EP2461040B1 - Vacuum pump and joint of shaft and rotary piston - Google Patents

Description

The invention relates to a vacuum pump with the features of the preamble of the first claim.

In many industrial applications, for example in chemistry or in coating technology, two-shaft vacuum pumps with contactlessly rotating pistons are an indispensable component of the vacuum system. These may be single-stage or multi-stage vacuum pumps whose pistons have, for example, Roots or claw profiles. For multi-stage pumps, it is quite common to select different profiles for different pumping levels.

One design feature of such vacuum pumps is the connection of shaft and piston. Basically, it is possible to manufacture shaft and piston in one piece, but this requires disadvantages in the housing design, for example, tight manufacturing tolerances. Therefore, shaft and piston are often made as separate components that must then be fastened together.

An example of a fastening of a piston on a shaft represents the EP 0 368 124 A1 in front. The basic idea here is to push through the shaft through a bore in the piston and to achieve a clamping action by clamping conical surfaces in the direction of the shaft axis. The disadvantage of this is that assembly and disassembly are difficult and expensive, especially in a multi-stage pumps. In addition, the attachment is based solely on frictional engagement, so that even the smallest assembly errors can cause a rotation of the piston during operation. This can lead to a mutual contact of the pistons in one stage.

As an alternative solution, a key is known. The piston has a bore through which the shaft is inserted. Shaft and piston each have grooves that are positioned congruent. In the resulting space, which extends over the shaft and piston, a positive locking element is arranged. The groove must be guided on the piston side to at least one of the end faces, so that the positive-locking element can be inserted. Disadvantage of this solution is the complicated and therefore expensive production. This ultimately results from the fact that the piston-side groove and the piston-side profile must be aligned very precisely with each other.

The prior art ( DE 36 89 054 T2 ) includes a rotor assembly for a Roots pump, in which a rotary piston has an axially formed therethrough axial bore. The rotary piston and a bearing shaft have at their axially central portions each pin holes. In these pin bores, a locking pin can be arranged. Also the JP 3 290082 presents a method for mounting rotary bodies or pistons on a shaft by means of pins and pin bores. The known pumps can be improved to the effect that the mounting of the pin is easier.

It is therefore an object of the invention to provide a connection between the piston and shaft of a vacuum pump, which is inexpensive to manufacture and allows easy assembly and disassembly.
This object is achieved by a vacuum pump having the features of the first claim. These advantages are deepened by the designs specified in subclaims 2 to 10.
It is provided that a piston recess is formed as a channel beginning on the piston profile surface, a first section of a form-fitting element is located in a shaft recess and a second section of the form-fitting element forms a positive connection with the channel in the direction of the shaft axis and the shaft circumference. The vacuum pump can be designed as a single-stage or multi-stage vacuum pump with non-contact rolling-off pistons, for example with Roots, screws or claw profile. It can also have gas inlets in more than one of the stages. The piston can be made in one or more parts. The vacuum pump may have more than two shafts.

The form-locking element forms a positive connection in the direction of shaft axis and shaft circumference. This allows a safe and highly accurate positioning of the piston in these two directions. This is made possible by the channel, through which the positive-locking element can be brought into position. The high-precision manufacturing of groove with respect to the piston profile is eliminated, so that the production is easier and less expensive. The improved positioning of the piston simplifies assembly and disassembly. It also allows to provide narrower gaps between the housing of the vacuum pump and the piston or between the pistons with each other. This improves the performance of the vacuum pump as unwanted backflow through these gaps from the discharge and suction sides is reduced. The cross section of the channel is basically not limited, but is advantageously carried out round, so that the channel can be designed inexpensively as a bore. The first section preferably has a maximum diameter which allows the interlocking element to be moved through the channel.
In particular, it is advantageous to provide a securing element which positions and fixes the positive-locking element in the channel. This allows a free design of the form-fitting element with a view to the introduction of force from the piston in the form-locking element or positive-locking element in the shaft. Such a design comprises flat surfaces of form-fitting element and shaft.
According to a further development, a plurality of pistons are arranged along the shaft axis on the shaft. The connection makes it possible to adjust the axial gap between the housing of the vacuum pump and piston by the simple axial fixability of the piston very accurately. It is also very easy to position the pistons with very little angular offset from each other, since both the shaft recesses to each other and piston profile and channel can be made precisely oriented to each other.

With reference to embodiments and their developments, the invention will be explained in more detail and the representation of its benefits to be deepened.

Fig. 1:

Schematischer Schnitt durch eine Vakuumpumpe;

Fig. 2:

Schnitt durch Welle und Kolben, senkrecht zur Wellenachse gemäß einem Beispiel, welches nicht unter den beanspruchten Schutzumfang fällt ;

Fig. 3:

Schnitt durch Welle und Kolben entlang I-I';

Fig. 4:

Schnitt entlang II-II';

Fig. 5:

Schnitt durch Welle und Kolben senkrecht zur Wellenachse gemäß Ausführungsbeispiel;

Fig. 6:

Schnitt durch Welle und Kolben entlang III-III';

Fig. 7:

Schnitt entlang IV-IV';

Fig. 8:

perspektivische Darstellung des Passstiftes gemäß Ausführungsbeispiel.

Fig. 9:

Schnitt durch eine Weiterbildung des Passstifts gemäß Ausführungsbeispiel.

Show it:

Fig. 1:

Schematic section through a vacuum pump;

Fig. 2:

Section through shaft and piston, perpendicular to the shaft axis according to an example, which does not fall under the claimed scope;

3:

Section through shaft and piston along I-I ';

4:

Section along II-II ';

Fig. 5:

Section through shaft and piston perpendicular to the shaft axis according to the embodiment;

Fig. 6:

Section through shaft and piston along III-III ';

Fig. 7:

Section along IV-IV ';

Fig. 8:

perspective view of the dowel pin according to the embodiment.

Fig. 9:

Section through a development of the dowel pin according to the embodiment.

A two-shaft vacuum pump with non-contact successive rolling piston shows Fig. 1 in a cut in the plane of the waves. In the housing 2 of the vacuum pump 1, first shaft 4 and second shaft 6 are rotatably supported in bearings 10 and 12 and 14 and 16. As a rule, these are bearings with grease or oil circulation lubrication. A drive 18, such as an asynchronous motor or brushless DC motor, rotates the first shaft. At the end opposite the drive of the first shaft, a synchronizing gear 22 is disposed within a gear chamber 20 on the shaft. It cooperates with a second synchronizing gear 24 on the second shaft and puts them into rotation at the same speed and solid phase but reversed sense of rotation.

The vacuum pump has an inlet 26 through which gas is sucked into the first pumping stage 30. There act a first, connected to the first shaft piston 40 and a second, connected to the second shaft piston 42 gas-promoting together. Between housing and piston, a sealing gap 38 is formed, between the two pistons of a pumping step, a sealing gap 38 '. The conductance of these sealing gaps determines the return flow against the conveying direction and thus the vacuum technical properties.

Gas is expelled from the first pumping stage and transferred by means of a first transfer channel 52 to the second pumping stage 32. In this act the pistons 44 and 46 together. Through a second transfer channel 54, the gas finally passes into the third pumping stage 34, where it is conveyed by the pistons 48 and 50 and finally expelled via the outlet 28 from the vacuum pump. The number of pumping stages depends on the objective of the vacuum pump, for example pumping speed and, in particular, achievable final pressure. The connection of piston and shaft described below can be used in single-stage and multi-stage vacuum pumps, but brings additional benefits in several stages. In several stages, it is important to be able to adjust the gap between the piston and the housing of the vacuum pump as closely as possible even with thermal expansion of shaft and piston, for which exact positioning is important. The connection described below allows this because it allows a very good axial positioning of the piston.

An example, which does not fall under the claimed scope, is in the Fig. 2 to 4 shown in different views. In Fig. 2 is a section shown perpendicular to the shaft axis 100, while Fig. 3 the section along the line II 'shows. A section along line II-II 'finally shows Fig. 4 ,

As in Fig. 2 shown, the piston 40 has a central hole 58 in which the shaft 4 is received. The piston is designed according to a Wälzkolbengeometrie and in the Fig. 2 shown with an approximately eight-shaped cross-section. Along the circumference, the piston profile surface 66 limits the piston. An excellent region of the piston is the piston head 68, which forms the sealing gap along with the housing during one revolution on one part of the track and on another part of the track together with the cooperating piston. Starting from the piston profile surface, a channel 60 is provided which extends to the central hole. It can advantageously be designed as a bore and have a thread 64, which is in engagement with a mating thread on a form-locking element 70. The positive-locking element extends with a second section 74 in the channel and with a first section 72 it extends into the shaft recess 62. The second section forms a positive connection with the channel both in the direction of the shaft axis 100 and in the circumferential direction 102, as shown in FIGS FIGS. 2 and 3 is apparent. In the direction of the shaft axis of the first portion forms a frictional engagement with the shaft recess, whereby the piston is axially fixed on the shaft. As in Fig. 4 Shown in detail, the extension 72 of the shaft recess in the direction of the shaft axis is greater than that of the first section, which has an approximately circular cross-section.

Preferably, the form-fitting element fills the channel up to the piston head, so that the dead volume contained in the channel between positive-locking element and piston profile surface is kept small.

The Fig. 5 to 8 represent an embodiment dar. It shows Fig. 5 a section perpendicular to the shaft axis 100 by the piston 40 and shaft 4. A section along the line III-III 'is in Fig. 6 stated while Fig. 7 the cut after the Line IV-IV 'off Fig. 6 shows. Fig. 8 Finally, a perspective and schematic representation of the positive-locking element itself.

Piston 40 and shaft 4 are designed as in the first example. The piston has a Wälzkolbengeometrie with a roughly achtförmigen cross-section and is limited by the piston profile surface 66 with respect to the suction chamber. In the region of the piston head, in which the piston profile surface has the greatest distance to the shaft axis 100, a channel 60 begins, which is preferably designed as a bore with a channel axis 104 and an internal thread 64. A form-locking element 80 has two sections, wherein the first section 82 forms a positive connection with a shaft recess 62. The second section 84 is designed and arranged in the channel so that it forms a positive connection in the circumferential direction 102 and the direction of the shaft axis 100 with this.

On the opposite side of the shaft of the positive-locking element, a securing element 78 is arranged in the channel. This securing element has a thread which is in engagement with the thread of the channel. As a result, a biasing force is generated on the positive-locking element, which presses this against the shaft. This ensures a frictional connection, which causes a fixing of the piston in the axial direction. The shaft recess has an extension 76 in the direction of the shaft axis, which is greater than that of the first portion, so that the piston is displaceable on the shaft before generating the biasing force. The first portion forms a positive connection in the circumferential direction 102. The securing element also prevents the displacement of the form-fitting element in the channel by the centrifugal forces occurring during rotation of the piston.

In a further development, the securing element largely fills the channel up to the piston head, so that the harmful volume is kept small, in which gas is trapped and transported from the discharge side to the suction side.

The perspective view in Fig. 8 explains further details of the positive-locking element according to the embodiment.

In the first section 82, the form-fitting element has planar contact surfaces 94 and 94 ', which cooperate with the shaft recess in the mounted state. It is advantageous to align the contact surface parallel to a plane spanned by channel axis 104 and shaft direction 100 and parallel to one another. This results in a planar contact between the first portion and shaft recess, wherein the acting forces are substantially perpendicular to the plane and act in the circumferential direction 102. The surface pressure on the material is significantly lower compared to a line contact, which improves the long-term stability of the connection, since plastic deformation under continuous load is prevented. A chamfer 92 on a lower end face 96 facilitates assembly, since tilting is prevented. The lower end face forms a frictional engagement with the shaft recess in the mounted state. The contact surfaces provide a positive connection in the circumferential direction and a frictional connection in the shaft direction.

Alternatively, the contact surface 94 and 94 'may be flat and form an acute angle with each other. Although there is a rather line-like pressure between the shaft recess and contact surfaces, the assembly is easier. If the vacuum technical requirements allow a low dynamic load of the connection of shaft and piston, the assembly advantage can outweigh the pressure disadvantage. In a further development, those surfaces of the shaft recess which contact the contact surfaces in the mounted state are designed parallel to these. It forms in the mounted state, a frictional engagement, which fixes the positive locking element and above the piston in the axial direction.

The second section 84 is designed as a cylindrical body. An upper end face 86 is in the mounted state with the securing element in contact. Here, a bore with an internal thread 88 is provided, which is accessible through the channel. Thus, the interlocking element can be very easily mounted and removed by means of a standing with this internal thread engaging tool and removed from the channel. Both manufacturing and separating the connection of shaft and piston are considerably simplified. A chamfer 90 between the upper face and cylinder supports this, in that it prevents jamming and jamming in the channel, in particular during disassembly.

The first section 82 may undergo further embodiments. So cone top, truncated cone, wedge and stump are favorable designs. In particular, a conical or wedge tip can be used to leave a plastic impression in the bottom of the shaft recess on the contact pressure, which prevents axial displacement by positive engagement.

In the case of a cylindrical or frusto-conical configuration of the positive connection can also by the design according to Fig. 9 be created. The lower end face 96 of the first section 82 of the positive-locking element 80 has a cutting edge 98. By biasing the positive-locking element in the channel, this cutting edge cuts into the shaft recess and thus forms a positive connection.

For both examples, the channel preferably begins in the region of the piston head. It may be so offset from the point with the greatest distance to the shaft axis, that it is not in the narrowest region of the sealing gap to lie comes. This reduces the influence on the vacuum properties of the piston.

Both examples are advantageous for multi-stage vacuum pumps. Due to manufacturing tolerances, an angular offset between the pistons on a shaft may occur in the prior art, i. the pistons 40, 44 and 48 are mutually twisted mounted on the shaft. This worsens the column. The connection according to the embodiments prevents this, since a channel, in particular a bore can be positioned with very small tolerances and backlash relative to the piston profile. The same applies to a plurality of mutually axially offset shaft recesses.

Claims (10)

1. Vacuum pump (1) with a shaft (4, 6) having a shaft axis (100) and a shaft circumference (102), with a piston (40, 42, 44, 46, 48, 50) having a piston profile face (66) and a hole (58) for receiving the shaft, with a shaft recess (62) provided on the shaft, with a piston recess provided in the piston, and with a positively-locking element (80) which is located with a first portion (82) in the shaft recess and a second portion (84) in the piston recess, the piston recess being formed as a channel (60) starting at the piston profile face, and the second portion forming a positive engagement with the channel (60) in the direction of the shaft axis (100) and the shaft circumference (102), characterised in that the positively-locking element has an internal thread (88) accessible through the radial channel.
2. Vacuum pump according to claim 1, characterised in that the shaft recess has a greater extent (76) along the shaft axis than the first portion, such that the first portion can be moved along the shaft axis in the shaft recess.
3. Vacuum pump according to either claim 1 or claim 2, characterised in that a securing element (78) is provided, which fixes the positively-locking element and exerts a compressive force on the form-locking connection element perpendicular to the shaft axis.
4. Vacuum pump according to claim 3, characterised in that the first portion comprises contact faces (94, 94') which are flat and parallel to one another and to a plane spanning a channel axis (104) and the shaft axis (100).
5. Vacuum pump according to any of the preceding claims, characterised in that the positively-locking element has a lower end face (96) which forms a frictional engagement with a basal face of the shaft recess.
6. Vacuum pump according to claim 5, characterised in that a cutting edge (98) is provided on the lower end face (96).
7. Vacuum pump according to claim 3, characterised in that the first portion (82) comprises contact faces which are flat and form an acute angle with one another.
8. Vacuum pump according to any of the preceding claims, characterised in that the piston profile face has a Roots-type piston profile.
9. Vacuum pump according to any of the preceding claims, characterised in that a plurality of pistons (40, 42, 44, 46, 48) are arranged on the shaft.
10. Vacuum pump according to any of the preceding claims, characterised in that the channel (60) is configured as a bore.

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