Ventilation – Vehicle – Having automatic control means
Patent
1996-08-29
1998-03-10
Wayner, William E.
Ventilation
Vehicle
Having automatic control means
454229, 165249, 73 2331, B61D 2700, E21B 4300
Patent
active
057254257
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention centers on a sensor system which controls the ventilation systems in vehicles, both for incoming air and recirculation mode, depending on the concentration of poisonous fumes in the atmosphere outside the vehicle, using a gas sensor element, the electrical resistance of which falls in case of reducing gases and which rises when oxidizing gases are present, together with an evaluation unit, the output of which is connected to the controls of the ventilation system.
BACKGROUND ART
It is known that by using gas sensor elements, for example tin dioxide elements, the presence of oxidable gases can be registered, for example the presence of carbon monoxide, hydrocarbons and hydrogen. During the process, a gas-sensitive layer within the gas sensor element, which can consist of conductive and heated tin dioxide, might be reduced by the oxidable gas; thus a reduction of the ohmic resistance of the gas-sensitive tin dioxide layer in the gas sensor element occurs. Such gas sensor elements are included in sensor systems which control ventilation systems in vehicles. Whenever the vehicle in question enters an area with a high concentration of poisonous fumes, the ventilation system will be switched to recirculation operation, ensuring that the fumes are kept out of the interior of the vehicle.
The usual sensor systems, especially those fitted with tin dioxide sensor elements, react to a very limited extent only to diesel exhaust emissions, although diesel emissions disturb vehicle passengers subjectively more than many petrol emissions, such as carbon monoxide, since these fumes may not be smelled as obviously as diesel emission fumes. The reason for this behavior lies in a masking effect which occurs, because diesel emissions contain not only oxidable gases, but also high levels of nitric oxide, which are gases which may be reduced and are thus oxidizing gases. The nitric oxide contained in the diesel emissions once again oxidises the gas sensitive tin dioxide layer of the gas sensor element, which has been reduced by the oxidable gases contained in the diesel emissions, so that the reducing and oxidizing effects created by the charging of the gas sensitive tin dioxide layer cancel each other out to a great extent.
For an explanation of the `Masking Effect`, see FIGS. 1-3. FIG. 1 shows a sensor circuit, which demonstrates a heated gas sensor element 1 and an external resistor 2. The external resistor 2 can also be replaced by a constant electrical source. The divider current UM measured between the heated gas sensor element 1 and the external resistor 2 is a function of the gas-altered ohmic resistance of heated gas sensor element 1.
FIG. 2 shows the change in the ohmic resistance in gas sensor element 1, when coated only with reducing gases or only with oxidizing gases. Impulse 3 shown in the figure is the result of gas sensor element contact with gases that can be oxidized, for example with carbon monoxide (CO). Impulse 4 is the result of gas sensor element 1 contact with gases that can be reduced, for example with nitric oxide (NOx).
FIG. 3 shows the `Masking Effect`, impulse 5 occurs through gas sensor element contact with reducing carbon monoxide that can be oxidized. In FIG. 3, impulse 5 is followed by impulse 6, which is achieved by a mixture of carbon monoxide and nitric oxide. In spite of the presence of nitric oxide in the mixture, the ohmic resistance of the gas sensor element remains lower than in the uncoated state. In spite of the presence of reducible and thus oxidizing nitric oxides in diesel exhaust emissions, the ohmic resistance of gas sensor element 1 remains under the level that it would have in an emission-free state. The effect occurs because of the oxidable and thus reducing gases which are present in diesel emissions. Under extreme conditions, the ohmic resistance of the gas sensor element 1 can show the same level following contact with mixed gas that would be reached by gas sensor element contact to fresh air. In any case, the value of the gas sensor signal
REFERENCES:
patent: 4437391 (1984-03-01), Eguchi et al.
patent: 4992965 (1991-02-01), Holter et al.
patent: 5252949 (1993-10-01), Kirby et al.
patent: 5320577 (1994-06-01), Tooru et al.
Hiller Jorg
Kiesewetter Olaf
Pieper Norbert
Rump Hanns
Auto Electronics Corporation
Malm Robert E.
Wayner William E.
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