EP3580455A1

EP3580455A1 - Oil-free vacuum pump having a prismatic piston and corresponding compressor

Info

Publication number: EP3580455A1
Application number: EP17822592.6A
Authority: EP
Inventors: Franz Pawellek; Conrad Nickel
Original assignee: Nidec GPM GmbH
Current assignee: Nidec GPM GmbH
Priority date: 2017-02-07
Filing date: 2017-12-11
Publication date: 2019-12-18
Anticipated expiration: 2037-12-11
Also published as: JP2020506321A; WO2018145795A1; DE102017102324A1; JP6830159B2; EP3580455B1; KR20190104203A; CN110249130A; KR102193199B1; US20200124036A1; CN110249130B

Abstract

The invention relates to an oil-free vacuum pump for evacuating gaseous media, comprising: an electric motor (4) which drives a shaft (3); a pump housing (1) having a pump chamber (10), as well as an inlet (15) and an outlet (16); a prismatic displacement piston (2) which is accommodated in the pump chamber (10) such that it is bidirectionally active and can be moved on a reciprocal working section; and at least one pressure valve (20) which releases an outflow of a gaseous medium out of the pump chamber (10) through the outlet (16) and blocks an inflow into the pump chamber (10). The displacement piston (2) has a slot (23) into which a drive force of the shaft (3) is introduced via a crankpin (33) by means of a rolling bearing (31).

Description

description

Oil-free vacuum pump with prismatic piston and accordingly

compressor

The present invention relates to an oil-free vacuum pump with a prismatic piston and a similar device for use as an oil-free running compressor.

Vacuum pumps are used in numerous application areas of pneumatics in process engineering processes or in vehicle construction. In the automotive sector, for example, they are required to adjust exhaust flaps, vanes on turbochargers with variable turbine geometry or a bypass for boost pressure control with a wastegate. You can also take over the function to operate a central locking or headlight flaps.

A special safety relevance is the function for evacuation of brake boosters to increase a force applied to the brake pedal force of the driver on the brake system. To obtain the amplification effect, a vacuum chamber of a brake booster is continuously evacuated when starting the vehicle and while driving. Therefore, in this application for operating a brake system of a vehicle, there is an increased demand on the reliability and longevity of the vacuum pump.

In addition, the packaging in the engine compartment of a modern vehicle with numerous auxiliary units only provides a very limited space for the vacuum pump. Furthermore, the vacuum pump in this application is exposed to strong temperature fluctuations.

In vehicle construction, predominantly rotary positive displacement pumps, such as vane pumps or rotary vane pumps, are used. Vane pumps made of metallic materials require the provision of a lubricating film between the rotating and stationary pump components in order to ensure a sufficiently gas-tight seal and a low frictional wear on the contact surfaces. Thus, for such vane pumps on the vehicle side, a lubricant supply or an integration into a circuit of a lubricant-carrying system must be provided.

In addition to this constructive restriction, the requirement of a lubricating film in a vacuum pump also raises a problem with regard to the temperature-dependent viscosity of the lubricant and the contamination by absorption of particles from the discharged air. These disadvantages come into effect under fluctuating environmental conditions of a mobile application and, in particular, in an installation in an engine compartment of a vehicle. In the past, vehicle manufacturers had to call for model recalls because of poor oil supply to such vacuum pumps under unfavorable circumstances, brake booster failure was to be feared.

In addition, vane pumps with Flächenpaarrungen from dry-able carbon materials are known, which are used for example in aviation. In addition to the costly materials such pumps are associated with the disadvantages of high friction losses and noise level.

Even outside of the automotive sector, there is a need in the process engineering for an oil-free running vacuum pump, which offers advantages in terms of low maintenance requirements waiving a regular lubrication of drive elements, or promotes gases that must not be contaminated by traces of lubricating oil.

Thus, in addition to circulating positive displacement pumps, double-stroke positive displacement pumps with oscillating components are known in the field of process engineering, and these require little lubricant at low coefficients of friction. In this case, a prismatic shape instead of a cylindrical shape of the piston has been found to be advantageous, creating a lower punctual load on a piston track is achieved by means of an improved area distribution of transverse forces or tilting moments.

Such pumps with prismatic pistons have been used in stationary applications. Accordingly, the prior art designs typically exhibit a relatively large size and design that is not suitable for installation in a vehicle or other mobile applications. A compact design of such a vacuum pump with prismatic

Piston is described in US 5,556,267 B. In addition to the compact construction of the pump assembly, which is shown without a drive, the advantages of high volumetric efficiency and low production costs are mentioned. The described Doppelhubpumpe is driven by an eccentric cam, which rotates in a sliding block, which in turn moves back and forth in a multi-part piston. The characteristic of a sliding block generally allows the conclusion that the drive can not be operated without a lubricating oil between piston, sliding block and eccentric cam. Furthermore, the piston is composed of several fits and parts whose sum complicates a realization of close running play in the cylinder bore and increases the complexity of manufacturing.

Accordingly, it is an object of the present invention to provide a vacuum pump with a simple, inexpensive structure that can be operated oil-free.

This object is achieved by an oil-free vacuum pump for the evacuation of gaseous media having the features of claim 1. This has an electric motor that drives a shaft; a pump housing having a pump chamber and an inlet and an outlet; a prismatic displacer, acting bidirectionally, on a reciprocal Working distance movable, is accommodated in the pump chamber, wherein the displacer exposes a connection between the inlet and the pump chamber in the range of two dead centers of the reciprocal working distance and covered in an intermediate region; and at least one pressure valve that releases a gaseous medium from the pump chamber through the outlet and blocks an inflow into the pump chamber; on.

The oil-free vacuum pump according to the invention is particularly characterized in that the displacement piston has a slot into which a driving force of the shaft is introduced via a crank pin by means of a roller bearing.

The invention thus provides for the first time a vacuum pump with an oil-free operable crank grinding mechanism as a drive kinematics for a prismatic displacement piston, which operates on the principle of double stroke or bidirectionally compacting effective.

By rolling friction, which receives the rolling bearing on the cotter pin in the slot, a large proportion of friction can be avoided compared to conventional drive kinematics in this application.

Due to the prismatic or rectangular shape of the piston is guided with low lateral forces in the raceway of the pump chamber. Furthermore, there are long sealing gaps along the rectangular shape. Thus, a low-cost electric, oil-free vacuum pump with few

Provided components that achieves excellent volumetric efficiency with low Verdrängerreibung.

In this case, the vacuum is based on the finding that the rolling friction of a grease-lubricated roller bearing, which initiates the rotational driving force of the crank pin on a translational engagement of the elongated hole, is advantageously suitable as a transmission means, the one permanently Low-wear drive of the piston in a power range of the vacuum pump to about 1 kW, without continuous or periodic supply of lubricating oil allows. The elimination of a lubricating oil, which emerges due to the oscillation and turbulence at gaps of the reciprocally moving components in the form of finely atomized droplets through the pump chamber and the outlet, provides various advantages.

The vacuum pump according to the invention requires no maintenance intervals for lubrication of the drive group. In the case of an application for evacuation of a brake booster or other pneumatically operated auxiliary equipment in a vehicle, the vacuum pump according to the invention can be flexibly positioned by eliminating a connection to a lubricant supply to the circumstances in the engine compartment of a vehicle, which also entails a lower assembly costs. Furthermore, the vacuum pump according to the invention is fail-safe with respect to a lubricant supply.

Compared with similar double-stroke pump types, the vacuum pump according to the invention can also be used in contamination-critical applications in process engineering.

In comparison to dry-running pump types, such as diaphragm pumps, the vacuum pump according to the invention has a superior power-dimension ratio.

In comparison with rotary vane-type rotary displacement pumps with components made of engineered carbon materials, the vacuum pump according to the invention, with a similar size or drive power, generates lower friction losses and a lower noise level.

Further advantageous developments of the vacuum pump according to the invention are the subject of the dependent claims. According to one aspect of the invention, the at least one pressure valve and at least one outlet channel, which establish a connection for the outflow of the gaseous medium between the pump chamber and the outlet of the pump housing, may be arranged in the displacement piston. Thus, areas of the structure that require the production of a more complex molding due to a channel guide or a valve seat can be laid exclusively in the component of the displacer for which such a requirement already exists for forming the slot. As a result, a portion of the pump housing forms the four walls of the pump chamber, in turn, be realized cost as a simple cast body in the form of a square profile.

According to one aspect of the invention, the piston may be formed integrally with the exception of the pressure valves as an integral body. As a result, the production of the component while avoiding mutual fits and assembly are simplified.

According to one aspect of the invention, two pressure valves can be arranged in the displacement piston, which are each assigned to a displacement surface. In the arrangement of a pressure valve to each displacement surface moments of inertia, which act on a resiliently biased valve body in the pressure valve, are advantageously used functionally.

According to one aspect of the invention, in the pump housing in the region of the outlet, an outlet pocket may be formed, which faces an opening of the outlet channel in the displacement piston, and whose extension overlaps with a reciprocal movement range of the mouth of the outlet channel. In this case, the outlet pocket, in overlap with a reciprocal range of movement of the mouth of the outlet channel in the displacer, easily establishes a permanent connection between the static housing sections of the pump chamber and the outlet channel of the oscillating displacer. According to one aspect of the invention, an inlet pocket may be formed in the pump housing in the region of the inlet that faces the displacement piston and that extends beyond positions of the displacement surfaces that are inward at the dead centers of the reciprocating working distance of the displacement piston. In this case, the inlet pocket forms, at the dead points of the reciprocal working distance of the displacer piston, two control slots in a simple manner, which establish a connection from the inlet, past an edge of an inward displacing surface of the displacer piston into the pump chamber. In contrast to an inlet guide with two separate control slots, the inlet pocket provides a larger flow area and an antechamber so that in the short Ansaugphasen at the dead center, there is a lower intake throttle or a larger intake volume can be implemented. As a result, the volumetric efficiency of the vacuum pump is increased.

According to one aspect of the invention, the dimensions of the pump chamber and the sliding surfaces of the prismatic displacement piston, which run parallel to the reciprocal working distance, form a gap seal. Thus, a friction and low-wear sealing is realized. By dispensing with seals assembly is further simplified. According to one aspect of the invention, the dimensions may be selected such that a gap surrounding the displacer in the pump chamber is a dimension of less than 50 .mu.m. In this measure, a sufficient seal between the displacement chambers on both sides of the piston in the pump chamber can be achieved in connection with the design-related large gap lengths along the prismatic piston. This can be dispensed with the use and installation of seals or piston rings.

According to one aspect of the invention, a noise damping element can be arranged inside or at the outlet. As a result, the noise level of the vacuum pump can be throttled by a flexible material having a porous structure in a cost effective manner. According to one aspect of the invention, the crankpin may be connected to a free end of the shaft. In this way, further storage in the axial region of the pump assembly can be avoided and a smaller overall axial dimension of the vacuum pump can be realized.

According to one aspect of the invention, the crankpin may be connected via a turntable to the free end of the shaft. The design of a disc-shaped connection turbulence in the rotation region between the drive and pump assembly and an imbalance of the crank pin can be minimized.

According to one aspect of the invention, a rotor of the electric motor may be connected to a free end of the shaft. As a result, further storage in the axial region of the drive assembly can also be avoided and a smaller overall axial dimension of the vacuum pump can be realized.

According to one aspect of the invention, the shaft may be supported by means of a single shaft bearing with two rows of rolling elements. By this embodiment, the achievement of a small overall axial dimension of the vacuum pump is further favored.

According to one aspect of the invention, the electric motor may be arranged in axial overlap with the shaft bearing and a housing portion for receiving the shaft bearing. This embodiment also favors the achievement of a smaller overall axial dimension of the vacuum pump.

According to one aspect of the invention, the vacuum pump having the aforementioned features can also be used as an oil-free running compressor. The advantage of the construction according to the invention that no atomized lubricating oil is permanently discharged from the outlet provides, in particular, an advantage with regard to inserts, such as laboratory applications, in which a contamination-sensitive system is to be supplied with compressed air. The invention will now be described in detail by means of an embodiment with reference to the accompanying drawings. In this show:

1 shows a cross-sectional view through the pump housing and the displacer with a plan view of the electric drive.

Figure 2 is a cross-sectional view through the pump housing and the displacer in the opposite direction to Fig. 2.

3 shows a longitudinal sectional view through the inlet and the outlet with a plan view of a displacement surface of the displacement piston;

Fig. 4 is a longitudinal sectional view through the crankpin and the rolling bearing; and

Fig. 5 is a longitudinal sectional view through the outlet channel of the displacement piston and the outlet.

As FIGS. 1 and 2 show, the pump housing 1 has four walls in the cross-sectional profile which enclose a rectangular pump chamber 10. In the pump chamber 10 is a rectangular or cuboid displacement piston 2, which moves linearly back and forth, slidably received. To the pump housing 1, an electric drive assembly is flanged. As shown in FIG. 3, the pump chamber 10 becomes a side which is the one

Drive assembly opposite, completed by a chamber wall 11, which occupies substantially the rectangular contour of the cross-sectional profile of the pump chamber 10. On the chamber wall 11, two nozzles are formed, through which an inlet 15 and an outlet 16 open into the pump chamber 10. On an opposite side of the chamber wall 11, the pump chamber 10 is closed by a housing part 13 to the drive assembly. The chamber wall 11, the pump housing 1 and the housing part 13 of the are screwed together. To the housing part 13, a motor housing 14 connects, in which an electric motor 4 is received. The electric motor 4 is substantially constituted by a stator 41 fixed in the motor housing 14 and a rotor 43 rotatably disposed radially inside the stator 41, which seats on and drives a shaft 3.

The shaft 3 is connected via a double row shaft bearing 31, e.g. a water pump bearing, mounted in a central axial portion of the shaft 3. The shaft bearing 31 is received in the housing part 13. A receiving portion of the housing part 13, in which the shaft bearing 31 is fitted, extends both radially and axially within the rotor 43. Thus, the rotor 43 on one side of the shaft bearing 31 is fixed against rotation at a free end of the shaft 3, and an electric motor effective A shell portion of the rotor 43, which faces the stator 41 and includes permanent magnetic elements, extends both radially and axially beyond a portion of the shaft bearing 31.

On the other side of the shaft bearing 31, a circular carrier disk 30 is arranged rotationally fixed at the other free end of the shaft 3. On the support plate 30 is offset in axial extension to the shaft end and to the axis of rotation of the shaft 3, a crank pin 33 is arranged. The carrier disk 30 is rotatably received in a corresponding rotationally symmetrical recess of the housing part 13.

As shown in Fig. 4, sits on the crank pin 33, a roller bearing 32 via which the crank pin 33 engages in a slot 23 which is excluded in the displacer 2. The slot 23 is aligned perpendicular or transversely to a working distance of the displacer 2 and excepted throughout.

In cooperation of the shaft 3, including the carrier disk 30, a crank grinding mechanism is formed via the crank pin 33 and the roller bearing 32, which engage in the elongated hole 23, which converts an eccentric drive movement into an alternating or reciprocal movement of the displacer piston 2. The rolling bearing 32 is a lubricated on its life bearings, by the rolling friction between the crank pin 33 and the slot 23, an introduction of the driving force on the displacer 2, without subsequent lubricant requirement is permanently and speed guaranteed.

By the crank mechanism, the displacer 2 is set in the rectangular pump chamber 10 in a reciprocal movement on a working distance between two dead centers. As a result of this mode of operation, two displacement regions are formed one after the other in the pump chamber 10 between the displacement surfaces 22 of the displacer piston 2 and the walls of the pump chamber 10 during one rotation of the shaft 3.

As can be seen in FIG. 2, in the region of an inlet of the inlet 15, an inlet pocket 17 is recessed in the chamber wall 11, which adjoins the displacer 2. The inlet pocket 17 has a rectangular contour whose dimension is centered to the middle of the working distance and extends on both sides beyond a position which is occupied at the dead centers of the displacer 2 of the respective inner and passive displacement surface 22.

Thus, in a period in which a change in direction of the displacer piston 2 takes place, the maximum increased volume of a displacement region can be filled with air, which by a vacuum based on the expanded volume, via the inlet 12, the inlet pocket 17 and an exposed gap between the inner or passive displacement surface 22 and the associated contour edge of the inlet pocket 17 is sucked into the pump chamber 10.

The displacer piston 2 has two pressure valves 20 which are each aligned and opened to one of the two displacement surfaces 22, as shown in FIG. 3 can be seen. The pressure valves 20 correspond to conventional check valves in which a spherical valve body is biased by a spring against an inlet-side valve seat before. As shown in FIG. 5, an outlet passage 21, which essentially forms a connecting path between the two pressure valves 20 and a bore oriented perpendicular thereto, which is aligned with the chamber wall 11, adjoins the interior of the displacer piston 2 behind the pressure valves 20. An opening of this bore of the outlet channel 21 performs the reciprocal movement of the displacer 2 with respect to the static chamber wall 11.

In the chamber wall 11, an outlet pocket 12 is excluded in the region of the outlet 16, which allocates to the displacer 2. The outlet pocket 12 has a rectangular contour and overlaps with the two positions of the mouth of the outlet channel 21, which occupies it at the dead points of the displacement piston 2. Thus, the outlet channel 21 following the pressure valves 20 always communicates with the outlet 16 via the outlet, over the entire reciprocal movement sequence of the displacer piston 2, via the outlet pocket 12.

In a subsequent to the filling period, the displacer 2 moves to the displacement region of the pump chamber 10 and the just sucked air is compressed. When the compressed air exceeds a set pressure of the pressure valves, an increasingly displaced volume of air escapes through the corresponding pressure valve 20, the outlet channel 21 and through its mouth, via the outlet pocket 12 and the outlet 16 from the pumping chamber 10. At the outlet 16 is a not connected noise damper comprising a porous sound-absorbing material, such as foam, whereby a noise level of the pulsation of the displacement operations is reduced.

The valve pressure at which the compressed air passes the valve body at the valve seat is adjusted by means of the elastic tension of the valve body. The valve pressure may be set substantially to the ambient pressure or atmospheric pressure, so that the pressure valve functionally only a blocking effect in a Return direction is true and a maximum volumetric efficiency is achieved. The valve pressure may also be selected in connection with the design of the pump geometry, such as a slight remaining dead space, and a desired operating speed to produce a small residual air cushion at the dead center of the displacer 2, the drive-side force introduction to overcome the inertia in the direction of change of the displacer 2 support. Thus, frictional forces and losses can be minimized.

The displacement piston 2 is a molded part, which is made of a sintered metallic material. The four sliding surfaces of the displacer 2, which run parallel to the working distance, are ground to a uniform level, which is selected to form a gap seal of less than 50 μπι in the piston raceway of the pump chamber 10.

The pump housing 1, which comprises four walls of the pump chamber 10, is made as a casting or profile part or sintered part, the inner wall surfaces are also ground to a corresponding degree of a gap seal to form a gap seal in the piston raceway of the pump chamber 10. Also, the chamber wall 11 including the nozzle for the inlet 15 and the outlet 16 and the housing part 13, which close the end face of the pump chamber 10 and form the piston race are made as a casting or sintered part and adjusted by a corresponding grinding treatment to the extent of a gap seal.

The sliding surfaces and the piston raceway may also have a dynamically functional surface structuring, not shown in detail, which promotes the formation of local air cushions in the micrometer range due to turbulent turbulences. As a result, a laminar flow of air in the circumferential gap between the sliding surfaces of the displacer 2 and the walls of the pump chamber 10 is disturbed, whereby a dynamic sealing effect of the gap seals and a low-friction dry-running capability of the surface pairing between the displacer 2 and the piston barrel is improved. The vacuum pump can also be used as a compressor. For this purpose, the inlet 15, which is connected in the vacuum pump with a vacuum line of a system to be evacuated, opened in the case of the compressor to the atmosphere. The outlet 16, which is opened to atmosphere via the silencer in the vacuum pump, is connected in the case of the compressor to a pressure line of a pneumatic system or the like.

In an alternative embodiment, the electric motor 4 may be configured as a reluctance motor. In this case, the rotor 43 has no permanent-magnetic elements but is made of a soft magnetic material such as a laminated sheet of electric sheet. Further, the cross-section of such a rotor has pole teeth and / or sectors with lamellar air-gap structures that produce an alternating magnetic permeability diametrically through the rotor.

Claims

Claims 1. An oil-free vacuum pump for evacuating gaseous media, comprising: an electric motor (4) driving a shaft (3); a pump housing (1) having a pump chamber (10) and an inlet (15) and an outlet (16); a prismatic displacer (2) bidirectionally movable on a reciprocal working path, received in the pump chamber (10), the displacer (2) communicating between the inlet (15) and the pump chamber (10) in the range of two Exposing dead centers of the reciprocal work path and covered in an intermediate area; and at least one pressure valve (20) which releases a gaseous medium from the pump chamber (10) through the outlet (16) and blocks inflow into the pump chamber (10); characterized in that the displacement piston (2) has a slot (23) into which a driving force of the shaft (3) via a crank pin (33) by means of a rolling bearing (31) is introduced.

2. oil-free vacuum pump according to claim 1, wherein the at least one pressure valve (20) and at least one outlet channel (21), which make a connection for the outflow of the gaseous medium between the pump chamber (10) and the outlet (16) of the pump housing, in the Displacer piston (2) are arranged.

3. Oil-free vacuum pump according to claim 1 or 2, wherein the displacer (2) is integrally formed as an integral body.

4. Oil-free vacuum pump according to claim 2 or 3, wherein in the displacement piston (2) two pressure valves (20) are arranged, which are each assigned to a displacement surface (22).

5. Oil-free vacuum pump according to one of claims 1 to 4, wherein in the pump housing (1) in the region of the outlet (16) an outlet pocket (12) is formed facing an opening of the outlet channel (21) in the Verdängcrkolben (2) is, and whose extension overlaps with a reciprocal movement range of the mouth of the outlet channel (21).

6. Ölfrcie vacuum pump according to one of claims 1 to 5, wherein in the pump housing (1) in the region of the inlet (15) an inlet pocket (17) is formed, which faces the displacement piston (2), and extending over positions of the Verdrängerflächen (22) which are at the dead centers of the reciprocal working distance of the displacer piston (2) inwardly extending beyond.

7. Oil-free vacuum pump according to one of claims 1 to 6, wherein the dimensions of the pump chamber (10) and the sliding surfaces of the prismatic displacement piston (2), which run parallel to the reciprocal working distance, form a gap seal.

8. Oil-free vacuum pump according to claim 8, wherein the dimensions are selected such that a displacement piston (2) circumferential gap in the pump chamber (10) is a measure of less than 50 μηι.

The oil-free vacuum pump according to any one of claims 1 to 8, wherein a noise-damping member is disposed inside or at the outlet.

10. Oil-free vacuum pump according to one of claims 1 to 9, wherein the crank pin (33) is connected to a free end of the shaft (3).

11. Oil-free vacuum pump according to claim 10, wherein the crank pin (33) via a turntable (30) with the free end of the shaft (3) is connected.

12. Oil-free vacuum pump according to one of claims 1 to 11, wherein a rotor (43) of the electric motor (4) with a free end of the shaft (3) is connected.

13. Oil-free vacuum pump according to claims 11 and 12, wherein the shaft (3) by means of a single shaft bearing (31) is mounted with two rows of rolling elements.

14. Oil-free vacuum pump according to claim 13, wherein the electric motor (4) in axial overlap with the shaft bearing (31) and a housing portion (13) for receiving the shaft bearing (31) is arranged.

15. Use of the oil-free vacuum pump as oil-free compressor with the features according to at least one of claims 1 to 14.