JPS63186955A - Air-fuel ratio control device - Google Patents

Abstract

PURPOSE:To prevent the deterioration of exhaust emission, by detecting an evaporation purge gas concentration according to a difference in control central values of feedback correction factors at idling and at low load, and decreasing a fuel injection quantity when the gas concentration is not less than a predetermined value. CONSTITUTION:An air-fuel ratio feedback device 200 controls a fuel injection valve 29 of an internal combustion engine 8 according to a signal from an air-fuel ratio sensor 21. An evaporated fuel gas in a fuel tank 31 connected to the fuel injection valve 29 is purged through a passage 36 into a suction passage 7. An engine load determining means such as an air flow meter 2 detects an idling condition and a low load condition, and means 300 detects a concentration of the evaporated fuel gas in the suction passage 7 according to a difference in control central values of feedback correction factors under the idling condition and under the low load condition. Means 400 decreases a fuel supply quantity to the fuel injection valve 29 according to a result of comparison between the detected gas concentration and a predetermined value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an air-fuel ratio control device that detects an air-fuel ratio using exhaust gas and feedback-controls the air-fuel mixture supplied to an engine to a predetermined air-fuel ratio based on this detection signal. .

[Prior art and problems]

Generally, in electronically controlled fuel injection engines, in order to prevent the fuel vapor from the fuel tank from being released into the atmosphere, the fuel vapor is adsorbed onto activated carbon as an adsorbent, and the adsorbed fuel vapor is transferred to the engine. In an engine that discharges (purges) air into the intake system during operation, the air-fuel ratio of the air-fuel mixture, that is, the output of the air-fuel ratio sensor, changes not only in relation to the fuel supplied from the fuel injection valve but also in relation to the amount of fuel evaporative gas released.

In other words, when using feedback control, the air-fuel mixture should be at the stoichiometric air-fuel ratio even if fuel vapor is purged into the intake system, but in reality, there is a delay in the control during engine transients, so the air-fuel ratio may be temporarily reduced. There is a problem in that it takes time to reach the stoichiometric air-fuel ratio from the rich side air-fuel ratio, and the exhaust emissions of 11C and Co increase during that time.

[Means for solving problems]

In order to solve the above problems, according to the present invention, the amount of fuel supplied to the engine is controlled based on the air-fuel ratio signal from the air-fuel ratio sensor, and the fuel gas from the fuel tank is transferred to the intake system when the engine is operating. In an electronically controlled fuel injection engine that purges the engine, the control central value of the feedback correction coefficient is calculated at engine idling and low load times, and the evaporative purge gas concentration is detected by the difference between the central values. An air-fuel ratio control device is provided, characterized in that it has means for incrementing the injection amount from the fuel injection valve when the amount exceeds the value.

[For production]

In general, in engines equipped with a mechanism to supply evaporative purge gas from the fuel tank to the intake system during engine operation, the supply part is located near the throttle valve, so when the engine is idling, the supply amount is almost zero. At low loads, the amount increases rapidly and reaches its maximum. The present invention makes use of this characteristic by determining the difference between the control center value of the air-fuel ratio feedback correction coefficient at idle (FAFa) and the control center value of the air-fuel ratio feedback correction coefficient at low load (FAFa'). The evaporative purge gas concentration is estimated, and based on the signal from the air-fuel ratio sensor when the gas concentration exceeds a predetermined value, the injection amount to the fuel injection valve is corrected and reduced by the evaporative purge gas, and the basic air-fuel ratio is reduced due to the evaporative purge gas. The objective is to prevent the engine from shifting toward the lynch side, and to prevent deterioration of exhaust emissions due to feedback control delay during that time.

〔Example〕

FIG. 1 is a diagram corresponding to claims of the present invention, in which an air-fuel ratio feedback device 200 controls a fuel injection valve 29 of an engine 8 based on an air-fuel ratio signal from an air-fuel ratio sensor 21. The fuel tank 31 is also connected to the fuel injection valve 29 and further includes a passage 36 for purging the fuel gas from the tank 31 into the intake passage 7. According to the present invention, in addition to the above-mentioned configuration, the idle state and low load state are detected by engine load determining means such as the air flow meter 2, and the control center value of the feed hack correction coefficient in the air-fuel ratio feedback control device 200 at that time is determined. An evaporative purge gas concentration detecting means 300 is provided to detect the concentration of fuel evaporative gas (evaporative purge gas) supplied to the intake passage 12 based on the difference, and the gas concentration determined by the evaporative purge gas concentration detecting means 300 is compared with a predetermined value described later. An evaporative purge correction control means 400 is provided which performs a correction on the amount of fuel supplied to the fuel injection valve 29 based on the comparison result.

The present invention will be explained in detail below.

FIG. 2 is a system diagram of an electronically controlled fuel injection engine to which the present invention is applied. Air taken in from the air cleaner 1 is sent to the combustion chamber 9 of the engine body 8 through an intake passage 7 including an air flow meter 2, a throttle valve 3, a surge tank 4, an intake boat 5, and an intake valve 6. The throttle valve 3 is linked to an accelerator pedal 10 in the driver's cab. The combustion chamber 9 is the cylinder head 1
1, a cylinder block 12, and a piston 13, and the exhaust gas produced by combustion of the air-fuel mixture is discharged to the atmosphere via an exhaust valve 14, an exhaust boat 15, an exhaust manifold 16, and an exhaust pipe 17.

An intake temperature sensor 18 is provided in the air flow meter 2 to detect the intake temperature, and a throttle position sensor 19 detects the opening degree of the throttle valve 3. The water temperature sensor 20 is attached to the cylinder block 10 and detects the cooling water temperature, that is, the engine temperature.
is attached to the collecting part of the exhaust manifold 16 to detect the oxygen concentration in the collecting part, and the crank angle sensor 22 is attached to the power distributor 2 connected to the crankshaft (not shown) of the engine main body 8.
The crank angle of the crankshaft is detected from the rotation of the shaft 24 of No. 3, and the vehicle speed sensor 25 detects the rotational speed of the output shaft of the transmission 26. These sensors 2゜1B, 19, 20
, 21 , 22 , and 25 and the voltage of the storage battery 27 are sent to an electronic control section 28 . A fuel injection valve 29 is provided near each intake boat 5 in correspondence with each cylinder, and a pump 30 supplies fuel from a fuel tank 31 to the fuel injection valve 29 via a fuel passage 32. The electronic control unit 28 calculates the fuel injection amount using input signals from each sensor as parameters, and sends an electric pulse having a pulse width corresponding to the calculated fuel injection amount to the fuel injection valve 29. The charcoal canister 33 accommodates activated carbon 34 as an adsorbent, connects the boat on the inlet side to the upper space of the fuel tank 31 via a passage 35, and connects the port on the outlet side to the purge port 3 via a passage 36.
Connected to 7.

The purge boat 37 is located upstream of the throttle valve 3 when the throttle valve 3 has an opening smaller than a predetermined opening, and is located downstream of the throttle valve 3 when the throttle valve 3 has an opening greater than the predetermined opening. and receive negative pressure in the intake pipe. The on-off valve 38 has a bimetal disc, and closes the passage 36 to stop releasing fuel evaporative gas into the intake system when the engine is at a low temperature lower than a predetermined temperature.

FIG. 3 shows details of the electronic control section 28.

CPU (central processing unit) consisting of a microprocessor
39, ROM (read-on memory) 40, RAM (
Random access memory) 41, another RAM as a non-volatile memory element that can be supplied with power from the auxiliary power supply and retain memory even when the engine is stopped 42, A/D with multiplexer
The (analog/digital) converter 43 and the buffered l10 (input/output) device 44 are connected to each other via a bus 45.

Air flow meter 2, intake temperature sensor 18, water temperature sensor 2
0. The output of the air-fuel ratio sensor 21 and the storage battery 27 is A/
The signal is sent to the D converter 43. Further, the outputs of the throttle position sensor 19 and the crank angle sensor 22 are output from the I10 device 44.
The fuel injection valve 29 is sent to the CP via the I10 device 44.
Receives input from U39.

FIG. 4 shows fuel injection amount calculation during feedbank control in which the fuel injection amount is calculated using the feedback signal from the air-fuel ratio sensor 21 as a parameter when the engine temperature is above a predetermined value, that is, after warm-up is completed. It is a flowchart of the program.

The data regarding the intake air flow rate Q and the engine rotational speed N stored in the RAM 41 are stored in steps 46 and 47.
The basic injection time τ is determined from these data in step 48. To calculate τ, a conventionally well-known calculation formula is used, for example, τ, = and - (where, is a constant). In step 49, FAF
2×K is calculated, and the effective injection time τ is obtained by further subtracting the correction time τ8v by the evaporative purge of the present invention, which will be described later. 7FAF Xτ, XK-τ. 9 is determined.

Then, in step 50, the effective injection time τ is determined.

The final injection time τ=τ, +τ9 is calculated from 9, which is the invalid injection time of the fuel injection valve 41, and at step 51, the final injection time τ=τ, +τ9 is calculated.
It is sent to the zero unit 44.

Hereinafter, τ in FIG. 9 will be explained.

As shown in Figure 5, the deviation of the actual air-fuel ratio from the stoichiometric air-fuel ratio due to the release of fuel evaporative gas into the intake system (evaporative purge) occurs when the engine is idling (section A in Figure 5). is 0, reaches its maximum when the engine is under low load (section B), and decreases when the engine is under high load (section C). Accordingly, from this characteristic analysis, if the deviation is greater than a predetermined value between AB, it can be determined that an air-fuel ratio deviation is occurring due to evaporative purge.

FIG. 6 is a flowchart of a program for calculating and storing the above deviation data.

In step 52, the average value of the intake air flow rate per two cycles of air-fuel ratio feedback control is calculated from the detection signal of the air flow meter 2. In step 53, the deviation between the average air-fuel ratio and the stoichiometric air-fuel ratio in the same two cycles as the two cycles in step 52 is calculated. Deviations on the lean side from the stoichiometric air-fuel ratio are positive, and deviations on the rich side from the stoichiometric air-fuel ratio are negative.

FIG. 7 illustrates the actual air-fuel ratio (also called return air-fuel ratio). Sl is the output of the air-fuel ratio sensor 21, and S2 is the integral value of the output of the air-fuel ratio sensor 21 as the feedback air-fuel ratio.

Note that this integral value is calculated by the CPU 39. The output of the air-fuel ratio sensor 21 is "1" when the air-fuel ratio is smaller than the stoichiometric air-fuel ratio, that is, when the air-fuel mixture is rich, and when the air-fuel ratio is larger than the stoichiometric air-fuel ratio, that is, when the air-fuel mixture is lean. It becomes “0”. The CPU 39 decreases the integral value S2 by a predetermined amount of ia at predetermined time intervals during a period in which the output S1 of the air-fuel ratio sensor 21 is maintained at "1", so that the output S1 of the air-fuel ratio sensor 21 is maintained at "0". During this period, the integral value S2 is increased by a predetermined amount a at a predetermined time interval.Furthermore, when the output S1 of the air-fuel ratio sensor 21 is reversed, the integral value S2 is increased or decreased by another predetermined value 1b (b>a).a , b are changed in relation to the vehicle speed, and b is set to improve responsiveness.The integral value S2 corresponds to the actual air-fuel ratio of the air-fuel mixture in the combustion chamber 9, that is, the return air-fuel ratio. do.

In step 54, it is determined whether or not the throttle switch of the throttle position sensor 19 is on. If the determination result is positive, the process proceeds to step 55, and if not, the process proceeds to step 66. In step 55, it is determined whether Ql<Q<Q2, that is, whether the operating state of the engine is in section A in FIG. If not, terminate this program.

In step 56, the first
The value 2 of the sum of MA and D in the memory section M1 is cleared when the engine operation is stopped. The reason why D is set to MA is to prevent MA from taking a completely unrelated value due to unforeseen causes and to improve the reliability of MA. Step 5
7, the value C1 of the first counter provided for section A is incremented by 1 and 3. The value C1 of the first counter is cleared when the engine operation is stopped. Step 58
Then, it is determined whether or not the value C1 of the first counter is 3 or more. If the determination result is positive, the process proceeds to step 59, and if not, the program is terminated.

For example, even if the first D contains an error of 0.1 (10%), by repeating step 57 three times, the MA error will be 0.025 (-2.5% = -10% ÷ 2 ÷ 2 ), which increases the reliability of MA. In step 59, the first flag bit FA is changed from 0 to 1, assuming that the deviation from the stoichiometric air-fuel ratio in section A has been determined. Flag FA=
1 means that the MA has become fully reliable. In step 66, whether or not Q3<Q<Q4,
That is, it is determined whether the operating state of the engine is in section B in FIG. 5, that is, whether the load is low or not. If the determination result is positive, the program proceeds to step 67, and if not, the program is terminated.

In step 67, the value Q of the storage unit of the intake air amount in section B is
, and the sum of 2 and 100 is a new Q.

Then, in the memory section of the injection time, try. The sum of % of the new pro 9
, 70 , 71 , 72 are the steps 56 , 5 described above.
7, 58.

Corresponds to 59. That is, in step 69, the value of the second counter provided for section B is set to 2, which is the sum of the value MB of the second storage section M2 provided for section B and D, as the new MB. Add 1 to C2. Step 7
1, it is determined whether or not the value C2 of the second counter is 3 or more. If the determination result is positive, the process proceeds to step 72, and if not, the program is terminated. In step 72, the second
The flag bit FB of is changed from 0 to 1.

FIG. 8 shows the evaporative purge gas concentration by determining the difference between the correction coefficient deviation MA of the feedback air-fuel ratio in the idle state (section A) obtained by executing the program explained above and the deviation MB in the low load state (section B). Calculate,
Furthermore, this is a program that determines the amount of reduction τ□ for controlling the evaporative purge correction based on the magnitude of the concentration. below,
Explain the program.

In steps 73 and 74, it is determined whether the learning shown in FIG. 6 has been completed, that is, whether the flags FA=1 and F13=1. If both determination results are positive, the process advances to step 75, and if not, the program is terminated. In step 75, the values MA and MB obtained in steps 56 and 69 in FIG.
ΔFAF=MA−MB corresponding to the difference in Fa is calculated. Next, in step 76, this ΔFAF is set to a predetermined value Y (for example, 0
．． 1) Determine whether or not it is larger than that to determine the degree of shadow caused by evaporation. If the determination result is positive, the evaporative purge correction execution flag F is changed from 0 to 1 in step 77, and then in step 78, it is determined whether ΔFAI' is larger than the set value X (for example, 0.02) taking into account the variation. Determine. This step is a step to stop the evaporative purge correction when the degree of shadow caused by the evaporative purge decreases due to the execution of the evaporative purge correction, and it is finally determined that there is almost no shadow.
The value of is set smaller than the value of Y in step 76.

If the determination result is positive in step 78, that is, it is determined that the influence of the evaporative barge is still large, the process proceeds to step 79, where the actual air-fuel ratio A/F is calculated from ΔFAF. below,
This calculation method will be explained. As mentioned above, ΔFAF corresponds to the difference between the control center value FAFA of the feedback correction coefficient in an idling state and the control center value FAFI of the feedback correction coefficient in a low load state, and this ΔFAF corresponds to the difference between the control center value FAFA of the feedback correction coefficient in an idle state and the control center value FAFI of a feedback correction coefficient in a low load state. This corresponds to the deviation from 7). In other words, the return air-fuel ratio A/F in a low load state is (l-ΔFAF
) X can be determined by the theoretical air-fuel ratio. This air-fuel ratio A/F is the intake air fflQ in the low load range.
g and the sum of the fuel injection amount (time) τ8 corresponding to the intake air LtQs and the fuel injection amount (time) τ8v corresponding to the fuel supplied by the evaporative barge, so the next step 80 Now, we take in Ql and τ calculated in steps 67 and 68 of the program in FIG. 6, and find τ, which is considered to be the shadow mouth of the Evapo barge. 9 is calculated using the following formula.

Therefore, K and p are constants for converting the fuel injection time into the injection amount.

111■, but if the determination is negative in step 76, there are two possibilities:
? ΔFAF is below Y without evaporative purge correction. Therefore, in step 81, it is determined whether the evaporative purge correction execution flag F is 1 at that time. If the sentencing result is positive, it is determined that there is a possibility that the evaporative purge correction will continue to be performed, and in step 78, it is verified whether or not it is larger than the set value X.
If the determination result is positive, the steps 79 and 8 described above
Execute 0.

If the determination result in step 81 is negative, it is determined that there is no need to perform the evaporative purge correction, and the evaporative purge correction fuel amount (injection time) τ and V are set to O using the steering knob 83.
Next, in step 84, the flags FA=1 and FB=1 are reset and the program ends.

By the way, after performing the evaporative purge correction, the final ΔF
If the AF becomes smaller than the set value X, that is, step 7
If it is determined no in step 8, the process proceeds to step 82 to stop the execution of the evaporative purge correction, resets the evaporative purge correction execution flag F to O, and proceeds to step 83 as described above.
, 84 are executed, and the program ends. Then, τ8 calculated by this program as described above
v is taken into step 67 of the program shown in FIG. 4 and is τ, which is obtained by subtracting τ from FAF Xτ, XK. The fuel is supplied from the fuel injection valve 29 (FIG. 2).

Note that this τ is cleared when the engine is stopped and set to prevent hack-up.

〔effect〕

FIG. 9 is a graph showing changes in the amount of fuel supplied to the combustion chamber of an engine by the air-fuel ratio control device of the present invention as engine conditions change; It shows the change in fuel amount in an engine without. As is clear from this figure and the above description, according to the present invention, when the engine changes to an idle-low load state, the increase in fuel due to evaporative purge is used. Since fuel is supplied to the engine from the fuel injector in an amount equal to the amount of fuel that is removed from the engine, the deterioration of exhaust emissions caused by a sudden increase in fuel as shown by diagonal lines can be avoided.

[Brief explanation of the drawing]

Figure 1 is a diagram corresponding to the claims of the present invention; Figure 2 is a system diagram of an electronically controlled fuel injection engine to which the present invention is applied; Figure 3 is a detailed diagram of the electronic control section; Figure 4 is a diagram of the fuel injection system of the present invention. Flowchart of the program; Figure 5 is a graph showing the air-fuel ratio deviation due to evaporative purge; Figure 6 is a flowchart of the program that calculates and stores the deviation data; Figure 7 is the output S1 of the air-fuel ratio sensor and the return air-fuel ratio S2 FIG. 8 is a flowchart of a program for determining the evaporative purge correction amounts τ and V from deviation data; FIG. 9 is a graph showing changes in the amount of fuel supplied from the fuel injection valve according to the present invention. 2... Air flow meter, 21... Air-fuel ratio sensor, 31... Fuel tank,
200... air-fuel ratio feedback control device, 300...
... Evaporative purge gas concentration detection means, 400... Evaporative purge correction control means.

Claims (1)

[Scope of Claims] 1. Electronically controlled fuel that controls the amount of fuel supplied to the engine based on an air-fuel ratio signal from an air-fuel ratio sensor, and purges evaporated fuel gas from the fuel tank into the intake system during engine operation. In an injection engine, a control center value of a feedback correction coefficient is calculated during engine idling and under low load, and the evaporative purge gas concentration is detected based on the difference between the center values, and when the gas concentration exceeds a predetermined value, the fuel An air-fuel ratio control device comprising: means for reducing and correcting the amount of injection from an injection valve.