DE19815502A1 - I.C. engine exhaust gas treatment unit - Google Patents

Abstract

The cold catalyst (8) in an I.C. engine exhaust gas treatment unit is charged with exhaust gas with low heat loss to a first side (7) via the first line (5). The exhaust gas leaves the catalyst at a second side (9). The hot catalyst is then charged with exhaust gas with low heat loss to the second side (9) via a second line (6). The exhaust gas then leaves at the first side (7).

Description

The invention relates to an exhaust system according to the Oberbe handle of claim 1.

According to DE-OS 34 39 998 it is known in an exhaust system ge for an internal combustion engine of a motor vehicle to feed two feed lines from the engine to the catalytic converter hen, these exhaust pipes are designed such that the heat losses of the hot exhaust gases in the various which supply lines are different by the Zulei different in length or under are differently insulated or in different ways Dimensionally cooled and therefore different heat release quantities to the environment before the Exhaust gases reach the catalytic converter. Shut-off devices, which one or the other supply line depending open from the exhaust gas temperature upstream of the catalytic converter or close, ensure that the catalyst at one Cold start process only with the warmer exhaust gas via the Zu line is fed with lower heat losses. After the catalyst reaches its starting temperature has the supply line through the shut-off devices released with the greater heat losses, so that in consequently an exhaust gas with reduced temperature to the kata lysator arrives. The catalyst may overheat so that can be prevented.  

Especially if the catalyst is a NOx adsorber cat lysator is designed as it is in internal combustion engines with extreme lean operation to reduce the ent higher NOx levels in the exhaust gas is required, then occurs in addition to the relatively high sensitivity to overheating The relatively fast old woman is another problem such a system.

The object of the invention is an exhaust system for a Internal combustion engine, in particular using a To create NOx adsorber catalyst, in addition to ei ner rapid heating of the catalyst after a cold start of the internal combustion engine and prevention overheating of the catalytic converter the aging of the kata lysators is significantly delayed.

According to the invention, this object is achieved through the features of Claim 1 solved.

Advantageous developments of the invention are counter stood the subclaims.

As a result of the different heat losses in the two alternatively switchable feed lines to the catalyst can at a cold start of the engine and at cold catalytic converter the exhaust gas relatively uncooled the kata lysator are supplied, on the side that in special way, e.g. B. by large-pore training of Catalyst body, to the exposure to hot exhaust gas is adjusted.

The large amount of heat transported with the hot exhaust gas quickly heats the catalyst up to its operating temperature rature, so that only a small amount of exhaust gas unpurified Exhaust system leaves.  

After reaching the operating temperature of the catalyst is triggered by heat sensors, the transport of the Exhaust gas from the engine to the catalyst vice versa switches to the supply line with the greater heat loss. The exhaust gas now reaches the other side of the catalytic converter tors and flows through the catalyst in the opposite Direction compared to the direction of flow during the warm-up phase. It can now be used as an inflow side of the catalytic converter this relatively constant operating temperature of the exhaust gas be adapted constructively.

Simply by changing the flow directions for the warm-up phase and the continuous operation phase can be a ver prolongation of the life of the catalyst is achieved the. Through special constructive adjustments of the one flow ranges to the different exhaust gas temperatures on both sides of the catalyst can moreover the life of the catalyst can be increased further.

In a particularly advantageous manner is a fiction moderate exhaust system for the arrangement of a NOx adsorber Ka talysators to an internal combustion engine with extreme lean operation, e.g. B. a direct injection gasoline engine, ge is suitable. The can alternately from both sides flowed catalyst out as a NOx adsorber catalyst leads, which is also preceded by a starting catalytic converter and a three-way catalyst can be arranged downstream.

An embodiment of the invention is below hand a drawing that is a schematic of an exhaust system shows, explained in more detail.

A designed for extreme lean operation Brennkraftma machine 1 is provided with an exhaust gas main pipe 2, in which a start catalyst is contained. 3 The main exhaust gas line 2 leads to a switching valve 4 , which switches the exhaust gas flow carried in the main exhaust gas line 2 either to a first exhaust gas supply line 5 with low heat loss or to a second exhaust gas supply line 6 with increased heat loss. The first feed line 5 leads to a first side 7 of a NOx adsorber catalyst 8 . The second feed line 6 leads to a second side 9 of the NOx adsorber catalyst 8 . From the first side 7 of the NOx adsorber catalyst 8 leads a diversion 10 , which can be closed or opened with a switching valve 11 , to an exhaust gas line 12 downstream of the NOx adsorber catalyst 8 . The exhaust line 12 begins on the second side 9 of the NOx adsorber catalytic converter 8 and leads to a three-way catalytic converter 13 . The exhaust pipe 12 is provided in its course between the second side 9 of the NOx adsorber catalyst 8 and the entry of the bypass 10 with a switching valve 14 which can open or close the passage of the exhaust pipe 12 . A Lei device 15 leads from the three-way catalyst 13 to a silencer, not shown, and from this to the outside.

In the event of a cold start of the internal combustion engine 1 and at a temperature of the NOx adsorber catalytic converter 8 below its starting temperature, the switching valve 4 is set by a control (not shown ) in such a way that free gas passage to the first supply line 5 is made possible from the main gas line 2 . At the same time, the valve 11 in the diversion 10 is closed and the valve 14 in the exhaust line 12 is opened.

The exhaust gas coming from the internal combustion engine 1 thus passes through the starting catalytic converter 3 and reaches the NOx adsorber catalytic converter 8 at a relatively high temperature through the first supply line 5 on the first side 7. This heats up to its starting temperature relatively quickly and can store NOx components. The exhaust gas leaves the NOx adsorber catalytic converter 8 on its second side 9 and passes through the exhaust pipe 12 into the three-way catalytic converter 13 , in which it is freed of harmful constituents in the usual way. From the three-way catalytic converter 13 , the exhaust gas reaches the outside through line 15 and the muffler.

The NOx constituents that arise during the lean phase of the internal combustion engine 1 and are stored in the NOx adsorber catalyst 8 are triggered at short intervals depending on a map or a signal from a NOx sensor by briefly switching the internal combustion engine to lambda 1 or lambda smaller than 1 converted into harmless connections.

As soon as the temperature of the NOx adsorber catalyst 8 exceeds a critical value, the switching valve 4 is set in such a way that a free gas passage to the second supply line 6 is made possible by the main exhaust gas line 2 . At the same time, the valve 11 opens in the diversion 10 and the valve 14 in the exhaust line 12 is closed.

The exhaust gas coming from the internal combustion engine 1 now passes after passing through the start catalytic converter 3 through the second feed line 6 with a relatively high heat loss to the second side 9 of the NOx adsorber catalytic converter 8 and flows through it in the opposite direction compared to the warming-up phase. As a result, the catalyst body is protected ge, while the function of the NOx adsorber catalyst 8 is retained even in this flow direction. The exhaust gas leaves the NOx adsorber catalytic converter 8 on its first side 7 and passes through the deflection 10 into the three-way catalytic converter 13 , from this through line 15 into the silencer and then into the atmosphere.

An exhaust system according to the invention thus enables Operation of a catalyst, in particular also a NOx Adsorber catalyst, within a fixed temperature limits and secures a compared to known systems increased lifespan.

Claims (4)

1. Exhaust system for an internal combustion engine with at least one catalyst for processing the harmful constituents of the exhaust gas, wherein an exhaust main line coming from the internal combustion engine is divided into two feed lines leading to the catalyst, the heat losses for the guided exhaust gases in the two feed lines are different and shut-off device lines are provided which alternatively activate the two supply lines, characterized in that the catalytic converter ( 8 ) is fed with exhaust gas in the cold state via the first supply line ( 5 ) with little heat loss on a first side ( 7 ) which weles a second side ( 9 ) leaves the catalytic converter ( 8 ) and the catalytic converter ( 8 ) is heated in the heated state via the second feed line ( 6 ) with high heat loss on its second side ( 9 ) with exhaust gas, which exhaust gas flows on its first side ( 7 ) leaves. 2. Exhaust system according to claim 1, characterized in that the supply via two feed lines ( 5 , 6 ) Ka talysator ( 8 ) is ausgebil Det as a NOx adsorber catalyst, which is a three-way catalyst ( 13 ) is arranged after. 3. Exhaust system according to claim 1 or 2, characterized in that the ver through two feed lines ( 5 , 6 ) ver catalytic converter ( 8 ) in the Abgashauptlei device ( 2 ) arranged start catalyst ( 3 ) is arranged. 4. Exhaust system according to at least one of claims 1 to 3, characterized in that the two alternatively used inflow sides of the catalytic converter ( 8 ) are specifically adapted to the prevailing exhaust gas temperature.