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A device for exhaust-gas purification utilizes reduction of nitrogen oxides which are present in the exhaust gas from internal combustion engines by way of gaseous ammonia with an SCR catalytic converter. The functions of the device are monitored with regard to their line paths with connections, val

A device for exhaust-gas purification utilizes reduction of nitrogen oxides which are present in the exhaust gas from internal combustion engines by way of gaseous ammonia with an SCR catalytic converter. The functions of the device are monitored with regard to their line paths with connections, valves and sensors by referring to these elements themselves using suitable control circuitry via the evaluation and control unit.

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1. A device for exhaust-gas purification involving reduction of nitrogen oxides, which are present in the exhaust gas from internal combustion engines, comprising an SCR catalytic converter using ammonia, at least one pressure vessel having a filling which releases gaseous ammonia when heat is suppl

1. A device for exhaust-gas purification involving reduction of nitrogen oxides, which are present in the exhaust gas from internal combustion engines, comprising an SCR catalytic converter using ammonia, at least one pressure vessel having a filling which releases gaseous ammonia when heat is supplied, and a metering unit downstream of the pressure vessel in a transition to the SCR catalytic converter, which metering unit is an ammonia source, wherein the pressure vessel filling is liquid ammonia, and at least the metering unit is arranged in a gastight, pressure-monitored housing.2. The device as claimed in one claim 1, wherein a heater is arranged at least one of detachably and separately with respect to the pressure vessel.3. The device as claimed in claim 1, wherein the pressure vessel is exchangeable.4. The device as claimed in claim 1, wherein a heat exchanger, which is configured to be fed with waste heat from an internal combustion engine, is operatively associated with the vessel.5. The device as claimed in claim 4, wherein the heat exchanger is heated from a cooling circuit of the internal combustion engine.6. The device as claimed in claim 5, wherein the heat exchanger is connected to the cooling circuit of the internal combustion engine.7. The device as claimed in claim 4, wherein the heat exchanger is heated by exhaust gas from the internal combustion engine.8. The device as claimed in claim 7, wherein the heat exchanger is heated by at least one of heat conduction and heat radiation.9. The device as claimed in claim 4, wherein the heat exchanger is a heat pipe.10. The device as claimed in claim 4, wherein a predetermined limit temperature of the pressure filling limits heating capacity which is introduced.11. The device as claimed in claim 1, wherein the pressure vessel is operatively associated with an electrical heater.12. The device as claimed in claim 11, wherein the pressure vessel is heated by heating elements which lie at least one of inside and outside thereof.13. The device as claimed in claim 11, wherein the pressure vessel is heated by a radiant heater.14. The device as claimed in claim 11, wherein an inductive heater is provided for the pressure vessel filling.15. The device as claimed in claim 1, wherein the pressure vessel is operatively associated with a holding vessel.16. The device as claimed in claim 15, wherein the holding vessel is a heat exchanger.17. The device as claimed in claim 15, wherein the holding vessel is of gastight construction.18. The device as claimed in claim 15, wherein the holding vessel is of insulated construction.19. The device as claimed in claim 15, wherein the holding vessel has a vessel opening which is selectively openable to atmosphere and to be blocked off.20. The device as claimed in claim 1, wherein the at lease one pressure vessel consists of a plurality of pressure vessels.21. The device as claimed in claim 20, wherein the pressure vessels are each operatively arranged in a holding vessel.22. The device as claimed in claim 20, wherein the pressure vessels are arranged operatively in a common holding vessel.23. The device as claimed in claim 20, wherein the pressure vessels are jointly operatively connected to the metering unit.24. The device as claimed in claim 20, wherein the pressure vessels are separately operatively connected to the metering unit.25. The device as claimed in claim 20, wherein the pressure vessels are switchably operatively connected to the metering unit.26. The device as claimed in claim 1, wherein the pressure vessel is operatively associated with a line-break safety device and, downstream of the latter, a vessel valve.27. The device as claimed in claim 26, wherein the metering unit and the vessel valve arranged on an outlet side of the pressure vessel, are located in the metering unit.28. The device as claimed in claim 1, wherein the metering unit is operatively connected downstream of the pressure vessel in a direction of the catalytic converter and comprising, in a direction of passage, a shut-off valve, a temporary store and a metering valve, having pressure recording provided on both sides thereof.29. The device as claimed in claim 28, wherein a pressure sensor for pressure recording is provided on sides of the metering valve.30. The device as claimed in claim 28, wherein a temperature sensor is provided between the temporary store and the metering valve.31. The device as claimed in claim 30, wherein the temperature sensor is arranged downstream of the pressure sensor which is mounted upstream of the metering valve.32. The device as claimed in claim 28, wherein a temperature sensor is arranged on both sides of the metering valve.33. The device as claimed in claim 28, wherein the shut-off valve and metering valve are as controllable valves.34. A method for operating a device for exhaust-gas purification involving reduction of nitrogen oxides which are present in the exhaust gas from a motor vehicle internal combustion engine, having an SOR catalytic converter using ammonia, at least one pressure vessel having a filling which releases gaseous ammonia when heat is supplied, a metering unit located downstream of a the pressure in a transition to the SCR catalytic converter and a temporary store (18) located between a shut-off valve and a metering valve, comprising alternatively filling the temporary store in a pressure-limited manner, from the pressure vessel when the metering valve is closed and then emptying the temporary store via the metering valve down to a minimum pressure when the shut-off valve is closed, wherein when the internal combustion engine is being switched off, the temporary store is emptied to a exhaust section of the internal combustion engine.35. The method as claimed in claim 34, wherein the exhaust section includes said SCR catalytic converter.36. A method for monitoring a device for exhaust-gas purification involving reduction of nitrogen oxides which are present in exhaust gas from a motor vehicle internal combustion engine, wherein the device has an SCR catalytic converter using ammonia, at least one pressure vessel having a filling which releases gaseous ammonia when heat is supplied, and a metering unit downstream of the pressure vessel in a transition to the SCR catalytic converter, which metering unit is an ammonia source, wherein the pressure vessel filling is liquid ammonia, and at least the metering unit is arranged in a gastight, pressure-monitored housing, comprising processing pressure values obtained from a pressure recording in the metering unit, and a housing which surrounds the metering unit in an evaluation and control unit and converting the processed pressure values into control signals for at least one of valves, heater and warning signals.37. The method as claimed in claim 36, wherein, in the event of a limit pressure being exceeded in a space surrounded by the housing and holding a vessel valve, a shut-off valve and the metering valve, the vessel valve is closed and, if the pressure limit continues to be exceeded, a line-pressure safety feature is activated.38. The method as claimed in claim 36, wherein, to check for leaks in a metering line leads from a metering valve to an exhaust section of the internal combustion engine, exhaust-gas back pressure on a side of the internal combustion engine is compared with a pressure on the a side of metering valve.39. The method as claimed in claim 38, further comprising to check sealing the metering valve, filling the temporary store between shut-off valve and metering valve, and checking that the pressure remains constant when the valves are closed.40. The method as claimed in claim 38, further comprising, to test a pressure sensor located upstream of a metering valve, observing a pressure curve of the pressure sensor during filling of the temporary store for correlation with a pressure curve stored in the evaluation and control unit.41. The method as claimed in claim 38, wherein the pressure on the metering valve side is recorded by a pressure sensor arranged downstream of the metering valve.42. The method as claimed in claim 41, wherein, to check correctness of the pressure determined by the pressure recording arranged downstream of the metering valve, the determined pressure is compared with the exhaust-gas back pressure when the metering valve is closed.43. The method as claimed in claim 41, further comprising, in the event of a fault, at least one of closing the pressure valve and emitting a warning signal.