EXHAUST SYSTEM OF AN INTERNAL COMBUSTION ENGINE

Abstract

An exhaust system for an internal combustion engine, in the exhaust duct of which a sensor is arranged for determining the exhaust gas composition. Furthermore, upstream of the sensor a guide vane is arranged, which is designed to increase the flow velocity of the exhaust gas in a local flow cross-section of the exhaust duct at the height of the sensor. This makes it possible to provide sufficiently high flow velocities of the exhaust gas at the sensor.

Claims

1. An exhaust system for an internal combustion engine of a vehicle, the exhaust system comprising: an exhaust duct; an exhaust aftertreatment system; at least one sensor arranged in the exhaust duct to determine the exhaust gas composition; and a guide vane arranged upstream of the sensor, the guide vane configured to increase a flow velocity of the exhaust gas in a local flow cross-section of the exhaust duct at a height of the sensor.

2. The exhaust system according to claim 1, wherein the flow cross-section of the exhaust duct at the height of the sensor is constant.

3. The exhaust system according to claim 1, wherein the at least one sensor for determining the exhaust gas composition is a lambda probe and/or an NO.sub.x sensor.

4. The exhaust system according to claim 1, wherein the guide vane is designed to increase the flow velocity of the exhaust gas at the height of the sensor to at least 5 m/s.

5. The exhaust system according to claim 1, wherein, by tilting or straightening the guide vane, an angle between the guide vane and the exhaust duct is variably adjustable.

6. The exhaust system according to claim 5, wherein the adjustment of the angle between the guide vane and the exhaust duct is carried out as a function of the flow velocity of the exhaust gas at a height of the sensor.

7. The exhaust system according to claim 6, wherein the flow velocity is calculated via a model or measured by a flowmeter.

8. The exhaust system according to claim 1, wherein a surface of the guide vane extending along the flow direction and overflowed by the exhaust gas rises ramp-like and in a direction of a center axis of the exhaust duct.

9. The exhaust system according to claim 1, wherein two side edges of the guide vane extending in the direction of flow protrude in the direction of the center axis and a surface of the guide vane overflowed by the exhaust gas is channel-shaped.

10. The exhaust system according to claim 1, wherein the guide vane is connected to the exhaust duct in a form- or material-locking manner.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

[0034] FIG. 1 illustrates an exhaust system according to the conventional art in a schematic view,

[0035] FIG. 2 illustrates a system structure according to the invention,

[0036] FIG. 3 illustrates a side view of an exhaust duct section according to the example of the invention shown in FIG. 2, and

[0037] FIG. 4 illustrates a view of the top of the guide vane and the lambda probe of an exhaust duct section according to the example of the invention shown in FIG. 2.

DETAILED DESCRIPTION

[0038] FIG. 1 shows an exhaust system 2′ according to the conventional art, which is arranged downstream of a not-shown internal combustion engine of a vehicle. The connection to the combustion engine is made via an exhaust duct 21. Downstream of the internal combustion engine, a first catalyst 221 is arranged. Downstream of this is a lambda probe 23, whose measuring head protrudes into the exhaust duct 21, whereby it is surrounded by the exhaust gas 3 (represented by an arrow, which also represents the flow direction of the exhaust gas) and measures the residual oxygen concentration in the exhaust gas 3. Also downstream of the first catalyst 221, a second catalyst 222 is arranged. The catalysts 221, 222 are used to reduce exhaust emissions and are part of the exhaust aftertreatment system 22. All the components mentioned above, which carry exhaust gas 3, are in flow connection to each other via an exhaust duct 21 that is not further subdivided.

[0039] The section 211 of the exhaust duct 21 which lies between the catalysts 221 and 222 and in which the lambda probe 23 is arranged has a reduced flow cross-section. This is done with the aim of increasing the flow velocity of the exhaust gas 3 in the constricted section 211 of the exhaust duct 21, so that the lambda probe 23 arranged there provides reliable measured values about the oxygen concentration in the exhaust gas 3. However, this flow influence affects the entire area within this section 211 of the exhaust duct 21. As a result, the flow resistance also increases, which results in an increased pressure loss and thus in increasing exhaust gas back pressure.

[0040] FIG. 2 shows an inventive system structure according to an embodiment of the present invention. Shown is an exhaust system 2, which is arranged downstream of an internal combustion engine 1 of a vehicle. Downstream of the internal combustion engine 1 is a first catalyst 221, which in this example is designed as a three-way catalyst. Downstream of the latter is a flowmeter 25 for measuring the exhaust gas mass flow. Following the flowmeter 25 is a lambda probe 23, which protrudes into the exhaust duct 21, whereby the lambda probe 23 is surrounded by the exhaust gas 3 (represented by an arrow, which also represents the flow direction of the exhaust gas) and measures the residual oxygen concentration 3 in the exhaust gas. Downstream of the lambda probe 23 is a second catalyst 222, which in this example is also designed as a three-way catalyst. The exhaust aftertreatment system 22 includes the catalysts used to reduce exhaust emissions. All the components mentioned above, which carry exhaust gas 3, are in flow connection with each other via an exhaust duct 21 that is not further subdivided.

[0041] Furthermore, upstream of the lambda probe 23, a guide vane 24 is arranged. The guide vane 24 is designed to increase the flow velocity of the exhaust gas in a local flow cross-section of the exhaust duct 21 at the height of the sensor. The flow cross-section of the exhaust duct 21 flowed through by exhaust gas 3 remains constant in the region of the lambda probe 23. There is no constriction in the region of the lambda probe 23.

[0042] In addition, the vehicle comprises an on-board computer, i.e., an engine control unit 4. This is used, among other things, for the preparation and evaluation of the signals, which are transmitted, among other things, by the lambda probe 23 and the flowmeter 25.

[0043] FIG. 3 shows a side view of an exhaust duct section of the exhaust duct 21 according to the embodiment of the invention shown in FIG. 2. It is the exhaust duct section on which the lambda probe 23 is arranged. To protect sensitive elements, a thermowell 231 is attached to the probe housing on the exhaust side. This protects the sensor element from solid combustion residues and condensation in the exhaust gas 3. For gas access, the thermowell 231 has inlet holes 232.

[0044] Upstream of the lambda probe 23, the guide vane 24 is arranged, which is connected to the exhaust duct 21, wherein it is attached directly to the duct wall. Two side edges 242 of the guide vane extending in the flow direction protrude in the direction of the center axis 212. A surface 241 of the guide vane 24 overflowed by the exhaust gas 3 is channel-shaped. In other words, there is a curvature of the overflowed surface 241, which is channel-shaped in a perspective oriented in the direction of flow of the exhaust gas 3. Furthermore, the surface 241 of the guide vane 24, which extends along the flow direction and is overflowed by the exhaust gas 3, rises ramp-like in the flow direction of the exhaust gas 3 and in the direction of the center axis 212 of the exhaust duct 21. In other words, the distance between the center axis 212 and the overflowed surface 241 decreases in the flow direction. Preferably, the surface 241 rises such that it has a curvature that comes close to a concave shape.

[0045] The guide vane 24 causes the exhaust gas 3 illustrated by arrows to experience an acceleration that is locally limited only to the flow velocity of the exhaust gas 3 at the height of the lambda probe 23. This favors an entry of the exhaust gas through the holes 232 of the thermowell 231 of the lambda probe 23 into the measuring volume. Nevertheless, the flow cross-section 211 of the exhaust duct 21 remains unchanged, so that the exhaust gas back pressure does not increase as a result of constriction of the exhaust duct 21. In addition, no structural and expensive measures to change the exhaust duct geometry are necessary.

[0046] FIG. 4 shows a view of the top of the lambda probe 23 and the guide vane 24 of the exhaust duct section according to FIG. 2. The perspective on the exhaust duct section was therefore rotated by 90° about the center axis 212 as compared to the view in FIG. 3, so that now a view of the top of the lambda probe 23 and the guide vane 24 is shown. The described surface 241 causes a significant deflection of the exhaust gas 3. Combined, therefore, both the protruding side edges 242 of the guide vane 24, the channel-shaped surface 241 and its ramp-like rise cause a deflection of the exhaust gas in several directional axes, so that a particularly pronounced acceleration can take place.

[0047] In an advantageous design, the guide vane 24 is adjustable, so that, among other things, an angle between the surface of the guide vane 24 facing away from the lambda probe 23 in FIG. 4 and a surface of the exhaust duct 21 facing this surface can be varied. As a result, the strength of the acceleration and thus the flow velocity of the exhaust gas 3 can be adjusted at the height of the lambda probe. This makes it possible to react optimally to different operating states and consequently to allow for a minimum pressure loss at a sufficiently high flow velocity. The setting can be specified by an engine control unit 4, wherein a flow velocity measured with the flowmeter 25 upstream of the lambda probe 23 serves as a basis for calculation. Alternatively, a flowmeter could be dispensed with, and the flow velocity could be determined on the basis of a model. The engine control unit 4 usually models the air volume on the basis of which the flow velocity of the exhaust gas 3 could be calculated.

[0048] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.