Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
2002-07-09
2003-11-18
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...
C060S298000, C060S320000, C060S321000, C060S305000, C060S292000
Reexamination Certificate
active
06647711
ABSTRACT:
PRIORITY CLAIM
This is a U.S. national stage of application No. PCT/EP00/11617, filed on Nov. 22, 2000. Priority is claimed on that application and on the following applications: Country: Germany, Applications No.: 199 59 141.5, filed: Dec. 08, 1999 and Country: Germany, Application No. 100 47 815.8, filed Sep. 27, 2000.
The invention concerns a device with multiple exhaust gas supply lines for supplying exhaust gases from an internal combustion engine to a catalytic converter, especially a storage catalytic converter, in accordance with the introductory clause of claim
1
.
To convert nitrogen oxides contained in automotive exhaust gases from Otto engines with direct fuel injection, NO
x
storage catalytic converters are preferably used. However, these provide sufficiently high conversion rates only within a relatively narrow window of exhaust gas temperatures. This results in a disadvantageous limitation of the high-performance lean operating range of an Otto engine. To achieve optimum reduction of the fuel consumption of direct-injection Otto engines by lean operation, the exhaust system must be adjusted to the engine in such a way that the exhaust gas temperatures immediately before the inlet to the storage catalytic converter fall within a well-defined window of operating temperatures over the greatest possible engine operating range. The upper limit of this window of operating temperatures is reached at high vehicle speeds or high engine loads. Exceeding this upper temperature limit has a negative impact on the operation and service life (durability) of the storage catalytic converter. Therefore, to extend the lean operating range of the Otto engine, the exhaust gases must be cooled before they enter the storage catalytic converter at high vehicle speeds or high engine loads. On the other hand, it is also necessary to ensure that, after a cold start of the direct-injection Otto engine, the storage catalytic converter reaches its so-called catalytic ignition point as fast as possible, i.e., the operating temperature for optimum pollutant conversion. To this end, it is necessary to take suitable measures, which, immediately after a cold start of the Otto engine, allow the least possible removal of heat from the exhaust gases to the surrounding environment before the exhaust gases enter the catalytic converter.
DE 199 05 345 A1 describes a generic device for supplying exhaust gases from an internal combustion engine to an exhaust gas treatment system with multiple exhaust gas supply lines. Several exhaust gas supply lines are installed between a three-way catalytic converter and an NO
x
trap. These multiple supply lines are designed to retain a relatively large proportion of the heat in the stream of exhaust gas at relatively low exhaust gas mass flows, whereas at higher mass flows, a relatively greater proportion of the heat is eliminated with the stream of exhaust gas.
Therefore, the goal of the present invention is to specify a generic device that allows reliable adjustment of the exhaust gas temperatures at the inlet of the exhaust gases into the catalytic converter.
This goal is achieved by a device with the features specified in claim
1
. This device is characterized by the fact that at least one exhaust gas supply line is designed as a heat-conveying line that promotes transfer of the exhaust gas heat to the catalytic converter, that at least one other exhaust gas supply line is designed as a heat exchanger that promotes extraction of heat from the exhaust gas upstream of the catalytic converter, and that a switchable control mechanism is provided to control a flow cross section of at least one of the exhaust gas supply lines. A device designed in this way is advantageously suited for maintaining the exhaust gas temperatures within a well-defined window of operating temperatures at the inlet of the catalytic converter for the greatest possible engine operating range (high vehicle speeds or high engine loads) as well as immediately after a cold start of the engine. This is accomplished with the use of a switchable control mechanism for controlling a flow cross section of at least one of the exhaust gas supply lines, i.e., the heat-conveying line or the heat exchanger. In this connection, the purpose of the heat-conveying line is to bring the catalyst to the catalytic ignition point as quickly as possible after a cold start of the Otto engine, while the purpose of the heat exchanger is to cool the exhaust gases upstream of the catalytic converter and thus to prevent unwanted exceeding of the upper temperature limit of the operating temperature window, especilly at high engine loads. During a cold start of the Otto engine, it is possible, for example, for the heat-conveying line to be open (maximum flow cross section) to allow maximum transfer of the heat of the exhaust gases to the catalytic converter, and for the heat exchanger to be partially or completely closed, so that as little exhaust gas heat as possible is transferred to the surrounding environment upstream of the catalytic converter and is used instead to heat the catalyst and thus to bring it to its ignition point as soon as possible after the cold start of the Otto engine. When the catalyst has reached the catalytic ignition point, and the Otto engine is being subjected to a higher load (higher vehicle speeds), it is advantageous to open the heat exchanger partially or completely and possibly to close the heat-conveying line partially or completely to prevent the upper temperature limit of the window of operating temperatures from being exceeded due to the transfer of too much heat to the catalytic converter by the exhaust gases. All of these adjustments with respect to the flow cross section of one or more exhaust gas supply lines are adapted to the given engine operating range for the purpose of controlling or regulating the amount of heat transferred to the catalytic converter by the exhaust gases and can be accomplished easily, precisely, and reliably by a switchable control mechanism.
The exhaust gas supply lines are preferably configured as pipes that are separated from one another. Since the exhaust gas supply lines are designed to have two different or opposing purposes, i.e., optimum transfer of exhaust gas heat to the catalytic converter (heat-conveying line) and minimum transfer of exhaust gas heat to the catalytic converter (heat exchanger), depending on the given engine operating range (cold start, higher engine load), it is advantageous to design the exhaust gas supply lines as separate pipes, which, preferably, are also spaced slightly apart. Separation of the heat-conveying line from the heat exchanger makes it possible to realize especially effective adjustment of the heat transfer to the catalytic converter by the exhaust gases.
In accordance with a refinement of the invention, the exhaust gas supply line that is designed as a heat-conveying line has a smaller flow cross section than the exhaust gas supply line that is designed as a heat exchanger. In this way, the surface area of heat transfer from the exhaust gas to the surrounding environment upstream of the catalytic converter can be limited to the smallest possible value with respect to the heat-conveying line and can be designed to be as large as possible with respect to the heat exchanger.
The exhaust gas supply lines are advantageously arranged as a bundle of pipes, the individual pipes of which are spaced some distance apart. The supply line that is designed as a heat-conveying line is arranged as an inner pipe in the bundle and is surrounded around its circumference by several exhaust gas supply lines that are designed as heat exchangers. Exhaust gas supply lines that are spaced some distance apart and grouped as a bundle of pipes allow a compact design of the device. In this type of arrangement, the exhaust gas supply lines that are designed as heat exchangers are preferably arranged on the outside of the bundle around the circumference of the inner heat-conveying line or lines to allow the most effective possible heat exchan
Pott Ekkehard
Spiegel Leo
Zillmer Michael
Denion Thomas
Tran Binh
Volkswagen AG
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