Dosing pump assembly for mixing an exhaust gas reducing fluid agent

Abstract

ASSEMBLY OF DOSING PUMP TO MIX A REDUCING FLUID AGENT IN EXHAUST GAS FLOW. Refers to a metering pump assembly for mixing a fluid reducing agent in an exhaust gas stream, which comprises a pre-mixing device (39) in which the supplied reducing agent is mixed in a mixing region (18) with a pressurized gas, where a first return valve (20) is arranged in the premix element (39) in a supply line (15) for the reducing agent, in front of the mixing region (18 ) in the direction of the flow.

Description

PI0517591-7 DOSING PUMP ASSEMBLY "FOR MIXING A REDUCING FLUID AGENT IN EXHAUST GAS STREAM". The invention relates to a metering pump assembly for mixing a fluid reducing agent into an exhaust gas stream. With self-ignition internal combustion engines, nitrous oxide rises in operation with excess oxygen, which is the case under most operating conditions and, specifically, with direct injection into the main combustion chamber, as is typically the case with diesel engines. It is known that a reducing catalyst is supplied to the exhaust gas stream in order to reduce these nitrous gas emissions. Typically, an aqueous solution of urea as a reducing agent is supplied to the exhaust gas in a finely distributed manner before entering the catalyst. Thus, the amount of urea supplied will be matched as much as possible to the combustion process in order to ensure the most complete reduction possible within the catalyst and, on the other hand, to avoid an excess of urea. A special metering pump for dosing and supplying the reducing agent to the exhaust gas stream is known in EP 1 435 458 Al. With this metering pump, the supplied reducing agent is mixed with or subjected to pressurized air in the metering pump assembly before being supplied to the exhaust gas stream. Because urea tends to crystallize in combination with air, it is It is important to vaporize the entire region that comes into contact with air and urea with air before stopping the installation so that no urea remains in this region. For this, a 3 / 2-way valve is placed on the dosing pump according to EP 1 435 458 Al, which, in a first position, carries the urea into a conduit section that is connected to a pressurized air conduit to impinge the urea with pressurized air. In a second position, the 3 / 2-way valve is connected so that no urea reaches the aforementioned conduit section, but pressurized air is supplied through a second 3 / 2-way valve inlet, so that the conduit section where the urea is subjected to pressurized air is vaporized with pressurized air. In this way, crystallization of the urea in the conduit section can be avoided. The construction of the dosing pump assembly according to EP 1 435 458 Al is very complicated due to the valve required for vaporization. Furthermore, the operation of the dosing pump assembly is further complicated because the vaporization of the part of the installation in contact with air and urea must always be checked when it is switched off. However, for cost and operational safety reasons, it is desirable to simplify the construction and operation of the dosing pump assembly. Therefore, the object of the invention is to present a dosing pump assembly. improved for mixing a fluid reducing agent in a The exhaust gas flow is constructed in a simpler and cheaper way, allowing for simpler operation. A metering pump assembly achieves this object with the characteristics specified in claim 1. Preferred configurations will be deduced from associated dependent claims, the subsequent description, and the figures. The metering pump assembly, according to the present invention, which contemplates the mixing of a fluid reducing agent (e.g., urea) in an exhaust gas stream, comprises a device in which, in a mixing region, the supplied reducing agent released by the metering pump is mixed with a pressurized gas. The metering pump releases the reducing agent from a tank, where the metering pump releases a controllable quantity of the reducing agent adapted to the momentary combustion process in the engine. For example, the metering pump can be created as a diaphragm or piston pump, where the quantity of reducing agent can be determined by the number of pump strokes and / or the stroke speed. The premixing element is created such that in a feed for the reducing agent, a first return valve is arranged in the flow direction ahead of the current mixing region.This return valve prevents pressurized gas, and in particular pressurized air, from entering the pressure duct where the reducing agent is released into the mixing region. This ensures that the reducing agent duct, located in front of the mixing region, is properly controlled. The flow is kept free of pressurized gas or pressurized air, so that it is possible to safely avoid the crystallization of the reducing agent, specifically urea, in this region. The reducing agent only contacts the pressurized gas behind the return valve in the direction of flow, i.e., in the mixing region, and from there it descends to an injection nozzle to inject the pressurized gas / reducing agent mixture into the exhaust gas flow. Since pressurized air is supplied to the mixing region anyway, this region where the reducing agent may contact the pressurized gas can always be automatically vaporized with the pressurized gas by cutting off the supply of the reducing agent, so that no residue of the reducing agent can crystallize or remain in this region. The inventive arrangement of the return valve in the reducing agent conduit in front of the mixing region thus eliminates the need for an additional vaporization procedure, shutting off the superfluous dosing pump assembly. Furthermore, no additional valve is required in the dosing pump assembly to initiate this vaporization procedure. Therefore, the construction and operation of the dosing pump assembly are considerably simplified, and greater operational safety is achieved. The mixture of pressurized gas and reducing agent in the context of the invention is not only to be understood as a homogeneous mixture with which the The reducing agent is finely distributed in the pressurized gas. However, the mixture can also be effective in such a way that, in each case, larger quantities of reducing agent are released by the pressurized gas; that is, for example, droplets of reducing agent and pressurized gas are released alternately in the duct, and the final homogeneous mixture is not effective until injected into the exhaust gas stream. The first return valve is, particularly and preferably, arranged directly adjacent to the mixing region where the reducing agent is mixed with the pressurized gas. This means that the pressurized gas flows preferably through the entire region behind the return valve in the direction of flow, so that when the supply of the reducing agent is shut off, this region can be completely vaporized by the pressurized gas and no residue of reducing agent will remain in this region. For this, the supply of pressurized gas to the mixing region is preferably created in such a way that pressurized gas flows directly over the outside of the return valve, where by closing the return valve, it is possible to prevent the pressurized gas from penetrating the supply of reducing agent. Specifically and preferably, the first return valve is an integral component of a mixing chamber, delimiting the mixing region. Thus, the return valve forms... Preferably, a section of a mixing chamber wall where pressurized gas is introduced for mixing with the reducing agent. The valve is thus integrated into the component defining the mixing chamber, so that it can be directly adjacent to the mixing region. For this purpose, the mixing chamber preferably comprises an inlet opening for the reducing agent, which is closed by the first return valve. Thus, the closing element of the return valve, preferably simultaneous, forms part of the inner wall of the mixing chamber. The pressurized gas introduced into the mixing chamber can thus flow through the outlet side of the return valve in order to vaporize the reducing agent located there, with the flow of pressurized gas outside the metering pump assembly through the injection nozzle in the exhaust gas flow. The supply lines for the reducing agent and the pressurized gas to the mixing region are, particularly and preferably, arranged concentrically to each other. For example, the reducing agent can be supplied through a central supply line, and the pressurized gas flows through an annular channel surrounding the central supply line in the mixing chamber. With this arrangement, not only is a uniform mixture achieved, but it is also possible to inflate the mixing chamber completely free of the reducing agent when pressurized gas is introduced into the mixing chamber. concentrically around the return valve. Preferably, the pressurized gas flows over the entire inner wall of the mixing chamber, so that any residual reducing agent adhering there can be expelled. The inlet opening for the reducing agent is preferably formed centrally on one end side of the mixing chamber. For example, the mixing chamber can be cylindrical in shape, and the inlet for the reducing agent can be formed on one end side or arranged on one end side of the mixing chamber. The cylindrical design of the mixing chamber is particularly advantageous with a concentric supply of pressurized gas and reducing agent, since the pressurized gas can be carried along the inner wall of the mixing chamber. The mixing chamber preferably comprises a perimeter wall, in particular a cylindrical perimeter wall, in which the inlet openings for the pressurized gas are formed. Thus, the inlet openings are preferably arranged and distributed uniformly around the entire perimeter, so that a uniform supply of pressurized gas is ensured in all regions of the mixing chamber. By means of this, the complete mixing chamber is successfully freed from residual agent. reduction in the activation / supply of the reducing agent. The check valve can, therefore For example, it can be created so that one end of the preferred cylindrical mixing chamber is created as a funnel, where the plate-shaped closing element of the first return valve is arranged in the funnel. An annular inlet of the reducing agent into the mixing chamber through the walls of the mixing chamber is obtained by means of this construction, so that a uniform mixture with the supplied pressurized gas can be ensured. Furthermore, the closing element with the surrounding wall in the closed condition forms a slightly wide inner wall, over which the incoming pressurized gas can flow in a uniform manner in order to remove any residue of the reducing agent. The first return valve in the reducing agent supply line preferably comprises a spring element that holds the return valve in a closed position, where the return valve can be moved to an open position by the pressure of the reducing agent fluid against the force of the spring element. It is ensured by means of the spring induction of the first return valve that the return valve is always kept closed when no reducing agent is pumped to the mixing chamber by the metering pump in order to prevent penetration of compressed gas into the reducing agent supply line or the reducing agent supply line. The closing of the return valve is thus ineffective, or at least ineffective, solely by the pressure of the compressed gas, but by the spring element that induces the return valve to its Closed position. Furthermore, through this arrangement, it is possible to make the return valve only open at a predefined fluid pressure in the reducing agent supply line, thereby ensuring a defined supply of reducing agent to the mixing chamber. Induction in the context of the spring element can also be achieved by means of other suitable elastic elements. According to another preferred configuration, the premixing device comprises a second return valve conduit for the pressurized gas. This return valve prevents the reducing agent from reaching the pressurized air supply conduit when the pressurized air supply is switched off or when the pressure in the pressurized gas supply conduit is reduced. Preferably, this second return valve is also arranged directly in a mixing chamber or mixing region where the mixing of the reducing agent and pressurized gas takes place. Thus, the second return valve can also be an integral component of the premixing device or the mixing chamber delimiting the mixing region. Furthermore, the second return valve is also induced so that it is kept closed in its inactive position. This can be achieved by spring elements or other elastic elements. Preferably, the second return valve is formed by an elastic sealing element that can be brought in to provide a seal. In the wall, no reducing agent or reducing agent / pressurized gas mixture can flow back through the gas supply line. In the open condition, the sealing element lifts from the wall and allows the flow of pressurized gas. Thus, the sealing element is held tightly against the wall of the supply conduit, preferably by induction, and can be moved by the pressure of the pressurized gas acting in the flow direction towards the mixing region in an open position away from the wall. This arrangement ensures that the sealing element of the second return valve, in the inactive condition, is always in the closed condition, so that no reducing agent can penetrate the pressurized gas conduit. Only when the pressure of the pressurized gas reaches a value that exceeds the induction force of the sealing element does the sealing element open, and the pressurized gas can then flow into the mixing region of the mixing chamber, where it is then ensured by the gas flow itself that no reducing agent can return to the pressurized gas conduit. Furthermore, preferably, the wall of the pressurized gas supply conduit is an outer cylindrical wall of a component containing the mixing region and the first reducing valve. This component forms the mixing chamber. The sealing element of the second return valve can thus be formed as an annular component that rests on the outer wall. For example, also a shoulder or a defined support region of the outer wall. Given a second return valve open, the pressurized gas then flows through the outer wall of the component or mixing chamber, so that the pressurized gas can be supplied to the mixing chamber in an annular flow. The concentric supply of pressurized gas and the reducing agent to the mixing chamber can be effective in this way. The sealing element of the second return valve is, preferably, created as an annular sleeve extending in the direction of the pressurized gas flow, inclined towards the wall. Thus, the sleeve is formed of an elastic material and is preferably created so that the induction of the elastic material retains the sleeve against the wall. In the direction of flow, the pressurized gas, given a suitably high pressure, can lift the sleeve from the wall, where the sleeve expands slightly and the pressurized gas flows through the wall to the mixing region. In the reverse direction, however, the inclined geometry has the effect that the sleeve is pressed against the wall by the pressure, and thus the return valve is closed, so that no reducing agent or pressurized gas / reducing agent mixture can return to the pressurized gas conduit. The invention is described below by way of example and by means of the attached figures. They are shown in: Figure 1 shows a circuit diagram of hydraulic components. of a dosing pump assembly according to the invention; Figure 2, in a sectional view, shows the pre-mixing device of a metering pump assembly according to Figure 1; Figure 3, in a separate sectional view, shows the premixing device as per Figure 2 with the return valves closed; Figure 4 shows the premixing device according to the Figure 3, with a return valve open. pressurized gas supply; and Figure 5 shows the premixing device according to the Figures 3 and 4, with a check valve open. for reducing the supply of the reducing agent and an open return valve for the supply of pressurized gas. Firstly, the basic function of an example configuration of a dosing pump assembly, according to the invention, is described by means of the circuit diaphragm in Figure 1. The main item in the dosing pump assembly is a dosing pump 2, which is designed as a diaphragm pump with an associated drive. The amount of reducing agent released by the dosing pump 2 can be determined by controlling the pump, and in particular, controlling the number of pump strokes, in order to adapt the amount of reducing agent precisely to the demand of the combustion process. The current in the motor. An aqueous urea solution is preferably used as a reducing agent. The reducing agent is kept ready in the reducing agent tank 4, from which it is drawn through the suction conduit 5 by the metering pump 2. In the known manner, in each case, a return valve 6 is arranged in front of and behind the metering pump 2, in the example shown, and these valves are an essential constituent in the diaphragm pump. Thus, the return valve 6 that is situated in front of the pump in the direction of flow ensures that the reducing agent is not released back into the reducing agent tank 4, given the pump stroke. The return valve 6 that is situated in the downward direction of the metering pump 2 in the direction of flow conversely ensures that with a suction, only the reducing agent is drawn out of the reducing agent tank 4 and is not drawn back into the pressure conduit. A return line 10 branches off at branch point 8 in a downward direction from the metering pump 2 and the second valve 6, and leads back to the reducing agent tank and serves to bleed the system during the initial operation of the metering pump 2. A shut-off or shut-off valve 12 is arranged in the return conduit 10 whereby the return conduit 10 can be closed, so that no reducing agent can return through the return conduit 10 to the reducing agent tank 4. In the inactive condition shown, the shut-off valve 12 is located in the open condition, where the return conduit 10 is released. A pressure sensor 14 detects the fluid pressure in front of the shut-off valve 12 and thus, In the downward direction from the metering pump 2 in the pressure conduit 16, it is arranged in the return conduit 10 in the upward direction from the shut-off valve 12 and in the downward direction from the branch point 8. 0 pressure conduit 16 It directs from the metering pump 2 through the branch point to the mixing region or mixing chamber 18 to a device where the reducing agent is impinged or mixed with the pressurized gas, in the case of pressurized air. A return valve 20 which, by means of induction, for example a spring, is maintained in the inactive position shown in a closed position and prevents a return flow of the reducing agent and, in particular, of the pressurized gas from the mixing region 18 in the pressure conduit 16, is arranged directly in front of the mixing region 18 in pressure duct 16, that is, at the end of pressure duct 16. A duct 22 leading to the injection nozzle in the exhaust gas system of the motor vehicle connects in the downward direction of the mixture region 18 in the direction of flow. The pressurized air used in this example as pressurized gas is prepared by a pressurized air supply 24 from the motor vehicle. These pressurized air supply systems are typically found in trucks, particularly to operate with the brakes. The metering pump assembly shown is connected to the central pressurized gas supply 24, wherein the mounting of the dosing pump on the inlet side comprises a solenoid or magnetic valve 26 which selectively connects the pressurized air duct 28 leading to the mixing region 18 to the pressurized air supply 24 or opens it to the atmosphere 30. The electrically activated magnetic valve 26 is induced so that it is maintained in its inactive condition in the position shown, wherein the pressurized air duct 28 is open to the atmosphere 30. In the pressurized air duct 28, a pressure regulator 32 is arranged downwards from the magnetic valve 26 in the direction of flow and a regulating valve 34 is arranged in the direction Descending pressure regulator. The pressurized air duct in the mixing chamber or mixing region 18 terminates in valve 36, which is induced so that it is closed in Inactive status shown and can be opened against your induction by activating the pressure in the pressurized air duct 28. It is thus ensured that the valve of Return valve 36 is always closed when no pressurized air flows from the pressurized air duct 28 into the mixing chamber 18, so that no reducing agent from the mixing region 18 can penetrate the pressurized air duct 28. The shut-off valve 12 in the return conduit 10 is activated by pressurized air and is connected to the pressurized air conduit 28 via an activation conduit 38, where the activation conduit 38 It is connected to the pressurized air conduit 28 between the pressure regulator 32 and the regulating valve 34. The activation conduit 38 ensures that, when the magnetic valve 26 is switched, so that the pressurized air conduit 28 is connected to the pressurized air supply 24, the activation conduit 38 is also pressurized. The prevailing air pressure in the activation conduit 38 then effects a switch-off valve 12 against its induction, so that the return conduit 10 is closed. The elements previously described as being within the limit indicated in Figure 1 by dashed lines D, namely, in particular the metering pump 2, the shut-off valve 12, the magnetic valve 26, the mixing point 18, the return valves and the conduits connecting these components, are all integrated into the metering pump assembly, so that the metering pump assembly, in addition to the electrical connections, has only four fluid connections to the outside, specifically for the connection to the pressurized air supply 24, for the connection of the conduit 22 leading to the injector nozzle, for the connection of the suction conduit 5 leading to the reducing agent tank 4 and for the connection of the return conduit 10 to the reducing agent tank 4. During the system startup operation, the magnetic valve 26 initially remains in its closed, inactive condition (position shown), in which The pressurized air duct 28 is separate from the supply. 24. First, the dosing pump 2 is put into operation, drawing the reducing agent out. from the reducing agent tank 4 through the suction conduit 5. The induction of the return valve 20 in the closed position shown is selected so that the pressure in pressure conduit 16 is not sufficient to open the backflow valve against induction, given a backflow conduit opening of 10. Since no pressure prevails in the pressurized air duct 28 initially, the activation duct 38 is also initially without pressure, so the shut-off valve 12 remains in its open, inactive position, and the return duct 10 is opened. In this way, the dosing pump 2 initially releases the reducing agent from the reducing agent tank 4. This serves to bleed the system in the initial operation, that is, to first ensure that the pressure duct 15 is completely filled with reducing agent. When the reducing conduit 16 and the return conduit 10 are completely filled with the reducing agent, the fluid pressure in the pressure conduit 16 and the return conduit 10 in the upward direction to the shut-off valve 12 reaches a certain limit value, which is detected by the pressure sensor 14. When this limit value is detected by the pressure sensor 14, a control switches the magnetic valve 26, so that the pressurized air conduit 28 is supplied with pressurized air through the pressurized air supply. 24 of the truck. The activation conduit 38 is also impeded with pressure through it, whereby the shut-off valve 12 is transferred against spring induction and the return conduit 10 is thus closed. As the pressure conduit 16 is no longer open to the reducing agent tank 4 through the return conduit 10, the fluid pressure in another operation of the metering pump 2 increases in the pressure conduit 16 until the pressure is sufficient to open the return valve 2 against its spring induction, so that the reducing agent can flow into the mixing region 18 and there be impeded with pressurized air from the pressurized air conduit 28. The reducing agent then travels together through conduit 22 to an injector nozzle in the truck's exhaust gas conduit. The amount of reducing agent... The reduction provided can be determined in operation by the number of pump strokes of the dosing pump. The flow of pressurized air through the pressurized air ducts 28 in the mixing region 18 is thus constant. If the installation is taken out of operation, in particular when switching off the vehicle, first the metering pump 2 is switched off, so that the reducing agent is no longer released from the reducing agent tank 4. This reduces the pressure in the pressure line 16 until the return valve 20 closes due to its induction, preventing another reducing agent from entering the mixing region 18. Like the magnetic valve 26, the In principle, it remains open, the pressurized air continues to flow through the return valve 36 into the mixing region 18 and there it flows out of the reducing agent residue that is still present there, through the conduit 22. When the magnetic valve 26 is closed by switching off the power supply, the pressurized airflow travels through the air duct 28 and the return valve 36 is also cut off, so that the entire system is stopped in operation. In this condition, the shut-off valve 12 returns to the inactive condition, i.e., the return duct 10 is opened. It is ensured by means of the arrangement of the return valve 20 that no air from the mixing chamber or the mixing region 18 can penetrate the pressure conduit 16. Thus, crystallization of the reducing agent in the pressure conduit 16 can be avoided. Furthermore, the mixing region 18 is automatically vaporized by the constant flow of pressurized air after the dosing pump 2 is switched off, thus preventing crystallization of the reducing agent in the mixing region 18 and in the conduit 22 that connects to it. The pressure sensor 14, which preferably emits an electrical signal, in addition to detecting the complete bleeding of the pressure conduit 16, also serves to recognize other undesirable operating conditions. Thus, a blocked return conduit 10 can be recognized by the pressure sensor 14, specifically when, given an open shut-off valve 12, the The pressure exceeds a pre-set limit value, which would not normally occur given an open return line 10. Furthermore, the pressure sensor 14 can also detect that the injector nozzle in the vehicle's exhaust gas line is blocked. Specifically, the pressure in the pressure line 16, given an open magnetic valve 26, similarly increases beyond the pre-set limit value, which would not normally occur when the injector nozzle is functioning correctly. Additionally, it is also possible to detect that the reducing agent tank 4 is empty via the pressure sensor 14. Specifically, in operation, the pressure in the pressure line 16 reduces below the pre-set limit value, which would not normally occur in normal operation given a closed return line 10. From this point on, an exemplary construction of the premixing device, consisting essentially of the mixing region 18 and the return valves 20 and 36, is described in figures 2 to 5. Figure 2 shows a sectional view of the premixing device 39 in a condition installed in a pump head. The pump head is essentially formed by a central plate 40 and an end plate 42 that rests on it, where the flow channels are formed and the premixing device 39 is arranged between plates 40 and 42. Conduit 22 on final plate 42 It is created as a connection, to which a fluid conduit flows. leads to an injector nozzle in the vehicle's exhaust gas system, it can be connected. The pressure duct 16, as well as the pressurized air duct 2 8 in the form of channels on the surface and connection holes to it, is formed on the central plate 40. The premixing device, as a central component, comprises a cylindrical casing 44 with a cylindrical outer wall 46. A neck 48, formed within the casing 44, divides the internal space of the casing 44 into two parts. The first part of the internal space, proceeding from the neck 48, widens like a funnel towards the first end side 50 of the casing 44. This region is in the actual mixing region 18 or in the mixing chamber 18 of the premixing device 39. Recesses, or openings, 52 are formed in the peripheral wall of the mixing region 18, uniformly distributed over the periphery, and serve as inlet openings for pressurized air. The opening surrounding the neck 48, inside the casing 44, serves as an inlet opening for the reducing agent in the mixing region 18. This region is closed by the piston 54 with an o-ring 56 applied in a peripheral groove.Thus, the O-ring 46, as shown in Figures 3 and 4, can support the funnel-shaped inner wall of the mixing region 19 within the housing 44, in a sealing manner. The piston 54 extends with a piston rod 55 through the neck 48 into a second region within the casing 44, to the second end side 58 which is distant from the first end side 50. A compression spring, which is supported with its first end on the neck 46, is arranged in the second part of the inner space of the casing 44. The opposite end of the compression spring 60, which is created as a helical spring, rests in a guide casing 62 around the piston rod 55, on a shoulder towards the neck 48. The guide casing 62 directs the piston rod and thus the piston 54 within the casing 44, where it rests on the inner wall of the casing 44. The guide casing 62 is supported by a spring ring 64 at a longitudinal end of the piston rod 55, which is distant from the piston 54. Thus, the compression spring 60 presses the piston rod 55 towards the second end side 58 of the casing 40, so that the piston 54, with the The O-ring 56 is pressed against the funnel-shaped or conical inner wall of the mixing region 18. In this way, the piston 54, which forms the return valve 20 in Figure 1, is held in its inactive position in the closed condition, as shown in Figures 3 and 4. The guide casing on this outer periphery comprises longitudinal grooves 66 (not shown in figures 3 to 5) through which the reducing agent can pass through the pressure conduit 16 into the casing 44 to the neck 48. The reducing agent is prevented from passing the casing 44 externally by means of the O-ring 58, encircling the casing 44 externally. In the inserted condition, the O-ring 68 seals the outer wall of the housing 44 to the inner wall of a recess, in which the housing 44 is arranged on the central plate 40. The fluid pressure in the pressure conduit 16 within the housing 44 acts on the piston 54 in the direction of the longitudinal axis of the piston rod 55. With a high fluid pressure in the pressure conduit 16, the actuating force due to the pressure on the piston 54 exceeds the spring force of the compression spring 60, so that the piston 54 with the piston rod 55 is displaced in the direction of the first end side 50 of the housing 44 and the piston 54 with the O-ring 56 rises from the conical inner wall to the mixing region 18, as shown in figures 2 and 5. Thus, an annular gap between the piston 54 or the O-ring 56 and the surrounding inner wall of the housing 44 or the mixing region 18 increases, through which the reducing agent can flow into the mixing region 18. The second return valve 3 6 of the premixing device 39 is formed by an annular elastic collar 70 which is fastened between the central plate 40 and the end plate 42. Thus, in particular, a thick region on the outer periphery of the collar 70 supports the central plate 40 as well as the end plate 42, so that the compressed air from the pressurized air duct 28 cannot exceed the outer periphery of the sleeve 70. Sleeve 70, on its inner periphery, extends like an envelope in an axial direction in direction to the final side 50 of the casing 44, so that the collar 72 is formed. This collar 72 extends in a slightly conical and inclined manner to the outer wall 46 of the casing 44 and comes to rest on it with this free terminal end. Thus, the sleeve 70 or the collar 72 is formed elastically, so that the collar, in its inactive position, is held sealingly on the outer wall 46 of the casing 44, as shown in figures 2 and 3. If pressurized air is introduced into the pressurized air duct 28, the pressurized air in the center plate 40, initially in the outer periphery 46, flows around the casing 44, since the recess that accommodates the casing 44, in the center plate 40, has a wider shape in the region furthest from the pressure duct 16 than the outer diameter of the casing 44. The compressed air then enters the region between the collar 72 of the sleeve 70 and the outer wall 46 of the casing 44, where the collar is pressed against the outer wall of the casing 46 by the air pressure, so that the annular gap 74 increases between the outer wall 46 and the inner periphery of the sleeve 70 or collar 72, through which the compressed air can travel to the recess 76 in which the casing 44 is arranged in the end plate 42.The pressurized air then flows from recess 46 through recess or openings 52 in the mixing region 18 and from there, together with the supplied reducing agent, through the duct or connection 22 further to the injector nozzle in the exhaust gas system. When the pressurized gas supply in pressurized gas conduit 28 is switched off, The sleeve 70, with its collar 72, due to its elasticity, again holds itself securely against the outer wall 46 of the sleeve 44. Because the collar 72 of the sleeve 70 projects into the recess 76, it is possible to achieve even greater pressure in the recess 76 by pressing the sleeve-shaped extension or the collar 72 of the sleeve 70 even more forcefully against the outer wall 46 and thus securely close the return valve 36. The recesses or openings 52 are designed so that they extend in the longitudinal direction of the casing 44 to the outer side of the piston 54. Furthermore, the recesses 52 are shaped so that they widen towards the casing 44, that is, towards the mixing region 18. In this way, it is possible to successfully allow the pressurized air flowing through the recesses 52 into the mixing region 18, completely traversing the entire mixing region 18 on its inner wall and, in particular, also the outer side of the piston 54, so that the residues of the reducing agent can be completely drained from the mixing region 18. LIST OF REFERENCE NUMBERS. 2 - dosing pump 4 - Reducing agent tank 5 - suction duct 6 - check valve 8 - branching point 10 - return conduit shut-off valve - pressure sensor - pressure conduit - mixing region - check valve - conduit - pressurized air supply - magneto valve - pressurized air duct - atmosphere - pressure regulator - regulating valve - check valve - channel of action - premixing device - center plate - final plate - casing - exterior wall - neck - final side - recesses piston - piston rod - O-ring - final side - compression spring - guide casing - spring ring 66 - longitudinal grooves 68 - O-ring 70 - manga 72 - collar 74 - gap 76 - recess D - Metering pump mounting limit

Claims

CLAIMS 1. "ASSEMBLY OF DOSING PUMP FOR MIXING A REDUCING FLUID AGENT IN EXHAUST GAS FLOW", comprising a premixing device (39) in which the supplied reducing agent (18) is mixed with the pressurized gas; characterized in that a first return valve (20) is arranged in the premixing element (39) in a supply conduit (15) for the reducing agent, in front of the mixing region (18) in the direction of flow.

2. "DOSING PUMP ASSEMBLY FOR MIXING A REDUCING FLUID AGENT IN EXHAUST GAS FLOW", as claimed in 1, characterized in that the return valve (20) is arranged directly adjacent to the mixing region (18), where the reducing agent is mixed with the pressurized gas.

3. "DOSING PUMP ASSEMBLY FOR MIXING A REDUCING FLUID AGENT IN EXHAUST GAS FLOW", as claimed in 1 or 2, characterized in that the first return valve (20) is an integral component of a mixing chamber delimiting the mixing region (18).

4. "DOSING PUMP ASSEMBLY FOR MIXING A REDUCING FLUID AGENT IN EXHAUST GAS FLOW", as claimed in 1 or 2, or 3, characterized in that the mixing chamber comprises an inlet opening (48) for the reducing agent, which is closed by the first return valve. (20.54).

5. "ASSEMBLY OF DOSING PUMP FOR MIXING A REDUCING FLUID AGENT IN EXHAUST GAS FLOW", as claimed in 1 or 2, or 3, or 4, characterized in that the supply conduits (16, 28) of the reducing agent and the pressurized gas to the mixing region (18) are arranged concentrically to each other.

6. "DOSING PUMP ASSEMBLY FOR MIXING A REDUCING FLUID AGENT IN EXHAUST GAS FLOW", as claimed in 5, characterized in that the inlet opening (48) for the reducing agent is formed concentrically on a final side of the mixing chamber (18).

7. "DOSING PUMP ASSEMBLY FOR MIXING A REDUCING FLUID AGENT IN EXHAUST GAS FLOW", as claimed in 3 or 4, or 5, or 6, characterized in that the mixing chamber (18) comprises a perimeter wall in which inlet openings (52) are formed for the pressurized gas.

8. "DOSING PUMP ASSEMBLY FOR MIXING A REDUCING FLUID AGENT IN EXHAUST GAS FLOW", as claimed in 3 or 4, or 5, or 6, characterized in that a final side of the mixing chamber (18) is created in the form of a funnel, where a plate-shaped closing element (54) of the first return valve (20) is arranged in the funnel.

9. "DOSING PUMP ASSEMBLY FOR MIXING A REDUCING FLUID AGENT IN EXHAUST GAS STREAM", as claimed in 1, 2, 3, or 4, or 5, or 6, or 7, or 8, characterized in that the return valve (20) is held in a closed position by the spring element (60) and can be moved to an open position by means of the fluid pressure of the reducing agent against the force of the spring element (60).

10. "DOSING PUMP ASSEMBLY FOR MIXING A REDUCING FLUID AGENT IN EXHAUST GAS FLOW", as claimed in 1 or 2, or 3, or 4, or 5, or 6, or 7, or 8, or 9, characterized in that a pre-mixing device (39) comprises a second return valve in a supply conduit (28) for the pressurized gas.

11. "ASSEMBLY OF DOSING PUMP FOR MIXING A REDUCING FLUID AGENT IN EXHAUST GAS FLOW", as claimed in 10, characterized in that the second return valve (36) is formed by an elastic sealing element (70, 72), which can be induced to hold itself by sealing on the wall (46) of the supply conduit.

12. "ASSEMBLY OF DOSING PUMP FOR MIXING A REDUCING FLUID AGENT IN EXHAUST GAS FLOW", as claimed in 11, characterized in that the elastic sealing element (70, 72) is held by sealing on the wall (46) of the supply conduit by means of induction and can be moved to an open position away from the wall (45) by means of the pressure of the pressurized gas, acting in the direction of flow towards the mixing region (18) against induction.

13. "DOSING PUMP ASSEMBLY FOR MIXING A REDUCING FLUID AGENT IN EXHAUST GAS FLOW", as claimed in 11 or 12, characterized in that the wall is preferably cylindrical, the outer wall (46) of a component (44) containing the mixing region (18) and the first return valve (20).

14. "DOSING PUMP ASSEMBLY FOR MIXING A REDUCING FLUID AGENT IN EXHAUST GAS FLOW", as claimed in 13, characterized in that the sealing element of the second return valve is created as an annular sleeve (70, 72:1) extending in the direction of the gas flow. pressurized inclined towards the wall (46).