EP2748439B1 - Metering system for a liquid reducing agent - Google Patents

Description

State of the art

In internal combustion engines that operate according to the diesel process, an SCR catalytic converter is often provided in the exhaust system in order to meet the environmental requirements. In order for the SCR catalyst to convert the NOx compounds contained in the exhaust into water and nitrogen, liquid urea or a liquid urea-water solution (reducing agent) must be injected into the exhaust line upstream of the SCR catalyst. For this purpose, a metering system comprising a tank, a pump and a metering module, which operates in a manner similar to the injector of a fuel injection system, is used. The pump is also referred to as a delivery module.

The task of the delivery module or the pump is to suck urea-water solution from a tank and build up a sufficient pressure on the pressure side, so that the liquid urea-water solution is finely atomized as soon as the dosing opens demand-controlled. The injector, like the delivery module, is connected to a control unit of the internal combustion engine and is opened and closed by it as required. The same applies to the operation of the feed pump. Since urea-water solution has the property of freezing at low temperatures and increasing its volume by about 11%, measures must be taken to prevent damage to the dosing system by freezing urea-water solution.

For this purpose is from the DE 10 2004 054 238 known to aerate urea-water solution leading lines. For this purpose, the pump is designed with a reversible conveying direction or a valve is provided for reversing the conveying direction of the pump.

From the DE 10 2009 029 408 It is known to integrate in the metering a 4/2 way valve. In a first switching position of the 4/2-way valve, the pump promotes reducing agent from the tank to the metering module. When the engine is to be stopped, the 4/2-way valve is brought into the second switching position, so that the pump of the delivery module promotes liquid reducing agent from the metering module into the tank and thereby ventilated parts of the metering system. This presupposes that the dosing module is open and that air or exhaust gas can flow from the exhaust gas tract into the dosing system.

Partial aeration of the metering system produces a compressible air bubble, so that when the remaining residues of the reducing agent in the metering system freeze, the resulting ice pressure is so low that no damage to the metering system occurs. However, such a 4/2-way valve is prone to failure and expensive.

The WO 2004/047963 describes a device for removing a reducing agent with a compressed air pump.

The DE 10 2009 029 408 discloses a method for monitoring an SCR catalyst system.

The WO 2012/093051 , a post-published document, shows a conveyor for supplying an exhaust aftertreatment system having two pumps.

Disclosure of the invention

The metering system according to the invention according to claim 1 is characterized in that it is very inexpensive and ensures a reliable emptying or ventilation of the metering after switching off the internal combustion engine. Because the ventilation pump according to the invention only serves to aerate or empty the dosing system, a very low flow rate is sufficient. Also, only low demands are placed on the delivery pressure of the ventilation pump. As a result, the ventilation pump according to the invention is less expensive than a 4/2-way valve. In addition, such a pump is less prone to failure than a switchable 4/2-way valve.

The feed pump according to the invention and / or the ventilation pump according to the invention are preferably designed as diaphragm pumps. However, the invention is not limited to diaphragm pumps. Other types known in the art may also be used.

It has proved to be particularly advantageous if the feed pump according to the invention and / or the venting pump is driven by an electromagnetic (linear) actuator, which is also referred to as a lifting magnet. Then namely, can be dispensed with an implementation of the rotational movement of an electric motor, for example in an oscillating conveying movement of the pump.

The direct drive of the diaphragm pump via an electromagnetic actuator allows to easily and inexpensively detect the injected amount of the reducing agent over the stroke of the actuator very accurately.

For example, can be deduced from the course of the armature current through the electromagnetic actuator to the stroke of the actuator. The stroke of the actuator is a direct measure of the amount of reducing agent delivered. Therefore, it is possible to dispense with a separate pressure sensor without degrading the metering accuracy of the metering system according to the invention.

In order to optimize the function of the feed pump and / or the venting pump, a check valve can be provided in each case on the suction side and / or the delivery side of both pumps. Alternatively, it is also possible that in each case a throttle or a diaphragm is provided on the suction side and / or the delivery side of the feed pump and / or the venting pump. In many applications, it is advantageous if a check valve is provided both on the suction side, as well as on the delivery side. Alternatively, it is also possible to provide either on the suction side or the delivery side, a throttle or a diaphragm on the pressure side or the suction side to provide a check valve.

In an advantageous embodiment of the metering system according to the invention, a second check valve is provided on the suction side of the aeration pump parallel to the first check valve, wherein the reverse direction of the second check valve is opposite to the reverse direction of the first check valve.

This makes it possible to use the ventilation pump according to the invention as a pressure compensation element. If an inadmissibly high pressure arises during operation of the feed pump in the pressure line, damage to the metering module or the pressure line can result.

In the metering system according to the invention, the ventilation pump is used during operation of the feed pump as a pressure compensation element. Namely, if in the pressure line such a high pressure prevails that it opens the first check valve on the suction side of the venting pump, then the high pressure from the pressure line acts on the membrane of the venting pump. This membrane can yield to this pressure by expanding towards the electric actuator. As a result, the volume on the pressure side of the metering system according to the invention increases and the pressure peak is reduced.

Alternatively, it is also possible to design the pressure-side check valve in the ventilation line so that it opens when an inadmissibly high pressure in the pressure line occurs and thus a portion of the pumped from the feed pump urea water solution from the pressure line flows back into the suction line. As a result, an effective pressure limitation is also achieved. Again, no additional costs are required.

Of course, a combination of the two variants, namely the elastic deformation of the membrane of the ventilation pump and the opening of the vent line can be realized.

According to the invention it is provided that a throttle or a diaphragm is provided on the pressure side of the ventilation pump parallel to the check valve. By this, the electric actuator can be made smaller. This reduces the electrical power consumption and reduces the weight and space requirements.

A particularly advantageous embodiment of the invention provides that in a diaphragm pump, the membrane vent line on the pressure side or the suction side of the venting pump closes when the actuator is de-energized. As a result, the ventilation pump according to the invention assumes the function of a switchable directional valve without additional expenditure of components. This is possible because the conveying work, ie when the membrane presses reducing agent from the pumping chamber into the venting line, from one to the membrane acting spring is done. This spring is biased by the electromagnetic actuator during the suction stroke of the feed pump.

By a suitable structural design, it is therefore easily possible that the membrane is pressed by the spring on the connection of the ventilation line in the pump housing and thus closes it.

In order to increase the sealing effect or the maximum pressure in the delivery chamber against which the diaphragm of the ventilation pump can shut off the ventilation line, a cross-sectional constriction in the housing can be provided. This cross-sectional constriction may be formed simultaneously as a throttle or aperture.

Furthermore, it is possible to increase the tightness or the maximum holding pressure / closing pressure of the diaphragm by forming an annular bead which surrounds the end of the pressure line or the suction line. This results in an increased surface pressure between the bead and the membrane, so that the tightness of the diaphragm pump used as a controllable directional control valve is increased. Again, the cost of the additional bead are negligible, since the housing of the pump is usually made as a plastic injection molded part or as a cast metal part and thus incur no additional manufacturing costs for the bead.

Alternatively, it is also possible, in the case of a currentless actuator of the delivery pump and / or the ventilation pump, to exert the membrane directly or indirectly a closing force on a valve member of the check valves. As a result, the tightness of the check valves is increased. Again, this can be achieved without additional manufacturing costs. This improved tightness makes it possible to simultaneously reduce the bias of the closing springs in the check valves. As a result, the delivery work to be applied by the electromagnetic actuator is reduced, and as a result, the electromagnetic actuator can be made smaller, more energy-efficient and inexpensive. This is an aspect that affects both the aeration pump and the delivery pump.

In order to achieve a particularly compact design, it is further provided that the ventilation pump is integrated in the feed pump. This not only has advantages in terms of the hydraulics of the dosing system, but also has the advantage that the signal lines for controlling both pumps can be guided together into the housing.

In addition, there is the advantage that with freezing reducing agent in the feed pump, the ventilated pumping chamber of the venting pump, which serves as a compensating volume for the reducing agent in the pump, is in the immediate vicinity of the pump and thus the pressure equalization between the two pumps is very possible ,

According to an advantageous embodiment of the dosing system according to the invention, at least one capacitor is present, so that the electrical charge stored in the capacitor can be used to energize the electric actuator of the ventilation pump. Since a capacitor can deliver the electrical charge stored in it very quickly, it is possible to act on the actuator of the ventilation pump very quickly and with large currents in an emergency, so that the membrane is suddenly raised and a very rapid suction of liquid reducing agents through the Ventilation pump takes place. Through this dynamic suction process, a so-called impulse back suction of liquid reducing agent takes place. This pulse back suction is ultimately nothing more than exploiting the elasticity of the pressure line and the liquid reducing agent pressurized therein. In the case of a sudden drop in pressure, the pressure line, as it were, springs together and thereby promotes a small amount of liquid reducing agent in the direction of the ventilation pump. This results in that at least a portion of the pressure line, but also the metering module is no longer filled with liquid reducing agent, but with air or exhaust gases. This has reduced the risk of ice pressure damage.

A further advantageous embodiment of the metering system according to the invention provides that the feed pump and / or the aeration pump comprises an electric actuator with a magnet and an armature, a diaphragm, a valve-membrane plate and a valve plate, and that between the Valve diaphragm plate and the valve plate is a rubber plate as a valve element and sealing element is present.

As a result of this sandwich-type construction of the delivery pump and / or the ventilation pump, the non-return valves according to the invention and / or throttles can be produced in the simplest and most cost-effective manner. For example, for an additional check valve to provide only an additional breakthrough in the valve plate and provide corresponding recesses acting as a valve element rubber plate.

Similarly, it is possible that the valve diaphragm plate and the diaphragm of the ventilation pump together with the electric actuator form a controllable shut-off valve. Again, no significant additional manufacturing costs are required.

In a further advantageous embodiment of the invention, a valve disc is formed on the armature, which works together with a sealing bead of the valve diaphragm plate as a switchable way or check valve. Furthermore, it is provided that the membrane is arranged offset in the stroke direction to the valve disk on the armature. This makes it possible, on the one hand, the pressure prevailing in the pumping chamber to some extent acts on the back of the valve disk and thus presses it against the sealing seat in the valve diaphragm plate. This increases the tightness. At the same time it is possible that the membrane evades in the stroke direction and thus degrades a pressure peak. Thus, the membrane can work as a pressure compensation element. In order to define the elasticity of the membrane structurally within narrow limits, it is advantageous to design the membrane in a wave-shaped cross-section. At the same time it is advantageous if the armature of the electric actuator limits the travel of the membrane in the stroke direction, so that no bursting or tearing of the membrane is to be feared when the membrane is subjected to impermissible high pressures.

Figur 1

ein Blockschaltbild eines Dosiersystems,

Figur 2

das Dosiersystem gemäß Figur 1 beim Belüften des Systems,

Figur 3

das Blockschaltbild eines zweiten Dosiersystems, bei dem die Belüftung als Membranpumpe ausgeführte Belüftungspumpe gleichzeitig als ein gesteuertes Rückschlagventil arbeitet im Normalbetrieb des Dosiersystems,

Figur 4

ein drittes Dosiersystem mit einer Drossel anstelle eines Rückschlagventils auf der Saugseite der Belüftungspumpe,

Figur 5

ein weiteres Dosiersystem mit einer Drossel auf der Druckseite / Förderseite der Belüftungspumpe,

Figur 6

ein weiteres Dosiersystems, bei dem die Membran der Förderpumpe als gesteuertes Rückschlagventil eingesetzt wird.

Figuren 7

ein weiteres Dosiersystem,

Figur 8

ein Ausfrühungsbeispiel eines erfindungsgemäßen Dosiersystems,

Figuren 9 bis 16

konstruktive Details verschiedener Belüftungspumpen.

Further advantages and advantageous embodiments of the invention are the following drawings, the description and the claims removable. Show it:

FIG. 1

a block diagram of a dosing system,

FIG. 2

the dosing system according to FIG. 1 when ventilating the system,

FIG. 3

the block diagram of a second metering system in which the ventilation as a diaphragm pump running aeration pump at the same time as a controlled check valve operates in normal operation of the dosing,

FIG. 4

a third metering system with a throttle instead of a check valve on the suction side of the ventilation pump,

FIG. 5

another dosing system with a throttle on the pressure side / delivery side of the aeration pump,

FIG. 6

Another dosing system, in which the diaphragm of the feed pump is used as a controlled check valve.

FIGS. 7

another dosing system,

FIG. 8

an early example of a dosing system according to the invention,

FIGS. 9 to 16

constructive details of various ventilation pumps.

In the FIG. 1 a dosing system is shown as a block diagram. In a tank 1 is liquid reducing agent (urea-water solution). Via a suction line 3, a feed pump 5 sucks liquid reducing agent from the tank as required and conveys it via a pressure line 7 to a metering module 9. The terms suction line 3 and pressure feed line 7 refer to the

Normal operation of the metering system, namely, when reducing agent is conveyed from the tank to the metering module 9.

The dosing module 9 can be represented in the block diagram as a combination of a throttle 11 and a switchable 2/2-way valve 13. The directional control valve 13 is closed in the de-energized state. Then no liquid reducing agent is injected into the exhaust system of the internal combustion engine (not shown). When the feed pump 5 delivers and thus the reducing agent in the pressure line 7 is under an elevated pressure, the directional control valve 13 can be opened by the engine control unit (not shown), so that liquid reducing agent is atomized by the throttle 11 in the metering module 9 and finely distributed is injected into the exhaust pipe of the internal combustion engine.

About the delivery pressure of the feed pump 5 and the opening time of the directional control valve 13, the injected into the exhaust tract amount of the liquid reducing agent can be controlled. In the metering system according to the invention, a ventilation pump 15 according to the invention is provided parallel to the feed pump, but with opposite conveying direction.

When the feed pump 5 is in operation, the aeration pump 15 is out of operation and vice versa. However, there are also operating states of the metering system according to the invention in which neither of the two pumps 5, 15 is in operation.

On the suction side and the delivery side of the feed pump 5, a check valve 17, 19 is provided in each case. In a corresponding manner, check valves 21 and 23 are also provided on the suction side and the pressure side of the aeration pump 15. Since the conveying directions of the feed pump 15 and the venting pump 15 are opposite, the locking directions of the check valves 17, 19 and 21, 23 are directed opposite.

The ventilation pump 15 is hydraulically integrated via a ventilation line 25 in the suction line 3 and the pressure line 7 of the feed pump 5. The suction-side section of the ventilation line with respect to the ventilation pump 15 25 has the reference numeral 25.1 The reference to the ventilation pump 15 pressure-side portion of the vent line 25 has the reference numeral 25.2

At the in FIG. 1 illustrated normal operation of the dosing shut off the check valves 21 and 23, the vent line 25, as long as the pressure in the pressure line 7 is below the opening pressure of said check valves.

In FIG. 2 the dosing system is shown in the aeration mode. In this case, the feed pump 5 is out of operation and the aeration pump 15 promotes liquid reducing agent from the metering module 9 in the tank 1 back. In order for the ventilation pump 15 to be able to ventilate the dosing module 9 as well as a part of the pressure line 7, the 2/2-way valve 13 of the dosing module 9 is opened. This switch position is in FIG. 2 shown.

At the in FIG. 2 shown ventilation of the metering block the check valves 17 and 17 sections of the suction line 3 and the pressure line 7, as long as the delivery pressure of the aeration pump 15 7 is below the opening pressure of said check valves.

Once the ventilation process is completed, the directional control valve 13 of the metering module 9 are closed again and the aeration pump 15 is turned off.

After the aeration process, both the dosing module 9 and parts of the pressure line 7, the ventilation line 25 and the aeration pump 15 are filled with air or exhaust gas. Thus, the still filled with liquid reducing agents areas of the dosing, namely especially the feed pump 5, the suction line 3 and a portion of the pressure line 7, the aforementioned air-filled areas are available as a compensating volume when the reducing agent freezes. As a result, the forces arising during the freezing of the reducing agent are reduced so much that no damage to the feed pump 5 or the lines 3, 7 are to be feared more. This is especially true when the feed pump 5 and the venting pump 15 are arranged in a common housing.

In the FIG. 3 a second dosing system is shown. An essential difference to the first metering system is that the venting pump 15 designed as a diaphragm pump is designed so that whenever the venting pump is de-energized, the membrane of the venting pump 15 closes the venting line 25. This is represented by a switchable directional control valve 26. Preferably, the section 25.2 of the vent line 25 is closed, although the directional control valve 26 is located in the section 25.1.

As soon as the actuator of the aeration pump 15 is energized, the membrane releases the ventilation line 25 again, so that it can be determined from the Figures 1 and 2 explained mode of operation again sets. The ventilation pump 15 according to the second embodiment thus additionally has the function of a controlled shut-off valve 26. Because this no additional components are needed, this additional functionality is achieved at no extra cost.

The use of the feed pump as a controlled shut-off valve 26 has the advantage that by appropriate design of the cross-section of the vent line 25, this can be sealed with a very low spring pressure acting on the membrane spring. This eliminates the need to design one of the two check valves 21, 23 in the ventilation line so that they are still tight relative to the operating pressure of the feed pump 5.

The opening pressure of the check valves 21 and 23 should be as low as possible because the electromagnetic actuator of the venting pump 15 must overcome the opening pressure at each stroke. The lower the opening pressure, the smaller and lighter the actuator can be made. Therefore, when using the diaphragm of the ventilation pump 15 as an additional shut-off valve, not only the opening pressure of the check valves 21, 23 can be reduced, but the electromagnetic actuator of the ventilation pump 15 can be made smaller, which saves costs and installation space. In addition, this also reduces the electrical energy required for the drive of the ventilation pump 15th

At the in FIG. 4 shown dosing is on the suction side of the venting pump 15 instead of a check valve 21 (see FIGS. 1 to 3 ), a suction throttle 27 is provided. Since the suction throttle 27 ultimately consists essentially only of a cross-sectional constriction in the ventilation line 25, thereby the number of required components is further reduced, which has a positive effect on the manufacturing costs and the robustness of the metering system according to the invention.

Like from the FIG. 5 it can be seen, the check valve 23 can be replaced on the pressure side of the venting pump 15 by a delivery throttle 29. It is important, however, that at least one check valve is present in the ventilation line 25.

It goes without saying that the membranes of the feed pump 5 and the venting pump 15 can be driven not only by an electromagnetic actuator, but also by an electric motor. It can also be another pump principle such. B. a piston pump, a gear pump, a vane pump u. a. be used more.

The check valves 17, 19, 21 and / or 23 can be loaded as required and design with spring elements, so that their opening pressure is adjustable by the biasing force of the springs within wide limits. You can as in the embodiments according to FIGS. 4 and 5 partially replaced by throttles.

Any necessary filters in the suction side 3, the pressure line 7 and / or the vent line 25 are partially required in practical applications, but not shown for reasons of clarity. The same applies to a pressure sensor or a flow sensor. If possible, however, the installation of such sensors is dispensed with, since they drive the costs upwards. If required, an additional electric heater can be installed. However, in many cases this is not necessary because the waste heat of the pump drive is generally sufficient to prevent the metering system from freezing. Of course, this does not apply to the liquid reducing agent in the tank 1. Here, in many cases, a heater is required at least for thawing the frozen reducing agent (not shown).

In the FIG. 6 another dosing system is shown. In this, the feed pump 5 is designed as a diaphragm pump and can in a similar manner as with reference to the FIG. 3 explained, can also be used as a switchable shut-off valve 28. Therefore, in this regard, in connection with the aeration pump 15 in FIG. 3 Said directed.

FIG. 7 is a block diagram of another dosing system. In this parallel to the first check valve 21 on the suction side of the aeration pump 15, a second check valve 31 is provided. The blocking directions and the passage directions of the check valves 21 and 31 are opposite.

If, for example, during operation of the feed pump 5 in the pressure line 7, an impermissibly high pressure occurs, then opens the first check valve 21. As a result, the membrane (not shown in FIG FIG. 7 ) of the aeration pump 15 is subjected to the higher pressure and the membrane deviates due to the higher pressure. As a result, the volume of the delivery chamber in the aeration pump 15 is increased and the pressure peak thereby partially reduced. As soon as the pressure in the pressure line 7 returns to normal values, the elastic diaphragm of the aeration pump 15 can push back via the second check valve 31 the amount of liquid urea water solution previously received in the delivery chamber back into the pressure line until a pressure equalization is achieved.

If the overpressure in the pressure line 7 is very high, it may also happen that the check valve 23 opens on the pressure side of the aeration pump 15 and thus part of the conveyed by the pump 5 liquid from the pressure line 7 is returned to the suction line 3 , This also causes a pressure reduction to permissible values or a pressure limitation. Thus, the system according to the invention is very robust and takes no damage even when impermissibly high pressures occur.

In the embodiment according to FIG. 8 is parallel to the check valve 23 on the pressure side of the aeration pump 15, a throttle 33 is provided.

Through this throttle, it is possible to make the electric actuator smaller. It has been found that, especially when the diaphragm of the venting pump 15 is formed as an additional shut-off valve 26 pressure holding valve 26, during the suction of the pump 5, a strong negative pressure in the delivery chamber of the venting pump 15 can form, because the delivery chamber via the vent line 25 and the check valve 23 is connected to the suction line 3. The blocking effect of the check valve 23 prevents a pressure equalization between the delivery chamber of the ventilation pump 15 and the suction line 3, when there is a negative pressure in the delivery chamber.

This negative pressure in the delivery room can only be overcome by a very strong electric actuator. The throttle according to the invention ensures that a pressure equalization can take place between the delivery chamber of the aeration pump 15 and the suction line 3 when negative pressure prevails in the delivery chamber. As a result, the drive power of the electric actuator can be reduced, which has a positive effect on space requirements and weight of the electric actuator. Further details can be found in the FIGS. 14-16 and their descriptions.

In FIG. 9 a longitudinal section through a venting pump 15 is shown.

The electric actuator 35 essentially comprises an electromagnet 37 and an armature 39. Between the magnet 37 and the armature 39, a spring 41 is present, which the armature 39 in the FIG. 9 pressed to the left against a membrane 43. The membrane 43 is sealingly clamped on the outside with a bead 44 in the housing 47 of the ventilation pump 15, so that in FIG. 9 right of the membrane 43 is no liquid. On the other side of the membrane 43, a delivery chamber 45 of the aeration pump 15 is formed in the housing 47. In the housing 47 of the ventilation pump 15, the connections of the sections 25.1 and 25.2 of the ventilation line 25 are indicated in addition to the delivery chamber 45. In this case, by the reference numeral 25.1, the suction-side connection of the ventilation pump 15 to the ventilation line 25th designated during the connection 25.2 the pressure-side connection of the ventilation pump 15 to the ventilation line 25. The check valves 21 and 23 are in the FIG. 9 not shown. In the region of the pressure-side connection 25.2, an annular sealing seat 49 is formed in the housing 47.

If the electric actuator is de-energized, then the spring 41 presses the armature 39 and with it the membrane 43 against the sealing seat 49, so that the connection 25.2 of the ventilation line 25 is closed. As soon as the electric actuator 35 is energized, the magnet 37 moves the armature 39 in FIG. 9 to the right, so that the membrane 43 lifts from the sealing seat 49 and thus a hydraulic connection between the terminal 25.1 and the pumping chamber 45 is made. Thus, the ventilation pump 15 according to the invention according to the embodiment of FIG. 9 at the same time a controllable directional control valve which closes the connection 25.2 of the ventilation line 25 when the actuator 35 is switched off. This functionality requires no additional components. It is achieved by a clever design and tuning of the diaphragm 43, the pump housing or the sealing seat 49 and the electric actuator 35. This results in no additional costs in the production.

When the electric actuator 35 is energized abruptly by the discharge of one or more capacitors (not shown), then the armature 39 is attracted very quickly and with great force, so that a strong and sudden pressure drop in the region of the pressure line 7 and a portion 25.1 of Ventilation line 25 takes place. Due to the elasticity of the pressure line 7 or the vent line 25 and the liquid therein and pressurized, the sudden pressure relief causes a portion of the liquid contained in the pressure line 7 is pressed by the venting pump 15 in the direction of the tank. This is also done with a. However, very fast conveying stroke of the aeration pump 15 ensures partial ventilation of the dosing module 9 and the pressure line 7, so that even during the subsequent freezing of the system no damage caused by ice pressure. This highly dynamic process is referred to in the context of the invention as pulse back suction and is also in all embodiments of dosing systems or ventilation pumps 15 according to the invention can be used.

In the FIG. 10 Another example of ventilation is also shown partially in section. In this example, a sandwich-like construction of the ventilation pump 15 is clearly visible. From top to bottom connects to the armature 39, the membrane 43 with its bead 44 and a valve-diaphragm plate 51 at.

In this example, it is also easy to see that at the in FIG. 10 lower end of the armature 39, a valve plate 53 is formed, which is molded with rubber or a similar elastic material. The membrane 43 is made of the same rubber material and is positively connected to the armature 39.

However, there is a certain distance between the valve disk 53 and the membrane 43 in the axial stroke direction of the armature 39, so that the pressure prevailing in the pumping chamber 45 also in FIG. 10 acts "from above" on the valve plate 53. As a result, the pressure prevailing in the delivery chamber 45 simultaneously acts as a hydraulic closing force, which presses the valve disk 53 against the sealing seat 49 in the valve membrane plate 51.

At the in FIG. 10 In the example shown, the membrane 43 is wave-shaped in cross-section. As a result, the membrane 43 becomes more elastic and can thus yield more easily when the pressure in the delivery chamber 45 increases. Then the membrane 43 gives in FIG. 10 upward in the direction of the armature 39 until it abuts the armature 39. This ensures that even with the occurrence of extremely large excess pressures in the delivery chamber 45, the membrane 43 does not tear.

In the valve diaphragm plate 51 are still more connections, namely the port 25.1 and a port 25.3 visible. The pressure-side outlet 25.2 of the ventilation pump 15 is in FIG. 10 obscured by the valve plate 53.

The port 25.3 provides the hydraulic connection to the second check valve 31 (see FIG. FIG. 7 ) ago, when the inventive Ventilation pump 15 is still used at the same time as a pressure compensation element.

FIG. 11 shows a detail of FIG. 10 further enlarged and supplemented by a valve plate 57 and a rubber plate 55. Below the valve diaphragm plate 51, a rubber plate 55 and a valve plate 57 are arranged. The valve diaphragm plate 51, the rubber plate 55 and the valve plate 57 form below the port 25.1, the check valve 21, the reverse direction in FIG. 11 runs from top to bottom. The passage direction is indicated by an arrow 59. To clarify which portions of the components 51, 55 and 57 form the check valve 21, these portions are enclosed by a dashed line.

In the valve plate 57, a circumferential ridge 61 is formed, which cooperates with a corresponding web 63 of the valve-diaphragm plate 51 so that it clamps the rubber plate 55 sealing. Coaxially with the web 61, a sealing seat 65 is formed in the valve plate 57, on which the rubber plate 55 rests when the check valve 21 is closed. The sealing seat 65 and the web 61 together with the rubber plate 55 define an annular channel 67. Above the annular channel 67, a plurality of arc-shaped openings 69 are recessed in the rubber plate 55.

Now, if the check valve 21 from the pressure line 7 (not shown in FIG FIG. 11 ) is acted upon by the vent line 25 with the pressure prevailing in the pressure line 7 and this pressure is greater than the opening pressure of the check valve 21, then lifts the rubber plate 55 from the sealing seat 65 and thereby creates a hydraulic connection to the annular channel 67 in the valve plate 57. From the annular channel 67, the reducing agent passes through openings 69 in the rubber plate 55 in the delivery chamber 45 of the ventilation pump flow.
This means that reducing agent can flow in the direction of the arrow 59 through the bore 69 in the valve plate 57, when the difference between that in the bore 71 and the delivery chamber 45 is large enough.

As soon as the pressure of the reducing agent in the section 25.1 of the ventilation line 25, which communicates with the pressure line 7, drops below the opening pressure of the check valve 21, the rubber plate 55 is lowered due to their elasticity back to the sealing seat 65 and thus closes the delivery chamber 45th

The second check valve 31 has the same structure but the opposite passage direction. Therefore, the annular channel 73 and the sealing seat 75 are disposed in the valve-membrane plate 51.

In the FIG. 11 are the belonging to the second check valve 31 openings 77 in the rubber plate 55 visible only to a small extent.

In comparison of the two check valves 21 and 31 it is clear that the sealing seat 75 of the second check valve 31 is smaller than the diameter of the sealing seat 65 of the first check valve 21. Thus, with the same thickness of the rubber plate 55, the opening pressure of the two check valves 21 and 31 can be adjusted , As already related to the FIG. 7 has been explained, it is advantageous if the opening pressure of the second check valve 31 is higher than that of the first check valve 21, which is structurally implemented by the smaller diameter of the sealing seat 75.

Already from the FIG. 11 It is clear that it is possible with minimal cost to integrate one or more check valve 21, 23, 31 in the ventilation pump 15 according to the invention. As a result, various variants of the ventilation pump 15 according to the invention can be produced by replacing the valve diaphragm plate 51 or the valve plate 57.

In FIG. 12 FIG. 12 is a side view of the example according to FIG FIG. 11 shown. In this, the check valve 23, which connects the delivery chamber 45 with the pressure-side section 25.2 of the ventilation line 25, can be clearly seen. The passage direction of the check valve 23 is indicated by an arrow 79. Again, the same structure is recognizable.

At the in FIG. 12 an example, an outer sealing seat 49.2 and an inner sealing seat 49.1 are formed in the valve diaphragm plate 51, on which the valve plate 53 rests when the actuator 35 is de-energized, so that a particularly good sealing of the pumping chamber 45 to the pressure side of

Ventilation pump 15 takes place. The inner sealing bead 49.1 results in a leakage-free sealing possible by the spring 41 applied closing forces. This is especially important if the vehicle is turned off and full running of the pressure line 7 and / or the dosing and / or the exhaust system to be safely prevented without the spring 41 and thus the magnet 37 must be larger than absolutely necessary.

In the valve-membrane plate 51, a sealing seat 81 and an annular channel 83 is formed, which forms the check valve 23 together with the rubber plate 55. In this illustration, it is easy to see how the valve plate 53 cooperates with the sealing seat 49 and thereby relieves the second check valve 23.

In FIG. 12 is also good to see that the magnet 37 has a toroidal recess which limits the stroke or the elastic deformation of the membrane 43. As a result, damage to the membrane 43 in the event of inadmissibly high pressures in the delivery chamber 45 can be avoided.

A shoulder 85 on the armature 39 on the one hand serves to support the compression spring 41 on the armature, on the other hand, this shoulder 85 can serve to guide the armature 39 in the magnet 37.

In the FIG. 13 the rubber plate 55 is transparent and "from below" shown, so that the sealing seats in the valve-diaphragm plate 51 and parts of the membrane 43 are visible. From this representation, the different diameters of the check valves 21, 23 and 31 become clear.

The check valve 23 has the largest bore, so that it opens at a small overpressure in the delivery chamber, if not the valve plate 53 closes this valve. As a result, the energy requirement is minimized during operation of the ventilation pump 15. In contrast, the second check valve 31 on the suction side of the aeration pump 15 has the smallest diameter of the sealing seat 75, so that this check valve opens only at a relatively high pressure.

In the FIGS. 14 to 16 another embodiment of a ventilation pump 15 is shown.

The check valves 21 and 23 are slightly different in construction than those described above. However, their function is unchanged. In the FIGS. 14 and 15 is easy to see how the membrane 43 on the sealing seat 49, which surrounds the port 25.1 in the valve plate 51, rests.

Especially in the FIG. 15 , which shows an enlarged detail of the FIG. 14 is also clearly visible that the membrane 43 rests on a further bead 87. The delivery chamber 45 thus has an annular geometry and is bounded radially on the outside by the bead 87 and on the inside by the sealing seat 49.

If now during operation of the feed pump 5 (see, for example, the FIG. 1 ) liquid reducing agent is sucked from the tank, the pressure in the suction line 3 decreases briefly. As a result, the check valve 23 opens in the pressure-side part in the ventilation line 25 and as a result, the pressure in the pumping chamber 45 also decreases. This low pressure in the delivery chamber 45 is maintained because of the blocking effect of the check valve 23 even if ambient pressure prevails in the suction line 3 again.

This low pressure in the delivery chamber 45 causes the membrane 43 is pulled against the valve plate 51 and against the sealing seat 49 and the bead 87, so to speak. This means that a very large force must be applied from the armature 39 or from the magnet 37 in order to lift off the armature 39 and with it the membrane 43 from the sealing seat 49 and the bead 87. This would require a large and expensive electric actuator 35.

Therefore, a throttle 33 is formed in the valve plate 57, which connects the delivery chamber 45 with the ventilation line 25.2 or indirectly with the suction line 3 (see the block diagram in FIG FIG. 8 and the FIG. 16 ). The throttle 33 ensures a pressure equalization between the suction line 3 and the delivery chamber 45, so that the forces that are required to lift the membrane 43 from the sealing seat 49 and the bead 87 are drastically reduced.

As a result, a smaller electrical actuator 35 can be used, which saves costs and installation space. In addition, the power requirement of the ventilation pump 15 according to the invention decreases.

Claims (16)

1. Dosing system for urea/water solution, comprising a delivery module having a delivery pump (5), and comprising a dosing module (9) and a tank (1), wherein the delivery pump (5) and the tank (1) are connected to one another via a suction line (3), and wherein the delivery pump (5) and the dosing module (9) are connected to one another via a pressure line (7), characterized in that an aeration pump (15) is arranged parallel to the delivery pump (5), and in that the aeration pump (15) is connected on the suction side to the dosing module (9) and on the pressure side to the tank (1), wherein on the suction side and on the delivery side of the aeration pump (15), a first check valve (21, 23) is provided in each case, and wherein on the pressure side (25.2) of the aeration pump (15), a throttle (33) or an aperture is provided parallel to the first check valve (23).
2. Dosing system according to Claim 1, characterized in that the delivery pump (5) and/or the aeration pump (15) is designed as a diaphragm pump.
3. Dosing system according to Claim 1 or 2, characterized in that the delivery pump (5) and/or the aeration pump (15) is driven by an electromagnetic actuator (35).
4. Dosing system according to one of the preceding claims, characterized in that a throttle (27, 33) or an aperture is provided on the suction side of the delivery pump (5) and/or of the aeration pump (15).
5. Dosing system according to one of the preceding claims, characterized in that, on the suction side of the aeration pump (15), a second check valve (31) is provided parallel to the first check valve (21), in that the blocking direction of the second check valve (31) is opposite to the blocking direction of the first check valve (21), and in that the opening pressure of the second check valve (31) is higher than the opening pressure of the first check valve (21).
6. Dosing system according to Claim 3, characterized in that when the actuator (35) of the delivery pump (5) and/or of the aeration pump (15) is not supplied with current, a diaphragm (43) closes off the pressure line (7), the suction line (3) or the aeration line (25).
7. Dosing system according to Claim 6, characterized in that that end of the pressure line (7), of the suction line (3) or of the aeration line (25) which is closed off by the diaphragm (43) when the actuator (35) is not supplied with current is surrounded by a sealing seat (49, 65, 81).
8. Dosing system according to Claim 6 or 7, characterized in that when the actuator (35) of the delivery pump (5) and/or of the aeration pump (15) is not supplied with current, the diaphragm (43) directly or indirectly exerts a closing force on a valve member of a check valve (17, 19, 21, 23).
9. Dosing system according to one of the preceding claims, characterized in that the aeration pump (15) is integrated in the delivery pump (5).
10. Dosing system according to one of the preceding claims, characterized in that at least one capacitor is present, and in that the electric charge of the capacitor stored in the capacitor is usable for supplying the electric actuator (35) of the aeration pump (15) with current.
11. Dosing system according to one of the preceding claims, characterized in that the delivery pump (5) and/or the aeration pump (15) comprises an electric actuator (35) having a magnet (37) and an armature (39), and comprises a diaphragm (43), a valve-diaphragm plate (51) and a valve plate (57), and in that a rubber plate (55) is present, as a valve element and sealing element, between the valve-diaphragm plate (51) and the valve plate (57).
12. Dosing system according to Claim 11, characterized in that the valve-diaphragm plate (51) and the diaphragm (45) of the aeration pump (15) form a controllable directional valve or check valve (26).
13. Dosing system according to Claim 11 or 12, characterized in that the valve-diaphragm plate (51), the rubber plate (55) and the valve plate (57) form a first suction-side check valve (21), a second suction-side check valve (31), a pressureside check valve (23) and/or a throttle (27, 29, 33).
14. Dosing system according to one of claims 11 to 13, characterized in that a valve disc (53) is formed on the armature (39), and in that the valve disc (53) is encapsulated with the material of the diaphragm (43), and in that the diaphragm (43) is arranged on the armature (39) so as to be offset with respect to the valve disc (53) in the stroke direction.
15. Dosing system according to one of the preceding claims, characterized in that the diaphragm (43) is of undulating form in cross section.
16. Dosing system according to one of Claims 11 to 15, characterized in that the armature (37) restricts the path of the diaphragm (43) in the stroke direction.

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