Sensor control device

Abstract

A sensor control device (6) is used for a gas sensor disposed in the exhaust pipe of an engine that is an internal combustion engine of a vehicle. The gas sensor has: a sensor unit (21) having an exhaust electrode (311), an atmospheric electrode (312) and a solid electrolyte (31); and a heater (22) for heating the sensor unit (21). The sensor control device (6) has a heater control unit (61) for controlling the heating of the sensor unit (21) by the heater (22). The heater control unit (61) heats the sensor unit (21) to the operating control temperature when the engine is running and to the stopping control temperature when the engine stops running, which is higher than the operating control temperature.

Description

[0001] Cross-references to related applications

[0002] This application is based on Japanese Patent Application No. 2020-130276, filed on July 31, 2020, and incorporates the contents thereof. Technical Field

[0003] This disclosure relates to a sensor control device for a gas sensor. Background Technology

[0004] Gas sensors are installed in the exhaust pipe of internal combustion engines to determine the engine's air-fuel ratio, oxygen concentration, and other parameters by detecting the exhaust gas flowing through the exhaust pipe. The gas sensor uses a sensor element comprising a solid electrolyte and a pair of electrodes. The solid electrolyte has oxide ion conductivity, and the pair of electrodes are disposed on the surface of the solid electrolyte. One electrode serves as the exhaust electrode exposed to the exhaust gas, and the other electrode serves as the atmospheric electrode, acting as the counter electrode for oxide ion conduction between the exhaust electrode and the exhaust electrode.

[0005] Furthermore, the atmosphere present in the engine compartment, etc., is introduced into the atmospheric electrode of the sensor element of the gas sensor. At this time, the atmosphere in the engine compartment contains gases such as siloxanes, which are compounds containing silicon and oxygen. These siloxanes may act as toxic substances and cause poisoning and deterioration of the atmospheric electrode.

[0006] For example, in the sensor control device of Patent Document 1, in order to suppress the poisoning and deterioration of the atmospheric electrode, it is configured such that when the atmospheric electrode is in a toxic environment, oxygen is pumped from the exhaust electrode to the atmospheric electrode. Furthermore, in the atmospheric channel in the sensor element where the atmospheric electrode is disposed, oxygen existing in the engine compartment is used for replacement instead of oxygen existing in the exhaust pipe via the exhaust electrode.

[0007] Existing technical documents

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2017-75794 Summary of the Invention

[0010] In the sensor control device of Patent Document 1, in order to suppress the poisoning and degradation of the atmospheric electrode, a design was implemented that only applied a voltage between the exhaust electrode and the atmospheric electrode to pump oxygen from the exhaust electrode to the atmospheric electrode. It has now been determined that in order to more effectively suppress the poisoning and degradation of the atmospheric electrode, not only oxygen pumping is required, but further design is also needed.

[0011] This disclosure aims to provide a sensor control device capable of suppressing poisoning of the atmospheric electrode of a gas sensor or enabling the atmospheric electrode to recover from poisoning.

[0012] One aspect of this disclosure is a sensor control device.

[0013] The sensor control device is used for a gas sensor, which has a sensor unit and a heater, and is disposed in the exhaust pipe of a vehicle's internal combustion engine. The sensor unit is formed by placing an exhaust electrode exposed to the exhaust gas and an atmospheric electrode exposed to the atmosphere opposite each other on a solid electrolyte. The heater is used to heat the sensor unit.

[0014] The sensor control device includes a heater control unit for controlling the heater's heating of the sensor unit, wherein...

[0015] The heater control unit is configured to heat the sensor unit to the operating temperature when the internal combustion engine is running, and to heat the sensor unit to a stop temperature higher than the operating temperature when the internal combustion engine stops running.

[0016] Another aspect of this disclosure is a sensor control device.

[0017] The sensor control device is used for a gas sensor, which has a sensor unit and a heater, and is disposed in the exhaust pipe of a vehicle's internal combustion engine. The sensor unit is formed by placing an exhaust electrode exposed to the exhaust gas and an atmospheric electrode exposed to the atmosphere opposite each other on a solid electrolyte. The heater is used to heat the sensor unit.

[0018] The sensor control device includes a voltage application unit that applies a voltage between the exhaust electrode and the atmospheric electrode, and a degradation detection unit that detects the degradation amount of the sensor unit's detection value during combustion operation or when combustion stops.

[0019] The voltage application unit is configured to: apply an operating voltage between the exhaust electrode and the atmospheric electrode during combustion operation of the internal combustion engine; and, provided that the amount of degradation detected by the degradation detection unit is above a predetermined value, apply a stopping voltage higher than the operating voltage between the exhaust electrode and the atmospheric electrode when combustion of the internal combustion engine stops, thereby reducing the silicon oxide attached to the atmospheric electrode.

[0020] (A sensor control device of one type)

[0021] In the aforementioned sensor control device, a heater control unit that controls the heating of the sensor unit by the heater is designed to suppress atmospheric electrode poisoning or enable the atmospheric electrode to recover from poisoning. Specifically, the heater control unit is configured to heat the sensor unit to a stop control temperature that is higher than the operating control temperature during combustion when the internal combustion engine stops. This structure prevents toxic gases such as siloxanes from reaching the atmospheric electrode due to oxidation within the gas sensor, thus suppressing the formation of an insulating poisoning film on the atmospheric electrode.

[0022] Furthermore, it is conceivable that poisons such as siloxanes have already adhered to the atmospheric electrode before the gas sensor and sensor control device are activated. In this state, if the gas sensor and sensor control device are activated, it is also conceivable that the heating of the atmospheric electrode would cause an oxidation reaction of the poisons, forming a poisonous film. In this case, by heating the sensor unit to the controlled temperature at which combustion of the internal combustion engine ceases, the poisonous film on the atmospheric electrode can be destroyed due to thermal stress, restoring the atmospheric electrode's function of ion activation of oxygen.

[0023] According to the sensor control device of the aforementioned method, it is possible to suppress the poisoning of the atmospheric electrode of the gas sensor or to restore the atmospheric electrode from poisoning.

[0024] (Another type of sensor control device)

[0025] In the other type of sensor control device, the voltage application unit that applies voltage between the exhaust electrode and the atmospheric electrode is designed to restore the atmospheric electrode from poisoning. Specifically, the voltage application unit is configured such that, when combustion of the internal combustion engine stops, a stop-time voltage higher than the operating voltage is applied between the exhaust electrode and the atmospheric electrode, provided that the amount of degradation detected by the sensor unit detected by the degradation detection unit is above a predetermined value, thereby reducing the silicon oxides adhering to the atmospheric electrode. This structure can reduce the silicon oxides that form a poisoning film on the atmospheric electrode due to toxic gases such as siloxanes adhering to it, restoring the atmospheric electrode's function of activating oxygen ions.

[0026] According to the sensor control device of the other method, the atmospheric electrode of the gas sensor can be recovered from poisoning.

[0027] Furthermore, the bracketed reference numerals of each component shown in the various embodiments of this disclosure indicate the correspondence with the reference numerals in the accompanying drawings of the embodiments, but do not limit each component to the content of the embodiments. Attached Figure Description

[0028] The objects, features, advantages, etc., of this disclosure will become more apparent from the following detailed description with reference to the accompanying drawings. The accompanying drawings are shown below.

[0029] Figure 1 This is an explanatory diagram showing the gas sensor of Embodiment 1 through cross-section.

[0030] Figure 2 This is an explanatory diagram showing the sensor element of Embodiment 1 through cross-section.

[0031] Figure 3 This refers to the sensor element of embodiment 1. Figure 2 Explanatory diagram of section III-III.

[0032] Figure 4 This refers to the sensor element of embodiment 1. Figure 2 Explanatory diagram of section IV-IV.

[0033] Figure 5 This is an explanatory diagram showing the gas sensor and sensor control device according to Embodiment 1.

[0034] Figure 6 This is an explanatory diagram showing the electrical structure of the gas sensor and sensor control device according to Embodiment 1.

[0035] Figure 7 This is a graph showing the relationship between the air-fuel ratio and the output current in Implementation Method 1.

[0036] Figure 8 This is an explanatory diagram showing the poisoning film formed on the atmospheric electrode in Embodiment 1.

[0037] Figure 9 This is a flowchart illustrating the control method of the sensor control device according to Embodiment 1.

[0038] Figure 10 It is a graph showing the changes in (a) vehicle speed over time, (b) siloxane concentration in the engine compartment over time, (c) excess air rate of the engine over time, and (d) heating temperature of the sensor unit by the heater control unit over time in Embodiment 1.

[0039] Figure 11 This is an explanatory diagram showing the electrical structure of the gas sensor and sensor control device according to Embodiment 2.

[0040] Figure 12 This is a graph showing the changes in (a) vehicle speed over time, (b) engine excess air ratio over time, and (c) voltage applied by the voltage application unit to the sensor unit over time in Embodiment 2.

[0041] Figure 13 This is a graph showing the relationship between voltage and current in the sensor unit of Embodiment 2.

[0042] Figure 14 The graph shows the changes in (a) the heating temperature of the sensor unit heated by the heater control unit over time, (b) the changes in the applied voltage of the voltage application unit to the sensor unit over time, (c) the changes in the output current generated in the sensor unit over time, and (d) the changes in the resistance value of the sensor unit over time in Embodiment 2.

[0043] Figure 15 This is a flowchart illustrating the control method of the sensor control device in Embodiment 2.

[0044] Figure 16 This is a graph showing the changes in (a) vehicle speed over time, (b) heating temperature of the sensor unit by the heater control unit over time, and (c) applied voltage of the voltage application unit to the sensor unit over time in Embodiment 3.

[0045] Figure 17 This is a graph showing the relationship between the temperature and the reduction potential of oxygen-deficient silica in Embodiment 3.

[0046] Figure 18 This is a flowchart illustrating the control method of the sensor control device in Embodiment 3.

[0047] Figure 19 This is a flowchart illustrating the control method of the sensor control device in Embodiment 4.

[0048] Figure 20 This is an explanatory diagram showing the electrical structure of the gas sensor and sensor control device according to Embodiment 5.

[0049] Figure 21 This is a flowchart illustrating the control method of the sensor control device in Embodiment 5. Detailed Implementation

[0050] A preferred embodiment of the aforementioned sensor control device will be described with reference to the accompanying drawings.

[0051] <Implementation Method 1>

[0052] like Figures 1 to 6As shown, the sensor control device 6 of this method is used for a gas sensor 1 disposed in the exhaust pipe 7 of an engine 5, which is an internal combustion engine of a vehicle. The gas sensor 1 has a sensor unit 21 and a heater 22 for heating the sensor unit 21. The sensor unit 21 has an exhaust electrode 311 exposed to the exhaust gas G, an atmospheric electrode 312 exposed to the atmosphere A, and a solid electrolyte body 31 in which the exhaust electrode 311 and the atmospheric electrode 312 are disposed opposite each other.

[0053] The sensor control device 6 includes a heater control unit 61 that controls the heating of the sensor unit 21 by the heater 22. For example... Figure 10 As shown, the heater control unit 61 is configured such that when the engine 5 is running, the heater 22 heats the sensor unit 21 to the running control temperature T1, and when the engine 5 stops running, the heater 22 heats the sensor unit 21 to the stop control temperature T2, which is higher than the running control temperature T1.

[0054] First, the gas sensor 1 of this method will be described in detail.

[0055] (Gas Sensor 1)

[0056] like Figure 1 and Figure 5 As shown, gas sensor 1 is disposed at the mounting port 71 of the exhaust pipe 7 of the vehicle's engine 5, and is used to detect the oxygen concentration and other parameters in the exhaust gas G flowing through the exhaust pipe 7. Gas sensor 1 can be used as an air-fuel ratio sensor (A / F sensor) to determine the air-fuel ratio in the engine 5 based on the oxygen concentration, unburned gas concentration, etc., in the exhaust gas G. The air-fuel ratio sensor can quantitatively and continuously detect the air-fuel ratio from a rich combustion state (where the fuel-to-air ratio is higher than the stoichiometric air-fuel ratio) to a lean combustion state (where the fuel-to-air ratio is lower than the stoichiometric air-fuel ratio). In addition to being an air-fuel ratio sensor, gas sensor 1 can also be used for various other purposes, such as determining oxygen concentration.

[0057] like Figure 5 As shown, a catalyst 72 for purifying harmful substances in the exhaust gas G is disposed in the exhaust pipe 7. The gas sensor 1 can be disposed either upstream or downstream of the catalyst 72 in the flow direction of the exhaust gas G in the exhaust pipe 7. Alternatively, the gas sensor 1 can also be disposed in a pipe on the intake side of a turbocharger that uses the exhaust gas G to increase the density of the air drawn into the engine 5. Furthermore, the pipe in which the gas sensor 1 is disposed can also be configured as a pipe in an exhaust gas recirculation mechanism that recirculates a portion of the exhaust gas G discharged from the engine 5 into the intake manifold of the engine 5.

[0058] like Figure 5As shown, the engine 5 in this embodiment is a gasoline engine, and a three-way catalyst 72 is disposed in the exhaust pipe 7. The gas sensor 1 in this embodiment is configured as an air-fuel ratio sensor 11 disposed in the exhaust pipe 7 upstream of the flow of the exhaust gas G, which is located further upstream than the three-way catalyst 72. In the air-fuel ratio sensor 11, a stacked sensor element 2 having a plate-shaped solid electrolyte body 31, as described later, can be used.

[0059] Alternatively, the gas sensor 1 can be configured as an oxygen sensor 12 positioned downstream of the exhaust gas G flow direction, further downstream than the three-way catalytic converter 72. In this configuration, the three-way catalytic converter 72 is arranged in multiple stages in the direction of exhaust gas G flow in the exhaust pipe 7. The oxygen sensor 12 is positioned adjacent to the downstream side of the upstream three-way catalytic converter 72 in the exhaust pipe 7. The oxygen sensor 12 can utilize a cup-shaped sensor element with a cup-shaped solid electrolyte body 31, as described later. The oxygen sensor can detect whether the air-fuel ratio of the engine 5, estimated by the exhaust gas G, is on the rich-fuel side or the lean-fuel side compared to the stoichiometric air-fuel ratio.

[0060] Furthermore, although the illustration is omitted, engine 5 can also be a diesel engine, and a reduction catalyst for reducing NOx (nitrogen oxides) can be configured on exhaust pipe 7, either together with or replacing the three-way catalytic converter 72. Such reduction catalysts include adsorption-type nitrogen oxide reduction catalysts (LNT) and selective reduction catalysts (SCR). Adsorption-type nitrogen oxide reduction catalysts cause carbon monoxide, hydrocarbons, etc., which are added to the exhaust gas G due to slightly excessive fuel injection in the engine, to react with the adsorbed NOx and be reduced to nitrogen. Selective reduction catalysts utilize ammonia to reduce NOx to nitrogen.

[0061] The gas sensor 1 can also be configured as a NOx sensor positioned upstream or downstream of the flow of exhaust gas G in the exhaust pipe 7, closer to the location of the reduction catalyst. In the sensor element 2 constituting the NOx sensor, a pump electrode is positioned upstream of the flow of exhaust gas G within the gas chamber 35 (described later) compared to the exhaust electrode 311, which serves as the detection electrode. This pump electrode pumps oxygen to the atmospheric electrode 312 by applying a voltage. The atmospheric electrode 312 is formed opposite the detection electrode and the pump electrode, separated by a solid electrolyte body 31. Furthermore, a diesel oxidation catalyst (DOC) can also be configured in the exhaust pipe 7 to oxidize soluble organic components (SOF), carbon monoxide, hydrocarbons, and other particulate matter contained in the exhaust gas G.

[0062] (Sensor element 2)

[0063] like Figures 2-4As shown, the sensor element 2 of this embodiment is a stacked structure in which insulators 33A, 33B and a heating element 34 are stacked on a plate-shaped solid electrolyte body 31 having an exhaust electrode 311 and an atmospheric electrode 312. Within the sensor element 2, a sensor unit 21 is formed, comprising the exhaust electrode 311, the atmospheric electrode 312, and the solid electrolyte body 31 sandwiched between the exhaust electrode 311 and the atmospheric electrode 312. The sensor unit 21 is formed on the front end portion of the elongated sensor element 2.

[0064] In this configuration, the direction in which the sensor element 2 extends into a long strip shape is called the length direction L. Furthermore, the direction orthogonal to the length direction L and in which the solid electrolyte 31, each insulator 33A, 33B, and the heating element 34 are stacked—in other words, the direction in which the sensor unit 21 and the heater 22 are stacked—is called the stacking direction D. Additionally, the direction orthogonal to both the length direction L and the stacking direction D is called the width direction W. Furthermore, along the length direction L of the sensor element 2, the side exposed to the exhaust gas G is called the front end side L1, and the opposite side of the front end side L1 is called the base end side L2.

[0065] (Sensor Unit 21)

[0066] like Figure 2 and Figure 3 As shown, the solid electrolyte 31 constituting the sensor unit 21 has oxide ions (O2) at a specified activity temperature. 2- The conductivity of the solid electrolyte body 31 is considered. An exhaust electrode 311, exposed to the exhaust gas G, is provided on the first surface 301 of the solid electrolyte body 31, and an atmospheric electrode 312, exposed to the atmosphere A, is provided on the second surface 302 of the solid electrolyte body 31. The exhaust electrode 311 and the atmospheric electrode 312 are positioned at the front end L1 exposed to the exhaust gas G along the longitudinal direction L of the sensor element 2, overlapping each other across the solid electrolyte body 31 in the stacking direction D. A first insulator 33A is stacked on the first surface 301 of the solid electrolyte body 31, and a second insulator 33B is stacked on the second surface 302 of the solid electrolyte body 31.

[0067] The solid electrolyte 31 is composed of zirconium oxide-based oxides, specifically stabilized or partially stabilized zirconium oxide, which is mainly composed of zirconium oxide (containing more than 50% by mass) and in which a portion of the zirconium oxide is replaced by rare earth or alkaline earth metal elements. A portion of the zirconium oxide constituting the solid electrolyte 31 can be replaced by yttrium oxide, scandium oxide, or calcium oxide.

[0068] The exhaust electrode 311 and atmospheric electrode 312 constituting the sensor unit 21 contain platinum, a noble metal that exhibits catalytic activity towards oxygen, and zirconium oxide, a shared material used with the solid electrolyte body 31. This shared material is used to maintain the bonding strength between the exhaust electrode 311 and atmospheric electrode 312 formed from the electrode material and the solid electrolyte body 31 when the slurry-like electrode material is printed (coated) onto the solid electrolyte body 31 and the solid electrolyte body 31 and the electrode material are sintered.

[0069] (Gas Chamber 35)

[0070] like Figure 2 and Figure 3 As shown, a gas chamber 35, surrounded by a first insulator 33A and the solid electrolyte body 31, is formed adjacent to the first surface 301 of the solid electrolyte body 31. The gas chamber 35 is formed at the front end L1 of the first insulator 33A along its length L at the location where the exhaust electrode 311 is housed. The gas chamber 35 is formed as a space enclosed by the first insulator 33A, the diffusion resistance section (gas inlet section) 32, and the solid electrolyte body 31. The exhaust gas G flowing in the exhaust pipe 7 is introduced into the gas chamber 35 through the diffusion resistance section 32.

[0071] (Diffusion resistance section 32)

[0072] like Figure 2 As shown, the diffusion resistance section 32 of this embodiment is disposed adjacent to the front end L1 of the gas chamber 35 in the longitudinal direction L. In other words, the diffusion resistance section 32 is formed on the front end face of the sensor element 2 in the longitudinal direction L. The diffusion resistance section 32 is formed in the first insulator 33A by disposing a porous material of metal oxide such as alumina into an inlet that is adjacent to the front end L1 of the gas chamber 35 in the longitudinal direction L. The diffusion velocity (flow rate) of the exhaust gas G introduced into the gas chamber 35 is determined by limiting the velocity of the exhaust gas G through the pores of the porous material in the diffusion resistance section 32.

[0073] The diffusion resistance portion 32 may also be formed adjacent to both sides of the gas chamber 35 in the width direction W. In this case, the diffusion resistance portion 32 is disposed in the first insulator 33A within the inlet port that is adjacent to both sides of the gas chamber 35 in the width direction W. Furthermore, in addition to being formed using a porous material, the diffusion resistance portion 32 may also be formed using a pinhole as a small through-hole communicating with the gas chamber 35.

[0074] (Atmospheric Channel 36)

[0075] like Figures 2-4As shown, an atmospheric channel 36, surrounded by a second insulator 33B and the solid electrolyte body 31, is formed adjacent to the second surface 302 of the solid electrolyte body 31. The atmospheric channel 36 extends from a portion of the second insulator 33B that houses the atmospheric electrode 312 in the longitudinal direction L to a base end position of the sensor element 2 exposed to the atmosphere A in the longitudinal direction L. At the base end position of the sensor element 2 in the longitudinal direction L, a base end opening 361, serving as an atmospheric inlet, is formed in the atmospheric channel 36. The atmospheric channel 36 extends from the base end opening 361 to a position where it overlaps with the gas chamber 35 along the stacking direction D, separated by the solid electrolyte body 31. Atmosphere A is introduced into the atmospheric channel 36 from the base end opening 361.

[0076] (Insulators 33A and 33B)

[0077] like Figure 2 and Figure 3 As shown, the first insulator 33A forms a gas chamber 35, and the second insulator 33B forms an atmospheric channel 36 and embeds a heating element 34. The first insulator 33A and the second insulator 33B are formed using metal oxides such as alumina. Each insulator 33A and 33B forms a dense body through which the exhaust gas G or atmosphere A cannot pass, and almost no pores are formed on each insulator 33A and 33B that allow gas to pass through.

[0078] (Heater 22)

[0079] like Figures 2-4 As shown, the heater 22 is formed by a heating element 34 embedded in the second insulator 33B. Alternatively, the heating element 34 may be embedded in the first insulator 33A. The heating element 34 has a heating portion 341 that heats up when energized and a heating element lead portion 342 connected to the base end side L2 of the heating portion 341 in the longitudinal direction L. The heating portion 341 is arranged in the stacking direction D of the solid electrolyte body 31 and each insulator 33A, 33B at a position that overlaps at least partly with the exhaust electrode 311 and the atmospheric electrode 312.

[0080] Furthermore, the heating element 341 is formed from a linear conductor that meanders through straight and curved portions. In this embodiment, the straight portion of the heating element 341 is formed parallel to the length direction L. The heating element lead portion 342 is formed from a straight conductor parallel to the length direction L. The resistance per unit length of the heating element 341 is greater than the resistance per unit length of the heating element lead portion 342. The heating element lead portion 342 extends from the heating element 341 to the base end side L2 in the length direction L. The heating element 34 contains a conductive metallic material.

[0081] The heating element 341 is positioned opposite the exhaust electrode 311 and the atmospheric electrode 312 in the stacking direction D, which is orthogonal to the length direction L. In other words, the heating element 341 is positioned at the front end L1 of the sensor element 2 in the length direction L, overlapping the exhaust electrode 311 and the atmospheric electrode 312 along the stacking direction D. When a voltage is applied to the pair of heating element leads 342, the heating element 341 heats up through Joule heating, thereby heating the periphery of the sensor unit 21 to the target temperature.

[0082] (Porous layer 37)

[0083] like Figure 1 As shown, a porous layer 37 is provided around the entire circumference of the front end L1 of the sensor element 2 in the longitudinal direction L for capturing toxic substances from the exhaust electrode 311, condensate generated in the exhaust pipe 7, and the like. The porous layer 37 is formed of a porous ceramic (metal oxide) such as alumina. The porosity of the porous layer 37 is greater than that of the diffusion resistance section 32, and the flow rate of the exhaust gas G that can pass through the porous layer 37 is greater than the flow rate of the exhaust gas G that can pass through the diffusion resistance section 32.

[0084] (Other sensor components 2)

[0085] Although the illustration is omitted, the sensor element 2 is not limited to having one solid electrolyte body 31, and may have two or more solid electrolyte bodies 31. The electrodes 311 and 312 provided on the solid electrolyte body 31 are not limited to the pair of exhaust electrode 311 and atmospheric electrode 312, and may be multiple sets of electrodes. When one or more solid electrolyte bodies 31 are provided with multiple sets of electrodes, the heating part 341 of the heating element 34 may also be provided in a position opposite to the multiple sets of electrodes.

[0086] Alternatively, the sensor element 2 can be configured as a cup-shaped structure comprising a solid electrolyte body with a bottomed cylindrical shape, an exhaust electrode 311 disposed on the outer side of the solid electrolyte body, and an atmospheric electrode 312 disposed on the inner side of the solid electrolyte body. In this case, toxic substances contained in the atmosphere A drawn into the atmosphere hoods 46A and 46B and flowing into the inner side of the solid electrolyte body may also reach the atmospheric electrode 312. Furthermore, in addition to detecting the electromotive force generated between the exhaust electrode 311 and the atmospheric electrode 312, the cup-shaped sensor element 2 can also be used to detect the air-fuel ratio or NOx using the voltage application unit 62.

[0087] (Other structures of gas sensor 1)

[0088] like Figure 1As shown, in addition to the sensor element 2, the gas sensor 1 also includes a first heat insulation body 42 for holding the sensor element 2, a housing 41 for holding the first heat insulation body 42, a second heat insulation body 43 connected to the first heat insulation body 42, and a contact terminal 44 held in the second heat insulation body 43 and in contact with the sensor element 2. Furthermore, the gas sensor 1 includes element covers 45A and 45B mounted on the front end L1 of the housing 41 and covering the front end portion of the sensor element 2, atmospheric covers 46A and 46B mounted on the rear end L2 of the housing 41 and covering the second heat insulation body 43, the contact terminal 44, etc., and bushings 47 for holding the lead wire 48 connected to the contact terminal 44 in the atmospheric covers 46A and 46B, etc.

[0089] The front end portion of sensor element 2 and element covers 45A and 45B are disposed inside the exhaust pipe 7 of engine 5. Gas passage holes 451 are formed on element covers 45A and 45B to allow the exhaust gas G, the gas to be detected, to pass through. Element covers 45A and 45B have a dual structure: an inner cover 45A and an outer cover 45B covering the inner cover 45A. Element covers 45A and 45B can also be a single structure. The exhaust gas G flowing into element covers 45A and 45B from the gas passage holes 451 is guided to the exhaust electrode 311 through the porous layer 37 and diffusion resistance portion 32 of sensor element 2.

[0090] like Figure 1 As shown, atmospheric shields 46A and 46B are disposed outside the exhaust pipe 7 of the engine 5. The gas sensor 1 in this configuration is for vehicle use, and the vehicle body with the exhaust pipe 7 constitutes the engine compartment where the engine 5 is located. Furthermore, gases generated from various rubbers, resins, lubricants, etc., in the engine compartment mix with the atmosphere A and flow to the periphery of atmospheric shields 46A and 46B. The gases generated in this engine compartment may contain toxic substances (toxic gases) that could potentially poison the atmospheric electrode 312. Examples of toxic substances generated in the engine compartment include Si (silicon) and S (sulfur).

[0091] In this configuration, the atmospheric covers 46A and 46B are constructed by a first cover 46A mounted on the housing 41 and a second cover 46B covering the first cover 46A. An atmospheric passage hole 461 for allowing atmospheric A to pass through is formed on both the first cover 46A and the second cover 46B. A waterproof filter 462 for preventing water from entering the first cover 46A is clamped at a position opposite to the atmospheric passage hole 461 between the first cover 46A and the second cover 46B.

[0092] The base opening 361 of the atmospheric channel 36 in sensor element 2 opens into the space inside the atmospheric shrouds 46A and 46B. Atmosphere A present around the atmospheric shrouds 46A and 46B via the atmospheric passage 461 is drawn into the atmospheric shrouds 46A and 46B through a waterproof filter 462. Furthermore, the atmospheric A that has passed through the waterproof filter 462 flows into the atmospheric channel 36 from the base opening 361 and is guided to the atmospheric electrode 312 within the atmospheric channel 36.

[0093] The principle of introducing atmospheric A containing toxic gases such as siloxanes into the atmospheric channel 36 equipped with atmospheric electrode 312 is considered to be as follows: After combustion in the engine 5 ceases, the exhaust pipe 7 and the gas sensor 1 gradually cool down from their heated state. Furthermore, the temperature of atmospheric A within the atmospheric covers 46A and 46B of the gas sensor 1 decreases along with the temperature of the gas sensor 1, causing the volume of atmospheric A within the atmospheric covers 46A and 46B to shrink. At this time, the atmospheric covers 46A and 46B become under negative pressure, with the pressure lower than atmospheric pressure. Atmospheric A containing toxic gases generated in the engine compartment is introduced into the atmospheric covers 46A and 46B via a waterproof filter 462. Then, atmospheric A containing toxic gases is introduced from the atmospheric covers 46A and 46B into the atmospheric electrode 312 within the atmospheric channel 36 of the sensor element 2.

[0094] Furthermore, when the gas sensor 1 is used as an air-fuel ratio sensor, a DC voltage is applied between the exhaust electrode 311 and the atmospheric electrode 312 via the voltage application unit 62, with the atmospheric electrode 312 as the positive side (the side with higher voltage). When the air-fuel ratio of the engine 5 is on the lean-burn side, oxide ions pass from the exhaust electrode 311 through the solid electrolyte 31 to the atmospheric electrode 312. On the other hand, when the air-fuel ratio of the engine 5 is on the rich-burn side, to react the unburned gases in the exhaust electrode 311, a countercurrent of oxide ions is generated from the atmospheric electrode 312 through the solid electrolyte 31 to the exhaust electrode 311. At this time, the atmosphere A inside the atmosphere shrouds 46A and 46B is drawn into the atmosphere passage 36, and the atmosphere A containing toxic gases introduced into the atmosphere shrouds 46A and 46B is introduced into the atmospheric electrode 312 in the atmosphere passage 36.

[0095] (Toxic substances)

[0096] Toxic substances in atmospheric A that could potentially poison the atmospheric electrode 312 include siloxane gases produced in the engine compartment of a vehicle. Siloxanes are compounds with a silicon and oxygen backbone, forming organosiloxanes, etc. The ambient gas outside the exhaust pipe 7 and other piping equipped with the gas sensor 1 mostly contains atmospheric A flowing in from the engine compartment. The term "toxic substances" for the atmospheric electrode 312 refers to substances that have the property of adhering to the atmospheric electrode 312 and degrading its performance.

[0097] (Sensor control device 6)

[0098] like Figure 1 , Figure 2 , Figure 5 and Figure 6 As shown, the sensor control device 6 cooperates with the engine control device 50, which controls the combustion operation of the vehicle's engine 5, to perform electrical control of the gas sensor 1. The sensor control device 6 is constructed using various control circuits, computers, etc. The sensor control device 6 can also be integrated into various control circuits, computers, etc., that constitute the engine control device. The sensor control device 6 includes a heater control unit 61 that energizes the heating element 34 constituting the heater 22, a voltage application unit 62 that applies a DC voltage between the exhaust electrode 311 and the atmospheric electrode 312, and a current measuring unit 63 that measures the current flowing between the atmospheric electrode 312 and the exhaust electrode 311. The air-fuel ratio of the engine 5 is calculated based on the output current of the current measuring unit 63.

[0099] The gas sensor 1 and sensor control device 6 are configured to operate not only during combustion operation of the engine 5, but also when combustion is stopped by the vehicle's battery after the engine 5 is switched off. In other words, the gas sensor 1 and sensor control device 6 are configured to be driven both during combustion operation and when combustion is stopped. The heater control unit 61 is configured to maintain the sensor unit 21 at the operating control temperature T1 by energizing the heating element 34 constituting the heater 22 during combustion operation.

[0100] In this embodiment, the operating temperature T1 of the sensor unit 21 is set to any temperature within the range of 600°C to 800°C. The operating temperature T1 is set to the temperature at which the conductivity of the oxide ions in the solid electrolyte 31 is activated. When the operating temperature T1 is below 600°C, it is difficult to activate the solid electrolyte 31; when it exceeds 800°C, the durability of the sensor element 2 containing the solid electrolyte 31 may decrease.

[0101] The heater control unit 61 is configured to maintain the sensor unit 21 at the shutdown control temperature T2 by energizing the heating element 34 constituting the heater 22 when combustion stops. The shutdown control temperature T2 is any temperature within the range of 660°C to 950°C, and is set to be higher than the operation control temperature T1. If the shutdown control temperature T2 is below 660°C, it is difficult to suppress the poisoning of the atmospheric electrode 312 or to achieve recovery from poisoning. If the shutdown control temperature T2 exceeds 950°C, the durability of the solid electrolyte 31 may decrease.

[0102] The difference between the control temperature T2 when stopped and the control temperature T1 when running is preferably 60°C or more, more preferably 100°C or more, and even more preferably 150°C or more.

[0103] Immediately after combustion in engine 5 has ceased, the engine compartment is extremely hot, and air circulation from vehicle movement and radiator fans is virtually nonexistent. Consequently, toxic gases are easily generated in the engine compartment, particularly at the atmospheric electrode 312, and these gases tend to remain trapped within the engine compartment. The heating of the sensor unit 21 to the stop-time control temperature T2, controlled by the heater control unit 61, preferably begins immediately after combustion in engine 5 has ceased. Alternatively, the heating controlled by the heater control unit 61 can also begin after a predetermined time has elapsed since combustion in engine 5 ceased.

[0104] In the gas sensor 1 installed in a vehicle without an idle stop function, the heater control unit 61 can heat the sensor unit 21 to the stop control temperature T2 each time combustion stops (when the engine 5 stops burning). Similarly, in the gas sensor 1 installed in a vehicle with an idle stop function, the heater control unit 61 can heat the sensor unit 21 to the stop control temperature T2 each time combustion stops (including combustion stops caused by idle stop). On the other hand, in this gas sensor 1, the heater control unit 61 can also heat the sensor unit 21 to the stop control temperature T2 each time combustion stops (other than combustion stops caused by idle stop). For example, the combustion stop caused by idle stop can be determined by sensing that combustion of the engine 5 restarts within 2 minutes after combustion stops.

[0105] (Treatment of toxic substances on atmospheric electrode 312)

[0106] The heater control unit 61 is configured to destroy the toxic substance attached to the atmospheric electrode 312 by heating the stop control temperature T2 through the sensor unit 21 when combustion stops. The toxic substance in this method is silicon oxide, and the heater control unit 61 is configured to cause the silicon oxide to crack by heating the stop control temperature T2 through the sensor unit 21.

[0107] When atmospheric atmosphere A, containing siloxanes, comes into contact with atmospheric electrode 312, a poisoning film of silicon oxide may sometimes form on the surface of atmospheric electrode 312. This poisoning film is an electrical insulator. If a poisoning film forms on the surface of atmospheric electrode 312, atmospheric electrode 312 will lose its active sites for oxygen ionization. In particular, in the air-fuel ratio sensor, when the air-fuel ratio of engine 5 is on the fuel-rich side, generating a countercurrent flow of oxide ions from atmospheric electrode 312 to exhaust electrode 311, the detection performance of the air-fuel ratio is reduced.

[0108] The reduction in the detection performance of the air-fuel ratio under rich conditions is, for example, as Figure 7 As shown. In a normally operating air-fuel ratio sensor, the change in output current in sensor unit 21 can be observed over a wide range, from the lean side (air-fuel ratio greater than 14.5) to the rich side (air-fuel ratio less than 14.5). On the other hand, if a poisoning film is formed on the atmospheric electrode 312, it is difficult to generate a change in the output current of sensor unit 21 representing the air-fuel ratio on the rich side. Figure 7 In the diagram, solid lines represent the normal situation, and dashed lines represent the situation where a toxic film has formed. Furthermore, the side with an air-fuel ratio less than 14.5 is represented as the rich-fuel side, and the side with an air-fuel ratio greater than 14.5 is represented as the lean-fuel side.

[0109] In this method, the oxygen-ionizing active sites of the atmospheric electrode 312 are restored by causing cracks in the poisoned film of the silicon oxide attached to the atmospheric electrode 312. Furthermore, the stopping temperature T2 of this method is set to a higher temperature than the temperature at which the thermal stress generated at the interface between the atmospheric electrode 312 and the silicon oxide attached to the atmospheric electrode 312 is greater than the tensile strength of the silicon oxide monomer.

[0110] In this method, the atmospheric electrode 312 is formed from platinum particles mixed with solid electrolyte particles, and the coefficient of linear expansion of the atmospheric electrode 312 is greater than that of silicon oxide. For example... Figure 8 As shown, when sensor unit 21 is heated, the thermal expansion of atmospheric electrode 312 is greater than that of the poisoning film M made of silicon oxide, by a larger amount of thermal expansion B2. At this time, thermal stress is generated between atmospheric electrode 312 and the poisoning film M, stretching the poisoning film M. Furthermore, when the thermal stress generated between atmospheric electrode 312 and the poisoning film M exceeds the tensile strength of the poisoning film M, fine cracks, i.e., microcracks C, are generated on the poisoning film M.

[0111] Silicon dioxide (SiO2), an oxide of silicon, exhibits a tensile strength of 50 N / mm². 2 To ensure that the thermal stress generated between the atmospheric electrode 312 and the poisoned membrane M exceeds 50 N / mm², 2 When stopping, the control temperature T2 is preferably set to be at least 60°C higher than the control temperature T1 during operation.

[0112] If the control temperature T2 is too high when the heating sensor unit 21 stops, the crystal structure of the zirconium oxide constituting the solid electrolyte 31 will change. Zirconia has three crystal systems: monoclinic, tetragonal, and cubic. At room temperature (around 25°C), it is in a monoclinic state. If the temperature increases, it changes to a tetragonal state, and if the temperature increases further, it changes to a cubic state. This crystal structure transformation is accompanied by a volume change; the transformation from monoclinic to tetragonal is accompanied by a volume shrinkage of about 4%.

[0113] The temperature at which the zirconium oxide constituting the solid electrolyte 31 transforms from monoclinic to tetragonal is 950°C or higher and 1200°C or lower. Therefore, the control temperature T2 at which the solid electrolyte 31 does not undergo a phase transformation is preferably set to 950°C or lower.

[0114] Based on the above, the stop-time control temperature T2 in this method is set to a temperature higher than the tensile strength of the silicon oxide monomer, where the thermal stress generated at the interface between the atmospheric electrode 312 and the silicon oxide attached to the atmospheric electrode 312 is greater than the thermal stress of the silicon oxide monomer, and lower than the temperature at which the crystal structure of the solid electrolyte 31 changes. Furthermore, by using the heater control unit 61 to heat the sensor unit 21 to the stop-time control temperature T2 when combustion stops, the poisoned film attached to the atmospheric electrode 312 is cracked, thus restoring the detection performance of the air-fuel ratio on the fuel-rich side.

[0115] (Control methods)

[0116] Reference Figure 9 The flowchart below describes the control method of the sensor control device 6 for gas sensor 1.

[0117] First, in response to the vehicle's ignition switch being turned on, combustion operation of the engine 5 begins (step S101). Additionally, in response to this, control of the gas sensor 1 and the sensor control device 6 begins (step S101). Then, the heater control unit 61 of the sensor control device 6 heats the sensor unit 21 to the operating control temperature T1 (step S102).

[0118] Next, it is determined whether the ignition switch is turned off, thus stopping the combustion operation of the engine 5 (step S103). Until the ignition switch is turned off, the engine 5 continues to operate by the engine control device 50 in response to the feedback of the air-fuel ratio from the gas sensor 1 and the sensor control device 6.

[0119] Next, when the combustion operation of the engine 5 stops, the heater control unit 61 of the sensor control device 6 heats the sensor unit 21 to the stop control temperature T2 (step S104). After a predetermined time has elapsed since the sensor unit 21 has been heated to the stop control temperature T2, the heater control unit 61 stops the heating.

[0120] Furthermore, when combustion in engine 5 ceases, a predetermined voltage can be applied between exhaust electrode 311 and atmospheric electrode 312 by voltage application unit 62 while the sensor unit 21 is heated to the stop control temperature T2 using heater control unit 61. This predetermined voltage can be set to the operating voltage V1 shown in Embodiment 2 described later.

[0121] (Effects)

[0122] In the sensor control device 6 of this method, the heater control unit 61, which controls the heating of the sensor unit 21 by the heater 22, is designed to suppress the poisoning of the atmospheric electrode 312 or to allow the atmospheric electrode 312 to recover from poisoning. Specifically, the heater control unit 61 is configured to heat the sensor unit 21 to a stop control temperature T2 that is higher than the operating control temperature T1 during combustion when the engine 5 stops. With this structure, toxic gases such as siloxane gas are isothermally oxidized in the atmospheric passage 36, making it difficult for them to reach the atmospheric electrode 312, thus suppressing the formation of an insulating poisoning film on the atmospheric electrode 312.

[0123] Furthermore, when combustion in engine 5 ceases, the sensor unit 21 is heated using the heater control unit 61, maintaining a high temperature inside the atmosphere shields 46A and 46B and the atmosphere passage 36. This prevents the volume of atmosphere A inside the atmosphere shields 46A and 46B from shrinking, making it difficult for atmosphere A containing siloxanes or the like to reach the atmosphere electrode 312 inside the atmosphere passage 36.

[0124] Furthermore, it is conceivable that poisons such as siloxanes may already be attached to the atmospheric electrode 312 before the gas sensor 1 and sensor control device 6 are activated. In this state, if the gas sensor 1 and sensor control device 6 are activated, it is also conceivable that the heating of the atmospheric electrode 312 could cause an oxidation reaction of the poisons, forming a poisoning film. In this case, by heating the sensor unit 21 to the stop-combustion control temperature T2 when the engine 5 stops combustion, the poisoning film in the atmospheric electrode 312 can be destroyed due to thermal stress, restoring the atmospheric electrode 312's function of ion activation of oxygen.

[0125] Thus, the sensor control device 6 of the gas sensor 1 according to this method can suppress the poisoning of the atmospheric electrode 312 of the gas sensor 1. Furthermore, in the event that the atmospheric electrode 312 is poisoned, recovery from the poisoning can be achieved.

[0126] Figure 10 (a), (b), (c), and (d) show the vehicle's status and the changes in the operation of the heater control unit 61 over time. Figure 10 (a) indicates the change in vehicle speed over time. The portion where the vehicle speed temporarily becomes zero indicates that engine 5 is idling. Figure 10 (b) represents the change in siloxane concentration in the engine compartment over time. The siloxane concentration increases when engine 5 is idling and when combustion in engine 5 stops. Idling refers to the state in which engine 5 operates at a specified low rotational speed when the vehicle speed is zero.

[0127] Figure 10 (c) represents the change of the excess air ratio λ of engine 5 over time. The excess air ratio tends to increase as the vehicle speed approaches zero. Figure 10 (d) indicates the change in heating temperature of sensor unit 21 by heater control unit 61 over time. When engine 5 is running, sensor unit 21 is heated to the running control temperature T1, and when engine 5 stops running, sensor unit 21 is heated to the stop control temperature T2.

[0128] In this method, when combustion of the engine 5, which has been in a state of high siloxane concentration in the engine compartment for an extended period, ceases, poisoning of the atmospheric electrode 312 can be suppressed by heating the sensor unit 21 to the control temperature T2 at which combustion ceases. Furthermore, in the event that the atmospheric electrode 312 has become poisoned, recovery from poisoning can be achieved.

[0129] The heater control unit 61 and heater 22 can also heat the sensor unit 21 to the stop control temperature T2 when the engine 5 is idling. After the vehicle has been in motion, when the engine 5 returns to idle, the concentration of siloxane in the engine compartment also increases. Therefore, in this case, heating to the stop control temperature T2 can also suppress the poisoning of the atmospheric electrode 312 or restore the atmospheric electrode 312 from poisoning.

[0130] <Implementation Method 2>

[0131] This method illustrates the situation where the atmospheric electrode 312 is restored from poisoning using the voltage application unit 62 in the sensor control device 6.

[0132] like Figure 2As shown, the voltage application unit 62 of this method is configured such that, during combustion operation and when combustion stops, the atmospheric electrode 312 is set to the positive side, and a DC voltage is applied between the exhaust electrode 311 and the atmospheric electrode 312. Furthermore, as... Figure 11 As shown, the sensor control device 6 of this method has a degradation detection unit 64, which detects the amount of degradation of the detection value of the sensor unit 21 during combustion operation or when combustion stops. The degradation detection unit 64 detects the amount of degradation of the detection performance of the sensor unit 21 on the rich-fuel side when the air-fuel ratio of the engine 5 changes to the rich-fuel side.

[0133] (Voltage application section 62)

[0134] like Figure 12 and Figure 13 As shown, the voltage application unit 62 is configured to apply an operating voltage V1 between the exhaust electrode 311 and the atmospheric electrode 312 during combustion operation of the engine 5. The operating voltage V1 is set to any voltage within a range above and below 0.6V where the voltage-current relationship of the sensor unit 21 exhibits limiting current characteristics. Figure 13 The limiting current characteristics based on the relationship between the applied voltage and the output current of sensor unit 21 under varying air-fuel ratio (A / F) conditions are shown.

[0135] The so-called limiting current characteristic refers to the characteristic that when the voltage applied between the exhaust electrode 311 and the atmospheric electrode 312 increases, the current flowing between the atmospheric electrode 312 and the exhaust electrode 311 becomes a limit state because the introduction of exhaust gas G into the exhaust electrode 311 is restricted by the diffusion resistance section 32. In other words, the limiting current voltage exhibits a situation where the current remains constant even if the voltage changes. The lower limit value of the operating voltage V1 can be set to, for example, 0.1V or higher. If the operating voltage V1 exceeds 0.6V, the sensor unit 21 is prone to deterioration.

[0136] like Figure 12 As shown, the voltage application unit 62 is configured such that, when combustion of the engine 5 stops, a stop voltage V2, higher than the operating voltage V1, is applied between the exhaust electrode 311 and the atmospheric electrode 312, provided that the amount of degradation detected by the degradation detection unit 64 is above a predetermined value, thereby reducing the silicon oxide adhering to the atmospheric electrode 312. Both the operating voltage V1 and the stop voltage V2 are applied with the atmospheric electrode 312 side as the positive side. When the amount of degradation detected by the degradation detection unit 64 is above the predetermined value, it is presumed that silicon oxide, as a poisoning film, has formed on the atmospheric electrode 312. In this case, when the stop voltage V2 is applied between the exhaust electrode 311 and the atmospheric electrode 312 by the voltage application unit 62 when combustion stops, the silicon oxide can be reduced, and the poisoning film can be removed from the atmospheric electrode 312.

[0137] The stop voltage V2 is set to any voltage within the range of more than 0.6V and less than 1.2V. By setting the stop voltage V2 to more than 0.6V, the silicon oxide on the atmospheric electrode 312 can be reduced. When the stop voltage V2 exceeds 1.2V, blackening may occur on the solid electrolyte 31, causing degradation of the sensor unit 21. Blackening refers to the reduction and metallization of zirconium oxide and other components constituting the solid electrolyte 31.

[0138] In this method, the stopping voltage V2 is set to be higher than the oxidation potential of the noble metal contained in the atmospheric electrode 312 and lower than the reduction voltage of the solid electrolyte 31. The oxidation potential of the noble metal contained in the atmospheric electrode 312 is any value within the range of more than 0.6V and less than 1.2V. The oxidation potential of the noble metal in the atmospheric electrode 312 is related to the principle of reducing the oxide of silicon attached to the atmospheric electrode 312.

[0139] By applying a direct current voltage between the exhaust electrode 311 and the atmospheric electrode 312, silicon dioxide (SiO2), specifically the silicon oxide that forms a poisoning film on the atmospheric electrode 312, is reduced in the following manner: Specifically, by applying a direct current voltage between the exhaust electrode 311 and the atmospheric electrode 312 with the atmospheric electrode 312 as the positive side (the side with higher voltage), the platinum (Pt), a noble metal contained in the atmospheric electrode 312, is oxidized. The oxidation reaction on the atmospheric electrode 312 proceeds via Pt→Pt 2+ +2e - This reaction can be represented by a formula.

[0140] Furthermore, electrons are transferred from the atmospheric electrode 312 to silicon dioxide, and the silicon dioxide is reduced at the atmospheric electrode 312 using these electrons. The reduction reaction of silicon dioxide at the atmospheric electrode 312 is carried out by SiO2 (Si... 4+ )+4e - The reaction can be represented by the equation →Si + O₂. Thus, starting with the oxidation of the noble metal platinum in the atmospheric electrode 312, the reduction of silicon oxide (silicon dioxide) in the atmospheric electrode 312 occurs. By reducing silicon dioxide, the active sites of the atmospheric electrode 312 used for oxygen ionization are restored.

[0141] The reduction voltage of the solid electrolyte 31 represents the voltage at which the solid electrolyte 31 blackens. It is the stopping voltage V2, and is a voltage in the range of 1V to 1.6V. The value of this reduction potential depends on the microcrystalline structure and grain size of the zirconium oxide constituting the solid electrolyte 31. The stopping voltage V2 is set to the voltage at which the solid electrolyte 31 does not blacken.

[0142] The application of the stop voltage V2 between the exhaust electrode 311 and the atmospheric electrode 312 by the voltage application unit 62 can be stopped after a predetermined time when combustion stops. The predetermined time for applying the stop voltage V2 is determined in advance by conducting experiments as the time required to reduce the silicon oxide attached to the atmospheric electrode 312. By setting the predetermined time for applying the stop voltage V2 to the minimum required to reduce the silicon oxide attached to the atmospheric electrode 312, it is possible to suppress power consumption in the vehicle, thermal load on the gas sensor 1, etc.

[0143] Furthermore, the specified time for applying the stop voltage V2 can be appropriately changed based on factors such as the engine combustion time required from the start to the stop of combustion in engine 5, the driving distance of the vehicle equipped with gas sensor 1, the sensor usage time of gas sensor 1 and sensor control device 6, and the history of the air-fuel ratio of engine 5. It is generally believed that the longer the engine combustion time, the vehicle driving distance, or the sensor usage time, the greater the amount of silicon oxide adhering to the atmospheric electrode 312. Additionally, it is generally believed that the longer the air-fuel ratio of engine 5 remains on the fuel-rich side, the greater the amount of silicon oxide adhering to the atmospheric electrode 312.

[0144] When the voltage application unit 62 stops applying voltage V2 between the exhaust electrode 311 and the atmospheric electrode 312, it can be done once or in multiple times when combustion stops.

[0145] (Deterioration Detection Department 64)

[0146] like Figure 12 As shown, the degradation detection unit 64 in this method is configured to detect the degradation amount of the sensor unit 21 during neutralization control C1 after a fuel cut-off operation FC that stops fuel supply to any cylinder of the engine 5. After the fuel cut-off operation FC, the exhaust pipe 7, where the three-way catalyst 72 is located, is in a state where the oxygen ratio is higher than the stoichiometric air-fuel ratio. Furthermore, during neutralization control C1, the environment in which the three-way catalyst 72 is located in the exhaust pipe 7 after the fuel cut-off operation FC is made close to the stoichiometric air-fuel ratio, so that in the cylinder where fuel supply has stopped, the fuel supply amount (fuel injection amount) is excessive compared to the stoichiometric air-fuel ratio. At this time, the air-fuel ratio of the exhaust gas G detected by the gas sensor 1 becomes on the rich-fuel side.

[0147] Furthermore, the degradation detection unit 64 compares the estimated air-fuel ratio, which is estimated based on the ratio of fuel supply to combustion air supply, with the detected air-fuel ratio detected by the output current of the gas sensor 1, and calculates the degradation amount of the detection value of the sensor unit 21 based on the difference between the detected air-fuel ratio and the estimated air-fuel ratio. Since the estimated air-fuel ratio is not affected by the poisoning degradation of the atmospheric electrode 312, it is used as a reference value for comparison.

[0148] If the degradation of the detected value by sensor unit 21 is significant, it is presumed that silicon oxide has adhered to the atmospheric electrode 312. Furthermore, when combustion stops (the combustion operation of engine 5 ceases), voltage application unit 62 applies a stop voltage V2 between exhaust electrode 311 and atmospheric electrode 312 if the degradation of the detected value exceeds a predetermined value. This reduces the silicon oxide adhering to atmospheric electrode 312.

[0149] Figure 12 (a), (b), and (c) show the vehicle's state and the changes in the operation of the voltage application unit 62 over time. Figure 12 (a) represents the change in vehicle speed over time. Figure 12 (b) represents the change of the excess air ratio λ of engine 5 over time. The excess air ratio becomes lean-burn side under fuel cut-off state FC, and then becomes rich-burn side under neutralization control C1. Under this neutralization control C1, a difference arises between the estimated air-fuel ratio and the detected air-fuel ratio. Figure 12 (c) indicates the change in voltage applied by voltage application unit 62 to sensor unit 21 (between exhaust electrode 311 and atmospheric electrode 312) over time. When the engine 5 is running, the operating voltage V1 is applied to sensor unit 21, and when the engine 5 stops running, the stopping voltage V2 is applied to sensor unit 21.

[0150] (Other structures of the deterioration detection unit 64)

[0151] The degradation detection unit 64 can also measure the current flowing between the atmospheric electrode 312 and the exhaust electrode 311 using the current measuring unit 63 when a predetermined voltage is applied between the exhaust electrode 311 and the atmospheric electrode 312 by the voltage applying unit 62. Based on the resistance value of the sensor unit 21 calculated according to the relationship between the voltage and current, the degradation amount of the sensor unit 21's detection value is detected. It is generally believed that the more silicon oxide adheres to the atmospheric electrode 312, the higher the resistance value. Furthermore, a higher resistance value indicates a greater degree of degradation. In addition, the degradation detection unit 64 can detect the degradation amount of the sensor unit 21's detection value during combustion operation or when combustion has stopped.

[0152] When the degradation detection unit 64 performs degradation detection during combustion operation, during the period when the voltage application unit 62 applies the voltage for degradation detection between the exhaust electrode 311 and the atmospheric electrode 312, the current flowing between the atmospheric electrode 312 and the exhaust electrode 311 is not used as the output value of the sensor utilizing the limiting current characteristic. Furthermore, during degradation detection, the voltage applied by the voltage application unit 62 between the exhaust electrode 311 and the atmospheric electrode 312 can be set to a value higher than the operating voltage V1.

[0153] When the deterioration detection unit 64 performs deterioration detection during combustion operation, when combustion stops, it determines whether the amount of deterioration detected by the deterioration detection unit 64 is above a specified value. When combustion stops, the voltage application unit 62 can apply the stop voltage V2 between the exhaust electrode 311 and the atmospheric electrode 312.

[0154] (Resumption of Judgment Section 65)

[0155] like Figure 11 As shown, the sensor control device 6 may also include a recovery determination unit 65, which determines the degree to which the degradation of the sensor unit 21's detection value has been recovered after the voltage application unit 62 applies the stop voltage V2. The recovery determination unit 65 can detect the resistance value between the exhaust electrode 311 and the atmospheric electrode 312 when the stop voltage V2 is applied between the exhaust electrode 311 and the atmospheric electrode 312 by the voltage application unit 62, and determine the degree of recovery of the sensor unit 21's detection value based on this resistance value. When the stop voltage V2 is applied between the exhaust electrode 311 and the atmospheric electrode 312 by the voltage application unit 62, the current flowing between the atmospheric electrode 312 and the exhaust electrode 311 can be measured by the current measuring unit 63, thereby detecting the resistance value. The voltage applied between the exhaust electrode 311 and the atmospheric electrode 312 to detect the resistance value can be set to an appropriate value such as the operating voltage V1. The recovery determination unit 65 can determine the degree of recovery of degradation when combustion stops.

[0156] Furthermore, the recovery determination unit 65 can also determine that the degradation of the detection value of the sensor unit 21 has been recovered when the resistance value becomes below a predetermined threshold value. The application of voltage and measurement of current (resistance value detection) by the recovery determination unit 65 can be repeated multiple times. Alternatively, the recovery determination unit 65 can determine that the degradation of the detection value of the sensor unit 21 has been recovered only when the resistance value repeatedly becomes below the predetermined threshold value.

[0157] The application of the stop voltage V2 by the voltage application unit 62 to the exhaust electrode 311 and the atmospheric electrode 312 can continue even when combustion stops, until the recovery determination unit 65 determines that the degradation of the detection value of the sensor unit 21 has been recovered. In other words, while the stop voltage V2 is applied by the voltage application unit 62, the current flowing between the atmospheric electrode 312 and the exhaust electrode 311 can be measured continuously or intermittently, and the application of voltage by the voltage application unit 62 can be stopped when the resistance value calculated based on the stop voltage V2 and the current falls below a predetermined threshold.

[0158] Figure 14 (a), (b), (c), and (d) show the changes in the operation of the recovery determination unit 65 over time. Figure 14 (a) indicates the change in heating temperature of sensor unit 21 heated by heater control unit 61 over time. Figure 14 (b) indicates the change in the voltage applied by the voltage application unit 62 to the sensor unit 21 over time. When the stop voltage V2 is intermittently applied to the sensor unit 21, voltage pulsation is generated. Figure 14 (c) indicates the change of the output current generated by sensor unit 21 over time. The output current generated by sensor unit 21 represents the output current flowing through solid electrolyte 31 between atmospheric electrode 312 and exhaust electrode 311. The output current generated by sensor unit 21 increases each time the degradation of atmospheric electrode 312 is restored by applying stop voltage V2.

[0159] Figure 14 (d) represents the change in resistance value of sensor unit 21 over time. Each time the atmospheric electrode 312 recovers from degradation by applying a stop voltage V2, the resistance value of sensor unit 21 decreases. When this resistance value falls below a predetermined threshold, it is determined that the poisoning degradation of atmospheric electrode 312 has recovered.

[0160] In addition to detecting the resistance value between the exhaust electrode 311 and the atmospheric electrode 312, the degradation detection unit 64 and the recovery determination unit 65 can also detect various physical property values ​​related to the poisoning of the atmospheric electrode 312 due to silicon oxide. Furthermore, the degradation detection unit 64 and the recovery determination unit 65 can also sense the amount of degradation or recovery based on various physical property values.

[0161] In addition, the recovery determination unit 65 can also be applied to the case shown in Embodiment 1 where the heater control unit 61 heats the sensor unit 21 to the stop control temperature T2, or simultaneously applies the stop voltage V2 of the voltage application unit 62 and heats the sensor unit 21 to the stop control temperature T2.

[0162] (Control methods)

[0163] Reference Figure 15 The flowchart below illustrates the control method of the sensor control device 6 in this embodiment.

[0164] First, in response to the vehicle's ignition switch being turned on, combustion operation of the engine 5 begins (step S201). Additionally, in response to this, control of the gas sensor 1 and the sensor control device 6 begins (step S201). Then, the voltage application unit 62 of the sensor control device 6 applies an operating voltage V1 between the exhaust electrode 311 and the atmospheric electrode 312 of the sensor unit 21, and the heater control unit 61 of the sensor control device 6 heats the sensor unit 21 to the operating control temperature T1 (step S202).

[0165] Next, the sensor control device 6 determines whether fuel cut-off operation (FC) has been performed by the engine control device (step S203). After fuel cut-off operation (FC) has been performed, the degradation detection unit 64 calculates the degradation amount of the detection value of the sensor unit 21 by comparing the estimated air-fuel ratio with the detected air-fuel ratio (step S204). The degradation detection unit 64 calculates the degradation amount of the detection value of the sensor unit 21 based on the difference between the estimated air-fuel ratio and the detected air-fuel ratio. Furthermore, if fuel cut-off operation (FC) has not been performed, the degradation amount detected by the degradation detection unit 64 is not calculated.

[0166] Next, it is determined whether the ignition switch is turned off, thus stopping the combustion operation of the engine 5 (step S205). Until the ignition switch is turned off, the engine 5 continues to operate in response to the feedback of the air-fuel ratio from the gas sensor 1 and the sensor control device 6.

[0167] Next, when the combustion operation of the engine 5 stops, it is determined whether the degradation amount of the detection value of the sensor unit 21 has been calculated by the degradation detection unit 64 (step S206). If the degradation amount has been calculated, the sensor control device 6 determines whether the degradation amount is above a predetermined value (step S207). If the degradation amount is above the predetermined value, the voltage application unit 62 applies a stop voltage V2 to the exhaust electrode 311 and the atmospheric electrode 312 for a predetermined time (step S208). At this time, the recovery determination unit 65 detects the resistance value between the exhaust electrode 311 and the atmospheric electrode 312 based on the current flowing between the exhaust electrode 311 and the atmospheric electrode 312 (step S209).

[0168] Then, the recovery determination unit 65 determines whether the detected resistance value has fallen below a predetermined threshold (step S210). The more the detection value of the sensor unit 21 deteriorates, in other words, the more the poisoned film adheres to the atmospheric electrode 312, the higher the resistance value. The predetermined threshold for the resistance value can be set as a value that is considered normal for the resistance value of the sensor unit 21.

[0169] If the detected resistance value is not below a predetermined threshold, it is assumed that the degradation of the detection value of the sensor unit 21 has not yet been recovered, and the voltage application unit 62 applies the stop voltage V2 to the exhaust electrode 311 and the atmospheric electrode 312 again for a predetermined time (step S208). Then, the recovery determination unit 65 detects the resistance value between the exhaust electrode 311 and the atmospheric electrode 312 again based on the current flowing between the exhaust electrode 311 and the atmospheric electrode 312 (step S209).

[0170] The application of the stop voltage V2 of the voltage application unit 62 and the detection of the resistance value are performed repeatedly as appropriate. When the detected resistance value falls below a predetermined threshold, the application of the stop voltage V2 of the voltage application unit 62 is stopped. In this way, by applying the stop voltage V2, the silicon oxide attached to the atmospheric electrode 312 is reduced, and the degradation of the detection value of the sensor unit 21 is restored. Furthermore, if the degradation amount is not calculated in step S206 or if the degradation amount is not above a predetermined value in step S207, the application of the stop voltage V2 of the voltage application unit 62 is not performed.

[0171] Furthermore, when combustion in the engine 5 ceases, the sensor unit 21 can be heated to a predetermined temperature by the heater control unit 61 when a stop voltage V2 is applied between the exhaust electrode 311 and the atmospheric electrode 312 via the voltage application unit 62. This predetermined temperature can be set to the operating control temperature T1 shown in Embodiment 1.

[0172] (Effects)

[0173] In the sensor control device 6 of this method, the voltage application unit 62, which applies voltage between the exhaust electrode 311 and the atmospheric electrode 312, is designed to restore the atmospheric electrode 312 from poisoning. Specifically, the voltage application unit 62 is configured such that, when combustion of the engine 5 stops, a stop-time voltage V2, higher than the operating voltage V1, is applied between the exhaust electrode 311 and the atmospheric electrode 312, provided that the amount of degradation detected by the degradation detection unit 64 is above a predetermined value, thereby reducing the silicon oxide adhering to the atmospheric electrode 312. With this structure, the silicon oxide that forms a poisoning film due to the adhering of toxic gases such as siloxane gas to the atmospheric electrode 312 can be reduced, restoring the atmospheric electrode 312's function of ion activation for oxygen.

[0174] Regarding the other structures and effects of the gas sensor 1 and sensor control device 6 in this embodiment, they are the same as those in Embodiment 1. Furthermore, in this embodiment, the constituent elements indicated by the same reference numerals as those in Embodiment 1 are the same as those in Embodiment 1.

[0175] <Implementation Method 3>

[0176] This method illustrates the use of the heater control unit 61 and voltage application unit 62 in the sensor control device 6 to suppress the poisoning of the atmospheric electrode 312 or to restore the atmospheric electrode 312 from poisoning.

[0177] like Figure 16 As shown in (a), (b), and (c), the sensor control device 6 of this method is configured such that, when combustion stops, the heater control unit 61 heats the sensor unit 21 to the stop control temperature T2, and the voltage application unit 62 applies the stop voltage V2 between the exhaust electrode 311 and the atmospheric electrode 312. Furthermore, by heating the sensor unit 21 to the stop control temperature T2 and applying the stop voltage V2 to the sensor unit 21 (between electrodes 311 and 312), the silicon oxide adhering to the atmospheric electrode 312 is reduced.

[0178] Figure 16 (a) represents the change in vehicle speed over time. Figure 16 (b) indicates the change in the heating temperature of the sensor unit 21 by the heater control unit 61 over time. When the engine 5 is running, the sensor unit 21 is heated to the operating control temperature T1, and when the engine 5 stops running, the sensor unit 21 is heated to the stopping control temperature T2. Figure 16 (c) indicates the change of the voltage applied by the voltage application unit 62 to the sensor unit 21 over time. When the engine 5 is running, the operating voltage V1 is applied to the sensor unit 21, and when the engine 5 stops running, the stopping voltage V2 is applied to the sensor unit 21.

[0179] As previously described, by applying a stop voltage V2 between the exhaust electrode 311 and the atmospheric electrode 312, silicon dioxide (SiO2), i.e., the silicon oxide that forms a poisoning film on the atmospheric electrode 312, is reduced. The reduction potential of this silicon dioxide decreases as the temperature of the atmospheric electrode 312 increases. In other words, the higher the temperature of the atmospheric electrode 312, the easier it is for the silicon dioxide adhering to the atmospheric electrode 312 to be partially reduced at a lower voltage.

[0180] The thermal oxidation of siloxanes produces silicon dioxide, but thermodynamically, this results in a certain degree of oxygen deficiency. It is generally believed that the reduction potential of oxygen-deficient silicon dioxide is lower than that of ordinary silicon dioxide. Figure 17 The relationship between temperature and reduction potential of oxygen-deficient silica is shown. Furthermore, within the temperature range of 660°C to 950°C for atmospheric electrode 312 and silica, the higher the temperature, the lower the reduction potential of oxygen-deficient silica, which varies between approximately 0.65V and approximately 0.42V.

[0181] In this method, the stopping control temperature T2 and the stopping voltage V2 are determined in relation to the reduction potential of silicon dioxide. Specifically, the stopping voltage V2 is determined to be the reduction potential of silicon dioxide at a specified temperature that is higher than the stopping control temperature T2 by 660°C to 950°C. Furthermore, the stopping control temperature T2 is set such that the stopping voltage V2 is higher than the reduction potential of silicon dioxide at that stopping control temperature T2.

[0182] (Control methods)

[0183] Reference Figure 18 The flowchart below illustrates the control method of the sensor control device 6 in this embodiment.

[0184] First, in response to the vehicle's ignition switch being turned on, combustion operation of the engine 5 begins (step S301). Additionally, in response to this, control of the gas sensor 1 and the sensor control device 6 begins (step S301). Then, the voltage application unit 62 applies an operating voltage V1 between the exhaust electrode 311 and the atmospheric electrode 312 of the sensor unit 21, and the heater control unit 61 heats the sensor unit 21 to the operating control temperature T1 (step S302).

[0185] Next, it is determined whether the ignition switch is turned off, thus stopping the combustion operation of the engine 5 (step S303). Until the ignition switch is turned off, the engine 5 continues to operate in response to the feedback of the air-fuel ratio from the gas sensor 1 and the sensor control device 6.

[0186] Next, when the combustion operation of the engine 5 stops, the voltage application unit 62 applies a stop voltage V2 between the exhaust electrode 311 and the atmospheric electrode 312, and the heater control unit 61 heats the sensor unit 21 to the stop control temperature T2 (step S304). After a predetermined time has elapsed, the application of voltage by the voltage application unit 62 is stopped, and the heating by the heater control unit 61 is also stopped.

[0187] (Effects)

[0188] In the sensor control device 6 of this embodiment, by simultaneously applying the stop voltage V2 of the voltage application unit 62 and heating the stop control temperature T2 by the heater control unit 61, the poisoning of the atmospheric electrode 312 and its recovery from poisoning can be more effectively suppressed. Other structures and effects of the gas sensor 1 and sensor control device 6 of this embodiment are the same as those of the gas sensor 1 and sensor control device 6 of Embodiments 1 and 2. Furthermore, in this embodiment, the constituent elements indicated by the same reference numerals as those shown in Embodiments 1 and 2 are the same as those in Embodiments 1 and 2.

[0189] <Implementation Method 4>

[0190] This method illustrates the situation where the atmospheric electrode 312 is recovered from poisoning using the heater control unit 61 in the sensor control device 6.

[0191] like Figure 11 As shown, the sensor control device 6 of this embodiment includes a degradation detection unit 64, which detects the amount of degradation of the sensor unit 21's detection value during combustion operation or when combustion stops. In this embodiment, when a predetermined voltage is applied between the exhaust electrode 311 and the atmospheric electrode 312 via the voltage application unit 62, the degradation detection unit 64 uses the current measurement unit 63 to measure the current flowing between the exhaust electrode 311 and the atmospheric electrode 312, and detects the amount of degradation of the sensor unit 21's detection value, or in other words, the amount of degradation of the atmospheric electrode 312, based on the resistance value calculated according to the relationship between the voltage and the current.

[0192] It is generally believed that the more silicon oxide adheres to the atmospheric electrode 312, the higher the resistance value, and the higher the resistance value, the greater the degradation. In this embodiment, the heater control unit 61 is configured such that, based on the condition that the degradation detected by the degradation detection unit 64 is above a predetermined value, the sensor unit 21 is heated to the shutdown control temperature T2 when combustion stops. Furthermore, the structure of the degradation detection unit 64 can be the same as that shown in Embodiment 2.

[0193] (Control methods)

[0194] Reference Figure 19 The flowchart below illustrates the control method of the sensor control device 6 in this embodiment.

[0195] First, in response to the vehicle's ignition switch being turned on, combustion operation of the engine 5 begins (step S401). Additionally, in response to this, control of the gas sensor 1 and the sensor control device 6 begins (step S401). Then, the voltage application unit 62 applies an operating voltage V1 between the exhaust electrode 311 and the atmospheric electrode 312 of the sensor unit 21, and the heater control unit 61 heats the sensor unit 21 to the operating control temperature T1 (step S402).

[0196] Next, it is determined whether the ignition switch has turned off, thus stopping the combustion operation of the engine 5 (step S403). Until the ignition switch turns off, the engine 5 continues to operate in response to the feedback of the air-fuel ratio from the gas sensor 1 and the sensor control device 6.

[0197] Next, when the combustion operation of the engine 5 stops, the degradation detection unit 64 applies a predetermined voltage lower than the stop voltage V2 between the exhaust electrode 311 and the atmospheric electrode 312, calculates the resistance value of the sensor unit 21, and calculates the degradation amount of the atmospheric electrode 312 (step S404). Then, the sensor control device 6 determines whether the degradation amount of the atmospheric electrode 312 is greater than or equal to a predetermined amount (step S405). Then, if the degradation amount of the atmospheric electrode 312 is greater than or equal to a predetermined amount, the heater control unit 61 heats the sensor unit 21 to the stop control temperature T2 (step S406).

[0198] Furthermore, the heater control unit 61 stops heating after heating to the stop control temperature T2 for a predetermined time. Additionally, heating to the stop control temperature T2 is not performed if the degradation of the atmospheric electrode 312 is not above a predetermined amount.

[0199] (Effects)

[0200] In the sensor control device 6 of this method, the sensor unit 21 is heated to the stop control temperature T2 only when the deterioration detection unit 64 detects deterioration of the atmospheric electrode 312, thereby restoring the deterioration of the atmospheric electrode 312. Thus, the sensor unit 21 is heated to the stop control temperature T2, which is higher than the operating control temperature T1, only when it is necessary to restore the detection value of the sensor unit 21. Therefore, it is possible to prevent the sensor unit 21 from being unnecessarily heated to a high temperature.

[0201] Regarding the other structures and effects of the gas sensor 1 and sensor control device 6 in this embodiment, they are the same as those in embodiments 1 to 3. Furthermore, in this embodiment, the constituent elements indicated by the same reference numerals as those shown in embodiments 1 to 3 are the same as those in embodiments 1 to 3.

[0202] <Implementation Method 5>

[0203] This method illustrates the use of the heater control unit 61 in the sensor control device 6 to restore the atmospheric electrode 312 from poisoning.

[0204] like Figure 20 As shown, the sensor control device 6 of this embodiment has a degradation estimation unit 66, which estimates the degree of degradation of the sensor unit 21 based on the usage condition of the engine 5 or the gas sensor 1. The degradation estimation unit 66 estimates the degree of degradation of the sensor unit 21 based on at least one of the following: the number of times the engine 5 stops combustion from the point when the sensor unit 21 is heated to the control temperature T2 at the time of combustion shutdown; the driving distance of the vehicle equipped with the gas sensor 1; and the usage time of the gas sensor 1 and the sensor control device 6.

[0205] The adhesion of silicon oxide to the atmospheric electrode 312 is most significant when the engine 5 stops. Therefore, the more times the engine 5 stops combustion, the more silicon oxide adheres to the atmospheric electrode 312. The greater the amount of silicon oxide adhered to the atmospheric electrode 312, the greater the degradation (deterioration) of the sensor unit 21. Furthermore, if the driving distance of the vehicle equipped with the gas sensor 1 or the usage time of the gas sensor 1 and sensor control device 6 increases, the number of times the engine 5 stops combustion will also increase. Therefore, the driving distance or usage time can be used instead of the number of times the engine 5 stops combustion.

[0206] Furthermore, the closer the air-fuel ratio of engine 5 is to the stoichiometric air-fuel ratio, the easier it is for silicon oxides to adhere to the atmospheric electrode 312. This can also be used to correct the situation where the historical air-fuel ratio is closer to the stoichiometric air-fuel ratio, the greater the degradation of sensor unit 21.

[0207] The heater control unit 61 in this embodiment is configured to heat the sensor unit 21 to the shutdown control temperature T2 when combustion stops, provided that the degree of degradation estimated by the degradation estimation unit 66 is at or above a predetermined value. The degradation estimation unit 66 in this embodiment is configured to count and store the number of times combustion of the engine 5 stops each time combustion stops. Furthermore, when the number of combustion stops exceeds a predetermined number, the degradation estimation unit 66 estimates that the degree of degradation of the sensor unit 21 has reached or exceeded a predetermined value.

[0208] Furthermore, when the gas sensor 1 and the sensor control device 6 are mounted on a vehicle with an idle stop function, the number of times the combustion of the engine 5 is stopped due to idle stop can be excluded from the number of times the combustion stops are estimated by the degradation estimation unit 66, as shown in Embodiment 1.

[0209] (Control methods)

[0210] Reference Figure 21 The flowchart below illustrates the control method of the sensor control device 6 in this embodiment.

[0211] First, in response to the vehicle's ignition switch being turned on, combustion operation of the engine 5 begins (step S501). Additionally, in response to this, control of the gas sensor 1 and the sensor control device 6 begins (step S502). Then, the voltage application unit 62 applies an operating voltage V1 between the exhaust electrode 311 and the atmospheric electrode 312 of the sensor unit 21, and the heater control unit 61 heats the sensor unit 21 to the operating control temperature T1 (step S503).

[0212] Next, it is determined whether the ignition switch is turned off, thus stopping the combustion operation of the engine 5 (step S504). Until the ignition switch is turned off, the engine 5 continues to operate in response to the feedback of the air-fuel ratio from the gas sensor 1 and the sensor control device 6.

[0213] Next, when the combustion operation of engine 5 stops, the number of times combustion stops is counted and stored (step S505). Next, it is determined whether the number of combustion stops is greater than or equal to a predetermined number (step S506). If the number of combustion stops is less than or equal to a predetermined number, the system waits until the combustion operation of engine 5 resumes (step S507). Next, after the combustion operation of engine 5 resumes, steps S502 to S507 are executed until the number of combustion stops in step S506 becomes greater than or equal to a predetermined number.

[0214] Next, when the number of combustion stops exceeds a predetermined number, the degradation estimation unit 66 estimates that the degradation degree of the sensor unit 21 is above a predetermined value (step S508). Then, the heater control unit 61 heats the sensor unit 21 to the stop control temperature T2 (step S509). Furthermore, after heating to the stop control temperature T2 for a predetermined time, the heater control unit 61 stops heating.

[0215] In addition, the degree of degradation of the degradation estimation unit 66 can be estimated during combustion operation, and the sensor unit 21 can be heated to the stop control temperature T2 when combustion stops.

[0216] (Effects)

[0217] In the sensor control device 6 of this method, the sensor unit 21 is heated to the stop control temperature T2 only when the degradation estimation unit 66 estimates degradation of the sensor unit 21, thereby restoring the degradation of the atmospheric electrode 312. Thus, the sensor unit 21 is heated to the stop control temperature T2, which is higher than the operating control temperature T1, only when it is necessary to restore the detection value of the sensor unit 21. Therefore, it is possible to prevent the sensor unit 21 from being unnecessarily heated to a high temperature.

[0218] Regarding the other structures and effects of the gas sensor 1 and sensor control device 6 in this embodiment, they are the same as those in embodiments 1 to 3. Furthermore, in this embodiment, the constituent elements indicated by the same reference numerals as those shown in embodiments 1 to 3 are the same as those in embodiments 1 to 3.

[0219] This disclosure is not limited to the various embodiments, and further different embodiments can be constructed without departing from its spirit. Furthermore, this disclosure includes various modifications and equivalent modifications. Moreover, various combinations and arrangements of constituent elements conceived from this disclosure are also included in the technical concept of this disclosure.

Claims

1. A sensor control device for a gas sensor, the gas sensor having a sensor unit and a heater, disposed in the exhaust pipe of an internal combustion engine of a vehicle, the sensor unit being formed by disposing of an exhaust electrode exposed to exhaust gas and an atmospheric electrode exposed to the atmosphere opposite to each other on a solid electrolyte, the heater being used to heat the sensor unit. The sensor control device is characterized by having: The heater control unit is configured to control the heater to heat the sensor unit, and to heat the sensor unit to a control temperature during combustion operation of the internal combustion engine, and to heat the sensor unit to a stop control temperature higher than the control temperature during combustion when the internal combustion engine stops; and The degradation estimation unit estimates the degree of degradation of the sensor unit based on at least one of the following: the number of times the internal combustion engine stops combustion during combustion operation or when combustion stops, the driving distance of the vehicle equipped with the gas sensor, and the usage time of the gas sensor and the sensor control device. The heater control unit is configured to heat the sensor unit to the control temperature at the time of combustion cessation, provided that the degree of degradation estimated by the degradation estimation unit is above a predetermined value. By using the heater control unit to heat the sensor unit to the controlled temperature at the time of cessation when combustion stops, the silicon oxide attached to the atmospheric electrode is caused to crack.

2. A sensor control device for a gas sensor, the gas sensor having a sensor unit and a heater, disposed in the exhaust pipe of an internal combustion engine of a vehicle, the sensor unit being formed by disposing an exhaust electrode exposed to exhaust gas and an atmospheric electrode exposed to the atmosphere opposite each other on a solid electrolyte, the heater being used to heat the sensor unit. The sensor control device includes a heater control unit for controlling the heater's heating of the sensor unit. The sensor control device is characterized in that... The heater control unit is configured to heat the sensor unit to a control temperature during combustion of the internal combustion engine, and to heat the sensor unit to a stop control temperature higher than the control temperature during combustion of the internal combustion engine when combustion stops. The stop temperature is set to be higher than the temperature at which the thermal stress generated at the interface between the atmospheric electrode and the silicon oxide attached to the atmospheric electrode is greater than the tensile strength of the silicon oxide monomer, and lower than the temperature at which the crystal structure of the solid electrolyte changes.

3. A sensor control device for a gas sensor, the gas sensor having a sensor unit and a heater, disposed in the exhaust pipe of an internal combustion engine of a vehicle, the sensor unit being formed by disposing of an exhaust electrode exposed to exhaust gas and an atmospheric electrode exposed to the atmosphere opposite to each other on a solid electrolyte, the heater being used to heat the sensor unit. The sensor control device includes a heater control unit for controlling the heater to heat the sensor unit and a voltage application unit for applying voltage between the exhaust electrode and the atmospheric electrode. The sensor control device is characterized in that... The heater control unit is configured to heat the sensor unit to a control temperature during combustion of the internal combustion engine, and to heat the sensor unit to a stop control temperature higher than the control temperature during combustion of the internal combustion engine when combustion stops. The voltage application unit is configured to: apply an operating voltage between the exhaust electrode and the atmospheric electrode during combustion operation, and apply a shutdown voltage higher than the operating voltage between the exhaust electrode and the atmospheric electrode when combustion stops. By using the heater control unit to heat the sensor unit to the stop-time control temperature when combustion stops, and by using the voltage application unit to apply the stop-time voltage between the exhaust electrode and the atmospheric electrode when combustion stops, the silicon oxide attached to the atmospheric electrode is reduced.

4. The sensor control device according to claim 3, characterized in that, The stop voltage is set to be higher than the oxidation potential of the noble metal contained in the atmospheric electrode and lower than the reduction voltage of the solid electrolyte.

5. A sensor control device for a gas sensor, the gas sensor having a sensor unit and a heater, disposed in the exhaust pipe of an internal combustion engine of a vehicle, the sensor unit being formed by disposing an exhaust electrode exposed to exhaust gas and an atmospheric electrode exposed to the atmosphere opposite to each other on a solid electrolyte, the heater being used to heat the sensor unit. The sensor control device includes a voltage application unit that applies a voltage between the exhaust electrode and the atmospheric electrode, and a degradation detection unit that detects the degradation amount of the sensor unit's detection value during combustion operation or combustion cessation of the internal combustion engine. The sensor control device is characterized in that... The voltage application unit is configured such that, during combustion operation, an operating voltage is applied between the exhaust electrode and the atmospheric electrode, and, provided that the amount of degradation detected by the degradation detection unit is above a predetermined value, when combustion stops, a stopping voltage higher than the operating voltage is applied between the exhaust electrode and the atmospheric electrode to reduce the silicon oxide attached to the atmospheric electrode.

Images