JP3003472B2 - Evaporative fuel evaporation prevention device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an apparatus for preventing evaporation of fuel vapor in a fuel reservoir such as a fuel tank.

[0002]

2. Description of the Related Art Conventionally, in order to prevent vaporized fuel vaporized in a fuel tank or the like of a vehicle from evaporating into the atmosphere and causing environmental destruction, a device for preventing evaporation of the vaporized fuel has been proposed. An apparatus as disclosed in Japanese Utility Model Application Laid-Open No. 58-151346 has been proposed.

As shown in FIG. 9, the fuel vapor generated in a fuel reservoir 16 such as a fuel tank 16 or a float chamber 40 of a carburetor is converted into a fuel such as a canister 10 filled with a fuel adsorbent 11 such as activated carbon. The adsorbent is temporarily adsorbed by the adsorbing means, and the external air communication passage is operated by the negative intake air pressure of the engine or the air pump 22 during operation of the engine.
The outside air is introduced into the canister 10 through 13, and when the introduced outside air passes through the adsorbent, the adsorbed evaporated fuel is desorbed (purge), and the desorbed evaporative fuel and the introduced evaporative fuel are introduced. A mixture (purge mixture) with the outside air is sucked into the intake manifold 2, or introduced into the exhaust passage 3 by an air pump 22 or the like to be oxidized, thereby preventing evaporation of the evaporated fuel into the atmosphere. ing.

[0004]

In general, when secondary air (fresh air) is introduced into the exhaust passage of an engine, the concentration of oxygen in the exhaust is increased, and unburned components, which are harmful components of the exhaust, are exhausted in the exhaust passage. Oxidation (purification) of (HC, CO, etc.) is promoted and, for example, in the case of a device provided with a catalytic converter, the temperature of the catalytic converter is raised by the reaction heat, thereby activating the catalytic converter at a low temperature. This has the advantage that the emission of unburned components and the like to the atmosphere can be suppressed.

Therefore, for example, the air-fuel mixture is introduced by the air pump 22 when the degree of activation of the catalytic converter 4 is low, such as when the engine is cold, so as to shorten the purging time and reduce the unburned components due to the secondary air. It is conceivable to purify the catalyst and activate the catalytic converter 4 at the same time. However, in such a case, there are the following problems. That is, since the air-fuel ratio of the purge air-fuel mixture has not been specified, the concentration of the unburned components in the exhaust gas may be increased, so that the unburned components cannot be sufficiently purified by the secondary air and the catalytic converter However, there is a problem that the amount of unburned components discharged into the atmosphere is increased due to a decrease in activation of the catalytic converter and the like.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is possible to prevent the air-fuel ratio of exhaust gas from deteriorating even if a purge mixture is introduced into an exhaust system of an engine. It is an object of the present invention to provide a device for preventing evaporated fuel from evaporating in an internal combustion engine capable of exhibiting good exhaust gas purification performance.

[0007]

For this reason, as shown in FIG. 1, the evaporative fuel evaporation prevention apparatus for an internal combustion engine according to the present invention temporarily removes the evaporative fuel accumulated in the fuel reservoir A by the adsorbing means B. The evaporative fuel is desorbed from the adsorbing means B in a predetermined engine operating state, and is guided to the exhaust passage C for processing. Pump means F for sucking and mixing a purge air-fuel mixture with desorption air and secondary air from the atmosphere via independent paths D and E and supplying the mixed air to an exhaust passage C; And a flow ratio control means G for controlling a flow ratio between the purged air-fuel mixture and the secondary air so that the air-fuel ratio of the air-fuel mixture of the air-fuel mixture and the secondary air approaches a target value.

[0008]

The evaporative fuel evaporation prevention device for an internal combustion engine according to the present invention having the above-described structure drives the pump means to desorb the evaporative fuel adsorbed by the adsorbing means and to remove the evaporative fuel desorbed from the adsorbed fuel. A purge mixture with desorption air and secondary air from the atmosphere are sucked and mixed through independent paths, and then discharged and supplied to an exhaust passage to process the evaporated fuel. At this time, the flow ratio between the purge mixture and the secondary air is controlled by the flow ratio control means so that the air-fuel ratio of the mixture of the purge mixture and the secondary air becomes the target air-fuel ratio. Therefore, for example, when the engine is cold, the unburned components (HC, CO) due to the secondary air while performing the purge process
Oxidation (purification) can be promoted, thereby reducing the load on the purge process during normal operation, suppressing the air-fuel ratio fluctuation accompanying the purge process, and thereby obtaining good operation performance and exhaust characteristics. .

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment according to the present invention will be described below with reference to the accompanying drawings. The same components as those in the related art shown in FIG. 9 are denoted by the same reference numerals. As shown in FIG. 2, an intake manifold 2 for guiding intake air is connected to the engine 1, while an exhaust passage 3 for discharging exhaust gas burned in a combustion chamber (not shown) of the engine 1 is connected to the intake manifold 2.

The exhaust passage 3 is provided with a three-way catalytic converter 4 for maximally purifying exhaust harmful components (NOx, CO, HC) near the stoichiometric air-fuel ratio. An acidity sensor 5 that outputs a signal corresponding to the oxygen concentration of the exhaust gas is provided upstream of the exhaust gas passage 3 of the three-way catalytic converter 4 so as to face the exhaust gas passage 3. The output signal of the acidity sensor 5 is input to the control unit 50.

An upstream portion of the exhaust passage 3 of the acidity sensor 5 and an upper chamber 14 of a canister 10 serving as an adsorbing means.
A check valve 21, an air pump 22, and an exhaust system purge flow control valve 23 are interposed in the exhaust system purge passage 20, respectively. The exhaust system purge passage 20 is bifurcated between the air pump 22 and the exhaust system purge flow control valve 23, and the fresh air (secondary air) introduction passage 24 on the branched side is fresh air. (Secondary air) A flow control valve 25 and an air filter 26 are interposed to communicate with the atmosphere.

Here, the exhaust system purge flow control valve 23 or the fresh air flow control valve 25 constitutes a flow ratio control means. The canister 10 has a built-in adsorbent 11 such as activated carbon, and the lower chamber 12 communicates with the atmosphere via an outside air communication passage 13. The upper chamber 14 communicates with an upper space of a fuel tank 16 via an evaporative fuel passage 15. Further, the upper chamber 14 is connected to one end of an intake system purge passage 17 for guiding a purge mixture to an engine intake system, and the other end thereof is connected to the intake manifold 2. An intake system purge flow control valve 18 for controlling the flow rate of the purge mixture is interposed in the intake system purge passage 17.

Further, a water temperature sensor 19 for detecting the temperature of the cooling water in the water jacket of the engine 1 is provided, and an output signal of the water temperature sensor 19 is input to the control unit 50. In the present embodiment, the output signal of the water temperature sensor 19 is used for determining the degree of activation of the three-way catalytic converter 4 as described later. By the way, the intake system purge flow control valve 18, the exhaust system purge control valve 23, the fresh air flow control valve
Numerals 25 can control the opening degree based on the drive signal from the control unit 50, respectively.

Here, the control unit 50
Performs a purge process as follows. With the above configuration, for example, the evaporated fuel generated in the fuel tank 16 is introduced into the upper chamber 14 of the canister 10 through the evaporated fuel passage 15 and is adsorbed by the adsorbent 11. Therefore, only the air that does not contain the evaporated fuel is discharged into the atmosphere via the outside air communication passage 13, so that the evaporation of the evaporated fuel into the atmosphere can be prevented.

During normal operation (when the degree of activation of the three-way catalytic converter 4 is high), the evaporated fuel adsorbed in the canister 10 is controlled based on a signal from the control unit 50 to control the purge flow rate of the intake system. The valve 18 is controlled to open, and is sucked into the intake manifold 2 together with the outside air introduced from the outside air communication passage 13 through the intake system purge passage 17 and subjected to combustion processing.

At this time, the control unit 50
Then, based on the rich / lean inversion signal of the acidity sensor 5, for example, the fuel injection amount from the fuel injection valve is feedback-controlled to maintain the air-fuel ratio in the vicinity of the stoichiometric air-fuel ratio, and the exhaust purification performance of the three-way catalytic converter 4 Make the most of
Exhaust harmful components are prevented from being discharged into the atmosphere.

On the other hand, in this embodiment, when the degree of activation of the three-way catalytic converter 4 is low at the time of engine cooling (at the time of starting, etc.), the emission of unburned components (HC, CO) to the atmosphere increases. Therefore, as described above, the secondary air is introduced into the exhaust passage 3 to effectively purify these exhaust harmful components, and the activation of the three-way catalytic converter 4 is promoted by utilizing the reaction heat. In addition, the purging process is performed even when the degree of activation of the three-way catalytic converter 4 is low by minimizing the emission of harmful components of exhaust gas into the atmosphere, thereby reducing the load of the purging process during the normal operation and reducing the purging. A change in air-fuel ratio, deterioration in drivability, and the like due to the processing are prevented.

That is, in the present embodiment, as will be described in detail below, when the degree of activation of the three-way catalytic converter 4 is low, the air pump 22 is driven,
The exhaust system purge flow control valve 23 and the fresh air flow control valve 25 are opened, whereby the purge mixing of the fresh air (atmosphere) introduced through the outside air communication passage 4 and the fuel vapor adsorbed by the canister 10 is performed. The mixture of air and fresh air (secondary air) introduced through the fresh air introduction passage 24 is introduced into the exhaust passage 3 while controlling the mixture to have a predetermined air-fuel ratio.

Hereinafter, the purge control performed by the control unit 50 at the time of cooling will be described.
First, the initial opening degree control of the exhaust system purge flow control valve 23 and the fresh air flow control valve 25 that is performed earlier when performing the cold purge control will be described. FIG. 3 shows a flowchart for setting the initial opening of the exhaust system purge flow control valve 23 and the fresh air flow control valve 25. This flow is executed only once when the start signal is input.

In step 1 (shown as S1 in the figure, the same applies hereinafter), it is determined whether or not the exhaust system purge flow control valve 23 has been initialized. If YES, go to step 2. If NO, the process proceeds to step 4 and initializes the exhaust system purge flow control valve 23, and then proceeds to step 2. In step 2, it is determined whether or not the fresh air flow control valve 25 has been initialized. If YES, proceed to step 3. On the other hand, if NO, the process proceeds to step 5, where the fresh air flow control valve 25 is initialized and the flow ends.

In step 3, the flag is set to "0", and the flow ends. Thus, the exhaust system purge flow rate control valve is set so that the ratio of the flow rate of the purge air-fuel mixture introduced from the canister 10 side to the flow rate of the fresh air introduced from the fresh air introduction passage 24 becomes the initial ratio. The opening degree of 23 and the fresh air flow control valve 25 is set. The initial ratio, that is, the initial opening setting of the exhaust system purge flow control valve 23 and the fresh air flow control valve 25 is sufficiently set when the canister 10 is purged from the state in which the fuel vapor is adsorbed to the maximum adsorption capacity. The air-fuel ratio (for example, λ = 1 to 1.
2) It is set to be. Therefore, the adsorbed amount of the canister 10 is often smaller than the maximum adsorbed amount, so that the air-fuel ratio of the air-fuel mixture of the purge air-fuel mixture and the secondary air guided to the exhaust passage 3 at the initially set opening degree is generally lower than the stoichiometric air-fuel ratio. Become lean.

Next, the cold purge control will be described with reference to the flowchart shown in FIG. This control is repeatedly executed at a predetermined time period. In step 11,
Canister 10 with fresh air introduced from fresh air passage 24
It is determined whether or not to introduce the purged mixture from the exhaust passage 3 into the exhaust passage 3. That is, it is a determination as to whether or not the three-way catalytic converter 4 is in an activated state. For example, if the cooling water temperature Tw is a temperature between the set water temperatures To ₁ and To ₂ , the process proceeds to step 12 and the air Step after turning on pump 22
Proceed to 13. On the other hand, in other cases, the process proceeds to step 17, the air pump 22 is turned off, and the present flow ends.

In step 13, the exhaust system purge flow control valve
In order to determine whether or not 23 is in the final setting state, it is determined whether the flag is 0 or 1. If the flag is 0, it is determined that the state is the initial setting state, and the process proceeds to step 14, where the flag is
In the case of, this flow is determined to be the final setting state, and this flow is terminated. In step 14, rich judgment of the air-fuel ratio is performed based on the output signal of the oxygen sensor 5 attached downstream of the exhaust gas from the position where the mixture of the purge mixture and the secondary air is introduced. If it is rich, go to step 15; if it is not rich, go to step 18. In the present embodiment, since the exhaust system purge flow control valve 23 and the fresh air flow control valve 25 are normally set to be lean by setting the initial opening degree, the step 18 in the case where it is determined to be lean is performed.
Is usually executed first.

In step 18, the exhaust gas purge flow control valve 23 is opened by a predetermined amount and the fresh air flow control valve 25 is closed by a predetermined amount in order to change the air-fuel ratio of the exhaust gas in the rich direction. Then, this flow is repeated until it is determined in step 14 that the vehicle is rich. Therefore, each time the flow is repeated, the opening degree of the exhaust system purge flow control valve 23 is increased stepwise at a constant rate, so that the purge flow rate increases and the opening degree of the fresh air flow control valve 25 also increases at a constant rate. , The fresh air flow rate is reduced. Thereby, as shown in FIG. 5, the air-fuel ratio in the exhaust passage 3 changes from lean to rich.

Thereafter, if it is determined in step 14 that the air-fuel ratio is rich, in step 15, the exhaust system purge flow control valve 23 is closed by a predetermined amount so as to change the exhaust air-fuel ratio in the lean direction. This allows the air-fuel ratio of the exhaust gas to be maintained at the target (slightly lean side) air-fuel ratio at which the three-way catalytic converter 16 can be activated satisfactorily while performing the purge process. After that, it proceeds to step 16.

In step 16, the opening of the exhaust system purge flow control valve 23 at this time is set and maintained as the final set opening, the flag is set to 1, and this flow is terminated. In the above control, the output change of the oxygen sensor 5 and each flow control valve
FIG. 5 shows a time chart of the change of the opening degree of 23 and 25 and the change of the actual air-fuel ratio of the exhaust gas. Here, FIG. 5 will be briefly described.

The output of the oxygen sensor 5 is shown in the upper part of FIG. 5. The output of the oxygen sensor 5 changes from lean to rich at the boundary of the air-fuel ratio of the exhaust at the slice level (stoichiometric air-fuel ratio). It changes step by step. In the middle,
The change in the opening of the exhaust system purge flow control valve 23 is indicated by a solid line, and the change in the opening of the fresh air flow control valve 25 is indicated by a broken line. actually,
As described above, these openings change stepwise,
Here, it is shown by a straight line.

Note that the lower part shows the actual air-fuel ratio of the exhaust gas. When the above flow is executed, the actual air-fuel ratio of the exhaust gas changes to the rich side with the passage of time, and when the air-fuel ratio becomes rich (exceeds the slice level of the oxygen sensor 5), the oxygen sensor The output of No. 5 is inverted stepwise to the rich side. Upon receiving the inversion signal, the exhaust system purge flow control valve 23 is changed by a predetermined amount in the closing direction (lean direction) and is kept constant. As a result, even when the purge process is performed, the air-fuel ratio of the exhaust gas can be maintained at a predetermined air-fuel ratio slightly on the lean side where activation of the three-way catalytic converter 16 can be favorably performed.

The above-mentioned cold purge control is performed until the three-way catalytic converter 4 is heated and activated. After a predetermined time has elapsed, the driving of the air pump 22 is stopped, and the exhaust system purge flow control valve 23 is operated. Then, the fresh air flow control valve 25 is also closed. The activation of the three-way catalytic converter 4 may be determined by providing a temperature sensor or the like at the three-way catalytic converter 4 or a downstream portion thereof and determining based on the temperature detected by the temperature sensor. Further, in the present embodiment, the opening degree of the exhaust system purge flow control valve 23 is changed in step 15, but of course, the fresh air flow control valve 25 may be simultaneously changed by a predetermined amount in the opening direction. However, it is also possible to adjust with only the fresh air flow control valve 25.

As described above, in this embodiment, the air-fuel ratio of the air-fuel mixture of the purge air-fuel mixture and the secondary air can be appropriately controlled. 4 has a low activation degree, the unburned component (H
As described above, secondary air is introduced into the exhaust passage 3 to effectively purify these exhaust harmful components, and the reaction heat is used by utilizing the reaction heat. The activation of the three-way catalytic converter 4 is promoted to minimize the emission of harmful exhaust components into the atmosphere, and the purging process is performed even when the degree of activation of the three-way catalytic converter 4 is low. The load of the purge process during operation can be reduced, and the fluctuation of the air-fuel ratio and the deterioration of drivability due to the purge process can be prevented (see FIG. 6).

Next, a second embodiment will be described with reference to the flowchart shown in FIG. In the second embodiment, an air-fuel ratio sensor 5 'which outputs an output signal corresponding to the air-fuel ratio is used as an air-fuel ratio detecting means, instead of the oxygen sensor 5 in the first embodiment. Note that step
Steps 21, 22, and 25 are the same as steps 11, 12, and 17 in the first embodiment, and thus description thereof will be omitted.

In step 23, it is determined whether or not the actual air-fuel ratio of the exhaust gas is the target air-fuel ratio based on the output of the air-fuel ratio sensor 5 '. If it is determined that the target (requested) air-fuel ratio is the target, the process proceeds to step 24. On the other hand, when it is determined that the air-fuel ratio is not the target air-fuel ratio, the present flow is terminated, and the flow is executed again after a predetermined time has elapsed. In step 24, when it is determined in step 22 that the actual exhaust air-fuel ratio is the target air-fuel ratio, the exhaust system purge flow rate is set to an amount corresponding to the difference between the target air-fuel ratio and the actual exhaust air-fuel ratio. Control valve 23
And the opening degree of the fresh air flow control valve 25 is changed, and this flow ends.

Therefore, according to the second embodiment, the first
As compared with the embodiment of the present invention, the target air-fuel ratio can be obtained more quickly, and the setting of the actual air-fuel ratio of the exhaust gas to the rich side can be excluded, so that the purification of the unburned components is accelerated accordingly. Therefore, the three-way catalytic converter 4 can be more quickly activated while performing the purging process, so that the emission of unburned components to the atmosphere can be reduced more effectively.

Next, a third embodiment will be described with reference to the flowchart shown in FIG. In the third embodiment, the air-fuel ratio of the purge mixture is predicted based on the weight of the canister 10 (that is, the weight of the adsorbed fuel vapor) and the temperature at the start of the purge. It is. Therefore, as shown in parentheses in FIG. 2, a weight sensor 30 for detecting the weight of the canister 10 and a canister temperature sensor 31 for detecting the temperature of the canister 10 are newly provided.

Steps 31 and 37 are the same as those in the first and second embodiments, and a description thereof will be omitted. In step 32, the weight W of the canister 10 is determined based on the output signal of the weight sensor 30.
, The process proceeds to step 33. In step 33, the temperature T of the canister 10 is detected based on the output signal of the canister temperature sensor 31, and the process proceeds to step.

In step 34, the obtained canister is determined with reference to a map determined in advance based on experimental results and the like.
The air-fuel ratio of the purge air-fuel mixture is retrieved from the weight W of the cylinder 10 and the temperature T of the canister 10. Then, the process proceeds to step 35.
In step 35, the opening degree of the exhaust system purge flow rate control valve 26 and the fresh air flow rate control valve 27, which is set and stored in advance, is referred to with reference to a map or the like in accordance with the air-fuel ratio of the purged air-fuel mixture searched in step 34. Search and set, and proceed to step 36.

In step 36, after the air pump 22 is driven, the present flow ends. Thus, in the third embodiment, it is not necessary to determine the actual air-fuel ratio of the exhaust gas, and the system can be simplified. Further, since the third embodiment employs feedforward control, the three-way catalytic converter 4 can be activated while purging more quickly than in the first and second embodiments. As a result, the emission of unburned components into the atmosphere can be reduced more effectively. Of course, the feed-forward control and the feedback control by detecting the air-fuel ratio in the first and second embodiments are combined to quickly and accurately control the actual exhaust air-fuel ratio to the target air-fuel ratio. You may do so.

In each of the above embodiments, the case where the three-way catalytic converter 4 is used has been described. However, the purge control at the time of cooling can be applied to the case where the oxidation catalytic converter is used. In addition, it is obvious that an apparatus without a catalytic converter is also effective in promoting the oxidation (purification) of unburned components in exhaust gas by secondary air while performing a purge process.

In each of the above embodiments, a fresh air flow control valve 25 is provided. However, even if the fresh air flow control valve 25 is not provided, a predetermined amount of fresh air is introduced.
By controlling the opening degree of only the exhaust system purge flow control valve 23,
The air-fuel ratio of the exhaust gas may be controlled to the target air-fuel ratio.

[0040]

As described above, according to the apparatus for preventing evaporation of fuel vapor in an internal combustion engine according to the present invention, the air-fuel ratio of the mixture of the purge mixture and the secondary air can be appropriately controlled. . Therefore, for example, when the engine is cold, the unburned components (HC, C
O) oxidation (purification) can be promoted, and the load of the purging process during normal operation can be reduced, and the air-fuel ratio fluctuation accompanying the purging process can be suppressed, so that good operating performance and exhaust characteristics can be obtained. Can be.

[Brief description of the drawings]

FIG. 1 is a block diagram according to an evaporative fuel evaporation prevention device for an internal combustion engine of the present invention.

FIG. 2 is an overall configuration diagram according to the first embodiment of the present invention.

FIG. 3 is a flowchart illustrating initial opening setting control according to the embodiment.

FIG. 4 is a flowchart for explaining purge control at the time of cooling according to the embodiment.

FIG. 5 is an explanatory diagram of the operation of the purge control at the time of cooling according to the embodiment.

FIG. 6 is a view for explaining one effect of the cold purge process according to the embodiment.

FIG. 7 is a flowchart illustrating a purge control at the time of cooling according to the second embodiment of the present invention.

FIG. 8 is a flowchart for explaining cold purge control according to a third embodiment of the present invention.

FIG. 9 is an overall configuration diagram of a conventional example.

[Explanation of symbols]

 Reference Signs List 1 engine 3 exhaust passage 4 three-way catalytic converter 5 oxygen sensor 10 canister 15 evaporative fuel passage 16 fuel tank 20 exhaust system purge passage 22 air pump 23 exhaust system purge flow control valve 24 fresh air introduction passage 25 fresh air flow control valve 50 control unit

Claims (1)

(57) [Claims] An evaporative fuel accumulated in a fuel reservoir is temporarily adsorbed by an adsorber, and the evaporative fuel is desorbed from the adsorber in a predetermined engine operating state, and is guided to an exhaust passage for processing. An evaporative fuel evaporation prevention device for an internal combustion engine, wherein a purged mixture of the desorbed evaporative fuel and desorption air and secondary air from the atmosphere are sucked through independent paths, mixed, and exhausted. Pump means for discharging and supplying to the passage; flow rate control means for controlling a flow rate ratio between the purge mixture and the secondary air such that an air-fuel ratio of the mixture of the purge air and the secondary air approaches a target value; An evaporative fuel evaporation prevention device for an internal combustion engine, comprising: