JPH05223018A - Evaporation purge system - Google Patents

Abstract

PURPOSE:To restrain vapor from being emitted to the atmosphere in an evapora tion purge system in which evaporated fuel in an internal combustion engine is adsorbed onto adsorbent in a canister, and thus adsorbed fuel is purged into the intake system of the internal combustion engine under a predetermined operating condition so as to be burnt. CONSTITUTION:The presence of leakage is detected if the variation rate of pressure in an evaporation purge system, when a vacuum is tightly held in the system for predetermined time, is higher than beta (step 101 to 11), and then a cut-off inhibiting flag is set (step 119) so as to inhibit the cut-off of a tank internal pressure change-over valve (VSV) so as to hold the opening condition of the tank internal pressure change-over valve (VSV).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention adsorbs evaporated fuel (vapor) of an internal combustion engine to an adsorbent in a canister, and releases the adsorbed fuel (purge) to an intake system of the internal combustion engine under predetermined operating conditions. The present invention relates to an evaporative purge system for burning, and more particularly to an evaporative purge system including a device for diagnosing a failure of the evaporative purge system.

[0002]

2. Description of the Related Art Fuel evaporated in a fuel tank (vapor)
In order to prevent air from being released to the atmosphere, each part is hermetically sealed, and the vapor is once adsorbed by the adsorbent in the canister, and the fuel adsorbed while the vehicle is running is sucked into the intake system and burned by an evaporative purge. In an internal combustion engine equipped with a system, the pressure in the fuel tank (tank internal pressure) is set to a positive pressure in order to suppress the generation of vapor during normal operation (for example, JP-A-1-151747). ..

Further, in such an internal combustion engine, when the vapor passage is damaged or the pipe is disconnected for some reason, the vapor is released to the atmosphere, and when the purge passage to the intake system is blocked. , The vapor in the canister overflows, and the vapor leaks to the atmosphere from the canister atmosphere introduction port. Therefore, it is necessary to diagnose whether such a failure of the evaporative purge system has occurred.

Therefore, the present applicant previously filed Japanese Patent Application No. 3-138.
No. 002 has a first control valve that opens and closes a purge passage that purges the evaporated fuel stored in the canister into the intake system of the internal combustion engine, and a second control valve that opens and closes an atmospheric hole of the canister. After closing the second control valve during failure diagnosis,
Failure diagnosis of the evaporative purge system that waits until a predetermined negative pressure is reached, closes the first control valve, maintains the airtightness for a predetermined time, and diagnoses the occurrence of a failure based on the degree of change in pressure at that time. Proposed a device.

[0005]

However, for example, in the evaporative purge system equipped with the above-mentioned failure diagnosis device, a device for setting the tank internal pressure to a positive pressure as in the above-mentioned JP-A-1-151747 is provided. When there is a leakage failure, the fuel vapor is released to the atmosphere from the leakage point when the tank internal pressure is returned to the normal state where it is maintained at a positive pressure after the failure diagnosis is completed. At this time, the leak amount of the fuel vapor increases as the differential pressure with the atmosphere increases in the same leak area.

The present invention has been made in view of the above points, and it is an object of the present invention to provide an evaporation purge system that solves the above problems by setting the tank internal pressure to atmospheric pressure when a leak failure is detected.

[0007]

FIG. 1 is a block diagram showing the principle of the present invention. In the figure, the failure diagnosis device of the present invention causes the evaporated fuel from the fuel tank 10 to be adsorbed by the adsorbent in the canister 12 through the vapor passage 11 and the adsorbed fuel in the canister 12 through the purge passage 13 during a predetermined operation. Evaporative Purge System 1 for purging 9 of intake passage 14
At the appropriate time during operation of the internal combustion engine, the internal pressure control valve 1
The valve 9 is opened to provide a failure diagnostic device 18 for determining the presence / absence of a failure of the evaporative purge system 1 and a passage between the fuel tank 10 and the inside of the canister 12, and the pressure inside the fuel tank 10 is controlled by the internal combustion engine 9. During operation, the internal pressure control valve 19 that controls the positive pressure and the valve opening means 20 that forcibly holds the internal pressure control valve 19 in the substantially open state when the failure diagnosis device 18 determines that there is a leakage failure. It is characterized by having and.

[0008]

In the present invention, the internal pressure control valve 19 keeps the internal pressure of the fuel tank 10 at a predetermined positive pressure during normal operation and suppresses the evaporation of the fuel in the fuel tank 10. The evaporation purge system 1 causes the evaporated fuel from the fuel tank 10 to be adsorbed by the adsorbent in the canister 12 through the vapor passage 11 and the adsorbed fuel in the canister 12 through the purge passage 13 into the intake passage 14 of the internal combustion engine 9 during a predetermined operation. Purge. The failure diagnosis device 18 opens the internal pressure control valve 19 at an appropriate time during operation to connect the intake passage 14 to the fuel tank 10 and then to the evaporative purge system 1
Diagnose whether there is any failure. At this time, the failure diagnosis device 18
If it is determined that there is a leakage failure by the valve opening means 20
As a result, the internal pressure control valve 19 is forcibly brought into a substantially open valve holding state, so that the pressure in the fuel tank 10 is not in the normal positive pressure state, but is brought to atmospheric pressure through the internal pressure control valve 19.

[0009]

FIG. 2 shows a system configuration diagram of an embodiment of the present invention. In the figure, after the air cleaner 22 measures the amount of intake air of the air from which dust and dirt in the atmosphere have been removed, the flow rate thereof is controlled by the throttle valve 25 in the intake pipe 24. Further, it flows through a surge tank 26 and an intake manifold 27 (which constitutes the intake passage 14 together with the intake pipe 24) into a combustion chamber (both not shown) of the internal combustion engine during a period in which the intake valve is open.

The opening of the throttle valve 25 is controlled in conjunction with an accelerator pedal (not shown), and the opening is detected by a throttle position sensor 28. Further, a fuel injection valve 29 is provided for each cylinder so that a part thereof projects into the intake manifold 27. The fuel injection valve 29 injects the fuel 31 in the fuel tank 30 into the air flow passing through the intake manifold 27 for a time designated by the microcomputer 21.

The fuel tank 30 is the fuel tank 10 described above.
Corresponding to, the fuel 31 is stored, and the vaporized fuel (vapor) generated inside is delivered to 32d of the vapor passages 32a to 32d (corresponding to the vapor passage 11). The canister 33 (corresponding to the canister 12 described above) is filled with an adsorbent such as activated carbon inside, and an air hole 34 is partially provided.

The atmosphere hole 34 is communicated with a canister atmosphere hole vacuum switching valve (VSV) 36 through an atmosphere passage 35. Canister vent V
The SV 36 is a control valve that connects or disconnects the atmosphere introducing hole 36 a and the atmosphere passage 35 based on a control signal from the microcomputer 21.

The canister 33 is in communication with the purge side VSV 38 via a purge passage 37. The purge-side VSV 38 is a control valve that connects or disconnects the other end of the purge passage 39, one end of which communicates with the surge tank 26, and the other end of the purge passage 37, based on a control signal from the microcomputer 21.

The pressure sensor 40 is provided in the middle of the vapor passage 32d, and detects the pressure in the vapor passage 32d to substantially detect the pressure in the space in the fuel tank 30 (tank internal pressure). The fuel tank internal pressure control valve 41 is a mechanical control valve that connects (opens) or shuts off the vapor passages 32a, 32c, and 32d. Is a value in the positive pressure direction, the diaphragm 41b
Are positioned as shown in the figure and the vapor passages 32a, 32c and 3
2d, and when the tank internal pressure has a value in the negative pressure direction from the set pressure of the spring 41a, the diaphragm 41
b moves downward to shut off between the vapor passages 32a and 32c and 32d. As a result, the tank internal pressure is maintained at a positive pressure, and the vapor generation amount is suppressed as low as possible. In addition,
Reference numeral 41c is an atmosphere opening port.

Further, in order to bypass the inlet and outlet of the fuel tank internal pressure control valve 41 via the vapor passages 32b and 32c, and to conduct (open) or cut off between the vapor passages 32b and 32c. The tank internal pressure switching valve (VSV) 42 is provided, and the tank internal pressure switching valve 42 is switched and controlled by the microcomputer 21. As will be described later, in the case of failure diagnosis of the evaporative purge system, after introducing a predetermined negative pressure into the fuel tank 30, VS
This is because it is necessary to close the V36 and V38, maintain the closed state for a predetermined time, and observe the pressure change in the held state. The warning lamp 43 is provided to notify the driver of the abnormality when the microcomputer 21 detects the abnormality.

In such a structure, the vapor generated in the fuel tank 30 is adsorbed to the activated carbon in the canister 33 via the vapor passages 32d and 32c, the tank internal pressure switching valve 42 which is in an open state at the time of purging, and the vapor passage 32b. As a result, release to the atmosphere is prevented. Normally, the canister atmosphere hole VSV36 is opened, and the purge side VSV38 is also opened when the evaporation purge system is operating. As a result, the negative pressure of the intake manifold 27 is used during the operation to allow the canister atmosphere hole VSV to flow from the atmosphere introduction port 36a.
The atmosphere is introduced into the canister 33 through the atmosphere passage 36 and the atmosphere passage 35.

Then, the fuel adsorbed on the activated carbon is desorbed, and the fuel is purged by the purge passage 37 and the purge side VSV3.
8 and the purge passage 39, respectively, to be sucked into the surge tank 26. In addition, the activated carbon is regenerated by the above desorption and prepared for the next adsorption of vapor.

Further, since the tank internal pressure switching valve 42 is closed during the normal operation of the internal combustion engine, the fuel tank 3
0 and the canister 33 are communicated with each other through the vapor passage 32d, the fuel tank internal pressure control valve 41, and the vapor passage 32d.

The microcomputer 21 is a control device for realizing the above-mentioned failure diagnosis and valve opening means 20 by software processing, and has a known hardware configuration as shown in FIG. 2, those parts which are the same as those corresponding parts in FIG. 2 are designated by the same reference numerals, and a description thereof will be omitted. In FIG. 3, a microcomputer 21 includes a central processing unit (CPU) 50 and a read only memory (RO) storing a processing program.
M) 51, random access memory (RAM) 52 used as a work area, backup RAM 53 that retains data even after the engine is stopped, input interface circuit 54 with multiplexer, A / D converter 56, input / output interface circuit 55, etc. , Which are connected via a bus 57.

The input interface circuit 54 receives the intake air amount detection signal from the air flow meter 23, the detection signal from the throttle position sensor 28, the pressure detection signal from the pressure sensor 40, etc. in parallel, and switches these input signals in sequence. And time-sequentially synthesizes it to form a serial signal, which is supplied to a single A / D converter 56 and analog
The signals are digitally converted and sequentially sent to the bus 57.

The input / output interface circuit 55 receives the detection signal from the throttle position sensor 28 and inputs it to the CPU 50 via the bus 57, while the bus 5 receives it.
Each signal inputted from 7 is selectively sent to the fuel injection valve 29, the canister atmosphere hole VSV 36, the purge side VSV 38, the tank internal pressure switching valve 42 and the warning lamp 43 to control them.

The CPU 50 of the microcomputer 21 having the above-mentioned configuration executes the processing of the flowchart described below according to the program stored in the ROM 51. FIG. 4 is a flow chart for explaining the operation of the embodiment of the main part of the present invention, which is activated by interruption every 65 ms, for example. In the figure, first, it is checked whether the execution flag is set (the value is "1") (step 101). Since the execution flag has been cleared (the value is "0") by the initial routine at the time of starting the engine, it is not initially set, so the routine proceeds to the next step 102.

In step 102, it is checked whether a leak determination flag, which will be described later, is set. Since the leak determination flag is also cleared by the initial routine, it is not initially set, and the process proceeds to the next step 103 first. In step 103, the tank internal pressure switching valve (VSV) 42
Is opened (valve open). Then the next step 104
The canister atmosphere hole VSV36 is shut off (valve closed), and the purge side VSV38 is opened (valve open) at step 105.

The tank internal pressure switching VSV 42 is opened at time t ₁ as shown in FIG. 5 (A), the canister atmosphere hole VSV 36 is closed and the purge side VSV is opened.
Assuming that the valve opening of 38 is performed at substantially the same time t _{1 as} shown in FIGS. 5 (C) and 5 (B), respectively, the negative pressure to the engine combustion chamber causes the purge passage 39 shown in FIG. Side VSV
38, purge passage 37, canister 33, vapor passage 3
2b, tank internal pressure switching VSV42 and vapor passage 32d
Through the fuel tank 30. As a result, the internal pressure of the fuel tank 30 (tank internal pressure) rapidly increases in the negative direction after time t _{1 as} shown in FIG. 5 (D).

Next, at step 106 in FIG. 4, it is judged whether the tank internal pressure is X Pa or less based on the detection signal of the pressure sensor 40. When it is X Pa or less, the negative pressure is being set, so this routine is finished. To do. Tank pressure is X
The above steps 101 to 106 are repeated every 65 ms until the pressure becomes larger than Pa on the negative pressure side. Then, if it is determined in step 106 that the tank internal pressure has become larger than X Pa on the negative pressure side, the purge side VSV 38 is shut off at time t ₂ as shown in FIG. 5B (step 107).

Since the two VSVs 36 and 38 are both closed at the time t ₂ , the pressure in the system from the VSV 38 on the purge side to the fuel tank 30 is maintained if there is no failure in the system, and becomes extremely gentle. It decreases to the atmospheric pressure side.

When the purge-side VSV 38 is shut off in step 107, the processing of the judgment means 18 is realized in steps 108-115. That is, first, it is determined whether or not the leak determination timer is "0" (step 108). Since the leak determination timer has been cleared to "0" by the above-mentioned initial routine, this step is first performed.
When 108 a determination is performed, "0" and it is determined the process proceeds to step 109, it is stored in the RAM52 the detected value of the current pressure sensor 40 as a diagnostic starting pressure value P _S.

Subsequently, a predetermined value is added to the value of the leak determination timer (step 110), the leak determination flag is set to "1" (step 111), and this routine is ended. The next time this routine is started again, the step
Since it is determined in step 102 that there is a leak determination, steps 103 to 10
Jump 6 and step via step 107
It reaches 108.

This time, it is determined in step 108 that the leak determination timer is not "0", so it is determined whether or not the value of the leak determination timer is equal to the diagnostic time (leak determination time) α (step 112), and when time α has not yet come, this routine is terminated via steps 110 and 111.

In this way, steps 101, 102, 107
, 108, 112, 110, 111 are repeated every 65 ms, and when the value of the leak determination timer reaches a value corresponding to the leak determination time α, the detected value of the pressure sensor 40 at that time is changed to the diagnostic end pressure value P _E. Stored in the RAM 52 as
113). Then, based on the pressure values P _S and P _E read out from the RAM 52, the rate of change in pressure is calculated from the formula (P _E −P _S ) / α (sec) (step 114).

Subsequently, it is determined whether the calculated rate of change is equal to or greater than a predetermined threshold value β (step 115). Above time t
The pressure change rate up to ₂ is gentle as shown in Fig. 5 (D),
If it is determined to be less than β in step 115, it is determined to be normal (no failure) because the leakage is below the specified value, and
After clearing the shutoff prohibition flag of the tank internal pressure switching VSV42 (step 116), the canister atmosphere hole VSV36.
Is opened at time t ₃ as shown in FIG. 5 (C) (step
120).

Then, it is checked whether the shutoff prohibition flag is set (step 121).
Since the shutoff prohibition flag is cleared at 116, it is determined that the flag is not set, and the routine proceeds to step 122 and FIG.
As shown at time t ₃ in (A), tank internal pressure switching VSV42
Is cut off. As a result, the passage between the canister 33 and the fuel tank 30 is connected only by the fuel tank internal pressure control valve 41 and the vapor passages 32a and 32d. Therefore, as shown in FIG. 5D, the tank internal pressure changes in the positive pressure direction set by the fuel tank internal pressure control valve 41 after time t ₃ .

On the other hand, when it is determined in step 115 that the rate of change is β or more, it is determined that the leakage is large and abnormal because the change in pressure is large, and the warning lamp 43 is turned on (step 117). After notifying the driver of the failure of the evaporative purge system, the leak failure fail code is stored in, for example, the backup RAM 53 (step 11).
8) After setting the interruption prohibition flag to "1" (step 119), proceed to step 120. The leakage failure fail code is read out from the backup RAM 53 at the time of subsequent repair and informs the cause of failure of the evaporative purge system.

In step 120, the canister atmospheric hole VSV3
After 6 is opened, it is determined in step 121 whether the shutoff prohibition flag is "1". When an abnormality is detected, this shutoff prohibition flag is "1", so step 122 is skipped to switch the tank internal pressure. Prohibit closing of VSV42. As a result, when an abnormality is detected, the open state of the tank internal pressure switching VSV 42 is maintained, and the canister atmosphere hole VSV 36 is opened in step 120, which causes the atmosphere introduction port 36 of FIG.
Since the atmosphere is introduced into the fuel tank 30 from the a through the canister atmosphere hole VSV36 and the tank internal pressure switching VSV42, the vapor discharge from the fuel tank 30 through the leak point is suppressed as much as possible.

Thereafter, the leak determination timer is cleared (step 123) and the execution flag is set to "1" (step 123).
124), the leak determination flag is further cleared to "0" (step 125), and the failure diagnosis process is terminated. After that,
Even if this routine is started, the execution flag is judged to be "1" in step 101, so this routine is not executed until it is restarted thereafter.

The present invention is not limited to the above embodiment, and for example, the pressure sensor 40 may be replaced by the fuel tank 30.
It is also possible to install it on the valve or to place the vapor purging portion near the throttle valve 25. Further, the shutoff prohibition flag may be stored in the backup RAM 53, and may be kept set until repaired (until the battery is removed) so that no determination is made.

Further, in the above embodiment, the fuel tank internal pressure control valve 41 is substantially opened by maintaining the tank internal pressure switching VSV 42 in the open state when an abnormality is detected. It is also possible to provide a function similar to that of the fuel tank internal pressure control valve 41, and to connect the atmosphere opening port 41c of the fuel tank internal pressure control valve 41 to the purge passage 39 through VSV.
The VSV can be forcibly turned on when a leakage abnormality is detected, and the fuel tank internal pressure control valve 41 can be forcibly turned on (open).

In the above-mentioned embodiment, the failure diagnosing device which introduces and holds the intake negative pressure into the system and diagnoses the failure by the change of the negative pressure is illustrated. However, as the failure diagnosing device, the negative pressure is introduced into the system, A type that determines whether there is a failure by whether the negative pressure becomes a predetermined value or more, a type that determines by comparing a vapor amount when a purge is provided with a vapor sensor in the purge passage with a predetermined value, There are two types, one is to judge by the change in the air-fuel ratio when the purge is stopped and the other is during the purge, a type that is judged by the change in the canister temperature at the time of vapor adsorption such as refueling, or at the time of purging, It is also possible to substitute various types of failure diagnosis devices, such as a type that determines whether or not the flow rate of the entire flowing fluid is a predetermined amount or more.

[0039]

As described above, according to the present invention, when a leak in the system of the evaporative purge system is detected, the internal pressure control valve provided in the passage between the fuel tank and the canister is forced. In addition, since the inside of the fuel tank is kept at atmospheric pressure with the valve open and held substantially, the amount of fuel vapor leaked from the leaking point to the atmosphere can be significantly reduced compared to the conventional method. It is a thing.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of the present invention.

FIG. 2 is a system configuration diagram of an embodiment of the present invention.

FIG. 3 is a configuration diagram of an example of hardware of the microcomputer in FIG.

FIG. 4 is a flowchart for explaining the operation of the embodiment of the main part of the present invention.

FIG. 5 is a time chart explaining the operation of each part of FIG. 4 in a normal state.

[Explanation of symbols]

10, 30 Fuel tank 11, 32, 32a to 32d Vapor passage 12, 33 Canister 13, 37, 39 Purge passage 14 Intake passage 18 Failure diagnosis device 19 Internal pressure control valve 20 Opening means 21 Microcomputer 36 Canister atmosphere hole vacuum switching・ Valve (VSV) 38 Vacuum switching valve on vapor side (V
SV) 40 Pressure sensor 41 Fuel tank internal pressure control valve 42 Tank internal pressure switching valve (VSV)

Claims (1)

[Claims] 1. An evaporation purge system for adsorbing evaporated fuel from a fuel tank to an adsorbent in a canister through a vapor passage and purging the adsorbed fuel in the canister through a purge passage into an intake passage of an internal combustion engine during a predetermined operation, Provided in a passage between the fuel tank and the inside of the canister, the pressure in the fuel tank during operation of the internal combustion engine,
An internal pressure control valve that controls to a positive pressure, a failure diagnosis device that opens the internal pressure control valve at an appropriate time during operation to diagnose a failure of the evaporative purge system, and a failure diagnosis device that determines that there is a leakage failure. And an valve opening means for forcibly holding the internal pressure control valve in a substantially valve-opened state.