JPH094489A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE: To restrict the deterioration of the exhausting performance by providing an additional charge time correction value presuming means for estimating the correction value of the air-fuel ratio controlled variable on the basis of a result of estimation of a purge gas concentration change presuming means. CONSTITUTION: In an exhaust passage 6, an air-fuel ratio sensor 7, which detects the concentration of the oxygen contained in the exhaust so as to detect the air-fuel ratio of the intake mixture, is provided in a manifold collecting part. A control unit 10 computes the fuel quantity corresponding to the target air-fuel ratio on the basis of values detected by various sensors. The injection pulse signal having a pulse width corresponding to this fuel quantity is output to a fuel injection valve 14. In the case there is the additional charge, since the quantity of displacement of the air-fuel ratio feedback correction coefficient can be estimated in response to that additional charge, even in the case there is the additional charge, the device can accurately cope with a stage difference of the air-fuel ratio, which is generated with a start of purge processing, with the excellent responsiveness. Deterioration of the exhausting performance can be thereby effectively restricted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control system for an internal combustion engine, and more particularly to an improvement of an air-fuel ratio control technique for an engine equipped with an evaporated fuel processing system (purge processing means).

[0002]

2. Description of the Related Art Conventionally, as a measure for preventing the spread of vaporized fuel generated in a fuel supply system such as a fuel tank into the atmosphere, the vaporized fuel is once adsorbed by an adsorption means called a canister. , The adsorbed fuel is purged from the canister during engine operation (purge gas) (a mixture of purge fuel and the outside air introduced into the canister at the time of desorption) is introduced into the intake air for treatment (hereinafter ,
There is known an evaporated fuel processing (purge processing) device that is configured to perform a purging process, and for example, there is one shown in FIG.

This one has a purge control valve 3 for opening and closing (ON / OFF) communication between a canister 5 communicating with an upper space of a fuel tank 11 via a check valve 12 and an intake passage 2 of an engine 1. It is interposed in the purge passage 4 and sucks the purge gas from the canister 5 into the intake system together with the outside air by the engine suction negative pressure when the purge control valve 3 is turned on. The opening of the purge control valve 3 (for example, when a duty control valve is used as the purge control valve, a predetermined ON / O
The ON time ratio in the FF cycle, etc.) is controlled based on the drive signal from the control unit 10 so that a predetermined purge rate (purge gas amount / fresh air intake air amount) can be obtained.

By the way, the purge gas is composed of purge fuel and
Since it is a mixture of the outside air introduced into the canister during desorption, it has a predetermined fuel concentration (hereinafter also referred to as purge concentration).
Having. Therefore, for example, based on the detection value of the air-fuel ratio sensor 7 provided in the exhaust passage 6, the air-fuel ratio of the engine intake air-fuel mixture is corrected by the air-fuel ratio feedback correction coefficient α set to increase or decrease so as to obtain the target air-fuel ratio. When the purge process is started during the so-called air-fuel ratio feedback control, a step difference occurs between the target air-fuel ratio and the actual air-fuel ratio due to the influence of the purge gas concentration, which deteriorates the exhaust performance and the like. Will be done. As shown in FIG. 13, the air-fuel ratio feedback correction coefficient α is gradually corrected so as to reduce the air-fuel ratio step, but it takes time until the air-fuel ratio step disappears. It is not possible to suppress deterioration of performance and the like.

[0005]

Therefore, in the conventional example, the above problem was solved in the following manner. The relationship between the cumulative purge amount (the total purge flow rate from the start of the purge process, which is determined from the purge control valve opening and time, etc.), and the purge concentration, which tends to gradually diminish over time after the start of the purge process (that is, the canister The desorption characteristic (see FIG. 10) is stored in advance in a table or the like.

The cumulative purge amount is calculated (always), and the purge concentration corresponding to the present time is obtained by searching the table of FIG. Based on the purge concentration obtained above and the current purge rate (calculated from the opening of the purge control valve 3 and the intake air flow rate), the air-fuel ratio feedback correction is performed based on the table of FIG. 11 which is preset and stored. Estimate the shift amount of the coefficient α.

Based on the deviation amount of the air-fuel ratio feedback correction coefficient α estimated above, the value of the air-fuel ratio feedback correction coefficient α is corrected so as to quickly eliminate the air-fuel ratio step, thereby reducing the exhaust performance and the like. I was trying to suppress it. However, in the above-mentioned conventional method, the relationship between the cumulative purge amount and the purge concentration shown in FIG. 10 is taken into consideration regarding so-called “additional charge” (a state in which evaporated fuel is generated in the fuel tank even during the purge process). If there is additional charge, the change in purge concentration due to this additional charge cannot be handled, and the deviation amount of the air-fuel ratio feedback correction coefficient α cannot be accurately estimated. Could not be corrected satisfactorily, and deterioration of exhaust performance and the like could not be sufficiently suppressed.

The present invention has been made in view of such a conventional situation. Even if additional charging is performed, it is possible to respond to the step of the air-fuel ratio during the purging process, particularly immediately after the start of the purging process with high responsiveness and high accuracy. Therefore, it is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine, which is capable of effectively suppressing deterioration of exhaust performance and the like.

[0009]

Therefore, as shown in FIG. 1, the air-fuel ratio control apparatus for an internal combustion engine according to the invention described in claim 1 temporarily uses the adsorbing means to temporarily hold the evaporated fuel accumulated in the fuel tank or the like. The purge processing means for adsorbing the vaporized fuel to the engine and introducing it into the engine intake system as a purge gas which is a mixture with the outside air and maintaining the air-fuel ratio of the engine intake mixture at a target value. As described above, in the air-fuel ratio control device of the internal combustion engine configured to include the air-fuel ratio control means for controlling the air-fuel ratio control amount, in the purge process, the fuel concentration change of the purge gas according to the progress state of the purge process is dealt with. In order to do so, a correction value setting means during purge processing for setting a correction value for the air-fuel ratio control amount, and an additional charge detection means for detecting an additional charge state in which evaporated fuel is generated in a fuel tank or the like during the purge processing. When the additional charge state is detected, the purge gas concentration change estimating means for estimating the fuel concentration change of the purge gas, and the additional charge for estimating the correction value of the air-fuel ratio control amount based on the estimation result of the purge gas concentration change estimating means And a time correction value estimating means.

According to a second aspect of the present invention, the purge gas concentration change estimating means estimates the fuel concentration of the purge gas based on the deviation of the air-fuel ratio control amount from the basic control value and the purge rate, and It is configured as a means for estimating the fuel concentration change of the purge gas based on the time change.

[0011]

In the invention according to claim 1 having the above-mentioned structure, even if additional charging is performed during the purge process, the fuel concentration of the purge gas corresponding to this (that is, the purge gas concentration).
In response to the change, it becomes possible to correct the air-fuel ratio control amount (for example, the fuel supply amount, the intake air flow rate, etc.) with high accuracy and responsiveness. Therefore, for example, when correcting the air-fuel ratio step difference at the start of the purging process, even if there is additional charging, it is possible to respond to this with high responsiveness and high accuracy, so that the exhaust performance during the purging process, etc. Can be suppressed to the maximum.

If the purge gas concentration change estimating means is constructed as described in claim 2, the change of the purge gas concentration can be detected with high accuracy by a simple structure utilizing the existing air-fuel ratio feedback control device. be able to.

[0013]

An embodiment of the present invention will be described below with reference to the accompanying drawings. It should be noted that common reference numerals to those shown in FIG. Referring to FIG. 2 showing the present embodiment, in an intake passage 2 of an engine 1, an intake air flow rate Q is interlocked with an air flow meter 9 for detecting an intake air flow rate Q of intake air sucked through an air cleaner (not shown) and an accelerator pedal. A throttle valve 8 for controlling the above is provided, and an electromagnetic fuel injection valve 14 is provided for each cylinder in the downstream manifold portion.

The fuel injection valve 14 is driven to open by an injection pulse signal set by a method described later in the control unit 10 containing a microcomputer, and injects and supplies a predetermined amount of fuel. A fuel pump 18 is mounted in the fuel tank 11, and the fuel pumped from the fuel pump 18 and adjusted to a predetermined pressure by a pressure regulator 19 is supplied to the fuel injection valve 14 through a fuel supply passage 20. To be done. Excess fuel from the pressure regulator 19 is returned to the fuel tank 11 via a return fuel passage 21.

The exhaust passage 6 is provided with an air-fuel ratio sensor 7 for detecting the air-fuel ratio of the intake air-fuel mixture by detecting the oxygen concentration in the exhaust gas at the manifold collecting portion. Downstream thereof, CO in the exhaust gas, An unillustrated three-way catalyst is provided as an exhaust gas purification catalyst that purifies exhaust gas by oxidizing HC and reducing NO _x . A crank angle sensor 15 is built in a distributor (not shown in FIG. 2), and the control unit 10 counts a crank unit angle signal output from the crank angle sensor 15 in synchronization with the engine rotation for a certain period of time. Alternatively, the cycle of the crank reference angle signal is measured to detect the engine rotation speed Ne.

The control unit 10 calculates a fuel amount corresponding to the target air-fuel ratio based on the values detected by the various sensors, and outputs an injection pulse signal having a pulse width corresponding to the fuel amount to the fuel injection valve 14 It is designed to output to. That is, from the intake air flow rate Q detected by the air flow meter 9 and the engine speed Ne obtained by counting the pulse signal of the crank angle sensor 15 for a certain period of time, the basic fuel injection pulse width (corresponding to the fuel injection amount) Yes) T
While setting p (Tp = k × Q / Ne, k is a constant), various correction coefficients COEF according to the engine operating state, air-fuel ratio feedback correction coefficient α, and learning correction coefficient K
_L and a correction amount Ts for correcting the change in the effective opening time of the electromagnetic fuel injection valve due to the battery voltage are respectively obtained, and the basic fuel injection pulse width is set so that the actual air-fuel ratio becomes the target air-fuel ratio. the Tp correction operation on is adapted to set a final fuel injection pulse width Ti = Tp · COEF · α · K L + Ts.

The various correction coefficients COEF are, for example,
For example, COEF = 1 + K_MR+ K_TW+ K _AS+ K_AI+ ...
Is calculated by the following formula, where K_MRIs the air-fuel ratio supplement
Positive coefficient, K_TWIs the water temperature increase correction coefficient, K_ASStart and start
Post-increase correction coefficient, K_AIIs the increase correction coefficient after idle
You. The air-fuel ratio feedback correction coefficient α is equal to the air-fuel ratio.
Proportional / product based on the exhaust air-fuel ratio detection result of the ratio sensor 7.
It is increased or decreased by minute control, etc.
The actual air-fuel ratio of the intake air-fuel mixture is set to the target air-fuel ratio (for example, theoretical
The air-fuel ratio) can be controlled. The correction coefficient
Rather than correction by α, the corrected fuel amount is compared with the basic fuel injection amount.
The target air-fuel ratio is controlled by adding and subtracting.
The same is true for success.

The reference value of the air-fuel ratio feedback correction coefficient α during the air-fuel ratio feedback control (for example, 1.0)
Deviations from, by determining the predetermined learned for each area of each engine operating state learning correction coefficient K _L, the In the calculation of the fuel injection amount, the learning correction coefficient a basic fuel injection amount Tp K _L And the operating condition is changed so that the target air-fuel ratio can be obtained by the fuel injection amount Ti calculated without correction by the air-fuel ratio feedback correction coefficient α (when α = 1.0). The air-fuel ratio control accuracy is improved with good responsiveness before the air-fuel ratio feedback correction coefficient α can be acquired.

By the way, the evaporated fuel accumulated in the upper space of the fuel tank 11 is guided to the canister 5 through the evaporated fuel passage 13 having the check valve 12 and is temporarily adsorbed to the canister 5. The vaporized fuel temporarily adsorbed in the canister 5 is purged through a purge control valve 3 whose opening is controlled by the control unit 10 so as to obtain a predetermined target purge rate under predetermined operating conditions. It is adapted to be introduced into the intake passage 2 downstream of the throttle valve 8 via the passage 4. The purge control valve 3, the purge passage 4, the canister 5, etc. constitute the hardware of the purge processing means of the present invention.

Here, the purge processing means, the air-fuel ratio control means, the purge value correction value setting means, the additional charge detection means, the purge gas concentration change estimation means, and the additional charge correction value estimation means of the present invention function as software. The air-fuel ratio control performed by the control unit 10 when switching from the non-purging process to the purging process will be described with reference to the flowchart of FIG.

Step (denoted by S in the figure, the same applies hereinafter)
At 1, it is determined whether or not the purge process has just started. The determination can be made based on, for example, the passage of time from the start of the purge process, the fact that the average value of the air-fuel ratio feedback correction coefficient α has stabilized within a predetermined range, and the like. YE
If S, go to step 2. If NO, the process proceeds to step 5, and the present flow is ended to perform normal air-fuel ratio feedback control and the like.

In step 2, subroutine B described later is executed.
The deviation amount x of the air-fuel ratio feedback correction coefficient α set by (the flowchart of FIG. 5) is read. In step 3, based on the deviation amount x, the fuel injection pulse width Ti ′ during the purging process (that is, the fuel injection amount) is calculated by the following equation.
Is calculated. 'In = Tp · COEF · (α- x) · K L + Ts Step 4, the Ti' Ti and transmitted as valve-opening drive signal of the fuel injection valve 14 and the flow ends. Here, the air-fuel ratio feedback correction coefficient α in the subroutine B
Subroutine A (purge concentration change detection routine) performed before detection of the deviation amount x will be described with reference to the flowchart of FIG.

In step 11, flag determination is performed.
If flag = 0, it is determined that it is the first time, and step 12
Proceed to. In step 12, the value of the air-fuel ratio feedback correction coefficient α is read and the current purge concentration is estimated.
For the estimation, a purge characteristic map as shown in FIG. 6 is stored in advance, and the current purge rate (calculated from the opening of the purge control valve 3 and the intake air flow rate Q) and the air-fuel ratio feedback correction coefficient α are calculated. The current purge concentration can be obtained from the value and the value by interpolation calculation or the like.

In step 13, after the purge concentration at the beginning of the purging process is calculated in step 12, the current state of the canister 5 is stored in advance as shown in FIG. At which point on the characteristic curve of the change in purge concentration with respect to the cumulative purge amount) in FIG. Then, the flag is set to 1 and the process returns to step 11.

By executing the steps 12 and 13, it is possible to eliminate the variation in the adsorbed state of the evaporated fuel at the beginning of the purge process of the canister 5, and to improve the accuracy of estimation / judgment in the subsequent steps. be able to. In step 11, the flag is set to 1 in step 13.
When it is confirmed that the additional charge is set, it is determined that it is the first time or later, and steps 14 and 15 are sequentially repeated until it is determined in step 16 that additional charge is present.

In step 14, as in step 12,
Referring to the purge characteristic map as shown in FIG. 6, the current purge rate (calculated from the opening of the purge control valve 3 and the intake air flow rate Q), the value of the air-fuel ratio feedback correction coefficient α,
Then, the current purge concentration is obtained by interpolation calculation or the like. In step 15, the purge concentration obtained in step 14 and
From the cumulative purge amount, the current state of the canister 5 is
The point on the pre-stored canister desorption characteristic (characteristic of change in purge concentration with respect to cumulative purge amount without additional charge) as shown in FIG. 7 is known.

That is, the steps 14 and 15 are used to know the tendency of the desorption state of the canister 5 during the purging process. In step 16, the canister desorption characteristics set in advance (without additional charge)
And the actual desorption characteristics of the canister 5 and the deviation amount x between
It is determined whether there is a predetermined value or more.

When the deviation amount x is equal to or larger than the predetermined value, it is determined that additional charge is present, and the process proceeds to step 17. If the deviation amount x is smaller than the predetermined value, it is determined that there is no additional charge,
Further, the process returns to step 14 in order to continuously monitor the change in the detached state of the canister 5. In step 17, when the predetermined purge amount is earned (when the grid point of the cumulative purge amount in FIG. 8 is reached), the current purge rate and the air-fuel ratio feedback are referred to with reference to the purge characteristic map as shown in FIG. The current purge concentration is obtained from the value of the correction coefficient α by interpolation calculation or the like.

At step 18, as shown in FIG. 9, the purge concentration at the previous cumulative purge amount grid point and the purge concentration at this time cumulative purge amount grid point are used to change the purge concentration with respect to the cumulative purge amount. Find the slope. And
Until the next cumulative purge amount grid point, it is estimated that the purge concentration will change due to the obtained gradient, and this flow is ended.

After that, the flowchart of the subroutine B shown in FIG. 5 is executed. In step 21, it is determined whether or not there is additional charge, based on the determination result of step 16 in the flowchart of FIG. If yes, then go to step 22, if no, then go to step 23.
In step 22, since there is additional charge, the purge concentration corresponding to the present time is estimated based on the predicted slope of the change in purge concentration (broken line in FIG. 9) obtained in step 18 of the flowchart in FIG.

In step 23, since there is no additional charge, the purge concentration corresponding to the present time is obtained based on the preset canister desorption characteristics as shown in FIG. In step 24, the deviation amount x of the air-fuel ratio feedback correction coefficient α is obtained from the purge concentration obtained in step 22 or step 23 and the current purge rate with reference to the table shown in FIG. 11. , This flow ends.

The deviation amount x thus obtained is read in step 2 of the flow chart of FIG. 3 described above, and the air-fuel ratio feedback correction coefficient α corresponding to the presence or absence of additional charge is corrected. As described above, according to the present embodiment, when there is additional charge, it is possible to estimate the deviation amount of the air-fuel ratio feedback correction coefficient α corresponding to the additional charge. It is possible to respond to the air-fuel ratio step difference due to the start of the purging process with high responsiveness and with high accuracy, and thus it is possible to effectively suppress the deterioration of the exhaust performance and the like.

Further, in this embodiment, since the air-fuel ratio feedback correction coefficient α is utilized to detect the additional charge and to estimate the change of the purge concentration during the additional charge, a dedicated device is provided independently. Since it is not necessary, the structure can be simplified. Note that, in the present embodiment, the description is made representatively immediately after the start of the purge processing, but the present invention is not limited to this, and the present invention can always respond to the change in the purge concentration due to the additional charge during the purge processing with high accuracy and promptly. It is a thing. In this embodiment, the fuel injection amount is corrected when the air-fuel ratio is corrected, but the intake air is introduced by a so-called auxiliary air introduction device or the like for introducing the intake air into the engine 1 from another route. The air flow rate may be corrected to obtain the target air-fuel ratio.

[0034]

As described above, according to the invention described in claim 1, even if there is additional charge, it is possible to respond to it with high responsiveness and high accuracy, so the air-fuel ratio during the purging process is improved. Control accuracy can be improved, and deterioration of exhaust performance and the like can be suppressed to the maximum. If the purge gas concentration change estimating means is configured as described in claim 2, it is possible to detect the change in the purge gas concentration with high accuracy by a simple configuration using an existing air-fuel ratio feedback control device.

[Brief description of drawings]

FIG. 1 is a diagram corresponding to a claim of the present invention.

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

FIG. 3 is a flowchart for explaining the air-fuel ratio control of the above embodiment.

FIG. 4 is a flowchart illustrating a subroutine A of the above embodiment.

FIG. 5 is a flowchart illustrating a subroutine B of the above embodiment.

FIG. 6 is a diagram showing an example of a table for estimating a purge concentration.

FIG. 7 is a diagram illustrating a change in purge concentration with respect to a cumulative purge amount.

FIG. 8 is a diagram illustrating a relationship between a cumulative purge amount and grid points.

FIG. 9 is a diagram illustrating estimation of a change in purge concentration with respect to a cumulative purge amount.

FIG. 10 is an example showing a relationship (change in canister desorption) of a change in purge concentration with respect to an accumulated purge amount.

FIG. 11 is a diagram showing a relationship between a purge concentration, a purge rate, and a deviation amount x of an air-fuel ratio F / B correction coefficient α.

FIG. 12 is an overall configuration diagram showing an example of a conventional evaporated fuel processing device.

FIG. 13 is a diagram illustrating a problem of conventional air-fuel ratio control at the start of purge processing.

[Explanation of symbols]

 1 engine 2 intake passage 3 purge control valve 4 purge passage 5 canister 6 exhaust passage 7 air-fuel ratio sensor 8 throttle valve 9 air flow meter 10 control unit 11 fuel tank 14 fuel injection valve 15 crank angle sensor

Claims (2)

[Claims] 1. An evaporative fuel accumulated in a fuel tank or the like is temporarily adsorbed by an adsorbing means, and the evaporative fuel adsorbed by the adsorbing means is introduced into an engine intake system as a purge gas which is a mixture with the outside air for processing. In the air-fuel ratio control device for an internal combustion engine, which includes a purge processing means and an air-fuel ratio control means for controlling the air-fuel ratio control amount so as to maintain the air-fuel ratio of the engine intake air-fuel mixture at a target value, the purge processing is performed. During the purging process, a correction value setting means for setting the correction value of the air-fuel ratio control amount in order to cope with the change in the fuel concentration of the purge gas according to the progress state of the purging process, the fuel tank, etc. during the purging process. Additional charge detecting means for detecting an additional charge state in which evaporated fuel is generated, and purge gas concentration change estimating means for estimating a fuel concentration change of purge gas when the additional charge state is detected An air-fuel ratio control apparatus for an internal combustion engine, comprising: an additional charge correction value estimation means for estimating a correction value of an air-fuel ratio control amount based on an estimation result of the purge gas concentration change estimation means. . 2. The purge gas concentration change estimation means estimates the fuel concentration of the purge gas based on the deviation of the air-fuel ratio control amount from the basic control value and the purge rate, and based on the time change of the estimation result, the purge gas concentration The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the air-fuel ratio control device is configured as means for estimating a change in fuel concentration.