Patent Application
20210222694
The present invention relates to a dry-running, oil-free orbiter vacuum pump, on which a friction-optimized surface is provided on components.
Vacuum pumps serve to evacuate gaseous media, such as e.g. for the purpose of generating a vacuum in a braking force booster. In the automotive sector, further applications of dry-running vacuum pumps also include e.g. the pneumatic adjustment of exhaust gas recirculation valves, exhaust flaps, guide vanes on turbochargers having a variable turbine geometry, and of a bypass for charging pressure regulation with a waste gate, and include the actuation of a central locking system, or for opening and closing headlight covers. In plant construction, dry-running vacuum pumps can serve in general to produce negative pressure in electro-pneumatic valves or pneumatic actuators.
Rotary displacement pumps, such as e.g. vane pumps or rotary vane pumps, are predominantly known for this purpose in the prior art and are very widely used. Some pumps require the provision of a lubricating film between the rotating and stationary pump components in order to ensure a sufficiently gas-tight seal as well as low frictional wear on contact surfaces. The requirement for a lubricating film in a vacuum pump gives rise to problems in terms of the temperature-dependent viscosity of the lubricant and the contamination caused by absorption of particles from the discharged air. These disadvantages are brought to bear under fluctuating ambient conditions of a mobile application and in particular to an increased extent in an installation in an engine compartment of a vehicle. Moreover, such pumps must always be connected to a lubricant supply or integrated into a lubricant-carrying system.
In order to avoid the aforementioned problem, dry-running vacuum pumps are known in the prior art. DE 10 2015 010 846 A1 by the same applicant describes an orbiter vacuum pump, of which the design of the pump assembly is similar to the design of the pump assembly of the present invention.
Dry-running vacuum pumps are generally lubricated by means of a solid lubricant, such as in particular by means of graphite. The solid lubricant graphite requires water or moisture for establishing a low-friction layer between a moving and a static pump part. The paucity of water in friction pairings in the vacuum leads to an increase in the coefficient of friction. As the inventors have established, the coefficient of friction of graphite increases in the vacuum of a dry-running vacuum pump. The inventors know that graphite, by reason of the behavior of the coefficient of friction, is not suitable in the desired manner as a solid lubricant for the application of a dry-running vacuum pump.
Therefore, the object of the invention is that of providing an alternative solution for a dry-running orbiter vacuum pump which, during vacuum operation, ensures a low loss of power from friction.
This object is achieved by means of an orbiter vacuum pump having the features of the main claim with respect to the present invention. The dry-running orbiter vacuum pump in accordance with the invention is characterized in particular in that at at least one of a radial air gap and an axial air gap formed in a cylindrical pump chamber between an orbiter eccentric piston and a 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.
The present invention provides for the first time a microstructure on a sliding surface at an air gap or between a moving and a static pump component in a dry-running pump for gaseous media.
In particular, the invention provides for the first time a sliding surface having a microstructure on an orbiter eccentric piston and/or a pump chamber wall of the pump housing of a dry-running orbiter vacuum pump.
In its most general form, the invention is based upon two aspects of decreasing a surface of the sliding surface and of producing an aerodynamic lubricating film in the air gap.
On the one hand, a friction-effective contact surface of the sliding surface is decreased by means of the cavities of the microstructure. The friction-effective contact surface of the sliding surface always contributes to friction resistance whenever friction contact occurs. Such friction contact occurs e.g. at the axial air gap by reason of a floating bearing arrangement of the orbiter eccentric piston in the pump chamber.
On the other hand, an aerodynamic lubricating film is produced by means of the cavities of the microstructure, as explained hereinafter. Such an aerodynamic lubricating film is produced in the air gap if suitable pressure ratios are present. These pressure ratios occur in particular at the radial air gap by reason of the displacement procedures of the orbiter eccentric piston. The radial air gap acts as a gap seal for separating the pump chamber into a negative pressure region and a pressure region on either side of the orbiter eccentric piston. The pressure difference gives rise to a leakage in the form of an airflow through the sealing gap or the corresponding air gap between the orbiter eccentric piston and the opposite chamber wall.
Each cavity of the microstructure produces a small turbulent swirl of the leakage airflow. Each small turbulent swirl bound locally over the cavity produces an effect equivalent to a small static air cushion bound locally over the cavity. Therefore, in comparison with a laminar flow of an airflow between two smooth surfaces, the sliding surface in accordance with the invention produces an aerodynamic lubricating film consisting of small turbulent air swirls which act in the same air gap in a manner equivalent to a sum of small static air cushions. A forcing-apart effect in terms of an air cushion or a friction-reducing effect in terms of the aerodynamic lubricating film consisting of locally bound turbulent swirls can be set on the basis of a number and surface distribution of the cavities in the microstructure.
The aerodynamic lubricating film which is provided in accordance with the invention and is produced by means of the microstructure of the sliding surface in accordance with the invention has several advantages.
The static pressure in the aerodynamic lubricating film ensures that, comparable to an air cushion, direct axial surface contact between end faces of the orbiter eccentric piston and the chamber wall are largely suppressed. As a result, very low wear occurs, thus achieving a long service life without any deterioration in the sealing effect of the corresponding air gap in terms of a gap seal.
Likewise, by reason of the lack of direct surface contact at the aerodynamic lubricating film, very low coefficients of friction are achieved which contribute to high energy efficiency of the orbiter vacuum pump.
Furthermore, the static pressure in the aerodynamic lubricating film constitutes a sealing-effective, separate pressure zone between an intake pressure and an outlet pressure of the orbiter vacuum pump. The locally bound turbulences over the cavities of the microstructure produce alternating, discrete zones of different pressures. Discrete zones of different pressures constitute in principle a barrier against the passage of a flow in a sealing gap or the corresponding air gap in the pump chamber. This principle is known e.g. from seals having grooves or chambers for providing a plurality of different pressure zones between two sealing sides. The aerodynamic lubricating film which is provided in accordance with the invention and is produced by means of the microstructure thus permanently achieves a sealing effect between a suction side and an outlet side of the orbiter vacuum pump which is better than in the case of a gap seal which is formed at the same air gap with the aid of smooth surfaces.
In summary, the aerodynamic lubricating film produced by means of the sliding surface in accordance with the invention, in avoiding direct friction contact, reduces static friction and sliding friction between the orbiter eccentric piston and the pump chamber, thus improving energy efficiency and wear resistance to the benefit of the service life and operating reliability of the orbiter vacuum pump. Moreover, the aerodynamic lubricating film produced by the sliding surface in accordance with the invention provides an improved sealing effect of the corresponding air gap between a negative pressure region and a pressure region in the pump chamber, whereby volumetric efficiency of the orbiter vacuum pump is improved.
Advantageous developments of the invention are provided in the dependent claims.
According to one aspect of the invention, the cavities of the microstructure can have a closed contour towards the surface of the at least one sliding surface. In comparison with a surface roughness, the topology of which includes any shapes of cavities having undefined contours, the closed contour of the cavities ensures a defined turbulent swirl on the surface and the local binding thereof to the closed contour, thus permitting targeted formation of the aerodynamic lubricating film in the air gap.
According to one aspect of the invention, the cavities of the microstructure can have a dimension of 10 to 100 μm in a depth direction to the surrounding surface of the at least one sliding surface. Within the stated range, an effectiveness of the cavities for producing turbulent swirls under the application-specific operating conditions and dimensions in the air gap of the orbiter vacuum pump is achieved.
According to one aspect of the invention, the cavities of the microstructure can 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. Even in this range, an effectiveness of the cavities for producing turbulent swirls under the application-specific operating conditions and dimensions in the air gap of the orbiter vacuum pump is achieved.
According to one aspect of the invention, the cavities of the microstructure can have the shape of a spherical cap, of an ellipsoid spherical cap, of an elongated hole or of a groove. In comparison with the shape of a spherical cap, the remaining shapes listed permit orientation and shape-optimization of the microstructure relating to the rotational direction or flow direction in the air gap.
According to one aspect of the invention, the microstructure of the at least one sliding surface can be produced at the corresponding surface of the pump housing or of the orbiter eccentric piston by means of laser-assisted melting of the material. This technique ensures particularly rapid and precise surface machining of the corresponding pump components.
According to one aspect of the invention, a material, on which the microstructure of the at least one sliding surface is produced, can be provided as a surface insert that is inserted into a component body of the pump housing or of the orbiter eccentric piston. This configuration means that, for a near-surface component region of the sliding surface, a harder or other optimized material, such as e.g. steel, can be selected, whereas, for the remaining component body of the piston or of the housing, a lighter and injection-moldable or other functionally optimized material, such as e.g. a synthetic material or aluminium, can be used.
According to one aspect of the invention, the microstructure of the at least one sliding surface can be produced on a metal material provided by the pump housing or by the orbiter eccentric piston. Different metal alloys provide preferred material properties with regard to hardness, surface quality and the machining capability thereof for producing the microstructure, in particular by means of a laser.
According to one aspect of the invention, the metal material, on which the microstructure of the at least one sliding surface is produced, can be surface hardened by means of hard anodizing. As a result, the wear resistance of the microstructure and thus the longevity of the advantageous effect can be improved by reason of the greater hardness of the material.
According to one aspect of the invention, the metal material, on which the microstructure of the at least one sliding surface is produced, can be provided as a sintered layer sintered on a material of the pump housing or of the orbiter eccentric piston. As a result, an alternative embodiment is proposed which, in turn, renders it possible to select a harder metal material for the sliding surface, while another optimized material can be used for the remaining component body.
According to one aspect of the invention, the at least one sliding surface can be 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. This embodiment ensures that it is possible to utilize the advantageous effect of the inventive sliding surface with the microstructure likewise in relation to a sliding movement and sealing arrangement between the blocking slide and the guide slot.
The invention will be explained in greater detail hereinafter with reference to different embodiments of the invention and the accompanying drawing. In the drawing:
As shown in
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.
The illustration in
As shown in
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.
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.
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.
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.
In the case of a first embodiment of the invention which is shown in
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2020 101 311.6 | Jan 2020 | DE | national |
