Directed secondary air supply into the exhaust pipe of an internal combustion engine

Abstract

The invention relates to a device for feeding a quantity of secondary air into an exhaust pipe (2) of an internal combustion engine, which has a flow path arranged downstream of a gas outlet of the internal combustion engine in the direction of the exhaust gas flow and an injection device designed to feed a quantity of secondary air into said flow path at a feed point, whereby the feed of secondary air takes place upstream of a first honeycomb body (3) and the secondary air is introduced into the flow section through injection pipes (5, 11) of the injection device, which are arranged outside the flow section and open into said flow section.

Description

[Technical field]

[0001] The present invention relates to a device for feeding a fixed amount of secondary air into the exhaust pipe of an internal combustion engine, the device having a flow path arranged downstream of a gas outlet of the internal combustion engine in the direction of the flow of the exhaust gases and an injection device designed to feed a fixed amount of secondary air into this flow path at a feed point. [Background technology]

[0002] For the aftertreatment of exhaust gases from internal combustion engines, various catalysts are used. In particular, catalysts are flow-through catalysts with a particularly large flow surface and a catalytically active coating that promotes the chemical conversion of pollutants contained in the exhaust gases into less harmful products. In particular, catalysts with a plurality of channels that can generate a flow along the main flow direction are known in the prior art. Typical catalysts for exhaust gas aftertreatment are made of ceramic material or designed as metallic honeycombs.

[0003] What these catalysts have in common is that they only achieve sufficient conversion of the respective pollutant when they reach a certain minimum temperature, the so-called light-off temperature, before which only insufficient conversion of the pollutant occurs.

[0004] In order to meet the requirements of current and future exhaust gas regulations, it is necessary to reach this light-off temperature as quickly as possible. To achieve a faster heating, prior art methods are known, such as secondary air injection. In this process, additional air is injected into the exhaust port of the internal combustion engine, which is then run with a higher proportion of fuel in order to increase the fuel content of the exhaust gases blown into the exhaust port. As a result, an exothermic reaction occurs in the exhaust pipe, which leads to heating of the catalyst.

[0005] The above-mentioned injection of secondary air into the exhaust pipe may also be carried out if an electrically heated catalytic converter is provided in the exhaust pipe. This represents another way of reducing the generation of pollutant emissions. Electrically heated catalytic converters only effect the conversion of pollutants when a light-off temperature, for example 300° C., is reached.

[0006] Preheating takes place when an electrically heated catalytic converter is supplied with energy before the internal combustion engine is started. The heating disk of the catalyst is heated by means of an electrical resistance. If the engine is not rotating, no exhaust gases are pumped into the exhaust pipe, so the heat from the electrically heated catalytic converter is transported by the secondary air flow by means of convection to the supporting catalyst of the downstream catalytic converter, for example the heating disk.

[0007] A particular disadvantage of the prior art devices is the indirection of the secondary air injection. The secondary air flow in the exhaust duct between the point where the secondary air is fed and the first honeycomb is usually not uniform. This means that the heating is not optimal and, in the extreme, local overheating of the honeycomb body can occur. This phenomenon is particularly detrimental if the first honeycomb body is formed by an electrically heatable heating disk. Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the present invention is therefore to create a device which allows a directed supply of secondary air into the exhaust pipe of an internal combustion engine, in particular to achieve a uniform distribution of the secondary air flow immediately before and at the first honeycomb body. [Means for solving the problem]

[0009] The problem with respect to the device is solved by an device having the features of claim 1.

[0010] One embodiment of the present invention relates to a device for feeding a quantity of secondary air into the exhaust pipe of an internal combustion engine, which has a flow path arranged downstream of a gas outlet of the internal combustion engine in the direction of the exhaust gas flow and an injection device designed to feed a quantity of secondary air into this flow path at a feed point, whereby the feed of secondary air takes place upstream of a first honeycomb body and the secondary air is introduced into the flow section through an injection pipe of the injection device, which is arranged outside the flow section and opens into this flow section.

[0011] The supply of exhaust gases through the injection pipe is particularly advantageous, since the precisely defined opening of the injection pipe and its precisely defined position inside the exhaust pipe allow the supply of secondary air to be precisely controlled. Inside the injection pipe, the flow of the secondary air can be preconditioned so that the secondary air entering the exhaust pipe is precisely adapted to the respective conditions in the exhaust pipe. This applies, for example, to the flow speed, flow direction and uniform distribution of the secondary air over the cross section through which it flows.

[0012] Locating the injection pipe outside the exhaust gas flow path does not adversely affect the internal exhaust gas flow: the exhaust gas can continue to flow freely and no unwanted back pressure is created.

[0013] It is particularly advantageous if the feed point for feeding the secondary air into the flow section is located downstream of the exhaust gas turbocharger.

[0014] This is advantageous in order to make the heat transfer from the electrically heatable catalytic converter easier and faster to the downstream catalyst, for example the support catalyst of a heat disk.

[0015] It is also advantageous if the initial honeycomb body is formed by an electrically heatable honeycomb body.

[0016] Electrically heatable honeycomb bodies are advantageous for achieving the fastest possible heating and thus reaching the light-off temperature of the individual catalysts as quickly as possible. In the electrically heatable honeycomb bodies, the secondary air can react strongly exothermically, in particular with the exhaust gases containing a high proportion of unused hydrocarbons, which enhances the heating effect. The secondary air can also be taken from the gas tank or from a filter used to filter free-floating hydrocarbons from the gas tank to ensure that the secondary air flow contains an increased proportion of unburned hydrocarbons therein. This is particularly advantageous when starting the engine at low temperatures, in particular at temperatures below freezing, where the engine is operated with a rich fuel mixture. By using the secondary air together with the unburned hydrocarbons, it is possible to ensure that the subsequent catalysts are operated stoichiometrically.

[0017] A preferred embodiment is characterized in that the injection tube has a cylindrical cross section.

[0018] A cylindrical cross-sectional area is particularly advantageous for generating the most uniform flow possible, especially since the downstream flow path in the exhaust pipe also typically has a cylindrical cross-sectional area.

[0019] It is also preferred that the injection tube has a cross section which widens conically towards the delivery point.

[0020] The conical widening creates a diffuser that can promote uniform flow distribution of the secondary air.

[0021] It is furthermore advantageous if the injection tube has a metallic substrate with a number of flow passages for directing the flow along the main flow direction towards the delivery point.

[0022] The metallic substrate in the injection tube may be formed by a honeycomb body that allows the flow to pass along multiple flow paths. Preferably, such a honeycomb body has a diameter of 30 mm to 40 mm and an axial length in the flow direction of 25 mm to 30 mm. The cell density of the honeycomb body is preferably 50 cpsi (cells per square inch) to 100 cpsi. The foil thickness of the metal foil used for the honeycomb body and the wall thickness of the honeycomb body are preferably 50 μm to 65 μm.

[0023] Furthermore, it is advantageous if the injection pipe is provided with elements for generating swirl in the secondary air flow.

[0024] The creation of vortex flows is particularly advantageous if one wishes to achieve the most uniform possible distribution of the secondary air quantity and the secondary air flow velocity over the cross section of the injection pipe and / or the flow path of the exhaust gases.

[0025] It is also advantageous if the elements for generating vortex flows are formed by a plate with openings arranged in the injection pipe, the flow through the openings taking place along preformed blade elements.

[0026] The vortices in the gas flow may be generated in various ways. Preferably, a vortex plate is used which has a number of openings through which the flow can pass. The openings have guide elements which contribute to the deflection of the flow. The guide elements can be, for example, any kind of guide surface.

[0027] It is furthermore advantageous if the secondary air flow in the injection pipe is cyclonic due to elements for generating vortex flows.

[0028] Such flow propagation is particularly advantageous for achieving the most uniform flow possible over the entire flow cross section.

[0029] It is furthermore advantageous if the injection tube is supplied with a secondary air flow via an air supply section, the injection tube being centrally located within the chamber, the secondary air being able to flow around the injection tube within the chamber, and the secondary air being able to flow from the chamber into the inlet opening of the injection tube.

[0030] The chamber may be used to precondition the secondary air flow. In particular, uniformity of the secondary air flow can be achieved and a favorable direction vector can be given to the flow. The chamber is located upstream of the injection tube in the flow direction and is therefore traversed by the secondary air before it flows through the injection tube or into the flow section.

[0031] The chambers may advantageously have further elements for influencing the secondary air flow, in particular fins, guide vanes or special surface coatings. Furthermore, the volume of the chambers and the respective shape may be varied depending on the specific application in each case.

[0032] Advantageous further embodiments of the invention are set forth in the dependent claims and in the following description of the drawings.

[0033] The present invention will now be described in detail with reference to the drawings, in which: FIG. [Brief description of the drawings]

[0034] [Figure 1] 1 shows a schematic diagram of an exhaust pipe from an exhaust gas turbocharger to an electrically heatable catalytic converter, with secondary air being fed into the exhaust pipe line. [Diagram 2] FIG. 1 shows a chamber for supplying secondary air into the injection tube. [Diagram 3] FIG. 2 shows a chamber for supplying secondary air into an injection tube in which a metal honeycomb is arranged. [Figure 4]FIG. 2 shows a cross-section of a chamber for supplying secondary air, on the left side a cylindrical injection tube and on the right side a conically expanding injection tube. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] 1 shows an exhaust gas turbocharger 1 and an exhaust gas pipe 2 downstream of the exhaust gas turbocharger 1. The exhaust gas pipe 2 leads the exhaust gases from the exhaust gas turbocharger 1 to an electrically heatable catalytic converter 3.

[0036] The electrically heatable catalytic converter 3 consists of an electrically heatable honeycomb body which can be connected to a voltage source via an electrical feedthrough (not shown). Downstream of the electrically heatable catalytic converter 3 there is a further catalytic converter 4, on which the electrically heatable catalytic converter 3 can be supported by support pins.

[0037] The exhaust pipe 2 has a feed point into which an injection pipe 5 opens. A secondary air flow can be fed into the exhaust pipe 2 via the injection pipe 5. For this purpose, the injection pipe 5 can have suitable means for directing the flow, for example nozzle elements, vanes or fins, which generate a directed flow of secondary air in the exhaust pipe 2.

[0038] In figure 2 an injection pipe 5 is shown, as already shown in figure 1. This injection pipe 5 is arranged in a chamber 6, to which secondary air can be supplied via a conduit 7. A possible flow of the secondary air is shown by streamlines 8.

[0039] The chamber 6 forms a closed housing designed to direct the secondary air entering via the conduit 7 into the injection pipe 5 as evenly as possible. For this purpose, guide elements may be provided in the chamber 6. Furthermore, the chamber 6 may have a shape different from the cylindrical shape shown in order to distribute and transport the flow from the conduit 7 into the injection pipe 5 in the best possible direction. In particular, with a change in the flow cross section inside the chamber 6, ridges may be provided in the walls of the chamber 6, which serve to guide the flow.

[0040] 2 has on its inlet side a number of air guide elements 9. These air guide elements 9 are formed by vanes and serve to direct the secondary air entering the injection tube 5 and thus generate an improved and uniform distribution of the secondary air within the injection tube 5.

[0041] Figure 3 shows an embodiment similar to that of figure 2. In contrast to figure 2, a metallic honeycomb body 10 is inserted into the injection pipe 5. This honeycomb body 10 has a number of channels running from the inlet side facing the chamber 6 to the outlet side forming the feed point into the exhaust gas line.

[0042] In an alternative embodiment, the honeycomb body may be made of a ceramic material. By adapting the structure of the honeycomb body, different properties can be produced. In particular, the cell density, wall thickness, length and diameter can be adapted. Furthermore, guide elements can be provided in the channels of the honeycomb body, and openings can be made to allow selective overflow between the multiple channels.

[0043] In the left-hand part of Figure 4, an injection pipe 5 is shown which has a cylindrical shape. In the right-hand part of the drawing, an injection pipe 11 is shown which widens conically from the inlet side to the outlet side. This injection pipe 11 on the right-hand side is an alternative embodiment to the injection pipe 5 on the left-hand side.

[0044] In both injection pipes 5, 11, a cyclone-like flow guidance of the secondary air flowing through these injection pipes 5, 11 is shown. Depending on the design of the injection pipes 5, 11, different spreading of the secondary air flow can be achieved.

[0045] Various features of the individual embodiment examples may be combined with one another.

[0046] In particular, the embodiments of FIGS. 1 to 4 are not of a limiting nature, but serve to illustrate the idea of ​​the present invention. [Explanation of symbols]

[0047] 01 Turbocharger 02 Exhaust gas pipe 03 Heatable catalyst 04 Catalyst 05 Injection pipe 06 Chamber 07 Conduit 08 Streamline 09 Guide Elements 10 Honeycomb body 11 Injection tube

Claims

1. A device for feeding a quantity of secondary air into an exhaust pipe (2) of an internal combustion engine, the device having a flow path arranged downstream of a gas outlet of the engine in the direction of the flow of the exhaust gases and an injection device designed to feed a quantity of secondary air into the flow path at a feed point, the secondary air is supplied upstream of the first honeycomb body (3), the secondary air being introduced into the flow section through the injection pipes (5, 11) of the injection device, the injection pipes (5, 11) being arranged outside the flow section and opening into it, The device is characterized in that the injection pipe (5, 11) has a metallic substrate (10) with a number of channels through which the flow passes along a main flow direction towards the feed point.

2. 2. The device according to claim 1, characterized in that the supply point for supplying the secondary air into the flow section is located downstream of an exhaust gas turbocharger (1).

3. 3. Apparatus according to claim 1 or 2, characterized in that the initial honeycomb body (3) is formed by an electrically heatable honeycomb body (3).

4. 2. Apparatus according to claim 1, characterized in that the injection tube (5) has a cylindrical cross section.

5. 2. Apparatus according to claim 1, characterized in that the injection pipe (11) has a cross section which widens conically towards the feed point.

6. 2. The device according to claim 1, characterized in that the injection pipe (5, 11) is supplied with a secondary air flow via an air supply section, the injection pipe (5, 11) is centrally arranged in a chamber (6), the secondary air can flow around the injection pipe (5, 11) inside the chamber (6), and the secondary air can flow from the chamber (6) into an inlet opening of the injection pipe (5, 11).

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