Gas concentration detecting device

Abstract

The sensor control device (5) of the gas concentration detection device (1) has a sensor detection section (51), a temperature sensing section (52), a heater control section (53), a change speed calculation section (54), and a correction output section (55). The change speed calculation section (54) calculates a change speed (AS) of a heater current (Ih) flowing through the heater (34) when the temperature of the sensor unit (21) sensed by the temperature sensing section (52) is maintained at a target temperature by the heater control section (53). The correction output section (55) corrects a sensor output, i.e., a sensor current (Is) detected by the sensor detection section (51), using the change speed (AS) of the heater current (Ih), and calculates a sensor correction output (Os) of the gas sensor (10).

Description

[0001] Cross-references to related applications

[0002] This application is based on Japanese Patent Application No. 2021-044216, filed on March 18, 2021, and incorporates the contents thereof. Technical Field

[0003] This disclosure relates to a gas concentration detection device. Background Technology

[0004] The gas concentration detection device consists of a gas sensor installed in the exhaust pipe of a vehicle, and a sensor control device that controls the operation of the gas sensor. The gas sensor has a sensor unit with a pair of electrodes on a solid electrolyte and a heater that heats the sensor unit by applying electricity. Considering the need for high-level response to load changes, the power supply to the heater is usually controlled by PWM (Pulse Width Modulation).

[0005] In the case of PWM control of the heater, a pulsed voltage is applied to the heater, and the duty cycle, which represents the on-off ratio in one cycle of the pulsed voltage, is appropriately changed to control the temperature of the sensor unit to the target temperature. For example, the device disclosed in Patent Document 1 is used as a gas concentration detection device for PWM control of the heater.

[0006] In the gas concentration detection device of Patent Document 1, the following design is implemented: When the energizing state of the heater changes from on to off, noise components superimposed on the output signal of the sensor unit are removed from the output signal through averaging. More specifically, when the heater is on, positive noise is generated in the output signal, and when the heater is off, negative noise is generated in the output signal. In the gas concentration detection device of Patent Document 1, averaging is performed in a manner that cancels out the noise components in the output signal, which are represented by opposite signs.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2004-093386 Summary of the Invention

[0010] However, through the inventors' research, it was discovered that in the noise components superimposed on the output signal of the sensor unit, besides the short-period noise component associated with the switching of power to and from the heater (referred to as the switching noise component), other noise components also exist. Specifically, it was discovered that when the temperature of the sensor unit is maintained at the target temperature by the heater's PWM control, a noise component with a larger period than the switching noise component (referred to as the temperature control noise component) superimposed on the sensor unit. It was also discovered that the temperature control noise component is captured as fluctuations or effective values ​​of temperature changes and has a different rate of change than the switching noise component.

[0011] Therefore, further design is needed to remove noise components from the output signal of the sensor unit and improve the detection accuracy of the gas concentration detection device.

[0012] This disclosure aims to provide a gas concentration detection device that eliminates the influence of noise components associated with changes in the applied voltage (which is an effective value) applied to the heater on the sensor output, thereby improving the detection accuracy of the gas sensor output.

[0013] One aspect of this disclosure is a gas concentration detection device, comprising:

[0014] A gas sensor comprising one or more sensor units having a pair of electrodes on a solid electrolyte body and a heater for heating the sensor units by means of an electric current; and a sensor control device for controlling the operation of the sensor units and the heater.

[0015] The sensor control device has:

[0016] The sensor detection unit detects the sensor current or sensor voltage generated by the sensor unit.

[0017] The temperature sensing unit senses the temperature of the sensor unit;

[0018] The heater control unit adjusts the voltage applied to the heater;

[0019] The rate of change calculation unit calculates at least one of the rate of change of the voltage applied to the heater and the rate of change of the heater current flowing through the heater when the temperature sensed by the temperature sensing unit is maintained at a target temperature by the heater control unit; and

[0020] The correction output unit uses the change rate calculated by the change rate calculation unit to correct the sensor current or sensor voltage detected by the sensor detection unit, i.e., the sensor output, and calculates the sensor correction output of the gas sensor.

[0021] In the sensor control device of the gas concentration detection apparatus of the aforementioned type, a rate of change calculation unit calculates at least one of the rate of change of the voltage applied to the heater and the rate of change of the heater current flowing through the heater when the temperature of the sensor unit sensed by the temperature sensing unit is maintained at a target temperature by the heater control unit. When the temperature of the sensor unit is affected by external disturbances, these rates of change are expressed as the rate of change calculated when the voltage applied to the heater is adjusted to prevent the temperature of the sensor unit from deviating from the target temperature.

[0022] When the temperature of the sensor unit is affected by external interference, and the sensor current or sensor voltage generated in the sensor unit is detected as the sensor output by the sensor detection unit, noise components that accompany the change in the applied voltage (which is the effective value) applied to the heater may be superimposed on the sensor output. Therefore, the sensor output is corrected by the correction output unit using the change rate calculated by the change rate calculation unit, and the sensor correction output of the gas sensor is calculated.

[0023] With this structure, the gas concentration detection device according to the above method eliminates the influence of noise components associated with changes in the applied voltage (effective value) applied to the heater on the sensor output, thereby improving the detection accuracy of the gas sensor output.

[0024] The "sensing of the temperature of the sensor unit by the temperature sensing unit" also includes the case of estimating the temperature based on various information.

[0025] Furthermore, the bracketed reference numerals of each component shown in one aspect of this disclosure indicate the correspondence between the reference numerals in the figures of the embodiment, but do not limit each component to the content of the embodiment. Attached Figure Description

[0026] The purpose, features, advantages, etc., of this disclosure will become more apparent from the detailed description following with reference to the accompanying drawings. The accompanying drawings of this disclosure are shown below.

[0027] Figure 1 This is a cross-sectional view of the gas sensor of the gas concentration detection device according to Embodiment 1.

[0028] Figure 2 This is a cross-sectional view of the sensor element of the gas sensor according to Embodiment 1.

[0029] Figure 3 This is implementation method 1. Figure 2 Section III-III.

[0030] Figure 4 This is implementation method 1. Figure 2Section IV-IV.

[0031] Figure 5 This is an explanatory diagram schematically showing the electrical structure of the sensor control device according to Embodiment 1.

[0032] Figure 6 It is a graph showing the changes over time of (a) the pulsed applied voltage, (b) the heater current, (c) the rate of change of the heater current, and (d) the sensor current before and after correction in Implementation 1.

[0033] Figure 7 This is the implementation method 1 Figure 6 (c) is a portion of the graph showing the rate of change of the heater current, enlarged.

[0034] Figure 8 This is a graph showing the relationship between the rate of change of the heater current and the amount of change of the sensor current in Embodiment 1.

[0035] Figure 9 This is a mapping that represents the relationship between the rate of change of the heater current in Implementation Method 1 and the correction amount of the sensor current.

[0036] Figure 10 This is a flowchart illustrating the control method of the gas concentration detection device according to Embodiment 1.

[0037] Figure 11 This is an explanatory diagram schematically showing the electrical structure of the sensor control device according to Embodiment 2.

[0038] Figure 12 This is a graph showing the changes over time of (a) the pulsed applied voltage, (b) the heater current, (c) the temperature change of the sensor unit, and (d) the sensor current before and after correction in Implementation 2.

[0039] Figure 13 This is a graph from Embodiment 2 that uses the rate of change of heater current as a parameter to represent the relationship between the change in temperature of the sensor unit and the change in sensor current.

[0040] Figure 14 This is the relationship mapping in Implementation 2, which uses the rate of change of the heater current as a parameter to represent the relationship between the changing temperature of the sensor unit and the correction amount of the sensor current.

[0041] Figure 15 The graph shows the changes over time of (a) heater current, (b) sensor unit temperature, and (c) sensor current of the comparative product of Embodiment 2.

[0042] Figure 16is a graph showing changes over time of (a) the heater current, (b) the temperature of the sensor unit, and (c) the sensor current, respectively, of the comparative product of Embodiment 2.

[0043] Figure 17 is a graph showing changes over time of (a) the heater current, (b) the temperature of the sensor unit, and (c) the sensor current, respectively, of the comparative product of Embodiment 2. DETAILED DESCRIPTION

[0044] The foregoing preferred embodiment of the gas concentration detecting device will be described with reference to the accompanying drawings.

[0045] <Embodiment 1>

[0046] As shown in Figures 1-4 , the gas concentration detecting device 1 of the present embodiment includes a gas sensor 10 and a sensor control device 5. The gas sensor 10 has one or more sensor units 21 provided with a pair of electrodes 311, 312 on a solid electrolyte body 31, and a heater 34 that heats the sensor units 21 by generating heat through electric conduction. The sensor control device 5 controls the operation of the sensor units 21 and the heater 34.

[0047] As shown in Figure 5 , the sensor control device 5 includes a sensor detecting section 51, a temperature sensing section 52, a heater control section 53, a change rate calculating section 54, and a correction output section 55. The sensor detecting section 51 is a constitutional section that detects a sensor current Is generated in the sensor units 21. The temperature sensing section 52 is a constitutional section that senses the temperature of the sensor units 21. The heater control section 53 is a constitutional section that adjusts an applied voltage Vh to the heater 34.

[0048] The change rate calculating section 54 is a constitutional section that calculates a change rate AS of the heater current Ih flowing through the heater 34 when the temperature of the sensor units 21 sensed by the temperature sensing section 52 is maintained at a target temperature by the heater control section 53. The correction output section 55 is a constitutional section that corrects a sensor output, i.e., the sensor current Is detected by the sensor detecting section 51, using the change rate AS of the heater current Ih calculated by the change rate calculating section 54 to calculate a sensor correction output Os of the gas sensor 10.

[0049] Hereinafter, the gas concentration detecting device 1 of the present embodiment will be described in detail.

[0050] (Gas Sensor 10)

[0051] As shown in Figure 1As shown, the gas sensor 10 is disposed at the mounting port 71 of the exhaust pipe 7 of the vehicle's internal combustion engine (engine) and is used to detect the oxygen concentration, specific gas concentration, etc., in the exhaust gas G flowing through the exhaust pipe 7. The gas sensor 10 can be used as an air-fuel ratio sensor (A / F sensor) to determine the air-fuel ratio in the internal combustion engine based on the oxygen concentration, unburned gas concentration, etc., in the exhaust gas G. The air-fuel ratio sensor can continuously detect the air-fuel ratio in a quantitative manner 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).

[0052] A catalyst for purifying harmful substances in the exhaust gas G is disposed on the exhaust pipe 7. The gas sensor 10 can be disposed on either the upstream or downstream side of the catalyst in the direction of the flow of the exhaust gas G in the exhaust pipe 7. Alternatively, the gas sensor 10 can also be disposed on the intake side of a turbocharger that uses the exhaust gas G to increase the density of the air drawn into the internal combustion engine. Furthermore, the piping on which the gas sensor 10 is disposed can also be configured as an exhaust gas recirculation mechanism that recirculates a portion of the exhaust gas G discharged from the internal combustion engine to the exhaust pipe 7 back into the intake manifold of the internal combustion engine.

[0053] (Sensor Unit 21)

[0054] like Figures 2-4 As shown, the sensor unit 21 and heater 34 of the gas sensor 10 are formed by the sensor element 2. The sensor unit 21 is composed of a solid electrolyte body 31 and an exhaust electrode 311 and an atmospheric electrode 312 disposed on the solid electrolyte body 31. Insulators 33A and 33B are stacked on the solid electrolyte body 31, and the heater 34 is composed of a heating element embedded in the insulators 33A and 33B.

[0055] In this embodiment, the sensor unit 21 is formed in the gas sensor 10 as a single unit to constitute an air-fuel ratio sensor. Alternatively, multiple sensor units 21 may be formed in the gas sensor 10, for example, to constitute a NOx (nitrogen oxides) sensor. In this case, the sensor unit 21 may also be configured as a pumping unit to reduce the oxygen concentration of the exhaust gas G, a monitoring unit to detect the residual oxygen concentration of the exhaust gas G, a detection unit to detect the NOx concentration of the exhaust gas G, etc.

[0056] Alternatively, the gas sensor 10 may also have multiple sensor units 21 for detecting air-fuel ratio, NOx concentration, etc. Multiple sensor units 21 may also be used to correct the sensor output using a change rate calculation unit 54 and a correction output unit 55.

[0057] (Sensor element 2)

[0058] like Figures 2-4 As shown, the sensor element 2 of this embodiment is formed into a long rectangular shape and includes a solid electrolyte body 31, an exhaust electrode 311 and an atmospheric electrode 312, a first insulator 33A, a second insulator 33B, a gas chamber 35, an atmospheric duct 36, and a heater 34. The sensor element 2 is a stacked type in which the insulators 33A, 33B and the heater 34 are stacked on the solid electrolyte body 31.

[0059] In this embodiment, the length direction L of the sensor element 2 refers to the direction in which the sensor element 2 extends into a long strip shape. Furthermore, the direction in which the solid electrolyte 31 and each insulator 33A, 33B are stacked, orthogonal to the length direction L, 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 emitted 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. In the gas sensor 10, the direction identical to the length direction L of the sensor element 2 is also called the length direction L.

[0060] (Solid electrolyte 31, exhaust electrode 311 and atmospheric electrode 312)

[0061] like Figures 2-4 As shown, the solid electrolyte 31 contains oxygen 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 their front end sides 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. At the front end side L1 of the sensor element 2 in the longitudinal direction L, a sensor unit 21 is formed, consisting of the portion of the exhaust electrode 311, the atmospheric electrode 312, and the solid electrolyte body 31 sandwiched between these electrodes 311 and 312. 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.

[0062] The solid electrolyte 31 is composed of zirconium oxide, specifically stable or partially stabilized zirconium oxide, which is mainly composed of zirconium oxide (containing more than 50% by mass) and is obtained by replacing a portion of the zirconium oxide with rare earth or alkaline earth metal elements. A portion of the zirconium oxide constituting the solid electrolyte 31 is replaced by yttrium oxide, scandium oxide, or calcium oxide.

[0063] The exhaust electrode 311 and the atmospheric electrode 312 contain platinum, a noble metal that exhibits catalytic activity towards oxygen, and zirconium oxide, which is the same material as the solid electrolyte 31. For example... Figure 1 and Figure 2 As shown, electrode lead portions 313 are connected to the exhaust electrode 311 and the atmospheric electrode 312 for electrically connecting these electrodes 311 and 312 to the external gas sensor 10. The electrode lead portions 313 are led out to the base end side L2 in the longitudinal direction L of the sensor element 2. A terminal connection portion 22 is formed at the end of the electrode lead portion 313 at the base end side L2 in the longitudinal direction L.

[0064] (Gas Chamber 35)

[0065] 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 32, and the solid electrolyte body 31. The exhaust gas G flowing through the exhaust pipe 7 is introduced into the gas chamber 35 through the diffusion resistance section 32.

[0066] (Diffusion resistance section 32)

[0067] like Figure 3 As shown, in this embodiment, the diffusion resistance section (gas inlet section) 32 is provided on both sides of the gas chamber 35 in the width direction W. The diffusion resistance section 32 is formed by distributing a porous material of metal oxide such as alumina in the inlet formed in the first insulator 33A. The diffusion velocity (flow rate) of the exhaust gas G in 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. Alternatively, the diffusion resistance section 32 may also be provided at the front end L1 of the gas chamber 35 in the length direction L.

[0068] (Atmospheric Pipeline 36)

[0069] like Figures 2-4 As shown, an atmospheric conduit 36, which is surrounded by the second insulator 33B and the solid electrolyte 31 and is introduced into the atmosphere A, is formed adjacent to the second surface 302 of the solid electrolyte 31. The atmospheric conduit 36 ​​is formed from the portion of the second insulator 33B that houses the atmospheric electrode 312 in the longitudinal direction L to the base position in the longitudinal direction L of the sensor element 2.

[0070] (Insulators 33A and 33B)

[0071] like Figures 2-4 As shown, the first insulator 33A forms a gas chamber 35, and the second insulator 33B forms an atmospheric duct 36 and embeds a heater 34. The first insulator 33A and the second insulator 33B are formed using metal oxides such as alumina (alumina). Each insulator 33A and 33B is formed as a dense body through which the exhaust gas G or atmospheric air A cannot pass.

[0072] (Heater 34)

[0073] like Figure 3 and Figure 4 As shown, the heater 34 is configured as a heating element and is embedded within the second insulator 33B forming the atmospheric conduit 36. The heater 34 has a heating section 341 that generates heat when energized and a heating element lead section 342 connected to the base end side L2 of the heating section 341 in the longitudinal direction L. The heating section 341 is positioned in the stacking direction D of the solid electrolyte body 31 and the insulators 33A and 33B, at least partially overlapping with the exhaust electrode 311 and the atmospheric electrode 312. The heater 34 is made of a conductive metallic material. A terminal connection section 22 is formed at the end of the heating element lead section 342 on the base end side L2 in the longitudinal direction L.

[0074] (Surface protective layer 37)

[0075] like Figure 1 As shown, a surface protective layer 37 covering the sensor unit 21 is formed at the front end L1 of the sensor element 2 along the longitudinal direction L. The surface protective layer 37 is composed of multiple ceramic particles bonded together, which are ceramic materials having pores through which the exhaust gas G can pass.

[0076] (Structure of other sensor element 2)

[0077] 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 exhaust electrode 311 and atmospheric electrode 312 pair, and may be multiple sets of electrodes. When multiple sets of electrodes are provided on one or more solid electrolyte bodies 31, the heating part 341 of the heater 34 can be provided at a position opposite to the multiple sets of electrodes from the stacking direction D.

[0078] (Other structures of the gas sensor 10)

[0079] like Figure 1As shown, the gas sensor 10 has a housing 41, an element holding material 42, a terminal holding material 43, a contact part 431, a contact terminal 44, a front end cover 45, a base end cover 46, an insulating sleeve 47, and a lead wire 48, etc., for the purpose of arranging the sensor element 2 on the exhaust pipe 7 and making electrical wiring to the sensor control device 5.

[0080] The housing 41 is used to secure the gas sensor 10 to the mounting port 71 of the exhaust pipe 7. The housing 41 holds the sensor element 2 via element holding material 42, etc. The sensor element 2 is held in the element holding material 42 by glass powder 421, and the element holding material 42 is held in the housing 41 by extrusion materials 422, 423, 424. At the base end L2 of the element holding material 42 in the longitudinal direction L, a terminal holding material 43 is connected to hold the contact terminal 44. The terminal holding material 43 is supported by the contact member 431 on the base end cover 46.

[0081] The contact terminal 44 contacts the base end of the electrode lead portion 313, which serves as the terminal connection portion 22, and the base end of the heating element lead portion 342, which also serves as the terminal connection portion 22, in the sensor element 2, thereby electrically connecting the electrode lead portion 313 and the heating element lead portion 342 to the lead wire 48. The contact terminal 44 is connected to the lead wire 48 via the connector 441 while being disposed within the terminal holding material 43.

[0082] like Figure 1 As shown, a front end cover 45 is provided on the front end L1 of the housing 41 along its length L, covering the sensor unit 21 of the sensor element 2. A gas flow hole 451 is formed in the front end cover 45, allowing the exhaust gas G, which contacts the sensor element 2, to flow through. The sensor unit 21 of the sensor element 2 and the front end cover 45 are disposed within the exhaust pipe 7 of the internal combustion engine. A portion of the exhaust gas G flowing through the exhaust pipe 7 enters the front end cover 45 through the gas flow hole 451. Furthermore, the exhaust gas G within the front end cover 45 is guided towards the exhaust electrode 311 through the surface protective layer 37 and the diffusion resistance portion 32 of the sensor element 2.

[0083] A base end cover 46 is provided on the base end side L2 of the housing 41 along the length L, and is used to cover the wiring portion located on the base end side L2 along the length L of the gas sensor 10 and protect the wiring portion from the influence of water and other substances in the atmosphere A. The wiring portion consists of a contact terminal 44, which is an electrical connection part with the sensor element 2, and a connection part (connector 441) between the contact terminal 44 and the lead wire 48.

[0084] On the inner circumference of the portion of the base end side L2 along the length L of the base end cover 46, an insulating sleeve 47 is provided to hold the plurality of leads 48. An atmospheric inlet hole 461 is formed in the base end cover 46 for introducing atmosphere A from the outside of the gas sensor 10. The atmospheric inlet hole 461 is covered by a waterproof filter 462. The base end of the atmospheric conduit 36 ​​in the sensor element 2 is open to the space within the base end cover 46, and atmosphere A is guided into the atmospheric electrode 312 within the atmospheric conduit 36.

[0085] (Sensor control device 5)

[0086] like Figure 1 As shown, lead 48 in gas sensor 10 is electrically connected to sensor control device 5, which controls gas detection in gas sensor 10. Sensor control device 5 cooperates with engine control device 6, which controls combustion operation in engine, to perform electrical control of gas sensor 10. Sensor control device 5 is constructed using various control circuits, computers, etc. Alternatively, sensor control device 5 can also be built into engine control device 6.

[0087] exist Figure 5 The electrical structure of the sensor control device 5 is schematically shown in the diagram. The sensor detection unit 51, temperature sensing unit 52, heater control unit 53, and heater current detection unit 56 are mainly composed of a control circuit, while the change rate calculation unit 54 and correction output unit 55 are mainly composed of a computer 50. In the sensor control device 5, the temperature of the sensor unit 21 sensed by the temperature sensing unit 52 is fed back, and the heater control unit 53 performs feedback control on the temperature of the sensor unit 21. Furthermore, in the sensor control device 5, the change rate ΔS of the heater current Ih sensed by the heater current detection unit 56 is calculated by the change rate calculation unit 54. And, based on the change rate ΔS, the sensor current Is sensed by the sensor detection unit 51 is corrected by the correction output unit 55, and a sensor correction output Os is calculated.

[0088] (Sensor Detection Unit 51)

[0089] like Figure 2As shown, the sensor detection unit 51 includes a voltage application circuit 511 that applies a DC voltage between the exhaust electrode 311 and the atmospheric electrode 312, and a current detection circuit 512 that measures the current flowing between the exhaust electrode 311 and the atmospheric electrode 312. The voltage application circuit 511 applies a DC voltage, the magnitude of which generates a limiting current characteristic in the sensor unit 21 due to the diffusion resistance of the diffusion resistance section 32 when the exhaust gas G flows into the gas chamber 35, to the electrodes 311 and 312. The voltage application circuit 511 applies a DC voltage between the electrodes 311 and 312 with the atmospheric electrode 312 as the positive side, to expel oxygen from the gas chamber 35.

[0090] In the sensor detection unit 51, when the exhaust gas G after combustion in a lean state in the internal combustion engine reaches the exhaust electrode 311, the sensor current Is on the positive side is mainly detected; when the exhaust gas G after combustion in a rich state in the internal combustion engine reaches the exhaust electrode 311, the sensor current Is on the negative side is mainly detected.

[0091] (Temperature sensing unit 52)

[0092] like Figure 2 As shown, the temperature sensing unit 52 includes a detection circuit 521 that detects the resistance or impedance of the sensor unit 21. The temperature sensing unit 52 is configured to sense the temperature of the sensor unit 21 using the resistance or impedance detected by the detection circuit 521. When the composition of the exhaust gas G is near the ideal ratio (stoichiometric air-fuel ratio), the sensor current Is detected by the sensor detection unit 51 is approximately zero. In states where the composition of the exhaust gas G varies little, such as this ideal ratio state, the resistance or impedance can be detected by detecting the current value when a voltage is applied between the electrodes 311 and 312 of the sensor unit 21. Furthermore, the temperature sensing unit 52 senses the temperature of the sensor unit 21 based on the correlation between the resistance or impedance and the temperature of the sensor unit 21.

[0093] The temperature sensing unit 52 can also be configured to estimate the temperature of the sensor unit 21 by detecting the resistance or impedance of the heater 34. In this case, it can also be configured in the same way as the case where the resistance or impedance of the sensor unit 21 is detected.

[0094] (Heater Control Unit 53)

[0095] like Figure 3As shown, the heater control unit 53 is configured to apply an applied voltage Vh, which is a pulsed AC voltage, to the heating element lead portion 342 of the heating element constituting the heater 34. The heater control unit 53 is formed using a power-on control circuit 531 that powers the heater 34. The heater control unit 53 is configured to adjust the pulse width modulation control (PWM control) of the applied voltage Vh applied to the heater 34 by changing the duty cycle of the pulsed applied voltage Vh.

[0096] like Figure 6 As shown in (a), when a pulsed applied voltage Vh is applied to the heater 34, an effective voltage Ve is substantially applied to the heater 34. This effective voltage Ve is the product of the on-time voltage of the pulsed applied voltage Vh and the duty cycle. The duty cycle is expressed as on-time voltage / 1 cycle, in other words, it is expressed as the proportion of the on-time voltage in 1 cycle of the AC voltage. The target temperature of the heating sensor unit 21 by the heater control unit 53 is set, for example, as the activation temperature of the sensor unit 21, to a predetermined temperature between 600 and 900°C.

[0097] (Heater current detection unit 56)

[0098] like Figure 3 As shown, the sensor control device 5 includes a heater current detection unit 56 that detects the heater current Ih flowing through the heater 34. The heater current detection unit 56 is formed using a current detection circuit 561 that detects the heater current Ih. The heater current detection unit 56 is configured to detect the effective current corresponding to the effective voltage Ve when a pulsed applied voltage Vh is applied to the heater 34 by the heater control unit 53. The heater current detection unit 56 is configured to detect the heater current Ih by measuring the voltage across a shunt resistor arranged in the energization control circuit 531 of the heater control unit 53 connected to the heater 34.

[0099] In this configuration, the heater current detection unit 56 detects the heater current Ih flowing through the heater 34 near the ideal air-fuel ratio controlled in the internal combustion engine. Within the exhaust pipe 7, where the gas sensor 10 is installed, when external interference exists that causes temperature fluctuations in the sensor unit 21, the heater current Ih will fluctuate because the heater control unit 53 aims to maintain the temperature of the sensor unit 21 at the target temperature. These external interferences include fluctuations in the temperature and flow rate of the exhaust gas G flowing through the exhaust pipe 7.

[0100] like Figure 6 (b) and Figure 7As shown, the sampling period t1 of the heater current detection unit 56 for detecting the heater current Ih is shorter than the period t2 of the pulsed applied voltage Vh of the heater control unit 53. This structure allows for appropriate detection of changes in the heater current Ih. Furthermore, in this embodiment, the sampling period t1 of the heater current detection unit 56 for detecting the heater current Ih is shorter than 1 / 10 of the period t2 of the pulsed applied voltage Vh of the heater control unit 53. The sampling interval for the sensor current Is detected by the sensor detection unit 51 and the sampling interval for the resistance value or impedance of the sensor unit 21 detected by the temperature sensing unit 52 can be set to be less than or equal to the sampling period t1 of the heater current detection unit 56 for detecting the heater current Ih. In addition, Figure 7 Extracted Figure 6 Part of (c).

[0101] (Change Rate Calculation Unit 54)

[0102] like Figure 3 , Figure 6 (b), (c) and Figure 7 As shown, the rate of change calculation unit 54 is configured to calculate the rate of change ΔS of the heater current Ih detected by the heater current detection unit 56. When the temperature of the sensor unit 21 sensed by the temperature sensing unit 52 is maintained at the target temperature by the heater control unit 53, it is assumed that the temperature of the sensor unit 21 fluctuates relative to the target temperature. Furthermore, when the heater control unit 53 controls the temperature of the sensor unit 21 to the target temperature, it is also assumed that the temperature of the sensor unit 21 may rise, fall, or remain essentially unchanged. In these cases, the heater current Ih fluctuates according to the amount of electricity supplied to the heater control unit 53, and the heater current Ih has a rate of change corresponding to this fluctuation.

[0103] In this method, such as Figure 6 As shown in (c), the rate of change ΔS of the heater current Ih calculated by the rate of change calculation unit 54 is calculated as the rate of change ΔS of the effective current in the heater 34 corresponding to the product of the voltage and duty cycle when the pulsed applied voltage Vh is turned on, i.e., the effective voltage Ve. The rate of change ΔS of the effective current does not reflect the change of the small-period noise component (called the switching noise component) that accompanies the switching of power supply to the heater 34 by the heater control unit 53. The rate of change ΔS of the effective current reflects the change of the larger-period noise component (called the temperature control noise component) when the temperature of the sensor unit 21 is maintained at the target temperature.

[0104] like Figure 6As shown in (b), in the rate of change calculation unit 54, the value of the heater current Ih detected by the heater current detection unit 56 is calculated as the average value a of the heater current Ih over a predetermined time period longer than the period t2 of the pulsed applied voltage Vh of the heater control unit 53. Furthermore, based on the amount of change (difference value), differential value, etc., of the value of the heater current Ih over a predetermined time period longer than the predetermined time for calculating the average value a of the heater current Ih, the rate of change ΔS of the heater current Ih is calculated. The rate of change ΔS is expressed as... Figure 6 The slope of the waveform of the heater current Ih in (b). The average value a of the heater current Ih can also be obtained by taking the period t2 of the period of the pulsed applied voltage Vh of the heater control unit 53 as an integer multiple.

[0105] When the heater control unit 53 continuously applies a pulsed voltage Vh with the same duty cycle to the heater 34, the average value a of the heater current Ih is constant, and the rate of change ΔS of the heater current Ih is zero. When the heater control unit 53 appropriately applies pulsed voltages Vh with different duty cycles to the heater 34, the average value a of the heater current Ih is not constant, and the rate of change ΔS of the heater current Ih has a predetermined value.

[0106] like Figure 6 As shown in (b) and (d), the rate of change ΔS of the heater current Ih represents the amount of variation (change) of the heater current Ih per unit time. It has been found that the amount of variation of the heater current Ih per unit time causes the sensor current Is of the sensor unit 21 detected by the sensor detection unit 51 to produce a change per unit time as a temperature control noise component. In other words, it has been found that the sensor current Is of the sensor unit 21 detected by the sensor detection unit 51 will produce a change corresponding to the change of the heater current Ih with appropriate phase delay ta.

[0107] (Corrected output section 55)

[0108] like Figure 2 , Figure 3 and Figure 6As shown in (d), the correction output unit 55 calculates the sensor correction output Os of the gas sensor 10 by reducing the impact of the change in heater current Ih per unit time on the sensor current Is detected by sensor detection unit 51, i.e., the sensor output. Specifically, the correction output unit 55 calculates the sensor correction output Os of the gas sensor 10 by removing the temperature control noise component contained in the sensor output. The correction output unit 55 calculates the sensor correction output Os by reflecting the amplitude and period of the change in heater current Ih, the phase delay ta until the change in heater current Ih manifests as a change in sensor current Is, etc. With this structure, the accuracy of the sensor correction output Os can be improved.

[0109] The correction output unit 55 uses the rate of change ΔS of the effective current of the sensor current Is to correct the sensor output to eliminate the induced current generated in the sensor unit 21, and calculates the sensor correction output Os. If the amplitude of the fluctuation of the heater current Ih increases, the amplitude of the temperature control noise component superimposed on the sensor current Is also tends to increase. In addition, if the period of the fluctuation of the heater current Ih decreases (if the frequency increases), the amplitude of the temperature control noise component superimposed on the sensor current Is also tends to increase. The amplitude and period of the fluctuation generated by the heater current Ih are reflected in the rate of change ΔS of the heater current Ih. Therefore, the larger the rate of change ΔS of the effective current of the heater current Ih, the greater the correction amount used by the correction output unit 55 to eliminate the temperature control noise component from the sensor current Is. With this structure, the temperature control noise component contained in the sensor current (sensor output) Is can be effectively removed.

[0110] In addition, such as Figure 6 As shown in (b) and (d), the phase delay ta of the temperature control noise component until the change in heater current Ih becomes apparent as a change in sensor current Is has an inherent value corresponding to the magnitude of the permeability, dielectric constant, etc., of the insulators 33A, 33B, atmospheric conduit 36, etc., disposed between the heater 34 and each electrode 311, 312, and each electrode lead portion 313. Here, permeability represents the ease with which magnetic flux passes from the heater 34 to each electrode 311, 312, and each electrode lead portion 313. The greater the permeability, the easier it is for magnetic flux to pass through.

[0111] Furthermore, the dielectric constant forms an electrostatic capacitance, which is a virtual capacitor formed between the heater 34 and each electrode 311, 312, and each electrode lead portion 313. The electrostatic capacitance increases proportionally to the dielectric constant. The larger the electrostatic capacitance, the slower the magnetic flux transmission speed.

[0112] The phase delay ta of the temperature control noise component can be obtained through experiments after the prototype gas sensor 10 is manufactured. Furthermore, the correction output unit 55 takes the phase delay ta into account when correcting the sensor current Is. In other words, the correction output unit 55 corrects the sensor current Is at a time that includes the phase delay ta, and calculates the sensor correction output Os.

[0113] The sensor current Is generated in sensor unit 21 includes, as a temperature control noise component, an induced current generated in the electrode leads 313 connected to the exhaust electrode 311 and atmospheric electrode 312 of sensor unit 21, corresponding to the effective current in heater 34. When heater 34 is pulse-width modulated using heater control unit 53, a current change occurs in heater 34 associated with the switching on and off of the pulsed applied voltage Vh, and a magnetic flux corresponding to this current change is generated around the wiring direction axis of heater 34. This magnetic flux induces a current in the electrode leads 313 connected to the exhaust electrode 311 and atmospheric electrode 312 of sensor unit 21, which overlaps with sensor current Is. Furthermore, this induced current overlaps with sensor current Is with a phase delay ta.

[0114] (Relational mapping M)

[0115] exist Figure 8 The diagram shows a graph illustrating the relationship between the rate of change ΔS [A / sec] of the heater current Ih and the change in sensor current Is [μA] of the sensor current Is when the applied voltage Vh from the heater control unit 53 to the heater 34 changes appropriately. The larger the rate of change ΔS of the heater current Ih, the larger the change in sensor current Is. Figure 8 In the figure, the change in sensor current Is relative to the rate of change ΔS of heater current Ih is plotted as a curve.

[0116] like Figure 9 As shown, the sensor control device 5 has a relationship mapping M that represents the relationship between the rate of change ΔS of the heater current Ih and the correction amount of the correction output unit 55 to the sensor current (sensor output) Is. It is generally believed that the change in the sensor current Is is a temperature control noise component, so the value of the change in the sensor current Is with a negative sign becomes the correction amount of the sensor current Is.

[0117] In the relational mapping M, regarding the rate of change ΔS of the heater current Ih, there exists a rate of change ΔS on the positive side (increasing heater current Ih) and a rate of change ΔS on the negative side (decreasing heater current Ih). In the relational mapping M, when the rate of change ΔS of the heater current Ih is on the positive side, there exists a relationship that the larger the rate of change ΔS of the heater current Ih becomes on the positive side, the larger the correction amount of the sensor current Is becomes on the negative side. Conversely, in the relational mapping M, when the rate of change ΔS of the heater current Ih is on the negative side, there exists a relationship that the larger the rate of change ΔS of the heater current Ih becomes on the negative side, the larger the correction amount of the sensor current Is becomes on the positive side.

[0118] The correction output unit 55 calculates the sensor correction output Os based on the correction amount of the sensor current Is determined by comparing the rate of change ΔS of the heater current Ih calculated by the rate of change calculation unit 54 with the relational mapping M. Furthermore, when calculating the sensor correction output Os, the correction output unit 55 utilizes the correction amount of the sensor output, calculated using the amount of time taken back by the phase delay ta of the temperature control noise component. By using the relational mapping M, the correction of the sensor current Is by the correction output unit 55 can be easily performed.

[0119] (Operation of gas concentration detection device 1)

[0120] exist Figure 6 In (a), the change of the pulsed applied voltage Vh applied to the heater 34 by the heater control unit 53 over time is shown. Additionally, in Figure 6 In (a), the effective value of the applied voltage Vh to heater 34 is also shown. Figure 6 In (b), the heater current Ih flowing through the heater 34, detected by the heater current detection unit 56, is shown. The heater current Ih has the same waveform as the effective value of the voltage Vh applied to the heater 34.

[0121] exist Figure 6 In (c), the rate of change ΔS of the heater current Ih, which represents the change in heater current Ih per unit time, calculated by the rate of change calculation unit 54, is shown as a function of time. The rate of change ΔS of the heater current Ih is obtained by the difference in heater current Ih within a time difference that is an integer multiple of the period of the pulsed applied voltage Vh.

[0122] exist Figure 6In (d), the change of sensor current Is over time, detected by sensor detection unit 51, is shown. Sensor current Is is detected as a waveform with a phase delay ta relative to the change of heater current Ih over time. Furthermore, the change of sensor current Is over time, which accompanies the change of heater current Ih over time, is considered as a temperature control noise component, and is corrected by taking the phase delay ta into account with the rate of change ΔS of heater current Ih. Therefore, the corrected sensor output Os is corrected to eliminate the influence of the temperature control noise component.

[0123] (Methods for detecting gas concentration)

[0124] The following is for reference Figure 10 The flowchart illustrates an example of a gas concentration detection method using gas concentration detection device 1.

[0125] Following the activation of the vehicle's internal combustion engine and engine control unit 6, the gas sensor 10 and sensor control unit 5 are also activated. In the sensor control unit 5, the heater control unit 53 performs pulse width modulation control of the heater 34, and the sensor unit 21 is heated by the heater 34 (step S101). Next, the temperature of the sensor unit 21 is detected by the temperature sensing unit 52 (step S102), and the sensor unit 21 is continuously heated until its temperature reaches the activation temperature (step S103). The activation temperature of the sensor unit 21 is the target temperature at which the sensor unit 21 is heated by the heater control unit 53.

[0126] Next, after the temperature of the sensor unit 21 sensed by the temperature sensing unit 52 becomes the activation temperature, the sensor current Is is detected by the sensor detection unit 51 at a predetermined sampling interval (step S104), and the heater current Ih is detected by the heater current detection unit 56 (step S105). Then, after a predetermined time interval of one or more calculations of the average value a of the heater current Ih has elapsed after multiple detections of the sensor current Is and the heater current Ih (step S106), the rate of change calculation unit 54 calculates the rate of change ΔS of the heater current Ih flowing through the heater 34 (step S107).

[0127] At this point, the rate of change ΔS of the heater current Ih is calculated by dividing the difference between the average value a of the heater current Ih at the current time point and the average value a of the heater current Ih at past time points by the time difference between the current time point and the past time point. The rate of change ΔS of the heater current Ih exists in both positive and negative directions.

[0128] Next, using the correction output unit 55, the rate of change ΔS of the heater current Ih is compared with the relationship mapping M to determine the correction amount of the sensor current Is (step S108). Furthermore, using the correction output unit 55, the correction amount of the sensor current Is, which is calculated by taking the time that the phase delay ta of the temperature control noise component has been traced back to the past, is calculated as the average value a of the heater current Ih at the current time point, and the sensor correction output Os is calculated (step S109).

[0129] Furthermore, if the correction value of the sensor current Is is negative, the correction value of the sensor current Is is subtracted from the average value a of the sensor current Is at the current time point. If the correction value of the sensor current Is is positive, the correction value of the sensor current Is is added to the average value a of the sensor current Is at the current time point. Then, steps S104 to S110 are repeated until the control of the sensor control device 5 is stopped (step S110).

[0130] (Effects)

[0131] In the sensor control device 5 of the gas concentration detection device 1 of this method, the rate of change ΔS of the heater current Ih flowing through the heater 34 when the temperature of the sensor unit 21 sensed by the temperature sensing unit 52 is maintained at the target temperature by the heater control unit 53 is calculated by the rate of change calculation unit 54. When the temperature of the sensor unit 21 is affected by external disturbances, this rate of change ΔS is expressed as the rate of change calculated when the applied voltage Vh to the heater 34 is adjusted to prevent the temperature of the sensor unit 21 from deviating from the target temperature.

[0132] When the temperature of sensor unit 21 is affected by external interference, and the sensor current Is generated in sensor unit 21 is detected as sensor output by sensor detection unit 51, the sensor output may contain temperature control noise components associated with the change in the applied voltage Vh applied to heater 34, which is an effective value. Therefore, using the rate of change ΔS of heater current Ih calculated by rate of change calculation unit 54, correction output unit 55 corrects the sensor output and calculates the sensor correction output Os of gas sensor 10.

[0133] With this structure, the gas concentration detection device 1 according to this method eliminates the influence of temperature control noise on the sensor output, thereby improving the detection accuracy of the gas sensor 10. Furthermore, by using the rate of change ΔS of the heater current Ih, the detection accuracy of the gas sensor 10 can be effectively improved.

[0134] <Implementation Method 2>

[0135] Regarding the gas concentration detection device 1 of this method, such as Figure 11 and Figure 12 As shown in (a), (b), (c), and (d), the correction output unit 55 of the sensor control device 5 corrects the sensor output, which is the sensor current Is, using not only the rate of change ΔS of the heater current Ih but also the temperature sensed by the temperature sensing unit 52. In this configuration, the correction output unit 55 considers the influence of the temperature of the sensor unit 21 on the magnitude of the sensor current Is and the influence of the temperature of the sensor unit 21 on the phase delay ta of the sensor current Is to correct the sensor current Ih and calculates the sensor correction output Os.

[0136] exist Figure 11 The electrical structure of the sensor control device 5 according to this embodiment is schematically shown in the diagram. In the sensor control device 5, the rate of change ΔS of the heater current Ih detected by the heater current detection unit 56 is calculated by the rate of change calculation unit 54. Furthermore, in the correction output unit 55, the sensor current Is detected by the sensor detection unit 51 is corrected based on the rate of change ΔS and the temperature change ΔT of the sensor unit 21 realized by the heater control unit 53, and the sensor correction output Os is calculated.

[0137] The temperature of the sensor unit 21 sensed by the temperature sensing unit 52 affects the magnitude of the temperature control noise component generated in the sensor current Is and the phase delay ta. The magnetic permeability of the insulators 33A, 33B, atmospheric ducts 36, etc., disposed between the heater 34 and each electrode 311, 312 and each electrode lead portion 313, increases with temperature. That is, the higher the temperature of the sensor element 2, the greater the change in the sensor current Is associated with the change in the heater current Ih. Furthermore, this is the opposite of the relationship where the resistance of the heater 34 increases and the heater current Ih is difficult to flow when the temperature increases.

[0138] Furthermore, the dielectric constant and electrostatic capacitance of the insulators 33A and 33B, atmospheric conduit 36, etc., disposed between the heater 34 and each electrode 311, 312, and each electrode lead portion 313 decrease with increasing temperature. Regarding the induced current generated in each electrode 311, 312, and each electrode lead portion 313 of the sensor unit 21 in response to the change in heater current Ih, the smaller the electrostatic capacitance, the shorter the phase delay ta until it overlaps with the sensor current Is. In other words, the higher the temperature of the sensor element 2, the shorter the phase delay ta of the change in sensor current Is relative to the change in heater current Ih.

[0139] exist Figure 12In (a) and (b), similar to Embodiment 1, the changes in the pulsed applied voltage Vh and the heater current Ih over time are shown. Figure 12 In (c), the changing temperature ΔT of sensor unit 21 as the heater current Ih changes is shown. Figure 12 Similarly, the change in temperature ΔT of sensor unit 21 relative to the heater current Ih is accompanied by a predetermined phase delay tb. It is generally assumed that the phase delay ta of the sensor current Is relative to the change in heater current Ih is the same as the phase delay tb of the change in temperature ΔT.

[0140] The sensor control device 5 of this method has a first relationship mapping M1 representing the relationship between the rate of change ΔS of the heater current Ih and the correction amount of the correction output unit 55 to the sensor current Is, and a second relationship mapping M2 representing the relationship between the temperature of the sensor unit 21 and the correction amount of the correction output unit 55 to the sensor current Is. The first relationship mapping M1 is consistent with that of Embodiment 1. Figure 9 The relational mapping M is the same.

[0141] exist Figure 13 The diagram shows a graph illustrating the relationship between the change in temperature ΔT [°C] and the change in sensor current Is [μA], representing the temperature rise of sensor unit 21, when the applied voltage Vh from heater control unit 53 to heater 34 changes. The graph uses the rate of change of heater current Ih ΔS [μA / sec] as a parameter. The change in temperature ΔT can be captured as the temperature change from the target temperature. The higher the change in temperature ΔT, the greater the change in sensor current Is. Furthermore, the greater the rate of change of heater current Ih ΔS, the greater the magnitude of the change in sensor current Is relative to the change in temperature ΔT.

[0142] exist Figure 13 In this context, the rate of change ΔS of the heater current Ih is expressed as 0.1 Hz, 0.2 Hz, and 0.3 Hz. Figure 13 In the figure, the values ​​of the sensor current Is, which is the change rate ΔS of the heater current Ih, relative to the change temperature ΔT, are connected into a curve.

[0143] like Figure 14As shown, the change in sensor current Is is generally considered a component of temperature control noise. Therefore, in the second relational mapping M2, the value of the change in sensor current Is with a negative sign becomes the correction amount for sensor current Is. The correction amount for sensor current (sensor output) Is has a relationship that the larger the rate of change ΔS of heater current Ih, the larger it is, and the higher the temperature change ΔT, the larger it is.

[0144] like Figure 14 As shown, in the second relationship mapping M2, regarding the changing temperature ΔT, there are cases where the changing temperature ΔT is on the rising side (positive side) and cases where the changing temperature ΔT is on the falling side (negative side). In the second relationship mapping M2, when the changing temperature ΔT is on the positive side, there is a relationship that the larger the changing temperature ΔT becomes on the positive side, the larger the correction amount of the sensor current Is becomes on the negative side. Furthermore, in the second relationship mapping M2, when the changing temperature ΔT is on the negative side, there is a relationship that the larger the changing temperature ΔT becomes on the negative side, the larger the correction amount of the sensor current Is becomes on the positive side.

[0145] The correction output unit 55 calculates the sensor correction output Os based on a first correction amount of the sensor current Is determined by comparing the rate of change of the heater current Ih ΔS with the first relationship mapping M1, and a second correction amount of the sensor current Is determined by comparing the rate of change of the heater current Ih ΔS and the temperature change ΔT with the second relationship mapping M2. Furthermore, when calculating the sensor correction output Os, the correction output unit 55 utilizes the first correction amount of the sensor current Is at a time point that has been retrospectively delayed by a phase delay ta, and the second correction amount of the sensor current Is at a time point that has been retrospectively delayed by a phase delay tb.

[0146] In other words, the correction output unit 55 of this method combines the first correction amount of the sensor current Is at a time point that has been back by a phase delay ta with the second correction amount of the sensor current Is at a time point that has been back by a phase delay tb, and calculates the sensor correction output Os. By using the first relational mapping M1 and the second relational mapping M2, the accuracy of the correction of the sensor current Is by the correction output unit 55 can be further improved.

[0147] (Operation of gas concentration detection device 1)

[0148] exist Figure 15 In (a), (b), and (c), the variation of the sensor current (sensor output) Is is shown in a conventional gas concentration detection device (comparative example) that does not have a rate of change calculation unit 54 and a correction output unit 55, when the temperature of the sensor unit 21 is controlled to the target temperature by the heater control unit 53, and the heater current Ih and the temperature of the sensor unit 21 change due to external interference. Figure 15 In (a), (b), and (c), the case in which the temperature of the exhaust gas G supplied to the gas sensor 10 is simulated to vary in a sinusoidal manner is shown.

[0149] exist Figure 15 The variation of the heater current Ih is shown in (a). Figure 15 (b) shows the temperature variation of sensor unit 21. Figure 15 The variation of the sensor current (sensor output) Is is shown in (c). Figure 15 As shown in (a), (b), and (c), it can be seen that when the heater current Ih and the temperature of the sensor unit 21 change, the sensor current Is changes with a specified phase delay ta.

[0150] exist Figure 16 In (a), (b), and (c), for the comparative example, the change in sensor current Is is shown when the temperature variation amplitude of sensor unit 21 decreases. It can be seen that when the temperature variation amplitude of sensor unit 21 decreases, the change in sensor current Is also decreases. Furthermore, although the illustration is omitted, if the period of heater current Ih becomes shorter (the frequency of vibration increases), the amplitude of sensor current Is increases.

[0151] exist Figure 17 In (a), (b), and (c), the variation of the sensor current (sensor output) Is is shown in the gas concentration detection device 1 (implementation) of Embodiment 2, which has a change rate calculation unit 54 and a correction output unit 55, when the temperature of the sensor unit 21 is controlled to the target temperature by the heater control unit 53, and the heater current Ih and the temperature of the sensor unit 21 change due to external interference. Figure 17 In (a), (b), and (c), the case in which the temperature of the exhaust gas G supplied to the gas sensor 10 is simulated to vary in a sinusoidal manner is also shown.

[0152] like Figure 17 As shown in (c), in the embodiment, by using the change rate calculation unit 54 and the correction output unit 55 to correct the sensor current Is, the change of the sensor current Is is suppressed to a small extent.

[0153] Regarding the other structures and effects of the gas concentration detection device 1 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 also the same as those in Embodiment 1.

[0154] <Other Implementation Methods>

[0155] The sensor detection unit 51 may also have a structure that converts the sensor current Is into a sensor voltage and detects it. In this case, the sensor voltage is corrected in the correction output unit 55 to calculate the sensor correction output Os.

[0156] Alternatively, the rate of change calculation unit 54 can calculate the rate of change of the applied voltage Vh to the heater 34 instead of calculating the rate of change ΔS of the heater current Ih. The applied voltage Vh to the heater 34 changes appropriately according to the temperature change of the sensor unit 21 sensed by the temperature sensing unit 52. The rate of change of the applied voltage Vh to the heater 34 is determined as the rate of change of the effective value of the applied voltage Vh. In this case, the correction output unit 55 preferably corrects the sensor current Is to also reflect the temperature change of the sensor unit 21 shown in Embodiment 2. Alternatively, the rate of change calculation unit 54 can use both the rate of change ΔS of the heater current Ih and the rate of change of the applied voltage Vh to the heater 34.

[0157] The heater control unit 53 can also replace pulse width modulation (PWM) control with pulse frequency modulation (PFM) control to apply an applied voltage Vh to the heater 34. In PFM control, the interval of the applied voltage Vh, which is a pulse of the same width, is appropriately varied.

[0158] 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 gas concentration detection device, characterized in that, have: A gas sensor comprising one or more sensor units having a pair of electrodes disposed on a solid electrolyte body, and a heater for heating the sensor units by means of an electric current; and A sensor control device controls the operation of the sensor unit and the heater; The sensor control device has: The sensor detection unit detects the sensor current or sensor voltage generated in the sensor unit. The temperature sensing unit senses the temperature of the sensor unit; The heater control unit adjusts the voltage applied to the heater; The rate of change calculation unit calculates at least one of the rate of change of the applied voltage to the heater and the rate of change of the heater current flowing through the heater when the temperature sensed by the temperature sensing unit is maintained at a target temperature by the heater control unit. as well as The correction output unit uses the rate of change calculated by the rate of change calculation unit to correct the sensor current or sensor voltage detected by the sensor detection unit, i.e., the sensor output, and calculates the sensor correction output of the gas sensor. The sensor control device also includes a heater current detection unit for detecting the heater current. The rate of change calculation unit calculates the rate of change of the heater current detected by the heater current detection unit. The correction output unit uses the rate of change of the heater current to correct the sensor output and calculates the sensor correction output. In addition to using the rate of change of the heater current, the correction output unit also uses the temperature sensed by the temperature sensing unit, and corrects the sensor output by taking into account the influence of the temperature on the magnitude of the sensor current and the influence of the temperature on the phase delay of the sensor current, and calculates the sensor correction output.

2. The gas concentration detection device according to claim 1, characterized in that, The heater control unit is configured to adjust the pulse width modulation control of the applied voltage to the heater by varying the duty cycle of the pulsed applied voltage. The sampling period for detecting the heater current by the heater current detection unit is shorter than the period of the pulsed applied voltage.

3. The gas concentration detection device according to claim 2, characterized in that, The rate of change of the heater current calculated by the rate of change calculation unit is calculated as the rate of change of the effective current in the heater corresponding to the effective voltage, which is the product of the voltage and duty cycle when the pulsed applied voltage is turned on.

4. The gas concentration detection device according to claim 3, characterized in that, The sensor detection unit is configured to detect the sensor current generated in the sensor unit. The sensor current generated in the sensor unit includes induced currents generated in the electrode leads of the pair of electrodes in the sensor unit, corresponding to the effective current in the heater. The correction output section uses the rate of change of the effective current to correct the sensor output to eliminate the induced current generated in the sensor unit, and calculates the sensor correction output.

5. The gas concentration detection device according to claim 4, characterized in that, The correction output section takes into account the phase delay caused by the heater current due to the induced current to correct the sensor output and calculates the sensor correction output.

6. The gas concentration detection device according to any one of claims 1 to 5, characterized in that, The sensor control device also has a relational mapping that represents the relationship between the rate of change and the correction amount of the correction output unit to the sensor output. The correction value output by the sensor has a relationship that the greater the rate of change, the larger the correction value. The correction output unit calculates the sensor correction output based on the correction amount of the sensor output determined by comparing the change rate calculated by the change rate calculation unit with the relationship mapping.

7. The gas concentration detection device according to claim 1, characterized in that, The sensor control device also has: The first relational mapping represents the relationship between the rate of change of the heater current and the correction amount of the correction output unit to the sensor output; as well as The second relational mapping represents the relationship between the temperature and the correction amount of the correction output unit to the sensor output; The correction value output by the sensor has a relationship that the greater the rate of change of the heater current, the greater the correction value, and the higher the temperature, the greater the correction value. The correction output unit calculates the sensor correction output based on a first correction amount of the sensor output determined by mapping the rate of change of the heater current to the first relationship and a second correction amount of the sensor output determined by mapping the change of the temperature to the second relationship.

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