JPH0579409A - Evaporative fuel control device for internal combustion engine - Google Patents

Abstract

(57) [Summary] [Object] The present invention provides an evaporative fuel control device for an internal combustion engine, which can accurately perform purge flow rate control and air-fuel ratio control, and can easily detect an abnormality of a mass flow meter. The purpose is to provide. According to the present invention, a flow meter 22 is provided in a purge passage 20, the opening of a purge control valve 21 is controlled based on an output value of the flow meter 22 and a calculated value of a purge flow rate, and the flow rate is controlled under a predetermined condition. The atmosphere was supplied to the total 22 to determine the abnormality of the flow meter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an evaporated fuel control device for an internal combustion engine, and more particularly to an evaporated fuel control device for an internal combustion engine for controlling the flow rate of purge gas supplied to an intake system of the engine.

[0002]

2. Description of the Related Art Conventionally, there has been widely used an evaporated fuel control device for preventing fuel vapor (evaporated fuel) generated in a fuel tank from being released into the atmosphere. In this type of device, fuel vapor is temporarily stored in a canister, and the stored fuel vapor is supplied (purged) to the intake system of the engine. Then, when the purge amount is small, the air-fuel ratio of the air-fuel mixture is promptly controlled by air-fuel ratio feedback control, although the air-fuel mixture supplied to the engine is momentarily enriched by purging the fuel vapor into the intake system. Since it returns to the target value, the air-fuel ratio hardly changes.

However, if the purge amount is large, the air-fuel mixture may become fuel-rich and the air-fuel ratio may fluctuate. Particularly, there is a possibility that a large amount of fuel vapor will be generated immediately after refueling, and in order to prevent such a change in the air-fuel ratio due to the purge immediately after refueling, the vehicle speed reaches a predetermined value after engine start immediately after refueling, and thereafter A purge flow rate control device has been proposed in which the purge amount is reduced until the integrated time in a state where it exceeds a predetermined value reaches a predetermined time (for example, Japanese Patent Laid-Open No. 63-111277).

An air-fuel ratio control device for predicting the amount of change of the air-fuel ratio correction coefficient at the time of a large amount of purge and suppressing the change of the air-fuel ratio even if the amount of purge is large, Have been proposed (for example, JP-A-62-62
-131962).

However, the above-mentioned conventional example has a drawback that it is difficult to perform accurate air-fuel ratio control because the actual fuel vapor flow rate is not detected in controlling the purge flow rate.

As means for solving such a drawback, a mass flow meter is provided in the conduit of the purge pipe, and the target fuel vapor flow rate is set based on the operating condition of the engine, and the output value of the mass flow meter and the target fuel flow rate are set. A method of controlling the purge flow rate by adjusting the opening of the purge control valve according to the vapor flow rate is conceivable.

In the above method, since the purge flow rate is directly measured by the flow meter, the fuel vapor flow rate can be accurately obtained and the air-fuel ratio control can always be performed accurately.

However, if the output of the mass flowmeter shows an abnormal value due to failure or deterioration of the mass flowmeter, the purge flow rate is controlled based on the abnormal value, and the following problems occur. Newly occurs.

That is, when the output value of the mass flowmeter shows an abnormally large value, excessive fuel vapor is supplied to the engine, the air-fuel ratio is greatly enriched, and the engine is stopped. A large amount of harmful components such as is discharged. On the other hand, when the output value of the mass flowmeter shows an abnormally small value, only too little fuel vapor is supplied to the engine,
Purge efficiency η (fuel vapor /
There is a problem that (air amount) + (fuel vapor)) decreases and the air-fuel ratio becomes lean.

In the purge control, the vapor flow rate correction coefficient is calculated to correct the air-fuel ratio correction coefficient according to the fuel vapor flow rate, and the valve opening time of the fuel injection valve is calculated by adding the vapor flow rate correction coefficient. Although it needs to be controlled, the vapor flow rate correction coefficient has a value that is inversely proportional to the fuel vapor flow rate. Therefore, if the output of the mass flowmeter shows an abnormal value and the vapor flow rate correction coefficient becomes excessively large, the vapor flow rate correction coefficient becomes small and the fuel injection amount becomes insufficient.Conversely, the vapor flow rate correction coefficient becomes too small. If so, the vapor flow rate correction coefficient becomes large, so that the fuel injection amount increases and the fuel becomes significantly rich, which causes a problem that the operating performance deteriorates in any case.

The present invention has been made in view of the above problems, and it is possible to accurately perform the purge flow rate control and the air-fuel ratio control, and to easily detect the abnormality of the mass flowmeter. An object is to provide an evaporated fuel control device for an engine.

[0012]

In order to achieve a steam object, the present invention is directed to a fuel tank, a canister for adsorbing and storing fuel vapor generated from the fuel tank, and a canister between the canister and an intake system of an internal combustion engine. Evaporative fuel control for an internal combustion engine having a purge passage for purging the air-fuel mixture containing the fuel vapor and a purge control valve for controlling the flow rate of the fuel vapor supplied to the engine intake system via the purge passage In the apparatus, a flow meter interposed in the purge passage, a purge flow rate calculating means for calculating a flow rate of an air-fuel mixture flowing in the purge passage based on an operating state of an engine, at least an output value of the flow meter and the purge. A purge control means for controlling the opening degree of the purge control valve based on the calculated value of the flow rate calculation means, and supplying the atmosphere to the flow meter under a predetermined condition. And an abnormality determining means for determining abnormality of the flowmeter based on an output value of the flowmeter when the atmosphere is being supplied to the flowmeter by the atmosphere supplying means. It has a feature.

Further, the output characteristic of the flow meter changes according to the concentration of the fuel vapor or the flow rate of the fuel vapor flowing through the conduit of the purge pipe and the purge flow rate.

[0014]

According to the above construction, when the flow meter is normal, the opening of the purge control valve is controlled by the purge control means, and the purge flow rate can be controlled to the desired flow rate.

Further, when the flowmeter is abnormal, the abnormality of the flowmeter can be detected by the atmosphere supply means and the abnormality determination means.

More specifically, the output characteristic of the flow meter changes according to the concentration of the fuel vapor, while the concentration of the fuel vapor during air supply is almost 0%. Therefore, based on these data. It is possible to detect abnormalities in the flow meter.

Further, since the fuel vapor flow rate is almost "0" when the air is supplied, the purge flow rate is almost 100 for air.
%, And the output characteristic changes depending on the flow rate of the fuel vapor flowing in the conduit of the purge pipe and the purge flow rate, and therefore abnormality of the flow meter can be detected based on these data.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is an overall configuration diagram showing an embodiment of an evaporated fuel control device for an internal combustion engine according to the present invention.

In the drawing, reference numeral 1 denotes an internal combustion engine having four cylinders (hereinafter, simply referred to as "engine"), a throttle body 3 is provided in the middle of an intake pipe 2 of the engine 1, and inside thereof is provided. A throttle valve 3'is provided. Further, the throttle valve 3 ′ has a throttle valve opening (θ
TH) sensor 4 is connected and outputs an electric signal according to the opening degree of the throttle valve 3 ′ and supplies it to an electronic control unit (hereinafter referred to as “ECU”) 5.

Further, a branch pipe 6 is provided downstream of the throttle valve 3'of the intake pipe 2, and an absolute pressure (PBA) sensor 7 is provided at the tip of the branch pipe 6. Also, PB
The A sensor 7 is electrically connected to the ECU 5, and the absolute pressure PBA in the intake pipe 2 detected by the PBA sensor 7 is converted into an electric signal and supplied to the ECU 5.

An engine water temperature (TW) sensor 25 composed of a thermistor or the like is attached to the cylinder peripheral wall filled with cooling water of the cylinder block of the engine 1, and the engine cooling water temperature TW detected by the TW sensor 25 is converted into an electric signal. It is converted and supplied to the ECU 5.

An engine speed (NE) sensor 8 is mounted around the cam shaft or crank shaft (not shown) of the engine 1.

The NE sensor 8 outputs a signal pulse (hereinafter referred to as "TDC signal pulse") at a predetermined crank angle position every 180 degrees rotation of the crankshaft of the engine 1, and the T
The DC signal pulse is supplied to the ECU 5.

Further, an oxygen concentration sensor (hereinafter referred to as "O ₂ sensor") 10 is provided in the exhaust pipe 9 of the engine 1, and the oxygen concentration in the exhaust gas detected by the O ₂ sensor 10 is detected. Is converted into an electric signal and supplied to the ECU 5.

The fuel injection valve 11 is provided for each cylinder between the engine 1 and the throttle valve 3'and slightly upstream of an intake valve (not shown) of the intake pipe 2. Further, each fuel injection valve 11 is connected to a fuel tank 14 via a fuel pump 13 by a fuel supply pipe 12 and electrically connected to the ECU 5, and a valve opening time of fuel injection is controlled by a signal from the ECU 5. It

A communication pipe 15 is provided above the fuel tank 14.
The fuel tank 14 can communicate with the canister 17 via the two-way valve 16. Canister 1
7 has an outside air intake port 18 and an internal adsorbent 19 such as activated carbon for adsorbing and storing the fuel vapor flowing from the fuel tank 14.

A purge pipe 20 is connected to the canister 17, and the tip of the purge pipe 20 (PC port 20a) is connected.
Is connected to the throttle body 3.

The PC port 20a is located downstream of the throttle valve 3'when the throttle valve 3'is opened, and the throttle valve 3'is closed when the throttle valve 3'is closed.
It is provided so as to be located on the upstream side.

A purge control valve 21 is provided in the conduit of the purge pipe 20, and the solenoid of the purge control valve 21 is connected to the ECU 5. The purge control valve 21 is controlled according to the signal from the ECU 5, and linearly changes the valve opening amount. That is, the ECU 5 outputs the control amount EPCV value to control the valve opening amount of the purge control valve 21.

Further, the canister 17 and the purge control valve 2
A hot-wire type flowmeter (mass flowmeter) 22 is provided in the conduit of the purge pipe 20 between the first and second purge pipes 1. This hot wire type flow meter 22
Utilizes the fact that when a platinum wire heated by passing an electric current is exposed to an air flow, its temperature decreases and its electrical resistance decreases. Its output characteristics depend on the fuel vapor concentration, flow rate, and purge flow rate. It changes and supplies the output signal according to these changes to ECU5.

Further, the canister 17 and the hot wire type flow meter 22.
A three-way solenoid valve 23 is interposed in the pipe line of the purge pipe 20 between and. The three-way solenoid valve 23 allows the canister 17 and the throttle body 3 to communicate with each other at normal times, and when the abnormality of the hot-wire flow meter 22 is determined, the three-way solenoid valve 23 is connected to the atmosphere and the throttle body 3 via the air filter 24. Are configured to be able to communicate with each other.

Therefore, the ECU 5 shapes the input signal waveforms from the various sensors described above, corrects the voltage level to a predetermined level, and converts the analog signal value into a digital signal value. An arithmetic processing circuit (hereinafter referred to as "CPU"), a storage unit that stores an arithmetic program executed by the CPU, an arithmetic result, and the like, and drive signals to the fuel injection valve 11, the purge control valve 21, and the three-way solenoid valve 23. And an output circuit for supplying.

The CPU discriminates various engine operating states such as a feedback control operating region and an open loop control operating region according to the oxygen concentration in the exhaust gas based on the above-mentioned various engine parameter signals, and also responds to the engine operating state. The fuel injection time Tout of the fuel injection valve 6 is calculated in synchronism with the TDC signal pulse based on the equation (1).

Tout = Ti × KO ₂ × VQKO ₂ × K1 + K2 (1) Here, Ti is a reference value of the injection time Tout of the fuel injection valve 6, and the engine speed NE and the intake pipe absolute pressure PBA.
Is read from the Ti map set in accordance with

KO ₂ is an air-fuel ratio correction coefficient, which is set in accordance with the oxygen concentration in the exhaust gas detected by the O 2 sensor 10 during feedback control, and is used in a plurality of open loop control operation regions where feedback control is not performed. It is set according to each operation area.

VQKO ₂ is a vapor flow rate correction coefficient, which is detected during purging and is set according to the vapor flow rate.

K1 and K2 are correction coefficients and correction variables calculated according to various engine parameter signals, respectively, and various characteristics such as fuel consumption characteristics and acceleration characteristics according to the engine operating state can be optimized for each cylinder. It is set to a predetermined value as shown.

In the evaporative fuel control system for the internal combustion engine constructed as above, when the fuel vapor generated in the fuel tank 14 reaches a predetermined set pressure, the two-way valve 16
Press the positive pressure valve (not shown) to open the canister 17
And is adsorbed and stored by the adsorbent 19 in the canister 17. The input port of the three-way solenoid valve 23 is normally switched to the canister 17 side so that the canister 17 and the throttle body 3 can communicate with each other. The purge control valve 21 is closed when its solenoid is not energized by the control signal from the ECU 5,
When the solenoid is energized according to the control signal, the purge control valve 21 opens by the valve opening amount corresponding to the energizing amount.
That is, the ECU 5 outputs the control amount EPCV value to the purge control valve 21 according to the output of the hot-wire flow meter 22, and the purge valve 21 opens by the valve opening amount according to the EPCV value.

Then, the fuel vapor stored in the canister 17 is generated by the negative pressure in the intake pipe 2,
It is sucked into the intake pipe 2 through the purge control valve 21 together with the outside air sucked from the outside air intake port 18 and is sent to each cylinder.

On the other hand, when a predetermined abnormality diagnosis condition is satisfied by the abnormality diagnosis program described later, the input port of the three-way solenoid valve 23 is switched to the atmosphere side and the air filter 2 is operated.
Atmosphere is sent to the hot-wire type flow meter 22 via 4 and it is inspected whether the hot-wire type flow meter 22 is out of order.

When the fuel tank 14 is cooled by the outside air and the negative pressure in the fuel tank increases, the negative pressure valve of the two-way valve 16 opens, and the evaporated fuel temporarily stored in the canister 17 becomes fuel. It is returned to the tank 14.

Next, based on FIGS. 2 to 7, the actual fuel vapor flow rate VQ (hereinafter referred to as "vapor flow rate") and the purge flow rate T
The calculation procedure of Q and the concentration β of fuel vapor (hereinafter referred to as “vapor concentration”) will be described in detail.

FIG. 2 shows the vapor flow rate VQ, the purge flow rate TQ,
It is a flowchart showing a procedure for calculating the vapor concentration β, and this program is executed by the CPU of the ECU 5.

First, in step S1, the basic PC flow rate PCQ0 is calculated according to the throttle valve opening degree θTH and the intake pipe absolute pressure PBA.

Here, the "PC flow rate" means the flow rate of the mixture of fuel vapor and air calculated based on the throttle valve opening θTH and the intake pipe absolute pressure PBA, and when the vapor concentration β is 0%. Only, coincides with the output value QH of the hot wire type flow meter 22, and in other cases, the output value QH as described later.
Have a certain relationship with.

The "basic PC flow rate" means that the purge control valve 21 is fully opened and the air amount is 100% (ie,
The PC flow rate when the vapor concentration β is 0%. Specifically, the basic PC flow rate PCQ0 corresponds to the predetermined throttle valve opening degree θTH and the predetermined intake pipe absolute pressure PBA.
It is calculated by searching the PCQ0 map in which the Q0 value is set and performing interpolation calculation.

FIG. 3 is a diagram showing an example of the relationship between the throttle valve opening degree θTH, the intake pipe absolute pressure PBA, and the basic PC flow rate PCQ0.

In the figure, the horizontal axis indicates the throttle valve opening θTH.
[%], The vertical axis represents the basic PC flow rate PCQ0 (l / min), and the curves A, B, and C show the intake pipe absolute pressure PBA of 36%, respectively.
The characteristics at 0 mmHg, 660 mmHg, and 710 mmHg are shown.

As is apparent from this figure, the basic PC flow rate PCQ0 has a larger value as the intake pipe absolute pressure PBA is smaller and the throttle valve opening degree θTH is larger.

Next, in step S2, the flow rate ratio ηQ is calculated according to the valve opening area VS of the purge control valve 21. The flow rate ratio ηQ [%] indicates the ratio of the PC flow rate corresponding to the valve opening area ratio VS [%] of the purge control valve 21, and specifically, ηQ corresponds to the predetermined valve opening area VS. It is calculated by searching the ηQ table in which the value is set and performing interpolation calculation.

FIG. 4 is a characteristic diagram showing the relationship between the flow rate ratio ηQ and the valve opening area VS, where the horizontal axis represents the valve opening area ratio VS.
[%], And the vertical axis represents the flow rate ratio ηQ [%].

As is clear from this figure, the flow rate ratio ηQ
Is directly proportional to the valve opening area VS.

Next, in step S3, the PC flow rate PCQ1 is calculated based on the equation (2).

PCQ1 = PCQ0 × ηQ (2) Next, after reading the output value QH of the hot-wire flow meter 22 in step S4, the VQ map is searched and interpolation calculation is performed in step S5 according to the QH value and the PCQ1 value. Then, the vapor flow rate VQ is calculated. The VQ map is one in which the vapor flow rate VQ is set in correspondence with the predetermined output value QH of the hot wire type flow meter 22 and the predetermined value of the PC flow rate PCQ1, and the vapor concentration VQ is calculated by searching the VQ map. It

In step S6, the purge flow rate TQ is calculated by searching the TQ map according to the QH value and the PCQ1 value and performing interpolation calculation. Similar to the VQ map, the TQ map has a predetermined output value QH of the hot wire type flow meter 22 and a PC flow rate P.
The purge flow rate TQ corresponding to CQ1 is set, and the purge flow rate TQ is calculated by searching the TQ map.

Finally, in step S7, equation (3)
Based on the above, the vapor concentration β is calculated, and this program ends.

[0058]

[Equation 1] FIG. 5 is a characteristic diagram showing the relationship between the vapor concentration β in the air-fuel mixture and the flow rate display change rate x, and the solid line in the figure is the hot-wire flow meter 2
2 shows the output value QH, and the broken line shows the PC flow rate PCQ1. Here, the flow rate display change rate x is the purge flow rate TQ.
Β is 0 with respect to the flow rate display value (that is, the steam QH value or the PCQ1 value) when β is 0% in the case of constant
This is a parameter indicating the ratio of the flow rate display value when%.
That is, the flow rate change rate x is QH for the purge flow rate TQ.
Value or ratio of PCQ1 value (QH / TQ or PC
Q1 / TQ), and as shown in FIGS. 6A and 6B, for example, when β = 0%, TQ = PCQ1 =
QH = 1 [l / min], but when β = 100%, PCQ1 = 1.69 for TQ = 1 [l / min]
[L / min] and QH = 4.45 [l / min].

FIG. 7 shows the output values QH and P of the hot wire type flow meter 22.
FIG. 6 is a characteristic diagram showing the relationship between the C flow rate PCQ1, the vapor concentration β, and the vapor flow rate VQ, showing the vapor concentration β and the vapor flow rate VQ according to the QH value and the PCQ1 value. Further, since the vapor concentration β is β = VQ / TQ, TQ =
The purge flow rate TQ can be calculated by calculating VQ / β.

As is clear from this figure, PC flow rate PCQ
1 is PCQ1 = QH when β = 0, and otherwise has a constant relationship with the QH value. Then, in this way, the output value QH and the PC flow rate PCQ1 of the hot-wire flow meter 22 are
Accordingly, the vapor concentration β, the vapor flow rate VQ, and the purge flow rate TQ are calculated.

FIG. 8 is a flowchart showing the procedure for calculating the vapor flow rate correction coefficient VQKO ₂ and the control amount EPCV value of the purge control valve 21, and this program is executed by the CPU of the ECU 5. Here, the vapor flow rate correction coefficient VQKO ₂ corrects the air-fuel ratio correction coefficient KO ₂ according to the vapor flow rate VQ, and the EPCV value controls the opening degree (opening area ratio VS) of the purge control valve 21. Is a control parameter value of. The larger the EPCV value,
The opening degree of the purge control valve increases, and the vapor flow rate VQ increases.

In the figure, in step S11, the amount QENG of air taken into the engine 1 by the mathematical expression (4).
To calculate.

QENG = Tout × NE × CEQ (4) Here, Tout is the fuel injection time calculated by the equation (1), and CEQ is a constant for converting the injection time into the intake air amount.

In step S12, the target vapor flow rate ratio KQPOBJ is calculated by searching the KQPOBJ map. KQPOBJ map shows the engine intake air amount QEN
A KQPOBJ value for G is a map set corresponding to a plurality of predetermined engine speeds NE and an intake pipe absolute pressure PBA, and the engine speed NE detected by the NE sensor 8 is searched by searching the KQPOBJ map.
And the absolute pressure P in the intake pipe detected by the PBA sensor 7.
A target vapor flow rate ratio KQPOBJ according to BA is calculated.

In step S13, the target vapor flow rate QPOBJ is calculated based on the equation (5).

QPOBJ = QENG × KQPOBJ (5) This target vapor flow rate QPOBJ may be appropriately corrected by the engine water temperature TW.

[0067] In step S14, temporarily stores the previously calculated value of VQKO ₂ value to a variable AVQKO _2. This is because the previously calculated value is used in step S17 described later.

In step S15, the vapor flow rate VQ [l / min] calculated by the program of FIG.
Convert to (g / min).

[0069]

[Equation 2] KVQ is a coefficient indicating the ratio of the gasoline vapor flow rate (l / min) included in the vapor flow rate VQ (l / min), and is 1 / 1.69. VMOL is a volume value of 1 mol and is represented by 22.4 l / MOL value at 0 ° C. Gasoline vapor molecular weight is about 64.

In step S16, the vapor flow rate correction coefficient VQKO ₂ is calculated based on the equation (7) using the gasoline weight equivalent amount GVQ (g / min).

[0071]

[Equation 3] The basic injection weight is a value obtained by converting the reference value Ti of the fuel injection time Tout into the fuel weight (g).

The vapor flow rate correction coefficient VQKO ₂ is 1.0 when the purge control valve 21 is closed and the purge is cut.
When the purge control valve 21 is opened and the purge is executed, the value becomes 1.0 or less.

In step S17, the air-fuel ratio correction coefficient KO ₂ is corrected by the equation (8).

KO ₂ = KO ₂ × VQKO ₂ / AVQKO ₂ (8) Using the KO ₂ value corrected in this way, Equation (1)
The fuel injection time Tout is calculated on the basis of the fuel injection time Tout, and the fuel injection valve 11 supplies the fuel amount to the engine 1 so as to suppress the fluctuation of the air-fuel ratio due to the magnitude of the purge amount.

Further, in step S18, the vapor flow rate VQ is the target vapor flow rate Q calculated in step S13.
It is determined whether POBJ or more.

The answer to step S18 is negative (NO), that is, the calculated vapor flow rate VQ is the target vapor flow rate QPOBJ.
If it is smaller, the control amount EPCV value corresponding to the valve opening amount of the purge control valve 21 is increased from the current value by the value C in order to increase the vapor amount and the fuel vapor emission suppressing ability (step S19). This program ends.
The value C is an update constant of the EPCV value. On the other hand, step S1
The answer of 8 is affirmative (YES), that is, the calculated vapor flow rate V
If Q is equal to or greater than the target vapor flow rate QPOBJ, the vapor amount is reduced to prevent the feedback control response from deteriorating, and the control amount EACV value of the purge control valve 16 is reduced from the current value by the value C (step S20), this program ends.

As described above, the actual vapor flow rate VQ is detected, and the fuel injection amount is corrected accordingly (step S1).
7) The change in the air-fuel ratio due to the purge is prevented, and the valve opening amount of the purge control valve 21 is controlled according to the detected vapor flow rate (steps S19 and S20), and the air-fuel ratio correction coefficient K is set.
The average value of O ₂ is prevented from deviating significantly from the value of 1.0. As a result, when the air-fuel ratio control shifts from the open loop mode to the feedback mode, the air-fuel ratio correction coefficient KO
It is possible to prevent deterioration of responsiveness of feedback control that occurs when the average value used as the initial value of ₂ deviates significantly from the value of 1.0.

Therefore, in the above evaporative fuel control device, when the hot-wire flow meter 22 is operating normally, it is possible to prevent the air-fuel ratio from changing due to the purge as described above. When the flow meter 22 is in an abnormal state due to a failure or the like, it does not output a normal value. Therefore, as described in detail in the section [Prior art and its problems], it causes variations in the air-fuel ratio and causes various changes. It causes deterioration of driving performance.

Therefore, the evaporative fuel control system of the present invention supplies the hot wire type flow meter 22 with the atmosphere, and the output value of the hot wire type flow meter 22 when the atmosphere is being supplied to the hot wire type flow meter 22 is set. Based on this, the abnormality of the hot wire type flow meter 22 is determined. That is, when the atmosphere is supplied to the hot-wire flowmeter 22, the vapor concentration β is β≈0, and when β = 0, QH = PCQ1 as described above (see FIG. 7).
Therefore, the output value QH (= PCQ1) when the vapor concentration β stored in the storage means of the ECU 5 is “0%”
On the other hand, the abnormality of the hot-wire flow meter 22 can be determined by whether or not the output value of the hot-wire flow meter 22 supplied with the atmosphere is within the allowable range.

FIG. 9 is a flow chart showing an abnormality diagnosis program, and this program is executed by the CPU of the ECU 5.

First, in step S31, it is determined whether or not the abnormality diagnosis condition is satisfied. For example, when the engine water temperature TW detected by the TW sensor 25 is equal to or higher than a predetermined value and the rate of change of operating parameters such as the intake pipe absolute pressure PBA and the engine speed NE is smaller than a predetermined value, it is determined that the abnormality diagnosis condition is satisfied. ..

Then, the answer to step S31 is negative (N
In the case of O), the input port of the three-way solenoid valve 23 is switched to the canister side to bring the canister 17 and the hot-wire flowmeter 22 into communication with each other (step S32), and this program ends.

On the other hand, the answer in step S31 is affirmative (YE
In the case of S), the input port of the three-way solenoid valve 23 is switched to the atmosphere side and the atmosphere is supplied to the hot-wire flow meter 22 (step S33). Next, in step S34, it is determined whether or not the output value QH of the hot-wire flow meter 22 is within the allowable range. Whether or not it is within the allowable range is determined when the vapor concentration β stored in the above-mentioned storage means is β = 0 when the atmospheric pressure is supplied (β≈0) with respect to the QH value (= PCQ1 value).
It is determined by whether or not the QH value of the hot-wire flow meter 22 in is within the allowable range (for example, ± 3%).

If the answer is affirmative (YES), it is judged to be normal (step S35), the program is terminated, and if the answer is negative (NO), it is judged to be abnormal (step S36). ) Exit this program.

As described above, the present invention can easily detect an abnormality in the hot-wire type flow meter 22 and can quickly respond even if the hot-wire type 22 becomes abnormal due to failure or deterioration.

Further, since the PC flow rate PCQ1 is calculated based on the engine operating parameters, the valve opening θTH of the throttle valve 3'and the intake pipe absolute pressure PBA, the PC port 20a is " Gap "
Even when it is attached in the state where the occurrence of the abnormality occurs, it is possible to detect the abnormality, and it is possible to quickly deal with a product defect or the like.

[0087]

As described above in detail, the present invention is provided between a fuel tank, a canister for adsorbing and storing fuel vapor generated from the fuel tank, and the canister and the intake system of the internal combustion engine. An evaporative fuel control system for an internal combustion engine, comprising: a purge passage for purging an air-fuel mixture containing fuel vapor; and a purge control valve for controlling a flow rate of fuel vapor supplied to an engine intake system via the purge passage. A flow meter interposed in the passage, a purge flow rate calculating means for calculating the flow rate of the air-fuel mixture flowing in the purge passage based on the operating state of the engine, and at least an output value of the flow meter and a calculation of the purge flow rate calculating means. Since it has a purge control means for controlling the opening degree of the purge control valve based on the value, when the flow meter is normal, it is supplied from the purge passage to the intake pipe. The fuel vapor flow rate can be obtained accurately, control of the air-fuel ratio of the fuel mixture, it is possible to accurately control of the purge control valve.

Further, the air supply means for supplying the air to the flow meter under a predetermined condition, and the flow meter based on the output value of the flow meter when the air is supplied to the flow meter by the air supply means. When the flowmeter is in an abnormal state, it is possible to quickly detect the abnormality of the flowmeter.

Specifically, since the concentration of fuel vapor at the time of air supply is almost 0%, the flowmeter is based on these data because its output characteristic changes according to the concentration of fuel vapor. It is possible to detect an abnormality of the flow meter.

Further, since the fuel vapor flow rate is almost "0" when the air is supplied, the purge flow rate is almost 100 for air.
%, The output characteristic of the flow meter changes according to the flow rate of the fuel vapor flowing through the conduit of the purge pipe and the purge flow rate. can do.

Therefore, according to the present invention, the erroneous input of the measured value due to the failure or deterioration of the flowmeter, or the defective product is prevented, the engine is stopped due to the misfire, the harmful components such as CO and HC are discharged, and the surging is performed. It is possible to prevent the occurrence of.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of an evaporated fuel control device for an internal combustion engine according to the present invention.

FIG. 2 is a flowchart of a program for calculating a fuel vapor flow rate (VQ), a purge flow rate (TQ), and a fuel vapor concentration (β).

FIG. 3 is a diagram showing a relationship between a throttle valve opening (θTH), an intake pipe absolute pressure (PBA), and a basic flow rate (PCQ0).

FIG. 4 is a characteristic diagram showing a flow rate characteristic of a purge control valve.

FIG. 5 is a characteristic diagram showing a relationship between a fuel vapor concentration (β) and a flow rate display change rate.

FIG. 6 is a diagram for explaining a relationship between a purge flow rate (TQ), a PC flow rate (PCQ1), and an output value (QH) of a hot-wire flow meter.

FIG. 7 is a characteristic diagram showing a relationship among a PC flow rate (PCQ1), an output value (QH) of a hot wire type flow meter, a vapor concentration (β) and a vapor flow rate (VQ).

FIG. 8 is a flow chart of a program for controlling a purge control valve opening degree and a fuel supply amount according to a fuel vapor flow rate (VQ).

FIG. 9 is a flowchart of an abnormality diagnosis program.

[Explanation of symbols]

 1 Internal Combustion Engine 2 Intake Pipe 5 Electronic Control Unit (ECU) 6 Fuel Injection Valve 14 Fuel Tank 17 Canister 21 Purge Control Valve 20 Purge Pipe 22 Hot Wire Flowmeter

Claims (3)

[Claims] 1. A fuel tank, a canister for adsorbing and storing fuel vapor generated from the fuel tank, and a purge provided between the canister and an intake system of an internal combustion engine for purging an air-fuel mixture containing the fuel vapor. In an evaporative fuel control system for an internal combustion engine having a passage and a purge control valve for controlling a flow rate of fuel vapor supplied to an engine intake system through the purge passage, a flow meter interposed in the purge passage, Purge flow rate calculation means for calculating the flow rate of the air-fuel mixture flowing through the purge passage based on the operating state of the engine, and opening of the purge control valve based on at least the output value of the flow meter and the calculated value of the purge flow rate calculation means. A purge control means for controlling the temperature, and an atmosphere supply means for supplying the atmosphere to the flowmeter under a predetermined condition; Evaporative fuel control system for an internal combustion engine, characterized in that said are provided with an abnormality judging means for judging the abnormality of the flow meter based on the output value of the flow meter when the air flow meter is supplied. 2. The evaporative fuel control system for an internal combustion engine according to claim 1, wherein the output characteristic of the flow meter changes according to the concentration of fuel vapor. 3. The evaporative fuel control for an internal combustion engine according to claim 1, wherein the output characteristic of the flow meter changes according to the flow rate of the fuel vapor flowing through the conduit of the purge pipe and the purge flow rate. apparatus.