Exhaust aftertreatment arrangement and method for dosing a reducing agent into the exhaust stream of an internal combustion engine

Abstract

Exhaust aftertreatment arrangement of an internal combustion engine (50), comprising a delivery unit (10) for a reducing agent (12), a storage container (8) for the reducing agent (12), a storage tank (30) for the reducing agent (12) and an injection valve (20) for metering the reducing agent (12) into an exhaust stream (60) of the internal combustion engine (50), wherein the storage tank (30) is arranged between the delivery unit (10) and the injection valve (20), wherein the storage tank (30) has a piston (32), wherein the piston (32) is movable in the storage tank (30) and delivers the reducing agent (12) from the storage tank (30) towards the exhaust stream (60), wherein auxiliary devices (35) for guiding and / or moving the piston (32) are arranged on the storage tank (30), characterized in that the auxiliary devices (35) comprise an electromagnet (96) or a linear motor (97).

Description

State of the art

[0001] The invention relates to an exhaust gas aftertreatment system of an internal combustion engine and to a method for metering a reducing agent into the exhaust system of an internal combustion engine according to the preamble of the independent claims. In internal combustion engines, for example in motor vehicles, the pollutant NOx, among others, must be reduced due to the stricter emissions legislation that will be introduced in the coming years. One method used is the so-called selective catalytic reduction (SCR process). In the SCR process, the pollutant NOx is reduced to nitrogen and water using a liquid reducing agent. DE 103 46 220 A1 discloses an exhaust gas aftertreatment system in which a liquid reducing agent is compressed by a delivery unit and fed to a storage volume, wherein the reducing agent is metered from the storage volume into the exhaust system of the internal combustion engine by means of an injection valve.In diesel engines, particulate filters are also frequently used to filter soot particles from the exhaust gas. To regenerate such a particulate filter, it is known from DE 10 2008 048 463 A1 to meter a fuel into the exhaust system of the internal combustion engine. The fuel is taken from the low-pressure circuit of a common-rail injection system of the internal combustion engine and is thus pressure-limited. DE 10 2008 000 594 A1 describes a device for emptying a reducing agent device of an internal combustion engine, DE 10 2009 014 436 A1 describes a delivery device for delivering an aqueous liquid with a reservoir interacting with a vent valve, and DE 198 19 579 C1 describes a device for exhaust gas aftertreatment with a pressure reservoir and a pressure sensor. revelation

[0002] The exhaust gas aftertreatment arrangement according to the invention and the method according to the invention for metering a reducing agent into the exhaust system of an internal combustion engine have the advantage that the accumulator has a piston, wherein the piston is movable in the accumulator and pumps the reducing agent from the accumulator towards the exhaust system. This allows the delivery unit to be designed to be small and cost-effective. In addition, a pressure can be achieved that is higher than the pressure available in the low-pressure circuit of a common rail system. Because the volume of the accumulator is reduced by the piston, the reducing agent pressure does not collapse immediately or only slightly, even when the reducing agent is metered into the exhaust system, so that continuous resupply of the reducing agent by a delivery unit is not required, which increases energy efficiency.To prevent uncontrolled injection of the reducing agent into the exhaust system, the injection valve should be designed as an active valve. In this case, aids for guiding and / or moving the piston are arranged on the accumulator. The piston can be moved hydraulically, pneumatically or mechanically and, with a sufficiently powerful aid, additional pressure can be built up in the accumulator. By guiding the piston, tilting and the associated increased force or jamming can be prevented. It is particularly advantageous if the aids comprise an electromagnet or a linear motor. By means of the electromagnet, preferably a linear motor, which acts on the piston, the piston can be moved, in particular against a provideable spring in the accumulator and can thus be preloaded similar to a crossbow.By deactivating the electromagnet or linear motor, the piston is accelerated by the spring, pushing the reducing agent toward the injector. A planned connection of the spring chamber to the return line ensures lubrication of the piston's sliding surfaces. Excessive leakage can be avoided by ensuring sufficient guide lengths.

[0003] The measures listed in the subclaims enable advantageous further developments and improvements of the proposed exhaust gas aftertreatment device and of the method for metering a reducing agent into the exhaust system.

[0004] An advantageous development consists in the accumulator having a spring which is operatively connected to the piston. A spring is a simple and effective means of exerting a force on the piston and displacing the piston in such a way that the reducing agent is delivered in the direction of the injection valve. The spring force can continue to exert a force on the piston and thus pressure on the reducing agent when the reducing agent is withdrawn from the accumulator. The spring should be dimensioned such that the spring is compressed under a reducing agent pressure generated by the delivery unit and relaxes accordingly when the delivery unit is switched off and exerts a force on the piston, whereby the reducing agent pressure generated by the spring and the piston roughly corresponds to the injection pressure of the exhaust gas aftertreatment system.

[0005] A further advantageous development consists in the provision of a check valve between the delivery unit and the reservoir. An injection valve arranged between the delivery unit and the reservoir, in particular an injection valve at the reservoir inlet, prevents or reduces backflow of the reducing agent from the reservoir toward the delivery unit, thus preventing or reducing pressure loss for the reducing agent in the reservoir.

[0006] Furthermore, it is advantageous for the delivery unit to comprise a pump. A pump is particularly suitable for building up the necessary reducing agent pressure to deliver the reducing agent into the reservoir. A discontinuously delivering pump is particularly advantageous, as it supplies a corresponding amount of reducing agent as needed and can otherwise be switched off, requiring no energy.

[0007] In a further development, it is advantageously provided that the piston separates a reducing agent chamber and a control chamber in the accumulator. This allows, for example, a gas to be compressed in the control chamber, whereby a pressure is built up in the control chamber which acts on the piston alone, in addition to the spring force or in addition to the force of an auxiliary device and conveys the reducing agent in the direction of the injection valve. It is particularly advantageous if the control chamber has a connection for a pressurised medium, in particular compressed air. By means of an external connection for a pressurised fluid, the force on the piston can be increased compared to a compression of the medium, whereby the force can also be exerted when the piston has already been displaced in the direction of the reducing agent chamber.

[0008] In a further development, it is provided that a pressure sensor is arranged on the accumulator for detecting the reducing agent pressure in the accumulator.

[0009] Such a pressure sensor can, for example, provide a signal to control the amount of reducing agent at the injection valve, but also to enable on-board diagnostics and functional testing of the exhaust aftertreatment system.

[0010] It is advantageous if the pressure sensor detects the reducing agent pressure in the accumulator and compares the pressure sensor with a reference pressure, such as the ambient pressure. This comparison can be used to determine whether the pressure sensor is still functioning properly, particularly when the internal combustion engine is started and the accumulator is empty. The function of the pressure sensor can also be tested during operation by increasing the pressure using the delivery device until the piston in the accumulator reaches its end stop. This mechanically / hydraulically specified pressure value can be compared with the sensor signal.

[0011] Furthermore, the pressure sensor can be used to detect the buildup of reducing agent pressure in the accumulator and compare it with the delivery line of the reducing agent delivery unit. Depending on the delivery rate of the delivery unit, preferably a stroke-by-stroke controllable piston pump, a pressure increase occurs when the accumulator is filled. By comparing the delivery rate and the pressure increase, any leak in the accumulator can be detected, thus identifying a functional impairment or failure of the exhaust gas aftertreatment system. Such a deviation can, for example, be forwarded to an error log and / or activate a warning light for the driver, indicating a defect in the exhaust gas aftertreatment system.

[0012] Furthermore, it is advantageously provided that when the reducing agent is metered into the exhaust system, a comparison is made between a drop in the reducing agent pressure in the accumulator due to the metered addition of the reducing agent and the metered-in amount of the reducing agent. This functionality allows the pressure sensor to detect whether the injected amount of reducing agent corresponds to the actually required amount of reducing agent.

[0013] A further advantageous development consists in that if a reference value for the reducing agent pressure in the accumulator is exceeded, the supply of reducing agent to the accumulator is stopped, for example by switching off the delivery unit, in particular a pump of the delivery unit. This maximum permissible pressure can also be detected by the pressure sensor on the accumulator and can advantageously prevent damage to the accumulator or the injection valve due to excessively high reducing agent pressure, as well as be used to control the delivery unit in order to switch off the delivery unit when the maximum reducing agent pressure in the accumulator is reached, thus saving energy. In addition, a second reference value can be specified, from which point the delivery unit is reactivated and refills the accumulator.

[0014] In some embodiments, it is advantageously provided that, in the event of a detected leak, the piston remains in the lower end position of the accumulator, i.e. the end position facing the injection valve, and thus seals the inlet to the accumulator, so that a refilling of the accumulator is prevented. Drawings

[0015] Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description. Fig. 1 shows an internal combustion engine with an exhaust aftertreatment arrangement. Fig. 2 shows another exhaust aftertreatment arrangement. Fig. 3 shows a memory of an exhaust aftertreatment arrangement. Fig. 4 shows the check valve of the accumulator Fig. 3. Fig. 5 shows a reservoir of an exhaust aftertreatment arrangement with means for moving a piston in the reservoir. Short description of the drawings

[0016] The invention and advantageous embodiments according to the features of the further claims are explained in more detail below with reference to the exemplary embodiments illustrated in the drawings. In the figures, identical components or components with identical functions are designated by the same reference numerals.

[0017] In the Fig. 1 shows an internal combustion engine 50 with an exhaust system 60, wherein an exhaust aftertreatment arrangement is arranged on the exhaust system 60. The exhaust aftertreatment arrangement comprises a reservoir 8 for a reducing agent 12, which is connected via a line 9 to a low-pressure circuit 15 of a fuel injection system. The low-pressure circuit 15 is connected via a further line 16 to a delivery unit 10, which includes a pump 80. The delivery unit 10 is connected via a line 18 to an accumulator 30, wherein a piston 32 and a spring 33 are arranged in the accumulator 30. At an inlet of the accumulator 30 there is a check valve 45, which prevents a backflow of reducing agent 12 from the accumulator 30 in the direction of the delivery unit 10. The accumulator 30 is connected via a pressure line 46 to an injection valve 20, which enables the metering of reducing agent 12 into the exhaust system 60.Additionally, a pressure sensor 47 is attached to the accumulator 30, via which a reducing agent pressure in a reducing agent chamber 38 of the accumulator 30 can be detected. The piston 32 divides the accumulator 30 into a reducing agent chamber 38 and a control chamber 39, wherein the control chamber 39 is connected by means of a return line 19 to a return line of the low-pressure circuit 15 and thus to the reservoir 8. The injection valve 20 and the accumulator 30 are arranged in a common housing 29, but alternatively they can also be surrounded by two separate housings. The injection valve 20, the pressure sensor 47, and the delivery unit 10 are connected to a control unit 70 via signal lines 71, 72, 73. The injection valve 20 is preferably cooled on the exhaust line 60, wherein the cooling is particularly preferably carried out with water, for example from the cooling water circuit of the internal combustion engine 50.

[0018] The reducing agent 12, here fuel, in particular diesel fuel, is sucked from the reservoir 8 and fed via line 9 to the low-pressure circuit 15 of the fuel injection system. From the low-pressure circuit, in which the reducing agent 12 circulates at a pressure of approximately 1 bar to 10 bar, the reducing agent 12 is withdrawn via line 16 and fed to the pump 80 of the delivery unit 10, which increases the reducing agent pressure to a pressure level of approximately 20 to 50 bar, for example, approximately 30 bar, and feeds the reducing agent 12 to the accumulator 30 via line 18. The reducing agent pressure presses the piston 32 in the accumulator 30 against the spring 33, expanding the volume of the reducing agent chamber 38.If a metering request is transmitted from the control unit 70 to the injection valve 20 via the signal line 73, the injection valve 20 opens and enables the metering of reducing agent 12 from the accumulator 30, in particular from the reducing agent chamber 38 of the accumulator 30, so that the reducing agent 12 is conveyed from the accumulator 30 via the pressure line 46 to the injection valve 20. The spring 33 presses on the piston 32, whereby the pressure in the reducing agent chamber 38 of the accumulator 30 remains almost constant even when the volume is reduced by the metering. The check valve 45 prevents the reducing agent 12 from flowing back from the accumulator 30 into the line 18. The reducing agent pressure in the reducing agent chamber 38 is detected by the pressure sensor 47 and transmitted to the control unit 70 via the signal line 72. Furthermore, the power of the pump 80 in the delivery unit 10 can be controlled or regulated via the signal line 71.

[0019] One application example for such an exhaust aftertreatment system is the reduction of nitrogen oxides in the exhaust gases of diesel engines. Direct supply to the injection valve 20 from the low-pressure circuit 15 of the fuel injection system is not possible in this case, since the reducing agent 12 must first be compressed by the delivery unit 10 and / or the accumulator 30 or auxiliary devices 35 interacting with the accumulator 30 to a reducing agent pressure higher than that prevailing in the low-pressure circuit 15. In this case, reducing agent 12 is metered into the exhaust system 60 by means of the injection valve 20 at short time intervals of approximately 2 to 5 seconds for 20 to 50 milliseconds each.A continuously delivering pump 80 without a reservoir 30 arranged between the pump 80 and the injection valve 20 is not very energy-efficient, since this pump 80 would have to deliver continuously; otherwise, the reducing agent pressure would collapse upon injection of reducing agent 12. This problem can be avoided by a demand-dependent pump 80, in particular a magnetic pump, and a reservoir 30, in particular a piston accumulator, arranged between the pump 80 and the injection valve 20.

[0020] In Fig. 2 shows a further exhaust gas aftertreatment arrangement. In this exemplary embodiment, the low-pressure circuit 15 comprises a pre-feed pump 13, which feeds the reducing agent 12 from the storage tank 8 into the low-pressure circuit 15 and from there on to a high-pressure pump (not shown). The low-pressure circuit 15 is connected to the pump 80 via the line 16, whereby the pump 80 is part of a feed unit 10, which can also have further control means in addition to the pump 80. The pump 80 is supplied by the pre-feed pump 13 from the low-pressure circuit 15 with reducing agent, which is at a low pressure of approximately 2 to 10 bar. Alternatively, the pump 80 can also be fed from the fuel return line of a fuel injection system, whereby the reducing agent pressure here is slightly above the ambient pressure in order to feed the reducing agent 12 back into the storage tank 8.In this exemplary embodiment, the pump 80 is designed as a magnetic pump, which delivers reducing agent 12 into the accumulator 30 as needed. In this exemplary embodiment, the check valve 45 is not arranged at the inlet of the accumulator 30, but rather at the pressure-side outlet 82 of the pump 80. The piston of the accumulator 30 is cup-shaped, with the spring 33 arranged in a recess 36 of the piston. Due to the cup-shaped design of the piston 32, the piston 32 is guided in the accumulator 30, and only minimal leakage occurs between the reducing agent chamber 38 of the accumulator 30 and the piston.In this way, the reducing agent pressure in the accumulator 30 can be kept almost constant. However, when the delivery unit 10 is shut down, the reducing agent pressure in the accumulator 30 slowly decreases, so that the accumulator 30 is emptied when the internal combustion engine 50 is shut down for a longer period of time, and the reducing agent 12 flows from the accumulator 30 back into the storage tank 8 via the return line 19. The reducing agent pressure in the accumulator 30, in particular in the reducing agent chamber 38, can be detected via the pressure sensor 47.

[0021] On-board diagnostics and / or functional monitoring of the exhaust gas aftertreatment system is possible via the pressure sensor 47. In a first step, the reducing agent pressure in the accumulator 30 can be compared with the ambient pressure via the pressure sensor 47 when the internal combustion engine is started, i.e. when the accumulator 30 has been emptied via the leak along the piston 32. If the determined reducing agent pressure deviates from the ambient pressure, this can indicate a malfunction of the pressure sensor 47 or damage to the accumulator 30, for example due to jamming of the piston 32 or a blocked return line 19. Furthermore, it is possible to compensate for the pressure build-up of the reducing agent pressure in the accumulator 30 as a function of the delivery rate of the pump 80 or the amount of reducing agent 12 delivered by the pump 80.If the pressure build-up when filling the accumulator 30 falls short of the pressure build-up expected in connection with the delivery capacity of the pump 80, this can be inferred from an inadmissible leak downstream of the pump 80. This can indicate either a defective, non-closed injection valve 20, a defective line 18, a defective pressure line 46, or an inadmissible leak at the accumulator 30. As a further functionality, the pressure sensor 47 can detect a maximum permissible fill level in the accumulator 30. If the reducing agent chamber 38 of the accumulator 30 is completely filled, i.e., either the spring 33 or the cup-shaped piston 32 reaches a stop, the pump 80 delivers against the compressibility of the reducing agent 12 in the reducing agent chamber 38. This leads to a sharp increase in the reducing agent pressure in the reducing agent chamber 38.The pump 80 can now either be switched off mechanically because it can no longer pump against the compressed reducing agent due to a lack of power, or preferably switched off electrically via the detected increase in the reducing agent pressure. This can prevent hydraulic overload of the accumulator 30 and / or the lines 18, 46. Since this increase in pressure occurs at a pressure determined by the mechanical / hydraulic design of the accumulator 30, this pressure value can also be used to calibrate the pressure sensor 47. As a further functionality, the signal from the pressure sensor 47 makes it possible to switch the pump 80 back on when the reducing agent pressure in the reducing agent chamber 38 of the accumulator 30 falls below a certain threshold.Additionally, it is possible to compare the pressure drop caused by the withdrawal of reducing agent 12 from the reservoir 30 during metering through the injection valve 20 with the injected amount of reducing agent 12, or with the delivered amount of reducing agent 12, according to the number of delivery strokes and the stroke volume. This provides another way to detect leaks in the proposed exhaust aftertreatment system.

[0022] In Fig. 3 shows another exhaust gas aftertreatment arrangement. The accumulator 30 is constructed in the form of a syringe, with a check valve 45 arranged at the inlet of the accumulator 30. The reducing agent chamber 38 of the accumulator 30 is filled via a supply line 44, at the end of which facing the accumulator 30 the check valve 45 is arranged. The accumulator 30 further has a piston 32, which is displaceable within a range of movement between the two end positions a and b within the preferably cylindrical housing 29 of the accumulator 30. The reducing agent chamber 38 is connected to the injection valve 20 via a pressure line 46, wherein the injection valve 20 can be designed either as a solenoid valve or as a piezoelectrically switched valve. Within the housing 29 of the accumulator 30, a control chamber 39 is separated by the piston 32, which has a connection opening 42.Piston 32 can be loaded both hydraulically and pneumatically via connection opening 42. This makes it possible to increase the reducing agent pressure in reducing agent chamber 38 relative to the reducing agent pressure in supply line 44. In this exemplary embodiment, a pre-feed pump or the low-pressure circuit of a fuel injection system can serve as the delivery unit 10; however, it is of course also possible to fill accumulator 30 via a separate pump. Alternatively, injection valve 20 and accumulator 30 can also form a single unit, in which case pressure line 46 can be omitted.

[0023] During operation of the exhaust aftertreatment system, the reducing agent chamber 38 of the accumulator is charged by the delivery unit 10. This effect, as well as the flow of the reducing agent 12 into the reducing agent chamber 38, can be further enhanced by a negative pressure in the control chamber 39, which pulls the piston 32 upwards. At certain time intervals, for example, every 5 seconds, or when the piston 32 has reached its end position a, a control medium, for example, compressed air, is introduced into the control chamber 39, thus pushing the piston 32 toward the injection valve 20, whereby the reducing agent 12 is metered from the accumulator 30 into the exhaust system 60.

[0024] In Fig. 4 is the check valve of the arrangement according to Fig. 3 in detail. The check valve 45 comprises a valve body 59 in which a sealing member 52 is slidably arranged. The sealing member 52 is pressed against a sealing seat 54 in the valve body 59 by a spring 53. The spring 53 is preloaded by an adjusting ring 58, which allows an opening pressure of the check valve 45 to be adjusted. The injection valve 20 is preferably designed as a solenoid valve, but other active injection valves are also possible in principle.

[0025] In Fig. 5 shows a memory 30. The structure of the memory basically corresponds to the structure of the memory in Fig.3. In addition, a spring 33 is arranged in the control chamber 39, which spring exerts a force on the piston 32 as soon as the reducing agent 12 in the reducing agent chamber 38 has displaced the piston 32 in the direction of the control chamber 39. The piston 32 is operatively connected to an auxiliary means 35, which in this exemplary embodiment is a linear motor 97 for electromagnetically displacing the piston. The piston 32 is pressed against the spring 33 by the linear motor 97, so that the spring 33 is under tension. In addition, a connection 42 for a control medium can also be present here, although this connection 42 can also be omitted in this embodiment variant. The reducing agent chamber 38 of the accumulator 30 is filled with reducing agent 12 and reducing agent 12 is to be metered into the exhaust system 60.If the power supply to the linear motor 97 is switched off, the piston 32 moves toward the injection valve 20 due to the spring tension, similar to a crossbow projectile, thereby delivering reducing agent 12 into the exhaust system 60. This "firing" of the piston 32 allows additional pressure to be built up on the reducing agent 12 in the accumulator 30, or the reducing agent pressure can be increased above the pressure level in the inlet 44. The check valve 45 prevents the reducing agent 12 from flowing back toward the delivery unit 10.

[0026] Alternatively, spring 33 can also be tensioned mechanically, for example, by a servomotor, or by means of an electromagnet acting on the piston. With a sufficiently high reducing agent pressure in the inlet 44 and a powerful linear motor 97, spring 33 may be dispensed with if the force of the linear motor 97 alone (without spring assistance) is sufficient to accelerate piston 32 toward the injection valve 20.

Claims

[1] Exhaust gas aftertreatment arrangement of an internal combustion engine (50), with a delivery unit (10) for a reducing agent (12), with a reservoir (8) for the reducing agent (12), with a reservoir (30) for the reducing agent (12) and with an injection valve (20) for metering the reducing agent (12) into an exhaust system (60) of the internal combustion engine (50), wherein the reservoir (30) is arranged between the delivery unit (10) and the injection valve (20), wherein the reservoir (30) has a piston (32), wherein the piston (32) is movable in the reservoir (30) and delivers the reducing agent (12) from the reservoir (30) in the direction of the exhaust system (60), wherein aids (35) for guiding and / or moving the piston (32) are arranged on the reservoir (30), characterized by that the aids (35) comprise an electromagnet (96) or a linear motor (97). [2] Exhaust aftertreatment arrangement according to claim 1, characterized bythat the accumulator (30) has a spring (33) which is operatively connected to the piston (32). [3] Exhaust aftertreatment arrangement according to claim 1 or 2, characterized by that a check valve (45) is arranged between the conveyor unit (10) and the reservoir (30). [4] Exhaust gas aftertreatment arrangement according to one of claims 1 to 3, characterized by that the delivery unit (10) comprises a pump (80), in particular a discontinuously delivering pump. [5] Exhaust gas aftertreatment arrangement according to one of claims 1 to 4, characterized by that the piston (32) separates a reducing agent chamber (38) and a control chamber (39) in the accumulator (30). [6] Exhaust aftertreatment arrangement according to claim 5, characterized by that the control chamber (39) has a connection for a pressurized medium, in particular compressed air. [7] Exhaust gas aftertreatment arrangement according to one of claims 1 to 6, characterized bythat a pressure sensor (47) for detecting the reducing agent pressure in the accumulator (30) is arranged on the accumulator (30). [8] Method for metering a reducing agent (12) into the exhaust system (60) of an internal combustion engine (50) with an exhaust aftertreatment arrangement according to one of the preceding claims, wherein the reducing agent (12) is supplied from a storage container (8) via a delivery unit (10) to a reservoir (30), wherein the reservoir (30) is arranged between a delivery unit (10) and an injection valve (20), characterized by that the reducing agent (12) is conveyed in the direction of the exhaust gas line (60) by a piston (32) movable in the accumulator (30). [9] Method according to claim 8, characterized by that a reducing agent pressure is detected in the accumulator (30) and this reducing agent pressure is compared with a reference value. [10] Method according to one of claims 8 or 9, characterized bythat when the internal combustion engine (50) is started, the reducing agent pressure in the accumulator (30) is compared with the ambient pressure. [11] Method according to one of claims 8 to 10, characterized by that the build-up of the reducing agent pressure in the accumulator (30) is detected and compared with the delivery capacity of the delivery unit (10). [12] Method according to one of claims 8 to 11, characterized by that when the reducing agent (12) is metered in, a comparison is made between a drop in the reducing agent pressure in the accumulator (30) due to the metering of the reducing agent (12) and the metered amount of the reducing agent (12). [13] Method according to one of claims 8 to 12, characterized by that when a reference value for the reducing agent pressure in the accumulator (30) is exceeded, a supply of reducing agent (12) to the accumulator (30) is stopped. [14] Method according to claim 9, characterized bythat the reducing agent pressure in the accumulator (30) is used to calibrate a pressure sensor (47) when the piston (32) hits the accumulator (30).

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