;

Figure 4 is an enlarged view of the pump shaft and adjacent structure shown in Figure 1;

Figure 5 is an exploded perspective view of the various elements comprising the embodiment ofthe pump shown in Figure l;

' Figure 6 is a diagrammatic perspective view of the main operating elements of the finishing stage of the pump shown in Figures 1 through 5, with parts broken away for clarity of illustration;

Figure 7 is a view similar to that of Figure 6, but illus- 2I trating the main operating elements of the roughing stage of the pump shown in Figures 1 through 5;

Figure 8 is a perspective view of the pump of Figures 1 through 7 as applied to a suitable pump mounting along with a motor for actuating same;

Figure 9 is a view illustrating one of our improvements in the pump shown in Figures l through 8, it being a sectional view vequivalent to a section along line 9-9 of Figure l, with the rotor, vanes, and pumping chamber of the roughing -stage shown Iin dotted lines;

Figure 9a is a cross sectional View along line 9a-9a of Figure 9;

Figure l0 is a View similar to that of Figure2, but on a larger scale and with parts broken away, illustrating another improvement in the pumpv illustrated in Figures 1 through 8;

Figure 11 isa view similar t'o that of Figure 3, showj ing the roughing'stage side of the plate shown in Figure 3', illustrating a further improvement; and Y Figure 12 is a view similar to that of Figure 4, further illustrating our improvements in the pump' shown in Figures 1 through 8.

But these drawings Vand the corresponding specific ldescription are used for the purpose of disclosure because they conform to embodiments thathave demonstrated their fitness for the purpose, and they are not intended to indicate the limits of the invention, which is susceptible of other embodiments.

Figures l through 8 illustrate the details of the pump described in said copending application.

The two-stage pump 10 shown in these figures generally comprises a center plate 12 (see Figures l and 5) having a finishing or intake stage 14 mounted on one side thereof, and a roughing or exhaust stage 16 mounted on the other side thereof. The two stages lare enclosed by a `casing 1 8 comprising a-pair -ofdished housing 'plates 20 fixed tothe center plate. The space enclosed by the casing is filled with lubricant, such as oil, to approximately the linelind'icated by referencenumeral 22. A shaft 24, rotatably mounted in the center plate 12 and operatively connected to suitable power means, actuates the linishingstage 1,4 and the roughing stage 16.

The specific components and features of pump 1Q are fully described in said copending application, the dis"- closure of which is specifically incorporated herein by this reference. For convenience for referring to said copend ing application, Figures v1-8 of the present application bear the reference numerals employed in the spejcication `of said copending application.

Our improvements Tests have shown that the operation of the pump described in said copending application can be improved by reducing the path that the oil to be injected must take to reach roughing stage pumping chamber 123 and :also'byproviding a positive way of evacuating spaces 238, 242, and 243. Referring to Figures l and 4, it `wil1 be noted that the oil follows a relatively long path Vbefore it is injected into chamber 123 in the pump of said copending application. Moreover, it must pass through a number of constricted passageways, which we have found has the effect of raising the'ternperature of the oil as it passes through or between-the-internal surfaces. of the pump. And, of course, evacuation of spaces 238, 242, and 243 and slots 119 is possible only through the passage provided by beveled roughing stage vanes 128 communicating with roughing stage pumping chamber 123 and this passage is in communication with pumping cham- ,ber 123 for only approximately 25 percent of a complete revolution of the roughing stage rotor. v i

In accordance 'with our invention, 'the oil to vbe -4iiijected into the roughing stage pumping chamber 123 ing stage stator,

passes directly into Athis chamber from a Aport adjacent the surface of the -oil bath through a single passageway. Referring to Figures 9 and 9a, which illustrate roughing stage end plate 116 as modilied in accordance with our invention, the passages 214 and 216 are eliminated, and a slot 300 is formedinthe surface .-117 Vofthis end plate It will be noted that the slot 3001extends from .the `top of the end plate, which is positioned adjacent thesurface 22 of the oil bath, down to the exhaust side, of roughing stage pumping chamber 123.

As each blade or vane `128 sweeps by the end of slot 300, lthe instantaneous pressure adjacent the trailing face of the blade or vane becomes quite low. Atmospheric pressure acting on the oil bath forces a metered amount of oil through slot 300 into chamber 123i. Although some oil may initially be forced backout of slot'300 when the next succeeding blade sweeps by, at low operating pressures, which are arrived atina short time, the pressure differential `between the vpressure in chamber 123 and atmgspheric `pressure is'so great that back tlow is impossi le.

As in the case of the pump described in said copending application, a substantial amount `of this extra oil is forced into the passages 150 by the' nextsucceeding blade so that the oil tends to fill up these passages. Thus, each time a quantity `of oil and air is forced into the passages, the strip 156 of valve 154 is lifted somewhat, to free the mixture of oil and air at the top of these passages.

Even though passages 214 and 216 have been eliminated, we have found that adequate oil reaches the linishing stage of the pump through the mounting for shaft 24. Sutiicient oil enters spaces 238, 242, `243, 244, 245, and 248 through the relatively close clearances between the vanes, center plate, stators, and end plates for accomplishing the functions of the pump hereinbefore described. We have also found that extra slots 34 and 119 formed in the respective rotors may be eliminated as unnecessary (see Figures 9 and 10 illustrating the roughing stage side of the pump).

Since the long injection path employed by the pump described in said copending applicationfis eliminated, the charnfer 227 of vane 128 is omitted, as indicated in Figure 10. Also, radially extending slots 222 have been eliminatedY as unnecessary since spaces 243 and 245 receive adequatelubricant from other sources.

A further improvement in accordance with our invention is indicated in Figures 1l and l2, wherein it will -be observed that the roughing stage side of center plate 12 is formed with recess 110e and slot 112:1 that correspond to recess y110 and slot 112 of the finishing stage side, and thus the roughing stage side is formed similarly to the finishing stage side of the center plate. The recess 113 of the center'plate is replaced by this recess 11011. Also, recess 172 is replaced by recess 172e having the same diameter as recess 110a so that spaces 238 and 242 will be in communication through the vane slots 126 of rotor 118. The action of the vanes orblades 128 in cooperation with port 106 and slot 112a is similar to that described in connection with port 104 and slot 112. However, the oil accumulating on .the bottom of passage 102 proceeds outwardly of the passage 102 together with any air that is passing into the roughing stage of the PllmP- This places spaces 238, 242, and 243 and the remaining slot 119 in positive communication with the pumping chamber 123 through slot 112e and slot 146 of the roughwhich insures fast evacuation ofthe former, since they are in communication with the intake side of the roughing stage during the entire revolution of said roughing stage rotor.

We have found that the oil injected intopum-ping chamber 123 directly from the oil bath need not be previously degassed, and even if it ,is not degassed, as in the illustrated embodiment, the'operation ofthe pump is not adversely affected. This isbecause the portion of lthis oilvthat is carried to the intake side of Vroughing stage pumping chamber 123 is immediately degassed, and the portion of thisroil whichreaches spaces 238 and.242 is ance with the principles of our invention which substantially reduces the noise of operation of the pump shown in Figures 1 throughs. It will be noted that the passage closer to the contact area between the stator 114 and the rotor 118 of the roughing stage is enlarged and is formed to taper outwardly as indicated at 150a. This arrangement gives the upper portion of the modified passage 150 a truncated conical conguration. In addilion, the strip 156 of the flap valve has been made wider with respect to passages 150 (compare Figures l and l2).

We have found that the larger contact surface that the oil in modified passage 150 has with the flap valve strip 156 has the eiect of deadening the usual noise of operation of this valve. We have also noticed that, `at low operating pressures, the escaping gas seems to come from the larger hole. Probably, this is because the modified passage 150 is closely adjacent the contact point between the rotor and the stator.

As shown in Figure 10, a depending flange 310 may be secured to the center plate side ofelement 160, which also aids in the deection of oil during the initial pumping stages.

As also is shown in Figure 12, pump shaft 24 may be mounted in a suitable bushing, such as bushing 312. The action of the lubricant passing in a thin film along the surface of shaft 24 from the roughing stage to the finishing stage of the pump is the same, however.

As indicated hereinbefore, these improvements have provided at least two important results. First of all, the reduction of both recovery time and pump down time is at least 50 percent. Also, we have achieved a substantial reduction-in operating temperatures; tests have shown that temperatures of the oil bath are reduced approximately 10 centigrade. It may be added that pump down time is that time required for a cold or newly assembled pump to provide the rated vacuum, while recovery time is that time required for a Warm pump to return to the rated vacuum of the pump.

The foregoing description and the drawings are given merely to explain and illustrate our invention and-the invention is not to be limited thereto, except in so far as the appended claim is so limited, since those skilled in the art who Vhave our disclosure before them will be able to make modifications and variations therein without departing from the scope of the invention.

We claim:

In a vacuum pump comprising a center plate having a stator iixedA to each side thereof, said stator-s each being formed withan internal rounded surface, a rotor eccentrically mounted within each stator and in contact with the respective rounded surfaces to provide a crescent shaped pumping chamber within each stator, `said stator-s each ybeing formed with inlet conduit means on theintake side thereof `and outlet conduit means on the exhaust sidey thereof, a pump inlet passage formed in said centcr plate and-leading to said inlet conduit means of one of said stators, said one stator and its rotor vcomprising a pump finishing stage, a pump outlet passage formed in said'center plate leading from the outlet conduit means vof the other of said stators, said other stator and its rotor comprising the roughing stage of the pump, said center plate being formed with a crosswse passage connecting said outlet conduit means of said nishing stage stator with said inlet conduit means of said roughing stage stator, vane means carried by each of said rotors, said vane means comprising a pair of diametrically opposed, outwardly biased, sliding blades having the outer ends thereof in contact with the respective internal surfaces of said stators, each of said stators having an end plate secured to the outwardly facing side thereof, a shaft rotatably mounted in said center plate and extending outwardly of each side of said center plate, said rotors being keyed to the respective ends of said shaft, and means for supplying lubricant to the mounting for said shaft and to said vanes and rotors, the improvement wherein said center plate is formedl with an annular recess on both the roughing and finishing stage sides thereof about said shaft, and conduit means extends between the annular recess and the end of said crosswse passage on each side of said center plate, said conduit means respectively merging into said ends of said crosswse passage at a point above the bottom of said crosswse passage.

References Cited in the ile of this patent UNITED STATES PATENTS 2,337,849 Dubrovin Dec. 28, 1943 FOREIGN PATENTS 620,465 Germany Oct. 22, 1935 678,962 Germany July 26, 1939

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