Humidity sensor diagnostics

Abstract

The diagnostic function of the humidity sensor is exposed to the outside world and is easily degraded. One form of the present invention comprises: an electrostatic capacitance voltage conversion circuit, which has a plurality of reference capacitors with different electrostatic capacitances and a switch for switching these reference capacitors, and outputs a voltage according to the electrostatic capacitance of the humidity sensor; and a diagnostic unit, which compares the output voltage of the electrostatic capacitance voltage conversion circuit with a reference voltage obtained based on the reference characteristics of the humidity sensor, and diagnoses the humidity sensor based on the comparison result. Furthermore, when the output voltage of the electrostatic capacitance voltage conversion circuit is within a certain range, the diagnostic unit changes the output voltage by changing the electrostatic capacitance of the electrostatic capacitance voltage conversion circuit using the switch, and compares the changed output voltage with the reference voltage.

Description

Technical Field

[0001] The invention relates to a humidity sensor diagnosis device for diagnosing a humidity sensor. Background Art

[0002] As a method for reducing harmful exhaust gas of automobiles and improving fuel efficiency and drivability, a feedback-type air-fuel ratio control device that controls the air-fuel ratio based on information on exhaust gas components of an internal combustion engine such as an engine has been put into practical use.

[0003] In the above-mentioned air-fuel ratio control device, there may be a situation where the exhaust gas component is abnormal or the control system cannot be reasonably controlled due to the failure or degradation of the air flow sensor (air quantity measurement) used. In recent years, in order to improve the accuracy of the air flow sensor, multifunctional sensors are used, including air flow sensors, intake air temperature sensors, humidity sensors, etc. In particular, when the air flow sensor is used to measure the intake air quantity, it will be exposed to the intake air quantity, causing pollutants to flow into the humidity sensor element (polymer sensitive film) and deteriorate or degrade the detection accuracy. Furthermore, the humidity detected by the humidity sensor is used to correct the intake air quantity, correct other controls, etc.

[0004] Vehicles for the North American market must comply with OBD2 regulations (a law that requires the installation of onboard self-diagnostic devices). If a malfunction such as a humidity sensor deteriorating to a level exceeding 1.5 times the emission regulation value occurs, the driver must be promptly warned of the abnormality and urged to make repairs. Therefore, if the detection accuracy of the humidity sensor decreases for some reason, appropriate measures such as replacement of the humidity sensor must be implemented (in the case of a multi-function sensor, each multi-function sensor must be replaced).

[0005] Therefore, the present invention seeks a technology for diagnosing a humidity sensor with high accuracy and provides a detection method thereof.

[0006] Patent document 1 discloses an invention related to humidity sensor diagnosis. In the technology disclosed in patent document 1, a first capacitor Ct1 and a second capacitor Ct2 (dielectric film) for diagnosis are provided on an abnormality detection component (humidity sensor itself) to determine the degradation of the characteristics of a first variable capacitor C1 and a second variable capacitor C2 that understand the change in humidity.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2014-10011 Summary of the invention

[0010] Problem that the invention aims to solve

[0011] However, in the technology described in Patent Document 1, since the first capacitor Ct1 and the second capacitor Ct2 as part of the diagnostic function are provided in the humidity sensor itself which is the abnormality detection component, the diagnostic function is exposed to the outside and is easily degraded.

[0012] Due to the above situation, the industry has been demanding a humidity sensor diagnosis device in which the detection accuracy of the diagnosis function is not easily deteriorated.

[0013] Technical means of solving problems

[0014] In order to solve the above-mentioned problem, a humidity sensor diagnostic device of one form of the present invention diagnoses a humidity sensor provided in an intake system of an internal combustion engine and detecting the humidity of intake air based on a change in electrostatic capacitance, and the humidity sensor diagnostic device comprises: an electrostatic capacitance voltage conversion circuit having a plurality of reference capacitors with different electrostatic capacitances and a switch for switching these reference capacitors, and outputting a voltage based on the electrostatic capacitance of the humidity sensor; and a diagnostic unit, which compares the output voltage of the electrostatic capacitance voltage conversion circuit with a reference voltage obtained based on a reference characteristic of the humidity sensor, and diagnoses the humidity sensor based on the comparison result. Furthermore, when the output voltage of the electrostatic capacitance voltage conversion circuit is within a certain range, the diagnostic unit changes the output voltage by changing the electrostatic capacitance of the electrostatic capacitance voltage conversion circuit using the switch, and compares the changed output voltage with the reference voltage.

[0015] Effects of the Invention

[0016] According to at least one form of the present invention, a configuration is adopted in which a plurality of reference capacitors with different electrostatic capacitances are provided in an electrostatic capacitance-to-voltage conversion circuit and the reference capacitors are switched to perform diagnosis. Thus, the plurality of reference capacitors are not exposed to the inflowing gas, and the detection accuracy of the diagnostic function is not easily deteriorated.

[0017] Other problems, structures, and effects than those described above will become clear through the following description of the embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a block diagram showing a configuration example of the humidity sensor diagnosis device according to the first embodiment of the present invention.

[0019] Figure 2 FIG. 1 is a diagram showing an example of an internal combustion engine system using the humidity sensor diagnosis device according to the first embodiment of the present invention.

[0020] Figure 3 This is a block diagram showing a configuration example of a multi-function sensor including a general humidity sensor (relative humidity sensor).

[0021] Figure 4 A diagram showing a configuration example of a humidity sensor.

[0022] Figure 5 A diagram for explaining the principle of a humidity sensor.

[0023] Figure 6 This is a graph showing an example of the relationship between the relative humidity RH and the electrostatic capacitance of the humidity sensor.

[0024] Figure 7 This is a conventional CV conversion circuit that outputs a voltage corresponding to the electrostatic capacitance of the humidity sensor.

[0025] Figure 8 This is a diagram for studying the factors (degradation patterns) of the humidity sensor degradation.

[0026] Fig. 9 This is a graph showing gain degradation, drift (offset) degradation, and response degradation.

[0027] Fig.10 It is a diagram showing an example of a CV conversion circuit provided in the humidity sensor diagnosis device according to the first embodiment of the present invention.

[0028] Fig.11 It is a diagram showing an example of a diagnostic sequence using the CV conversion circuit according to the first embodiment of the present invention.

[0029] Fig.12 Graphs showing a method for detecting gain degradation in the humidity sensor diagnosis device according to the first embodiment of the present invention.

[0030] Fig.13 This is a graph showing a method for detecting drift (offset) degradation by the humidity sensor diagnosis device according to the first embodiment of the present invention.

[0031] Fig.14 FIG. 1 is a time chart showing an example of the response degradation behavior of the humidity sensor when the heater is turned on.

[0032] Fig.15 1 is a diagram showing a method for detecting response degradation of a humidity sensor when a heater is turned on, by the humidity sensor diagnosis device according to the first embodiment of the present invention.

[0033] Fig.16 1 is a diagram showing an example of the detection result of the humidity sensor response degradation when the heater is turned on by the humidity sensor diagnosis device according to the first embodiment of the present invention.

[0034] Fig.171 is a diagram showing a method for detecting response degradation of a humidity sensor when a heater is turned off, by the humidity sensor diagnosis device according to the first embodiment of the present invention.

[0035] Fig.18 This is a flowchart showing an example of a procedure of a gain / drift diagnosis region determination process performed by the gain / drift diagnosis region determination unit according to the first embodiment of the present invention.

[0036] Fig.19 This is a flowchart showing an example of output processing by the CV conversion circuit of the humidity sensor diagnosis device according to the first embodiment of the present invention.

[0037] Fig. 20 This is a flowchart showing an example of a procedure for gain / drift degradation detection processing performed by the humidity sensor diagnosis device according to the first embodiment of the present invention.

[0038] Fig.21 This is a flowchart showing an example of a procedure of a response degradation diagnosis region determination process when a heater is turned on, performed by the humidity sensor diagnosis device according to the first embodiment of the present invention.

[0039] Fig. 22 This is a flowchart showing an example of a procedure of a process for detecting a decrease in response degradation when a heater is turned on, performed by the humidity sensor diagnosis device according to the first embodiment of the present invention.

[0040] Fig.23 This is a flowchart showing an example of the procedure of the rising response degradation detection process when the heater is turned on, which is performed by the humidity sensor diagnosis device according to the first embodiment of the present invention.

[0041] Fig.24 This is a flowchart showing an example of a procedure of a response degradation diagnosis region determination process when the heater is off, which is performed by the humidity sensor diagnosis device according to the first embodiment of the present invention.

[0042] Fig.25 The flowchart shows an example of the procedure of the process of detecting the degradation of the falling response when the heater is off, which is performed by the humidity sensor diagnosis device according to the first embodiment of the present invention.

[0043] Fig.26 It is a diagram showing an example of a CV conversion circuit provided in the humidity sensor diagnosis device according to the second embodiment of the present invention. DETAILED DESCRIPTION

[0044] Hereinafter, examples of specific embodiments of the present invention will be described with reference to the accompanying drawings. In this specification and the accompanying drawings, components having substantially the same function or configuration are denoted by the same reference numerals, and repeated descriptions are omitted.

[0045] <1. First embodiment>

[0046] First, a humidity sensor diagnosis device and a diagnosis method thereof according to a first embodiment of the present invention will be described in detail. In this embodiment, an example of diagnosing a humidity sensor provided in an intake system of an internal combustion engine in a vehicle will be described.

[0047] [Composition of humidity sensor diagnostic device]

[0048] Figure 1 It is a block diagram showing a configuration example of the humidity sensor diagnosis device according to the first embodiment.

[0049] The humidity detector 101 includes a humidity sensor 102, an electrostatic capacitance voltage conversion circuit 103, a temperature sensor 104 (temperature and humidity sensor), and a heater 105 for heating the humidity sensor 102. The humidity sensor 102 is provided in an internal combustion engine 240 (see Figure 2 ) intake system.

[0050] Figure 1 The humidity sensor diagnosis device 130 shown is composed of the electrostatic capacitance voltage conversion circuit 103 and the diagnosis unit 110. Hereinafter, the electrostatic capacitance voltage conversion circuit is referred to as a "CV conversion circuit".

[0051] The humidity detector 101 including the humidity sensor 102 with the heater 105 detects humidity by converting it into a voltage. Here, the humidity sensor 102 detects humidity by utilizing the phenomenon that electrostatic capacitance changes according to humidity. The humidity sensor 102 is controlled at a constant temperature by the temperature sensor 104 and the heater 105. The CV conversion circuit 103 outputs a voltage according to the electrostatic capacitance of the humidity sensor 102, and can be said to be a circuit that converts electrostatic capacitance into a voltage.

[0052] The humidity sensor 102 degradation that the humidity sensor diagnostic device 130 can detect includes gain degradation, drift (offset) degradation, and response degradation. These degradations will be Figure 8 and Fig. 9 Detailed description in.

[0053] The diagnosis unit 110 includes a gain / drift diagnosis region determination unit 111, a gain / drift reference characteristic comparison unit 112, a reference capacitor switching determination unit 113, and a gain / drift determination unit 114. In addition, the diagnosis unit 110 includes a heater-on response degradation diagnosis region determination unit 115, a heater-on response degradation diagnosis time constant detection unit 116, and a heater-on response degradation determination unit 117. In addition, the diagnosis unit 110 includes a heater-off response degradation diagnosis region determination unit 118, a heater-off response degradation diagnosis time constant detection unit 119, and a heater-off response degradation determination unit 120. The gain / drift determination unit 114, the heater-on response degradation determination unit 117, and the heater-off response degradation determination unit 120 constitute a normal / abnormal determination unit 121, respectively. Furthermore, the diagnosis unit 110 includes a correction unit 122 for each control based on the humidity sensor.

[0054] The gain / drift diagnostic region determination unit 111 determines whether the state of the system (the internal combustion engine system in this embodiment) using the humidity sensor 102 matches the gain / drift diagnostic region in which the detection process of gain degradation or drift degradation of the humidity sensor 102 can be performed. Then, the gain / drift diagnostic region determination unit 111 outputs its determination result to the reference capacitor switching determination unit 113 and the gain / drift reference characteristic comparison unit 112.

[0055] The gain / drift reference characteristic comparison unit 112 operates when the state of the target system matches the gain / drift diagnosis area. The gain / drift reference characteristic comparison unit 112 compares the characteristic of the humidity sensor 102 with the normal reference characteristic based on the output voltage of the CV conversion circuit 103, and outputs the comparison result (e.g., the deviation amount from the normal reference characteristic) to the gain / drift determination unit 114. The details will be referred to later. Fig.12 and Fig.13 to explain.

[0056] The reference capacitor switching determination unit 113 operates when the state of the target system matches the gain / drift diagnosis region. The reference capacitor switching determination unit 113 determines the voltage detection sequence applied to the CV conversion circuit 103, and outputs an instruction to switch the reference capacitor to the CV conversion circuit 103 according to the determined voltage detection sequence (refer to the following description). Fig.10 , Fig.11 ).

[0057] The gain / drift determination section 114 determines whether the gain or drift of the humidity sensor 102 is normal or abnormal based on the comparison result of the gain / drift reference characteristic comparison section 112. Then, the gain / drift determination section 114 outputs the determination result to the heater-on response degradation diagnosis area determination section 115 and the heater-off response degradation diagnosis area determination section 118.

[0058] The heater-on response degradation diagnosis region determination unit 115 determines whether the state of the system (the internal combustion engine system in this embodiment) using the humidity sensor 102 matches the heater-on response degradation diagnosis region (the first response degradation diagnosis region) in which the response degradation detection process of the humidity sensor 102 when the heater is turned on can be performed. The heater-on response degradation diagnosis region determination unit 115 outputs the determination result to the heater-on response degradation diagnosis time constant detection unit 116. The heater-on response degradation diagnosis region determination unit 115 is an example of the first response degradation diagnosis region.

[0059] The heater-on response degradation diagnosis time constant detection unit 116 calculates the inverse of the time constant of the output voltage drop during charging and the inverse of the time constant of the output voltage rise during discharging based on the output voltage of the CV conversion circuit 103 in the response degradation diagnosis of the humidity sensor 102 when the heater is on. Fig.14 and Fig.15 Wait for explanation.

[0060] Heater-on response degradation determination unit 117 determines whether the responsiveness of heater-on is normal or abnormal based on the inverse of the output voltage drop time constant during charging and the inverse of the output voltage rise time constant during discharging detected by heater-on response degradation diagnosis time constant detection unit 116 .

[0061] The heater-off response degradation diagnosis region determination unit 118 determines whether the state of the system (the internal combustion engine system in the present embodiment) using the humidity sensor 102 corresponds to the heater-off response degradation diagnosis region (the second response degradation diagnosis region) in which the response degradation detection process when the humidity sensor 102 is heater-off can be performed. The heater-off response degradation diagnosis region determination unit 118 outputs the determination result to the heater-off response degradation diagnosis time constant detection unit 119. The heater-off response degradation diagnosis region determination unit 118 is an example of the second response degradation diagnosis region.

[0062] The heater off response degradation diagnosis time constant detection unit 119 calculates the rise time constant of the output voltage when the heater is off based on the output voltage of the CV conversion circuit 103 in the response degradation diagnosis of the humidity sensor 102 when the heater 105 is switched from on to off, and further converts the reciprocal of the rise time constant of the output voltage during the discharge when the heater is on to a time constant (time constantization). Details will be referred to later. Fig.17 Wait for explanation.

[0063] The heater-off response degradation determination unit 120 compares the output voltage rise time constant when the heater is off with a value obtained by time-constantizing the output voltage rise time constant when the heater is on, and determines whether the responsiveness when the heater is off is normal or abnormal based on the comparison result.

[0064] The correction unit 122 corrects the control that can improve the accuracy in the humidity detection by the humidity sensor 102 .

[0065] The above is an overview of the humidity detector 101 and the humidity sensor diagnosis device 130 according to the first embodiment of the present invention. Next, an internal combustion engine system provided with the humidity sensor 102 to which the present invention is applied will be described.

[0066] [Internal combustion engine system]

[0067] Figure 2 An example of an internal combustion engine system using the humidity sensor diagnostic device 130 is shown. The internal combustion engine system 250 is composed of an internal combustion engine 240, an intake system, and an exhaust system. The internal combustion engine 240 is equipped with an ignition device 201, a fuel injection device 202, and a speed detection device 203. The air flowing from the intake port through the air filter 200 is regulated in flow by a throttle valve 213, and then the flow is measured by a flow detection device 204.

[0068] like Figure 3 As shown, the flow rate detection device 204 is a multifunctional detector (multi-sensor) having an air flow sensor 310, an intake air temperature sensor 320, and a humidity detector 101 built therein. The air flowing into the intake pipe is mixed with the fuel injected at a predetermined angle from the fuel injection device 202 and supplied to each cylinder 214. In addition, in the exhaust system, an air-fuel ratio sensor 205 (an example of a pre-catalyst oxygen sensor), a three-way catalyst 206, and an oxygen sensor 215 (an example of a post-catalyst oxygen sensor) are installed. The exhaust gas of the internal combustion engine 240 is purified by the three-way catalyst 206 and then discharged to the atmosphere.

[0069] The internal combustion engine control device 220 is a control device that controls the internal combustion engine system 250 by transmitting and receiving various signals and data with the internal combustion engine system 250. As an example, an ECU (Electronic Control Unit) is used. The internal combustion engine control device 220 includes an analog input circuit 221, a digital input circuit 222, an A / D conversion circuit 223, an I / O unit 224, an MPU 225, a clock 226, a ROM 227, a RAM 228, a timer / counter 229, and an output circuit 230.

[0070] The MPU (Micro-Processing Unit) 225 is a processor (control unit) that operates in synchronization with the clock signal output from the clock 226. The MPU 225 reads the control program stored in the ROM 227 to the RAM 228 for execution. The timer / counter 229 measures time or the number of occurrences of the measurement object phenomenon according to the instruction of the MPU 225. When the MPU 225 detects an abnormality of the diagnosis object according to the control program, it turns on the warning lamp 235 provided on the instrument panel. The humidity sensor diagnosis device 130 ( Figure 1 ) The functions of each block are realized by executing the control program stored in ROM by MPU 225.

[0071] The internal combustion engine control device 220 reads the output signal Qa of the flow rate detection device 204 and the rotation speed Ne of the drive gear or gear plate 208 obtained by the rotation speed detection device 203, calculates the fuel injection amount Ti, and controls the injection amount of the fuel injection device 202. The internal combustion engine control device 220 uses the air-fuel ratio sensor 205 to detect the air-fuel ratio in the internal combustion engine 240 and performs air-fuel ratio feedback control to correct the fuel injection amount Ti so that the air-fuel ratio in the internal combustion engine 240 becomes the theoretical air-fuel ratio. In addition, the internal combustion engine control device 220 uses the oxygen sensor 215 to detect the air-fuel ratio after catalysis.

[0072] On the other hand, the fuel in the fuel tank 209 is sucked and pressurized by the fuel pump 210, and then guided to the fuel inlet of the fuel injection device 202 through the fuel pipe 212 equipped with the pressure regulator 211, and the excess fuel is returned to the fuel tank 209. The above is the structure of the internal combustion engine system 250 that is the operating object of the humidity sensor diagnosis device 130.

[0073] The humidity sensor for measuring the humidity of the intake system is exposed to the intake air, and pollutants flow into the inside of the humidity sensor element (polymer sensitive film), causing deterioration of the detection accuracy or degradation of the humidity sensor itself. In such an environment, if a structure for realizing the diagnostic function is set on the humidity sensor itself, the diagnostic function is also easy to deteriorate. Therefore, after repeated research, the inventor of the present application came up with a method for diagnosing a humidity sensor that can prevent the degradation of the diagnostic function as described in the specification and drawings of the present application.

[0074] Next, humidity sensor diagnosis device 130 will be described in detail.

[0075] Figure 3 This is a block diagram showing a configuration example of a flow rate detection device 204 (multi-function sensor) including a general humidity sensor (relative humidity sensor). In this embodiment, it is assumed that a relative humidity sensor is used as the humidity sensor 102. Relative humidity (RH) is expressed as a ratio (%) of the actual amount of water vapor (water vapor pressure) to the saturated amount of water vapor (saturated water vapor pressure).

[0076] As described above, the flow rate detection device 204 has built-in air flow sensor 310, intake air temperature sensor 320, and humidity detector 101 having humidity sensor 102. In addition, the flow rate detection device 204 has LSI (Large-Scale Integration) 330 and MCU (Micro-Control Unit) 340. The air flow sensor 310 is a sensor for measuring the flow rate of air in the intake system, and the intake air temperature sensor 320 is a sensor for measuring the temperature of air in the intake system. In addition, the humidity sensor 102 is a sensor for measuring the humidity of air in the intake system.

[0077] The air flow sensor 310 and the intake air temperature sensor 320 output voltages to the LSI 330 as their respective detection results. In addition, the humidity sensor 102 (CV conversion circuit 103) and the temperature sensor 104 output voltages to the LSI 350 as their respective detection results. Then, the LSI 330 and the LSI 350 respectively send data corresponding to the received voltages to the internal combustion engine control device 220 having the diagnosis unit 110 via the MCU 340. The LSI 330 and the LSI 350 are equipped with circuits for processing the voltages input from the sensors, such as sampling circuits, noise removal circuits, and amplifier circuits, as appropriate, and detailed descriptions are omitted.

[0078] The diagnosis unit 110 of the internal combustion engine control device 220 performs a diagnosis on the humidity sensor 102 based on the detection results of the humidity sensor 102 and the temperature sensor 104. Fig.10 The command for the reference capacitor shown is output to the LSI 350 via the MCU 340 , and the reference capacitor of the CV conversion circuit 103 is switched by the LSI 350 .

[0079] [Structure of humidity sensor]

[0080] Figure 4 A configuration example of the humidity sensor 102 using electrostatic capacitance is shown. Figure 4 The structure of the humidity sensor 102 shown is a well-known structure. Figure 4 As shown on the upper side, as an example, a humidity sensor 102 is formed using a humidity sensitive film 401. The humidity sensitive film 401 has a comb-shaped positive electrode 403 and a negative electrode 402 inside, and the positive electrode 403 and the negative electrode 402 are arranged in a state where one comb tooth is engaged with the other comb tooth. The humidity sensitive film 401 is made of polyimide (relative dielectric constant ε'=3) or the like.

[0081] When the humidity of the environment changes, the relative dielectric constant of water (ε'=80) will affect the humidity sensitive film 401 (relative dielectric constant of polyimide ε'=3), causing the relative dielectric constant ε' of the humidity sensitive film 401 to change, thereby causing the electrostatic capacitance C related to humidity to change. Figure 4 As shown in the figure below, the equivalent circuit of the humidity sensor 102 has a structure equivalent to that of a parallel plate capacitor. That is, the electrostatic capacitance C can be expressed by equation (1).

[0082]

[0083] ε0: Dielectric constant in vacuum = 8.854×10 -12 [F / m]

[0084] ε': Relative dielectric constant, one of the electrical properties of a substance (the dielectric constant of the substance is obtained by taking the product with ε0)

[0085] S: surface area, d: gap length, C: electrostatic capacitance

[0086] Figure 5 A diagram for explaining the principle of a humidity sensor. Figure 4 The cross section obtained by cutting along the A-A' line on the upper side. The surface of the moisture sensitive film 401 ( Figure 5The upper and lower surfaces in the figure are covered with a protective film 404. The humidity sensitive film 401 is a porous material having numerous polymer pores 501. A positive electrode 403 and a negative electrode 402 are alternately arranged inside the humidity sensitive film 401. When the power is turned on, electric lines of force are generated between the positive electrode 403 and the negative electrode 402. In the humidity sensor 102, when water molecules 502 pass through the protective film 404 and mix into the humidity sensitive film 401, the water molecules 502 enter the polymer pores 501, and the relative dielectric constant ε' of the humidity sensitive film 401 changes. As a result, the electrostatic capacitance C of the humidity sensor 102 increases.

[0087] Figure 6 This is a graph showing an example of the relationship between the relative humidity RH [% RH] and the electrostatic capacitance C [F] of the humidity sensor. Figure 6 It is found that when the relative humidity increases due to the influence of the relative dielectric constant of water (ε'=80), the electrostatic capacitance of the humidity sensor also increases linearly.

[0088] [Conventional CV conversion circuit]

[0089] Figure 7 This is a conventional CV conversion circuit that outputs a voltage based on the electrostatic capacitance of a humidity sensor.

[0090] The positive side of the humidity sensor 102 is connected to the inverting input terminal of the operational amplifier 710 via the switch SWT, and the negative side thereof is grounded. The capacitor Cs is an equivalent capacitor (electrostatic capacitance) of the humidity sensor 102, and is hereinafter referred to as "equivalent capacitor Cs". In addition, the connection midpoint between the positive side of the humidity sensor 102 and the switch SWT is connected to the power supply Vc via the switch SWC. The reference capacitor C is connected in parallel to the output terminal and the inverting input terminal of the operational amplifier 710. REF2 and switch SWR. Reference capacitor C REF2 The operational amplifier 710 has an electrostatic capacitance that serves as a reference when detecting humidity (hereinafter also referred to as “reference electrostatic capacitance”). The non-inverting input terminal of the operational amplifier 710 is grounded.

[0091] The voltage applied to the output terminal of the operational amplifier 710 is taken out as the output voltage Vo of the CV conversion circuit 700 and output to the LSI 350. The output voltage Vo changes according to the electrostatic capacitance of the equivalent capacitor Cs, and thus can be said to be the “equivalent voltage” of the humidity sensor 102.

[0092] The CV conversion circuit 700 turns on the switch SWC, turns off the switch SWT, and turns on the switch SWR during charging, and charges the equivalent capacitor Cs. On the other hand, the CV conversion circuit 700 turns off the switch SWC, turns on the switch SWT, and turns off the switch SWR during discharging, and discharges the charge from the equivalent capacitor Cs, outputting the output voltage Vo. The state at this time can be expressed by equation (2). Here, the output voltage Vo takes a negative value.

[0093]

[0094] [Degradation Mode]

[0095] Figure 8 This is a diagram for studying the factors (degradation patterns) of humidity sensor degradation. In particular, poisoning by volatile organic compounds (VOCs) and the like can lead to degradation. The degradation caused by the poisoning mainly includes gain degradation, response degradation, and drift (offset) degradation. Therefore, the humidity sensor diagnostic device 130 of the present invention detects these three types of degradation. Each degradation is briefly described.

[0096] [Gain Degradation]

[0097] When the relative humidity sensor (humidity sensor 102) deteriorates, a certain slope is generated between the humidity detected by the relative humidity sensor and the actual humidity, and this is considered to be an error in the output of the relative humidity sensor or a response degradation of the relative humidity sensor. When the deterioration factor is an error in the output of the relative humidity sensor, if the slope is too large or too small, these must be detected through diagnosis.

[0098] [Response Deterioration]

[0099] When the factor of degradation is response degradation of the relative humidity sensor, the response degradation is detected.

[0100] [Drift (offset) degradation]

[0101] When the poisoning characteristic is not just a linear slope (characteristic with an intercept), the degradation of the characteristic caused by poisoning is detected. Before poisoning (before the humidity sensor is used), it is confirmed that the original characteristic of the relative humidity sensor has no deviation.

[0102] Furthermore, if the above three types of degradation are shown in the figure, Fig. 9 The figure shown is used to represent it.

[0103] Fig. 9 This is a graph showing gain degradation, drift (offset) degradation, and response degradation. Fig. 9(1) Gain degradation on the upper side and Fig. 9 In the graph of (2) drift (offset) degradation in the center, the horizontal axis represents relative humidity RH (capacitance of equivalent capacitor Cs), and the vertical axis represents the absolute value of the output voltage Vo of the CV conversion circuit 700. Fig. 9 In the graph of (3) response degradation on the lower side, the horizontal axis represents time and the vertical axis represents the relative humidity sensor voltage Vo.

[0104] like Fig. 9 As shown in the upper side, the slope of the normal reference characteristic 910 of the relative humidity sensor shown by the dotted line is Vc / C REF2 When gain degradation occurs, the slope changes. When the slope becomes too large, the relative humidity sensor becomes characteristic 911, and when the slope becomes too small, the relative humidity sensor becomes characteristic 912.

[0105] like Fig. 9 As shown in the center, when drift degradation occurs, the slope remains constant while the intercept changes (shifts). When the output voltage |Vo| shifts toward an increase, the relative humidity sensor becomes characteristic 921, and when the output voltage |Vo| shifts toward a decrease, the relative humidity sensor becomes characteristic 922.

[0106] exist Fig. 9 On the lower side, the on and off of the relative humidity sensor (output voltage Vo) are repeated periodically. The behavior of the output voltage Vo of the relative humidity sensor in normal state is shown as the response characteristic 930 indicated by the dotted line. Here, when response degradation (abnormality) occurs, the behavior of the output voltage Vo of the relative humidity sensor becomes slower as shown by the response characteristic 931 of the solid line, so the time (time constant τ) until reaching about 63.2% of the final target value becomes longer than normal. Fig. 9 The lower side shows an example of response degradation with respect to the rise and fall of the output voltage.

[0107] [CV conversion circuit]

[0108] Next, the configuration of the CV conversion circuit which is a feature of the present invention will be described.

[0109] Fig.10 An example of a CV conversion circuit provided in humidity sensor diagnosis device 130 is shown. Fig.10 The CV conversion circuit 103 shown in the figure is provided with a capacitor parallel circuit 1000 and a switch SW1 instead of Figure 7 The reference capacitor C of the CV conversion circuit 700 shown in FIG. REF2 That is, a circuit in which the capacitor parallel circuit 1000 and the switch SW1 are connected in series is connected in parallel between the inverting input terminal and the output terminal of the operational amplifier 710 .

[0110] In the capacitor parallel circuit 1000, a plurality of reference capacitors C having different reference electrostatic capacitances are provided. REF1 ~C REF3 In this embodiment, the size of the reference electrostatic capacitance is set to C REF3 >C REF2 >C REF1 The switch SW1 is connected to the reference capacitor C REF1 ~C REF3 The switches SWC, SWT, SWR and SW1 are driven by a switch control signal from the internal combustion engine control device 220.

[0111] In this way, a plurality of reference capacitors C are prepared to detect gain degradation and drift (offset) degradation. REF* ( Fig.10 In the example, * is 1, 2, 3), and it is set that the reference capacitors C can be switched by switch SW1. REF* At this time, the output voltage Vo of the CV conversion circuit 103 is expressed by equation (3).

[0112]

[0113] As can be understood from the above formula (3), in the CV conversion circuit 103, it is possible to change Figure 7 The denominator of formula (2) explained in the previous section is to change the denominator described later. Fig.12 and Fig.13 The measurement point on the horizontal axis (reference capacitor C REF* ). In addition, in this embodiment, three reference capacitors C are provided. REF1 ~C REF3 , but C can also be omitted REF2 The number may be set to 2, or may be set to 4 or more.

[0114] [Diagnostic sequence]

[0115] Fig.11 An example of a diagnostic sequence using the CV conversion circuit 103 is shown.

[0116] like Fig.11 As shown, the diagnostic unit 110 performs a diagnostic sequence through the CV conversion circuit 103 after the heater 105 is turned on. The diagnostic unit 110 switches the reference capacitor C REF* And find the reference capacitor C REF* For example, in the first diagnostic sequence (1), the diagnostic unit 110 first switches to the reference capacitor C REF3Then, the diagnostic unit 110 switches to the reference capacitor C REF1 The output voltage Vo is detected and finally switched to the reference capacitor C REF2 After the first diagnostic sequence (1) is completed, the second diagnostic sequence (2) is implemented in the same manner.

[0117] In this specification, if the reference capacitor is C REF1 , then the output voltage Vo detected at this time is set to V1. In addition, if the reference capacitor is C REF2 , then the output voltage Vo at this time is set to V2 (V2a or V2b). The difference between V2a and V2b will be explained separately. Furthermore, if the reference capacitor is C REF3 , then the output voltage Vo at this time is set to V3.

[0118] Furthermore, the switching to the reference capacitor C can be omitted. REF2 The voltage detection sequence (V2a, V2b) will be described later. Fig.12 is described in.

[0119] [Gain degradation detection method]

[0120] Fig.12 : is a graph showing a method of detecting gain degradation by humidity sensor diagnosis device 130 . Fig.12 2 shows an example of a case where the poisoning substance IPA (ε′=18) flows into the humidity sensor 102. Fig.12 The horizontal axis represents the reference capacitor (C REF* ), the vertical axis represents the absolute value of the output voltage Vo of the CV conversion circuit 103. Fig.12 and the following Fig.13 The premise is that the relative humidity RH [% RH] of the inhaled air is kept constant.

[0121] (Gain Normal)

[0122] First, the diagnostic unit 110 switches the reference capacitor of the CV conversion circuit 103 to C REF2 , the output voltage Vo detected at this time is set to V2a. Next, the diagnostic unit 110 switches the reference capacitor to C REF3 Then, the output voltage Vo at this time is set to V3. Next, the diagnostic unit 110 sets the reference capacitor to C REF3 The output voltage Vo obtained based on the normal reference characteristic 1210 is set to V3r. Then, the diagnosis unit 110 compares V3 with V3r to determine whether V3 is within the range of the upper limit margin H and the lower limit margin L with respect to V3r.

[0123] Here, if V3 ≒ V3r, that is, V3 is within the range of the upper limit margin H and the lower limit margin L relative to V3r, the diagnosis unit 110 then switches the reference capacitor to C REF1 Then, the output voltage Vo at this time is set to V1. Next, the diagnostic unit 110 sets the reference capacitor to C REF1 The output voltage Vo obtained based on the normal reference characteristic 1210 is set as V1r. Then, the diagnosis unit 110 compares V1 with V1r to determine whether V1 is within the range of the upper limit margin H and the lower limit margin L with respect to V1r.

[0124] Here, if V1 ≒ V1r, that is, V1 is within the range of the upper limit margin H and the lower limit margin L relative to V1r, the diagnosis unit 110 then switches the reference capacitor to C REF2 , and the output voltage Vo at this time is set to V2b. Thereafter, the diagnostic unit 110 compares the V2b detected this time with the V2a detected last time, and determines whether V2b is within the range of the upper limit margin H and the lower limit margin L relative to V2a. Then, if V2b≒V2a, that is, V2b is within the range of the upper limit margin H and the lower limit margin L relative to V2a, the diagnostic unit 110 can determine that the humidity is in a fixed state, and therefore determines that the gain is normal.

[0125] (Gain Abnormality)

[0126] On the other hand, gain abnormality can be detected as follows. First, the diagnostic unit 110 sets the reference capacitor to C REF2 The output voltage Vo is set to V2a. Then, the reference capacitor is switched to C REF3 , the output voltage Vo at this time is set to V3. At this time, the output voltage Vo obtained based on the normal reference characteristic 1210 is set to V3r. If V3≠V3r (there is a difference exceeding the upper and lower limit margins), it is determined to be a gain abnormality. For example, the measurement point 1241 on the measured characteristic 1240 exceeds the upper limit margin H, so it is determined to be abnormal (NG).

[0127] Similarly, the diagnostic unit 110 switches the reference capacitor to C REF1 , the output voltage Vo at this time is set to V1. At this time, the output voltage obtained based on the normal reference characteristic 1210 is set to V1r. If V1≠V1r (there is a difference exceeding the upper and lower limit margins), it is determined to be a gain abnormality. For example, the measurement point 1242 on the measured characteristic 1240 also exceeds the upper limit margin H, so it is determined to be abnormal (NG).

[0128] In addition, similarly, the diagnostic unit 110 switches the reference capacitor to C REF2, the output voltage Vo at this time is set to V2b. Then, if V2b≠V2a (there is a difference exceeding the upper and lower limit margins), it is determined that the gain is abnormal.

[0129] In this way, when the humidity (output voltage Vo under the same conditions) is within a certain range, the reference capacitor C REF* In the case of , if any one of the output voltage Vo exceeds the upper limit margin H or falls below the lower limit margin L, it is determined that the gain is degraded. The upper limit margin H and the lower limit margin L can be set to appropriate values ​​according to the intake air temperature measured by the intake air temperature sensor 320 .

[0130] Furthermore, as a method of confirming that the humidity during diagnosis is within a certain range, the reference capacitor C REF3 or C REF1 Instead of the reference capacitor C REF2 To measure the output voltage Vo multiple times, determine whether the difference of multiple output voltages Vo is within a certain range. For example, in one diagnostic sequence ( Fig.11 ) and switches to the reference capacitor C twice REF3 It is confirmed whether the difference between the secondary output voltages Vo (V3a, V3b) is within the range of the upper limit margin H and the lower limit margin L. This method of confirming that the humidity in the diagnosis is within a certain range is also the same as the method of detecting drift (offset) degradation.

[0131] In addition, in order to confirm that the humidity during diagnosis is within a certain range, the reference capacitor is switched to C REF2 Although V2a and V2b are measured as output voltage Vo and compared, this process can be omitted. The reason is that the interval between measuring V2a and V2b is very short, so it is usually unlikely that the humidity will change to a degree that affects the diagnosis result during this period. This simplifies the diagnostic procedure.

[0132] [Drift (offset) degradation detection method]

[0133] Fig.13 : is a graph showing a method of detecting drift (offset) degradation by humidity sensor diagnosis device 130 . Fig.13 2 shows an example of a case where the poisoning substance IPA (ε′=18) flows into the humidity sensor 102. Fig.13 The horizontal axis represents the reference capacitor (C REF* ), the vertical axis represents the absolute value of the output voltage Vo of the CV conversion circuit 103.

[0134] like Fig.13As shown in FIG. 1 , drift (offset) degradation refers to a degradation state in which the slope is the same as that of the normal reference characteristic 1210 but there is an offset (intercept). The drift (offset) detection method is basically the same as Fig.12 The detection method of gain degradation is the same as that shown in the figure. Therefore, gain degradation and drift (offset) degradation cannot be distinguished and detected, but it can be judged as normal or abnormal as one of the characteristic abnormalities.

[0135] For example, Fig.13 , the slope of the measured characteristic 1340 is the same as the normal reference characteristic 1210, but the measurement point 1341 on the characteristic 1340 exceeds the upper limit margin H, so it is judged to be abnormal (NG). Similarly, the measurement point 1342 on the characteristic 1340 also exceeds the upper limit margin H, so it is judged to be abnormal (NG).

[0136] Thus, in the diagnosis of drift (offset) degradation, when the humidity (output voltage Vo under the same conditions) is within a certain range, the reference capacitor C is changed. REF* In the case of , as long as one of the output voltage Vo exceeds the upper limit margin H or is lower than the lower limit margin L, it is determined to be drift degradation. The upper limit margin H and the lower limit margin L can be set to appropriate values ​​according to the intake air temperature measured by the intake air temperature sensor 320.

[0137] [Detection method of response degradation]

[0138] Next, a method for humidity sensor diagnosis device 130 to detect degradation in the response of the temperature sensor will be described.

[0139] The detection method of response degradation is different when the heater is on and when the heater is off. Fig.14 1 is a time chart showing an example of the response degradation behavior of the humidity sensor 102 when the heater is turned on. Fig.14 The timing of the switch SWC, the switch SWT, the switch SWR and the output voltage Vo (equivalent voltage) are shown in FIG. Fig.14 The contents of the time graph include Fig. 9 Lower side and Fig.11 In the description, the dotted line represents the response characteristics in a normal state, and the solid line represents the response characteristics when the response is degraded.

[0140] The response degradation is detected when the output voltage Vo drops during charging, and the response degradation is detected when the output voltage Vo rises during discharging. When gain degradation or drift (offset) degradation occurs, the humidity corresponding to the environment cannot be detected, so the response degradation diagnosis is not performed (refer to the following description). Fig.21 and Fig.24). When the gain and drift (offset) are normal, response degradation diagnosis is performed. The significance of detecting response degradation is that when the time constant of the output voltage Vo is extremely long, charging and discharging may switch before reaching the voltage corresponding to the humidity corresponding to the environment, and the correct humidity may no longer be detected.

[0141] Fig.15 A method for humidity sensor diagnosis device 130 to detect the response degradation of the humidity sensor when the heater is turned on is shown. Fig.15 The timing of switches SWC, SWR and output voltage Vo is shown in FIG.

[0142] When the response degradation of the output voltage Vo is a first-order hysteresis response, in the response degradation during discharge, the expression (4) regarding the response degradation index holds. The expression in parentheses "()" corresponds to the output voltage Vo. The rise time constant is detected during discharge.

[0143]

[0144] Furthermore, in formula (4), since T>τ holds, formula (5) holds.

[0145]

[0146] That is, the response degradation index is a parameter that is inversely proportional to the time constant τ of the response speed. Basically, the situation during charging is the same as that during discharging, and the response degradation index is inversely proportional to the time constant τ. During charging, the falling time constant is detected. Fig. 22 In the example, the descending response degradation index is set to Id, Fig.23 The rising response degradation index is set to Iu.

[0147] [Detection results of response degradation when heater is turned on]

[0148] Fig.16 An example of the detection result of the humidity sensor response degradation when the heater is turned on by the humidity sensor diagnosis device 130 is shown. This detection result is a simulation result of the humidity sensor under a certain condition.

[0149] Fig.16 The above figure shows the relationship between the rise time constant τ and the rise response degradation index when the heater is turned on due to poisoning. It can be seen that Fig.16The detection result of the response degradation shown in the above figure is the result during discharge, and the rising response degradation index is inversely proportional to the time constant. Therefore, a threshold value Th1 for determining the abnormality of the rising response is set, and it is determined to be normal when the rising response degradation index is above the threshold, and it is determined to be abnormal when the rising response degradation index is less than the threshold. The area determined to be abnormal indicates a state with a long time constant. Furthermore, the threshold can also be set in the form of a table (lookup table) of intake air temperatures that have a high correlation with humidity. That is, it is preferred to make the threshold variable according to the intake air temperature measured by the intake air temperature sensor 320.

[0150] Fig.16 The figure below shows the relationship between the falling time constant τ and the falling response degradation index when the response degradation occurs when the heater is turned on due to poisoning. The degradation detection of the falling response degradation index is the same as that of the rising response degradation index. In other words, the falling response degradation index and the time constant are inversely proportional. The threshold Th2 for determining the abnormality of the falling response is set. When the falling response degradation index is above the threshold, it is determined to be normal, and when the falling response degradation index is less than the threshold, it is determined to be abnormal. The falling situation is the response degradation detection during charging.

[0151] The above is a method for detecting the response degradation when the heater is turned on. Next, a method for detecting the response degradation when the heater is turned off from the heater on state will be described.

[0152] [Detection results of response degradation when heater is off]

[0153] Fig.17 The following is a method for detecting the response degradation of the humidity sensor when the heater is turned off by the humidity sensor diagnostic device 130. Fig.17 As shown, the detection of response degradation when the heater is turned off is to detect the response degradation just after the heater 105 changes from on to off. In this case, the time constant when the heater is turned off is directly measured. The time taken for the output voltage Vo to rise to 0.632 times the final value Vf of the output voltage Vo when the heater is turned on when the heater is turned off is measured. In other words, it is the time taken for the output voltage Vo to reach a voltage equivalent to 63.2% from 0% when the final value "Vf" is set to 0% and the output voltage "0" is set to 100%. This time is the time constant when the heater is turned off. As shown Fig.17 As shown, the time constant τ2 when responding to an abnormality is larger than the time constant τ1 when responding to a normality.

[0154] The response degradation index when the heater is turned on is the inverse of the time constant, so the time constant when the heater is turned on can be obtained by calculating the inverse of the response degradation index when the heater is turned on. The time constant when the heater is turned on is compared with the measured time constant when the heater is turned off. If the two time constants are the same, it is determined to be normal. If the time constant when the heater is turned off is longer than the time constant when the heater is turned on, it is determined to be abnormal.

[0155] [Absolute humidity]

[0156] In the above, the detection methods of gain degradation, drift degradation and response degradation are described for relative humidity RH. However, in reality, the degradation state of absolute humidity must be detected. Absolute humidity SH can be expressed by equation (6).

[0157] SH=0.662×1000×E / (PE)···· (6)

[0158] Water vapor pressure E = RH × EW / 100 [kPa]

[0159] Saturated water vapor pressure EW = α × exp (β × T / (λ + T)) [kPa]

[0160] α: 0.6112, β: 17.62, λ: 243.5

[0161] 0.662: Molecular weight of water / molecular weight of dry air

[0162] RH: Relative humidity [%RH], T: Temperature [℃], P: Atmospheric pressure [kPa]

[0163] When gain degradation, drift degradation, or response degradation occurs in the relative humidity RH, the absolute humidity SH will also be degraded in the same manner as a result. Therefore, by detecting each abnormality with respect to the relative humidity RH, gain degradation, drift degradation, and response degradation of the absolute humidity SH can be detected.

[0164] Next, the humidity sensor diagnostic device 130 (refer to Figure 1 ) describes the order of processing performed by each block.

[0165] [Gain / Drift Diagnosis Area Judgment Processing]

[0166] Fig.18 1 is a flowchart showing an example of a procedure of a gain / drift diagnosis region determination process performed by the gain / drift diagnosis region determination unit 111 . Fig.18 Each step represents the diagnosis area determination condition in gain / drift diagnosis.

[0167] First, in step S1, the gain / drift diagnostic area determination unit 111 checks whether the rotational speed of the internal combustion engine 240 is within the specified range (specified value A≤rotational speed≤specified value B). If the rotational speed is within the specified range (Yes in S1), the process proceeds to step S2; if the rotational speed is not within the specified range (No in S1), the process proceeds to step S13.

[0168] Then, in step S2, the gain / drift diagnostic region determination unit 111 checks whether the load of the internal combustion engine 240 is within a specified range (specified value A≤load≤specified value B). If the load is within the specified range (Yes in S2), the process proceeds to step S3. If the load is not within the specified range, the process proceeds to step S13 (No in S2). The load of the internal combustion engine 240 can be obtained, for example, in the form of a ratio of air flow to rotation speed or torque.

[0169] Then, in step S3, the gain / drift diagnostic area determination unit 111 checks whether the temperature of the cooling water (water temperature) is within the specified range (specified value A≤water temperature≤specified value B). If the water temperature is within the specified range (Yes in S3), the process proceeds to step S4. If the water temperature is not within the specified range (No in S3), the process proceeds to step S13.

[0170] Then, in step S4, the gain / drift diagnostic area determination unit 111 checks whether the vehicle speed is within the specified range (specified value A≤vehicle speed≤specified value B). If the vehicle speed is within the specified range (Yes in S4), the process proceeds to step S5. If the vehicle speed is not within the specified range (No in S4), the process proceeds to step S13.

[0171] Then, in step S5, the gain / drift diagnostic area determination unit 111 checks whether the intake air temperature is within the specified range (specified value A≤intake air temperature≤specified value B). If the intake air temperature is within the specified range (Yes in S5), the process proceeds to step S6. If the intake air temperature is not within the specified range (No in S5), the process proceeds to step S13.

[0172] Then, in step S6, the gain / drift diagnostic area determination unit 111 checks whether the atmospheric pressure is above the specified value (atmospheric pressure ≥ specified value). If the atmospheric pressure is within the specified range (Yes in S6), the process proceeds to step S7. If the atmospheric pressure is not within the specified range (No in S6), the process proceeds to step S13.

[0173] Then, in step S7, the gain / drift diagnostic area determination unit 111 checks whether the battery voltage is within the specified range (specified value A≤battery voltage≤specified value B). If the battery voltage is within the specified range (Yes in S7), the process proceeds to step S8. If the battery voltage is not within the specified range (No in S7), the process proceeds to step S13.

[0174] Then, in step S8, the gain / drift diagnostic region determination unit 111 checks whether fuel cut is not being performed. If fuel cut is not being performed (YES in S8), the process proceeds to step S9, and if fuel cut is being performed (NO in S8), the process proceeds to step S13.

[0175] Then, in step S9, the gain / drift diagnostic region determination unit 111 checks whether the air-fuel ratio control feedback is in progress. If so (Yes in S9), the process proceeds to step S10; if not (No in S9), the process proceeds to step S13.

[0176] Then, in step S10, the gain / drift diagnostic region determination unit 111 checks whether the used sensor is not faulty. If the sensor is normal (Yes in S10), the process proceeds to step S11, and if the sensor is faulty (No in S10), the process proceeds to step S13. The determination target sensor is various sensors including the humidity sensor 102 provided in the target system (internal combustion engine system 250).

[0177] Then, in step S11, the gain / drift diagnosis region determination unit 111 checks whether the heater 105 is turned on. If the heater 105 is turned on (Yes in S11), the process proceeds to step S12; if the heater 105 is turned off (No in S11), the process proceeds to step S13.

[0178] Then, in step S12 , that is, when all the conditions in steps S1 to S11 are satisfied, the gain / drift diagnostic region determination unit 111 determines that the state of the internal combustion engine system 250 is within the gain / drift diagnostic region.

[0179] On the other hand, in step S13, that is, when any one of the conditions in steps S1 to S11 is not satisfied, the gain / drift diagnostic region determination unit 111 determines that the state of the internal combustion engine system 250 is not within the gain / drift diagnostic region. After the processing in step S12 or S13, the process returns to step S1.

[0180] The processing of step S8 (in the process of fuel cut-off) and step S9 (in the process of air-fuel ratio feedback) described above may also be omitted. Fig.21 and Fig.24 The same determination processing steps in the flowchart may also be omitted.

[0181] [Output processing of CV conversion circuit]

[0182] Fig.19FIG. 1 is a flowchart showing an example of output processing of the CV conversion circuit 103 of the humidity sensor diagnosis device 130. Fig.18 When it is determined that the state of the internal combustion engine system 250 is within the gain / drift diagnosis region, the output voltage Vo of the CV conversion circuit 103 is measured.

[0183] In step S21, the output voltage Vo of the CV conversion circuit 103 is converted into digital form by the A / D conversion circuit 223. Then, in step S22, the digitalized output voltage Vo is directly stored in the RAM 228 according to the instruction of the MPU 225 or directly. Here, the output voltage Vo is stored in the RAM 228 every 10 ms. In this embodiment, an example of operating in a 10 ms task is shown, but it is not limited to this.

[0184] [Gain / Drift Deterioration Detection Processing]

[0185] Fig. 20 1 is a flowchart showing an example of a procedure of a gain / drift degradation detection process performed by the gain / drift reference characteristic comparison unit 112 and the gain / drift determination unit 114 .

[0186] First, in step S31, the gain / drift reference characteristic comparison unit 112 compares Fig.11 The number of times the diagnostic sequence has been implemented (diagnostic sequence number) Ns is initialized (set to zero). Then, in step S32, the gain / drift reference characteristic comparison unit 112 receives the determination result of the gain / drift diagnostic region determination unit 111 and checks whether the state of the internal combustion engine system 250 is within the gain / drift diagnostic region. If the state of the internal combustion engine system 250 is within the gain / drift diagnostic region (Yes in S32), the process proceeds to step S33. If the state of the internal combustion engine system 250 is not within the gain / drift diagnostic region (No in S32), the process proceeds to step S44.

[0187] Then, in step S33, the gain / drift reference characteristic comparison unit 112 switches the CV conversion circuit 103 ( Fig.10 ) is switched to the reference capacitor C REF2 Then, the gain / drift reference characteristic comparison unit 112 sets the output voltage Vo of the CV conversion circuit 103 detected at this time as V2a. As described above, the switching of the reference capacitor is determined by the reference capacitor switching determination unit 113.

[0188] Next, in step S34, the gain / drift reference characteristic comparison section 112 switches the reference capacitor of the CV conversion circuit 103 to the reference capacitor C via the switch SW1. REF3Then, in step S35, the gain / drift reference characteristic comparison unit 112 compares the normal reference characteristic 1210 ( Fig.12 , Fig.13 )The output voltage Vo obtained is set to V3r.

[0189] Then, in step S36, the gain / drift reference characteristic comparison unit 112 determines whether the condition (V3r+H≥V3 and V3r-L≤V3) is satisfied. If the condition is satisfied (Yes in S36), it is considered that the output voltage Vo is within the margin of the normal reference characteristic 1210, and the process moves to step S37. On the other hand, if the condition in step S36 is not satisfied (No in S36), the gain / drift determination unit 114 determines in step S43 that the gain or drift of the humidity sensor 102 is abnormal.

[0190] Next, if the process proceeds to step S37, the gain / drift reference characteristic comparison unit 112 switches the reference capacitor of the CV conversion circuit 103 to the reference capacitor C via the switch SW1. REF1 Then, in step S38, the gain / drift reference characteristic comparison unit 112 compares the normal reference characteristic 1210 ( Fig.12 , Fig.13 )The output voltage Vo obtained is set to V1r.

[0191] Then, in step S39, the gain / drift reference characteristic comparison unit 112 determines whether the condition (V1r+H≥V1 and V1r-L≤V1) is satisfied. If the condition is satisfied (Yes in S39), it is considered that the output voltage Vo is within the margin of the normal reference characteristic 1210, and the process moves to step S40. On the other hand, if the condition in step S39 is not satisfied (No in S39), the gain / drift determination unit 114 determines that the gain or drift of the humidity sensor 102 is abnormal in step S43.

[0192] Next, when the process moves to step S40, the gain / drift reference characteristic comparison unit 112 switches the reference capacitor of the CV conversion circuit 103 to the reference capacitor C via the switch SW1. REF2 , the output voltage Vo detected at this time is set to V2b.

[0193] Then, in step S41, the gain / drift reference characteristic comparison unit 112 determines whether the condition (V2a+H≥V2b and V2a-L≤V2b) is satisfied. If the condition is satisfied (Yes in S41), the gain / drift determination unit 114 determines in step S42 that the gain or drift of the humidity sensor 102 is normal. The determination process in step S41 is to check the condition that the humidity is in a fixed state during diagnosis.

[0194] On the other hand, if the condition of step S41 is not satisfied (No in S41), the process proceeds to step S44. Then, in step S44, the diagnostic sequence number Ns is incremented (Ns=Ns+1). In addition, after the gain / drift is determined to be normal in step S42 and after the gain / drift is determined to be abnormal in step S43, the process proceeds to step S44.

[0195] Then, in step S45, if the number of diagnostic sequence times Ns has reached the prescribed number of times (Yes in S45), the diagnosis is considered to be completed. If the number of diagnostic sequence times Ns has not reached the prescribed number of times (No in S45), the process is transferred to step S32, i.e., the diagnostic region determination process of gain / drift. In addition, the upper limit margin H and the lower limit margin L appearing in this flowchart may be constants or may be a table defined in relation to the intake air temperature.

[0196] [Response Deterioration Diagnosis Region Determination Processing When Heater is On]

[0197] Fig.21 1 is a flowchart showing an example of a procedure of a response degradation diagnosis region determination process when the heater is on, which is performed by the heater-on response degradation diagnosis region determination unit 115 . Fig.21 The steps are diagnosis region determination conditions in the diagnosis of response degradation when the heater is turned on.

[0198] Fig.21 The processing of steps S51 to S61 shown in FIG. Fig.18 Since steps S1 to S11 are the same, detailed description is omitted. In each of steps S51 to S61, when the determination condition is not satisfied, the process proceeds to step S64.

[0199] After the determination process in step S61, in step S62, the heater-on response degradation diagnosis region determination unit 115 checks Fig. 20 Then, the heater on response degradation diagnosis region determination unit 115 transfers to step S63 when the diagnosis result of the gain / drift degradation diagnosis is normal (Yes in S62), and transfers to step S64 when the diagnosis result of the gain / drift degradation diagnosis is abnormal (No in S62).

[0200] Next, in step S63 , that is, when all the conditions in steps S51 to S62 are satisfied, the heater-on response degradation diagnosis region determination unit 115 determines that the state of the internal combustion engine system 250 is within the heater-on response degradation diagnosis region.

[0201] On the other hand, in step S64, that is, when at least one of the conditions in steps S51 to S62 is not satisfied, the heater-on response degradation diagnosis region determination unit 115 determines that the state of the internal combustion engine system 250 is not within the heater-on response degradation diagnosis region. After the processing of step S63 or S64, the processing of this flowchart is repeated.

[0202] [Degradation detection process of heater-on response]

[0203] Fig. 22 1 is a flowchart showing an example of a procedure of a heater-on response degradation diagnosis time constant detection unit 116 and a heater-on response degradation determination unit 117 for detecting a decrease in response degradation during heater-on.

[0204] First, in step S71, the heater-on response degradation diagnosis time constant detection unit 116 decreases the response degradation indicator Id and Fig.11 The number of times the diagnostic sequence has been implemented (diagnostic sequence number) Nd is initialized (set to zero).

[0205] Then, in step S72, the heater-on response degradation diagnosis time constant detection unit 116 obtains the determination result of the heater-on response degradation diagnosis region determination unit 115, and checks whether the state of the internal combustion engine system 250 is within the heater-on response degradation diagnosis region. If the state of the internal combustion engine system 250 is within the heater-on response degradation diagnosis region (Yes in S72), the process proceeds to step S73, and if the state of the internal combustion engine system 250 is not within the heater-on response degradation diagnosis region (No in S72), the process proceeds to step S82.

[0206] Then, in step S73, the heater-on response degradation diagnosis time constant detection unit 116 determines whether the switch SWC of the CV conversion circuit 103 is on, the switch SWT is off, and the switch SWR is on. If the switches SWC, SWT, and SWR satisfy the conditions (Yes in S73), the process proceeds to step S74, and if the conditions are not satisfied (No in S73), the process proceeds to step S82.

[0207] If the answer is NO in step S72 or NO in step S73 , in step S82 , heater-on response degradation diagnosis time constant detection unit 116 initializes the drop response degradation indicator Id and the diagnosis sequence number Nd.

[0208] Then, if the result of step S73 is YES, in step S74, the heater-on response degradation diagnosis time constant detection unit 116 differentiates the signal (time series data) of the output voltage Vo. That is, the heater-on response degradation diagnosis time constant detection unit 116 calculates the difference value ΔVo between the output voltage Vo measured by the previous diagnosis sequence and the output voltage Vo measured by the current diagnosis sequence.

[0209] Then, in step S75, heater-on response degradation diagnosis time constant detection unit 116 calculates the square of difference value ΔVo. Then, in step S76, heater-on response degradation diagnosis time constant detection unit 116 adds (integrates) the square of difference value ΔVo to falling response degradation indicator Id.

[0210] Then, in step S77, the heater-on response degradation diagnosis time constant detection unit 116 increments the diagnosis sequence number Nd (Nd=Nd+1). Here, in step S78, the heater-on response degradation diagnosis time constant detection unit 116 determines whether the diagnosis sequence number Nd has reached the first predetermined number. Then, if the diagnosis sequence number Nd has reached the first predetermined number, the process proceeds to step S79, and if the diagnosis sequence number Nd has not reached the first predetermined number, the process proceeds to step S73.

[0211] Then, in step S79, the heater-on response degradation diagnosis time constant detection unit 116 compares the down-response degradation indicator Id with a preset first threshold value. Then, when the down-response degradation indicator Id is greater than the first threshold value (Yes in S79), the process proceeds to step S80, and when the down-response degradation indicator Id is less than the first threshold value (No in S79), the process proceeds to step S81.

[0212] Then, if the answer is YES in step S79, the heater-on response degradation determination unit 117 determines in step S80 that the falling response when the heater is turned on is normal. If the answer is NO in step S79, the heater-on response degradation determination unit 117 determines in step S81 that the falling response when the heater is turned on is abnormal. After any of the processes in steps S80 to S82 is completed, the process of this flowchart is repeated.

[0213] The falling response degradation indicator Id indicates the inverse of the time constant of the output voltage Vo. Furthermore, the first threshold value may be a table defined in relation to the intake air temperature.

[0214] [Detection process of deterioration of rising response when heater is turned on]

[0215] Fig.231 is a flowchart showing an example of the sequence of the heater-on response degradation diagnosis time constant detection unit 116 and the heater-on response degradation determination unit 117 for detecting the heater-on rise response degradation. Fig. 22 The descending response degradation index Id is replaced by the ascending response degradation index Iu, and the diagnosis sequence number Nd is replaced by the diagnosis sequence number Nu, which has the same Fig. 22 Similar processing steps.

[0216] First, in step S91, the heater-on response degradation diagnosis time constant detection unit 116 calculates the rising response degradation index Iu and Fig.11 The number of times the diagnostic sequence has been implemented (diagnostic sequence number) Nu is initialized (set to zero).

[0217] Then, in step S92, the heater-on response degradation diagnosis time constant detection unit 116 obtains the determination result of the heater-on response degradation diagnosis region determination unit 115, and checks whether the state of the internal combustion engine system 250 is within the heater-on response degradation diagnosis region. If the state of the internal combustion engine system 250 is within the heater-on response degradation diagnosis region (Yes in S92), the process proceeds to step S93, and if the state of the internal combustion engine system 250 is not within the heater-on response degradation diagnosis region (No in S92), the process proceeds to step S102.

[0218] Then, in step S93, the heater-on response degradation diagnosis time constant detection unit 116 determines whether the switch SWC of the CV conversion circuit 103 is off, the switch SWT is on, and the switch SWR is off. If the switches SWC, SWT, and SWR satisfy the conditions (Yes in S93), the process proceeds to step S94, and if the conditions are not satisfied (No in S93), the process proceeds to step S102.

[0219] If the answer is NO in step S92 or NO in step S93 , in step S102 , heater-on response degradation diagnosis time constant detection unit 116 initializes rising response degradation indicator Iu and diagnosis sequence number Nu.

[0220] Then, if the result of step S93 is YES, in step S94, the heater-on response degradation diagnosis time constant detection unit 116 differentiates the output voltage Vo. That is, the heater-on response degradation diagnosis time constant detection unit 116 calculates the difference value ΔVo between the output voltage Vo measured by the previous diagnosis sequence and the output voltage Vo measured by the current diagnosis sequence.

[0221] Then, in step S95, heater-on response degradation diagnosis time constant detection unit 116 calculates the square of difference value ΔVo. Then, in step S96, heater-on response degradation diagnosis time constant detection unit 116 adds (integrates) the square of difference value ΔVo to rising response degradation indicator Iu.

[0222] Then, in step S97, the heater-on response degradation diagnosis time constant detection unit 116 increments the diagnosis sequence number Nu (Nu=Nu+1). Here, in step S98, the heater-on response degradation diagnosis time constant detection unit 116 determines whether the diagnosis sequence number Nu has reached the second predetermined number. Then, if the diagnosis sequence number Nu has reached the second predetermined number, the process proceeds to step S99, and if the diagnosis sequence number Nu has not reached the second predetermined number, the process proceeds to step S93.

[0223] Then, in step S99, the heater-on response degradation diagnosis time constant detection unit 116 compares the rising response degradation index Iu with a preset second threshold value. Then, when the rising response degradation index Iu is greater than the second threshold value (Yes in S99), the process proceeds to step S100, and when the rising response degradation index Iu is less than the second threshold value (No in S99), the process proceeds to step S101.

[0224] Then, if the answer is YES in step S99, the heater-on response degradation determination unit 117 determines in step S100 that the rising response when the heater is turned on is normal. If the answer is NO in step S99, the heater-on response degradation determination unit 117 determines in step S101 that the rising response when the heater is turned on is abnormal. After any of the processes in steps S100 to S102 is completed, the process of this flowchart is repeated.

[0225] As in the case of the above-mentioned fall response degradation detection, the rise response degradation index Iu indicates the inverse of the time constant of the output voltage Vo. In addition, the second threshold value may be a table defined in relation to the intake air temperature.

[0226] [Response Deterioration Diagnosis Area Determination Processing When Heater OFF]

[0227] Fig.24 1 is a flowchart showing an example of a procedure of a response degradation diagnosis area determination process when the heater is off, which is performed by the heater-off response degradation diagnosis area determination unit 118 . Fig.24 The steps are diagnosis area determination conditions in the response degradation diagnosis when the heater is off.

[0228] Fig.24 The processing of steps S111 to S120 shown in FIG. Fig.21Since steps S51 to S60 are the same, detailed description is omitted. In each of steps S111 to S120, when the determination condition is not satisfied, the process proceeds to step S124.

[0229] After the determination process of step S120, in step S121, the heater-off response degradation diagnosis area determination unit 118 checks whether the heater 105 is turned off. Then, if the heater 105 is turned off (Yes in S121), the process moves to step S122, and if the heater 105 is still turned on (No in S121), the process moves to step S124.

[0230] Then, in step S122, the heater-off response degradation diagnosis region determination unit 118 checks Fig. 20 Then, when the diagnosis result of the gain / drift degradation diagnosis is normal (Yes in S122), the heater-off response degradation diagnosis area determination unit 118 transfers to step S123, and when the diagnosis result of the gain / drift degradation diagnosis is abnormal (No in S122), the heater-off response degradation diagnosis area determination unit 118 transfers to step S124.

[0231] Next, in step S123 , that is, when all the conditions in steps S111 to S122 are satisfied, heater-off response degradation diagnosis region determination unit 118 determines that the state of internal combustion engine system 250 is within the heater-off response degradation diagnosis region.

[0232] On the other hand, in step S124, that is, when any one of the conditions in steps S111 to S122 is not satisfied, heater-off response degradation diagnosis region determination unit 118 determines that the state of internal combustion engine system 250 is not within the heater-off response degradation diagnosis region. After the processing in step S123 or S124, the processing in this flowchart is repeated.

[0233] [Heater OFF rising response degradation detection process]

[0234] Fig.25 1 is a flowchart showing an example of the procedure of the rising response degradation detection process at the time of heater OFF performed by the heater OFF response degradation diagnosis time constant detection unit 119 and the heater OFF response degradation determination unit 120 .

[0235] First, in step S131, the heater-off response degradation diagnosis time constant detection unit 119 sets the output voltage Vo of the CV conversion circuit 103 when the heater is off (when switching from heater-on to heater-off) to the final value Vf ( Fig.17 ).

[0236] Then, in step S132, the heater-off response degradation diagnosis time constant detection unit 119 obtains the determination result of the heater-off response degradation diagnosis region determination unit 118, and checks whether the state of the internal combustion engine system 250 is within the heater-off response degradation diagnosis region. If the state of the internal combustion engine system 250 is within the heater-off response degradation diagnosis region (Yes in S132), the process moves to step S133, and if the state of the internal combustion engine system 250 is not within the heater-off response degradation diagnosis region (No in S132), the detection process ends.

[0237] Then, in step S133 , heater-off response degradation diagnosis time constant detection unit 119 measures the time Tu until the voltage rises to the final value Vf×0.632 times. Fig.17 In the example, the time Tu is equivalent to the time constant τ1 or τ2.

[0238] Then, in step S134, heater-off response degradation diagnosis time constant detection unit 119 calculates (constant / Iu) ( Fig.23 ) is compared with Tu. When (constant / Iu) is greater than Tu (Yes in S134), the process proceeds to step S135. When (constant / Iu) is less than Tu (No in S134), the process proceeds to step S136.

[0239] Then, if it is YES in step S134, in step S135, the heater-off response degradation determination unit 120 determines that the rising response when the heater is off is normal. Also, if it is NO in step S134, in step S136, the heater-off response degradation determination unit 120 determines that the rising response when the heater is off is abnormal. If it is NO in step S132, or the processing of step S135 or S136 is completed, the processing of this flowchart is repeated.

[0240] Regarding (constant / Iu), since the rising response degradation index Iu is the reciprocal of the time constant, it is converted into the time constant by taking the reciprocal, and can be compared with the time Tu.

[0241] According to the above-described embodiment, more accurate functional diagnosis (gain degradation, drift (offset) degradation, response degradation) of the humidity sensor 102 can be performed, and this state will continue.

[0242] As described above, the humidity sensor diagnostic device (humidity sensor diagnostic device 130) of the present embodiment is a humidity sensor diagnostic device that diagnoses a humidity sensor (humidity sensor 102) that is provided in the intake system of an internal combustion engine and detects the humidity of intake air based on a change in electrostatic capacitance. The humidity sensor diagnostic device includes: an electrostatic capacitance voltage conversion circuit (CV conversion circuit 103) having a plurality of reference capacitors (C REF1 ~C REF3 ) and a switch (switch SW1) for switching the reference capacitor, outputting a voltage according to the electrostatic capacitance of the humidity sensor; and a diagnostic unit (diagnostic unit 110) which compares the output voltage (Vo) of the electrostatic capacitance voltage conversion circuit with a reference voltage obtained according to the reference characteristic (normal reference characteristic 1210) of the humidity sensor, and diagnoses the humidity sensor according to the comparison result. When the output voltage of the electrostatic capacitance voltage conversion circuit is within a certain range, the diagnostic unit changes the output voltage by changing the electrostatic capacitance of the electrostatic capacitance voltage conversion circuit using the switch, and compares the changed output voltage with the reference voltage.

[0243] In the first embodiment constructed in the above manner, a plurality of reference capacitors with different electrostatic capacitances are provided in the electrostatic capacitance voltage conversion circuit. Furthermore, when the output voltage of the electrostatic capacitance voltage conversion circuit is maintained in a state within a certain range, the output voltage is changed by changing the electrostatic capacitance of the electrostatic capacitance voltage conversion circuit, and the changed output voltage is compared with the reference voltage obtained based on the reference characteristic, thereby diagnosing the humidity sensor. According to the first embodiment, the humidity sensor element itself is not equipped with a diagnostic function (a reference capacitor for diagnosis) but the reference capacitor of the electrostatic capacitance voltage conversion circuit is switched, so that the plurality of reference capacitors are not exposed to the inflowing gas and the plurality of reference capacitors are not easily degraded. Therefore, the detection accuracy of the diagnostic function of the humidity sensor diagnostic device is not easily degraded. It is possible to implement a more accurate functional diagnosis of the humidity sensor, and this state will continue.

[0244] Furthermore, the present embodiment has a smaller number of switches than the technique described in Patent Document 1, so the possibility of misdiagnosis due to switch failure is reduced.

[0245] In the first embodiment, a heater (heater 105) is provided to heat the humidity sensor, and the temperature of the humidity sensor is kept constant by the heater. Thus, the temperature of the humidity sensor can be kept constant during diagnosis, so that accurate diagnosis can be performed.

[0246] In addition, in the above-mentioned first embodiment, the above-mentioned diagnostic unit (diagnostic unit 110) is configured to compare the output voltage (Vo) of the electrostatic capacitance voltage conversion circuit (CV conversion circuit 103) with a reference voltage calculated based on the reference characteristics (normal reference characteristics 1210) of the humidity sensor (humidity sensor 102), and when the difference between the output voltage and the reference voltage is within a specified value (upper limit margin H, lower limit margin L), it is determined that the humidity sensor is normal; when the difference between the output voltage and the reference voltage exceeds a specified value, it is determined that the humidity sensor has an abnormality caused by gain degradation or drift degradation.

[0247] According to the present embodiment having the above-described configuration, the gain degradation diagnosis or the drift degradation diagnosis of the humidity sensor can be performed more accurately, and this state can continue.

[0248] Furthermore, in the first embodiment, the diagnosis unit (diagnosis unit 110 ) is configured to shift to the humidity sensor response degradation diagnosis when the gain degradation or drift degradation of the humidity sensor (humidity sensor 102 ) is not detected.

[0249] According to the present embodiment configured as above, response degradation diagnosis can be performed when the characteristics (gain, drift (offset)) of the humidity sensor are normal, thereby enabling both characteristic diagnosis and response diagnosis. In addition, since response degradation diagnosis is performed when the gain and drift are normal, more accurate response degradation diagnosis can be performed on the humidity sensor.

[0250] In the first embodiment, the diagnosis unit (diagnosis unit 110) is configured to calculate the time constant of the output voltage drop during charging and the time constant of the output voltage rise during discharging for the electrostatic capacitance voltage conversion circuit (CV conversion circuit 103) in the diagnosis of the response degradation of the humidity sensor (humidity sensor 102) when the heater is turned on. With such a configuration, it is possible to diagnose the response degradation of the output voltage drop and rise when the heater is turned on.

[0251] In the first embodiment, the diagnostic unit (diagnostic unit 110) is configured to differentiate the signal of the output voltage (Vo) during charging, then square the differentiated value, and then integrate the squared value to calculate the inverse of the output voltage drop time constant (response degradation index Id). Furthermore, the diagnostic unit (diagnostic unit 110) is configured to determine that the response characteristic of the output voltage drop is normal when the inverse of the output voltage drop time constant is greater than the threshold value (Th2), and to determine that the response characteristic of the output voltage drop is abnormal when the inverse of the output voltage drop time constant is less than the threshold value.

[0252] With such a configuration, the diagnosis unit can diagnose the fall response degradation by comparing the inverse of the fall time constant of the output voltage with the threshold value ( Th2 ) as a fall response degradation index.

[0253] In the first embodiment, the diagnostic unit (diagnostic unit 110) is configured to calculate the inverse of the rising time constant of the output voltage (response degradation index Iu) by differentiating and squaring the signal of the output voltage (Vo) during discharge and then integrating the signal. Furthermore, the diagnostic unit (diagnostic unit 110) is configured to determine that the response characteristic of the rise of the output voltage is normal when the inverse of the rising time constant of the output voltage (Vo) is greater than the threshold value (Th1), and to determine that the response characteristic of the rise of the output voltage is abnormal when the inverse of the rising time constant of the output voltage (Vo) is less than the threshold value (Th1).

[0254] With such a configuration, the diagnosis unit can diagnose the rise response degradation by comparing the inverse of the rise time constant of the output voltage with the threshold value ( Th1 ) as a rise response degradation index.

[0255] In addition, in the first embodiment, the diagnosis unit (diagnosis unit 110) is configured to calculate the rise time constant (Tu) of the output voltage when the heater is turned off for the electrostatic capacitance voltage conversion circuit (CV conversion circuit 103) in the response degradation diagnosis of the humidity sensor (humidity sensor 102) when the heater (heater 105) is switched from on to off, and further take the reciprocal (constant / Iu) of the rise time constant of the output voltage when the heater is turned on to perform time constantization, and compare the rise time constant of the output voltage when the heater is turned off with the value obtained by time constantization based on the rise time constant of the output voltage when the heater is turned on. And, when the rise time constant of the output voltage when the heater is turned off is less than the value obtained by time constantization, the diagnosis unit determines that the response characteristic of the output voltage when the heater is turned off is normal, and when the rise time constant of the output voltage when the heater is turned off exceeds the value obtained by time constantization, the response characteristic of the output voltage when the heater is turned off is abnormal.

[0256] According to the present embodiment having the above configuration, it is possible to diagnose the response degradation of the drop and rise of the output voltage when the heater is turned off.

[0257] Furthermore, in the first embodiment, the diagnosis unit (diagnosis unit 110) includes a gain / drift diagnosis region determination unit (gain / drift diagnosis region determination unit 111) that determines whether the state of the internal combustion engine (internal combustion engine 240) is consistent with the gain / drift diagnosis region in which the detection process of gain degradation or drift degradation of the humidity sensor (humidity sensor 102) can be performed. And, the diagnosis unit is configured to be able to shift to the process of detecting gain degradation or drift degradation of the humidity sensor when the gain / drift diagnosis region determination unit determines that the state of the internal combustion engine is consistent with the gain / drift diagnosis region.

[0258] According to the present embodiment configured as above, when the state of the internal combustion engine matches the gain / drift diagnosis region, the process shifts to detecting gain degradation or drift degradation of the humidity sensor. Therefore, gain degradation or drift degradation can be detected more accurately.

[0259] In addition, in the first embodiment, the diagnosis unit (diagnosis unit 110) includes a first response degradation diagnosis area determination unit (heater-on response degradation diagnosis area determination unit) that determines whether the state of the internal combustion engine (internal combustion engine 240) corresponds to a first response degradation diagnosis area in which the response degradation detection process when the humidity sensor (humidity sensor 102) is able to be performed. And, the first response degradation diagnosis area determination unit determines that the state of the internal combustion engine does not correspond to the first response degradation diagnosis area at least when the heater (heater 105) is turned off or when gain degradation or drift degradation is detected, and the diagnosis unit receives the determination result of the first response degradation diagnosis area determination unit without shifting to the response degradation detection process when the heater is turned on.

[0260] According to the present embodiment constructed as above, at least when the heater is disconnected or gain degradation or drift degradation is detected, the determination result of the first response degradation diagnostic area determination unit is received without transferring to the response degradation detection processing when the heater is turned on, thereby preventing the deterioration of the detection accuracy of the response degradation when the heater is turned on.

[0261] In addition, in the first embodiment, the diagnosis unit (diagnosis unit 110) includes a second response degradation diagnosis area determination unit (heater off response degradation diagnosis area determination unit) that determines whether the state of the internal combustion engine (internal combustion engine 240) is consistent with the second response degradation diagnosis area in which the response degradation detection process when the humidity sensor (humidity sensor 102) is able to be performed. And, the second response degradation diagnosis area determination unit is configured so that at least when the heater (heater 105) is turned on or when gain degradation or drift degradation is detected, the second response degradation diagnosis area determination unit determines that the state of the internal combustion engine does not correspond to the second response degradation diagnosis area, and the diagnosis unit receives the determination result of the second response degradation diagnosis area determination unit without shifting to the response degradation detection process when the heater is off.

[0262] According to the present embodiment constructed as above, at least when the heater is turned on or gain degradation or drift degradation is detected, the determination result of the second response degradation diagnostic area determination unit is received without transferring to the response degradation detection processing when the heater is turned off, thereby preventing the deterioration of the detection accuracy of the response degradation when the heater is turned off.

[0263] In addition, in the above-mentioned first embodiment, the electrostatic capacitance voltage conversion circuit (CV conversion circuit 103) outputs a voltage (Vo) equivalent to the humidity based on the electrostatic capacitance (Cs) that changes under the relationship between the relative dielectric constant of moisture in the air and the substance (humidity sensitive film 401) having a relative dielectric constant different from that of water arranged in the humidity sensor.

[0264] In the first embodiment, the diagnostic unit (diagnostic unit 110) is switched twice to the same reference capacitor (eg, C REF2 ), confirming that the difference between the two output voltages (Vo) obtained by the electrostatic capacitance voltage conversion circuit (CV conversion circuit 103) when switching to the reference capacitor is within a certain range. With such a configuration, it is possible to confirm that the environment of the humidity sensor during diagnosis is fixed, thereby making an accurate diagnosis.

[0265] <2. Second Embodiment>

[0266] The second embodiment is a CV conversion circuit 103 (see Fig.10 ) A circuit for amplifying the electrostatic capacitance of the reference capacitor is provided to replace the structure of the capacitor parallel circuit 1000.

[0267] Fig.26 An example of a CV conversion circuit provided in the humidity sensor diagnosis device according to the second embodiment will be described. Fig.26In the CV conversion circuit 103A shown, the capacitance amplifier circuit 2600 is connected in parallel between the inverting input terminal and the output terminal of the operational amplifier 710, so that the diagnosis of the present invention can be implemented even for a small capacitance.

[0268] The electrostatic capacitance amplifier circuit 2600 is composed of a fixed reference capacitor C REF , a resistor parallel circuit 2610 (resistor R2), a switch SW1, an operational amplifier 2620, a resistor R1, and a resistor R3. Fixed reference capacitor C REF The series circuit of the resistor parallel circuit 2610 (resistor R2) and the switch SW1 is connected in parallel between the inverting input terminal and the output terminal of the operational amplifier 710. The resistor parallel circuit 2610 is composed of three reference resistors R REF1 ~R REF3 The parallel circuit uses switch SW1 to select any reference resistor R REF* In addition, capacitor C REF The connection midpoint with the resistor parallel circuit 2610 is connected to the non-inverting input terminal of the operational amplifier 2620, and the output terminal of the operational amplifier 710 is connected to the output terminal of the operational amplifier 2620 via the resistor R3. Furthermore, the resistor R1 is connected between the inverting input terminal and the output terminal of the operational amplifier 2620. In addition, the switch SWR is connected between the inverting input terminal and the output terminal of the operational amplifier 710.

[0269] In the above configuration, the reference capacitor C in the capacitance amplifier circuit 2600 REF* The electrostatic capacitance can be expressed by formula (7). By switching the reference resistor R2 REF1 ~R REF3 , the reference capacitor C REF* The electrostatic capacitance is amplified.

[0270]

[0271] Generally speaking, when the electrostatic capacitance of a capacitor increases, its housing also increases, so the area and volume of the circuit increase. As a countermeasure, an electrostatic capacitance amplifier circuit 2600 can also be used while maintaining the degree of integration. The diagnostic method itself is the same as the first embodiment, by using the switch SW1 to adjust the resistor R2 (reference resistor R REF1 ~R REF3 ) is switched to switch the reference capacitor C REF* The electrostatic capacitance of the device is used to perform the diagnosis. Even if the resistivity increases, the resistance does not change much, so using this circuit is effective in miniaturizing the circuit. In addition, the material of the resistor is mostly a composite material of aluminum oxide (alumina) and glass, and the resistor is less likely to deteriorate over time than the capacitor.

[0272] Furthermore, the capacitance may be switched by switching the resistor R3 instead of the resistor R2 using a switch.

[0273] Industrial Applicability

[0274] Humidity sensor diagnosis device 130 can accurately diagnose gain degradation, drift (offset) degradation, and response degradation of humidity sensor 102 installed in internal combustion engine system 250, and is a technology suitable for strengthening vehicle self-diagnosis regulations.

[0275] Furthermore, the present invention is not limited to the above-described embodiments, and various other application examples and modified examples can of course be employed without departing from the gist of the present invention described in the claims.

[0276] For example, the above embodiments are detailed and specific descriptions of the configuration of the humidity sensor diagnostic device to help understand the present invention, and are not necessarily limited to having all the components described. In addition, other components may be added, replaced, or deleted from part of the configuration of each embodiment.

[0277] In addition, the above-mentioned components, functions, processing units, etc. can be implemented in part or in whole by hardware, for example, by designing with integrated circuits. As hardware, FPGA (Field Programmable Gate Array), ASIC (Application Specific Integrated Circuit), etc. can be used. In addition, the above-mentioned components, functions, etc. can also be implemented in software by interpreting and executing programs that implement each function by a processor (such as MPU 225) equipped in a computer. Information such as programs, tables, files, etc. that implement each function can be placed in a recording device such as a semiconductor memory (ROM 227), a hard disk, an SSD (Solid State Drive), or a recording medium such as an IC card, an SD card, or an optical disk.

[0278] Furthermore, in the flowchart described in the first embodiment, a plurality of processes may be executed in parallel or the order of processes may be changed within a range that does not affect the processing results.

[0279] In addition, in the above-mentioned embodiment, the control lines and information lines are shown as those considered necessary for explanation, and not all the control lines and information lines may be shown on the product. In fact, it can be considered that almost all the components are connected to each other.

[0280] Explanation of symbols

[0281] 101 ... humidity detector, 102 ... humidity sensor, 103, 103A ... CV conversion circuit, 104 ... temperature sensor, 105 ... heater, 110 ... diagnosis unit, 111 ... gain / drift diagnosis region determination unit, 112 ... gain / drift reference characteristic comparison unit, 113 ... reference capacitor switching determination unit, 114 ... gain / drift determination unit, 115 ... heater-on response degradation diagnosis region determination unit (first response degradation diagnosis region determination unit), 116 ... heater-on response degradation diagnosis time constant detection unit, 117 ... heater-on response degradation determination unit, 118 ... heater-off response degradation diagnosis region determination unit (second response degradation diagnosis region determination unit), 119 ... heater-off response degradation diagnosis time constant detection unit, 120 ... heater-off response degradation determination unit, 121 ... normal / abnormal determination unit, 122 ... correction unit for each control based on the humidity sensor, 13 0...humidity sensor diagnostic device (CV conversion circuit 103, diagnostic unit 110), 200...air filter, 201...ignition device, 202...fuel injection device, 204...flow rate detection device (multi-sensor), 205...air-fuel ratio sensor, 206...three-way catalyst, 215...oxygen sensor, 220...internal combustion engine control unit (ECU), 225...MPU, 227...ROM, 235...warning lamp, 240...internal combustion engine, 250…Internal combustion engine system, 310…Air flow sensor, 320…Intake air temperature sensor, 401…Humidity sensitive film, 710…Operational amplifier, 910…Normal reference characteristics, 911, 912, 921, 922…Characteristics, 930, 931…Response characteristics, 1000…Capacitor parallel circuit, 1210…Normal reference characteristics, 2600…Electrostatic capacitance amplifier circuit, 2610…Resistance parallel circuit, 2620…Operational amplifier, C S …equivalent capacitor, C REF …fixed reference capacitor, C REF* , C REF1 ~C REF3 ...reference capacitor, R2, R3...resistor, R REF1 ~R REF3 ...reference resistor, SW1...switch, Th1, Th2...threshold, V O …output voltage, τ, τ1, τ2…time constants.

Claims

1. A humidity sensor diagnostic device for diagnosing a humidity sensor provided in an intake system of an internal combustion engine and detecting the humidity of intake air based on a change in electrostatic capacitance, the humidity sensor diagnostic device comprising: an electrostatic capacitance voltage conversion circuit including a plurality of reference capacitors having different electrostatic capacitances and a switch for switching the reference capacitors, and outputting a voltage according to the electrostatic capacitance of the humidity sensor; and a diagnosis unit that compares the output voltage of the electrostatic capacitance voltage conversion circuit with a reference voltage obtained based on a reference characteristic of the humidity sensor, and diagnoses the humidity sensor based on the comparison result; When the output voltage of the electrostatic capacitance voltage conversion circuit is within a certain range, the diagnostic unit changes the output voltage by changing the electrostatic capacitance of the electrostatic capacitance voltage conversion circuit using the switch, and compares the changed output voltage with the reference voltage.

2. The humidity sensor diagnostic device according to claim 1, characterized in that: The temperature of the humidity sensor is kept fixed by a heater.

3. The humidity sensor diagnostic device according to claim 2, characterized in that: The diagnostic unit compares the output voltage of the electrostatic capacitance voltage conversion circuit with the reference voltage calculated based on the reference characteristics of the humidity sensor, and determines that the humidity sensor is normal when the difference between the output voltage and the reference voltage is within a specified value; and determines that the humidity sensor has an abnormality caused by gain degradation or drift degradation when the difference between the output voltage and the reference voltage exceeds a specified value.

4. The humidity sensor diagnostic device according to claim 3, characterized in that: The diagnosis unit may shift to response degradation diagnosis of the humidity sensor when gain degradation or drift degradation of the humidity sensor is not detected.

5. The humidity sensor diagnostic device according to claim 4, characterized in that: In the diagnosis of response degradation of the humidity sensor when the heater is turned on, the diagnosis unit calculates a time constant of a decrease in the output voltage of the electrostatic capacitance voltage conversion circuit during charging and calculates a time constant of a rise in the output voltage during discharging.

6. The humidity sensor diagnostic device according to claim 5, characterized in that: The diagnostic unit differentiates the output voltage signal during charging, squares the differentiated value, and then integrates the squared value, thereby calculating the inverse of the falling time constant of the output voltage.

7. The humidity sensor diagnostic device according to claim 5, characterized in that: The diagnostic unit differentiates the output voltage signal during discharge, squares the differentiated value, and then integrates the squared value, thereby calculating the inverse of the rise time constant of the output voltage.

8. The humidity sensor diagnostic device according to claim 6, characterized in that: The diagnosis unit determines that the response characteristic of the output voltage drop is normal when the inverse of the output voltage drop time constant is equal to or greater than a threshold value, and determines that the response characteristic of the output voltage drop is abnormal when the inverse of the output voltage drop time constant is less than the threshold value.

9. The humidity sensor diagnostic device according to claim 7, characterized in that: The diagnosis unit determines that the response characteristic of the increase of the output voltage is normal when the inverse of the increase time constant of the output voltage is greater than or equal to a threshold value, and determines that the response characteristic of the increase of the output voltage is abnormal when the inverse of the increase time constant of the output voltage is less than the threshold value.

10. The humidity sensor diagnostic device according to claim 4, characterized in that: In the response degradation diagnosis of the humidity sensor when the heater is switched from on to off, the diagnostic unit calculates the rise time constant of the output voltage of the electrostatic capacitance voltage conversion circuit based on the signal of the output voltage when the heater is off, and further, differentiates the signal of the output voltage during discharge when the heater is on, then squares the differentiated value, and integrates the squared value to calculate the reciprocal of the rise time constant of the output voltage during discharge when the heater is on, and then calculates the time-constantized value by taking the reciprocal of the reciprocal of the rise time constant of the output voltage. The rise time constant of the output voltage when the heater is turned off is compared with a value obtained by taking the inverse of the rise time constant of the output voltage when the heater is turned on and converting the result into a time constant. When the rising time constant of the output voltage when the heater is turned off is equal to or less than the value obtained by time-constantizing the reciprocal of the rising time constant of the output voltage during discharge when the heater is turned on, it is determined that the response characteristic of the output voltage when the heater is turned off is normal. When the rising time constant of the output voltage when the heater is off exceeds a value obtained by time-constantizing the inverse of the rising time constant of the output voltage during discharge when the heater is on, it is determined that the response characteristic of the output voltage when the heater is off is abnormal.

11. The humidity sensor diagnostic device according to claim 3, characterized in that: The diagnosis unit includes a gain / drift diagnosis region determination unit configured to determine whether the state of the internal combustion engine corresponds to a gain / drift diagnosis region in which a detection process of gain degradation or drift degradation of the humidity sensor can be performed. The diagnosis unit may shift to a process of detecting gain degradation or drift degradation of the humidity sensor when the gain / drift diagnosis region determination unit determines that the state of the internal combustion engine corresponds to the gain / drift diagnosis region.

12. The humidity sensor diagnostic device according to claim 4, characterized in that: The diagnosis unit includes a first response degradation diagnosis area determination unit that determines whether the state of the internal combustion engine corresponds to a first response degradation diagnosis area in which a response degradation detection process when the heater of the humidity sensor is turned on can be performed. The first response degradation diagnostic area determination unit determines that the state of the internal combustion engine does not conform to the first response degradation diagnostic area at least when the heater is disconnected or the gain degradation or drift degradation is detected, and the diagnostic unit receives the determination result of the first response degradation diagnostic area determination unit without transferring to the response degradation detection processing when the heater is turned on.

13. The humidity sensor diagnostic device according to claim 4, characterized in that: The diagnosis unit includes a second response degradation diagnosis area determination unit that determines whether the state of the internal combustion engine corresponds to a second response degradation diagnosis area in which a response degradation detection process when the heater of the humidity sensor is turned off can be performed. The second response degradation diagnostic area determination unit determines that the state of the internal combustion engine does not conform to the second response degradation diagnostic area at least when the heater is turned on or the gain degradation or drift degradation is detected, and the diagnostic unit receives the determination result of the second response degradation diagnostic area determination unit without transferring to the response degradation detection processing when the heater is turned off.

14. The humidity sensor diagnostic device according to claim 1, characterized in that: The electrostatic capacitance voltage conversion circuit outputs a voltage corresponding to humidity based on the electrostatic capacitance that changes in relation to the relative dielectric constant of moisture in the air and a substance provided in the humidity sensor and having a relative dielectric constant different from that of moisture.

15. The humidity sensor diagnostic device according to claim 1, characterized in that: The diagnosis unit switches to the same reference capacitor twice by the switch, and checks whether the difference between two output voltages obtained by the electrostatic capacitance-voltage conversion circuit when switching to the reference capacitor is within the certain range.

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