JPH0452385B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an air-fuel ratio control device for an internal combustion engine using an oxygen concentration detector (lean sensor).

Conventional technology In recent years, as a fuel efficiency measure as well as preventing exhaust pollution,
A lean burn system is adopted in which the internal combustion engine (hereinafter referred to as the engine) is operated at a lean air-fuel ratio. One of them is Utsukai Showa 57-92159.
There is a system in which a lean sensor is provided in the exhaust pipe of the engine, and the output signal of the lean sensor is used to feedback-control the air-fuel ratio of the engine to an arbitrary value on the lean side.

However, in the lean burn system described above, it is advantageous in terms of fuel efficiency if the air-fuel ratio of the engine is significantly shifted to the lean side, but if individual variations and characteristic deterioration of the engine and fuel injection valves are taken into consideration, feedback control is necessary. If the control air-fuel ratio is set to a lean region that is close to the misfire limit, misfires may occur and drivability may deteriorate. Therefore, in reality, the air-fuel ratio is set in a stable region that is 2 or more richer than the misfire limit in terms of air-fuel ratio. Nevertheless, if the characteristics of the lean sensor change over time, there is a risk that the air-fuel ratio of the engine will approach the misfire limit and cause a misfire.

OBJECT OF THE INVENTION In view of the above-mentioned problems of the conventional type, an object of the present invention is to detect combustion fluctuations in the engine to detect that the air-fuel ratio of the engine approaches the misfire limit. When the fuel ratio approaches the misfire limit, a limit is set on the air-fuel ratio of the air-fuel ratio feedback to prevent the air-fuel ratio from moving further toward the lean side, thereby preventing misfires and deterioration of drivability. .

Structure of the Invention The structure of the present invention for achieving the above object is shown in FIG. In FIG. 1, the lean air-fuel ratio sensor detects the lean air-fuel ratio of the engine and generates an air-fuel ratio signal D, and the combustion fluctuation amount detection means detects the combustion fluctuation amount ΔN _n ·max of the engine. Further, the lean air-fuel ratio sensor determining means determines whether the lean air-fuel ratio sensor is normal or abnormal based on the frequency with which the detected combustion fluctuation amount ΔN _n ·max exceeds a predetermined value C4. As a result, when the lean air-fuel ratio sensor is determined to be normal, the lean air-fuel ratio feedback control means feedback-controls the air-fuel ratio of the engine so that the output D of the lean air-fuel ratio sensor becomes a predetermined required lean air-fuel ratio C2. On the other hand, when the lean air-fuel ratio sensor is determined to be abnormal, the lean air-fuel ratio limit feedback control means feedback-controls the air-fuel ratio of the engine so that the combustion fluctuation amount ΔN _n ·max becomes a predetermined required combustion fluctuation amount C6. It is something to do.

Embodiment An embodiment of the present invention will be described with reference to FIG. 2 and subsequent figures.

FIG. 2 is a graph for explaining the principle of the present invention. In Figure 2, CO, HC, and NO _x represent three harmful components in exhaust gas, and the air-fuel ratio A/F
When the engine becomes lean and approaches the misfire region (shaded area), the NO _x component in particular decreases. Further, the fuel consumption rate FC also decreases, but increases rapidly when entering the misfire region, and furthermore, the engine torque change Δτ also increases rapidly when entering the misfire region. Therefore, in order to prevent exhaust pollution and take fuel efficiency measures, it is preferable to set the air-fuel ratio A/F to the lean side. The condition may be that the torque change Δτ is controlled to be within a certain range. In other words, since the point where the torque change Δτ suddenly rises is the lean limit point, the torque change Δτ
By controlling the air-fuel ratio supplied to the engine in a feedback manner so that the ratio is always constant, operation at the lean limit point, which is optimal in terms of fuel efficiency, is possible.

The engine torque change described above is due to engine combustion fluctuations, that is, it corresponds to the pulsating rotational speed fluctuations that appear during the engine's explosive stroke (see FIG. 9C). Further, as shown in FIGS. 3A and 3B, the amount of variation in rotational speed is proportional to the amount of variation in cylinder pressure of the engine. Therefore, in the present invention, the air-fuel ratio A/F is adjusted based on engine combustion fluctuations, such as engine speed fluctuations, torque fluctuations detected by a torque sensor, or cylinder pressure fluctuations detected by a cylinder pressure sensor.
By monitoring F, it is determined whether or not to cancel the lean control based on the lean air-fuel ratio feedback control.

In FIGS. 3A and 3B, σ〓 _N indicates the standard deviation of the engine rotational speed fluctuation amount, and σ _pi indicates the standard deviation of the engine cylinder pressure.

FIG. 4 is an overall schematic diagram showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention.

The engine 1 is a spark ignition type engine for an automobile, and combustion air is taken into the combustion chamber of the engine 1 through an air cleaner 2, an air flow meter 3, and an intake conduit 4. The suction conduit 4 is provided with a throttle valve 5 that can be operated arbitrarily by the driver. Fuel is injected and supplied from an injector 6 installed in the intake conduit 4. The mixture of fuel and air is combusted in the fuel chamber and discharged into the atmosphere via the exhaust conduit 7.

The control circuit 10 calculates the amount of fuel supplied to the engine 1 according to the operating state of the engine 1, drives the injector 6, and controls the amount of fuel supplied to the engine 1. The input of the control circuit 10 includes an air flow meter 3 that detects the intake air amount of the engine 1;
Reference sensor 8, angle sensor 9, and exhaust conduit 7
The signal from the lean sensor 11 for air-fuel ratio detection is input.

In this embodiment, the signal from the air flow meter 3 is used as the intake air amount to the engine 1.
Instead of the air flow meter 3, the intake air amount may be determined from the intake pipe negative pressure generated downstream of the throttle valve 5 of the engine 1 and the engine rotation speed. The rotation signal may be detected from a camshaft or the like.

As the reference sensor 8 and the angle sensor 9, for example, known magnetoresistive elements are used, and a signal is output by changing the magnetic circuit due to the unevenness of the teeth of the flywheel and the iron piece built in the distributor, which is a magnetic material. . This flywheel has teeth with a period of 30° CA. As a result, as shown in FIG. 9A, the reference sensor 8 outputs a TDC signal with a 720° CA cycle, and the angle sensor 9 outputs an angle signal with a 30° CA cycle.

The air flow meter 3 is, for example, a known vane type air flow meter.

The lean sensor 9 is a limiting current type oxygen concentration sensor as disclosed in Utility Model Application No. 57-92159, and the limiting current value of the lean sensor 9, which is the output, changes depending on the oxygen concentration in the exhaust gas, as shown in Fig. 5. do.

Next, the control circuit 10 will be explained with reference to FIG. The TDC signal from the reference sensor 8 is sent to the shaping circuit 1
01 formatted CPU 107 and comparator 11
The CPU 107 uses this signal as an interrupt signal for calculating the amount of fuel to be injected, and the comparator 110 uses it as a signal for starting the injection pulse of the injector 5. Further, the angle signal from the angle sensor 9 is shaped by a shaping circuit 102 and input to a rotational speed counting circuit 103, a CPU 107, and a comparator 110. The rotational speed counting circuit 103 is composed of a 16-bit binary counter, and calculates the angle signal.
Count the period of 30゜CA and input/output interface 1
Send binary data to CPU107 via 04
The CPU 107 calculates the reciprocal of this value to obtain the rotation speed. The angle signal input to the CPU 107 acts as an interrupt signal for the CPU 107, which reads the rotation speed and calculates the rotation speed fluctuation (combustion fluctuation).
The angle signal input to the comparator 110 is used to count the angle of injection timing. The output voltage of the air flow meter 3 is converted into a digital value by the A-D conversion circuit 105, and read into the CPU 107 to calculate the intake air amount Q. Since the output of the lean sensor 9 is obtained as a current output as shown in FIG.
It becomes a digital value in the D conversion circuit 105 and is sent to the CPU 1.
07, and it is possible to know the oxygen concentration in the exhaust gas, that is, the air-fuel ratio of the fuel mixture.

The A-D conversion circuit 105 is a known 12-bit A-D converter.
A converter (eg, Burr-Brown ADC80) is used, and the CPU 107 is a known 16-bit microcomputer TMS9900 made by Texas Instruments. Further, the comparator 110 converts the binary data of the injection time (valve opening time) of the injector 5 calculated by the CPU 107 into a pulse width, and the injector 6 is driven by this pulse via the drive circuit 111. Ru.

Further, the ROM 108 stores programs such as a main routine and a fuel injection time calculation routine, constants necessary for processing these programs, map data, etc., and the RAM 109 stores temporary data.

Next, the operation of the control circuit 10 shown in FIG. 4 will be explained with reference to the flowchart shown in FIG. 7. The flowchart in FIG. 7 is a part of the main routine or an interrupt routine executed at every predetermined crank angle. From start step 701 to step 702
Then, the data D of the lean sensor 11 is fetched from the A-D conversion circuit 105. In step 703, A
-Intake air amount data Q from the D conversion circuit 105
In step 704, the rotation speed counting circuit 103
Retrieve rotational speed data N from . Next step 7
At step 05, the amount of intake air B1 per engine rotation is determined by calculating B1=K1×QN. In step 706, a two-dimensional map is created from B1 and N.
Find flag F1 using MAP1. This MAP
1 is for setting the range of A/F control by lean sensor 11 or lean limit control, and the control range by lean sensor 11 is F1=
F1 is "0", and the lean limit control region is F1="1". Therefore, in step 707, F1="0"
If so, the process advances to step 708, and if F1="1", the process advances to step 722 to execute lean limit control. In step 708, the error flag F2 of the lean sensor 11 is checked, and if F2="1", the process proceeds to a loop of step 722. That is, this flag F2 is set in steps 715 to 721, which will be described later.
If it is determined that the lean sensor 11 is abnormal, control by the lean sensor is stopped and lean limit control is performed.

Steps 709 to 714 are an air-fuel ratio routine performed by the lean sensor 11. That is, in step 709, a two-dimensional map MAP2 is created from B1 and N.
Using this, the required A/F under the engine condition determined by B1 and N, that is, the required value C2 of the data D of the lean sensor 11 is determined. In step 710, a two-dimensional map MAP3 is similarly used from B1 and N to obtain a coefficient C3 for calculation to obtain the required A/F.
In step 711, the data D and the required value C2 are compared, and if D>C2, it is determined that the A/F is leaner than the required value, and rich correction is performed in step 712.
If not, lean correction is performed in step 713. Here, K2 is the integral value of the coefficient for feedback controlling the A/F, and α is the amount of A/F correction per time. In step 714, the valve opening time τ of the injector 6 is calculated from C3, K2, and B1 calculated above.

Steps 715 to 721 are a routine for determining whether the lean sensor 11 is abnormal. That is, in step 715, a two-dimensional map MAP4 is used from B1 and N to determine a determination level C4 of the rotational speed fluctuation ΔN at which the lean sensor should be determined to be abnormal. If the lean sensor 11 is normal,
The required A/F and judgment level C4 are determined from B1 and N, and the output of the lean sensor 11 is determined based on the required A/F.
matches.

Therefore, the determination level C4 is determined as a value corresponding to the output of the lean sensor 11. Here, C4 is data of ΔN around the misfire region of A/F=21.5 in the characteristic graph shown in FIG. 3, for example, and engine misfire or combustion fluctuation immediately before misfire is detected. In step 716, C4 is compared with the maximum value ΔN n _,nax of the rotational speed fluctuation ΔN _n during the calculation cycle of this flowchart.

In steps 716 to 721 and 730, the frequency of occurrence of ΔN _n,nax >C4 is determined, and it is determined whether this frequency is greater than or equal to a predetermined value E. For this purpose, a calculation number counter n1 and an occurrence frequency counter n2 are provided. and steps 717 and 71 respectively.
At 8, the count is incremented by 1. Furthermore, judgment level C4
is determined to be a relatively large value in order to prevent misdiagnosis from occurring due to variations in the lean sensor or changes over time. Step 719,7
20 is ΔN _n,nax of the calculations in the past 100 cycles >
If the number of times n2 at C4 is equal to or greater than E, a lean sensor abnormality flag is set at step 721,
Lean limit feedback control step 722
~727 will be executed. Step 72
At step 1', the counters n1 and n2 are set to 0 in preparation for the calculation from the next cycle.

Next, to explain lean limit control, in step 722, a two-dimensional map is created from B1 and N.
Using MAP5, calculate the calculation coefficient C5 to obtain the required A/F under the engine conditions determined by B1 and N. In step 723, similarly, from B1 and N, the set value C6 of the rotational speed fluctuation ΔN _n to achieve the A/F at the lean limit point is determined using MAP6. Step 724 calculates the maximum value ΔN _n,nax of the rotational speed fluctuation ΔN _n during the calculation cycle of this flowchart.
and C6 are compared, and if it is small, the combustion fluctuation is small, so a lean correction is performed in step 726, and if it is large, the combustion fluctuation is large, so a rich correction is performed in step 725. Here, K3 is the integral value of the coefficient for feedback controlling the A/F, and β is the amount of A/F correction per time. Step 727 calculates the valve opening time τ of the injector 6 from C5, K3, and B1 calculated above.

In step 728, the valve opening time τ of the injector 6 obtained in step 715 or 727 is set in the comparator 110. As a result,
The drive circuit 111 energizes the injector 6 for a time corresponding to the time τ. The routine of FIG. 7 then ends at step 729.

Next, details of the measurement calculation of the rotational speed fluctuation ΔN _n will be explained with reference to the flowchart of FIG. 8. An interrupt step 801 is started by an angle signal of 30° CA, which is the output signal of the angle sensor 8 in FIG.
In step 802, the register value is transferred to RAM10.
Evacuate to 9. Next, step 803 is for checking the TDC signal of FIG. 9A,
If YES, that is, TDC, the rotational position counter m is set to 0 in step 805, and if NO, the counter is incremented by 1 in step 804. At step 806, the counter m is set to 1, 3, 7, 9, 13, 1.
5, 19, or 21, step 80
The process proceeds to step 7 and thereafter, and otherwise jumps to step 814. In step 807, period data is fetched from the rotational speed counting circuit 103, and in step 80
In step 809, the rotational speed A2 is obtained by performing reciprocal calculation, and in step 809, it is stored in the RAM area Nc _,n . This RAM
Eight regions N _c,n are prepared corresponding to possible values of the counter m, that is, 1, 3, 7, 9, 13, 15, 19, and 21. In other words, in the region N _c,1 , the crankshaft is 30
The average rotation speed when the crankshaft rotates from 90 degrees to 60 degrees is stored, and the memory N _{c,21 stores the} average rotation speed when the crankshaft rotates from 90 degrees to 120 degrees during the explosion stroke of the second cylinder, which is the last cylinder in the rotation speed fluctuation measurement cycle. The average rotational speed when rotating is stored. At step 810, the contents of counter m are 3, 9, 15, 2.
1, the process proceeds to step 811 and subsequent steps; otherwise, the process jumps to step 814.
In step 811, steps 807, 808,
The average rotational speed at a predetermined crankshaft rotation angle of a predetermined cylinder calculated in step 809 and stored in the RAM area N _c,n , and the average rotation speed at a predetermined crankshaft rotation angle calculated in the previous measurement cycle and stored in memories N _a,n and N _b,n. The rotation speed fluctuation ΔN _n of the predetermined cylinder is calculated from the average rotation speed of the predetermined cylinder at a predetermined crankshaft rotation angle.
That is, ΔN _n = {(N _a,n-2 −N _a,n )−(N _b,n-2 −N _b,n )}−{(
N _b,n-2 −N _b,n )−(N _c,n-2 −N _c,n )} is calculated. In the above formula, m has values of 3, 9, 15, and 21 corresponding to the first, third, fourth, and second cylinders. To explain the above formula in detail, (N _a,n-2 −N _a,n ), (N _b,n-2 −N _b,n ), (N _c,n-2 −
N _c,n ), it is possible to obtain a value that corresponds to engine combustion and is not affected by road surface conditions. Furthermore, it is not affected by changes in sensitivity caused by changes in rotational speed during transient conditions.

In steps 812 and 813, the contents of the RAM area N _b,n are moved to Na _,n , and the contents of N _c,n are moved to N _b,n . In step 814, the contents of the register before the interrupt, which were saved in the memory at the beginning of the arithmetic program, are restored, and in step 815, the routine of FIG. 8 ends.

The rotational speed fluctuation calculation program shown in FIG. 8 is activated every time the angle signal _of 30 _° CA shown in FIG _. The average rotational speed as schematically shown in Figure C is stored. The height of the bar graph in the figure indicates the magnitude of the average rotational speed, and the upper part of each graph indicates the memory in which each average rotational speed is stored.

The average rotational speed of the crankshaft every 30 degrees exhibits periodic pulsations as shown by the dotted line in the figure as the explosion stroke of each cylinder occurs. As shown in the flowchart in Figure 8, for the explosion stroke of each cylinder, the flankshaft ranges from 30 degrees to 60 degrees and from 90 degrees to 120 degrees.
It only calculates the average rotational speed up to degrees. This is shown by the solid line in the figure. For example, the rotational speed fluctuation ΔN ₁ of the first cylinder is ΔN ₁ = {(N _a,1 −N _a,3 )−(N _b,1 −N _b,3 )}−{(N _b,1
−N _b,3 )−(N _c,1 −N _b,3 )}, and the output fluctuation of the first cylinder is known from this rotational fluctuation ΔN ₁ .

In the above embodiment, engine output fluctuations are detected based on rotational speed fluctuations, but as described above, similar detection is also possible using changes in torque or cylinder pressure.

In addition, in the above example, the average rotational speed every 30°CA is used as the rotational speed, but if the average rotational speed is used at intervals shorter than 30°CA, the correlation between combustion and the engine will be further improved. Can be done.

Furthermore, in the above embodiment, the integral value K2 of the coefficient for A/F control in the flowchart of FIG.
Although only one K3 is used, the control speed and controllability can be improved by providing the engine conditions determined by B1 and N respectively.

Further, by statistically processing the rotational speed fluctuation value ΔN _n obtained in the flowchart of FIG. 8 of the above embodiment to obtain, for example, the standard deviation,
The detection accuracy of rotational speed fluctuations can be further improved.

Effects of the Invention As explained above, according to the present invention, lean control of the A/F using a lean sensor and lean limit control of the A/F to the best fuel efficiency point immediately before a misfire are performed by detecting engine combustion fluctuations. , it is possible to simultaneously achieve purification of exhaust gas and improvement of fuel efficiency.
Furthermore, in the present invention, even during A/F control using the lean sensor, the combustion fluctuation detector (in this embodiment, the rotational speed fluctuation ΔN is determined) constantly measures the combustion fluctuation of the engine. Even if the lean sensor changes over time (changes in characteristics toward the lean side), the A/F controlled to the lean side shifts further to the lean side, and a misfire occurs, this misfire can be detected. In this case, there is an excellent effect that the A/F control by the lean sensor can be stopped and the A/F can be prevented from entering the misfire range.

[Brief explanation of the drawing]

Fig. 1 is an overall block diagram for explaining the configuration of the present invention, Fig. 2 is an air-fuel ratio characteristic diagram for explaining the principle of the present invention, and Figs. 3 A and B are engine rotational speed changes and engine cylinders. A graph showing the relationship with internal pressure, FIG.
6 is a detailed block diagram of the control circuit 10 of FIG. 4, and FIG. 7 is a detailed block diagram of the control circuit 10 of FIG.
8 are flowcharts for explaining the operation of the control circuit 10 of FIG. 4, and FIGS. 9A, B, and C are timing charts for explaining the flowchart of FIG. 8. 1... Engine main body, 3... Air flow meter, 6... Injector, 8... Reference sensor, 9... Angle sensor,
10...Control circuit, 11...Lean sensor.

Claims (1)

[Claims] 1. A lean air-fuel ratio sensor 11 that detects a lean air-fuel ratio of an internal combustion engine and generates an air-fuel ratio signal D; and a combustion fluctuation amount detection unit that detects a combustion fluctuation amount (ΔN _n・max) of the engine. means, lean air-fuel ratio sensor determining means for determining whether the lean air-fuel ratio sensor is normal or abnormal based on the frequency with which the detected combustion fluctuation amount is equal to or higher than a predetermined value C4; and the lean air-fuel ratio sensor is determined to be normal. lean air-fuel ratio feedback control means for feedback-controlling the air-fuel ratio of the engine so that the output of the lean air-fuel ratio sensor becomes a predetermined required lean air-fuel ratio C2; and when the lean air-fuel ratio sensor is determined to be abnormal; an air-fuel ratio control device for an internal combustion engine, comprising: lean air-fuel ratio limit feedback control means for feedback-controlling the air-fuel ratio of the engine so that the combustion fluctuation amount becomes a predetermined required combustion fluctuation amount C6. 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the combustion fluctuation amount is a rotational speed fluctuation of the engine. 3. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the combustion fluctuation amount is a torque fluctuation of the engine. 4. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the combustion fluctuation amount is a cylinder pressure fluctuation of the engine.