SE538969C2 - Valve arrangement for controlling the exhaust gas flow through an oxidation catalyst - Google Patents

Abstract

The present invention relates to a valve arrangement for controlling the flow of exhaust gas 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 flow direction of the exhaust gases in the oxidation catalyst (4). 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, 19,200) which changes shape depending on the temperature of the exhaust gases. The valve arrangement is adapted to control exhaust gas fate through the oxidation catalyst (4) so that the oxidation catalyst capacity to oxidize nitrogen monoxide (NO) to nitrogen dioxide (NO 2) is reduced when the bimetallic component (15c, 16, 19, 20c) is in contact with exhaust gases having a too high temperature. . (Figs)

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 nitric oxide NOX from internal combustion engines, a technology called SCR (Selective Catalytic Reduction) is used. This technique means that a solution of urea and water is 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 atomized urea solution is evaporated in contact with the hot exhaust gases to form ammonia. The mixture of ammonia and exhaust gases is then passed through an SCR catalyst. The nitrogen in the nitrogen oxide in the exhaust gases reacts here with the nitrogen in the ammonia so that nitrogen gas is formed. The oxygen in the nitrogen oxide reacts with the hydrogen in the ammonia to form water. The nitrogen oxide in the exhaust gases is thus reduced in the catalyst to nitrogen gas and water vapor. nitric oxide is greatly reduced.

Nitric oxide NOX in exhaust gases consists of nitrogen monoxide NO and nitrogen dioxide NO2. The ability of conventional SCR catalysts 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 nitric 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 known to arrange an oxidation catalyst DOC (Diesel OxidationCatalyst) in the exhaust line in a position upstream of the SCR catalyst. Enoxidation 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 fate of the exhaust gases. The oxidation catalyst's capacity to oxidize nitrogen monoxide to nitrogen dioxide is greatest at exhaust temperatures around 300 ° C and low exhaust fumes. Under 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 nitric oxide decreasing drastically at the same time as nitrous oxide is formed, which is a very powerful greenhouse gas. Ammonia grinding increases as well. It is thus a problem when an oxidation catalyst supplies exhaust gases to an SCR catalyst containing nitric 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 an oxidation catalyst capacity to oxidize oxide. to nitrogen dioxide at operating times when the oxidation catalyst risks supplying nitrogen oxide with an excess of nitrogen dioxide.

This object is achieved with the valve arrangement of the kind mentioned in the introduction, which is characterized by the features stated in the characterizing part of claim 1. The valve arrangement thus comprises a bimetallic component which is influenced by the exhaust gas temperature. A bimetallic component consists of two thinly joined metal elements with different thermal expansion capacity. When the bimetallic component heats up, it bends because 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 exhaust gases with a high temperature are led to an oxidation catalyst, it obtains an increased capacity and there is thus a risk that it oxidizes nitrogen monoxide to nitrogen dioxide an excessive amount. When the exhaust gases have a temperature above a predetermined value, the valve arrangement controls the exhaust flow through the oxidation catalyst so that the oxidation catalyst's capacity to oxidize nitrogen monoxide to nitrogen dioxide is reduced. The bimetallic component affects the valve arrangement so that said control is exhausted by the oxidation catalyst. The bimetallic component can affect the valve arrangement so that it abruptly changes as 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 care. 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 care. Such a reduction in the capacity of the oxidation catalyst results in the downstream SCR catalyst being able to receive nitrogen oxides even at high exhaust gas temperatures 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 which is less than a predetermined care. The capacity of an oxidation catalyst to oxidize nitrous oxide to nitrogen dioxide is thus also dependent on the exhaust gas oxidation catalyst. A small and then slow fl fate of exhaust gases through the oxidation catalyst means that the exhaust gases are in contact with the active catalyst material for a longer period of time, which leads to a larger proportion of the nitrous oxide having time to oxidize to nitrogen dioxide before it leaves the oxidation catalyst. In this case, the valve arrangement thus takes into account the temperature and fate of both exhaust gases. The predetermined care of the exhaust gases regarding temperature and år years related to each other and defines different operating conditions at 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 control 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 not more than 50% nitrogen dioxide. The ability of an SCR catalyst to reduce nitrogen oxide is optimal as it contains 50% nitrogen monoxide and 50% nitrogen dioxide. If the proportion of nitrogen monoxide is greater than 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 greater 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 appropriate for an oxidation catalyst to be dimensioned so that it can deliver nitrous oxide with a proportion of nitrogen dioxide which is in the range of 40-50% during most operating conditions and to reduce the oxidation catalyst capacity with the valve arrangement at operating times when the exhaust gases have a high temperature and low nitrogen content. of nitrogen dioxide never exceeds 50%.

According to an embodiment of the invention, the valve arrangement comprises a duct receiving exhaust gases in connection with the oxidation catalyst and a valve which regulates the exhaust flow through the duct and thus the exhaust gas flow through the connecting oxidation catalyst. By means of such an alternative fate channel for the exhaust gases, the exhaust gas flow through the oxidation catalyst is changed in such a way 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. Thus, in this case, some of the exhaust gases are passed past the oxidation catalyst instead of 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 a bore of, for example, a central pair of deoxidation catalyst. This does not make the channel space-consuming. Said channel can also be constituted by a tube extending around the oxidation catalyst.

According to another embodiment of the invention, said duct is connected to the co-oxidation catalyst so that the exhaust gas flow through the duct results in a corresponding exhaust gas fl in a region of the oxidation catalyst. When the valve blocks the exhaust gas through the duct, no exhaust gas is obtained in the said area of the oxidation catalyst. The exhaust gases in this case are forced to pass through a limited area of the oxidation catalyst which results in the oxidation catalyst capacity to oxidize nitrogen monoxide to nitrogen dioxide being reduced. Said channel can be formed by wall elements which are attached 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 channel depending on the size of the incoming exhaust flow. In this case, the spring element affected by the incoming exhaust gas fate and the bimetallic component affected by the temperature of the exhaust gases can be arranged so that at a high exhaust temperature and a low exhaust fate they provide exhaust exhaust through the channel resulting in the oxidation catalyst obtaining reduced oxide or oxide. According to one embodiment, the spring element is said bimetallic component. This utilizes the ability of both the bimetallic component to change shape during temperature changes and resilience properties as it is affected by the incoming exhaust gases. The components of the valve can then 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 flame and a substantially closed flame. The substantially closed lid causes a minimum exhaust gas fl to be passed through the duct so that the bimetallic component has the ability to substantially continuously sense the temperature of the incoming exhaust gases. The bimetallic component sensing the temperature of the exhaust gases can provide a force acting on the valve body. 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 constitute the valve body which blocks the channel in a substantially closed flame and exposes it in an open flame.

The invention also 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 shows a part of an exhaust line comprising a valve arrangement according to a first embodiment of the present invention, Fig. 2 shows a valve of the valve arrangement of Fig. 1 in more detail, Fig. 3 shows an alternative valve of the valve arrangement of Fig. 1, Fig. 4 shows a valve arrangement according to a second embodiment of the present invention, Fig. 5 shows a valve of the valve arrangement of Figs. Fig. 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 engine l. The diesel engine 1 is equipped with a single exhaust line 2 which contains a container 3 for exhaust gas treatment components. The exhaust gas treatment components can of course be arranged in your 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 ability to oxidize nitrogen monoxide 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. The ability of an oxidation catalyst 4 to oxidize nitrogen monoxide NO to nitrogen dioxide NO 2 depends on the temperature and fate of the exhaust gases.

The container 3 comprises downstream the oxidation catalyst 4 a second exhaust gas purifying component in the form of a particle filter 5 which can be called DPF (Diesel ParticulateFilter). A particle filter 5 comprises elongate parallel channels with stop surfaces which are arranged in suitable places. The stop surfaces force the exhaust gases to be led into adjacent elongate channels in the particle filter 5. The walls of the channels are made of porous material with fine pores that allow the passage of exhaust gases but not soot particles. The soot particles then become stuck inside the particle filter 5. The particle filter 5 is continuously regenerated without active measures by oxidizing the soot particles with NO 2 and / or actively by heat-raising measures which accelerate the oxidation with either NO 2 or oxygen.

The container 3 comprises downstream of the particle 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 means that a reducing agent in the form of a urea solution is injected into the exhaust gases. In this case, the urea solution is stored in a tank 7 and is led, via a line 8, to an injection means 9 which injects the urea solution into a space 3a in the container. A control unit 10 controls the supply of the urea solution with information regarding specific motor parameters 11. A pump 12 transports the urea solution to the injector 9.

The container 3 comprises downstream of the SCR catalyst 6 a fourth exhaust gas purifying component in the form of an ammonia slip catalyst 13 ASC (Ammonia Slip Catalyst). The task of the ammonia slip catalyst 13 is to eliminate any excess ammonia which is not reduced in the SCR catalyst. An ammonia abrasive catalyst generally 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 as load and speed the amount of 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 injector 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 leads to the SCR catalyst 6. In the SCR catalyst 6, the nitrogen of the nitrogen oxide reacts with the nitrogen in the ammonia to form nitrogen gas. The oxygen of the nitric oxide reacts with the hydrogen 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 ability of the SCR catalyst 6 to reduce nitric oxide is related to exhaust gas temperature. 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 nitric oxide is reduced. The exhaust gas through the SCR catalyst is also a factor that affects 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 nitrous oxide has time to be reduced. The nitrogen oxide NOX in exhaust gases consists of nitrogen monoxide NO and nitrogen dioxide NO2. The ability of an SCR catalyst 6 to remove nitric oxide from exhaust gases also depends on the ratio of nitric oxide NO to nitrogen dioxide NO2. An SCR catalyst's ability to reduce the amount of nitric oxide in exhaust gases is optimal as the exhaust gases contain as much 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 an amount such that the SCR catalyst 6 receives nitric oxide NOX which ideally contains the same amount of nitrogen monoxide NO and nitrogen dioxide NO2.

The oxidation catalyst 6 has been provided with a continuous centrally arranged channel 14. A valve 15 has been arranged in the channel 14. The valve 15 is adapted to regulate exhaust gas through the channel 14. Some of the exhaust gases reaching the oxidation catalyst 4 will be led through the continuous passages of the oxidation catalyst 4 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 NO 2. A remaining part of the exhaust gases is led through the duct 14 by means of the valve 15 in unchanged form. When the valve 15 is in a closed position, substantially all of the exhaust gas is passed through the oxidation catalyst 4. With the aid of the valve 15, a variable proportion of the exhaust gases can thus be led to the bypass catalyst 4. The larger the proportion of exhaust gas passed through the duct 14 unchanged form, the less nitrogen oxide is oxidized to nitrogen dioxide. oxidation catalyst 4.

Fig. 2 shows the valve 15 which is arranged in the channel 14 in more detail. The valve 15 includes a valve housing 15a. The valve housing 15a comprises one or more inlet openings 15b for receiving exhaust gases. A bimetallic component 15c is provided inside the inlet openings 15b. The bimetallic component 15c consists of a metal sheet which comprises two, side by side, arranged thin metal plates which are made of different materials with different heat-expanding properties. The bimetallic component 15c is attached to the housing 15a in a curved condition. The bimetallic component 15c is in a transverse directional grinder than the inner width of the housing 15a so that exhaust gases can pass the bybimetal component 15 inside the housing 15a. Alternatively, the bimetallic component 15 may include through openings for the passage of exhaust gases. The bimetallic component 15 is attached between a wall surface adjacent to the inlet opening 15b of the valve housing and a front side of a valve body 15d. The valve body 15d is movably arranged in relation to a valve seat 15e between a closed position and a more or less open position. The valve body 15d is arranged on a valve rod 15f which is movably attached to holes extending through a wall adjacent to the inlet opening 15b of the valve housing and a wall adjacent to the outlet opening 15g of the valve housing. A spring member 15h is attached between one side of the valve body 15d and an inner wall surface of the valve housing 15a adjacent to the outlet opening 15 g.

The bimetallic component 15c acts with a spring force on the valve body 15d which strives to bring it towards the valve seat 15e and thus close the valve arrangement 15. The two metal plates included in the bimetallic component are arranged relative to each other so that the spring force bimetallic component 15c rises with the valve body exhaust temperature. Spring member 15h acts with spring force on the valve body 15d which seeks to move it from the valve seat 15e and thus open the valve arrangement 15. This spring force is substantially constant during all operating conditions. The exhaust gas acts with a force on the valve body l5d which seeks to move the valve body l5d towards the valve seat l5e and thus the shut-off valve arrangement l5. The force exerted by the exhaust on the valve body is related to the size of the exhaust. The position of the valve body 15c in relation to the valve seat 15e is thus determined by the temperature and fate of the exhaust gases, i.e. co-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 NO 2. The capacity of the oxidation catalyst 4 to perform this task is at most when the exhaust gases have a high temperature and a low fate. In such operating times, a conventional oxidation catalyst oxidizes nitrogen dioxide NO 2 in an amount so that the content of nitrogen dioxide risks exceeding 50% of the total amount of nitric oxide NOx leaving the oxidation catalyst 4 and being passed to the SCR catalyst 6. The SCR catalyst's ability to reduce nitrogen oxides the nitrogen dioxide content NO2 in the exhaust gases exceeds 50% of the total amount of nitrogen oxide NOX. The oxidation catalyst 4 should for that reason supply nitric oxide NOX to the SCR catalyst 6 which contains 50% nitrogen dioxide NO2 but no more. Preferably it supplies nitric oxide with a proportion of nitrogen dioxide NO2 in the range 45-50%.

The bimetallic component l5c and the spring member l5h are dimensioned so that the bimetallic component l5c together with the incoming exhaust gas håll holds the valve arrangement l4 in a closed position at operating times when there are low exhaust temperatures and low exhaust gas fl deserts, high exhaust gases höga high exhaust gases and high exhaust gases. At these operating times, the capacity of the oxidation catalyst to oxidize nitrogen monoxide to nitrogen dioxide is not entirely optimal and it delivers a nitrogen dioxide content of NO 2 which is less than 50% of the total amount of nitric oxide NOX. In the case of operation, the exhaust gases have a high temperature and low fl feats, the oxidation catalyst 4 has an optimum capacity. The high exhaust temperature affects the bimetallic component l5c so that it exerts a reduced spring force on the valve body l5d at the same time as the exhaust gas exerts a relatively small force on the valve body l5d towards the closed position. The spring means 15h now has the capacity to displace the valve means 15d towards an open position so that some of the exhaust gases are passed through the open valve 15 and the duct 14 without oxidizing the oxidation catalyst 4. As some of the exhaust gases pass the pre-oxidation catalyst 4, the nitrogen dioxide content in the nitric oxide NOx as the downstream SCR catalyst 6 is reduced. The valve body 15c moves the spring means 15h to an open position which may be more or less open depending on the temperature and fate of the exhaust gases. The flow through the valve arrangement 15 can thus be varied steplessly within a certain area. The components of the valve arrangement 15 are dimensioned so that the valve body 15d opens and leads past a part of the exhaust gases in the duct 14 so that the nitrogen dioxide content NO 2 in the exhaust gases downstream of the oxidation catalyst 4 becomes at most 50% of the total amount of nitric oxide NOx.

Fig. 3 shows an alternative embodiment of a valve 16 which can be arranged in a channel 14 extending through an oxidation catalyst 4. The valve arrangement 16 in this case comprises only a bimetallic component 16 in the form of a metal plate. The metal plate has an internal edge surface 16a which is fixed in the duct 14 and a free edge surface 16b which is located in a position upstream of the fixed edge surface 16a with respect to the flow direction of the exhaust gases in the duct 14. The bimetallic component 16 has the property that it is curved, i.e. bends downwards towards a successively more open position increasing exhaust temperatures. However, the exhaust gas in the channel 14 supplies a force which tends to bend the bimetallic component 16 upwards, i.e. against a closed position.

The bimetallic component 16 is dimensioned to hold the duct 14 in a closed position at operating times when there are low exhaust temperatures and low exhaust fumes, high exhaust temperatures and high exhaust fumes and low exhaust temperatures and high exhaust fumes. At these operating times, the capacity of the oxidation catalyst to oxidize nitrogen monoxide to nitrogen dioxide is not entirely optimal and it delivers a nitrogen dioxide content of NO 2 which is less than 50% of the total amount of nitric oxide NOx. At operating times, the exhaust gases have a high temperature and low den feats, the oxidation catalyst 4 has an optimum capacity. The high exhaust temperature affects the bimetallic component 16 so that it is curved and the free end surface bends downwards. The low exhaust gas flow has not been able to supply a force which can lift the free end surface 16b upwards towards a closed position in which the free end surface abuts against an upper surface of the duct 14. This creates an opening for the exhaust gases between the free end surface 16b and the upper surface of the duct 14. . This opening holds a size that varies with the temperature and fate 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 sheet oxide in an amount such that nitric oxide NOX is supplied to a downstream SCR catalyst which contains at most 50% nitrogen dioxide NO2. In this case, a part 4 of the outlet side 4a of the oxidation catalyst 4 is provided with wall elements 17 which define 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 throughput is regulated. When the valves 19 are in a closed position, the flow through the adjoining areas of the oxidation catalyst 4 and then the oxidation of nitric oxide NO to nitrogen dioxide NO2 in these areas is deoxidized by the catalyst 4. The valves 19 are adapted to close at operating times when the total amount of nitrogen dioxide is at risk. nitrogen oxides NOX reaching the SCR catalyst 6. Such operating times occur when the exhaust gases have a high temperature and a low flow. In this case, the valve 19 is adapted to close and block adjacent areas of the oxidation catalyst 4. Thus, the oxidation catalyst 4 delivers nitric oxide NOX to the downstream SCR catalyst 6 with a proportion of nitrogen dioxide not exceeding 50%.

Fig. 5 shows two such valves 19 in more detail. The valves 19 in this case only comprise 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 channel 18 and a free edge surface 19b which is located in a position downstream of the fixed edge surface 19a with respect to the exhaust gas flow direction in the channel 18. The bimetallic component 19 here has the property that it curves i.e. bends upwards towards a closed position at rising exhaust temperatures. The exhaust gas flow in the duct 14 supplies a force which strives to bend the bimetallic component 18 downwards, i.e. towards an open position. The bimetallic component 19 is dimensioned so that it holds the duct 18 in an open position at operating times when there are low exhaust temperatures and low exhaust fumes, high exhaust temperatures and high exhaust fumes and low exhaust temperatures and high exhaust fumes. In these operating cases, the capacity of the oxidation catalyst to oxidize nitrogen monoxide to nitrogen dioxide is not completely optimal and it delivers a nitrogen dioxide content of N02 which is less than 50% of the total amount of nitrogen oxide N0X. At operating times when the exhaust gases have a high temperature and low den fates, the oxidation catalyst 4 has an optimal capacity. The high exhaust temperature affects the bimetallic component 19 so that it is curved and the free end surface 12 bends upwards. The low exhaust gas flow does not have the capacity to apply a force which pressurizes the free end surface 19b from the substantially closed position. Subsequently, the gas is substantially blocked by the areas of the oxidation catalyst 4 which have outlet openings in connection with said channels 18.

Fig. 6 shows an alternative valve 20 which can be used to regulate the exhaust flow through the ducts 18. The valve 20 comprises corresponding components as the valve in Fig. 2 but they have been arranged so that the valve closes instead of opens at operating times when the exhaust gases have a high temperature and a low de destiny. The valve arrangement 20 includes a straight 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 inside the inlet openings 20b. The bimetallic component 20c is in a transverse direction narrower than the inside width of the housing 20a so that exhaust gases can pass the bimetallic component 20c inside the housing 20a. The bimetallic component 20c is attached between a wall surface adjacent the inlet opening 20b of the valve housing and a first side of a valve body 20d. The valve body 20d is movably arranged relative to a valve seat 20e between a substantially closed position and a more or less open position. The valve body 20d is arranged on a valve rod 20f which is movably fixed in holes extending through a single wall adjacent to the inlet opening 20b of the valve housing and a wall adjacent 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 wall 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 strives to move it from the valve seat 20e and thus towards an open position. The spring force that the bimetallic component 20 acts on the valve body 20d decreases with rising exhaust temperature. The spring means 20h acts with a spring force on the valve body 20 which strives to bring it towards the valve seat 20e and thus the shut-off valve arrangement 20. This spring force is substantially constant under all operating conditions. The exhaust flow acts with a force on the valve body 20d which strives to move the valve body 20d towards an open position. The force exerted by the exhaust body 20d on the valve body 20d is related to the size of the exhaust fate. The position of the valve body 20d relative to the valve seat 20e is thus determined by the temperature and fate of the exhaust gases.

The oxidation catalyst 4 thus has the highest capacity as the exhaust gases have a high temperature and a low fate. The bimetallic component 20c and the spring member 20h are 13 dimensioned to hold the valve arrangement 20 in an open low mode of operation when there are low exhaust temperatures and low exhaust fumes, high exhaust temperatures and high exhaust fumes and low exhaust temperatures and high exhaust fumes. In these operational cases, the capacity of the oxidation catalyst to oxidize nitrous oxide to nitrogen dioxide is not entirely optimal and it delivers a nitrogen dioxide content NO2 that is less than 50% of the total amount of nitrogen oxide NOx. In the event of an operation, the exhaust gases have a high temperature and low fl feats, the oxidation catalyst 4 has an optimal capacity. The high exhaust temperature affects the bimetallic component 20c so that it exerts a reduced kraft force on the valve body 20d while the exhaust d adds a relatively small force on the valve body 20d to the open lid. The spring means 20h now has the capacity to displace the valve means 20d towards the closed lid so that the desolate exhaust gases through the valve 20 and the duct 18 are substantially blocked. As the full capacity of the canoxidation catalyst 4 is not utilized and it delivers a reduced content of nitrogen dioxide NO 2 in the nitrogen oxide NOX to the downstream SCR catalyst 6 is reduced. The flow through the valve arrangement 20 can vary steplessly from a fully open flame to a successively substantially closed flame as a minimum 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 part of the oxidation catalyst. the oxidation catalyst 4 becomes 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 claims.

Claims (10)

Valve arrangement for controlling the fate 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 flow direction 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 NO 2, the valve arrangement comprising a channel (14, 18) pre-receiving exhaust gases in connection with the oxidation catalyst and a valve (15, 16, 19, 20) which regulates exhaust gas flow through the duct (14, 18) and thus through the connecting oxidation catalyst (4) and a bimetallic component (15c, 16, 19, 20c) which is in contact with the exhaust gases in the duct (14, 18) and adapted to regulate exhaust gas through the duct (14, 18) by changing shape depending on the temperature of the exhaust gases, characterized in that the valve (15, 16, 19, 20) comprises a spring element (15h, 16, 19,20h) which is in contact with the exhaust gases in the duct (14, 18) and adapted to control the exhaust gas flow through the duct (14, 18) depending on the incoming exhaust gas size, the valve arrangement being adapted to control the exhaust flow through the duct (14, 18) and thus through the oxidation catalyst by means of the bimetallic component (15c, 16, 19, 20c) and the core element (15h, 16, 19, 20h) so that the oxidation catalyst capacity to oxidize nitrogen monoxide (NO) to nitrogen dioxide (NO2) is reduced when the metal component (15c, 16, 19, 20c) is in contact with exhaust gases having a temperature exceeding a predetermined value and then the exhaust gases have a flow below a predetermined value. Valve arrangement according to claim 1, characterized in that it is adapted that the control flow through the oxidation catalyst (4) so that the oxidation catalyst capacity is reduced to a level at which the downstream SCR catalyst (6) receives nitric oxide NOX containing not more than 50% nitrogen dioxide NO 2. Valve arrangement according to claim 1 or 2, characterized in that said duct (14) is a bypass line with which exhaust gases can be led past the oxidation catalyst (4). Valve arrangement according to claim 3, characterized in that said channel (14) extends through the oxidation catalyst (4). Valve arrangement according to claim 1 or 2, characterized in that said duct (18) is connected to an area of the oxidation catalyst (4) so that an exhaust gas genom through the duct (18) results in a corresponding exhaust fl fate through said area of the oxidation catalyst (4). Valve arrangement according to claim 5, characterized in that said channel (18) is formed by wall elements (17) which are attached to an outlet side (4a) of the oxidation catalyst (4). Valve arrangement according to any one of the preceding claims, characterized in that the spring element is comprised of said bimetallic component (16, 19). Valve arrangement according to 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 position and a substantially closed position. Valve arrangement according to claim 8, characterized in that the valve body is comprised of said bimetallic component (16, 19). Exhaust system for an internal combustion engine, characterized in that it comprises a valve arrangement (5) according to any one of claims 1-9.