JP7373380B2 - Humidity sensor diagnostic device and humidity sensor diagnostic method - Google Patents

Description

The present invention relates to a device and a diagnostic method for diagnosing an abnormality in a humidity sensor provided in an engine control device equipped with an exhaust gas recirculation system (EGR).

Conventionally, in order to reduce nitrogen oxides (NOx) contained in the exhaust gas of an internal combustion engine, an exhaust gas recirculation device is known that connects an exhaust pipe and an intake pipe to take a part of the exhaust gas into the intake air. Furthermore, a configuration in which a supercharged internal combustion engine is provided with a high-pressure exhaust gas recirculation device and a low-pressure exhaust gas recirculation device is also known. Specifically, the high-pressure exhaust gas recirculation device connects the exhaust pipe upstream of the turbine and the intake pipe downstream of the compressor, and recirculates the exhaust gas to the intake side. Further, the low-pressure exhaust gas recirculation device communicates the downstream side of the turbine in the exhaust pipe with the upstream side of the compressor in the intake pipe, and recirculates the exhaust gas to the intake side. Each of the high-pressure exhaust gas recirculation device and the low-pressure exhaust gas recirculation device is equipped with a valve (EGR valve) for adjusting the amount of recirculation, and each valve is controlled by an electronic control unit. (For example, see Patent Document 1)

Japanese Patent Application Publication No. 2016-196871

In the low-pressure exhaust gas recirculation device, since the exhaust gas temperature is lower than that near the high-pressure exhaust gas recirculation device, condensed water is likely to be generated. When condensed water is generated, there is a risk that the piping of the low-pressure exhaust gas recirculation device and the valve for regulating the flow rate of exhaust gas that flows back through the low-pressure exhaust gas recirculation device will corrode. Therefore, in the low-pressure exhaust gas recirculation device, the exhaust temperature and the amount of recirculation are controlled by an electronic control unit so that no condensed water is generated. In this control, a humidity sensor may be placed in the intake pipe and its output value may be used.

The electronic control unit performs various fault diagnosis. If the output value of the humidity sensor cannot be obtained due to an electrical disconnection or short circuit, the electronic control unit determines that the humidity sensor is malfunctioning. On the other hand, even when the electronic control unit obtains the output value of the humidity sensor, there has been a desire for a technique that can accurately diagnose whether there is an abnormality in the humidity sensor based on the output value.

The present invention has been made in view of the above situation, and it is an object of the present invention to provide a humidity sensor diagnostic device and a humidity sensor diagnostic method that improve diagnostic accuracy regarding the presence or absence of an abnormality in a humidity sensor.

In order to achieve the object of the present invention, the humidity sensor diagnostic device according to the present invention includes:
a high pressure exhaust recirculation passage;
a low pressure exhaust recirculation passage;
a humidity sensor that is provided in an intake pipe for introducing air into the engine and measures the humidity of the air in the intake pipe;
an electronic control unit configured to be able to control the amount of exhaust gas recirculated in each of the high-pressure exhaust recirculation passage and the low-pressure exhaust recirculation passage;
The electronic control unit includes:
a receiving unit that receives the output value of the humidity sensor;
an output value storage unit that stores the output value of the humidity sensor received by the reception unit;
a diagnostic unit that determines that the humidity sensor is normal when a difference between a maximum value and a minimum output value of the humidity sensor within a predetermined time exceeds a predetermined threshold;
It is configured to include.

Furthermore, in order to achieve the object of the present invention, the humidity sensor diagnosis method according to the present invention includes:
a high pressure exhaust recirculation passage;
a low pressure exhaust recirculation passage;
a humidity sensor that is provided in an intake pipe for introducing air into the engine and measures the humidity of the air in the intake pipe;
A method for diagnosing a humidity sensor in an engine control device, comprising: an electronic control unit configured to be able to control the amount of exhaust gas recirculated in each of the high-pressure exhaust recirculation passage and the low-pressure exhaust recirculation passage;
The electronic control unit includes:
a receiving step in which a receiving unit receives an output value of the humidity sensor;
an output value storage step in which an output value storage unit stores the output value of the humidity sensor received by the reception unit;
a diagnostic step in which the diagnostic unit determines that the humidity sensor is normal when the difference between the maximum and minimum output values of the humidity sensor within a predetermined time exceeds a predetermined threshold;
It is configured to include.

According to the present invention, in an engine control device equipped with an exhaust gas recirculation device, it is possible to improve the accuracy of diagnosis regarding the presence or absence of abnormality in a humidity sensor.

1 is a configuration diagram showing a configuration example of an engine control device according to an embodiment of the present invention. 1 is a block diagram showing the configuration of a portion of an electronic control unit that constitutes an engine control device according to a first embodiment of the present invention; FIG. It is a subroutine flowchart showing an example of the operation of the electronic control unit in the first embodiment of the present invention. FIG. 2 is a block diagram showing the configuration of a portion of the electronic control unit that constitutes the engine control device in the present invention, according to a second embodiment of the present invention. It is a subroutine flowchart which shows the operation example of the electronic control unit in the 2nd Embodiment of this invention.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings as appropriate. Note that the members, arrangement, etc. described below do not limit the present invention, and can be variously modified within the scope of the spirit of the present invention. Further, in each figure, the same reference numerals indicate the same elements, and the description thereof will be omitted as appropriate.

First, a configuration example of an engine control device 100 including an exhaust gas recirculation device (hereinafter also referred to as "EGR") according to an embodiment of the present invention will be described with reference to FIG.

The exhaust gas recirculation device according to the embodiment of the present invention has a configuration in which two exhaust gas recirculation passages, a high-pressure exhaust recirculation passage 5 and a low-pressure exhaust recirculation passage 6, are provided, and this configuration itself is conventional. It is known from In engine control device 100 according to the embodiment of the present invention, engine 1 as an internal combustion engine is, for example, a diesel engine.

An intake pipe 2 for taking in air necessary for combustion of fuel is connected to an intake manifold 4a of the engine 1, and an exhaust pipe 3 for exhausting air is connected to an exhaust manifold 4b.

A high-pressure exhaust recirculation passage 5 is provided between an appropriate portion of the intake pipe 2 near the intake manifold 4a and an appropriate portion of the exhaust pipe 3 near the exhaust manifold 4b, which communicate the two. The high-pressure exhaust recirculation passage 5 includes a high-pressure EGR valve 7 for adjusting the communication state of the high-pressure exhaust recirculation passage 5 from the intake pipe 2 side, in other words, the amount of recirculation of exhaust gas, and a high-pressure EGR valve 7 for cooling the exhaust gas passing therethrough. High-pressure EGR coolers 8 are arranged in order to perform this.

Further, the high-pressure exhaust gas recirculation passage 5 near both ends of the high-pressure EGR cooler 8 is provided with a bypass passage 9 that communicates the vicinity of both ends of the high-pressure EGR cooler 8 . A bypass valve 10 is provided on the upstream side of the bypass passage 9, that is, at the end on the exhaust manifold 4b side, so that the amount of bypass can be adjusted.

Further, a variable turbo 11 having a known configuration whose main components include a compressor 13 provided in the intake pipe 2 and a variable turbine 12 provided in the exhaust pipe 3 is provided. That is, the compressor 13 is located at an appropriate position in the intake pipe 2 upstream of the high-pressure exhaust recirculation passage 5, and the variable turbine 12 is located at an appropriate position in the exhaust pipe 3 downstream from the high-pressure exhaust recirculation passage 5. , respectively. In the variable turbo 11, the compressor 13 is rotated by the rotational force obtained by the variable turbine 12, and the compressed air can be sent to the intake manifold 4a as intake air.

Further, the intake pipe 2 is provided with a water-cooled intercooler 14 for cooling intake air at an appropriate position between the high-pressure exhaust gas recirculation passage 5 and the variable turbo 11 described above. Furthermore, an intake throttle valve 16 is provided between the water-cooled intercooler 14 and the high-pressure exhaust recirculation passage 5 for adjusting the amount of intake air.

Furthermore, low-pressure exhaust recirculation passages 6 are provided at appropriate locations in the intake pipe 2 on the upstream side of the compressor 13 and the exhaust pipe 3 on the downstream side of the variable turbine 12, which communicate the two. A low pressure EGR cooler 19 and a low pressure EGR valve 20 are provided in this low pressure exhaust recirculation passage 6 in this order from the exhaust pipe 3 side.

Further, in the exhaust pipe 3 between the low-pressure exhaust recirculation passage 6 and the variable turbine 12, a nitrogen oxide storage reduction catalyst (NOx Storage Catalyst) for purifying exhaust gas is installed downstream from the variable turbine 12 side. 17 and a diesel particulate filter 18 are provided in this order.

On the other hand, on the upstream side of the portion communicating with the low-pressure exhaust recirculation passage 6 in the intake pipe 2, from the upstream side to the downstream side, there is an air filter 21, an air mass sensor 22 for measuring the amount of intake air, and a low-pressure throttle valve. 23 are provided in order. Note that the air mass sensor 22 has a built-in temperature sensor, and can measure the intake air temperature.

Further, the engine control device 100 according to the embodiment of the present invention is provided with various sensors described below. First, a humidity sensor 31 is provided between the air filter 21 of the intake pipe 2 and the air mass sensor 22. The humidity sensor 31 detects the relative humidity of intake air taken into the intake pipe 2.

Further, an intake pressure sensor 32 and an intercooler downstream temperature sensor 33 are provided between the connection portion of the intake pipe 2 with the high-pressure exhaust gas recirculation passage 5 and the intake throttle valve 16. The intake pressure of the engine 1 can be detected by the intake pressure sensor 32, and the downstream temperature of the water-cooled intercooler 14 can be detected by the intercooler downstream temperature sensor 33.

Furthermore, in the exhaust pipe 3, between the variable turbine 12 and the nitrogen oxide storage reduction catalyst (hereinafter referred to as "NSC") 17, a first exhaust temperature sensor 34 and a first lambda sensor are installed from the upstream side. 36 are provided in order. Further, a second exhaust temperature sensor 35 is provided between the NSC 17 and the diesel particulate filter (hereinafter referred to as "DPF") 18, while a connecting portion of the exhaust pipe 3 with the low pressure exhaust recirculation passage 6 A second lambda sensor 37 is provided between the DPF 18 and the DPF 18 .

Further, an exhaust differential pressure sensor 38 is provided at the location where the DPF 18 is provided, and the pressure difference before and after the DPF 18 can be detected. Further, a low-pressure differential pressure sensor 39 is provided in the low-pressure exhaust recirculation passage 6 at the position of the low-pressure EGR valve 20, so that the pressure difference before and after the low-pressure EGR valve 20 can be detected.

The operations of the above-mentioned high pressure EGR valve 7, bypass valve 10, intake throttle valve 16, low pressure EGR valve 20, low pressure throttle valve 23, etc. are controlled by an electronic control unit 50. Furthermore, the operations of the variable turbine 12 and the like mentioned above are also controlled by the electronic control unit 50.

The electronic control unit 50 is, for example, mainly equipped with a microcomputer having a known and well-known configuration, and includes storage elements (not shown) such as RAM and ROM, as well as an input/output interface circuit (not shown). It is composed of the main components.

This electronic control unit 50 includes an air mass sensor 22, a humidity sensor 31, an intake pressure sensor 32, an intercooler downstream temperature sensor 33, a first exhaust temperature sensor 34, a first lambda sensor 36, and a second exhaust temperature sensor. 35, together with the detection signals of the second lambda sensor 37, the exhaust differential pressure sensor 38, and the low pressure differential pressure sensor 39, various signals necessary for vehicle operation control detected by sensors (not shown), such as large Barometric pressure, outside temperature, engine speed, accelerator opening, etc. are input.

The various detection signals input to the electronic control unit 50 as described above are used for controlling the operation of the engine 1, diagnosing the humidity sensor in the embodiment of the present invention, etc. to be described later.

Next, a configuration example of the electronic control unit 50 according to the first embodiment of the present invention will be described with reference to FIG. 2. FIG. 2 is a block diagram showing the configuration of a portion of the electronic control unit 50 according to this embodiment.

The electronic control unit 50 includes a diagnosis condition acquisition section 502, a diagnosis possibility determination section 504, a reception section 506, an output value storage section 508, and a diagnosis section 510.

The diagnostic condition acquisition unit 502 acquires outside air temperature and atmospheric pressure as environmental conditions, and notifies the diagnosis possibility determination unit 504. The outside air temperature and atmospheric pressure are values measured by a sensor (not shown), and can be used in an engine control process that is executed separately from the present invention. Alternatively, in carrying out the present invention, a new sensor may be provided.

The diagnosability determination unit 504 determines whether or not the humidity sensor 31 can be diagnosed based on the environmental conditions and the presence or absence of disconnection or short circuit. Specifically, the diagnosis possibility determining unit 504 determines that the environmental conditions are satisfied when the outside air temperature exceeds a predetermined reference value and the atmospheric pressure exceeds a predetermined reference value. Further, the diagnosis possibility determining unit 504 determines that no disconnection or short circuit has occurred when the electronic control unit 50 is receiving the signal from the humidity sensor 31. That is, the diagnosis possibility determination unit 504 permits diagnosis of the humidity sensor 31 when the above-mentioned environmental conditions are satisfied and no disconnection or short circuit occurs.

The reason why the diagnosis possibility determining unit 504 uses the above environmental conditions as a condition for permitting diagnosis of the humidity sensor 31 is as follows. Diagnosis of the humidity sensor 31 in the present invention utilizes the difference between the maximum value and the minimum value of the output value of the humidity sensor 31 in a predetermined period of time (details will be described later). In an environment where the outside air temperature is low or at a high altitude where the atmospheric pressure is low, the saturated water vapor pressure of the outside air decreases, so the amount of change in the relative humidity of the intake air is small, and the accuracy of diagnosis decreases. Therefore, the diagnosis availability determining unit 504 uses the above-mentioned environmental conditions as a condition for permitting the diagnosis of the humidity sensor 31.

Note that predetermined reference values for the outside air temperature and atmospheric pressure for allowing the diagnosis possibility determination unit 504 to diagnose the humidity sensor 31 are set in advance through tests, simulations, or the like.

The receiving unit 506 acquires the output value of the humidity sensor 31 when the diagnosis is permitted by the diagnosis availability determining unit 504.

The output value storage unit 508 stores the output value of the humidity sensor 31 acquired by the reception unit 506. Acquisition of the output value of the humidity sensor 31 by the receiving unit 506 is continued until a predetermined time has elapsed from the start of the acquisition. The output value storage unit 508 stores the output value of the humidity sensor 31 for a predetermined period of time, and also extracts the maximum value and minimum value from the stored output values.

Note that the above-mentioned predetermined time period during which the receiving unit 506 repeatedly acquires the output value of the humidity sensor 31 is set in advance through a test, simulation, or the like.

After the predetermined time has elapsed, the diagnostic unit 510 calculates the difference between the maximum and minimum output values of the humidity sensor 31 stored in the output value storage unit 508. Furthermore, the diagnostic unit 510 diagnoses the humidity sensor 31 by comparing the difference with a predetermined threshold. In diagnosis, a predetermined threshold value with which the difference is compared is set in advance through tests, simulations, or the like.

Next, a procedure for diagnosing the humidity sensor 31 executed by the electronic control unit 50 will be described with reference to the subroutine flowchart shown in FIG. The subroutine flowchart shown in FIG. 3 is repeatedly executed at a predetermined cycle while the engine 1 is operating.

When the diagnostic process for the humidity sensor 31 is started, first in step S102, the diagnostic condition acquisition unit 502 acquires diagnostic conditions. Specifically, as described above, the outside temperature and atmospheric pressure are acquired.

In the following step S104, the diagnosis possibility determining unit 504 determines whether the environmental conditions acquired in step S102 satisfy the conditions for diagnosing the humidity sensor 31. Specifically, the diagnosis possibility determining unit 504 determines that the conditions for diagnosing the humidity sensor 31 are satisfied when the outside air temperature exceeds a predetermined reference value and the atmospheric pressure exceeds a predetermined reference value. judge. If it is determined in step S102 that the acquired diagnostic conditions satisfy the conditions for diagnosing the humidity sensor 31 (in the case of YES), the process proceeds to step S106. On the other hand, if it is determined in step S102 that the acquired environmental conditions do not satisfy the conditions for diagnosing the humidity sensor 31, the process returns to the main routine (not shown).

In step S<b>106 , the diagnosis possibility determining unit 504 determines whether the electronic control unit 50 has received the output signal of the humidity sensor 31 . If it is determined that the electronic control unit 50 is receiving the signal from the humidity sensor 31 (in the case of YES), the process proceeds to step S108. On the other hand, if it is determined that the electronic control unit 50 has not received the signal from the humidity sensor 31 (in the case of NO), the process proceeds to step S120.

In step S108, the receiving unit 506 acquires the output value of the humidity sensor 31, and the process proceeds to step S110. In step S110, the output value storage unit 508 stores the output value of the humidity sensor 31 acquired by the reception unit 506 in step S108, and the process proceeds to step S112.

In step S112, the output value storage unit 508 determines whether a predetermined time has elapsed since acquisition of the output value of the humidity sensor 31 in step S108 started. If it is determined that the predetermined time has elapsed (in the case of YES), the process advances to step S114. On the other hand, if it is determined that the predetermined time has not elapsed (in the case of NO), the processes from step S108 to step S112 are repeated.

Furthermore, in step S110, the maximum value and minimum value are also extracted from the stored data while the processes of step S108 and step S110 are repeated for a predetermined period of time.

In step S114, the diagnostic unit 510 calculates the difference between the maximum and minimum output values of the humidity sensor 31 extracted in step S110, and the process proceeds to step S116.

In step S116, the diagnostic unit 510 compares the difference calculated in step S114 with a predetermined threshold. If the difference calculated in step S114 is larger than the predetermined threshold (in the case of YES), the process proceeds to step S118, and it is determined that the humidity sensor 31 is normal.

This is due to the following points of view. That is, the humidity of the intake air changes depending on the temperature and atmospheric pressure of the outside air, or the operating conditions of the engine control device 100. Therefore, when the difference between the maximum value and the minimum value of the output values of the humidity sensor 31 acquired over a predetermined period of time is larger than a predetermined threshold value, it is determined that the humidity sensor 31 is normal.

On the other hand, if it is determined in step S116 that the difference calculated in step S114 is equal to or less than a predetermined threshold value (in the case of NO), or in step S106, the electronic control unit 50 If it is determined that the signal from the sensor 31 has not been received (in the case of NO), the process proceeds to step S120, where it is determined that the humidity sensor 31 is abnormal, and predetermined processing such as warning the driver is performed.

Further, in step S120, instead of immediately determining that the humidity sensor 31 is abnormal, it may be determined that the humidity sensor 31 is abnormal when the flow reaches step S120 a predetermined number of times or more.

(Second embodiment)
A second embodiment of the present invention will be described below. In the second embodiment, when diagnosing the humidity sensor 31, the time from the previous stop to the current start of the engine 1 (hereinafter referred to as "engine stop time") is taken into consideration.

A second embodiment of the present invention will be described with reference to FIGS. 4 and 5. Note that descriptions of parts that overlap with those of the first embodiment will be omitted as appropriate.

FIG. 4 is a block diagram showing the configuration of a portion of the electronic control unit 50 according to the second embodiment of the present invention. The second embodiment further includes a timer section 500 and a measurement time calculation section 505 in addition to the first embodiment.

The timer unit 500 measures engine stop time, which is the time from the previous stop of the engine 1 to the current start, while the engine 1 is stopped. Furthermore, the measurement time calculation unit 505 calculates the storage time of the output value of the humidity sensor 31 to be stored in the output value storage unit 508 based on the engine stop time measured by the timer unit 500.

Next, a second embodiment of the present invention executed by the electronic control unit 50 will be described with reference to the subroutine flowchart shown in FIG. In the second embodiment, the diagnosis of the humidity sensor 31 is performed only once when the engine 1 is started.

When the diagnostic process for the humidity sensor 31 is started, first in step S102, the diagnostic condition acquisition unit 502 acquires diagnostic conditions. In the first embodiment, the diagnostic condition acquisition unit 502 acquires the outside temperature and atmospheric pressure as environmental conditions, but in the second embodiment, in addition to this, Obtain the engine stop time, which is the time from start to current start. The engine stop time is a value measured by the timer section 500.

In step S104 and step S106, the diagnosis possibility determination unit 504 performs the same processing as in the first embodiment. That is, in step S104, it is determined whether the environmental conditions satisfy the conditions for diagnosing the humidity sensor. Furthermore, in step S106, it is determined whether the electronic control unit 50 is receiving the signal from the humidity sensor 31. If YES is determined in both steps S104 and S106, the process advances to step S107.

In step S107, the measurement time calculation unit 505 calculates, as the measurement time, the time for repeating the acquisition of the output value of the humidity sensor 31 in step S108 and the storage of the output value in step S110. The measured time is used as a predetermined time in step S112. The measured time is calculated based on the engine stop time measured by the timer unit 500 using a predetermined arithmetic expression, map search, or the like.

The measurement time calculated in step S107 is set shorter as the engine stop time is longer, and becomes a constant value when the engine stop time exceeds a certain time. This is due to the following reasons.

After the engine stops, the temperature in the engine room gradually decreases. When the engine 1 is started in a state where the temperature in the engine room has decreased, the temperature in the engine room increases relatively rapidly. Therefore, the humidity of the intake air measured by the humidity sensor 31 also changes in a relatively short time. Therefore, when the engine 1 is started after a long engine stop time, the time it takes to repeat the processes of step S108 and step S110 can be shortened.

On the other hand, if engine 1 is restarted after a relatively short period of time has passed after engine 1 has stopped, the temperature change in the engine room after restart is small because the temperature drop in the engine room at the time of restart is small. . In this case, since the change in the output value of the humidity sensor 31 is also small, the time required to repeat the processes of step S108 and step S110 is longer than when the engine is started after a long engine stop time.

After a certain amount of time passes after the engine is stopped, the temperature inside the engine room becomes approximately equal to the outside temperature, so the measurement time calculated in step S107 is set to a constant value. The engine stop time at which the measured time calculated in step S107 becomes a constant value can be approximately 6 to 8 hours, although it depends on the specifications of the vehicle and engine.

If it is determined in step S112 that the predetermined time has elapsed (in the case of YES), the process proceeds to step S114. The processes from step S114 to step S120 are the same as those in the first embodiment described above, so the description here will be omitted.

In the present embodiment, it has been explained that the diagnosis of the humidity sensor 31 is performed only once when the engine 1 is started. This is because when the engine 1 is started, the temperature in the engine room is low, so changes in the output value of the humidity sensor 31 are likely to appear, and highly accurate diagnosis is possible.

However, in this embodiment as well, in step S120, it is not determined that the humidity sensor 31 is abnormal immediately, but when the flow reaches step S120 a predetermined number of times or more, it is determined that the humidity sensor 31 is abnormal. You can also do it. That is, this flow is repeated only when step S120 is reached, and when step S120 is reached a predetermined number of times or more, it is determined that the humidity sensor 31 is abnormal, and predetermined processing such as a warning to the driver is performed. You can also do that.

Furthermore, in this embodiment, it has been explained that in step S107, the measured time calculation unit 505 calculates the measured time based on the engine stop time. However, in step S107, the measured time calculation unit 505 may calculate the measured time based on the engine stop time and the previous operating time of the engine 1 using a predetermined calculation formula, map search, etc. .

When the engine 1 was operated for a short time last time, the temperature in the engine room when the engine 1 was stopped is lower than when the engine 1 was operated for a long time. In such a case, even if the engine stop time is short, the condition approaches the condition when the engine stop time is long, so it is possible to shorten the measurement time.

As described above, according to the present invention, it is possible to diagnose the humidity sensor 31 with high accuracy.

1: Engine, 2: Intake pipe, 5: High pressure exhaust recirculation passage, 6: Low pressure exhaust recirculation passage, 31: Humidity sensor, 50: Electronic control unit, 500: Timer section, 502: Diagnostic condition acquisition section, 504: Diagnosis possibility determination unit, 505: Measurement time calculation unit, 506: Receiving unit, 508: Output value storage unit, 510: Diagnosis unit

Claims (4)

a high pressure exhaust recirculation passage;
a low pressure exhaust recirculation passage;
a humidity sensor that is provided in an intake pipe for introducing air into the engine and measures the humidity of the air in the intake pipe;
an electronic control unit configured to be able to control the amount of exhaust gas recirculated in each of the high-pressure exhaust recirculation passage and the low-pressure exhaust recirculation passage;
The electronic control unit includes:
a receiving unit that receives the output value of the humidity sensor;
an output value storage unit that stores the output value of the humidity sensor received by the reception unit;
a diagnostic unit that determines that the humidity sensor is normal when a difference between a maximum value and a minimum output value of the humidity sensor within a predetermined time exceeds a predetermined threshold;
a timer unit that measures the stopping time of the engine from the previous stop to the current start ;
a measured time calculation unit that calculates the predetermined time based on the stop time measured by the timer unit;
including;
The determination by the diagnostic unit is performed at the time of starting the engine,
In the humidity sensor diagnostic device, the predetermined time is shorter as the stop time is longer, and is set to a constant value when the stop time exceeds a predetermined time. The electronic control unit includes:
a diagnostic condition acquisition unit that acquires conditions for determining whether or not the humidity sensor can be diagnosed;
a diagnosability determination unit that determines whether or not the humidity sensor can be diagnosed based on the conditions acquired by the diagnosis condition acquisition unit;
2. The humidity sensor diagnostic device according to claim 1, wherein the diagnosability determination unit determines whether or not the humidity sensor can be diagnosed based on at least outside air temperature and atmospheric pressure. 3. The humidity sensor diagnostic device according to claim 2, wherein the diagnosis possibility determining unit permits diagnosis of the humidity sensor when outside air temperature and atmospheric pressure exceed respective set thresholds. a high pressure exhaust recirculation passage;
a low pressure exhaust recirculation passage;
a humidity sensor that is provided in an intake pipe for introducing air into the engine and measures the humidity of the air in the intake pipe;
A method for diagnosing a humidity sensor in an engine control device, comprising: an electronic control unit configured to be able to control the amount of exhaust gas recirculated in each of the high-pressure exhaust recirculation passage and the low-pressure exhaust recirculation passage;
The electronic control unit includes:
a measuring step in which the timer unit measures the stopping time of the engine from the previous stop to the current start;
a measurement time calculation step in which the measurement time calculation unit calculates a predetermined time used for diagnosing the humidity sensor based on the stop time measured by the timer unit;
a receiving step in which a receiving unit receives an output value of the humidity sensor;
an output value storage step in which an output value storage unit stores the output value of the humidity sensor received by the reception unit;
a diagnostic step in which the diagnostic unit determines that the humidity sensor is normal when a difference between a maximum value and a minimum output value of the humidity sensor within the predetermined time exceeds a predetermined threshold;
including;
The diagnostic step is performed when starting the engine,
The predetermined time is shorter as the stop time is longer, and is set to a constant value when the stop time exceeds a predetermined time.

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