Device for supplying ammonia to a reduction catalyst arranged in an exhaust system of an internal combustion engine

Abstract

In a device for supplying ammonia (NH3) to a reduction catalytic converter arranged in an exhaust system of an internal combustion engine comprising a container for storing a precursor body capable of generating ammonia when heated by a heating device disposed in the container for the thermolytic decomposition of the precursor material, the heating device includes a heating surface arranged adjacent the precursor body and means are provided for biasing the precursor material body in firm contact with the heating device surface for direct heat transfer to the precursor body, and the heating device is connected to a control unit for controlling the energization of the heating device depending on the NH3 requirements of the reduction catalytic convertor.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation-in-part application of international application PCT/IB2004/050127 filed Feb. 18, 2004 and claiming the priority of German applications 103 06 843.0 filed Feb. 18, 2003, 103 08 257.3 filed Feb. 25, 2003, 103 13 998.2 filed Mar. 27, 2003 and 203 08 348.2 filed May 26, 2003.

BACKGROUND OF THE INVENTION

This invention relates to a device for supplying ammonia in a gas phase to a reduction catalytic converter disposed in an exhaust gas duct of an internal combustion engine, particularly a Diesel engine, comprising a container having an outlet connected to the exhaust duct by a supply line and serving as a storage of a precursor which, when heated releases NH₃. The precursor may be, for example, ammonium carbonate. The storage container includes a heating device for inducing the thermolytic release of NH₃ from the NH₃ precursor.

In addition to carbon monoxide (CO) particulate matter and hydrocarbons (HC) particularly nitrogen-oxides (NO_x) are the primary environmentally objectionable emissions which are directly emitted during operation of internal combustion engines, particularly Diesel engines. Three-way catalytic converters as they are used in gasoline engines can not be used in connection with Diesel engines because diesel engines exhaust gases include an excess amount of oxygen. For this reason, for the reduction of the nitrogen oxide emissions of Diesel engines, a selectively operating SCR catalytic converter Selective Catalytic Reduction catalytic converter) has been developed in which with an added oxidation means, that is, ammonia (NH₃), the nitrogen oxides emitted from the engine are reduced to the air components N₂ and H₂O.

Such an apparatus for supplying ammonia in a gaseous phase to the exhaust gas duct of an internal combustion engine of a motor vehicle is known from DE 197 20 209 C1. This nitrogen removal apparatus comprises a gas-tight and pressure resistant converter in which a medium or a medium mixture, a so-called NH₃ precursor, is disposed which thermolytically releases NH₃. The medium may be for example, ammonium carbonate. The converter is connected to the exhaust gas duct of a diesel engine via a supply line wherein the supply line is connected to the exhaust gas duct in the flow direction of the exhaust gases ahead of the inlet end of a SCR catalytic converter. A closing device, a periodically operated valve, is provided which is controlled by a control unit so that the required NH₃ amount can be injected into the exhaust gas flow depending on certain engine operating data. The converter consists essentially of a pressure resistant reaction container which is surrounded by a heating device in the form of a heat exchange tube. The heating device is in communication with the cooling circuit of the diesel engine via a hot water supply and a return line.

By heating, the ammonium carbonate serving as NH₃ precursor is decomposed into NH₃ and CO₂. This gas mixture is collected in the pressure resistant reaction container until a certain internal pressure is built up. When a certain pressure has been reached in this reaction container an equilibrium is established so that no additional ammonium carbonate is decomposed. Under engine operating conditions, whenever the cooling water flowing through the heating device generally has a temperature of 80° to 100° C. there is an equilibrium pressure in the reaction container which for ammonium carbonate is about 3-4 bar. In order to be able to provide a sufficient amount of NH₃ for injection into the exhaust gas flow during dynamic operation of the diesel engine, the connector serves also as a reaction storage device in which a certain reaction gas amount or respectively the NH₃ contained therein is stored.

This known system operates in accordance with the principle that in the convertor a certain amount of NH₃ under a certain pressure is always stored so that the required NH₃ dose needed for the removal of the NO_x from the exhaust gases is always available. The system has the advantage over the carrying along of NH₃ in pressure cylinders in that only a relatively small amount of NH₃ needs to be carried along.

Furthermore, apparatus are known wherein NH₃ gas is released from the precursor for the NO_x reduction on a “just in time” basis. Such an apparatus is known for example from DE 34 22 175 A1. The NH₃ is generated by heating the NH₃ precursor wherein at any time only such an amount of NH₃ is generated as is needed in accordance with the respective momentary engine load. In accordance with DE 34 22 175 A1, the required NH₃ amount is generated by controlling the heat input. According to the state of the art, the NH₃ precursor is stored in a container which includes a heated decomposition chamber in which the NH₃ precursor is subjected to thermolysis (thermal decomposition). The outlet of the decomposition chamber is, by a supply line, to the exhaust duct of the internal combustion engine. As heating devices, electrical resistance heaters or infrared radiation heaters are proposed.

Such an arrangement is suitable for use in connection with stationary plants which generally are subjected only to few load changes which, furthermore, are predetermined. For use in connection with motor vehicles for example, in trucks or passenger cars, this technology is not suitable since the reaction time of the system is too long and the system is therefore too slow to be able to accommodate the rapid motor load changes as they occur during vehicle operation unexpectedly and in rapid succession with correspondingly different NO_x emissions. When an engine operating state is determined at a certain point in time and a certain NH₃ dose is calculated therefrom, first the NH₃ generating precursor material amount needed for the production of the NH₃ gas mixture must be supplied to the decomposition chamber so as to be heated therein. Under normal operating conditions, particularly in city traffic, the engine of the motor vehicle, however, is subjected to constant and unpredictable load changes so that the last supplied NH₃ amount is not adapted to the newest engine operating state. If an insufficient amount of NH₃ is supplied, the NO_x conversion is incomplete and if the NH₃ amount supplied is excessive, unoxidized NH₃ is discharged from the catalytic converter.

Based on the state of the art as discussed above, it is the object of the present invention to provide a device for supplying gaseous ammonia to a reduction catalyst arranged in the exhaust duct of an internal combustion engine in the required amount, particularly during a dynamic engine operation.

SUMMARY OF THE INVENTION

In a device for supplying ammonia (NH₃) to a reduction catalytic converter arranged in an exhaust system of an internal combustion engine comprising a container for storing a precursor body capable of generating ammonia when heated by a heating device disposed in the container for the thermolytic decomposition of the precursor material, the heating device includes a heating surface arranged adjacent the precursor body and means are provided for biasing the precursor material body in firm contact with the heating device surface for direct heat transfer to the precursor body, and the heating device is connected to a control unit for controlling the energization of the heating device depending on the NH₃ requirements of the reduction catalytic convertor.

Such a device combines in one container, the NH₃ precursor and the heating device wherein both are in direct contact with each other. This system, in principle, is a closed system and the NH₃ precursor is not heated in accordance with the principle of a flow-through heater. The heating device may, for example, be a resistance heater with a heating element such as a heating plate with which the NH₃ precursor is in direct contact. The NH₃ precursor may basically be present in liquid or in solid form. For practical purposes, however, the use of a solid NH₃ precursor is preferred. This may be a pressed body whose front side is in contact with the heating element of the heating device.

With the direct heat transfer from the heating device or, respectively, the heating element thereof to the adjacent NH₃ material, a reaction gas amount containing NH₃ corresponding to the respective operating state of the internal combustion engine can be made available within a very short time, so that the nitrogen oxides formed during combustion can be reduced in the reduction catalytic converter. As a result of the direct heat transfer, for example, by the direct contact of the NH₃ precursor with the surface of the heating element, the areas of the NH₃ precursor disposed adjacent the heating element are not only rapidly heated but they are also heated with relatively little energy consumption.

With such a device, the required reaction gas or, respectively, NH₃ amount can be produced in a “just in time” fashion so that, depending on the engine load situation the required NH₃ amount can be readily made available. With such a device also the NH₃ storage capacity of the reduction catalyst may be utilized in such a way, that during operation of the internal combustion engine such as a diesel engine, the NH₃ charge of the reaction catalyst is recorded and maintained at such a level that even with sudden load changes an amount of NH₃ gas sufficient for the conversion of the nitrogen oxide gases discharged from the engine is available. In such a control procedure, the storage capacity of the reduction catalyst with respect to an NH₃ charge and the delay of the device generating the NH₃ are used as basic control valves. By utilizing the NH₃ storage capacity of the reduction catalyst, the described device for the generation of NH₃ may be relatively small, since the NH₃ peak requirements can be satisfied by NH₃ stored in the reaction catalyst.

The provision of an electric heating device is not only expedient with regard to a rapid response behavior, but also because of the simple control required therefore. To this end, the heating device is connected to a control unit by which the heating device is controlled. Control may be established by simple on and off switching and/or by changing the heating power.

Such a “just-in-time” NH₃ production is also desirable because of safety requirements since when the amount of NH₃ present in a gaseous state can be reduced to a minimum.

If a NH₃ precursor is a solid body, such as a rod-shaped body is present as NH₃ precursor, it is expedient to bias this body by a piston into contact with the surface of a heating element with a certain engagement pressure. Then it is ensured that the NH₃ precursor is in contact with the surface of the heating element under any operating condition and, if used in connection with a motor vehicle, also when driving on bumpy roads. In such an arrangement it is expedient if the container is divided by the piston into two container sections which are separated from each other in a gas tight manner. In the first container section there is the NH₃ precursor together with the heating device. In a particular embodiment, the other container section is connected to external means for providing the desired engagement pressure for example by pressurizing the second container section. To this end, an external pressure storage device for example in the form of a nitrogen gas spring may be provided. If the device is on board of a motor vehicle which includes a compressed air system such as a truck with air brakes, the second container section may be connected to the compressed air system. Then the required pressure is provided by the compressor of the compressed air system. If necessary, a pressure reducing valve may be disposed between the compressed air system and the second container section. Basically, the second container section may also be connected to a hydraulic system in order to obtain the desired contact pressure. It is furthermore possible to fill the second container section with a pressurized medium, such as nitrogen, so that the necessary contact preserve is provided from within this container section. The pressure generated, in the second container section which may be called gas space, by filling the second container section for example with nitrogen may be utilized with regard to a consumption of the ammonium carbonate disposed in the other container section and the resulting volume reduction with increasing consumption of the ammonium carbonate, the gas space that is the second container section is increased and consequently the pressure is reduced proportionally with the volume increase of the gas space there is a corresponding volume decrease of the first container section which includes the ammonium carbonate.

A pressure can be applied to the NH₃ precursor disposed in the container preferably in the form of a pressed body also by mechanical means. There may be provided for example a scissor drive or a spindle drive which is effective on the piston dividing the container into the two container sections either directly or by way of a pressure disc. An actuator for driving such an engagement mechanism is arranged expediently outside the container and is connected to the engagement structure by a releasable coupling device. A drive, expediently a self-locking transmission such as a spindle drive, is provided for driving the scissor structure. In such a mechanical engagement system, a pressure sensor may be arranged between the piston and engagement device in order to control the mechanical engagement structure on the basis of the sensed pressure.

A piston for dividing the container into the two container sections as described above expediently a rolling bellows piston is used which has the specific advantage of providing a good gas seal between the two chambers and easy movability of the piston.

The heating device expediently includes a heating element, a heating plate which abuts the pressed NH₃ precursor body. The heating plate may include channels or channel-like depressions by way of which the reaction gas formed during operation of the heating device can flow out of the contact area between the heating element and the pressed body. Basically, the provision of such channels or channel-like depressions is not necessary since the NH₃ containing reaction gas formed by the thermolysis flows out of the area where it has been generated already because of the pressure generated during the thermolysis. However, occasionally, as a result the pressure device may be shortly lifted off the surface of the heating element during the thermolysis of the NH3 precursor body depending on the engagement pressure applied to the pressed body by the engagement device. Therefore, the provision of the channels and/or channel-like depressions is expedient so that the reaction gas formed by the thermolysis can easily flow away from the area where it has been generated.

In accordance with another embodiment, the surface of the heating element which may be a heating plate may be provided adjacent the NH₃ precursor body with a nep-structure. When the heating element is energized for the first time, the neps projecting from the heating element protrude into the adjacent surface of the NH₃ precursor body and as a result increase the effective heat transfer surface area and at the same time fix the NH₃ precursor body in the place of the heating element.

Since generally, during operation of the heating device the outlet of the container is open for supplying the NH₃ generated by the thermolysis to the engine exhaust duct there is a substantial pressure difference between the gas pressure generated during the thermolysis and the pressure in the exhaust duct so that the reaction gases generated by the thermolysis will automatically flow out of area where they have been generated.

The arrangement described comprises a heating device with at least one heatable surface which as described above, may be in the form of a heating plate. In a particular embodiment, the heating device may include several heating surface areas, each provided with its own pressed precursor body. The heatable surfaces of such a heating device may be commonly or separately controlled. In another embodiment, the apparatus may include several containers each with its own heating device which can then be operated commonly or accummulatively. With the use of several independently controllable heating devices or one heating device with several independently controllable heating elements, the NH₃ production can be controlled, and adapted to a great extent to dynamic engine operating load situations.

The container of such an arrangement expediently includes a separation plane for opening the container. After consumption of the NH₃ precursor contained therein preferably in the form of a solid body, the container can be opened, a new NH₃ precursor material body can be inserted and the container can then again be closed. Such a container is also usable in connection with a multi-way system. Then, the container forms a closed system from which NH₃ containing reaction gas is only released when the container is connected by means of a coupling, to the supply line leading to the exhaust gas duct. With such an arrangement in which the container is exchangeable the two container parts are expediently so interconnected that the container can be opened only with special tools. This can be achieved for example by the use of a clamping ring of an engagement structure by which the two flanges of the container parts are joined in a firm-locking manner. Opening and refilling of the container is then performed only by commercial operations which also has the advantage that such a procedure is performed after the container has cooled off. The changeover of a container of a vehicle in operation or of a motor vehicle which is at operating temperature is easily possible since only the connections have to be established by interconnecting the complementary coupling parts. The coupling parts are without any pressure, particularly if a magnetic valve is integrated into the container. The magnetic valve may also be an integral part of the container.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail on the basis of particular embodiments with reference to the accompanying drawings, in which:

FIG. 1 shows a device for supplying ammonia to a reduction catalytic convertor which is disposed in an exhaust duct of an internal combustion engine and which is shown in a first operating position;

FIG. 2 shows the device of FIG. 1 at a later operating stage;

FIG. 3 shows another embodiment of the device shown in FIG. 1;

FIG. 4 shows a device according to FIG. 1, in which the container is different however;

FIG. 5 shows another device for supplying ammonia to a reduction catalyst disposed in the exhaust duct of an internal combustion engine with a valve connected thereto and shown in an open position; and,

FIG. 6 shows the valve of FIG. 5 in a closed position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 a device for supplying ammonia (NH₃) to a reduction catalytic converter disposed in the exhaust duct of an internal combustion engine is indicated in FIG. 1 overall by the reference numeral 1. This device 1 comprises a container 2 for generating ammonia (NH₃) by thermolytic decomposition of an NH₃, precursor. In the shown embodiment pressed ammonium carbonate bodies 3, 3′,3″ are used as NH₃ precursors. The pressed ammonium carbonate bodies 3, 3′,3″ are disc-like bodies formed by compressing ammonium carbonate powder into the bodies as shown in the figures. The ammonium carbonate bodies 3, 3′,3″ are circular in cross-section. Three ammonium carbonate bodies are disposed in the container 2; part of the lowermost ammonium carbonate body 3 has already been consumed. The container 2 includes also a heating device 4. The heating device 4 is an electric resistance heater of which in FIG. 1 the heater plate 5 is shown schematically in cross-section without the electrical components. The top side of the heating plate 5 shown in FIG. 1 represents in this embodiment the heating surface 6 heated by the heating device 4. On this top surface 6, the bottom side of the respective lowest pressed ammonium carbonate body 3, 3′ or 3″ is disposed depending on how much ammonium carbonate has already been consumed during operation of the device 1. The heating plate 5 is connected to a control unit via a connecting cable 7 and a connector plug 8 in a way which is not disclosed in detail herein. The heating device 4 is controlled by a control unit. For controlling the energy supply to the heating device 4, the heating device may be periodically switched on and off or the amount of energy supplied to the heating device is controlled continuously.

The heating plate 5 of the heating device 4 includes a plurality of channels K extending therethrough, especially of circular cross-sections. Several channels K form together a circular structure so that the channels K of the heating plate 5 are arranged in several concentric circular structures. Additionally channel-like recess KV are formed into the heating plate 5 which extend radially. The channels K and the channel-like recesses KV form passages for the connection of the top side 6 of the heating plate 5 with the outlet area 9 of the container 2. The outlet area 9 of the container 2 is that area from which the reaction gas formed during operation of the device 1 can be withdrawn from container 2. The outlet area 9 is therefore also provided with the actual container outlet 10. The outlet 10 is connected by a rapid coupling 11 to the supply line 12 which extends to the exhaust duct of the Diesel engine in flow direction of the exhaust gas ahead of this reduction catalytic convertor. The rapid coupling 11 has two coupling parts 13, 13′ which are interconnected in a basically gas-tight manner. The coupling parts only open when both coupling parts 13, 13′ are joined and sealed. Disposed in the supply line 12 is a magnetic valve 14, which in this embodiment shown in the figures is arranged in flow direction of the reaction gas after the coupling 11.

The container 2 includes a rolling bellows piston 15 which divides the interior of the container 2 into a first container section 16 and a second container section 17. By the rolling piston 15, the two container sections 16, 17 are separated in a gas-tight manner. The first container section 16 includes the heating device 4 and the ammonium carbonate pressed bodies 3, 3′ 3″ as well as the outlet 10. In the second container section 17, an engagement structure is disposed, which is designated by the reference numeral 18 and by which the ammonium carbonate bodies 3, 3′ 3″ can be biased toward the heating device 4. As a result, the lower surface of the lower most pressed ammonium carbonate body 3 abuts the top side 6 of the heating device 4 with a certain pressure which improves the reaction capability of the device 1 for providing the required reduction amount of NH₃. In the embodiment shown in FIG. 1, a mechanical structure is used as a biasing structure 18. The mechanical biasing structure 18 comprises a scissor-jack structure 19 which is actuated by a threaded spindle 20. With the actuation of the scissor-jack mechanism by a spindle 20, the biasing structure becomes self-locking. A back-up movement is only possible if and when the spindle 20 is operated accordingly. The scissor-jack structure 19 includes at the end therefor opposite the spindle 20 a support plate 21 which abuts the rear side of the rolling piston 15 and, consequently the top side of the uppermost ammonium carbonate body 3″. The spindle 20 extends to the outside of the container 2 and is connected by a releasable clutch or coupling 22 to an electric motor 23 for driving the spindle 20. The electric motor 23 is connected to a control unit by way of which the electric motor 23 is energized for operating the biasing structure 18. The control unit may be the same control unit which is used for controlling the heating device 4. The opening through which the spindle 20 extends through the wall of this container 2 serves at the same time as a venting opening for the container section 17.

In order to provide for a constant engagement pressure between the respective lower most pressed ammonium carbonate body 3, 3′ 3″ on the top side of the heating device 4, the biasing structure 18 includes means for determining the pressure generated by the biasing structure 18. This can be achieved, for example, by an evaluation of operating data of the electric motor 23 such as the current supply to the electric motor. It is also possible to provide between the pressure plate 21 and the back side of the rolling piston 15 a pressure sensor by way of which the pressure applied by the biasing structure 18 to the ammonium carbonate bodies 3, 3′ 3″ is determined. The output signals of such a pressure sensor are supplied to the control unit for controlling the electric motor 23 so that it can be controlled in accordance with the measured actual engagement pressure.

In the embodiment shown, the container 2 comprises several parts including an upper cover section 24, a cylindrical intermediate section 25 and an outlet section 26. The intermediate section 25 is connected to the cover and the outlet sections 24, 26 by flanged joints. For sealing the joints between the intermediate section and the cover section 24 an end of the rolling piston 15 is used which is engaged between the facing sides of the flanges. The joint between the intermediate section 25 and the cover section 24 is firmly held together by a clamping ring 27. The joint between the intermediate section 24 and the outlet section 26 is of corresponding design wherein for sealing purposes a seal ring 28 is disposed between the facing flange surfaces. Also, this joint is held together by a clamping ring in a gas-tight manner. The clamping rings 27, 29 are so designed that they can not be easily opened. An opening of the containers 2 by the user is not intended. The container 2 is by design an exchange container. After consumption of the ammonium carbonates contained in the container 2, this container is disconnected by removal of the plug in connector 8 from the motor vehicle based components of the device 1 and is replaced by a refilled container.

In the shown embodiment, the biasing structure 18 is also used in order to hold the heating device 4 in the container section 16 in its predetermined position. The heating device 4 includes projections Z arranged at the side thereof opposite the surface 6. The radial projections Z are for centering the heating plate 5 in the container 2 and holding the heating plate 5 at a distance from the lowest end of the container 2. The projections Z disposed on the side opposite the surface 6 provide for the outlet area 9 which collects the reaction gas from the channels K and the channel-like recesses KV. By the pressure exerted by the biasing structure 18 on the ammonium carbonate bodies 3, 3′,3″ also the heating plate 5 is held in the position as shown in the figures. At the inside of the lower section 26 of the container 2, there is a groove N into which one of the radial projections Z extends for the coded installation and to prevent rotation as this is shown in FIG. 1.

During operation of the Diesel engine, the NO_x content of the exhaust gas is directly or indirectly determined in order to introduce, dependent on this valve, by way of the device 1 together with the reaction gas formed by the thermolysis a certain NH₃ amount into the exhaust duct upstream of the reduction catalytic convertor so as to provide a sufficient amount of NH₃ for the reduction of the nitrogen oxides contained in the exhaust gas. When the ammonia supply device 1 is not in operation, the magnetic valve 14 is closed. When the heating device 4 is energized for the thermal decomposition of ammonium carbonate in order to generate the needed NH₃, the magnetic valve 14 is opened. The heating device 4 is designed such that the upper side 6 of the heating element 5 reaches its operating temperature essentially instantly whereby the ammonium carbonate of the ammonium carbonate body 3 which abuts the top surface 6 under the pressure imbued by the biasing device 18 (see FIG. 1) is thermolytically decomposed. This thermolytic decomposition results in the pressure increase in the lower container section 16. Since with the rapid coupling 11 established and the magnetic valve 14 open, a communication is established between the lower container section 16 and the exhaust duct a pressure differential is established toward the exhaust duct so that reaction gas generated at the surface 6 flows through the channels K and the channel-like recesses KV to the outlet area 9 of the container 2 and through the outlet 10 to the exhaust duct. The passage required for conducting the reaction gas to the exhaust duct are so designed that their flow resistance is as small as possible. This can be achieved by providing correspondingly large flow cross-sections.

With the method as described above, the reaction gas generated is supplied to the exhaust duct without interim storage. Also, no pressure-buildup is provided by the thermolysis caused by the energization of the heating device 4. The magnetic valve 4 is closed only after the heating device 4 is de-energized.

With the underside of the ammonium carbonate body 3 being in direct contact with the top side 6 of the heater plate 5, the ammonium carbonate is rapidly heated since only a single heat transfer barrier has to be overcome that is the heat needs to be transferred only from the heating element 5 to the ammonium carbonate. This heat transfer is furthermore facilitated by the engagement pressure which is generated by the biasing structure 18 and with which the ammonium carbonate body is in contact with the top side 6 of the heating plate 5. The ammonium carbonate body 3 abuts the top side 6 of the heating plate 5 always with its smooth underside. Originally, uneven surface areas formed during the manufacture of the body 3, 3′,3″ or formed by the later handling thereof are equalized when the uneven surface is in contact with the top side 6 of the heating plate 5 during operation of the heating device 4.

As a result of the thermolytic decomposition of the ammonium carbonate at the top surface 6 of the heating plate 5 and the gas generated by consumption of ammonium carbonate the engagement pressure provided by the biasing structure 18 is reduced. The ammonium carbonate consumption can be detected by the pressure sensor disposed between the pressure plate 21 and the back side of the rolling piston 15 so that, upon detection of such an arrangement pressure loss, the electric motor 23 for operating the spindle 20 for opening the scissor structure 19 can be energized until the denoted engagement pressure is established. With the biasing device 18 of the embodiment presented herein a travel distance recorder may be coupled whereby the momentary ammonium carbonate remaining in the container 2 could be determined. To this end however, also separate sensors may be used. Also the characteristic data of the electric motor could be used for calculating the travel distance of the pressure plate 21. If the electric motor 23 is a connected DC motor, the travel distance or the position of the pressure plate 21 can be determined by ripple counting.

FIG. 2 shows the arrangement of FIG. 1 wherein, however, the ammonium carbonate is used up to a large extent. The ammonium carbonate bodies 3, 3′,3″ are consumed. Only a remaining part of the ammonium carbonate body 3″ abuts the top side 6 of the heating plate 5. The scissor structure 19 is substantially expanded and continues to engage the back side of the ammonium carbonate body 3″ with the desired engagement pressure.

The container 2 of the device 1 is disposed at an exchange location of the motor vehicle. The respective connecting parts between the container and the vehicle-side components of the arrangement are so designed that with the installation of the container 2 or respectively, its removal from that location, the required connections with the respective supply lines are automatically established.

FIG. 3 shows another embodiment of the ammonium supply device according to the invention. This device 30 for supplying ammonia to a reduction catalytic converter disposed in an exhaust duct of a Diesel engine includes two containers 31, 31′ in which ammonium carbonate is thermally decomposed. The containers 31, 31′ are basically of the same design as that of the previous embodiment. In contrast to the container 2 however, the containers 31, 31′ have container sections opposite the heating device which are connected to the air pressure system of the truck in which the device 30 is installed. The air pressure system is indicated in FIG. 3 by the reference numeral 32. By means of the air pressure system 32, which also includes a compressor for generating the necessary air pressure, the rear container sections is pressurized, so as to provide the engagement pressure at the contact area between the ammonium carbonate and the adjacent side of the heating element. The respective container sections are expediently connected to the pressurized air storage tank of the air pressure system 32.

As pointed out, the device 30 includes two containers 31, 31′ each of which includes a heating device. The heating devices of the two containers 31, 31′ are independently controllable and can therefore be energized individually or in unison as with different energy inputs in order to satisfy the NH₃ requirements at a certain load state of the Diesel engine, particularly during rapid load changes. To this end, the heating devices are connected to a common control unit.

FIG. 4 shows another embodiment with a container 33 of essentially the same design as the container 2 of the device 1. Functionally identical elements are therefore identified by the same reference numerals. Different from the container 2 of the device 1, the rolling piston 34 of the container 33 is mounted in the area of the outlet 35 of the container 33. The container 33 only has one separation area, where the container 33 is divided into the two container parts 36 and 37. The advantage of this concept resides in the fact that the space remaining in the container 33 is reduced to a minimum and the container basically needs only a single joint. Consequently, the space required for the container is reduced to a minimum wherein, upon down cooling of the container 33 ammonium carbonate can be reformed from the reaction gas generated earlier.

Instead of the arrangement 30 as described in FIG. 3, a single container may be used whose heating device includes a single heating plate with two opposite heating surfaces as two heating plates which are controllable independently of each other. For providing the desired engagement pressure between the ammonium carbonate and respective heated surface, the container includes two pistons, preferably in the form of rolling pistons.

In an arrangement with two or even more containers, it is advantageous that not only peak demands for NH₃ can be accommodated, but limited installation spaces in a vehicle can be more effectively utilized. If the containers are exchangeable containers, they are of course also relatively small and therefore easier to handle.

Instead of the biasing structure 18 as described earlier, which is a mechanical scissor-like structure, other devices may be used such as spindle devices or telescope spindle devices.

In another embodiment which is not shown in the figures, the magnetic valve is included in the container and is in heat transferring connection with the heating device. Thus, the heat generated by the heating device is utilized to decompose ammonium carbonate which may have been formed during engine start down from the reaction mixture and may have been deposited on the magnetic valve, whereby the magnetic valves continued operability is ensured.

Another device 38 for supplying ammonia (NH3) to a reduction catalytic converter arranged in the exhaust duct of a Diesel engine of a motor vehicle is shown in FIG. 5. This device 38 operated like the earlier described devices 1, 30 wherein, however, for providing the engagement pressure between the NH₃ precursor 39, the container section 41 separated by the rolling piston 40 is connected to a pressurized air supply system D. In addition to the precursor 39, this section of the container includes a heating device 42 designated over all by the reference numeral 42. The heating device 42 comprises a radiation heater. The radiation heater consists in the embodiment shown of three individual heating elements 43, 43′, 43″ which have a spiral configuration and are interleaved. The individual heating elements 43, 43′, 43″ of the heating device 42 are controllable independently of one another so that the heat generation and/or cause of a heating phase can be controlled depending on the amount of the heating elements 43, 43′, 43″ which are being energized. The heating device 42 is disposed in a lower container part 44 of the device 38. Below the heating elements 43, 43′, 43″ a heat insulation structure 45 is arranged. Above, and in spaced relationship from, the radiation heater there is a heating plate 46 which is another component of the heating device 42. The heating plate 46 consists in the embodiment shown of a transparent glass-ceramic material which is permeable for the heat radiation generated by the heating device 42. The side of the heating plate 46 facing the ammonium carbonate body 39 has a surface structure with neps or protrusions projecting therefrom. At the bottom end of the container, a tube section 47 is connected to the heating plate 46 and extends downwardly therefrom. The tube section 47 forms a connecting passage 48 leading to a supply line 49 which extends to an exhaust duct of the Diesel engine.

FIG. 5 shows the device 38 and particularly the container 44 with the ammonium carbonate body 39 disposed therein before an initial operation. For this reason, the bottom surface of the ammonium carbonate body 39 is disposed on top of the nep structure of the heating plate 46. After an initial operation of the device 38 by energization of the heating device 42 a certain amount of ammonium carbonate will have been decomposed thermolytically so that the neps will have been embedded into the surface of the ammonium carbonate body and fix the body in position.

The heating device 42 is so designed that at the side of the heating plate 46 facing the ammonium carbonate body 39 the temperature remains below the decomposition temperature of the reaction gas or gas mixture formed during the theromolysis of the ammonium carbonate. This is achieved largely by the glass-ceramic heating plate 46. As a result, the heating device 42 combines the advantages of a radiation heater which are a rapid reaction capability and, consequently a spontaneous decomposition of ammonium carbonate with the advantages of heating devices which rely on heat transfer by direct contact.

The supply line 49 includes a valve 50 which is shown in FIG. 5 in an open position. The valve 50 comprises a movable element or Peltier element 51 which can be moved to its open position by an operating member 52. The operating member 52 may be for example, an electromagnet. In the closed portion as shown in FIG. 6, the valve 50 can be closed by the force stored in the compressor spring 53 as a result of movement of the Peltier element 51. The Peltier element 51 forms With its surface 54 the valve surface and therefore forms the control element for the valve 50. The membrane 55 seals the valve chamber 56 circumferentially in the open position of the valve 50 as shown in FIG. 5.

In the open position of the valve 50, reaction gas formed by thermolysis flows through the valve chamber 56 into the supply line 49 by way of which the reaction gas mixture is supplied to the exhaust duct. When the valve 50 is being closed as shown in FIG. 6, the Peltier element 51 is, at the same time, energized for cooling the valve surface 54 thereof. By engagement of the valve surface 54 thereof with this seals 57 sealing the connecting passage 48—the valve seal—and as a result of the condensation effect caused by the cooling, reaction gas present in the two branches of the supply line 49 is attracted to the then cold surface 54 which, in this case serves as a cold trap. As a result, the supply lines 49 are kept open after de-energization of the heating device 42 so that a reformation of ammonium carbonate from the reaction gas and the deposit thereof on the walls of the supply line 49 is essentially prevented. Upon opening of the valve 50 or shortly ahead of the opening the Peltier element 51 is so energized that it acts as a heating element whereby ammonium carbonate formed as a result of the cold trap action is again decomposed so that the valve 50 becomes operable and functions as desired.

Ammonium carbonate is the preferred NH₃ precursor material for use in connection with the device described. It is advantageous in that its thermolytic decomposition occurs to a substantial extent already at temperatures above 70° C. This relatively low thermolysis temperature also has the advantage that ammonium carbonate which has been reconstituted and deposited in the outlet area of the container and/or the supply ducts and the valves disposed in the supply ducts is again decomposed by the reaction gas which is expediently heated to higher temperatures so that upon initial operation of the device the walls of the devices and of all the passages are cleared for unobstructed flow of the reaction gas to the exhaust duct.

It is apparent from the description of the device that with a minimum of hardware expenses a “just in time” production of NH₃ can be provided from a NH₃ precursor, particularly ammonium carbonate, and the NH₃ can be supplied in amounts as needed for an effective nitrogen oxide reduction in the reduction catalytic convertor also when the internal combustion engine, that is the Diesel engine, is operated under full load for an extended period. During the operation of the device advantageously also the storage capability of the reduction catalytic converter with respect to the reduction medium (NH₃) may be utilized.

Claims

1. A device (1; 30; 38) for supplying ammonia (NH3) to a reduction catalyst arranged in an exhaust duct of an exhaust system of an internal combustion engine, said device comprising a container (2; 31, 31′; 33; 44) for storing a precursor body (3, 3′, 3″; 39) capable of generating ammonia (NH3) when subjected to heat, said container (2; 31; 31′; 33; 44) having an outlet (10; 35; 48) connected to a supply line (12; 49) extending to said exhaust duct and a heating device (4, 42) for heating areas of said precursor body (3, 3′, 3″; 39) for the thermolytic decomposition thereof resulting in the generation of an NH3 containing gas, said heating device (4, 42) having a heating surface (6) arranged adjacent said precursor body (3, 3′, 3″; 39) for a direct heat transfer to said precursor body (3, 3′, 3″; 39) and said heating device (4, 42) being connected to a control unit for controlling the energization of the heating device (4, 42).

2. A device according to claim 1, wherein said precursor body (3, 3′, 3″; 39) contained in the container is in the form of a solid, pressed rod-shaped body.

3. A device according to claim 2, wherein biasing means (19, 20, 21, D) are provided for biasing the body (3, 3′, 3″; 39) into firm contact with the heating surface (6) of the heating device (4, 42).

4. A device according to claim 3, wherein the container (2) is divided by a piston (15) into two sections (16, 17) which are separated from each other by the piston (15) in a gas-tight manner, one of the container sections (16) including the NH3 precursor (3, 3′, 3″) and the heating device (4) and the other container section (17) including said biasing means which comprises a mechanical pressure generator device (18).

5. A device according to claim 4, wherein said biasing means includes an activator (23) which is arranged outside the container (2) and coupled to the biasing structure (18) disposed within the container (2).

6. A device according to claim 3, wherein the container (2) is divided by a piston (15) into two sections (16, 17) which are separated from each other in a gas-tight manner, one of the container sections (16) including the NH3 precursor (3, 3′, 3″) and the heating device (4) and the other container section (17) including a gas under pressure for biasing the NH3 precursor in contact with the heating device.

7. A device according to claim 3, wherein said container is divided into two sections (16, 17) by a rolling piston (15).

8. A device according to claim 1, wherein said heating device (4, 42) comprises a heating plate (5, 46) arranged in the area of the outlet (10; 35; 48) of the container (2; 31, 31′; 33; 44) and the precursor body (3, 3′, 3″; 39) is biased into firm contact with the heating plate (5, 46).

9. A device according to claim 8, wherein on the side of the heating plate (46) remote from the precursor body (39) an electric radiation heating device (43, 43′, 43″) is arranged.

10. A device according to claim 9, wherein the side of the heating plate (46) adjacent the NH3 precursor (39) is provided with a nep-structured surface.

11. A device according to claim 9, the heating plate (46) consists of a transparent glass-ceramic material.

12. A device according to claim 1, wherein the container (2; 31, 31′; 33) with its content of components of the device (1, 30) is removably supported and the outlet (10; 35) of the container (2; 31, 31′; 33) is connected to the supply line (12) leading to the exhaust duct by a coupling structure (13, 13′).

13. A device according to claim 1, wherein the heating device comprises several independently controllable heating elements, each being provided with its own NH3 precursor storage structure.

14. A device according to claim 1, wherein the ammonia supply device (30) comprises several containers (31, 31″), each including its own heating device.

15. A device according to claim 1, wherein the NH3 supply line (49) extending from the device includes a controllable valve (50).

16. A device according to claim 15, wherein the controllable valve (50) includes a stationary valve part (57) forming a valve seat and a movable valve plate (54) which forms the heat exchange surface of a Peltier element (51) for cooling and, respectively heating the movable valve plate (54).