DE102004045178A1 - Diesel engine vehicle exhaust system has a pre-filter which removes a fixed proportion of particulates and to enable its continual partial regeneration by nitrogen oxides is heated by mounting close to the engine - Google Patents

Abstract

Exhaust system for a diesel vehicle comprises a storage pre-filter (24) mounted near to the engine (10) and upstream of a particulates filter (36) to retain an essentially constant proportion of larger particles. The high temperature of the pre-filter allows on-going partial regeneration by NO 2 oxidation of deposited carbon; an oxidation catalyst may be incorporated to increase the temperature.

Description

The Invention relates to an exhaust system of a motor vehicle with a diesel engine, having a particle filter unit.

Such particle filters, also referred to as soot filters, are intended to reduce the particulate emissions of the exhaust gases. The particle filter units have as their core a substrate, in particular of SiC, which is accommodated in its own outer housing, wherein the exhaust pipe opens downstream and upstream of the particulate filter unit in the housing. The particulate filter cartridge itself, ie the substrate, must be regenerated from time to time by burning off the particulates accumulated on the filter surface. One of the most promising possibilities of regeneration is to introduce fuel into the exhaust gas, preferably in vapor form, immediately before the particulate filter unit, in order, among other things, not to cool the exhaust gas too much. This is for example in the EP 1 369 557 A1 described.

In addition, there are efforts to make the particulate filter units more cost-effective. The high cost of the particulate filter units arise, for example, by the very expensive SiC material of the substrate and by the complex storage of the substrate via bearing mats in the outer housing of the diesel particulate filter unit. As far as the integration into the housing, the effort is, inter alia, that the particle filter units are to be mounted as close to the engine or provided with heaters because of the NO ₂ - oxidation effect. The NO ₂ oxidation effect is that carbon oxidizes with the NO ₂ in the exhaust gas at temperatures above 230 ° C, producing nitrogen and CO ₂ . However, this regeneration effect, which is less effective than combustion with oxygen, should be exploited in the particle filter unit. If, however, one arranges the particle filter unit close to the engine, extreme requirements with regard to the storage of the substrate and the durability of substrate and housing are to be met due to the high vibrations in the section of the exhaust system close to the engine. In addition, the exhaust system near the engine provides little space for the voluminous particulate filter units. There is thus a bundle of partially contradictory and, at first glance, factors that exclude the design and arrangement of the particulate filter unit for a more cost effective design.

Ideas for accommodating a main filter and a prefilter in the particle filter unit itself, ie in the same outer housing, are, for example, from US 5 053 062 and the EP 1 205 228 A1 as well as the EP 0 957 241 A1 known. However, these ideas do not provide for a really significant reduction in the cost of a particulate filter unit and for a significantly simplified placement of the exhaust system in the vehicle.

The invention provides these desired advantages in an exhaust system of the type mentioned in that upstream of the particulate filter unit, a close-coupled particulate receiving memory is arranged, which binds a subset of the particles contained in the exhaust stream and flows through the other subset of the particles contained in the exhaust stream to the particulate filter unit, said the particulate receiving accumulator is located so close to the engine that it is regenerated during operation due to the NO ₂ oxidation effect.

In contrast to the aforementioned prior art with a pre-filter disposed in the particulate filter unit near the substrate, the invention provides a particulate receiving reservoir structurally separate and disposed outside the particulate filter unit, which binds a portion of the particulate and expels it again via the NO ₂ oxidation effect The filter cartridge of the particulate filter unit (substrate) and the insert in the particulate trap are separated by at least 300 mm, and the particulate trap steadily absorbs a subset of the incoming particulates to release a portion of it as CO _2. This subset of particulates must are no longer taken up by the particle filter unit, so that it fills with particles much more slowly and must also be regenerated much less frequently, which allows the particle filter unit to be arranged much further away from the engine than actually started With increasing distance from the engine, there are also fewer vibrations in the exhaust system, so that the particulate filter unit can be equipped on the one hand with a less expensive substrate and on the other hand less effort for housing integration is required. Due to the structural separation of particle receiving storage and particle filter unit, it is possible to accommodate these parts at completely different locations in the vehicle, which is very desirable due to the already low, available space. Since combustion of a certain amount of soot, although not actively initiated by a separate device, also occurs in the particulate receiving reservoir, an increase in the exhaust gas temperature caused by the combustion will take place downstream of the particulate matter reservoir in the exhaust gas system according to the invention.

The particle receiving memory allows before regardless of the degree of filling, ie of the amount of particles in it, always a certain subset of exhaust gas including particles, which are collected only in the particle filter unit. That is, the particle receiving memory can not lock. In this respect, the particle receiving memory differs from a conventional pre-filter in the prior art, in which larger particles are to be collected in the pre-filter and only smaller particles reach the main filter. The particle storage tank should be able to store particles as large and small as possible and allow large particles to pass through even with a high degree of filling. This effect also means that it can not come to a high back pressure (back pressure) due to a near-engine, almost completely filled with soot filter in the exhaust system according to the invention.

According to the preferred embodiment, the particulate receiving accumulator is only able to bind a smaller amount of particulates than the particulate filter unit. The particulate receiving reservoir is also preferably designed to bind the smaller portion (less than 50 weight percent) of the particles flowing into it. This makes it possible to construct the particulate receiving memory structurally relatively small, so that it can actually be arranged very close to the engine. However, as the motor becomes closer, it has a higher temperature, which in turn improves the NO ₂ oxidation effect, so that the particulate receiving memory has a high performance in terms of the particulate uptake capacity. The smaller size and lower weight make smaller requirements for storage in the near-engine range. In addition, due to the smaller size and the lower volume requirements higher quality material can be used. Conversely, the motor remote arrangement of the particulate filter unit allows the use of less expensive substrate material, in particular cordierite.

Of the Particle storage is, as already mentioned, preferably by a Exhaust pipe connected to the particulate filter unit fluidly or structurally separated. Of course, the exhaust pipe has one much smaller outer cross-section as the particulate filter unit.

Between the particulate filter unit and the particulate receiving memory is according to the preferred embodiment a vibration decoupling device in the exhaust pipe provided the sections with particle filter unit and particle receiving memory connects with each other. This vibration decoupling device is already known per se, it preferably separates the manifold section the exhaust system of the so-called underbody section. This embodiment it allows even more, then the vibration largely decoupled from the engine Particle filter unit cheaper out, what the material of the substrate as well as the integration into the outer casing and execution of the outer casing itself As.

The preferred embodiment provides that the Particulate storage in the manifold area or is arranged directly adjacent to this.

The However, the particulate filter unit should be positioned in the underbody portion of the exhaust gas purifier be where more space for this large volume Unit available stands.

In the exhaust system is preferably a turbocharger. The particle receiving storage should be located immediately in front of the turbocharger to its Reduce exposure to particulate matter, or immediately after it be arranged. This arrangement ensures in each case that the particle receiving memory is arranged close to the engine.

Downstream of the Particle storage and if possible immediately upstream the particle filter unit may optionally have a regeneration device be provided, which the particle filter unit discontinuously and preferably dependent on the loading level of the substrate, sensor-controlled regenerated. This should lead to a complete regeneration of the substrate in the particulate filter unit.

The Regeneration device is in particular a fluid or fuel introduction system, at the e.g. CO or HC for catalytic exothermic oxidation and Combustion of accumulated carbon is initiated.

Prefers can of course a fluid evaporator can be used.

to increase the temperature in the particulate filter unit is this an oxidation catalyst assigned.

This Oxidation catalyst can either be upstream unit or be designed as a section of the particulate filter unit.

Also the particle receiving memory can be assigned to an oxidation catalyst be to raise the exhaust gas temperature in the particle receiving memory to lead. Also here would be Naturally to coat a part of the storage material accordingly, or It may be the particulate receiving memory a separate oxidation catalyst upstream.

The Invention also ensures Advantages of exhaust systems with exhaust gas recirculation, via the exhaust gas to the engine again supplied can be. Namely, the particulate receiving memory is preferably so in the Exhaust system arranged that the recirculated exhaust gas passes the particulate receiving memory. This means that with less Particles provided exhaust gas and especially hot exhaust gas fed back to the engine can be.

Of the Particulate storage should be upstream of one in an exhaust gas recirculation line sitting radiator be arranged as possible even upstream one of the radiator upstream bypass valve. This will reduce the load on radiator and Valve reduced by particles.

Further, it is advantageous if the particulate receiving memory is followed by a NO _x storage.

A preferred embodiment of the particle receiver is a foamed ceramic or metal insert to store the particles.

Further Features and advantages of the invention will become apparent from the following Description and from the following drawings, to the reference is taken. In the drawings show:

1 a schematic view of a motor vehicle diesel engine with an exhaust system according to the invention and

2 a flowchart of a diesel engine with an exhaust system according to a second embodiment.

1 shows a diesel engine 10 a motor vehicle and a downstream exhaust system 12 , The exhaust system 12 has one up to a flange 14 reaching elbow section 16 and one downstream of the manifold section 16 subsequent underbody section 18 , which via a vibration decoupling device 20 connected to each other.

To the diesel engine 10 closes an exhaust pipe with a first pipe section 22 to a particle receptacle 24 leads, which close to the engine in the exhaust system 12 is arranged.

The particle receiving storage 24 contains a bet 26 made of foamed ceramic or metal, in an outer casing 28 of the particulate receiving memory 24 is arranged. Upstream of the insert 26 sits an oxidation catalyst 30 , Usually, however, the oxidation catalyst 30 omitted since the upstream part of the insert 26 coated accordingly. The oxidation catalyst 30 So it's usually in the mission 26 integrated.

Immediately downstream of the particle receiving reservoir 24 a turbocharger sits 32 in the manifold section 16 , Alternatively, the positions of particulate trapping memory could 24 and turbocharger 32 also be reversed. Also in the manifold section 16 , after the particulate receiving memory 24 and the turbocharger 32 is a NO _x memory 33 arranged. Due to the downstream location of the NO _x storage tank 33 to the particle receiving memory 24 the former is less heavily loaded with nitrogen oxides, since the particle receiving memory 24 already reduced a certain amount of NO _X.

The vibration decoupling device 20 consists of such a flexible material that in the elbow section 16 if possible not initiated engine vibrations in the underbody section 18 or at least strongly subdued be forwarded to this section. The underbody section 18 includes an elongated exhaust pipe 34 leading to a particle filter unit 36 leads. In the particle filter unit 36 it is a conventional diesel particulate or soot filter, with a substrate or filter cartridge 38 made of cordierite and an upstream oxidation catalyst 40 , Again, the oxidation catalyst 40 omitted when the upstream part of the filter cartridge 38 coated accordingly. The particle filter unit 36 is outwardly by its own outer housing 42 completed, which significantly larger cross-sectional dimensions than the exhaust pipe 34 and the subsequent piece of pipe 36 the exhaust pipe has. The outer case 28 . 42 are thus widely spaced and through at least one simple exhaust pipe 34 separated from each other.

Immediately upstream of the oxidation catalyst 40 sits a regeneration device 43 for the particulate filter unit 36 , with an evaporator 44 for introduced diesel fuel. Alternatively, the regeneration device could 43 also in the particle filter unit 36 be integrated.

In the exhaust system 12 Of course, even more filter units can be installed, to which it does not matter directly in the following, so they have been omitted for simplicity.

The exhaust gas flows over the pipeline 22 in the oxidation catalyst 30 and then in the insert 26 , This is designed so that it is a subset of the particles located in the exhaust gas, especially soot particles, absorbs and stores. The use 26 regardless of its Partikelfüllgrad always exhaust gas flow through it, including particles that are not used 26 be bound. The particle absorption capacity of the insert 26 is so limited. Thus the use 26 but in any case passes particles, he has channels that have a larger diameter than the largest in the exhaust gas soot particles. For example, the irregular inner walls of the insert can be thought of as walls that have protruding, upstream, open gills that can accumulate particles regardless of their size.

Due to the proximity of the particulate matter storage 24 to the engine 10 have the exhaust and thus the particulate matter storage 24 in operation a high temperature. This high temperature, which is beyond 250 ° C, promotes use 26 adjusting NO ₂ oxidation effect. This causes the particle receiving memory 24 is constantly regenerated during operation.

The proposed oxidation catalyst 30 increases the temperature in the exhaust and thus the temperature of the insert 26 , The use 26 permanently absorbs less than 50% of the incoming particles and allows the remaining particles to flow through them. The exhaust gas reaches the turbocharger 32 ,

The exhaust gas with the remaining particles passes over the exhaust pipe 34 to the particle filter unit 36 , in their outer casing 42 yes, if necessary already the oxidation filter 40 can be accommodated. In the filter insert 38 Then almost all other particles are filtered out of the exhaust gas. These particles settle in inlet channels 50 From and can the partitions to exhaust ports 52 do not penetrate.

Because the particle filter unit 36 in the underbody section 18 is arranged, the filter element 38 only brought to a much lower temperature than the insert 26 , This means that the NO ₂ -oxidation effect takes place to a much lesser extent or, preferably, not at all. It is therefore a purposeful discontinuous regeneration of the particulate filter unit 36 necessary. When in the filter cartridge 38 There would be an NO ₂ oxidation effect, where carbon would first be oxidized, excessive carbon oxidation, flow fluctuations, and eventually "hot spots" that could be detrimental to the filter cartridge.

As soon as therefore the filter cartridge 38 has exhausted its capacity is via the regeneration device 43 and a fuel introduction system 54 vaporized fuel into the exhaust pipe 34 initiated. The vaporized fuel contains HC and CO, which is in the oxidation catalyst 40 leads to a catalytic catalytic oxidation of the fuel and the exhaust gas temperature significantly increased, which in turn leads to the combustion of the particles in the filter cartridge 38 leads.

In one embodiment according to 2 an exhaust gas recirculation is provided. The particle receiving storage 24 is located upstream or downstream of the turbocharger 32 , Again, the separate, from the particle receiving memory 24 spatially separated particle filter unit 36 provided in the underbody section. The particle filter unit 36 turn is a muffler 60 downstream. Downstream of the particulate matter storage 24 directs an exhaust gas recirculation line 62 Exhaust, which already has a smaller amount of particles due to the particulate matter storage 24 has, to a radiator bypass valve 64 , From there, exhaust can either through a radiator 66 or directly to a so-called EGR valve 68 stream. The exhaust gas then passes through the exhaust gas recirculation line 62 in an air supply line 72 between the air intake 74 and an air mass flow sensor 76 which is an air temperature sensor 78 is downstream.

Through the particle receiving storage 24 Manages to exhaust with significantly fewer particles than before the engine 10 attributed again. This reduces the risk that the particles in systems of the air supply 72 like the air mass flow sensor 76 or the air temperature sensor 78 cause damage. Also the valves 64 . 68 and the performance of the cooler 66 are reduced due to the lower particulate or soot loading in the exhaust gas recirculation system. It results in a higher reliability and a longer life of the parts in the air supply line 72 and in the exhaust system, which reduces overall costs.

Claims (20)

Exhaust system of a motor vehicle with diesel engine ( 10 ) containing a particulate filter unit ( 36 ), characterized in that upstream of the particulate filter unit ( 36 ) a close-coupled particulate receiving memory ( 24 ) is arranged, which binds a subset of the particles contained in the exhaust stream and by the other subset of the particles contained in the exhaust stream to the particle filter unit ( 36 ) flows, wherein the particle receiving memory ( 24 ) so close to the engine ( 10 ) is arranged to be at least partially regenerated during operation due to the NO ₂ oxidation effect. Exhaust system according to claim 1, characterized in that the particulate receiving reservoir ( 24 ) is designed so that it is independent of filling level, a subset of the particles contained in the exhaust gas flow to the particle filter unit ( 36 ). Exhaust system according to claim 1 or 2, characterized in that the particulate receiving memory ( 24 ) binds a smaller amount of particles than the particle filter unit ( 36 ). Exhaust system according to one of the preceding claims, characterized in that the particulate receiving reservoir ( 24 ) via an exhaust pipe ( 34 ) with the particle filter unit ( 36 ) is fluidly connected. Exhaust system according to claim 4, characterized in that between the particulate receiving memory ( 24 ) and the particulate filter unit ( 36 ) a vibration decoupling device ( 20 ) at a between particle receiving memory ( 24 ) and particle filter unit ( 36 ) arranged exhaust pipe ( 34 ) is provided. Exhaust system according to one of the preceding claims, characterized in that the particulate receiving reservoir ( 24 ) in the manifold section ( 16 ) of the exhaust system or directly to these is subsequently arranged. Exhaust system according to one of the preceding claims, characterized in that the particle filter unit ( 36 ) in the underbody section ( 18 ) of the exhaust system is arranged. Exhaust system according to one of the preceding claims, characterized in that in the exhaust system a turbocharger ( 32 ) and the particulate receiving memory ( 24 ) immediately before or after the turbocharger ( 32 ) is arranged. Exhaust system according to one of the preceding claims, characterized in that the particle filter unit ( 36 ) a cordierite-containing filter cartridge ( 38 ) having. Exhaust system according to one of the preceding claims, characterized in that downstream of the particulate receiving memory ( 24 ) one of the particle filter unit ( 36 ) associated regeneration device ( 43 ) is provided, which the particle filter unit ( 36 ) is regenerated discontinuously. Exhaust system according to claim 10, characterized in that the regeneration device ( 43 ) a fluid, in particular fuel introduction system ( 54 ) Has. Exhaust system according to claim 11, characterized in that the regeneration device ( 43 ) a fluid evaporator ( 44 ) to introduce steam into the exhaust gas. Exhaust system according to one of the preceding claims, characterized in that the particle filter unit ( 36 ) an oxidation catalyst ( 40 ) to increase the temperature in the particulate filter unit ( 36 ) assigned. Exhaust system according to one of the preceding claims, characterized in that the particulate receiving memory ( 24 ) an oxidation catalyst ( 30 ) for increasing the temperature of the exhaust gas in the particle receiving storage ( 24 ) assigned. Exhaust system according to one of the preceding claims, characterized in that it is equipped with an exhaust gas recirculation, via the exhaust gas to the engine ( 10 ) can be supplied, wherein the particulate receiving memory ( 24 ) is arranged in the exhaust system, that the recirculated exhaust gas, the particulate receiving memory ( 24 ) happens. Exhaust system according to claim 15, characterized in that the particulate receiving memory ( 24 ) upstream of an exhaust gas recirculation line ( 62 ) sitting radiator ( 66 ) is arranged. Exhaust system according to claim 16, characterized in that the particulate receiving memory ( 24 ) upstream of a in the exhaust gas recirculation line ( 62 ), the radiator ( 66 ) upstream bypass valve ( 64 ) sits. Exhaust system according to one of the preceding claims, characterized in that the particulate receiving reservoir ( 24 ) has a foamed ceramic or metal insert for storing the particles. Exhaust system according to one of the preceding claims, characterized in that a NO _x reservoir ( 33 ) downstream of the particle receiver ( 24 ) is provided. Exhaust system according to one of the preceding claims, characterized in that the particle filter unit ( 36 ) in operation so removed from diesel engine ( 10 ) is arranged that takes place in her due to low operating temperature no steady NO ₂ Oxidationsseffekt.