Sensor element

Details Sensor element Sensor element

1997-11-07

1999-05-11

Tung, T.

Chemistry: electrical and wave energy

Apparatus

Electrolytic

204426, G01N27/407

Patent

active

059024704

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a sensor element for an electrochemical measuring sensor for determining the oxygen content of gases, particularly for determining the oxygen content in exhaust gases of internal combustion engines, the sensor element having the features cited in the preamble of claim 1.


STATE OF THE TECHNOLOGY

Sensor elements of the generic type are known. They are designed, e.g., as so-called planar sensor elements, having a first electrode on a solid electrolyte formed as a carrier, which electrode is exposed to a gas to be measured, and a second electrode exposed to a reference gas. For various applications, the sensor element must be heated to a certain temperature. For this purpose, it is known to allocate to the sensor element a heating device which usually has heating conductors extending below the electrode that is exposed to the reference gas.
In order to supply a reference gas to the reference gas electrode, a reference gas conduit is provided within the planar sensor element which is constructed in layers, which conduit extends, for example, in the longitudinal direction of the sensor element. This reference gas conduit extends between the reference gas electrode and the heating conductors.
An electrochemical measuring sensor with a sensor element of this type is disclosed, e.g., in DE 29 28 496. It has the drawback that the reference gas conduit is a poor heat conductor for the thermal energy emitted by the heating device so that the sensor element can only be heated to its operating temperature with an increased heating energy or after a correspondingly long heating time. The heat transfer to the sensor element is poor, particularly in sensor elements in which the heating conductors are in direct connection with the reference gas conduit.


ADVANTAGES OF THE INVENTION

In contrast, the sensor element according to the invention having the features stated in claim 1 offers the advantage that a heat transfer from the heating device to the sensor element is considerably improved. Since the reference gas conduit is designed so as to be divided, at least in the region of the heating device, there is the possibility of matching the layout of the reference gas conduit and/or of the heating device in such a manner that a heat conduction between the heating device and the sensor element can be assumed by the substrate disposed between the divided (branched) reference gas conduits. This substrate has a much better thermal conductivity than the reference gas in the reference gas conduits so that heat can be transferred more quickly and more effectively. Thus it is possible, in particular, to accomplish a shorter heating-up period for the sensor element or a higher sensor element temperature with a predetermined heating power of the heating device. On the other hand, it is possible to reduce the heating power of the heating device while maintaining the heating-up time and the same sensor element temperature so that an improved long-term stability of the heating device and an improved thermal shock behavior of the sensor element can be accomplished. In addition, the branching of the reference gas conduit in the region of the heating device increases the mechanical stability of the entire planar sensor element because ribs remaining between the individual branches of the reference gas conduit provide for a smaller unsupported width of the reference gas conduit.
A further advantage of the sensor element according to the invention results from the fact that there is no longer any overlap between the width of the reference gas conduit and an insulating system for the heating conductors. This prevents damage to the insulating system in the region of the heating conductors during the production of the sensor elements, particularly during the lamination of the individual layers of the sensor elements. Minimizing or excluding any damage of the insulating system results in an improved leakage current behavior of the heating conductors.
Advantageous embodiments of the invention ensue from the remaining fe

REFERENCES:
patent: 4541900 (1985-09-01), Mase et al.
patent: 4900412 (1990-02-01), Ker et al.
patent: 5296112 (1994-03-01), Seger et al.
patent: 5395506 (1995-03-01), Duce et al.

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