Injection valve and metering system for an exhaust aftertreatment system

Abstract

Injection valve for an exhaust aftertreatment device of an internal combustion engine with a valve needle (33), a valve seat (27), a valve spring (39) and a spring retainer (37), wherein the valve needle (33) has a stem (35) and a valve disc (31) with a frustoconical seat surface (30), characterized in that the seat surface (29) of the valve seat (27) has a cone angle (θ) of 55° to 75°, that a rotationally symmetrical transition surface (40) is present between the stem (35) and the seat surface (30), and that an angle difference (θ) between the seat surface (29) of the valve seat (27) and the transition surface (40) of the valve disc (31) is between 2° and 20°.

Description

Prior ArtDE 10 2004 053 351 A1, U.S. Pat. No. 6,109,549 A and U.S. Pat. No. 5,685,492 A disclose valves for injecting fuel into the combustion chamber of an internal combustion engine. These injectors operate at relatively high injection pressures. When driven, they open for a very short time and then close without bouncing or scrubbing. Due to the high pressure level and because they do not snore, they are not suitable for injecting fuel into the exhaust tract.DE 10 2006 057 425 A1 discloses a device for regenerating diesel particulate filters and / or catalytic converters. This device makes it possible to regenerate the particle filter with a targeted injection of diesel fuel into the exhaust system. In this case, the diesel fuel is injected into the exhaust tract above the oxidation catalytic converter. The injected fuel reacts with unburned oxygen in the exhaust gas, so that the exhaust gas temperature increases to about 600° C. as it flows through the oxidation catalyst. At this exhaust gas temperature, the soot stored in the particle filter arranged downstream burns off and the particle filter is regenerated.This object is achieved according to the invention in a generic injection valve for an exhaust gas aftertreatment device of an internal combustion engine having the characterizing features of claim 1.It has been found in practical tests that particularly fine atomization of the injected fuel takes place within the claimed range. At the same time, the chatter of the valve, i.e. the short-term opening and closing of the injection valve, is also assisted at an approximately constant and stable frequency over the entire range of possible operating pressures. This scrubbing is a desirable effect which also contributes to particularly fine atomization of the fuel. The sonar frequencies of injection valves of this type are between 700 Hz and 1500 Hz, other frequencies also being possible. Due to the geometry according to the invention of the seat surface of the valve seat with a seat angle β of 55° to 75°, particularly preferably of 60° to 70°, it is possible on the one hand to achieve a sufficiently large sealing surface between the valve disk and the valve seat. The service life of the injection valve is thereby increased. On the other hand, the surface pressure is also large enough to ensure reliable sealing.It has been found in experiments that in a cone-cone-seat variant, as is shown for example in FIG. 3, a width of the annular sealing surface of 20 μm is sufficient. This width of the sealing line has proven to be a good compromise between good sealing behavior and a high service life due to a sufficiently low surface pressure. In a cone-ball seat variant, as is illustrated for example in FIG. 4, the width of the annular sealing surface can be even smaller in the new state.In a further advantageous embodiment of the invention, it is provided that an angle difference between the seat angle β of the valve seat and the frustoconical seat surface of the valve disk is 2°. With this angle difference, the formation of a very fine spray and consequently very small fuel droplets can be achieved particularly well and stably.Alternatively, it is also possible that a side of the valve disk facing the valve seat is curved in cross section and / or that this curved side of the valve disk contacts the valve seat tangentially when the valve needle is closed. As a result, the fine atomization of the fuel according to the invention can also be achieved reliably and reliably with little outlay and also with injection valves produced on a large scale.The object underlying the invention is also achieved by a metering system according to independent claim 7, in that an injection valve according to the invention is used.Further advantages and advantageous embodiments of the invention can be derived from the following description and the patent claims. All features disclosed in the drawings, their description and the patent claims can be essential to the invention both individually and in any combination with one another.DRAWINGThe following are shown: FIG. 1 shows a schematic illustration of an internal combustion engine with an exhaust gas aftertreatment device according to the invention; FIG. 2 shows a section through an exemplary embodiment of an injection valve according to the invention, and FIGS. 3 and 4 show embodiments of valve needles according to the invention.FIG. 1 shows an internal combustion engine 1 with an exhaust gas aftertreatment device 3 in a greatly simplified and schematic manner. The exhaust gas after-treatment device 3 comprises an exhaust pipe 5, an optional oxidation catalyst 6 and a particle filter 7. the particle filter 7 is usually arranged downstream of the oxidation catalyst 6. The direction of flow of the exhaust gas through the exhaust pipe 5 is indicated by arrows.The fuel injection system of the internal combustion engine 1 is shown in FIG. 1 in a very greatly simplified manner and reduced to the essence. A prefeed pump or low-pressure pump 11 delivers fuel from a fuel tank 13 to a high-pressure fuel pump 15. The low-pressure pump 11 has a delivery pressure of approximately four to six bar and supplies the high-pressure fuel pump 15 with fuel from the fuel tank 13.In order to be able to regenerate the particle filter 7, a metering system is provided which comprises a fuel line 19, a metering unit 21 designed as a 2 / 2-way valve and an injection valve 9. The injection valve 9 is arranged upstream of the oxidation catalytic converter 6. Alternatively and not shown in FIG. 1, the dosing unit 21 can also be connected to the return line (not shown) of the injectors 17.In order to be able to inject the fuel into the exhaust pipe 5 with the aid of the injection valve 9, the delivery head of the low-pressure pump 11 is sufficient. Therefore, the injection valve 9 is supplied with fuel from the low-pressure pump 11 via a fuel line 19. The injection valve 9 is a passive component and opens as soon as a pressure prevails in the fuel line 19.2 which is greater than or equal to the opening pressure of the injection valve 9. The opening pressure of the injection valve 9 is lower than the delivery pressure of the low-pressure pump 11 or the pressure in the return system of the injectors 17.The fuel line 19 is separated from the dosing unit 21 into a first section 19.1 and a second section 19.2. When the dosing unit 21 is closed, as shown in FIG. 1, the second section 19.2 of the fuel line 19 is pressureless and the injection valve 9 is closed.When the particle filter 7 is to be regenerated, the dosing unit 21 is controlled by an engine control unit (not shown) or a separate control unit into the second switching position (not shown), so that a hydraulic connection is established between the first section 19.1 and the second section 19.2 of the fuel line 19. As a result, the injection valve 19 is acted upon by the delivery pressure of the low-pressure pump 11 and opens. As a result, a finely divided fuel spray is injected into the exhaust pipe 5 by the injection valve 9.Since oxygen is still present in the exhaust pipe 9 because of the excess air of the internal combustion engine 1, the fuel injected by the injection valve 9 can react with the oxygen in the exhaust gas, so that the temperature of the exhaust gases increases to approximately 600° C. This temperature is sufficient to trigger and support the regeneration, i.e. the oxidation of deposited soot, in the particle filter 7. The aim here is to inject the fuel as finely as possible into the exhaust pipe 5.FIG. 2 shows an exemplary embodiment of an injection valve 9 according to the invention in cross section. Some terms will be explained based on this representation.The injection valve 9 comprises a housing 23 with a centrally arranged bore 25, which in the illustrated exemplary embodiment is also stepped. In the exemplary embodiment shown, the valve seat 27 is fixed in a shoulder of the housing 23 by crimping. The valve seat 27 has a frustoconical seating surface 29. The cone angle of this seat surface 29, also referred to as seat angle, is denoted by the reference sign β in FIG. 2. It has been found in experiments that seat angles β in a range from 55° to 75°, preferably in a range from 60° to 70°, bring about particularly fine atomization of the fuel and are therefore particularly advantageous.The valve seat 27 interacts with a valve disk 31 of a valve needle 33. In addition to the valve disk 31, the valve needle 33 also comprises a shank 35. The spring plate 37 serves to transmit the closing force provided by a valve or closing spring 39 to the valve needle 33. The closing spring 39 is supported at one end against the valve seat 27 and at the other end against the spring plate 37.The entire interior of the injection valve 9 and with it the bore 25 are filled with fuel during operation of the injection valve 9. As soon as the pressure of the fuel, triggered by the opening of the metering unit 21, exceeds the opening pressure of the injection valve 9, the valve disk 31 of the valve needle 33 lifts off from the seat surface 29. As a result, a narrow annular gap is released between the valve plate 31 and the seat surface 29 and the fuel is injected in a finely atomized manner into the exhaust pipe (not shown).By suitable coordination of the spring rate and prestress of the closing spring 39, of the stepped bore 25, in particular its diameter d, and of the valve needle 33 and of the valve disk 31, a pulsating or oscillating movement of the valve needle in the axial direction can be brought about. This oscillating movement is stable over the entire pressure range, which is easily detectable with a uniform noise. This oscillating movement leads to a spray jet which is interrupted briefly again and again and particularly fine atomization of the fuel and is therefore desired.In FIGS. 3 and 4, advantageous embodiments of the valve seat 27 and of the valve seat 31 are shown in detail and enlarged. It is common to all these exemplary embodiments that they bring about very fine atomization of the fuel and at the same time are very wear-resistant.In FIG. 3, a seat or sealing surface 30 of the valve disk 31 is clearly visible on account of the enlarged illustration. When the injection valve 9 is closed, the valve disk 31 lies in the region of the sealing surface 30 on the seat surface 29 of the valve seat 27.In this exemplary embodiment, the frustoconical sealing surface 30 of the valve disk 31 is designed with a cone angle which is equal to the seat angle β of the valve seat 27.Between the shank 35 and the sealing surface 30, a likewise frustoconical transition surface 40 is present. The cone angle of the transition surface 40 and the seat angle β of the valve seat 27 enclose an angle γ of 2°. However, it is also possible for the angle difference γ to be increased up to 20°. In experiments, with angle differences γ of between 2° and 20°, preferably 10°, very good formation of small droplets has been established during the injection of fuel.The combination according to the invention of the seat angle β in a range between 55° and 75° and the angle difference γ in a range between 2° and 20° likewise results in very good formation of small droplets during the injection of fuel.The wear behavior of the injection valve 9 according to the invention can be improved if necessary by enlarging the diameter of the valve seat 27 and correspondingly also of the valve disk 37. A larger sealing surface 30 is then available between the valve disk 31 and the seat surface 29 of the valve seat 27.In the exemplary embodiment according to FIG. 4, the upper side of the valve disk 31 has a curve in the form of a circular arc in cross section or in longitudinal section.The radius r of the upper side of the valve disk 31 curved in the shape of a circular arc and its position are selected such that the valve disk 31 rests tangentially on the seat surface 29 of the valve seat 27 in some areas. The sealing surface is then formed there.

Claims

Injection valve for an exhaust gas aftertreatment device of an internal combustion engine, having a valve needle (33), a valve seat (27), a valve spring (39) and a spring plate (37), wherein the valve needle (33) has a shank (35) and a valve plate (31) having a frustoconical seating surface (30), characterized in that the seating surface (29) of the valve seat (27) has a cone angle (β) of 55° to 75°, in that a rotationally symmetrical transition surface (40) is present between the shank (35) and the seating surface (30), and in that an angle difference (γ) between the seating surface (29) of the valve seat (27) and the transition surface (40) of the valve plate (31) is between 2° and 20°.Injection valve according to Claim 1, characterized in that a side of the valve disc (31) facing the valve seat (27) is curved in cross section.Injection valve according to Claim 2, characterized in that the side of the valve disc (31) facing the valve seat (27), when the injection valve (9) is closed, touches the valve seat (27) tangentially in some regions.Injection valve according to one of the preceding claims, characterized in that the width of an annular sealing surface (30) is approximately 20 μm.Injection valve according to one of the preceding claims, characterized in that the seat surface (29) of the valve seat (27) has a cone angle (β) of 60° to 70°.Injection valve according to one of the preceding claims, characterized in that the angle difference (γ) between the seat surface (29) of the valve seat (27) and the transition surface (40) of the valve disc (31) is 10°.Dosing system comprising a dosing unit (21) and an injection valve (9), characterized in that the injection valve (9) is an injection valve according to one of the preceding claims.

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