US3402880A

US3402880A - Flexible rotor vacuum pump

Info

Publication number: US3402880A
Application number: US614291A
Authority: US
Inventors: David B Webb
Original assignee: David B. Webb
Current assignee: DAVID B WEBB
Priority date: 1967-02-06
Filing date: 1967-02-06
Publication date: 1968-09-24
Anticipated expiration: 1985-09-24

Description

United States Patent O 3,402,880 FLEXIBLE ROTOR VACUUM PUMP David B. Webb, 181 Easy St., Alamo, Calif. 94507 Filed Feb. 6, 1967, Ser. No. 614,291 12 Claims. (Cl. 230-147) ABSTRACT F THE DISCLOSURE A vacuum pump employing a generally annular flexible rotor with a radially projecting guide which reciprocates in a guide slot in the pump housing.

Background of the invention The present invention relates to vacuum pumps; more particularly it relates to vacuum pumps employing a exible rotor having a radially projecting guide which reciprocates in a guide slot in the pump housing.

The closest related art which has been determined is U.S. Patent No. 1,501,596 for Rotary Blower and Rotary Engine issued to Max Guttner on July 15, 1924. However, the device shown and described therein is not suitable for use as a vacuum pump for reasons which will hereinafter become apparent.

One of the main considerations in the art of making vacuum pumps is providing a device which will pump gas out of a partially evacuated volume without backow. To `do this, it is usually necessary to employ an internal configuration in the pump, if it is of the reciprocating variety as opposed to a diffusion pump, having close tolerances or contact between the moving parts.

A basic problem which occurs in the numerous types of reciprocating vacuum pumps is wear on the close tolerance or contacting surfaces which reduces the pumping eiliciency and performance of the pump. In most vacuum pumps there is an average of tive to seven moving parts upon which wear may occur, Applicants invention reduces the number of moving parts which are used whereby fewer wear points are present, less heat is produced by friction, and less energy is consumed in operating the pump.

It will be noted that if one were to build a vacuum pump based on the teachings of the cited prior art reference, many disadvantages become immediately apparent. Since the rotor elements (pistons 7 and 8) are made of a solid construction, they must either contact and drag along the wall of the housing 1 during rotation or be accurately machined to have a very close clearance therewith for proper sealing. Although a rubbing contact between parts is generally avoided whenever possible in making any kind of a machine, vacuum pumps often use a contacting arrangement between the parts to eiTect the seals necessary for ypulling a vacuum. However, the dragging and interference between the parts which would be effected by a configuration constructed in accordance with the prior art reference would cause considerable friction which would more than likely be unacceptable. The second alternative of providing close tolerances would be expensive to construct, and, as wear occurred on the journals of the rotary elements, contact would likewise again occur creating the problems of friction and increased clearance between the parts which would permit internal leakage and prevent a vacuum from being maintained.

A further objection to the use of a vacuum pump constructed according to the prior art reference is due to the journalling of the elements 9 and 10 called the links. These are articulated in rotational cylinder sections which are unnumbered in the patent. As such a pump operates, there would be wear between the articulated links and 3,402,880 Patented Sept. 24, 1968 Mice the rotational cylinder sections and also between the cylinder sections and the casing. Each of these wear surfaces would increase the clearance between the elements of the pump which would permit leakage.

It is a further problem in the prior art of vacuum pumps lthat such pumps usually must be driven at relatively low rotational speeds because of their complicated internal structure, numerous moving parts, and contacting seals. Generally they cannot be operated at the same speed as the motors by which they are driven. The present invention comprises a vacuum pump which may be directly driven by a motor.

It is therefore an object of the present invention to provide a vacuum pump which has a minimum of moving parts.

It is another object of the present invention to provide a vacuum pump which can be mounted on a motor and driven directly thereby.

It is a further object of the present invention to provide a vacuum pump which incurs only a minimum of wear internally thereof whereby the efficiency ofthe pump is maintained over a relatively long period of time.

It is still another object of the present invention to provide a vacuum pump which is self-compensating for internal wear.

It i-s still a further object of the present invention to provide a two-stage vacuum pump in which the stages can be operated in parallel for exhausting large volumes or in series for pulling higher vacuums.

And yet another object of the present invention is to provide a vacuum pump of simple construction characterized by securing ilat plates together.

Summary of the present invention The present invention is a vacuum pump which is characterized by a stator body defining a generally circular internal cavity wall having a guide slot. An arcuate seal is formed in the cavity wall surrounding the guide slot. Intake and exhaust ports are disposed one on each side of the guide slot in the arcuate seal, and they communicate through the stator body with the internal cavity. A oneway valve constricts the exhaust port. A generally annular flexible rotor is disposed in the cavity and has a projecting guide disposed in the guide Slot and formed for reciprocation therein. Shoulders are formed on the rotor on both sides of the guide. An eccentrically juornalled cam is disposed internally of the rotor. Drive means are provided for rotating the cam while a relief means is provided for permitting the pump to start under load.

Descriptionv of the drawings FIGURE 1 is a side elevation in partial section showing a preferred embodiment of the present invention;

FIGURE 2 is an end sectional elevation taken along lines 2-2 of FIGURE 1 with the pump casing removed;

FIGURE 3 is a sectional view of one of the cavity plates taken along lines 3 3 of FIGURE 2 with the internal elements removed.

Description of the preferred embodiments Reference is made concurrently to FIGURES 1 and 2 of the drawings for a description of a preferred embodiment of the present invention which includes a pair of basic pumping elements which are similar to each other and arranged in series. The basic element of the vacuum pump contemplates a stator body 11 dening a generally circular internal cavity wall 13 having a radial guide slot 15 formed therein and a rst circular wall portion 17 disposed opposite the guide slot.

A second circular wall portion 19 is provided in the cavity wall surrounding the guide slot and forms an arcuate seat in the cavity wall which extends from both sides of the guide slot. The second circular wall portion is formed of a lesser diameter than the first wall portion and extends for a total of approximately between 30 and 45 degrees of angular generation.

Intake and

exhaust ports

21, 23 respectively are disposed proximate the guide slot, one on each side thereof, in the arcuate seat r second circular wall portion. The intake and exhaust ports communicate through the stator body with the internal cavity. A one-way valve 25 constricts the exhaust port to prevent backflow into the pumping chamber 27.

A generally annular fiexible rotor 29 is disposed in the cavity of the body and has a radial guide 0r web 31 projecting therefrom disposed in the guide slot of the cavity Wall. The guide is formed for reciprocation in the guide slot. The annular rotor has shoulders 33 formed on each side of the guide.

An eccentrically journalled circular cam 35 is disposed internally of the annular rotor. The rotor is tangent to the pump body at the point of greatest eccentricity of the cam. In other words, the peripheral surface of the cam describes an arc of travel which at its maximum radial extension from the center of rotation of the cam is spaced from the first wall portion of the cavity a distance equal to the thickness of the annular portion of the rotor.

A driving means, such as an electric or other type motor 37, is provided for rotating the cam.

This heretofore described basic element of the invention employs a single vacuum pumping chamber 27. However, for most practical vacuum purposes, it is more efiicient to operate a number of these vacuum pumping charnbers in stages, either in parallel or in series, most usually in series.

The preferred embodiment of the present invention comprises a pair of basic elements which are created in a unique manner. The stator body is constructed by assembling a series of plates which define the separate internal cavities for the first and second stages and the sealing partitions at both ends of the pumping cavities. By utilizing a series of plates for effecting the construction of the pump body, numerous advantages and unique features are obtained which will hereinafter become apparent.

A first end plate 39 is secured to one end of an electric motor 37. The drive shaft 41 of the motor extends through the first end plate in sealed relation. This permits the motor and the pump to be securely engaged and reduces to a minimum the overall dimensions of the combined pumping and driving units since there is virtually no lost space between them.

A first cavity plate 43, which in effect is an irregular annular ring, is secured against the first end plate and sealed therewith. The first cavity plate defines a generally circular internal cavity wall 13 having a radial guide slot 15. The guide is substantially a rectangular groove milled on a radial line into the internal wall of the casing.

The cavity wall has a first circular wall portion 17 disposed opposite the guide slot. This comprises substantially all but about 30 to 45 degrees of the angular generation of the internal cavity wall. The second circular Wall portion 19 which forms the arcuate seat has a lesser diameter of generation than the first Wall portion. It is created by milling on a smaller radius which is taken from a point along the radial line forming the center line of the guide slot. This second circular wall portion forms an arcuate seal which takes up the remaining 30 to 45 degrees of angular generation on both sides of the guide slot. This is the total angle of generation and does not mean 30 to 45 degrees to each side of the guide slot. However, the range 30 to 45 degrees is an approximate value and could be considerably more or less depending upon the size of the pump.

An intermediate plate 45 is secured to and seals with the first cavity plate. The drive shaft extends through the intermediate plate in sealed relation.

A second cavity plate thicker than the `first cavity plate is secured to and seals with the intermediate cavity plate. By being thicker, the second cavity plate provides a working or pumping chamber of greater volume than the first cavity plate.

In operation however, the second cavity plate fonrns the initial or first stage of the pump. The second pumping stage can have a smaller volumetric capacity because the gas which is vented to it from the first stage is under pressure relative to the pressure the rst stage pulls on.

The second cavity plate is similar to the first cavity plate. By the use of the term similar, it is meant a structure having the same features or characteristics as the element to which it is referred. In other Words, it defines an internal cavity having the same limitations as the first cavity plate, but the elements may be of a different size or of different proportions.

The relief valves 49 provided for each of the guide slots in the stator body to permit the pump to start under load include reed valves 51 secured to the external side of the cavity plates and covering vent ports 53. The ports communicate with the guide slots and have a portion with a larger cross-sectional area operating the valve than vents the slots. This is effected by providing a counter sink 55 of a relatively large diameter with respect to the vent hole at the discharge end of the port 53 whereby the pressure in the guide slot operates on the reed valve over a larger surface area than that provided by the cross-sectional area of the vent hole and provides a mechanical advantage for opening the valve. In other words, this reduces the pressure required to operate the valve.

A second end plate 57 is secured to and seals with the second cavity plate.

`Porting means are provided which in the basic element include simply an exhaust port 23 disposed on one side of the guide slot 15 and an intake port 21 disposed on the other side. Both of the ports terminate at one end thereof in the arcuate seat 19 and communicate through the stator body 11.

`In the preferred embodiment, the porting means include a transfer passage 59 formed in the cavity plates and the intermediate plate. This passage is formed by drilling aligned holes through the cavity plates and the intermediate plate. The transfer passage includes communication ports at both ends thereof formed by cutting a slot through the internal lwall of the cavity plate in the arcuate seat portion to connect with the passages. The

elongated ports

21, 23 effect the best possible seals with the rotor. One of the communication ports for the transfer passage is formed in the second circular wall portion of the rst cavity plate on the intake side of the guide slot and the other is formed at the other end of the passage in the second circular wall portion of the second cavity plate on the exhaust side of the guide slot.

The porting means in the preferred embodiment also includes an intake passage in the second cavity plate having a communication port in the second circular Wall portion of the second cavity plate on the intake side of the guide slot. The other end of the intake passage is provided with means for attaching the pump to whatever volume is to be evacuated. This includes a passage or tube 63 which extends from the outer periphery of the second cavity plate through the end wall 65 of the pump casing (which is actually the end plate of the motor).

The porting means of the preferred embodiment also includes an exhaust passage 23 which has a communication port at one end in the second circular wall portion of the rst cavity plate on the exhaust side of the guide slot.

In the preferred embodiment, a reed valve 25 is utilized as the one-way valve for constricting the exhaust port. It is disposed on the outer end of the exhaust passage on the external surface of the first cavity plate.

The intake and exhaust passages are likewise formed by drilling holes laterally through the cavity plates and then by milling the

communication ports

21, 23 through the internal cavity wall in the arcuate seat portion. The passage portions 67 of the ports extend through the cavity wall by means of obliquely drilled holes which communicate with the laterally drilled passages.

A generally annular exible rotor 29 is disposed within each of the cavity plates. The rotors have a thickness equal to that of the cavity plates whereby they each seal with the adjacent end plate and the intermediate plate. The shoulders 33 or projections formed on the rotor on each side of the guide increase the radial depth of the rotor for a small amount of angular generation to each side of the guide. In operation, these shoulders form seals for the ports of the intake and exhaust ports of each cavity.

An individual eccentrically journalled generally cylindrical cam 35 secured to the drive shaft 41 of the motor is provided for each of the rotors. The major eccentricity of each of these earns is disposed at a re- -lation of 180 degrees with respect to each other whereby the two rotors are exactly out of phase. This tends to balance the reciprocating weight of the pump.

The various moving parts of the present invention must he sealed in order to evacuate the major portion of air or gas for any given volume. The seals must be sufficient to prevent leakage within the pump or movement of air or gas from `one part of the cycle to another within the pump. The best means for achieving seals for these pumps has proved to be the use of an oil of the proper characteristics which acts as an eicient sealing medium between the parts.

An external casing 69 secured to the en-d plate 65 of the motor is provided for containing the sealing oil. The intake passage of the porting means communicates through the casing by means of the aforementioned tube 63. The exhaust port vents directly into the Oil reservoir, which is at atmospheric pressure because of a vent located in the end plate 65 of the motor which is the top end of the oil reservoir. As the expelled gas is vented `by the exhaust port into the oil, it migrates to the surface and out the vent before any appreciable pressure builds up to Ihold the exhaust port closed.

With each exhaust cycle, oil is expelled from the pumping chambers. It is therefore necessary that means be provided for replacement of the oil to the internal working parts of the pump. This is effected by a passage 71 which extends through the upper plates of the pump to vent into the rst stage by an oil hole in the second cavity plate positioned in such a manner whereby it is covered by the tiexible rotor which abuts the end and intermediate plates in sealing relation. The passage could be an oil tube, but either has its intake in or near the iirst end plate high in the oil reservoir. This passage permits oil to be drawn into the pump from the external reservoir to enter the pumping chamber at a point which is continually covered by the end face of the rotor. The oil hole is located high in the reservoir so it does not pick up particles or impurities which may have been exhausted into the oil reservoir. The suction in the pump pulls the oil into it while the flexible rotor prevents air from leaking out. Exhaust oil from the irst stage in the second cavity plate lubricates the second stage.

As a result of using oil as a sealing medium, a problem is created which is taken care of by the relief valves provided for each of the guide slots. When the pump is stopped under load, or with a vacuum in the internal chambers, oil migrates into the guide slot area and collects in the space at the end of the slot whereby the slots fill with oil. At the time of restart, the oil must be forced out of the gap to permit the web to travel and to prevent a lock-up. Hydraulic action of the oil will not permit it to ow around the web to the exhaust during the start up. Therefore, the relief valves are required. During start up, oil is forced out of the Valve by the piston like action of the guide. The one-way action of the reed valves prevent oil or air from re-entering the guide slot.

During operation, the motor drives the cam whereby the rotor is forced around the internal cavity wall of the rotor body or the cavity plates with the web or guide ilexing at its connection with the rotor where it enters the guide slot. By providing the intake and exhaust ports on opposite sides of the guide slot, the pump draws air through the intake port into the pumping chamber 27 formed between the body wall and the rotor. As the cam revolves, the rotor forces the air around the internal cavity in the pumping chamber ahead of the tangent point of the rotor with the body and forces it out of the exhaust port. The expanding chamber behind the point of tangency draws air into the pump through the intake port.

The web of the rotor in the guide slot eifectively seals the exhaust port from the intake port. The one-way valve which constricts the exhaust port prevents the exhaust air or oil from the oil reservoir from leaking into the pump by backilowing through the exhaust port. The two end plates and the intermediate sealing plate of the pump body provide end seals to the flexible rotors. They also seal the laterally drilled portions of the intake and exhaust passages as well as the drive shaft.

An important feature of the present invention is the provision for the arcuate seat, or the second circular wall portion of the pumping cavity, which extends on both sides of the guide slot, and the mating shoulders on the rotors which are provided on both sides of the guide. These increase the degree of tangency between the pump body and the exible rotor at the intake and exhaust ports. The reason for this feature will be appreciated when two circles of different diameter are considered with one inside the other and having a tangential point of contact. The tangential relationship means that there is space between the two circles on both sides of, and adjacent, the point of tangency. Hence, when an exhaust or intake port is located directly under the point of tangential contact of the rotor with the stator, or pump body, there is not a complete seal on the port, unless that port is very thin (theoretically a line). To improve the sealing of the intake and exhaust ports, the arcuate seat in the cavity walls and the shoulders on the rotor are provided to increase the degree of tangency between the body and the rotor.

In practice, the arcuate seat is formed by machining an eccentric bore into the wall of the body from a center of generation located on the radial center line of the guide. The shoulders formed on the rotor are of a comparable diameter to the arcuate seat so that the rotor hasa larger degree of Contact with the cavity walls when the major eccentricity of the cam passes through the angular rotation of approximately 30 to 45 degrees surrounding the guide slot.

The vacuum pump of the preferred embodiment can be operated in parallel as well as in series, or valving means can be provided for permitting the pump to be operated either in parallel or series. To operate the pump in parallel, the intake ports of both stages need to be connected to a common intake tube; the exhaust ports for both stages would require one-way exhaust valves, and an oil hole would be needed to lubricate the second stage. A valving means to permit either switching between two stage parallel operation and series operation requires simply a valving arrangement for switching from the parallel arrangement by connecting the exhaust from the first stage to the intake of the second stage. This can be effected by any number of means and no particular one is a preferred means.

There are numerous advantages to the preferred ernbodiment of the present invention. A pump constructed in accordance with the present teachings uses a minimum of moving parts which, in number, are comparably onehalf to one-fourth the number of those used in competitive sized units. Fewer moving parts means fewer wear points, less Wear, less heat from friction, less maintenance, higher efiiciency, and lower power requirements.

The flexible rotor reduces wear on the internal surface of the body by virtue o-f its relatively soft composition and its mode of operation. During operation, the web is centrifugallyv held against the internal wall of the cavity plates and in the larger size units it stretches an incremental amount to actually walk around the internal surface of the pump body with very little or no relative motion between the rotor and the stator. This prevents all but a very minimum of Wear on the pump body with a very positive sealing action. When the rotor becomes worn out, it is easily replaced and replacing such a rotor is considerably less expensive than having to replaced machined parts.

The use of the flexible rotor has the additional feature of compensating for any wear between the rotor and the pump body by virtue of centrifugal force keeping the rotor tightly sealed against the internal surface of the stator. The rotor can be made of various materials to suit individual needs such as for resistance to corrosive attack.

Because of the particular design of this device, the unit can be operated at driving motor speed. This permits a direct drive operation and vertical mounting which eliminates a main portion of the oil leakage problem which is usually associated with horizontal design vacuum pumps. A direct drive eliminates the power transmission means, such as pulleys and belts or other speed reduction and drive elements whereby still fewer parts are required. As a result of the direct drive, a lighter pump having smaller envelope dimensions than competitive designs is effected.

It will be apparent from the foregoing description of the invention, in its preferred form, that it will fulfill all of the objects attributable thereto. While it has been illustrated and described in considerable detail, the invention is not to be limted to such details as have been set forth except as may be necessitated by the appended claims.

I claim:

1. A vacuum pump comprising a stator body defining a generally circular internal cavity wall having a guide slot,

an arcuate seat formed in said cavity wall surrounding said guide slot,

intake and exhaust ports disposed one on each side of said guide slot in said arcuate seat and communicating through said stator body with said cavity,

a one-way valve constricting said exhaust port,

a generally annular flexible rotor disposed in said cavity Vand having a projecting guide disposed in said slot formed for reciprocation therein,

shoulder-s formed on said rotor on both sides of said guide,

an eccentrically journalled cam in said rotor,

drive means for rotating said cam, and

relief means for permitting said pump to start under load.

2. The vacuum pump of claim 1 wherein the relief means for permitting said pump to start under load includes a relief valve for venting said guide slot.

3. The vacuum pump of claim 2 wherein said relief valve for said guide slot includes a reed valve and a port of larger cross-sectional area operating said valve than vents said slots.

4. The vacuum pump of claim 1 wherein a second vacuum pump similar to said first vacuum pump is hooked in series to said rst pump by having its intake port connected to the exhaust port of said first vacuum pump, the cam of said second pump is driven by the same means provided for rotating the cam of the first pump, and

a one-way valve constricts the exhaust port of only the second of said pumps.

5. The vacuum pump of claim 1 wherein said arcuate seat in said cavity wall extends for approximately between 30-45 degrees of angular generation substantially centered with respect to said guide slot.

6. A vacuum pump comprising a stator body defining at least one generally circular internal cavity Wall having a radial guide slot, said cavity having a first circular wall portion disposed opposite said guide slot and a second circular wall portion of a les-ser diameter than said first wall portion extending on both sides of said guide slot for a total of approximately between 30-45 degrees of angular generation,

a reed relief valve venting said guide slot,

intake and exhaust port disposed proximate said guide slot, one on each side thereof and formed in said cavity second wall portion, said ports communicating through said stator body with said cavity,

a one-way reed valve covering the external end of said exhaust port,

a generally annular flexible rotor disposed in said cavity and having a radial guide projecting therefrom disposed in said guide slot and formed for reciprocation therein, said rotor having shoulders on said rotor on each side of said guide,

an eccentrically journalled circular cam disposed internal of said annular rotor, the rotor being tangent to the first circular wall portion at the point of greatest eccentricity of the cam, and

driving means for rotating said cam. l

7. The vacuum pump of claim 6 deleting the one-way valve on said exhaust port and including a Second stage wherein said stator body defines a second generally circular cavity similar to said first cavity but of a larger volume than said first cavity, the cam in ysaid second cavity driven by same means that drives the cam in said first cavity, and

porting means connecting the exhaust port of said first stage with the intake port of said second stage, and

a one-way reed valve on the exhaust port of said second stage.

8. The vacuum pump of claim 7 wherein said body comprises a series of assembled plates including a first end plate, a first cavity plate defining said first cavity, an intermediate sealing plate, a second cavity plate defining said second cavity, and a second end plate.

9. The vacuum pump of claim 6 including an external casing for containing oil and an oil inlet through said stator body continually covered by said rotor.

10. A vacuum pump comprising a first end plate having a drive shaft extending there- Ithrough in sealed relation,

a first cavity plate secured against and sealing with said first end plate and defining a generally circular internal cavity wall having a radial guide slot, said cavity wall having a first circular wall portion disposed opposite said guide slot and a second circular wall portion of a lesser diameter than said first wall portion extending on both sides of said guide slot for a total of approximately between 30-45 degrees of angular generation,

an intermediate plate secured to and sealing with said first cavity plate and having said drive shaft extending therethrough in sealed relation,

a second cavity plate thicker than and similar to said first cavity plate secured to-and sealed with said intermediate cavity plate,

reed relief valves venting the guide slots of said first and second cavity plates, said relief valves having ports of larger cross-sectional area operating said reed valves than vent said slots,

a second end plate secured against and sealed with said second cavity plate,

porting means including a transfer passage formed in said plates and having a communication port at one end thereof formed in the second circular wall portion of said first cavity plate on the intake side of said guide slot and a communication port at the other end of said passes formed in the second circular wall portion of said second cavity plate on the eX- haust side of the guide slot,

an intake passage including a communication port in the second circular wall portion of said second cavity plate on the intake side of said guide slot and connecting means at the other end thereof for attaching to the volume to be evacuated, and

an exhaust passage including a communication port at one end of said passage in the second circular wall portion of said rst cavity plate on the exhaust side of the guide slot and a one-way reed valve disposed at the other end of said exhaust passage,

a generally annular ilexible rotor disposed within each of said cavity plates sealing with the adjacent plates and having radially projecting guides disposed within the respective guide slots and formed for reciprocation therein, said rotors having shoulders formed on each side of said guide,

an eccentrically journalled generally cylindrical cam disposed within each of said rotors and secured to said d-rive shaft, and

means for rotating said drive shaft.

References Cited UNITED STATES PATENTS Evans 91-56 Guttner 230-147 Mallory 230-147 Smith 230-147 Karasick 230-147 Van Ranst 103-132 Balogh 103-132 Gordinier 10S-132 FRED C. MATTERN, JR., Primary Examiner. 25 WILBUR J. GOODLIN, Assistant Examiner.