Gas sensor and manufacturing method therefor

Abstract

A sensor element has a cross-sectional area that increases either uniformly or gradually from a positive (+) electrode side toward a negative (−) electrode side, thereby leading a hot spot, which attempts to move to the negative electrode side, to a lower resistance side. A position that is at nearly equal distances from paired electrodes formed on either end of the sensor element is set as a hot spot generating position, so as to avoid damage to the electrodes due to heat emitted by the hot spot.

1 . A gas sensor made from a ceramic sintered body for detecting as gas concentration, either change in an electric current value or change in a resistance value measured when a voltage is applied to a sensor element, wherein
 the sensor element has a shape in which a cross-sectional area changes from one electrode side toward the other electrode side of paired electrode parts formed on either longitudinal end.   
     
     
         2 . The gas sensor according to  claim 1 , wherein the cross-sectional area increases or decreases either uniformly or gradually from the one electrode side toward the other electrode side. 
     
     
         3 . The gas sensor according to  claim 2 , wherein the sensor element has a constant thickness, and a width that increases or decreases either uniformly or gradually from the one electrode side toward the other electrode side. 
     
     
         4 . The gas sensor according to  claim 2 , wherein the sensor element has thickness and width increasing or decreasing either uniformly or gradually from the one electrode side toward the other electrode side. 
     
     
         5 . The gas sensor according to  claim 1 , wherein of the paired electrode parts, an electrode part formed on one side where cross-sectional area of the sensor element is larger is set as a negative electrode, and an electrode part formed on another side where the cross-sectional area is smaller is set as a positive electrode. 
     
     
         6 . The gas sensor according to  claim 5 , wherein either the negative electrode and the positive electrode have nearly the same size, or size of the negative electrode is larger than that of the positive electrode. 
     
     
         7 . The gas sensor according to  claim 5 , wherein either both the negative electrode and the positive electrode are formed on the same side of the sensor element, or one of the negative electrode or the positive electrode is formed on an upper surface of the sensor element and the other is formed on an under surface of the sensor element. 
     
     
         8 . A manufacturing method for a gas sensor made from a ceramic sintered body for detecting as gas concentration, either change in an electric current value or change in a resistance value measured when a voltage is applied to a sensor element; comprising the steps of:
 manufacturing a green sheet from slurry formed by mixing together raw materials of the sensor element;   manufacturing a ring-shaped first green sheet by punching out the green sheet so as to form a punched hole having a predetermined diameter;   manufacturing a ring-shaped second green sheet by forming belt-like shaped electrodes along periphery of the punched hole of the first green sheet and a ring-shaped outer periphery of the first green sheet;   manufacturing a ring-shaped laminated body by coaxially stacking a plurality of the first green sheet with the second green sheet as a top surface;   cutting the laminated body along a plurality of diametral virtual lines of the ring-shaped laminated body that is formed by rotating around the axis of the ring-shaped laminated body every fixed angle in the circumferential direction; and   baking a sensor element divided into individual pieces through said cutting, and forming paired electrodes on either end part in the longitudinal direction.   
     
     
         9 . The manufacturing method for a gas sensor according to  claim 8 , wherein in the step of cutting the ring-shaped laminated body, cutting of the laminated body is carried out either by rotating the laminated body around its axis every fixed angle in the circumferential direction, and moving a cutter part arranged on an upper part of the laminated body a predetermined distance vertically downward in sync with said rotating, or by fixing the laminated body and moving a cutter part arranged on an upper part of the laminated body a predetermined distance vertically downward while rotating around the axis of the laminated body every fixed angle in the circumferential direction. 
     
     
         10 . A manufacturing method for a gas sensor made from a ceramic sintered body for detecting as gas concentration, either change in an electric current value or change in a resistance value measured when a voltage is applied to a sensor element, comprising the steps of:
 manufacturing a long green sheet from slurry formed by mixing together raw materials of the sensor element;   manufacturing a sensor element piece with a nearly trapezoidal shape, in a planar view, by cutting the green sheet in a zigzag shape at predetermined intervals in a direction crossing a longitudinal direction of the green sheet; and   baking the sensor element piece and forming paired electrodes on either end part in the longitudinal direction.   
     
     
         11 . The gas sensor according to  claim 6 , wherein either both the negative electrode and the positive electrode are formed on the same side of the sensor element, or one of the negative electrode or the positive electrode is formed on an upper surface of the sensor element and the other is formed on an under surface of the sensor element.