JPS59158356A - Air-fuel ratio control device in engine - Google Patents

Abstract

PURPOSE:To carry out always the optimum feed-back control of the air-fuel ratio of an engine in which the feed-back control of the air-fuel ratio is made, by compensating the control gains of a control system so that the detection value of responsiveness and stability of the control system falls within a predetermined allowable range. CONSTITUTION:A microcomputer 11 receives outputs from a rotational speed sensor 10, a negative pressure sensor 5, and an O2 sensor 8. An ROM14 stores the map of basic fuel injection pulses and the map of reference values of the responsiveness and stability of the control system of an engin, and an RAM15 stores the map of control gains. In a feed-back control range the output of the O2 sensor 8 is received to carry out the feed-back control of mixture wire the use of control gains in the RAM15 to obtain a desired air-fuel ratio. Thus, the optimum feed-back control of the air-fuel ratio may be carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control device for an engine.

Generally, as an air-fuel ratio control device for an engine, an exhaust sensor is installed in the exhaust system to detect the air-fuel ratio of the air-fuel mixture, and the air-fuel ratio of the air-fuel mixture is feedback-controlled to the target air-fuel ratio. In conventional air-fuel ratio control devices, the air-fuel ratio of the mixture repeatedly fluctuates between lean and rich due to the detection time delay caused by detecting the air-fuel ratio in the exhaust system. A loose hunting phenomenon occurs, and in this case, if the hunting width is large, the stability of the control system will be poor, the exhaust gas purification performance will deteriorate, and unpleasant engine vibrations will occur. This causes a problem that the responsiveness of the control system deteriorates and it takes time to reach the target air-fuel ratio when the operating range changes.

Therefore, in some conventional air-fuel ratio control devices, the control gain of the control system is set so that both the response and stability of the control system are within a predetermined tolerance range. In the system disclosed in Japanese Patent Publication No. 51-124739, the control gain is changed between idling and other operating times.

However, in such conventional air-fuel ratio control devices, the control gain of the control system is determined in advance through experiments, so there may be individual differences in engine characteristics due to manufacturing errors.
Or, if the engine characteristics change due to aging, the above control gain may deviate from the optimal value.
There was a problem in that the responsiveness or stability of the control system deteriorated.

In view of these conventional problems, the present invention provides an engine that receives the output of an air-fuel ratio sensor provided in the exhaust system and performs feedback control using a predetermined control gain so that the air-fuel ratio of the air-fuel mixture becomes a target air-fuel ratio. In this method, the control gain is stored in a storage device, the responsiveness and stability of the control system are constantly detected, and the control gain of the control system is corrected so that both of the detected values are within a predetermined tolerance range. Moreover, by rewriting the control gain value in the storage device with the corrected value, it is possible to perform optimal feedback control for changes in engine characteristics due to individual differences in engines and changes over time. An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an air-fuel ratio control device for an engine according to an embodiment of the present invention. In the figure, reference numeral 1 denotes an engine; an intake passage 2 of the engine 1 is provided with a fuel injection valve 4, which is a fuel supply device, upstream of a throttle valve 3;
A negative pressure sensor 5 for detecting intake negative pressure is attached downstream of the throttle valve 3 , and the upstream end of the intake passage 2 is connected to an air cleaner 6 . Further, the exhaust passage 7 of the engine 1 is provided with an 02 sensor 8, which is an air-fuel ratio sensor that detects the air-fuel ratio of the air-fuel mixture from the oxygen concentration in the exhaust gas. 9 is interposed. Here, this 02 sensor 8 has a fifth detection characteristic.
As shown in Figure (a), when the air-fuel ratio of the air-fuel mixture is richer than the target air-fuel ratio, signal 11' is output, and when it is lean, signal 1 is output.
It has a characteristic of outputting 0''.

Furthermore, a rotation sensor 10 is attached to the engine 1 to detect the engine speed, and the output of the rotation sensor 10, the negative pressure sensor 5, and the 02 sensor 8 are input to a microcomputer 11. This microcomputer 11 has an input/output interface 12. CPU
13. It is composed of 0M14 and non-volatile RAM15, and the RUM14 has basic fuel injection, S
), and a map of reference values for control system responsiveness and stability is stored, and the RAM 15 also stores a map of control gain. And the above CPU
1 Bit, read out the basic fuel injection pulse from the ROM 14 based on the engine speed and intake negative pressure, and set the feed I < ivy control during engine high-load operation, etc.
) In the non-feedback region, the above-mentioned basic fuel injection, <)res is applied as is to the fuel injection valve 4 and fuel injection is performed, while in the feed/ick region where feedback control is performed at times such as when the engine is under low or medium load ( In response to the output of the sensor 8, the control system 1 in the RAM 15 performs feedback control 1 on the air-fuel ratio of the air-fuel mixture to the target air-fuel ratio.
In addition, the control system constantly detects the responsiveness and stability of the control system, modifies the control gain so that both of them meet a predetermined tolerance range, and rewrites the control gain value in the RAM 15 with the modified value. It is something to do.

Further, FIGS. 2 to 4 show flowcharts of the arithmetic processing of the CPUI 3. Figure 2 shows the main menu, and in the figure, 16 is the step of initializing the register inside the cpul 3, 17 is the step of reading the output of the negative pressure sensor 5 from the interface 12, and 18 is the step of rotating from the interface 12. A step 19 reads the output of the sensor 10, a determination step 19 determines whether the current operating region is a feedback region based on the read engine speed and intake negative pressure, and 20 reads the ROM 14 and KAM 15 based on the engine speed and intake negative pressure. Step 21 specifies whether the stability of the control system I KR-KL 1 is less than or equal to the reference value m. A judgment step 22 is a correction value △ from the control gain ■.
Step 23 is to subtract iI, store it in the register, and rewrite the value of the map in RAM 15 with that value (■-△iI). Step 23 is to determine whether the responsiveness n of the control system is less than or equal to the reference value. Step 24 is a step of adding the correction value △i2 to the control gain ■, storing it in the register, and rewriting the value of the map in the RAM 15 with that value (I + △12). .

FIG. 3 shows the first interlaced routine in which the CPU 13 performs arithmetic processing when the engine 1 reaches the fuel injection timing, for example, when the piston reaches the compression top dead center "I'I)C". , 25 is a step of reading the output of the rotation sensor 1o from the interface 12, 2
6 is a step of reading the output of the negative pressure sensor 5 from the interface 12, 27 is a length step of reading the basic fuel injection pulse 1゛i by addressing the ROM 14 based on the read engine speed and intake negative pressure, and 28 is a reading step. a determination step of determining whether the current operating region is a feedback region based on the engine rotation speed and intake negative pressure;
9 is a step of calculating a final fuel injection pulse T from the basic fuel injection pulse Ti and the air-fuel ratio deviation rate, and 30 is a step of applying a fuel injection pulse to the fuel injection valve 4 to execute fuel injection.

Furthermore, FIG. 4 shows the CP at each predetermined timing of engine 1
U13 is the second interwoven routine that performs arithmetic processing, and in the figure, 31 reads the output of the '02 sensor 8 from the interface 12 and determines whether it is inverted, that is, from rich to lean or from lean to rich. A determination step 32 determines whether the current air-fuel ratio is rich or not from the output of the 02 sensor 8. A determination step 33.34 determines the control gain ■ currently stored in the register. The air-fuel ratio deviation rate K (Fig. 5(b)
Step 35 is the step of calculating the responsivity n.
Step of adding 1 to 36 is the responsiveness value n =
37 is a step of storing Q in the register; 37 is a determination step of determining the reversal direction of the output of the 02 sensor 8; 38
．． 39 is a step in which the air-fuel ratio deviation rate K obtained in steps 33 and 34 is stored in the register as the maximum air-fuel ratio deviation rate KR, KL.

Next, the general operation of this device will be explained.

When the engine is started, the accelerator pedal (not shown)
The throttle valve 3 rotates in accordance with the amount of depression of the throttle valve 3, and an amount of air corresponding to the opening degree of the throttle valve 3 is sucked into the intake passage 2 from the air cleaner 6, and this air is mixed with fuel injected from the fuel injection valve 4. The mixture is mixed and inhaled into the engine 1. Further, exhaust gas from the engine 1 is discharged into the exhaust passage 7, and after being purified by the exhaust gas purification device 9, it is released into the atmosphere.

At this time, the negative pressure sensor 5 detects the intake negative pressure downstream of the throttle valve 3, the rotation sensor 10 detects the engine rotation speed, and the 02 sensor 8 detects the oxygen concentration in the exhaust gas. The output of .8 is the microcomputer 11.
added to. In this microcomputer 11, the CPU 13 reads the basic fuel injection pulse Ti from the ROM 14 according to the engine speed and intake negative pressure, and also controls whether the current operating range is low or medium depending on the engine speed and intake negative pressure. Determine whether it is in a feedback area such as a load area. If the current operating range is a non-feedback range such as during high-load operation, the basic fuel injection pulse 1'i is applied as is to the fuel injection valve 4, and the
From this point on, fuel is injected in an amount determined by the operating state of the engine.

Furthermore, when the current operating range is a feedback range such as low or medium load, ct'u13 determines whether the current air-fuel ratio of the air-fuel mixture is rich or lean from the output of sensor 8.
Reduce the current air-fuel ratio deviation rate K by using the control gain in the RAM 15 so that it becomes lean when it is rich, and greatly modify the above air-fuel ratio deviation rate K so that it becomes rich when it is lean.'Refer to Fig. 5 (b). ), a final fuel injection pulse T is calculated from this air-fuel ratio deviation rate and the basic fuel injection pulse Ti, and the fuel injection pulse 1' is applied to the fuel injection valve 4. Therefore, the injected fuel is the fuel injection amount determined by the engine operating condition, increased or decreased according to the output of the 02 sensor 8, and in this way, the air-fuel ratio of the mixture is feedback-controlled to the target air-fuel ratio. . Then, the CPU 13 further calculates the responsiveness and stability of the control system from the current control gain I, corrects the side 1 gain I so that both the responsiveness and stability fall within a predetermined tolerance range, and makes this correction. The control gain value in the RAM 15 is rewritten with the value.

Next, the operation will be explained in detail using the flowcharts shown in FIGS. 2 to 4.

In this apparatus, (: In the main routine, the PU 13 first initializes the inside of the CPol 3 in step 16, reads the output of the negative pressure sensor 5 from the interface 12 in step 17, and reads the output of the negative pressure sensor 5 from the ink face 12 in step 18. The output of step 10 is read, and it is determined whether the current operating region is the feedback region or not based on the engine rotational speed and intake negative pressure read in step 19.

If it is not the feedback region, the process returns from step 19 to step 17, and if it is the feedback region, in step 20, the map in the 0M14 and RAM 15 is addressed using the engine speed and intake negative pressure, and the current For the reference values of control gain I and responsiveness/stability according to the operating range, m is read out and stored in a register, and in step 21, the maximum value obtained in steps 38 and 39 of the second interwoven routine to be described later is used. From the air-fuel ratio ratio, , from KL to the control system stability IK, -, l
is determined, and it is determined whether it is less than the reference value m.

If the stability IKR-KL1 of the control system is greater than the reference value m, in step 22 the correction value Δil is subtracted from the readout control gain ■, and it is stored in the register and the value (I- Δ1.) RAM15
After rewriting the values in the map, the process advances to step 23. If the stability IK, -KLl of the control system is less than the reference value m, the process proceeds directly to step 23, where the response n of the control system obtained in step 35 of the second interwoven routine described later becomes the reference value. If it is less than or equal to the reference value, the process returns from step 23 to step 17; if it is greater than the reference value, the process proceeds from step 23 to step 24, and in step 24, the control gain I in the register is set to a corrected value. After adding .DELTA.i, storing it in the register and rewriting the value of the map in the RAM 15 with that value (I+.DELTA.12), the process returns to step 17.

When a predetermined period of time has elapsed while cycling through the main routine in this way, the CPol 3 moves from the main routine to the second interwoven routine, reads the output of the 02 sensor 8 from the interface 12 in step 31, and reads the output of the 02 sensor 8 from the interface 12. It is determined whether the output of No. 8 has been reversed, that is, whether the air-fuel ratio of the air-fuel mixture has changed from rich to lean or from lean to rich. If it has not been reversed, step 3
In step 2, determine whether the current air-fuel ratio of the mixture is rich or not.
In the case of rich, the process proceeds to step 33, and in the case of lean, the process proceeds to step 34. In steps 33 and 34, the air-fuel ratio ratio 1 (is calculated (K) using the control gain ■ in the register.
= to -aI or C to = to +aI) (,, Store it in the register, proceed to step 35, and perform this step 31
, 32.33 or 31. The number of times the path '32°34 has been passed is counted and set as the value of responsiveness n, and the process returns to the main routine. Furthermore, if the output of the 02 sensor 8 is inverted in step 31, CP(Jl 3 follows the path from step 31 to steps 36 and 37, and in step 36, the value of the number of passages in the register, that is, the value of the responsiveness) With n set to 0, the inversion direction of the output of the 02 sensor 8 is determined in step 37.

And if the reversal direction is lean but rich, step 3
8, and in the opposite case, proceed to step 39, and in step 38 or 39, the air-fuel ratio deviation rate obtained in the above steps 33 and 34 is stored in the register as the maximum air-fuel ratio deviation rate KR, KL, and the main routine Return to

Also, when cpuia is cycling through the main routine,
When the engine 1 reaches a predetermined injection timing, that is, when the piston reaches the compression top dead center 1" DC, the CP013 moves from the main routine to the first interwoven routine, and in step 25, the output of the rotation sensor 1o is sent from the interface 12. In step 26, read the output of the negative pressure sensor 5 from the interface 12, and in step 27, calculate R using the engine speed and intake negative pressure read above.
Addressing the basic fuel injection pulse map in the OM 14 reads out the basic fuel injection pulse ri, and in step 28 determines whether the current operating region is the feedback region from the engine speed and intake negative pressure; In the case of the feedback region, in step 29, a final fuel injection pulse is calculated from the basic fuel injection pulse 1'i and the air-fuel ratio deviation rate obtained in step 33 or 34 of the second interwoven routine. In step 30, the injection pulse T is applied to the fuel injection valve 4 to execute fuel injection, and then the process returns to the main routine. If it is not the feedback area, the CPU 13 directly goes from step 28 to step 3.
0, and the basic fuel injection pulse ri is the final pulse 1.
°, the fuel injection valve 4 is added, and the process returns to the main routine.

In the device of this embodiment as described above, the control gain of feedback control is always corrected and rewritten to be optimal, so even if engine characteristics change due to individual differences in engines or changes over time, optimal feedback control is always performed. be able to.

Note that in the above embodiment, the fuel supply amount is adjusted according to the output of the 02 sensor, but this may be done by adjusting the intake air amount. Further, the fuel supply device may be a carburetor instead of a fuel injection valve. Further, the air-fuel ratio sensor may be other than the 0□ sensor as long as it detects the air-fuel ratio of the air-fuel mixture from the concentration of a specific component in the exhaust gas. Further, the arithmetic processing of the CPU 13 may be performed by a flow different from that shown in FIGS. 2 to 4 as long as the same function is achieved.

As described above, according to the air-fuel ratio control device for an engine according to the present invention, in an engine having an air-fuel ratio sensor provided on the exhaust line, the control gains are stored ν, t:, 4.
(Write in ji:f) to constantly detect the responsiveness and stability of the control system, and ensure that the detected values are both within the predetermined tolerance if
The control gain of the control system is corrected so that , j < within the song, and the control gain value in the go record storage device is rewritten with the correction value, so that the change due to individual differences in the engine or changes over time is avoided. This has the advantage of being able to perform optimal feedback control in response to changes in engine characteristics.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an engine air-fuel ratio control device 1' according to an embodiment of the present invention, FIGS. 2 to 4 are flowcharts of arithmetic processing of the CPU 13 in the above device, and FIG. (a) is the above device; 0 at x
2. The output waveform diagram of the sensor 8, FIG. 5(b) is a diagram showing changes in the air-fuel ratio deviation rate () which is effective for the above device. 1...Engine, 4...Fuel injection valve ( fuel supply device), 8...02 sensor (air-fuel ratio sensor), 13...
CPU (control means, detection means, correction≠switching means), 1
5...R, AM (storage device). Figure 1 Figure 2 Figure 3 Figure 4 332

Claims (1)

[Claims] (1) A fuel supply device that supplies fuel to the engine;
A storage device that stores the control gain of the control system, an air-fuel ratio sensor that detects the concentration of a specific component in the exhaust gas, and an air-fuel ratio sensor that receives the output of the air-fuel ratio sensor so that the air-fuel ratio of the mixture becomes the target value. a control means for feedback controlling the fuel supply amount or intake air amount of the fuel supply device using the control gain in the storage device; a detection means for calculating and detecting the responsiveness and stability of the control system; and correction/rewriting means for correcting the control gain so that the stability falls within a predetermined tolerance range and rewriting the control gain value in the storage device with the corrected value. 〉・Air-fuel ratio control device.