GAS SENSOR

Abstract

Gas sensor (10), comprising: a sensor element (12); a plurality of element contact points (200a to 200e) formed on a rear end section of the sensor element (12); and a plurality of contact elements (20a to 20e) designed to hold the rear end section of the sensor element (12) and to electrically connect it to the plurality of element contact points (200a to 200e), wherein at least one contact element of the plurality of contact elements (20a to 20e) has a smaller width (Wt) than other contact elements of the plurality of contact elements (20a to 20e) and wherein the smaller width (Wt) of the at least one contact element (20e) is 0.121 times to 0.273 times the width (W) of the sensor element (12).

Description

Field of invention:

[0001] The present invention relates to a gas sensor. Description of the state of the art:

[0002] The technology disclosed in the Japanese patent with publication number 2001-141689 has the task of providing a gas sensor that is less prone to short circuits of connecting wires, metal connection elements, etc., and that provides a stable sensor output.

[0003] To solve the problem, the technique disclosed in the Japanese patent with publication number 2001-141689 comprises first guide sections (531) formed at the front ends of individual first through holes in an elastic insulating element (5) and second guide sections (331) formed at the proximal ends of second through holes in an insulator (3), wherein the first guide sections (531) and the second guide sections (331) restrict the movement of connecting wires (161) and metal terminals (49).

[0004] German patent application DE 10 2017 211 498 A1 describes a gas sensor comprising a scanning element that includes an electrode connection surface, metal connections, and a separator having insertion holes in which the metal connections are held. The metal connections comprise the main bodies and elastic sections that are integrally connected to the main bodies and elastically connected to the electrode connection surfaces at predetermined contact points. The main bodies comprise the limiting sections of the front end face and the limiting sections of the rear end face, which come into contact with the wall surfaces of the insertion holes when the main bodies begin to move in a direction intersecting the direction of an axial line O, and which limit the movement.The contact points are located between the confining sections of the front end face and the confining sections of the rear end face in the direction of the axial line. The confining sections of the front end face and the confining sections of the rear end face are connected to each other in a state in which the flat plate sections, which form part of the metal connections, are positioned between them. SUMMARY OF THE INVENTION

[0005] According to the gas sensor described in the Japanese patent publication number 2001-141689, a plurality of contact elements (female contacts) that provide conductivity in direct contact with the sensor element have the same widths. The distance between adjacent contact elements thus decreases as the width of the contact elements increases, leading to an increased probability of a short circuit.

[0006] Furthermore, in gas sensors for use in vehicles, a greater width of a contact element increases the area of ​​the element contact point that is paired with the contact element, thus increasing the amount of material used to form the element contact point, such as Pt (platinum), which leads to increased costs.

[0007] The present invention was made taking these problems into consideration, and one object of the present invention is to provide a gas sensor that can solve the aforementioned problems, i.e., that can prevent the occurrence of a short circuit between adjacent contact elements and can reduce the amount of material used to form element contact points.

[0008] A gas sensor according to one aspect of the present invention comprises: a sensor element; a plurality of element contact points formed on a rear end section of the sensor element; and a plurality of contact elements designed to hold the rear end section of the sensor element and to electrically connect it to the plurality of element contact points, wherein at least one contact element of the plurality of contact elements has a smaller width than the other contact elements of the plurality of contact elements, and wherein the smaller width of the at least one contact element is 0.121 to 0.273 times the width of the sensor element.

[0009] According to the present invention, the occurrence of a short circuit between adjacent contact elements can be prevented and the amount of material used to form the element contact points can be reduced.

[0010] The foregoing and further tasks, features and advantages of the present invention will become clearer from the following description when it is considered together with the accompanying drawings, in which a preferred embodiment of the present invention is shown by means of an illustrative example. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a cross-section of a gas sensor according to one embodiment; Fig. Figure 2 is a schematic cross-section that schematically shows an exemplary structure of a sensor element; Fig. 3 is the cross-section along line III-III in the Fig. 1; and Fig. Table 1, which shows the results of the evaluation of examples 1 to 7 and comparison examples 1 to 3, is shown in Table 4. DESCRIPTION OF PREFERRED EXECUTION FORMS

[0011] The gas sensor according to the present invention is described in detail below in connection with preferred embodiments, with reference to the accompanying drawings.

[0012] As it is in the Fig. As shown in Figure 1, a gas sensor 10 according to this embodiment comprises a sensor element 12. The sensor element 12 has an elongated, rectangular parallelepiped shape. The longitudinal direction of the sensor element 12 (the left-right direction in the Fig. 2) is defined as the front-back direction and the thickness direction of the sensor element 12 (the top-bottom direction in the Fig. 2) is defined as the up-down direction. The width direction of the sensor element 12 (a direction perpendicular to the front-back and up-down directions) is defined as the left-right direction.

[0013] As it is in the Fig. As shown in Figure 1, the gas sensor 10 comprises the sensor element 12, a protective cover 14 for protecting the front end of the sensor element 12, and a sensor assembly 20 which includes a ceramic housing 16. The ceramic housing 16 holds a rear end section of the sensor element 12 and acts as a connector 24 by means of terminal elements 18 that are electrically connected to the sensor element 12 attached to it.

[0014] As shown in the drawing, the gas sensor 10 is attached, for example, to a line 26, such as an exhaust line of a vehicle, and is used to measure concentrations of specific gases, such as NOx, O2, etc., which are contained in the exhaust gas, which is a gas to be measured (also referred to as the measuring gas).

[0015] The protective cover 14 comprises a tubular inner protective cover 14a with a base, which covers the front end of the sensor element 12, and a tubular outer protective cover 14b with a base, which covers the inner protective cover 14a. A plurality of holes are formed in the inner protective cover 14a and the outer protective cover 14b, through which a gas to be measured can flow into the interior of the protective cover 14. A sensor element chamber 22 is formed as a space enclosed by the inner protective cover 14a, and the front end of the sensor element 12 is arranged within the sensor element chamber 22.

[0016] The sensor assembly 20 comprises an element sealing body 30 for sealing and fixing the sensor element 12, a nut 32 attached to the element sealing body 30, an outer tube 34, and the connector 24. The connector 24 is in contact with and electrically connected to electrodes (not shown) formed on the surfaces (upper and lower surfaces) of the rear end of the sensor element 12.

[0017] The element sealing body 30 comprises a tubular main fitting 40 and a tubular inner tube 42, which is welded to and coaxially attached to the main fitting 40. The element sealing body 30 includes ceramic holders 44a to 44c, green press-molded (powder-pressed) bodies 46a, 46b, and a metal ring 48, which are encapsulated in an internal through-hole within the main fitting 40 and the inner tube 42. The sensor element 12 is located on the central axis of the element sealing body 30 and penetrates the element sealing body 30 in a front-to-back direction. The inner tube 42 has a reduced-diameter section 42a and a reduced-diameter section 42b. The reduced-diameter section 42a presses the green press-molded body 46b in the direction of the central axis of the inner tube 42.The reduced-diameter section 42b pushes the ceramic holders 44a to 44c and the green molded parts 46a, 46b forward through the metal ring 48. The compressive forces from the reduced-diameter sections 42a, 42b press the green molded parts 46a, 46b between the main molded part 40 and the inner tube 42 and the sensor element 12. The green molded parts 46a, 46b thus provide a seal between the sensor element chamber 28 in the protective cover 14 and a space 50 in the outer tube 34 and secure the sensor element 12.

[0018] The nut 32 is coaxially fixed to the main component 40 and has an external threaded section formed on its outer circumferential surface. The external threaded section of the nut 32 is inserted into a fixing element 52, which is welded to the line 26 and has an internal thread formed on its inner circumferential surface. The gas sensor 10 is thus fixed to the line 26 such that the front end of the sensor element 12 and the protective cover 14 protrude into the line 26.

[0019] The outer tube 34 encloses the inner tube 42, the sensor element 12, and the connector 24. A plurality of connecting wires 54, which are connected to the connector 24, extend from the rear end of the outer tube. The connecting wires 54 are electrically connected to electrodes of the sensor element 12 via the connector 24 (as described later). The gap between the outer tube 34 and the connecting wires 54 is sealed by an elastic insulating element 56, which is formed from a sealing disc or the like. The space 50 in the outer tube 34 is filled with a reference gas (air in this embodiment). The rear end of the sensor element 12 is located within this space 50.

[0020] On the other hand, as it is in the Fig. As shown in Figure 2, the sensor element 12 is a device formed from a laminate in which, for example, six layers are laminated in the following order from the bottom of the drawing. The six layers comprise a first substrate layer 60, a second substrate layer 62, a third substrate layer 64, a first solid electrolyte layer 66, a spacer layer 68, and a second solid electrolyte layer 70. Each of the six layers consists of an oxygen-ion-conducting solid electrolyte layer, such as zirconium oxide (ZrO2). Furthermore, the solid electrolyte forming the six layers has a high density and is gas-tight. The sensor element 12 is manufactured, for example, by applying a predefined processing method and printing circuit structures onto ceramic green layers corresponding to the respective layers, laminating these layers together, and then integrating the layers by sintering.

[0021] A plurality of diffusion control sections and a plurality of internal chambers, which will be described next, are located between the lower surface of the second solid electrolyte layer 70 and the upper surface of the first solid electrolyte layer 66 on the side of one end of the sensor element 12 (on the left side in the Fig. 2) formed. That is, a gas inlet 80, a first diffusion control section 82, a buffer chamber 84, a second diffusion control section 86, a first inner cavity 88, a third diffusion control section 90, a second inner cavity 92, a fourth diffusion control section 94 and a third inner cavity 96 are formed in such a way that they are connected and adjacent in this order.

[0022] The gas inlet 80, the buffer chamber 84, the first inner cavity 88, the second inner cavity 92, and the third inner cavity 96 are formed by hollowing out the spacer layer 68. Each of the buffer chamber 84 and the others is a space within the sensor element 12, divided by the lower surface of the second solid electrolyte layer 70 at the top, the upper surface of the first solid electrolyte layer 66 at the bottom, and the side surfaces of the spacer layer 68 on the sides.

[0023] The first diffusion control section 82, the second diffusion control section 86, and the third diffusion control section 90 are each configured as two horizontally elongated slots (the longitudinal direction of their openings is perpendicular to the drawing sheet). The fourth diffusion control section 94 is configured as a horizontally elongated slot, which forms a gap below the lower surface of the second solid electrolyte layer 70 (the longitudinal direction of its openings is perpendicular to the drawing sheet). The section from the gas inlet 80 to the third inner cavity 96 is also referred to as the measuring gas passage.

[0024] A reference gas introduction chamber 98 is provided in a position located further away from the aforementioned end than the measurement gas passage. The reference gas introduction chamber 98 is formed between the upper surface of the third substrate layer 64 and the lower surface of the spacer layer 68 and is divided laterally by a side surface of the first solid electrolyte layer 66. A reference gas for measuring the NOx concentration, such as air (the atmosphere within chamber 50 in the Fig. 1), is introduced into the reference gas introduction chamber 98.

[0025] An atmosphere introduction layer 100 is a layer made of ceramic, such as porous aluminum oxide, etc., and is exposed in the reference gas introduction chamber 98. The reference gas is introduced into the atmosphere introduction layer 100 through the reference gas introduction chamber 98. The atmosphere introduction layer 100 is configured to cover a reference electrode 102. The atmosphere introduction layer 100 introduces the reference gas into the reference gas introduction chamber 98 to the reference electrode 102 while a given diffusion resistance is exerted on the reference gas. The atmosphere introduction layer 100 is configured such that it is exposed to the interior of the reference gas introduction chamber 98 only on a rear end face of the sensor element 12, which is located behind the reference electrode 102 (on the right side in the Fig. 2) In other words, the reference gas introduction chamber 98 is not located in a position directly above the reference electrode 102. However, the reference electrode 102 can be located directly below the reference gas introduction chamber 98 in the Fig. 2 be trained.

[0026] The reference electrode 102 is an electrode formed between the upper surface of the third substrate layer 64 and the first solid electrolyte layer 66, and, as mentioned above, the atmosphere introduction layer 100, which is connected to the reference gas introduction chamber 98, is provided around it. The reference electrode 102 is formed directly on the upper surface of the third substrate layer 64 and is covered by the atmosphere introduction layer 100, except in sections that contact the upper surface of the third substrate layer 64. Furthermore, as will be described later, the oxygen concentrations (oxygen partial pressures) in the first inner cavity 88, the second inner cavity 92, and the third inner cavity 96 can be measured using the reference electrode 102. The reference electrode 102 is configured as a porous cermet electrode (e.g., a cermet electrode made of Pt and ZrO2).

[0027] In the measuring gas passage, the gas inlet 80 to the outside chamber is open, and the measuring gas is drawn into the sensor element 12 from the outside chamber through the gas inlet 80. The first diffusion control section 82 is a section that provides a defined diffusion resistance for the measuring gas drawn in through the gas inlet 80. The buffer chamber 84 is a chamber that directs the measuring gas introduced by the first diffusion control section 82 to the second diffusion control section 86.

[0028] The second diffusion control section 86 is a section that provides a given diffusion resistance for the sample gas, which is directed from the buffer chamber 84 into the first inner cavity 88. A case is described below in which the sample gas is introduced into the first inner cavity 88 from the outside of the sensor element 12 by a pressure fluctuation of the sample gas in the outer chamber. The pressure fluctuation can be caused by exhaust pressure pulsations if the sample gas is motor vehicle exhaust. The sample gas, which has been rapidly drawn into the sensor element 12 from the gas inlet 80 due to the pressure fluctuation, is not introduced directly into the first inner cavity 88. A concentration variation of the sample gas is canceled out by the first diffusion control section 82, the buffer chamber 84, and the second diffusion control section 86, and then the sample gas is introduced into the first inner cavity 88.

[0029] Accordingly, the concentration variation of the measuring gas introduced into the first inner cavity 88 has become almost negligible. The first inner cavity 88 is a chamber that adjusts the oxygen partial pressure in the measuring gas introduced through the second diffusion adjustment section 86. The oxygen partial pressure is adjusted by the operation of a main pump cell 110, which is described next.

[0030] The main pump cell 110 is an electrochemical pump cell consisting of an inner pump electrode 112, an outer pump electrode 114, and the second solid electrolyte layer 70. The inner pump electrode 112 is provided on the inner surfaces of the first inner cavity 88. The outer pump electrode 114 is formed on a section of the upper surface of the second solid electrolyte layer 70, corresponding to the inner pump electrode 112, such that it faces the outer space (the sensor element chamber 28 in the Fig. 1) is exposed. The second solid electrolyte layer 70 is arranged between the inner pump electrode 112 and the outer pump electrode 114.

[0031] The inner pump electrode 112 is formed on the upper and lower solid electrolyte layers (the second solid electrolyte layer 70 and the first solid electrolyte layer 66) that divide the first inner cavity 88, and on the spacer layer 68, which forms the side walls. In particular, an upper electrode section 112a of the inner pump electrode 112 is formed on the lower surface of the second solid electrolyte layer 70, which forms the upper surface of the first inner cavity 88. A lower electrode section 112b is formed directly on the upper surface of the first solid electrolyte layer 66, which forms the lower surface of the first inner cavity 88.Side electrode sections (not shown) are formed on the side wall surfaces (inner surfaces) of the spacer layer 68, which form both side walls of the first inner cavity 88, such that the side electrode sections connect the upper electrode section 112a and the lower electrode section 112b. That is, the inner pump electrode 112 is designed as a tunnel-shaped structure.

[0032] The inner pump electrode 112 and the outer pump electrode 114 are designed as porous cermet electrodes (e.g., cermet electrodes made of Pt and ZrO2 containing 1% Au). The inner pump electrode 112, which contacts the sample gas, is made of a material with a reduced reduction capacity for NOx components in the sample gas.

[0033] In the main pump cell 110, a desired pump voltage Vp0 is applied to the inner pump electrode 112 and the outer pump electrode 114, causing a pump current Ip0 to flow in the positive or negative direction between the inner pump electrode 112 and the outer pump electrode 114. This allows the main pump cell 110 to pump the oxygen in the first inner cavity 88 out to the outer cavity or to pump the oxygen in the outer cavity into the first inner cavity 88.

[0034] The sensor element 12 further comprises an oxygen partial pressure detection sensor cell for the main pump control 120 for detecting the oxygen concentration (oxygen partial pressure) in the atmosphere in the first inner cavity 88. This sensor cell 120 is an electrochemical sensor cell which includes the inner pump electrode 112, the second solid electrolyte layer 70, the spacer layer 68, the first solid electrolyte layer 66 and the reference electrode 102.

[0035] The oxygen concentration (oxygen partial pressure) in the first inner cavity 88 is known by measuring an electromotive force V0 in the oxygen partial pressure sensing sensor cell for the main pump control 120. Furthermore, the pump current Ip0 is adjusted by regulating the pump voltage Vp0 of a variable power supply 122 such that the electromotive force V0 is kept constant. The oxygen concentration in the first inner cavity 88 can therefore be maintained at a specific constant value.

[0036] The third diffusion control section 90 is a section that provides a given diffusion resistance for the measuring gas, whose oxygen concentration (oxygen partial pressure) has been set by the operation of the main pump cell 110 in the first inner cavity 88, and that directs the gas to be measured into the second inner cavity 92.

[0037] The second inner cavity 92 is provided as a chamber in which the measuring gas, which has undergone oxygen concentration adjustment (oxygen partial pressure) in the first inner cavity 88 and is then introduced into the chamber through the third diffusion adjustment section 90, undergoes a further oxygen partial pressure adjustment by an auxiliary pump cell 124. The oxygen concentration in the second inner cavity 92 can therefore be kept very precisely constant, enabling the gas sensor 10 to perform a very accurate NOx concentration measurement.

[0038] The auxiliary pump cell 124 is an electrochemical auxiliary pump cell comprising an auxiliary pump electrode 126, which is provided on the inner surface of the second inner cavity 92, the outer pump electrode 114, and the second solid electrolyte layer 70. A suitable electrode outside the sensor element 12 is sufficient as the outer pump electrode 114.

[0039] The auxiliary pump electrode 126 has a tunnel-shaped structure similar to that of the inner pump electrode 112, which is provided in the first inner cavity 88, and is arranged in the second inner cavity 92. That is, an upper electrode section 126a is formed on the second solid electrolyte layer 70, which forms the upper surface of the second inner cavity 92. Furthermore, a lower electrode section 126b is formed directly on the upper surface of the first solid electrolyte layer 66, which forms the lower surface of the second inner cavity 92. Additionally, side electrode sections (not shown), which connect the upper electrode section 126a and the lower electrode section 126b, are formed on both wall surfaces of the spacer layer 68, which forms the side walls of the second inner cavity 92, thereby forming a tunnel-shaped structure.Like the inner pump electrode 112, the auxiliary pump electrode 126 is also made of a material with a reduced reduction capacity for NOx components in the measuring gas.

[0040] In the auxiliary pump cell 124, a desired voltage Vp1 is applied to the auxiliary pump electrode 126 and the outer pump electrode 114, so that oxygen in the atmosphere is pumped out of the second inner cavity 92 to the outside space or oxygen is pumped into the second inner cavity 92 from the outside space.

[0041] Furthermore, in order to adjust the oxygen partial pressure in the atmosphere in the second inner cavity 92, an electrochemical sensor cell, i.e., an oxygen partial pressure detection sensor cell for auxiliary pump control 130, is formed from the auxiliary pump electrode 126, the reference electrode 102, the second solid electrolyte layer 70, the spacer layer 68 and the first solid electrolyte layer 66.

[0042] The auxiliary pump cell 124 performs pumping with a variable power supply 132, which is voltage-controlled based on an electromotive force V1 detected by the oxygen partial pressure sensing sensor cell for auxiliary pump control 130. Consequently, the oxygen partial pressure in the atmosphere in the second inner cavity 92 can be set to such a low partial pressure that the NOx measurement is not significantly affected.

[0043] Furthermore, a pump current Ip1 is used to control the electromotive force V0 of the oxygen partial pressure sensing sensor cell for the main pump control 120. Specifically, the pump current Ip1 is fed into the oxygen partial pressure sensing sensor cell for the main pump control 120 as a control signal, thus controlling the electromotive force V0. This provides control such that the gradient of the oxygen partial pressure in the measuring gas, which is introduced from the third diffusion control section 90 into the second inner cavity 92, can always be kept constant. When the gas sensor is used as a NOx sensor, the main pump cell 110 and the auxiliary pump cell 124 can operate in such a way that the oxygen concentration in the second inner cavity 92 is maintained at a constant value of approximately 0.001 ppm.

[0044] The fourth diffusion control section 94 is a section that provides a given diffusion resistance for the sample gas, whose oxygen concentration (oxygen partial pressure) in the inner cavity 92 has been set by the operation of the auxiliary pump cell 124, and that directs the sample gas into the third inner cavity 96. The fourth diffusion control section 94 serves to limit the amount of NOx flowing into the third inner cavity 96.

[0045] The sample gas, whose oxygen concentration (oxygen partial pressure) has been set in the second inner cavity 92, is introduced through the fourth diffusion control section 94 into the third inner cavity 96. That is, the third inner cavity 96 is provided as a chamber in which the sample gas introduced therein is subjected to a method for measuring the concentration of nitrogen oxides (NOx) in the sample gas. The measurement of the NOx concentration is primarily carried out in the third inner cavity 96 by operating a measuring pump cell 140.

[0046] The measuring pump cell 140 measures the NOx concentration in the sample gas in the third inner cavity 96. The measuring pump cell 140 is an electrochemical pump cell consisting of a measuring electrode 134, which is formed directly on the upper surface of the first solid electrolyte layer 66 facing the third inner cavity 96, the outer pump electrode 114, the second solid electrolyte layer 70, the spacer layer 68, and the first solid electrolyte layer 66. The measuring electrode 134 is a porous cermet electrode. The measuring electrode 134 also acts as an NOx reduction catalyst, reducing the NOx present in the atmosphere within the third inner cavity 96.

[0047] In the measuring pump cell 140, the oxygen produced by the decomposition of nitrogen oxide in the atmosphere around the measuring electrode 134 is pumped out, and the amount of oxygen produced can be recorded as pump current Ip2.

[0048] Furthermore, an electrochemical sensor cell, i.e., an oxygen partial pressure detection sensor cell for measuring pump control 142, is formed around the measuring electrode 134 to detect the oxygen partial pressure. This cell consists of the first solid electrolyte layer 66, the measuring electrode 134, and the reference electrode 102. A variable power supply 144 is controlled based on an electromotive force V2 detected by the oxygen partial pressure detection sensor cell for measuring pump control 142.

[0049] The sample gas, which is directed into the second inner cavity 92, reaches the measuring electrode 134 in the third inner cavity 96 through the fourth diffusion control section 94 in a state where the oxygen partial pressure is set. The nitrogen oxide in the sample gas around the measuring electrode 134 is reduced, so that oxygen is produced (2NO → N2 + O2). The produced oxygen is then pumped through the measuring pump cell 140. During this process, a voltage Vp2 of the variable power supply 144 is controlled such that the electromotive force V2, which is detected by the oxygen partial pressure sensing sensor cell for the measuring pump control 142, is kept constant. The amount of oxygen produced around the measuring electrode 134 is proportional to the concentration of nitrogen oxide in the sample gas. Accordingly, the nitrogen oxide concentration in the sample gas is calculated using the pump current Ip2 of the measuring pump cell 140.

[0050] Furthermore, an electrochemical sensor cell 146 is formed from the second solid electrolyte layer 70, the spacer layer 68, the first solid electrolyte layer 66, the third substrate layer 64, the outer pump electrode 114, and the reference electrode 102. The oxygen partial pressure in the measuring gas outside the sensor can be detected by an electromotive force Vref, which is generated by the sensor cell 146.

[0051] Furthermore, an electrochemical reference gas adjustment pump cell 150 is formed from the second solid electrolyte layer 70, the spacer layer 68, the first solid electrolyte layer 66, the third substrate layer 64, the outer pump electrode 114, and the reference electrode 102. The reference gas adjustment pump cell 150 performs a pumping action when a voltage Vp3, applied by a variable power supply 152 connected between the outer pump electrode 114 and the reference electrode 102, causes a control current Ip3 to flow. The reference gas adjustment pump cell 150 consequently pumps oxygen into a chamber (atmosphere introduction layer 100) around the reference electrode 102 from another chamber (the sensor element chamber 28 in the Fig. 1) around the outer pump electrode 114. The voltage Vp3 of the variable power supply 152 is specified as such a direct (DC) voltage that the control current Ip3 has a given value (a direct current with a constant value).

[0052] In the gas sensor 10, which is constructed as described above, the main pump cell 110 and the auxiliary pump cell 124 are operated such that the measuring pump cell 140 is supplied with the measuring gas in which the oxygen partial pressure is always maintained at a constant low value. This constant low value of the oxygen partial pressure represents a value that does not significantly influence the NOx measurement. Consequently, the NOx concentration in the measuring gas can be determined based on the pump flow rate Ip2, which is essentially proportional to the NOx concentration in the measuring gas when the oxygen produced by NOx reduction is pumped out through the measuring pump cell 140.

[0053] The sensor element 12 further comprises a heating unit 160, which serves as a temperature control device by heating the sensor element 12 and maintaining the temperature, thus increasing the oxygen ion conductivity of the solid electrolyte. The heating unit 160 comprises a heating element connector electrode 162, a heating element 164, a through-hole 166, a heating element insulating layer 168, a pressure relief hole 170, and a connecting wire 172.

[0054] The heating device connector electrode 162 is an electrode that is in contact with the lower surface of the first substrate layer 60. The heating device connector electrode 162 is connected to an external power supply for supplying electricity to the heating device unit 160 from the outside.

[0055] The heating element 164 is an electrical resistor located between the second substrate layer 62 below and the third substrate layer 64 above. The heating element 164 is connected to the heating element connector electrode 162 via the connecting wire 172 and the through-hole 166. By being supplied with electricity externally through the heating element connector electrode 162, the heating element 164 generates heat, which warms the solid electrolyte forming the sensor element 12 and keeps it hot or warm.

[0056] Furthermore, the heating device 164 is included in the entire area from the first inner cavity 88 to the third inner cavity 96, so that the entire sensor element 12 can be set to temperatures at which the solid electrolyte is activated.

[0057] The heating element insulating layer 168 is an insulating layer formed on the upper and lower surfaces of the heating element 164 and is made of porous aluminum oxide, which is formed from an aluminum oxide insulator, etc. The heating element insulating layer 168 is designed to provide electrical insulation between the second substrate layer 62 and the heating element 164, and electrical insulation between the third substrate layer 64 and the heating element 164.

[0058] The pressure relief hole 170 passes through the third substrate layer 64, so that it is connected to the reference gas introduction chamber 98 in order to reduce the internal pressure increase caused by a temperature rise in the heating device insulation layer 168.

[0059] The one in Fig. The two variable power supplies 122, 144, 132, 152, etc. shown are in practice connected by connecting wires (not shown) formed in the sensor element 12 and the connector 24 and connecting wires 54 in the Fig. 1 connected to electrodes.

[0060] In this embodiment, the rearward-extending connection elements 18 are electrically connected to element contact points 200 exposed at the rear end section of the sensor element 12. The ceramic housing 16 is provided around the rear end section of the sensor element 12. The connection elements 18 are fitted between the element contact points 200 and the ceramic housing 16, thereby pressing (squeezing) the element contact points 200 of the sensor element 12 and the connection elements 18, and then electrically connecting them. That is, the ceramic housing 16 is provided with the connection elements 18, which are electrically connected to the sensor element 12, and holds the rear end section of the sensor element 12. As shown in the Fig. As shown in Figure 3, the element contact points 200 comprise a first element contact point 200a, a second element contact point 200b, a third element contact point 200c, a fourth element contact point 200d, and a fifth element contact point 200e. As shown in the Fig. As shown in Figure 3, the connection elements 18 further comprise a first connection element 18a, a second connection element 18b, a third connection element 18c and a fourth connection element 18d.

[0061] The rear ends of the connecting elements 18 extend rearward beyond the rear section of the ceramic housing 16 and are electrically connected by soldering, etc., to the connecting wires 54, which are inserted into the elastic insulating element 56. A plurality of through-holes 202 are formed in the elastic insulating element 56 along the axial direction of the sensor element 12. The connecting wires 54 are inserted through the through-holes 202, and the connecting elements 18 extending from the sensor element 12 and the connecting wires 54 are electrically connected by soldering, etc.

[0062] In particular, as stated in the Fig. As shown in Figure 3, the gas sensor 10 of this embodiment has the four connection elements 18 (first to fourth connection element 18a to 18d) on the inside of the ceramic housing 16, which extends along the front-back direction inside the outer tube 34.

[0063] The ceramic housing 16 comprises two ceramic parts (a first ceramic part 16a and a second ceramic part 16b) facing inwards, and two further ceramic parts (a third ceramic part 16c and a fourth ceramic part 16d) also facing inwards. The first connection element 18a and the second connection element 18b are each provided on the two ceramic parts. Furthermore, the third connection element 18c and the fourth connection element 18d are each provided on the further two ceramic parts.

[0064] The first ceramic part 16a and the second ceramic part 16b as well as the third ceramic part 16c and the fourth ceramic part 16d are provided in the housing 16 such that they are directed towards each other.

[0065] Furthermore, a first contact element 20a is provided on a main surface of the first terminal element 18a (a surface facing the third terminal element 18c), with a first positioning layer 210a arranged between them. In particular, the first contact element 20a is arranged at a position facing the first element contact point 200a formed on a main surface of the sensor element 12. A second contact element 20b is provided on a main surface of the second terminal element 18b (a surface facing the fourth terminal element 18d), with a second positioning layer 210b arranged between them. In particular, the second contact element 20b is arranged at a position facing the second element contact point 200b formed on one of the main surfaces of the sensor element 12.

[0066] Accordingly, a third contact element 20c is formed on a main surface of the third terminal element 18c (a surface facing the first terminal element 18a), with a third positioning layer 210c arranged between them. In particular, the third contact element 20c is arranged at a position facing the third element contact point 200c, which is formed on the other main surface of the sensor element 12, for example, on the left side. A fourth contact element 20d is formed on a main surface of the fourth terminal element 18d (a surface facing the second terminal element 18b), with a fourth positioning layer 210d arranged between them. In particular, the fourth contact element 20d is arranged at a position facing the fourth element contact point 200d, which is formed on the other main surface of the sensor element 12.

[0067] Furthermore, a fifth contact element 20e is provided between the first terminal element 18a and the second terminal element 18b. The width We of the fifth contact element 20e, excluding the width Wt of its end section 20t, is approximately twice the width (Wa, Wb, etc.) of the first contact element 20a, etc. Conversely, the width Wt of the end section 20t is smaller than the width (Wa, Wb, etc.) of the first contact element 20a, etc. The fifth contact element 20e is positioned such that the end section 20t faces the fifth element contact point 200e, which is formed on one of the main surfaces of the sensor element 12.

[0068] Furthermore, it is preferred that the width Wt of the end section 20t of the fifth contact element 20e is greater than or equal to 40% and less than or equal to 90% of the width (Wa, Wb, etc.) of the outer contact elements (first contact element 20a, etc.).

[0069] Furthermore, it is preferred that the ratio of the width Wt of the end section 20t of the fifth contact element 20e to a width W of the sensor element 12 (Wt / W) is greater than or equal to 12.1% and less than or equal to 27.3%.

[0070] The following is an example of an experiment. In this example experiment, gas sensors from examples 1 to 7 and gas sensors from comparison examples 1 to 3 were manufactured, and each gas sensor was subjected to a heating and vibration test to check for the presence / absence of a short circuit using signal monitoring and for the presence / absence of anomalies in the contact elements.

[0071] The heating and vibration test was performed under the following conditions, with each gas sensor attached to an exhaust pipe of a propane burner which was attached to a vibration test device. Gas temperature: 900 °C Vibration condition: 30-minute cycle of 50 Hz → 100 Hz → 150 Hz → 250 Hz Acceleration: 30 G, 40 G, 50 G Testing time: 150 hours [Assessment procedure] Assessment 1: The presence / absence of signal variation due to a short circuit during the heating and vibration test was examined. The criteria for Assessment 1 were defined as follows. A: During the heating and vibration test, no disturbance of the sensor signal (Ip2) due to a short circuit was detected. B: During the heating and vibration test, a disturbance of the sensor signal (Ip2) due to a short circuit was detected. Assessment 2: The presence / absence of anomalies in contact elements after the heating and vibration test was examined. The criteria for Assessment 2 were defined as follows. A: No anomaly B: Breakage of contact elements [Example 1]

[0072] The ratio of the width Wt of the end section 20t of the fifth contact element 20e to the width (Wa, Wb, etc.) of the outer contact elements (first contact element 20a, etc.) is 90%.

[0073] The ratio of the width Wt of the end section 20t of the fifth contact element 20e to the width W of the sensor element 12 is 27.3%.

[0074] The width of the outer contact elements is 1 mm and the width of the sensor element 12 is 3.3 mm; the same applies to the following examples. [Example 2]

[0075] The ratio of the width Wt to ​​the width of the outer contact elements is 80% and the ratio of the width Wt to ​​the width W of the sensor element 12 is 24.2%. [Example 3]

[0076] The ratio of the width Wt to ​​the width of the outer contact elements is 70% and the ratio of the width Wt to ​​the width W of the sensor element 12 is 21.2%. [Example 4]

[0077] The ratio of the width Wt to ​​the width of the outer contact elements is 60% and the ratio of the width Wt to ​​the width W of the sensor element 12 is 18.2%. [Example 5]

[0078] The ratio of the width Wt to ​​the width of the outer contact elements is 50% and the ratio of the width Wt to ​​the width W of the sensor element 12 is 15.2%. [Example 6]

[0079] The ratio of the width Wt to ​​the width of the outer contact elements is 45% and the ratio of the width Wt to ​​the width W of the sensor element 12 is 13.6%. [Example 7]

[0080] The ratio of the width Wt to ​​the width of the outer contact elements is 40% and the ratio of the width Wt to ​​the width W of the sensor element 12 is 12.1%. [Comparison example 1]

[0081] The ratio of the width Wt to ​​the width of the outer contact elements is 100% and the ratio of the width Wt to ​​the width W of the sensor element 12 is 30.3%. [Comparative example 2]

[0082] The ratio of the width Wt to ​​the width of the outer contact elements is 35% and the ratio of the width Wt to ​​the width W of the sensor element 12 is 10.6%. [Comparative example 3]

[0083] The ratio of the width Wt to ​​the width of the outer contact elements is 30% and the ratio of the width Wt to ​​the width W of the sensor element 12 is 9.1%.

[0084] Table 1 of Fig.Figure 4 shows the assessment results and details of the preceding examples 1 to 7 and comparative examples 1 to 3.

[0085] Based on the results shown in Table 1, it is preferred that the width Wt of the end section 20t of the fifth contact element 20e is greater than or equal to 40% and less than or equal to 90% of the widths (Wa, Wb, etc.) of the outer contact elements (of the first contact element 20a, etc.). Furthermore, it is preferred that the ratio (Wt / W) of the width Wt of the end section 20t of the fifth contact element 20e to the width W of the sensor element 12 is greater than or equal to 12.1% and less than or equal to 27.3%.

[0086] The embodiments described above can be summarized as follows. [1] A gas sensor (10) according to the embodiment comprises: a sensor element (12); a plurality of element contact points (200a to 200e) formed on a rear end section of the sensor element (12); and a plurality of contact elements (20a to 20e) formed for holding the rear end section of the sensor element (12) and for electrically connecting to the plurality of element contact points (200a to 200e), wherein at least one contact element (20e) of the plurality of contact elements (20a to 20e) has a smaller width (Wt) than the other contact elements.

[0087] This increases the distance between adjacent contact elements and thus helps to prevent short circuits. Furthermore, reducing the width of a contact element or elements reduces the amount of material used to form the element contact points (200a to 200e), such as Pt (platinum), which leads to lower costs.

[0088] [2] In the embodiment, of three or more contact elements (20a to 20e), at least one contact element (20e), which is located in the middle, has the smaller width (Wt).

[0089] Consequently, when three or more contact elements are provided, the width (Wt) of at least one contact element (20e) located in the middle is reduced, which increases the distance between the adjacent contact elements and thus makes it possible to prevent the occurrence of a short circuit. Furthermore, reducing the width (Wt) of the contact element (20e) reduces the amount of material used to form the element contact point (200e), such as Pt (platinum), which allows for a cost reduction.

[0090] [3] In the embodiment, of the three contact elements (20a, 20e, 20b), one contact element (20e), which is located in the middle, has the smaller width (Wt).

[0091] Consequently, when three contact elements (20a, 20e, 20b) are provided, the width (Wt) of the contact element (20e) located in the middle is reduced, which increases the distance between the adjacent contact elements and thus helps prevent short circuits. Furthermore, reducing the width (Wt) of the contact element (20e) reduces the amount of material, such as platinum (Pt), used to form the contact point (200e), thereby reducing costs.

[0092] [4] In this embodiment, the smaller width (Wt) of the contact element (20e) is 0.4 to 0.9 times the width of the other contact elements (20a to 20d). Setting the width (Wt) to less than 0.4 times the width of the other contact elements (20a to 20d) cannot maintain the durability of the contact element (20e), and setting the width (Wt) to more than 0.9 times the width of the other contact elements (20e) is ineffective.

[0093] [5] In this embodiment, the smaller width (Wt) of the contact element (20e) is 0.121 to 0.273 times the width (W) of the sensor element (12). Setting the width (Wt) to less than 0.121 times the width cannot maintain the durability of the contact element, and setting the width (Wt) to more than 0.273 times the width is ineffective.

[0094] Implementations of the present invention can be provided with various devices to improve reliability as a motor vehicle component without deviating from the concept of the present invention.

Claims

[1] Gas sensor (10), comprising: a sensor element (12); a plurality of element contact points (200a to 200e) formed on a rear end section of the sensor element (12); and a plurality of contact elements (20a to 20e) designed to hold the rear end section of the sensor element (12) and to electrically connect it to the plurality of element contact points (200a to 200e), wherein at least one contact element of the plurality of contact elements (20a to 20e) has a smaller width (Wt) than other contact elements of the plurality of contact elements (20a to 20e) and wherein the smaller width (Wt) of the at least one contact element (20e) is 0.121 times to 0.273 times the width (W) of the sensor element (12). [2] Gas sensor according to claim 1, wherein of three contact elements (20a, 20e, 20b) of the contact elements one (20e) of the three contact elements, which is arranged in the middle, has a smaller width (Wt). [3] Gas sensor according to claim 1 or 2, wherein of three or more contact elements (20a to 20e) of the contact elements at least one (20e) of the three or more contact elements, which is arranged in the middle, has a smaller width (Wt). [4] Gas sensor according to claim 1, wherein the smaller width (Wt) of the at least one contact element (20e) is 0.4 times to 0.9 times the width (Wa, Wb) of the other contact elements (20a to 20d).

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