Dosing system with dosing pump with ejecting spring

Description

[0001] The invention relates to a reducing agent dosing system for introducing a reducing agent into the exhaust gas stream of an internal combustion engine for selective catalytic reduction, comprising at least one feed pump, by means of which reducing agent is sucked from a reducing agent tank via a suction line and conveyed via at least one pressure line and introduced into the exhaust gas stream of the internal combustion engine via at least one nozzle, wherein the feed pump is a reciprocating piston pump.

[0002] Furthermore, the invention relates to a method for operating a reducing agent dosing system for injecting a reducing agent into the exhaust gas stream of an internal combustion engine for selective catalytic reduction with at least one feed pump, by means of which reducing agent is sucked from a reducing agent tank via a suction line, conveyed via at least one pressure line and introduced into the exhaust gas stream of the internal combustion engine via at least one dosing point.

[0003] Such dosing systems and methods for operating such dosing systems are known from DE 10 2007 035 938 A1 and DE 10 2011 01231 A1. The reducing agent is typically introduced into the exhaust stream of the combustion engine in the form of an aerosol, with the aerosol evaporating due to the high exhaust temperatures.

[0004] Selective catalytic reduction (SCR) catalysts are used to reduce nitrogen oxide emissions from diesel engines, combustion plants, waste incineration plants, industrial facilities, and the like. A reducing agent is injected into the exhaust system using a dosing device. The reducing agent is ammonia, an ammonia solution, or another reducing agent.

[0005] Since the transport of ammonia in vehicles is safety-critical, urea is used in an aqueous solution with a typical 32.5% urea content, particularly in accordance with DIN 70070. In the exhaust gas, the urea decomposes into gaseous ammonia and CO2 at temperatures above 150°C. The parameters for the decomposition of urea are essentially time (evaporation and reaction time), temperature, and droplet size of the injected urea solution. In these SCR catalysts, nitrogen oxide emissions are reduced by approximately 90% through selective catalytic reduction.

[0006] The term "reducing agent solution" or "reducing agent" encompasses any reducing agent suitable for selective catalytic reduction; preferably, a urea solution according to DIN 70070 is used for this purpose. However, the invention is not limited to this. The terms "reducing agent dosing system" and "dosing system" are used synonymously within the meaning of the invention. The terms "nozzle" and "injection nozzle" are also used synonymously.

[0007] After the urea is injected in aqueous solution into the exhaust system, ammonia (NH 3 ) must first be formed for the SCR reaction. The reducing ammonia is released through the thermal decomposition of urea (thermolysis) and the hydrolysis of the resulting isocyanic acid. The treatment is therefore divided into the following two reaction steps: Thermolysis (NH 2 ) 2 CO → NH 3 + HNCO Hydrolysis HNCO + H 2 O → NH 3 + CO 2

[0008] In the first reaction, thermolysis, urea is converted into ammonia (NH 3 ) and isocyanic acid (HNCO) under the influence of temperature. In the second step, hydrolysis occurs in the presence of water, in which the isocyanic acid is also converted into ammonia, forming carbon dioxide (CO 2 ). To ensure the desired course of these reactions, the required amount of reducing agent solution and the generation of a finely dispersed aerosol are required.

[0009] In the known reducing agent dosing systems for injecting a reducing agent into the exhaust gas stream of an internal combustion engine for selective catalytic reduction, a distinction can be made between systems in which the dosing quantity is defined via the feed pump and systems in which a pre-pressure is generated and the dosing quantity is defined via a dosing valve.

[0010] The problem with both systems is the uniform and continuous provision of the required flow rates and the generation of the desired finely dispersed aerosol.

[0011] The object of the invention is therefore to further develop a reducing agent dosing system for introducing a reducing agent into the exhaust gas flow of an internal combustion engine for selective catalytic reduction in such a way that the required delivery quantities can be provided under a uniform pressure.

[0012] This object is achieved according to the invention by a reducing agent dosing system according to claim 1 and a method for operating a reducing agent dosing system according to claim 10. Advantageous developments of the invention are specified in the dependent claims. For the purposes of the invention, the terms "reducing agent dosing system" and "dosing system" are used synonymously.

[0013] Particularly advantageous in the reducing agent dosing system for injecting a reducing agent into the exhaust gas flow of an internal combustion engine, in particular of a vehicle, for selective catalytic reduction with at least one feed pump, by means of which reducing agent is sucked in from a reducing agent tank via a suction line and fed via at least one pressure line to at least one nozzle for introduction into the exhaust gas flow of the internal combustion engine, is that the feed pump is a reciprocating piston pump, wherein the feed stroke and the suction stroke are carried out simultaneously by a stroke of the piston up to the top dead center by means of a spring, wherein after the end of the stroke the piston is retracted electromagnetically against the spring force of the spring up to the bottom dead center by means of a switchable coil and the spring is tensioned.

[0014] According to the invention, the feed pump is designed so that the delivery stroke and the suction stroke are executed simultaneously by a spring. The spring-driven feed allows for a uniform pressure during the injection phase, independent of line variations and any partial blockages in the dosing line and nozzle.

[0015] Once the dosing process is complete, the piston and thus the spring are electromagnetically retracted by the coil, thereby tensioning the spring and simultaneously recirculating the reducing agent within the feed pump. During the feed stroke, the spring again ensures a very smooth and largely continuous injection process without overloading the nozzle.

[0016] Preferably, the pressure line opens into a spray nozzle, through which the reducing agent can be introduced into the exhaust stream of the combustion engine. Spray nozzles require a flow that is as continuous as possible to achieve good spray quality. This is ensured by the feed pump according to the invention and the feed by means of the spring.

[0017] Preferably, the pressure line opens into a spray nozzle, which has a check valve. The provision of a check valve can prevent dripping.

[0018] Preferably, the pressure line opens into a spray nozzle, wherein the spray nozzle is formed by a swirl nozzle. The use of a swirl nozzle achieves a very good spray quality when injecting the reducing agent into the exhaust stream of the combustion engine.

[0019] The pressure line between the feed pump and the nozzle is preferably designed to be pressure-resistant. This is advantageous because the flow rate required by the nozzle is quickly achieved and the spray quality is produced. The spraying process must also be completed quickly to avoid a deterioration in spray quality at the end of injection. This is ensured by a pressure-resistant pressure line between the feed pump and the nozzle.

[0020] Preferably, the pressure line between the feed pump and the nozzle has at least one volume expansion element.

[0021] Preferably, the pressure line between the feed pump and the nozzle is designed to be pressure-resistant up to a defined limit pressure and has at least one volume expansion element which releases an additional volume for pressure equalization above the limit pressure.

[0022] The reducing agent is typically a urea-water solution with a 32.5% urea content. This urea-water solution freezes at -11°C and then expands by approximately 10%. To make the reducing agent dosing system frost-resistant, one or more volume expansion elements are installed in the pressure line. These elements are pressure-resistant in the dosing pressure range up to a defined limit pressure of, for example, 10 bar. Above this limit pressure of, for example, 10 bar, they release additional volume for pressure equalization in frost conditions.

[0023] Preferably, a control device is arranged by means of which the feed pump is controlled.

[0024] Particularly preferably, a control device is arranged by means of which the feed pump is monitored; in particular, the feed pump can be monitored by means of an evaluation of the piston movement.

[0025] With this setup, dosing can be monitored via the pump by recording the piston stroke and evaluating it using the control unit. Based on the evaluation of the piston movement, blockages and line breaks can be reliably detected.

[0026] Particularly advantageous in the method for operating a reducing agent dosing system for injecting a reducing agent into the exhaust gas flow of an internal combustion engine, in particular of a vehicle, for selective catalytic reduction with at least one feed pump, by means of which reducing agent is sucked from a reducing agent tank via a suction line from the tank, conveyed via at least one pressure line and introduced into the exhaust gas flow of the internal combustion engine via at least one nozzle, is that a reciprocating piston pump is used as the feed pump, wherein the delivery stroke and the suction stroke are carried out simultaneously by a stroke of the piston up to the top dead center by means of a spring, wherein after the end of the stroke the piston is retracted electromagnetically against the spring force of the spring up to the bottom dead center by means of a switchable coil and the spring is tensioned.

[0027] The reducing agent is preferably introduced into the exhaust stream via a swirl nozzle. As explained above, this ensures particularly good spray quality.

[0028] Preferably, the feed pump is controlled by a control unit. This control unit allows for precise control of the feed pump, taking into account other influencing parameters such as exhaust gas mass flow, exhaust gas temperature, etc.

[0029] Particularly preferably, the feed pump is monitored by a control unit; in particular, the feed pump can be monitored by evaluating the piston movement. With this arrangement, dosing can be monitored via the pump by detecting the piston stroke and evaluating it using the control unit. Based on the evaluation of the piston movement, blockages and line breaks can be reliably detected.

[0030] An embodiment of the invention is illustrated in the figures and explained below. They show: Fig. 1A schematic representation of a reducing agent dosing system; Fig. 2A section of the feed pump of the reducing agent dosing system according to Figure 1 .

[0031] Figure 1shows a schematic representation of a reducing agent dosing system for injecting a reducing agent into the exhaust stream of a vehicle's internal combustion engine (not shown) for selective catalytic reduction, comprising a feed pump 2, by means of which reducing agent is sucked from a reducing agent tank 1 via a suction line 3 and conveyed via a pressure line 4 to a nozzle 5 for introduction into the exhaust stream of the internal combustion engine. In this exemplary embodiment, the reducing agent dosing system is thus formed by the feed pump 2, the suction line 3, the pressure line 4, and the nozzle 5. In a further embodiment (not shown), the tank 1 is also an integral component of the reducing agent dosing system.

[0032] The feed pump 2 is in Figure 2 shown in a sectional view. The Figure 2A suction line (not shown) opens into the reducing agent inlet 21 of the feed pump 2. The reducing agent is sucked into the feed pump 2 via the open intake valve 22. The overflow valve 23 is closed during a delivery stroke.

[0033] To execute the simultaneous suction stroke and delivery stroke of the pump piston 24, the pump piston 24 is displaced by the spring 25 toward the top dead center of the pump piston 24. Due to the spring force of the spring 25, a uniform pressure is always maintained during the delivery stroke. The reducing agent is delivered via the open outlet valve 27 via the pressure line 4 to the swirl nozzle 5. The reducing agent is injected via the swirl nozzle 5 into the exhaust stream of an internal combustion engine (not shown in the figure).

[0034] After the pump piston 24 has reached top dead center and the delivery stroke has ended, the pump piston is magnetically retracted to bottom dead center by means of the coil 26, thereby tensioning the spring 25. This results in a recirculation of the reducing agent sucked in during the previously simultaneously executed suction stroke and delivery stroke within the delivery pump 2. After the coil 26 is deactivated, the next suction stroke and delivery stroke occur due to the spring force of the tensioned spring 25.

[0035] A pressure relief module 40 with an opening pressure of > 10 bar is integrated into pressure line 4 to prevent frost damage. If the melting temperature of the reducing agent being pumped falls below -11°C for the reducing agent typically used, the reducing agent freezes and expands by up to 10%. The pressure relief module 40 in pressure line 4 thus serves to prevent frost damage by releasing an additional volume when the limit pressure of 10 bar is exceeded.

[0036] It has surprisingly been shown that pushing out the feed pump 2 via the spring 25 produces a very good and uniform spray. During the delivery stroke, a virtually constant pressure is maintained, which cannot be achieved with pulsed dosing using a magnetic piston pump. Swirl nozzles such as the swirl nozzle 5 used here are usually operated with a constant pre-pressure. With pulsating delivery, spray formation is generally problematic because the nozzle quickly goes outside its operating range. Pushing out the feed pump 2 via the spring 25, on the other hand, offers the advantage of delivery with constant force and thus with constant pressure on the delivery side of the feed pump 2. This ensures optimal spray formation.

Claims

1. Reducing agent metering system for injecting a reducing agent into the exhaust gas flow of an internal combustion engine, in particular of a vehicle, for selective catalytic reduction, with at least one feed pump (2), by means of which reducing agent is suctioned from a reducing agent tank (1) via a suction line (3) and is fed via at least one pressure line (4) to at least one nozzle (5) for introduction into the exhaust gas flow of the internal combustion engine, wherein the feed pump (2) is a reciprocating piston pump, characterized in that the delivery stroke and the suction stroke are executed simultaneously by a stroke of the piston (24) to top dead center by means of a spring (25), wherein the piston (24) is retracted electromagnetically against the spring force of the spring (25) to the bottom dead center after completion of the stroke by means of a switchable coil (26) and the spring (25) is tensioned and the reducing agent is simultaneously circulated within the delivery pump during this process.

2. Reducing agent metering system according to claim 1, characterized in that the pressure line (4) opens into a spray nozzle (5), via which the reducing agent can be introduced into the exhaust gas flow of the internal combustion engine.

3. Reducing agent metering system according to claim 1 or claim 2, characterized in that the pressure line (4) opens into a spray nozzle (5), wherein the spray nozzle (5) has a non-return valve.

4. Reducing agent metering system according to any one of the previous claims, characterized in that the pressure line (4) opens into a spray nozzle (5), wherein the spray nozzle (5) is formed by a swirl nozzle.

5. Reducing agent metering system according to any one of the preceding claims, characterized in that the pressure line (4) between the feed pump (2) and the nozzle (5) is configured to be pressure-resistant.

6. Reducing agent metering system according to any one of the preceding claims, characterized in that the pressure line (4) between the feed pump (2) and the nozzle (5) has at least one volume expansion element (40).

7. Reducing agent metering system according to any one of the preceding claims, characterized in that the pressure line (4) between the feed pump (2) and the nozzle (5) is configured to be pressure-resistant up to a defined limit pressure and has at least one volume expansion element (40) which releases an additional volume for pressure equalization above the limit pressure.

8. Reducing agent metering system according to any one of the preceding claims, characterized in that a control unit is arranged by means of which the feed pump (2) is controlled.

9. Reducing agent metering system according to any one of the preceding claims, characterized in that a control unit is arranged, by means of which the feed pump (2) is monitored, in particular in that the feed pump (2) is monitored by means of an evaluation of the piston movement.

10. Method for operating a reducing agent metering system for injecting a reducing agent into the exhaust gas flow of an internal combustion engine, in particular a vehicle, for selective catalytic reduction with at least one feed pump (2), by means of which reducing agent is suctioned out of a reducing agent tank (1) via a suction line (3) from the tank, conveyed via at least one pressure line (4) and introduced into the exhaust gas flow of the internal combustion engine via at least one nozzle (5), wherein a reciprocating piston pump is used as the feed pump (2), characterized in that the feed stroke and the suction stroke are executed simultaneously by a stroke of the piston (24) to top dead center by means of a spring (25), wherein the piston (24) is retracted electromagnetically by means of a switchable coil (26) against the spring force of the spring (25) to bottom dead center after completion of the stroke and the spring (25) is tensioned and the reducing agent is simultaneously circulated within the feed pump during this process.

11. Method according to claim 10, characterized in that the reducing agent is introduced into the exhaust gas flow via a swirl nozzle (5).

12. Method according to claim 10 or 11, characterized in that the feed pump (2) is controlled by means of a control unit.

13. Method according to any one of claims 10 to 12, characterized in that the feed pump (2) is monitored by means of a control unit, in particular in that the feed pump (2) is monitored by means of an evaluation of the piston movement.