Measuring and testing – Vehicle chassis – Steering
Patent
1994-09-08
1997-04-01
Chilcot, Richard
Measuring and testing
Vehicle chassis
Steering
123697, F02D 4114
Patent
active
056168357
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a system for operating a heating element for a ceramic sensor in a motor vehicle.
BACKGROUND INFORMATION
A system for operating a heating element for a ceramic sensor in a motor vehicle is described in U.S. Pat. No. 4,348,583. There, a constant current is fed to a heating element during a first time interval. During a second time interval, the current is pulsed so that reduced power is used for heating during the second time interval. Using this type of triggering of the heating element, a high heating power is made available during the first time interval in order to attain a desired temperature as rapidly as possible. During the second time interval, reduced power is used for heating in order to maintain the temperature.
An oxygen sensor serves to measure the oxygen content of the exhaust gas and to provide an apparatus for controlling the air/fuel ratio. Until now, the oxygen sensor was generally situated very far forward in the exhaust channel, i.e., near to the internal combustion engine, in order to guarantee that the oxygen sensor was heated rapidly by the exhaust gases of the internal combustion engine.
In order to heat the oxygen sensor even more rapidly, it is generally equipped with an electrical heating element. Moreover, it can be ensured by way of the heating element that the oxygen sensor is maintained at operating temperature even under operating conditions whereby the exhaust temperature is low and/or only a very small quantity of exhaust gases are present.
However, problems can arise if the oxygen sensor is situated near to the internal combustion engine: long time, a large quantity of very hot exhaust gases will be produced which can possibly heat the oxygen sensor to an intolerably high temperature. This can reduce the service life of the oxygen sensor. the oxygen sensor in the exhaust channel near to the internal combustion engine from which the exhaust gases from all cylinders of the internal combustion engine can be measured.
These difficulties can be circumvented by situating the oxygen sensor downstream, i.e., away from the internal combustion engine, in the exhaust channel. However, this second installation site entails a new problem. In the initial phase after starting a cold internal combustion engine, the exhaust channel upstream from the oxygen sensor will remain relatively cold. This will result in the condensation of the water contained in the exhaust gases. If the condensed water droplets are, for example, pulled loose from the wall of the exhaust passage by the exhaust gases streaming by and slung onto the oxygen sensor, the oxygen sensor will be cooled down very rapidly at the local points of impingement. This cooling can result in damage to the oxygen sensor (e.g., cracks in the ceramics). The risk of damage is particularly high if the oxygen sensor is already at a high temperature.
SUMMARY OF THE INVENTION
The underlying object of the present invention is, in a system of the type described above for operating a heating element for a ceramic sensor in a motor vehicle, to set different sensor temperatures depending on the operating state of an internal combustion engine powering the motor vehicle.
A further object of the present invention is to protect the ceramic sensor from damage due to impinging liquid. At the same time, the ceramic sensor should be ready for operation as rapidly as possible and the sensor signals should suffer as little impairment as possible. Moreover, the invention allows protection of the ceramic sensor with no structural alterations whatsoever to the sensor or with only minor structural alterations, and without incurring significant additional expense.
The present invention makes it possible to influence the temperature TSe of the oxygen sensor through appropriate triggering of the heating element such that the risk of damage to the oxygen sensor due to impinging condensed water can be held very low.
An advantage of the present invention is that it allows the setting of the temperatur
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Blischke Frank
Henkelmann Konrad
Mallebrein Georg
Schnaibel Eberhard
Schneider Erich
Chilcot Richard
McCall Eric S.
Robert & Bosch GmbH
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