JP4289778B2 - Humidity sensor failure determination device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a failure determination device for a humidity sensor that detects the humidity of exhaust gas discharged from an internal combustion engine.
[0002]
[Prior art]
Generally, in an exhaust system such as a gasoline engine, a three-way catalyst is provided in the middle of an exhaust pipe in order to purify harmful substances (hydrocarbon, carbon monoxide and nitrogen compounds) in the exhaust gas. However, immediately after the cold start of the engine (for example, about 30 to 40 seconds from the start), the three-way catalyst is not activated, so that harmful substances are not sufficiently purified. It may be discharged to the outside. For this reason, in order to prevent this, some exhaust pipes are provided with an adsorbent for adsorbing hydrocarbons in addition to the three-way catalyst. Such an adsorbent is provided in the bypass exhaust passage branched from the middle of the main exhaust passage of the exhaust pipe provided with the three-way catalyst. And the switching valve provided in the branch part of the exhaust pipe switches the exhaust gas exhaust passage to the main exhaust passage and the bypass exhaust passage according to the state of the three-way catalyst. As a result, the exhaust gas immediately after the cold start of the engine is purified by adsorbing hydrocarbons on the adsorbent, and then discharged to the outside.
[0003]
The adsorbent has, for example, zeolite on its surface, and when the exhaust gas passes through the bypass passage, hydrocarbon molecules enter the pores of the zeolite, thereby adsorbing hydrocarbons. Moreover, such an adsorbent desorbs hydrocarbons once adsorbed when heated to a predetermined temperature or higher (for example, 100 to 250 ° C.) by exhaust gas. The desorbed hydrocarbon is recirculated to the engine via an EGR pipe or the like. As described above, although the adsorption and desorption of hydrocarbons are repeated in the adsorbent, hydrocarbons that could not be desorbed gradually remain in the adsorbent due to long-term use of the adsorbent, or the pores of the adsorbent May break. As a result, the adsorbent is deteriorated, that is, the adsorbable amount of hydrocarbons in the adsorbent is gradually reduced. If the engine is repeatedly started in such a state, hydrocarbons that have not been adsorbed by the adsorbent will be discharged to the outside. For this reason, to control the engine for desorbing hydrocarbons (such as increasing the temperature of the adsorbent) in order to eliminate the deterioration of the adsorbent, or to inform the driver of the deterioration of the adsorbent The applicant has already proposed a deterioration detection device for detecting the deterioration of the adsorbent in Japanese Patent Application No. 2000-66443.
[0004]
In this deterioration detection device, a humidity sensor is provided on the downstream side of the adsorbent in the bypass exhaust passage, and the humidity of the exhaust gas that has passed through the adsorbent is detected by the humidity sensor. Based on the detection result, the adsorbent is detected. Deterioration is detected. This utilizes the fact that the adsorbing capacity of hydrocarbon and moisture in the adsorbent is proportional to each other, and the humidity sensor detects the humidity of the exhaust gas that has passed through the adsorbent, thereby carbonizing the adsorbent. It is possible to detect a decrease in the adsorption capacity of hydrogen and moisture, that is, deterioration of the adsorbent.
[0005]
[Problems to be solved by the invention]
Although the deterioration detection device can properly detect the deterioration of the adsorbent, if the humidity sensor of the deterioration detection device fails, the deterioration of the adsorbent cannot be detected properly. There is a risk that the above-described engine control and notification to the driver cannot be performed properly. Therefore, there is room for improvement in the above-described deterioration detection device.
[0006]
The present invention has been made to solve the above-described problems, and a failure of a humidity sensor that detects the humidity of exhaust gas discharged from an internal combustion engine can be appropriately determined with a simple configuration. An object of the present invention is to provide a humidity sensor failure determination device.
[0007]
[Means for Solving the Problems]
In order to achieve this object, the invention according to claim 1 of the present application is a failure determination device for a humidity sensor that detects the humidity of exhaust gas discharged from the internal combustion engine 1, and is an operation that detects the operating state of the internal combustion engine. State detection means (in the embodiment (hereinafter the same in this section) ECU 25, steps 131, 133 and 134 in FIG. 7), and the internal combustion engine determines whether the humidity sensor 22 has failed according to the detection result of the operation state detection means. The failure determination execution determination means (ECU 25, steps 131, 133 and 134 in FIG. 7) for determining whether or not the operation state is capable of executing the operation, and the failure determination execution determination means can execute the failure determination of the humidity sensor. Humidity sensor failure determination means (ECU 25, FIG. 10) for determining whether or not the humidity sensor has failed based on the detection result of the humidity sensor. And step 151-157), provided with an exhaust passage of the exhaust gas, the bypass exhaust gas is disposed between the main exhaust passage 13, hydrocarbons and moisture in exhaust gas can adsorb adsorbents (HC adsorbent 16) in the middle The humidity sensor 22 is arranged on the downstream side of the adsorbent in the bypass exhaust passage, and the failure determination execution determination means is configured so that the exhaust passage is switched to the bypass exhaust passage. When the adsorbent is adsorbing hydrocarbons in the exhaust gas introduced to the bypass exhaust passage, it is determined that the failure determination of the humidity sensor can be executed .
[0008]
According to this configuration, when the failure determination execution determination unit determines that the internal combustion engine is in an operation state in which the failure determination of the humidity sensor can be executed based on the operation state of the internal combustion engine, the humidity sensor failure determination unit Based on the detection result of the humidity sensor, the presence / absence of a failure of the humidity sensor is determined. Depending on the operating state of the internal combustion engine, if the detected value of the humidity sensor is not within the predetermined range even though the detected value of the humidity sensor is within the predetermined range, the humidity sensor may fail. Therefore, it is possible to correctly determine the failure of the humidity sensor at an appropriate timing. In addition, since the humidity sensor failure determination is performed using the detection value of the humidity sensor, the failure determination apparatus can be realized with a relatively simple configuration without requiring a special apparatus.
[0010]
Further , since the humidity sensor is provided on the downstream side of the adsorbent in the bypass exhaust passage, the exhaust gas that has passed through the adsorbent being adsorbed, that is, the exhaust gas after adsorption of hydrocarbons and moisture by the adsorbent (after adsorption) The humidity of the exhaust gas) can be detected. Then, when the adsorbent is adsorbing the hydrocarbon in the exhaust gas guided to the bypass exhaust passage, it is determined that the failure determination of the humidity sensor can be executed. Since the adsorption capacity of hydrocarbons and moisture in the adsorbent is proportional to each other, the humidity of the exhaust gas after adsorption has a high correlation with the actual adsorption state of hydrocarbons in the adsorbent. Thereby, when the adsorbent is adsorbing hydrocarbons, for example, when the adsorption of hydrocarbons is nearing completion, the detected value of the humidity sensor should be within a predetermined range. Based on the detection value of the sensor, it is possible to determine the failure of the humidity sensor. As described above, by selecting when the adsorbent is adsorbing hydrocarbons as the operating state of the internal combustion engine suitable for determining the failure of the humidity sensor, it is possible to appropriately determine the failure of the humidity sensor.
[0011]
The invention according to claim 2, in the fault determination apparatus for a humidity sensor according to claim 1, by the exhaust passage is switched to the main exhaust passage is configured such hydrocarbons are desorbed from the adsorbent, from the adsorbent The desorption state detection means (ECU 25, steps 161 to 163 in FIG. 12) for detecting the desorption state of the hydrocarbon is further provided. At the end of the previous operation, it is determined whether or not the failure determination of the humidity sensor can be executed according to the desorption state detected by the desorption state detecting means.
[0012]
According to this configuration, whether or not the failure determination of the humidity sensor can be performed according to the hydrocarbon desorption state from the adsorbent detected by the desorption state detection means at the end of the previous operation of the internal combustion engine. Since the determination is made, it is possible to execute an appropriate failure determination in consideration of the adsorbent desorption state that affects the detection value of the humidity sensor. That is, for example, if the desorption of hydrocarbons in the adsorbent is not completed during the previous operation, the transition of the detection value of the humidity sensor changes, so the timing for properly performing the failure determination shifts. In such a case, erroneous determination can be avoided by performing failure determination only when hydrocarbon desorption is completed during the previous operation without performing failure determination.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an internal combustion engine to which an embodiment of the present invention is applied. As shown in the figure, an exhaust system 2 of the internal combustion engine (hereinafter referred to as “engine”) 1 exhausts exhaust gas discharged from the engine 1 to the outside (in the atmosphere) while purifying it, and a part thereof Is recirculated (EGR) to the engine 1 and has an exhaust pipe 4 connected to the engine 1 via an exhaust manifold 3.
[0014]
In the middle of the exhaust pipe 4, there are a catalyst device 6 having two three-way catalysts 5 and 5 and a hydrocarbon adsorption catalyst device 7 for adsorbing hydrocarbons as exhaust gas purification catalysts for purifying exhaust gas. Is provided. The two three-way catalysts 5 and 5 of the catalyst device 6 are arranged adjacent to each other along the exhaust pipe 4, and are activated when they become a predetermined temperature (for example, 300 ° C.) or more, thereby Harmful substances (hydrocarbon, carbon monoxide and nitrogen compounds) in the exhaust gas passing through the device 6 are purified by oxidation / reduction action.
[0015]
On the other hand, the hydrocarbon adsorption catalyst device 7 is disposed downstream of the catalyst device 6 in the exhaust pipe 4, and the engine 1 is started in a state where the three-way catalysts 5 and 5 are not activated (for example, at the time of start-up). For about 30 to 40 seconds), the hydrocarbons in the exhaust gas are adsorbed, thereby significantly reducing the hydrocarbons in the exhaust gas discharged to the outside. As shown in FIGS. 1 and 2, the hydrocarbon adsorption catalyst device 7 is connected to the downstream end of the catalyst device 6 via an exhaust passage switching device 8 and constitutes a substantially cylindrical outer shell. 11, a bypass exhaust pipe 12 disposed inside the case 11, and a columnar shape for adsorbing hydrocarbons in the exhaust gas filled in the bypass exhaust pipe 12 and flowing into the bypass exhaust pipe 12. HC adsorbent 16 (adsorbent).
[0016]
As shown in FIG. 2, the case 11 has an upstream end that is bifurcated up and down, and the upper opening 11 a communicates with the exhaust passage of the exhaust pipe 4 and the bypass exhaust pipe in the case 11. 12, the lower opening 11 b communicates with the space inside the bypass exhaust pipe 12 (bypass exhaust passage 14).
[0017]
The bypass exhaust pipe 12 has an upstream end connected to the inner surface of the lower opening 11 b of the case 11 and a downstream end connected to the inner surface of the downstream end of the case 11 in an airtight state. Further, at the position near the downstream end of the bypass exhaust pipe 12, a plurality of (for example, five) long communication holes 12a are formed at equal intervals in the circumferential direction, and these communication holes 12a are interposed through the communication holes 12a. Thus, the downstream ends of the main exhaust passage 13 and the bypass exhaust passage 14 in the case 11 communicate with each other.
[0018]
The HC adsorbent 16 is composed of a metal honeycomb core (not shown) carrying zeolite on its surface, and when the exhaust gas flowing into the bypass exhaust passage 14 passes through the inside of the HC adsorbent 16, The hydrocarbons and moisture in the exhaust gas are adsorbed on the zeolite. Zeolite has high heat resistance and adsorbs hydrocarbons at low temperatures (for example, less than 100 ° C.), and once adsorbed hydrocarbons at predetermined temperatures (for example, 100 to 250 ° C.). Is detached. The desorbed hydrocarbons are recirculated to the engine 1 via a branch pipe portion 18b described later of the exhaust passage switching device 8 and an EGR pipe 17 having both ends connected to the intake pipe 1a of the engine 1 respectively. The engine 1 burns. The zeolite is not particularly limited as long as it can adsorb hydrocarbons and moisture, but in this embodiment, USY (Y type), Ga-MFI and ferrierite are mixed. It was used.
[0019]
The exhaust passage switching device 8 connects the hydrocarbon adsorption catalyst device 7 having the above configuration to the catalyst device 6, and the exhaust passage of the exhaust gas that has passed through the catalyst device 6 depends on the active state of the three-way catalyst 5. This is for selectively switching between the main exhaust passage 13 and the bypass exhaust passage 14. The exhaust passage switching device 8 includes a substantially cylindrical connecting pipe 18 and a switching valve 15 provided in the connecting pipe 18 for switching the exhaust passage. The connecting pipe 18 branches from a main pipe part 18a that communicates the downstream end part of the catalyst device 6 and the main exhaust passage 13 of the hydrocarbon adsorption catalyst apparatus 7 in an airtight state, and an upstream part of the main pipe part 18a. The downstream end portion of the device 6 and the branch exhaust pipe portion 18b that communicates the bypass exhaust passage 14 of the hydrocarbon adsorption catalyst device 7 in an airtight state.
[0020]
On the other hand, the switching valve 15 has a disc-shaped valve body 15a and an arm 15c having a predetermined shape that supports the valve body 15a at one end. A switching valve drive device 19 (see FIG. 1) controlled by an ECU 25, which will be described later, rotates the valve body 15a with a predetermined angle around the other end so that the valve body 15a also rotates. One of the part 18a and the branch pipe part 18b is opened and the other is closed. Therefore, as shown in FIG. 2, when the valve main body 15a opens the main pipe portion 18a and closes the branch pipe portion 18b, the exhaust gas that has passed through the catalytic device 6 passes through the main pipe portion 18a. It flows to the main exhaust passage 13 in the case 11. Conversely, when the valve body 15a closes the main pipe portion 18a and opens the branch pipe portion 18b (see the two-dot chain line in FIG. 2), the exhaust gas that has passed through the catalyst device 6 passes through the branch pipe portion 18b. And flows into the bypass exhaust passage 14. Note that a torsion coil spring (not shown) is provided at the other end of the arm 15c. With this torsion coil spring, the valve body 15a normally opens the main pipe portion 18a as shown in FIG. And the branch pipe part 18b is closed.
[0021]
In the exhaust passage switching device 8 configured in this way, normally, immediately after the engine 1 is started, the valve body 15a that closes the branch pipe portion 18b is rotationally driven to open the branch pipe portion 18b and The main pipe part 18a is closed. As a result, the exhaust gas that has passed through the catalyst device 6 flows through the branch pipe portion 18 b to the bypass exhaust passage 14, where hydrocarbons and moisture are adsorbed by the HC adsorbent 16 and pass through the HC adsorbent 16. The exhaust gas thus flowed further downstream is discharged to the outside. Then, as will be described later, when it is determined that the adsorption of hydrocarbons in the HC adsorbent 16 is completed, the valve main body 15a that has closed the main pipe portion 18a is driven to rotate again, whereby the main pipe portion 18a is opened and the branch pipe part 18b is closed. Thereby, the exhaust gas that has passed through the catalyst device 6 flows through the main pipe portion 18 a to the main exhaust passage 13 in the case 11 and flows through the communication hole 12 a at the downstream end of the bypass exhaust pipe 12. , Flows into the bypass exhaust pipe 12, flows further downstream, and is discharged to the outside.
[0022]
The case 11 of the hydrocarbon adsorption catalyst device 7 is provided with a downstream humidity sensor 22A for detecting the humidity (hereinafter, simply referred to as “downstream humidity”) D downstream of the HC adsorbent 16 in the bypass exhaust passage 14. The detection signal is output to the ECU 25. The ECU 25 is also connected with an intake air temperature sensor 27 that detects the intake air temperature TA. The ECU 25 (operating state detection means, failure determination execution determination means, humidity sensor failure determination means, desorption state detection means) includes the switching valve 15 and the engine 1 and the engine 1 based on the detection results of these sensors 22A and 27. Various controls of the exhaust system 2 are performed.
[0023]
The downstream humidity sensor 22A is attached to the downstream end of the case 11 so that the sensor element 22a at the front end faces the bypass exhaust passage 14 via one of the communication holes 12a of the bypass exhaust pipe 12. As described above, the downstream humidity D is detected, and the detection signal is sent to the ECU 25. This detection signal is treated as a relative humidity detection signal in the ECU 25 when a hydrocarbon adsorption condition by the HC adsorbent 16 described later is established, while when the adsorption condition is not established, the absolute humidity is detected. Treated as a detection signal. The downstream humidity sensor 22A is provided with a heater 28 for heating the sensor element 22a. The heater 28 is controlled by the ECU 25, and operates for a predetermined time when a predetermined condition described later is satisfied, and heats the sensor element 22a of the downstream humidity sensor 22A. The details of the downstream humidity sensor 22A have been described in Japanese Patent Application No. 2000-23085 already proposed by the present applicant, and are therefore omitted here.
[0024]
In addition to the downstream humidity sensor 22A, an upstream sensor that is the same humidity sensor as the downstream humidity sensor 22A is also provided upstream of the HC adsorbent 16 as shown by a two-dot chain line in FIGS. 22B may be provided. The upstream humidity sensor 22B detects the upstream humidity (hereinafter simply referred to as “upstream humidity”) DF of the HC adsorbent 16 in the bypass exhaust passage 14. In the following description, when the downstream humidity sensor 22A and the upstream humidity sensor 22B are not particularly distinguished, these sensors are collectively referred to as “humidity sensor 22”.
[0025]
The engine 1 is provided with a crank angle sensor 32, and outputs a CRK signal and a TDC signal, which are pulse signals, to the ECU 25 for each predetermined crank angle as the crankshaft (not shown) of the engine 1 rotates. . As the TDC signal, for example, one pulse is output to the ECU 25 every time the crankshaft rotates 180 degrees.
[0026]
The ECU 25 is composed of a microcomputer including an I / O interface, CPU, RAM, ROM, and the like. The detection signals from the various sensors such as the humidity sensor 22 and the intake air temperature sensor 27 described above are each input to the CPU after A / D conversion and shaping by the I / O interface. The CPU detects the operating state of the engine 1 according to a control program stored in the ROM in accordance with detection signals from various sensors, and performs various controls according to the detected operating state. For example, when the ECU 25 determines that the humidity sensor 22 is out of order, the ECU 25 outputs a control signal to the warning lamp 26, whereby the warning lamp 26 is turned on, and the failure of the humidity sensor 22 is notified to the driver. Inform.
[0027]
Next, the control process executed by the ECU 25 will be specifically described with reference to FIGS. FIG. 3 shows an execution determination process for humidity detection. This process is started immediately when the ignition switch is turned on to start the engine 1. In this process, first, in step 101 (illustrated as “S101”, the same applies hereinafter), it is determined whether or not the heater 28 for heating the humidity sensor 22 is operating. When the determination result is Yes, that is, when the heater 28 is operating, this program is ended as it is. On the other hand, when the determination result in step 101 is No, that is, when the heater 28 is not operating, the process proceeds to the subsequent step 102 to determine whether or not the engine 1 is before starting, specifically, whether or not cranking is started. . When the determination result is Yes, that is, when the engine 1 is not started, the process proceeds to the subsequent step 103, and whether or not the intake air temperature TA detected by the intake air temperature sensor 27 is lower than a predetermined determination value TA_HT_JDG (for example, 50 ° C.). Is determined.
[0028]
When the determination result in step 103 is Yes, that is, when the intake air temperature TA is smaller than the determination value TA_HT_JDG, the heater 28 is operated for a predetermined time (for example, 10 seconds) (step 104), and this program is terminated. The heater 28 is controlled for the following reason. That is, when the ambient temperature is low when the engine 1 is started, condensation is likely to occur in the sensor element 22a of the humidity sensor 22, and if the humidity detection is performed in this state, the actual value cannot be detected accurately. This is because water droplets due to condensation are removed from the sensor element 22a by actuating. On the other hand, when the determination result in step 103 is No, that is, when the intake air temperature TA is equal to or higher than the determination value TA_HT_JDG, it is determined that there is no possibility of condensation on the sensor element 22a, and a humidity detection process in step 106 described later is executed. Exit the program.
[0029]
On the other hand, when the determination result in step 102 is No, that is, after the engine 1 is started, the process proceeds to the subsequent step 105, where it is determined whether or not the idling of the engine 1 has continued for a predetermined time (for example, 10 seconds). When idling continues for a predetermined time or longer, condensation may occur on the sensor element 22a of the humidity sensor 22. Therefore, when the determination result in step 105 is Yes, water droplets should be removed from the sensor element 22a as described above. Then, the heater 28 is operated for a predetermined time (step 104), and this program is terminated. When the determination result in Step 105 is No, that is, when the idling is continued for less than the predetermined time, the process proceeds to Step 106.
[0030]
FIG. 4 shows a humidity detection process based on the detection result of the humidity sensor 22 executed in step 106. In this process, first, in step 111, the detection value D detected by the downstream humidity sensor 22A is set as the current value Hum_R (n) of the downstream humidity.
[0031]
Next, at step 112, it is determined whether or not the engine 1 is before starting. When the determination result is Yes, that is, when the engine 1 is not started, in the subsequent step 113, the current upstream value Hum_F_hat (n) of the upstream estimated humidity is set to the downstream humidity Hum_R (n) set in step 111. Since the exhaust gas from the engine 1 has not yet flowed into the bypass exhaust passage 14 before the engine 1 is started, the downstream humidity Hum_R (n) is set as the upstream estimated humidity Hum_F_hat (n). In step 113, the previous value Hum_F_hat (n-1) of the upstream estimated humidity is set to the current value Hum_F_hat (n).
[0032]
Thereafter, in step 114, it is determined whether or not the upstream humidity sensor 22B is provided. As shown by a two-dot chain line in FIGS. 1 and 2, when the upstream humidity sensor 22 </ b> B is provided on the upstream side of the HC adsorbent 16, the detected value DF detected thereby is used as the upstream humidity. The current value Hum_F (n) is set (step 115), and the program is terminated. On the other hand, if the upstream side humidity sensor 22B is not provided (step 114: No), the process proceeds to step 117, and the upstream side estimated humidity Hum_F_hat (n) set in step 113 or calculated in step 116 described later. Is set as the upstream humidity Hum_F (n), and this program ends.
[0033]
When the determination result in Step 112 is No, that is, after the engine 1 is started, the process proceeds to Step 116, where the maximum humidity Hum_MAX that is the maximum value of the relative humidity and the previous value Hum_F_hat (n−1) of the upstream side estimated humidity are used, The current value Hum_F_hat (n) of the estimated upstream humidity is calculated from the following equation (1) (step 116).
Hum_F_hat (n) = ALF × Hum_MAX + (1−ALF) × Hum_F_hat (n−1) (1)
ALF in the equation (1) is a weighting coefficient obtained by experiment and takes a value in the range of 0 <ALF <1.0. In step 116, along with the above calculation, the previous upstream value Hum_F_hat (n-1) of the upstream side estimated humidity is set to the upstream side estimated humidity Hum_F_hat (n) at the time of the current main processing, and the process proceeds to step 114. .
[0034]
As described above, in the humidity detection process, when there is the upstream humidity sensor 22B, the detection value DF of the upstream humidity sensor 22B is used as the current value Hum_F (n) of the upstream humidity. If there is no upstream humidity sensor 22B, the upstream estimated humidity Hum_F_hat (n) estimated in step 113 or 116 is used based on the detection value D of the downstream humidity sensor 22A.
[0035]
Further, when both the humidity sensors 22A and 22B have low responsiveness, a response delay occurs in the detection values D and DF. In order to compensate for this, the response of the humidity sensor 22 shown in FIG. Delay compensation processing is executed. As shown in the figure, in this compensation processing, the upstream side humidity Hum_F (n) is obtained from the following equations (2) and (3) using the current detection values D and DF and the previous detection values D_old and DF_old. Then, the downstream humidity Hum_R (n) is calculated (step 121).
Hum_F (n) = 1 / ALF1 (DF− (1−ALF1) × DF_old) (2)
Hum_R (n) = 1 / ALF2 (D− (1−ALF2) × D_old) (3)
Here, ALF1 and ALF2 are obtained by experiments for each specification of the humidity sensor 22, and are correction coefficients for compensating for response delay, and are in the range of 0 <ALF1 <1.0 and 0 <ALF2 <1.0. Takes a value. For example, the above equation (2) is
Hum_F (n) = 1 / ALF1 (DF−DF_old) + DF_old
As the correction coefficients ALF1 and ALF2 increase, the degree of compensation decreases, and as their values approach 1, the upstream humidity Hum_F (n) and the downstream humidity Hum_R (n) Each approaches the current values DF and D as much as possible. On the other hand, the smaller the correction coefficients ALF1, ALF2, the greater the degree of compensation.
[0036]
Next, in step 122, the current values DF and D are set as the previous values DF_old and D_old, respectively, so as to be used as the previous values in the next compensation process, and the program ends. When both of the humidity sensors 22A and 22B have high responsiveness, the detected values D and DF are directly used as the downstream humidity Hum_R (n) and the upstream humidity Hum_F (n), respectively. Used, and the compensation process is not executed.
[0037]
6A, 6B, and 6C show the actual humidity (true value) obtained for the upstream humidity of the HC adsorbent 16, the detected value DF of the upstream humidity sensor 22B, and the detected value DF, respectively. Is shown an example of each transition of the upstream humidity Hum_F (n) after the compensation process. As shown in FIG. 5A, for example, when the engine 1 is started, the humidity of the exhaust gas rises immediately after the start and then changes to a substantially constant value. When the humidity is detected by the sensor, the detection value DF changes in a state delayed from the true value as shown in FIG. On the other hand, since the upstream humidity Hum_F (n) is calculated by the above-described equation (2), a humidity that changes at substantially the same timing as the true value is obtained, whereby the response of the upstream humidity sensor 22B. Delay can be compensated.
[0038]
If there is no upstream humidity sensor 22B, for example, the compensated downstream humidity Hum_R (n) calculated in step 121 in FIG. 5 is used in steps 113 and 116 in FIG. The compensated appropriate upstream humidity Hum_F (n) can be obtained.
[0039]
FIG. 7 shows a main flow of a series of execution procedures of the hydrocarbon adsorption state and desorption state estimation process in the HC adsorbent 16 and the humidity sensor 22 failure determination process. This process is executed in synchronization with the TDC signal from the crank angle sensor 32 being input to the ECU 25, for example. In this process, first, it is determined whether or not the hydrocarbon adsorption condition by the HC adsorbent 16 is satisfied (step 131). Specifically, as shown by a two-dot chain line in FIG. 2, the valve body 15a of the switching valve 15 is in a state where the main exhaust passage 13 is closed and the bypass exhaust passage 14 is opened, that is, exhaust from the engine 1. It is determined whether or not the gas is guided to the bypass exhaust passage 14.
[0040]
When the determination result of step 131 is Yes, that is, when the above-described adsorption condition is satisfied, the process proceeds to step 132, and the HC adsorption state estimation process is executed. FIG. 8 shows a subroutine of the process for estimating the HC adsorption state. By this process, the hydrocarbon adsorption state in the HC adsorbent 16 is estimated. In this process, first, using the upstream humidity Hum_F (n) and the downstream humidity Hum_R (n) calculated in the humidity detection process of FIG. 4, the difference accumulated value deltasum of both humidity is calculated from the following equation (4) (step). 141).
deltsum = deltsum + Hum_F (n) −Hum_R (n) (4)
When the engine 1 is started, the upstream humidity and the downstream humidity usually change as shown in FIG. That is, the upstream humidity rises before the downstream humidity (time tF), and gradually increases in value as time elapses, and changes so as to converge to a constant value. On the other hand, the downstream humidity rises later (time tR) after the upstream humidity has increased to some extent, and thereafter the value increases so that the hydrocarbon adsorption on the HC adsorbent 16 is completed. (Time tS), it converges to almost the same value as the upstream humidity. Therefore, by repeatedly executing this processing, the difference accumulated value deltasum, that is, the area of the hatched portion shown in FIG. 9, is calculated by the above equation (4), and this is the amount of moisture adsorbed on the HC adsorbent 16. Equivalent to. The moisture adsorption amount is proportional to the hydrocarbon adsorption amount adsorbed on the HC adsorbent 16, and has a high correlation with this.
[0041]
Next, the routine proceeds to step 142, where it is determined whether or not the absolute value of the difference between the upstream humidity Hum_F (n) and the downstream humidity Hum_R (n) is smaller than a predetermined determination value D_H_JDG (for example, 10%). . When the determination result is No, it is determined that the hydrocarbon adsorption in the HC adsorbent 16 is not completed because the deviation between the upstream humidity Hum_F (n) and the downstream humidity Hum_R (n) is large (step 145). ), This program ends. On the other hand, when the determination result in step 142 is Yes, that is, when the deviation between the upstream humidity Hum_F (n) and the downstream humidity Hum_R (n) is small, the process proceeds to step 143.
[0042]
In step 143, it is determined whether or not the difference accumulated value deltasum calculated in step 141 is larger than a predetermined determination value TRAP_JDG (for example, 2000%). When the determination result is No, it is determined that the difference accumulated value deltasum is small and the hydrocarbon adsorption on the HC adsorbent 16 is not completed (step 145), and this program is terminated. On the other hand, when the determination result of step 143 is Yes, that is, when the difference accumulated value deltasum exceeds the determination value TRAP_JDG, it is determined that the hydrocarbon adsorption in the HC adsorbent 16 is completed (step 144), and this program is terminated. .
[0043]
As described above, in this estimation process, when the deviation between the upstream humidity Hum_F (n) and the downstream humidity Hum_R (n) is smaller than the determination value D_H_JDG and the difference accumulated value deltasum is larger than the determination value TRAP_JDG. Then, it is determined that the hydrocarbon adsorption in the HC adsorbent 16 is completed. As described above, when the engine 1 is started, the deviation gradually decreases as the adsorption of hydrocarbons in the HC adsorbent 16 is completed, and the accumulated difference value deltasum is equal to the hydrocarbon in the HC adsorbent 16. It has a high correlation with the amount of adsorption. Therefore, the hydrocarbon adsorption state in the HC adsorbent 16, that is, the carbonization in the HC adsorbent 16, based on the detection result of the downstream humidity sensor 22A or the upstream humidity sensor 22B in addition to the above processing. Completion of hydrogen adsorption can be appropriately determined.
[0044]
Returning to FIG. 7, in step 133 following the HC adsorption state estimation process in step 132 described above, it is determined whether or not a predetermined time (for example, 10 seconds) has elapsed after the engine 1 is started, and the previous engine is determined. During the operation of 1 (at the end of the operation), it is determined whether or not the later-described desorption of hydrocarbons in the HC adsorbent 16 has been completed (step 134). If any of these determination results is No, it is determined that the condition for executing the failure determination process of the humidity sensor 22 is not satisfied, and this program is terminated. On the other hand, when the determination results of step 133 and step 134 are both Yes, the failure determination process is performed assuming that the condition for executing the failure determination process of the humidity sensor 22 is satisfied (step 135).
[0045]
As described above, the determination of steps 133 and 134 in order to execute the failure determination process of the humidity sensor 22 is performed for the following reason. That is, first, in step 133, the condition that a predetermined time has elapsed after the engine 1 is started is that a certain amount of time has passed since the engine 1 was started, so that the hydrocarbons in the HC adsorbent 16 are reduced. Since the suction is completed, the detected value of the humidity sensor 22 is stabilized to a substantially constant value (see FIGS. 9 and 11B). Therefore, when the detected value is stable, the failure determination of the humidity sensor 22 is performed. This is because appropriate determination can be performed. On the other hand, in step 134, the condition for completion of hydrocarbon desorption during the previous operation is that the humidity sensor 22 detects that the hydrocarbon desorption from the HC adsorbent 16 has not been completed during the previous operation. As the transition of the value changes, the timing for properly performing the failure determination shifts. In such a case, the failure determination is not performed and the hydrocarbon desorption is completed during the previous operation. This is to avoid erroneous determination by performing failure determination only at times.
[0046]
FIG. 10 shows a subroutine of the failure determination process executed in step 135, and with this process, it is determined whether or not there is a failure in the downstream humidity sensor 22A. In this process, first, in step 151, it is determined whether or not the failure determination completion flag is set to “1”. This failure determination completion flag is reset to “0” when the ignition switch is turned on, and is set to “1” in step 156 to be described later when the failure determination of the downstream humidity sensor 22A is completed. . When the determination result of step 151 is Yes, that is, when the failure determination completion flag is set to “1”, this program is ended as it is. Thus, when the failure determination of the downstream humidity sensor 22A has already been completed, the failure determination is not performed thereafter, that is, this failure determination is executed only once when the engine 1 is started.
[0047]
If the determination result in step 151 is No, that is, if the failure determination of the downstream humidity sensor 22A is not completed in this process, the integrated value sgm_tout is expressed by the following formula (5) using the fuel injection time tout of all cylinders of the engine 1. 5) (step 152).
sgm_tout = sgm_tout + tout (5)
This equation (5) is for estimating the total amount of heat given from the engine 1 to the exhaust system 2 from the start.
[0048]
Next, it is determined whether or not the calculated integrated value sgm_tout is larger than the predetermined determination value SGM_JDGR (step 153). When this determination result is No, it is determined that the temperature of the sensor element 22a of the downstream humidity sensor 22A is not sufficiently increased because the total heat amount is small, and the failure determination of the downstream humidity sensor 22A is not performed, and this Exit the program.
[0049]
On the other hand, when the determination result in step 153 is Yes, it is determined that the temperature of the sensor element 22a has sufficiently increased, and the process proceeds to step 154, where the downstream humidity Hum_R (n) is smaller than the determination value H_R_JDG (for example, 90%). Determine whether or not. As shown in FIG. 11A, the integrated value sgm_tout increases as time elapses from the start of the engine 1, and when the determination value SGM_JDGR is exceeded (time tK), the temperature of the sensor element 22a is sufficient. The downstream humidity Hum_R (n) has a substantially constant value because the adsorption of hydrocarbons in the HC adsorbent 16 is completed or close to completion. The determination value H_R_JDG is set as a predetermined value slightly lower than this fixed value. Therefore, when the determination result in step 154 is No, that is, when the downstream humidity Hum_R (n) is equal to or higher than the determination value H_R_JDG, it is determined that the downstream humidity sensor 22A is normal, while the determination result is Yes, that is, the downstream humidity. When Hum_R (n) is smaller than the determination value H_R_JDG, it is determined that the downstream humidity sensor 22A has failed. Then, the failure determination completion flag is set to “1” (step 156), and this program is terminated.
[0050]
Through the above processing, failure determination of the downstream humidity sensor 22A can be appropriately performed based on the detection result. When the upstream humidity sensor 22B is present, the failure determination process is performed in the same manner as the failure determination of the downstream humidity sensor 22A, only by changing the magnitudes of the two determination values (SGM_JDGR, H_R_JDG). be able to.
[0051]
Returning to FIG. 7, when the determination result of step 131 is No, that is, when the adsorption condition is not satisfied, the routine proceeds to step 136, where it is determined whether or not the hydrocarbon desorption condition by the HC adsorbent 16 is satisfied. Specifically, it is determined whether or not EGR is being executed. When the determination result in step 136 is Yes, that is, when the desorption condition is satisfied, the process proceeds to step 137, and the HC desorption state estimation process is executed. FIG. 12 shows a subroutine of the process for estimating the HC desorption state. By this process, the desorption state of hydrocarbons from the HC adsorbent 16 is estimated. In this process, in step 161, it is determined whether or not the downstream humidity Hum_R (n) is smaller than a predetermined determination value REL_JDG (for example, 15%).
[0052]
As shown in FIG. 11 (b), when desorption of hydrocarbons from the HC adsorbent 16 is started, initially, moisture is desorbed from the HC adsorbent 16 together with hydrocarbons, thereby reducing the downstream humidity. Hum_R (n) is maintained at a substantially constant value, and thereafter, the amount of moisture remaining in the HC adsorbent 16 decreases, and the amount of desorption decreases, thereby reducing the downstream humidity Hum_R (n). To do. Therefore, when the determination result of step 161 is Yes, that is, when the downstream humidity Hum_R (n) is smaller than the determination value REL_JDG, the downstream humidity Hum_R (n) is small, and the desorption of hydrocarbons from the HC adsorbent 16 is completed. It is determined that the program has been completed (step 162), and the program is terminated. On the other hand, when the determination result in step 161 is No, that is, when the downstream humidity Hum_R (n) is equal to or higher than the determination value REL_JDG, it is determined that the desorption of hydrocarbons is not completed (step 163), and this program ends. To do.
[0053]
Through the above estimation process, completion of hydrocarbon desorption from the HC adsorbent 16 can be appropriately determined based on the detection result of the downstream humidity sensor 22A.
[0054]
FIG. 13 shows a flow chart of the switching valve control process. By this process, the exhaust passage is selectively switched between the main exhaust passage 13 and the bypass exhaust passage 14. In this process, in step 171, it is determined whether or not the hydrocarbon adsorption on the HC adsorbent 16 is completed. This determination is made based on whether or not step 144 in FIG. 8 is executed. When the determination result in step 171 is No, the hydrocarbon adsorption in the HC adsorbent 16 is not completed and is in the middle of adsorption, so the switching valve 15 is maintained as it is. That is, the valve main body 15a of the switching valve 15 holds the main exhaust passage 13 closed and the bypass exhaust passage opened (step 173).
[0055]
On the other hand, when the determination result in step 171 is Yes, hydrocarbon adsorption in the HC adsorbent 16 is completed, so the main exhaust passage 13 is opened and the bypass exhaust passage is opened by the valve body 15a of the switching valve 15. Close (step 172). After that, EGR is performed through the EGR pipe 17 so that hydrocarbons are desorbed from the HC adsorbent 16.
[0056]
With the above processing, the switching valve 15 can be switched at an appropriate timing based on the detection result of the downstream humidity sensor 22A.
[0057]
As described above in detail, according to the present embodiment, based on the downstream humidity Hum_R (n) having a high correlation with the actual adsorption state of hydrocarbons in the HC adsorbent 16, the HC adsorbent 16 The adsorption state and desorption state of hydrocarbons can be estimated appropriately. Then, according to the adsorption state and desorption state of hydrocarbons in the HC adsorbent 16, the failure determination of the humidity sensor 22 can be performed correctly at an appropriate timing based on the detection result. Moreover, since the failure determination of the humidity sensor 22 is performed using the detection value of the humidity sensor 22, a failure determination device for the humidity sensor can be realized with a relatively simple configuration without requiring a special device. Can do.
[0058]
In addition, this invention can be implemented in various aspects, without being limited to the said embodiment described. For example, in the embodiment, as the exhaust gas purification catalyst, the catalyst device 6 having the three-way catalyst 5 and the hydrocarbon adsorption catalyst device 7 having the HC adsorbent 16 are provided in the exhaust pipe 4 separately from each other. The present invention is also applicable to a so-called hybrid type exhaust gas purification catalyst in which these are configured as a single device. It is also possible to integrate the humidity sensor 22 using the same housing as the air-fuel ratio sensor.
[0059]
【The invention's effect】
As described above in detail, the failure determination device for a humidity sensor according to the present invention can appropriately determine a failure of a humidity sensor that detects the humidity of exhaust gas discharged from an internal combustion engine with a simple configuration. Has an effect.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an internal combustion engine to which an embodiment of the present invention is applied.
FIG. 2 is an enlarged cross-sectional view of a hydrocarbon adsorption catalyst device.
FIG. 3 is a flowchart showing an execution determination process for humidity detection.
FIG. 4 is a flowchart showing a humidity detection process.
FIG. 5 is a flowchart showing a response delay compensation process of a humidity sensor.
FIG. 6 is an image diagram for explaining response delay compensation processing of a humidity sensor, where (a) shows actual humidity (true value), (b) shows detected value of the humidity sensor, and (c) shows detected value. An example of transition of upstream humidity after compensation processing is shown.
FIG. 7 is a flowchart showing an execution procedure of a process for estimating a hydrocarbon adsorption state and a desorption state in an HC adsorbent and a humidity sensor failure determination process.
FIG. 8 is a flowchart showing an HC adsorption state estimation process.
FIG. 9 is a time chart showing an example of changes in upstream humidity and downstream humidity from the start of the engine.
FIG. 10 is a flowchart showing a humidity sensor failure determination process.
FIGS. 11A and 11B are diagrams showing an example of transition of various data from the start of the engine, where FIG. 11A shows a fuel injection time integrated value, FIG. 11B shows downstream humidity, and FIG. 11C shows sensor element temperature.
FIG. 12 is a flowchart showing an HC desorption state estimation process.
FIG. 13 is a flowchart showing control processing of a switching valve.
[Explanation of symbols]
1 Internal combustion engine 4 Exhaust pipe 13 Main exhaust passage 14 Bypass exhaust passage 15 Switching valve 15a Valve body 16 HC adsorbent (adsorbent)
22 Humidity sensor 22A Downstream humidity sensor 22B Upstream humidity sensor 25 ECU (Operating state detection means, failure determination execution determination means, humidity sensor failure determination means, desorption state detection means)
D Detected value of downstream humidity DF Detected value of upstream humidity Hum_R (n) Downstream humidity Hum_F (n) Upstream humidity

Claims (2)

A failure determination device for a humidity sensor that detects the humidity of exhaust gas discharged from an internal combustion engine,
An operating state detecting means for detecting an operating state of the internal combustion engine;
A failure determination execution determination unit that determines whether or not the internal combustion engine is in an operation state capable of executing a failure determination of the humidity sensor according to a detection result of the operation state detection unit;
When the failure determination execution determination unit determines that the failure determination of the humidity sensor can be executed, the humidity sensor failure determination determines whether the humidity sensor has failed based on the detection result of the humidity sensor. Means,
Equipped with a,
The exhaust gas exhaust passage is configured to be switched to a main exhaust passage and a bypass exhaust passage in which an adsorbent capable of adsorbing hydrocarbons and moisture in the exhaust gas is disposed in the middle.
The humidity sensor is disposed on the downstream side of the adsorbent in the bypass exhaust passage,
The failure determination execution determination means is configured to switch the exhaust passage to the bypass exhaust passage so that the adsorbent is adsorbing hydrocarbons in the exhaust gas guided to the bypass exhaust passage. A humidity sensor failure determination apparatus that determines that a failure determination of a humidity sensor is feasible . The exhaust passage is configured to be desorbed from the adsorbent by switching to the main exhaust passage,
A desorption state detection means for detecting the desorption state of the hydrocarbon from the adsorbent, further comprising:
The failure determination execution determination means is configured to detect the hydrocarbon sensor from the adsorbent at the end of the previous operation of the internal combustion engine according to the desorption state detected by the desorption state detection means. The humidity sensor failure determination apparatus according to claim 1, wherein it is determined whether failure determination is feasible .

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