JPS58148947A - Electric resistance type detection element for exhaust gas component - Google Patents

Abstract

PURPOSE:To obtain a small-sized element having good detection accuracy and giving a good linearity for its resistance value corresponding to the variation of gas components even in a low temperature range of exhaust gas temperature, by forming a gas sensitive body consisting essentially of WO3 on a comb-shaped electrode formed on the surface of a ceramic substrate. CONSTITUTION:A comb-shaped electrode is formed on the surface of a ceramic substrate by printing gold paste and Pt lead wire is fixed to a terminal part with the gold paste and hereafter, is baked. Next, paste added SiO2 to WO3 powder for increasing adhesive strength is put into 100 mesh screen print on the comb-shaped electrode and said electrode is calcined at 600-1,000 deg.C after drying to complete a detection element. Hereby, resistance value of this element has a good linearity corresponding to the variation of exhaust gas components of internal combustion engine of a motor car etc. and the equivalent ratio of air- fuel is measured in the range of 200-500 deg.C with good accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electric resistance type exhaust gas composition detection element, and more particularly, to an electric resistance type exhaust gas composition detection element used for controlling an air-fuel ratio, for example, to detoxify internal combustion engine exhaust gas and improve fuel efficiency. The present invention relates to an exhaust gas composition sensing element.

Conventional S n Ox * T 10x t Ce Os
Electrical resistance type exhaust gas detection elements, which are mainly used by NFO* etc., show resistance changes depending on the exhaust gas composition, but the resistance changes greatly with temperature, and the resistance against changes in the air-fuel ratio. Because the linearity of the value change is poor, it is only used for so-called large senna, which is formed by adding a catalyst*1 to the element and controls the air-fuel ratio by switching due to a large resistance value change around the ideal air-fuel ratio. It has become limited. However, due to recent demands for reducing fuel consumption, it has been desired to control the air-fuel ratio on the air-excess side.

In addition, in the oxygen concentration battery type oxygen sensor using zirconia that is currently in practical use, the exhaust gas temperature is 400°C.
The drawback is that the output voltage drops significantly in the low temperature range below, making it difficult to use. Therefore, it is desired to develop an element that has a sufficient ability to detect the exhaust gas composition even in the region where the exhaust gas temperature is still low at the time of starting the internal combustion engine, especially in the relatively low temperature region where the exhaust gas i1 degree is 400 degrees Celsius or less. It was desired to develop an element whose resistance value changes little with temperature.

Therefore, it is an object of the present invention to exhibit good linearity in the change in resistance value corresponding to changes in exhaust gas composition, and to have a small temperature change in resistance value after the exhaust gas temperature reaches 400°C, and a good detection degree. An object of the present invention is to provide a compact electric resistance type exhaust gas composition sensing element.

Hereinafter, the electrical resistance type exhaust gas composition sensing element of the present invention will be explained in more detail based on preferred embodiments thereof.

The electrical resistance type exhaust gas composition sensing element (hereinafter simply referred to as the sensing element) of the present invention includes a comb-shaped electrode and a ceramic substrate with A+T-leads. On one side of the cut alumina plate,
Twelve pairs of comb-shaped electrodes with a spacing of 0.2 m and an overall size of 5 cm x 15 electrodes are printed and molded using gold paste, and a lead edge of 0.21 diameter of platinum is attached to the seventh terminal using gold paste. It is fixed and baked at 860°C.

Next, 810s t-8% by weight is added to tungsten trioxide (WOs) powder to increase adhesive strength, mixed well, and the mixed powder is kneaded with a suitable resin and solvent, and yeast for screen printing is added. 100 meshes of the paste were screen-printed on the comb-shaped electrodes of the ceramic substrate mentioned above, and after drying, 60
Baking is performed at 0° C. to 100° C. for about 1 hour, thereby producing a sensing element.

In such a sensing element, the resistance value change of the scissors sensing element due to the change in the exhaust gas composition corresponding to the air-fuel equivalence ratio in the internal combustion engine at an exhaust gas temperature of 400°C is the first
This is shown in the graph in Figure. The main components of the exhaust gas at this time are I'h, CO, and COs.

Hz * Ox. As shown in FIG. 1, the sensing element of the present invention exhibits a large resistance value change and good linearity when the air-fuel equivalence ratio is in the range of α9 to 1.5 at an exhaust gas temperature of 400°C. It shows.

Further, the graph in FIG. 2 shows an example of a temperature change of the detection element in an exhaust gas atmosphere. This at! As is clear from FIG. 2, according to the detection element, there is little temperature change in the resistance value in the exhaust gas temperature range of 200° C. to 500° C., and stable detection can be obtained against temperature fluctuations. Note that the graph shown in Figure 2 was for the case where the air-fuel equivalence ratio was 1.35, but
Even in an exhaust gas atmosphere with an air-fuel equivalence ratio other than the above, the temperature change in resistance value was approximately the same as in the graph of FIG. 2 in the temperature range from 200° C. to 50 (Jul).

The graph in FIG. 3 shows the temperature change in the resistance value of the sensing element in the atmosphere. In the sensing element of the present invention, as shown in the graph of FIG. In the atmosphere, the temperature is between 200℃ and 600℃.
The resistance value changes greatly over a range of 1000°C. The reason for this difference in temperature characteristics from that in exhaust gas is that the atmosphere contains almost no CO, C (h, Hz), so the true temperature characteristics of the element's sensitive body itself and the CU + CO wealth +
This is because there is no canceling effect between the temperature characteristics of the adsorption state on the 1-1 m sensitive body.

Furthermore, FIGS. 4 and 5 respectively show changes in resistance value at exhaust gas temperature [400° C.] with respect to changes in zero snow concentration and CO concentration in the tooth gas of the detection element in the present invention. As shown by Dala 7 in each of these figures, the sensing element of the present invention exhibits an increase or decrease in resistance value for each gas component depending on the nature of the gas component, and the overall effect is Depending on the composition of exhaust gas corresponding to the fuel ratio, if &! Indicates resistance value change with characteristics.

As described above, the sensing element of the present invention has significantly improved the shortcomings of conventional elements, and has CO, CCh, gas, and Ns as main components in the temperature range of 250°C to 500°C, which is sensitive to exhaust gas composition. The temperature change in the resistance value in the exhaust gas atmosphere is small, and the resistance value change shows good linearity with respect to the exhaust gas composition change.Furthermore, the sensing element of the present invention can easily be used with a thick film gas sensitive material. Compared to electrochemical oxygen sensors, it can be easily manufactured in smaller sizes and has a smaller heat capacity, so a small heater can quickly increase the element temperature
The temperature can be raised to 250°C to 400°C, and good exhaust gas detection is possible.

As mentioned above, according to the electrical resistance type exhaust gas composition detection element of the present invention, among the main components of the exhaust gas composition of internal combustion engines, changes in concentration of each of the seven gas components, Ox, CO, and Hl, are detected. On the other hand, the resistance value of O2, which is an unburnt gas, increases as the concentration increases, and the resistance value of O2, which is a reducing gas, increases as the concentration increases.
On the contrary, it has the characteristic that the resistance value decreases and Nt, 0! , C(h.

In the exhaust gas of internal combustion engines, etc. whose main components are CO and Hx, the overall adsorption effect of the exhaust gas components on the gas 16 reactants of the element, as well as the temperature change of the gas adsorption state and the truth of the resistance value of the sensitive body. Due to the offsetting effect of temperature changes, resistance changes with good linearity in response to changes in exhaust gas composition corresponding to the air-fuel equivalence ratio, which are extremely useful characteristics, and good resistance changes in exhaust gas. It has temperature characteristics of resistance value.

The electrical resistance type exhaust gas composition sensing element of the present invention can be used as a sensor for controlling the air-fuel ratio in internal combustion engines such as automobile engines, Mailer-1 heaters, and the like.

[Brief explanation of drawings]

FIG. 1 is a graph showing the change in resistance value with respect to exhaust gas composition at 400° C. for the sensing element according to the present invention, and FIG. FIG. 3 is a graph showing temperature changes in resistance value in the corresponding exhaust gas; FIG. 3 is a graph showing temperature changes in resistance value of the sensing element of the present invention in the atmosphere;
The figure and FIG. 5 show the detection element of the present invention in tooth gas at 0! It is a graph showing changes in resistance value at 400° C. with respect to changes in concentration and CO concentration. Agent Shin Kuzuno - Figure 1! wL power consumption 1 quantity kt diagram m/l (・C1 Fig. 3 Fig. 4

Claims (1)

[Claims] (1) An electric resistance type exhaust gas composition sensing element characterized in that a material containing tungsten trioxide (WOs) as a main component is used as a gas sensitive member. (2. In the electric resistance type exhaust gas composition sensing element according to claim 1, the sensing element is provided on the surface of the ceramic substrate by screen printing and baking treatment (on the ribbon-shaped electrode, A thick film-like gas sensitive body formed by screen printing a paste containing powder of the gas sensitive body and then baking it, and an element heating element formed on the back surface of the ceramic substrate by screen printing and baking processing. An electric resistance type exhaust gas composition detection element equipped with a heater.