Sensor element for limit current sensors to determine the .lambd

Details Sensor element for limit current sensors to determine the .lambd Sensor element for limit current sensors to determine the .lambd

1993-04-12

1994-05-24

Niebling, John

Chemistry: electrical and wave energy

Apparatus

Electrolytic

204412, 204415, 204424, 204426, 204429, G01N 2726

Patent

active

053146042

DESCRIPTION:

BRIEF SUMMARY
STATE OF THE ART

The point of departure for the present invention is a sensor element according to the species defined in the main claim. These types of sensor elements, which operate on the diffusion limit current principle, measure the diffusion limit current while a constant voltage is applied to the two electrodes of the sensor element. In an exhaust gas resulting from combustion processes, this current is dependent on the oxygen concentration as long as the diffusion of gas to the pump electrode determines the speed of the occurring reaction. It is known to construct these types of sensors, which operate on the polarographic measuring principle, in such a way that both anode and cathode are exposed to the gas to be measured, with the cathode providing a diffusion barrier in order to achieve a performance in the diffusion limit current region.
The known limit current sensors generally serve to determine the .lambda.-value of gas mixtures, which refers to the ratio "total oxygen/oxygen required for the complete combustion of fuel" of the air/fuel mixture combusted in a cylinder, with the sensors indicating the oxygen content of the exhaust gas via a limit current measurement, with a pump voltage lying in a predetermined range.
Due to a simplified and cost-effective production method, it has been found to be advantageous in practice in recent years to produce sensor elements by means of ceramic-sheet and screen-printing technology.
In a simple and efficient manner, it is possible to produce planar sensor elements starting with oxygen-conducting solid electrolytes, for example, of stabilized zircon dioxide, in the shape of platelets or sheets, with the electrolytes each being coated with an interior and exterior pump electrode and the associated conductor paths. In this case, the interior pump electrode is advantageously disposed in the edge region of a diffusion channel through which the measuring gas is supplied and which serves as gas diffusion resistance.
Sensor elements and detectors are also disclosed in DE-OS (unexamined published patent application) 3,543,759 and EP 0,142,993, 0,188,900, and 0,194,082 which have in common that each is provided with a pump cell and a sensor cell, which comprise two platelet or sheet-shaped oxygen-conducting solid electrolytes, two electrodes arranged thereon, and a common diffusion channel.
One drawback of the sensor elements of the type described is that the forward portion of the interior pump electrode facing the supplied measuring gas is more heavily used than the rearward portion of the pump electrode facing away from the supplied measuring gas. This results in high polarization of the electrodes which requires a high pump voltage. The latter, in turn, involves the danger of the electrolyte disintegrating in the region of the interior pump electrode.
In order to overcome this drawback, it is known from DE-OS 3,728,618 to arrange at least two interior pump electrodes in the diffusion channel of a sensor element for limit current sensors. This results in a marked reduction in the disadvantageous electrode polarization which easily occurs in sensor elements having only one interior pump electrode. At the same time, improved utilization of the noble metal required for the configuration of the pump electrode is achieved.
European Patent EP 0,194,082 also discloses a sensor element for determining the concentration of a gas component in gases, in particular, the exhaust gases from internal combustion engines. This sensor element comprises essentially a pump cell including two pump electrodes and a sensing cell including two further electrodes. However, construction of this sensor element is comparatively expensive, involving the impression of an auxiliary pump current on the exhaust gas side of the Nernst cell electrode and resulting in a comparatively high oxygen partial pressure both above the cathode of the pump cell and above the exhaust gas side of the Nernst cell electrode.


ADVANTAGES OF THE INVENTION

By contrast, the sensor element according to the presen

REFERENCES:
patent: 4732663 (1988-03-01), Kato et al.
patent: 4818363 (1989-04-01), Bayha et al.
patent: 4824549 (1989-04-01), Hamada et al.
patent: 4839018 (1989-06-01), Yamada et al.
patent: 5098549 (1992-03-01), Friese et al.
patent: 5137615 (1992-08-01), Friese et al.

Affiliated with

Also associated with

Rating

Sensor element for limit current sensors to determine the .lambd does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Sensor element for limit current sensors to determine the .lambd, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Sensor element for limit current sensors to determine the .lambd will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1970929