Exhaust gas recirculation system for an internal combustion engine

Abstract

Exhaust gas recirculation system (10) for an internal combustion engine (2), comprising an exhaust gas channel (6) to which an exhaust gas recirculation channel (8) is connected at a branch point (24) in which an exhaust gas recirculation valve (26) is arranged, - wherein the exhaust gas recirculation channel (8) connects the exhaust gas-side branch point (24) and a fresh air-side exhaust gas supply point, - wherein the exhaust duct (6) has a deflection area (38) and a flow element (30, 40) in the area of ​​the branch point (24), - wherein the flow element (30, 40) is formed by the exhaust gas recirculation valve (26), and - wherein the flow element (30, 40) does not extend into the exhaust gas channel (6) when the exhaust gas recirculation valve (26) is closed, and is positioned as a flow resistance in the deflection area (38) when the valve is open.

Description

[0001] The invention relates to an exhaust gas recirculation system for an internal combustion engine, comprising an exhaust gas channel, in particular designed as an exhaust manifold, to which an exhaust gas recirculation channel is connected at a branch point, in which an exhaust gas recirculation valve is arranged.

[0002] Exhaust gas recirculation systems of the type mentioned above can be found, for example, in DE 10 2010 038 326 A1 or DE 10 2010 007 092 A1. These systems are often used to reduce nitrogen oxide emissions, which are produced during fuel combustion in internal combustion engines. From an environmental protection perspective, it is advantageous to minimize the formation of nitrogen oxides during the combustion process itself.

[0003] When exhaust gas is mixed with the fresh air used for combustion, the oxygen concentration of the gas mixture decreases. This reduces the reaction rate and the combustion temperature for the fuel molecules within the combustion engine. Due to the exponential dependence of the reaction rate of nitrogen oxide formation on the combustion temperature, this reduces nitrogen oxide formation during the combustion process.

[0004] Especially in diesel engines, exhaust gas recirculation is one of the most important measures for reducing nitrogen oxide emissions and complying with prescribed emission regulations, as the use of exhaust aftertreatment (for example by means of an exhaust catalyst) alone is not sufficient for this purpose.

[0005] The amount of recirculated exhaust gas, or rather the exhaust gas recirculation mass flow rate, depends on the opening degree of the exhaust gas recirculation (EGR) valve. Opening the EGR valve creates a flow connection between the exhaust system and the intake air system of the combustion engine. Typically, the exhaust system is tapped by the EGR valve in the area between an exhaust valve and the turbocharger of the combustion engine. The diverted exhaust gas is then fed back into the intake air system downstream of the turbocharger. With the EGR valve fully open, the maximum possible EGR mass flow rate is determined by the pressure differential between the exhaust gas outlet and the intake air outlet.

[0006] To meet increasingly stringent emissions regulations, ever-higher exhaust gas recirculation (EGR) mass flows are required. However, these higher EGR mass flows negatively impact the efficiency of modern exhaust gas turbochargers. As a result of continuous improvements in turbocharger technology, the pressure differential required for the EGR mass flow decreases. Therefore, with the current state of technology, the increasing demand for higher EGR mass flows is limited, as these are directly influenced by the pressure differential.

[0007] Throttle valves can be used to increase the exhaust gas recirculation rate. By selectively adjusting the throttle in the exhaust gas recirculation system, an increased pressure differential can be generated. However, this type of throttling also increases the vehicle's fuel consumption.

[0008] In DE 697 04 322 T2, an exhaust gas recirculation device is described which is able to prevent the occurrence of condensation within an exhaust gas recirculation pipe after the engine has stopped and of corrosion within the exhaust gas recirculation pipe, an EGR valve, a reed valve, etc., and which is ultimately able to improve the durability and service life of the engine.This exhaust gas recirculation device comprises an exhaust gas recirculation pipe with an EGR valve for controlling an exhaust gas recirculation quantity, connected between an exhaust port and an intake port in an internal combustion engine equipped with a compressor, and a check valve to prevent intake air from flowing into the exhaust gas recirculation pipe when an internal pressure of the exhaust gas recirculation pipe is lower than an internal pressure of the intake port, arranged at the connection between the exhaust gas recirculation pipe and the intake port, wherein the check valve has a gap for the connection between the exhaust gas recirculation pipe and the intake port while the engine is stopped.

[0009] DE 33 39 592 A1 discloses an exhaust gas recirculation system in an internal combustion engine with an intake system and an exhaust system, which includes an exhaust gas recirculation line connecting the intake and exhaust systems. This line can be closed by a shut-off device that can be actuated by auxiliary energy. To redirect the exhaust gas flow using simple mechanical means, the shut-off device is used in the exhaust gas recirculation position to divert the exhaust gas flow into the exhaust gas recirculation line.

[0010] The invention is based on the objective of providing an exhaust gas recirculation system for an internal combustion engine that is optimized as much as possible with regard to the exhaust gas recirculation rate for existing and future emissions regulations. In particular, the aim is to achieve the highest possible exhaust gas recirculation rates while simultaneously minimizing fuel consumption.

[0011] This problem is solved according to the invention by an exhaust gas recirculation system with the features of claim 1 and by a motor vehicle with such an exhaust gas recirculation system. Advantageous embodiments and further developments are the subject of the dependent claims.

[0012] An exhaust gas recirculation system for an internal combustion engine comprises an exhaust manifold to which an exhaust gas recirculation channel is connected at a branch point. This recirculation channel contains an exhaust gas recirculation valve. The exhaust manifold is preferably formed by an exhaust manifold, which is referred to as the exhaust manifold in the following text. A flow element is located at the branch point and can be moved into the flow path of the exhaust manifold. This flow element creates additional flow resistance for the exhaust gas, generating a controlled increase in exhaust back pressure during operation. This back pressure increases the pressure differential between the exhaust-side branch point and a fresh air-side exhaust inlet. This increased pressure allows for higher exhaust gas recirculation rates.

[0013] By increasing the achievable exhaust gas recirculation rates due to the additional exhaust backpressure generated, improved emission values ​​can be met in accordance with stricter (future) emissions regulations. Furthermore, a reduction in fuel consumption is achievable compared to the use of throttle valves in the exhaust gas recirculation system.

[0014] In one embodiment according to the invention, the flow element is formed by the exhaust gas recirculation valve. This generates exhaust gas back pressure in addition to the adjustable cross-sectional opening when the valve is opened.

[0015] To prevent any negative influence on the main flow path from the exhaust valves of the combustion engine to an exhaust gas turbocharger, for example through generated turbulence or eddies, the flow element in a further development according to the invention does not extend into the exhaust manifold when the exhaust gas recirculation valve is closed.

[0016] To ensure that the exhaust gas flow of the main flow path is not negatively affected, a suitable design provides in particular that the flow element is aligned with a wall of the exhaust manifold when the exhaust gas recirculation valve is closed.

[0017] In a particularly fluid-efficient embodiment according to the invention, the exhaust manifold has a deflection area in the region of the branch point into which the flow element can be positioned. In a preferred embodiment, the branch point is approximately T-shaped. The vertical leg of the T corresponds to the supply line from the exhaust manifold, while the horizontal leg corresponds to the supply line to the exhaust tract and a turbine of the exhaust gas turbocharger on the one hand, and to the supply line to the exhaust gas recirculation channel on the other. The deflection area is, for example, a bulge in the corner region between the horizontal and the vertical legs of the T. The exhaust gas recirculation channel is advantageously arranged between two engine-side exhaust ports of the exhaust manifold.

[0018] In a preferred embodiment, the exhaust gas recirculation valve is a poppet valve comprising a valve poppet and a valve stem. The valve poppet and the valve stem essentially form or encompass the flow element when the valve is open and extends at least partially into the exhaust gas channel of the exhaust manifold.

[0019] In a suitable further development, the flow element is specifically molded onto the back of the valve disc. The back is therefore specially designed to increase the dynamic pressure and thus has a larger flow area compared to a conventional valve disc.

[0020] In an advantageous embodiment, the flow element has, in particular, an inclined flow surface, wherein the flow surface is preferably shaped like a paddle. In an advantageous embodiment, the flow surface serves, in particular, as a flow guide element and is, for example, designed as a concavely curved cone or truncated cone. Preferably, the height of the cone or truncated cone is greater than 20%, and in particular greater than 50%, of the valve disc diameter.

[0021] The design of the valve disc back with flow surfaces creates a scooping effect that ensures the additional utilization of the exhaust back pressure. In particular, as the valve opens, the corresponding geometric shape of the flow surfaces gradually comes into play, so that the proportion of the "sketched" exhaust mass flow increases.

[0022] An embodiment of the invention is explained in more detail below with reference to a drawing. The drawing shows: Fig. 1 in schematic representation an internal combustion engine with an exhaust gas turbocharger, an exhaust gas manifold and an exhaust gas recirculation system, Fig. 2 in perspective view the exhaust manifold with an exhaust gas recirculation channel connected to it, Fig. 3 in top view the exhaust manifold with the exhaust gas recirculation channel connected to it, Fig. 4 in sectional view along line III-III according to Fig. 3 the exhaust manifold and the exhaust gas recirculation channel with a closed exhaust gas recirculation valve, and Fig. 5 in sectional view along line III-III according to Fig. 3 the exhaust manifold and the exhaust gas recirculation channel with an open exhaust gas recirculation valve.

[0023] Corresponding parts in all figures are always marked with the same reference symbols.

[0024] The in Fig. The combustion engine 2 shown in Figure 1 is equipped with an exhaust gas turbocharger 4 and an exhaust manifold 6, to which an exhaust gas recirculation channel 8 is connected as part of an exhaust gas recirculation system 10. In this embodiment, the combustion engine 2 has four cylinders 12, schematically represented by circles, of which only one is provided with a reference numeral for illustrative purposes. The combustion engine 2 is connected to a fresh air intake tract 14 for supplying the cylinders 12 with oxygen-containing fresh air F and to an exhaust gas intake tract 16 for removing exhaust gases A.

[0025] Exhaust gases A, produced during fuel combustion in cylinders 12, are routed through the exhaust manifold 6 and fed through the exhaust tract 16 to a turbine 18 of the exhaust gas turbocharger 4. The turbine 18 drives a fresh air-side compressor 20 of the exhaust gas turbocharger 4 in a manner not shown in detail. Downstream of the compressor 20, a fresh air cooler 22 is arranged, which cools the fresh air F to a specific temperature.

[0026] In an exemplary embodiment of a high-pressure exhaust gas recirculation system, exhaust gases A are diverted upstream of the turbine 18 via the exhaust gas recirculation channel 8 at a branch point 24 and fed upstream to the fresh air cooling system 22 for mixing with the fresh air F. The recirculated exhaust gas mass flow rate depends on the opening degree of an exhaust gas recirculation valve 26. With a fully open exhaust gas recirculation valve 26, the maximum possible exhaust gas recirculation mass flow rate within the exhaust gas recirculation channel 8 is determined by the pressure difference ΔP between the exhaust gas-side pressure P and the pressure on the exhaust side. A in the area of ​​a branch point 24 upstream of turbine 18, as well as the fresh air side pressure P F The exhaust gas temperature is influenced in the area of ​​the exhaust gas inlet upstream of the fresh air cooling system 22. To regulate the exhaust gas temperature, the exhaust gas recirculation system 10 includes an exhaust gas cooler 28.

[0027] In the Fig. 2, Fig. 3, Fig. 4 to Fig. Figure 5 shows the exhaust manifold 6, the exhaust gas recirculation channel 8, and the branch point 24 in more detail. The exhaust gas recirculation valve 26 is, in particular, a poppet valve with a valve disc 30 as a shut-off element and a valve stem 32, which is coupled to an electric motor 34 for actuation. The electric motor 34 allows the exhaust gas recirculation valve 26 to be moved from a closed position to an open position within the exhaust manifold 6.

[0028] In Fig. 4 and Fig. Section 5 explains the structure and function of the exhaust gas recirculation valve 26 in more detail. The corresponding exhaust gas mass flow from the exhaust manifold 6 is shown schematically by means of arrows. In the closed state ( Fig. 4) Through the exhaust gas recirculation valve 26, the entire exhaust gas mass flow from the cylinders 12, via the exhaust manifold 6, past the branch point 24 to the turbine 18 in the exhaust tract 16. The valve plate 30 seals the exhaust gas recirculation channel 8 essentially hermetically against the exhaust manifold 6. The underside, or belly, of the valve plate 30 is flush with the walls of the exhaust manifold 6.

[0029] The exhaust gas recirculation channel 8 is arranged on the exhaust manifold between two engine-side manifold stubs, offset from them by approximately 90°. Opposite the exhaust gas recirculation channel 8 is the common exhaust-side manifold stub. The central axis of the exhaust gas recirculation channel 8 generally preferably aligns with the central axis of this exhaust-side manifold stub. The engine-side manifold stubs and the exhaust-side manifold stub are therefore also offset by approximately 90°, so that a deflection section 38 of the exhaust manifold 6 is formed in the area of ​​the exhaust gas recirculation channel 8. The branch point 24 is therefore approximately T-shaped. The vertical leg of the T corresponds to the engine-side flow channel of the exhaust manifold 6. The horizontal leg of the T forms, on the one hand, the exhaust-side inlet to the exhaust tract 16 with the turbine 18 of the exhaust gas turbocharger 4, and on the other hand, the exhaust gas recirculation channel 8.The deflection area 38 is essentially a bulge in the corner region between the horizontal and vertical T-legs. The valve plate 30 is moved into this deflection area 38 by the electric motor 34 to open the exhaust gas recirculation channel 8.

[0030] When open ( Fig. 5), in which the valve plate 30 has moved into the chamber of the exhaust manifold 6, exhaust gases A flow at least partially through the exhaust gas recirculation system 10 to the fresh air tract 14. For the purpose of increasing the exhaust gas recirculation rate of the exhaust gases A, the valve plate 30 of the exhaust gas recirculation valve 26 has a flow surface 40 formed on its back surface, which defines a flow element.

[0031] The flow area 40 is - as in Fig. 4 and Fig.5 is evident – ​​essentially designed as a concave curved surface of a truncated cone, which is aligned with the valve stem 32 on its end face. The flow surface 40 is generally oriented at an angle to the incident exhaust gas mass flow of the exhaust manifold 6, i.e., at an angle to the longitudinal axis of the engine-side flow channel of the exhaust manifold 6. At the same time, the flow surface 40 is also oriented at an angle to the valve stem 32 and has, in particular, an approximately scoop-like cross-sectional profile.

[0032] In the open operation of the exhaust gas recirculation valve 26, the flow area 40 serves, on the one hand, as a flow resistance to generate an exhaust gas back pressure P due to the thereby increased surface area of ​​the valve disc 30. S . Due to the additional exhaust back pressure Ps, the pressure difference ΔP increases and thus the exhaust gas recirculation rate of the exhaust gas recirculation system 10.

[0033] On the other hand, the flow surface 40, due to its special geometric shape, is designed as a flow guide element for deflecting the exhaust gas mass flow. This ensures optimal utilization of the increased pressure difference ΔP for deflecting the largest possible exhaust gas mass flow into the exhaust gas recirculation channel 8.

[0034] The invention is not limited to the embodiment described above. Rather, other variants of the invention can also be derived by a person skilled in the art without departing from the subject matter of the invention. In particular, all individual features described in connection with the various embodiments can also be combined with one another in other ways without departing from the subject matter of the invention.

Claims

[1] Exhaust gas recirculation system (10) for an internal combustion engine (2), comprising an exhaust gas channel (6) to which an exhaust gas recirculation channel (8) is connected at a branch point (24) in which an exhaust gas recirculation valve (26) is arranged, - wherein the exhaust gas recirculation channel (8) connects the exhaust gas-side branch point (24) and a fresh air-side exhaust gas supply point, - wherein the exhaust duct (6) has a deflection area (38) and a flow element (30, 40) in the area of ​​the branch point (24), - wherein the flow element (30, 40) is formed by the exhaust gas recirculation valve (26), and - wherein the flow element (30, 40) does not extend into the exhaust gas channel (6) when the exhaust gas recirculation valve (26) is closed, and is positioned as a flow resistance in the deflection area (38) when the valve is open. [2] Exhaust gas recirculation system (10) according to claim 1, characterized by, that the flow element (30) is aligned with a wall of the exhaust gas channel (6) when the exhaust gas recirculation valve (26) is closed. [3] Exhaust gas recirculation system (10) according to claim 1 or 2, characterized by , that the exhaust gas recirculation valve (26) is a poppet valve with a valve poppet as a flow element (30) and a valve stem (32). [4] Exhaust gas recirculation system (10) according to claim 3, characterized by , that a flow surface (40) is formed on the back of the valve plate (30). [5] Exhaust gas recirculation system (10) according to claim 3 or 4, characterized by , that the flow element (30,40) has an obliquely inclined flow surface (40). [6] Exhaust gas recirculation system (10) according to claim 5, characterized by , that the flow surface (40) is shaped like a paddle. [7] Motor vehicle with an internal combustion engine (2) and an exhaust gas recirculation system (10) coupled thereto according to one of claims 1 to 6.

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