EP3580455B1 - Oil-free vacuum pump having a prismatic piston and corresponding compressor - Google Patents

Description

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

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

The function for evacuating brake boosters is of particular safety relevance in order to increase the force exerted on the brake pedal by the driver on the brake system. To achieve the boosting effect, a vacuum chamber of a brake booster is continuously evacuated when the vehicle is started and while driving. Therefore, in this application for operating a brake system of a vehicle, there is an increased requirement for the reliability and durability of the vacuum pump.

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

In vehicle construction, rotating displacement pumps such as vane pumps or rotary vane pumps are predominantly 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 low frictional wear on the contact surfaces. Thus, a lubricant supply or an integration into a circuit of a lubricant-carrying system must be provided on the vehicle side for such vane pumps.

In addition to this structural restriction, the requirement of a lubricating film in a vacuum pump also raises problems with regard to the temperature-dependent viscosity of the lubricant and the contamination through absorption of particles from the discharged air. These disadvantages come into play under fluctuating environmental conditions of a mobile application and, in particular, to a greater extent in the case of installation in an engine compartment of a vehicle. In the past, vehicle manufacturers had to recall models because, under unfavorable circumstances, a failure of the brake booster was to be feared due to an inadequate supply of lubricating oil to such vacuum pumps.

In addition, vane pumps with surface pairings made of dry-running carbon materials are known, which are used, for example, in aviation. In addition to the cost-intensive materials, pumps of this type are associated with the disadvantages of high friction loss and noise level.

Outside of the automotive sector, there is also a need in process engineering for an oil-free vacuum pump that offers advantages in terms of low maintenance requirements while dispensing with the need for regular lubrication of drive elements, or which conveys gases that must not be contaminated by traces of lubricating oil.

In addition to circulating displacement pumps, process engineering also discloses double-stroke displacement pumps with oscillating components that manage with little lubricant at low coefficients of friction. A prismatic shape instead of a cylindrical shape of the piston has been found to be advantageous, whereby a lower point loading on a piston raceway is achieved by means of an improved area distribution of transverse forces or tilting moments.

Such pumps with prismatic pistons have so far been used in stationary applications. Accordingly, the designs known in the prior art typically have relatively large dimensions and an unfavorable design which is not suitable for installation in a vehicle or other mobile applications.

A compact version of such a vacuum pump with a prismatic piston is shown in the U.S. 5,556,267 B described. In addition to the compact design of the pump assembly, which is shown without a drive, the advantages of high volumetric efficiency and low manufacturing costs are mentioned.

The double stroke pump described is driven by an eccentric cam that 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 cannot be operated without a lubricating oil between the piston, sliding block and eccentric cam. Furthermore, the piston is composed of several fits and parts, the sum of which makes it difficult to achieve tight running clearances in the cylinder barrel and increases the complexity of production. A generic oil pump with the features of the preamble of claim 1 is also from DE 10 2016 102 654 A1 known.

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 according to the invention by an oil-free vacuum pump for evacuating gaseous media with the features of claim 1.

This has an electric motor that drives a shaft; a pump housing with a pump chamber and an inlet and an outlet; a prismatic displacement piston, which acts bidirectionally and is movable on a reciprocal working path, is received in the pump chamber, the displacement piston exposing a connection between the inlet and the pump chamber in the area of two dead points of the reciprocal working path and covering it in an area lying in between; and at least one pressure valve, which releases an outflow of 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 an elongated hole into which a drive 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 a slider crank mechanism that can be operated oil-free as drive kinematics for a prismatic displacement piston which works effectively according to the principle of the double stroke or bi-directionally compressing.

Due to the rolling friction that the roller bearing absorbs on the cube pin in the elongated hole, a large amount of friction can be avoided in this area of application compared to conventional drive kinematics.

Due to the prismatic or rectangular shape, the piston is guided in the path of the pump chamber with low side forces. Furthermore, there are long sealing gaps along the rectangular shape.

Thus, an inexpensive electric, oil-free vacuum pump with few components is provided, which realizes an excellent volumetric efficiency with low displacement friction.

The vacuum pump is based on the knowledge according to the invention that the rolling friction of a grease-lubricated roller bearing, which initiates the rotational drive force of the crank pin on a translational engagement of the elongated hole, is advantageously suitable as a transmission means that provides a permanently low-wear drive of the piston in a performance range of Vacuum pump up to about 1 kW, without continuous or periodic supply of lubricating oil. Dispensing with a lubricating oil, which, due to the oscillation and turbulence at the gaps in the reciprocally moving components, emerges in the form of finely atomized droplets through the pump chamber and the outlet, provides various advantages.

The vacuum pump according to the invention does not require any maintenance intervals to lubricate the drive group.

In the case of an application for evacuating a brake booster or other pneumatically operated auxiliary equipment in a vehicle, the vacuum pump according to the invention can be flexibly positioned according to the conditions in the engine compartment of a vehicle due to the omission of a connection to a lubricant supply, which also results in less installation effort. Furthermore, the vacuum pump according to the invention is fail-safe with regard to a lubricant supply.

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

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

Compared to rotating displacement pumps of the vane cell type with components made of dry-running components made of technical carbon materials, the vacuum pump according to the invention generates lower friction losses and a lower noise level with similar dimensions or drive power.

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, can be arranged in the displacement piston. Thus, areas of the structure that require the production of a more complex molded part due to a duct or a valve seat can be relocated exclusively to the component of the displacement piston for which such a requirement already exists for the formation of the elongated hole. As a result, a section of the pump housing can form the four walls of the pump chamber, again being implemented cost-effectively as a simple cast body in the form of a square profile.

According to one aspect of the invention, with the exception of the pressure valves, the piston can be designed as an integral body in one piece. This simplifies the manufacture of the component while dispensing with mutual fits and the assembly.

According to one aspect of the invention, two pressure valves can be arranged in the displacement piston, each of which is assigned to a displacement surface. When a pressure valve is arranged for each displacement surface, moments of inertia which act on an elastically pretensioned valve body in the pressure valve are used in a functionally advantageous manner.

According to one aspect of the invention, an outlet pocket can be formed in the pump housing in the area of the outlet, facing an opening of the outlet channel in the displacement piston, and the extent of which overlaps with a reciprocal movement area of the opening of the outlet channel. The The outlet pocket, in an overlap with a reciprocal movement range of the mouth of the outlet channel in the displacement piston, creates a permanent connection between the static housing sections of the pump chamber and the outlet channel of the oscillating displacement piston in a simple manner.

According to one aspect of the invention, an inlet pocket can be formed in the pump housing in the area of the inlet which faces the displacement piston and which extends beyond positions of the displacement surfaces that are inwardly at the dead points of the reciprocal working path of the displacement piston. The inlet pocket easily forms two control slots at the dead points of the reciprocal working path of the displacement piston, which establish a connection from the inlet past an edge of an inward displacement surface of the displacement piston into the pump chamber. In contrast to an inlet guide with two separate control slots, the inlet pocket provides a larger flow cross-section and an antechamber, so that there is less suction throttling at the dead points in the short suction phases or a larger suction volume can be implemented. This increases the volumetric efficiency of the vacuum pump.

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 path, can form a gap seal. A low-friction, low-wear seal is thus achieved. By dispensing with seals, assembly is also simplified.

According to one aspect of the invention, the dimensions can be selected in such a way that a gap in the pump chamber surrounding the displacement piston is less than 50 μm. With this dimension, in connection with the construction-related large gap lengths along the prismatic piston, a sufficient seal can be achieved between the displacement chambers on both sides of the piston in the pump chamber. This also makes it possible to dispense with the use and assembly of seals or piston rings.

According to one aspect of the invention, a noise-damping element can be arranged inside or on the outlet. As a result, the noise level of the vacuum pump can be throttled in a cost-effective manner by means of a flexible material with a porous structure.

According to one aspect of the invention, the crank pin can be connected to a free end of the shaft. In this way, a further bearing in the axial area 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 crank pin can be connected to the free end of the shaft via a rotary plate. By designing a disk-shaped connection, turbulence in the area of rotation between the drive and pump assembly and an imbalance in the crank pin can be minimized.

According to one aspect of the invention, a rotor of the electric motor can be connected to a free end of the shaft. In this way, a further bearing in the axial area 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 can be supported by means of a single shaft bearing with two rows of rolling elements. This configuration further promotes the achievement of a small overall axial dimension of the vacuum pump.

According to one aspect of the invention, the electric motor can be arranged in an axial overlap with the shaft bearing and a housing section for receiving the shaft bearing. This configuration also promotes the achievement of a smaller overall axial dimension of the vacuum pump.

According to one aspect of the invention, the vacuum pump with the features mentioned above can also be used as an oil-free compressor. The advantage of the structure according to the invention that no atomized lubricating oil is permanently discharged from the outlet provides an advantage in particular with regard to applications such as laboratory applications in which a contamination-sensitive system has to be supplied with compressed air.

Fig. 1

eine Querschnittsansicht durch das Pumpengehäuse und den Verdrängerkolben mit Draufsicht auf den elektrischen Antrieb;

Fig. 2

eine Querschnittsansicht durch das Pumpengehäuse und den Verdrängerkolben in entgegengesetzter Richtung zu Fig. 1;

Fig. 3

eine Längsschnittansicht durch den Einlass und den Auslass mit Draufsicht auf eine Verdrängerfläche des Verdängerkolbens;

Fig. 4

eine Längsschnittansicht durch den Kurbelzapfen und das Wälzlager; und

Fig. 5

eine Längsschnittansicht durch den Auslasskanal des Verdängerkolbens und den Auslass.

The invention is described in detail below using an exemplary embodiment with reference to the accompanying drawings. In this show:

Fig. 1

a cross-sectional view through the pump housing and the displacement piston with a plan view of the electric drive;

Fig. 2

a cross-sectional view through the pump housing and the displacement piston in the opposite direction Fig. 1 ;

Fig. 3

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

Fig. 4

a longitudinal sectional view through the crank pin and the roller bearing; and

Fig. 5

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

As the Figures 1 and 2 show, the pump housing 1 has four walls in cross-sectional profile which enclose a rectangular pump chamber 10. A rectangular or cuboid-shaped displacement piston 2, which moves linearly back and forth, is slidably received in the pump chamber 10. An electric drive assembly is flanged to the pump housing 1.

As in Fig. 3 is shown, the pump chamber 10 is closed on a side opposite the drive assembly by a chamber wall 11, which in the Essentially the rectangular contour of the cross-sectional profile of the pump chamber 10 assumes. Two nozzles, through which an inlet 15 and an outlet 16 open into the pump chamber 10, are formed on the chamber wall 11. On an opposite side of the chamber wall 11, the pump chamber 10 is closed off from the drive assembly by a housing part 13. The chamber wall 11, the pump housing 1 and the housing part 13 of are screwed together.

A motor housing 14, in which an electric motor 4 is accommodated, connects to the housing part 13. The electric motor 4 is essentially formed by a stator 41, which is fixed in the motor housing 14, and a rotor 43 which is arranged so as to be rotatable radially inside the stator 41 and which is seated on a shaft 3 and drives it.

The shaft 3 is supported by a double row shaft bearing 31, e.g. a water pump bearing, mounted in a central axial section of the shaft 3. The shaft bearing 31 is received in the housing part 13. A receiving section of the housing part 13, in which the shaft bearing 31 is fitted, runs both radially and axially inside the rotor 43. Thus, the rotor 43 is rotatably fixed on one side of the shaft bearing 31 at a free end of the shaft 3, and is more effective by an electric motor The casing section of the rotor 43, which faces the stator 41 and comprises permanent magnetic elements, extends both radially and axially beyond a part of the shaft bearing 31.

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

As in Fig. 4 is shown, sits on the crank pin 33 a roller bearing 32, via which the crank pin 33 engages in an elongated hole 23 in the displacement piston 2 is excluded. The elongated hole 23 is aligned perpendicularly or transversely to a working section of the displacement piston 2 and is recessed throughout.

In cooperation with the shaft 3 including the carrier disk 30, a crank loop 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 displacement piston 2. The roller bearing 32 is a roller bearing that is grease-lubricated for its service life and whose rolling friction between the crank pin 33 and the elongated hole 23 ensures that the drive force is introduced to the displacement piston 2 without any subsequent need for lubricant.

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

As in Fig. 2 As can be seen, an inlet pocket 17 is cut out in the chamber wall 11 in the region of a confluence of the inlet 15 and faces the displacer piston 2. The inlet pocket 17 has a rectangular contour, the dimension of which is centered on the middle of the working section and extends on both sides beyond a position that is assumed at the dead points of the displacement piston 2 by the respective inner or passive displacement surface 22.

Thus, in a period of time in which the displacement piston 2 changes direction, the maximum increased volume of a displacement area can be filled with air, which is generated by a negative pressure based on the expanded volume, via the inlet 12, the inlet pocket 17 and an exposed gap between the inside or passive displacement surface 22 and the associated contour edge of the inlet pocket 17 is sucked into the pump chamber 10.

The displacement piston 2 has two pressure valves 20 which are each aligned with one of the two displacement surfaces 22 and open, as in FIG Fig. 3 can be seen. The pressure valves 20 correspond to conventional check valves in which a spherical valve body is tensioned by a spring against an inlet-side valve seat.

As in Fig. 5 is shown, an outlet channel 21 connects inside the displacement piston 2 behind the pressure valves 20, which essentially forms a connecting path between the two pressure valves 20 and a bore aligned perpendicular thereto, which is aligned with the chamber wall 11. An opening of this bore of the outlet channel 21 executes the reciprocal movement of the displacement piston 2 with respect to the static chamber wall 11.

In the chamber wall 11, in the area of the outlet 16, an outlet pocket 12 is cut out, which points towards the displacement piston 2. The outlet pocket 12 has a rectangular contour and overlaps with the two positions of the mouth of the outlet channel 21, which it occupies at the dead points of the displacement piston 2. The outlet channel 21, which follows the pressure valves 20, is therefore always connected to the outlet 16 via the outlet pocket 12 through its mouth, over the entire reciprocal movement sequence of the displacement piston 2.

In a period of time following the filling, the displacement piston 2 moves towards the displacement area of the pump chamber 10 and the air that has just been sucked in 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 its mouth, via the outlet pocket 12 and outlet 16 from the pump chamber 10.

A noise damper (not shown) is connected to the outlet 16 and comprises a porous sound-absorbing material, such as for example foam, as a result of which the noise level of the pulsation of the displacement processes is reduced.

The valve pressure from which the compressed air passes the valve body on the valve seat is set by means of the elastic bracing of the valve body. The valve pressure can essentially be set to the ambient pressure or atmospheric pressure, so that the pressure valve only has a functional blocking effect in one return direction and maximum volumetric efficiency is achieved. The valve pressure can also be used in connection with the design of the pump geometry, e.g. a slight remaining dead space and a desired operating speed must be selected in order to generate a small residual air cushion at the dead center of the displacement piston 2, which supports the introduction of force on the drive side to overcome the inertia when changing direction of the displacement piston 2. Thus, frictional forces and losses can be minimized.

The displacement piston 2 is a molded part made from a sintered metal material. The four sliding surfaces of the displacement piston 2, which run parallel to the working section, are ground to a uniform dimension that is selected to form a gap seal of less than 50 μm in the piston path of the pump chamber 10.

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

The sliding surfaces and the piston raceway can also have a dynamic, functional surface structure (not shown in more detail), which, through turbulent eddies, favors the formation of local air cushions in the micrometer range. This disrupts a laminar air flow in the circumferential gap between the sliding surfaces of the displacement piston 2 and the walls of the pump chamber 10, which improves the dynamic sealing effect of the gap seals and the low-friction dry-running ability of the surface pairing between the displacement piston 2 and the piston raceway.

The vacuum pump can also be used as a compressor. For this purpose, the inlet 15, which in the case of the vacuum pump is connected to a negative pressure line of a system to be evacuated, is opened to the atmosphere in the case of the compressor. The outlet 16, which in the vacuum pump is open to the atmosphere via the noise damper, 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 can be designed as a reluctance motor. In this case, the rotor 43 has no permanent magnetic elements, but consists of a soft magnetic material, such as a laminated package made of electrical steel. Furthermore, the cross section of such a rotor has pole teeth and / or sectors with lamellar air gap structures, which generate an alternating magnetic permeability diametrically through the rotor.

Claims (15)

1. An oil-free vacuum pump for evacuating gaseous media, comprising:

   an electric motor (4) that drives a shaft (3);

   a pump housing (1) with a pump chamber (10) and an inlet (15) and an outlet (16);

   a prismatic displacement piston (2) that, acting bi-directionally and movable over a reciprocal operating path, is accommodated within the pump chamber (10), the displacement piston (2) having an elongated hole (23) into which a driving force of the shaft (3) is introduced via a crankpin (33); and

   at least one pressure valve (20) that releases a flow of gaseous medium out of the pump chamber (10) through the outlet (16) and blocks a flow into the pump chamber (10);

   characterised in that

   the displacement piston (2) releases a connection between the inlet (15) and the pump chamber (10) in the region of two dead centers of the reciprocal operating path and overlapping in a region lying in between, and

   the driving force of the shaft (3) is introduced by means of a roller bearing (31).
2. The oil-free vacuum pump according to Claim 1, wherein the at least one pressure valve (20) and at least one outlet channel (21) that establish a connection for the outflow of the gaseous medium between the pump chamber (10) and the outlet (16) of the pump housing are disposed within the displacement piston (2).
3. The oil-free vacuum pump according to Claim 1 or 2, wherein the displacement piston (2) is formed in one part as an integral body.
4. The oil-free vacuum pump according to Claim 2 or 3, wherein two pressure valves (20), which are respectively assigned to a displacement surface (22), are disposed within the displacement piston (2).
5. The oil-free vacuum pump according to any of Claims 1 to 4, wherein an outlet pocket (12) is formed in the pump housing (1) in the region of the outlet (16), which faces an opening of the outlet channel (21) within the displacement piston (2), and the extension of said outlet pocket coincides with a reciprocal range of movement of the opening of the outlet channel (21).
6. The oil-free vacuum pump according to any of Claims 1 to 5, wherein an inlet pocket (17) is formed in the pump housing (1) in the region of the inlet (15), which faces the displacement piston (2) and which extends beyond positions of the displacement surfaces (22) that lie inwards at the dead centers of the reciprocal operating path of the displacement piston (2).
7. The oil-free vacuum pump according to any of Claims 1 to 6, wherein the dimensions of the pump chamber (10) and of the sliding surfaces of the prismatic displacement piston (2) that run parallel to the reciprocal operating path form a gap seal.
8. The oil-free vacuum pump according to Claim 7, wherein the dimensions are selected such that a gap in the pump chamber (10) running round the displacement piston (2) measures less than 50 µm.
9. The oil-free vacuum pump according to any of Claims 1 to 8, wherein a noise dampening element is disposed within or at the outlet.
10. The oil-free vacuum pump according to any of Claims 1 to 9, wherein the crankpin (33) is connected to a free end of the shaft (3).
11. The oil-free vacuum pump according to Claim 10, wherein the crankpin (33) is connected to the free end of the shaft (3) by means of a rotary plate (30).
12. The oil-free vacuum pump according to any of Claims 1 to 11, wherein a rotor (43) of the electric motor (4) is connected to a free end of the shaft (3).
13. The oil-free vacuum pump according to Claims 11 and 12, wherein the shaft (3) is mounted by means of a single shaft bearing (31) having two rows of rolling elements.
14. The oil-free vacuum pump according to Claim 13, wherein the electric motor (4) is arranged so as to axially overlap the shaft bearing (31) and a housing portion (13) receiving the shaft bearing (31).
15. The use of the oil-free vacuum pump having the features according to at least one of Claims 1 to 14 as an oil-free compressor.

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