JP3339258B2 - Evaporative fuel treatment system 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 apparatus for treating fuel vapor from a fuel system of an internal combustion engine, and more particularly to a technique for improving exhaust gas purification performance by increasing the processing capacity.

[0002]

2. Description of the Related Art As a conventional evaporative fuel processing apparatus for an internal combustion engine, there is a technique disclosed in, for example, Japanese Patent Application Laid-Open No. H5-215020. According to this method, a vapor mixture generated by temporarily adsorbing vaporized fuel generated in a fuel tank or the like to a canister, releasing the adsorbed vaporized fuel under predetermined engine operating conditions and mixing with purge air is supplied to a purge control valve. By performing suction processing on the intake system of the engine while controlling the flow rate, evaporation of the evaporated fuel into the outside air is prevented.

On the other hand, in an internal combustion engine equipped with an electronically controlled fuel injection device, it is possible to perform feedback control by a feedback correction amount that is increased or decreased so that the air-fuel ratio approaches a target air-fuel ratio (stoichiometric air-fuel ratio) under predetermined operating conditions. Done. By the way, in a device provided with the air-fuel ratio feedback control device, a limit value is generally set for the feedback correction amount. This is to fix the feedback correction amount to the limit value when a failure occurs in the air-fuel ratio feedback control system (for example, a failure of the sensor that detects the air-fuel ratio) or when the feedback correction amount falls outside the appropriate range due to a transient cause. This prevents the feedback correction amount from becoming an abnormal value.

In an engine equipped with the above-described evaporative fuel processing device and the air-fuel ratio feedback control device, the purge process is performed while performing the air-fuel ratio feedback control, so that the air-fuel ratio to be enriched by the purge process is supplied to the fuel supply device. The purge process can be performed while maintaining the target air-fuel ratio by correcting the amount by decreasing the amount. However, if the purge process and the air-fuel ratio feedback control are performed in parallel when the concentration of the purge mixture is high, the feedback correction amount reaches the limit value for leaning the air-fuel ratio (hereinafter referred to as the lower limit value). As a result, the air-fuel ratio is controlled to the rich side, and the exhaust gas purification performance decreases. If the purge mixture is estimated to be rich in order to prevent this, and if the flow rate of the purge mixture is set to a low value, the purge processing capacity will decrease, and the exhaust gas purification performance will also decrease.

In view of this point, there is one in which the setting of the lower limit of the feedback correction amount is released in a state where the purge concentration is estimated to be high to allow lean correction of the air-fuel ratio (Japanese Patent Laid-Open No. Sho 64). -69746).

[0006]

However, in the above-mentioned conventional method of expanding the lower limit of the feedback correction amount, the purge concentration is estimated based on the internal pressure of the fuel tank. However, the following problems have arisen because the influence of the concentration of fuel vapor has not been considered.

First, the state of the purge concentration with respect to the flow rate of the purge gas mixture will be described with reference to FIG. 5. Evaporated fuel in the purge gas mixture departs from the canister and evaporates from the fuel tank (float not adsorbed by the canister). Minutes). Among them, the amount desorbed from the canister is sucked into the engine at a concentration substantially proportional to the adsorbed amount of the canister with respect to the flow rate of the purged mixture gas. Therefore, a substantially constant purge concentration is maintained with respect to a change in the flow rate of the purge mixture (characteristic B
See).

On the other hand, the amount of evaporation from the fuel tank is determined by the fuel temperature, the fuel volatility, the remaining amount of fuel, and the like, and is sucked in as a fixed amount independent of the flow rate of the purge mixture. The value is inversely proportional (see characteristic A). It is necessary to consider the purge concentration by taking into account the amount of departure from the canister and the amount of evaporation from the fuel tank. The purge concentration is a value that can vary depending on the flow rate of the purge mixture. Can not be estimated with the internal pressure of

Therefore, if the threshold value of the purge concentration estimated based on the tank internal pressure is set to a low value, the setting of the lower limit value is likely to be canceled because the purge concentration is not so high in practice, and the air-fuel ratio feedback control system may fail. May fail to operate. Therefore, the threshold value of the purge concentration must be set higher. However, in such a case, the region where the lower limit value is maintained as it is in spite of the fact that the purge concentration is high actually increases, and in this region, there is no space. As a result, the fuel ratio is enriched and the exhaust gas purification performance is reduced.

When the setting of the lower limit is released, there is a margin for increasing the flow rate of the purge mixture, but the purge rate remains constant, so that the purging capacity can be more positively improved. Was not. Further, simply canceling the setting of the lower limit value or simply increasing the lower limit value as described above causes the feedback correction amount to gradually decrease when the purge concentration is high. However, it is inevitable that the exhaust gas purification performance deteriorates due to the enrichment of the air-fuel ratio during that time (see FIG. 6).

The present invention has been made in view of such a conventional problem. The present invention expands the lower limit value of the feedback correction amount in the air-fuel ratio feedback control only when the purge concentration is actually high, so that the entire operation range can be improved. It is a first object of the present invention to maintain an air-fuel ratio during a purge process satisfactorily and maintain exhaust gas purification performance without impairing a lower-limit fail-safe function.

It is a second object of the present invention to increase the purging capacity as much as possible by increasing the flow rate of the purge mixture in accordance with the increase in the feedback correction amount. It is a third object of the present invention to maintain an excellent air-fuel ratio and secure exhaust purification performance even in a transient state in which the purge concentration changes.

[0013]

For this reason, the present invention according to claim 1 has a feedback correction amount such that the air-fuel ratio of the entire air-fuel mixture supplied to the engine approaches the target air-fuel ratio as shown by a solid line in FIG. Feedback control by
While the air-fuel ratio feedback control means in which the limit value of the feedback correction amount in the air-fuel ratio lean correction direction is provided, the evaporated fuel generated from the fuel system is temporarily adsorbed by the adsorbing means and desorbed from the adsorbing means. In an evaporative fuel processing apparatus for an internal combustion engine, a purge mixture obtained by mixing evaporative fuel with air for purging is guided to an engine intake system while controlling the flow rate by a purge control valve, and the purge during the desorption process of the evaporative fuel is performed. Evaporative fuel concentration detecting means for detecting the concentration of the evaporative fuel in the air-fuel mixture; and evaporative fuel concentration detected by the evaporative fuel concentration detecting means being higher than a predetermined value.
When it is determined that the air-fuel ratio is large, the limit value of the feedback correction amount in the air-fuel ratio lean correction direction is set to the lean correction of the air-fuel ratio.
And a feedback correction amount limit value changing unit that expands in a direction that allows positive .

With this arrangement, when the purge concentration becomes higher than the predetermined value in accordance with the flow rate of the purge mixture, the flow is increased.
Of the feedback correction amount to allow the air-fuel ratio to lean.
The limit value has been expanded to allow for lean correction of the air-fuel ratio.
Therefore , the enrichment of the air-fuel ratio at the time of the purge processing at the time of the high purge concentration is suppressed while ensuring the fail-safe function by the limit value, and the exhaust gas purification performance can be maintained satisfactorily.

According to a second aspect of the present invention, as shown by a dashed line in FIG. 1, when the fuel vapor concentration changes, the detected fuel vapor concentration and the limit value of the feedback correction amount to be changed are changed. And a purge rate changing means for changing the ratio of the flow rate of the purged air-fuel mixture to the flow rate of the intake air. If you do this,
Since the purge rate can be increased so as to maintain the feedback correction amount just near the limit value of the changed feedback correction amount, the purge processing capacity can be increased as much as possible.

According to a third aspect of the present invention, as shown by a dotted line in FIG. 1, when the fuel vapor concentration changes, an amount corresponding to a change in the feedback correction amount predicted by the change is obtained. The present invention is characterized by including a feedback correction amount transient correction means for initial correction of the feedback correction amount. In this way, even if the limit value of the feedback correction amount is changed as described above, the feedback correction amount alone gradually changes to reach the target air-fuel ratio, and the air-fuel ratio during that time is shifted. However, the feedback correction amount transient correction means can maintain the air-fuel ratio near the target air-fuel ratio from the beginning of the change by initially correcting the amount corresponding to the change in the feedback correction amount in advance. Enrichment is suppressed, and the exhaust gas purification performance can be favorably maintained. In the case where the purge rate is changed when the fuel vapor concentration changes as in the second aspect of the present invention, the amount corresponding to the change in the feedback correction amount estimated including the change in the purge rate is changed. May be initially corrected.

Further, the invention according to claim 4 is characterized in that the evaporation concentration detecting means is configured to perform the feedback control based on the feedback correction amount when the air-fuel ratio feedback control is performed by the air-fuel ratio feedback control means during the evaporative fuel separation process. The method is characterized in that the fuel vapor concentration is estimated and detected, and the detected value is stored and updated for each purged mixture gas flow rate region.

In this way, if the air-fuel ratio feedback control is performed during the evaporative fuel release process, the feedback correction amount changes according to the purge concentration. Therefore, the purge concentration is estimated based on the feedback correction amount. By performing the detection for each purge air-fuel mixture flow rate and updating the storage, when the purge air-fuel mixture flow rate changes and the purge concentration can change, the stored value can be used. The purge concentration can be immediately detected. And, by such estimation detection, it is not necessary to provide a sensor for density detection specially.

[0019]

FIG. 2 shows an embodiment of the present invention. Air is drawn into an internal combustion engine 1 through a throttle chamber 2 and an intake manifold 3. The throttle chamber 2 is provided with a throttle valve 4 interlocked with an accelerator pedal (not shown) to control an intake air flow rate Q. The intake manifold 3 is provided with an electromagnetic fuel injection valve 5 for each cylinder. Fuel is fed from a fuel pump (not shown) and controlled to a predetermined pressure by a pressure regulator to inject and supply the fuel into the intake manifold 3. . The control of the fuel injection amount by the fuel injection valve 5 is performed by a control unit 6 with a built-in microcomputer.

Further, the engine 1 includes an evaporative fuel treatment device.
21 are provided. The evaporative fuel processing apparatus 21 adsorbs and collects the evaporative fuel of the fuel generated in the fuel tank 20 with an adsorbent 23 such as activated carbon filled in a canister 22 as an adsorbing means, and adsorbs the adsorbent 23 on the adsorbent 23. The supplied fuel is supplied to the intake passage downstream of the throttle valve 4 via the purge passage 24.

The evaporative fuel in the fuel tank 20 is introduced into the canister 22 through an evaporative fuel passage 26 provided with a check valve 25 which opens when the positive pressure in the fuel tank 20 exceeds a predetermined value. An electromagnetically driven purge control valve 26 controlled based on a control signal from the control unit 6 is provided in the purge passage 24.
Is interposed.

An air flow meter 51 for detecting an intake air flow rate Q of the internal combustion engine 1, a rotation speed sensor 52 for detecting an engine rotation speed N, a water temperature sensor 53 for detecting a water temperature Tw, an oxygen concentration in exhaust gas, etc. An air-fuel ratio sensor 54 for detecting an air-fuel ratio is provided, and a fuel temperature sensor 55 for detecting a fuel temperature is provided in the fuel tank 20, and their detection signals are output to the control unit 6.

The control unit 6 controls the air-fuel ratio by controlling the amount of fuel injected by the fuel injection valve 5 based on the signals from the various sensors.
By controlling the purge control valve 26 under predetermined operating conditions, the fuel vapor is purged into the intake system so as to maintain the air-fuel ratio constant. The control of the fuel injection amount from the fuel injection valve 5 by the control unit 6 and the control of the flow rate of the purge mixture by the purge control valve 26 performed in connection with this will be described with reference to the flowchart shown in FIG.

Step (S in the figure; the same applies hereinafter) 1
Then, the intake air flow rate Q detected by the air flow meter 51, the engine rotation speed N detected by the rotation speed sensor 52, and the water temperature Tw detected by the water temperature sensor 53 are input. In step 2, the basic fuel injection amount _TP (= kQ / N) is calculated based on the intake air flow rate Q and the engine speed N.

In step 3, it is determined whether or not an operating condition for performing feedback control to a target air-fuel ratio (for example, a stoichiometric air-fuel ratio) based on each of the detected values. When it is determined in step 3 that the condition is the air-fuel ratio feedback control condition, the process proceeds to step 4 and it is determined whether the operating condition for performing the purge process is based on each of the detected values.

When it is determined that the purge condition is satisfied, the routine proceeds to step 5, where the air-fuel ratio learning under the purge condition is performed. This is based on a signal from the air-fuel ratio sensor 54. The air-fuel ratio feedback correction coefficient is set by increasing or decreasing the air-fuel ratio from the target air-fuel ratio (the stoichiometric air-fuel ratio) to rich or lean.
It is set by averaging the (multiplied is the basic fuel injection quantity T _P). Specifically, as is well known, the average value of the air-fuel ratio correction coefficient at the time of inversion of rich and lean is updated and set as a learning value as it is, or the air-fuel ratio correction coefficient deviates from a reference value (for example, 1). In order to eliminate the error, the initial value (for example, 1) by a predetermined ratio of the deviation between the average value and the reference value
The learning value GTBL is obtained by, for example, updating the learning value by adding the learning value GTBL to the target purge mixture gas flow rate (set in proportion to the intake air flow rate so that the purge rate is constant). Is updated and stored in the map.
Here, when the purge concentration is higher than the target air-fuel ratio, the feedback correction amount is set in the direction of decreasing the air-fuel ratio, and when the purge concentration is lower than the target air-fuel ratio, the feedback correction amount is set in the direction of increasing the air-fuel ratio. Since the deviation is set to be shifted to the learning value GTBL so as to eliminate the deviation of the feedback correction amount from the reference value due to the purge concentration, the learning value GTBL after the learning is advanced is The value indicates the purge concentration. Therefore, the air-fuel ratio learning function at the time of purging in step 5 constitutes a purge concentration detecting means.

On the other hand, if it is determined in step 4 that the non-purge condition is not satisfied, the process proceeds to step 6 where the opening control amount of the purge control valve 26 is set to 0, the valve is fully closed, and the purge is stopped.
Proceeding to step 15, the air-fuel ratio learning at the time of non-purge is performed in the same manner as the air-fuel ratio learning at the time of purge at step 10. However, region for learning, may be segmented by the engine rotational speed Ne and basic fuel injection quantity T _P. Here, the air-fuel ratio learning value at the time of non-purge is stored and updated in a map for non-purge at a time different from the map at the time of purge, so that air-fuel ratio learning is performed independently at the time of purge and at the time of non-purge.

Next, at step 7, the fuel injection valve 5 is determined by using the air-fuel ratio learning value GTBL at the time of purging or not purging.
The fuel injection quantity T _I from the set by the following equation. T _I = T _P · COEF · GTBL · α + T _S Here, COEF is various correction coefficients set by the water temperature Tw or the like, and α is the air that is increased or decreased by PI control or the like based on a signal from the air-fuel ratio sensor 54. The fuel ratio feedback correction coefficient, T _S, is the amount of invalid injection due to the battery voltage. The upper limit and the lower limit are set so that α does not become an abnormal value when a failure or the like occurs. In particular, in the present invention, the lower limit is an air-fuel ratio during a purge process when a purge concentration described later is high. It is expanded and corrected in a direction that allows leaning.

In step 8, an injection pulse signal having an injection pulse width corresponding to the fuel injection amount T _I is supplied to the fuel injection valve.
By outputting to 54, feedback control to the stoichiometric air-fuel ratio is performed. Therefore, the functions of steps 3, 5 to 8 together with the hardware such as the fuel injection valve 5 and the air-fuel ratio sensor 54 constitute an air-fuel ratio feedback control means.

If it is determined in step 3 that the condition is not the air-fuel ratio feedback control condition, that is, that the condition is the air-fuel ratio feedforward control condition, the process proceeds to step 9.
The air-fuel ratio feedforward control is performed with the air-fuel ratio feedback correction coefficient α fixed at a predetermined value, for example, 1.0. Next, a description will be given of a routine for correcting the lower limit of the feedback correction coefficient α of the air-fuel ratio according to the present invention and for initially correcting the amount of change predicted in the feedback correction coefficient α when the flow rate of the purge mixture changes. .

In step 11, it is determined whether the air-fuel ratio feedback control condition and the purge process condition are satisfied. If the conditions in step 11 are not met,
Exit this routine and if satisfied, step
Proceed to 12. In step 12, a learned value GTBL as a detected value of the air-fuel ratio purge concentration corresponding to the current purged air-fuel mixture flow rate region (n) is retrieved from a map storing the learned value at the time of the purge processing and inputted.

In step 13, it is determined whether or not the learned value GTBL is smaller than a predetermined value EVPDEN. Here, as described above, the learning value GTBL is a value representing the purge concentration. However, when the purge rate is changed as described later, the evaporation is performed when the purge rate is large even at the same purge concentration. As the fuel supply amount increases, the feedback correction amount becomes a smaller value, and as a result, the learning value GTBL
Is also smaller, the purge concentration can be more accurately estimated if the value obtained by multiplying the learning value GTBL by the purge rate is used as the estimated value of the purge concentration.

[0033] Then, when said learned value GTBL (or value it multiplied by the purge rate) is determined to be smaller than the predetermined value EVPDEN the purge concentration is high the air-fuel ratio feedback control in the purge gas mixture flow area At this time, it is determined that the feedback correction coefficient α is stuck to the lower limit (initial value L1), and the process proceeds to step 14, where the lower limit is expanded to allow lean correction of the air-fuel ratio (changed to L2).
I do.

Further, the process proceeds to step 15, where the feedback correction amount is maintained at the limit of the expanded lower limit value based on the expansion range of the lower limit value of the feedback correction amount and the currently detected purge concentration. And set the purge rate as follows. With this configuration, the purge processing capacity and, consequently, the exhaust gas purification performance can be increased as much as possible by setting the maximum purge mixture flow rate as large as possible within a range where the air-fuel ratio can be maintained near the target air-fuel ratio by the air-fuel ratio feedback control. Can be.

Next, the routine proceeds to step 16, where the purge concentration
(Purge mixture flow rate range) is determined to have changed at the beginning, the change from the feedback correction amount before the change to the feedback correction amount after the change (after the steady state) due to the change in the purge concentration and the change in the purge rate. The feedback correction amount is corrected by a corresponding amount. However, in the case of performing the air-fuel ratio learning, the correction of the change in the feedback correction amount due to only the change in the purge concentration is performed by switching the learning value GTBL in accordance with the change in the purge mixture gas flow rate range. What is necessary is just to correct by the change by the change. When the purge concentration is detected by a sensor, an initial correction amount is set by predicting a change in the feedback correction amount due to a change in the purge concentration.

In this way, the feedback correction coefficient α is corrected in advance by the initial correction amount corresponding to the change due to the change in the purge concentration and the change in the purge rate, so that the feedback correction coefficient α is maintained near the target air-fuel ratio from the beginning of the change. Thus, the air-fuel ratio is prevented from being enriched even during the transition, and the exhaust gas purification performance can be maintained satisfactorily (see FIG. 6). Further, when said learned value GTBL (or value it multiplied by the purge concentration) is determined to be the predetermined value EVPDEN than the determination of step 13, the air-fuel ratio lower purged concentration in the purge gas mixture flow area Feedback correction coefficient α during feedback control
Is determined not to stick to the lower limit (initial value), the process proceeds to step 17 , and the lower limit is set to the initial value.

Then, the process proceeds to a step 15, wherein the purge rate is changed such that the feedback correction amount of the air-fuel ratio is maintained near the lower limit set to the initial value.

[0038]

As described above, according to the first aspect of the present invention, the limit value in the direction in which the air-fuel ratio lean correction of the feedback correction amount is allowed in accordance with the increase in the purge concentration is set.
Since it is expanded in a direction that allows lean correction of the air-fuel ratio,
The enrichment of the air-fuel ratio at the time of the purge processing at the time of a high purge concentration is suppressed while ensuring the fail-safe function by the limit value, and the exhaust gas purification performance can be maintained satisfactorily.

According to the second aspect of the present invention, the purge rate can be increased so as to maintain the feedback correction amount almost at the limit of the changed feedback correction amount. Can be enhanced. According to the third aspect of the invention, when the purge concentration changes, the amount corresponding to the change in the feedback correction amount is initially corrected, so that the target air-fuel ratio can be maintained near the target air-fuel ratio from the beginning of the change. Even during the transition, the air-fuel ratio is prevented from being enriched, and the exhaust gas purification performance can be maintained satisfactorily.

According to the fourth aspect of the invention, when the purge concentration changes, the purge concentration can be immediately detected from the value stored by the air-fuel ratio learning, and no special sensor for concentration detection is provided. I'm done.

[Brief description of the 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 according to an embodiment of the present invention.

FIG. 3 is a flowchart showing air-fuel ratio feedback control of the embodiment.

FIG. 4 is a flowchart showing feedback correction amount lower limit expansion control according to the embodiment.

FIG. 5 is a diagram showing the relationship between the flow rate of a purge mixture and the purge concentration.

FIG. 6 is a diagram showing a state of a change in an air-fuel ratio feedback correction coefficient due to a change in purge concentration between a conventional example and the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Internal combustion engine 5 Fuel injection valve 6 Control unit 20 Fuel tank 21 Evaporative fuel processor 22 Canister 24 Purge passage 26 Purge control valve 54 Air-fuel ratio sensor

Claims (4)

(57) [Claims] An air-fuel ratio of the whole air-fuel mixture supplied to the engine is feedback-controlled by a feedback correction amount so as to approach a target air-fuel ratio, and a limit value of the feedback correction amount in an air-fuel ratio lean correction direction is set. While the air-fuel ratio feedback control means is provided, a purge air-fuel mixture in which the evaporated fuel generated from the fuel system is temporarily adsorbed by the adsorbing means and the evaporative fuel desorbed from the adsorbing means is mixed with the purge air is purged. An evaporative fuel processing device for an internal combustion engine, wherein the evaporative fuel concentration detecting means detects the concentration of the evaporative fuel in the purged mixture during the desorption process of the evaporative fuel. , when the fuel vapor concentration fuel vapor concentration detected by the detecting means is judged to be larger than the predetermined value, the full Check the limit value of the air-fuel ratio lean correction direction of the readback correction amount
An evaporative fuel processing apparatus for an internal combustion engine, comprising: a feedback correction amount limit value changing unit that expands in a direction allowing a lean correction of a fuel ratio . 2. A purge system for changing a ratio of a flow rate of a purge mixture to an intake air flow rate based on a detected fuel vapor concentration and a limit value of a feedback correction amount to be changed when the fuel vapor concentration changes. 2. The apparatus according to claim 1, further comprising a rate changing unit. 3. A feedback correction amount transient correction means for initially correcting the feedback correction amount by an amount corresponding to a change amount of the feedback correction amount predicted by the change when the fuel vapor concentration changes. The evaporative fuel processing apparatus for an internal combustion engine according to claim 1 or 2, wherein the apparatus is configured. 4. An evaporative concentration detecting means for estimating and detecting an evaporative fuel concentration based on a feedback correction amount when the air-fuel ratio feedback control is performed by the air-fuel ratio feedback control means during the evaporative fuel separation process. And
4. The evaporative fuel processing apparatus for an internal combustion engine according to claim 1, wherein the detected value is stored and updated for each purged mixture flow rate region.