WO2005005799A1

WO2005005799A1 - Cooled device for metering reducing agent to the exhaust gas of a combustion engine

Info

Publication number: WO2005005799A1
Application number: PCT/DE2004/001256
Authority: WO
Inventors: Bernhard Bonse
Original assignee: Robert Bosch Gmbh
Priority date: 2003-07-09
Filing date: 2004-06-17
Publication date: 2005-01-20
Also published as: DE10332114A1

Abstract

The invention relates to device for metering reducing agent to the exhaust gas of a combustion engine (12), comprising an injector (22) to which reducing agent is supplied from a reservoir (35) via an inlet (32). The injector (22) has a sealing seat (24) and a moving plunger (26) that, when lifting from the sealing seat (24), enables a flow of reducing agent to the exhaust gas. The device is characterized in that the piston (26) is lifted from the sealing seat (24) by a pressure of the reducing agent.

Description

Cooled device for dosing reducing agent to the exhaust gas of an internal combustion engine

State of the art

The invention relates to a device for metering the reducing agent to the exhaust gas of an internal combustion engine, with an injector, the reducing agent is supplied from a storage tank via an inlet, the injector ^'a sealing seat, and a movable piston comprises the at

Lifting off the sealing seat releases a flow of reducing agent to the exhaust gas.

Such a device is known per se

The metering of a reducing agent into the exhaust gas of the internal combustion engine is required for various exhaust gas aftertreatment systems. Examples of such exhaust gas aftertreatment systems are soot particle filters and DeNOX catalysts.

The reducing agent is usually metered in via a metering module which is electrically controlled. In order to be able to use the known technology of commercially available fuel injection valves, When the injector is installed, there are no impermissibly high temperatures. If certain temperature threshold values are exceeded, the functionality of the valve could be damaged by impairing its seals and / or the insulation and contacting of its coils. In addition, the metering module could become blocked due to solid deposits, which could impair the function of the metering module or even make it inoperable. The solids are deposited because the contact of the injection valve with the exhaust gas results in comparatively large heat inputs into the injection valve, which allow the liquid components of the reducing agent to evaporate.

In order to prevent deposits of solids, it is known per se to cool the metering module by means of a partial reducing agent stream which is fed back into the storage tank. Another partial flow is injected directly. By returning a partial reducing agent flow, reducing agent is passed through the injection valve even when the injection valve is not open, in order to produce a cooling effect.

In the known device, an injection valve is used in which a nozzle needle, actuated electromagnetically, lifts off a sealing seat and releases a flow cross section. Reducing agent is metered to the exhaust gas via the flow cross section. In the known device, the supply of reducing agent should take place at a distance from the injection opening, so that it must be directed inside the injection valve in the direction of the injection opening. This should provide a large area for heat transfer. However, it has been shown that, despite the large heat transfer surfaces, deposits occur cannot be reliably excluded during the generally long operating times.

Against this background, the object of the invention is to provide an inexpensive device which can be operated in a long-term stable manner with a further reduced formation of deposits.

This object is achieved in a device of the type mentioned in the introduction in that the piston is lifted from its sealing seat by a pressure of the reducing agent.

Advantages of the invention

Such pressure-controlled injection valves generally have a comparatively large internal volume which is filled with the liquid to be injected. An increase in pressure in this volume acts on the piston via a pressure cone, which is generally conical in shape, and is usually pressed onto a sealing seat by spring force. When an opening pressure predetermined by the spring force and the geometry of the arrangement is exceeded, the piston is lifted off a sealing seat and releases an injection cross section. It is just that close to

Injection cross section and thus arrangement of the internal fuel volume adjacent to the exhaust pipe in connection with its comparatively large content, which leads to improved cooling of the exhaust-side end of the device. It is the improved cooling of this area of the device which leads to a further reduced formation of deposits in the long term. The fact that pressure-controlled injection valves are used according to the invention means that these Advantages can be provided with low unit costs and with reduced development effort.

It is preferred that the inj ector ^'a Drosselzapfendüse is.

Throttle pin nozzles are particularly well suited for this purpose because their internal fluid-absorbing volume (the pressure chamber) is relatively large and is close to the end face of the injection valve. As a result, the thermally particularly stressed end face of the injection valve is cooled particularly well by the reducing agent flowing through the pressure chamber.

A particularly preferred embodiment is characterized in that the injector is a throttle pin nozzle, as is used in swirl chamber diesel engines.

Throttle pin nozzles are characterized by the fact that the flow rate is directly dependent on the piston stroke.

Throttle pin nozzles are the standard injection nozzles for Wirbelka merdieselmotoren. Due to the number of pieces manufactured with sophisticated methods for this purpose, these injection nozzles, which have been tried and tested over many years, are available inexpensively on the market. When using such nozzles, the adaptation to the new purpose can be limited to an adaptation of the closing force of the elastic element to the changed pressure conditions (1 to 2 orders of magnitude lower opening pressure). However, perforated nozzles are also possible, as are generally used in diesel engines with direct injection. Both nozzles are presented, for example, in the Automotive Paperback, 22nd edition, pages 524 to 529. It is also preferred that the pressure of the reducing agent in the throttle pin nozzle is determined by an opening cross section of a flow control valve which is arranged in the inlet.

This configuration has the advantage that the control of the device can be spatially separated from the injection valve, so that the thermal and mechanical loads on the flow control valve can be reduced.

It is further preferred that the injector additionally has a return line via which the reducing agent is returned to the storage tank.

This configuration has the particular advantage that reducing agent flows through the internal volume, that is to say the pressure chamber, even when the injection valve is closed, and is therefore cooled particularly reliably and uniformly. Another advantage is that this

Design can be easily implemented in terms of construction and manufacturing technology with a throttle pin nozzle.

It is further preferred that the piston has a pressure shoulder and movably seals a pressure chamber which is hydraulically connected to the inlet and to the return.

These features, which can also be realized with other pressure-controlled injection valves such as perforated nozzles, can be easily manufactured and enable effective cooling of the exhaust-side end of the injection valve. In addition, heat absorbed by the movable piston (the nozzle needle) can be transferred to the liquid via the pressure shoulder, which is generally wide due to the pressure control are emitted, which flows through the pressure chamber to the return or to the open injection cross section.

It is also preferred that the pressure in the pressure chamber is determined by an inlet pressure, a throttle arranged in the return and an opening cross section of a flow control valve, via which a flow of reducing agent in the circuit from the inlet, injector and return to the storage tank is controlled.

These features enable a structurally simple and sufficiently precise control of the dosage of reducing agent to the exhaust gas to be achieved. The dimensioning of the throttle allows the flow of liquid through the internal volume to be matched to the inlet pressure provided by a pump so that the pressure-controlled injection valve is open

Flow control valve closes and opens when the pressure increases, which results from the opening cross-section being closed. As a rule, one

Low pressure pump used, which delivers a pressure in the order of 1 to 10 bar.

It is further preferred that a throttle is alternatively or additionally arranged in the inlet.

Such an additional throttle allows an even better coordination of the fuel flow to the injection valve required for sufficient cooling and for generating sufficient pressure differences. On its own, such a throttle completely takes over the adjustment of the fuel flow and thus enables a configuration without a return. Another preferred embodiment is characterized by a flow control valve arranged in the return.

It is also preferred that the flow control valve is arranged in the flow direction behind the pressure chamber and in front of the throttle. It is further preferred that the flow control valve, if present, can be actuated electromagnetically. It is particularly preferred that the flow control valve is open when de-energized.

Electromagnetic actuation is reliable and inexpensive. The arrangement mentioned ensures that the injection valve is cooled even when the flow control valve is defective. The result of the arrangement is that the pressure in the pressure chamber rises when the flow control valve is closed and decreases when the injection valve is open. If a flow control valve that is open when de-energized is used, then in the event of a defect if the flow control valve no longer closes, it is ensured that a cooling flow is not interrupted. In the less likely case of a defective closed flow control valve, the injection valve is cooled by a permanent injection.

It is further preferred that a part of the injector protruding into the exhaust gas is at least partially covered by a shield that is thermally insulating against the exhaust gas flow.

These features can already reduce the heat input into the injection valve, so that the cooling power requirement is reduced accordingly. It is further preferred that the injector is arranged such that an injection direction of the reducing agent largely coincides with the flow direction of the exhaust gases.

This configuration ensures good mixing of the reducing agent with the exhaust gas and thus good further transport of the reducing agent within the exhaust gas aftertreatment system.

Further advantages result from the description and the attached figures.

It goes without saying that the features mentioned above and those yet to be explained below not only in the combination indicated in each case, but also in others

Combinations or alone can be used without leaving the scope of the present invention.

drawings

Exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the description below. Show it:

Fig. 1 shows schematically a first embodiment of the invention; and

Fig. 2 shows a second embodiment of the invention.

Description of the embodiments

In FIG. 1, the number 10 denotes the entirety of an internal combustion engine 12 with an exhaust gas aftertreatment system 14. The exhaust gas aftertreatment system 14 shown in FIG. 1 has one Particle filter 16 with an upstream oxidation catalytic converter and an SCR catalytic converter 18, which is arranged in the flow direction of the exhaust gases behind the particle filter 16 with an upstream oxidation catalytic converter. This exhaust gas aftertreatment system 14 is a CRT system (CRT = Continuously Regenerating Trap). Such a CRT system is a typical representative of exhaust gas aftertreatment systems in which a reducing agent is metered into the exhaust gas. However, it goes without saying that the invention is not limited to an application in CRT systems, but can be used in all exhaust gas aftertreatment systems in which a reducing agent is metered into the exhaust gas.

In the exemplary embodiment in FIG. 1, reducing agents are metered into an exhaust pipe section 20 which is arranged between the particle filter 16 with an upstream oxidation catalytic converter and the SCR catalytic converter 18 (SCR = Selective Catalytic Reduction).

The function of such a CRT system is briefly explained below in order to clarify the need for metering reducing agents into the exhaust gas. The particle filter 16 has a porous structure in which soot particles from the exhaust gas are deposited. In order to avoid an inadmissibly high exhaust gas back pressure due to particle residues, the particle filter 16 must be regenerated. The regeneration takes place within the framework of the CRT system from particle filter 16 with an upstream oxidation catalyst in that the

Oxidation catalyst first converts nitrogen monoxide from the exhaust gas of the internal combustion engine 12 with oxygen to nitrogen dioxide and that the carbon present in the form of soot particles in the subsequent particle filter 16 there with the nitrogen dioxide to form CO ₂ and Nitrogen monoxide is converted, both of which are discharged from the particle filter with the remaining exhaust gas. Through these reactions, the particle filter 16 is continuously regenerated during normal operation of the internal combustion engine 12.

The nitrogen monoxide formed during the regeneration of the particle filter 16 is reduced in the subsequent SCR catalytic converter 18 together with raw nitrogen oxide emissions from the internal combustion engine 12 by the eponymous selective catalytic reduction to molecular nitrogen. For this purpose, a directly reducing substance such as ammonia or a preliminary product is added to the exhaust gas, which only releases reducing substances in the exhaust gas. For example, a urea-water solution can be used as a preliminary product. Alternatively, hydrocarbons and thus fuel can also be used as reducing agents. It is also known to operate SCR catalysts without an upstream CRT system in order to convert engine-generated nitrogen oxides.

In the exemplary embodiment in FIG. 1, the reducing agent is dosed to the exhaust gas by an injector 22, which is arranged in the exhaust pipe section 20 between the particle filter 16 and the SCR catalytic converter 18. The injector 22 has a sealing seat 24, onto which a piston 26 is pressed by an elastic element 28, for example a steel spring. Furthermore, the injector 22 has a pressure chamber 30 in its interior, which is supplied with reducing agent via an inlet 32. The reducing agent is conveyed by a pump 34 from a storage tank 35 via a throttle 36 and a flow control valve 38 to the inlet 32. The pump 34 is, for example, an electrically driven one or a mechanical one from the internal combustion engine 12 driven low-pressure pump that pumps the reducing agent at a pressure of a few bar.

The flow control valve 38 is controlled by a control unit 40, which is preferably the control unit of the internal combustion engine 12, which also controls the other functions of the internal combustion engine 12. The reducing agent requirement of the exhaust gas aftertreatment system 14 depends on the operating states of the internal combustion engine 12. The controller 40 controls the flow through the flow control valve 38 in accordance with the

Reducing agent requirement of the exhaust gas aftertreatment system 14, which can be determined in the control unit 40, for example, from the operating parameters present there by modeling. When open

Flow control valve 38 sets a reducing agent pressure 30 in the inlet 32 and thus also in the pressure chamber 30, as is structurally predetermined by the reducing agent pressure provided by the pump 34 and the dimensions of the throttle 36.

In any case, in the embodiment according to FIG. 1, when the flow control valve 38 is opened, there is an increase in pressure behind the flow control valve 38, which increases in the inlet 32 and thus in the pressure chamber 30 and on the pressure shoulder 42 of the piston 26 a directed against the closing force of the elastic element 28 Power creates. As soon as the pressure force on the pressure shoulder 42 becomes greater than the closing force of the elastic element 28, the piston 26 lifts off from its sealing seat 24 under pressure control and gives one

Injection cross section free, via which reducing agent is metered into the exhaust gas within the exhaust pipe section 20 via a spray hole 44. In a preferred embodiment of the invention, the injector 22 is a throttle pin nozzle, as is used in swirl chamber diesel engines for injecting fuel into combustion chambers of the internal combustion engine. When using such throttle pin nozzles for dosing reducing agent to the exhaust gas, only the closing force of the elastic element 28 has to be adapted to the reduced pressures. A characteristic of a throttle pin nozzle is the control of the outflow cross section, that is to say the flow rate, in a direct dependence on the stroke of the piston 26. Throttle pin nozzles show a very flat cross-sectional profile in the area of small piston strokes. In this stroke range, the throttle pin or throttle pin 46, ie a pin-shaped extension of the piston 26, still remains in the spray hole 44. Only the small annular area between the somewhat larger spray hole 44 and the throttle pin 46 is available as the flow cross section. With large piston stroke values, the throttle pin 46 completely clears the spray hole 44 and the flow cross section increases significantly.

Pressure-controlled injectors 22 in general and throttle pin nozzles in particular are characterized in that the pressure chamber 30 is arranged very close to the exhaust-side end 48 (end face) of the injector 22. As a result, the heat which is introduced into the injector 22 by the exhaust gas via the end face 48 can be absorbed particularly well by the reducing agent in the pressure chamber 30. Another advantage can be seen in the fact that heat, which is introduced into the piston 26 via the throttle pin 46 and the sealing seat 24, is also released very close to the exhaust-side end of the injector 22 via the wide pressure shoulder 42 to the reducing agent in the pressure chamber 30 can. The heated reducing agent in the pressure chamber 30 is injected into the exhaust gas when the injector 22 is opened, which takes place by lifting the piston 26 from the sealing seat 24, and by flowing, cooler

Reducing agent from the storage tank 35 replaced. In conjunction with the special geometric properties of the pressure-controlled injector 22, this results in a very good cooling effect. However, the cooling effect still depends heavily on the flow through the

Injector 22, that is, from the amount of reducing agent metered via injector 22. The larger this amount, the better the cooling effect. The embodiment according to FIG. 1 also has the disadvantage that after a certain time, when the injector 22 is closed

Temperature compensation between the reducing agent in the pressure chamber 30 and the injector 22 sets. In this case, the reducing agent does not cause any further cooling until the next injection. However, this can be tolerable in some applications because the operating points of the internal combustion engine 12 with a low reducing agent requirement of the exhaust gas aftertreatment system 14 are generally characterized by low exhaust gas temperatures and thus by a reduced cooling power requirement. In addition, the cooling power requirement can be further reduced by a thermally insulating cladding 50 of the exhaust-side end 40 of the injector 22. The thermal insulation 50 can have the shape of a cup, for example, which has an opening 52 in its base through which the reducing agent can get into the exhaust gas. Particularly suitable materials for the thermal insulation 50 are high-temperature-resistant plastics or ceramic materials, which are distinguished by a reduced thermal conductivity in comparison to the metal of the injector 22. Figure 2 shows a particularly preferred embodiment of the invention, which is characterized by a further improved cooling effect. The subject of FIG. 2 differs from the subject of FIG. 1 in particular by an additional return 54, via which the reducing agent supply from the storage tank 35 to the pressure chamber 30 is expanded to form a closed circuit. The particular advantage of this embodiment is that when the flow control valve 38 is open, there is a flow of reducing agent through the pressure chamber 30 even when the injector 22 is closed. In this way, the reducing agent can also remove heat from the injector 22, in particular from its exhaust-side end 48, even when the injector 22 is closed. The additional return 54 can be produced in conventional throttle pin nozzles in a simple manner by one or more additional holes.

This is preferred in this embodiment

Flow control valve 38 arranged on the return side of the injector 22 and designed as a normally open, electromagnetically actuated valve. In the open state, there is a flow in the circuit from the storage tank 35, pump 34, inlet 32,

Pressure chamber 30, return 54 and flow control valve 38, as specified by the flow resistances of the circuit and the pressure generated by the pump 34. The flow resistances are preferably set with a throttle 56 arranged on the return side and, if appropriate, with an additional throttle 36 which is provided with an inlet soap. With the valve 38 open, a reducing agent pressure is thus established in the pressure chamber 30, which pressure is in any case lower than the maximum pressure provided by the pump 34. When closing the Through lusssteuerventils 38 by the engine control unit 40, the pressure in the pressure chamber 30 increases and finally lifts the piston 26 from the sealing seat 24 via its force acting on the pressure shoulder 42, and thus releases an injection opening to the exhaust gas.

In a particularly preferred embodiment, the exemplary embodiment according to FIG. 2 is also equipped with thermal insulation of the exhaust-side end 48 of the injector 22. It can be advantageous here

Bevel end face 48 of injector 22 in the manner shown. The bevel, which is also shown in the form of the bevels 58 of the thermal insulation 50, can be adapted to the contour of the pressure chamber 30. In this way, the heat-absorbing area of the injector 22 exposed to the exhaust gas is reduced. By adapting to the contour of the pressure chamber 30, the reduction takes place without an inadmissible reduction in the remaining wall thickness between the pressure chamber 30 and the exhaust gas. Such a bevel is possible in particular because the pressure-controlled injectors 22 as injection nozzles for diesel engines are generally designed for significantly higher injection pressures and thus for significantly higher mechanical loads.

In all configurations, the injector can be arranged such that an injection direction of the reducing agent largely corresponds to the flow direction of the exhaust gases. This can be brought about by an oblique arrangement of the injector which deviates from the right-angled arrangement according to FIGS. 1 and 2 and / or by an arrangement of the injector on a bend (a knee or kink) of the exhaust pipe. 1 and 2, the exhaust pipe 20 could for example, bend down below the injector 22.

Claims

Expectations

1. Device for dosing reducing agent to the exhaust gas of an internal combustion engine (12), with an injector (22) to which reducing agent is fed from a storage tank (35) via an inlet (32), the injector (22) having a sealing seat (24) and a movable piston (26) which releases during lifting from the sealing seat (24) a flow of reducing agent to the exhaust gas, characterized in that the piston (26) is lifted by a pressure of ^• reducing agent from its seat (24).

2. Device according to claim 1, characterized in that the injector (22) is a throttle pin nozzle.

3. Device according to claim 2, characterized in that the injector (22) is a throttle pin nozzle, as is used in swirl chamber diesel engines.

4. The device according to claim 2 or 3, characterized in that the pressure of the reducing agent in the throttle pin nozzle is determined by an opening cross section of a flow control valve (38) which is arranged in the inlet.

5. Device according to one of claims 1 to 4, characterized in that the injector (22) additionally one Return (54), via the reducing agent is returned to the storage tank (35).

6. The device according to claim 5, characterized in that the piston (26) has a pressure shoulder (42) and movably seals a pressure chamber (30) which with the

Inlet (32) and hydraulically connected to the return (54).

7. The device according to claim 6, characterized in that the pressure in the pressure chamber (30) by an inlet pressure, a throttle (56) arranged in the return and an opening cross section of a flow control valve

(38) is determined, via which a flow of reducing agent in the circuit of inlet (32), injector (22) and return

(54) to the storage tank (35) is controlled.

8. The device according to claim 5, characterized in that a throttle (36) is alternatively or additionally arranged in the inlet (32).

9. The device according to claim 7 or 8, characterized in that the flow control valve (38) is arranged in the return (54).

10. The device according to claim 9, characterized in that the flow control valve (38) is arranged in the S ^' flow direction behind the pressure chamber (30) and in front of the throttle (56).

11. The device according to one of claims 4 to 10, characterized in that the flow control valve (38), if present, can be actuated electromagnetically.

12. The apparatus according to claim 11, characterized in that the flow control valve (38) is open when de-energized.

13. Device according to one of the preceding claims, characterized in that a part of the injector projecting into the exhaust gas is at least partially covered by a shield (50) which is thermally insulating against the exhaust gas flow.

14. Device according to one of the preceding claims, characterized in that the injector is arranged such that an injection direction of the reducing agent largely corresponds to the flow direction of the exhaust gases.