JP4304826B2 - Abnormality diagnosis device for fuel vapor purge system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an abnormality diagnosis device for a fuel vapor purge system. In particular, the present invention relates to an abnormality diagnosing device for diagnosing whether or not there is an abnormality in a component (particularly, a control valve of other type) of a fuel vapor purge system.
[0002]
[Prior art]
In general, a so-called fuel vapor purge system is employed in a vehicle having a tank of volatile liquid fuel. According to a typical charcoal canister type purge system, the fuel vapor generated in the fuel tank is once collected in the canister, and the collected fuel vapor is appropriately purged (released) into the intake passage of the engine. In order to ensure the reliability of the fuel vapor purge system, the system often incorporates an abnormality diagnosis device for detecting leaks due to holes or lacerations. This abnormality diagnosis device includes, for example, a pressure sensor for detecting an internal pressure of a fuel tank and a region communicating with the fuel tank, and a control valve for opening and closing a negative pressure introduction passage (bypass passage) that connects the fuel tank and the canister. . Further, such an abnormality diagnosis device incorporates a diagnosis program for detecting an abnormality (operation failure) of each device component such as the pressure sensor and the control valve, thereby further ensuring the reliability of the purge system. ing.
[0003]
One of the applicants of the present patent application requires that strict preconditions be established in the prior application (Japanese Patent Application No. 2000-59314) for the diagnosis of the abnormality of the control valve provided in the negative pressure introduction passage (bypass passage). We have proposed a new valve abnormality diagnosis device that can be performed relatively frequently. The new diagnostic method is that statistically the follow-up of the internal pressure of the fuel tank to a sufficient change in the internal pressure of the canister in a situation where a suction negative pressure is applied to the purge system and a valve closing command is issued to the control valve. In the case where the control valve interposed in the negative pressure introduction passage (bypass passage) connecting the fuel tank and the canister is stuck in an open state (open sticking) is determined. is there.
[0004]
[Problems to be solved by the invention]
This case relates to several improvements for further enhancing the degree of completion of an abnormality diagnosis apparatus that employs the new diagnostic method. Specifically, the improvement from the following viewpoints was tried.
[0005]
(1) In the abnormality diagnosis device, the canister is not provided with a pressure sensor for directly measuring the internal pressure, and as an alternative measure, the canister internal pressure is determined based on other available information (purge flow rate, etc.). Estimated. At that time, the estimated value of the canister internal pressure (simulated canister internal pressure) is calculated with reference to the characteristic map regarding the correlation between the purge flow rate and the internal pressure estimated value prepared in advance through experiments, etc. Only the disclosure up to that point). In subsequent studies, various studies were made on the factors that reduce the accuracy of calculation of the simulated canister internal pressure. As a result, when calculating the simulated canister internal pressure based on the purge flow rate, a correction calculation method has been devised so that the simulated canister internal pressure can truly reflect the actual canister internal pressure.
[0006]
(2) In connection with the above-described calculation of the simulated canister internal pressure, the preferred mode of the characteristic map relating to the correlation between the purge flow rate and the internal pressure estimated value was also investigated.
(3) In the new diagnostic method, the number of changes in the simulated canister internal pressure as a premise for statistically grasping the degree of significant follow-up (correlation rate) of the fuel tank internal pressure to the sufficient change in the simulated canister internal pressure. A counter is assigned to each of the number of significant changes in the internal pressure of the fuel tank. At this time, when there is no change or very small change in the internal pressure of the fuel tank, an algorithm is employed that decrements (subtracts) the value of the counter for counting the number of changes in the internal pressure of the fuel tank. However, in the subsequent examination, because there are not enough examination items (or pre-judgment items) for decrementing the counter value, the final judgment is made even if the valve abnormality cannot be detected or the abnormality can be detected. It has been found that there is a possibility that a considerable amount of time will occur. In this case, the cause was investigated, and improvements were made to the diagnostic method to prevent the occurrence of such inconvenient situations. In other words, it fixes a bug in the diagnostic program.
[0007]
An object of the present invention is to provide an abnormality diagnosis device for a fuel vapor purge system, which is further improved from the above viewpoint and further improved in completeness.
[0008]
[Means for Solving the Problems]
The invention of claim 1 includes a fuel tank, a canister, a passage for introducing air into the canister, a purge passage for purging fuel vapor from the canister to an engine intake passage, a bypass passage for connecting the canister and the fuel tank, and a bypass passage therefor An abnormality diagnosis apparatus incorporated in a fuel vapor purge system provided with a bypass control valve provided in a tank, wherein a tank internal pressure detecting means for detecting an internal pressure of the fuel tank, and a fuel remaining amount in the fuel tank Fuel remaining amount grasping means for grasping, purge flow amount grasping means for grasping the purge flow rate of fuel vapor from the canister to the engine intake passage, fuel tank internal pressure detected by the tank internal pressure detecting means, and canister internal pressure Based on the above, it is diagnosed whether there is an abnormality in the components of the fuel vapor purge system Disconnection control means, and the diagnosis control means variably sets a correction coefficient according to the fuel remaining amount grasped by the fuel remaining amount grasping means, and the purge flow amount grasped by the correction coefficient and the purge flow amount grasping means. The gist of the abnormality diagnosis device for the fuel vapor purge system is to calculate a simulated canister internal pressure as the canister internal pressure based on the above.
[0009]
According to the present invention, based on the mutual relationship between the fuel tank internal pressure and the canister internal pressure, it is diagnosed whether or not there is an abnormality in a component (for example, a bypass control valve) of the fuel vapor purge system. At this time, the fuel tank internal pressure is detected by the tank internal pressure detecting means, and the simulated canister internal pressure calculated by the diagnostic control means is used as the canister internal pressure. That is, the simulated canister internal pressure is an estimated value of the canister internal pressure calculated based on the purge flow rate of fuel vapor from the canister to the engine intake passage and the correction coefficient. This case is based on the knowledge that the deviation between the simulated canister internal pressure and the true canister internal pressure can be minimized by variably setting the correction coefficient according to the fuel remaining amount in the fuel tank. Will be described in the embodiment). Therefore, if the simulated canister internal pressure as in the present case is used as the estimated value of the canister internal pressure, the reliability of the abnormality diagnosis by the diagnostic control means is improved.
[0010]
According to a second aspect of the present invention, in the abnormality diagnosis device for a fuel vapor purge system according to the first aspect, the diagnostic control means holds a map relating to a correlation between the purge flow rate and the temporary canister internal pressure as internal data, The temporary canister internal pressure is calculated from the purge flow rate grasped by the purge flow rate grasping means by referring to the map, and the simulated canister internal pressure is calculated by multiplying the calculated temporary canister internal pressure by the correction coefficient. And
[0011]
This limits the method for calculating the simulated canister internal pressure to the best embodiment. The technical significance thereof will become clear in the description of the embodiments of the invention described later.
According to a third aspect of the present invention, in the abnormality diagnostic device for a fuel vapor purge system according to the first or second aspect, the diagnostic control means applies a negative suction pressure to the entire purge system including a canister and applies to the bypass control valve. On the other hand, when a significant follow-up of the fuel tank internal pressure is statistically recognized with respect to the change in the simulated canister internal pressure in a situation where the valve closing command is issued, an abnormality occurs in which the bypass control valve is stuck in the open state. It is determined that it is present.
[0012]
This clarifies the principle of abnormality diagnosis when the bypass control valve is an element to be diagnosed. If the bypass control valve is normal under conditions where a suction negative pressure is applied to the entire purge system including the canister and a valve closing command is issued to the bypass control valve, the bypass control valve is closed and there is no communication between the fuel tank and the canister. Even if the canister internal pressure changes, the fuel tank internal pressure does not follow it. On the other hand, if there is a significant follow-up of the fuel tank internal pressure to the change in the canister internal pressure under the same circumstances, and this is also statistically recognized, the communication between the fuel tank and the canister exists. That is, it can be recognized that the bypass control valve is stuck in the open state.
[0013]
A fuel tank, a canister, a passage for introducing air into the canister, a purge passage for purging fuel vapor from the canister to an engine intake passage, a bypass passage for connecting the canister and the fuel tank, and a bypass passage therefor An abnormality diagnosis apparatus incorporated in a fuel vapor purge system provided with a bypass control valve provided in a tank, wherein tank internal pressure detection means for detecting the internal pressure of the fuel tank, and fuel from the canister to the engine intake passage Based on the purge flow rate grasping means for grasping the steam purge flow rate, the fuel tank internal pressure detected by the tank internal pressure detection means, and the canister internal pressure, it is determined whether or not there is an abnormality in the components of the fuel vapor purge system. A diagnostic control means for diagnosing the temporary control canister internal pressure. A map or formula that associates both of them so as to be a quadratic function of the flow rate is stored as internal data, and the internal pressure of the temporary canister is calculated from the purge flow rate grasped by the purge flow rate grasping means using the map or formula. The gist of the abnormality diagnosis device for a fuel vapor purge system is to calculate a simulated canister internal pressure as the canister internal pressure based on the calculated temporary canister internal pressure and the correction coefficient.
[0014]
According to this configuration, the temporary canister internal pressure is calculated from the purge flow rate by using a map or expression held as internal data by the diagnosis control means, and the simulated canister internal pressure is obtained by adding a correction coefficient thereto. be able to. In that case, in the said map or expression, both are related so that the temporary canister internal pressure becomes a quadratic function of the purge flow rate, and this correlation is in accordance with the relationship between the pressure and the flow velocity in hydrodynamics. Therefore, the range in which the correlation between the temporary canister internal pressure and the purge flow rate is reasonable is wide, and the simulated canister internal pressure obtained from the temporary canister internal pressure calculated from the map or the formula does not greatly deviate from the true canister internal pressure. . Therefore, if the simulated canister internal pressure obtained in this way is employed, the reliability of the abnormality diagnosis by the diagnostic control means is improved.
[0015]
According to a fifth aspect of the present invention, in the abnormality diagnosis device for a fuel vapor purge system according to the fourth aspect, the map or expression held as the internal data by the diagnosis control means is the purge when the bypass control valve is opened. It is created based on data obtained by actually measuring the relationship between the purge flow rate at that time and the tank internal pressure detected by the tank internal pressure detecting means in a state where the suction negative pressure is applied to the system.
[0016]
This limits the method of creating the map or the method of deriving the equation, and the technical significance thereof will become clear in the description of the embodiments of the invention described later.
According to a sixth aspect of the present invention, in the abnormality diagnostic apparatus for a fuel vapor purge system according to the fourth or fifth aspect, the diagnostic control means applies a negative suction pressure to the entire purge system including a canister and applies to the bypass control valve. On the other hand, when a significant follow-up of the fuel tank internal pressure is statistically recognized with respect to the change in the simulated canister internal pressure in a situation where the valve closing command is issued, an abnormality occurs in which the bypass control valve is stuck in the open state. It is determined that it is present.
[0017]
This clarifies the principle of abnormality diagnosis when the bypass control valve is an element to be diagnosed, and its technical significance is the same as in the case of claim 3.
The invention of claim 7 includes a fuel tank, a canister, a passage for introducing air into the canister, a purge passage for purging fuel vapor from the canister to an engine intake passage, a bypass passage for connecting the canister and the fuel tank, and a bypass passage therefor An abnormality diagnosis device incorporated in a fuel vapor purge system provided with a bypass control valve provided in a canister internal pressure detection means for detecting the internal pressure of the canister, and for detecting the internal pressure of the fuel tank The tank internal pressure detecting means, a first counter for counting the number of changes in the canister internal pressure, a second counter for counting the number of changes in the fuel tank internal pressure, and a suction negative pressure in the entire purge system including the canister In the situation where the valve closing command is issued to the bypass control valve. An abnormality in which the operation of two counters is allowed and the bypass control valve is stuck in an open state when a correlation rate obtained by dividing the value of the second counter by the value of the first counter is equal to or greater than a predetermined threshold value Diagnostic control means for determining that the fuel tank internal pressure has occurred, the diagnostic control means increments the second counter when the amount of change in the fuel tank internal pressure is greater than or equal to the first predetermined amount, and When the change amount is less than the second predetermined amount and the fuel tank internal pressure at that time is larger than the detection lower limit value of the tank internal pressure detecting means, the second counter is decremented, and neither the increment condition nor the decrement condition is satisfied The gist of the present invention is an abnormality diagnosis device for a fuel vapor purge system characterized by maintaining the second counter value.
[0018]
According to this configuration, the number of changes in the canister internal pressure and the number of changes in the internal pressure of the fuel tank are monitored under a situation where a suction negative pressure is applied to the entire purge system and a valve closing command is issued to the bypass control valve. Recorded in the first and second counters. When the correlation rate obtained by dividing the value of the second counter by the value of the first counter is equal to or greater than a predetermined threshold, significant follow-up of the fuel tank internal pressure is statistically recognized with respect to the change in the canister internal pressure. It is determined that there is an abnormality that the bypass control valve is stuck in the open state. At this time, the method of addition / subtraction of the second counter that counts the number of changes in the fuel tank internal pressure becomes a problem. In the present invention, when the amount of change in the fuel tank internal pressure is equal to or greater than the first predetermined amount, the second counter is incremented (added by 1) assuming that the follow-up of the fuel tank internal pressure to the change in the canister internal pressure can be clearly recognized. . On the other hand, when the change amount of the fuel tank internal pressure is less than the second predetermined amount and the fuel tank internal pressure at that time is larger than the detection lower limit value of the tank internal pressure detecting means, the change in the fuel tank internal pressure with respect to the change in the canister internal pressure The second counter is decremented (subtracted by 1) on the assumption that follow-up cannot be positively recognized. In the case of decrementing, an incidental condition is that the fuel tank internal pressure is larger than the detection lower limit value of the tank internal pressure detecting means. This is because when the pressure detected by the tank internal pressure detecting means is equal to the detection lower limit value, the fuel tank internal pressure is actually more likely to be lower than the detection lower limit value. In the first place, it is doubtful that the amount of change in the internal pressure of the fuel tank is less than the second predetermined amount. Therefore, when the decrement operation of the second counter, which leads to denying the follow-up of the fuel tank internal pressure to the change in the canister internal pressure, is performed, the incidental condition is imposed. Even if the apparent change amount of the fuel tank pressure is less than the second predetermined amount, if the fuel tank internal pressure is equal to the detection lower limit value of the tank internal pressure detecting means, the decrement of the second counter is prohibited. Thereby, the omission and delay of the abnormality detection of the bypass control valve are prevented, and the reliability and quickness of the abnormality diagnosis are improved.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, specific examples of a fuel vapor purge system for a vehicle and an abnormality diagnosis device thereof will be described with reference to the drawings.
[0020]
As shown in FIG. 1, the engine 10 includes a combustion chamber 11, an intake passage 12, and an exhaust passage 13. When the engine 10 is operated, fuel stored in the fuel tank 30 (for example, gasoline) is pumped out by the fuel pump 31 and sent to the delivery pipe 12a through the fuel supply passage, and then in the intake passage 12 by the fuel injection valve 12b. Is supplied by injection. A throttle valve 12c that makes the flow passage area of the intake passage 12 variable based on a depression operation of an accelerator pedal (not shown) is provided upstream of the intake passage 12. Further upstream, an air cleaner 12d for purifying the intake air and an air flow meter 12e for detecting the amount of intake air to the engine 10 are provided.
[0021]
The fuel vapor purge system 20 includes a canister 40 that collects fuel vapor generated from the fuel tank 30 and a purge passage 71 that purges the collected fuel vapor into the intake passage 12 of the engine 10. In the purge system 20, a pressure sensor 32 as a tank internal pressure detecting means and a breather control valve 33 are provided on the ceiling portion of the fuel tank 30. The pressure sensor 32 detects the pressure in the fuel tank 30 and a region communicating with the tank 30 on the basis of the atmospheric pressure. The atmospheric pressure reference means that the pressure corresponding to the atmospheric pressure is detected as zero. The detection lower limit L of the pressure sensor 32 is −4.0 kPa (kilopascal) = − 30 mmHg, and the lower limit L (= −4.0 kPa) is output when the pressure is lower than that. The breather control valve 33 is a diaphragm type differential pressure valve. When the internal pressure of the fuel tank becomes higher than the pressure in the breather passage 34 by a predetermined amount or more during refueling, the breather control valve 33 autonomously opens to let the fuel vapor pass through the breather passage 34. Through the canister 40.
[0022]
Further, the fuel tank 30 can communicate with the canister 40 via a vapor passage 35 having a smaller inner diameter than the breather passage 34. A tank internal pressure control valve 60 provided between the vapor passage 35 and the canister 40 is a diaphragm type differential pressure valve having the same function as the previous breather control valve 33. The diaphragm valve element 61 in the tank internal pressure control valve 60 opens the tank internal pressure control valve 60 only when the pressure in the fuel tank 30 is higher than the pressure in the canister 40 by a predetermined pressure or more.
[0023]
The canister 40 includes an adsorbent (for example, activated carbon) in the inside thereof, adsorbs fuel vapor on the adsorbent, temporarily stores the fuel vapor, and then adsorbs the adsorbent by placing it under a pressure lower than atmospheric pressure. It is the structure which can make the fuel vapor made to detach again. Hereinafter, in the present specification, a pressure lower than the atmospheric pressure is referred to as a negative pressure, and a pressure higher than the atmospheric pressure is referred to as a positive pressure. The canister 40 can communicate with the fuel tank 30 via the breather passage 34 and the vapor passage 35, can communicate with the intake passage 12 via the purge passage 71, and can further communicate with the air introduction passage via the atmospheric valve 70. 72 and the air discharge passage 73. A purge control valve 71a composed of an electromagnetic valve or VSV (vacuum switching valve) is provided in the purge passage 71. An air introduction valve 72a made of an electromagnetic valve or VSV is provided in the middle of the air introduction passage 72 communicating with the air cleaner 12d.
[0024]
In the atmospheric valve 70, two diaphragm valve bodies 74 and 75 each having a different function are provided. The first diaphragm valve body 74 has a space 74a on the back side thereof communicating with the purge passage 71. When the purge passage 71 is in a negative pressure state equal to or lower than a predetermined pressure, the first diaphragm valve body 74 opens and is opened from the atmosphere introduction passage 72 into the canister 40. Allow inflow of outside air into On the other hand, the second diaphragm valve body 75 opens when the inside of the canister 40 reaches a positive pressure equal to or higher than a predetermined pressure, and discharges excess air from the canister 40 to the atmosphere exhaust passage 73.
[0025]
The interior of the canister 40 is partitioned into a first adsorbent chamber 42 and a second adsorbent chamber 43 by a partition plate 41. Although both adsorbent chambers 42 and 43 are filled with an adsorbent (activated carbon), both chambers communicate with each other via a breathable filter 44 at the bottom of the canister. The fuel tank 30 can communicate with the first adsorbent chamber 42 on the one hand via the vapor passage 35 and the tank internal pressure control valve 60 and on the other hand via the breather control valve 33 and the breather passage 34. Further, the air introduction passage 72 and the air discharge passage 73 can communicate with the second adsorbent chamber 43 through the air valve 70. The purge passage 71 provided with the purge control valve 71a connects the first adsorbent chamber 42 of the canister 40 and the downstream position of the throttle valve 12c of the intake passage 12 for opening the purge control valve 71a. Accordingly, the first adsorbent chamber 42 communicates with the downstream position of the throttle valve 12c. That is, the fuel vapor introduced from the vapor passage 35 and the breather passage 34 is temporarily adsorbed in the first adsorbent chamber 42 and then carried to the purge passage 71. Further, even when the second diaphragm valve body 75 constituting the atmospheric valve 70 is opened and excess air in the canister 40 is discharged from the atmospheric discharge passage 73, the fuel vapor remaining in the gas phase in the canister 40 Is adsorbed by the adsorbent inside the second adsorbent chamber 43 and does not leak outside.
[0026]
In addition, the fuel vapor purge system 20 includes a bypass passage 80 for introducing a negative pressure so as to connect the tank internal pressure control valve 60 (or one end portion of the vapor passage 35) and the second adsorbent chamber 43 of the canister. Is provided. In the middle of the bypass passage 80, a bypass control valve 80a (a valve to be diagnosed in this example) made of an electromagnetic valve or VSV is provided. When the bypass control valve 80a is opened, the second adsorbent chamber 43 and the fuel tank 30 are directly communicated with each other via the bypass passage 80 and the vapor passage 35. In particular, when the purge control valve 71a is in an open state, the entire purge passage 71 is fueled via the first adsorbent chamber 42 → the air permeable filter 44 → the second adsorbent chamber 43 → the bypass passage 80 → the vapor passage 35. It communicates with the tank 30. Further, since the space in the breather passage 34 is also in communication with the first adsorbent chamber 42, the same space as the purge passage 71 is shared. As described above, the common space in the fuel vapor purge system 20 that communicates with each other by opening the bypass control valve 80a in a state where the negative pressure is introduced into the canister 40 by opening the purge control valve 71a is provided in the same system. This is the evaporation route at 20. The abnormality diagnosis device for the fuel vapor purge system according to the present embodiment diagnoses the presence or absence of the abnormality by determining the presence or absence of leakage in the evaporation path. In addition, an abnormality or malfunction of the bypass control valve 80a is also diagnosed.
[0027]
Furthermore, the engine 10 and the fuel vapor purge system 20 include an electronic control unit (ECU) 50 that serves as a control system and a diagnostic system for the engine. As shown in FIG. 2, the ECU 50 is configured around a microcomputer 51. The microcomputer 51 includes a CPU 51a that executes various processes related to engine control and system diagnosis, a ROM 51b that is a read-only memory storing various programs related to the control and diagnosis, a RAM 51c that is a volatile memory that can be freely read and written, and a read A backup RAM 51d, which is a non-volatile memory in which stored contents are retained even after the engine 10 is stopped by being backed up by a battery, is provided. Further, the microcomputer 51 includes a first counter 52, a second counter 53, and an internal timer 54. However, the first and second counters 52 and 53 do not need to be provided when the internal register of the CPU 51a plays the role of a counter. In addition to the pressure sensor 32 and the air flow meter 12e, various sensors necessary for operation control of the engine 10, such as a rotation speed sensor and a cylinder discrimination sensor, are directly or indirectly connected to the input side of the microcomputer 51. . On the output side of the microcomputer 51, a fuel injection valve 12b, a fuel pump 31, a purge control valve 71a, an air introduction valve 72a, and a bypass control valve 80a are connected via respective drive circuits.
[0028]
The ECU 50 executes engine control such as fuel injection control and air-fuel ratio control based on various information provided from each sensor. The ECU 50 recognizes an output signal from the pressure sensor 32 and appropriately controls opening and closing of the purge control valve 71a, the air introduction valve 72a, and the bypass control valve 80a, thereby diagnosing abnormality of the purge system (that is, leakage of the evaporation path). In order to ensure the accuracy or reliability of the purge system abnormality diagnosis, in particular, abnormality diagnosis of the bypass control valve 80a is executed. In this sense, the ECU 50 is positioned as “diagnosis control means”.
[0029]
(Outline of fuel purge by fuel vapor purge system 20)
When the fuel in the fuel tank 30 is vaporized and the vapor pressure reaches a predetermined pressure or higher, the tank internal pressure control valve 60 is opened autonomously to allow fuel vapor to flow from the fuel tank 30 into the canister 40. In addition, when the vapor pressure of the fuel vapor suddenly increases in the fuel tank 30 as in fuel refueling, for example, the breather control valve 33 opens autonomously, and the fuel tank 30 enters the canister 40. Larger amounts of fuel vapor are allowed to enter. The fuel vapor that has flowed into the canister 40 is once adsorbed by the adsorbent in the canister 40. Thereafter, as shown in FIG. 3, for example, when the coolant temperature of the engine 10 reaches a predetermined purge start water temperature (80 ° C. in this embodiment), the closed purge control valve 71a is opened based on a control signal from the ECU 50. At the same time, the open state of the air introduction valve 72a is maintained. Then, suction negative pressure is introduced from the intake passage 12 into the canister 40 through the purge passage 71, and fresh air is introduced from the air cleaner 12 d into the canister 40 through the atmosphere introduction passage 72. By introducing the negative pressure and fresh air, the fuel vapor is desorbed from the adsorbent and purged to the intake passage 12 through the purge passage 71.
[0030]
(Outline of leakage diagnosis of evaporation path of fuel vapor purge system 20)
In performing the leakage diagnosis of the evaporation path, it is a precondition that the cooling water temperature of the engine 10 reaches the purge start water temperature and the purge is started, and that the tank internal pressure Pt of the fuel tank 30 is stable. . For example, as shown in FIG. 3, a pressure change amount ΔP1 for a predetermined time (for example, 15 seconds) of the tank internal pressure Pt is calculated based on the pressure detected by the pressure sensor 32, and the pressure change amount ΔP1 is equal to or less than a predetermined value. If it is continuously checked, it is determined that the tank internal pressure Pt is stable. At the time (time t0) when the preconditions for the leakage diagnosis are satisfied, the air introduction valve 72a is closed and the purge control valve 71a is opened according to a command from the ECU 50. As a result, the canister 40 is cut off from the atmosphere. As a result, a negative pressure is introduced into the canister 40 from the intake passage 12 through the purge passage 71. In addition, by opening the bypass control valve 80a, the fuel tank 30, the canister 40, the breather passage 34, the vapor passage 35, and the purge passage 71 (that is, the entire evaporation passage) are in a negative pressure state. The internal pressure of the evaporation path is detected by a pressure sensor 32 on the ceiling of the fuel tank 30.
[0031]
When the purge control valve 71a is once closed at time t1 when the entire evaporation path is depressurized to some extent (for example, depressurization to −2.67 kPa = −20 mmHg with respect to atmospheric pressure), the inside of the evaporation path is sealed in a negative pressure state. At this time, if there is no abnormality such as perforation in the evaporation path, the fuel in the fuel tank 30 evaporates, so that the internal pressure of the evaporation path gradually approaches the equilibrium pressure of the air and fuel vapor remaining in the path. (In other words, it should rise slowly). On the other hand, when there is a leak in the evaporation path, the internal pressure of the evaporation path rapidly approaches the external pressure (atmospheric pressure). In any case, the evaporation path internal pressure increases after time t1, but the degree of the internal pressure increase differs depending on the presence or absence of leakage. In the present embodiment, at time t2 when the evaporation path internal pressure (= Pt) again reaches the predetermined negative pressure (−2.00 kPa = −15 mmHg), the pressure change rate ΔP (−15) (kPa / sec) as the pressure change degree. Or mmHg / sec). Then, based on the pressure change rate ΔP (−15), it is determined whether or not there is an abnormality such as a hole in the evaporation path.
[0032]
(Abnormality diagnosis of valves constituting the fuel vapor purge system 20)
In order for the evaporative path leakage diagnosis to be reliable, it is necessary to always confirm that the valves and sensors constituting the system are operating normally. In the following, a method for diagnosing abnormality or malfunction of the bypass control valve 80a provided in the bypass passage 80 will be described. In the actual system, abnormality diagnosis is performed for other valves and sensors, but the description thereof is omitted.
[0033]
4 and 5 are flowcharts showing an outline of a valve abnormality diagnosis routine for diagnosing the presence or absence of abnormality of the bypass control valve 80a. This routine is executed by the ECU 50 as a periodic interruption process every predetermined time (for example, several tens to several hundreds of milliseconds). This diagnostic process is particularly aimed at detecting an abnormality (open sticking) where the bypass control valve 80a sticks in the open state. Before entering this abnormality diagnosis routine as a preliminary preparation, at least the purge control valve 71a is open, and a valve closing drive signal (valve closing command) is issued from the ECU 50 to the bypass control valve 80a.
[0034]
When there is an interrupt request, the ECU 50 first calculates a simulated canister internal pressure Pc in step 110. This step estimates the canister internal pressure based on other information that can be obtained because the canister 40 is not equipped with a pressure sensor that directly detects the internal pressure. The estimated value is the simulated canister internal pressure Pc. And as shown in FIG. 4, the process of step 110 is subdivided into five steps of steps 111-115.
[0035]
First, at step 111, the ECU 50 calculates a purge flow rate Qp. “Purge flow rate” means the flow rate of gas released to the intake passage 12 via the purge passage 71 during the fuel purge operation, that is, the amount of inflow air flowing into the canister via the air introduction passage 72. If the valve opening of the purge control valve 71a and the degree of the negative pressure of the purge passage 71 are found, the purge flow rate Qp is calculated based on these, or a map (map format database) obtained by calculation or experiment or computer simulation is used. It can be calculated by referring to it. Here, since the opening degree of the purge control valve 71a is controlled by the ECU 50, the ECU 50 holds information regarding the opening degree of the purge control valve 71a as internal data. On the other hand, the degree of negative pressure in the purge passage 71 has a correlation with the engine load, and the relationship between the two is mapped into a characteristic map through experiments and the like for each vehicle. The engine load can be calculated based on the rotational speed data from the engine rotational speed sensor and the intake air amount data from the air flow meter 12e. That is, the degree of negative pressure in the purge passage 71 can be grasped based on data from various sensors, and the purge flow rate Qp can also be calculated based on external data and internal data. In this sense, the engine speed sensor, the various sensors including the air flow meter 12e, and the ECU 50 constitute "purge flow rate grasping means".
[0036]
In step 112, the ECU 50 calculates a temporary canister internal pressure Pc ′. In general, there is a close correlation between the canister internal pressure and the purge flow rate Qp in accordance with the characteristics of the atmospheric valve 70 of the canister, and the relationship between both can be made into a characteristic map through experiments and the like for each vehicle. The graph of FIG. 6 conceptually shows the relationship between Qp and Pc ′ in the characteristic map. The characteristic line drawn in this graph is almost a quadratic function curve (Pc ′ = A · Qp) over the entire assumed range of Qp and Pc ′. ² + B, where A and B are arbitrary numbers). This is based on the law derived from Bernoulli's theorem, which is the fundamental theorem of fluid mechanics, "if the fluid density is constant, the pressure is proportional to the square of the flow velocity". Such a quadratic function characteristic map is held as internal data by the ECU 50, and by referring to this, regardless of the value of the purge flow rate Qp within the assumed variable range, an appropriate temporary value is obtained from the Qp value. The canister internal pressure Pc ′ can be calculated. The reason why the temporary canister internal pressure Pc ′ is merely “temporary” will become clear later. Further, if the quadratic term coefficient A and the zeroth term coefficient B in the quadratic function curve equation are respectively fixed to specific values, Pc ′ can be directly calculated from the value of Qp according to the above equation without preparing map format data. It can also be calculated.
[0037]
In step 113, the ECU 50 grasps the remaining amount of fuel in the fuel tank 30. There are various methods for determining the remaining amount of fuel, but the simplest method is to refer to the output of a fuel meter incorporated in the instrument panel of the vehicle driver's seat. The ECU 50 can grasp the remaining fuel amount based on the electrical output from the fuel meter. Alternatively, in the fuel vapor purge system, the remaining amount of fuel is determined based on the total volume of the fuel tank 30 and the time required to reduce the internal pressure of the tank from the atmospheric pressure level to a predetermined reduced pressure level (negative pressure introduction time). A method for estimating the amount is well known, and the remaining fuel amount may be indirectly grasped by this known method. In these senses, the ECU 50 constitutes fuel remaining amount grasping means.
[0038]
In step 114, the ECU 50 calculates a smoothing coefficient K as a correction coefficient from the remaining fuel amount obtained in the previous step. The technical significance of this “annealing coefficient K” will be described later. The ECU 50 holds in advance a trend map as shown in FIG. 7 as internal data, and determines the smoothing coefficient K from the remaining fuel amount with reference to this map. As shown in FIG. 7, the smoothing coefficient K approaches 1.0 as the amount of remaining fuel in the tank increases (that is, the volume of the gas phase portion decreases). On the other hand, the smaller the remaining amount of fuel in the tank (that is, the larger the volume of the gas phase portion), the closer the smoothing coefficient K approaches 0 (however, K is never zero).
[0039]
In step 115, the ECU 50 calculates a normal simulated canister internal pressure Pc by multiplying the smoothing coefficient K and the temporary canister internal pressure Pc ′ (Pc = K · Pc ′). That is, the annealing coefficient K is a kind of correction coefficient when calculating the normal simulated canister internal pressure Pc from the temporary canister internal pressure Pc ′. The correction coefficient itself is a variable parameter that is appropriately changed according to the remaining fuel amount as shown in step 114.
[0040]
The reason why the correction by the “annealing coefficient K” is necessary is as follows. In the description of the step 112, it has been described that there is a close correlation between the canister internal pressure and the purge flow rate Qp, and the relationship between the two is mapped through an experiment or the like. Is not provided with a pressure sensor for directly measuring its internal pressure, and a map cannot be created by directly measuring the correlation between the canister internal pressure and the purge flow rate Qp. Therefore, as an alternative measure, instead of the internal pressure of the canister alone, the bypass control valve 80a is opened, the tank internal pressure in a state where the canister 40 and the fuel tank 30 are communicated is measured by the pressure sensor 32, and the measured tank internal pressure The map is created by measuring the relationship with the purge flow rate Qp. That is, the temporary canister internal pressure Pc ′ is actually the internal pressure of the fuel tank in the communication state with the canister. For this reason, a gap naturally exists between the temporary canister internal pressure Pc ′ and the true canister internal pressure. The correction coefficient for filling the gap is the smoothing coefficient K, and the smoothing coefficient K is of a nature set so that the canister internal pressure can simulate the fuel tank internal pressure. As described above, the smoothing coefficient K is not the correlation map between the canister internal pressure and the purge flow rate Qp, but the actual condition associated with the alternative adoption of the correlation map between the fuel tank internal pressure and the purge flow rate Qp in the communication state with the canister. This is a correction coefficient to compensate for the deviation.
[0041]
Further, the reason why the smoothing coefficient K as the correction coefficient is variably set according to the remaining fuel amount is as follows. As described above, the tank internal pressure in the state where the bypass control valve 80a is opened and the canister 40 and the fuel tank 30 are in communication is measured by the pressure sensor 32, and the relationship between the measured tank internal pressure and the purge flow rate Qp is measured. When creating the correlation map, the case where the fuel remaining in the fuel tank 30 is about half (for example, 40%) is represented as an average state, and a plurality of maps are prepared for each fuel remaining amount. Do not mean. However, in reality, the remaining space volume (volume of the gas phase part) and the vapor-liquid equilibrium state of the fuel in the tank change depending on the amount of remaining fuel, which is related to the relationship between the tank internal pressure and the actual canister internal pressure. The effect on it cannot be ignored. As a currently known phenomenon, when the remaining amount of fuel in the fuel tank 30 is relatively large under the open state of the bypass control valve 80a, the change in the tank internal pressure (= temporary canister internal pressure Pc ′) due to the purge suction is compared. The gap between the temporary canister internal pressure Pc ′ obtained in step 112 and the actual canister internal pressure is also small. On the other hand, when the remaining amount of fuel in the fuel tank 30 is relatively small under the open state of the bypass control valve 80a, the change in the tank internal pressure (= temporary canister internal pressure Pc ′) due to the purge suction is relatively dull. The gap between the temporary canister internal pressure Pc ′ obtained at 112 and the actual canister internal pressure tends to increase (at least instantaneously, the pressure is not equalized). That is, if the smoothing coefficient K is variably set according to the amount of remaining fuel, the actual condition is met. The fact that the annealing coefficient K is large (that is, close to 1.0) means that the degree of correction (or annealing) for the temporary canister internal pressure Pc ′ is reduced. On the other hand, the fact that the annealing coefficient K is small (that is, close to 0) means that the degree of correction (or annealing) for the temporary canister internal pressure Pc ′ is increased.
[0042]
As described above, the simulated canister internal pressure Pc is calculated through the processing of steps 111 to 115, and the reliability and accuracy of the simulated canister internal pressure Pc as an estimated value of the canister internal pressure based on the purge flow rate Qp is ensured. In this sense, the ECU 50 constitutes a canister internal pressure detection unit that indirectly detects the internal pressure of the canister 40.
[0043]
Next, in step 121, the ECU 50 determines whether or not the elapsed time from the previous zero clear of the internal timer 54 has reached a predetermined time TM (for example, 15 seconds). If the predetermined time TM has elapsed at that time, the process of step 122 is executed. If the predetermined time TM has not been reached, the process of step 122 is skipped. That is, the process of step 122 is performed every predetermined time TM (for example, 15 seconds).
[0044]
Step 122 is a reset operation every predetermined time TM. Here, first, the internal timer 54 is cleared to zero. Further, the simulated canister internal pressure Pc obtained in step 110 is set as the temporary canister reference internal pressure Pcs, and the detected pressure (tank internal pressure Pt) of the pressure sensor 32 at that time is set as the temporary tank reference internal pressure Pts. That is, the simulated canister internal pressure Pc when the predetermined time TM has elapsed is stored as a provisional comparison reference value (or reference point) Pcs, and the tank internal pressure Pt when the predetermined time TM has elapsed is used as the temporary comparison reference value (or The reference point is stored as Pts (see FIG. 8). That is, in step 122, the temporary canister reference internal pressure Pcs and the temporary tank reference internal pressure Pts are updated every predetermined time TM.
[0045]
Steps 123 to 125 are a series of processes for counting the number of times the simulated canister internal pressure Pc has changed from the temporary canister reference internal pressure Pcs by a predetermined pressure value α or more. Specifically, in step 123, the absolute value of the difference ΔPc between the simulated canister internal pressure Pc and the temporary canister reference internal pressure Pcs at that time, that is, the absolute value of the amount of change in the canister internal pressure from the reference point is determined as a predetermined pressure value α ( For example, it is determined whether it is 0.67 kPa = 5.0 mmHg) or more. If the determination in step 123 is YES (positive), in step 124, the value C1 of the first counter 52 assigned for counting the number of canister internal pressure changes is incremented (added by 1). In the same manner, the zero clear of the internal timer 54 and the temporary canister reference internal pressure Pcs are reset (see FIG. 8). The predetermined pressure value α is set to a magnitude that can exclude the change in the simulated canister internal pressure Pc, which is only a slight fluctuation, from the count target.
[0046]
If the determination in step 123 is NO (No), the amount of change in the simulated canister internal pressure Pc and the tank internal pressure Pt is not checked at all (that is, the first and second counters 52 and 53 are not added or subtracted at all). Skip to step 141. This is because it is not appropriate to rely on the valve abnormality determination method of the present embodiment when the change in the simulated canister internal pressure Pc is too small.
[0047]
After step 125, the process proceeds to step 131 in FIG. In step 131, the absolute value of the difference ΔPt between the tank internal pressure Pt and the provisional tank reference internal pressure Pts at that time, that is, the absolute value of the change amount of the tank internal pressure from the reference point is the predetermined pressure value β as the first predetermined amount. It is determined whether or not (for example, 0.47 kPa = 3.5 mmHg) or more. If the determination in step 131 is YES, in step 132, the value C2 of the second counter 53 assigned for counting the number of tank internal pressure changes is incremented (added by 1). That is, when the determination at step 123 is YES and the determination at step 131 is YES, it is determined that the followability corresponding to the change in Pt with respect to the change in Pc is recognized (positive followability of the followability), and the counter values C1, C2 As a result, both are plus one. The predetermined pressure value β is set to a value smaller than the value α (β <α).
[0048]
On the other hand, if the determination in step 131 is NO, in step 133, the ECU 50 determines whether the tank internal pressure Pt (current Pt) at that time is larger than the detection lower limit L (= −4.0 kPa) of the pressure sensor 32. Determine whether or not. If the determination at step 133 is YES, the process proceeds to step 134. On the other hand, when the determination at step 133 is NO, that is, when the detected pressure is stuck to the lower limit value L, the actual tank internal pressure Pt may be lower than the lower limit value L, and the detected value of the pressure sensor 32 It is not possible to proceed to the determination of step 134 by trusting. Therefore, in that case, steps 134 and 135 are skipped.
[0049]
If the determination in step 133 is YES, in step 134, the ECU 50 determines that the absolute value of the difference ΔPt between the tank internal pressure Pt and the temporary tank reference internal pressure Pts, that is, the absolute value of the change amount of the tank internal pressure from the reference point is the second place. It is determined whether or not the pressure is less than a predetermined pressure value γ (for example, 0.11 kPa = 0.8 mmHg). If the determination in step 134 is YES, the value C2 of the second counter 53 is decremented (subtracted by 1) in step 135. That is, if the determination at step 123 is YES and both the determination at step 133 and step 134 are YES, it is determined that no clear followability is recognized in the change in Pt despite the sufficient Pc change (follow-up performance). The result of subtracting 1 from the counter value C2 despite the increase in the counter value C1. The predetermined pressure value γ is set to a value smaller than the value β (γ <β).
[0050]
If the determination in step 134 is NO, that is, if γ ≦ | ΔPt | <β, the second counter 53 is not added or subtracted at all. That is, in this case, the change in Pt is halfway despite a sufficient change in Pc, and it is impossible to positively affirm or deny the followability of the change in Pt with respect to the change in Pc. Therefore, the counter value C2 is maintained as it is despite the increase of the counter value C1.
[0051]
Prior to step 134 determination, the prior determination regarding the current Pt magnitude is performed at step 133 because the change amount ΔPt of the tank internal pressure does not actually satisfy the determination condition of step 134. This is to prevent the second counter value C2 from being decremented by mistake. More specifically, if the purge suction is strong (for example, if the remaining amount of fuel is high and the engine is in a high load operation state) in a state where the bypass control valve 80a is abnormally fixed in an open state, The tank internal pressure Pt may fall below the detection lower limit L of the pressure sensor 32. In such a case, the change amount ΔPt of the tank internal pressure should not satisfy the determination condition of step 134, but because the detection lower limit L of the pressure sensor 32 is higher than the actual tank internal pressure Pt. In addition, there may occur a situation where the change amount ΔPt of the tank internal pressure is apparently zero. Then, the second counter value C2 is decremented, so that it becomes impossible to reach the determination result (conclusion that the valve is open abnormally) with the follow-up correlation of the change in Pt with respect to the change in Pc in relation to the processing in step 141 and later described later. Even if it can be reached, there is a risk that it will be extremely slow. In order to avoid such a problem, an algorithm is employed in which the decrement of the second counter value C2 is avoided when the determination at step 133 is NO.
[0052]
After the processing of step 132, 133, 134 or 135, in step 136, the ECU 50 resets the temporary tank reference internal pressure Pts in the same manner as in step 122, and prepares for the determination in the next cycle. After step 136 or after the determination at step 123 is NO, the process proceeds to a final determination procedure after step 141.
[0053]
In step 141, it is determined whether or not the value C1 of the first counter is equal to a predetermined determination value DA (for example, 10 times). When the first counter value C1 is less than the determination value DA, it is considered that the number of changes in the simulated canister internal pressure Pc has not reached the prescribed number and that there is no appropriate abnormality diagnosis, and whether or not there is an abnormality in the valve. The interrupt processing shown in FIGS. 4 and 5 is temporarily terminated without making any diagnosis. That is, the determination value DA is the minimum prescribed number for ensuring statistical reliability in determining the followability of the change in Pt with respect to the change in Pc. Naturally, increasing the determination value DA statistically increases the reliability of the determination, but on the other hand, it takes a certain amount of time to reach a conclusion.
[0054]
If the determination in step 141 is YES (C1 = DA), it is determined that the number of changes in the simulated canister internal pressure Pc has reached a specified number that allows appropriate abnormality diagnosis, and the determination in step 142 is performed. In step 142, it is determined whether or not the value C2 of the second counter is equal to or greater than a predetermined determination value DB (for example, 7 times). This determination value DB is set to a value equal to the determination value DA (DB = DA) or a value close thereto (provided that DB <DA).
[0055]
If the determination in step 142 is YES, it is determined that the bypass control valve 80a is broken in the open state (open abnormality) (step 143). The satisfaction of the determination condition of step 142 means that the tank internal pressure change count C2 is equal to or very close to the canister internal pressure change count C1, and the change trend of the simulated canister internal pressure Pc and the tank internal pressure Pt change. This is because it shows that there is a high correlation with the trend, that is, it is possible to reasonably recognize the followability of the Pt change with respect to the Pc change. Even if a valve closing command is issued to the bypass control valve 80a provided in the passage connecting the fuel tank 30 and the canister 40, there is a close correlation between the change trends of the two internal pressures Pc and Pt. This means that the two regions are clearly in communication, and it can be determined that there is a high possibility that the bypass control valve 80a is open and malfunctioning. In this case, the processing of steps 141 and 142 implicitly obtains the correlation rate or tracking rate R calculated by C2 / C1, and the correlation rate R is equal to or greater than a predetermined threshold (in this example, 7/10 = 70% or more) can be understood as a process for determining that the bypass control valve 80a is abnormally open. When it is determined that the opening is abnormal, a warning display (for example, installed in the instrument panel of the vehicle) for notifying the person of the abnormality of the fuel vapor purge system is turned on.
[0056]
On the other hand, if the determination in step 142 is NO, it is determined that the bypass control valve 80a has no abnormality in the open state (normal) (step 144). This is regarded as such as a flip in the case of an abnormal opening. That is, not satisfying the determination condition of step 142 means that there is no significant correlation between the change trend of the simulated canister internal pressure Pc and the change trend of the tank internal pressure Pt, that is, the Pt change relative to the Pc change. This is because it indicates that it cannot be asserted until followability is reasonably recognized. In terms of the correlation rate R, the ratio R does not reach a predetermined threshold (70% in this example). Accordingly, it cannot be asserted that the bypass control valve 80a is in an abnormally open state and the fuel tank 30 and the canister 40 are in communication with each other. It is judged passively that it has been. Incidentally, when the bypass control valve 80a is normally closed, the fuel tank 30 should be in an isolated space, and in this case, the tank internal pressure Pt is substantially constant as shown by a one-dot chain line in FIG. The value should be maintained.
[0057]
By the way, the predetermined time TM of step 121 in FIG. 4 is understood to be the time limit until the timer is cleared and the provisional reference internal pressures Pcs and Pts are forcibly reset in step 122 when the determination of step 123 is not easy. be able to. That is, in the diagnostic procedure of FIGS. 4 and 5, if the change amount ΔPc of the simulated canister internal pressure is not greater than the predetermined pressure value α within the time limit, a meaningful (or suitable for diagnosis) change in the simulated canister internal pressure can be obtained. It is assumed that there was not, and the diagnosis is performed again without changing the count value. It is meaningless even if the step 123 determination is YES over a long time. A preferable range of the predetermined time TM as the time limit is empirically a range of 10 to 20 seconds (preferably around 15 seconds).
[0058]
(Effect) According to the present embodiment, the following effects can be obtained.
In the fuel vapor purge system of the present embodiment, the simulated canister internal pressure Pc as an estimated value of the canister internal pressure can be obtained by calculation processing based on information such as the purge flow rate Qp, the remaining fuel amount, and the smoothing coefficient K. That is, it is not necessary to provide a special pressure sensor for measuring the internal pressure of the canister 40, and it is possible to suppress an increase in cost associated with an increase in the number of assembly steps required to ensure the airtightness of the sensor (reduction in manufacturing cost). .
[0059]
The smoothing coefficient K for correcting the temporary canister internal pressure Pc ′ derived from the purge flow rate Qp by referring to the map is variably set according to the remaining amount of fuel in the fuel tank 30. For this reason, even if the remaining fuel amount at the time of valve abnormality diagnosis deviates from the remaining fuel condition at the time of acquiring the map data of Qp vs. Pc ′, the deviation is compensated by the variable smoothing coefficient K, so that the simulated canister The calculated value of the internal pressure Pc can reflect the true canister internal pressure almost accurately. Therefore, the accuracy of valve abnormality diagnosis is improved.
[0060]
The characteristic line drawn in the map of Qp vs. Pc ′ (see FIG. 6) is a quadratic function curve, and the above-mentioned physical law “if the fluid density is constant, the pressure is proportional to the square of the flow velocity” It matches. For this reason, even if the purge flow rate Qp changes in a wide range, the temporary canister internal pressure Pc ′ can be accurately specified over almost all of the wide range. In particular, even when the vehicle engine is in a high load operation state and the purge flow rate Qp is large, the correct temporary canister internal pressure Pc ′ can be obtained from the purge flow rate Qp at that time. That is, even when the purge flow rate Qp increases (or decreases), the calculated value of the simulated canister internal pressure Pc does not greatly deviate from the actual canister internal pressure.
[0061]
As described above, when the detected value of the pressure sensor 32 indicates the detection lower limit L (that is, when the determination at step 133 is NO), the detected value of the sensor does not reflect the actual tank internal pressure. In view of the above, an algorithm is employed in which the decrement of the second counter value C2 is avoided. For this reason, an erroneous determination that there is no followability or correlation in the presence of the followability or correlation of the tank internal pressure Pt with respect to the change in the simulated canister internal pressure Pc can be avoided. Can do. Further, even when no erroneous determination is made, it is possible to prevent the time required to reach the correct determination from becoming extremely long.
[0062]
In the present embodiment, the valve (bypass) to be diagnosed is determined based on whether or not the tank internal pressure Pt follows the change in the simulated canister internal pressure Pc or whether there is a close correlation between the Pc change and the Pt change. The presence or absence of an abnormal opening of the control valve 80a) is diagnosed. That is, regardless of the absolute value of Pt, it is possible to diagnose the presence or absence of an abnormal valve opening by focusing only on the relative relationship between Pc and Pt. Thus, since the vehicle, engine, or tank internal pressure Pt is not determined as a precondition for entering the diagnosis process, for example, the valve abnormality diagnosis is performed even when the vehicle is traveling on a rough road. It can be carried out. According to the present embodiment, it is possible to frequently perform abnormality diagnosis without being restricted by the establishment of strict preconditions.
[0063]
Even when it is determined that the valve to be diagnosed is in an abnormal open state, there is a statistically reasonable correlation between the change trend of the simulated canister internal pressure Pc and the change trend of the tank internal pressure Pt. This is a condition for judgment. That is, the valve opening abnormality is determined only when the correlation rate R is large enough to be statistically certain. Therefore, it is excellent in accuracy and reliability of valve abnormality diagnosis.
[0064]
(Another example) The above embodiment may be modified as follows.
Only in the invention described in claim 7, the canister 40 is provided with the second pressure sensor to measure the canister internal pressure without relying on the simulated canister internal pressure Pc which is an estimated value of the internal pressure based on indirect data. (It may be detected directly). In this case, the second pressure sensor serves as canister internal pressure detection means.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a fuel vapor purge system and its abnormality diagnosis device.
FIG. 2 is a block diagram showing an outline of an electrical configuration related to abnormality diagnosis.
FIG. 3 is a timing chart showing an outline of leakage diagnosis of a purge system.
FIG. 4 is a flowchart of a valve abnormality diagnosis procedure.
FIG. 5 is a flowchart of a valve abnormality diagnosis procedure following FIG. 4;
FIG. 6 is a graph showing the correlation between the purge flow rate and the temporary canister internal pressure.
FIG. 7 is a graph that suggests a correspondence relationship between the remaining amount of fuel and the smoothing coefficient.
FIG. 8 is a timing chart showing several patterns related to the correlation between the canister internal pressure and the tank internal pressure when the valve is abnormal.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Engine, 12 ... Intake passage, 12e ... Air flow meter (purge flow rate grasping means), 20 ... Fuel vapor purge system, 30 ... Fuel tank, 32 ... Pressure sensor (tank internal pressure detecting means), 40 ... Canister, 50 ... ECU (Fuel remaining amount grasping means, purge flow amount grasping means, canister internal pressure detecting means and diagnostic control means), 52... First counter, 53... Second counter, 71... Purge passage, 72. 80a ... Bypass control valve (valve to be diagnosed), C1 ... First counter value, C2 ... Second counter value, K ... Smoothing coefficient (correction coefficient), L ... Detection lower limit value, R ... Correlation rate.

Claims (7)

A fuel tank, a canister, a passage for introducing air into the canister, a purge passage for purging fuel vapor from the canister to an engine intake passage, a bypass passage for connecting the canister and the fuel tank, and a bypass control valve provided in the bypass passage An abnormality diagnosis apparatus incorporated in a fuel vapor purge system comprising:
Tank internal pressure detection means for detecting the internal pressure of the fuel tank;
Fuel remaining amount grasping means for grasping the fuel remaining amount in the fuel tank;
A purge flow rate grasping means for grasping a purge flow rate of fuel vapor from the canister to the engine intake passage;
Diagnostic control means for diagnosing whether there is an abnormality in the components of the fuel vapor purge system based on the fuel tank internal pressure detected by the tank internal pressure detection means and the canister internal pressure;
The diagnostic control means variably sets a correction coefficient according to the fuel remaining amount grasped by the fuel remaining amount grasping means, and the canister internal pressure based on the correction coefficient and the purge flow amount grasped by the purge flow amount grasping means. An apparatus for diagnosing abnormality of a fuel vapor purge system, characterized in that the internal pressure of a simulated canister is calculated as The diagnostic control means holds a map relating to the correlation between the purge flow rate and the temporary canister internal pressure as internal data, and calculates the temporary canister internal pressure from the purge flow rate grasped by the purge flow rate grasping means by referring to the map. 2. The abnormality diagnosis device for a fuel vapor purge system according to claim 1, wherein the simulated canister internal pressure is calculated by multiplying the calculated temporary canister internal pressure by the correction coefficient. The diagnosis control means applies a negative suction pressure to the entire purge system including the canister and issues a valve closing command to the bypass control valve. The abnormality diagnosis of the fuel vapor purge system according to claim 1 or 2, wherein when the follow-up is statistically recognized, it is determined that an abnormality occurs in which the bypass control valve is stuck in an open state. apparatus. A fuel tank, a canister, a passage for introducing air into the canister, a purge passage for purging fuel vapor from the canister to an engine intake passage, a bypass passage for connecting the canister and the fuel tank, and a bypass control valve provided in the bypass passage An abnormality diagnosis apparatus incorporated in a fuel vapor purge system comprising:
Tank internal pressure detection means for detecting the internal pressure of the fuel tank;
A purge flow rate grasping means for grasping a purge flow rate of fuel vapor from the canister to the engine intake passage;
Diagnostic control means for diagnosing whether there is an abnormality in the components of the fuel vapor purge system based on the fuel tank internal pressure detected by the tank internal pressure detection means and the canister internal pressure;
The diagnostic control means holds, as internal data, a map or an expression in which the temporary canister internal pressure is a quadratic function of the purge flow rate, and the purge flow rate grasping means uses the map or the expression. An abnormality diagnosing device for a fuel vapor purge system, wherein a temporary canister internal pressure is calculated from the grasped purge flow rate, and a simulated canister internal pressure is calculated as the canister internal pressure based on the calculated temporary canister internal pressure and a correction coefficient . The map or expression held as internal data by the diagnostic control means is a state in which a negative suction pressure is applied to the purge system when the bypass control valve is opened, and the purge flow rate at that time and the tank internal pressure detection means are The abnormality diagnosis device for a fuel vapor purge system according to claim 4, wherein the abnormality diagnosis device is prepared based on data obtained by actually measuring a relationship with a tank internal pressure to be detected. The diagnosis control means applies a negative suction pressure to the entire purge system including the canister and issues a valve closing command to the bypass control valve. 6. The abnormality diagnosis of a fuel vapor purge system according to claim 4 or 5, wherein when the follow-up is statistically recognized, it is determined that an abnormality occurs in which the bypass control valve is stuck in an open state. apparatus. A fuel tank, a canister, a passage for introducing air into the canister, a purge passage for purging fuel vapor from the canister to an engine intake passage, a bypass passage for connecting the canister and the fuel tank, and a bypass control valve provided in the bypass passage An abnormality diagnosis apparatus incorporated in a fuel vapor purge system comprising:
Canister internal pressure detecting means for detecting the internal pressure of the canister;
Tank internal pressure detection means for detecting the internal pressure of the fuel tank;
A first counter for counting the number of changes in the canister internal pressure;
A second counter for counting the number of changes in the fuel tank internal pressure;
The negative counter is allowed to operate under a situation where a suction negative pressure is applied to the entire purge system including the canister and a valve closing command is issued to the bypass control valve, and the value of the second counter is set to the second counter value. Diagnostic control means for determining that the bypass control valve is stuck in an open state when a correlation rate obtained by dividing by one counter value is equal to or greater than a predetermined threshold,
The diagnosis control means increments the second counter when the change amount of the fuel tank internal pressure is equal to or greater than the first predetermined amount, and the change amount of the fuel tank internal pressure is less than the second predetermined amount and the fuel tank at that time The fuel vapor purge, wherein the second counter is decremented when the internal pressure is larger than the detection lower limit value of the tank internal pressure detecting means, and the second counter value is maintained when neither the increment condition nor the decrement condition is satisfied. System abnormality diagnosis device.

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