JPH07166975A - Control device for purging fuel vapor - Google Patents

Abstract

PURPOSE:To secure accuracy in cases where a small valve-opening duty is required particularly at the start of purging so as to avoid excessive purging by controlling a duty period if the opening duty of a purge control valve is small. CONSTITUTION:A control device for purging fuel vapor has a purge control valve 24 in a purge passage 22 connecting a canister 21 to the intake system of an internal combustion engine 1, and causes fuel vapor adsorbed to the canister to be purged into the intake system 2 by opening the purge control valve 24 under predetermined engine operating conditions. In this case, the opening duty of the purge control valve 24 is set by a valve-opening duty setting means (control unit) 6 according to the engine operating conditions so that the desired purge rate of fuel vapor is attainable. When the set valve-opening duty is in a range less than a predetermined value, the duty period is set greater by the duty period setting means 6 than in the case of a range not less than the predetermined value, and the purge control valve 24 is controlled based on the set valve-opening duty and the duty period.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for temporarily adsorbing fuel vapor generated from a fuel tank or the like of an internal combustion engine in a canister, and then sucking it into an intake system of the engine through a purge control valve for combustion treatment. In regard to the above, in regard to the improvement of the control method of the duty-controlled purge control valve, in particular, to the technique of improving the accuracy in the region where the valve opening duty is small.

[0002]

2. Description of the Related Art As a conventional control method of a purge control valve in a fuel vapor processing apparatus, the following is known. In JP-A-59-399575, the purge control valve is operated in relation to the load of the engine, and the purge flow rate is controlled in proportion to the intake air flow rate, thereby suppressing fluctuations in the air-fuel ratio of the air-fuel mixture. What has been done is disclosed.

Further, Japanese Patent Laid-Open No. 61-19962 discloses a purge control valve in which duty control is used and the purge flow rate is controlled according to the intake air flow rate. Further, in JP-A-2-245461, the higher the fuel concentration of the purge gas is, the slower the opening speed of the purge control valve is to prevent a large amount of purge gas from suddenly flowing into the intake system at the beginning of the purge. However, it is disclosed that the air-fuel ratio is prevented from being transiently enriched.

[0004]

However, by integrating these techniques, the purge flow rate is controlled in proportion to the intake air flow rate by using a generally used duty control type purge control valve, and the purge flow rate is controlled. Even if an attempt is made to prevent the air-fuel ratio from becoming rich by reducing the valve opening speed of the purge control valve in the initial stage of the start, it has been difficult to realize with the conventional control method due to the following problems.

First, in today's engines, especially in engines for vehicles, the dynamic range of the intake air flow rate is increasing due to the higher rotation speed and higher output, and it is required to increase the dynamic range of the purge flow rate accordingly. But,
This basically means that it is difficult to ensure accuracy on the low flow rate side. Second, at the beginning of the purge, the fuel vapor filled in the canister is pushed into the air for mixing and is sucked in an extremely rich state without being mixed, so it is necessary to keep the flow rate low. Accuracy is required in the low flow rate range.

That is, it has been difficult to meet the contradictory requirements of ensuring high accuracy on the low flow rate side while ensuring a maximum flow rate by increasing the opening area in order to secure a sufficient purge flow rate. The present invention has been made in view of the above conventional problems, and a fuel vapor purge control device that solves the above problems by improving the control system without changing the structure of a duty-controlled purge control valve. The purpose is to provide.

[0007]

Therefore, the present invention is based on FIG.
As shown in FIG. 4, a duty control purge control valve is provided in a purge passage that connects a canister for adsorbing fuel vapor and an intake system of an internal combustion engine, and the purge control valve is opened under a predetermined engine operating condition to open the canister. In a fuel vapor purge control device configured to purge the fuel vapor adsorbed in the intake system into the intake system, the valve opening duty of the purge control valve is changed according to the engine operating state so as to obtain a target purge rate of the fuel vapor. In the area where the valve opening duty setting means for setting the valve opening duty of the purge control valve set by the valve opening duty setting means is less than a predetermined value, the duty cycle is set to be larger than that in the area of the predetermined value or more. Duty cycle setting means, and a duty control for duty-controlling the purge control valve based on the set valve opening duty and duty cycle. Characterized by being configured to include a tee control means.

Further, the valve opening duty cycle setting means may be configured to increase the duty cycle as the valve opening duty becomes smaller, in a region where the valve opening duty of the purge control valve is less than a predetermined value. Further, the valve opening duty setting means may be configured to set the target purge rate by averaging past values and present values.

[0009]

In the region where the valve opening duty of the purge control valve set by the valve opening duty setting unit is less than the predetermined value, that is, in the region on the low flow rate side of the purge flow amount, the duty cycle setting unit sets a large duty cycle. As a result, the valve opening time per cycle can be increased, so that it becomes easy to ensure control accuracy.

On the other hand, in the region where the valve opening duty is equal to or more than a predetermined value and it is easy to ensure the accuracy even if the cycle is shortened, the cycle is set small to shorten the interval between the valve opening and the valve non-opening. By performing the purge evenly, it is possible to reduce the fluctuation of the air-fuel ratio. Further, in a region where the valve opening duty of the purge control valve is less than the predetermined value, the duty cycle is set to be larger as the valve opening duty becomes smaller, so that the cycle becomes larger as the flow rate becomes lower, that is, it becomes difficult to secure accuracy. By doing so, fluctuations in the air-fuel ratio due to intermittent purging can be suppressed to be small without increasing the cycle more than necessary.

Further, if the target purge rate of the fuel vapor is set by averaging the past value and the present value,
Since the purge rate gradually increases at the start of purging, it is possible to prevent a large amount of fuel vapor from being purged and deterioration of exhaust gas purification performance and operating performance.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. 2, an intake passage 2 of an internal combustion engine 1 is provided with a throttle valve 3 interlocking with an accelerator pedal (not shown) to control an intake air flow rate Q. The throttle valve 3 has an opening θ of the throttle valve 3.
Is connected to a throttle sensor 31 including an idle switch that is turned on when the throttle valve opening degree is equal to or less than a predetermined value. Further, an idle control valve 41 for controlling the auxiliary air flow rate at the time of idling to control the idle rotation speed is provided in the auxiliary air passage 4 bypassing the throttle valve 3, and a passage bypassing other throttle valves (Fig. (Not shown) is provided with an idle-up control valve that increases the auxiliary air flow rate stepwise according to the drive load of the auxiliary machine or the like at the time of idling, and an air regulator for promoting warm-up. The intake passage 2 is provided with an electromagnetic fuel injection valve 5 for each cylinder, and injects fuel into the intake manifold 3 which is pressure-fed from a fuel pump (not shown) and is controlled to a predetermined pressure by a pressure regulator. To do. The control of the fuel injection amount by the fuel injection valve 5 is
The control unit 6 with a built-in microcomputer is used.

Further, the internal combustion engine 1 is provided with a processing device for the fuel vapor generated from the fuel tank. The fuel vapor processing apparatus causes an adsorbent such as activated carbon filled in the canister 21 to adsorb and collect the fuel vapor of the fuel generated in the fuel tank, and to purge the fuel adsorbed by the adsorbent into the purge passage 22. It is supplied to the intake passage on the downstream side of the throttle valve 3 via.

The fuel vapor in the fuel tank 20 is introduced into the canister 21 through a fuel vapor introducing passage 23 provided with a check valve that opens when the positive pressure in the fuel tank exceeds a predetermined value. In addition, the purge passage 22 is provided with an electromagnetic purge control valve 24 which is driven based on a duty control signal from the control unit 6.

An air flow meter 51 for detecting the intake air flow rate Q of the internal combustion engine 1, a rotation speed sensor 52 for detecting the engine rotation speed N, and a water temperature sensor 53 for detecting the cooling water temperature are provided. It is used to determine the purge control conditions for fuel vapor. The control unit 6 is
The fuel injection amount of the fuel injection valve 5 and the like are controlled based on signals from the various sensors, and the valve opening duty of the purge control valve 27 is controlled based on an operating state (intake air flow rate) under predetermined operating conditions. By doing so, the fuel vapor is purged into the intake system so as to keep the air-fuel ratio constant.

The fuel vapor purge control according to this embodiment by the control unit 6 will be described below.
First, the setting of the valve opening duty of the purge control valve 24 is performed as shown in FIG.
It will be described according to the flowchart shown in FIG. This routine corresponds to the valve opening duty setting means. In step (denoted as S in the figure. The same applies hereinafter) 1, it is determined whether or not the purge condition of the fuel vapor is satisfied. Specifically, the cooling water temperature of the internal combustion engine 1 detected by the water temperature sensor 53 is equal to or higher than a predetermined value, the canister 21 is sufficiently adsorbed with fuel vapor, and the idle switch is off, that is, the non-idle state, that is, the fuel vapor. The purging conditions of the fuel vapor are satisfied except in the idle state where the influence of the enrichment of the air-fuel ratio due to the purging is large.

If the purge condition is satisfied, the routine proceeds to step 2, where the throttle valve opening θ is read from the throttle sensor 31, and the throttle opening area A _TVO corresponding to the throttle valve opening θ is stored in the ROM. Theta-A _TVO
It is obtained by searching the conversion table (see the figure). In step 3, the total bypass opening area A _AAC obtained by summing the opening areas of the idle up control valve and the air regulator for controlling the flow rate of the air bypassing the idle control valve 41 and the throttle valve 4 is set in the same manner as above. Obtained by searching from.

In step 4, the throttle opening area A _{TVO found} in step 2 and the total bypass opening area A _{AAC found in} step 3 are added to obtain the total opening area A of the intake system.
_Ask for _INT . In step 5, the target purge rate (fuel vapor flow rate / intake air flow rate) RATIO is calculated by the following equation.

[0019] _{RATIO = RATIO · τ R + RATIO} 0 · (1-τ R) where, RATIO ₀ is the target purge rate which is previously calculated,
τ _R is a weighting factor (0 <τ _R <1), and such averaging
By performing the (annealing) process, it is possible to prevent the fuel vapor filling the canister 21 from suddenly flowing in at the start of purging and deteriorating the exhaust purification performance and the operating performance.

In step 6, the total opening obtained in step 4
Mouth area A_INTAnd the target purge calculated and set in step 5
Effective opening surface of purge control valve 22 based on rate RATIO
Product A _PRATIO = A_P/ (A_INT+ A_P) Relationship
It is calculated by the following formula obtained from the above. A_P= A_INT-RATIO / (1-RATIO) In step 7, the purge control obtained as described above is
Effective opening area A of the control valve 22_POpening duty D corresponding to
UTY is the effective opening area A_PIt is obtained from the functional expression of.

The method of determining the valve opening duty DUTY in this way is, for example, the intake air flow rate Q and the engine rotation speed N.
On the other hand, as compared with the method of mapping the valve opening duty DUTY, there is an effect that the purge rate becomes stable with respect to a change in atmospheric pressure due to altitude or the like. That is, the valve opening duty DUTY is set with the intake air flow rate Q as one parameter.
When defining the, in the highlands but is defective as purge rate reduces the amount of purge for the same Q by a decrease in the atmospheric pressure is reduced occurs, in the above method and the amount of air changes in the atmospheric pressure is passed through the A _{IN T} because they act on both the purge amount passing through the a _P will be kept constant as the purge rate.

If the purge control condition is not satisfied in step 1, the process proceeds to step 8 and the target purge rate RA
Reset TIO and valve opening duty DUTY to zero. Next, the duty cycle switching control according to the purge rate according to the present invention will be described. First, the reason for variably controlling the duty cycle will be described. FIG. 4 shows a schematic timing chart of the duty signal and the operation of the purge control valve 22. DUTY is the valve opening duty, T is the cycle of the duty signal, τ ₀ is the valve opening delay, τ _C is the valve closing delay, t ₀ is the valve opening time, and t _C is the valve closing time. Figure 5
Shows the relationship between the flow rate Q _P of the purge control valve 22 at a duty signal DUTY a predetermined condition. Q _P is approximately DUTY accuracy falls in the small side. That is, DUTY ≦ τ ₀ / T
Then, Q _P ≈0, and since the valve is not substantially opened, the DUT
Y> τ ₀ / T is set, and at this time, Q _P = k _P · {D
UTY− (τ ₀ −τ _C ) / T}. FIG. 6 shows the elapsed time after the start of purging and the fuel vapor flow rate Q _E actually purged.
Shows the relationship between (and Aru shown as a percentage of purge flow Q _P in the drawing). As is clear from the figure, immediately after the start of purging, a large amount of fuel vapor is purged and the air-fuel ratio is likely to be disturbed, so it is necessary to suppress the purge flow rate.

Therefore, it is necessary to set the DUTY small when starting the purge when the flow rate of the intake air is low. However, if the DUTY is simply decreased, the influence of the error becomes large and it becomes difficult to secure the accuracy. However, D
In UTY control, accuracy is affected not only by the flow rate but also by the duty cycle. That is, the smaller the flow rate error / flow rate is, the higher the accuracy is. That is, it is difficult to secure the accuracy on the low flow rate side. However, the flow rate error is a characteristic of the purge control valve, and the flow rate is large or small per opening (duty operation). Since the same amount is generated regardless of the above, the smaller the number of times of opening and closing per unit time, that is, the larger the duty cycle, the smaller the total amount of flow rate error and the higher the accuracy.

As described above, the accuracy can be improved by increasing the duty cycle, but there is a problem in uniformly increasing the cycle over the entire area. That is, when the duty cycle is increased, the state where the fuel vapor at the time of valve opening is purged and the state where it is not purged are clearly separated, and since the average purge cannot be performed, the variation range of the air-fuel ratio is large, Not desirable in terms of exhaust purification performance and operating performance. In particular, in the high purge flow rate region where the valve opening duty is set large, it is preferable to disperse the purge as much as possible because the air-fuel ratio is likely to become excessively rich if the purge time for each time is prolonged. Since it may be easier to ensure accuracy compared to the flow rate region, it is preferable not to increase the cycle more than necessary.

Therefore, in the present invention, the duty cycle is controlled to be large in the low purge flow rate region and to be decreased in the high purge flow rate region. The duty cycle control according to the present invention is performed according to the flowchart shown in FIG. This routine corresponds to duty cycle setting means. In step 11, the duty cycle T corresponding to the valve opening duty DUTY is set by searching the table map having the characteristics shown in FIG. Here, the duty cycle T is set to increase as the DUTY decreases in a region where the valve opening duty DUTY is less than or equal to a predetermined value, whereby the intermittent purging is performed without increasing the cycle more than necessary. The influence can be avoided as much as possible.

Further, in a region where the valve opening duty DUTY is larger than the predetermined value, the cycle T is kept constant at a minimum value. This minimum value is a valve opening time (= DUTY ·
T) is larger than the valve opening delay time τ ₀ (T> τ ₀ / D
UTY) It is set to ensure accuracy. Based on the valve opening duty DUTY and the duty cycle T set as described above, the duty control is performed as shown in FIG. This routine is executed in time synchronization. Further, this routine corresponds to duty control means.

In step 21, the count value t of the timer counter is incremented. In step 22, it is determined whether or not the count value t has reached the set duty cycle T. When it is determined that the duty cycle T has been reached, the routine proceeds to step 23, where after the count value t of the timer counter is reset to 0, the routine proceeds to step 24 where the energization of the purge control valve 22 is started.

After the energization is started, step 21, step
After going through step 22, go to step 25, compare the count value t with the valve opening time (= T · DUTY) per time, and proceed to step 24 until the count value t exceeds the valve opening time and purge. Continue to energize control valve 22 and step 26 after exceeding
Then, the power is cut off, and the cutoff state is maintained until the count value t reaches the duty cycle T next. By repeating this, duty control is performed according to the set valve opening duty and duty cycle.

[0029]

As described above, according to the present invention, since the duty control of the purge control valve is controlled so that the duty cycle becomes large when the opening duty of the purge control valve is small. It is possible to secure the accuracy when it is required to reduce the valve duty, and it is possible to suppress excessive purging and satisfy both the exhaust purification performance and the operating performance.

Further, by controlling so that the duty cycle becomes larger as the valve opening duty becomes smaller in a region where the valve opening duty is less than a predetermined value, the increase of the cycle is kept to a necessary minimum and the air-fuel ratio due to intermittent purging is reduced. It is possible to secure the purge control accuracy while avoiding fluctuation as much as possible. Further, by setting the purge rate by averaging, it is possible to prevent a large amount of fuel vapor from being rapidly purged at the start of purging, and it is possible to avoid deterioration of exhaust purification performance and deterioration of operating performance.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration and functions of the present invention.

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

FIG. 3 is a flowchart showing a routine for setting the valve opening duty of the purge control valve of the above embodiment.

FIG. 4 is a time chart showing a relationship between duty control and opening / closing of a purge control valve.

FIG. 5 is a diagram showing a relationship between valve opening duty and purge flow rate.

FIG. 6 is a diagram showing the relationship between the elapsed time after the start of purging and the actual fuel vapor flow rate / purge flow rate.

FIG. 7 is a flowchart showing a routine for similarly setting a duty cycle.

FIG. 8 is a flowchart showing a duty control routine of the same.

[Explanation of symbols]

 1 Internal combustion engine 2 Intake passage 3 Throttle valve 6 Control unit 21 Canister 22 Purge passage 24 Purge control valve 41 Idle control valve 51 Air flow meter 52 Rotation speed sensor 53 Water temperature sensor

Claims (3)

[Claims] 1. A canister that has a purge control valve that is duty-controlled in a purge passage that connects a canister that adsorbs fuel vapor and an intake system of an internal combustion engine, and opens the purge control valve under predetermined engine operating conditions. In the fuel vapor purge control device configured to purge the fuel vapor adsorbed in the intake system into the intake system, in order to obtain the target purge rate of the fuel vapor, the opening duty of the purge control valve is changed according to the engine operating state. In the area where the valve opening duty of the purge control valve set by the valve opening duty setting means is less than a predetermined value, the duty cycle is set to be larger than that in the area of the predetermined value or more. A duty cycle setting means, and a duty cycle control means for duty-controlling the purge control valve based on the set valve opening duty and duty cycle. Purge control device of the fuel vapor, characterized in that configured to include a tee control means. 2. The valve opening duty cycle setting means sets the duty cycle such that it becomes larger as the valve opening duty becomes smaller in a region where the valve opening duty of the purge control valve is less than a predetermined value. 5. The fuel vapor purge control device according to. 3. The valve opening duty setting means is adapted to set the target purge rate by averaging past values and present values.
5. The fuel vapor purge control device according to.