DE102014010948A1 - Reduktionsmitteldosiersystem with damping of the reducing agent promotion - Google Patents

Abstract

The invention relates to a reducing agent metering system (10) for injecting a reducing agent into the exhaust gas flow of an internal combustion engine for selective catalytic reduction, with a delivery pump (20), by means of which reducing agent from a reducing agent tank (40) via a suction line (30) from the tank (40). sucked and conveyed via a pressure line (50) and via at least one nozzle (60) is introduced into the exhaust gas stream of the internal combustion engine, wherein the suction line (30) has a bidirectional rubber valve (70).

Description

The invention relates to a Reduktionsmitteldosiersystem for injection of a reducing agent in the exhaust stream of an internal combustion engine for selective catalytic reduction, with a feed pump, sucked by means of which reducing agent from a reducing agent tank via a suction line from the tank and conveyed via a pressure line and via at least one nozzle in the exhaust stream of the Internal combustion engine is initiated.

Furthermore, the invention relates to a method for operating a Reduktionsmitteldosiersystems for injecting a reducing agent into the exhaust stream of an internal combustion engine for selective catalytic reduction, with a magnetic piston pump as a feed pump, sucked by means of which reducing agent from a reducing agent tank via a suction line from the tank and conveyed via a pressure line and over at least one nozzle is introduced into the exhaust gas flow of the internal combustion engine, wherein the piston movement is brought about by driving one or more cylindrical coils.

Selective Catalytic Reduction (SCR) catalysts are used to reduce the NOx emissions of diesel engines, combustion plants, incinerators, industrial plants, and the like. For this purpose, a reducing agent is injected into the exhaust system with a metering device. The reducing agent used is ammonia or an ammonia solution or another reducing agent.

Since the entrainment of ammonia in vehicles is safety-critical, urea is in aqueous solution with usually 32.5% urea content in particular according to DIN 70070 used. In the exhaust gas, the urea decomposes at temperatures above 150 ° Celsius into gaseous ammonia and CO ₂ . Parameters for the decomposition of the urea are essentially time (evaporation and reaction time), temperature and droplet size of the injected urea solution. In these SCR catalysts, selective catalytic reduction (SCR) reduces the emission of nitrogen oxides by about 90%.

In the known Reduktionsmitteldosiersystemen for injecting a reducing agent in the exhaust stream of an internal combustion engine for selective catalytic reduction, the reducing agent solution is conveyed by means of a magnetic piston pump to the nozzle. It has been shown that occurs by the pulse in the delivery line after a delivery stroke of the magnetic piston pump uncontrolled subsequent delivery of the reducing agent. Furthermore, it has been shown that due to a high piston speed in a delivery stroke, the hydraulic fluid does not flow as desired through the control bores out of the cylinder, but instead hydraulic fluid is conveyed even before closing the control bores, resulting in a promotion of too much reducing agent due to increased deflection of the conveyor diaphragm , which makes an exact dosage difficult.

Furthermore, it has been shown that due to a high piston speed after a delivery stroke, the hydraulic fluid is not supplied as desired via the control bores the cylinder and piston, but instead hydraulic fluid is still sucked from the diaphragm chamber, resulting in a suction of too much reducing agent, which is an exact Dosage difficult.

The object of the invention is to form a Reduktionsmitteldosiersystem of the type mentioned on and provide a method for operating a Reduktionsmitteldosiersystems, so that an exact dosage of the reducing agent allows and unwanted over-promotion or Nachförderung after a delivery stroke is reliably prevented.

This object is achieved by a Reduktionsmitteldosiersystem according to claim 1. Advantageous developments of the invention are specified in the dependent claims.

Particularly advantageous in the Reduktionsmitteldosiersystem for injecting a reducing agent in the exhaust stream of an internal combustion engine for selective catalytic reduction, sucked with a feed pump by means of which reducing agent from a reducing agent tank via a suction line from the tank and conveyed via a pressure line and at least one nozzle in the exhaust stream of It is that the suction line has a bidirectional rubber valve.

In particular, the reducing agent metering system may comprise a pump unit containing the feed pump. This pump unit may have additional components, in particular switching valves and / or sensors, in addition to the delivery pump.

The term "suction line" designates the delivery line from the reducing agent tank to the suction mouth of the delivery pump. In this suction line a bidirectional rubber valve is arranged. Such a bi-directional rubber valve is a passive component which automatically opens upon occurrence of a corresponding pressure difference between the two sides of the bidirectional rubber valve and the Flow channel releases and vice versa falls below the required pressure difference to both sides of the bidirectional rubber valve again automatically closes the flow channel. As a result, an undesired Nachfördern the reducing agent due to the pulse in the delivery line after a delivery stroke of the feed pump is reliably prevented.

With the term of the pressure line while that conveying line is referred to, in which the pressure side of the feed pump opens and via which the reducing agent is conveyed from the pump to the nozzle.

The terms reducing agent metering system or metering system are used synonymously in the context of the invention. The term reducing agent solution or reducing agent includes any reducing agent suitable for selective catalytic reduction, preferably a urea solution according to DIN 70070 for use. However, the invention is not limited thereto.

In a preferred embodiment, the pressure line has a throttle. It has been shown that especially the arrangement of a bidirectional rubber valve in the suction line in combination with a throttle in the pressure line allows a particularly accurate dosing of the reducing agent and reliably prevents unwanted over-delivery or Nachförderung after a delivery.

The system preferably has a component carrier on which the delivery pump is mounted, and wherein a suction channel to the pump inlet and a pressure channel adjoining the pump outlet are integrated into the component carrier, wherein the component carrier has a mounting region in which the rubber valve is integrated into the suction channel is.

By such a component carrier, a particularly advantageous arrangement of the pump and the bidirectional rubber valve in the suction line is possible. It is possible to pre-assemble the components arranged on and / or on the component carrier to form an assembly. This results in a simpler installation of the dosing and a saving of the required space by combining several components to a space-saving assembly.

In a preferred overall arrangement, the reducing agent metering system has a tank to which the suction line is connected. In this case, the reducing agent solution is filled into the tank and stored in the tank for the operation of the system. For dosing, the reducing agent solution is removed from the tank and conveyed by means of the feed pump and introduced via at least one nozzle in the exhaust gas stream of the internal combustion engine.

Particularly preferably, the system has a compressed air supply and the reducing agent is atomized inside or outside the nozzle by means of compressed air. In this case, the compressed air supply may have a switching valve and / or a pressure regulating valve. This switching valve is used to control, d. H. the switching on and off of the compressed air supply for all or part of the dosing system.

Alternatively or cumulatively, the compressed air supply may have a pressure regulating valve. In this way, the compressed air can be adjusted to a desired level for atomization of the reducing agent by means of compressed air pressure level. The compressed air itself can be taken from an on-board compressed air system, such as a commercial vehicle, in the exhaust system, the dosing is arranged without the prevailing system pressure in the compressed air system is a limitation, since the pressure of the compressed air can be lowered to the desired pressure.

In a preferred embodiment of the Reduktionsmitteldosiersystems therefore a compressed air supply is provided, wherein the reducing agent is atomized inside or outside the nozzle by means of compressed air. For atomizing the reducing agent, a mixing chamber may be provided, within which an atomization of the reducing agent by means of the compressed air takes place even before the introduction into the exhaust gas tract. In a preferred embodiment, however, the nozzle is designed as an externally mixing two-substance nozzle in which the reducing agent solution emerges from a first nozzle opening and compressed air emerges from a second nozzle opening, wherein the two nozzle openings are aligned with one another such that the compressed air atomizes the reducing agent outside the nozzle, so that the nozzle is designed as an external mixing two-fluid nozzle and the aerosol formation takes place outside the nozzle. In particular, the second opening of the nozzle is positioned in such a way, in particular positioned at an angle relative to the jet direction of the first opening of the nozzle, that by means of the compressed air emerging from the second opening, the reducing agent emerging from the first opening is atomized.

Preferably, the pressure line is connected via a switching valve or control valve to a compressed air supply to free the pressure line and the nozzle after completion of the dosage by means of compressed air from reducing agent.

In this preferred embodiment of the Reduktionsmitteldosiersystems thus a compressed air supply is provided, wherein the reducing agent-conveying pressure line and thus the nozzle are connected via a switching valve to the compressed air supply to free them after completion of the dosage by means of compressed air from reducing agent.

As a result, the reducing agent-conveying pressure line and the nozzle and / or a metering chamber and / or the dosing can be freed after completion of the dosage by means of the compressed air from the reducing agent solution to prevent freezing or crystallization of the reducing agent solution. This can effectively prevent frost damage and blockage.

The compressed air can thus be used alternatively or cumulatively for atomizing the reducing agent in the exhaust line and for cleaning the reducing agent-carrying lines after the end of the dosage.

Preferably, the pressure in the pressure line is detected and monitored by means of a pressure sensor. By such detection and monitoring of the pressure in the reducing agent leading pressure line and the correct operation of the feed pump and the dosage can be monitored continuously.

The system preferably has a heating device for heating the reducing agent solution. The widely used reducing agent solution according to DIN 70070 freezes due to its water content at approx. -11 ° C. Therefore, it is necessary to provide a heating device, for example inside the tank and / or in thermal coupling to the suction line and / or pressure line for heating the reducing agent solution in the case of very low ambient temperatures.

The feed pump is preferably a piston pump, in particular a magnetic piston pump. In such a magnetic piston pump, one or more cylindrical coils, by means of which a magnetic field is generated, arranged. The piston movement of the magnetic piston is controlled by the magnetic field generated by the coils.

In the case of a magnetic piston pump, it is particularly advantageous that it can be actuated and controlled precisely by a corresponding control of the coils producing the magnetic field.

Accordingly, in a method for operating a reducing agent metering system for injecting a reducing agent into the exhaust gas stream of a selective catalytic reduction internal combustion engine, it is possible to suck it from a reducing agent tank via a suction line from the tank and convey it via a pressure line by means of a magnetic piston pump and is introduced via at least one nozzle in the exhaust stream of the internal combustion engine, wherein the piston movement is controlled by driving one or more cylindrical coils, by means of which a magnetic field is generated, to provide that a pulse-width modulated control of the / the solenoid / n depending on the current Position, speed and direction of movement of the piston takes place.

By the term of the control of the / the cylindrical coil / n is meant the time-variable energization of the coil / n, by each of which a resulting magnetic field is generated, which exerts a resultant force on the magnetic piston. By the resulting magnetic force of the piston is reciprocated in the cylinder of the magnetic piston pump between the top dead center and the bottom dead center and thereby accelerated or decelerated.

By a pulse-width modulated control of the / the solenoid / n the duty cycle, d. H. the ratio of duty cycle to power-off duration of the solenoid (s) during a cycle varies, resulting in a time-varying resulting magnetic field of the solenoid (s). This in turn follows a time-varying resulting on the piston resulting magnetic force and the resulting variable piston acceleration or piston speed. By varying the duty cycle, the arithmetic mean of the electrical voltage can be changed. Accordingly, by a pulse width modulated control of the solenoid / n a magnetic piston pump, the resulting force acting on the piston magnetic force can be controlled.

The application of the method for operating a Reduktionsmitteldosiersystems can be done alternatively to the development of the invention also in a generic Reduktionsmitteldosiersystem according to the prior art. However, it is also possible to apply the method for operating a reducing agent metering system cumulatively in a reducing agent metering system developed according to the invention.

The control of the cylinder coil (s) is preferably carried out such that the piston is slowed down during a delivery stroke at the level of the control bores via which hydraulic fluid is supplied.

The control of the cylinder coil (s) is preferably carried out such that the piston is slowed down during a suction stroke at the level of the control bores via which hydraulic fluid is supplied.

Preferably, the control of the / of the cylinder / n is such that the piston is decelerated to complete a delivery stroke before top dead center.

By slowing down the piston at the level of the control bores via which hydraulic fluid is supplied and discharged to the cylinder in which the piston is guided, the desired flow of the hydraulic fluid through the control bores is optimized, since at too high piston speeds in the intake stroke, an undesired suction of too much hydraulic fluid is to be observed from the diaphragm chamber during a suction stroke, while during the delivery cycle due to an excessive piston speed, an undesired delivery of hydraulic fluid into the diaphragm chamber. These unwanted effects both during a suction stroke and during a delivery stroke can be significantly reduced by a corresponding pulse-width-modulated control of the / of the cylindrical coil / s and a braking of the piston in the region of the control bores.

An unrestrained impact of the piston on the baffle plate to the end of a delivery stroke leads to a significant impulse in the pressure line of the metering system, with the result that due to this pulse, the inlet valve opens and an uncontrolled and unwanted promotion of reducing agent. This undesirable effect can be suppressed by braking the piston just before top dead center. By avoiding a hard impact of the piston on the baffle plate of the occurring pulse is reduced in the pressure line, so that an undesired further conveying of reducing agent after completion of the delivery stroke is omitted. To decelerate the piston, a corresponding reduction of the duty cycle of the current supply of the / the cylindrical coil / n.

An embodiment of the invention is illustrated in the figures and will be explained in more detail below. Show it:

1 a schematic representation of a Reduktionsmitteldosiersystems;

2 an enlarged view of the dosing according to 1 on average;

3 the bidirectional rubber valve after the 1 and 2 in different views;

4 a schematic representation of the feed pump according to 2 on average;

5 the section of the feed pump during the phase B of a delivery stroke according to 9 ;

6 the section of the feed pump during the phase C of a delivery stroke according to 9 ;

7 the section of the feed pump during the phase D of a delivery stroke according to 9 ;

8th the section of the feed pump during the phase E of a delivery stroke according to 9 ;

9 the course of the piston travel s and the PWM duty cycle of the control of the feed pump over the time t during a delivery cycle of the feed pump;

1 shows a schematic representation of the Reduktionsmitteldosiersystems 10 for injecting a reducing agent into the exhaust gas flow of an internal combustion engine, not shown, for selective catalytic reduction.

By means of the feed pump 20 is via the suction line 30 Reducing agent solution from the tank 40 sucked in and over the pressure line 50 to the injection nozzle 60 promoted. About the injector 60 the reducing agent is injected into the exhaust gas flow of the internal combustion engine. According to the invention is in the suction line 30 a bidirectional rubber valve 70 arranged.

An enlarged view of the dosing according to 1 shows 2 on average. Here is the pump 20 on a component carrier 15 arranged. In the component carrier 15 integrated are the integrated suction line 30 ' and the integrated pressure line 50 ' , The pump 20 as well as the component carrier 15 are adapted to each other in such a way that in the component carrier 15 integrated suction line 30 ' directly into the pump inlet of the pump 20 opens and also the pump outlet of the pump 20 directly into the component carrier 15 integrated pressure line 50 ' empties.

Furthermore, in 2 recognizable in the component carrier 15 integrated valve seat 16 for receiving the bidirectional rubber valve 70 , The bidirectional rubber valve 70 is fixed in the valve seat by the valve carrier 31 , which in turn is an integral part of the suction line 30 is. The suction line 30 is with the in 2 not shown tank connected. The valve carrier 31 is against the valve seat 16 in the component carrier 15 by means of the sealing surface of the bidirectional rubber valve and additionally by means of an O-ring 35 sealed.

3 shows the bi-directional rubber valve 70 in a plan view and the section AA. Recognizable in the plan view of the rubber valve 70 is the opening slot 71 , When a corresponding pressure difference across the bidirectional rubber valve 70 opens the opening slot 71 automatically. Conversely, the opening slot closes 71 due to its restoring forces automatically at the moment when the required pressure difference across the bidirectional rubber valve 70 falls below the required opening pressure.

The arrangement of this bidirectional rubber valve 70 in the suction line 30 of the dosing system 10 leads to an attenuation of the reducing agent promotion in particular to the end of a delivery stroke, as without this integrated bi-directional rubber valve 70 the pulse in the pressure line 50 the dosing would cause an undesirable Nachförderung of reducing agent from the tank. Through that into the suction line 30 on the suction side of the pump 20 integrated valve 70 This unwanted Nachförderung is reliably prevented.

In 4 is a view of the pump 20 shown in section. At the pump 20 it is an electromagnetic piston pump in which the piston 21 by building up a corresponding magnetic field by means of a solenoid 22 that is, by means of a cylindrical coil 22 generated magnetic field and the resulting on the piston 21 is moved by acting magnetic force.

The drive of the piston 21 by a corresponding control of the solenoid 22 takes place in the extension direction of the piston 21 that is, during a delivery stroke of the piston 21 towards the top dead center. The piston is reset 21 by means of a spring 23 like this in 4 is recognizable.

The space surrounding the piston with the solenoid is filled with hydraulic fluid, with lubrication of the piston and filling of the displacement via respective control bores 24 he follows. The actual delivery volume of the pump 20 is formed by the cylinder volume 25 ,

The suction takes place via the inlet channel 26 , The pushing out takes place via the outlet channel 27 , The inlet channel 26 and the outlet channel 27 covers the membrane 28 ,

The control of the solenoid 22 depending on the piston position, piston speed and direction of movement will be explained below with reference to the other figures.

In the 4 to 8th are the respective piston positions during a Förderzyklusses recognizable, the individual phases A to G according to 9 correspond.

In a 100 percent control of the solenoid during a first phase A starting from the bottom dead center of the piston, the bias and the construction of a strong magnetic field by 100 percent driving the solenoid takes place. This results in a large acceleration of the piston from the bottom dead center UT at the beginning of a delivery stroke, as shown by the in 4 illustrated position of the piston 21 is recognizable. At the beginning of phase A is the piston 21 at the bottom dead center UT. With improved control by means of a pulse width modulation of the current is now in the in 9 Phase A shown with a large pulse width modulation only the current i set, which is necessary to adjust the magnetic field so that the piston 21 is moving with only a slight acceleration.

The first phase A with 100 percent control is followed by a second phase B at high speed of the piston. During phase B, a displacement of the hydraulic fluid in the designated control bores 24 take the pump, as in 5 represented and by the arrows 24 ' is indicated schematically. During this movement phase B during the delivery stroke, the hydraulic fluid normally flows not only through the control bores provided in advance 24 but also a part to the membrane chamber. To avoid that the hydraulic fluid is driven in front of the piston, rather than in the designated control bores 24 to drain, the piston is in the in 9 shown movement phase B with reduced duty cycle of the pulse width modulation kept at a low speed, as indicated by the lower slope of the travel curve s of the piston over the time t in 9 is recognizable. The position of the piston at the level of the pilot holes 24 during the phase B is in the sectional drawing according to 5 indicated accordingly. Also in 5 registered is the height level 25 ' according to the control edge 25 ' the tax holes 24 , in which the actual cylinder volume of the piston pump begins and is pressed as a delivery volume to the diaphragm chamber.

After the piston the control bores 24 and their control edges 25 ' and at the beginning of the actual cylinder volume 25 at the level of the level 25 ' arrives, as in 6 is indicated, then follows in the further course of time, the phase C according to 9 , In this phase C, in turn, a control of Cylinder coil with a higher duty cycle, so that the piston is accelerated again, as can be seen from the path-time diagram of the 9 the piston movement is readable and also in 9 Registered duty cycle can be seen. During the movement phase C, the actual promotion of the cylinder volume takes place 25 the pump 20 ,

An unrestrained impact of the piston 21 At the baffle plate at top dead center OT would give a significant boost in the pressure line 50 effect the dosing. This impact and also the resulting pulse would in turn be so large in the dosing line that the inlet valve opens and reducing agent flows across the pump until the pulse has dissipated. This would lead to an undesirable Nachförderung and thus to an uncontrolled dosage.

To prevent this effect, a hard impact of the piston 21 prevented at the baffle plate at top dead center OT, that during the movement phase C at the end of the delivery stroke of the piston is decelerated, as in the path-time diagram of the piston movement according to 9 is recognizable. The deceleration of the piston 21 before the top dead center OT again takes place at the end of the movement phase C in that the duty cycle in the pulse width modulated control of the solenoid is extremely reduced to a minimum. This is the in 9 plotted course of the duty cycle during the period T4 removed.

After reaching the top dead center OT, the piston 21 by means of the spring 23 moved back to the bottom dead center, whereby a corresponding suction of reducing agent via the suction line 30 he follows.

Phase D, indicated by the position of the piston 21 according to 7 at top dead center OT or shown in 9 begins when the piston has reached top dead center OT.

During the return travel of the piston in phase E by the spring force of the return spring, hydraulic fluid is sucked out of the diaphragm chamber during the stroke volume travel. Since too fast a piston movement when returning to bottom dead center UT in the area of the control bores 24 This causes hydraulic fluid to continue to be drawn from the diaphragm and not just from the control bores 24 like this in 8th through the arrows 24 '' is shown here in phases E and F according to 9 the piston during its return travel by the spring force of the return spring also by a corresponding pulse width modulated control of the solenoid in the field of control bores 24 slowed down as in 9 during the movement phase E and F can be seen. Clearly readable in 9 is the lower piston speed at the level of the control bores 24 from the lower control edge 25 ' the tax holes. As soon as the piston has swept over the control bores, the slower piston speed with the low duty cycle in phase F makes it easier to draw in hydraulic fluid from the control bores 24 like this by the arrows 24 '' in 8th is indicated schematically.

The entire movement cycle is in 9 presented in a general overview. In the upper part after 9 is the path-time diagram of the piston stroke s over time t during an entire delivery and Ansaugzyklus. Entered are the bottom dead center UT, the top dead center OT and the control edge 25 ' the tax holes 24 the pump. Recognizable in the path-time diagram are the sections A-D during the delivery stroke and subsequently the phase E to G corresponding to the intake stroke of the pump.

The corresponding pulse width modulated control of the solenoid, ie the respective change of the duty cycle, is out of phase with respect to the individual motion phases A to G, since on the one hand the corresponding magnetization must be done and further it requires a certain reaction time until the piston reacts to the changed magnetic field accordingly. This is in the lower part to 9 the respective duty cycle in the control of the solenoid can be seen, that is, it is the course of the turn-on or shutdown in the energization of the solenoid of the piston pump shown.

During a first time period T1, the required magnetization occurs with a high duty cycle resulting in a correspondingly small acceleration and low movement speed of the piston during phase A. This is followed by a constant low speed of the piston by a drive with a reduced duty cycle during a second time period T2 in the movement phase B on. This is followed by a drive with a slightly increased duty cycle during the period T3 approximately corresponding to the movement phase C, that is during the actual promotion of the reducing agent followed by a control of the solenoid with a minimum duty cycle during a period T4 to brake the piston at the end the movement phase C before reaching the top dead center OT. At the top dead center OT in the period T5 in the phase D, the duty cycle is increased again to prevent a collision and to ensure a secure holding of the piston. Starting from top dead center OT, the piston is activated by the spring force of the return spring in the direction of the bottom dead center UT retracted, wherein during a subsequent period T6 with a minimum duty cycle, the magnetic influence of the piston is almost omitted, whereby only the speed of the piston is somewhat limited. In the following period of time T7 with increased duty cycle, a deceleration of the piston at the level of the control bores 24 starting at the height of the control edge 25 ' brought about. This is followed by another period of time T8, in which the piston is again kept at a low speed with a somewhat reduced duty cycle, and is returned to the bottom dead center UT. Shortly before the impact of the piston at bottom dead center UT, the piston is braked again with an increased duty cycle in the time period T9 in order to prevent an impact here as well. After the end of the cycle, that is to say after the end of the time period T9, the delivery cycle starts again from the beginning after a corresponding pause time, depending on the dosing quantity requirement.

This variable pulse width modulated control of the solenoid of the piston pump, the piston is at the control bores 24 slowly approached and passed. As a result, less hydraulic fluid is delivered to the membrane and sucked back from the membrane. This results in a straighter delivery characteristic over the pump back pressure, ie the system is counterpressure independent. Since this control slows the piston, the period of a piston stroke is greater than at a constant unmodulated control of the solenoid. The maximum possible delivery frequency decreases as a result. Since it has been shown that at high frequency, a back pressure in the pressure line of the metering system is built up by the high flow rate, the possibility for reducing the respective duty cycles in the individual periods is given in the vicinity of the maximum delivery frequency of the pump. Thus, the maximum delivery frequency can be achieved. The displayed values of the duty cycles, times and paths are only symbolic.

The special pulse width modulated control increases the dosing accuracy of a diaphragm or piston pump. Further, we reduce the conveying speed of the reducing agent during a delivery stroke of a diaphragm or piston pump by the special pulse width modulated control and thus the formation of a finer spray is given with a two-fluid nozzle.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• DIN 70070 [0004]
• DIN 70070 [0013]
• DIN 70070 [0026]

Claims (8)

Reducing agent dosing system ( 10 ) for injecting a reducing agent into the exhaust gas stream of a selective catalytic reduction internal combustion engine, with a delivery pump ( 20 ), by means of which reducing agent from a reducing agent tank ( 40 ) via a suction line ( 30 ) from the tank ( 40 ) and via a pressure line ( 50 ) and via at least one nozzle ( 60 ) is introduced into the exhaust gas stream of the internal combustion engine, characterized in that the suction line ( 30 ) a bidirectional rubber valve ( 70 ) having. Dosing system ( 10 ) according to claim 1, characterized in that the pressure line ( 50 ) has a throttle. Dosing system ( 10 ) according to claim 1 or 2, characterized in that the system ( 10 ) a component carrier ( 15 ), on which the feed pump ( 20 ) and wherein in the component carrier ( 15 ) a suction channel ( 30 ' ) to the pump inlet and to the pump outlet subsequent pressure channel ( 50 ' ), the component carrier ( 15 ) a mounting area ( 16 ), in which the valve ( 70 ) fluidically into the suction channel ( 30 ' ) is integrated. Dosing system ( 10 ) according to one of the preceding claims, characterized in that the system ( 10 ) a reducing agent tank ( 40 ), to which the suction line ( 30 ) connected. Dosing system ( 10 ) according to one of the preceding claims, characterized in that the system has a compressed air supply and the reducing agent is atomized inside or outside the nozzle by means of compressed air, in particular that the compressed air supply has a switching valve and / or a pressure control valve. Dosing system ( 10 ) according to any one of the preceding claims, characterized in that it is at the nozzle ( 60 ) is an externally mixing two-fluid nozzle, in which emerges from at least one first opening reducing agent and at least one second opening compressed air exits, wherein the second opening is positioned, in particular at an angle to the beam direction of the first opening is employed that by means of the second opening escaping compressed air which is atomized from the first opening reducing agent. Dosing system ( 10 ) according to one of the preceding claims, characterized in that the pressure line ( 50 ) is connected via a switching valve or control valve to a compressed air supply to the pressure line ( 50 ) and the nozzle ( 60 ) After completion of the dosage by means of compressed air of reducing agent to free. Dosing system ( 10 ) according to one of the preceding claims, characterized in that it is in the feed pump ( 20 ) is a piston pump, in particular a magnetic piston pump.

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