JPS62131962A - Air-fuel ratio control device for engine - Google Patents

Abstract

PURPOSE:To prevent fluctuations in air-fuel ratios by calculating, according to the fluctuations in feedback coefficients when the purging quantity of evaporation gas is small, the predictors for feedback coefficients when the purging quantity is made larger. CONSTITUTION:As a control performed by a control unit 23, when both main and auxiliary purge valves 20, 22 are in their closed states, and evaporation gas is not being purged, if purging conditions are satisfied, then, the auxiliary purge valve 22 is caused to open, and a '10% purging' is carried out for a fixed period of time. In addition, after the lapse of the fixed time, by way of adding a value 10 times as much as the variation in the feedback coefficients during the '10% purging' to a feedback coefficient stored immediately before starting the purging operation, a predicted feedback coefficient at the time of '100% purging' is calculated. Simultaneously with this, a '100% purging' is carried out in a state where the auxiliary purge valve 22 is being closed and the main purge valve 20 is being opened, and the then feedback coefficients are caused to replace the predictors.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an air-fuel ratio control device for an engine.

(Prior art) Some engine air-fuel ratio control devices control the amount of fuel supplied to the engine based on the air-fuel ratio of exhaust gas (generally oxygen concentration) to maintain a predetermined air-fuel ratio of the air-fuel mixture. There are many cases where the value is set to .

-4. The engine intake system is supplied with evaporative gas (evaporated fuel) that has been adsorbed in a canister in advance, but when this evaporative gas is supplied to the intake system, the air-fuel ratio is slightly overrich. The problem arises that it becomes

For this reason, in the past, the purge amount of evaporative gas was kept extremely small, or, as shown in Japanese Patent Application Laid-Open No. 192858/1984, an optimum purge amount was calculated depending on the operating condition of the engine, and the optimum purge amount was determined. A system has also been proposed in which the air-fuel ratio of the air-fuel mixture is prevented from changing as much as possible by driving a purge pump.

(Problem to be solved by the invention) However, if the purge amount is always kept small as in the above conventional method, large fluctuations in the air-fuel ratio can be prevented, but the evaporative gas adsorbed in the canister cannot be completely purged. It takes a long time to complete the process, and considering the adsorption capacity of the canister, it is practically difficult to use. Furthermore, as described in the above publication, even if an attempt is made to obtain the optimum purge amount using a purge pump, since the absolute amount of evaporative gas adsorbed in the canister itself differs from time to time when purging is attempted, the same purge will not work. Pump operation status!
In other words, even if the purge amount is the same, the amount occupied by evaporated gas varies from time to time, and this is not a fundamental solution to preventing fluctuations in the air-fuel ratio.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an air-fuel ratio control device for an engine that can quickly purge evaporative gas and effectively prevent fluctuations in the air-fuel ratio caused by this purging.

(Means and effects for solving the problem) In order to achieve the above-mentioned object, the present invention provides feedback on the air-fuel ratio of the air-fuel mixture supplied to the engine, that is, the amount of fuel supplied, based on the air-fuel ratio of exhaust gas. Based on the premise of what is being controlled, this feedback control is designed to actively utilize fluctuations in the feedback coefficient. That is,
The purge amount of evaporative gas is initially small and then increased. Based on the fluctuation of the feedback coefficient when the purge amount is small, the sub-measurement value of the feedback coefficient when the purge amount is increased is calculated. The predicted value is used as a feedback coefficient in synchronization with increasing the purge amount. Specifically, as shown in FIG. 1, there is a fuel adjustment means for adjusting the amount of fuel supplied to the intake system of the engine, an air-fuel ratio sensor for detecting the air-fuel ratio of exhaust gas, and a fuel-adjusting means for adjusting the amount of fuel supplied to the intake system of the engine, an air-fuel ratio sensor for detecting the air-fuel ratio of exhaust gas, and a air-fuel ratio control means that performs feedback control on the fuel adjustment means so that the air-fuel ratio of the air-fuel mixture supplied to the engine becomes a predetermined value based on the output; and evaporative gas adjustment means that adjusts the amount of evaporative gas purged to the intake system. and purge amount control means that controls the evaporative gas adjusting means to increase the purge amount of the evaporative gas after keeping it in a small state; and receiving outputs from the purge amount #JI control means and the air-fuel ratio sensor, Calculate a sub-measurement value of the feedback coefficient when the purge amount is increased based on the fluctuation of the feedback coefficient in the air-fuel ratio control means when the purge amount is small, and calculate the feedback coefficient when the purge amount is increased. and a correction means for changing the feedback coefficient to the predicted value.

With this configuration, regardless of fluctuations in the absolute amount of evaporated gas adsorbed in the canister, this purge can be performed quickly while controlling fluctuations in the air-fuel ratio to an extremely small level when the purge amount is increased. can be done. Of course, the small amount of purge that is performed in advance to obtain the sub-measurement value of the feedback coefficient can be made small enough that fluctuations in the air-fuel ratio do not pose a problem in practice, so no equivalent problem will occur in this respect either. be.

(Example) Embodiments of the present invention will be described below with reference to the accompanying drawings.

In FIG. 2, an engine 1 has a combustion chamber 3 defined by a reciprocating piston 2, and an intake boat 4, an exhaust boat 5, an intake valve 6, or an exhaust valve 7 opening into the combustion chamber 3. Therefore, it is opened and closed at a known timing in synchronization with the output shaft of the engine l.

An air cleaner 9, an air flow meter 1O, a throttle valve 11, and a fuel injection valve 12 are disposed in the intake passage 8 connected to the intake port 4 in this order from the upstream side. Further, in the exhaust passage 13 connected to the exhaust port 4, an oxygen sensor 14 as an air-fuel ratio sensor,
A three-way catalyst 15 is provided.

16 in FIG. 2 is a canister, and this canister 16 is
It is connected to the fuel tank 18 via piping 17, and
It is connected to the intake passage 8 between the throttle valve 11 and the fuel injection valve 12 via a pipe 19 serving as a purge passage. An electromagnetic main purge valve 20 is connected to the purge pipe 19, and the main purge valve 2
A narrow bypass passage 21 is provided to bypass 0. A sub purge valve 22 is connected to this bypass passage 21. These purge valves 20 and 22 have different effective opening areas when opened, and in the embodiment, the effective opening area of the sub purge valve 22 is 10% of the effective opening area of the main purge valve 20. There is.

The canister 16 adsorbs the evaporative gas from the fuel tank 17 onto an adsorbent 16a therein, and temporarily stores the evaporative gas therein. By opening either one of both purge valves 20.22 under predetermined operating conditions of the engine 1, the evaporated gas adsorbed by the adsorbent 16a is removed from the atmosphere communication port 1 in the canister 16.
It will be purged into the intake passage 8 together with the air from 6b. The amount of evaporative gas purged into the intake passage 8 is large when the purge is performed through the main purge valve 20, and is small when the purge is performed through the auxiliary purge valve 22, and the ratio of the purge gas between the two purge valves 20 and 2 is
Considering the setting of the effective aperture area described above with 2, lO:1
It is said that

The aforementioned fuel injection valve 12 and both purge valves 20.2
2 is controlled by an FJHH unit 23 consisting of a microcomputer. In order to perform this control, the control unit 23 receives signals from the rotational speed sensor 24 that detects the engine rotational speed in addition to the signals from the air flow meter 10 and the oxygen sensor 14 described above. .

Next, an example of control by the control unit 23 will be described with reference to the flowchart shown in FIG. First, in step S1, the intake air amount Q and the engine speed N detected by the air flow meter 10 are read, and then in step S2, based on the intake air amount Q, the engine speed N is taken into account. In a well-known manner, the basic injection pulse width Tp for the fuel injection valve 12 is calculated. After this, in step S3, the current purge state of the evaporative gas, that is, whether or not purge is being performed (both purge valves 20 and 22 are closed), is determined as ``rlO% purge''.
(Sub purge valve 22 is open) or "100% purge"
(The main purge valve 20 is open) is determined.

When it is determined in step S3 that the evaporative gas is not purged, the process proceeds to step S4, where it is determined whether the conditions for purging the evaporative gas are satisfied. The conditions for performing this purge are such that even if the evaporative gas is purged, the operation of the engine will not be significantly affected.For example, the conditions are that the engine cooling water temperature is above a predetermined value and that the vehicle is running steadily. When it is determined in this step S4 that the purge condition is not satisfied, in step S5, the current feedback coefficient CFB is temporarily stored as a memory value MFB, and then (
The initial value of the feedback coefficient CFB is "1"), and in step S6, the feedback coefficient CF
An increase/decrease (correction) of H is made. After this, step S7
, the basic injection pulse width T obtained in step S2
The final injection pulse width Ti is calculated by multiplying P by the flap coefficient CFB that has been corrected to increase or decrease in step S6, and this calculated injection pulse Ti is applied to the fuel injection valve 12 in step S8. is output to.

The part explained above is the feedback control of the air-fuel ratio when both purge valves 20 and 22 are closed and the evaporative gas is not purged, and is essentially the same as what has been done in the past. .

When it is determined in step S4 that the purge condition is satisfied, first, in step S9, the sub purge valve 22 is opened (the main purge valve 20 is closed), and a small purge amount, that is, "rlO% purge" is performed. Thereafter, in step S10, since this 10% purge is to be performed only at a predetermined time, a timer is set to the predetermined time K. After this, step S mentioned above
5 and subsequent steps are performed, and the feedback coefficient CFB in step S6 is naturally corrected to increase or decrease as the 10% purge is performed.

In the above step S9, in the case of the route passing through SIO, the process moves from step S3 to step Sll since it is currently "10% purge". This step Sl
In step 1, it is determined again whether or not the purge condition is satisfied, and if the purge condition is still satisfied, the timer set in step S10 is counted down in step 512, and then in the subsequent step S1.
When it is determined in step 3 that the countdown has not ended (when K=0 is not achieved), feedback control of the air-fuel ratio is performed while performing the processes from step S6 onwards, that is, the "10% purge".

When it is determined in step 513 that the predetermined time K for performing "rlO% purge" has elapsed (when K=O)
In step S14, the predicted value rMFB+10 (CFB-MFB) J of the feedback coefficient predicted when performing "100% purge" is calculated, and 1 This calculated predicted value is used as a new feedback It is set as coefficient CFB.

That is, CFB in the above formula for calculating the predicted value is the feedback coefficient when performing "10% purge", and MFB is the "10% purge" in step S5.
This is the most recent feedback coefficient just before performing "0% purge". And the constant "10" is r for "rlO%"
100%, which is a tenfold ratio. To explain more specifically, rCFB-MFB
J means the variation in the feedback coefficient when "10% purge" is performed, and the variation predicted when "rloo% purge" is performed is rlo(CFB-MFB)J. And this predicted fluctuating molecule l O(CF
B-MFB) By adding J to the stored value (feedback coefficient MFB) that was stored just before the purge, the overall A feedback coefficient CFB is obtained.

In step S14, the feedback coefficient CF
In order to synchronize with the change to the predicted value of B, in the subsequent step S15, the main purge valve 20 is opened (the sub purge valve 22 is closed), and a "100% purge" is performed.

After this, the processes from step S6 described above are performed, but when this "100% purge" is being performed, as long as the purge condition is satisfied, the steps from step s3 to step S18 are performed, and the process continues as it is. Processing from S6 onwards is performed. By this "100% purge", the evaporative gas is quickly purged.

Note that if the purge condition is not satisfied during the "10% purge" or "100% purge", the value MFB stored in step S5 is used as the feedback coefficient, and the main or sub The purge valves 20 and 22 are closed (steps Sll and S16).
．． 517c7) Root or step S18, S1
9, S20 route).

Although the embodiments have been described above, the present invention is not limited thereto, and includes, for example, the following cases.

(2) The purge amount can be adjusted to be large or small by providing one duty or beam replacement in the piping 19 instead of providing two purge valves 20 and 22. In addition, without adjusting the effective opening area of the piping 19 as a purge passage, a dilution air passage opening into the intake passage 8 is separately provided in parallel with the piping 19, and the purge amount can be controlled by supplying dilution air. While reducing the purge amount, the purge amount may be increased by stopping the supply of dilution air.

(2) The timing of switching from a small purge amount to a large purge amount may not be based on time (K at step 510), but may be performed when the feedback coefficient at this small purge amount becomes stable. In addition, the feedback coefficient at a small purge amount, which is used to predict the fluctuation of the feedback coefficient at a large purge amount, is the average value over a certain period of time in the past, especially the feedback coefficient for this averaging, which is stable as described above. By using the feed/nine-turn coefficient at the time, a predicted value of the feedback coefficient at a large purge amount can be obtained more accurately.

(2) When the control unit 23 is constituted by a microcomputer, it may be of either a digital type or an analog type.

(Effects of the Invention) As is clear from the above description, the present invention can quickly purge evaporative gas while effectively preventing fluctuations in the air-fuel ratio caused by this purging.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of the present invention. FIG. 2 is an overall system diagram showing one embodiment of the present invention. FIG. 3 is a flowchart showing a control example of the present invention. l: Engine 8: Intake passage 12: Fuel injection valve 13: Exhaust passage 14: # Elementary sensor 16: Canister 17: Fuel tank 19: Piping 20: Main purge valve (for large purge amount) 21: Bypass passage 22: Sub-purge valve ( (for small purge amount) 23: Control unit

Claims (1)

[Claims] (1) A fuel adjustment means for adjusting the amount of fuel supplied to the intake system of the engine; an air-fuel ratio sensor for detecting the air-fuel ratio of exhaust gas; and an air-fuel mixture to be supplied to the engine based on the output from the air-fuel ratio sensor. an air-fuel ratio control means for feedback-controlling the fuel adjustment means so that the air-fuel ratio of the air-fuel ratio becomes a predetermined value; an evaporative gas adjustment means for adjusting an amount of evaporative gas purged to the intake system; and an evaporative gas adjustment means for controlling the evaporative gas adjustment means; purge amount control means for increasing the purge amount of the evaporative gas after it is in a small state; and feedback in the air-fuel ratio control means when the purge amount is small by receiving outputs from the purge amount control means and the air-fuel ratio sensor. a correction means for calculating a predicted value of a feedback coefficient when the purge amount is increased based on a variation in the coefficient, and changing the feedback coefficient to the predicted value in synchronization with increasing the purge amount; An air-fuel ratio control device for an engine, characterized by comprising: