Single-Shaft Vacuum Positive Displacement Pump

Abstract

A single-shaft vacuum positive displacement pump (10) comprises two pump stages (12,14) each provided with a pump rotor (13,15) and a drive motor (16). The drive motor (16) is axially arranged between the two pump stages (12,14), wherein the shaft (22) supports the pump rotors (13,15) and the motor rotor (17).

Description

The invention relates to a single-shaft vacuum positive replacement pump comprising two or more pump stages arranged one behind the other and a drive motor.

Conventional single-shaft vacuum positive replacement pumps comprising two pump stages are configured as two-stage rotary piston pumps or rotary vane pumps, for example. Usually, the two pump stages are axially arranged one behind the other, wherein the drive motor is disposed at a longitudinal end of one of the two pump stages and drives the common shaft of the two pump stages. Both the drive motor and the two pump stages are arranged in their own housings such that the shaft passes through a plurality of housing openings. For shaft supporting purposes at least two shaft bearings are provided in the drive motor, and in the region of the pump stages three shaft bearings are normally arranged.

It is an object of the invention to provide a simplified single-shaft vacuum positive replacement pump.

According to the invention, this object is achieved through the features of claim 1.

In the positive replacement pump according to the invention, the drive motor is axially arranged between the two pump stages, wherein a single common shaft supports the two pump rotors and the motor rotor. The vacuum positive replacement pump thus only comprises a single one-piece shaft, which offers a number of constructional advantages. In particular two common shaft bearings can be used for supporting the drive motor rotor and the two axially adjacent pump rotors. In this manner, the number of shaft bearings can be reduced to only a few bearings. When the two pump rotors are supported in a cantilevered position, the overall positive replacement pump does not require more than two shaft bearings. Due to the single-shaft configuration a coupling is not required, which further simplifies the layout. Thus a simple two-stage positive replacement pump of compact design, which is inexpensive to manufacture, is provided. To the two pump stages arranged adjacent to the drive motor further pump stages facing away from the drive motor may be axially attached.

Preferably, the gas connection between the two pump stages is defined by the gap between the motor rotor and the motor stator. Formation of a gap between the motor rotor and the motor is unavoidable. This gap serves as a connecting conduit between the two pump stages, namely between the prevacuum stage and the high-vacuum stage. A separate connecting conduit between the two pump stages thus need not be provided. This allows for a simple configuration and an inexpensive manufacture. An additional separate connecting conduit is to be provided merely in the case of a larger pumping capacity.

According to a preferred embodiment, the gap between the motor rotor and the motor stator is cylindrical, i.e. the motor rotor is of cylindrical configuration on the outside, and the motor stator is of cylindrical configuration on the inside.

According to a preferred embodiment, the motor rotor comprises a helical pump groove. The helical rotating pump groove improves the axial gas transport from the high-vacuum stage to the pre-vacuum stage through the gap between the motor rotor and the motor stator.

According to a preferred embodiment, the motor rotor acts as a lubricant pump pumping the lubricant from the upstream to the downstream pump stage. In wet-type vacuum positive replacement pumps, i.e. in positive replacement pumps lubricated with a flowing lubricant, the pump groove is suitable for transporting even the liquid lubricant from the high-vacuum stage to the pre-vacuum stage. Therefore a separate lubricant pump is not required. The lubricant further cools the drive motor and in particular the motor rotor such that a separate motor cooling device may possibly be omitted.

Preferably, a single stator housing surrounds the shaft, wherein the stator housing does not comprise any shaft sealings. The stator housing thus surrounds the two pump stages and the motor rotor, and may possibly define the stators of the pump stages and the drive motor. Since no shaft sealings are provided, all problems and costs associated therewith are avoided. In particular any undesired oil and gas leakage can thus be prevented to a large extent.

Preferably, the stator housing is surrounded by a lubricant housing. The stator housing is arranged in spaced relationship in the lubricant housing such that the lubricant is disposed between the stator housing and the lubricant housing, and is allowed to flow from the outlet to a lubricant pump.

Preferably, the two pump stages are configured as rotary piston or rotary vane pump stages. Multistage rotor stages or claw-type pump stages or other types of pump stages may also be provided.

An embodiment of the invention will now be described in greater detail with reference to the drawings.

The FIGURE shows a longitudinal section of a single-shaft vacuum positive replacement pump according to the invention comprising two rotary vane pump stages.

The FIGURE shows a vacuum positive replacement pump 10 comprising two pump stages 12,14 each configured as a rotary vane pump stage, and a drive motor 16 axially arranged between the two pump stages 12,14. The inlet-side pump stage 14 is connected with a gas inlet 18 and defines the high-vacuum stage. The pump stage 12 arranged downstream as seen in the direction of gas flow is the pre-vacuum stage which pumps gas against the atmospheric pressure out of the gas outlet 20. The two pump stages 12,14 each comprise a pump rotor 13,15, and the drive motor 16 comprises a motor rotor 17. The pump rotors 13,15 and the motor rotor 17 are permanently fixed to a common one-piece shaft 22. The motor rotor 17 is permanently excited.

The gas connection between the two pump stages 12,14 is realized by a cylindrical gap 24 which is defined on the inside by the motor rotor 17 and on the outside by a motor stator 28. The motor rotor 17 comprises a helical groove 30 provided in the cylindrical outside of the motor rotor 17. The gas connection may further be realized by an external channel, e.g. in the case of larger pumping capacities.

The shaft 22 is supported by two shaft bearings 32,34 configured as roller bearings. Slide bearings or gas bearings may also be used. The pump rotors 13,15 are supported in a cantilevered position such that the shaft 22 is supported by the two shaft bearings 32,34 alone.

The two pump stages 12,14 and the drive motor 16 as well as the shaft 22 are supported and fully surrounded by a stator housing 40. The stator housing 40 does not comprise any shaft sealings. The stator housing 40, in turn, is arranged in a lubricant housing 41 which serves for receiving the lubricant and transporting it from the pre-vacuum side to the high-vacuum side.

At the high-vacuum end of the shaft 22 a gear pump 44 is arranged which pumps the liquid lubricant 46 into the gap 24 between the motor rotor and the motor stator via a channel 48. Through a corresponding inlet a small portion of the lubricant delivered by the gear pump 44 is transported directly into the working chamber of the high-vacuum pump stage 14. The mixture of the gas and the lubricant leaving the high-vacuum pump stage 14 is pumped to the pre-vacuum pump stage 12 via the helical pump groove 30, whereby the motor rotor 17 and the motor stator 28 are lubricated and cooled.

Adjacent to the pump chamber outlet of the pre-vacuum pump stage 12 an oil separator 50 is arranged which separates the lubricant dripping down and the the gas pumped off against the atmosphere. The lubricant flows between the lubricant housing 41 and the stator housing 40 and back to the gear pump 44.

Claims

1. A single-shaft vacuum positive displacement pump comprising: two pump stages, each stare including a pump rotor; anda drive motor said drive motor being axially arranged between said two pump stages, and a shaft supporting pump rotors of said pump stages and a motor rotor.

2. The single-shaft positive displacement pump according to claim 1, wherein a gas connection between the two pumps stages is defined by a gap between the motor rotor and a motor stator.

3. The single-shaft positive displacement pump according to claim 2, wherein the gap between the motor rotor and the motor stator is cylindrical.

4. The single-shaft positive displacement pump according to claim 2, wherein the motor rotor comprises a helical pump groove.

5. The single-shaft positive displacement pump according to claim 1, wherein a stator housing surrounds the shaft, wherein the stator housing does not comprise any sealings.

6. The single-shaft positive displacement pump according to claim 1, wherein exactly two roller bearings are provided between the motor rotor and the pump rotors.

7. The single-shaft positive displacement pump according to claim 1, wherein a stator housing is surrounded by a lubricant housing.

8. The single-shaft positive displacement pump according to claim 1, wherein the motor rotor acts as a lubricant pump which pumps a lubricant from a high-vacuum one of the pump stages to a downstream pre-vacuum one of the pump stages.

9. The single-shaft positive displacement pump according to claim 1, wherein the two pump stages are configured as rotary piston or rotary vane pump stages.

10. The single-shaft positive displacement pump according to claim 1, wherein a first bearing and a first of the pump stage rotors are supported on the shaft on one side of the motor rotor and a second bearing and a second of the pump stage rotors are supported on the shaft on an opposite side of the motor rotor.

11. A pump comprising: a motor stator;a motor rotor rotatably mounted in the motor stator on a shaft, the motor rotor and the motor stator defining a fluid passage therebetween;a first pump stage having a rotor mounted on the shaft on one side of the rotor to pump fluid from a fluid inlet into the fluid passage between the motor rotor and the motor stator; anda second pump stage having a rotor mounted on the shaft on an opposite side of the rotor from the first pump stage rotor to pump fluid from the fluid passage between the motor rotor and the motor stator to an outlet.

12. The pump according to claim 11 further including: a first bearing supporting the shaft between the motor rotor and the first pump stage rotor; anda second bearing supporting the shaft between the motor rotor and the second pump stage rotor.