DE19850373A1 - Exhaust system with adsorber for internal combustion engine, in which fresh air flow can be mixed with exhaust gas downstream of adsorber and upstream of catalytic converter - Google Patents

Abstract

The exhaust system includes a catalytic converter (8) with an adsorber (6) in front of it for the short-term storage of at least one component of the exhaust gas after a cold start. A fresh air flow can be mixed with the exhaust gas downstream of the adsorber and upstream of the catalytic converter. This fresh air stream as previously been brought into heat-exchange connection with the exhaust gas flow upstream of the adsorber.

Description

The invention relates to an exhaust system of an internal combustion engine with a catalyzer sator for converting harmful exhaust gas components as well as with one switched adsorber, in which in particular after a cold start of the combustion Engine at least one component of the internal combustion engine exhaust gas can be saved at short notice. For technical reasons, reference is made to the US 5,538,698.

To meet increasingly stringent exhaust gas limits on internal combustion engines driven motor vehicles, it is generally advantageous to start a normal gas catalyst after a cold start of the internal combustion engine if possible to quickly bring it up to its operating temperature. A well-known means of doing this is to heat this catalyst in particular with electrical energy. Is also a System known that the ejected after the engine start A large part of hydrocarbons in a so-called adsorber, at least holds low temperatures and only at higher temperatures (the adsor bers) again. These are then essentially already in the meantime heated catalyst and provided downstream of the adsorber. On such system is in the above. Scripture shown.  

Another known measure by means of which an exhaust gas catalytic converter quickly turns on its operating temperature can be brought down to the internal combustion engine operate with a rich air-fuel mixture immediately after starting, so that the hydrocarbons and carbon monoxides emitted together with a fresh air stream supplied to the exhaust gas in the catalytic converter by exothermic Reactions bring about the desired heating. In addition, a Be drove this to a spark ignition internal combustion engine with late firing angles accelerate the heating up of the catalytic converter by hotter exhaust gas.

A disadvantage of these known procedures is that the relatively hot and pollutant-rich exhaust gases from the internal combustion engine, particularly the Adsorbing hydrocarbons and arranged in front of the catalyst About heating in an undesirable manner, so that this the adsorbed exhaust gas (s) component (s), especially hydrocarbons, at one point in time emits at which the subsequent catalyst does not yet reach its operating temperature has reached completely.

It is the task of pointing out a remedial measure for this problem of the present invention.

The solution to this problem is characterized in that the internal combustion engine Engine exhaust gas fresh downstream of the adsorber and upstream of the catalytic converter Airflow is admixed, which previously upstream with the exhaust gas flow in the adsorber a heat-exchanging connection is brought. It is preferably provided for this one branching off from the intake tract of the internal combustion engine and in which the combustion engine exhaust leading exhaust pipe downstream of the adsorber as well upstream of the catalyst opening fresh air line, through which the Exhaust gas supplying the adsorber exhaust pipe provided heat exchanger is guided, and in which there is a quantity control member and / or a conveyor for the fresh air flow.

The content of the invention is thus to improve the behavior of the adsorber influence that the exhaust gas in front of the adsorber part of the un at this point  Desired heat is withdrawn and fed upstream of the catalyst.

According to the invention this is done in that the early start of the Fresh air supplied to the catalyst, i. H. the so-called secondary air, via a upstream of the adsorber heat exchanger is passed, this Fresh air / secondary air absorbs as much of the exhaust gas heat as possible and this then upstream of the catalyst when mixed with the Introduces exhaust gas flow again. In this way, the early on as desired remains jumping behavior of the catalyst unchanged, while the adsorber less is heated up quickly and thus its desired function as a long time Storage device for at least one exhaust gas component, in particular hydro fabrics, can perceive.

The invention is explained in more detail with reference to one in the attached single figure illustrated preferred embodiment.

Reference number 1 denotes a four-cylinder, mixture-compressing, externally ignited internal combustion engine, the cylinders of which are supplied with fresh gas via an intake tract 2 . A fuel injection device, by means of which fuel is added to the fresh gas, is not shown. This mixture is then burned as usual in the internal combustion engine cylinders and discharged into the environment as exhaust gas via the exhaust gas system, designated in its entirety by reference number 3 .

The exhaust system 3 consists of a the exhaust gases of the individual cylinders collect the exhaust manifold 4 , to which an exhaust pipe 5 connects, which opens into an adsorber 6 . From this adsorber 6 , the internal combustion engine exhaust gases are fed via a further exhaust line 7 to a catalyst designated in its entirety with the reference numeral 8 . This catalyst 8 consists of an electrically heatable so-called E-catalyst 8 a and an adjoining three-way main catalyst 8 b. From the latter, the gas flow from the internal combustion engine 1 passes through an exhaust pipe 9 to a muffler, not shown, and from this ultimately into the environment.

In the catalytic converter 8 , harmful exhaust gas constituents are converted into harmless substances when this catalytic converter 8 has reached its operating temperature. In order to accelerate the achievement of this operating temperature following a cold start of the internal combustion engine 1 , the e-catalyst 8 a is electrically heated. The electrical energy supplied not only brings the E-catalyst 8 a faster to its operating temperature, but also the three-way main catalyst 8 b, since a part of this energy and the latter is supplied via the exhaust stream.

In the adsorber 6 , in particular after a cold start of the internal combustion engine 1, at least one component of the internal combustion engine exhaust gas can be stored for a short time, and desirably until the catalytic converter 8 has reached its operating temperature. In particular, this short-term storable exhaust gas component is hydrocarbons. Such adsorbers are known and mostly work on a zeolite basis. It is also known that the storage ability of the adsorber 6 not only decreases over time, but also with increasing temperature. If the adsorber 6 , which is of course warmed up by the hot exhaust gases of the internal combustion engine 1 , has reached a certain critical temperature of approximately 100 ° C. to 200 ° C., it then gives the initially stored exhaust gas component (s). off again. Desirably, the catalytic converter 8 should already have reached its operating temperature at this point in time, so that it can then - in addition to the continuously supplied exhaust gas components - also convert the exhaust gas pollutants initially stored by the adsorber 6 and now released again. However, the latter is not always guaranteed.

For this reason, a further measure for accelerated heating of the catalytic converter 8 is hen hen a cold start of the internal combustion engine 1 . As a result, unburned hydrocarbons, which are still in the exhaust gas stream downstream of the adsorber 6 , can be afterburned in the catalytic converter 8 , specifically by adding fresh air to the exhaust gas stream. This fresh air flow is introduced via a fresh air line 10 into the exhaust line 7 downstream of the adsorber 6 and upstream of the catalytic converter 8 . This fresh air line 10 branches off from the intake tract 2 of the internal combustion engine 1 .

As can be seen, this fresh air line 10 is guided in such a way that the fresh air flow carried therein before the introduction into the exhaust line 7 is brought into a heat-exchanging connection with the exhaust gas flow on the adsorber 6 . For this purpose, the fresh air line 10 is guided through a heat exchanger 11 surrounding the exhaust gas line 5 (upstream of the adsorber 6 ). Since the fresh air flow branched off from the intake tract 2 is of course considerably colder than the exhaust gas flow from the internal combustion engine 1 , the latter is cooled at least slightly in the heat exchanger 11 , ie the fresh air flow takes part of the heat quantity contained in the exhaust gas flow and is itself heated here.

This at least slight cooling of the flue gas stream upstream of the Adsor bers 6 has for its result that the adsorber 6 is less it is heated by the exhaust gas flow, and it hence the above-mentioned critical temperature, upon reaching wel cher it the previously stored off-gas component (s) releases again, reached later from a cold start. However, the heat removed from the exhaust gas stream upstream of the adsorber 6 by the fresh gas stream is advantageously not lost, ie this amount of heat is still available for the desired heating of the catalytic converter 8 after this amount of heat is fed back to the exhaust gas stream upstream of the catalytic converter 8 via the fresh air stream, and through the described introduction into the exhaust gas line 7 .

The fresh air line 10 can be at least partially insulated in order to prevent undesired heat exchange with the surroundings (ie heating upstream of the heat exchanger 11 and cooling downstream thereof). Furthermore, a quantity control element can be provided in the fresh air line 10 , which is integrated here in a conveying device 12 for the fresh air flow, but this and a large number of further details, in particular of a constructive type, can be designed quite differently from the exemplary embodiment shown, without leaving the content of the claims . In particular, the ad sorber 6 itself can also be additionally provided with a catalytically active coating, ie, after its operating temperature has been reached, it can additionally act as a catalyst.

Reference list

1

Internal combustion engine

2nd

Intake tract

3rd

Exhaust system

4th

Exhaust manifold

5

Exhaust pipe (between

4th

and

6

)

6

Adsorber

7

Exhaust pipe (between

6

and

8th

)

8th

catalyst

8th

a electrically heated e-catalyst

8th

b Three-way main catalytic converter

9

Exhaust pipe (downstream of

8th

b)

10th

Fresh air line

11

Heat exchanger

12th

Conveyor

Claims (2)

1. Exhaust system of an internal combustion engine ( 1 ) with a catalyst ( 8 ) for converting harmful exhaust gas components and with an upstream adsorber ( 6 ), in which at least one component of the internal combustion engine exhaust gas can be stored for a short time, particularly after a cold start of the internal combustion engine ( 1 ) , characterized in that the internal combustion engine exhaust gas downstream of the adsorber ( 6 ) and upstream of the catalyst ( 8 ) can be admixed with a fresh air stream which is previously brought into a heat-exchanging connection with the exhaust gas stream on the adsorber ( 6 ). 2. Exhaust system according to claim 1, characterized by a from the intake tract ( 2 ) of the internal combustion engine ( 1 ) branching and in the exhaust gas line leading to the internal combustion engine exhaust gas ( 7 ) downstream of the adsorber ( 6 ) and upstream of the catalyst ( 8 ) opening fresh air line ( 10 ) which is guided through a heat exchanger ( 11 ) provided on the exhaust gas line ( 5 ) supplying the adsorber ( 6 ), and in which a quantity control element and / or a conveying device ( 12 ) is provided for the fresh air flow.