JP2013221783A - Gas sensor controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas sensor controller capable of preventing deterioration in sensor responsiveness.SOLUTION: A gas sensor controller 10 comprises: a gas sensor 50 disposed in an exhaust passage 29 of an internal combustion engine 1 and including a sensor element and a porous protective layer which covers at least one portion of the sensor element; a heater provided in the gas sensor 50, for heating the sensor element; and a heater controller 32 for controlling energization of the heater. The porous protective layer contains ceramic particles, and the ceramic particles have an average particle diameter of 12 μm or less and a specific surface area of 20 m/g or less. The heater controller 32 can execute startup energization processing to energize the heater so that a temperature of the sensor element reaches a prescribed startup temperature at start-up of the internal combustion engine 1, and normal energization processing to energize the heater so that after the startup energization processing, the temperature of the sensor element is maintained at an activation temperature of the sensor element.

Description

  The present invention relates to a control device for a gas sensor.

Conventionally, a gas sensor using a gas detection element has been used to detect a specific gas in the atmosphere. This type of gas sensor can detect the concentration of a specific gas component such as hydrocarbon (HC) or oxygen (O ₂ ) contained in the exhaust gas of an automobile, for example, so that it can be used in an exhaust passage of an internal combustion engine such as an automobile engine. It is provided and used for control of internal combustion engines and exhaust gas purification devices.

As an oxygen sensor element for detecting the oxygen concentration in exhaust gas, for example, an oxygen concentration electromotive force type element using a ZrO ₂ solid electrolyte is known. As shown in FIG. 17, the oxygen sensor element 90 is a bottomed cylindrical body in which an inner electrode 94a, a solid electrolyte layer 92, an outer electrode 94b, and a diffusion resistance layer 96 are laminated in this order. A heater 97 is inserted inside the inner electrode 94a. The exhaust gas reaches the outer electrode 94b through the minute holes of the diffusion resistance layer 96, and obtains a sensor output between the outer electrode 94b and the inner electrode 94a. The diffusion resistance layer 96 is formed of a dense porous ceramic coating film in order to limit the flow rate of exhaust gas reaching the outer electrode 94b and to protect the outer electrode 94b.

  When this type of gas sensor element is used in an exhaust gas sensor for automobiles, it must be heated and activated in a high-temperature atmosphere of 500 ° C. or higher. Therefore, when water droplets in the exhaust gas adhere to the gas sensor, thermal stress due to partial quenching occurs. There is a problem that the gas sensor is cracked. Therefore, in order to solve the above-mentioned problem, there is a technique for relaxing the thermal stress by covering the periphery of the gas sensor with a porous protective layer 98 (see FIG. 17) so that the water droplet does not directly hit the gas sensor even when it gets wet. Proposed. Patent Document 1 describes that in a gas sensor provided with a porous protective layer, the porous protective layer is formed of alumina particles. In this publication, the porous protective layer is formed of alumina particles having an average particle diameter of 22 μm ± 4 μm and alumina particles having a particle diameter of 10 μm or less.

JP2011-252894A

By the way, when the internal combustion engine is started, exhaust gas may condense in the exhaust passage after the previous engine stop and water may remain in the exhaust passage. As a result of various studies on the gas sensor having the porous protective layer described above, the present inventor cannot obtain stable sensor characteristics when condensed water remaining in the exhaust passage adheres to the gas sensor, and sensor responsiveness. I found a problem that decreased. Specifically, the inventor has focused on the Mn component contained in the condensed water. That is, Mn components contained in gasoline or the like are concentrated in the condensed water, and when such Mn concentrated condensed water adheres to the gas sensor, it deposits as Mn oxide on the porous protective layer. When exhaust gas having a high oxygen concentration flows into the gas sensor in this state, the Mn oxide deposited on the porous protective layer is oxidized, and the oxidation reaction of Mn ₃ O ₄ + O ₂ → Mn ₂ O ₃ proceeds, Oxygen is consumed. Therefore, the oxygen concentration of the exhaust gas reaching the sensor electrode becomes lower than actual, and this state continues until the oxidation reaction is completed. Therefore, until the oxidation reaction ends, the value becomes lower than the actual oxygen concentration, and the response when the high oxygen concentration exhaust gas flows into the gas sensor is delayed.

On the other hand, when exhaust gas having a low oxygen concentration flows into the gas sensor, the Mn oxide deposited on the porous protective layer is reduced, and the reverse reaction, that is, the reduction reaction of Mn ₂ O ₃ → Mn ₃ O ₄ + O ₂ proceeds. As a result, oxygen is released into the exhaust gas. Therefore, the oxygen concentration of the exhaust gas reaching the sensor electrode becomes higher than actual, and this state continues until the reduction reaction is completed. Therefore, until the reduction reaction is completed, the value becomes higher than the actual oxygen concentration, and the response when the low oxygen concentration exhaust gas flows into the gas sensor is delayed. Thus, when Mn in the condensed water adheres to the gas sensor, an OSC reaction due to Mn oxidation-reduction (delay of oxygen concentration detection due to a valence change of Mn oxide) occurs, so that the responsiveness of the sensor decreases. Therefore, there is a demand for a mechanism that can effectively prevent the adhesion of Mn to the gas sensor.

  The present invention has been created to solve the above-described problems, and a main object thereof is to provide a gas sensor control device capable of preventing a decrease in sensor response.

  The present inventor has conceived that the cause of the decrease in sensor responsiveness in the gas sensor provided with the porous protective layer is the OSC reaction due to oxidation and reduction of Mn deposited on the porous protective layer. As a mechanism to prevent the accumulation of gas, it has been found that it is effective to use ceramic particles with a small diameter and a low specific surface area in the porous protective layer, and to heat the gas sensor to a high temperature immediately after the engine is started. did.

That is, the gas sensor control device provided by the present invention is provided in the gas sensor, which is disposed in the exhaust passage of the internal combustion engine and includes a sensor element and a porous protective layer covering at least a part of the sensor element. And a heater unit that heats and activates the sensor element, and a heater control unit that controls energization of the heater unit. The porous protective layer contains ceramic particles, and the ceramic particles have an average particle diameter of 12 μm or less based on a laser scattering method and a specific surface area of 20 m ² / g or less based on a nitrogen adsorption method. . Here, the heater control unit performs a start-up energization process for energizing the heater unit and a start-up energization process so that the temperature of the sensor element becomes a predetermined start temperature when the internal combustion engine is started. Thereafter, a normal energization process for energizing the heater unit can be performed so that the temperature of the sensor element is maintained at the activation temperature of the sensor element.

In the structure of this invention, the ceramic particle which comprises the porous protective layer of a gas sensor is adjusted to the small diameter (12 micrometers or less) and the low specific surface area (20 m < ² > / g or less). Thus, when a porous protective layer is comprised from the ceramic particle of a small diameter and a low specific surface area, it becomes difficult for a condensed water to permeate into a porous protective layer. Therefore, it becomes difficult for Mn contained in the condensed water to adhere to the porous protective layer. Further, in the gas sensor control device disclosed herein, the gas sensor is temporarily heated to a high temperature immediately after the engine is started, so that Mn adhering to the gas sensor is blown off together with the condensed water and hardly adheres to the gas sensor. This appropriately prevents Mn from adhering to the porous protective layer and keeps the gas sensor clean. Therefore, according to the present invention, the sensor response delay due to Mn adhesion as in the prior art is suitably prevented, and the sensor response is significantly improved.

  The predetermined start temperature in the start-up energization process is preferably set to a temperature at which condensed water adhering to the gas sensor does not penetrate into the porous protective layer. If the starting temperature is too low, when the condensed water adheres to the gas sensor, the porous protective layer tends to penetrate. When condensed water soaks into the porous protective layer in this way, Mn in the condensed water is deposited on the porous protective layer and causes an oxidation-reduction reaction, so that the sensor response is lowered. Therefore, it is preferable that the starting temperature is set to a temperature at which the condensed water adhering to the gas sensor does not soak into the porous protective layer. For example, the starting temperature in the start-up energization process may be set to a temperature equal to or higher than the activation temperature of the sensor element (preferably higher than the activation temperature). The starting temperature is desirably set to a temperature exceeding 700 ° C., for example, 750 ° C. or higher (for example, 750 ° C. to 900 ° C.), preferably 800 ° C. or higher, particularly preferably 900 ° C. or higher. When the start-up energization process is performed within such a temperature range, the condensed water adhering to the gas sensor can be suitably repelled.

  The average particle size of the ceramic particles disclosed here is approximately 12 μm or less. For example, it is preferable to use ceramic particles having an average particle diameter of about 10 μm or less, more preferably 8 μm or less, and particularly preferably 6 μm or less. If the average particle size of the ceramic particles is too larger than 12 μm, the water resistance improvement effect due to the use of small-sized ceramic particles for the porous protective layer tends to decrease. In addition, Mn blown off by the start-up energization process easily adheres to the ceramic particles. Therefore, even if the start-up energization process is performed, the desired effect may not be sufficiently exhibited.

The ceramic particles disclosed herein preferably have a BET specific surface area in a range of approximately 20 m ² / g or less. Ceramic particles satisfying such a BET specific surface area can be used for a porous protective layer of a gas sensor and can stably exhibit higher performance. For example, it is possible to form a gas sensor with little soaking even when it comes into contact with moisture in the exhaust gas (for example, the soaking depth is suppressed to 80 μm or less). The suitable range of the BET specific surface area is usually 20 m ² / g or less, preferably 15 m ² / g or less, particularly preferably 10 m ² / g or less.

  In a preferred aspect of the gas sensor control device disclosed herein, a temperature sensor is disposed in the exhaust passage, and the heater control unit is electrically connected to the temperature sensor. Here, the heater control unit measures the temperature in the exhaust passage by the temperature sensor during the start-up energization process, and the measured value of the temperature exceeds a predetermined reference value. The start-up energization process is configured to end. The reference value for the temperature of the start-up energization process may be set within a range of 100 ° C. to 150 ° C., for example. According to such a configuration, the start-up energization process can be ended immediately after the condensed water remaining in the exhaust passage is vaporized, that is, immediately after there is no possibility that the condensed water adheres to the gas sensor. As a result, it is possible to prevent the start-up energization process from becoming unnecessarily long and to switch to the normal energization process at an appropriate timing. The reference value for the temperature is more preferably set within a range of 100 ° C to 120 ° C.

  In a preferred aspect of the gas sensor control device disclosed herein, the heater control unit is configured to end the start-up energization process when the duration of the start-up energization process exceeds a predetermined reference value. Has been. According to this configuration, it is not necessary to arrange a temperature sensor in the exhaust passage, so that the device configuration can be simplified. More preferably, the reference value for the duration is set within a range of approximately 400 seconds to 500 seconds, for example, 7 minutes to 8 minutes.

  In a preferred aspect of the gas sensor control device disclosed herein, the maximum thickness of the porous protective layer is 80 μm or less. By setting the minimum thickness of the porous protective layer to 80 μm or less, the responsiveness of the gas sensor can be further improved.

It is the figure which showed typically the exhaust gas purification apparatus and gas sensor control apparatus which concern on one Embodiment of this invention. It is sectional drawing which showed typically the gas sensor which concerns on one Embodiment of this invention. It is a flowchart for demonstrating the control flow of the gas sensor control apparatus which concerns on one Embodiment of this invention. It is a graph which shows the relationship between engine starting time and exhaust pipe temperature. It is a flowchart for demonstrating the control flow of the gas sensor control apparatus which concerns on other embodiment of this invention. It is a flowchart for demonstrating the control flow of the gas sensor control apparatus which concerns on other embodiment of this invention. It is a graph which shows the relationship between the specific surface area of a ceramic particle, and the penetration depth. It is a graph which shows the relationship between the average particle diameter of ceramic particles, and the penetration depth. It is a graph which shows the relationship between sensor control temperature and a penetration depth. 2 is a cross-sectional SEM image of the gas sensor according to Example 1 after a Mn durability test. It is a cross-sectional SEM image after the Mn endurance test of the gas sensor concerning comparative example 1. It is a cross-sectional SEM image after the Mn endurance test of the gas sensor concerning comparative example 2. It is a cross-sectional SEM image after the Mn endurance test of the gas sensor concerning comparative example 3. 6 is a graph showing sensor output responses before and after the Mn durability test of the gas sensor according to Example 1; It is a graph which shows the sensor output response before and behind the Mn endurance test of the gas sensor concerning comparative example 1. It is a graph which shows the sensor output response before and behind the Mn endurance test of the gas sensor concerning comparative example 3. It is the figure which showed the conventional gas sensor typically.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in the field. The present invention can be carried out based on the contents disclosed in the present specification and common general technical knowledge in the field.

(First embodiment)
Here, first, the configuration of the exhaust gas purification apparatus according to an embodiment of the present invention will be described. The exhaust gas purifying apparatus disclosed here is provided in an exhaust system of an internal combustion engine. Hereinafter, an internal combustion engine and an exhaust gas purification apparatus will be described with reference to FIG. FIG. 1 is a diagram schematically showing an internal combustion engine 1 and an exhaust gas purification device 100 provided in an exhaust system of the internal combustion engine 1.

<Internal combustion engine>
An internal combustion engine (engine) is supplied with an air-fuel mixture containing oxygen and fuel gas. The internal combustion engine burns the air-fuel mixture and converts the combustion energy into mechanical energy. The air-fuel mixture combusted at this time becomes exhaust gas and is discharged to an exhaust system described later. Although the internal combustion engine 1 having the configuration shown in FIG. 1 is mainly composed of a gasoline engine of an automobile, an engine other than a gasoline engine (for example, a diesel engine) can be used.

  In the internal combustion engine 1 configured as shown in FIG. 1, a cylinder head 13 is connected to a cylinder block 12. A plurality of cylinder bores 14 are formed in the cylinder block 12. Pistons 15 are fitted to the cylinder bores 14 so as to be movable up and down. A crankshaft (not shown) is rotatably supported on the lower portion of the cylinder block 12. Each piston 15 is connected to a crankshaft via a connecting rod 16. In the following, only one cylinder will be described.

  The combustion chamber 17 includes a cylinder block 12, a cylinder head 13, and a piston 15. An intake port 18 and an exhaust port 19 communicate with the combustion chamber 17. A lower end portion of the intake valve 20 is located between the intake port 18 and the combustion chamber 17. The intake port 18 is opened and closed by the vertical movement of the intake valve 20. A lower end portion of the exhaust valve 21 is located between the exhaust port 19 and the combustion chamber 17. The exhaust port 19 is opened and closed by the vertical movement of the exhaust valve 21. In the following description, a system that is provided upstream of the intake port 18 and supplies air (oxygen) to the internal combustion engine 1 is referred to as an “intake system”, and is provided downstream of the exhaust port 19. A system that exhausts the exhaust gas generated in step 1 to the outside is referred to as an “exhaust system”.

  The intake system of the internal combustion engine 1 will be described. An intake manifold 22 is connected to the intake port 18 for communicating the internal combustion engine 1 with the intake system. The intake manifold 22 is connected to an intake pipe 23, and an air cleaner 24 is connected to the intake pipe 23. An air flow meter (not shown) is disposed downstream of the air cleaner 24 (internal combustion engine 1 side). The air flow meter is a sensor that detects the amount of intake air supplied to the intake pipe 23. A throttle valve 25 is provided further downstream of the air flow meter in the intake pipe 23. By opening and closing the throttle valve 25, the amount of air supplied to the internal combustion engine 1 can be adjusted. Further, a throttle sensor (not shown) for detecting the opening degree of the throttle valve 25 may be disposed in the vicinity of the throttle valve 25.

  Next, the exhaust system of the internal combustion engine 1 will be described. An exhaust manifold 28 is connected to the exhaust port 19 for communicating the internal combustion engine 1 with the exhaust system. The exhaust manifold 28 is connected to an exhaust pipe 29 through which exhaust gas flows.

<Exhaust gas purification device>
The exhaust gas purifying apparatus disclosed here is provided in the exhaust system of the internal combustion engine 1. This exhaust gas purifying apparatus includes a catalyst unit 40 and a control unit 30 and contains harmful components (for example, carbon monoxide (CO), hydrocarbon (HC), nitrogen oxide (NO _x )) contained in the exhaust gas discharged. ) Purify.

<Catalyst part>
Next, the catalyst unit 40 will be described in detail. The catalyst unit 40 is provided in the exhaust pipe 29 that communicates with the engine 1. Specifically, as shown in FIG. 1, the catalyst unit 40 is provided on the downstream side of the exhaust pipe 29. The kind of catalyst part 40 is not specifically limited. The catalyst unit 40 may be a monolith catalyst on which a noble metal such as platinum (Pt), palladium (Pd), rhodium (Rd) is supported, for example. The catalyst unit 40 disclosed herein is composed of a base material, a support supported on the base material, and a noble metal catalyst (typically a metal catalyst belonging to the platinum group) supported on the support. Yes. As a base material, the thing of the various raw materials and form used for this kind of conventional use can be used. For example, cordierite having high heat resistance, a honeycomb substrate having a honeycomb structure formed of ceramics such as silicon carbide (SiC) or an alloy (stainless steel, etc.) can be suitably employed. The shape of the substrate may be a foam shape, a pellet shape, etc. in addition to the honeycomb shape. In addition to the cylindrical shape, the overall shape of the base material may be an elliptical cylindrical shape or a polygonal cylindrical shape. The catalyst unit 40 may be a DPF or the like on which a noble metal is supported. The exhaust pipe 29 may be provided with an exhaust system fuel injection valve that injects fuel into the exhaust gas. The exhaust system fuel injection valve can adjust the air-fuel ratio (A / F) of the exhaust gas supplied to the catalyst unit 40 by injecting fuel into the exhaust gas.

  A gas sensor 50 is disposed in the exhaust pipe 29 downstream of the catalyst unit 40. The gas sensor 50 is a sensor that detects the concentration of a specific gas component (here, oxygen) in the exhaust gas flowing through the exhaust pipe 29 downstream of the catalyst unit 40, and is a sensor that detects the air-fuel ratio of the exhaust gas. . The arrangement position of the gas sensor 50 is not limited to the position illustrated in FIG. 1 as long as the oxygen concentration of the exhaust gas can be measured. The gas sensor 50 may be any sensor that can detect that at least the air-fuel ratio is on the rich side or the lean side. For example, the gas sensor may be a sensor (for example, a limiting current oxygen sensor) that linearly detects an air-fuel ratio in accordance with the oxygen concentration in the exhaust gas. Alternatively, an oxygen sensor that outputs an electromotive force of the sensor element may be used as the gas sensor 50. The gas sensor 50 may be disposed in the exhaust pipe 29 on the upstream side of the catalyst unit 40. The number is not limited to one, and a plurality of gas sensors 50 may be arranged. For example, the gas sensors 50 may be arranged on both the upstream side and the downstream side of the catalyst unit 40.

<Control unit (ECU: Engine Control Unit)>
The control unit (ECU) 30 is mainly composed of a digital computer, and functions as a control device in the operation of the exhaust gas purification device 100. The control unit 30 includes, for example, a ROM that is a read-only storage device, a RAM that is a readable / writable storage device, a CPU that performs arbitrary computation and determination, an input port, and an output port. The control unit 30 is a unit that performs control between the engine unit 1 and the gas sensor 50, and is electrically connected to the engine 1 and the gas sensor 50. An output signal from the gas sensor 50 is input to an input port of the control unit 30 via a corresponding AD converter (not shown). On the other hand, the output port of the control unit 30 is connected to the injector 26, a step motor for driving the throttle valve 25, a spark plug 27, and the like via corresponding drive circuits. The control unit 30 controls energization to the gas sensor 50 and performs air-fuel ratio feedback control of the engine 1 based on the output from the gas sensor 50. For example, the control unit 30 determines the fuel injection timing of the injector 26, the ignition timing of the spark plug 27, and the like based on the detected operating air amount, throttle opening (or accelerator opening), engine speed, and the like. It is possible to control.

<Gas sensor control device>
As part of the exhaust gas purification apparatus 100, the gas sensor control apparatus 10 according to the present embodiment is provided. Hereinafter, the gas sensor control device 10 will be described.

<Gas sensor>
First, the structure of the gas sensor 50 will be described with reference to FIG. FIG. 2 is a schematic diagram showing an example of the configuration of the main part of the gas sensor of the present embodiment, and shows a cross section thereof. The gas sensor 50 includes a sensor element 60 for detecting the oxygen concentration in the exhaust gas, a heater unit 70 for heating the sensor element 60, and a porous member that protects the sensor element 60 and the heater 70 from moisture in the exhaust gas. And a quality protective layer 52.

  The sensor element 60 includes a solid electrolyte body 62. The solid electrolyte body 62 is composed of a solid electrolyte having oxygen ion conductivity. Examples of such a solid electrolyte include zirconia (for example, yttria stabilized zirconia (YSZ)). A measurement electrode 64a is formed outside the solid electrolyte body 62, and a measurement gas space 66a into which exhaust gas can be introduced while forming the solid electrolyte body 62 as one wall surface is formed outside the measurement electrode 64a. ing. The measurement gas space 66 a is defined by the solid electrolyte body 62, the diffusion resistance layer 68, and the shielding layer 69. The shielding layer 69 has an internal structure impermeable to gas, and is made of alumina here. The diffusion resistance layer 68 is provided at positions (here, both ends in the width direction of the measurement gas space 66a) that define the measurement gas space 66a around the measurement electrode 64a in order to regulate the amount of exhaust gas introduced into the measurement electrode 64a. The exhaust gas is introduced into the measurement gas space 66a through the diffusion resistance layer 68. As a material of the diffusion resistance layer 68, a material that can constitute a porous material such as alumina, zirconia, or ceria may be used. On the other hand, a reference electrode 64b is formed inside the solid electrolyte body 62, and a reference gas space 66b into which a reference gas such as the atmosphere can be introduced is formed so as to surround the reference electrode 64b. The reference gas space 66 b is defined by the solid electrolyte body 62 and the protective layer 65. The protective layer 65 has an internal structure impermeable to gas, and is made of alumina here. Both the reference electrode 64b and the measurement electrode 64a are made of a noble metal having high catalytic activity such as platinum.

  The heater unit 70 includes an insulating base 72 mainly composed of alumina, and a heating resistor 74 laminated on the insulating base 72. The solid electrolyte body 62 made of zirconia or the like exhibits insulating properties at room temperature, but becomes activated when exposed to a high temperature environment, and exhibits high oxygen ion conductivity. The heater unit 70 is heated and controlled so that the heating region of the solid electrolyte body 62 is formed and the activation temperature thereof is reached. In this embodiment, the heater unit 70 is disposed on the outer layer of the protective layer 65 on the reference electrode 64 b side of the solid electrolyte body 62. The heating resistor 74 is made of a resistor such as platinum, for example.

  The porous protective layer 52 is composed of a porous body in which a large number of ceramic particles are bonded, and is provided to prevent moisture from reaching the sensor element 60 and causing the sensor element 60 to be subject to water cracking. Yes. In this embodiment, the sensor element 60 and the heater unit 70 are notched in a tapered shape in the illustrated cross-sectional shape. The thickness of the porous protective layer 52 is adjusted. In this embodiment, the thicknesses t1 to t5 are different for each part. It is preferable that the maximum thickness of the porous protective layer 52 that is different for each part is approximately 80 μm or less. When the thickness of the porous protective layer 52 is 80 μm or less, the sensor activation time of the gas sensor 50 is improved. Therefore, for example, it becomes possible to fall below the sensor activation time that satisfies the regulations regarding the emission amount in EuroVI. That is, in FIG. 2, the porous protective layer 52 is preferably formed so that the largest thickness among the thicknesses t1 to t5 is 80 μm. On the other hand, if the thickness of the porous protective layer 52 is too thin, it may not be possible to prevent moisture from reaching the sensor element 60 and causing the sensor element 60 to be cracked by water. Therefore, the minimum thickness is usually about 30 μm or more ( It is preferable to form a porous protective layer 52 of preferably 40 μm or more, particularly preferably 50 μm or more.

  The porous protective layer 52 is made of ceramic particles such as a metal oxide mainly composed of alumina, spinel, mullite, or the like, or a metal carbide such as silicon carbide. You may make a ceramic particle carry | support a noble metal particle as needed. As such noble metal particles, palladium or rhodium alone or two or more alloys of palladium, rhodium and platinum can be used.

  The average particle size of the ceramic particles is approximately 12 μm or less. For example, it is preferable to use ceramic particles having an average particle diameter of about 10 μm or less, more preferably 8 μm or less, and particularly preferably 6 μm or less. By forming the porous protective layer 52 from the small-diameter ceramic particles in this way, the water resistance of the porous protective layer 52 is improved and the condensed water is less likely to permeate. For example, it is possible to form a gas sensor that does not soak even when it comes into contact with moisture in the exhaust gas (for example, a gas sensor in which the penetration depth is suppressed to 80 μm or less). This coincides with the thickness of the porous protective layer 52 of 80 μm or less for ensuring the desired sensor activation time (for example, sensor activation time or less satisfying the regulations regarding emission emission in EuroVI, typically 5 seconds or less). To do. If the average particle size of the ceramic particles is too large, the effect of improving water resistance due to the above-mentioned reduction in diameter tends to decrease, and Mn blown off by the energization treatment at the time of starting described later tends to adhere to the ceramic particles. Become. For this reason, even if the start-up energization process is performed, the desired effect may not be sufficiently exhibited. On the other hand, if the average particle size of the ceramic particles is too small, gas diffusibility is hindered and the sensor output changes. Therefore, it is usually preferable to use ceramic particles having an average particle size of about 1 μm or more. The average particle size of the ceramic particles can be determined by a method known in the art, for example, measurement based on a laser scattering method.

The ceramic particles constituting the porous protective layer 52 disclosed herein preferably have a BET specific surface area in a range of approximately 20 m ² / g or less. Ceramic particles satisfying such a BET specific surface area can be used for a porous protective layer of a gas sensor, and can form a gas sensor that stably exhibits higher performance. For example, it is possible to form a gas sensor that does not soak even when it comes into contact with moisture in exhaust gas. This means that a desired sensor activation time (for example, a sensor activation time equal to or less than the sensor activation time that satisfies the regulations regarding emission emissions in EuroVI, for example, The thickness of the porous protective layer 52 for guaranteeing (second or less) is equal to or less than 80 μm. The suitable range of the BET specific surface area is usually 20 m ² / g or less, preferably 15 m ² / g or less, particularly preferably 10 m ² / g or less. The lower limit value of the specific surface area of the ceramic particles is not particularly limited, but is, for example, 0.1 m ² / g or more. In addition, as a value of the specific surface area, a measured value by a general nitrogen adsorption method can be adopted.

  As the method for forming the porous protective layer 52, a slurry in which ceramic particles (typically granular) and other porous protective layer forming components (for example, a binder, a dispersant, etc.) are dispersed in an appropriate solvent (for example, water) is used. A method of preparing and applying this slurry to the surfaces of the sensor element 60 and the heater unit 70 and firing can be preferably employed.

  In the gas sensor 50 configured as described above, the solid electrolyte body 62 and the pair of electrodes 64a and 64b on both surfaces thereof function as an oxygen concentration detection cell that generates an electromotive force according to the oxygen concentration between both electrodes. That is, a voltage having a phase difference between the oxygen concentration difference and the current is applied to the pair of electrodes 64a and 64b, the measured gas is brought into contact with one electrode (measurement electrode) 64a, and the other electrode (reference electrode). A reference gas such as the atmosphere is brought into contact with 64b, the current value generated between the electrodes is measured according to the difference in oxygen concentration between the two, and the air-fuel ratio of the engine can be specified based on the measured current.

  In the gas sensor 50 covered with the porous protective layer 52, exhaust gas may condense in the exhaust passage after the engine stops and water may remain, and when Mn contained in the condensed water adheres to the gas sensor 50, Due to Mn adhering to the gas sensor 50, there is a problem that the sensor responsiveness is lowered. That is, when Mn contained in the condensed water adheres to the gas sensor 50, it is deposited as Mn oxide on the porous protective layer 52. In this case, since the oxygen concentration of the exhaust gas reaching the measurement electrode 64a is changed by the oxidation-reduction reaction of the Mn oxide, the sensor responsiveness is lowered during the period until the oxidation-reduction reaction is completed. Therefore, in this embodiment, as a mechanism for preventing the deposition of Mn, ceramic particles having a small diameter and a low specific surface area are used in the porous protective layer 52, and the gas sensor is temporarily heated to a high temperature immediately after the engine is started. It was.

  That is, in the gas sensor control device 10 having the configuration shown in FIGS. 1 and 2, the control unit (ECU) 30 includes a heater control unit 32. The heater control unit 32 is configured to execute a start-up energization process for energizing the heater unit 70 so that the temperature of the sensor element 60 becomes a predetermined start temperature when the engine is started. In addition, after the start-up energization process, the heater control unit 32 executes a normal energization process for energizing the heater unit 70 so that the temperature of the sensor element 60 is maintained at the activation temperature of the sensor element 60. Is configured to do.

  The predetermined start temperature in the start-up energization process is preferably set to a temperature at which condensed water adhering to the gas sensor does not penetrate into the porous protective layer. Specifically, as shown in FIG. 9, if the starting temperature is too low, when the condensed water adheres to the gas sensor 50, the porous protective layer 52 is likely to penetrate. When the condensed water soaks into the porous protective layer 52 in this way, Mn in the condensed water is deposited on the porous protective layer 52 and causes an oxidation-reduction reaction, so that the sensor response decreases. Therefore, the starting temperature is preferably set to a temperature at which the condensed water adhering to the gas sensor 50 does not soak into the porous protective layer 52. For example, based on the graph of FIG. 9, it is desirable that the starting temperature is set to a temperature higher than 700 ° C., preferably 750 ° C. or higher, more preferably 800 ° C. or higher, and particularly preferably 900 ° C. or higher. When the start-up energization process is performed within such a temperature range, the condensed water adhering to the gas sensor 50 can be suitably repelled. The predetermined starting temperature in the starting energization process is preferably set to a temperature equal to or higher than the normal control temperature (preferably higher than the normal control temperature). For example, the starting temperature is preferably set to a temperature that is 50 ° C. or higher (eg, 50 ° C. to 200 ° C. or higher) higher than the normal control temperature. In this way, the heater is energized and controlled at a temperature higher than a normal control temperature (for example, 550 ° C.), and the gas sensor is heated to a temperature higher than the normal (for example, 750 ° C.). You can play effectively. The above-described starting temperature value may be set in the control unit 30 in advance.

  The activation temperature (normal control temperature) in the normal energization process is preferably set within a temperature range in which the sensor element 60 is preferably activated. For example, when the gas sensor 50 is an oxygen sensor, it is preferably set within a temperature range of 500 ° C to 600 ° C. Further, when the gas sensor 50 is a full-range air-fuel ratio sensor, it is preferably set within a temperature range of 700 ° C to 800 ° C. When the normal energization process is performed within the above temperature range, the sensor element 60 can be activated preferably. The normal control temperature value described above may be set in the control unit 30 in advance.

  The gas sensor control device 10 having the configuration shown in FIG. 1 includes a heater control circuit 34. The heater control circuit 34 is electrically connected to the control unit 30. The heater control circuit 34 is connected to the heating resistor 74 of the heater unit 70 provided in the gas sensor 50, and applies a voltage across the heating resistor 74. As a result, the heating resistor 74 is caused to generate heat, and the sensor element 60 is heated. The control unit 30 is electrically connected to an ignition switch (not shown). When the ignition switch is turned on, the control unit 30 outputs a startup energization processing pulse signal to the heater control circuit 34. The heater control circuit 34 that has received the signal responds to the start-time energization processing pulse signal output from the control unit 30 so that the temperature of the sensor element 60 becomes a predetermined start temperature. Apply voltage to Thereby, the sensor element 60 is heated so that it may become predetermined | prescribed starting temperature.

  In the gas sensor control device 10 disclosed herein, the temperature sensor 54 is disposed in the exhaust passage 29. The temperature sensor 54 is electrically connected to the control unit 30. The controller 30 measures the temperature in the exhaust passage 29 with the temperature sensor 54 while the start-up energization process is being performed, and when the measured value of the temperature exceeds a predetermined reference value, It is comprised so that an electricity supply process may be complete | finished. Specifically, when the measured value of the temperature in the exhaust passage 29 exceeds a predetermined reference value, the control unit 30 outputs a normal energization processing pulse signal to the heater control circuit 34. The heater control circuit 34 that has received the signal maintains the temperature of the sensor element 60 at the activation temperature (for example, 550 ° C.) of the sensor element 60 in accordance with the normal energization processing pulse signal output from the control unit 30. Thus, a voltage is applied across the heating resistor 74. Thereby, the temperature of the sensor element 60 is maintained at the activation temperature. The reference value for the temperature is preferably set to a temperature at which the condensed water accumulated in the exhaust passage 29 is completely vaporized. For example, the reference value for the temperature may be a value set within a range of 100 ° C. to 150 ° C. (preferably 100 ° C. to 120 ° C.).

  The operation of the gas sensor control device 10 configured as described above will be described. FIG. 3 is a flowchart showing an example of a processing routine executed by the gas sensor control device 10 according to the present embodiment.

  First, in the gas sensor control device 10 according to the present embodiment, an engine start request is determined in step S10. This determination is made based on the input ignition signal. If the control unit 30 has not received the ignition engine start request signal, it is determined (NO) that there is no engine start request, and the processing routine ends without performing the following control. On the other hand, when the control unit 30 has received the ignition engine start request signal, it is determined (YES) that “the engine start request is present”, and step S11 is performed.

  If the determination result of the engine start request is YES, a start-time energization process for energizing the heater unit 70 is executed so that the temperature of the sensor element 60 becomes a predetermined start temperature in step S11. Specifically, the control unit 30 outputs a start-time energization processing pulse signal to the heater control circuit 34, and the heater control circuit 34 that has received the signal detects that the temperature of the sensor element 60 is a predetermined start temperature. A voltage is applied across the heating resistor 74 so that Thereby, the sensor element 60 is heated so that it may become predetermined | prescribed starting temperature.

  Next, in step S12, the control unit 30 determines whether or not the temperature (T) in the exhaust passage 29 has exceeded a predetermined reference value tem. When it is determined that the temperature (T) in the exhaust passage 29 does not exceed the predetermined reference value tem (that is, T ≦ tem), the process returns to step S11 to continue the start-up energization process. On the other hand, when it is determined that the temperature (T) in the exhaust passage 29 has exceeded the predetermined reference value tem (that is, T> tem), it is determined that it is time to end the start-up energization process, and the next step S13 is performed. move on.

  In step S13, the heater control of the sensor is switched from the startup energization process to the normal energization process. That is, the control unit 30 performs a normal energization process for energizing the heater unit 70 so that the temperature of the sensor element 60 is maintained at the activation temperature of the sensor element. Specifically, the control unit 30 outputs a normal energization processing pulse signal to the heater control circuit 34, and the heater control circuit 34 that has received the signal causes the temperature of the sensor element 60 to be equal to a predetermined activation temperature. Thus, a voltage is applied to both ends of the heating resistor 74. Thereby, the temperature of the sensor element 60 is maintained at the activation temperature, and normal sensor control is performed thereafter. Thus, after heating the gas sensor immediately after the engine is stopped to a high temperature (for example, 750 ° C. or higher), it is possible to switch to a normal energization process.

  According to the gas sensor control device 10 disclosed herein, since the gas sensor 50 is heated to a high temperature immediately after the engine is started, Mn adhering to the gas sensor 50 or existing around the gas sensor 50 is blown off together with the condensed water, and the gas sensor 50 Almost no adhesion. Therefore, adhesion of Mn to the porous protective layer 52 is appropriately prevented, and the gas sensor 50 is kept clean. Therefore, according to the gas sensor control apparatus 10, a response delay of the sensor due to the Mn adhesion as in the conventional case is suitably prevented, and the sensor response is remarkably improved.

  In this embodiment, the control unit 30 measures the temperature in the exhaust passage 29 by the temperature sensor 54 during the start-up energization process, and the measured value of the temperature is a predetermined reference value (for example, 100 ° C.). ) Is exceeded, the start-up energization process is terminated. According to such a configuration, the start-up energization process can be terminated immediately after the condensed water accumulated in the exhaust passage 29 is vaporized, that is, immediately after there is no possibility that the condensed water adheres to the gas sensor 50. As a result, it is possible to prevent the start-up energization process from becoming unnecessarily long and to switch to the normal energization process at an appropriate timing.

According to the study of the present inventor, the gas sensor including ceramic particles having a large diameter (for example, 20 μm or more) and a high specific surface area (for example, 70 m ² / g or more) has been described. It was confirmed by a test example described later that the same level of effect could not be obtained with the use of (see the graph of FIG. 9). Therefore, by applying the sensor heating immediately after starting the engine and the gas sensor 50 including ceramic particles having a small diameter and a low specific surface area, as a synergistic effect by such a combination, gas sensor control in which Mn adhesion is more effectively suppressed. An apparatus can be provided.

(Second Embodiment)
The heater control method executed in the gas sensor control device 10 according to one embodiment of the present invention has been described above. Next, a heater control method that can be executed by the gas sensor control device 10 according to another embodiment of the present invention will be described.

  In this embodiment, the control unit 30 is configured to end the start-up energization process when the duration of the start-up energization process exceeds a predetermined reference value. The reference value for the duration of the start-up energization process is that the temperature in the exhaust pipe 29 has reached 100 ° C. since the engine started, that is, the condensed water in the exhaust pipe 29 is vaporized. Sometimes, it is preferable to set so that the start-up energization process is terminated. Specifically, as shown in FIG. 4, when the engine is started in an idling state where the outside air temperature is −10 ° C., the temperature in the exhaust pipe 29 increases, and reaches approximately 100 ° C. after approximately 400 seconds. In this case, the reference value for the duration of the start-up energization process is desirably set to approximately 400 seconds or more, preferably 400 seconds to 600 seconds, and particularly preferably 7 minutes to 8 minutes.

  The operation of the gas sensor control device 10 configured as described above will be described. FIG. 5 is a flowchart showing an example of a processing routine executed by the gas sensor control device 10 according to this embodiment.

  First, in the gas sensor control device 10 according to the present embodiment, an engine start request is determined in step S20. This determination is made based on the input ignition signal. If the control unit 30 has not received the ignition engine start request signal, it is determined (NO) that there is no engine start request, and the processing routine ends without performing the following control. On the other hand, when the control unit 30 receives the ignition engine start request signal, it determines that “engine start request is present” (YES), and performs step S21.

  If the determination result of the engine start request is YES, the control unit 30 performs start-up energization processing for energizing the heater unit 70 so that the temperature of the sensor element 60 becomes a predetermined start temperature in step S21. Run. As a result, the temperature of the sensor element 60 rises to a predetermined starting temperature. In addition, the control unit 30 starts an internal timer and starts measuring the duration (A) of the start-up energization process. Next, in step S22, the control unit 30 determines whether or not the duration (A) of the start-up energization process has reached a predetermined reference value a1. If the determination result here is NO, the process returns to step S21 to continue the start-up energization process. On the other hand, if the determination result is YES, it is determined that it is time to end the energization process at startup, and the process proceeds to the next step S23.

  In step S23, the heater control of the sensor is switched from the startup energization process to the normal energization process. That is, the control unit 30 performs a normal energization process for energizing the heater unit 70 so that the temperature of the sensor element 60 is maintained at the activation temperature of the sensor element. Thereby, the temperature of the sensor element 60 is maintained at the activation temperature, and normal sensor control is performed thereafter. In this manner, the gas sensor immediately after the engine is stopped can be heated to a high temperature (for example, 750 ° C. or higher), and then the normal energization process can be performed. According to such a configuration, since it is not necessary to arrange the temperature sensor 54 in the exhaust pipe 29, the device configuration can be simplified as compared with the first embodiment described above.

(Third embodiment)
The heater control method executed in the gas sensor control device 10 according to one embodiment of the present invention has been described above. Next, a heater control method that can be executed by the gas sensor control apparatus 10 according to another embodiment of the present invention will be described with reference to the flowchart of FIG.

  First, in the gas sensor control device 10 according to the present embodiment, an engine start request is determined in step S30. This determination is made based on the input ignition signal. If the control unit 30 has not received the ignition engine start request signal, it is determined (NO) that there is no engine start request, and the processing routine ends without performing the following control. On the other hand, when the control unit 30 receives the ignition engine start request signal, it determines that “the engine start is requested” (YES), and performs step S31.

  In step S31, the control unit 30 executes a start-time energization process for energizing the heater unit 70 so that the temperature of the sensor element 60 becomes a predetermined start temperature. As a result, the temperature of the sensor element 60 rises to a predetermined starting temperature. In addition, the control unit 30 starts an internal timer and starts measuring the duration (A) of the start-up energization process. Next, in step S32, the control unit 30 determines whether or not the duration (A) of the start-up energization process has reached a predetermined reference value a1. If the determination result here is YES, it is determined that it is time to end the energization process at the start, and the process proceeds to step S34. On the other hand, if the determination result is NO, the process proceeds to the next step S33.

  In step S33, the control unit 30 determines whether or not the temperature T in the exhaust passage 29 has reached a predetermined reference value tem. If the determination result here is NO, the process returns to step S31 to continue the start-up energization process. On the other hand, if the determination result is YES, it is determined that it is time to end the energization process at start-up, and the process proceeds to the next step S34. In step S34, the heater control unit 32 executes a normal energization process for energizing the heater unit 70 so that the temperature of the sensor element 60 is maintained at the activation temperature of the sensor element. Thereby, the temperature of the sensor element 60 is maintained at the activation temperature, and normal sensor control is performed thereafter. Thus, after heating the gas sensor immediately after the engine stops to a predetermined starting temperature, it is possible to shift to a normal energization process.

  According to such a configuration, switching between the start-up energization process and the normal energization process is performed based on the duration of the start-up energization process, and when the temperature in the exhaust pipe 29 rises faster than expected depending on the operating state, The start-up energization process can be immediately terminated. As a result, it is possible to prevent the start-up energization process from becoming unnecessarily long and to switch to the normal energization process at an appropriate timing.

  Hereinafter, although the test example regarding this invention is demonstrated, it is not intending to limit this invention to what is shown to the following test examples.

<Test Example 1: Relationship between specific surface area and penetration depth>
Test pieces were prepared by varying the specific surface area of the alumina particles constituting the porous protective layer of the gas sensor, and a test was conducted to verify the penetration depth of moisture in each test piece. Here, each gas sensor was heated to 700 ° C., and 0.3 μL of water droplets were dropped on the porous protective layer. And the penetration depth of the water droplet (the film thickness of the portion where the water droplet penetrated) was measured. In addition, as the value of the specific surface area, a value measured by a nitrogen adsorption method was adopted (hereinafter the same). The results are shown in FIG. FIG. 7 is a graph showing the relationship between the specific surface area (horizontal axis) of the porous protective layer and the moisture penetration depth (vertical axis).

As shown in FIG. 7, the penetration depth tended to decrease as the specific surface area of the porous protective layer decreased. In the case of the gas sensor used here, by setting the specific surface area to 20 m ² / g or less, a very low penetration depth of 80 μm or less could be achieved. From the viewpoint of reducing the penetration depth, the specific surface area is suitably 20 m ² / g or less, preferably 15 m ² / g or less, particularly preferably 10 m ² / g or less.

<Test Example 2: Relationship between average particle size and penetration depth>
Gas sensors (test pieces) were prepared by variously changing the average particle diameter of alumina particles constituting the porous protective layer of the gas sensor, and a test for verifying the penetration depth of moisture in each test piece was performed. Here, each gas sensor was heated to 700 ° C., and 0.3 μL of water droplets were dropped on the porous protective layer. And the penetration depth of the water droplet was measured. In addition, the average particle diameter (D50 diameter) of the alumina particles was obtained by measurement based on a laser scattering method (hereinafter the same). The results are shown in FIG. FIG. 8 is a graph showing the relationship between the average particle size (vertical axis) and the penetration depth (horizontal axis).

  As shown in FIG. 8, the penetration depth tended to decrease as the average particle size of the ceramic particles constituting the porous protective layer became smaller. In the case of the gas sensor used here, an extremely low penetration depth of 80 μm or less could be achieved by setting the average particle size to 12 μm or less. From the viewpoint of reducing the penetration depth, the average particle size of the ceramic particles is suitably 12 μm or less, preferably 10 μm or less, particularly preferably 5 μm or less.

<Test Example 3: Relationship between sensor control temperature and penetration depth>
A gas sensor (test piece) equipped with a porous protective layer made of alumina particles with a small diameter (8 μm) and a low specific surface area (0.9 m ² / g) was created. A test was conducted to verify this. For comparison, a gas sensor (test piece) with a porous protective layer made of alumina particles with a large diameter (20 μm) and high specific surface area (70 m ² / g) was created, and the penetration depth was verified using the same method. did. The results are shown in FIG. FIG. 9 is a graph showing the relationship between the sensor control temperature (horizontal axis) and the penetration depth (vertical axis).

  As shown in FIG. 9, the penetration depth tended to decrease as the control temperature of the sensor increased. In the case of the gas sensor used here, by using alumina particles having a small diameter and a low specific surface area and setting the control temperature of the sensor to 700 ° C. or more, a very low penetration depth of 50 μm or less could be achieved. From the viewpoint of reducing the penetration depth, it is appropriate that the control temperature of the sensor is 700 ° C. or higher, preferably 750 ° C. or higher, particularly preferably 900 ° C. or higher. From this figure, it was confirmed that the effect of preventing penetration by heating the sensor immediately after starting the engine is particularly effective when ceramic particles having a small diameter and a low specific surface area are used.

As a preferred example of the gas sensor control device disclosed herein, the ceramic particles constituting the porous protective layer have an average particle size of 12 μm or less, a specific surface area of 20 m ² / g or less, and a start temperature immediately after engine start is 750. Ceramic particles having an average particle size of 10 μm or less, a specific surface area of 15 m ² / g or less, and a starting temperature immediately after starting the engine of 800 ° C. or more In which the average particle size is 5 μm or less, the specific surface area is 10 m ² / g or less, and the starting temperature immediately after engine starting is set to 900 ° C. or higher. By setting the average particle size, specific surface area, and starting temperature of such ceramic particles, it is possible to better suppress the penetration of condensed water (and hence the adhesion of Mn).

<Test Example 4: Mn durability test>
(1) Example 1
In this example, as shown in Table 1, a gas sensor (see FIG. 2) provided with a porous protective layer made of alumina particles having a small diameter and a low specific surface area was prepared. The maximum thickness of the porous protective layer was 80 μm. About this gas sensor, the Mn endurance test was done. In the Mn durability test, 5 μL of a Mn aqueous solution (Mn concentration: 6000 ppm) in which the Mn concentration contained in the condensed water in the exhaust pipe was concentrated 10 times was dropped on the porous protective layer of the gas sensor heated to 750 ° C. The cycle of dropping was repeated 50 times. A cross-sectional SEM image of the gas sensor after the Mn durability test is shown in FIG. In the SEM image of FIG. 10, there was no discoloration of the porous protective layer, and no Mn adhesion was observed.
(2) Comparative Example 1
In this example, similarly to Example 1, a gas sensor including a porous protective layer made of alumina particles having a small diameter and a low specific surface area was prepared. About this gas sensor, the Mn endurance test was done like Example 1. However, the gas sensor was not heated, and the temperature of the sensor element was room temperature. A cross-sectional SEM image of the gas sensor after the Mn durability test is shown in FIG. In the SEM image of FIG. 11, the porous protective layer was slightly discolored in black, and a slight amount of Mn was observed.
(3) Comparative Example 2
In this example, as shown in Table 1, a gas sensor including a porous protective layer made of alumina particles having a large diameter and a high specific surface area was prepared. About this gas sensor, the Mn endurance test was done like Example 1. A cross-sectional SEM image of the gas sensor after the Mn durability test is shown in FIG. In the SEM image of FIG. 12, the porous protective layer was discolored black, and adhesion of Mn was recognized.
(4) Comparative Example 3
In this example, as in Comparative Example 2, a gas sensor including a porous protective layer made of alumina particles having a large diameter and a high specific surface area was prepared. For this gas sensor, a Mn durability test was conducted in the same manner as in Comparative Example 2. However, the gas sensor was not heated, and the temperature of the sensor element was room temperature. A cross-sectional SEM image of the gas sensor after the Mn durability test is shown in FIG. In the SEM image of FIG. 13, the porous protective layer was discolored in black, and adhesion of Mn was observed.

  From the comparison of the SEM images of FIGS. 10 to 13, by using a gas sensor having a porous protective layer made of alumina particles having a small diameter and a low specific surface area, and heating the gas sensor to 750 ° C., after the Mn durability test Further, it was confirmed that discoloration of the porous protective layer and thus adhesion of Mn can be appropriately prevented.

<Test Example 5: Sensor response test>
About the gas sensor of the said Example 1 and Comparative Examples 1-3, the sensor response output before and behind the above-mentioned Mn durability test was measured. The sensor response output was measured by assembling the gas sensor of each example to a gas detector and holding the sensor in a test gas having a predetermined oxygen concentration. At that time, the heater was energized so that the temperature of the sensor element was maintained at 700 ° C. The sensor response output measurement was performed before and after the Mn durability test described above. FIG. 14 shows sensor response outputs before and after the Mn durability test according to the first embodiment. FIG. 15 shows sensor response outputs before and after the Mn durability test according to Comparative Example 1. FIG. 16 shows sensor response outputs before and after the Mn durability test according to Comparative Example 3.

As shown in FIG. 14, in Example 1 in which a gas sensor provided with a porous protective layer made of alumina particles having a small diameter and a low specific surface area was used and the gas sensor was heated to 750 ° C., the sensor response output was before and after the Mn durability test. Almost unchanged, good results were obtained. On the other hand, as shown in FIGS. 15 and 16, in Comparative Examples 1 and 3 in which the gas sensor was not heated during the Mn durability test, the sensor output response after the Mn durability test was delayed as compared with that before the durability test. Although omitted here, the same tendency as in Comparative Examples 1 and 3 was obtained for Comparative Example 2. In Comparative Examples 1 to 3, it is understood that the delay is caused by Mn adhering to the porous protective layer.
From the above, by using a gas sensor having a porous protective layer made of alumina particles having a small diameter and a low specific surface area, and heating the gas sensor to 750 ° C., adhesion of Mn to the porous protective layer is prevented, It was confirmed that the sensor response delay caused by Mn can be eliminated.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

1 Internal combustion engine
10 Gas sensor control device 29 Exhaust pipe (exhaust passage)
30 control unit 32 heater control unit 34 heater control circuit 40 catalyst unit 50 gas sensor 52 porous protective layer 54 temperature sensor 60 sensor element 62 solid electrolyte body 64a measurement electrode 64b reference electrode 65 protection layer 66a measurement gas space 66b reference gas space 68 diffusion Resistance layer 69 Shielding layer 70 Heater 72 Insulating substrate 74 Heating resistor 100 Exhaust gas purification device

Claims (9)

A gas sensor disposed in an exhaust passage of the internal combustion engine and including a sensor element and a porous protective layer covering at least a part of the sensor element;
A heater provided in the gas sensor for heating the sensor element;
A heater control unit that controls energization of the heater unit,
The porous protective layer contains ceramic particles,
The ceramic particles have an average particle size based on a laser scattering method of 12 μm or less, and a specific surface area based on a nitrogen adsorption method of 20 m ² / g or less,
Here, the heater control unit
A start-up energization process for energizing the heater unit so that the temperature of the sensor element becomes a predetermined start temperature at the start of the internal combustion engine;
After the start-up energization process, a normal energization process for energizing the heater unit can be performed so that the temperature of the sensor element is maintained at the activation temperature of the sensor element. Gas sensor control device.   The gas sensor control device according to claim 1, wherein a start temperature in the start-up energization process is set to a temperature equal to or higher than an activation temperature of the sensor element.   The gas sensor control device according to claim 2, wherein a start temperature in the start-up energization process is set in a range of 750 ° C to 900 ° C. A temperature sensor is disposed in the exhaust passage,
The heater control unit is electrically connected to the temperature sensor,
Here, the heater control unit measures the temperature in the exhaust passage by the temperature sensor while performing the start-up energization process,
The gas sensor control device according to any one of claims 1 to 3, wherein the start-up energization process is terminated when a measured value of the temperature exceeds a predetermined reference value.   5. The gas sensor control device according to claim 4, wherein a reference value for the temperature of the start-up energization process is a value set in a range of 100 ° C. to 150 ° C. 6.   The heater control unit is configured to end the start-up energization process when a duration of the start-up energization process exceeds a predetermined reference value. The gas sensor control apparatus according to 1.   The gas sensor control device according to claim 6, wherein a reference value for a duration of the start-up energization process is a value set in a range of 400 seconds to 600 seconds.   The gas sensor control device according to any one of claims 1 to 7, wherein a maximum thickness of the porous protective layer is 80 µm or less. An exhaust gas purification apparatus in which an exhaust gas purification catalyst for purifying exhaust gas discharged from an internal combustion engine is disposed in an exhaust passage of the internal combustion engine,
An exhaust gas purification device comprising the gas sensor control device according to claim 1.