SE1351282A1 - Valve arrangement for controlling the exhaust gas flow through an oxidation catalyst - Google Patents

Abstract

The present invention relates to a valve arrangement for regulating the flow of exhaust gases through an oxidation catalyst (4) in an exhaust line (2) which also comprises an SCR catalyst (6) which is arranged in a position downstream of the oxidation catalyst (4) with respect to the intended exhaust gases. flow direction in the exhaust line (2). The oxidation catalyst (4) is adapted to oxidize nitrogen monoxide NO in the exhaust gases to nitrogen dioxide NO2. The valve arrangement comprises a bimetallic component (15c, 16, 19, 20c) which changes shape depending on the temperature of the exhaust gases. The valve arrangement is adapted to regulate exhaust flow through the oxidation catalyst (4) so that the oxidation catalyst's capacity to oxidize nitrogen monoxide (NO) to nitrogen dioxide (NO2) is reduced when the bimetallic component (15c, 16, 19, 20c) is in contact with exhaust gases having a temperature exceeding predestined cairn.

Description

BACKGROUND OF THE INVENTION AND PRIOR ART The present invention relates to a valve arrangement for regulating the exhaust flow through an oxidation catalyst according to the preamble of claim 1.

To reduce emissions of nitrogen oxide NOx flan internal combustion engines, e.g. a technique called SCR (Selective Catalytic Reduction). This technique meant that a solution of urea and water was supplied in a certain dose to the exhaust gases in an exhaust line. The urea solution can be sprayed into the exhaust line, after which the finely divided urea solution is evaporated in contact with the hot exhaust gases so that ammonia is formed. The mixture of ammonia and exhaust gases is then passed through an SCR catalyst. The nitrogen of the nitrogen oxide in the exhaust gases reacts with the nitrogen in the ammonia so that nitrogen gas is formed. The oxygen of the nitrogen oxide reacts with the water in the ammonia so that water is formed. The nitrogen oxide in the exhaust gases is thus reduced in the catalyst to nitrogen gas and water vapor. With a correct dosage of urea, the emission of nitrogen oxide by the internal combustion engine can be greatly reduced.

Nitric oxide NOx in exhaust gases consists of nitrogen monoxide NO and nitrogen dioxide NO2. Conventional SCR catalysts' ability to remove nitrogen oxide from exhaust gases depends on the ratio between nitrogen monoxide NO and nitrogen dioxide NO2. The ability of an SCR catalyst to reduce the amount of nitrogen oxide in exhaust gases is optimal as the exhaust gases contain the same amount of nitrogen monoxide and nitrogen dioxide. Exhaust gases from diesel engines in particular usually contain a much smaller proportion of nitrogen dioxide than nitrogen monoxide. In order to increase the proportion of nitrogen dioxide in the exhaust gases which is led to an SCR catalyst, it is advisable to arrange an oxidation catalyst DOC (Diesel Oxidation Catalyst) in the exhaust line in a position upstream of the SCR catalyst. An oxidation catalyst oxidizes nitrogen monoxide to nitrogen dioxide. Thus, the proportion of nitrogen dioxide in the exhaust gases can be increased.

The capacity of an oxidation catalyst to oxidize nitrogen monoxide to nitrogen dioxide depends on the temperature and flow of the exhaust gases. The capacity of the oxidation catalyst to oxidize nitrogen monoxide to nitrogen dioxide is greatest at exhaust temperatures around 300 ° C and 2 layers of exhaust gas. During such operating conditions, the oxidation catalyst oxidizes nitrogen monoxide to nitrogen dioxide in an amount such that the SCR catalyst receives nitrogen oxide which contains more nitrogen dioxide than nitrogen monoxide. The excess nitrogen dioxide results in the SCR catalyst's ability to eliminate nitrogen oxide dropping drastically at the same time as nitrous oxide is formed, which is a very powerful greenhouse gas. Ammonia grinding also increases. It is thus a problem when an oxidation catalyst supplies exhaust gases to an SCR catalyst containing nitrogen oxide with an excess of nitrogen dioxide.

SUMMARY OF THE INVENTION The object of the present invention is to provide a simple and reliable valve arrangement with which it is possible to reduce the capacity of an oxidation catalyst to oxidize nitrogen monoxide to nitrogen dioxide in operational cases when the oxidation catalyst risks supplying nitrogen oxide with an excess of nitrogen dioxide.

This object is achieved with the valve arrangement of the type mentioned in the introduction, which can be characterized by the features stated in the characterizing part of the claim 1.

The valve arrangement thus comprises a bimetallic component which is affected by the temperature of the exhaust gases. A bimetallic component consists of two thinly joined metal elements with different thermal expansion capabilities. When the bimetallic component is heated, it is flexed to the extent that one metal expands more than the other. Common metals that can be used in bimetals are, for example, copper and steel. Bimetals are simple components that have a reliable function.

When the high temperature exhaust gases are led to an oxidation catalyst, it acquires an increased capacity and there is a risk that it oxidizes nitrogen monoxide to nitrogen dioxide a large amount. The exhaust gases have a temperature above a predetermined value. The valve arrangement regulates the exhaust flow through the oxidation catalyst catalyst. capacity to oxidize nitrogen monoxide to nitrogen dioxide is reduced.

The bimetallic component affects the valve arrangement so that said control of the exhaust gas flow through the oxidation catalyst is obtained when the exhaust gases reach the predetermined value. The bimetallic component can affect the valve arrangement so that it strikes abruptly when the exhaust gas temperature exceeds the predetermined value. However, the valve arrangement can advantageously have a construction so that it gradually begins to reduce the capacity of the oxidation catalyst when the temperature of the exhaust gases exceeds the predetermined value. The valve arrangement can in this case reduce the capacity of the oxidation catalyst depending on how much the temperature of the exhaust gases exceeds the predetermined value. Such a reduction in the capacity of the oxidation catalyst results in the SCR catalyst arranged downstream, even at high exhaust gas temperatures, being able to receive nitrogen oxides with a nitrogen monoxide / nitrogen dioxide ratio which gives a good reduction of the nitrogen oxide in the exhaust gases.

According to an embodiment of the invention, the valve arrangement is adapted to regulate exhaust gas flow through the oxidation catalyst so that the capacity of the oxidation catalyst to oxidize nitrogen monoxide to nitrogen dioxide is reduced when the exhaust gases have a flow below a predetermined value. The capacity of an oxidation catalyst to oxidize nitrogen monoxide to nitrogen dioxide is thus also dependent on the exhaust gas flow through the oxidation catalyst. A small and damn slow flow of exhaust gases through the oxidation catalyst means that the exhaust gases are in contact with the active catalyst material for a long time, which leads to a stone proportion of the nitrogen monoxide having time to oxidize to nitrogen dioxide before it leaves the oxidation catalyst. In this case, the valve arrangement thus takes into account both the temperature of the exhaust gases and the width. The predetermined values of the exhaust gases with respect to temperature and flow are related to each other and define different operating conditions in which the capacity of the oxidation catalyst should be reduced so that the nitrogen oxide in the exhaust gases that the oxidation catalyst delivers to the SCR catalyst does not contain too much nitrogen dioxide.

According to a preferred embodiment of the invention, the valve arrangement is adapted to regulate the flow through the oxidation catalyst so that the capacity of the oxidation catalyst is reduced to a level so that the downstream SCR catalyst receives nitrogen oxide containing at most 50% nitrogen dioxide. An SCR catalyst capable of reducing nitrogen oxide is optimal as it contains 50% nitrogen monoxide and 50% nitrogen dioxide. If the proportion of nitrogen monoxide is the same as the proportion of nitrogen dioxide, the SCR catalyst works relatively well even if it does not have an optimal capacity. If the proportion of nitrogen dioxide is stone than the proportion of nitrogen monoxide, the capacity of the SCR catalyst to eliminate nitrogen oxide is significantly reduced while emitting nitrous oxide and ammonia. It is advisable that an oxidation catalyst be dimensioned so that it can supply nitrogen oxide with a proportion of nitrogen dioxide which is in the range of 40-50% during the most operating conditions and to reduce the oxidation catalyst capacity by 4 valve arrangement at operating times when the exhaust gases have a high temperature and a laid flow so that the nitrogen oxide's share of nitrogen dioxide never exceeds 50%.

According to an embodiment of the invention, the valve arrangement comprises a duct for receiving exhaust gases in connection with the oxidation catalyst and a valve which regulates the exhaust gas flow through the duct and thus the exhaust solder through the connecting oxidation catalyst. By means of such an alternative flow channel for the exhaust gases, the exhaust gas flow through the oxidation catalyst can be changed on a sieve so that it obtains a reduced capacity to oxidize nitrogen monoxide to nitrogen dioxide.

According to an embodiment of the invention, said duct is a bypass line with which exhaust gases can be passed past the oxidation catalyst. In this case, a part of the exhaust gases is thus passed past the oxidation catalyst instead of passing through it. Since only a reduced part of the exhaust gases is passed through the oxidation catalyst, the proportion of nitrogen dioxide in the exhaust line in a position downstream of the oxidation catalyst becomes lower.

Advantageously, said channel extends through the oxidation catalyst. Said channel can be formed by drilling out, for example, a central pan of the oxidation catalyst. This means that the channel does not require space. Said channel can also be constituted by a tube extending around the oxidation catalyst.

According to another embodiment of the invention, said channel is connected to the oxidation catalyst so that the exhaust gas flow through the channel results in a corresponding exhaust flow in an area of the oxidation catalyst. Since the valve blocks the exhaust flow through the duct, no exhaust flow is obtained in said area of the oxidation catalyst either. The exhaust gases in this case are forced to pass through a limited area of the oxidation catalyst, which results in the capacity of the oxidation catalyst to oxidize nitrogen monoxide to nitrogen dioxide being reduced. The nananda channel may be formed of rocker elements fixed to an outlet side of the oxidation catalyst. Preferably, a plurality of such channels are provided on the outlet side of the oxidation catalyst so that they can stop or reduce the flow through a relatively large area of the oxidation catalyst.

According to an embodiment of the invention, the valve comprises a spring element which is adapted to regulate the exhaust flow through the duct depending on the size of the incoming exhaust flow. In this case, the spring element affected by the incoming exhaust gas and the bimetallic component affected by the exhaust gas temperature can be arranged so that at a high exhaust temperature and a laid exhaust flow they provide an exhaust flow through the channel resulting in the oxidation catalyst obtaining a reduced capacity to oxidize nitrous oxide. According to one embodiment, the feeder element is said bimetallic component. In this, both the bimetallic component's shape is used to different shape at temperature changes and resilient properties as it is affected by the incoming exhaust gases. The valve's input components can thus be reduced.

According to an embodiment of the invention, the valve comprises a valve body which is adapted to regulate the flow through the channel by being displaced between an open bearing and a substantially closed bearing. The substantially closed layer means that a minimal exhaust gas flow is led through the duct, so that the bimetallic component has the possibility of substantially continuously sensing the temperature of the incoming exhaust gases. The bimetallic component that senses the exhaust gas temperature can provide a force acting on the valve body in one direction and the feeder element affected by the exhaust flow can provide a force acting on the valve body in an opposite direction. Alternatively, the valve body may be included in said bimetallic component. In this case, the bimetallic component can not only actuate the valve but also form the valve body which blocks the channel in a substantially closed bearing and exposes it in an open bearing.

The invention relates to an exhaust system which comprises a valve arrangement according to any of the embodiments defined above.

BRIEF DESCRIPTION OF THE DRAWINGS In the following, by way of example, preferred embodiments of the invention are described with reference to the accompanying drawings, in which: Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 4 shows a part of an exhaust line comprising a valve arrangement according to a first embodiment of the present invention shows a valve of the valve arrangement in Fig. 1 in more detail, shows an alternative valve of the valve arrangement in Fig. 1, shows a valve arrangement according to a second embodiment of the present invention, shows a valve of the valve arrangement in Figs. 4 in more detail and Fig. 6 shows an alternative valve for valve arrangement in Fig. 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Fig. 1 shows an internal combustion engine in the form of a diesel electric motor 1. The diesel engine 1 may be intended as a drive motor for a heavier vehicle. The diesel engine 1 is provided with an exhaust line 2 which contains a container 3 for exhaust gas treatment components. The exhaust gas treatment components can of course be arranged in several separate containers. The container 3 can be a muffler. The container 3 in this case contains a first exhaust gas treatment component in the form of an oxidation catalyst DOC 4 (Diesel Oxidation Catalyst). An oxidation catalyst 4 comprises elongate channels with an inner layer of a catalyst material in the form of a noble metal. The oxidation catalyst 4 has damned i.a. capable of oxidizing nitric oxide NO to nitrogen dioxide NO2. Thus, the proportion of nitrogen dioxide NO2 in the exhaust gases can be increased. Exhaust gases from diesel engines in particular contain a much smaller proportion of nitrogen dioxide than nitrogen monoxide. An oxidation catalyst 4 capable of oxidizing nitrogen monoxide NO to nitrogen dioxide NO2 is dependent on the temperature and Wide of the exhaust gases.

The container 3 comprises the downstream oxidation catalyst 4 a second exhaust gas purifying component in the form of a particulate filter 5 which may be called DPF (Diesel Particulate Filter). A particle filter 5 comprises elongate parallel channels with stop surfaces arranged on suitable stalls. The stop surfaces force the exhaust gases to be led into adjacent elongate channels in the particle filter 5. The cradles of the channels are made of a porous material with fine pores that allow the passage of exhaust gases but not of soot particles. The soot particles then get stuck inside the particle filter 5. The particle filter 5 is regenerated continuously without active action by oxidizing the soot particles with NO2 and / or actively by heat-raising & Orders which accelerate the oxidation with either NO2 or oxygen.

The container 3 comprises downstream of the particulate filter 5 a third exhaust gas purifying component in the form of an SCR catalyst 6 for catalytic exhaust gas purification according to the method called SCR (Selective Catalytic Reduction). This method involved injecting a reducing agent in the form of a urea solution into the exhaust gases. In this case, urea discharge is stored in a tank 7 and is led, via a line 8, to an injection means 9 which injects the urea discharge into a space 3a in the container. A control unit 10 controls the supply 7 of the urea discharge with information regarding specific motor parameters 11. A pump 12 transports the urea discharge to the injection means 9.

The container 3 comprises downstream the SCR catalyst 6 a fourth exhaust gas purifying component in the form of an ammonia slip catalyst 13 ASC (Ammonia Slip Catalyst). The function of the ammonia abrasive catalyst 13 is to eliminate any excess ammonia that has not been reduced in the SCR catalyst. An ammonia abrasive catalyst usually comprises a coating of a noble metal such as platinum which oxidizes ammonia to nitrogen gas, nitrogen oxide and nitrous oxide.

During operation of the internal combustion engine 1, the control unit 10 calculates with the aid of information regarding engine parameters 11 such as load and speed the amount of the urea solution that needs to be added in order for the nitrogen oxide in the exhaust gases to be reduced in an optimal way. The control unit 10 activates the pump 12 which transports the urea solution in the calculated amount to the injection means 9 which injects the urea solution into the exhaust gases. The supplied urea solution is heated by the exhaust gases in the container 3 so that it evaporates and is converted into ammonia. The mixture of ammonia and the exhaust gases is led to the SCR catalyst 6. In the SCR catalyst 6, the nitrogen of the nitrogen oxide in the exhaust gases reacts with the nitrogen in the ammonia to form nitrogen gas. The oxygen of the nitrogen oxide reacts with the water in the ammonia to form water. The nitrogen oxide in the exhaust gases is thus reduced in the catalyst 6 to nitrogen gas and water vapor.

The shape of the SCR catalyst 6 to reduce nitrogen oxide is related to the temperature of the exhaust gases. An optimal temperature can be in the range 300-450 ° C. At higher and lower exhaust temperatures, the capacity of the SCR catalyst to reduce nitrogen oxide is reduced. The exhaust flow through the SCR catalyst is an alien factor affecting the capacity of the SCR catalyst. The faster the exhaust gases pass through the SCR catalyst, the smaller the proportion of the exhaust gas content of nitrogen oxide has time to be reduced. The nitrogen oxide NOx in exhaust gases consists of nitrogen monoxide NO and nitrogen dioxide NO2. An SCR catalyst 6 capable of removing nitrogen oxide from exhaust gases is Liven dependent on the ratio between nitrogen monoxide NO and nitrogen dioxide NO2. The ability of an SCR catalyst to reduce the amount of nitrogen oxide in exhaust gases is optimal as the exhaust gases contain the same amount of nitrogen monoxide NO and nitrogen dioxide NO2. The task of the oxidation catalyst 4 is to oxidize nitrogen monoxide NO to nitrogen dioxide NO2 in a quantity said that the SCR catalyst 6 receives nitrogen oxide NOx which ideally contains the same amount of nitrogen monoxide NO and nitrogen dioxide NO2. The oxidation catalyst atom 6 has been continued with a through-centrally arranged channel 14. A valve 15 has been arranged in the channel 14. The valve 15 is adapted to regulate the exhaust flow through the channel 14. Some of the exhaust gases reaching the oxidation catalyst 4 will be passed through the oxidation catalyst 4 through passages in contact with the active layers of catalyst material in the oxidation catalyst 4 and obtain an oxidation of nitrogen monoxide NO to nitrogen dioxide NO2. A remaining part of the exhaust gases is led through the duct 14 with the aid of the exhaust valve 15 in unchanged form. Since the valve 15 is in a closed position, substantially the entire exhaust gas flow is led through the oxidation catalyst 4. Thus, with the aid of the valve 15, a variable proportion of the exhaust gases can be passed past the oxidation catalyst 4. The larger proportion of the exhaust gas flow through the duct 14 in unchanged form, the less nitrogen monoxide oxidized to nitrogen dioxide in the oxidation catalyst 4.

Fig. 2 shows the valve 15 which is arranged in the channel 14 in more detail. The valve comprises a valve housing 15a. The valve housing 15a comprises one or more inlet openings 15b for receiving exhaust gases. A bimetallic component 15c is arranged internally about the inlet openings 15b. The bimetallic component 15c consists of a metal sheet comprising two, side by side, arranged thin metal plates which are made of different materials with different thermal expansion properties. The bimetallic component 15c is attached to the housing 15a in a hooked condition. The bimetallic component 15c is narrower in a transverse direction than the internal width of the housing 15a so that exhaust gases can pass past the bimetallic component 15 inside the housing 15a. Alternatively, the bimetallic component 15 may include through-holes for the passage of exhaust gases. The bimetallic component 15 is attached between a cradle surface adjacent to the valve housing inlet port 15b and a first side of a valve body 15d. The valve body 15d is movably arranged in relation to a valve set 15e between a closed bearing and a more or less open bearing. The valve body 15d is arranged on a valve rod 15f which is movably attached to a hall which extends through a cradle adjacent to the inlet opening 15b of the valve housing and a cradle adjacent to the outlet opening 15g of the valve housing. A spring member 15h is fixed between a second side of the valve body 15d and an inner cradle surface of the valve housing 15a adjacent to the outlet opening 15g.

The bimetallic component 15c operates with a spring force of. the valve body 15d which strives to guide it against the valve seat 15e and thus close the valve arrangement 15. The two metal plates forming in the bimetallic component are arranged in relation to each other so that the spring force with which the bimetallic component 15c acts on the valve body 15d decreases with rising exhaust temperature. The spring member 15h acts with a spring force on the valve body 15d which strives to guide the free valve seat 15e and thus open the valve arrangement 15. This spring force is substantially constant during all operating conditions. The exhaust flow acts with a force on the valve body 15d which strains to guide the valve body 15d towards the valve stem 15e and thus closes the valve arrangement 15. The force with which the exhaust flow acts on the valve body is related to the size of the exhaust flow. The position of the valve body 15c in relation to the valve seat 15e is thus determined by the temperature and flow of the exhaust gases, i.e. the same parameters that affect the oxidation catalyst's capacity to oxidize nitrogen monoxide NO to nitrogen dioxide NO2.

The oxidation catalyst 4 has the task of oxidizing nitrogen monoxide NO to nitrogen dioxide NO2. The capacity of the oxidation catalyst 4 to perform this task is highest as the exhaust gases have a high temperature and a laid flow. In such operating cases, a conventional oxidation catalyst oxidizes nitrogen dioxide NO / in an amount such that the content of nitrogen dioxide risks exceeding 50% of the total amount of nitric oxide NOx which leaves the oxidation catalyst 4 and is led to the SCR catalyst 6. The SCR catalyst's ability to reduce nitrogen oxides however, the exhaust gases decrease radically if the nitrogen dioxide content NO2 in the exhaust gases exceeds 50% of the total amount of nitrogen oxide NOx. For this reason, the oxidation catalyst 4 bar supplies nitric oxide NOx to the SCR catalyst 6 which contains 50% nitrogen dioxide NO2 but no more. Lamply, it delivers nitrogen oxide with a proportion of nitrogen dioxide NO2 within the range of 50%.

The bimetallic component 15c and the spring means 15h are dimensioned so that the bimetallic component 15c together with the incoming exhaust flow holds the valve arrangement 14 in a closed position at operating times when it rows low exhaust temperatures and low exhaust flow, high exhaust temperatures and high exhaust flow and low exhaust flow and low exhaust flow. In these operating cases, the oxidation catalyst's capacity to oxidize nitrogen monoxide to nitrogen dioxide is not entirely optimal and it delivers a nitrogen dioxide content of NO2 that is less than 50% of the total amount of nitrogen oxide NOx. In the case of operation when the exhaust gases have a high temperature and the raga river, the oxidation catalyst 4 has an optimal capacity. The high exhaust gas temperature affects the bimetallic component 15c sa. that it exerts a reduced spring force on the valve body 15d at the same time as the exhaust flow tiff & a relatively small force on the valve body 15d against the closed layer. The spring means 15h now has the capacity to displace the valve means 15d towards an open layer so that a part of the exhaust gases is passed through the open valve 15 and the duct 14 without being oxidized in the oxidation catalyst 4. As some of the exhaust gases pass the oxidation catalyst 4, the content of nitrogen dioxide NO2 in the nitrogen oxide NOx which when the downstream SCR catalyst 6 is reduced. The valve body 15c is driven by the spring means 15h to an open position which can be more or less open depending on the temperature and flow of the exhaust gases. The flow through the valve arrangement 15 can be varied varied steplessly within a certain range. The components of the valve arrangement 15 are dimensioned so that the valve body 15d opens and leads past some of the exhaust gases in the duct 14 so that the nitrogen dioxide content NO2 in the exhaust gases downstream of the oxidation catalyst 4 is at most 50% of the total amount of nitrogen oxide NOx.

Fig. 3 shows an alternative embodiment of a valve 16 which can be arranged in a channel 14 which extends through an oxidation catalyst 4. The valve arrangement 16 in this case comprises only a bimetallic component 16 in the form of a metal sheet.

The metal sheet has an inner edge surface 16a which is fixed in the channel 14 and a free edge surface 16b which is coated in a position upstream of the fixed edge surface 16a with respect to the flow direction of the exhaust gases in the channel 14. The bimetallic component 16 has the property that it hooks i.e. bend neatly towards a gradually more open layer at rising exhaust temperatures. However, the exhaust flow in the duct 14 supplies a force which strains after bending the bimetallic component 16 upwards, i.e. against a barred team.

The bimetallic component 16 is dimensioned so that it holds the duct 14 in a closed position at operating times as it rows low exhaust temperatures and low exhaust flow, high exhaust temperatures and high exhaust flow and low exhaust temperatures and high exhaust flow. In these operating cases, the oxidation catalyst's capacity to oxidize nitrogen monoxide to nitrogen dioxide is not entirely optimal and it delivers a nitrogen dioxide content of NO2 that is less than 50% of the total amount of nitrogen oxide NOx. In the case of operation when the exhaust gases have a high temperature and the low river, the oxidation catalyst 4 has an optimal capacity. The high exhaust temperature affects the bimetallic component 16 so that it is curved and the free end surface is not bent. The low exhaust flow does not have the capacity to supply a force which can lift the free end face 16b upwards against a rod bearing in which the free end face abuts against an upper surface of the channel 14. This creates an opening for the exhaust gases between the free end face 16b and the channel. 14 upper surface. This opening receives a size that varies with the temperature and flow of the exhaust gases. The size of the opening defines how much of the exhaust gases is passed past the oxidation catalyst 4, via the duct 14. How much of the exhaust gases passed through the duct 14 is related to the reduction of the oxidation catalyst capacity.

Fig. 4 shows another principle for preventing an oxidation catalyst 4 from oxidizing nitrogen oxide in an amount such that nitrogen oxide NOx is delivered to a downstream SCR catalyst which contains at most 50% nitrogen dioxide NO2. In this case, a part of the outlet side 4a of the oxidation catalyst 4 has been continued with rocking elements 17 defining short channels 18 for receiving exhaust gases leaving certain areas of the oxidation catalyst 4. Each of the channels 18 comprises a valve 19 with which the continuous flow is regulated. Since the valves 19 are in a closed position, the exhaust gas flow is substantially blocked by the connecting areas of the oxidation catalyst 4 and the armed oxidation of nitrogen oxide NO to nitrogen dioxide NO2 in these areas of the oxidation catalyst 4. The valves 19 are adapted to close during operation as the percentage of nitrogen dioxide exceeds 50%. of the total amount of nitrogen oxides NOx that reaches the SCR catalyst 6. Such operating cases occur when the exhaust gases have a high temperature and a laid flow. In this case, the valve 19 is adapted to shut off and block the connecting areas of the oxidation catalyst 4. Thus, the oxidation catalyst 4 delivers nitrogen oxide NOx to the downstream coated SCR catalyst 6 with a proportion of nitrogen dioxide which is at most 50%.

Fig. 5 shows two such valves 19 in more detail. The valves 19 in this case comprise only a bimetallic component 19 in the form of a metal plate. The bimetallic component 19 has an inner edge surface 19a which is fixed in the duct 18 and a free edge surface 19b which is coated in a position downstream of the fixed edge surface 19a with respect to the flow direction of the exhaust gases in the duct 18. The bimetallic component 19 has the property that it hooks ie. bent upwards towards a rod 'age at rising exhaust temperatures. The exhaust flow in the duct 14 tiff & a force that strains after bending the bimetallic component 18 down, ie. against an appet make. The bimetallic component 19 is dimensioned so that it hails the duct 18 in the open at operating times when it fades low exhaust temperatures and low exhaust flow, high exhaust temperatures and high exhaust flow and low exhaust temperatures and high exhaust flow. In these operating cases, the oxidation catalyst's capacity to oxidize nitrogen monoxide to nitrogen dioxide is not very optimal and it delivers a nitrogen dioxide content of NO2 which is less than 50% of the total amount of nitrogen oxide NOx. At operating times when the exhaust gases have a high temperature and raga Widen, the oxidation catalyst 4 has an optimal capacity. The high exhaust temperature affects the bimetallic component 19 so that the crank and the free 12 end face are pooped upwards. The low exhaust gas flow does not have the capacity to apply a force that can depress the free end surface 19b from the substantially closed bed. Thereby, the exhaust gas flow is substantially blocked through the areas of the oxidation catalyst 4 which have outlet openings adjacent to said channels 18.

Fig. 6 shows an alternative valve 20 which can be used to regulate the exhaust gas flow through the channels 18. The valve 20 comprises corresponding components as the valve in Fig. 2 but they have been arranged so that the valve closes in the stable for opening at operating times when the exhaust gases have a high temperature and a laid flOde. The valve arrangement 20 comprises a valve housing 20a. The valve housing 20a includes one or more inlet openings 20b for receiving the exhaust gases. A bimetallic component 20c is provided internally about the inlet openings 20b. The bimetallic component 20c is in a transverse direction narrower than the internal width of the housing 20a so that exhaust gases can pass past the bimetallic component 20c inside the housing 20a. The bimetallic component 20c is fixed between a cradle surface adjacent to the valve housing inlet port 20b and a first side of a valve body 20d.

The valve body 20d is movably arranged in relation to a valve set 20e between a substantially closed bearing and a more or less open length. The valve body 20d is arranged on a valve rod 20f which is movably attached to a hole which projects through a cradle adjacent to the inlet opening 20b of the valve housing and a cradle adjacent to the outlet opening 20g of the valve housing. A spring member 20h is attached between a second side of the valve body 20d and an inner cradle surface of the valve housing 20a adjacent to the outlet opening 20g.

The bimetallic component 20c acts with a spring force on the valve body 20d which tends to guide it from the valve seat 20e and thus towards an open bearing. The spring force with which the bimetallic component 20 acts on the valve body 20d decreases with increasing exhaust temperature. The spring member 20h acts with a spring force on the valve body 20d which springs to guide it against the valve seat 20e and thus closes the valve arrangement 20. This spring force is substantially constant during all operating conditions. The exhaust flow acts with a force on the valve body 20d which strains to move the valve body 20d towards an open bearing. The force with which the exhaust flow acts on the valve body 20d is related to the size of the exhaust flow. The position of the valve body 20d in relation to the valve insert 20e is thus determined by the temperature and flow of the ayga gases.

The oxidation catalyst 4 thus has the highest capacity as the exhaust gases have a high temperature and after flow. The bimetallic component 20c and the spring means 20h are dimensioned so that they hail the valve arrangement 20 in an open position at the operating supply where the father low exhaust temperatures and low exhaust flow, high exhaust temperatures and high exhaust flow and low exhaust temperatures and high exhaust flow. In these operating conditions, the oxidation catalyst's capacity to oxidize nitrogen monoxide to nitrogen dioxide is not entirely optimal and it delivers a nitrogen dioxide content of NO2 which is less than 50% of the total amount of nitrogen oxide NOx. In the case of operation when the exhaust gases have a high temperature and cook the river, the oxidation catalyst 4 has an optimal capacity. The high exhaust temperature affects the bimetallic component 20c so that it exerts a reduced feed force on the valve body 20d while the exhaust flow tiff & a relatively small force on the valve body 20d towards the open layer. The spring means 20h now has the capacity to displace the valve means 20d towards the closed layer so that the flow of exhaust gases through the valve 20 and the duct 18 is substantially blocked. As a result, the full capacity of the oxidation catalyst 4 can not be utilized and it thus delivers a reduced content of nitrogen dioxide NO2 in the nitrogen oxide NOx to the SCR catalyst 6 arranged downstream. The flow through the valve arrangement 20 can be varied steplessly from a completely open layer to a successively substantially closed layer as a minimal flow of exhaust gases is passed through the valve arrangement 20. The components of the valve arrangement 20 are dimensioned so that the valve body 20d closes and blocks the flow in parts of the oxidation catalyst 4. NO2 in the exhaust gases downstream of the oxidation catalyst 4 is at most 50% of the total amount of nitric oxide NOx.

The invention is not limited to the embodiment described above, but it can be varied freely within the scope of the patent claims. 14

Claims (13)

Patent claims Valve arrangement for regulating the flow of exhaust gases through an oxidation catalyst (4) in an exhaust line (2) which also comprises an SCR catalyst (6) which is arranged in a position downstream of the oxidation catalyst (4) with respect to the intended direction of flow of the exhaust gases in the exhaust line. (2), wherein the oxidation catalyst (4) is adapted to oxidize nitrogen monoxide NO in the exhaust gases to nitrogen dioxide NO2, characterized in that the valve arrangement comprises a bimetallic component (15c, 16, 19, 20c) which changes shape depending on the temperature of the exhaust gases, the valve arrangement being adapted to regulate exhaust flow through the oxidation catalyst (4) so that the oxidation catalyst's capacity to oxidize nitrogen monoxide (NO) to nitrogen dioxide (NO2) is reduced when the bimetallic component (15c, 16, 19, 20c) is in contact with exhaust gases having a temperature exceeding a predetermined value. Valve arrangement claim 1, characterized in that it is adapted to regulate exhaust flow through the oxidation catalyst (4) so that the oxidation catalyst's capacity to oxidize nitrogen monoxide (NO) to nitrogen dioxide (NO2) is reduced when the exhaust gases have a Wide below a predetermined value. Valve arrangement according to Claim 1 or 2, characterized in that it is adapted to regulate the flow through the oxidation catalyst (4) so that the capacity of the oxidation catalyst is reduced to a level at which the downstream SCR catalyst (6) receives nitrogen oxide NOx containing a maximum of 50%. nitrogen dioxide NO2 Valve arrangement according to the preceding claim, characterized in that the valve arrangement comprises a channel (14, 18) for receiving exhaust gases in connection with the oxidation catalyst and a valve (15, 16, 19, 20) which regulates the exhaust flow through the channel (14, 18 ) and thus through the connecting oxidation catalyst (4). Valve arrangement according to claim 4, characterized by said channel (14) is a bypass line with which exhaust gases can be led past the oxidation catalyst (4). Valve arrangement according to claim 5, characterized by said channel (14) extending through the oxidation catalyst (4). Valve arrangement according to claim 4, characterized in that said channel (18) is connected to the oxidation catalyst (4) A. that an exhaust flow through the channel (18) results in a corresponding exhaust flow through said area of the oxidation catalyst (4). Valve arrangement according to claim 7, characterized in that said channel (18) is formed by cradle elements (17) which are fixed to an outlet side (4a) of the oxidation catalyst (4). Valve arrangement according to any one of claims 4-7, characterized in that the valve (15, 16, 19, 20) comprises a spring element (15h, 16, 19, 201i) which is adapted to regulate the exhaust flow through the duct (14, 18) in depending on the size of the incoming exhaust flow. Valve arrangement according to claim 9, characterized in that the spring element is comprised of said bimetallic component (16, 19). Valve arrangement according to any one of the preceding claims, characterized in that the valve (15, 16, 19, 20) comprises a valve body (15d, 16, 19, 20d) which is adapted to regulate the flow through the channel (14, 18) by displacing between an open ldge and a substantially closed ldge. A valve arrangement according to claim 11, characterized in that the valve body is comprised of said bimetallic component (16, 19). Exhaust system has an internal combustion engine, characterized in that it comprises a valve arrangement (5) according to any one of claims 1-12. 10