Housing for vacuum pump

Abstract

A housing 10 for a vacuum pump, such as a two-shaft screw vacuum pump, comprises a housing element 12 defining at least partially an elongated pump chamber 18 having a first axial end 14 and an opposi

Description

The present invention relates to a housing for a vacuum pump and in particular for a 2-shaft vacuum pump. Further, the present invention relates to a vacuum pump comprising such a housing. Conventional 2-shaft vacuum pumps and here in particular screw pumps comprise a housing having an inlet and an outlet. By the housing a pump chamber is defined, wherein two rotors are arranged in the pump chamber. Each rotor comprises a rotor shaft and at least one rotor element connected to the rotor shaft, wherein the rotor elements in the case of a screw pump are provided by meshing screw shaped or helical shaped structures. The rotors are rotated by an electromotor and by interaction of the two rotors, a gaseous medium is conveyed from the inlet to the outlet. Therein, positioning of the rotors relative to each other and also relative to the housing is crucial in order to minimize back-flow through gaps between the rotor elements and the housing or the rotor elements of the two rotors. Conventional vacuum pumps are constructed to have a housing element and a headplate at each end of the housing element. This concept is known as "tunnel" stator in which the housing element, defining the pump chamber, is accessible from both end faces. However, assembly of the headpiates which usually carries one of the bearings rotatably supporting the rotor is less accurate and time consuming. Due to this difficulty larger gaps between the rotor elements and the housing or the respective rotor elements of the two rotors are accepted as safety margin reducing the overall pump performance of the vacuum pump. It is an object of the present invention to provide a housing for a vacuum pump which enables positioning of a rotor with higher precision. Further, it is an object of the present invention to provide a vacuum pump with higher performance. The problem is solved by a housing for a vacuum pump according to claim 1 and a vacuum pump according to claim 13. The housing for a vacuum pump according to the present invention is in particular a housing for a 2-shaft vacuum pump such as roots pumps, claw pumps or screw pumps. However, the present invention is not limited to 2-shaft vacuum pumps and can be also implemented into vacuum pumps comprising only one shaft or more than two shafts. The housing comprises a housing element defining at least partially an elongated pump chamber configured to receive the one or more rotors of the vacuum pump. Therein, the inner surface of the pump chamber serves as stator for the vacuum pump interacting with the rotor. The elongated pump chamber has a first end and an opposite second end along the axial direction which is also defined by the extension of the rotor, i.e. coincides with the axis of rotation of the one or more rotors. A ratio L / D of a length L of the pump chamber to a diameter D of the pump chamber is larger than three. Therein, for a non-constant inner diameter of the pump chamber, D may be the smallest diameter. In particular, to achieve high pressure ratios between the inlet and the outlet, it is desirable to increase the ratio L / D of the length L of the pump chamber to the diameter D of the pump chamber. Thus, with larger ratio, high performance vacuum pumps can be provided and in particular a larger number of wraps in the example of a screw pump can be disposed in the pump chamber. According to the present invention first headplate at the first end of the housing element closing the first end of the pump chamber. Therein, the first headplate comprises at least one opening configured to receive a shaft of the rotor of the vacuum pump. Thus, the shaft of the rotor is extending through the opening of the headplate. On a side of the first headplate opposite to the pump chamber, the rotor shaft may be arranged in a gear box or otherwise connected to an electromotor for rotation. In particular, the first headplate may have more than one opening and preferably, the number of openings corresponds to the number of rotors such that the shaft of each rotor extends through one of the openings of the first headplate. A second headplate at the second end of the housing element closes the second end of the pump chamber. Therein, according to the present invention the first headplate and the housing element are integrally formed. In other words, the first headplate and the housing element are one piece. Positioning of the opening of the first headplate and the pump chamber is crucial for alignment of the rotor within the pump chamber. Thus, by building the first headpiate and the housing element as one piece, precision of positioning of the rotor inside the pump chamber is improved. In particular, aligning the position of the rotor inside the pump chamber is simplified since the position of the first headplate and, including with the first headplate, also the at least one opening of the first headplate is fixed and can be provided with higher precision. Consequently, the safety margins for the gaps between the rotor elements of the rotors and / or the inner surface of the pump chamber can be reduced, re-ducing backflow inside the pump chamber. Hence, by integrally forming the first headplate and the housing element, pump performance of a vacuum pump, implementing such a housing, can be improved. In addition, the number of parts can be reduced simplifying the assembly and reducing the costs. Preferably, the housing element and the first headplate are made from a single casting. Consequently, the housing element and the first headplate are machined in the same machining step when forming the pump chamber. Consequently, the relative position of the first headplate and the housing element, I. e. the pump chamber, is fixed and can be provided with high precision. Preferably, by the housing element and the first headplate a bucket stator design is provided. In particular, the pump chamber is provided by a recess in the housing element, wherein the recess is closed by the first headplate. Preferably, the first end is arranged towards an outlet of the housing and in particular the vacuum pump. The second end is arranged towards an inlet of the housing and in particular the vacuum pump. Hence, the first headplate, integrally build with the housing element, is arranged at the high-pressure side of the housing, wherein the second headplate is arranged towards the low pressure or high vacuum end of the vacuum pump. Vacuum pumps are sensitive to radial clearance. However, the clearances on the inlet side are less critical compared to the clearances at the exhaust side. By integrally forming the first headplate at the exhaust side, the required clearances can be achieved. Preferably, the second headplate is plate-shaped and thus, the pump chamber is entirely formed by the housing element. By in the plate shaped second headplate, the second end of the pump chamber is dosed. In particular, the number of parts which need to be aligned with high precision with respect to each other can be reduced. In particular, if the second headplate is arranged towards the inlet of the vacuum pump, i.e. towards lower pressures and higher vacuums, the position of the second headplate needs to be aligned with less precision relative to the housing element. This is in particular the case, if the one or more rotors are cantilevered and only rotatably supported at the first end of the housing. Preferably, the second headplate comprises at least one opening configured to receive the shaft of the rotor. Therein, the number of openings in the second headplate may correspond to the number of shafts implemented in the vacuum pump. Hence, the rotor is fed through the second headplate. In particular, a bearing may be connected to the second headplate in order to rotatably support the second end of the rotor. Preferably, the second headplate comprises a recess, wherein by the recess a part of the pump chamber is provided. Hence, the rotor of the vacuum pump extends into the recess of the second headplate. Hence, the pump chamber is combinedly defined by the housing element and the recess of the second head-plate. Consequently, the length of the pump chamber is split into the length of the pump chamber defined by the housing element and the length of the recess. Machining of either the housing element and / or the second headplate is simplified. However, the second headplate needs to be precisely adjusted with respect to the housing element in order to provide a continuous pump chamber. Preferably, the elongated pump chamber comprises a first section having a first diameter, a second section having a second diameter and an inclined section in between the first section and the second section having an inclined diameter. Therein, the first diameter is different than the second diameter. Further, the first section has a constant diameter along the entire length of the first section, the second section has a constant diameter along the entire length of the second section and the inclined section has a changing diameter along the entire length of the inclined section. Hence, by the first diameter and the second diameter the pump volume can be gradually decreased and adapted in order to provide sufficient compression of the gaseous medium, I. e. a high inner volume ratio. Preferably, the first section is arranged towards the first end and the second section is arranged towards the second end, wherein the first diameter is smaller than the second diameter. Hence, higher compression and smaller inner volume of the rotor is achieved towards the high-pressure section, i. e. the outlet of the housing or vacuum pump. Preferably, the inclined section has a diameter changing from the first diameter to the second diameter, i. e. connecting the first section having the first diameter with the second section having the second diameter. Therein, change of diameter can be linear or may have any other continuous form. Preferably, the ratio L / Di of a length L of the pump chamber to the first diameter Di of the pump chamber is larger than three. In other words, the ratio L / D with .... g ... D being the smallest inner diameter of all the sections is larger than three. Wherein for the continuous pump chamber only one section having a constant diameter D is present, in the case of more than one sections with different inner diameters the diameter of the smallest section is considered for the ratio L / D. Hence, in particular, the first diameter Di is used in order to determine the ratio of the length L of the vacuum chamber to the diameter D of the pump chamber. Preferably, the volume ratio between the inlet and the outlet of the vacuum pump is larger than 5 and in particular between 5 and 12. Preferably, a bearing is attached to the first headplate and / or the second headplate rotatably supporting a rotor of the vacuum pump. Preferably, one or more cooling elements are directly connected to the housing element and the first headplate. Hence, the one or more cooling elements extend from the housing element to the first headplate. In a conventional "tunnel" design of a stator difficulties arise implementing cooling of the first headplate and in particular a bearing connected to the first headplate. Due to the integral design of the first headplate and the housing element provided by the present invention, the one or more cooling elements can be formed together on the housing element and the first headplate. Therein, the cooling element may be one or more cooling fins extending on the outer surface of the housing element and the outer surface of the first headplate. Additionally or alternatively, one or more cooling elements are provided by an active cooling such as a water cooling or cooling by any other liquid coolant. Thus, the first headplate and any bearing connected to the first headplate can be easily cooled together with the housing element which leads to a reduced complexity and lower costs in fabrication. In another aspect of the present invention a vacuum pump is provided comprising a housing as described before and at least one rotor having at least one rotor element. By rotation of the rotor, a gaseous medium is conveyed from an inlet of the housing towards an outlet of the housing. Preferably, the vacuum pump comprises a single rotor. Alternatively, the vacuum pump comprises two or more rotors. Preferably, the vacuum pump is further built along the features as described before with respect to the housing. Preferably, the rotor comprises a first section having a diameter corresponding to the first diameter of the first section of the housing, a second section having a second diameter corresponding to the second diameter of the second section of the housing and an inclined section between the first section and the second section having a diameter corresponding to the diameter of the inclined section of the housing. Consequently, the diameter of the rotor follows the diameter of the pump chamber in the first section, second section and inclined section. Hence, in each section a small gap or clearance between the rotor and the inner wall of the pump chamber is obtained reducing backflow. Preferably, the vacuum pump is a screw pump comprising two screw rotors 'wherein preferably each rotor comprises more than 4 and more preferably more than 6 wraps. Preferably, the vacuum pump is a roots pump, a claw pump or the like. In the following the present invention is described in more detail with reference to the accompanying figures. The figures show: Figure 1 present invention, a first embodiment of a vacuum pump according to the Figure 2 a second embodiment of a housing according to the pre sent invention and Figure 3 another embodiment of a housing according to the pre sent invention. It is referred to the embodiment of Figure 1 showing a vacuum pump with a housing 10 having a housing element 12 with a first end 14 and a second end 16. By the housing element 12 a pump chamber 18 is defined with an inner wall 30. The pump chamber 18 has an axial length L and a constant diameter D over the full length of the pump chamber 18. The first end 14 of the pump chamber 18 is closed by a first headplate 22, Therein, the first headplate 22 is integrally formed with the first end 14 of the housing element 12. Thus, the housing element 12 and the first headplate 22 are built as single piece in particular from a single casting. The second end 16 of the vacuum chamber 18 is closed by a second headplate 24, which is in the embodiment of figure 1 plate-shaped. The second headplate Is a separate element and assembled to the housing element by conventional means such as bolts. The entire pump chamber 18 is formed within the housing element 12. The first headplate 22 may have one or more openings 26, wherein a shaft 44 of a rotor 40 of the vacuum pump may extend through the opening 26 of the first headplate 22. A bearing (not shown) may be attached to the outer side 28 of the first headplate 22 in order to rotatably support the rotor 40 within the pump chamber 18. Therein, the rotor 40 can be built in a cantilevered design and only supported at the first end 14 or also the second headplate 24 may comprise an opening such that the shaft 44 of the rotor 40 may extend also through the second headplate 24 and is supported by a bearing connected to the second headplate 24. By rotation of the rotor 40 within the pump chamber 18, a gaseous medium is conveyed from the Inlet 20 to an outlet (not shown). Therein, the first headpiate 22, which is integrally formed with the first end 14 of the housing element 12 is arranged at the high pressure end of the housing 10, wherein the second end 16 is arranged towards the inlet 20 or the low pressure or high vacuum end of the vacuum pump or the vacuum chamber 18. Thus, by the design of the present invention the number of parts necessary in order to form the vacuum chamber 18 is reduced. In fact, according to the embodiment of Figures 1 and 2, in order to define the pump chamber 18 only the housing element 12 integrally formed with the first headplate 22 is necessary in combination with the second headplate 24. In particular, the positioning of the opening 26 in the first headpiate 22 is fixed relative to the pump chamber 18 and can be provided with high precision without additional alignment. Hence, the rotor 40 within the pump chamber 18 can be positioned with high precision such that backflow is minimized and performance of the vacuum pump can be increased. Therein, it has been shown a ratio L / D of the length L of the pump chamber 18 to the diameter D of the pump chamber 18 is larger than 3 in order to achieve sufficient high compression rates and sufficient pump performance. Also shown in Figure 1 is the rotor 40 having a schematically represented rotor element 42 disposed in the pump chamber 18. The pump element 42 may be a screw or helically shaped structure. Although in Figure 1 only one rotor 40 is shown, the vacuum pump of Figure 1 may comprise 2 or more rotors. In particular, the vacuum pump is built as screw pump. Consequently, the vacuum pump may have two screw rotors meshing with each other. For simplicity, in Figures 2 and 3 no rotor Is shown and these Figures are reduced to the housing. It is referred to the embodiment of Figure 2. Therein, the vacuum chamber 18 comprises a first section 32 having a first diameter Di, a second section 36 having a second diameter Dz and an Inclined section 34 in between the first section 32 and the second section 36. Therein, the first diameter Di is smaller than the second diameter Dz. The smaller diameter Di is arranged towards the region of higher pressure, i. e. towards the outlet of the vacuum pump reducing the pump volume generated by the one or more rotors 40. The inclined section 34 connects the diameter Di of the first section 32 to the second diameter D2 of the second section 36. Although shown in Figure 2 that the change of diameter in the inclined section 34 is linear, other possibilities exist to continuously connect the first diameter to the second diameter. Referring to Figure 3. In Figure 3 the second headplate 24' comprises a recess 38, which forms part of the pump chamber 18. Hence, the pump chamber 18 is defined by the housing element 12 as described before in connection with the recess 38 of the second headplate 24’. In particular, the inlet 20 is arranged in the headplate 24'. Therein, as shown in Figure 3, the second section 36 may be built by the recess 38, wherein the housing element 12 contains the inclined section 34 and the first section 32. Other possibilities also exist. By the present invention an efficient vacuum pump is provided, wherein the housing 10 according to the present invention allows for a precisely aligned rotor 40 in the pump chamber 18 due to integrally forming the first headplate 22 with the housing element 12. No additional alignment between a separate first headplate is necessary at the first end 14 of the housing element 12. Reference List: 10 housing 12 housing element 14 first end 16 second end 18 pump chamber 20 inlet 22 first headplate 24 second headplate 26 opening 28 outer side 30 inner wail 32 first section 34 inclined section 36 second section 38 recess 40 rotor 42 rotor element 44 rotor shaft

Claims

1. Housing for a vacuum pump, in particular a 2-shaft vacuum pump, comprising:a housing element defining at least partially an elongated pump chamber having a first axial end and an opposite second axial end, wherein a ratio L / D of a length L of the pump chamber to a diameter D of the pump chamber is larger than 3; anda first headplate at the first end of the housing element closing the first end of the pump chamber, wherein the first headpiate comprises at least one opening configured to receive a shaft of a rotor; anda second headplate at the second end of the housing element closing the second end of the pump chamber;wherein the first headplate and the housing element are integrally formed.

2. Housing according to claim 1, characterized in that the housing element and the first headplate are made from a single casting.

3. Housing according to claim 1 or 2, characterized in that the first end is arranged towards an outlet and the second end is arranged towards an inlet.

4. Housing according to any of claims 1 to 3, characterized in that the second headplate is plate shaped and preferably comprises at least one opening configured to receive a shaft of a rotor.

5. Housing according to any of ciaims 1 to 3, characterized in that the second headplate comprises a recess, wherein by the recess a part of the pump chamber is provided.

6. Housing according to any of claims 1 to 5, characterized in that the elongated pump chamber comprises a first section having a first diameter, a second section having a second diameter and an inclined section in between the first section and the second section having an inclined diameter, wherein the first diameter is different than the second diameter.

7. Housing according to claim 6, characterized in that the first section is arranged towards the first end and the second section is arranged towards the second end and the first diameter is smaller than the second diameter.

8. Housing according to claim 6 or 6, characterized in that the inclined section has a diameter changing from the first diameter to the second diameter.

9. Housing according to any of claims 6 to 8, characterized in that the ratio of a length of the pump chamber to the first diameter of the pump chamber is larger than 3.

10. Housing according to any of claims 1 to 9, characterized in that the volume ratio is larger than 5 and in particular between 5 and 12.

11. Housing according to any of claims 1 to 10, characterized in that a bearing is attached to the first headplate and / or the second headplate rotatably supporting a rotor of the vacuum pump.

12. Housing according to any of claims 1 to 11, characterized in that one or more cooling elements are directly connected to the housing element and the first headplate.

13. Vacuum pump comprising a housing according to any of claims 1 to 12 and at least one rotor comprising at least one rotor element.

14. Vacuum pump according to claim 13, characterized in that the rotor comprises a first section having a first diameter corresponding to the first diameter of the first section of the housing, a second section having a second diameter corresponding to the second diameter of the second section of the housing, and an inclined section between the first section and the second section having a diameter corresponding to the diameter of the inclined section of the housing.

15. Vacuum pump according to claim 13 or 14, characterized in that the vacuum pump is a screw pump comprising two screw rotors, each preferably comprising more than 4 and more preferably more than 6 wraps.

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