JP2004270501A - Evaporated fuel treating device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To diagnose leakage for an evaporated fuel treating device without deteriorating operability and exhaust gas emission, and to increase frequency of leak diagnosis. <P>SOLUTION: The evaporated fuel treating device for an internal combustion engine is provided with a bypass passage 8 connecting a fuel tank 3 and an intake pipe 6 while passing around a canister 2, and a bypass valve 13 for opening and closing the bypass passage 8. Upon diagnosing the leakage, depending on operation conditions of the engine, a leak diagnosis with negative pressure introduced from the bypass passage 8 or a leak diagnosis with negative pressure introduced form a purge passage 7 is selectable. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an evaporative fuel processing apparatus for an internal combustion engine, and more particularly to an evaporative fuel processing apparatus for an internal combustion engine that performs a leak diagnosis by introducing a negative pressure in an intake pipe.
[0002]
[Prior art]
The evaporative fuel processing device of the internal combustion engine temporarily adsorbs the evaporative fuel generated in the fuel tank to the canister, and desorbs the adsorbed evaporative fuel by using the suction negative pressure according to the operating condition of the engine, The desorbed fuel vapor is sucked into an intake pipe of the engine to perform a combustion process. In order to prevent evaporative fuel from being directly released into the atmosphere due to a poor sealing at a pipe joint or the like, there is known an apparatus that diagnoses the presence or absence of a leak in an apparatus (for example, see Patent Document 1).
[0003]
[Patent Document 1]
JP-A-2002-161814
[Problems to be solved by the invention]
However, in the conventional evaporative fuel processing apparatus as described in Patent Document 1, by opening a purge control valve provided in a purge passage that connects the canister and the intake pipe, the inside of the intake pipe is removed from the purge passage. Since the leak diagnosis is performed by introducing the negative pressure into the apparatus, there are the following problems.
[0005]
That is, when the negative pressure is introduced, the gas in the device is sucked into the intake pipe, and if a leak diagnosis is performed in a state where a large amount of fuel vapor is adsorbed in the canister, a rich air-fuel mixture is generated in the intake pipe. The exhaust A / F is greatly shifted due to the air being sucked, and the operability and the exhaust emission are deteriorated.
[0006]
For this reason, the evaporated fuel generated in the fuel tank is adsorbed after the engine is stopped, and immediately after the start of the cold operation, where a large amount of the evaporated fuel is likely to be adsorbed to the canister, the adsorbed evaporated fuel is desorbed to some extent. It is necessary to perform the leak diagnosis afterwards (that is, after the purging process has been performed to some extent), which has been an obstacle in increasing the frequency of the leak diagnosis.
[0007]
The present invention has been made in order to solve the above-described conventional problems, and performs a leak diagnosis without deteriorating operability and exhaust emission even at the time of cold start in which a large amount of evaporative fuel is adsorbed in a canister. Accordingly, it is an object of the present invention to provide an evaporative fuel processing apparatus for an internal combustion engine which can improve the frequency of diagnosis.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, an evaporative fuel treatment apparatus according to the present invention includes a bypass passage that bypasses a canister and communicates with a fuel tank and an intake pipe, and a bypass valve that opens and closes this bypass passage. First leak diagnosis means for performing a leak diagnosis by introducing a negative pressure in the intake pipe from the bypass passage by opening the bypass valve with the cut valve and the purge control valve closed, a drain cut valve and a bypass valve A second leak diagnosis means for performing a leak diagnosis by introducing a negative pressure in the intake pipe from the purge passage by opening the purge control valve in a state where the valve is closed, and a first leak diagnosis according to the operating conditions of the engine. And means for selecting either one of the means and the second leak diagnosis means.
[0009]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to the evaporative fuel processing apparatus for an internal combustion engine according to the present invention, when performing a leak diagnosis, the leak diagnosis is performed by selecting a leak diagnosis unit that does not affect the drivability and exhaust emission according to the operating conditions of the engine. It can be carried out.
[0010]
For example, when the canister is likely to adsorb a large amount of evaporative fuel and the generation of evaporative fuel in the fuel tank is small, for example, at the time of cold start, the first leak diagnostic means is selected and the bypass passage is selected. The leak diagnosis is performed by introducing a negative pressure from the fuel tank side. On the other hand, after a certain period of time has elapsed from the start of the engine, the amount of fuel vapor generated in the fuel tank increases, but the fuel vapor adsorbed in the canister is purged and reduced. In such a case, the second leak diagnosing means is selected, and a negative pressure is introduced from the canister side through the purge passage to perform a leak diagnosis as in the related art. As described above, since the leak diagnosis can be changed according to the operating conditions, it is possible to prevent a rich air-fuel mixture from being sucked into the intake pipe at the time of the leak diagnosis, and to suppress deterioration in operability and exhaust emission. In addition, the leak diagnosis can be performed even at the time of cold start, where the leak diagnosis could not be performed conventionally, and the diagnosis frequency can be improved.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram of an evaporative fuel processing apparatus for an internal combustion engine according to an embodiment of the present invention. As shown in the figure, the evaporative fuel processing apparatus 1 communicates a canister 2, an evaporative fuel passage 4 that communicates the canister 2 with a fuel tank 3, and an intake pipe 6 downstream of the canister 2 and a throttle valve 5. And a bypass passage 8 that bypasses the canister 2 and communicates with the fuel tank 3 and the intake pipe 6.
[0012]
The canister 2 contains an adsorbent such as activated carbon, and the evaporative fuel generated in the fuel tank 3 is guided by the evaporative fuel passage 4 to be temporarily adsorbed. An atmosphere communication passage 10 communicating with the atmosphere via a water separation box 9 is connected to an atmosphere communication port provided in the canister 2. The atmosphere communication passage 10 is constituted by a normally open solenoid valve. A drain cut valve 11 is provided. That is, by opening and closing the drain cut valve 11, the atmosphere communication port of the canister 2 communicates with the atmosphere or is shut off. The drain cut valve 11 is energized and closed when a predetermined condition is satisfied.
[0013]
The purge passage 7 is provided with a purge control valve 12 composed of a normally closed solenoid valve. Then, when the purge control valve 12 is energized and opened, the suction negative pressure in the intake pipe 6 acts on the canister 2 and air is introduced into the canister 2 from the atmosphere communication passage 10. The evaporative fuel adsorbed on the canister 2 is desorbed by the introduced atmosphere, and a purge gas containing the desorbed evaporative fuel is sucked into the intake pipe 6 through the purge passage 7, and thereafter, the combustion of the engine is performed. It is burned (purged) in the room.
[0014]
Further, as a characteristic configuration of the present embodiment, a bypass passage 8 that bypasses the canister 2 (without passing through) and directly communicates the fuel tank 3 with the intake pipe 6 is provided. Is provided with a bypass valve 13 composed of a normally closed solenoid valve. In this embodiment, the fuel tank 3 and the intake pipe 6 are communicated with each other by the bypass passage 8 that connects the upper surface of the fuel tank 3 and the purge passage 7 on the intake pipe 6 side of the purge control valve 12. A configuration may be adopted in which the upper surface of the tank 3 and the intake pipe 6 downstream of the throttle valve 5 are connected by a bypass passage.
[0015]
A control unit (C / U) 20 incorporating a microcomputer has a pressure sensor (pressure detecting means) for detecting a pressure P in the device (more specifically, a bypass valve 13 to a fuel tank 3 to a purge control valve 12). ) 21, a temperature sensor (fuel temperature detecting means) 22 for detecting the fuel temperature Tf in the fuel tank 3, a water temperature sensor (water temperature detecting means) 23 for detecting the cooling water temperature Tw of the engine, and other various sensors (not shown). The detection signal has been input.
[0016]
The C / U 20 performs various controls on the engine and controls the purge control valve 12 according to the operating conditions of the engine to process the evaporated fuel adsorbed on the canister 2. Further, a leak diagnosis for diagnosing the presence or absence of a leak in the fuel vapor treatment apparatus 1 is performed by controlling the drain cut valve 11, the purge control valve 12, and the bypass valve 13.
[0017]
Here, the leak diagnosis according to the present embodiment executed by the C / U 20 will be described with reference to the flowcharts shown in FIGS. Note that such a diagnosis flow is executed every predetermined time (for example, every 100 ms).
[0018]
In step 1 (referred to as S1 in the figure, the same applies hereinafter), it is determined whether the cooling water temperature Tw at the time of starting is lower than a predetermined temperature (for example, set at 30 to 40 ° C.), and if it is lower than the predetermined temperature. If so, go to step 2. By this step, it is possible to determine whether the engine is to be started immediately after the stop, which is likely to generate fuel vapor in the fuel pump 3, or to start after a while after the stop.
[0019]
In step 2, it is determined whether the fuel temperature Tf in the fuel tank 3 is lower than a predetermined temperature (for example, set at 20 to 30 ° C.), and if it is lower than the predetermined temperature, the process proceeds to step 3. By this step, it is possible to determine whether or not the fuel vapor is generated in the fuel tank 3 (or the amount of fuel vapor generated).
[0020]
In step 3, it is determined whether or not the elapsed time from the start of the engine is shorter than a predetermined time T1, and if not, the process proceeds to step 4. By this step, it can be determined that the purge process has hardly been performed after the start, that is, a state in which there is a high possibility that a large amount of fuel is adsorbed in the canister 2.
[0021]
Steps 1 to 3 correspond to the selection means according to the present invention, and when the conditions of steps 1 to 3 are satisfied, a suction diagnosis is performed by introducing a suction negative pressure through the bypass passage 8 from step 4 onward. Leak diagnosis).
[0022]
It should be noted that, similarly to the fuel temperature itself, the increase in the fuel temperature also has a large contribution to the generation and amount of fuel vapor in the fuel tank 3, so that the fuel temperature increases from the start (current fuel temperature- The fuel temperature may be lower than a predetermined temperature.
[0023]
In step 4, while the drain cut valve 11 and the purge control valve 12 are closed, the bypass valve 13 is opened to start pull-down (introducing negative pressure). Thereby, the suction negative pressure in the intake pipe 6 is introduced through the bypass passage 8, and the inside of the device is made negative pressure. When the engine is started, the purge control valve 12 is normally in a closed state.
[0024]
After the pull-down is started, it is determined in step 5 whether a predetermined time T2 set in advance has elapsed, and in step 6, the internal pressure P detected by the pressure sensor 21 has reached the target negative pressure. Is determined (whether the pressure has become equal to or lower than the target negative pressure). If the target negative pressure has not been reached, pull-down is continued, and if the target pressure has been reached, the routine proceeds to step 8. If the internal pressure P does not reach the target negative pressure before the predetermined time T2 elapses, the routine proceeds to step 7, where "leakage" is diagnosed, and this control is terminated.
[0025]
In step 8, the bypass valve 13 is closed and the leak down is started. By closing the bypass valve 13, the inside of the apparatus is sealed. Therefore, when no leak is generated in the canister 2, the fuel tank 3, the pipes, and the like, the negative pressure in the device is maintained. However, when a leak is generated, the negative pressure in the device is gradually reduced. Will change.
[0026]
In step 9, it is determined whether or not a leak-down ending condition (for example, a predetermined time T3 has elapsed from the start of the leak-down) is satisfied. If the leak-down ending condition is satisfied, the process proceeds to steps 10 and 14. move on.
[0027]
In step 10, a change ΔP of the internal pressure of the apparatus with respect to the elapsed time from the start of the leak down, that is, a deviation between the internal pressure at the start of the leak down and the internal pressure at the lapse of the predetermined time T3, is calculated as a parameter for leak diagnosis. I do.
[0028]
In step 11, the calculated leak diagnosis parameter is compared with an evaluation reference value (criterion) set in advance. If the change ΔP in the internal pressure of the apparatus is larger than the evaluation reference value, the routine proceeds to step 12, where it is diagnosed that “there is a leak”. In this case, the driver is notified by turning on the warning light. On the other hand, if the change ΔP in the internal pressure of the apparatus is equal to or smaller than the evaluation reference value, the process proceeds to step 13 and diagnoses as “no leak”. Steps 4 to 13 described above correspond to a first leak diagnosis unit according to the present invention.
[0029]
In step 14, in parallel with the leak diagnosis, the drain cut valve 11 and the purge control valve 12 are opened, the normal purge control is returned, and the present control is terminated.
[0030]
FIG. 5 is a timing chart of the first leak diagnosis described above.
The drain cut valve 11 and the purge control valve 12 are closed, and the pull-down is started by opening the bypass valve 13, and the pressure is reduced until the internal pressure of the apparatus reaches the target negative pressure (for example, -20 mmHg). Thereafter, the bypass valve 13 is closed to start the leak down. When a leak occurs, the pressure in the device increases (negative pressure decreases) as indicated by the broken line in the figure, while when no leak occurs, the pressure in the device hardly changes. Therefore, the leak diagnosis is performed as described above.
[0031]
When the cold start is performed, the fuel vapor generated in the fuel tank 3 after the stop of the engine is likely to cause a large amount of fuel vapor to be adsorbed to the canister 2. Has not occurred. For this reason, when the pull-down is performed from the fuel tank 3 side by the bypass passage 8, the influence on the exhaust A / F at the time of pull-down is performed via the purge passage 7, that is, a second leak diagnosis (described later) (Indicated by a dashed line)).
[0032]
Returning to FIG. 2, when the conditions of the above steps 1 to 3 are not satisfied, the suction negative pressure is introduced through the purge passage 7 from step 15 onward (FIG. 4), and the same leak diagnosis as the conventional one (the second leak diagnosis) is performed. Diagnosis).
[0033]
First, in step 15, it is determined whether or not a predetermined leak diagnosis condition is satisfied. If the leak diagnosis condition is satisfied, the process proceeds to step 16, and if not, the control ends. In order to prevent erroneous diagnosis due to sudden generation of evaporative fuel or the like, it is assumed that the engine speed is equal to or lower than a predetermined value, the vehicle speed is equal to or lower than a predetermined speed, and the like.
[0034]
In step 16, while the drain cut valve 11 is closed, the purge control valve 12 is opened and pull-down (introduction of negative pressure) is started. At this time, the bypass valve 13 is in the closed state. As a result, the suction negative pressure in the intake pipe 6 is introduced through the purge passage 7, and the inside of the device is made negative as in the first leak diagnosis.
[0035]
Steps 17 to 19 after the start of the pull-down are the same as steps 5 to 7 described above. When the internal pressure P detected by the pressure sensor 21 reaches the target negative pressure, the process proceeds to step 20.
[0036]
In step 20, the purge control valve 12 is closed and the leak down is started.
Steps 21 to 26 are the same as steps 10 to 14 described above. When the leak-down ending condition is satisfied, a leak diagnosis is performed by calculating a leak diagnosis parameter, and the drain cut valve 11 and the purge control valve 12 is opened to return to normal purge control, and this control is ended.
[0037]
Steps 15 to 25 described above correspond to a second leak diagnosis unit according to the present invention, and a timing chart of the second leak diagnosis is shown in FIG.
As described above, in the present embodiment, the bypass passage 8 that connects the fuel tank 3 and the intake pipe 6 without passing through the canister 2, the bypass valve 13 that opens and closes the bypass passage 8, When a cold start is performed, a suction diagnosis is performed by introducing a suction negative pressure into the device through the bypass passage 8 (first leak diagnosis). In other cases, the purge passage 7 is provided similarly to the conventional case. A leak diagnosis (second leak diagnosis) is performed by introducing a suction negative pressure into the device through the.
[0038]
That is, at the time of cold start, a negative pressure in the intake pipe 6 is introduced from the fuel tank 3 side where almost no evaporative fuel is generated by the bypass passage 8 which does not pass through the canister 2 where a large amount of evaporative fuel is adsorbed. Since the leak diagnosis (first leak diagnosis) is performed, the influence on the exhaust A / F at the time of pull-down can be suppressed, and the deterioration of drivability and exhaust emission can be prevented. As a result, the leak diagnosis can be performed even at the time of cold start where the leak diagnosis cannot be performed conventionally, and the frequency of the diagnosis can be greatly improved.
[0039]
Further, the first leak diagnosis is performed when the cooling water temperature Tw of the engine is lower than the predetermined temperature, when the fuel temperature Tf in the fuel tank 3 is lower than the predetermined temperature, and when the elapsed time from the start is lower than the predetermined time T1. Thus, the first leak diagnosis can be performed after confirming a state in which the amount of fuel vapor generated in the fuel tank 3 is small. As a result, deterioration of drivability and exhaust emission can be more effectively prevented.
[0040]
Further, since the bypass passage 8 is connected to the upper surface of the fuel tank 3, the negative pressure in the intake pipe 5 can be introduced into the device from the bypass passage 12 regardless of the amount of fuel.
[0041]
In the first leak diagnosis, a negative pressure in the intake pipe 6 is introduced by opening the bypass valve 13 in a state in which the drain cut valve 11 and the purge control valve 12 are closed, and the pressure in the device becomes a predetermined value. When the pressure falls below the pressure, the bypass valve 13 is closed to close the inside of the device, so that the presence or absence of a leak can be diagnosed based on a subsequent pressure change, that is, a pressure change with respect to an elapsed time after the valve is closed.
[0042]
Further, if the pressure in the apparatus does not decrease below the predetermined pressure by the elapse of the predetermined time T2 from the start of the introduction of the negative pressure into the apparatus, it is determined (diagnosed) that there is a leak. It can be carried out.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an evaporative fuel processing apparatus according to an embodiment of the present invention.
FIG. 2 is a flowchart illustrating a leak diagnosis process of the evaporated fuel processing device.
FIG. 3 is a flowchart showing a leak diagnosis process.
FIG. 4 is a flowchart showing a leak diagnosis process.
FIG. 5 is a timing chart of a first leak diagnosis.
FIG. 6 is a timing chart of a second leak diagnosis.
[Explanation of symbols]
2 canister, 3 fuel tank, 4 evaporative fuel passage, 6 intake pipe, 7 purge passage, 8 bypass passage, 11 drain cut valve, 12 purge control valve, 13 bypass valve, 20 control Unit, 21: Pressure sensor, 22: Fuel temperature sensor, 23: Water temperature sensor

Claims (8)

A canister having an atmosphere communication port; a drain cut valve for opening and closing the atmosphere communication port; an evaporative fuel passage communicating the canister with a fuel tank; a purge passage communicating the canister with an intake pipe; and a purge passage. A purge control valve that opens and closes the fuel vapor treatment device for an internal combustion engine,
A bypass passage bypassing the canister and communicating the fuel tank with the intake pipe;
And a bypass valve for opening and closing the bypass passage.
A first leak diagnosis for diagnosing a leak by introducing a negative pressure in the intake pipe from the bypass passage by opening the bypass valve in a state where the drain cut valve and the purge control valve are closed. Means,
A second leak diagnosis for diagnosing the presence or absence of a leak by introducing the negative pressure in the intake pipe from the purge passage by opening the purge control valve with the drain cut valve and the bypass valve closed. Means,
Selecting means for selecting either the first leak diagnosing means or the second leak diagnosing means in accordance with operating conditions of the engine;
An evaporative fuel processing apparatus for an internal combustion engine, comprising: 2. The apparatus according to claim 1, wherein the selection unit selects the first leak diagnosis unit at the time of cold start. Water temperature detection means for detecting the temperature of the cooling water of the engine,
3. The apparatus according to claim 2, wherein the selection unit selects the first leak diagnosis unit when the detected coolant temperature is lower than a predetermined temperature. Fuel temperature detecting means for detecting the fuel temperature in the fuel tank,
4. The apparatus according to claim 2, wherein the selection unit selects the first leak diagnosis unit when the detected fuel temperature is lower than a predetermined temperature. The evaporative fuel processing apparatus for an internal combustion engine according to any one of claims 2 to 4, wherein the selection unit selects the first leak diagnosis unit until a predetermined time has elapsed from the start of the engine. The apparatus according to claim 1, wherein the bypass passage is connected to an upper surface of the fuel tank. A pressure detecting means for detecting a pressure in the device,
The first leak diagnosing means closes the bypass valve when the detected pressure falls below a predetermined pressure, and diagnoses the presence or absence of a leak based on a pressure change with respect to an elapsed time since the closing. The fuel vapor treatment device for an internal combustion engine according to any one of claims 1 to 6. 8. The apparatus according to claim 7, wherein the first leak diagnosis unit diagnoses that there is a leak when the internal pressure of the apparatus does not decrease to the predetermined pressure or less before a predetermined time elapses after opening the bypass valve. A fuel vapor treatment device for an internal combustion engine according to claim 1.

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