Cooling device for an exhaust system

Abstract

A device arranged on the underside of the vehicle for air cooling the exhaust system of an internal combustion engine, comprising a first functional area (118, 312) for flow enhancement and a second functional area (120, 314) for forced flow guidance, wherein the second functional area (120, 314) surrounds the exhaust system (104, 304, 306) on the downstream side in a jacket-like manner, so that a cooling air flow is forced around the exhaust system (104, 304, 306).

Description

[0001] According to the preamble of claim 1, the invention relates to a device arranged on the vehicle underbody for air cooling the exhaust system of an internal combustion engine.

[0002] NO is often used for exhaust gas aftertreatment, particularly in lean-burn gasoline engines such as naturally aspirated or direct-injected engines. X -Storage catalysts are used. The exhaust gases from the internal combustion engine are usually led via the exhaust system from the internal combustion engine through the engine compartment into the underbody area, where one or more flowable NO X -Storage catalysts are arranged.

[0003] At high exhaust gas temperatures, such as those that occur at high loads, the NO Xstorage catalyst to the point of irreversible damage. In this context, it is necessary to design the exhaust system in such a way that the airflow ensures the best possible circulation and thus cooling of its surface, especially in the area upstream of the NO X -storage catalyst.

[0004] If the exhaust pipes are not sufficiently cooled, cooling by enriching the exhaust gas is necessary, corresponding to engine operation with λ<1, which results in significantly increased fuel consumption. Furthermore, when the engine is operated with λ<1, complete purification of the exhaust gas by means of the catalytic converter is no longer possible.

[0005] An example is DE 100 38 796 A1, which is used for exhaust gas cooling before the NO XThe storage catalytic converter requires a multi-flow exhaust system. No further measures are taken to ensure effective cooling of the exhaust system, so exhaust cooling relies solely on increasing the surface area. The disadvantage is that this results in a very high overall weight of the exhaust system and poses the risk of heat buildup in poorly ventilated areas between the individual pipes.

[0006] Although it is proposed according to one embodiment to provide a housing which surrounds the pipes and which can be acted upon by means of a coolant, this measure is also considered to be very complex and further increases the weight of the exhaust system.

[0007] A high exhaust system weight is not only disadvantageous in terms of the overall vehicle weight and the known associated disadvantages, it also hinders the necessary rapid heating of the catalytic converter system due to the greater heat capacity, so that lean operation, which is favorable for consumption and emissions, can only be carried out at a relatively late point in time.

[0008] Document DE 101 25 989 A1 relates to a method for cooling motor vehicle exhaust gases in an air-cooled exhaust gas heat exchanger through which the exhaust gases flow. It proposes guiding incoming ambient air through the exhaust gas heat exchanger at an acute angle α relative to the exhaust gas flow direction. The exhaust gas heat exchanger is to have a plurality of exhaust gas and cooling ducts arranged alternately next to one another transversely to the exhaust gas flow direction. The flow of circulating air to the exhaust gas heat exchanger is to be controlled by a control device with at least one first air or louvre flap device on the air inlet and / or air outlet side, which is arranged at a specific distance and a specific inclination relative to the exhaust gas heat exchanger.

[0009] Document DE 197 11 336 A1 relates to a floor structure at the rear of a motor vehicle, comprising an upper floor and a lower floor spaced therefrom, and comprising an exhaust system extending adjacent to the floor structure. It is proposed that the floor structure, on the one hand, comprise a storage compartment for motor vehicle parts, and that the upper floor of the storage compartment be spaced from the lower floor by webs. Side walls formed beneath the storage compartment, together with the floors and the webs, form flow channels that comprise inlet openings at their front end and outlet openings at their rear, rear end and on the side walls.

[0010] Document US 5 813 491 A relates to an improved underbody structure of a motor vehicle, by which the fuel tank is effectively cooled during operation of the vehicle. The underbody structure comprises a lower cover arranged below the engine compartment. The lower cover is formed with a longitudinally extending groove whose opening is directed downwards to come into contact with air of a relatively low temperature. A floor panel is formed with a longitudinally extending tunnel whose opening is directed downwards. The tunnel accommodates the exhaust piping therein without contacting it. A heat-insulating plate extends into and along the tunnel in such a way that an air flow channel is defined in the tunnel, which is insulated from the exhaust piping. The air flow channel has a rear open end directed toward the fuel tank.A connecting channel is provided to connect the groove of the bottom cover with the air flow channel defined in the tunnel of the base plate.

[0011] The object of the invention is to achieve effective airflow-induced cooling of the exhaust system in a simple and cost-effective manner, but without significantly restricting the underbody clearance of the vehicle.

[0012] The problem is solved by a device having the features of claim 1.

[0013] Advantageous embodiments and further developments of the invention are the subject of the dependent claims.

[0014] According to a particularly preferred embodiment, the first functional area is arranged upstream of the second functional area in the direction of travel, so that the first and then the second functional area are affected by the airflow.

[0015] It is very advantageous if the first functional area causes a flow increase in the direction of the exhaust system due to negative pressure.

[0016] The air flow is expediently directed by means of the first functional area in such a way that an optimized flow to the second functional area occurs.

[0017] Furthermore, it is considered particularly advantageous if the second functional area is used to force the air flow to flush the exhaust system.

[0018] According to a preferred embodiment of the invention, both the first and the second functional region are arranged above a predetermined underbody clearance line, so that the underbody clearance of the vehicle is at least not significantly restricted.

[0019] It is advisable for a vehicle with an exhaust system that emits NO X-Storage catalyst includes the device in the inlet area of ​​the exhaust system into the underbody and in the flow direction in front of the NO X -Storage catalyst is arranged.

[0020] According to a preferred embodiment, the first functional region has a guide surface that rises in the direction of flow and has a narrow inlet and a wide outlet. The second functional region has a guide surface that rises in the direction of flow and has an inlet and outlet of at least approximately the same width, which is substantially shorter but rises more steeply than the guide surface of the first functional region. According to a further embodiment, the first functional region has a guide surface that rises in the direction of flow and has an at least approximately constant width over its length.

[0021] A particularly preferred embodiment of the invention is explained in more detail below with reference to figures, which show schematically and by way of example Fig. 1a a flow pattern in the pre-pipe area, Fig. 1b a flow increase towards the exhaust pipe by means of negative pressure, Fig. 1c a forced air flow to flush the exhaust pipes, Fig. 1d a combination of the operating principles of flow increase and forced guidance, Fig. 2 an air baffle to increase the flow, Fig. 3a a cooling device for an exhaust system from below, as well as Fig. 3b a cooling device for an exhaust system in section.

[0022] Catalytic converters are commonly used for exhaust gas aftertreatment in internal combustion engine-powered vehicles. For example, in intake manifold and direct injection gasoline engines, NO X Storage catalysts are used. At high exhaust temperatures, such as those encountered during high engine loads, there is a risk that the catalysts will overheat and be irreversibly damaged, so cooling the exhaust pipes using an airflow induced by the headwind is attempted.

[0023] In this context, Fig. 1 shows the course of an underbody flow 100a caused by the airstream in the front pipe area below an underbody clearance line 102. The exhaust pipe 104, which carries the hot exhaust gas 106, runs in this area from the internal combustion engine toward the vehicle underbody, passes through it, and continues to the rear of the vehicle. The exhaust system includes catalytic converters (not shown in detail here). No special measures have been taken to direct the flow around the exhaust pipe 104; the flow 100a essentially flows past the exhaust pipe 104 without any corresponding cooling effect.

[0024] According to Fig. 1b, an air guidance measure based on the principle of increasing the flow through negative pressure is used to circulate the cooling air around the exhaust pipe 104. An air guide plate 108 is provided that rises slightly in the direction of flow, creating a negative pressure upon inflow in the area 110, so that the underbody flow 110b is increased in the direction of the exhaust pipe 104, thus achieving improved heat dissipation. An increase in flow is possible without restricting the vehicle's underbody clearance; however, the air flow 100b only flows relatively ineffectively from below the exhaust pipe. A further increase in flow up to the height of the pipe's center axis is not possible due to the risk of flow separation, with the result that the cooling measure would not be sufficiently effective.

[0025] Fig. Figure 1c shows an air baffle 112, which represents an air guidance measure based on the principle of forced air flow for air circulation. The underbody-side airflow 100c, caused by the airstream, flows against the air baffle 112, which rises in the direction of flow. This results in a strong deflection and forced flow around the exhaust pipe 104 by the air flow 114. At the same time, due to the negative pressure at the rear of the air baffle, an air flow 116 is directed toward the exhaust pipe 104, which also contributes to cooling. For this arrangement to be sufficiently effective, it is necessary for the air baffle 112 to protrude relatively downward, thus limiting the vehicle's underbody clearance.

[0026] A combination of the two in the Fig. 1b and Fig. 1c shows the principles of action Fig. 1d. A first air baffle 118, which is arranged substantially above the underbody clearance line 102, rises slightly in the direction of the underbody flow 100d caused by the airstream, so that a separation-free rise in the flow in the region 122 occurs. A second air baffle 120 is arranged downstream of the first air baffle 118 in the flow direction. Due to the already raised flow, the second air baffle 120 can also be structurally arranged substantially above the underbody clearance line 102 and is nevertheless effectively exposed to the raised air flow. The air baffle 120 rises more sharply in the flow direction than the air baffle 118, thereby forcing the exhaust pipe 104 to be flushed with the air flows 124, 126 (cf. Fig. 1c). Even if only one exhaust pipe 104 is shown here, the exhaust system can of course also comprise several parallel exhaust pipes.

[0027] An embodiment of an air baffle 200 for realizing a Fig. 1b shown air guidance measure by flow increase, is in Fig. 2. The air baffle 200 rises slightly in the flow direction 202, so that a flow increase occurs on the underside 208 of the baffle due to the negative pressure without separation. Lateral guides 204, 206 are provided for the targeted flow onto the exhaust pipe or a second air baffle.

[0028] A structural design of a cooling device 300 for an exhaust system according to the Fig. The principle shown in Figure 1d shows Fig. 3a from below and Fig. 3b in section. In the illustrated embodiment, the exhaust system comprises two exhaust pipes 304, 306, through which air flows in the direction of the arrow 308. The exhaust pipes 304, 306 lead from the internal combustion engine (not shown here) into the area of ​​the vehicle underbody 302 and further to the rear of the vehicle. The airflow 310 on the underbody side, caused by the airstream, is used to cool the exhaust pipes in accordance with the Fig.1d is used. To increase the air flow, a first air guiding device 312 is provided, while the second air guiding device 314 directs the air flow to the exhaust pipes 304, 306, so that effective air circulation is achieved while maintaining high ground clearance. The first air guiding device 312 has a skirt 316 for attachment to the vehicle underbody, for example by means of screws 320. It is designed to rise slightly in the flow direction 310, with the width increasing; a flow increase without separation is achieved. The second air guiding device 314 is shorter in the flow direction, but is arranged with a steeper and progressive rise, and is designed like a wing in the inflow area. On the downstream side 318, the air guiding device 314 surrounds the two exhaust pipes 304, 306 like a jacket, so that the cooling air flow flows around the exhaust pipes 304, 306 in a forced manner.Catalysts not shown in detail here, such as a NO. X -Storage catalyst, for example, are arranged further downstream of the cooling device 300.

Claims

[1] Device arranged on the underbody of the vehicle for air cooling the exhaust system of an internal combustion engine, comprising a first functional area (118, 312) for increasing the flow and a second functional area (120, 314) for forced flow guidance, wherein the second functional area (120, 314) surrounds the exhaust system (104, 304, 306) on the downstream side in a jacket-like manner, so that a cooling air flow flows around the exhaust system (104, 304, 306) in a forced manner. [2] Device according to claim 1, characterized by that the first functional area (118, 312) is arranged upstream of the second functional area (120, 314) in the direction of travel. [3] Device according to claim 1 or 2, characterized by that by means of the first functional area (118, 312) a flow increase (122) in the direction of the exhaust system (104) takes place due to negative pressure. [4] Device according to one of the preceding claims, characterized bythat by means of the first functional area (118, 312) the flow (100d) is directed in such a way that an optimized flow onto the second functional area (120, 314) takes place. [5] Device according to one of the preceding claims, characterized by that the second functional area (120, 314) is used to force the air flow (124, 126) to flush the exhaust system (104). [6] Device according to one of the preceding claims, characterized by that both the first and the second functional area are arranged above a predetermined underbody clearance line (102). [7] Device according to one of the preceding claims, wherein the exhaust system comprises a NO X -Storage catalyst includes, characterized by that the device is located in the inlet area of ​​the exhaust system (104, 304, 306) in the underbody (302) and in the flow direction in front of the NO X -Storage catalyst is arranged. [8] Device according to one of the preceding claims, characterized by that the first functional area (118) has a guide surface (312) rising in the direction of flow with a narrow inlet and an extended outlet. [9] Device according to one of the preceding claims, characterized by that the first functional area (118) has a guide surface (208) which rises in the direction of flow and has a width which is at least approximately constant over the length. [10] Device according to one of the preceding claims, characterized by that the second functional area (120) has a guide surface (314) which rises in the direction of flow and has an inlet and outlet of at least approximately the same width, which is substantially shorter but rises more steeply than the guide surface (208, 312) of the first functional area (118).

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