Power plants – Internal combustion engine with treatment or handling of... – Material from exhaust structure fed to engine intake
Reexamination Certificate
1999-03-15
2001-03-20
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Material from exhaust structure fed to engine intake
C123S572000, C123S568190, C073S001010, C073S118040
Reexamination Certificate
active
06202408
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application claims the priority of German Application No. 198 10 973.3 filed Mar. 13, 1998, which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
For reducing the pollutant component in exhaust gases (waste gases) of internal-combustion engines and firing installations, particularly small firing devices, the composition of the exhaust gas has to be monitored and the fuel component has to be varied by suitable control devices. In internal-combustion engines additionally exhaust gas treating devices are provided. In internal-combustion engines operating with varying load requirements, particularly in internal-combustion engines for automotive vehicles, the exhaust gas treating device has to be submitted to a follow-up regulation dependent upon the load requirement and the different contents of pollutants resulting therefrom, particularly nitrogen oxides and hydrocarbons.
To perform the above-outlined regulations, exhaust gas (waste gas) sensors are provided which, however, are exposed in an environment characterized by a changing gas composition, high temperature fluctuations and also high temperature gradients. The exhaust gas sensors, however, do not remain stable, because they have a limited operating range as concerns an upper temperature limit and are also exposed to a “drift”, that is, because of the changing temperature and concentration their zero-point is affected.
Several methods for calibrating measuring devices are known:
German Offenlegungsschrift (application published without examination) 42 17 893 describes a method of calibrating gas sensors for smoke gas analyses. This method uses air as the reference or calibrating gas for calibrating the measuring value for determining an O
2
-concentration.
German Offenlegungsschrift 39 39 166 describes a calibration of sensors by using electrochemical effusion cells. Here too, the object is to set the concentration signal with the aid of a calibrating device.
In German Offenlegungsschrift 35 46 409 for the calibration of chemical sensors a calibrating gas is admitted under pressure to the sensor surrounded by the liquid to be analyzed. The calibrating gas displaces the liquid at the sensor and by capturing the pressure and temperature values at the sensor the concentration of the components of the gas to be calibrated may be determined by computation and compared with the sensor signal.
In German Offenlegungsschrift 31 26 647 a quasi-electric calibration is described in which an electric resistance is used to expand in time the calibration of the measuring instrument by calibration gases with the aid of an alignment of the constant electric resistance with the simulated measuring values.
The above-outlined known methods in all instances presuppose the existence of a measuring value or a measuring value indication, that is, a value which is above the zero-point because only in such a case can a deviation be determined. The “wandering” or “drifting” of the zero point cannot be determined with the known methods and thus can also not be taken into account in a regulating device.
It is further feasible to detect the drift and also to achieve a stability of indication by taking into account the changing influences with the aid of different algorithms in the software of the regulating device. For such a proceeding, however, an independent reference system is not available which also has a certain stability as concerns aging.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved apparatus of the above-outlined type by means of which the drift of an exhaust gas sensor may be compensated for and also, in case of high waste (exhaust) gas temperatures, the working temperature range of the exhaust gas sensor may be maintained.
This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the apparatus for a zero-point stabilization of an exhaust gas sensor installed in an apparatus for a thermal energy conversion of gaseous fuel while producing an exhaust gas stream, includes an arrangement for alternatingly exposing the exhaust gas sensor to a flow of exhaust gas and a flow of fresh air.
By virtue of the arrangement as outlined above, a reference system is provided for the exhaust gas sensor, since it is repeatedly exposed all around to fresh air so that, accordingly, in such operational phases the same initial value, that is, the “zero point” is necessarily indicated. By virtue of aging effects, temperature effects and the like, the signal which is considered to be the zero point signal may change, that is, it may drift, and thus the invention provides the possibility for the regulating device to detect such a drift during the phases of the fresh air exposure by a comparison with a predetermined value and then to correct such value by the regulating device. Thus, the arrangement provides for the possibility to continuously restore the regulating device to the zero point even during the operation of the exhaust gas sensor. The invention further provides that at a given temperature of the fresh air, for example, at an environmental temperature, the exhaust gas sensor is cooled and, corresponding to the temperature difference, may be maintained within its operating temperature range.
The term “apparatus for converting thermal energy” in the meaning of the present invention also encompasses firing systems, particularly small firing devices in addition to combustion engines, particularly piston-type engines. The term “gaseous fuels” encompasses fuels which are initially in gaseous form as they are used for small firing devices, as well as liquid fuels which are atomized and/or vaporized in preparation for the energy conversion.
According to an advantageous feature of the invention, the alternation between exhaust gas exposure and fresh gas exposure is effected by a controllable valve assembly. This arrangement makes possible to control the duration and the alternating frequency of the exhaust gas exposure and the fresh air exposure dependent on the mode of use and as a function of the changing load conditions. Thus, in small firing devices which have essentially a constant fuel flow rate during the operating period, the sensor needs to be only infrequently exposed to the fresh air flow. The method may be coupled with the regulating device in such a manner that an alternation between the exposure to exhaust gas and the exposure to fresh gas is effected only when the fuel is actually combusted. In contrast, in an internal-combustion engine, particularly in an engine for an automotive vehicle which has varying load requirements and therefore varying components of pollutants in the exhaust gas and, last but not least, because of the substantially higher exhaust gas temperature, a frequent alternation between an exposure to the exhaust gas and an exposure to the fresh air has to be performed. In this manner, it is not only ensured that by means of the exhaust gas sensor the after-connected regulating device always receives the “actual” exhaust gas data but also, during the period of exposure to fresh air, a cooling of the exhaust gas sensor is achieved so that the latter may be held in its operating temperature range.
According to a further advantageous feature of the invention, the exhaust gas sensor is exposed to an exhaust gas flow which is branched off the main exhaust gas stream. This measure which also results in small flow cross sections in the exposure region for the exhaust gas sensor, ensures not only a superior flow pattern in the contact region with the exhaust gas sensor but the partial stream may be taken out from a core zone of the main exhaust gas stream so that external interferences are excluded to a substantial extent. While in principle it is possible to introduce the fresh air into the exposure zone of the exhaust gas sensor by an additional fan, according to a further advantageous feature of the invention the fresh air is introduced to the exhaust gas s
Lepperhoff Gerhard
Meyerdierks Dietrich
Denion Thomas
FEV Motorentechnik GmbH & Co. KG
Kelemen Gabor J.
Trieu Thai-Ba
Venable
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