JP2018100961A - Gas sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress temperature fluctuations of a detection element.SOLUTION: A NOx sensor 1 comprises: a gas sensor element 3; a metallic body 21; and a metallic protector 5. The metallic body 21 has a cylindrical shape extending in a direction of axis DA. The gas sensor element 3 is accommodated inside the body 21. The NOx sensor 1 has a mounting part 22 that has a cylindrical shape extending in the direction of axis DA and is disposed in such a manner that a space 23 extending in the direction of axis DA is formed between the mounting part 22 and the body 21. The gas sensor element 3 has an oxygen-ion-conducting solid electrolyte layer, an oxygen-concentration-detecting cell 140 having a pair of detection electrodes and a reference electrode formed on the solid electrolyte layer, and a heater for heating the oxygen-concentration-detecting cell 140 to a predetermined temperature. The oxygen-concentration-detecting cell 140 is disposed inside the space 23.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a gas sensor that detects a specific gas contained in a gas to be measured.

  As disclosed in Patent Document 1, a gas sensor is known that is capable of detecting the concentration of a specific gas contained in a gas to be measured by being heated to a predetermined activation temperature or higher. Such a gas sensor is provided with a heater so that a specific gas concentration can be detected at an early stage after activation (ie, an activated state).

  In addition, the internal resistance of the detection element formed with the solid electrolyte body has a characteristic that changes in a form having a correlation with the temperature of the detection element. Therefore, the sensor control device that controls the detection element detects this internal resistance, and drives the heater based on the temperature calculated using the detected internal resistance so that the detection element becomes the target temperature. Can be controlled.

JP 2012-18050 A

However, if the temperature of the detection element deviates from the target temperature due to a temperature change around the gas sensor, the detection accuracy of the specific gas concentration by the gas sensor may be reduced.
An object of the present disclosure is to suppress temperature fluctuation of a detection element.

  One aspect of the present disclosure is a gas sensor including a detection element, a metal housing member, and a metal protector. The detection element is formed in a long shape and detects a specific gas contained in the gas to be measured. The accommodating member is formed in a cylindrical shape extending in the axial direction, and accommodates the detection element inside itself.

The protector has a vent hole through which the gas to be measured passes, and is fixed to the housing member so as to cover the tip of the detection element.
In addition, the gas sensor of the present disclosure includes a space forming member that is formed in a cylindrical shape extending in the axial direction, and is arranged so as to form an annular or end annular space extending in the axial direction between the housing member and the gas sensor.

  The detection element includes a detection cell having a solid electrolyte body having oxygen ion conductivity and a pair of electrodes formed on the solid electrolyte body, and a heater for heating the detection cell to a predetermined temperature. The detection cell is arranged inside the space. Note that “arranged inside the space” means that it is arranged inside the space in the radial direction.

  In the gas sensor of the present disclosure configured as described above, the detection cell includes a space forming member, a space, and a portion in which the metal housing member is stacked along the radial direction (hereinafter referred to as a stacked portion). Covered.

  For this reason, one path in which the temperature change around the gas sensor affects the temperature of the detection cell of the gas sensor is a path through which the heat around the gas sensor conducts through the above-described stacked portion and reaches the detection cell.

  In the laminated portion, a space is formed between the space forming member and the housing member. That is, gas exists between the space forming member and the metal housing member. And gas has a lower thermal conductivity than metal. For this reason, in the gas sensor of the present disclosure, it is difficult for heat around the gas sensor to be conducted to the detection cell through the stacked portion, and temperature fluctuation of the detection cell can be suppressed. And the temperature fluctuation of a detection element can be suppressed by suppressing the temperature fluctuation of a detection cell.

  In one aspect of the present disclosure, the space forming member may be disposed so as to cover at least a part of the outer peripheral surface of the housing member in a state where a space is formed between the space forming member and the housing member. In one aspect of the present disclosure, the space forming member is disposed inside the housing member so as to cover at least a part of the inner peripheral surface of the housing member in a state where a space is formed between the space forming member and the housing member. It may be.

  In one embodiment of the present disclosure, the detection element includes a measurement chamber, a pumping cell, and an oxygen concentration detection cell, the oxygen concentration detection cell is a detection cell, and the pumping cell detects more than the oxygen concentration detection cell. You may make it arrange | position at the front end side of an element and the inside of an accommodating member. A measurement gas is introduced into the measurement chamber. The pumping cell has a first solid electrolyte body having oxygen ion conductivity and a pair of pumping electrodes formed on the first solid electrolyte body, and is measured by flowing a pumping current between the pair of pumping electrodes. Pumps or pumps oxygen in the gas to be measured introduced into the chamber. The oxygen concentration detection cell has an oxygen ion conductive second solid electrolyte body, a detection electrode and a reference electrode formed on the second solid electrolyte body, and the detection electrode is arranged facing the measurement chamber, An electromotive force is generated according to a difference in oxygen concentration between the detection electrode and the reference electrode.

  In the gas sensor of the present disclosure configured as described above, since the pumping cell is disposed inside the housing member, the periphery of the pumping cell in the radial direction is covered with the housing member. For this reason, the gas sensor according to the present disclosure can suppress heat around the gas sensor from reaching the pumping cell by the housing member. Thereby, the gas sensor of this indication can further control the temperature variation of a detection element.

1 is a cross-sectional view of a NOx sensor 1. FIG. FIG. 3 is a diagram showing a schematic configuration of an element body 31 and a sensor control device 170. FIG. 3 is a cross-sectional view around the detection unit 31a in the NOx sensor 1.

(First embodiment)
Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.
The NOx sensor 1 of this embodiment is mounted on a vehicle and detects nitrogen oxides (hereinafter referred to as NOx) contained in exhaust gas discharged from an internal combustion engine.

  As shown in FIG. 1, the NOx sensor 1 includes a metal shell 2, a gas sensor element 3, a holding unit 4, a protector 5, an outer cylinder 6, a plurality of lead wires 7, a plurality of connection terminals 8, A separation unit 9 and a grommet 10 are provided. In FIG. 1, the lower end side of the NOx sensor 1 is referred to as a front end side FE, and the upper end side of the NOx sensor 1 is referred to as a rear end side BE.

The metal shell 2 is a member formed in a cylindrical shape with a heat-resistant metal such as stainless steel. The metal shell 2 includes a main body portion 21 and an attachment portion 22.
The main body 21 is a member formed in a cylindrical shape extending in the direction of the axis O of the NOx sensor 1 (hereinafter referred to as the axis direction DA). The main body 21 includes a through hole 21a penetrating along the axial direction DA. On the inner peripheral wall of the through hole 21a, a stepped portion 21b is formed that protrudes radially inward.

  The attachment portion 22 is a cylindrical member that surrounds the main body portion 21 so as to be rotatable with respect to the main body portion 21, and includes a hexagonal portion 22a and a screw portion 22b. A cylindrical space 23 extending in the axial direction DA is formed between the outer peripheral surface of the main body 21 and the inner peripheral surface of the attachment portion 22. The space 23 has a ring shape with ends and is a space closed in the radial direction. More specifically, in the cross-sectional view of FIG. 1, the space 23 is uniformly formed with a predetermined thickness in the axial direction and the radial direction, but the inner peripheral surface of the mounting portion 22 and the outer peripheral surface of the main body portion 21 are different from each other. Some are touching. Accordingly, the space 23 has an end ring shape (C shape).

  The hexagonal portion 22a extends outward from the outer periphery of the main body portion 21 along the radial direction, and the outer periphery is formed in a hexagonal plate shape. The hexagonal portion 22a is a portion for fitting an attachment tool such as a hexagon wrench when the NOx sensor 1 is attached to the exhaust pipe.

  The screw portion 22b is located on the tip side FE from the hexagonal portion 22a, extends outward from the outer periphery of the main body portion 21 along the radial direction, and has a male screw formed on the outer periphery. The male screw has a shape that can be fitted into an attachment screw hole provided in the exhaust pipe in order to attach the NOx sensor 1 to the exhaust pipe of the internal combustion engine.

  The gas sensor element 3 includes an element main body 31 and a protective layer 32. The element body 31 is formed in a long plate shape extending in the axial direction DA. And detection which detects the density | concentration of the specific gas (this embodiment NOx) contained in the to-be-measured gas (this embodiment exhaust gas of an internal combustion engine) to which the gas sensor element 3 is exposed to the front end side FE of the element main body 31 A portion 31a is formed. The protective layer 32 is made of porous alumina, and is disposed on the front end side FE of the element main body 31 so as to cover at least the detection unit 31a.

The holding unit 4 includes a ceramic holder 41, talc powder 42, a ceramic sleeve 43, and a packing 44.
The ceramic holder 41 is an alumina member formed in a substantially cylindrical shape that can be accommodated in the through hole 21 a of the main body 21 while being supported by the stepped portion 21 b of the main body 21. A through hole penetrating along the axial direction DA is formed in the ceramic holder 41, and the gas sensor element 3 is inserted into the through hole.

The talc powder 42 is filled in the through hole 21a of the main body 21 on the rear end side BE from the ceramic holder 41.
The ceramic sleeve 43 is an alumina member formed in a substantially cylindrical shape that can be accommodated in the through hole 21 a of the main body 21. A through hole penetrating along the axial direction DA is formed in the ceramic sleeve 43, and the gas sensor element 3 is inserted into the through hole. Thereby, the ceramic sleeve 43 is accommodated in the through hole 21 a of the main body 21 on the rear end side BE from the talc powder 42.

  The packing 44 is a member formed in an annular shape that can be accommodated in the through hole 21 a of the main body 21. The packing 44 is disposed between the ceramic sleeve 43 and the end portion 21 c on the rear end side BE in the main body portion 21. The end 21c of the main body 21 is crimped so as to press the ceramic sleeve 43 against the distal end FE via the packing 44. As a result, the talc powder 42 is compressed and filled, and the holding portion 4 has the front end side FE of the gas sensor element 3 projecting from the front end side FE of the ceramic holder 41 and the rear end side BE of the gas sensor element 3 is behind the metal shell 2. The gas sensor element 3 is held in a state protruding from the end side BE.

  In addition, the step part 21b of the main-body part 21 is arrange | positioned at the back end side BE from the screw part 22b. For this reason, the holding | maintenance part 4 is accommodated in the through-hole 21a of the main-body part 21 by BE rear end BE from the screw part 22b. Thereby, the holding | maintenance part 4 hold | maintains the gas sensor element 3 in the state by which the detection part 31a is arrange | positioned in the through-hole 21a by the front end side FE from the step part 21b.

  Further, an oxygen concentration detection cell 140 (described later) provided inside the detection unit 31a has a space 23 along the axial direction DA at the front end FE from the holding unit 4 in the through hole 21a of the main body unit 21. It arrange | positions to the range Rs1 to carry out. The length in the radial direction of the through hole 21a in the range Rs1 (that is, the inner diameter of the through hole 21a) is the length in the radial direction of the screw portion 22b of the main body 21 in the range Rs1 (that is, the thickness of the screw portion 22b). Bigger than).

  The protector 5 is a metal member formed in a cylindrical shape so as to cover the end portion of the front end side FE of the gas sensor element 3 protruding from the metal shell 2. A plurality of gas intake holes 5 a are formed in the protector 5. The protector 5 is joined to the outer periphery of the front end side FE of the metal shell 2 by welding.

  The protector 5 has a double structure and includes an outer protector 51 and an inner protector 52. A bottomed cylindrical outer protector 51 is disposed on the outer side, and a bottomed cylindrical inner protector 52 is disposed on the inner side.

  The outer cylinder 6 is a metal member formed in a cylindrical shape extending in the axial direction DA. The outer cylinder 6 is fixed in a state in which a portion of the main body 21 of the metal shell 2 located on the rear end side BE from the attachment portion 22 is fitted into the opening 6a at the end of the front end side FE.

  The plurality of lead wires 7 are provided corresponding to each of a plurality of electrode pads (not shown) formed on the rear end BE of the element main body 31, and drive-controls the element main body 31 and the gas sensor element 3. It is a conducting wire for electrically connecting the sensor control device 170. In FIG. 1, two lead wires 7 are shown. Further, the sensor control device 170 is not shown in FIG. 1 but shown in FIG.

The plurality of connection terminals 8 are provided corresponding to each of the plurality of lead wires 7 and attached to one end of the corresponding lead wire 7.
The separation unit 9 includes a separator 91 and a holding member 92. The separator 91 is a ceramic member formed in a cylindrical shape extending in the axial direction DA, and is disposed in the outer cylinder 6. Inside the separator 91, a space capable of accommodating the plurality of connection terminals 8 and a part of the rear end BE of the element main body 31 is formed. The separator 91 maintains the state in which the rear end BE of the plurality of connection terminals 8 protrudes from the rear end BE of the separator 91 and the plurality of connection terminals 8 are not in contact with each other. Accommodate. In addition, the separator 91 maintains a state in which the plurality of connection terminals 8 are in contact with the electrode pads of the element main body 31. In addition, a flange 91a is formed on the outer peripheral surface of the rear end BE of the separator 91 so as to extend outward along the radial direction.

  The holding member 92 includes a main body portion 92a and a bending portion 92b. The main body 92a is a metal member formed in a cylindrical shape extending in the axial direction DA. The curved portion 92b is a member that extends from the rear end BE of the main body portion 92a and is bent into a U shape. The holding member 92 is installed so as to be positioned between the outer cylinder 6 and the separator 91 on the front end side FE from the flange portion 91a. As a result, the main body portion 92a comes into contact with the inner peripheral surface of the outer cylinder 6, and the curved portion 92b comes into a state of pressing the flange portion 91a of the separator 91 toward the inside thereof. For this reason, the separator 91 is held in the outer cylinder 6 by the holding member 92.

  The grommet 10 is an elastic member made of fluororubber formed in a cylindrical shape extending in the axial direction DA. Grommet 10 is formed with a plurality of through holes penetrating along axial direction DA. The plurality of through holes are provided corresponding to each of the plurality of lead wires 7, and the corresponding lead wires 7 are inserted into the plurality of through holes, respectively.

  The grommet 10 is disposed inside the opening 6 b at the end of the rear end BE in the outer cylinder 6 and is crimped in the radial direction via the outer cylinder 6. Thereby, the opening part 6b of the edge part of the rear end side BE in the outer cylinder 6 is obstruct | occluded.

  As shown in FIG. 2, the element main body 31 of the gas sensor element 3 includes an insulating layer 113, a ceramic layer 114, an insulating layer 115, a ceramic layer 116, an insulating layer 117, a ceramic layer 118, an insulating layer 119, and an insulating layer 120 in order. It is configured by stacking. The insulating layers 113, 115, 117, 119, 120 are formed mainly of alumina.

  The element main body 31 includes a first measurement chamber 121 formed between the ceramic layer 114 and the ceramic layer 116. The element body 31 is exhausted from the outside to the inside of the first measurement chamber 121 via the diffusion resistor 122 disposed between the ceramic layer 114 and the ceramic layer 116 so as to be adjacent to the first measurement chamber 121. Introduce gas. The diffusion resistor 122 is made of a porous material such as alumina.

The element body 31 includes a first pumping cell 130. The first pumping cell 130 includes a solid electrolyte layer 131 and pumping electrodes 132 and 133.
The solid electrolyte layer 131 is formed mainly of zirconia having oxygen ion conductivity. A portion of the ceramic layer 114 in the region in contact with the first measurement chamber 121 is removed, and a solid electrolyte layer 131 is filled instead of the ceramic layer 114.

  The pumping electrodes 132 and 133 are formed mainly of platinum. The pumping electrode 132 is disposed on the surface that contacts the first measurement chamber 121 in the solid electrolyte layer 131. The pumping electrode 133 is disposed on the surface of the solid electrolyte layer 131 on the side opposite to the pumping electrode 132 with the solid electrolyte layer 131 interposed therebetween. The insulating layer 113 in the region where the pumping electrode 133 is disposed and the surrounding region is removed, and the porous body 134 is filled instead of the insulating layer 113. The porous body 134 allows gas (for example, oxygen) to enter and exit between the pumping electrode 133 and the outside.

The element main body 31 includes an oxygen concentration detection cell 140. The oxygen concentration detection cell 140 includes a solid electrolyte layer 141, a detection electrode 142, and a reference electrode 143.
The solid electrolyte layer 141 is formed mainly of zirconia having oxygen ion conductivity. A portion of the ceramic layer 116 in the region on the rear end side (that is, the right side in FIG. 2) from the solid electrolyte layer 131 is removed, and the solid electrolyte layer 141 is filled instead of the ceramic layer 116.

  The detection electrode 142 and the reference electrode 143 are formed mainly of platinum. The detection electrode 142 is disposed on the surface in contact with the first measurement chamber 121 in the solid electrolyte layer 141. The reference electrode 143 is disposed on the surface of the solid electrolyte layer 141 on the side opposite to the detection electrode 142 with the solid electrolyte layer 141 interposed therebetween.

  The element main body 31 includes a reference oxygen chamber 146. The reference oxygen chamber 146 is a through hole formed by removing the insulating layer 117 in the region where the reference electrode 143 is disposed and the surrounding region.

  The element body 31 includes a second measurement chamber 148. The second measurement chamber 148 is formed through the solid electrolyte layer 141 and the insulating layer 117 on the rear end side of the detection electrode 142 and the reference electrode 143. The element main body 31 introduces exhaust gas discharged from the first measurement chamber 121 into the second measurement chamber 148.

The element body 31 includes a second pumping cell 150. The second pumping cell 150 includes a solid electrolyte layer 151 and pumping electrodes 152 and 153.
The solid electrolyte layer 151 is formed mainly of zirconia having oxygen ion conductivity. The ceramic layer 118 in the region in contact with the reference oxygen chamber 146 and the second measurement chamber 148 and its surrounding region is removed, and a solid electrolyte layer 151 is filled instead of the ceramic layer 118.

  The pumping electrodes 152 and 153 are formed mainly of platinum. The pumping electrode 152 is disposed on the surface in contact with the second measurement chamber 148 in the solid electrolyte layer 151. The pumping electrode 153 is disposed on the surface of the solid electrolyte layer 151 on the side opposite to the reference electrode 143 across the reference oxygen chamber 146. A porous body 147 is disposed inside the reference oxygen chamber 146 so as to cover the pumping electrode 153.

  The element body 31 includes a heater 160. The heater 160 is a heating resistor that is formed mainly of platinum and generates heat when energized. The heater 160 is disposed between the insulating layer 119 and the insulating layer 120.

  The element main body 31 is connected to the sensor control device 170. The sensor control device 170 controls the element body 31 and calculates the NOx concentration in the exhaust gas based on the detection result of the element body 31.

The sensor control device 170 includes a control circuit 180 and a microcomputer 190 (hereinafter referred to as a microcomputer 190).
The control circuit 180 is an analog circuit arranged on the circuit board. The control circuit 180 includes an Ip1 drive circuit 181, a Vs detection circuit 182, a reference voltage comparison circuit 183, an Icp supply circuit 184, an Rpvs detection circuit 185, a Vp2 application circuit 186, an Ip2 detection circuit 187, and a heater drive circuit 188.

  The pumping electrode 132, the detection electrode 142, and the pumping electrode 152 are connected to a reference potential. The pumping electrode 133 is connected to the Ip1 drive circuit 181. The reference electrode 143 is connected to the Vs detection circuit 182, the Icp supply circuit 184, and the Rpvs detection circuit 185. The pumping electrode 153 is connected to the Vp2 application circuit 186 and the Ip2 detection circuit 187. The heater 160 is connected to the heater drive circuit 188.

  The Ip1 drive circuit 181 supplies the first pumping current Ip1 by applying the voltage Vp1 between the pumping electrode 132 and the pumping electrode 133, and detects the supplied first pumping current Ip1.

The Vs detection circuit 182 detects the voltage Vs between the detection electrode 142 and the reference electrode 143, and outputs the detected result to the reference voltage comparison circuit 183.
The reference voltage comparison circuit 183 compares the reference voltage (for example, 425 mV) with the output of the Vs detection circuit 182 (that is, the voltage Vs), and outputs the comparison result to the Ip1 drive circuit 181. The Ip1 drive circuit 181 controls the flow direction of the first pumping current Ip1 and the magnitude of the first pumping current Ip1 so that the voltage Vs becomes equal to the reference voltage, and also controls the oxygen concentration in the first measurement chamber 121. , And adjust to a predetermined value that does not decompose NOx.

  The Icp supply circuit 184 flows a weak current Icp between the detection electrode 142 and the reference electrode 143. As a result, oxygen is sent from the first measurement chamber 121 to the reference oxygen chamber 146 via the solid electrolyte layer 141, so that the reference oxygen chamber 146 is set to a predetermined oxygen concentration as a reference.

  The Rpvs detection circuit 185 instantaneously supplies a current Ir between the detection electrode 142 and the reference electrode 143 of the oxygen concentration detection cell 140, and between the detection electrode 142 and the reference electrode 143 generated by the supplied current Ir. The voltage Vr is detected. The microcomputer 190 calculates the internal resistance Rpvs of the oxygen concentration detection cell 140 based on the current Ir and the voltage Vr. Since the internal resistance Rpvs corresponds to the temperature of the oxygen concentration detection cell 140, the temperature of the oxygen concentration detection cell 140 can be calculated from the internal resistance Rpvs as is well known.

  The Vp2 application circuit 186 applies a constant voltage Vp2 (for example, 450 mV) between the pumping electrode 152 and the pumping electrode 153. Thereby, in the second measurement chamber 148, NOx is dissociated by the catalytic action of the pumping electrodes 152 and 153 constituting the second pumping cell 150. Oxygen ions obtained by this dissociation move through the solid electrolyte layer 151 between the pumping electrode 152 and the pumping electrode 153, whereby a second pumping current Ip2 flows. The Ip2 detection circuit 187 detects the second pumping current Ip2.

  The heater driving circuit 188 drives the heater 160 by applying a positive voltage for energizing the heater to one end of the heater 160 that is a heating resistor and applying a negative voltage for energizing the heater to the other end of the heater 160. .

The microcomputer 190 includes a CPU 191, a ROM 192, a RAM 193, and a signal input / output unit 194.
The CPU 191 executes a process for controlling the NOx sensor 1 based on a program stored in the ROM 192. The signal input / output unit 194 is connected to the Ip1 drive circuit 181, the Vs detection circuit 182, the Rpvs detection circuit 185, the Ip2 detection circuit 187, and the heater drive circuit 188.

  The CPU 191 calculates the NOx concentration in the exhaust gas and the temperature of the oxygen concentration detection cell 140 based on signals input from the circuits 181, 182, 185, 187 via the signal input / output unit 194. The CPU 191 controls the heater 160 by outputting a drive signal to the heater drive circuit 188 via the signal input / output unit 194.

Next, an example of the operation of the gas sensor element 3 will be described.
First, when the sensor control device 170 is activated, the sensor control device 170 supplies power to the heater 160. The heater 160 heats the first pumping cell 130, the oxygen concentration detection cell 140, and the second pumping cell 150 to the activation temperature.

  When each cell 130, 140, 150 is heated to the activation temperature, the sensor control device 170 causes the first pumping current Ip1 to flow through the first pumping cell 130. Accordingly, the first pumping cell 130 moves oxygen between the pumping electrode 132 and the pumping electrode 133 via the solid electrolyte layer 131, so that the oxygen contained in the exhaust gas flowing into the first measurement chamber 121 is transferred. Pump in and out.

  The sensor control device 170 supplies the first pumping current Ip1 that flows through the first pumping cell 130 so that the voltage Vs between the detection electrode 142 and the reference electrode 143 of the oxygen concentration detection cell 140 becomes a reference voltage (for example, 425 mV). Control. The voltage Vs of the oxygen concentration detection cell 140 is a value corresponding to the oxygen concentration in the detection electrode 142 with the oxygen concentration in the reference oxygen chamber 146 as a reference. By this control, the oxygen concentration in the first measurement chamber 121 is adjusted to the extent that NOx is not decomposed.

The exhaust gas whose oxygen concentration is adjusted in the first measurement chamber 121 further flows toward the second measurement chamber 148.
The sensor control device 170 applies a constant voltage Vp2 between the pumping electrode 152 and the pumping electrode 153 of the second pumping cell 150. This voltage is set to such a voltage that the NOx gas in the exhaust gas is decomposed into oxygen and nitrogen gas. Thereby, NOx in the exhaust gas is decomposed into nitrogen and oxygen. A second pumping current Ip2 flows through the second pumping cell 150 so that oxygen generated by the decomposition of NOx is pumped out of the second measurement chamber 148. Since there is a proportional relationship between the second pumping current Ip2 and the NOx concentration, the NOx concentration in the exhaust gas can be detected by detecting the current value of the second pumping current Ip2.

  Further, the sensor control device 170 uses the temperature of the oxygen concentration detection cell 140 calculated based on the internal resistance Rpvs to supply current to the heater 160 via the heater drive circuit 188 so that the gas sensor element 3 reaches a target temperature. The control which supplies is performed.

  The NOx sensor 1 configured as described above includes a gas sensor element 3, a metal main body 21, and a metal protector 5. The gas sensor element 3 is formed in a long shape and detects NOx contained in the exhaust gas. The main body 21 is formed in a cylindrical shape extending in the axial direction DA, and houses the gas sensor element 3 inside itself. The protector 5 is formed with a gas intake hole 5a through which exhaust gas passes, and is fixed to the main body 21 so as to cover the end of the front end side FE of the gas sensor element 3.

  The NOx sensor 1 includes a mounting portion 22 that is formed in a cylindrical shape extending in the axial direction DA and disposed so as to form an end-shaped annular space 23 extending in the axial direction DA between the NOx sensor 1 and the main body portion 21. The attachment portion 22 is disposed so as to cover at least a part of the outer peripheral surface of the main body portion 21 with a space 23 formed between the attachment portion 22 and the main body portion 21.

  The gas sensor element 3 includes an oxygen concentration detection cell 140 having an oxygen ion conductive solid electrolyte layer 141, a pair of detection electrodes 142 and a reference electrode 143 formed on the solid electrolyte layer 141, and an oxygen concentration detection cell 140. And a heater 160 for heating to a predetermined temperature. The oxygen concentration detection cell 140 is disposed inside the space 23.

  As described above, in the NOx sensor 1, the oxygen concentration detection cell 140 includes the oxygen concentration by the portion (hereinafter, the first laminated portion) in which the attachment portion 22, the space 23, and the metal main body portion 21 are laminated along the radial direction. The periphery of the detection cell 140 is covered.

  For this reason, one path in which the temperature change around the NOx sensor 1 affects the temperature of the oxygen concentration detection cell 140 is that the heat around the NOx sensor 1 is conducted through the first stacked portion and the oxygen concentration detection cell. This is a route to 140.

  In the first laminated portion, a space 23 is formed between the attachment portion 22 and the main body portion 21. That is, gas exists between the attachment portion 22 and the metal main body portion 21. And gas has a lower thermal conductivity than metal. For this reason, the NOx sensor 1 becomes difficult to conduct the heat around the NOx sensor 1 to the oxygen concentration detection cell 140 via the first stacked portion, and the temperature variation of the oxygen concentration detection cell 140 can be suppressed. And the temperature fluctuation of the gas sensor element 3 can be suppressed by suppressing the temperature fluctuation of the oxygen concentration detection cell 140.

  Further, in the NOx sensor 1, the gas sensor element 3 includes a first measurement chamber 121 and a first pumping cell 130, and the first pumping cell 130 is disposed on the distal side FE of the gas sensor element 3 with respect to the oxygen concentration detection cell 140. And disposed inside the main body 21.

  Exhaust gas is introduced into the first measurement chamber 121. The first pumping cell 130 includes an oxygen ion conductive solid electrolyte layer 131 and a pair of pumping electrodes 132 and 133 formed on the solid electrolyte layer 131, and the first pumping cell 130 is connected between the pair of pumping electrodes 132 and 133. By flowing one pumping current Ip1, oxygen in the exhaust gas introduced into the first measurement chamber 121 is pumped out or pumped in. The oxygen concentration detection cell 140 includes a solid electrolyte layer 141, a detection electrode 142 and a reference electrode 143 formed on the solid electrolyte layer 141, and the detection electrode 142 faces the first measurement chamber 121. An electromotive force corresponding to the difference in oxygen concentration between the detection electrode 142 and the reference electrode 143 is generated.

  As described above, in the NOx sensor 1, the first pumping cell 130 is disposed inside the main body 21, and thus the first pumping cell 130 is covered with the main body 21 in the radial direction. For this reason, the NOx sensor 1 can suppress the heat around the NOx sensor 1 from reaching the first pumping cell 130 by the main body 21. Thereby, the NOx sensor 1 can further suppress the temperature fluctuation of the gas sensor element 3.

The NOx sensor 1 corresponds to a gas sensor, the gas sensor element 3 corresponds to a detection element, the main body 21 corresponds to a housing member, and the gas intake hole 5a corresponds to a vent hole.
The mounting portion 22 corresponds to a space forming member, the space 23 corresponds to a ring-shaped end space, the solid electrolyte layer 141 corresponds to a solid electrolyte body, and the detection electrode 142 and the reference electrode 143 correspond to a pair of electrodes. The oxygen concentration detection cell 140 corresponds to a detection cell.

The exhaust gas corresponds to the gas to be measured, and NOx corresponds to the specific gas.
The first measurement chamber 121 corresponds to a measurement chamber, the solid electrolyte layer 131 corresponds to a first solid electrolyte body, the pumping electrodes 132 and 133 correspond to pumping electrodes, and the first pumping cell 130 corresponds to a pumping cell. The solid electrolyte layer 141 corresponds to a second solid electrolyte body.

(Second Embodiment)
Hereinafter, a second embodiment of the present disclosure will be described with reference to the drawings. In the second embodiment, parts different from the first embodiment will be described. Common components are denoted by the same reference numerals.

The NOx sensor 1 of the second embodiment is different from the first embodiment in that the configuration of the metal shell 2 is changed.
Specifically, as shown in FIG. 3, the metal shell 2 includes a main body portion 21, an attachment portion 22, and a space forming member 25.

The space forming member 25 is a metal member formed in a cylindrical shape extending in the axial direction DA. The space forming member 25 includes a cylindrical portion 25a and an enlarged diameter portion 25b.
The cylindrical portion 25a is formed in a cylindrical shape so that its diameter is smaller than the diameter of the through hole 21a in the distal end side FE from the stepped portion 21b.

  The enlarged diameter portion 25b is formed in a shape that extends from the end portion of the rear end side BE in the cylindrical portion 25a and increases in diameter toward the rear end side BE. The diameter-enlarged portion 25b is formed so that the diameter of the opening on the rear end side BE is smaller than the diameter of the through hole 21a on the rear end side BE than the stepped portion 21b.

  The space forming member 25 is held in the through hole 21a when the enlarged diameter portion 25b is sandwiched between the stepped portion 21b and the ceramic holder 41. Thereby, the cylindrical part 25a is arrange | positioned in the through-hole 21a in the front end side FE from the step part 21b. A cylindrical space 26 extending in the axial direction DA is formed between the outer peripheral surface of the cylindrical portion 25a and the inner peripheral surface of the through hole 21a.

  The oxygen concentration detection cell 140 provided inside the detection unit 31a is within the range Rs2 in which the space 26 exists along the axial direction DA at the front end side FE from the holding unit 4 in the through hole 21a of the main body unit 21. Be placed. The radial length of the cylindrical portion 25a in the range Rs2 (that is, the inner diameter of the cylindrical portion 25a) is the radial length of the screw portion 22b of the main body portion 21 in the range Rs2 (that is, the thickness of the screw portion 22b). Bigger than).

  The NOx sensor 1 configured in this way is formed in a cylindrical shape extending in the axial direction DA, and is arranged so that an annular space 26 extending in the axial direction DA is formed between the body portion 21 and the space forming member. 25. The space forming member 25 is disposed inside the main body 21 so as to cover at least a part of the inner peripheral surface of the main body 21 in a state where the space 26 is formed between the space forming member 25 and the main body 21.

  The oxygen concentration detection cell 140 is arranged such that the space 26 is positioned on a straight line (hereinafter referred to as a radial straight line) passing through the oxygen concentration detection cell 140 along a direction perpendicular to the axial direction DA (hereinafter referred to as a radial direction). Be placed.

  As described above, in the NOx sensor 1, the oxygen concentration detection cell 140 includes a portion in which the metal space forming member 25, the space 26, and the metal main body portion 21 are stacked along the radial direction (hereinafter referred to as a second stacked portion). ) Covers the periphery of the oxygen concentration detection cell 140.

  For this reason, one path in which the temperature change around the NOx sensor 1 affects the temperature of the oxygen concentration detection cell 140 is that the heat around the NOx sensor 1 is conducted through the second stacked portion and the oxygen concentration detection cell. This is a route to 140.

In the second stacked portion, a space 26 is formed between the space forming member 25 and the main body portion 21. That is, gas exists between the space forming member 25 and the metal main body 21. And gas has a lower thermal conductivity than metal. For this reason, the NOx sensor 1 becomes difficult to conduct the heat around the NOx sensor 1 to the oxygen concentration detection cell 140 through the second stacked portion, and the temperature variation of the oxygen concentration detection cell 140 can be suppressed.
The space 26 corresponds to an annular space.

As mentioned above, although one embodiment of this indication was described, this indication is not limited to the above-mentioned embodiment, and can carry out various modifications.
For example, in the above-described embodiment, the space 23 formed by the inner peripheral surface of the attachment portion 22 and the outer peripheral surface of the main body portion 21 is a ring-shaped end space, but may be an annular space.
In the above embodiment, the NOx sensor for detecting the NOx concentration in the exhaust gas has been described as the gas sensor for detecting the concentration of the specific gas contained in the gas to be measured. However, the gas sensor of the present disclosure is limited to the NOx sensor. There is nothing. The gas sensor of the present disclosure may be a gas sensor having a cell to which a detection current is supplied in order to detect internal resistance, and examples thereof include a full-range air-fuel ratio sensor.
Further, in the above embodiment, the current is supplied between the detection electrode and the reference electrode of the oxygen concentration detection cell, and the internal resistance Rpvs of the oxygen concentration detection cell is calculated. And the internal resistance may be calculated from the current generated by the supplied voltage. Further, when there is another physical quantity correlated with the internal resistance of the detection element, the heater may be driven based on the physical quantity instead of the internal resistance of the detection element.

  In the above embodiment, the oxygen concentration detection cell 140 is arranged in the range Rs1 or Rs2. As described above, in order to arrange the oxygen concentration detection cell 140 in the ranges Rs1 and Rs2, the arrangement of the gas sensor elements 3 in the main body 21 may be changed, or the arrangement of the gas sensor elements 3 may be changed. Alternatively, the arrangement of the oxygen concentration detection cells 140 in the gas sensor element 3 may be changed.

  The functions of one component in each of the above embodiments may be shared by a plurality of components, or the functions of a plurality of components may be exhibited by one component. Moreover, you may abbreviate | omit a part of structure of each said embodiment. In addition, at least a part of the configuration of each of the above embodiments may be added to or replaced with the configuration of the other above embodiments. In addition, all the aspects included in the technical idea specified from the wording described in the claims are embodiments of the present disclosure.

  DESCRIPTION OF SYMBOLS 1 ... NOx sensor, 2 ... Main metal fitting, 3 ... Gas sensor element, 5 ... Protector, 5a ... Gas intake hole, 21 ... Main-body part, 22 ... Mounting part, 23, 26 ... Space, 25 ... Space formation member, 140 ... Oxygen concentration detection cell, 141 ... solid electrolyte layer, 142 ... detection electrode, 143 ... reference electrode, 160 ... heater

Claims (4)

A detection element that is formed in a long shape and detects a specific gas contained in the gas to be measured;
A metal housing member that is formed in a cylindrical shape extending in the axial direction and houses the detection element inside itself;
A gas sensor comprising a metal protector formed with a vent hole through which the gas to be measured passes and fixed to the housing member so as to cover a tip of the detection element;
A space forming member that is formed in a cylindrical shape extending in the axial direction, and is disposed so that an annular or end annular space extending in the axial direction is formed between the housing member and the housing member;
The detection element includes a detection cell having an oxygen ion conductive solid electrolyte body and a pair of electrodes formed on the solid electrolyte body;
A heater for heating the detection cell to a predetermined temperature;
The detection cell is a gas sensor arranged inside the space. The gas sensor according to claim 1,
The said space formation member is a gas sensor arrange | positioned so that at least one part of the outer peripheral surface of the said accommodation member may be covered in the state in which the said space was formed between the said accommodation members. The gas sensor according to claim 1,
The said space formation member is a gas sensor arrange | positioned inside the said accommodation member so that at least one part of the internal peripheral surface of the said accommodation member may be covered in the state in which the said space was formed between the said accommodation members. The gas sensor according to any one of claims 1 to 3,
The detection element is
A measurement chamber into which the gas to be measured is introduced;
An oxygen ion conductive first solid electrolyte body and a pair of pumping electrodes formed on the first solid electrolyte body, and a flow of a pumping current between the pair of pumping electrodes, thereby allowing the measurement chamber to A pumping cell for pumping or pumping oxygen in the measurement gas introduced into
An oxygen ion conductive second solid electrolyte body, and a detection electrode and a reference electrode formed on the second solid electrolyte body, wherein the detection electrode is disposed facing the measurement chamber, and the detection electrode And an oxygen concentration detection cell that generates an electromotive force according to a difference in oxygen concentration between the reference electrode and the reference electrode,
The oxygen concentration detection cell is the detection cell;
The said pumping cell is a gas sensor arrange | positioned inside the said accommodating member while being arrange | positioned rather than the said oxygen concentration detection cell at the front end side of the said detection element.

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