JP2003247462A - Fuel vapor processor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel vapor processor which can preferably prevent fluctuation or the like of air/fuel ratio resulting from a difference between a target purge flow rate and an actual purge flow rate, by carrying out precise flow rate control which suppresses the above purge flow rate difference. <P>SOLUTION: A maximum purge flow rate Qmax in accordance with a load factor L is calculated, and a maximum duty ratio Dmax from which the maximum purge flow rate Qmax can be obtained is variably set in accordance with a load factor L. At this time, at the load factor in a region where a saturation point does not appear in flow rate characteristics of a purge valve, the maximum duty ratio Dmax is set at 100%. At the load factor in a region where a saturation point appears, a duty ratio at the saturation point is set at the maximum duty ratio Dmax. A target duty ratio D is calculated by making use of the maximum duty ratio Dmax, the maximum purge flow rate Qmax and the target purge flow rate PQ, and an opening degree of the purge valve is controlled according to the target duty ratio D. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel vapor processing apparatus which is used, for example, in a vehicle-mounted internal combustion engine to suppress the release of fuel vapor generated in the fuel tank thereof into the atmosphere.

[0002]

2. Description of the Related Art Conventionally, in a vehicle internal combustion engine, in order to prevent the fuel vapor generated in the fuel tank from being released into the atmosphere, the fuel vapor in the fuel tank is filled with activated carbon. There is known a fuel vapor treatment device which is introduced into a canister and which adsorbs fuel vapor with this activated carbon. In this fuel vapor processing device, since the amount of fuel vapor adsorbed by the activated carbon in the canister is limited, the fuel vapor is desorbed from the activated carbon in the canister during engine operation and introduced into the intake passage through the purge passage. Then, a so-called purging process is performed in which the fuel is burned in the combustion chamber. By performing such a purging process, the fuel vapor adsorption performance of activated carbon is also restored.

Further, normally, when carrying out this purging process,
By controlling the opening degree of the purge valve provided in the purge passage, the flow rate of the fuel vapor introduced from the canister to the intake passage, that is, the purge flow rate is adjusted. Then, in the control of the purge valve, the actual purge flow rate is obtained based on the intake pressure and the opening degree of the purge valve at that time, and the actual purge flow rate and the target purge flow rate set based on the engine operating state are The opening of the purge valve is feedback-controlled so that they match.

When the purging process is performed, fuel vapor introduced from the canister separately from the fuel injected from the fuel injection valve is also introduced into the engine combustion chamber. Therefore, normally, as described in, for example, JP-A-8-109844, when the air-fuel ratio of the internal combustion engine is controlled, the fuel injection amount is calculated in consideration of the fuel amount by the purge process. ing. As described above, when the purge process is performed, the fuel amount, that is, the fuel injection amount is calculated in consideration of the target purge flow rate, thereby suppressing the disturbance of the air-fuel ratio even when the purge process is performed. As a result, the stoichiometric air-fuel ratio can be maintained.

[0005]

By the way, in recent years, along with the stricter regulation of the amount of fuel vapor released into the atmosphere, the adsorption capacity of activated carbon in the canister is surely recovered in a short time,
It is desired to improve the fuel adsorption capacity as a canister. Then, as one method for responding to this demand, attempts have been made to increase the number of executions of the purge process.

However, in order to increase the number of executions of the purging process, the purging process is intentionally performed even in the situation where the purging process has not been conventionally executed.
The following problems will occur.

For example, when the engine load is low and the intake pressure in the intake passage is low (increased to the negative pressure side), the flow velocity of the fuel vapor passing through the purge valve is high, and the pressure loss in the valve is small. Increase. Therefore,
As indicated by a solid line at 0, even if the opening degree of the purge valve (opening degree command value) is increased, the actual purge flow rate is saturated at a certain level and the flow rate exceeds a certain flow rate.

Even if the engine load is higher than the above engine load and the intake pressure in the intake passage has not decreased enough to cause saturation of the purge flow rate, depending on the characteristics of the purge valve, FIG. As shown by the solid line and the broken line, when the opening degree becomes equal to or larger than a predetermined opening degree, the flow rate characteristic may change from the opening degree area up to then due to the pressure loss. In addition, even if the opening of the purge valve is small, if the flow velocity characteristic of the fuel vapor passing through the valve changes to a predetermined opening or less, such as when the flow velocity of the fuel vapor is extremely small, the flow rate characteristics differ from those of the previous opening. There is also.

When the flow rate characteristics in the high opening range and the low opening range of the purge valve change as described above, the linear relationship between the purge valve opening and the purge flow rate in the entire opening range is not established.

However, in the above-described calculation of the actual purge flow rate, when the intake pressure is constant, the linear relationship between the opening of the purge valve and the purge flow rate is established without changing in the entire opening range. It is based on the assumption that Specifically, as indicated by the broken line in FIG. 10, the purge flow rate is based on the assumption that the opening of the purge valve linearly increases until it reaches the maximum opening. Then, the opening of the purge valve corresponding to the target purge flow rate is also calculated based on the maximum opening of the valve and the maximum purge flow rate. Therefore, in the operating region where the linear relationship between the opening degree of the purge valve and the purge flow rate is lost, the actual purge flow rate cannot be accurately calculated based on the maximum opening degree of the purge valve. The calculation accuracy is greatly reduced. Then, in this case, a deviation also occurs between the target purge flow rate and the actual purge flow rate, and this deviation also affects the air-fuel ratio control when the purging process is performed, and the air-fuel ratio is disturbed. Cause deterioration of emissions, which is inevitable. Note that such a deviation may occur due to, for example, non-linearity of the drive characteristic of the drive circuit that drives the purge valve to open and close, in addition to the non-linearity of the flow rate characteristic of the purge valve itself.

The present invention has been made in view of the above circumstances, and an object thereof is to control the purge flow rate by performing a more accurate flow rate control that suppresses a deviation between the target purge flow rate and the actual purge flow rate. An object of the present invention is to provide a fuel vapor processing apparatus capable of suitably suppressing the disturbance of the air-fuel ratio due to the deviation.

[0012]

[Means for Solving the Problems] Means for attaining the above-mentioned objects and their effects will be described below. The invention according to claim 1 is a canister for collecting the fuel vapor generated in the fuel tank, a purge passage for purging the fuel vapor desorbed from the canister into the intake passage of the internal combustion engine,
In a fuel vapor processing apparatus provided with a purge valve provided in the purge passage for adjusting a purge flow rate of fuel vapor, the opening degree of the purge valve corresponding to an inflection point at which the flow rate characteristic of the purge flow rate changes is set as a limit opening degree. It is said that a control means for controlling the opening of the purge valve according to the target purge flow rate is provided while variably setting this based on the engine operating state.

In the structure according to the first aspect, the opening degree of the purge valve corresponding to the inflection point at which the flow rate characteristic of the purge flow rate changes is set as the limit opening degree, which is variably set based on the engine operating state. . Therefore, even if the flow rate characteristic of the purge flow rate changes in the opening area exceeding the limit opening degree, the limit value of the purge valve opening degree can be determined by following the flow rate characteristic. A linear relationship with the flow rate will be maintained.
As a result, even when the number of executions of the purge process or the target purge flow rate is increased, it is possible to perform more accurate flow rate control that suppresses the deviation between the target purge flow rate and the actual purge flow rate. Turbulence, and eventually deterioration of exhaust emission and the like can be suitably suppressed.

According to a second aspect of the present invention, in the fuel vapor processing apparatus according to the first aspect, the inflection point changes when the purge flow rate reaches a saturation amount as the opening degree of the purge valve increases. When it is a turning point, the control means variably sets the limit opening as the maximum opening of the purge valve based on the engine operating condition.

When the purge flow rate of the fuel vapor passing through the purge valve reaches the saturation amount, the purge flow rate does not increase even if the opening of the purge valve is further increased. Therefore, the actual purge flow rate is calculated without considering this. Then, the deviation from the target purge flow rate also becomes large. In this respect, according to the configuration described in claim 2, the maximum opening of the purge valve at which the purge flow rate reaches the saturation amount is variably set based on the engine operating state, and the opening of the purge valve is increased. The linear relationship between the opening of the purge valve and the purge flow rate in the above is maintained.
Therefore, even in the above-described situation in which the deviation between the actual purge flow rate and the target purge flow rate becomes large, the deviation can be suppressed appropriately.

The invention according to claim 3 is the invention according to claim 1 or 2.
In the fuel vapor treatment apparatus described in the paragraph 1, when the inflection point is an inflection point when the flow rate characteristic of the purge flow rate changes as the opening degree of the purge valve decreases, the control means causes the limit opening. Degree as the lower limit opening degree of the purge valve and variably set it based on the engine operating state,
The purge valve is closed when the purge valve opening calculated based on the target purge flow rate is less than the variably set lower limit opening of the purge valve.

According to the third aspect of the present invention, the control of the opening of the purge valve is restricted in the opening region where the linear relationship between the opening of the purge valve and the purge flow rate is lost. become. In other words, since the purge valve opening is controlled only in the opening region where the linear relationship between the purge valve opening and the purge flow rate is established, the target purge flow rate and the actual purge flow rate are controlled. It becomes possible to suppress the gap between and.

According to a fourth aspect of the present invention, in the fuel vapor processing apparatus according to any of the first to third aspects, the purge valve is divided based on an inflection point at which the flow rate characteristic of the purge flow rate changes. For each control opening region, a storage means for storing the relationship between the control amount of the purge valve and the purge flow rate corresponding thereto is further provided, and the control means includes the control amount of the purge valve stored in the storage means and the control amount. The opening degree of the purge valve is controlled based on the relationship with the corresponding purge flow rate.

According to the fourth aspect of the present invention, the control opening area is divided with the inflection point where the flow rate characteristic of the purge flow rate changes as a boundary line, and the purge valve of each purge opening area is applied. The opening degree of the purge valve is controlled based on the relationship between the control amount and the purge flow rate corresponding thereto. As a result, even if the flow rate characteristic of the purge flow rate in the purge valve changes, the deviation between the target purge flow rate and the actual purge flow rate can be suppressed.

According to a fifth aspect of the present invention, in the fuel vapor processing apparatus according to any of the first to fourth aspects, the control means controls the load factor of the internal combustion engine, the intake air amount, and the intake pressure. Based on either of them, the limit opening of the purge valve is variably set.

The inflection point at which the flow rate characteristic of the purge flow rate changes changes as the intake pressure in the intake passage changes. Further, the intake pressure in the intake passage also changes as the amount of intake air taken into the cylinder changes. In the internal combustion engine, the intake pressure and the intake air amount have a correlation with the engine load factor.
Therefore, according to the configuration described in claim 5, the limit opening degree of the purge valve is appropriately set according to the engine operating state, and the effects of the invention described in any one of claims 1 to 4 are also obtained. This can be obtained easily and surely.

According to a sixth aspect of the present invention, a canister for collecting the fuel vapor generated in the fuel tank, a purge passage for purging the fuel vapor desorbed from the canister into the intake passage of the internal combustion engine, and the purge passage And a purge valve for adjusting the purge flow rate of the fuel vapor, which controls the opening of the purge valve based on the target purge flow rate according to the engine operating state and opens the purge valve. The control means is configured to close the purge valve on the basis of detection of an engine operating state in which the opening degree corresponds to an inflection point at which the flow rate characteristic of the purge flow rate changes.

The linear relationship between the opening degree of the purge valve and the purge flow rate is lost when there is an inflection point in the flow rate characteristic of the purge flow rate, and this inflection point depends on the engine operating state. It will appear. Therefore, in the configuration according to claim 6, the engine operating state in which the opening of the purge valve becomes the opening corresponding to the inflection point at which the flow rate characteristic of the purge flow rate changes is detected, and the purge valve is closed at this time. ing. Therefore, the purge is stopped when the linear relationship between the opening degree of the purge valve and the purge flow rate is lost. In other words, the purge is performed when the linear relationship between the opening degree of the purge valve and the purge flow rate is established. As a result, even when the number of executions of the purge process or the target purge flow rate is increased, it is possible to perform more accurate flow rate control that suppresses the deviation between the target purge flow rate and the actual purge flow rate. Turbulence, and eventually deterioration of exhaust emission and the like can be suitably suppressed.

According to a seventh aspect of the present invention, in the fuel vapor processing apparatus according to the sixth aspect, the control means is based on any one of the load factor of the internal combustion engine, the intake air amount, and the intake pressure. It is assumed that the engine operating state in which the opening of the purge valve corresponds to the inflection point at which the flow rate characteristic of the purge flow rate changes is detected.

The inflection point at which the flow rate characteristic of the purge flow rate changes changes as the intake pressure in the intake passage changes. Further, the intake pressure in the intake passage also changes as the amount of intake air taken into the cylinder changes. In the internal combustion engine, the intake pressure and the intake air amount have a correlation with the engine load factor.
Therefore, in the configuration according to claim 7, it becomes possible to preferably detect the engine operating state in which the opening of the purge valve corresponds to the inflection point at which the flow rate characteristic of the purge flow rate changes. The effect of the invention described in Item 6 can be easily and surely obtained.

According to an eighth aspect of the invention, a canister for collecting the fuel vapor generated in the fuel tank, a purge passage for purging the fuel vapor desorbed from the canister into the intake passage of the internal combustion engine, and the purge passage In a fuel vapor processing apparatus provided with a purge valve for adjusting the purge flow rate of the fuel vapor, the opening degree of the purge valve corresponding to the inflection point at which the flow rate characteristic of the purge flow rate changes,
The control amount and the purge flow rate corresponding thereto are obtained in advance,
When controlling the opening degree of the purge valve based on the target purge flow rate according to the engine operating state, a control means for controlling the opening degree of the purge valve using the obtained control amount and the purge flow rate corresponding thereto is provided. It is supposed to be one.

According to the structure of claim 8, the opening degree of the purge valve is controlled based on the control amount of the purge valve corresponding to the inflection point at which the flow rate characteristic of the purge flow rate changes and the purge flow rate corresponding thereto. As a result, even if the flow characteristics of the purge flow rate change when the number of executions of the purge process or the target purge flow rate is increased, highly accurate flow rate control that suppresses the deviation between the target purge flow rate and the actual purge flow rate. Will be able to do. Therefore, it is possible to preferably suppress the disturbance of the air-fuel ratio due to such a deviation of the purge flow rate, and further, the deterioration of the exhaust emission and the like.

According to a ninth aspect of the present invention, in the fuel vapor processing apparatus according to the eighth aspect, a control amount of the purge valve is set for each control opening range of the purge valve divided based on the inflection point. The control means further comprises a storage means for storing a relationship with a purge flow rate corresponding thereto, wherein the control means controls the purge valve based on the relationship between the control amount of the purge valve stored in the storage means and the corresponding purge flow rate. It is supposed to control the opening.

According to the ninth aspect of the present invention, the control opening area is divided with the inflection point where the flow rate characteristic of the purge flow rate changes as the boundary line, and the purge valve of each of the opening areas is applied. The opening degree of the purge valve is controlled based on the relationship between the control amount and the purge flow rate corresponding thereto. As a result, even if the flow rate characteristic of the purge flow rate in the purge valve changes, the deviation between the target purge flow rate and the actual purge flow rate can be suppressed.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION
The above-mentioned problem that the linear relationship between the opening degree of the purge valve and the purge flow rate is lost, and the deviation between the target purge flow rate and the actual purge flow rate is caused, reduces the pressure loss in the purge valve. Can be improved to some extent. However, when the capacity of the purge valve is increased in order to reduce the pressure loss, the purge flow rate changes greatly even with a slight change in the opening, so the control accuracy of the purge flow rate decreases and variations in the purge flow rate increase. A new problem arises. Therefore, eventually, it also affects the air-fuel ratio control when the purging process is performed, causing the air-fuel ratio to be disturbed, and consequently the deterioration of the emission cannot be avoided. On the other hand, in each of the following embodiments, by performing highly accurate flow rate control that suppresses the deviation between the target purge flow rate and the actual purge flow rate, the turbulence of the air-fuel ratio caused by the deviation of the purge flow rate is performed. It is possible to suitably suppress the deterioration of exhaust emission and the like resulting from this.

(First Embodiment) Hereinafter, a first embodiment in which the fuel vapor processing apparatus according to the present invention is embodied as a fuel vapor processing apparatus for an on-vehicle internal combustion engine will be described with reference to FIGS.

FIG. 1 is a schematic diagram showing the basic system configuration of the fuel vapor processing apparatus of this embodiment. As shown in FIG. 1, this fuel vapor processing apparatus includes a canister 2 for adsorbing fuel vapor, and a vapor line 4 for sucking fuel vapor in the canister 2 into an intake passage 5.
2, a purge valve 43 provided in the middle of the vapor line 42 for adjusting the purge flow rate, and an evaporation line 4 for introducing the fuel vapor in the fuel tank 1 into the canister 2.
1, an air flow meter 51 that measures the intake air amount Qa in the intake passage 5, and an EC that totally controls the purging process
It has a U (control device) 7.

FIG. 2 is an enlarged view showing the sectional structure of the canister 2. As shown in FIG. 2, the canister 2 has perforated plates 23 and 24 therein. The space sandwiched between the perforated plates 23, 24 serves as a fuel adsorption chamber 22. The fuel adsorption chamber 22 is filled with activated carbon 34 for adsorbing fuel vapor. In addition, the perforated plate 23,
Filters 28 and 29 for preventing the activated carbon 34 from falling off are provided between the fuel cell 24 and the fuel adsorption chamber 22. An air chamber 25 is provided between one end of the case 21 of the canister and the porous plate 23. Air chambers 26 and 27 are provided between the other end of the canister case 21 and the porous plate 24. The air chamber 26 and the air chamber 27 are partitioned by a partition plate 33 to prevent the fuel vapor introduced from the fuel tank 1 from being released to the outside of the canister 2 without being adsorbed by the activated carbon 34. An evaporation port 30 and a purge port 31 are provided at the end of the case 21 on the side where the air chambers 26 and 27 are provided. On the other hand, an air port 31 is provided at the end of the case 21 on the air chamber 25 side. Here, one end of the evaporation port 30 is communicated with the air chamber 26, and the other end is connected to the evaporation line 41 via an appropriate control valve (not shown). The purge port 31 has one end communicating with the air chamber 27 and the other end connected to the purge line 42 via an appropriate control valve (not shown). The air port 32 has one end at the air chamber 2
5, and the other end is open to the atmosphere via an appropriate control valve (not shown).

Further, in FIG. 1, the purge line 4 is used.
The purge valve 43 provided in No. 2 is an electromagnetic valve whose opening degree is variably set according to the duty ratio of the control signal output from the ECU 7. Here, when the duty ratio of the control signal is 0%, the valve is fully closed, when the duty ratio is 100%, it is fully opened, and when the duty ratio is 0 to 100%, the opening is in accordance with the duty ratio. That is, this duty ratio is the control amount of the purge valve 43. In the present embodiment, the purge valve 43 is assumed to have the characteristics illustrated in FIG.

Further, the purge valve 4 is provided in the ECU 7.
A storage element (R which stores various maps for controlling
OM, etc.) and a CPU for performing various calculations.
Then, parameters indicating the operating state of the internal combustion engine (not shown) are input to the ECU 7, and the opening degree of the purge valve 43 is duty-controlled based on these parameters and the map. The ECU 7 performs not only purge control including duty control of the purge valve 43, but also various engine controls such as air-fuel ratio control.

Next, the purging process performed by this fuel vapor processing apparatus will be described. Normally, when refueling or when the outside temperature rises, fuel vapor is generated in the fuel tank 1 accordingly. The fuel vapor generated in the fuel tank 1 is introduced into the canister 2 through the evaporation line 41, diffused in the air chamber 26, and then adsorbed by the activated carbon 34 in the fuel adsorption chamber 22.

On the other hand, when the engine is in operation, a process of desorbing the fuel vapor adsorbed by the activated carbon 34 to restore the adsorption capacity of the activated carbon 34 is performed. That is, the pressure in the intake passage 5 is lower than the atmospheric pressure when the engine is operating,
When the purge valve 43 is opened, the pressure in the purge line 42 drops, and the outside air is introduced into the canister 2 from the atmosphere port 32. Then, this outside air is introduced into the fuel adsorption chamber 22 while being diffused in the air chamber 25, and activated carbon 34
Acts to desorb the adsorbed fuel vapor.
The fuel vapor desorbed from the activated carbon 34 is sucked into the intake passage 5 through the purge line 42 while the flow rate of the fuel vapor is controlled by the purge valve 43, and the fuel injected along with the fuel injection valve (not shown) together with the combustion chamber of the engine. Burned in.

In the purging process, the amount of the fuel vapor introduced into the intake passage 5 (intake amount), that is, the purge flow rate, is determined by controlling the opening of the purge valve 43 through the ECU 7.

FIG. 3 shows the ECU 7 during the purging process.
FIG. 3 shows a processing procedure for controlling the opening degree of the purge valve 43 executed by the process shown in FIG.
The processing relating to the purge valve opening control according to the present embodiment will be described in detail with reference to FIG. It should be noted that this process is repeatedly executed as an interrupt process at predetermined time intervals.

When this processing is started, it is first determined whether or not the purge condition is satisfied based on the engine operating state (step S101). The establishment of the purge condition is, for example, when the air-fuel ratio feedback control is being performed. When such a purge condition is not established, the purge valve 43 is closed (step S11).
2) Then, this process ends.

On the other hand, when the purge condition is satisfied, the intake air amount Qa is measured based on the output from the air flow meter 51 (step S102), and the load factor L of the internal combustion engine is calculated by the following equation (1). Calculated (step S10
3). Note that Qwot is the intake air amount when the engine is fully loaded, and is a predetermined value that is obtained in advance.

L = Qa / Qhot (1) Next, the maximum purge flow rate Qmax at the calculated load factor L is obtained from the map illustrated in FIG. 4 (step S104). Here, as can be seen from FIG. 4, the maximum purge flow rate Qmax increases as the load factor L decreases. This is because when the load factor L is small, the opening degree of the throttle valve 5a provided in the intake passage is small, and the intake pressure in the intake passage 5 is low (increases to the negative pressure side). This is because the pressure difference becomes large and the amount of fuel vapor drawn from the canister 2 increases. Further, when the load factor L becomes a predetermined value or less, the load factor L
Even if becomes smaller, the maximum purge flow rate Qmax becomes a substantially constant value. This is because the flow rate of the fuel vapor sucked from the canister 2 becomes faster when the load factor L becomes a certain value or less. That is, since the pressure loss in the fluid passage is proportional to the square of the fluid velocity, the flow velocity of the fuel vapor increases, so that the pressure loss in the purge valve 43 increases, and as a result, the purge flow rate does not increase, that is, it is saturated. Will end up.

Next, the target purge rate P is set (step S105). Incidentally, the purge rate is the ratio of the purge flow rate to the intake air amount, and the target purge rate P
Is a value that is set each time as a target value of the purge rate based on the engine operating state and the like. For example, the target purge rate P immediately after the start of purging is kept low, and the target purge rate P is set high by continuing the purging process.

Thereafter, the target purge flow rate PQ is calculated from the following equation (2) using the target purge rate P thus set and the calculated intake air amount Qa (step S106).

PQ = P · Qa (2) Next, the maximum duty ratio Dmax at the calculated load factor L is obtained from the map illustrated in FIG. 5 (step S107). The maximum duty ratio Dmax is a duty ratio when the maximum purge flow rate Qmax is obtained. Further, in the present embodiment, as illustrated in FIG. 5, even if the control duty ratio of the purge valve 43 is increased, the maximum duty ratio Dmax is set to 100% in the engine load region where the purge flow rate is not saturated. . On the other hand, in the engine load region where the flow rate characteristic of the purge valve 43 changes as the control duty ratio of the purge valve 43 increases, that is, in the engine operating state in which the purge flow rate is saturated, when the purge flow rate reaches the saturation amount, The control duty ratio of the valve 43 is set to the maximum duty ratio Dm.
Set to ax.

In this way, the maximum duty ratio Dmax
By setting the maximum duty ratio Dmax
The ratio between the target duty ratio D and the target duty ratio D is as shown in the following equation (3).
And will match the ratio with. Therefore, in the present embodiment, the target duty ratio D is calculated using the equation (4) obtained by modifying the equation (3) (step S108).

Qmax: PQ = Dmax: D (3) D = (PQ / Qmax) Dmax (4) Next, in this processing, it is determined whether the target duty ratio D is equal to or more than the lower limit duty ratio D0. (Step S
109). The lower limit duty ratio D0 is a duty ratio at an inflection point where the linear relationship between the purge flow rate and the duty ratio is not established, and is also a value set according to the load factor L.

The target duty ratio D is the lower limit duty ratio D
When it is 0 or more, the opening degree of the purge valve 43 is controlled by the target duty ratio D (step S110). on the other hand,
When the target duty ratio D is less than the lower limit duty ratio D0, the relationship between the purge flow rate and the duty ratio is non-linear, and the purge flow rate cannot be controlled accurately, so the purge valve 43 is closed. (Step S111).

Thereafter, step S10 is performed until it is determined in step S101 that the purge condition is no longer satisfied.
The processing of 1-111 is repeatedly executed. As described above, according to the fuel vapor processing apparatus of the first embodiment, the following effects can be obtained.

(1) The maximum duty ratio Dmax capable of obtaining the maximum purge flow rate Qmax is variably set according to the load factor L of the internal combustion engine. Accordingly, the duty control of the purge valve 43 is performed within the range of 0 to Dmax, and the actual purge flow rate is 0 to Qmax.
Within the range of, it changes linearly without becoming saturated. Therefore, even if the number of executions of the purging process or the target purge flow rate is increased, it is possible to perform highly accurate flow rate control while suppressing the deviation between the target purge flow rate PQ and the actual purge flow rate. . As a result, it becomes possible to suitably suppress the disturbance of the air-fuel ratio and the deterioration of exhaust emission resulting from this.

(2) The inflection point opening at which the linear relationship between the purge flow rate and the duty ratio is not established is set as the lower limit duty ratio D0, and the calculated target duty ratio D is the lower limit duty ratio D0. When it is less than the target value, the target duty ratio D is ignored and the purge valve 43 is closed. As a result, the opening of the purge valve 43 is controlled only in the region where the linear relationship between the purge flow rate and the duty ratio is established, and in this respect also, the target purge flow rate PQ and the actual purge flow rate are It becomes possible to suppress the gap.

(Second Embodiment) Next, a second embodiment of the fuel vapor processing apparatus according to the present invention will be described based on FIG. 6 focusing on the difference from the first embodiment. explain.

In the present embodiment, the processes of steps S201 and 203 are added to the process of FIG. 3 in the first embodiment, the process of step S107 is omitted, and the maximum duty ratio Dmax is 100% in the process of step S108. The difference is that it is fixed to. Note that, in FIG. 6, steps indicating the same processing as in FIG. 3 in the first embodiment are given the same step numbers.

When the process shown in FIG. 6 is started, first, the processes of steps S101 to 103 described above are performed, and the load factor L of the internal combustion engine is calculated in the same manner as described above. Next, it is determined whether the load factor L is equal to or higher than the saturation load factor L0 (step S201). As shown in FIGS. 4 and 5, the saturation load factor L0 gradually shows a saturation point in the flow rate characteristic of the purge flow rate controlled by the purge valve 43 when the load factor L is gradually changed. It is the load factor when. In other words, it is the maximum load factor in the load region where the saturation point appears and is a fixed value that has been obtained in advance by experiments or the like. When it is determined in this step S201 that the load factor L is less than the saturated load factor L0, a saturation point appears in the flow rate characteristic, and the linear relationship between the purge flow rate and the duty ratio is lost and the target is reached. There may be a gap between the purge flow rate and the actual purge flow rate. Therefore,
In the present embodiment, in such a case, the purge valve 43
Is closed (step S203), and the process is once ended. On the other hand, when the load factor L is equal to or higher than the saturated load factor L0, the above-described steps S104 to S1 to advance the purging process.
The processing of 06 is performed.

After that, the target duty ratio D is calculated using the following equation (5) (step S202). D = (PQ / Qmax) · 100 (5) In this equation (5), “Dmax” in the above equation (4) is changed to “10.
It is fixed to "0". This is the purge valve 43
The maximum purge flow rate Qmax
This is because it has been determined in advance through step S201 that the maximum duty ratio Dmax at which the above is obtained is always 100%.

After the target duty ratio D is calculated in this way, the same processing as in the first embodiment (FIG. 3) is performed. As described above, according to the fuel vapor processing apparatus of the second embodiment, the following effects can be obtained.

(1) The saturated load factor L0, which is the maximum load factor in the load region where the saturation point appears in the flow rate characteristic of the purge flow rate controlled by the purge valve 43, is set, and the calculated load factor L and saturated load factor L0 are set. When the load factor L is less than the saturated load factor L0, the purge valve 43 is once closed. Therefore, the purging process is not performed in the load region in which the saturation point appears in the flow rate characteristic, in other words, the purging process is performed only in the load region in which the saturation point does not appear. A linear relationship is maintained. As a result, even when the number of executions of the purging process or the target purge flow rate is increased, it is possible to suppress the deviation between the target purge flow rate PQ and the actual purge flow rate.

(2) Calculated load factor L and saturated load factor L0
When the load factor L is equal to or higher than the saturated load factor L0, the maximum duty ratio is set to 100% and the target duty ratio D is calculated. Therefore, it is not necessary to variably set the maximum duty ratio Dmax, and as a result, the map illustrated in FIG. 5, that is, the map for calculating the maximum duty ratio with respect to the load factor becomes unnecessary. Therefore, the calculation load on the ECU 7 (FIG. 1) is reduced, the memory capacity to be saved by the ECU 7 is also reduced, and the processing speed is improved and the cost is reduced.

(Third Embodiment) Next, a third embodiment of the fuel vapor processing apparatus according to the present invention will be described with reference to FIG.
~ It demonstrates based on FIG.

In the third embodiment, the purge valve 4
3 is intended for characteristic compensation when using the purge valve having the flow rate characteristics illustrated by the solid line and the broken line in FIG. 11 above, and is equal to or less than the inflection point on the side controlled by the low duty ratio of the valve. Even in the region above the inflection point on the side controlled by the high duty ratio, the purge control with a small flow rate error is executed.

In the following, as shown in FIG. 8, the inflection point on the side controlled by the low duty ratio is the inflection point C1, and the inflection point on the side controlled by the high duty ratio is the inflection point. Let it be C2. Further, since the purge flow rate and the duty ratio at the inflection points C1 and C2 change according to the load rate, in the present embodiment, the purge flow rate and the duty ratio at the inflection points C1 and C2 with respect to the load rate, respectively. The relationship of is obtained in advance by experiments or the like. Then, a map illustrated in FIG. 9 is created in advance based on the obtained result and stored in the ROM or the like of the ECU 7. The map illustrated in FIG. 9 is
The number of inflection points is prepared.

FIG. 7 shows a processing procedure for controlling the opening degree of the purge valve according to the third embodiment, which will be described below with reference to FIG. The details of the processing performed will be sequentially described. The process shown in FIG. 7 is also repeatedly executed as an interrupt process at every predetermined time.

When this process is started, it is first determined whether or not the purge condition is satisfied based on the operating state of the internal combustion engine (step S501). The establishment of the purge condition is, for example, when the air-fuel ratio feedback control is being performed. When such a purge condition is not satisfied, the purge valve 43 is closed (step S513), and this processing ends.

On the other hand, when the purge condition is satisfied, the intake air amount Qa based on the output from the air flow meter 51 is measured (step S502), and the equation (1) is obtained.
Thus, the load factor L is calculated (step S503). It has been described above that Qwot is the intake air amount at the full load of the engine and is a predetermined value that is obtained in advance.

Next, from the map illustrated in FIG. 4 above, the maximum purge flow rate Qmax at the calculated load factor L is obtained.
Is required. Further, from the map illustrated in FIG. 9, the inflection point purge flow rate Qc1 and the inflection point duty ratio Dc1 at the inflection point C1, and the inflection point purge flow rate Qc2 and the inflection point duty ratio Dc2 at the inflection point C2. Are obtained respectively (step S504).

Next, the target purge rate P is set based on the engine operating state and the like (step S505), and the target purge rate P and the measured intake air amount Qa are used to calculate from the equation (2). The target purge flow rate PQ is calculated (step S506).

Next, the calculated target purge flow rate PQ
Is determined to be smaller than the inflection point purge flow rate Qc1 (step S507). When the target purge flow rate PQ is smaller than the inflection point purge flow rate Qc1, the target duty ratio D is calculated from the following equation (6) using the target purge flow rate PQ, the inflection point purge flow rate Qc1, and the inflection point duty ratio Dc1. (Step S508). Then, the opening of the purge valve 43 is controlled by the target duty ratio D (step S509).

D = (PQ / Qc1) · Dc1 (6) On the other hand, when it is determined in step S507 that the target purge flow rate PQ is equal to or greater than the inflection point purge flow rate Qc1, the target purge flow rate PQ is Inflection point purge flow rate Qc
It is further determined whether it is smaller than 2 (step S5).
10). The target purge flow rate PQ is the inflection point purge flow rate Qc2.
If smaller, the target purge flow rate PQ, the inflection point purge flow rates Qc1, Qc2, and the inflection point duty ratios Dc1, D
The target duty ratio D is calculated from the following equation (7) using c2 (step S511). Then, the opening of the purge valve 43 is controlled by the target duty ratio D (step S509).

D = {(D2c-Dc1) / (Qc2-Qc1)} · (PQ-Qc1) + Dc1 (7) On the other hand, in step S510, the target purge flow rate PQ is equal to or greater than the inflection point purge flow rate Qc2. If it is determined that the target purge flow rate PQ and the inflection point purge flow rate Qc
2, inflection point duty ratio Dc2, and maximum purge flow rate Q
The target duty ratio D is calculated from the following equation (8) using max (step S512). Then, the opening of the purge valve 43 is controlled by the target duty ratio D (step S509).

D = {(100−Dc2) / (Qmax−Qc2)} · (PQ−Qc2) + Dc2 (8) After that, until it is determined in step S501 that the purge condition is not satisfied, step S501. ~ S512
The process of is repeatedly executed.

As described above, according to the fuel vapor processing apparatus of the third embodiment, the following effects can be obtained. (1) Inflection point purge flow rate Qc at each inflection point where the flow rate characteristic of the purge flow rate controlled by the purge valve 43 changes
The relationship between the inflection point duty ratio Dc and the inflection point duty ratio Dc is stored in the ROM or the like of the ECU 7 as a map so that it can be referred to based on the load factor L. Further, the control opening regions of the purge valve 43 are divided for each inflection point purge flow rate Qc, and the inflection point purge flow rate Qc and the inflection point duty ratio are set in the control opening regions according to the target purge flow rate PQ. The target duty ratio D is calculated based on Dc. Therefore, even if the flow rate characteristic of the purge flow rate changes, the target duty ratio is calculated in accordance with the change, so that the deviation between the target purge flow rate PQ and the actual purge flow rate can be suppressed. become able to. Furthermore, since the entire opening area of the purge valve 43 can be used,
The number of executions of the purge process can be increased, and the fuel vapor adsorption performance of the canister 2 can be improved.

(Other Embodiments) The above-described embodiments may be modified as follows, and even in that case, the actions and effects according to the respective embodiments can be obtained.

In the first embodiment, the map illustrated in FIG. 5 is used as a map for obtaining the maximum duty ratio with respect to the load factor. However, the above equation (1)
As is clear from the above, the intake air amount Qwot is a fixed value, and the load factor L corresponds to the change in the intake air amount Qa. Therefore, the maximum duty ratio Dmax may be set based on the intake air amount Qa. Further, normally, when the intake air amount Qa decreases, the opening degree of the throttle valve 5a in the intake passage 5 also decreases, and the intake pressure decreases (becomes larger on the negative pressure side). On the contrary, when the intake air amount Qa increases, the opening degree of the throttle valve 5a in the intake passage 5 also increases, and the intake pressure increases (decreases toward the negative pressure side). That is, there is a close relationship between the intake air amount and the intake pressure in the intake passage. Therefore, an appropriate intake pressure sensor may be provided instead of the air flow meter 51, and the maximum duty ratio may be set based on the intake pressure detected by the intake pressure sensor. Even in this case, the operational effects according to the first embodiment can be obtained.

In the second embodiment, the judgment as to whether to perform the purging or to temporarily stop (step S201 in FIG. 6) is made based on the load factor L. The amount and the intake pressure are correlated with each other. Therefore,
The intake air amount when the saturation point begins to appear in the flow rate characteristic of the purge valve 43 is set as the saturated intake air amount Qa0, and the purge process is performed or temporarily stopped by comparing the saturated intake air amount Qa0 and the intake air amount Qa. It may be possible to make such a judgment. Further, the intake pressure PM in the intake passage 5 is measured based on the output of the intake pressure sensor, and the intake pressure when the saturation point begins to appear in the flow rate characteristic of the purge valve 43 is set to the saturated intake pressure PM0. It may be possible to determine whether to perform purging or to temporarily stop by comparing PM0 with the intake pressure PM. Even in this case, the operational effects according to the second embodiment can be obtained.

In the second embodiment, the saturation load factor L0
Is a fixed value, but may be a variable value set based on the engine operating state such as the engine speed. By doing so, the determination in step S201 of FIG. 6 can be made more accurate. Further, the saturated intake air amount Qa0 and the saturated intake pressure PM0 are also set to variable values set based on the engine operating state such as the engine speed, so that the determination as to whether or not to perform the purging process is also performed. It can be highly accurate.

In the third embodiment, the purge flow rate and the duty ratio at the inflection point were calculated based on the load factor. However, since the load factor, the intake air amount, and the intake pressure are correlated with each other as described above, the purge at the inflection point is performed based on the intake air amount or the intake pressure detected by the pressure sensor provided in the intake passage 5. The flow rate and the duty ratio may be obtained. Even in this case, the operational effect according to the third embodiment can be obtained.

The third embodiment may be applied to the first embodiment. That is, the opening of the valve 43 when the fuel vapor passing through the purge valve 43 reaches the saturation amount is set as the maximum opening, and the maximum opening and the maximum purge flow rate at the same opening and the purge valve at each inflection point are set. The opening of the purge valve 43 may be set based on the opening and the purge flow rate. For example, in the third embodiment, when the inflection point C2 is the saturation point, the inflection point purge flow rate Qc2 is set to the maximum purge flow rate Qmax, and the inflection point duty ratio Dc2 is set to the maximum duty ratio Dmax.
Further, the lower limit duty ratio D in the first embodiment
0 is the inflection point duty ratio Dc1, and the purge flow rate at the lower limit duty ratio D0 is the inflection point purge flow rate Qc1. By doing so, it becomes possible to suppress the deviation between the target purge flow rate PQ and the actual purge flow rate, and even when the purge flow rate is saturated,
The entire opening control region of the purge valve 43 can be used, and the number of purges can be increased. That is, the fuel vapor adsorption performance of the canister 2 can be improved.

In addition, the technical ideas that can be understood from the above-described respective embodiments or modifications thereof will be described below along with their effects. (1) In the fuel vapor processing apparatus according to claim 8 or 9, a control amount for the opening degree of the purge valve corresponding to an inflection point at which the flow rate characteristic of the purge flow rate obtained in advance changes, and a purge flow rate corresponding thereto. A fuel vapor processing apparatus, wherein and are obtained as values according to various operating states of the engine.

According to this fuel vapor processing apparatus, even if the relationship between the purge valve control amount at the inflection point and the corresponding purge flow rate changes depending on the engine operating state.
The change can be captured with certainty. Therefore, the precision of the value used when calculating the opening degree of the purge valve required for the purge process is improved, and the purge flow rate can be controlled with high precision.

(2) In the fuel vapor processing apparatus described in (1) above, various operating states of the engine are any one of a load factor, an intake air amount, and an intake pressure of the engine. Fuel vapor treatment device.

The inflection point at which the flow rate characteristic of the purge flow rate changes changes as the intake pressure in the intake passage changes. Further, the intake pressure in the intake passage also changes as the amount of intake air taken into the cylinder changes. In the internal combustion engine, the intake pressure and the intake air amount have a correlation with the engine load factor.
Therefore, according to this fuel vapor processing apparatus, it becomes possible to easily and surely obtain each value obtained in the fuel vapor processing apparatus described in (1) above.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a first embodiment of a fuel vapor processing apparatus according to the present invention.

FIG. 2 is a sectional view showing a sectional structure of the canister shown in FIG.

FIG. 3 is a flowchart showing a purge valve opening control procedure according to the first embodiment.

FIG. 4 is a graph showing a map structure for obtaining a maximum purge flow rate from a load factor.

FIG. 5 is a graph showing a map structure for obtaining a maximum duty ratio from a load factor.

FIG. 6 is a flowchart showing a purge valve opening control procedure according to a second embodiment of the fuel vapor processing apparatus according to the present invention.

FIG. 7 is a flowchart showing a purge valve opening control procedure according to a third embodiment of the fuel vapor processing apparatus of the present invention.

FIG. 8 is a graph showing inflection points defined in the third embodiment.

FIG. 9 is a graph showing a map structure for obtaining the purge flow rate and the duty ratio at the inflection point defined above.

FIG. 10 is a graph showing a flow rate characteristic example of a purge valve in an engine low load region.

FIG. 11 is a graph showing a flow rate characteristic example of a purge valve having an inflection point in a low engine load region.

[Explanation of symbols]

1 ... Fuel tank, 2 ... Canister, 5 ... Intake passage, 5a
... Throttle valve, 7 ... ECU, 19 ... Filter case,
21 ... Case, 22 ... Fuel adsorption layer, 23 ... Perforated plate, 24
... perforated plate, 25 ... air layer, 26 ... air layer, 27 ... air layer, 28 ... filter, 30 ... evaporation port, 31 ... purge port, 32 ... atmosphere port, 33 ... partitioner, 34 ... activated carbon, 41 ... evaporation line, 42 … Vapor line, 43
... Purge valve, 51 ... Air flow meter.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Naoya Kato             14 Iwatani Shimohakaku-cho, Nishio-shi, Aichi Stock Association             Company Japan Auto Parts Research Institute (72) Inventor Masaki Takeyama             14 Iwatani Shimohakaku-cho, Nishio-shi, Aichi Stock Association             Company Japan Auto Parts Research Institute (72) Inventor Yuji Miyano             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Car Co., Ltd. (72) Inventor Kenji Kasashima             1 Toyota Town, Toyota City, Aichi Prefecture Toyota Auto             Car Co., Ltd. F-term (reference) 3G044 BA16 CA05 DA02 EA03 EA23                       FA18

Claims (9)

[Claims] 1. A canister for collecting fuel vapor generated in a fuel tank, a purge passage for purging fuel vapor desorbed from the canister into an intake passage of an internal combustion engine, and a purge passage provided in the purge passage for collecting the fuel vapor. In a fuel vapor processing apparatus provided with a purge valve for adjusting the purge flow rate, the opening degree of the purge valve corresponding to an inflection point at which the flow rate characteristic of the purge flow rate changes is set as a limit opening degree, which is variably set based on the engine operating state. At the same time, the fuel vapor processing apparatus is provided with control means for controlling the opening degree of the purge valve according to a target purge flow rate. 2. When the inflection point is an inflection point when the purge flow rate reaches a saturation amount with an increase in the opening degree of the purge valve, the control means sets the limit opening degree of the purge valve. The fuel vapor processing apparatus according to claim 1, wherein the maximum opening degree is variably set based on the engine operating state. 3. When the inflection point is an inflection point when the flow rate characteristic of the purge flow rate changes as the opening degree of the purge valve decreases, the control means sets the limit opening degree to the purge valve. The lower limit opening of the purge valve is variably set based on the engine operating state, and when the purge valve opening calculated based on the target purge flow rate is less than the lower limit opening of the variably set purge valve, the purge valve is closed. The fuel vapor processing device according to claim 1 or 2. 4. The fuel vapor processing device according to claim 1, wherein each purge valve control opening area is divided based on an inflection point at which the flow rate characteristic of the purge flow rate changes. The purge valve control amount further includes a storage unit that stores a relationship between the purge flow rate and the purge flow rate corresponding thereto, and the control unit is a relationship between the purge valve control amount stored in the storage unit and the corresponding purge flow rate. The fuel vapor processing apparatus is characterized in that the opening of the purge valve is controlled based on the above. 5. The load ratio of the internal combustion engine,
The fuel vapor processing apparatus according to any one of claims 1 to 4, wherein the limit opening degree of the purge valve is variably set based on any one of the intake air amount, the intake air amount, and the intake pressure. 6. A canister for collecting fuel vapor generated in a fuel tank, a purge passage for purging fuel vapor desorbed from the canister into an intake passage of an internal combustion engine, and a purge passage provided in the purge passage for collecting the fuel vapor. In a fuel vapor processing apparatus having a purge valve for adjusting the purge flow rate, the opening of the purge valve is controlled based on the target purge flow rate according to the engine operating state, and the opening of the purge valve is the flow rate of the purge flow rate. A fuel vapor processing apparatus comprising: a control unit that closes the purge valve based on detection of an engine operating state that has an opening corresponding to an inflection point where the characteristic changes. 7. The load ratio of the internal combustion engine,
7. The engine operating state in which the opening degree of the purge valve becomes the opening degree corresponding to the inflection point at which the flow rate characteristic of the purge flow rate changes is detected based on any of the intake air amount, the intake air amount, and the intake pressure. Fuel vapor treatment equipment. 8. A canister for collecting fuel vapor generated in a fuel tank, a purge passage for purging the fuel vapor desorbed from the canister into an intake passage of an internal combustion engine, and a purge passage provided in the purge passage for collecting the fuel vapor. In a fuel vapor processing apparatus including a purge valve that adjusts a purge flow rate, a control amount and a purge flow rate corresponding thereto are obtained in advance for an opening of the purge valve that corresponds to an inflection point at which the flow rate characteristic of the purge flow rate changes. When controlling the opening degree of the purge valve based on the target purge flow rate according to the engine operating state, a control means for controlling the opening degree of the purge valve using the obtained control amount and the purge flow rate corresponding to the control amount is provided. A fuel vapor processing device comprising: 9. The fuel vapor processing apparatus according to claim 8, wherein a control amount of the purge valve and a purge flow rate corresponding thereto are set for each control opening region of the purge valve divided based on the inflection point. A storage unit storing a relationship, wherein the control unit controls the opening degree of the purge valve based on the relationship between the control amount of the purge valve stored in the storage unit and the corresponding purge flow rate. Characteristic fuel vapor treatment device.