WO2008031418A2

WO2008031418A2 - Diaphragm pump

Info

Publication number: WO2008031418A2
Application number: PCT/DE2007/001630
Authority: WO
Inventors: Jörg STERN; Thomas Rolland; Thorsten Hillesheim; Dietrich Ginsberg; Olaf OHLIGSCHLÄGER; Dieter Paul
Original assignee: Thomas Magnete Gmbh; Paul, Sascha; Paul, Ailien
Priority date: 2006-09-16
Filing date: 2007-09-11
Publication date: 2008-03-20
Also published as: EP2061971A2; WO2008031418A3

Abstract

The invention relates to a diaphragm pump (1) for delivering and metering an especially liquid medium. Said pump comprises a delivery compartment which can be filled with a liquid medium, a pressure compartment, filled with a hydraulic liquid, a diaphragm (7) that separates the delivery compartment from the pressure compartment and that is fastened to freely oscillate between the two, a piston working compartment (16) provided in the pressure compartment and being fluidically connected to the diaphragm, and a hydraulic diaphragm drive having a piston (15) that can be longitudinally displaced in the direction of the diaphragm. Said piston interacts with the piston working compartment (16) with its lower face facing the diaphragm, the piston (15) being displaceable by a predetermined distance in the direction of the membrane. The piston working compartment (16) has a bottom surface (20) against which the piston (15) abuts with its lower face (34) during its movement inside the piston working compartment (16) so that the piston (15) reaches a lower dead point when contacting the bottom surface (20).

Description

diaphragm pump

The invention relates to a diaphragm pump for conveying and metering a fluid, in particular a liquid medium.

Dosing pumps in the form of piston pumps are known in the prior art, for example from DE 4328621 A1 and DE 10 2004 002 245 A1. Here are the parts of the drive, namely the electromagnetic armature and the plain bearing / piston combination in the medium to be conveyed run. The moving parts of the piston pump are in contact with the fluid to be pumped and are possibly lubricated by it. An aggressive fluid tends to crystallize in the case of drying. As a result, operation of the piston pump would be disturbed or at least impaired by jamming or settling of the moving parts as a result of the solid fluid. In the case of a liquid urea solution, in the case of drying, the stated crystallization of solids may occur. Therefore, such piston pumps are not suitable for delivering an aggressive fluid such as a urea solution.

When dosing flowable substances, especially liquids, the use of feed pumps in the form of diaphragm pumps is known, which are characterized by a leak-free operation. In contrast to a directly driven reciprocating pump, a displacer is not directly connected to a pumping fluid in a diaphragm pump. Such feed pumps are used in particular in the promotion of an aggressive fluid such as a urea-water solution for an exhaust gas purification process in automotive diesel engines. Such an exhaust gas purification process is also known as "selective catalytic reduction", abbreviated SCR. By means of the SCR technology, a diesel engine is set to maximum efficiency and compliant particle emissions. By using this technology, the threshold levels Euro 4 and Euro 5 can be achieved for nitrogen oxide emissions. This denitrification technology requires a reduc- tion agent. In most cases, AdBlue ™ is used as the reducing agent. This is an aqueous urea solution which is injected into the exhaust gas stream and releases the required reducing agent, namely ammonia, for the SCR reactions in the catalyst. As a result, the NO _x emissions of the diesel exhaust gases are effectively reduced while optimizing the diesel engine to a low efficiency out. This advantageously results in low fuel consumption and low particulate emissions.

Due to its specific properties, the AdBlue ™ reducing agent sets very stringent design requirements for the exhaust gas aftertreatment systems with which denitrification is carried out, with regard to frost resistance, clogging at elevated temperatures due to crystallization and material compatibility of the medium-carrying components.

DE 10 2004 011 123 A1 shows a delivery pump for an exhaust aftertreatment medium, in particular a urea-water solution for diesel engines, which is used in an SCR process. However, the metering of the medium requires, in addition to the feed pump, an additional metering device. Another disadvantage of this pump is that because of a direct mechanical drive of a membrane by a solenoid comparatively high driving forces are required. This can also lead to inaccurate production rates.

In addition to a direct mechanical drive of a membrane, which is controlled directly by a solenoid, especially in the field of chemical pumps, those are known in which a membrane is hydraulically driven. The oscillating movement of a delivery piston is transmitted via a hydraulic template in a membrane working space on a membrane, which is the actual delivery chamber, with the fluid to be delivered filled, seals against the atmosphere. In contrast to a diaphragm driven directly by a reciprocating piston, a hydraulically supported diaphragm always works with pressure equalization and is therefore suitable for higher delivery pressures with higher outputs. In comparison to a mechanical direct drive of the diaphragm, a higher dosing accuracy also arises due to the high pressure rigidity of the hydraulic principle.

DE-U-8437633 shows a hydraulically driven diaphragm pump in which a hydraulic chamber comprises a diaphragm working space and a pumping chamber separated therefrom by the diaphragm. The precise delivery and metering amount of the pumped fluid in the delivery chamber of the pump adjusts itself here by the stroke length of the piston in the membrane working space. The stroke length of the piston varies between a piston start and piston end position depending on drive elements such as the piston length and the frequency of movement. Due to a variety of parameters to be taken into account an exact dosage of the medium to be delivered is not possible. Especially with small displacement and low stroke of the piston, these disadvantages are noticeable.

Another disadvantage of the pump according to DE-U-8437633 is that it is not suitable for installation in a motor vehicle due to its robust design. In order to be able to vent gas bubbles from the membrane working space, venting channels are connected to the geodetically highest point of the membrane working space, which open out into the open or into a suitable container. In this respect, an operation of this pump in a predetermined position orientation is required. In other words, operation of this pump is not possible regardless of location.

DE 21 04 783 describes a diaphragm pump in the form of a Membranpump- device in which a liquid to be pumped by a movable

Membrane is promoted. The membrane is arranged between a first chamber for the liquid to be pumped and a second chamber. In the second chamber, a drive piston is arranged longitudinally displaceable, the is driven by a swash plate. The drive piston is biased by a spring, which is provided between an end face of the drive piston and the diaphragm, in the direction of the swash plate. An accurate stop position for the drive piston in the Druckhub position when the displaced towards the diaphragm is not provided.

DE 195 35 314 C1 describes a diaphragm pump according to the preamble of claim 1, in which a delivery chamber for a delivery fluid is separated by a membrane from a hydraulic space filled with a hydraulic fluid. In the hydraulic chamber, a displacer piston is provided, which is sealed in a corresponding bore of a guide block back and forth. On one of the membrane opposite side of a rod of the displacer lock nuts are provided, which come into contact with the guide block in a Druckhub position of the displacer and thereby prevent further movement of the displacer in the direction of the membrane. An adjustment of the lock nuts leads to a disadvantageous tolerance for displaceability of the displacement piston with respect to or within the bore and thus to a non-exact volume of hydraulic fluid which acts on the diaphragm.

Accordingly, the invention is based on the object to provide a diaphragm pump that allows accurate metering of a fluid to be delivered with simple and robust means.

This object is achieved by a diaphragm pump having the features of claim 1. Advantageous developments of the invention are defined in the dependent claims.

A membrane pump according to the invention comprises a delivery chamber, which may be filled with a liquid medium, a pressure chamber which is filled with a hydraulic fluid, and a membrane which separates the delivery chamber from the pressure chamber and is freely suspended therebetween. The membrane pump further comprises a piston chamber provided in the pressure chamber. Working space, which is in fluid communication with the membrane, and a hydraulic diaphragm drive having a longitudinally displaceable in the direction of the membrane piston, the piston with its lower, the membrane facing the end face, cooperating with the piston working space.

At least one control bore opens laterally into the piston working space, through which the piston working chamber is fed with the hydraulic fluid of the pressure chamber. When the piston with its lower end face passes over a membrane edge of the lower control bore, the piston working space is separated from the control bore. The membrane is deformable by a hydraulic fluid volume displaced by the piston, which is determined by the product of the area of the face of the piston with the distance by which the piston within the piston working space moves from the lower edge of the control bore towards the diaphragm. The piston working space has a bottom surface against which the piston with its lower end face abuts when moving within the piston working space, so that the piston reaches a bottom dead center when in contact with the bottom surface.

An advantage of the diaphragm pump according to the invention is that the volume which is displaced by the piston within the piston working space in the direction of the membrane and thus acts on the side of the pressure chamber on the membrane, regardless of drive elements of the membrane drive or a length of the piston. The hydraulic fluid volume acting on the diaphragm is governed solely by the diameter of the piston, ie, the area of the piston face which cooperates with the piston working space and the distance that the piston moves towards the diaphragm from the lower edge of the control becomes. By contacting the piston with the bottom surface of the piston working space, an accurate bottom dead center is defined, which thus does not depend on further tolerances. Accordingly, this results in an exact dosage of the medium to be delivered on the pressure side. In other words, an exact metering of the medium to be delivered on the pressure side can thus be achieved simply and in particular independently of drive elements. The exact one Volume of the liquid medium to be conveyed and metered on the side of the pumping chamber results from the exact hydraulic fluid volume which is displaced by the piston in the direction of the diaphragm on the side of the pressure chamber.

In an advantageous embodiment of the invention, the piston can be moved by a predetermined distance in the direction of the membrane. This means that the piston within the piston working space is moved by the predetermined distance in the direction of the diaphragm after passing over the lower edge of the control bore. This results in an exact, displaced in the direction of the membrane volume of the hydraulic fluid, and thus a precisely predetermined deformation of the membrane in the direction of the pressure chamber to dose the liquid medium in the desired amount and pressure. Preferably, the piston working space has a bottom surface, against which the piston abuts with its end face during the movement within the piston working space, so that the piston reaches a bottom dead center when it comes into contact with the bottom surface. By this bottom dead center, the distance by which the piston of the piston working space can shift from the lower edge of the control bore, defined, which has a positive effect, especially at a high frequency of the piston oscillation.

In contrast to known metering pumps, in which the accuracy of a delivery of several variables depends on the diaphragm pump according to the invention, the accuracy of the flow rate depends only on the distance to which the piston with its lower end side starting from the lower edge of the control bore in the direction the membrane is moved. As explained, this distance may simply be limited by a stop surface, for example in the form of the bottom surface of the piston working space.

In an advantageous embodiment of the invention, the piston may have on its lower end face a survey that comes at the bottom dead center of the piston in contact with the bottom surface. A side edge of the piston end abuts at the bottom dead center not against the bottom surface of the piston working space and is thus not subject to wear. This has a positive effect on a dosing accuracy and on a long service life of the metering pump, since the side edge of the piston end face acts as a control edge when the lower edge of the control bore is passed over. A high and above all constant accuracy of fit of this control edge ensures leakage-free displacement of the hydraulic fluid in the piston working chamber by the piston.

In an advantageous embodiment of the invention, the survey may be formed centrally on the lower end side. In this case, the lower end side is stepped from the elevation to its peripheral edge, so that, as explained, the peripheral edge does not come into contact with the bottom surface at the bottom dead center of the piston. Conveniently, the survey is formed integrally with the piston, and can be produced, for example, as a turned part or as a casting.

In an advantageous embodiment of the invention, the piston can be moved in a direction away from the membrane to a top dead center, wherein the lower end face of the piston, the control bore at least partially releases. As a result, the pressure in the piston working chamber drops to the pressure prevailing in the pressure chamber, wherein at the same time the diaphragm is deformed in the direction of the pressure chamber in order to suck the fluid medium again in the pumping chamber. During the subsequent displacement of the piston back into the piston working space, the previously sucked in liquid medium is expelled again metered into the pressure chamber by the resulting deformation of the membrane.

In an advantageous development of the invention, the diaphragm drive may comprise a lifting magnet with an armature piston enclosed by a magnetic coil. The solenoid drives in its displacement in the magnetic field generated by the magnetic field, the piston at least in the direction of the membrane. Recovery of the piston away from the diaphragm or out of the piston working space is preferably accomplished by spring means biasing the piston in a direction away from the diaphragm. A fixed connection between the armature piston and the piston is thus not required to displace the piston in a direction away from the membrane. A particularly space-saving arrangement of the spring device results from the fact that it is designed as a spiral spring which surrounds the piston at its upper end side adjacent to the armature piston. Such a membrane drive is characterized by a small number of movable portions, wherein the magnetic drive allows precise control in a large adjustment. In addition, the magnetic drive allows a stepless stroke adjustment for the piston during its displacement in the piston working space and an exact adjustability of the pump frequency. This is reflected in a larger flow and in a precise dosage.

In an advantageous embodiment of the invention, the piston can be guided in the piston working space without play in order to obtain an exact metered quantity of the liquid medium to be conveyed. Such a play-free guidance of the delivery piston can be achieved by a stationary in a pump housing held guide or bearing sleeve, in which the piston is guided displaceably. The interior of the sleeve defines a portion of the piston working space, with the control bore opening into a wall of the sleeve.

The control bore is designed with its edge adjacent to the piston working space substantially at right angles. The control bore is thus formed at its mouth to Kolbenarbeitsraum sharp without chamfers or rounded to achieve when crossing the peripheral edge of the piston face an exact separation of the piston working chamber from the pressure chamber.

In an advantageous embodiment of the invention may be formed in the bottom surface of the piston working space, a passage opening leading to a membrane working space. The membrane working space immediately adjoins the membrane, whereby the membrane can deform into the membrane working space. The diaphragm working space is a part of the piston working space and is in fluid communication with the part of the piston working space which is connected to the piston or its end face by means of the passage opening. acts. It is understood that the passage opening has a smaller diameter than the part of the working space in which the piston is slidably received. Thus, the bottom surface of the piston working space advantageously forms an abutment shoulder which defines the abovementioned bottom dead center of the piston. Although the passage opening is smaller in diameter than the piston working space in which the piston is displaceably guided, it is dimensioned sufficiently large that when displacing the hydraulic fluid after passing over the lower edge of the control bore through the piston no significant flow losses or even backflow occur.

In an advantageous embodiment of the invention, the pressure chamber, which is formed in a pump housing, comprise a drive space in which the armature piston is slidably received. By energizing the magnetic coil, the armature piston is driven in the direction of an upper end side of the piston, thereby to move with a displacement of the piston whose lower end side into the piston working space. In the pump housing, at least one control line is preferably formed, which is connected to the at least one control bore and opens into the drive chamber. If this control line extends substantially parallel to the longitudinal axis of the piston, advantageously results in a compact design of the membrane according to the invention.

The diaphragm pump according to the invention is suitable for all pumping tasks in which an exact dosage is required. A particularly advantageous

The use of the diaphragm pump is in the area of SCR exhaust gas purification systems used in diesel vehicles. In the SCR process, the diesel exhaust gases are treated in a special catalyst with a urea-water solution, which are introduced from a reservoir into the exhaust stream or injected. The ammonia resulting from the urea decomposition reduces the nitrogen oxides in the exhaust gas flow to the fission products nitrogen and water. By means of the membrane pump according to the invention can be with respect to the urea-water solution pressure and Set flow rate exactly to the values that are mandatory for a desired droplet size during injection. An additional metering device for injecting the urea-water solution into the exhaust gas flow is no longer required. It is understood that the metering pump according to the invention is not only suitable for metering aggressive media such as a urea-water solution, but can also be used for injecting fuel.

A membrane according to the invention, which is intended for use in a hydraulically driven diaphragm pump, separates a delivery chamber from a pressure chamber of the diaphragm pump. In the delivery chamber may be contained a fluid to be metered, in particular a liquid medium. The pressure chamber contains a hydraulic fluid acting on the membrane, by means of which a deformation of the membrane is forced. In the membrane, a recess is formed on the side of the delivery chamber, through which an exact delivery volume for the fluid to be metered or the liquid medium to be metered is defined. The membrane has a hybrid structure, wherein the membrane on the side of the pressure chamber has a metallic membrane body and on the side of the delivery chamber an elastomeric rubber which is attached to the metallic membrane body.

Conventionally known pumps are usually problematic when dry aspirating. By dry aspiration is meant a beginning of the Fördems and the dosing of a fluid when the pumping chamber is not filled with the fluid, but with air. In order to produce a large negative pressure in the intake passage of the diaphragm pump, the delivery space between the intake and discharge channel must be brought to a very small volume during the intake tract. An essential advantage of the invention is that an exact delivery volume or stroke volume for the medium to be metered is metered through the recess in the membrane. At the beginning of the dry suction, the membrane is deformed into the delivery chamber against the opposite surface of the pump head, and thereby comes into contact with this surface. Apart from a minimal residual volume, the arises due to usual tolerances of the membrane or on the surface of the pump head, the air from the pumping chamber is almost completely expelled in this process. This results in a sufficiently large negative pressure when the membrane is then deformed in the opposite direction, ie in the direction of the pressure chamber and away from the intake passage or the discharge channel. Accordingly, a sufficiently large amount of the fluid to be metered is sucked into the delivery space through the intake passage. In the subsequent ejection tract, when the membrane again moves against the surface of the pump head, the previously aspirated fluid is expelled again.

The recess according to the invention in the membrane can advantageously be produced accurately and simply. With respect to the membrane, the recess may be preferably circular, and is provided in particular in the central region of the membrane. As a result, the recess is arranged symmetrically between the suction channel and the discharge channel when the membrane is pressed against the opposite surface of the pump head at the beginning of Trockenansaugens. If the membrane has a round shape, the recess may be formed substantially concentric with the edge of the membrane. A uniform arrangement of the through

Recess defined delivery volume can be achieved in that the recess in the middle of the membrane has its greatest distance with respect to a plane which is spanned by an edge region of the membrane. This can be done by a configuration of the recess in the form of a concave dome, which is directed away in the relaxed state of the membrane from the opposite surface of the pump head.

In an advantageous embodiment of the invention, the membrane may have a so-called hybrid structure, wherein the membrane on the side of the pressure chamber comprises a metallic membrane body and on the side of the delivery chamber, ie opposite to the surface of the pump head comprises an elastomeric rubber. The elastomeric rubber is suitable, attached to the metallic membrane body, for example by gluing, vulcanization or the like. Particularly easy is the production of the recess in the hybrid membrane then, if it is provided in the elastomeric rubber. In particular, a concave calotte can easily be produced in the elastomer rubber.

In an advantageous development of the invention, in the case of the hybrid membrane, the metallic membrane body can have wave-like steps along its longitudinal extent, which have orthogonal high deformability of the membrane in one direction _. to ensure their surface. Conveniently, the wave-like steps facing the pressure chamber, wherein an opposite side of the metallic base body is formed substantially flat. The attachment of the elastomeric rubber to such a flat surface is easier and prevents unwanted detachment of the elastomeric rubber.

In an advantageous embodiment of the invention, the pump head may have an intake passage and an exhaust passage, which are in line connection with the delivery chamber. Both the intake passage and the discharge passage can be closed by a valve, depending on the intake tract or discharge tract. The valves are arranged substantially directly adjoining the delivery chamber, so that a volume of the intake duct or of the discharge duct between the respective valve and the delivery chamber is minimal. This advantageously results in a minimal "dead space volume", since the membrane can not penetrate into the line connection between the valves and the mouth in the delivery chamber at the beginning of Trockenansaugens

Contact the membrane remains with the surface of the pump head in the pumping chamber, minimal, resulting in the explained large negative pressure during the subsequent suction.

In an advantageous embodiment of the invention, the recess, which is formed in the opposite surface of the diaphragm of the pump head, take the form of a dome. In order to define an exact delivery volume, the surface of the pump head is bordered on its edge. zend to the inlet valve and the outlet valve is substantially planar, wherein the recess is formed exclusively in a substantially central region of the surface. As a result, even small volumes of the fluid can be precisely conveyed and metered. By virtue of such a relatively small delivery volume, which is defined by the recess, there are likewise advantages for dry aspiration, in which initially a negative pressure must be generated in the delivery space.

In an advantageous embodiment of the invention, the recess may be formed in the surface of the pump head in the form of a substantially cylindrical recess.

In an advantageous embodiment of the invention may be formed in the surface of the pump head opposite to the membrane at least one groove extending between the intake passage and the outlet passage. Such a groove promotes a flow of the fluid to be metered within the pumping chamber from an opening of the intake duct to a mouth of the discharge channel, which is reflected in a constant dosing.

The membrane according to the invention or the pump head according to the invention ensure problem-free dry aspiration in a hydraulically driven diaphragm pump since the diaphragm is deformed with its recess against the surface of the pump head or in the case of a planar diaphragm into the recess of the surface of the pump head and thereby between the diaphragm and the surface of the pump head remains a minimum volume of air. In other words, during dry aspiration, the volume of air from the delivery chamber, ie between the membrane and the adjacent surface of the pump head can be almost completely pushed out. This results in a sufficient negative pressure during subsequent re-deformation of the membrane for suction of the fluid.

It is understood that the features mentioned above and those yet to be explained not only in the combination specified in each case, but also usable in other combinations or in a single division, without departing from the scope of the present invention.

The invention is illustrated schematically below with reference to several embodiments in the drawing and will be described in detail with reference to the drawing.

Show it:

Figure 1 is a cross-sectional view of an inventive

2 shows a cross-sectional view of a further embodiment of the diaphragm pump according to the invention in a fully assembled state, Figure 3 shows the area B of Figure 1 in an enlarged view, Figure 4 is a cross-sectional view of a delivery piston, Figure 5 shows the area A of Figure 4 in an enlarged view,

FIG. 6 shows a cross-sectional view of a further embodiment of the diaphragm pump according to the invention with a compensation volume,

FIG. 7 shows a cross-sectional view of a further embodiment of the membrane pump according to the invention, with a compensation volume,

8 shows a cross-sectional view of a pump head according to the invention for a diaphragm pump, FIG.

9 shows a cross-sectional view of a further embodiment of the pump head according to the invention, FIG. 10 shows a cross-sectional view of a further embodiment of the pump head according to the invention, with connecting leads mounted thereon,

FIG. 11 shows a cross-sectional view of a pump head which interacts with a membrane according to the invention, FIG. 12 shows a cross-sectional view of the membrane according to the invention of FIG.

Figure 11, Figure 13 is a partial cross-sectional view of an inventive

Check valve, Figure 14 is a plan view of Figure 13,

Figure 15a is a cross-sectional view of a portion of a pump head with check valves according to the invention mounted therein

Fig. 13,

Figure 15b is a plan view from the direction of the arrow C of Figure 15a, Figure 16 is a cross-sectional view of an inventive

FIG. 17 is a plan view of a spring diaphragm of the invention used in the check valve of FIG. 16. FIG. 18 is a cross-sectional view of another embodiment of a spring diaphragm of the present invention for use with a check valve

Check valve,

FIG. 19 shows a plan view of the spring diaphragm of FIG. 18, FIG. 20 shows a cross-sectional view of a further embodiment of a check valve according to the invention, with the spring diaphragm of FIG. 18 or 19,

Figure 21 is a sectional view taken along line I-I of Figure 20, and Figure 22 is a simplified principal view of a device according to the invention

Exhaust gas aftertreatment system, in which a diaphragm pump according to Figure 1 or 2 is arranged in a line from a reducing agent tank to an injection nozzle arranged in front of a catalyst.

The diaphragm pump 1 serves to convey a fluid, in particular a liquid medium. Without being understood as limiting, the fluid to be delivered is referred to hereinafter only as a liquid medium. Of the

Intake passage 9 is connected via a line connected to the coupling pipe 13 with a (not shown) tank containing the liquid medium. The discharge channel 10 is connected via a to the corresponding coupling connected 13 connected line with a nozzle or the like, to which the liquid medium is to be metered. The diaphragm pump 1 is based on the principle that in the delivery chamber 8 by means of the membrane 7 alternately a suction pressure or an overpressure is generated. At a suction pressure, the liquid medium is sucked as indicated by an arrow in Figure 1 through the coupling neck through the intake passage 9 into the delivery chamber 8 in, as a result of the suction pressure, the first check valve 11 opens and the second check valve 12 closes. By sucking the delivery chamber 8 is substantially completely filled with the liquid medium. At a pressure reversal in the delivery chamber 8, ie at an overpressure, which results from a deformation of the diaphragm 7 in the direction of the pump head 3, the liquid medium is expelled from the delivery chamber 8 through the discharge channel 10, wherein the second check valve 12 as a result of the overpressure opens in the discharge channel 10 and the first check valve 11 in the intake passage 9 closes. By continuously forming a negative and positive pressure in the delivery chamber 8, the liquid medium is metered by means of the diaphragm pump 1.

The diaphragm pump 1 has a hydraulic diaphragm drive, with which the membrane 7 is acted upon from the side of the pressure chamber 5 forth with a hydraulic volume. The membrane 7 is therefore not driven directly by means of a mechanical element which is attached to the membrane 7, but undergoes a forced deformation by the hydraulic fluid 6, which is contained in the pressure chamber 5. In detail, the hydraulic diaphragm drive 14 comprises a longitudinally displaceable piston in the form of a delivery piston 15. In the pump body 2, a piston working space 16 is formed, which is part of the pressure chamber 5. In a centrally formed in the pump body 2 bore a guide sleeve 17 is enclosed, within which the delivery piston 15 is guided longitudinally displaceable. As far as the guide sleeve 17 is not filled by the delivery piston 15, it is filled with the hydraulic fluid 6 and thus also forms part of the pressure chamber 5. Adjacent to a foot portion 18 of the guide sleeve 17, a stop block 19 is enclosed in the pump body 2. With his the guide sleeve 17 facing Surface of the stop block 19 forms a bottom surface 20 for the piston working space. In a central region of the stop block and coaxial with the longitudinal axis of the delivery piston 15, a passage opening 21 is formed, which passes through the stop block coaxially to the longitudinal axis of the delivery piston 15 in length. Accordingly, this passage opening 21 opens to the membrane 7, wherein below the stop block 19, a membrane working chamber 22 is formed. Also, the membrane working space 22 is part of the pressure chamber 5 and thus filled with the hydraulic fluid 6.

In the pump body 2 and in the upper housing part 4 matched recesses are formed, which form a drive chamber 23 when mounted upper housing part 4. Within the drive space 23, a drive piston 24 is slidably received in the form of an armature piston. The delivery piston 15 passes above the guide sleeve 17 through the pump body 2 with a clearance, its upper end face 25 protruding into the drive space 23. The drive space 23 is formed so that the drive piston 24 displaceable therein is aligned with a longitudinal axis coaxial to the longitudinal axis of the delivery piston 15. Since the drive space 23 is also part of the pressure chamber, it is filled with the hydraulic fluid 6. In other words, the drive piston 24 is surrounded by the hydraulic fluid 6, so that it is lubricated by the hydraulic fluid 6 during its longitudinal displacement in the drive chamber 23. The same applies to the delivery piston 15, which is also lubricated by the hydraulic fluid at a displacement in the guide sleeve.

The armature piston 24 is forcibly moved within the drive space 23 by generating a magnetic field. For this purpose, at least one magnetic coil 26 is fixed between the upper housing part 4 and the pump body 2, which surrounds at least a part of the armature piston 24. Between an inner end face 27 of the upper housing part 4 and an adjoining part of the pump body 2, a recess 28 is provided which forms a lateral circumferential opening within the drive chamber 23. Thus, a magnetic field is generated during energization of the Magnet coil 26 is generated, not shielded by a mostly metallic material of the pump body 2 and / or the upper housing part 4 and can act on the armature piston 24. As a result, the armature piston 24 is forcibly displaced during energization of the solenoid 26 within the drive chamber 23 down, ie in the direction of the delivery piston 15. The magnetic coil 26 is connected to electrical lines 29, which are upwards, ie opposite to the membrane 7, led out of the upper housing part 4.

In order to create a pressure equalization for the hydraulic fluid 6 contained in the drive chamber 23, the armature piston 24 has a passage opening 30 which is substantially parallel to the longitudinal axis of the armature piston 24 and opens into both end faces of the armature piston 24. Thus, the hydraulic fluid 6 can pass through the passage opening 30 during a displacement of the armature piston 24, which leads to a pressure equalization on both end sides of the armature piston 24 and thus does not hinder a displacement.

The bore in which the guide sleeve 17 is enclosed within the pump body 2 has, above the guide sleeve 17, a shoulder portion 31 which narrows the bore. The delivery piston 15 extends with its shaft through the shoulder portion 31 therethrough. Opposite to the guide sleeve 17 sits on the shoulder portion 31, a coil spring 32 which surrounds the shaft of the delivery piston 15. A head portion 33 of the upper end face 25 of the delivery piston 15 has a larger diameter than the shaft of the delivery piston 15. Accordingly, the coil spring 32 engages the head portion 33, whereby the delivery piston 15 is pressed in its longitudinal axis in the drive chamber 23 into it. In other words, the delivery piston 15 is biased by the coil spring 32 in a direction away from the diaphragm 7 and the piston working space 16, respectively.

With a lower end face 34 of the delivery piston 15 cooperates with the piston working chamber 16. This means that the delivery piston 15 with his the lower end face 34 is in contact with the hydraulic fluid and this displaced during a displacement of the delivery piston 15. For this purpose, it is important that the delivery piston at the edge of the lower end face is matched with an exact fit to the inner diameter of the guide sleeve 17, so that a leakage-free displacement of the hydraulic fluid is achieved.

The operation of the hydraulic diaphragm drive 14 now works as follows:

In an initial state, the armature piston 24 is in an upper region of the drive chamber 23, in which position it is pressed by the upper end face 25 of the delivery piston 15, due to the bias of the coil spring 32. When energizing the solenoid 26, the armature piston 24 in Sequence of the generated magnetic field downwards, ie moved against the upper end face 25 of the delivery piston 15. Since the field strength of the magnetic field is sufficiently strong, the displacement of the armature piston 24 against the bias of the coil spring 32 can take place. As the armature piston 24 drives the delivery piston 15 in the direction of the piston working space, the lower end face 34 of the delivery piston displaces the hydraulic fluid 6 within the pressure chamber 5 or the piston working space 16. As a result, a defined volume of the hydraulic fluid 6 passes through the passage opening 21 of the stop block 19 displaced into the membrane working chamber 22, so that the membrane 7 is forcibly deformed into the delivery chamber 8. The liquid medium contained in the delivery chamber 8 or residual air contained therein is pushed out of the delivery chamber 8 through the discharge channel 10 by the resulting overpressure. When the solenoid 26 is de-energized, the coil spring 32 pushes the head portion 33 into the drive space 23. At the same time, the contact of the upper end face 25 of the armature piston 24 in FIG. 1 is pushed back upwards into the drive space 23. As explained above, the through hole 30 formed in the armature piston ensures pressure equalization in the drive space 23 when the armature piston 24 is reciprocated therein. By means of a suitable control of the magnetic coil 26, a stroke and a frequency of the movement of the armature piston 24 can be adjusted continuously. This becomes linear via the coupling of the armature piston 24 with the delivery piston 15 to the volume of hydraulic fluid 6, with which the diaphragm 7 is deformed. As a result, therefore, a flow rate and a delivery pressure for the liquid medium to be metered can be set exactly.

Although the armature piston 24 and the delivery piston 15 are in contact with each other during their translatory movement in both directions, they are not firmly connected to one another. When the magnet coil 26 is energized, the armature piston 24 acts on the delivery piston 15 and presses it in the direction of the piston working space 16. An important feature of this drive is that the drive piston 24 is decoupled from the delivery piston 15 in a direction away from the piston working space. Only by the bias of the spiral spring 32 do the two pistons remain in abutting contact with each other when the magnetic coil 26 is de-energized. This has the advantage that transverse forces to which the armature piston 24 will be exposed transversely to its longitudinal or displacement direction as a result of the magnetic field will not be transmitted to the delivery piston 15. Accordingly, the delivery piston 15 remains free of such transverse forces, and is driven exclusively in one direction, substantially parallel to its longitudinal axis, by the armature piston. This results in less wear for the delivery piston and a correspondingly long service life. In addition, this supports an exact axial guidance of the delivery piston 15 within the guide sleeve 17th

The various basic elements of the diaphragm pump 1, ie the pump body 2, the pump head 3 and the upper housing part 4 are suitably connected to each other, for example by screw thread, fittings, mating dimensions or the like. A sufficient tightness of the diaphragm pump 1 is achieved by suitable sealing means, such as O-rings 35. An O-ring 35 is received in a groove which is formed on the pump body 2 laterally encircling and adjacent to the pump head 3. Furthermore, O-rings 35 are in the pump body 2 and the upper housing part. 4 adjacent to a wall of the solenoid 26 is provided to prevent leakage of the hydraulic fluid from the working space 23 and the laterally circumferential opening 28 adjacent to the coils. Further O-rings are provided between the foot portion 18 and the stopper block 19, the stopper block 19 and the pump body 2, and the first and second check valves 11, 12 and the corresponding suction and discharge ports 9, 10.

With the diaphragm pump 1, a media separation between the pressure chamber 5 and the delivery chamber 8 is achieved, which means that on the side of the pressure chamber, ie in Figure 1 above the membrane 7, almost any materials for the elements of the diaphragm pump 1 can be used. Such materials need not be compatible with either the base material or any surface treatment with the liquid medium to be delivered. Thus, these materials can be optimized for their magnetic, mechanical, manufacturing or economic properties, without taking into account a material compatibility with a potentially aggressive liquid medium. This is especially true when the liquid medium is an aqueous urea solution.

The said separation between pressure and delivery chamber allows on the side of the delivery chamber, i. In the area of the pump head, a relatively free choice of materials, since only the functions of the housing parts lead medium, withstand pressure and receiving the membrane, valve and connection parts are of importance. In addition to metallic components and inexpensive plastic solutions are correspondingly feasible. In particular, a possible high degree of integration of plastic parts allow almost any arrangement of the coupling stub 13 and other hydraulic connections.

The representation of Figure 1 shows that the diaphragm pump 1 is formed substantially rotationally symmetrical. This advantageously results in a compact installation space, which makes the diaphragm pump 1 particularly suitable in mobile applications. FIG. 2 shows a cross-sectional view of a further embodiment of the diaphragm pump 1 according to the invention. This embodiment largely corresponds to that of Figure 1, wherein the same components are designated by the same reference numerals and are not explained again to avoid repetition.

In the membrane pump 1 shown in FIG. 2, a surface of the membrane working space 22 opposite the membrane 7 is not cone-shaped, but is formed in a dome-shaped manner. In the center of the dome opens the passage opening 21, which allows a passage from the piston working space above the stop block 19 up to the membrane 7. As explained above, the membrane working chamber 22 below the stop block 19 is also part of the pressure chamber 5 and the piston working chamber 16. The functioning of the membrane 7 within the delivery chamber 8 does not change due to the dome-shaped formation of the surface of the membrane working space 22.

Another difference in the embodiment of Figure 2 are attached to a bottom of the pump head 3 coupling stub 13 ', which are designed to be much longer. Thus, the coupling stubs 13 'are suitable for connecting flexible hoses or the like, which are easily forced over a respective outer peripheral surface of the coupling stub 13'.

In the same way as in the embodiment according to FIG. 1, in the embodiment according to FIG. 2, compensation bores 36 are formed within the pump body 2 and extend substantially vertically and thus parallel to the longitudinal axis of the delivery piston 15. The compensation holes 36 open with their upper ends in each case in the drive space 23rd

The guide sleeve 17, which forms with its interior part of the piston working space 16, has two control bores 37 laterally above the foot portion 18. The control bores 37 open with their one end on the inner peripheral surface of the guide sleeve 17, and with its other end in a The compensation bores 36 each open into the recess 38. Thus, the compensation bores 36 form a connecting line between the drive chamber 23 and the recess 38. Accordingly, the hydraulic fluid 6 can pass from the drive chamber 23 the compensation bores 36, the recess 38 and the control bores 37 are fed into the piston working chamber 16, with which the lower end face 34 of the delivery piston 15 cooperates.

To clarify the displacement of the hydraulic fluid 6 in the piston working chamber 16 through the lower end face 34 of the delivery piston 15 during its displacement in the direction of the membrane, the region B of Figure 1 in Figure 3 is shown enlarged. It is understood that the embodiment according to Figure 2 is constructed analogously with respect to the region B of Figure 1.

The delivery piston 15 is displaceably guided within the guide sleeve 17, wherein its lower end face points in the direction of the piston working chamber 16 and displaces therein the hydraulic fluid 6. In the wall of the guide sleeve 17, the two control bores 37 are formed, which provide a fluid connection between the piston working space below the lower end face 34 and the part of the recess 38 outside of the guide sleeve 17. The delivery piston 15 passes over the two control bores 37 when it is displaced within the guide sleeve 17 with a peripheral edge of the lower end face 34. In the illustration of FIG. 3, the mouths of the control bores 37 on the inner circumferential surface of the guide sleeve 17 are only partially covered by the delivery piston 15 , The entire piston working chamber 16, i. Also, the through hole 21, which extends into the stop block 19 in the membrane working chamber 22, is filled with the hydraulic fluid 6.

When the delivery piston 15, starting from the position shown in Figure 3, is further displaced in the direction of the membrane, the peripheral edge of the lower end face 34 completely passes over the two control bores 37. If the peripheral edge of the lower end face 34, a lower edge 39 of a respective Overflowed control bore 37, then the remaining piston working space 16 is separated below the lower end face 34 of the control bores 37. This has the consequence that this part of the piston working space is then no longer supplied with the outside of the guide sleeve 17 hydraulic fluid 6. After said passing over of the lower edge 39 by the peripheral edge of the lower end face 34, a closed volume is thus present in the piston working space 16. The volume of the hydraulic fluid 6, which is displaced in the direction of the membrane 7 as a result of the downward displacement through the passage opening 21, determined from the product of the surfaces of the lower end face 34 of the delivery piston 15 with the distance to which the delivery piston within of the piston working space from the lower edge 39 in the direction of the diaphragm 7, ie in the direction of the bottom surface 20, moves. With the diaphragm pump 1, in particular, a small volume of the hydraulic fluid can be metered exactly in the direction of the diaphragm 7. This results in only slight deformation of the diaphragm 7 and correspondingly only small delivery volume for the liquid medium per working cycle, with nevertheless high delivery pressures.

The distance by which the delivery piston 15 can be moved with its lower end face 34 in the direction of the membrane 7 is limited by the bottom surface 20. At the lower end face 34, a survey 40 is formed, which comes in the displacement of the delivery piston 15 in Figure 3 down in contact with the bottom surface 20. If the elevation 40 touches the bottom surface 20, thereby a bottom dead center of the delivery piston 15 is defined. The elevation 40 is formed only in a central area of the lower end face 34 and bounded by a groove 41. An outer peripheral edge of the lower end face 34 jumps radially inwardly from the groove 41 inwardly, so that the projection 40 protrudes in a plane perpendicular to the longitudinal axis of the delivery piston 15 via the outer peripheral edge of the lower end face 34. This has the effect that, when the bump 40 contacts the bottom surface 20, the outer peripheral edge of the lower end face 34 does not come into contact with the bottom surface. Accordingly, this outer peripheral surface is not subject to wear when the delivery piston 15 with its lower end face 34th oscillating against the bottom surface 20 abuts. Thus, since an edge of the peripheral edge of the lower end face 34, which separates the piston working chamber 16 from the control bore 37 after passing over the control bore 37, is not worn, a very exact volume within the piston working space is due to the movement of the delivery piston 15 possible. This is of great importance, in particular with small displaced volumes in the piston working space, or with only slight membrane movements for a small volume of the liquid medium to be metered. In addition, a long service life arises.

At the peripheral edge of the lower end face 34 of the delivery piston, which cooperates with an inner wall surface of the guide sleeve 17, no sealing means in the form of a piston ring or the like is required. The contact of the peripheral edge with the inner wall surface corresponds to a metal-metal pairing. Due to the high viscosity of the hydraulic fluid, a leakage flow is prevented by a suitably small gap between this metal-metal pairing and ensures a correspondingly accurate displacement of hydraulic fluid through the lower end face 34.

In Figure 4, the delivery piston 15 is shown in a side sectional view. The area A of FIG. 4 is shown enlarged again in FIG. The boss 40 is made to protrude from a peripheral edge of the lower end face 34, and is separated therefrom by the circumferential circular groove 41. Upon contact of the lower end face 34 with the bottom surface 20 of the peripheral edge of the lower end face 34 remains spaced from the bottom surface 20 and is therefore not subject to wear.

As a result of the displacement of the delivery piston 15 within the guide sleeve 17 beyond the lower edge of the control bores 37, a defined volume of hydraulic fluid is displaced in the direction of the membrane 7. This results in the hydraulic chamber 5, a negative pressure, which corresponds substantially to the displaced volume of the hydraulic fluid. For this reason, it is for a displacement of the delivery piston 15 as possible low flow resistance important to create a pressure equalization in the pressure chamber 5. For this purpose, the upper housing part 4, a ventilation opening 42 (Figure 2), which opens into the environment or a suitable surge tank. Through the ventilation opening 42, the pressure chamber 5 may be in connection with ambient air, so that in the pressure chamber 5 there is atmospheric pressure. When moving the delivery piston 15 to its bottom dead center, an air volume passes through the ventilation opening 42 into the pressure chamber 5, which volume of air corresponds to the volume of hydraulic fluid displaced by the delivery piston 15 from the lower edge 39 of the control bore 37 into the piston working space 16. At an upper end side of the armature piston 24 thus no negative pressure, whereby an operation of the hydraulic diaphragm drive 14 with the lowest possible flow resistance is possible.

The vent 42 may remain unlocked during operation of the diaphragm pump. In the embodiment of Figure 1, the vent opening 42 is closed by a screw 43. The screw 43 is penetrated by a through hole (not shown), which in turn opens into the environment or a pressure equalization tank. By the screw 43, a free diameter of the vent opening 42 is advantageously minimized, but still sufficiently large to ensure the pressure equalization with air. By the screw 43 penetration of dirt particles or the like through the ventilation opening 42 is excluded.

FIG. 6 shows, in a cross-sectional view, a further embodiment of the diaphragm pump 1 according to the invention, which is suitable for position-independent operation. The embodiments according to FIGS. 1 and 2 are to be operated substantially in the illustrated position in order to prevent leakage of the hydraulic fluid 6 from the ventilation opening 42. This takes place in that the ventilation opening 42 forms the geodetically highest point of the diaphragm pump 1. In contrast, the pressure chamber of the diaphragm pump 1 according to the form of effect of Figure 6 is closed to the outside. Therefore, this diaphragm pump 1 can also be operated with a pressure compensation in any position.

The pressure compensation principle of the diaphragm pump 1 according to FIG. 6 will be described in detail below. The basic mode of operation of the diaphragm pump according to FIG. 6 corresponds to the previously explained embodiments, wherein identical components are designated by the same reference numerals and are not explained again to avoid repetition.

The diaphragm pump 1 according to FIG. 6 has, above the drive space 23, an additional chamber 44, which is formed in the upper housing part 4. The additional chamber 44 is open at the top. A housing cover 45 is fastened from above on the upper housing part 4. At an upper edge of the additional chamber 45, an additional membrane 46 is provided, which is inserted into a circumferential groove 47 of the upper housing part 4 and applied by the latter

Housing cover 45 is clamped. Thus, the additional chamber 44 is closed at the top by the additional membrane 46. The supplemental membrane 46 is made of an elastic rubber or of an elastically deformable thin sheet metal, and may deform slightly into or out of the auxiliary chamber 44.

The housing cover 46 has a ventilation opening 48 which leads into the environment or a pressure equalization tank. The area between an upper surface of the auxiliary diaphragm 46 and an inner surface of the housing cover 45 is filled, for example, with air at atmospheric pressure. Thus, the pressure above the auxiliary membrane 46, i. on its side opposite to the pressure chamber 5 constant.

In the upper housing part 4, a bore 49 is formed below the additional chamber 44, which opens into the additional chamber 44 and leads on its opposite side into the drive chamber 23, in which the armature piston 24 is slidably received. The bore 49 has a smaller diameter than the additional chamber 44 and the drive space 23. The bore 49 is however, sufficiently sized to provide fluid communication between the auxiliary chamber 44 and the drive space 23. Since the diameter of the bore 49 is smaller than that of the drive space 23, stop shoulders 31 are formed on the upper end wall of the drive space, which define a top dead center for the armature piston 24. The additional chamber 44 is also part of the pressure chamber 5 and filled with the hydraulic fluid 6.

The pressure equalization in the diaphragm pump 1 according to FIG. 6 now works as follows:

When the armature piston 23 drives the delivery piston 15 starting from the position shown in FIG. 6 in the direction of the diaphragm 7, after passing over the lower edge 39 of the control bore 37 through the lower end face 34 of the delivery piston 15 a defined volume of hydraulic fluid in the direction of the diaphragm 7 displaced. As a result of this, a negative pressure in the pressure chamber 5 arises as explained above. This negative pressure may have an effect in the additional chamber 44 through the compensation bores 36, the drive chamber 23 and the passage openings 30 in the armature piston 23 and the bore 49. This negative pressure causes the additional diaphragm 46 to deform into the auxiliary chamber 44. In other words, the deformation of the additional diaphragm 46 in the auxiliary chamber 44 causes the generation of a compensation volume. The compensating volume formed by the deformation of the additional diaphragm 46 corresponds to the volume displaced by the delivery piston 15 during its displacement within the pressure chamber 5 or within the piston working chamber 16.

If in the pressure chamber 5, an overpressure arises as a result of the movement of the delivery piston 15 in a direction away from the membrane 7 and out of the piston working space 16, a compensation of this overpressure by the additional membrane 46 on the same principle. At an overpressure in the pressure chamber 5, which affects into the additional chamber 44, the additional membrane 46 in the direction of the housing cover 45, that is deformed outwardly. Such a deformation of the additional membrane 46 creates an same volume, which corresponds to the volume, which is displaced by the delivery piston 15 and the anchor piston 23 at a suction stroke of the diaphragm pump 1.

The additional membrane 46 closes the upwardly open additional chamber 44. This prevents that the hydraulic fluid 6 can escape from the additional chamber 44. This is true even if the diaphragm pump 1 is operated upside down. Leakage of the hydraulic fluid 6 is prevented in any case. Since the pressure chamber 5 is closed by the additional diaphragm 46, the above-explained pressure compensation functions as a result of the deformation of the additional diaphragm 46 in any operating position of the diaphragm pump 1. This results in a position independence for the operation of the diaphragm pump 1 or its installation in one Vehicle.

FIG. 7 shows a further embodiment of the membrane pump 1, in which a compensation volume can be generated in the pressure chamber 5 and thus a position of independent operation is possible.

In contrast to the embodiment of Figure 6, a capsule 50 is provided in the embodiment of Figure 7 instead of the additional membrane 46, which is secured to an upper edge of the additional chamber 44 between the upper housing part 4 and the housing cover 45. The capsule 50 is inserted with its side edges 51 in the circumferential groove 47 and clamped therein by the applied housing cover 45 therein. The capsule 50 forms a hollow body with elastically deformable walls. For example, the capsule 50 may be made of a thin metal sheet having these elastic properties and being resistant to the hydraulic fluid 6.

The additional chamber 44 is closed off from the outside through the housing cover 45. As a result, an undesired escape of the hydraulic fluid 6, which is contained in the additional chamber 44, in any position of the diaphragm pump 1 is not possible. The capsule 50 thus does not close the additional chamber 44 on the outside, but is defined by the fixing of their side edges 51 in the circumferential groove 47 held within the additional chamber 44.

The pressure equalization by means of the capsule 50 now works as follows:

If there is a negative pressure in the pressure chamber 5, the capsule expands, thereby increasing its volume. This increase in volume corresponds to a compensation volume and thus to the volume displaced by the delivery piston 15 in the direction of the membrane 7. With an overpressure within the pressure chamber 5, the pressure equalization works analogously. The capsule 50 is compressed and thereby reduces its volume. The volume decrease corresponds to the volume that is conveyed back into the pressure chamber 5 during a suction stroke by the delivery piston 15.

When a start-up of the diaphragm pump 1 is still no liquid medium in the delivery chamber 8. Only by a suction stroke of the diaphragm 7, the liquid medium is sucked through the intake passage 9 into the delivery chamber 8, and then by an opposite movement of the membrane 7 back out of the Ejection channel 10 ejected. For membrane pumps, this process is called dry aspiration. Particularly in the case of small volumes with which the liquid medium is to be conveyed and metered, dry aspiration presents itself critically. FIGS. 8 to 12 show various embodiments for the pump head 3 and the membrane 7, which optimize dry aspiration.

FIG. 8 shows the pump body 2 and the attached pump head 3 in a simplified cross-sectional view. The membrane 7 is mounted swinging freely between the pump body 2 and the pump head 3 and separates the pressure chamber 5 from the delivery chamber 8. On the side of the pressure chamber 5 above the membrane 7 is the membrane working space 22, in which the

Through opening 21 opens. In the pump head 3, the suction channel 9 and the discharge channel 10 are formed, which open into the delivery chamber 8 below the membrane 7. On a surface of the pump head 3, which faces the membrane 7, a recess 52 is formed in the form of a dome, namely in the part, the surface which is located between the mouths of the intake passage 9 and the ejection channel 10. Thus, the surface of the pump head 3 opposite to the membrane 7 with the exception of the cap 52 is formed substantially flat. In conjunction with such a pump head 3 is a membrane 7 is used, which is substantially flat in its relaxed state.

The volume which encloses the dome 52 with respect to a plane defined by the outer surface areas of the surface of the pumphead 3 defines a lift volume in the delivery space. At the beginning of the dry suction, the hydraulic fluid 6 is displaced into the diaphragm working chamber 22, so that the diaphragm 7 is deformed in the direction of the pump head 3 and comes into contact with the calotte 52. In this case, a residual air from the delivery chamber is ejected substantially completely through the discharge channel 10, by a corresponding overpressure in the delivery chamber. During a subsequent suction stroke of the diaphragm pump 1, the diaphragm 7 is deformed upwards by discharging the hydraulic fluid 6 out of the diaphragm working chamber 22, whereby a negative pressure is generated in the pumping chamber 8. By this negative pressure opens the first check valve 11 in the intake passage 9, so that the liquid medium is sucked into the delivery chamber 8 in. In the subsequent delivery cycle, hydraulic fluid 8 is in turn displaced into the membrane working chamber 22, which deforms the membrane 7 in the direction of the pump head 3 and generates an overpressure in the delivery chamber 8. As a result, the second check valve 12 opens in the discharge passage 10, whereby the liquid medium is discharged from the delivery space 8.

It is important for problem-free dry aspiration that an exact volume is defined between the membrane and a surface of the pump head 3, which volume can be filled by the membrane 7 at the start of dry suction. It is also important that at the first printing Clock, when the membrane 7 deforms into the cap 52, as little residual air in the delivery chamber 8 remains. The less residual air remains in the delivery chamber 8 at the first pressure cycle, the greater is the. Negative pressure during the subsequent suction stroke. For this purpose, it is important that the delivery chamber 8 has the smallest possible dead space volume that can not be filled by the diaphragm 7 during its deformation.

Figure 9 shows a simplified cross-sectional view of the pump head 3 with first and second check valves 11, 12 mounted therein. The membrane shown herein is made of a metallic membrane body 7a which is planar on the side of the delivery space and has wave-like steps on the side of the pressure space , The wave-like steps ensure elastic deformability of the metallic membrane body.

From the arrangement of the check valves 11, 12 according to Figure 9 it can be seen that the ball seats of these valves are in close proximity to the surface of the pump head 3 adjacent to the membrane. As a result, the bores 54 that lead from the ball seat into the pumping chamber 8 in the pump head 3 are very short. The membrane 7 can not deform into the bores 54 when it dries dry. Because of the short length of the holes, however, the dead space volume formed thereby is minimal or negligible.

In Figure 10, the pump head 3 is also shown in a cross-sectional view. Herein, the first and second check valves 11, 12 are also shown in section to illustrate their operation. As already explained with reference to FIG. 1, the coupling stubs 13 are fastened to the lower part of the pump head 3. At the opposite part of the pump head 3, ie adjacent to the pump body 2, the pump head 3 has recesses 55, which serve to receive an end face of the pump body 2 (see FIG. In Figure 10, the pump body 2 is not shown for simplicity. FIGS. 11 and 12 illustrate a membrane according to the invention for a hydraulically driven diaphragm pump. Figure 12 shows a cross-sectional view through such a membrane T. The membrane T shows a hybrid construction and comprises a metallic membrane body 55 with wave-like steps. To the metallic membrane body 55, an elastomeric rubber 56 is attached, which has on its surface a recess 57 in the form of a dome. When using such a membrane T, the surface of the pump head 3 adjacent to the membrane is substantially planar and not provided with a recess. The recess 57 in the elastomeric rubber fulfills the same function as the above-described recess 52 in the surface of the pump head 3. In its relaxed state, the cap 57 of the elastomeric rubber 56 encloses with the opposite surface of the pump head 3 a volume which is exact Delivery volume defined for the liquid medium to be metered. At the beginning of Trockenansaugens the hybrid membrane T is pressed against the pump head 3, so that the metallic membrane body 55 and the elastomer rubber 56 deform so far that the membrane T is substantially completely applied to the surface of the pump body 3. As a result, air is forced out of the delivery chamber 8 in order to produce a greater negative pressure in the subsequent intake stroke can.

FIG. 11 shows the installation of the hybrid membrane T in the membrane pump 1. In order to achieve improved delivery properties of the membrane pump 1, an elongated groove 58 is formed in the surface of the pump head 3 adjacent to the hybrid membrane 7 ', extending between the respective mouths of the intake channel 9. of the ejection channel 10 extends. The elongated groove 58 supports a flow of the liquid medium within the pumping chamber 8 from the suction channel 9 to the discharge channel 10. However, the elongated groove is provided in its width or depth with small dimensions, so that only slightly increased by the dead space volume within the pumping chamber becomes. When dosing a small delivery volume of the liquid medium is important that the check valves, which are provided in the intake passage or the discharge channel, even at low forces and yet respond precisely. In addition, for a good response of the diaphragm pump, only a small dead space volume of the check valves is important.

FIGS. 13 to 15 b show a check valve 78 according to the invention, which fulfills the requirements just mentioned.

Fig. 13 shows the check valve 78 in a cross-sectional view in one half. In a housing of the check valve, a passage opening 79 is formed, into which a retaining disk 80 is pressed. The retaining disk has two bores 81 which pass through the retaining disk in its height, that is to say in a flow direction X of the non-return valve. The holes 81 are arranged acentrically. In the illustration according to FIG. 13, only one of the two bores 81 in the Schmitt is shown along its longitudinal axis because of the symmetrical construction of the check valve.

The housing has a step-shaped recess, with a step 82, which reduces the diameter of the passage opening 79. The check valve 78 comprises a disc membrane 83 which rests on the step 82. The retaining disk 80 is pressed into the passage opening 79 adjacent to the disk membrane 83. As a result, the disk membrane is firmly held in the passage opening 79.

The disk membrane 83 is penetrated by two openings 84, of which in the sectional view of FIG. 13, only one opening is shown. In the plan view of Fig. 14 it can be seen that the two openings 84 are formed in the shape of a semicircle. An edge of the respective openings is arranged adjacent to the peripheral edge of the disc membrane 83. Through the openings 84 is formed in each case a web 85, which extends radially inwardly to the center of the disk membrane 83. The webs are each elastically in a direction substantially perpendicular to the longitudinal extent of the disc membrane. bran 83 deformable, as indicated in Fig. 13 by truncated lines. For this purpose, the disk membrane is made of a flexible sheet metal.

The openings 84 of the Scheibenmebran are radially offset from the respective bores 81 of the retaining disc 80. Thus, the holes 81 are covered and closed in the closed state of the check valve 78 by the abutting disc membrane 83, as shown in Fig. 13 by solid lines.

The check valve 78 functions as follows:

If a fluid impinging on the side of the holding disk 80 exceeds an opening pressure determined by the spring rate of the disk membrane, the webs 85 are bent upwards correspondingly to the side facing away from the pressure (shown in FIG. 13 downwards, truncated). The fluid can then flow out through the bores 81 and the openings 84 to the side facing away from the pressure. The opening pressure at which the webs lift off the retaining disk 80 to open the check valve 78 can be specified by the geometrical ratio of the openings 84, the base material of the disk membrane and its thicknesses. Through the two semicircular openings 84 and the webs 85, a large throughput through the check valve 78, in conjunction with a good response at low fluid pressures.

The retaining disk 78 is provided on its side facing the membrane with an elastomer layer (not shown) against which the webs 85 of the disk membrane 83 rest in the closed state of the check valve 78. This improves the noise behavior and the tightness of the check valve 78. In addition or as an alternative to the holding plate 78, the disc membrane can be coated with the elastomer material on its side facing the holding membrane, from which the advantages mentioned above likewise result. Fig. 15a shows the pump head 3 with the suction channel 9 and the discharge channel 10 in a simplified cross-sectional view. The check valve 78 is installed in each of the intake passage 9 and the discharge passage 10. Here, the channels 9, 10 each act as a housing part for the check valve 78, wherein the passage opening (Fig. 13) is formed by the interior of the channels. In the sectional view, only one of the two holes 81 of the retaining disk 80 is shown. It is understood that the check valve 78 is installed in the discharge channel 10 in comparison to the intake passage 9 rotated by 180 °. The representation of the check valve 78 in Fig. 13 corresponds to an installation in the discharge channel, since the web 85 bends down when opening the valve.

The check valve 78 has a low overall height, so that when installed in the pump head 3, a correspondingly low dead space volume results. In Fig. 15a it can be seen that the check valve 78 is arranged on the side of the ejection channel with the bore 81 immediately adjacent to a surface of the pump head, and thus to the delivery chamber 8. On the side of the intake passage, only a thin web of material 86 above the disc membrane 83 is required to form the step 82 or a holder for resting the disc membrane. In the material web 86, an opening 87 is formed to provide a fluid connection between the intake passage 9 to the delivery chamber 8 through the check valve 78 therethrough. The small height of the material web 86 also ensures a small dead volume for the side of the intake duct.

In Fig. 15b, the pump head 3 is again shown in a plan view, from the direction of the arrow C of Fig. 15a.

As an alternative to the above-described embodiment, and in correspondence with the representation of FIG. 15 a, it is also possible to provide only an acentric bore 81 in the retaining disk 80. As a result, the production of the retaining disk 80 is simplified. FIGS. 16 to 21 illustrate a spring diaphragm according to the invention or a further embodiment of a check valve 78 'according to the invention, in which a very low response force for opening the valve and at the same time a small dead volume for the delivery chamber 8 are achieved.

FIG. 16 shows a cross-sectional view of the check valve 78 'according to the invention. It is understood that this may be the first check valve 11 in the intake passage 9 or the second check valve 12 in the discharge passage 10. The check valve 78 'comprises a housing insert 59 made of plastic or of metal or steel, in particular

Stainless steel is made. The housing insert 59 is received with its Außenumfangs- surface in the intake passage 9 and the discharge passage 10 and fitted therein. The housing insert 59 is penetrated along its longitudinal axis by a through opening 60, which allows a passage of a fluid or the like. In the housing insert 59 is in the passage opening 60, a sealing member 61, for example, enclosed in the form of a rubber seal. The rubber seal 61 tapers in its lower part in the form of a funnel. On the flanks of this funnel sits a ball 62, for example a stainless steel ball.

At an edge of the housing insert 59 opposite to the funnel-shaped taper of the rubber seal 61, a diaphragm spring 63 is held, which engages with its peripheral edge in a groove or the like. In the closed state of the check valve, the diaphragm spring 63 presses from above on the ball 62, so that it rests on the flanks of the funnel-shaped taper of the rubber seal 61. From the direction of the arrow z according to FIG. 16, the check valve can not be flowed through since the ball 62 locks with the rubber seal 61. If a pressure from the direction of the arrow a according to FIG. 16 is large enough, the ball 62 is lifted upwards against the pretension of the membrane spring 63 out of the funnel-shaped taper of the rubber seal 61. The arrow a in FIG. 20 thus indicates the direction of flow through the return flow valve 78 '. Analogous to an overpressure from the direction of Arrow a, the ball 62 can also be lifted by a negative pressure acting from the direction of the arrow z, to open the valve of the rubber seal 61.

FIG. 17 shows the diaphragm spring 63 in a plan view. The diaphragm spring 63 is penetrated by a plurality of circular segment-shaped recesses 64. The plurality of recesses 64 weaken the diaphragm spring 63 with respect to the spring force in a direction perpendicular to the surface extension of the diaphragm spring 63. The more recesses 64 the diaphragm spring 63 has, the flatter the corresponding spring characteristic. Compared to a diaphragm spring which has no recesses, the diaphragm spring 63 can be deformed according to Figure 16 or 17 easier in a direction transverse to its surface extension. This results for the check valve 11 and 12, a smaller clamping force and a better response at low compressive forces.

In FIGS. 18 and 19, the diaphragm spring is shown in a further embodiment 63 '. Compared to the diaphragm spring 63 according to Figure 17, this embodiment 63 'is not in the form of a plate, but annular, with a ring 65 of the diaphragm spring 63' abuts the ball 62. Laterally on the ring 65 S-shaped extending spring legs 66 are formed on opposite sides, which act like a leaf spring. FIG. 20 shows the installation of the diaphragm spring 63 'in the housing insert 59. The spring legs 66 are bordered with their free ends in a groove of the housing insert 59. At a sufficiently high pressure from the direction a of Figure 20, the ball 62 presses from below against the ring 65 of the diaphragm spring 63 ', whereby the spring legs 66 deform. In this case, the ball 62 lifts off from the funnel-shaped taper of the rubber seal 61, so that a fluid flows through the check valve 11, 12 in the direction of arrow a. The closing of this embodiment is analogous to the explanation of Figure 16. If the valve is depressurized or from the direction of arrow a, a fluid pressure is smaller than the spring force, the diaphragm spring 63 'presses the ball 62 against the rubber seal and closes the valve. Figure 21 shows the check valve 78 'of Figure 20 in a plan view. The ball 62 is centrally bordered by the ring 65, which is held with its laterally molded spring legs 66 in the housing insert 59.

The check valve 78 'explained above has, in addition to a very good response at only low compression forces, the further advantage that it has a low overall height because of the use of the diaphragm spring 63 for biasing the ball 62. The ball seat is located immediately adjacent to an end opening of the check valve, which is located downstream when flowing through the valve. From the small height of such a check valve 78 'results in a correspondingly small dead volume for the delivery chamber 8, so that the dry suction behavior of the diaphragm pump is improved.

FIG. 22 shows a system 70 according to the invention for after-treatment of an exhaust gas of an internal combustion engine with a reducing agent. The system 70 operates on the principle of the SCR process, in which a reducing agent in the form of an aqueous urea-water solution is injected into the exhaust gases of a diesel engine upstream of an SCR catalyst.

With the system 70 according to the invention, the limit value levels Euro 4 and Euro 5 can be met and the advantages of the SCR method mentioned in the introduction can be achieved. The diaphragm pump 1 is due to the aforementioned media separation between the pressure chamber 5 and the delivery chamber 8 is excellent for dosing an aggressive reducing agent, for example AdBlue ™.

Hereinafter, the system 70 will be explained in detail.

The system 70 includes a tank 71 containing the urea-water solution. A connection line 72 leads to an injection nozzle 73, which is fixed upstream of a catalytic converter 74 to an exhaust pipe 75 of a diesel internal combustion engine (not shown). In the connecting line 72, a diaphragm pump 1 is arranged, the oebn with reference to the Figures 1, 2, and in particular Figs. 6 and 7 is explained. The diaphragm pump 1 serves as a metering pump in the system 70 to meter the urea-water solution from the tank 71 to the injector 73 and to inject it into the exhaust pipe 75.

The diaphragm pump 1 is connected to a control unit 76, which in turn is connected to a motor control 77. By means of the control unit, the energizing of the solenoid 26 is controlled, thereby setting a stroke and a frequency for the armature piston 23. This results in a variable delivery volume for the urea-water solution. The so-called liquid medium in the above explanation of the diaphragm pump 1 is to be understood in the system 17 as the aqueous urea-water solution.

The control unit 76 may be connected via the engine control 77 to various operating conditions of the engine, such as e.g. Idle, full throttle or the like adapted. As a result, different operating conditions can be achieved for the diaphragm pump 1, which are adapted to the respective engine operating state, with respect to the amount of urea-water solution to be injected.

The system 70 has only one connecting line 72 which leads from the tank 71 to the injection nozzle 73. There is no further return from the nozzle 73 back to the tank 71 is provided. With the diaphragm pump 1, sufficiently high pressures can be achieved so that the urea-water solution with the desired dispersion is injected into the exhaust pipe 75. For example, with the diaphragm pump 1 pressures greater than 10 bar can be generated.

With the diaphragm pump 1 according to the invention and its associated components according to the invention, an extremely precise and backpressure-independent metering of fluids up to several atmospheric back pressure is possible, for example with pressure values of greater than 10 bar. By the separation of the pressure chamber 5 from the delivery chamber 8 by means of the membrane 7 is It is also possible to meter aggressive media, for example an aqueous urea-water solution. With the lubrication of the armature piston 23 and the delivery piston 15 by the hydraulic fluid 6, a long life of the diaphragm pump is achieved as a result of low wear of the moving elements. Another advantage of the membrane pump 1 is excellent dry aspiration at the beginning of the metering operation, thanks to a minimized dead space volume and a precisely defined delivery volume within the delivery chamber 8. As a result of the compensation volume which can be generated in the additional chamber 44 through the additional membrane 46 or the capsule 50 , a bearing-independent operation of the diaphragm pump 1 is possible. This is particularly advantageous when installed in motor vehicles.

It is understood that the diaphragm pump 1 is not only suitable for metering an aggressive fluid, but also for metering other fluids, in particular liquids.

Claims

Diaphragm pump (1) for conveying and metering a particularly liquid medium, comprising a delivery chamber (8) which can be filled with the liquid medium, a pressure chamber (5) filled with a hydraulic fluid, a membrane (7) which separates the delivery chamber (8) from the pressure chamber (8). 5) separates and between them freely suspended, one in the pressure chamber (5) provided piston working space (16), which is in fluid communication with the membrane (7), and a hydraulic diaphragm drive (14), one in the direction of the membrane (7) longitudinally displaceable piston (15), with its lower end facing the membrane (34) with the

Piston working space (16) cooperates, wherein the piston (15) by a predetermined distance in the direction of the diaphragm (7) is movable. wherein in the piston working space (16) laterally at least one control bore (37) opens, through which the piston working chamber (16) with the hydraulic fluid (6) of the pressure chamber (16) is fed, said

Piston working space (16) is separated from the control bore (37) when the piston (15) with its lower end face (34) one of the membrane (7) facing lower edge (39) of the control bore (37) passes over, wherein the membrane (7 ) is deformable by a hydraulic fluid volume displaced by the piston, which volume is determined from the product of the area of the lower end face (34) of the piston (15) with the distance by which the piston (15) within the piston working space (16 ) is moved from the lower edge (39) of the control bore (37) in the direction of the diaphragm (7), characterized in that the piston working chamber (16) has a bottom surface (20) against which the piston (15) with its lower end face (20). 34) abuts when moving within the piston working chamber (16), so that the Piston (15) when in contact with the bottom surface (20) reaches a bottom dead center.

2. Membrampumpe according to claim 1, wherein the piston (15) at its lower end face (34) has a survey (40) which reaches the bottom dead center of the piston (15) in contact with the bottom surface (20).

3. diaphragm pump (1) according to claim 2, wherein the elevation (40) is formed centrally on the lower end face (34), wherein the lower end face (34) of the elevation (40) is stepped towards its peripheral edge, so that the peripheral edge at the bottom dead center of the piston (15) does not come into contact with the bottom surface.

4. The diaphragm pump (1) according to any one of claims 1 to 3, wherein the piston (15) in a direction away from the diaphragm (7) to an upper

Dead point is movable, wherein the lower end face of the piston (15) at least partially releases the control bore (37).

5. Diaphragm pump (1) according to one of claims 1 to 4, wherein the diaphragm drive comprises a lifting magnet with an enclosed by a solenoid coil armature (24) through which the piston (15) at least in the direction of the membrane (7) can be driven.

6. The diaphragm pump (1) according to claim 5, wherein the diaphragm drive comprises a spring device (32) which biases the piston (15) in a direction away from the diaphragm (7), wherein the armature piston (24) and the piston (15 ) are not firmly connected.

7. Diaphragm pump (1) according to claim 6, wherein the spring means is a coil spring (32) which surrounds the piston (15) at its upper end side adjacent to the armature piston (24).

8. Diaphragm pump (1) according to one of claims 1 to 7, wherein the lower edge of the control bore (37) at an orifice to the piston working chamber (16) is formed substantially at right angles.

9. diaphragm pump (1) according to one of claims 1 to 8, wherein the piston (15) is displaceably mounted in a guide sleeve (17), so that its lower end face (34) without play in the piston working space (16) is displaceable.

10. Diaphragm pump (1) according to any one of claims 1 to 9, wherein the at least one control bore (37) outside the Kolbenarbeits- space (16) a control line (36) is connected, via which the piston working space (16) with the hydraulic fluid is supplied.

11. Diaphragm pump (1) according to claim 10, wherein the control line leads to a drive space (23), in which the armature piston (24) is slidably received.

12. Diaphragm pump (1) according to claim 10 or 11, wherein the control line (36) extends substantially parallel to a longitudinal axis of the piston (15).

13. Use of a diaphragm pump (1) according to one of claims 1 to 12 as a metering pump in an SCR exhaust gas purification system for diesel motor vehicles.

14. membrane (7 ') for a hydraulically driven diaphragm pump (1), which membrane (7, 55, 56) a delivery chamber (8) containing a liquid medium to be metered, and a pressure chamber (5) having a on the Containing diaphragm (7 ') acting hydraulic fluid (6), separated from each other, wherein in the membrane (7') on the side of the delivery chamber (8) has a recess (57) is formed, defined by the exact delivery volume for the medium to be metered is, characterized the membrane (7 ') has a hybrid construction, the membrane (7') having on the side of the pressure chamber a metallic membrane body (55) and on the side of the delivery chamber an elastomeric rubber (56) attached to the metallic membrane body (55) is attached.

15. membrane (7 ') according to claim 14, which is formed substantially circular.

16. membrane (7 ') according to claim 14 or 15, wherein the recess (57) in the central region of the membrane (7') is provided.

17. membrane (7 ') according to claim 15 or 16, wherein the recess (57) is formed substantially concentric with the edge of the membrane (7').

18, membrane (7 ') according to claim 17, wherein the recess (57) in the middle of the membrane (7') has its greatest distance with respect to a plane which is spanned by an edge region of the membrane (7 ').

19. A membrane (7 ') according to any one of claims 14 to 18, wherein the recess (57) has the shape of a concave dome.

20. A membrane (7 ') according to claim 19, wherein the recess (57) is formed in the elastomeric rubber.

21. A membrane (7 ') according to claim 19 or 20, wherein the metallic membrane body (55) along its longitudinal extension has wave-like steps, so that a high deformability in a direction orthogonal to

Surface of the membrane (7 ') is guaranteed.

22, membrane (7 ') according to claim 21, wherein the wave-like steps facing the pressure chamber (5).

23. A hydraulically driven diaphragm pump (1) having a diaphragm (7 ¹ ) according to any one of claims 14 to 22, wherein the membrane (7 ¹ ) is in a dry suction in contact with a surface of a pump head (3), so that the Volume between the membrane (7 ') and the surface is minimal.