JP3376172B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an 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.

[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 evaporative fuel treatment device which is called a purge process, and there is, for example, 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.

[0004]

By the way, the purge gas is composed of the purge fuel and the outside air introduced into the canister during desorption.
Therefore, it has a predetermined fuel concentration (hereinafter, also referred to as purge concentration). Therefore, in order to obtain the target air-fuel ratio even during the purging process, the fuel amount injected from the fuel injection valve 14 is determined based on the detection value of the air-fuel ratio sensor 7 provided in the exhaust passage 6. It is necessary to perform so-called air-fuel ratio feedback control for controlling (or the intake air flow rate), but in such a case, the detection delay of the air-fuel ratio sensor 7 and the purge gas amount and purge concentration may change over time. And the opening 4 of the purge passage 4
Since A is separated from the fuel injection valve 14, the air-fuel ratio sensor 7 and the like, if the fuel injection amount from the fuel injection valve 14 is corrected based on the detection value of the air-fuel ratio sensor 7 by a method similar to the conventional one, for example, , A phase shift occurs between the change of the purge amount and the change of the purge concentration over time and the fuel correction that is supposed to be corrected, and in the worst case, the control hunting, that is, the change of the air-fuel ratio is large. There was a fear of becoming.

The present invention has been made in view of the above-mentioned conventional circumstances, and provides an air-fuel ratio control device for an internal combustion engine capable of further improving the accuracy of the air-fuel ratio control during the purging process. With the goal.

[0006]

Therefore, as shown in FIG. 1, an air-fuel ratio control system for an internal combustion engine according to a first aspect of the present invention temporarily adsorbs evaporated fuel generated in a fuel tank or the like. And adsorbing means for storing the adsorbing means and the passage connecting the adsorbing means and the engine intake system, and purging the evaporated fuel stored in the adsorbing means as purge gas under the predetermined engine operating conditions. In an air-fuel ratio control device for an internal combustion engine that includes a purge control valve that is controlled to a predetermined opening degree to be introduced, a fuel supply amount that sets the fuel supply amount supplied from the fuel supply means according to the engine operating state. Setting means, air-fuel ratio detecting means for detecting a specific component concentration in the exhaust gas to detect the air-fuel ratio of the engine intake air-fuel mixture, and air-fuel ratio for detecting an air-fuel ratio change amount based on the detection value of the air-fuel ratio detecting means. Change detection hand When the purge variation amount detecting means for detecting a purge amount of change in the fuel vapor during the purge, the purge variation amount storage means for storing the detected purged change amount for each predetermined time, a purge gas is introduced into the intake system Based on the calculated purge detection delay time and the purge detection delay calculation means for calculating the purge detection delay time from the above to the detection by the air-fuel ratio detection means, the air-fuel ratio change amount at the present time is affected. Detected purge change amount specifying means for specifying the purge change amount via the purge change amount storage means, and purge combustion delay calculation means for calculating the purge combustion delay time from when the purge gas is introduced into the intake system to when it is burned. And based on the calculated purge combustion delay time, the purge change amount to be burned at the next combustion is specified through the purge change amount storage means. Based on the combustion purge change amount specifying unit, the specified detected purge change amount, the current air-fuel ratio change amount, and the specified combustion purge change amount, set by the fuel supply amount setting unit. And a fuel supply amount correction means for correcting the fuel injection amount for the next combustion.

According to the second aspect of the present invention, the purge control for correcting the opening of the purge control valve so that the air-fuel ratio change amount detected by the air-fuel ratio change amount detecting means is maintained at a predetermined value. The valve opening correction means is included. Claim 3
In the invention described in the above paragraph, the purge detection delay calculation means is based on the intake transportation delay time, the correction time by the filling efficiency, the exhaust passage length to the air-fuel ratio detection means, and the response delay time of the air-fuel ratio detection means. Then, the purge detection delay time is calculated.

According to the fourth aspect of the present invention, the purge combustion delay calculating means is configured to calculate the purge combustion delay time based on the intake transportation delay time and the correction time based on the charging efficiency.

[0009]

According to the first aspect of the invention having the above-described structure, the purge gas concentration (amount) scheduled to be burned next time is made to correspond to the change in the exhaust air-fuel ratio while taking into account the transport delay of the purge gas. Enables correction of fuel supply. As a result, it becomes possible to suppress the control hunting of the air-fuel ratio control during the purging process, and consequently the air-fuel ratio fluctuation.

According to the second aspect of the present invention, since the opening of the purge control valve is corrected so that a predetermined (for example, substantially constant) air-fuel ratio change, that is, a predetermined purge change amount is obtained, the purge gas is purged. Since it is possible to further suppress the fluctuation of the air-fuel ratio, it is possible to further improve the accuracy of the air-fuel ratio control. According to the third and fourth aspects of the invention, the purge detection delay time and the purge combustion delay time are calculated based on the factors that affect the purge detection delay time and the purge combustion delay time. It is possible to easily match the purge detection delay time and the purge combustion delay time with the actual values by appropriately changing the characteristics of each factor without performing an experiment or the like for each time or for each design change.

[0011]

An embodiment of the present invention will be described below with reference to the accompanying drawings. It should be noted that common reference numerals shown in FIG. In FIG. 2, an intake passage 2 of an engine 1 includes an air flow meter 9 for detecting an intake air flow rate Q of intake air drawn through an air cleaner (not shown) and a throttle valve for controlling the intake air flow rate Q in conjunction with an accelerator pedal. 8 is provided, and an electromagnetic fuel injection valve 14 is provided for each cylinder in the downstream manifold portion. A throttle sensor 8A that detects the opening TVO of the throttle valve 8 (may be an idle switch that detects a fully closed state) is provided.

The fuel injection valve 14 is opened and driven by an injection pulse signal set by a method which will be described later in the control unit 10 having a built-in 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 is adjusted to a predetermined pressure via a fuel supply passage 20 having a pressure regulator 19 interposed therebetween, and the fuel injection valve 14 Is supplied to. 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 as an air-fuel ratio detecting means of the present invention 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, and the downstream thereof. on the side, a predetermined air-fuel ratio (e.g., stoichiometric air-fuel ratio) CO in the exhaust at the bottom, three-way catalyst (not shown) as an exhaust purifying catalyst for purifying performing the reduction of oxidation and nO _X of HC is provided.

A crank angle sensor 15 is built in a distributor (not shown in FIG. 2), and a crank unit angle signal output from the crank angle sensor 15 in synchronization with the engine rotation is counted for a certain period of time. Alternatively, the engine speed Ne is detected by measuring the cycle of the crank reference angle signal. 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 like this.

That is, the engine rotation speed Ne obtained by counting the intake air flow rate Q detected by the air flow meter 9 and the pulse signal of the crank angle sensor 15 for a certain period of time.
From the following, while the basic fuel injection pulse width (corresponding to the fuel injection amount) Tp (Tp = k × Q / Ne, k is a constant) is set, various correction coefficients COEF according to the engine operating state are set.
, The air-fuel ratio feedback correction coefficient α, the learning correction coefficient K _L, and the correction amount Ts for correcting the change in the effective opening time of the electromagnetic fuel injection valve due to the battery voltage, respectively, and the actual air-fuel ratio is calculated. so that a target air-fuel ratio, a final fuel injection pulse width the basic fuel injection pulse width Tp correction operation to Ti = Tp · COEF · α · K L + Ts
Is set. The setting of the fuel injection amount by the control unit 10 corresponds to the fuel supply amount setting means of the present invention.

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
It 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 air-fuel ratio
The control performed by the feedback correction coefficient α is the so-called empty
It corresponds to the fuel ratio feedback control. The correction coefficient α
The correction fuel amount to the basic fuel injection amount
Controlled to the target air-fuel ratio by adding, subtracting, etc.
May be

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.

Here, the air-fuel ratio change amount detecting means of the present invention,
Purge change amount detecting means, purge change amount storing means, purge detection delay calculating means, detected purge change amount specifying means, purge combustion delay calculating means, combustion purge change amount specifying means, fuel supply amount correcting means, purge control valve opening correction The air-fuel ratio control and purge control performed by the control unit 10 functioning as a means will be described with reference to the flowchart (main routine) of FIG. Here, the idle operation will be described, but the present invention is not limited to this, and the control can be performed in another operation region in a steady state.

Step (denoted by S in the figure. The same applies hereinafter)
In No. 1, it is determined whether or not the current operating state is the idle operating state based on the engine rotation speed Ne, the detection signal from the throttle sensor 8A, and the like. If YES, the process proceeds to step 2, and if NO, this flow ends. It should be noted that the steady operation state may be detected. In step 2, a subroutine A is executed to calculate the purge delay time and the like.

In the subroutine A, the flowchart shown in FIG. 4 is executed. That is, in step 11,
The purge delay time T is calculated. The purge delay time T corresponds to a delay time (purge detection delay time) until the purge gas released from the opening 4A is detected by the air-fuel ratio sensor 7. For example, the purge delay time T is
It can be calculated based on “intake passage transport delay time + correction time obtained from a function of intake charge efficiency + exhaust delay time + air-fuel ratio sensor response delay time and the like”.

In step 12, as shown in the flow,
Every predetermined time (for example, air-fuel ratio sensor
Change amount (ΔPurg)
e, the ΔPurge is the change in the opening control amount of the purge control valve 3
It can be calculated from the amount. Also, ΔO described later₂/ S request
You can also turn on the table)
It corresponds to before the purge delay time T, and
Output of the air-fuel ratio sensor 7 [ΔO₂/ S_n= O₂/ S
_n(Current air-fuel ratio sensor output value)- O₂/ S _n-1(Previous
Purge that affects the air-fuel ratio sensor output value)
Amount of change (ΔPurge_n-3).

In step 13, ΔO ₂ / S _n is regarded as corresponding to the change in the air-fuel ratio due to the purge change amount (ΔPurge _n-3 ) before the purge delay time T, and the subsequent change in the air-fuel ratio due to the purge change amount is considered. In order to prevent this, referring to the table described in step 12, the purge change amount (ΔPurge) that is burned by the next air-fuel ratio detection and affects the air-fuel ratio.
_{n− 2} ) and search for the function f [ΔPurge _n-2 , (ΔO ₂ /
S _n ) / ΔPurge _{n −3} ] based on the fuel correction coefficient x. That is, the purge change amount (ΔPurge) is corrected by correcting the fuel injection amount until the next air-fuel ratio detection with the correction coefficient x.
It is designed to prevent the air-fuel ratio from fluctuating under the influence of ( _n-2 ).

It should be noted that the search for the purge change amount (ΔPurge _{n− 2} ) that is burned and has an influence by the next air-fuel ratio detection is the purge change amount before the purge delay time T, and is scheduled to be burned next time. It suffices to retrieve the purge change amount before T ₀ (purge combustion delay time) in the above. Step 14
Then, the correction amount PD of the purge change amount (ΔPurge) is obtained.

[0025] That is, with reference to the table shown in the flow, as ΔO ₂ / S _n falls within a predetermined range, for example, to maintain the ΔO ₂ / S _n in the vicinity 0 (in other words,
In order to maintain the air-fuel ratio of the air-fuel mixture introduced into the cylinder at the target air-fuel ratio, the purge control valve opening is reduced when the purge concentration is higher than the target air-fuel ratio, and the purge control valve opening is corrected to be small when the purge concentration is thin. Then, the correction amount PD of the purge change amount (ΔPurge) is obtained, and this flow ends.

Now, let us return to the description of the main routine. As described above, after executing the subroutine A in step 2, the process proceeds to step 3. In step 3, the exhaust air-fuel ratio is rich (R) (ΔO ₂ / S based on the detection value of the air-fuel ratio sensor 7). _n > 0) or lean (L)
(ΔO _{2 n} / S <0) or stoichiometry (S)
It is determined whether or not (ΔO ₂ / S _n = 0).

If rich, go to step 4, if lean, go to step 5, and if stoichiometric, go to step 6. In step 4, the fuel injection amount is reduced and corrected by the fuel correction coefficient x obtained in step 13 of the subroutine A. The air-fuel ratio feedback correction coefficient α may be fixed to a reference value (for example, 1.0).

In step 5, the fuel injection amount is increased and corrected by the fuel correction coefficient x obtained in step 13 of the subroutine A. The air-fuel ratio feedback correction coefficient α may be fixed to a reference value (for example, 1.0). In step 6, it is assumed that there is no air-fuel ratio fluctuation even in the current state, that is, the purge concentration and the target air-fuel ratio substantially match, and normal air-fuel ratio feedback control is performed.

In step 7, it is determined whether or not the purge is completed (determined based on whether the total purge amount has reached a target or the purge control valve 3 has reached a predetermined opening). If YES, this flow ends. N
If O, go to step 8. In step 8, the correction amount PD obtained in step 14 of subroutine A is read, and the total purge amount (Total Purge _n ) up to now is calculated based on the following equation.

Total Purge _n = Total Purge _n-1 + ΔPurge _n × PD In step 9, the total purge amount (or rate) and the purge control valve 3 reference are made by referring to a preset table as shown in the flow. Based on the relationship with the opening degree, the opening degree (duty) of the purge control valve 3 is set, the purge control valve 3 is driven, and this flow ends.

As described above, according to this embodiment, the fuel injection amount corresponding to the purge change amount can be corrected on the basis of the change in the exhaust air-fuel ratio, while taking into account the transport delay of the purge gas. The control hunting during the purging process and the variation of the air-fuel ratio can be suppressed, and the opening degree of the purge control valve is corrected so that the desired (substantially constant) amount of change in purge is corrected. Fluctuations can be further suppressed, and thus the occurrence of control failure of the air-fuel ratio control due to changes in the purge gas amount and the purge concentration can be prevented more reliably.

FIG. 5 is a functional block diagram showing the control flow of the present invention. As shown in FIG. 5, the intake passage transport delay time, the correction time obtained from the function of the intake charging efficiency, the exhaust delay time, the air-fuel ratio sensor response delay time, etc. are input independently, and each correction amount is calculated from these input data. If it is obtained, that is, if it is modeled, even if the model is changed or the design of the intake system and the exhaust system is changed, the matching can be made easy, and the matching can be achieved. The number of steps can be reduced.

By the way, in this embodiment, the fuel correction coefficient x and the correction amount PD of the purge change amount are calculated based on the change ΔO ₂ / S of the output value of the air-fuel ratio sensor 7. Based on a change in deviation of the average value of the correction coefficient α from the reference value, the air-fuel ratio variation, and thus the purge change amount, is obtained, and thereby the fuel correction coefficient x and the purge change amount correction amount PD are obtained. You can also

In this embodiment, the purge control valve opening is also corrected. However, the fuel injection amount is corrected based on the change in the exhaust air-fuel ratio while taking into account the delay of the purge gas transportation. Only by itself, the control accuracy of the air-fuel ratio control can be improved.

[0035]

As described above, according to the first aspect of the present invention, the purge gas concentration (amount) scheduled to be burned next time is based on the change in the exhaust air-fuel ratio while considering the purge gas transportation delay. ), It is possible to correct the fuel supply amount so that the control hunting of the air-fuel ratio control during the purging process and, consequently, the fluctuation of the air-fuel ratio can be suppressed, thereby improving the accuracy of the air-fuel ratio control during the purging process. Can be improved.

According to the second aspect of the present invention, the opening degree of the purge control valve is further corrected so that a predetermined (for example, substantially constant) air-fuel ratio change, that is, a predetermined purge change amount is obtained. Therefore, the fluctuation of the air-fuel ratio due to the purge gas can be further suppressed, so that the accuracy of the air-fuel ratio control can be further improved. According to the third and fourth aspects of the invention, it is possible to reduce the matching man-hours of the purge detection delay time and the purge combustion delay time.

[Brief description of drawings]

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

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

FIG. 3 is a flowchart illustrating a main routine of air-fuel ratio control / purge control according to the embodiment.

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

FIG. 5 is a functional block diagram illustrating a control flow of the present invention.

FIG. 6 is an overall configuration diagram showing an example of a conventional evaporated fuel processing device.

[Explanation of symbols]

1 organization 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 14 Fuel injection valve 10 Control unit 11 Fuel tank 15 crank angle sensor

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) F02M 25/08 301 F02D 41/02 330 F02D 45/00 368

Claims (4)

(57) [Claims] 1. An adsorbing means for temporarily adsorbing and storing evaporative fuel generated in a fuel tank or the like, and a passage connecting the adsorbing means and an engine intake system,
An air-fuel ratio of an internal combustion engine configured to include a purge control valve controlled to a predetermined opening degree so as to purge the evaporated fuel stored in the adsorbing means and introduce the evaporated fuel into the intake system as purge gas under predetermined engine operating conditions. In the control device, the fuel supply amount setting means for setting the fuel supply amount supplied from the fuel supply means in accordance with the engine operating state, and the air-fuel ratio of the engine intake air-fuel mixture by detecting the concentration of the specific component in the exhaust gas A fuel ratio detection unit, an air-fuel ratio change amount detection unit that detects an air-fuel ratio change amount based on a detection value of the air-fuel ratio detection unit, and a purge change amount detection unit that detects a purge change amount of the evaporated fuel during purging, Purge change amount storage means for storing the detected purge change amount at every predetermined time, and the purge change amount detection means for introducing the purge gas into the intake system until it is detected by the air-fuel ratio detection means. Purge detection delay calculating means for calculating the purge detection delay time, and the purge change amount storing means for storing the purge change amount that has influenced the current air-fuel ratio change amount based on the calculated purge detection delay time. The purge combustion delay amount specifying means for specifying the purge combustion delay amount specifying means for calculating the purge combustion delay time for calculating the purge combustion delay time from when the purge gas is introduced into the intake system until it is burned, Based on this, the purge change amount to be combusted at the next combustion, the combustion purge change amount specifying means for specifying via the purge change amount storage means, the specified detected purge change amount, and the current air-fuel ratio change amount And a fuel supply amount correction means for correcting the fuel injection amount for the next combustion set by the fuel supply amount setting means based on the specified combustion purge change amount. An air-fuel ratio control device for an internal combustion engine, comprising: 2. A purge control valve opening correction means for correcting the opening of the purge control valve so that the air-fuel ratio change amount detected by the air-fuel ratio change amount detecting means is maintained at a predetermined value. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein 3. The purge detection delay calculation means is based on an intake transportation delay time, a correction time based on charging efficiency, an exhaust passage length to the air-fuel ratio detection means, and a response delay time of the air-fuel ratio detection means. The air-fuel ratio control device for an internal combustion engine according to claim 1 or claim 2, wherein the purge detection delay time is calculated. 4. The purge combustion delay calculation means, based on the intake transportation delay time and the correction time based on the charging efficiency,
The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the air-fuel ratio control device is means for calculating a purge combustion delay time.