Friction-Optimized Vacuum Orbiter Pump

Abstract

The present invention relates to a dry-running, oil-free orbiter vacuum pump, on which a friction-optimized surface is provided on components. The dry-running orbiter vacuum pump comprises inter alia a pump housing with a cylindrical pump chamber and an orbiter eccentric piston with a guide slot and a cylindrical exterior surface, a cylindrical cross-section of the orbiter eccentric piston being smaller than a cylindrical cross-section of the pump chamber. At at least one of a radial air gap and an axial air gap formed in the cylindrical pump chamber between the orbiter eccentric piston and the pump housing at least one sliding surface is arranged in a manner exposed to the air gap; wherein the at least one sliding surface comprises a microstructure including cavities for decreasing an exposed surface of the at least one sliding surface.

Claims

1. A dry-running orbiter vacuum pump comprising: a pump housing with a cylindrical pump chamber; an orbiter eccentric piston with a guide slot and a cylindrical exterior surface, a cylindrical cross-section of the orbiter eccentric piston being smaller than a cylindrical cross-section of the pump chamber; a shaft for driving the orbiter eccentric piston by means of an eccentric crankpin that meshes with the orbiter eccentric piston; a blocking slide received in the guide slot of the orbiter eccentric piston, one end of the blocking slide being pivotably mounted at the pump housing between an inlet and an outlet; characterized in that at at least one of a radial air gap and an axial air gap formed in the cylindrical pump chamber between the orbiter eccentric piston and the pump housing at least one sliding surface is arranged in a manner exposed to the air gap; wherein the at least one sliding surface comprises a microstructure including cavities for decreasing an exposed surface of the at least one sliding surface.

2. The dry-running orbiter vacuum pump according to claim 1, wherein the cavities of the microstructure have a closed contour towards the surface of the at least one sliding surface.

3. The dry-running orbiter vacuum pump according to claim 1, wherein the cavities of the microstructure have a dimension of 10 to 100 μm in a depth direction to the surrounding surface of the at least one sliding surface.

4. The dry-running orbiter vacuum pump according to claim 1, wherein the cavities of the microstructure have a dimension of 10 to 1000 μm in an extension direction of a contour to the surrounding surface of the at least one sliding surface.

5. The dry-running orbiter vacuum pump according to claim 1, wherein the cavities of the microstructure have the shape of a spherical cap, of an ellipsoid spherical cap, of an elongated hole or of a groove.

6. The dry-running orbiter vacuum pump according to claim 1, wherein the microstructure of the at least one sliding surface is produced at the corresponding surface of the pump housing or of the orbiter eccentric piston by means of laser-assisted melting of the material.

7. The dry-running orbiter vacuum pump according to claim 1, wherein a material, on which the microstructure of the at least one sliding surface is produced, is provided as a surface insert that is inserted into a component body of the pump housing or of the orbiter eccentric piston.

8. The dry-running orbiter vacuum pump according to claim 1, wherein the microstructure of the at least one sliding surface is produced on a metal material provided by the pump housing or by the orbiter eccentric piston.

9. The dry-running orbiter vacuum pump according to claim 8, wherein the metal material, on which the microstructure of the at least one sliding surface is produced, is surface hardened by means of hard anodizing.

10. The dry-running orbiter vacuum pump according to claim 8, wherein the metal material, on which the microstructure of the at least one sliding surface is produced, is provided as a sintered layer sintered onto a material of the pump housing or of the orbiter eccentric piston.

11. The dry-running orbiter vacuum pump according to claim 1, wherein the at least one sliding surface is additionally also arranged at at least one surface of the blocking slide, wherein the at least one sliding surface at the blocking slide also comprises the microstructure including cavities for decreasing an exposed surface of the at least one sliding surface.

Description

[0030] The invention will be explained in greater detail hereinafter with reference to different embodiments of the invention and the accompanying drawing. In the drawing:

[0031] FIG. 1 shows a cross-section of the pump chamber of an orbiter vacuum pump according to one embodiment of the invention;

[0032] FIG. 2 shows an axial cross-section of the orbiter vacuum pump according to one embodiment in FIG. 1; and

[0033] FIG. 3 shows an enlarged section Z of the orbiter vacuum pump according to one embodiment in FIG. 2.

[0034] As shown in FIG. 1, the orbiter vacuum pump according to one embodiment of the invention is formed from a pump housing 1 which comprises a pump chamber 2 with a cylindrical chamber wall. In the pump chamber 2, an orbiter eccentric piston 3 performs a circular movement, wherein a circumferential sliding contact of the orbiter eccentric piston 3 with the cylindrical chamber wall is maintained. Arranged in the orbiter eccentric piston 3 is a guide slot 4 in which a blocking slide 5 is slidably received. The blocking slide 5 extends through the pump chamber 2 into the orbiter eccentric piston 3 and is pivotably mounted at a free end. For this purpose, a pivot bearing 14 is arranged in the chamber wall between an inlet opening 6 and an outlet opening 7. The pump inlet has a nozzle for connecting a vacuum hose.

[0035] In dependence upon the position of the orbiter eccentric piston 3 in the circular movement in the pump chamber 2, a portion of the blocking slide 5 located opposite the pivotably mounted end slides in and out in the guide slot 4. As a result, the pump chamber 2 is divided, either side of the blocking slide 5, into two volumes, of which one communicates with the inlet opening 6 and one communicates with the outlet opening 7. The volumes on each side of the blocking slide 5 vary with the circumferential sliding contact between the orbiter eccentric piston 3 and the cylindrical chamber wall in equal proportions oppositely to one another such that a cyclical displacement procedure which is explained hereinafter is completed.

[0036] The illustration in FIG. 1 shows a position of the orbiter eccentric piston 3 approximately halfway prior to a top dead center, in which the increasing volume of the pump chamber 2 which communicates with the inlet 6 and through which a gas is sucked in reaches an almost maximum volume. After passing over the top dead center, i.e. after the orbiter eccentric piston 3 has passed over the sliding bearing 14 and the inlet opening 6, during the next revolution in the clockwise direction the previously sucked-in gas is pushed out through the outlet 7 by reason of a decreasing volume on a leading side of the circumferential sliding contact between the orbiter eccentric piston 3 and the cylindrical chamber wall, whereas at the same time and to the same extent new gas is then sucked through the inlet 6 into the pump chamber 2 by reason of an increasing volume on a trailing side of the circumferential sliding contact.

[0037] As shown in FIG. 2, a shaft 8 is arranged in the pump housing 1 in such a manner as to be rotatably mounted by means of a shaft bearing. The shaft 8 is driven by means of an electric motor 9. An eccentric disk 12 with an eccentrically arranged crankpin 13 is fixed on the shaft 8. The crankpin 13 engages into the center point of the orbiter eccentric piston 3. During a rotation of the shaft 8, the eccentric disk 12 performs the circular movement of the orbiter eccentric piston 3 in the pump chamber 2 via the crankpin 13. The orbiter eccentric piston 3 is designed in a cylindrical manner in the form of a piston drum. Preferably, the orbiter eccentric piston 3 is manufactured as a molded part by means of injection-molding from a synthetic material, in particular a fiber-reinforced synthetic material.

[0038] The outlet opening 7 is provided by means of an axially oriented bore which issues into the pump chamber 2. It forms, in conjunction with a pressure valve 17, an outlet to the environment. The pressure valve 17 is provided by means of a bent sheet-metal part which covers a rear side of the outlet opening 7 and is urged back by means of a delivery pressure of a gas exiting the pump chamber 2. One side of the pump housing 1, on which the electric motor 9 is received, is closed off by means of a motor cover 19. Furthermore, electronics for controlling an electric drive power are arranged in the motor cover 19.

[0039] FIG. 3 shows an enlarged section Z of FIG. 2 which relates to a region of the sliding contact between the orbiter eccentric piston 3 and the cylindrical chamber wall of the pump housing 1 in the pump chamber 2. At the apex of the sliding contact, there is generally a small radial air gap R which for illustrative purposes is shown in an exaggerated manner. Likewise, there is an axial air gap A between the orbiter eccentric piston 3 and an end-face chamber wall of the pump housing 1. On a side illustrated on the left, the end-face chamber wall of the pump housing 1 is formed by means of a pump lid 11.

[0040] On the one hand, the radial air gap R and the axial air gap A in the pump chamber 2 are necessary in order to ensure a low-friction circular movement of the orbiter eccentric piston 3 in the pump chamber 2 within the scope of manufacturing and fitting tolerances. Furthermore, the radial air gap R and the axial air gap A ensure that the orbiter eccentric piston 3 cannot become jammed during the circular movement even by small, particulate impurities, which can be sucked in with a gas flow. The dimension of the radial air gap R and of the axial air gap A is preferably several 10 μm, e.g. 50 μm for the radial air gap R and either side of the orbiter eccentric piston 3 in each case 30 μm for the axial air gap A. The orbiter eccentric piston 3 is mounted in a floating manner in the axial direction, i.e. is received in a freely movable manner on the crankpin 13, such that an equilibrium of flows and pressure zones in the axial air gaps A on either side means that an axial position of the orbiter eccentric piston 3 is achieved in an automatically displaceable manner.

[0041] Nevertheless, axial movements, external effects such as vibrations or accelerations in a system environment, moisture, impurities, temperature fluctuations or otherwise caused material stresses or material expansions bring about temporary or permanent reductions in the contact-free gap dimension of the axial air gap A or of the radial air gap R to a gap dimension of 0 μm such that there is contact between opposing surfaces. Therefore, between the orbiter eccentric piston 3 and the chamber walls of the pump housing 1 friction-effective sliding contacts also exist at certain points or in a planar manner in the axial air gap A or in the radial air gap R.

[0042] In various embodiments of the invention, orbiter vacuum pumps are provided having different arrangements and configurations of sliding surfaces which reduce disruption of the pump operation or impairment of efficiency by friction-effective sliding contacts in the axial air gap A or in the radial air gap R.

[0043] In the case of a first embodiment of the invention which is shown in FIG. 3, a specific sliding surface 30, which is explained hereinafter, is provided on the radial outer surface of the orbiter eccentric piston 3. The sliding surface 30 comprises a microstructure with cavities which is illustrated by checkered hatching. The cavities are arranged in a regular pattern distributed uniformly over the sliding surface 30. Furthermore, the cavities comprise a closed contour towards the surface, i.e. each cavity is separated with respect to an adjacent cavity in any direction by means of an intermediate portion of the surface of the sliding surface 30. As a result, the sliding surface 30 comprises a decreased surface area in relation to friction contact in the radial air gap R.

[0044] The cavities of the microstructure are produced at the sliding surface by means of a laser, wherein material is partially removed by the melting of material on the surface. The shape of the cavities is selected in favor of a machining speed preferably corresponding to a projected shape of the impinging laser beam or a mask. Therefore, a contour of the cavities preferably has a simple shape without angles, such as spherical cap or an elliptical spherical cap. The cavities comprise a depth of 10 to 100 μm and a diameter of 10 to 1000 μm in an extension direction of the contour. In an exemplified embodiment, the microstructure of the sliding surface 30 comprises round cavities having a depth of 20 μm and a diameter of 100 μm.

[0045] The material of the sliding surface 30 at which the microstructure with the cavities is produced consists of a hard-anodized metal alloy. More specifically, a metal layer is applied on the body—designed as a piston drum—of the orbiter eccentric piston 3 which is manufactured from a fiber-reinforced synthetic material. The metal layer is sintered on the material of the orbiter eccentric piston 3 in the form of a sintered metal layer consisting of a sintered alloy. Moreover, the sintered metal layer is subjected to a process of surface hardening by means of hard anodizing.

[0046] In alternative variants of the first embodiment, a metal layer for producing the sliding surface 30 as an annular or cylindrical material insert is provided on the outer surface of the orbiter eccentric piston 3, or the entire body of the orbiter eccentric piston 3 consists of a corresponding metal, such as a stainless steel.

[0047] In a not-illustrated, second embodiment of the invention, a sliding surface 20 comprising a microstructure with cavities is arranged on the cylindrical chamber wall of the pump housing 1 which is exposed to the radial air gap R. The microstructure of the sliding surface 20 corresponds in all configurations of the cavities to the previously explained microstructure of the sliding surface 30 of the first embodiment. Likewise, a material selection of a metal having a hard-anodized surface for the sliding surface 20 corresponds to the preferred material selection for the sliding surface 30 of the first embodiment. However, in the second embodiment, the material for the sliding surface 20 is provided such that the entire body of the pump housing 1 is manufactured from a corresponding metal.

[0048] In alternative variants of the second embodiment, only a metal layer for producing the sliding surface 20 is provided on the pump housing. The metal layer is provided as an annular or cylindrical material insert consisting of a stainless steel on the inner surface of the cylindrical chamber wall of the pump housing 1, or in the same region the metal layer is sintered on the material of the pump housing 1 in the form of a sintered metal layer consisting of a sintered alloy. In the case of these variants, the body of the pump housing 1 can be manufactured from another metal, such as an injection-moldable light metal alloy or even from a synthetic material.

[0049] In a not-illustrated, third embodiment of the invention, sliding surfaces 10 comprising a microstructure with cavities are arranged on the end-face chamber walls of the pump housing 1 and the pump cover 11 which are exposed to the axial air gap A. The microstructure of the sliding surfaces 10 corresponds in all configurations of the cavities to the previously explained microstructure of the sliding surface 30 of the first embodiment. Likewise, a material selection of a metal having a hard-anodized surface for the sliding surfaces 10 corresponds to the preferred material selection for the sliding surface 30 of the first embodiment. However, in the third embodiment, the material for the sliding surfaces 10 is provided such that the pump cover 11 and the entire body of the pump housing 1 are manufactured from a corresponding metal.

[0050] In alternative variants of the third embodiment, only a metal layer for producing the sliding surfaces 10 is provided on the pump housing 1 and the pump cover 11. The metal layer is provided as a planar material insert in the form of a steel sheet on the inner surface of the pump cover 11 and the end-face chamber wall of the pump housing 1, or in the same regions the metal layer is sintered on the material of the pump cover 11 and the material of the pump housing 1 in the form of a sintered metal layer consisting of a sintered alloy. In the case of these variants, the body of the pump cover 11 and the body of the pump housing 1 can be manufactured from another metal, such as an injection-moldable light metal alloy or even from a synthetic material.

[0051] In a fourth embodiment of the invention, sliding surfaces comprising a microstructure with cavities are arranged additionally on the surfaces of the blocking slide 5 which are exposed to the guide slot 4 of the orbiter eccentric piston 3. The microstructure of these sliding surfaces likewise corresponds in all configurations of the cavities to the previously explained microstructure of the sliding surface 30 of the first embodiment. Likewise, a material selection of a metal having a hard-anodized surface for these sliding surfaces corresponds to the preferred material selection for the sliding surface 30 of the first embodiment. In this case, the material for these sliding surfaces is provided such that the body of the blocking slide 5 is manufactured from a corresponding metal, such as a stainless steel.

[0052] In a further alternative embodiment of the invention, sliding surfaces comprising a microstructure with cavities are arranged additionally on axial surfaces of the orbiter eccentric piston 3 which are exposed to the axial air gap A. The microstructure of such sliding surfaces likewise corresponds in all configurations of the cavities to the previously explained microstructure of the sliding surface 30 of the first embodiment. Likewise, a material selection of a metal having a hard-anodized surface for such sliding surfaces corresponds to the preferred material selection for the sliding surface 30 of the first embodiment.

[0053] It should be noted that the various embodiments and their alternative variants can be combined with one another and in particular can be added to one another in order to provide an orbiter vacuum pump in accordance with the invention having the previously described advantages.

LIST OF REFERENCE NUMERALS

[0054] 1 pump housing [0055] 2 pump chamber [0056] 3 orbiter eccentric piston [0057] 4 guide slot [0058] 5 blocking slide [0059] 6 inlet/inlet opening [0060] 7 outlet/outlet opening [0061] 8 shaft [0062] 9 electric motor [0063] 10 axial sliding surfaces of the pump housing/of the pump cover [0064] 11 pump cover [0065] 12 eccentric disk [0066] 13 crankpin [0067] 14 pivot bearing [0068] 17 pressure valve [0069] 19 motor cover [0070] 20 radial sliding surface of the pump housing [0071] 30 radial sliding surface of the orbiter eccentric piston [0072] A axial air gap [0073] R radial air gap [0074] Z enlarged section