EP0980966B1 - Exhaust system with reservoir for an internal combustion engine - Google Patents

Description

The invention relates to an exhaust system of an internal combustion engine with a storage volume, according to the features in the preamble of claim 1.

In addition to DE 43 42 296 C1, DE 40 25 becomes the known prior art 565 A1 to GB 1 349 051 and in particular to US 3,645,098, of which this Registration runs out, referenced.

As is known, the exhaust gases of a motor vehicle internal combustion engine have to be cleaned become, d. H. are at least partially freed from harmful components, for which exhaust gas catalysts are used in particular. Need to know these catalytic converters have a certain operating temperature so that they have their Function to convert harmful exhaust gas components. This so-called light-off temperatures reach modern exhaust gas catalysts directly afterwards to a (cold) start of the internal combustion engine in normal exhaust gas test cycles only after approx. 25 seconds, so that the following also during this period is referred to as the "critical" period of time, the engine exhaust gas quasi got into the environment unpurified.

As a remedial measure for this problem, it has already been proposed in US 3,645,098 the internal combustion engine exhaust gas during this (critical) Time span of, for example, 25 seconds to convey into a storage volume and there save until the catalytic converter reaches its light-off temperature has or generally until the exhaust gas purification device is ready for operation. After that the amount of exhaust gas in the storage volume can then be ready for operation Emission control device for cleaning and / or the internal combustion engine (or their combustion chambers) for further combustion.

The storage volume is similar to that of a bellows (that of a pump) sucked empty and kept empty by a check valve at the outlet can be. After the internal combustion engine starts, a flap closes behind the exhaust gas purification device that the exhaust gas into the overhead pipe, such that the exhaust gas through a further line into the storage volume is led, which is inflated by the exhaust gas. The disadvantage of this solution is the uncontrolled inflation of the storage volume with exhaust gas. Depending on the The degree of filling of the storage volume has different pressure ratios in the exhaust system that influence the charge change of the internal combustion engine. This is particularly disadvantageous after a start (restart) of the internal combustion engine, because the mixture formation processes are negatively influenced, resulting in a very restless Internal combustion engine run can result.

The object of the present invention is after the start of the internal combustion engine Defined pressure ratios in the exhaust line during filling of the storage volume to have with exhaust gas. This task is characterized by the feature in characterizing part of claim 1 solved.

So can the internal combustion engine exhaust gas flow to the storage volume leading branch line a control valve for metered filling of the Storage volume may be provided, which then follows a start the internal combustion engine with the associated desired Filling the storage volume the negative pressure initially present therein not abruptly, but quasi-dosed degradation. This is a suction of internal combustion engine exhaust gas from the internal combustion engine exhaust pipe possible over a longer period. Preference is given to the best possible Implementation of this method in addition to a pressure value in the Storage volume-sensing pressure sensor a the vacuum pump and / or suitably controlling the control valve based on the pressure sensor signals Control unit provided.

Otherwise, a suitable adsorber material can be stored in the storage volume an undesirable exhaust gas component may be provided, so that in the Storage volume introduced exhaust gases at least partially cleaned at the same time before they expire after the desired or required storage period back into the exhaust pipe of the internal combustion engine be delivered.

In a further particularly advantageous embodiment, the exhaust system partially double-walled, so that two essentially Exhaust gas lines running coaxially to one another are present, wherein Via the first, preferably inner exhaust pipe, the exhaust gas from the internal combustion engine led away and via the second, preferably outer exhaust pipe is led to the storage volume.

With a partially double-walled exhaust system - one such is shown, for example, in DE-AS 22 22 498 - the internal combustion engine exhaust gases thus initially in a first exhaust line from the internal combustion engine led away and then in a coaxial or concentric of this first exhaust line running second exhaust line to the storage volume passed, namely back towards the internal combustion engine. This double-walled section of the exhaust system thus resembles a counterflow heat exchanger. By this measure, the exhaust system in the double-walled section warms up, which means faster start of the catalytic converter is beneficial, i.e. the exhaust gas purification device reaches its operating temperature earlier with this measure.

This increased warming is accompanied by an increased cooling of the to the storage volume led exhaust gas flow, whereby the volume of the Exhaust gas volume or exhaust gas mass actually to be stored according to the physical State equation for gases is reduced. in a limited space Storage volume can therefore a larger amount of exhaust gas or exhaust gas mass get saved. It is particularly advantageous if the Transition between the first and the second exhaust pipe with respect to the Internal combustion engine provided downstream of the exhaust gas purification device is, while a diversion from the second exhaust line into a Storage volume leading branch line between the internal combustion engine and the exhaust gas purification device. Then there is the exhaust system double-walled also in the area of the exhaust gas cleaning device trained, whereby the latter through a particularly intense heating experiences the engine exhaust gases.

Another advantage of an exhaust system according to the invention is that the partially double-walled exhaust system itself is part of the Storage volume forms, with a minimal additional space requirement, so that the actual storage volume is made smaller accordingly can be. For the rest, it is particularly recommended to start with amount of exhaust gas stored during the so-called "critical" period after the operational readiness of the exhaust gas cleaning device has been reached to feed the internal combustion engine for (re) combustion, so that the storage volume is preferably arranged near the internal combustion engine should be. Then it is advantageous with one according to the invention Exhaust system is a relatively simple exhaust system for close to the internal combustion engine arranged storage volume possible.

The invention is explained in more detail with reference to two preferred exemplary embodiments, which are each shown in the form of a schematic diagram in the attached FIGS. 1, 2 . The same components are always provided with the same reference numbers.

Reference number 1 thus designates an (here four-cylinder reciprocating piston) internal combustion engine, the exhaust gases of which are first passed via exhaust manifolds 2 into (here two parallel side by side) electrically heatable pre-catalysts 3. Via exhaust pipes 4 (referred to as first exhaust pipe in FIG. 2 ) or exhaust pipes 4 ′ ( FIG. 1 ), the internal combustion engine exhaust gases then enter a main catalytic converter 5 and from there through an exhaust pipe 4, which has at least one silencer 19, finally into the Surroundings. A shutoff flap 6 is provided in the exhaust line 4 downstream of the sound damper 19, by means of which the exhaust line 4 can be shut off essentially completely, ie when the shutoff flap 6 is closed, the exhaust gas flow flowing through the muffler 19 cannot get into the environment.

In the following, reference is now made to the exemplary embodiment according to FIG. 1 . Here, when the shut-off flap 6 is closed, the exhaust gas flow conducted in the exhaust gas line 4 ′ is conducted via a branch line 7 branching off upstream of the main catalytic converter 5 into a storage volume 8. Alternatively, the exhaust gas flow with the shut-off flap 6 closed can also be taken downstream of the main catalytic converter 5 or - as shown here via the branch line 7 ′ shown in dashed lines - downstream of the silencer 19 from the exhaust line 4 and fed to the storage volume 8. Of course, both a control valve 9 provided in the branch line 7 and a further shut-off valve 10a designed as a three-way valve 10 must be suitably connected for this purpose, ie these two valves 9, 10a, the function of which will be discussed in more detail later, must flow through the exhaust gas release the branch line 7 at least partially.

As explained at the beginning, the introduction of the exhaust gas flow just described is intended in the storage volume 8 especially after a (cold) start of the Internal combustion engine 1, so if the pre-catalysts 3 and the main catalyst 5 have not yet reached their light-off temperature and thus are unable to remove harmful exhaust gas components (especially hydrocarbons) to convert for a certain period of time (e.g. 25 Seconds). Have after this so-called "critical" period at least the pre-catalysts 3 have reached their starting temperature and can then perform their function, the locking flap 6 is opened so that then the exhaust gas stream is cleaned, i.e. of at least the essential ones Free pollutant components, is discharged into the environment.

If the state just described is reached, the storage volume can 8 to be emptied for a later (new) start or cold start the internal combustion engine 1 to be able to again during the said Time span of, for example, 25 seconds of exhaust gas flow take. This required emptying of the storage volume 8 can either in the suction system 11 of the internal combustion engine 1 or in the exhaust pipe 4 'into it. One of the storage volume is provided for this 8 branching drain line 17, which is in a branch valve 20th in a first line branch 17 'opening into the suction system 11 and in branches a second line branch 17 ″ opening into the exhaust gas line 4 ′. Depending on the switching position of the branch valve 20, the initially, the amount of exhaust gas stored in the storage volume 8 is either for "cleaning" (or aftertreatment) by the then functional Main catalyst 5 out, or alternatively in the intake system 11 of the internal combustion engine 1 initiated. In the latter case, the previously in the storage volume 8 stored amount of exhaust gas thus when this storage volume is emptied 8 suitable for repeated post-combustion fed to the internal combustion engine combustion chambers for combustion Fresh gas stream added, preferably at such operating points the internal combustion engine 1, in which this admixture for a flawless Run of the internal combustion engine 1 is not a hindrance.

In this context, the other elements shown in FIG. 1 in the periphery of the internal combustion engine 1 are briefly explained: As usual, the (here four) combustion chambers of the internal combustion engine 1 are supplied with fresh gas via the intake system 11 already mentioned. As usual, a throttle valve 13 is provided in an intake line 12 leading to the intake system 11 for controlling the power of the internal combustion engine 1. At the free end of the intake line 12 there is a conventional intake air filter 14. From this, in addition to the intake line 12, a secondary air line 15, which opens into the exhaust manifold 2 and is known to the person skilled in the art, branches off, in which, as usual, a secondary air pump 16 is provided, but for the present invention is immaterial.

Returning to the above-mentioned emptying of the storage volume 8 via the emptying line 17, a vacuum pump 18 can be seen in this in addition to a shut-off valve 10b, which in turn is part of the three-way valve 10 already mentioned or forms this three-way valve 10 together with the other already mentioned shut-off valve 10a If the shut-off valve 10a is now closed and the shut-off valve 10b is open, ie if the three-way valve 10 assumes the switch position shown in FIG. 1 , the storage volume 8 is sucked empty and thus evacuated when this vacuum pump 18 is operated at the same time, since this vacuum pump 18 adopts with its suction side the storage volume 8 is connected. As already mentioned, the vacuum pump 18 then conveys the amount of exhaust gas located in the storage volume 8 via the emptying line 17 either into the suction system 11 or into the exhaust line 4 '.

This just described conveying the stored amount of exhaust gas the storage volume 8 in the suction system 11 is not the only one Function of the vacuum pump 18, since this with the shut-off valve 10b due to - as is known to the expert - at least temporarily in the Suction system 11 (with throttle valve 13 at least partially closed) existing vacuum would also take place almost automatically. Another Rather, the function of the vacuum pump 18 is in the storage volume 8 generate an essentially absolute vacuum, which then by appropriate switching of the three-way valve 10 or of the two check valves 10a, 10b is held.

When the internal combustion engine 1 is operating, at least after the pre-catalysts 3, generally an exhaust gas purification device, their Have reached / have reached operating temperature and after that in the storage volume 8 removed amount of exhaust gas from the storage volume 8 removed an essentially absolute vacuum was created in the storage volume 8, which due to the absolutely tightly closed shutoff valves 10a, 10b, even after the internal combustion engine 1 has been switched off, up to the latter next start is held.

If the internal combustion engine comes to a standstill even after a long-term shutdown 1 restarted and are then started simultaneously - as already mentioned above described - the shut-off flap 6 in the exhaust pipe 4 closed as well the control valve 9 and the check valve 10a opened, so due to the the vacuum present in the storage volume 8 of the main catalyst 5 leaving exhaust gas stream sucked into the storage volume 8. Of course As a result, the vacuum in the storage volume 8 is continuous mined, however, due to the relatively high at least initially Vacuum in the storage volume ensures that those in the already mentioned "Critical" period of time accruing amount of exhaust gas safely into the storage volume 8 arrives.

With a suitable dimensioning or a suitable volume of the storage volume 8, the entire amount of exhaust gas occurring during the “critical” period of time can even be conveyed into the storage volume 8 by said initial vacuum; deviating from the exemplary embodiment shown here, however, a feed pump (already shown in the prior art mentioned at the outset) can additionally be provided, which enables the accumulation of exhaust gas amount to be stored in the storage volume 8 under excess pressure, as a result of which this storage volume 8 can be dimensioned smaller. Such a feed pump is usually shown in FIG. 2 , which will be explained later, under reference number 24. Compared to the known state of the art, due to the generation of negative pressure in the storage volume 8, a less powerful feed pump (24) can now be used, or - as in DE 43 42 296 C1, which has also already been mentioned - the internal combustion engine 1 can be adapted by adapting its valve timing to compress the exhaust gas are used after an absolutely safe introduction of the exhaust gas flow into the storage volume 8 is ensured by the vacuum prevailing initially (ie when the internal combustion engine 1 is started) in the storage volume 8.

Es ist bekannt, daß die in der bereits mehrfach genannten, im Hinblick auf die Abgasemissionen der Brennkraftmaschine 1 anschließend an einen Start derselben sog. "kritischen" Zeitspanne von bspw. 25 Sekunden anfallende Abgasmenge nur bei Erzeugung eines Druckgefälles gegenüber dem Umgebungsdruck bzw. Atmosphärendruck in einem Speichervolumen (hier mit der Bezugsziffer 8 bezeichnet) untergebracht werden kann. Bei der vorliegenden Erfindung wird nun dieses Druckgefälle durch das zunächst im Speichervolumen 8 vorliegende Vakuum hergestellt.

This effect according to the invention is explained again in other words in the following:

It is known that the amount of exhaust gas occurring in the already mentioned several times, with regard to the exhaust gas emissions of the internal combustion engine 1 after a start of the same so-called "critical" time period of, for example, 25 seconds, only when a pressure gradient is generated in relation to the ambient pressure or atmospheric pressure in a storage volume (here designated by reference numeral 8) can be accommodated. In the present invention, this pressure drop is now produced by the vacuum initially present in the storage volume 8.

Um nämlich zu verhindern, daß mit einem Öffnen des Sperrventiles 10a der Unterdruck im Speichervolumen 8 schlagartig abgebaut wird, kann dieses Regelventil 9 geeignet gesteuert eine Drosselstelle bilden, die nur einen allmählichen, über einen längeren Zeitraum, d.h. insbesondere über die genannte Zeitspanne von bspw. 25 Sekunden währenden Abbau des Unterdruckes im Speichervolumen 8 ermöglicht. Wäre hingegen eine derartige Drosselstelle bspw. in Form des geeignet gesteuerten Regelventiles 9 nicht vorhanden, so könnte über allgemein in der Abgasanlage bzw. insbesondere über an der Sperrklappe 6 unvermeidbar vorhandene Undichtigkeitsstellen auch Umgebungsluft in das Speichervolumen 8 gesaugt werden, wodurch dessen Speicherkapazität für die Abgasmenge herabgesetzt werden würde. Dieser unerwünschte Effekt kann durch das geeignet gesteuerte und hierbei als einstellbare Drosselstelle wirkende Regelventil 9 vermieden werden, wobei dieser Regelventil 9 bspw. derart eingestellt werden kann, daß im Mündungsbereich der Zweigleitung 7 in die Abgasleitung 4 während der genannten "kritischen" Zeitspanne im wesentlichen gleichbleibend ein Unterdruck in der Größenordnung von bspw. 0,75 bar anliegt. Auf diese Weise kann der den Hauptkatalysator 5 verlassende Abgasstrom sicher und zuverlässig in das Speichervolumen 8 gefördert werden.

For the described filling of the storage volume 8 by means of the vacuum originally prevailing therein, previously generated by the vacuum pump 18 and held by the shut-off valves 10a, 10b, the control valve 9 already briefly mentioned, which is arranged in the branch line 7, can now be particularly advantageous:

In order to prevent the vacuum in the storage volume 8 from being abruptly reduced when the shut-off valve 10a is opened, this control valve 9 can be suitably controlled to form a throttle point which is only a gradual one, over a longer period of time, ie in particular over the period of time mentioned, for example. The vacuum in the storage volume 8 can be reduced for 25 seconds. If, on the other hand, such a throttle point were not present, for example in the form of a suitably controlled control valve 9, ambient air could also be sucked into the storage volume 8 via leak points which are inevitably present in the exhaust system or in particular via the locking flap 6, as a result of which its storage capacity for the amount of exhaust gas would be degraded. This undesirable effect can be avoided by the suitably controlled control valve 9, which acts as an adjustable throttle point, this control valve 9 being able to be set, for example, in such a way that in the area where the branch line 7 opens into the exhaust line 4 during the said “critical” period of time, it remains essentially constant there is a negative pressure in the order of magnitude of, for example, 0.75 bar. In this way, the exhaust gas stream leaving the main catalyst 5 can be conveyed safely and reliably into the storage volume 8.

Indem nämlich während der besagten "kritischen" Zeitspanne von bspw. 25 Sekunden, während derer die anfallende Abgasmenge in das Speichervolumen 8 eingeleitet werden muß, diese Abgasmenge aus der Abgasleitung 4 bzw 4' aufgrund des im Speichervolumen 8 herrschenden Unterdruckes sicher abgesaugt wird, sind an die Dichtheit der Sperrklappe 6 keine so hohen Anforderungen zu stellen, wie im bekannten, eingangs genannten Stand der Technik.

In this context, it should be pointed out that in a simplified embodiment, a simple, rigid throttle point in the branch line 7 may be sufficient instead of the control valve 9 shown here. In this context, reference should also be made to a particular advantage of an exhaust gas system according to the invention with a storage volume 8 acting as it were as a vacuum accumulator:

This is because, during the said "critical" period of, for example, 25 seconds, during which the amount of exhaust gas to be introduced into the storage volume 8, this amount of exhaust gas is safely sucked out of the exhaust line 4 or 4 'due to the negative pressure prevailing in the storage volume 8, are on the tightness of the locking flap 6 does not have to be as demanding as in the known prior art mentioned at the beginning.

If it has to be guaranteed that in the said critical period of time no exhaust gas gets into the environment at all known prior art only possible in that in the exhaust pipe 4 required (and here designated by reference numeral 6) flap is absolutely tightly closed. In contrast, in the present invention this absolute tightness requirement is not given, because due to the - if necessary controlled by the control valve 9 - abutting the exhaust pipe 4 Negative pressure, which comes from the open storage volume 8, which in this exhaust pipe 4 exhaust gas always safely and reliably into the Storage volume 8 is sucked off.

An electronic control unit, in particular, is not shown in the figure, among others the shut-off flap 6 and the three-way valve 10, i.e. the check valves 10a and 10b positioned according to the respective requirements. This Control unit can also - preferably using the signals of a in particular provided in the storage volume 8 and the respective current one The pressure sensor detecting the pressure value here - the appropriate control the control valve 9 and the vacuum pump 18. At a Can fill the storage volume 8 during the "critical" period this control unit (possibly using further signals or boundary conditions) by suitable control of the control valve 9 in the mouth area the branch line 7 or 7 "into the exhaust line 4 'or 4 one set an approximately constant vacuum of, for example, 0.75 bar. At a later emptying of the storage volume 8, this control unit can ensure that this emptying and the associated admixture the amount of exhaust gas collected in the storage volume 8 for the internal combustion engine combustion chambers fresh gas flow supplied only in those operating points the internal combustion engine 1 takes place in which this admixture is not a hindrance to the smooth running of the internal combustion engine. Furthermore, in the subsequent build-up of the negative pressure in the storage volume 8 said control unit operates the vacuum pump Monitor 18 such that the desired negative pressure in the storage volume 8 is generated in the desired order. In this context it should be noted that it is fundamentally desirable after emptied of the storage volume 8 during the operation of the Internal combustion engine 1 in this storage volume 8 once the desired Build vacuum and then keep it closed the check valves 10a, 10b over a long period of time - in particular also after the internal combustion engine 1 has been switched off until its next start - to be liable. However, it is also possible to set the vacuum in the storage volume 8 to be continuously monitored and also when the internal combustion engine is at a standstill 1 to ensure by temporarily operating the vacuum pump 18, that in the storage volume 8 always for a restart of the internal combustion engine 1 desired (or in view of the reduction that can be achieved with this of the exhaust gas emissions) is present. Alternatively it is also possible to start the internal combustion engine 1 only at all enable or allow if the desired volume in the storage volume 8 Vacuum is present. Possibly. So before starting the internal combustion engine 1 - similar to the preheating in self-igniting internal combustion engines - initially the vacuum pump 18 are operated until the vacuum is generated in the storage volume 8.

If the vacuum pump 18 even when the internal combustion engine 1 is stopped should be operated, the conveying side should be connected to the environment be, for example. About the drain line 17 "and the exhaust pipe 4. In this context it should be pointed out that that the delivery side of the vacuum pump 18 with the suction system 11 Internal combustion engine 1 is connectable, requires a reduced pump output if, in addition - as is known to the person skilled in the art - in the Suction system 11 at a variety of engine operating points (and particularly intensively at idle) prevailing negative pressure becomes. In view of this, the control unit already mentioned can be the vacuum pump 18 operate appropriately.

With reference to the exemplary embodiment according to FIG. 1, it should also be pointed out that with a branch line 7 ′ branching downstream of the muffler 5 from the exhaust gas line 4, not only the main catalytic converter 5 (and of course also the pre-catalytic converters 3) through the engine after the engine 1 has started Exhaust gas stream passed through is heated in the desired manner, but at the same time the exhaust gas stream is cooled, whereby the volume of the amount of exhaust gas to be stored (according to the physical equation of state for gases) is reduced. A larger amount of exhaust gas, more precisely exhaust gas mass, can thus be stored in the storage volume 8.

The detailed structure of the storage volume 8 is not to be discussed in detail. In essence, this can be a suitable vacuum storage that is stable when the evacuation is complete. Of course, ideally, an absolute tightness is required not only of the vacuum accumulator or the accumulator volume 8, but also of the check valves 10a, 10b (or the three-way valve 10) as well as the drain line 17 and the branch line 7.
Finally, an adsorber material can also be provided in the storage volume 8, which itself stores at least one undesired exhaust gas component for a certain period of time or, as known to the person skilled in the art, for example, as activated carbon, has an adsorbent effect on pollutants.

In the following, FIG. 2 and the essential differences of this second exemplary embodiment compared to that according to FIG. 1 are now described:
While in normal continuous engine operation the internal combustion engine exhaust gases ultimately reach the environment through the so-called first exhaust pipe 4, as shown by the flow arrow, via the main catalytic converter 5 and via the muffler 19, the internal combustion engine will also start during this 1 subsequent "critical" period, during which neither the pre-catalytic converters 3 nor the main catalytic converter 5 have reached their starting or operating temperature, the shut-off flap 6 provided downstream of the muffler 19 in the exhaust pipe 4 is closed, so that the first exhaust pipe 4 is connected to it Is essentially completely closed off. When the shut-off flap 6 is closed, the exhaust gas flow flowing through the muffler 19 cannot get into the environment, but is directed into a storage volume 8. In the exemplary embodiment according to FIG. 2, this takes place in the following way:

Between the sound damper 19 and the exhaust flap 6, ie upstream of it, a transition 21 is provided in the first exhaust line 4 into a second exhaust line 22, into which the exhaust gas flow - as shown by flow arrows - enters with the shut-off valve 6 closed. This second exhaust line 22 is arranged coaxially or concentrically to the first exhaust line 4 or envelops the first exhaust line 4, an annular space (not specified in more detail) being present between the outer wall of the first exhaust line 4 and the inner wall of the second exhaust line 22, through which the internal combustion engine exhaust gases then be guided in the second exhaust line 22. This second exhaust line 22 extends from the transfer line 21 in the direction of the internal combustion engine 1 (back) to a so-called diversion 23, which is upstream of the pre-catalytic converter 3 on the left-hand side with respect to the flow direction in the second exhaust-gas line 22, and for the pre-catalytic converter on the right-hand side 3 is provided between this pre-catalyst 3 and the internal combustion engine 1.
In the area between the discharge line 23 and the transfer line 21, the internal combustion engine exhaust system shown is thus double-walled, with not only the exhaust line 4 but also the exhaust gas purification devices in the form of the main catalytic converter 5 and the pre-catalytic converter 3 on the right being encased by the exhaust gas line 22.

At the outlet 23 or at the end of the first exhaust pipe 4 is preferred coaxially enveloping second exhaust line 22 now closes the in Connection with the first exemplary embodiment already explained branch line 7, which ultimately also in the storage volume 8, which has also already been explained empties. When the shut-off flap 6 is closed, the internal combustion engine exhaust gases via the second exhaust line 22 and the adjoining one Branch line 7 introduced into the storage volume 8. Of course here also the one provided in the branch line 7 as a three-way valve 10 formed check valve 10a can be switched suitably, i.e. this Check valve 10a must allow the flow of exhaust gas flow through the branch line 7 release. In this context, let's look at those in the branch line 7 provided feed pump 24 indicated, with the help of which in the Storage volume 8 initiated internal combustion engine exhaust gas in the storage volume 8 can be compressed so that this storage volume 8 a for storing the accumulated in the "critical" time period Exhaust gas volume still has reasonable volume.

As explained at the beginning, the introduction of the exhaust gas flow just described is intended in the storage volume 8 especially after a (cold) start the internal combustion engine 1, so if the pre-catalysts 3 and the main catalyst 5 have not yet reached their light-off temperature and thus are unable to remove harmful exhaust gas components (especially hydrocarbons) to convert for a certain period of time (e.g. 25 Seconds). Have after this so-called "critical" period at least the pre-catalysts 3 have reached their starting temperature and can then perform their function, the locking flap 6 is opened so that then the exhaust gas stream is cleaned, i.e. of at least the essential ones Free pollutant components, is discharged into the environment.

If the state just described is reached, the storage volume can 8 to be emptied for a later (new) start or cold start the internal combustion engine 1 to be able to again during the said Time span of, for example, 25 seconds of exhaust gas flow take. This required emptying of the storage volume 8 takes place in this second exemplary embodiment, only in the suction system 11 the internal combustion engine 1, namely via the drain line 17, wherein a targeted quantity control of those taken from the storage volume 8 and the suction system 11 fed and thus recirculated exhaust gas amount by means of a control valve provided in the drain line 17 25 takes place.

In the emptying line 17 there is also the vacuum pump 18 already explained in connection with the exemplary embodiment according to FIG. 1. When the internal combustion engine 1 is in operation, after at least the pre-catalysts 3, generally an exhaust gas cleaning device, have / have reached their operating temperature and after that the amount of exhaust gas previously collected in the storage volume 8 was removed from the storage volume 8 - an essentially absolute vacuum was created with this vacuum pump 18 in the storage volume 8. Due to the absolutely tightly closed shut-off valves 10a, 10b, this is held until after the internal combustion engine 1 is switched off until it is started again or, if appropriate, is generated again by starting the vacuum pump 18 before the internal combustion engine 1 is started.

Indem das Brennkraftmaschinen-Abgas vor einer Einleitung in das Speichervolumen 8 zunächst über die erste Abgasleitung 4 durch die Vorkatalysatoren 3 und durch den Hauptkatalysator 5 hindurchströmt und anschließend daran - geführt in der zweiten Abgasleitung 22 - nicht nur diese Abgasreinigungsvorrichtungen (nämlich den Hauptkatalysator 5 sowie ggf. den Vorkatalysator 3), sondern auch die Abgasleitung 4 außenseitig umströmt, werden diese soeben genannten Elemente der Brennkraftmaschinen-Abgasanlage in gewünschter Weise beschleunigt erwärmt, so daß die Abgasreinigungsvorrichtung(en) seine/ihre Anspring- oder Betriebstemperatur schneller erreichen, wodurch die sog. "kritische" Zeitspanne verkürzt und somit die im Speichervolumen 8 unterzubringende Abgasmenge reduziert wird.

Vorteilhafterweise wird hiermit gleichzeitig der Abgasstrom abgekühlt, wodurch das Volumen der zu speichernden Abgasmenge (nach der physikalischen Zustandsgleichung für Gase) verringert wird, so daß in einem in seinem Rauminhalt vorgegebenen Speichervolumen 8 somit eine größere Abgasmenge, d.h. Abgasmasse gespeichert werden kann.

Returning to the introduction of the internal combustion engine exhaust gas into the storage volume 8 during the so-called “critical” time period following a start of the internal combustion engine 1, the essential advantages of the exhaust system, which is in some cases double-walled, are repeated:

In that the internal combustion engine exhaust gas, before being introduced into the storage volume 8, first flows through the primary catalytic converter 3 and through the main catalytic converter 5 via the first exhaust pipe 4 and then - not guided in the second exhaust pipe 22 - not only these exhaust gas purification devices (namely the main catalytic converter 5 and possibly . The precatalyst 3), but also flows around the exhaust pipe 4 on the outside, these elements of the internal combustion engine exhaust system, which have just been mentioned, are heated in an accelerated manner in the desired manner, so that the exhaust gas cleaning device (s) reach its starting or operating temperature more quickly, so that the so-called. "Critical" time span is shortened and thus the amount of exhaust gas to be accommodated in the storage volume 8 is reduced.

Advantageously, the exhaust gas stream is hereby simultaneously cooled, as a result of which the volume of the amount of exhaust gas to be stored (according to the physical equation of state for gases) is reduced, so that a larger amount of exhaust gas, ie exhaust gas mass, can thus be stored in a storage volume 8 predetermined in terms of its volume.

It should be expressly pointed out that these effects mentioned occur in that the exhaust system is partially double-walled is, so that the engine exhaust gas in this area in one first exhaust pipe 4, which contains the exhaust gas purification device (s), led away from the internal combustion engine 1 and coaxially in a second this first extending exhaust pipe 22 in the manner of a counterflow heat exchanger returned in the direction of the internal combustion engine 1, ultimately, however, is introduced into the storage volume 8. It is not absolutely necessary to achieve these advantageous effects that the first exhaust pipe 4 is the inner one and the second one Exhaust line 22 around the outer exhaust line of the double-walled, an exhaust system having an annular space. Rather can also the first exhaust line 4 on the outside and the second exhaust line 22 be provided on the inside, the latter then the exhaust gas purification devices, i.e. the main catalytic converter 5 and the precatalyst (s) 3 would penetrate.

Of course, a variety of other modifications of the described Embodiment possible without the content of the claims to leave. So the transition 21 or the beginning of the second exhaust pipe 22 also between the silencer 19 and the main catalytic converter 5, or upstream of the same. It is particularly advantageous whenever a certain area of the exhaust system is described in the Way is double-walled, it should be noted that this double-walled area of the exhaust system is also a partial volume, so to speak of the storage volume 8 forms, so that the latter advantageously can have a correspondingly reduced volume.

Although not in more detail on the detailed structure of the storage volume 8 is received - essentially this can be a suitable one and in the embodiment shown here in connection with the vacuum pump 18 stable vacuum accumulator even with complete evacuation act - be briefly a special one not shown here advantageous embodiment of the storage volume 8 mentioned, after which the Storage volume 8 can be designed in two parts. In addition to a first Partial volume that can be evacuated in the manner described can be a second partial volume can be provided, in which the internal combustion engine exhaust gas stored compressed using the feed pump 24. Besides can of course be a variety of other details, especially constructive Kind of completely different from the illustrated embodiments be designed without leaving the content of the claims.

LIST OF REFERENCE NUMBERS

1

Internal combustion engine

2

exhaust manifold

3

precatalyzer

4

(first) exhaust pipe

4 '

exhaust pipe

5

main catalyst

6

blocking flap

7

branch line

7 '

Branch line (alternatively guided)

8th

storage volume

9

control valve

10

Three-way valve consisting of 10a, 10b

10a

check valve

10b

check valve

11

suction

12

suction

13

throttle

14

Intake air filter

15

Secondary air line

16

Secondary air pump

17

drain line

17 '

first line branch of 17, ending in 11

17 "

second line branch of 17, ending in 4 '

18

Vacuum pump

19

silencer

20

Branch valve in 17th

21

Reconciliation (between 4 and 22)

22

second exhaust pipe

23

Diversion = transition from 22 to 7

24

feed pump

25

control valve

Claims (9)

1. An engine exhaust system comprising an exhaust-gas cleaning device (3, 5) and an evacuatable storage chamber (8) into which at least a part of the stream of engine exhaust gas can be introduced for a certain time, especially after a start of the engine (1), the storage chamber being adapted to be closed by a shut-off valve (10, 10a, 10b) at its outlet opening,
   characterised in that a negative pressure pump (18) is provided for generating a negative pressure in the storage chamber (8) which can be maintained by the shut-off valve (10, 10a, 10b) when the engine (1) is inoperative.
2. An engine exhaust system according to claim 1,
   characterised in that the delivery side of the negative-pressure pump (18) connected via its suction side to the storage chamber (8) is connectable to the suction system (11) of the engine (1) and/or to the exhaust pipe (4') upstream of the exhaust-gas cleaning device (main catalyser 5).
3. An engine exhaust system according to claim 1 or claim 2,
   characterised in that a control valve (9) for metered filling of the storage chamber (8) is provided in a branch pipe (7) conveying the stream of exhaust gas from the engine to the storage chamber (8), in addition to a shut-off flap (6) provided in the exhaust system downstream of the exhaust-gas cleaning device (5).
4. An engine exhaust system according to any of the preceding claims,
   characterised by a pressure sensor for detecting the pressure in the storage chamber (5) and by a control unit which suitably controls the negative pressure pump (18) and/or the control valve (9) in accordance with the signals from the pressure sensor.
5. An engine exhaust system according to any of the preceding claims,
   characterised in that at least one adsorber material for an undesired exhaust-gas component is provided in the storage chamber (8).
6. An exhaust-gas system according to any of the preceding claims,
   characterised in that the exhaust system is double-walled in places, resulting in two substantially coaxial exhaust pipes (4, 22), wherein the exhaust gas is conveyed away from the engine (1) via the first, preferably inner, exhaust pipe (4) and is supplied to the storage chamber (8) via the second, preferably outer, exhaust pipe (22).
7. An engine exhaust system according to claim 6,
   characterised in that a transfer pipe (21) to the second, preferably outer, exhaust pipe (22) is provided upstream of a shut-off flap (6) provided in the first, preferably inner, exhaust pipe (4) downstream of the exhaust-gas cleaning device (5).
8. An engine exhaust system according to claim 6 or 7,
   characterised in that a pipe (23) leading out of the second, preferably outer exhaust pipe (22) into a branch pipe (17) leading to the storage chamber (8) is provided in the portion between the engine (1) and an exhaust-gas cleaning device in the form of a precatalyser (3).
9. An engine exhaust system according to any of the preceding claims,
   characterised in that a delivery pump (24) is provided in the branch pipe (17) conveying the engine exhaust gas to the storage chamber (8).

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