Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
1999-02-25
2001-02-27
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
By means producing a chemical reaction of a component of the...
C060S301000, C060S303000, C060S276000, C060S291000, C422S105000, C423S213200
Reexamination Certificate
active
06192676
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a device for NO
x
reduction in the exhaust gas of an internal combustion engine operated with excess air. The engine is controlled with a control unit. The device includes a reduction catalytic converter that works according to the so-called SCR principle in the exhaust system. A reducing agent metering system has a reducing agent injection valve upstream of the reduction catalytic converter in the exhaust system. The reducing agent is metered in on the basis of catalytic converter operating parameters and the exhaust gas composition.
The so-called selective catalytic reduction (SCR) method is known for reducing the NO
x
content in the exhaust gas of an internal combustion engine operated with excess air. A reducing agent is thereby injected into the exhaust gas at a point upstream of a catalytic converter (in terms of the exhaust gas flow direction), and the NO
x
contained in the exhaust gas is thus reduced in a reduction catalytic converter to form nitrogen gas N
2
. In this regard, reference may be made to the publication by Schöppe et al., “Ein geregeltes Abgasnachbehandlungssystem zur Erfüllung zukünftiger Emissionsgrenzwerte bei PKW-Dieselmotoren” [A controlled exhaust gas post-treatment system for meeting future emission restrictions in automobile diesel engines], 17th International Wiener Motorensymposium, 1996, Vol. 1. Ammonia can serve as the reducing agent, although for reasons of convenience it is customary to use an aqueous urea solution or powdered urea. It is also known to employ fuel or derivatives as the reducing agent.
In the known SCR system, the target quantity for the reducing agent metering is calculated continuously by the control unit of the internal combustion engine. For this, the control unit needs the instantaneous reducing agent demand. This is calculated from operating parameters of the internal combustion engine, such as mass of air, operating temperature or load. Together with the catalytic converter temperature, these values form the basis for metering the reducing agent. NO
x
reduction using the SCR system allows reduction rates in excess of 60%, but presupposes the determination of individual emission characteristics for the internal combustion engines, which have to be stored in a control unit in order to control the metering.
The NO
x
reduction therefore requires significant equipment outlay with extensive data interchange between the control unit of the internal combustion engine and the reducing agent metering system. It has to date been possible only with great outlay to retrofit vehicles which are already being used and have internal combustion engines operated with excess air, with an exhaust gas post-treatment system based on the SCR principle, or to equip internal combustion engines originally developed without NO
x
reducing exhaust gas treatment with SCR catalysts.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a simplified device for reducing the NO
x
content in the exhaust gas of a vehicle internal combustion engine operated with excess air, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which makes it possible to use catalytic converters working on the basis of the SCR principle without the outlay on conventional devices, and in particular makes it possible to retrofit vehicles already available with acceptable outlay.
With the foregoing and other objects in view there is provided, in accordance with the invention, a device for reducing a NO
x
content in exhaust gas of a vehicle internal combustion engine, wherein a control unit is provided and the engine is operated with excess air, the device comprising:
an exhaust system conducting an exhaust gas flow in an exhaust gas flow direction;
an SCR catalytic converter disposed in the exhaust system;
a reducing agent metering system including:
a source of reducing agent and a reducing agent injection valve communicating with the source of reducing agent, the injection valve being disposed to inject reducing agent into the exhaust system upstream of the SCR catalytic converter in the exhaust gas flow direction;
a temperature sensor, an NO
x
measuring sensor, and an exhaust gas flow sensor connected to the exhaust system;
a reducing agent control unit directly connected to the temperature sensor, to the NO
x
measuring sensor, and to the exhaust gas flow sensor;
the reducing agent control unit determining an amount of reducing agent to be injected, from measurements of the temperature sensor, the NO
x
measuring sensor, and the exhaust gas flow sensor without recourse to data available in the control unit of the internal combustion engine, and driving the reducing agent metering system and metering the reducing agent based on the measurement.
The novel device is a self-contained unit. The metering of the reducing agent is no longer carried out with recourse to data present in the control unit of the internal combustion engine, but is derived from the signals of a volume flow sensor, a temperature measuring sensor and an NO
x
measuring sensor. To this end, a generally simplified NO
x
characteristic is stored in the reducing agent control unit. It is possible to do without test rig calibration for determining emission characteristics individual to the internal combustion engines. To configure the device when retrofitting, only the maximum volume throughput and the maximum permissible exhaust gas back pressure on the internal combustion engine need to be taken into account. The simple structure of the overall system, by reducing the sensing hardware to the components exhaust gas temperature measuring sensor, or catalytic converter temperature measuring sensor, NO
x
measuring sensor and volume flow measuring sensor, make it possible to fit almost all the components directly to the SCR system, by means of which the previous elaborate wiring may be omitted.
In accordance with an added feature of the invention, urea is used as the reducing agent and the source of reducing agent includes a storage container and a pump for pumping the urea from the storage container to the injection valve.
In accordance with an additional feature of the invention, the reducing agent control unit is mounted on the storage container.
In a preferred configuration of this embodiment, a further measuring sensor is provided, which is sensitive to NH
3
as a component of the exhaust gas. It is, however, also possible to provide an NO
x
measuring sensor which is sensitive to NH
3
as a function of the operating temperature. The reducing agent control unit continues to meter urea until a predetermined maximum NH
3
content is indicated by the measuring sensor.
In accordance with an alternative feature of the invention, fuel is used as the reducing agent and the reducing agent metering system communicates with the fuel supply of the internal combustion engine, for feeding fuel to the reducing agent injection valve. The reducing agent metering system delivers the fuel to the reducing agent injection valve from a connection to the fuel supply of the internal combustion engine. In a preferred configuration of this embodiment, a further measuring sensor is provided which is sensitive to HC as a component of the exhaust gas. It is also possible to use an NO
x
measuring sensor which is sensitive to HC as a function of the operating temperature.
In accordance with another feature of the invention, the exhaust gas flow sensor is a volume flow measuring sensor disposed in the exhaust system for measuring an exhaust gas volume flow rate.
In accordance with a further feature of the invention, the exhaust gas flow sensor is a pressure sensor disposed upstream of the SCR catalytic converter for measuring a exhaust gas back pressure in front of the SCR catalytic converter, as a measure of an exhaust gas volume flow rate.
In accordance with various further embodiments of the invention, the exhaust gas flow sensor is formed of a plura
Dolling Winfried
Latsch Reinhard
Tost Rainer
Zurbig Jurgen
Denion Thomas
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
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