Fault diagnosis method and apparatus for evaporation fuel processing device

Abstract

The present invention performs stage 1 and stage 2 diagnostics as fault diagnostics for two purge control valves 8A, 8B in an evaporated fuel processing device. The stage 1 diagnostics are performed during normal purging to determine if a purge passage pressure is at or below a first threshold Lim1 when the two purge control valves 8A, 8B are both controlled to be open. An NG counter is incremented if the first threshold Lim1 is exceeded, and when the counter value reaches a certain value, a fault is determined and the stage 2 diagnostics are performed. In stage 2, the purge control valves 8A, 8B are forcibly controlled to be open one at a time, and it is determined whether the purge passage pressure is at or below a second threshold Lim2. With this arrangement, the fault location can be ultimately identified.

Description

Technical Field

[0001] The present invention relates to a failure diagnosis method and apparatus for diagnosing failures such as closing and sticking of a plurality of purge control valves in an evaporation fuel processing apparatus using a canister.

Background Art

[0002] An evaporation fuel processing apparatus is widely used in which evaporation fuel generated in a fuel tank of a vehicle is temporarily adsorbed by a canister using an adsorbent such as activated carbon so as not to flow out to the outside, and then, during operation of an internal combustion engine, fuel components are purged from the canister by introduction of fresh air and introduced into the intake system of the internal combustion engine.

[0003] Patent Document 1 discloses that in an evaporation fuel processing apparatus provided with two purge control valves in parallel in a purge passage, by operating the two purge control valves individually, failure diagnosis (for example, diagnosis of closing and sticking) of each purge control valve is performed. When pulsation of the tank internal pressure is not detected when one purge control valve is operated at an appropriate duty ratio, it is determined that the purge control valve is faulty. Such diagnosis is sequentially performed for the two purge control valves.

[0004] However, if only one purge control valve is operated for failure diagnosis and the other purge control valve is kept non-operating in this way, during that time, the purge amount flowing from the canister to the intake system of the internal combustion engine is substantially halved, which becomes a factor in delaying the processing of the fuel components adsorbed by the canister. And such a problem becomes more prominent if failure diagnosis is frequently performed.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

[0006] This invention relates to a failure diagnosis of an evaporative fuel treatment device in which a plurality of purge control valves are arranged in parallel with each other in a purge passage between a canister and an intake system of an internal combustion engine, and a first diagnosis of the purge system is performed based on the pressure in the purge passage when the plurality of purge control valves are all open-controlled, and when it is determined in this first diagnosis that there is a failure in the purge system, a second diagnosis is performed to identify the failure location based on the pressure in the purge passage in each state by open-controlling the plurality of purge control valves one by one.

[0007] The second diagnosis is not executed unless it is determined in the first diagnosis that there is some failure. Therefore, the purge from the canister to the intake system for failure diagnosis is minimized.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0009] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a configuration explanatory diagram showing the configuration of an evaporative fuel treatment device to which the failure diagnosis of one embodiment of the present invention is applied. In one embodiment, the vehicle is a so-called series hybrid vehicle that runs on a motor, and the internal combustion engine 1 is an internal combustion engine for power generation that drives a generator. Therefore, the internal combustion engine 1 repeats operation and stop according to the power demand based on the SOC of the battery, etc., and during operation, it is basically operated under specific operating conditions (load and rotational speed) that achieve the best fuel efficiency.

[0010] The evaporative fuel treatment device is configured mainly by a canister 3 filled with an adsorbent such as activated carbon inside to treat the evaporative fuel generated in the fuel tank 2 of the vehicle during vehicle parking or the like without allowing it to flow out to the outside. The canister 3 has a charge port 3a and a purge port 3b at one end of the internal flow path, and a drain port 3c at the other end. The charge port 3a communicates with the upper space of the fuel tank 2 via a charge passage 4, while the purge port 3b communicates with the intake passage 7 of the internal combustion engine 1 via a purge passage 5. The drain port 3c is open to the atmosphere via a drain passage 6. The drain passage 6 is provided with a drain cut valve 10 composed of a solenoid valve that can close the drain passage 6 in order to seal the system during leakage diagnosis or the like.

[0011] For example, the evaporative fuel generated during vehicle parking or refueling is introduced into the canister 3 via the charge passage 4 and adsorbed by the adsorbent in each part while flowing toward the drain port 3c through the adsorbent. The fuel components adsorbed in this way are purged from the adsorbent when air is taken in through the drain passage 6 due to the negative pressure generated in the intake system during the operation of the internal combustion engine 1, and are introduced into the intake system of the internal combustion engine 1 via the purge passage 5, and finally burned together with the fuel from the fuel injection valve in the combustion chamber of the internal combustion engine 1.

[0012] The illustrated internal combustion engine 1 is a four-stroke cycle spark ignition engine, and for example, it is equipped with a turbocharger 11 as a supercharger. Therefore, the intake passage 7 of this internal combustion engine 1 is provided with a compressor 11A of the turbocharger, and a water-cooled intercooler 12 and a throttle valve 13 are arranged downstream of this compressor 11A. Further, an admission valve 14, which is, for example, a butterfly valve for generating a negative pressure in the intake passage 7, is arranged upstream of the compressor 11A in the intake passage 7. The tip of the purge passage 5 is connected to the intake passage 7 between the admission valve 14 and the compressor 11A. Therefore, even in the supercharged region, a negative pressure is generated by the action of the admission valve 14, and purge of the canister 3, that is, introduction of purge gas into the intake passage 7, is possible due to the pressure difference from the atmospheric pressure on the drain passage 6 side.

[0013] Note that the turbine 11B of the turbocharger 11 is located on the relatively upstream side of the exhaust passage 15, and a catalytic device 16 is provided downstream of the turbine 11B. An air flow meter 17 is arranged upstream of the admission valve 14 in the intake passage 7.

[0014] A pair of purge control valves 8, which are solenoid valves, are provided in the purge passage 5 for controlling the purge gas flow rate. Specifically, a part of the purge passage 5 branches into a pair of purge passages 5a and 5b that are parallel to each other, and a first purge control valve 8A and a second purge control valve 8B are arranged respectively. That is, the two purge control valves 8A and 8B are arranged in parallel with each other. Hereinafter, when there is no need to distinguish between the two, they are collectively referred to as the purge control valve 8. In one embodiment, the first purge control valve 8A and the second purge control valve 8B are basically solenoid valves of the same capacity and the same type. The first purge control valve 8A and the second purge control valve 8B may be solenoid valves with different capacities from each other.

[0015] The two purge control valves 8 are duty-controlled by the engine controller 9. The engine controller 9 performs various controls of the internal combustion engine 1 (including fuel injection control, ignition control, throttle valve 13 opening control, admission valve 14 opening control, supercharging pressure control, etc.), performs purge control via the purge control valves 8, and further performs failure diagnosis of the purge system including the two purge control valves 8 as described later.

[0016] In one embodiment, the two purge control valves 8 that are duty-controlled under the same driving frequency are controlled to have the same opening degree (i.e., on-duty ratio) with each other during the operation of the internal combustion engine 1. In this specification, "opening control" means operating the purge control valve 8 with an appropriate on-duty ratio. In other words, it means controlling the opening degree of the purge control valve 8 by duty control to an appropriate opening degree other than 0. "Closing control" means setting the on-duty ratio to 0. Neither means opening and closing in pulse units according to the driving frequency of the duty control. In this way, when purging the canister 3, when the two purge control valves 8 are both under opening control, the purge gas flows in parallel through the two purge control valves 8, and the pressure loss generated in the purge control valves 8 is suppressed. Therefore, a sufficient purge gas flow rate can be ensured with the negative pressure generated by the admission valve 14.

[0017] On the other hand, regarding the control in terms of driving pulse units in the duty control, the first purge control valve 8A and the second purge control valve 8B are driven to open in a form with a 180° different phase. Therefore, microscopically, the first purge control valve 8A and the second purge control valve 8B open and close alternately, and the pressure pulsation generated in the intake passage 7 etc. with the opening and closing of the purge control valve 8 becomes smaller.

[0018] The purge passage 5 is provided with a pressure sensor 18 for detecting the purge passage pressure. Specifically, the pressure sensor 18 is provided within a range between the purge port 3b of the canister 3 and the purge control valve 8 (preferably closer to the canister 3 than the branch portions 5a, 5b), and detects the pressure within the purge passage 5 at a portion on the canister 3 side with respect to the purge control valve 8. Therefore, in a state where the purge control valve 8 is opened for control and purge gas flows from the canister 3 to the intake passage 7, the negative pressure generated by the admission valve 14 is introduced into the purge passage 5, and the pressure detected by the pressure sensor 18 (this is referred to as the purge passage pressure) decreases toward the negative pressure side.

[0019] Next, the failure diagnosis of the two purge control valves 8 will be described. The explanatory diagram in Fig. 3 summarizes the failure diagnosis process of an embodiment into the stage 1 in the left column, the stage 2 in the center, and the diagnosis result in the right column. As shown in the figure, when it is determined that OK (no abnormality) in the diagnosis of stage 1 (the first diagnosis), the diagnosis of stage 2 (the second diagnosis) is not performed and it is determined that there is no failure. When it is determined that NG (abnormality exists) in the diagnosis of stage 1, the diagnosis of stage 2 is executed, and the final diagnosis result is obtained according to the result as described later.

[0020] In this embodiment, the diagnosis of Stage 1 is not particularly specified in terms of the timing of diagnosis execution and is continuously (in other words, repeatedly) performed during normal vehicle driving. In the diagnosis of Stage 1, the purge passage pressure is read while both of the two purge control valves 8 are under open control, and it is determined whether this purge passage pressure is equal to or lower than a first threshold value set on the negative pressure side. This diagnosis is performed on the condition that the on-duty ratio in the open control is equal to or higher than a predetermined diagnosis permission duty ratio (set to a relatively high value near 100%, for example). When it is determined that the purge passage pressure is higher than the first threshold value while both of the two purge control valves 8 are under open control, the NG counter is incremented. If the value of this NG counter reaches a predetermined value during continuous execution of the diagnosis of Stage 1, the diagnosis result of Stage 1 becomes NG, and the diagnosis proceeds to Stage 2.

[0021] In the diagnosis of Stage 2, each of the two purge control valves 8 is controlled to open one by one, and it is determined whether the purge passage pressure in this state is equal to or lower than a second threshold value set on the negative pressure side.

[0022] Figure 2 is a time chart showing the diagnosis of Stage 1 and the diagnosis of Stage 2 in series for easy understanding. In order from the top of the figure, (a) the on-duty ratio of the first purge control valve 8A (abbreviated as PCVA in the figure), (b) the on-duty ratio of the second purge control valve 8B (abbreviated as PCVB in the figure), (c) the purge passage pressure (kPa), (d) the NG counter value, and (e) the open / closed state of the drain cut valve 10 (abbreviated as DCV in the figure) are shown respectively.

[0023] In the diagnosis of stage 1 shown in the first half of the time chart of FIG. 2, as shown in the figure, along with the intermittent operation of the internal combustion engine 1 according to the power demand etc., the first purge control valve 8A and the second purge control valve 8B are simultaneously opened with a duty ratio close to 100%, so the purge passage pressure at that time is compared with the first threshold value Lim1. If the first purge control valve 8A and the second purge control valve 8B are operating normally, as shown by line OK1 in column (c), the purge passage pressure decreases relatively greatly and becomes equal to or lower than the first threshold value Lim1. On the other hand, when the purge passage pressure is higher than the first threshold value Lim1 as shown by line NG1, the NG counter shown in column (d) is incremented. Here, in consideration of the delay in pressure change, the purge passage pressure after an appropriate delay period has elapsed since the start of the opening control of the purge control valve 8 is read and compared with the first threshold value Lim1. Also, as shown in column (e), during the diagnosis of stage 1, the drain cut valve 10 remains open. In other words, the diagnosis of stage 1 is executed while normal purging is being performed.

[0024] As described above, the illustrated example is the internal combustion engine 1 for power generation in a series hybrid vehicle, so the operation of the internal combustion engine 1 is intermittent. In the time chart of FIG. 2, the increase and decrease changes in the duty ratio shown in columns (a) and (b) correspond to the intermittent operation of the internal combustion engine 1. In the illustrated example, since the internal combustion engine 1 is operated under specific operating conditions (load and rotational speed) that result in the best fuel efficiency when the internal combustion engine 1 is operated, basically the duty ratio becomes a substantially constant value of 100% or a value close thereto. When the internal combustion engine 1 is stopped, the duty ratio is 0. Depending on the operating conditions of the internal combustion engine 1, the duty ratio can be a lower value, so if the duty ratio becomes lower than the diagnosis permission duty ratio DL, the diagnosis of stage 1 is not executed. By thus limiting the execution of the diagnosis to the diagnosis permission duty ratio DL or higher, misdiagnosis due to differences in the duty ratio can be avoided.

[0025] In the example of FIG. 2, in the diagnosis of stage 1, every time the internal combustion engine 1 is operated, if it is determined that the purge passage pressure is equal to or lower than the first threshold value Lim1, the NG counter increases. When the NG counter reaches a predetermined value (3 in the illustrated example for explanation), it is determined that there is some failure in the purge system, and the diagnosis proceeds to stage 2. Note that the NG counter value may be reset at the end of the vehicle operation (end of trip), or may be held as it is. By appropriately setting the NG counter value, it is possible to prevent excessive and frequent transitions to stage 2 due to some false detections or the like.

[0026] In the diagnosis of stage 2, as shown in column (e), the drain cut valve 10 is closed. As shown in columns (a) and (b), the first purge control valve 8A and the second purge control valve 8B are each forcibly opened with a relatively high constant on-duty ratio (for example, 100% or in the vicinity thereof). That is, with the on-duty ratio of the second purge control valve 8B set to 0, the on-duty ratio of the first purge control valve 8A is set to, for example, 100%. Then, after an appropriate delay period considering the pressure change delay, the purge passage pressure is read and compared with the second threshold value Lim2 set on the negative pressure side. Next, with the on-duty ratio of the first purge control valve 8A set to 0, the on-duty ratio of the second purge control valve 8B is set to, for example, 100%. Then, after an appropriate delay period, the purge passage pressure is read and compared with the second threshold value Lim2 set on the negative pressure side.

[0027] Note that this diagnosis of stage 2 is executed during the operation of the internal combustion engine 1 that is intermittently operated (that is, under the condition that negative pressure is generated in the intake passage 7). The operation of the internal combustion engine 1 may be actively requested to perform the diagnosis of stage 2.

[0028] If the purge control valves 8A and 8B are operating correctly and negative pressure is introduced from the intake passage 7 to the purge passage 5, as shown by line OK2 in column (c), the purge passage pressure drops relatively significantly and becomes equal to or lower than the second threshold value Lim2. On the other hand, when the purge passage pressure is higher than the second threshold value Lim2, as shown by line NG2, it is determined as an abnormality.

[0029] In one embodiment, considering that one of the purge control valves 8 is closed, the second threshold value Lim2 is set to a pressure relatively higher (a negative pressure closer to atmospheric pressure) than the first threshold value Lim1. However, the present invention is not limited to this, and it can be optimally set respectively considering various conditions during diagnosis.

[0030] Also, in the above example, during the diagnosis at stage 2, by closing the drain cut valve 10, the purge system including the canister 3 is sealed, and negative pressure is introduced into this sealed space through the purge control valve 8. Therefore, the drop in the purge passage pressure when the purge control valve 8 and the like are normal occurs more reliably. For example, even when the negative pressure generated by the admission valve 14 is relatively weak, high diagnostic accuracy can be obtained.

[0031] As shown in FIG. 2, in the diagnosis at stage 2 of the illustrated example, the forced opening control of the first purge control valve 8A and the second purge control valve 8B is performed only once each to determine the presence or absence of an abnormality. However, after repeatedly performing each opening control and pressure determination a plurality of times, the final presence or absence of an abnormality may be determined.

[0032] Next, based on the explanatory diagram of FIG. 3, the finally obtained diagnostic result will be described. First, if there is no abnormality in the diagnosis of stage 1, that is, if the purge passage pressure is equal to or less than the first threshold value Lim1, as described above, the final diagnosis is "no failure" without performing the diagnosis of stage 2. On the other hand, when it is determined that there is some failure in the diagnosis of stage 1 (the NG counter value has reached a predetermined value), the diagnosis of stage 2 is executed as described above. In the diagnosis of stage 2, as long as there is no misdiagnosis due to some factor, when the diagnosis of the first purge control valve 8A is normal and the diagnosis of the second purge control valve 8B is abnormal, when the diagnosis of the second purge control valve 8B is normal and the diagnosis of the first purge control valve 8A is abnormal, or when the diagnoses of both the first purge control valve 8A and the second purge control valve 8B are abnormal, it will be any one of these three cases.

[0033] As shown in FIG. 3, when the diagnosis of the first purge control valve 8A is normal (OK) and the diagnosis of the second purge control valve 8B is abnormal (NG) in the diagnosis of stage 2, the final diagnosis is that the second purge control valve 8B is stuck closed or the passage (purge passage 5b) before and after it is clogged. When the diagnosis of the second purge control valve 8B is normal (OK) and the diagnosis of the first purge control valve 8A is abnormal (NG), the final diagnosis is that the first purge control valve 8A is stuck closed or the passage (purge passage 5a) before and after it is clogged. When the diagnoses of both the first purge control valve 8A and the second purge control valve 8B are abnormal (NG), the final diagnosis is that both the purge passages 5a and 5b (or the purge passage 5 in the non-branched part) are clogged, or the two purge control valves 8 are stuck closed, or there is a leak in the purge system (that is, inflow of air) due to disconnection of the hose, etc.

[0034] In the case of any failure, a failure code corresponding to each is generated and stored in the memory of the engine controller 9. Also, in order to notify that there is a failure, for example, the warning light (MIL) on the driver's seat is turned on.

[0035] As described above, in the fault diagnosis of the above embodiment, the diagnosis of stage 1 is executed during the operation of the normal internal combustion engine 1. In the diagnosis of this stage 1, the purge from the canister 3 continues as usual. And until it is diagnosed that there is some fault in the diagnosis of stage 1, the diagnosis of stage 2 is not executed, so the purge from the canister 3 is not impaired by the fault diagnosis.

[0036] In addition, in a series hybrid vehicle or the like where the operation frequency of the internal combustion engine 1 is low, since the opportunity for purging the canister 3 is small, it is not preferable that the purge is impaired by the fault diagnosis. In the fault diagnosis of the above embodiment, basically there is no influence on the purge.

[0037] As described above, one embodiment of the present invention has been described in detail. However, the present invention is not limited to the above embodiment, and various modifications are possible. In the above embodiment, an example applied to the internal combustion engine for power generation in a series hybrid vehicle has been described. However, the present invention can be similarly applied to vehicles other than series hybrid vehicles, that is, vehicles in which the internal combustion engine serves as the vehicle driving power source. Also, it can be similarly applied when three or more purge control valves are provided. In addition, if it is a naturally aspirated internal combustion engine, the negative pressure generated downstream of the throttle valve can be utilized.

Claims

1. A method for diagnosing a failure of an evaporative fuel processing apparatus in which a plurality of purge control valves are arranged in parallel with each other in a purge passage between a canister and an intake system of an internal combustion engine, comprising: performing a first diagnosis on the purge system based on the pressure of the purge passage when the plurality of purge control valves are all under open control; when it is determined in this first diagnosis that there is a failure in the purge system, opening the plurality of purge control valves one by one, and performing a second diagnosis for identifying the failure location based on the pressure of the purge passage in each state; A method for diagnosing a failure of an evaporative fuel processing apparatus.

2. In the first diagnosis, it is determined as abnormal when the pressure of the purge passage is higher than a first threshold value on the negative pressure side, and in the second diagnosis, it is determined as abnormal when the pressure of the purge passage is higher than a second threshold value on the negative pressure side, and the first threshold value is set to a pressure lower than the second threshold value, The method for diagnosing a failure of an evaporative fuel processing apparatus according to claim 1.

3. The first diagnosis is performed on the condition that the on-duty ratio of each purge control valve is equal to or higher than a diagnosis permission duty ratio. The method for diagnosing a failure of an evaporative fuel processing apparatus according to claim 1.

4. In the second diagnosis, when the purge passage pressure during the open control of any one of the purge control valves is abnormal and the purge passage pressure during the open control of the other purge control valves is not abnormal, it is identified that the one purge control valve has failed. The method for diagnosing a failure of an evaporative fuel processing apparatus according to claim 1.

5. In the second diagnosis, when the purge passage pressure during the open control of all the purge control valves is abnormal, it is identified that all the purge control valves have failed or there is a leak in the purge passage. The method for diagnosing a failure of an evaporative fuel processing apparatus according to claim 1.

6. When performing the second diagnosis, the drain passage of the canister is closed. The method for diagnosing a failure of an evaporative fuel processing apparatus according to claim 1.

7. A failure diagnosis device for an evaporative fuel processing apparatus, comprising a canister to which a charge port is connected to a fuel tank, a purge passage connecting the purge port of the canister and the intake system of the internal combustion engine and having a plurality of purge control valves arranged in parallel with each other, and a pressure sensor provided in the purge passage, performing a first diagnosis on the purge system based on the pressure of the purge passage when the plurality of purge control valves are all under open control; If it is determined in this first diagnosis that there is a failure in the purge system, a second diagnosis is performed to identify the failure location based on the pressure in the purge passage in each state by controlling the opening of a plurality of purge control valves one by one, a failure diagnosis device for an evaporative fuel processing device.

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