VACUUM PUMP WITH ECCENTRICALLY DRIVEN VANE (ECCENTRIC PUMP DESIGN WITH CRANK PIN)

Abstract

A vacuum pump includes a housing defining a cavity having an inlet and an outlet; a vane member for a rotary driven movement inside the cavity; a drivable rotor inside the cavity; and a rotatable central shaft extending to the cavity. The vane member is slidably arranged in the rotor. The rotor is rotatable together with the vane member. The central shaft comprises a crank pin configured to engage a respective guiding recess of the rotor for driving the rotor at least along a first predetermined rotational angle.

Claims

1: A vacuum pump, comprising: a housing defining a cavity having an inlet and an outlet; a vane member for a rotary driven movement inside the cavity; a drivable rotor inside the cavity; and a rotatable central shaft extending to the cavity; wherein the vane member is slidably arranged in the rotor, wherein the rotor is rotatable together with the vane member; and wherein the central shaft comprises a crank pin configured to engage a respective guiding recess of the rotor for driving the rotor at least along a first predetermined rotational angle.

2: The vacuum pump according to claim 1, wherein the guiding recess is in the form of a groove.

3: The vacuum pump according to claim 2, wherein the groove extends in a direction substantially perpendicular to a plane defined by the vane member.

4: The vacuum pump according to claim 1, wherein the guiding recess comprises at least one narrow portion having a first width substantially corresponding to an outer diameter of the crank pin, and at least one wide portion having a second width substantially larger than the outer diameter of the crank pin.

5: The vacuum pump according to claim 4, wherein an axial length of the wide portion is in a range of of a moving length of the crank pin in the guiding recess.

6: The vacuum pump according to claim 4, wherein the guiding recess is formed such that the first predetermined rotational angle is in the range of 20 to 5.

7: The vacuum pump according to claim 1, wherein the guiding recess is formed as a blind recess.

8: The vacuum pump according to claim 1, wherein the crank pin comprises a pin sleeve for contacting wall portions of the guiding recess.

9: The vacuum pump according to claim 1, wherein the vane member is coupled to the central shaft by means of an eccentric element on the central shaft.

10: The vacuum pump according to claim 9, wherein the rotor is configured to be rotatable together with the vane member upon rotation of the vane member for at least a second predetermined rotational angle.

11: The vacuum pump according to claim 1, wherein the vane member is drivable and the guiding recess is formed such that the crank pin engages the rotor when a drive moment on the vane member becomes low.

12: The vacuum pump according to claim 9, wherein the eccentric element is formed as an eccentric bushing which is eccentrically arranged on the drive shaft.

13: The vacuum pump according to claim 9, wherein the eccentric element is non-rotatable coupled to the drive shaft by the crank pin.

14: The vacuum pump according to claim 9, wherein the vane member comprises a central hollow jacket and the vane member is rotatably seated about the eccentric element by the central hollow jacket.

15: The vacuum pump according to claim 14, wherein the vane member is formed as a single one-piece vane member having first and second vanes on the central hollow jacket protruding in a radial direction on opposing sides of the central hollow jacket.

16: The vacuum pump according to claim 9, wherein the first offset of the rotational axis of the central shaft relative to the rotational rotor-axis of the rotor is substantially identical to the second offset of the point of action of the vane member relative to the rotational axis of the central shaft.

17: The vacuum pump according to claim 1, wherein the rotor comprises at least one bearing journal for bearing the rotor against a bottom plate and/or an end plate of the cavity.

18: A method for driving a vacuum pump, the method comprising: directly driving a rotor along a first predetermined rotational angle; and directly driving a vane member along a second predetermined rotational angle.

19: The method according to claim 18, wherein the rotor is indirectly driven by means of a vane member when the vane member is directly driven, and wherein the vane member is indirectly driven when the rotor is directly driven.

20: The method according to claim 18, wherein the first predetermined rotational angle is in the range of 20 to 5.

Description

[0039] For a more complete understanding of the invention, the invention will now be described in detail with reference to the accompanying drawings. The detailed description will illustrate and describe what is considered as a preferred embodiment of the invention. It should of course be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention may not be limited to the exact form and detail shown and described herein, nor to anything less than the whole of the invention disclosed herein and as claimed hereinafter. Further the features described in the description, the drawing and the claims disclosing the invention may be essential for further developments of the invention considered alone or in combination. In particular, any reference signs in the claims shall not be construed as limiting the scope of the invention. The wording comprising does not exclude other elements or steps. The wording a or an does not exclude a plurality. The wording, a number of items, comprises also the number one, i.e. a single item, and further numbers like two, three, four and so forth.

[0040] In the accompanying drawings:

[0041] FIG. 1 shows a perspective view of a vacuum pump;

[0042] FIG. 2 shows a top view of a vacuum pump without housing;

[0043] FIG. 3 shows a cross section along the plane Z-Z of FIG. 2;

[0044] FIG. 4 shows a cross section along the plane Y-Y of FIG. 2;

[0045] FIG. 5 shows an elevated view of the vacuum pump of FIGS. 2 to 4;

[0046] FIG. 6 shows another elevated view of the vacuum pump of FIG. 5;

[0047] FIG. 7 shows a bottom view into the cavity of the vacuum pump;

[0048] FIG. 8 shows a bottom view of the rotor;

[0049] FIG. 9 shows an elevated view of the rotor;

[0050] FIG. 10 shows another elevated view of the rotor;

[0051] FIG. 11 shows an exploded view of the vacuum pump of FIGS. 2 to 6;

[0052] FIG. 12 shows another exploded view of the vacuum pump of FIG. 11;

[0053] FIG. 13 shows an elevated view of the central shaft;

[0054] FIG. 14 shows an elevated view of an eccentric bushing;

[0055] FIG. 15 shows another elevated view of the eccentric bushing of FIG. 14; and

[0056] FIGS. 16a to 16d illustrate different rotational positions of the vacuum pump.

[0057] A vacuum pump 1 (FIG. 1) comprises a housing 50. The housing 50 comprises a demountable end plate 102, in which an outlet 104 of the vacuum pump 1 is formed. The housing 50 further more comprises an inlet 106 which is provided with a connecting piece 108 which may receive a hose or the like of a consumer. The vacuum pump 1 is connected to a drive motor 110 having a motor housing 112.

[0058] According to FIGS. 2 to 4, a vacuum pump 1, which is for the sake of simplicity shown without housing 50, is connected with a drive motor 110, from which only the rotor 2 is shown. The rotor 2 comprises a motor shaft 4, connected to a central shaft 6 of the vacuum pump 1.

[0059] The vacuum pump 1 furthermore comprises a drivable rotor 8, which is rotatable about a rotation axis AR. The rotor 8 comprises a circumferential outer wall 10 having a slot 12, in which a vane member 14 is slidable arranged. The rotor 8 thus is being rotatable together with the vane member 14. The central shaft 6 comprises a crank pin 16 (cf. also FIG. 13) which engages a guiding recess 18 integrally formed in the rotor 8. Due to the engagement between the crank pin 16 and the guiding recess 18, the rotor 8 is drivable along a first predetermined angle a, as will be described later.

[0060] According to this embodiment, also the vane member 14 is coupled to the drive shaft 6 and thus driven. This is not mandatory, the scope of the invention also covers vacuum pumps in which the vane 14 is passive and only indirectly driven by means of the rotor. Furthermore, alternative driving mechanisms for directly driving the vane member, at least along a second predetermined angle , are preferred.

[0061] According to this embodiment, the vane member is seated about an eccentric element 20 on the central shaft 6. The eccentric element 20 according to this embodiment is formed as an eccentric bushing 20, which is fixed in a positive fitting connection to the crank pin 16 of the central shaft 6 (cf. also FIGS. 12, 14, 15). The eccentric element 20 comprises a cylindrical outer wall 22 and the vane member 14 comprises a central hollow jacket 24, which is rotatably seated about the circumferential outer surface 22 of the eccentric bushing 20. From the hollow jacket 24, two vanes 26, 28 extend in a common plane and protrude through the slot 12 formed in the rotor 8.

[0062] As can be seen in FIG. 3, the rotor comprises a rotational axis AR, which is offset to a rotational axis AS of the central shaft 6, and which both are offset of the central axis of the eccentric bushing 20, which forms the rotational axis AE of the vane member 14 relative to the eccentric bushing 20.

[0063] The rotor 8 furthermore comprises a shaft end 30 extending along the rotational axis AR of the rotor and being received in a cover of the vacuum pump 1 (not shown) for bearing the rotor 8.

[0064] The rotor 8 comprises first and second circumferentially protruding rims 32, 34, one rim 32 at the bottom side 36 of the rotor 8 and the other rim 34 at the top side 38 of rotor 8. Both rims 32, 34 are received in respective recesses in a bottom and a top wall of the cavity 52 (cf. FIG. 7), thus forming a labyrinth seal. The rims 32, 34 are part of a bearing journal 37 formed between the bottom side 36 of the rotor and a bottom plate 41, and a bearing journal 39 formed between the top side 38 of the rotor 8 and an end plate (not shown in figures), which closes the cavity 52 at the top end (cf. FIG. 7). To further enhance sealing, respective sealing elements 40, 42 are arranged in respective recesses 44, 46 at the ends of the vanes 26, 28 respectively (cf. FIG. 5). Such sealing elements 40, 42 are particularly preferred when the vacuum pump is used as a lubricated vacuum pump, however, maybe avoided when used as a dry running vacuum pump without contact between the vane member 14 and an inner circumferential wall of the cavity.

[0065] In FIG. 7, the vacuum pump 1 is shown with a housing 50. The housing 50 defines a cavity 52 having an inlet and an outlet, which are arranged in the bottom plate, which is not shown in FIG. 7. The cavity 52 includes an inner circumferential wall 54. The cavity 52 is divided into two working chambers 56, 58 by means of the vane member 14. The vane member 14 is formed as a single one-piece member 14 having the central hollow jacket 24 from which the two vanes 26, 28 protrude in opposing directions. The vanes 26, 28 are symmetrically shaped and have the same length measured in radial direction. By means of the central hollow jacket 24, the vane member 14 is coupled to the eccentric element 20 (not shown in FIG. 7). The rotor 8 furthermore comprises a rotor wall 60 which defines a substantially cylindrical outer shape. The rotor wall 60 further defines an inner space 62 in which the drive shaft 6, the eccentric bushing 20 and the hollow jacket 24 are arranged. Thus, the rotor 8 radially encloses the eccentric bushing 20 and the central shaft 6 as well as the hollow jacket 24. The rotor 8 has a fixed position within the cavity 52 and only rotates about its rotational axis AR (cf. FIG. 3).

[0066] Furthermore, according to FIG. 7, the guiding recess 18 can be seen. The guiding recess 18 has an axis AG, which runs perpendicular to the plane E defined by the vanes 26, 28 of the vane member 14. The guiding recess 18 is formed such that the crank pin 16 of the drive shaft 6 engages the rotor 8 at predetermined rotational angles a of a revolution of the rotor 8 inside the cavity 52.

[0067] In FIG. 8, a bottom view of the rotor 8 is shown. The rotor 8 comprises a rotor wall 60 and a slot 12 formed in the rotor wall 60 and extending along a plane containing the rotational axis AR of rotor 8. Rotor wall 60 defines an inner space 62 (cf. FIG. 7). The guiding recess 18 is formed in a top wall 64. The longitudinal axis AG of the guiding recess 18, which is formed as a groove 17, namely a blind recess 19, is substantially perpendicular to plane E which is defined by the slot 12 and by the vane member 14 (cf. FIG. 7). The guiding recess 18 comprises a wide portion 66 and two narrow portions 68a, 68b. The wide portion 66 has a width W1, which is substantially larger than a diameter DC of the crank pin 16 (cf. FIG. 13). The two narrow portions 68a, 68b are arranged at opposing end portions of the guiding recess and comprise a width W2 perpendicular to longitudinal axis AG, which substantially equals the outer diameter DC of the crank pin. When a crank pin 16 travels through the guiding recess 18 along the longitudinal axis AG, upon rotation of the central shaft 6, the crank pin 18 engages the rotor 8, when in the range of the narrow portions 68a, 68b, but disengages the rotor 8, when in the wide portion 66. For a more even rotation between the wide portion 66 and the narrow portions 68a, 68b, two transition portions 69a, 69b are provided with tapered surfaces. Such a configuration of the guiding recess 18, with a wide portion 66, is preferred, when the vacuum pump 1 comprises a second drive for driving the vane member 14, as it has been described with respect to FIGS. 2 to 5 in particular.

[0068] When the vane member 14 is not driven but only passive, it may be provided that the guiding recess 18 has the same width W2 along its axial extension and does not comprise a narrow portion W1. When the crank pin is in the narrow portion W1, force cannot be transmitted from the central shaft 6 to the rotor 8. Due to the arrangement of the guiding recess and the offset of the rotational axis AR of the rotor and rotational axis AS of the driving shaft, the rotor 8 will travel at half speed of the rotational speed of the central shaft 6, which thus allows using an electric motor for driving the vacuum pump, while at the same time keeping the rotational speed of the vacuum pump 1 low, which is beneficial with respect to friction and maintenance issues.

[0069] According to this embodiment (FIG. 8) the overall length LW of the wide portion 66 is approximately two-thirds of the total length LT of the guiding recess 18, measured from the outermost points of travel of the crank pin, that is from centers of the radius of the rounded end portions of a guiding recess 18. In rotation this leads to an engagement between the crank pin 16 and guiding recess 18 for a first predetermined angle of approximately 15 at rotational positions of 90 and 270 of the rotor (cf. FIGS. 16a to 16d).

[0070] The rotor 8 is formed out of a plastic material preferably by means of injection molding as can be inferred from FIGS. 8 to 10. The rotor 8 does not comprise any undercuts and thus is easy to manufacture.

[0071] FIGS. 11 and 12 illustrate the assembly of the vacuum pump 1, in particular the moving parts, namely rotor 8, vane member 14, eccentric bushing 20, drive shaft 6 and rotor shaft 4.

[0072] The central shaft 6 comprises an opening 70 which receives a tip of the motor shaft 4. The central shaft 6 furthermore comprises a connection portion 72 having a cylindrical outer surface. The connection portion 72 is adapted to be received in a corresponding recess 74 of the eccentric bushing 20. The recess 74 is eccentrically arranged in the bushing 20 with respect to the central axis AE of the eccentric bushing 20. Inside the recess 74 is a through hole 76 formed through which the crank pin 16 can protrude. Due to the recess 74 and the through hole 76, the central shaft 6 and the eccentric bushing are non-rotatingly to each other connected by means of a form-fit. After exiting the through hole 76, the crank pin 16 is received in a pin sleeve 78, which is rotatingly provided on the crank pin 16. The pin sleeve 78 forms the outer surface of the crank pin and comes into contact with the inner wall portions of the guiding recess 18. The pin sleeve 78 is not mandatory, but beneficial with respect to friction reduction.

[0073] The eccentric bushing 20 is received inside the space 80 of the hollow jacket 24, forming a rotatable connection, and the vane member 14 is received in the rotor 8 by means of the two vanes 26, 28 which are seated in the slot 12. Furthermore, sealing elements 40, 42 are received in recesses 44, 46 respectively.

[0074] Now turning to FIGS. 14 and 15 in particular, the eccentric bushing 20 is shown. From FIG. 14, a bottom view is shown, in which the recess 74 and the through hole 76 can be seen. In FIG. 14, a respective top view is shown. It can be seen that in the top section of the bushing 20 a first substantial planar recess 82 is formed and a second recess 84 which has a greater depth and is curved and opposingly arranged with respect to the crank pin 16. When forming the recesses 82, 84 appropriately and choosing materials of the central shaft 6 and the eccentric bushing 20 appropriately, it is possible to balance inertia forces, generated by means of the eccentric arrangement of the crank pin 16 and the eccentric bushing 20 with respect to the drive shaft 4. According to this arrangement, an additional balance weight or the like is not necessary.

[0075] Now turning to FIGS. 16a to 16d, the drive mechanism will be explained, when using the two drive mechanisms, the eccentric one for driving the vane member 14 and the crank pin 16 for driving the rotor 8 in a predetermined angle a. FIGS. 16a to 16d illustrate the movement of the moving parts during an operation. It is shown how the rotor 8 rotates and how the vane member 20 moves upon a full rotation of the central shaft 6, and how the crank pin 16 moves within the guiding recess 18. The main parts are indicated with reference signs in FIG. 16a; in FIGS. 16b to 16d, these reference signs are left away to simplify the illustration. It will be understood that FIGS. 16a to 16d show the same parts as in FIG. 16a, however, in different rotational positions as now will be described.

[0076] The rotor 8, the central shaft 6 and the vane member 14 are provided with indicators I1, I2, I3 in the form of arrows for indicating a rotational position of these parts. According to FIG. 16a, all three indicators I1, I2, I3 direct to the bottom of FIG. 16a and thus, compared to a watch, all three indicators I1, I2, I3 direct to the six o'clock position. When now for example the central shaft 6 is rotated in a clockwise direction about 90 about its rotational axis AS (cf. FIGS. 2, 11 and 13), the eccentric bushing 20 which is seated on the central shaft 6 is rotated about 90 degree as well as the central axis AE of the eccentric bushing 20 and thus, the point of action of the eccentric bushing 20 moves on a circle segment about 90 from the six o'clock position to the nine o'clock position. In the same manner also the crank pin 16 moves. Since the vane member 14 engages the eccentric bushing 20 in that the central hollow jacket 24 is seated about the eccentric bushing 20, the point of action of the vane member 14, which is identical to the central axis AE of the eccentric bushing 20, is moved to the 9 o'clock position accordingly. However, since the vane member 14 is not freely movable, but positively coupled to the rotor 8 by means of the slot 12 (cf. also FIGS. 2, 5 and 7 in particular), the vane member 14 cannot move in a direction perpendicular to the vanes 26, 28 of the orientation of FIG. 16a without rotation. Therefore, the vane member 14 and the rotor 8 are forced to rotate about 45 together as indicated by the indicators I2, I3 accordingly to FIG. 16b. Since the crank pin 16 is coupled to the drive shaft 6 and the guiding recess 16 is formed in the rotor 18, also the crank pin 16 travels inside the guiding recess 18, while in the positions shown in FIGS. 16a and 16b, the crank pin 16 is still remaining in the wide portion 66 and not engaging the rotor 8. Thus, the vacuum pump 1 is moved from a first rotational position P1 to an intermediate position PI (cf. FIG. 16b).

[0077] When the central shaft 6 rotates on to a 180 position (cf. FIG. 16c), the indicator I1 directs to the 12 o'clock position and the point of action of the vane member 14, which is again identical to the central axis AE of the eccentric bushing 20, is further rotated about the rotational axis AS of the central shaft 6 and thus, both, the vane member 14 and the rotor 8 are rotated about 19, so that the indicators 12,13 direct to the nine o'clock position. In this position, it can be seen that the resulting force F acting from the eccentric bushing 20 on the vane member 14 is parallel to a plane defined by the vanes 26, 28 while at the same time the central axis AE of the eccentric bushing 20 crosses the rotational axis AR of the rotor 8. A moment arm in this position P2 (FIG. 16c) becomes zero and no rotational force is induced to the vane member 14, but the vane member 14 only is pushed along the plane defined by the vanes and with respect to FIG. 16c to the right hand side. This could lead to a contact between the right hand side vane and the circumferential wall of the vacuum pump 1, thus resulting in wear. According to the present invention however, the crank pin 16 has further travelled through the guiding recess 18 and is now (cf. FIG. 16c) in the narrow portion 68 of the guiding recess thus engaging the rotor 8. The crank pin 16 in this position cranks the rotor 8 and pushes the rotor 8 by means of a pushing force FC into rotation, thus indirectly driving the vane member 14.

[0078] Upon further rotation (from position P2 to position P3, FIG. 16d) rotor 8 and vane member 14 are further rotated and the crank pin 16 travels back through the guiding recess 18 to the white portion 66, thus engaging the rotor 8, while the vane member 14 again is driven by means of the eccentric bushing 20. In the first position P1 and the intermediate position PI, the driving force F from the eccentric bushing 20 to the vane member 14 is substantially perpendicular to the plane of the vane member 14 (cf. FIG. 16a) or at least acute (cf. FIG. 16b). In these positions, the crank pin 16 disengages the rotor 8, while in the position shown in FIG. 16c, the crank pin 16 engages the rotor 8 via the guiding recess 18. This happens in two positions of the total revolution of the rotor 8, namely in the 90 and to 170 positions (the 170 position is similar to FIG. 16c, while indicators 12, 13 would direct to the right hand side and indicator I1 to the bottom). As also can be seen from FIGS. 16a to 16d, rotor 8 and vane member 14 travel at half speed of the speed of the drive shaft 6.

LIST OF REFERENCE SIGNS (PART OF THE DESCRIPTION)

[0079] 1 vacuum pump

[0080] 2 rotor of motor

[0081] 4 motor shaft

[0082] 6 central shaft

[0083] 8 drivable rotor

[0084] 10 outer wall

[0085] 12 slot

[0086] 14 vane member

[0087] 16 crank pin

[0088] 17 groove

[0089] 18 guiding recess

[0090] 19 blind recess

[0091] 20 eccentric element

[0092] 21 eccentric bushing

[0093] 22 surface of eccentric bushing

[0094] 24 central hollow jacket

[0095] 26, 28 vanes

[0096] 30 shaft end

[0097] 32, 34 circumferentially protruding rims

[0098] 36 bottom side

[0099] 37 bearing journal

[0100] 38 top side

[0101] 39 bearing journal

[0102] 40, 42 sealing elements

[0103] 41 bottom plate

[0104] 44, 46 recesses

[0105] 50 housing

[0106] 52 cavity

[0107] 54 inner circumferential wall

[0108] 56, 58 working chambers

[0109] 60 rotor wall

[0110] 62 inner space

[0111] 64 top wall

[0112] 66 wide portion

[0113] 68a, 68b narrow portions

[0114] 69a, 69b transition portions

[0115] 70 opening

[0116] 72 connection portion

[0117] 74 recess

[0118] 76 through hole

[0119] 78 pin bushing

[0120] 80 space

[0121] 82, 84 recesses

[0122] First (predetermined) rotational angle

[0123] Second (predetermined) rotational angle

[0124] AE Point of action (of the vane member)

[0125] AS Rotational axis (of the central shaft)

[0126] AR Rotational rotor-axis

[0127] e1 First offset

[0128] e2 Second offset

[0129] LT Moving length (of the wide portion)

[0130] LW Axial length (of the crank pin)

[0131] w1 Second width

[0132] w2 First width