The present invention relates to a lubricant-sealed vacuum pump, particularly a rotary vane pump.

Lubricant-sealed vacuum pumps such as e.g. rotary vane pumps comprise a pump housing in which a suction chamber is defined. Within the suction chamber, at least one rotor element is arranged. In a rotary vane pump, the rotor element is arranged eccentrically within a cylindrical suction chamber. The rotor element is provided with a plurality of sliding vanes which are radially slideable in the rotor element, with the outer edge of the sliding vanes being in abutment on the inner wall of the suction chamber. As a result of the eccentric arrangement of the rotor element, the volume of the individual chambers formed by the sliding vanes will be changing so that the to-be-conveyed medium will be compressed . Via a lubricant supply duct, lubricant is supplied to the at least one rotor element. The lubricant is provided to achieve a sealing between the rotor element and the inner wall of the suction chamber. Thus, in a rotary vane pump, the lubricant serves for generating a sealing effect between the sliding vanes connected to the rotor element, and the inner wall of the suction chamber. In rotary vane pumps, the lubricant supply duct normally extends within the rotor, wherein the lubricant will be supplied to the recesses of the rotor in which the sliding vanes are held for radial displacement. Under the effect of the centrifugal forces, the lubricant will then reach the outer edge of the sliding vane that has the inner wall of the suction chamber abutting on it.

The rotor element is enclosed by a housing in which the shaft is arranged. Normally, the shaft is driven by an electric drive motor. Particularly in the area where the shaft passes through the pump housing, a main seal is provided. The latter normally comprises a sealing lip which is in abutment on the shaft surface or e.g . also on an outer side of a shell which is connected to the shaft in this area. In this arrangement, the provision of a shell may, depending on the given circumstances, have advantages in the assembly process and/or the advantage that the shell can be formed of a material improving the sealing tightness. Even in seals of high quality, leakages may happen to occur, particularly after many hours of use. Such leakages may be caused e.g . by particles intruding into the lubricant. These particles may intrude into the lubricant e.g . as a result of abrasion or the like, or they may enter the lubricant out of the medium which is to be conveyed by the vacuum pump. If such particles happen to reach the area between the sealing lip of the seal and the shaft surface or the outer side of the shell surrounding the shaft, leakages will occur on the shaft seal.

It is an object of the invention to improve the sealing tightness of such shaft seals in lubricant-sealed vacuum pumps and respectively to extend the useful life of such seals.

The above object is achieved by the lubricant-sealed vacuum pump defined in claim 1.

According to the invention, the lubricant-sealed vacuum pump comprises, apart from the main seal, an additional seal. The main seal normally comprises a seal lip arranged in abutment on the shaft surface or on an outer side of a shell surrounding the shaft. According to the invention, the preferably annular additional seal is arranged on an inner side of the main seal that is facing toward the suction chamber. The additional seal comprises a sealing lip arranged in abutment on the shaft surface or on the outer side of the shell surrounding the shaft. Thus, according to the invention, two seals are provided directly adjacent to each other, wherein it is preferred that both seals comprise a sealing lip arranged in abutment on the shaft surface or on the outer side of the shell .

By providing a main seal and an additional seal, it is e.g . possible to produce the sealing lip of the additional seal within a mold and or to produce it from a material which is especially suited to prevent the intrusion of particles into the area between the additional seal and the main seal and respectively to reduce the risk of such an intrusion. Thus, the additional seal serves as a kind of filter preventing the transport of particles in the direction of the main seal. As a result, it is then possible to produce particularly the sealing lip of the main seal from a softer material because the danger is reduced that particles of a possible damaging effect on the main seal might reach the latter. The material for the main seal can thus be selected substantially under the aspect of achieving the best possible sealing effect, while the material for the additional seal will be selected substantially under the aspect of a safe retention of damaging particles. As material for the main seal, the use of Viton, FKM, FPM, PTFE and/or EPDM is preferred. The additional seal is preferably made of textile fiber and/or non-woven textile. It is possible to use organic or non-organic textiles.

According to a preferred embodiment, the additional seal is connected to the main seal, particularly fixedly. For instance, the additional seal can be fixedly connected to an inner side of the main seal by bonding, locking engagement or the like. Preferably, the additional seal comprises a particularly annular projection extending into a particularly annular recess of the main seal. Thereby, on the one hand, there can be realized or improved a connection between the additional seal and the main seal and, on the other hand, the stiffness and respectively the position of the additional seal can be improved. According to a preferred embodiment of the invention, the additional seal comprises a holding element. The holding element carries the sealing element of the additional comprising the sealing lip. In this arrangement, the sealing element can be connected to the holding element e.g . by bonding, welding or the like. By designing the additional seal from two elements, it is particularly possible to use different materials.

In case that the additional seal is provided with a holding element, it is preferred that the holding element is connected - particularly fixedly - to the main seal and, according to a preferred embodiment, comprises the above described projections for connection to the main seal . Further, the holding element can also be connected to the main seal in one piece.

Further, according to a preferred embodiment of the additional seal, it is preferred that the sealing lip is arranged at an inclination and is facing in the direction of the suction chamber. Achieved in this manner is a better retention of particles and respectively a better filtering effect of the additional seal.

Particularly in case of a sealing lip arranged at an inclination, it is preferred that the holding element comprises a support element which supports the sealing lip and respectively has the sealing lip resting on it. In this arrangement, the support element is preferably arranged at an inclination in the direction of the suction chamber. The inclination of the support element and/or of the sealing lip relative to the shaft surface and respectively the outer side of the shell is preferably in an angular range from 10° to 60°.

According to a further preferred embodiment of the invention, an outer side of the main seal has an annular cover element connected to it. Herein, the outer side of the main seal is the side of the main seal that faces away from the suction chamber. Said cover element, which particularly can also be formed as an annular protrusion, is preferably formed in one piece with the main seal and is connected to it by bonding, welding, locking engagement of the like. By the annular cover element, there is formed a collection chamber for lubricant existent outside the main seal. In cases where, particularly after long operating periods and particularly in spite of the provision of the additional seal, lubricant should happen to issue from the main seal, this lubricant will be trapped in said collection chamber.

In the embodiment of the invention wherein a shell is arranged on the shaft, it is preferred that an outer edge of the cover element faces in the direction of the shaft and has a smaller diameter than the outer diameter of the shell. Thus, the cover element covers the shell in radial direction. In this manner, there is formed an additional collection chamber for the lubricant because the lubricant, when passing along the outer side of the shell, will get to the outside and then will be retained by the cover element. Due to the occurring centrifugal forces, the lubricant will be held in a collection chamber which particularly surrounds the shell at least partially.

For further improvement of the useful life, a particularly preferred embodiment of the invention additionally provides a conveying element arranged on the inner side of the collection chamber. With the aid of said conveying element, the lubricant that has reached the collection chamber will be conveyed in the direction of the suction chamber. This could be realized e.g . by a transverse bore which, starting from an inner side of the collection chamber, extends inwards, wherein this opening should be formed at an inclination so as to effect a corresponding lubricant conveyance due to the centrifugal force. With particular preference, said conveying element is formed as a feed screw arranged on the inner side of the collection chamber. Due to the movement of the lubricant in the collection chamber, a conveyance in the direction of the suction chamber is effected . Particularly, there is effected a conveyance in the direction of the sealing lip of the main seal so that, in this area, the lubricant that has emerged will be conveyed back again in the direction of the suction chamber. Further, in this manner, a counter- pressure will be generated on the outer side of the sealing lip of the main seal, thus reducing the danger of leakage of lubricant. With particular preference, the inner side of the collection chamber, particularly in the area where the conveying element is arranged, has a - particularly continuously - decreasing diameter in the direction of the suction chamber. In this manner, returning the lubricant in the direction of the suction chamber is improved . Particularly, it is thereby rendered possible in a simple manner, by providing a projection or a groove, to form a helical conveying means on the inner side of the collection chamber.

According to a further preferred embodiment, there is additionally provided a collection element for lubricant on an outer side of the main seal and/or on an outer side of the housing that surrounds the main seal. Thereby, a further extension of the useful life can be achieved . The function of said collection element resides in that, if lubricant should issue from the collection chamber, this lubricant will be received or sucked by the collection element. Said collection element herein is particularly formed similar to a sponge or the like. For instance, the collection element can be of an annular shape and surround the shaft particularly entirely. The provision of such a collection element has the advantage that, on the one hand, the lubricant will not run along on an outer side of the housing, drip onto a factory floor, or the like and, on the other hand, that a leakage of lubricant will be easily visible to the user.

The provision of a cover element on the outer side of the main seal, particularly in connection with the collection element on the outer side of the main seal and/or the outer side of the housing, represents an invention in its own right that is independent from the additional seal provided on the inner side of the main seal. However, the combination of the two inventions is preferred.

The invention will be explained in greater detail hereunder by way of a particularly preferred embodiment with reference to the accompanying drawings. In the drawings:

Fig. 1 is a largely simplified schematic sectional view of a rotary vane pump,

Fig. 2 is a view of a preferred embodiment of the shaft seal according to the invention, and

Fig. 3 is an enlarged schematic view of a part of the shaft sealing .

A rotary vane pump comprises a suction chamber 10 formed by a housing 12. Suction chamber 10 is connected to an inlet 14. Inlet 14 is connected to a chamber, not shown, which is to be evacuated, and again comprises an inlet valve, not shown. Within suction chamber 10, a rotor element 16 is eccentrically arranged, so that different chambers 18 are formed in the cylindrical suction chamber 10. Said chambers 18 are respectively delimited by sliding vanes 20 which are held in the rotor element in slots and respectively recesses 22 in a manner allowing for radial displacement of the vanes therein. Said recesses 22 are connected to lubricant supply channels 24 (only schematically outlined in the Figures). Rotor element 16 is carried by a rotor shaft 26. Thereby, the rotor element 16 and the rotor shaft 26 can be made of one part. Further, the smallest chamber 18 has an outlet 28 connected to it. On said outlet 28, in turn, an outlet valve is provided, particularly in the form of an oil-sealed valve plate or the like.

In the particularly preferred embodiment of the shaft seal according to the invention as shown in Fig. 2, the two inventions, related to an additional seal arranged within the main seal, and related to the collection chamber arranged outside the main seal and to the collection element, are combined .

In the illustrated exemplary embodiment, the shaft 26 is surrounded by a shell 30 or sleeve ring . The shell 30 is e.g . pressed onto the shaft 26. Fur- ther, shell 30 is surrounded by a main seal 32. In the illustrated exemplary embodiment, the main seal 32 comprises a sealing lip 34 arranged in abutment on an outer side 36 of shell 30. For improving the abutment force, an annular metallic spring 38 could be arranged on the inner side of the sealing lip 34. Connected to the sealing lip 34 is a C-shaped annular element 40 of the main seal 32. The main seal 32 is arranged in an annular recess of housing 12.

On an inner side 42 of main seal 32 facing in the direction of the suction chamber 10, an annular additional seal 44 is arranged . In the illustrated exemplary embodiment, the additional seal 44 is of a two-part design and comprises a sealing element 46 and a holding element 48. The sealing element 46 forms a sealing lip 50 which again is arranged in sealing abutment on the outer side 36 of shell 30. The sealing lip 50 serves for filtering out or retaining particles so that these cannot advance in the direction of the sealing lip 34 of main seal 32. Sealing lip 50 is inclined and respectively arranged at an inclination in the direction of the suction chamber 10. Further, the additional seal 44 comprises a holding element 52 supporting this portion of sealing element 46. The supporting element 52 is not in contact with the rotating sleeve 30. There is a radial clearance between the supporting element 52 and the sleeve 30.

In the illustrated exemplary embodiment, the holding element 48 of the additional seal 44 further comprises one or two axial annular projections 54,56. These serve particularly for connection to the C-shaped element 40 of main seal 32. For this purpose, the two projections 54,56 extend into the opening 58 of main seal 32 formed by C-shaped element 40. The additional seal 44 is connected to the main seal 32 by clamping or gluing of annular ring 54 in the C-shaped element 40.

In the illustrated exemplary embodiment, a cover element 62 is arranged on an outer side 60 (Figure 3) of the main seal 32. Said cover element 62 which in the illustrated exemplary embodiment is formed as a part-ring- shaped projection, comprises an outer edge 64 facing in the direction of a shaft surface 65, but not in contact with it. There is a clearance between the static lip 64 and the rotating surface 65. The diameter of said outer edge 64 is smaller than the outer diameter of shell 30. In this manner, there is formed a collection chamber 66 for collection of lubricant which may happen to leak out in the area of sealing lip 34. For returning such leaked lubricant in the direction of the collection chamber 66, as illustrated by the arrow 68, a conveying element 72, particularly formed as a spiral, is arranged on an inner side 70 of collection chamber 66. Particularly because, in the area of the conveying element 72, said inner side 70 has a decreasing diameter in the direction of the suction chamber, possibly leaking lubricant will be reliably conveyed back from the collection chamber 66 into the suction chamber 10.

According to the preferred embodiment, it is further possible to provide a likewise annular collection element 74 (Figure 2) on the outer side 60 of main seal 32 or fixed on the surface 75 of the housing 12. By this collection element 74, lubricant which may happen to leak out from collection chamber 66 can be sucked and stored. Collection element 74 is preferably made from an organic or non-organic sponge-like material.