JPH02176138A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To stabilize an air-fuel ratio after warming up run by updating, by a learning means, a learning value per temperature region, which is provided in every temperature region of an engine, so that a torque fluctuating rate becomes a prescribed value, and adjusting the air-fuel ratio in response to the above learning value per temperature region by an air-fuel ratio adjusting means, when an engine is in the state of warming up run. CONSTITUTION:The torque fluctuating rate of an engine is calculated by a torque fluctuating rate calculating means, and it is discriminated by a warming up condition discriminating means whether the engine is in a warming up condition or not. As a result, a learning value Wi per temperature region, which is provided in every temperature region of the engine, is updated by a learning means so that the torque fluctuating rate becomes a prescribed value. Further, when the engine is in the warming up condition, an air-fuel ratio of the engine is adjusted by an air-fuel ratio adjusting means, in response to the learning value Wi per temperature region. Namely, during warming up, the learning value per temperature region is updated, therefore, since an air-fuel ratio lean limit control is operated in response to the temperature of the engine, the air-fuel ratio after warming up is stabilized without influencing a learning per load region after warming up, so that emission of HC, CO, NOx, fuel consumption and the like can be prevented from worsening.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a lean burn system for an internal combustion engine that utilizes torque fluctuations.

[Conventional technology]

In recent years, a lean burn system has been adopted in which the engine is operated at a lean air-fuel ratio to prevent exhaust pollution and to reduce fuel consumption.

One such method is to provide a lean mixture sensor in the exhaust pipe of the engine, and use the output of the lean mixture sensor to feedback control the air-fuel ratio of the engine to a desired lean air-fuel ratio. However, in a lean burn system using a lean mixture sensor, the control air-fuel ratio is adjusted to the very edge of the misfire limit (lean limit) by taking into account variations in components such as the lean mixture sensor, fuel injection valves, aging, and secular changes. If the engine is set to the lean range, misfires will occur and drivability will deteriorate. Therefore, the air-fuel ratio is normally controlled in a stable region on the lean side of the lean limit, and as a result, emissions reduction and fuel efficiency improvement are insufficient.

Therefore, the applicants of the present application have already proposed a lean burn system that does not use a lean mixture sensor (see Japanese Patent Laid-Open No. 122234/1982). That is, the second
As shown in the figure, when the air-fuel ratio A/F becomes lean and approaches the misfire region (shaded area), the exhaust gas components, especially N
Although the Ox component decreases and the fuel consumption rate FC also decreases, it increases rapidly when entering the misfire region, and furthermore, the engine torque fluctuation amount ΔTRQ also increases rapidly. Therefore, in order to prevent exhaust pollution and reduce fuel consumption, it is preferable to set the air-fuel ratio A/F to the lean side. The condition may be that the amount ΔTRQ is controlled to be within a certain range. In other words, torque fluctuation amount ΔTRQ
The lean limit point is the point where It becomes possible. For this reason, in the above-mentioned Japanese Patent Application Laid-Open No. 60-122234, the amount of combustion pressure fluctuation is detected as the amount of engine torque fluctuation, and the amount of intake air per revolution and the rotational speed of the engine are detected for each load region of the engine. The learning value for each load region provided for each region is updated, that is, the feedper is controlled so that the amount of combustion pressure fluctuation becomes a predetermined value. in this case,
This predetermined value corresponds to the lean limit point of the air-fuel ratio.

[Problem to be solved by the invention]

However, the lean limit point of the air-fuel ratio is actually
As shown in Figure 3, it is greatly affected by the engine temperature.

That is, when the engine cooling water temperature THW is low, the lean limit air-fuel ratio becomes small;
The lean limit air-fuel ratio increases as . Therefore, if the air-fuel ratio of the engine is controlled during warm-up using the load range-specific learning value that is learned by the load range in the state after warm-up, there is a problem that the engine becomes unstable and tends to misfire. Moreover, since the learned values for each load area are updated even during warm-up, the learned values for each load area fluctuate greatly during warm-up, and as a result, even though the learned values for each load area stabilize after warming up. It takes time, and during this time, HC, Co, No.
, there are also problems such as deterioration of emissions, deterioration of drivability, deterioration of fuel efficiency, etc.

Therefore, an object of the present invention is to prevent misfires (but also to prevent misfires from occurring).
, Co, N0wAn object of the present invention is to provide a lean burn system using a torque fluctuation amount that prevents deterioration of emissions, drivability, fuel efficiency, etc.

[Means to solve the problem]

A means for solving the above problem is shown in FIG.

In FIG. 1, the torque fluctuation amount calculating means calculates the torque fluctuation amount of the engine, and the warm-up state determining means determines whether or not the engine is warmed up. As a result, when the engine is warmed up, the learning means updates the temperature region-specific learning value W provided for each temperature region of the engine so that the torque fluctuation amount becomes a predetermined value. Then, when the engine is warmed up, the air-fuel ratio adjusting means adjusts the air-fuel ratio of the engine in accordance with the learned value W for each temperature range.

[For production]

'According to the above means, the learning value for each temperature range is updated during warm-up, and therefore the air-fuel ratio lean limit control is performed according to the temperature of the engine. has no effect.

〔Example〕

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. In FIG. 4, a pressure sensor 3 is provided in an intake passage 2 of an engine body 1. As shown in FIG.

The pressure sensor 3 directly measures the progressive pressure PM of the intake air pressure, and is, for example, a semiconductor sensor, and generates an analog voltage output signal corresponding to the intake air pressure. This output signal is supplied to an A/D converter 101 with a built-in multiplexer of the control circuit 10. The distributor 4 has a crank angle sensor 5 whose shaft generates a reference position detection pulse signal every 720 degrees in terms of crank angle, and a crank angle sensor 5 which generates a reference position detection pulse signal every 30 degrees in terms of crank angle. A crank angle sensor 6 is provided. The pulse signals of these crank angle sensors 5.6 are supplied to the input/output interface 102 of the control circuit 10, and the output of the crank angle sensor 6 is sent to the CPU.
103 interrupt terminal.

Further, the intake passage 2 is provided with a fuel injection valve 7 for supplying pressurized fuel from a fuel supply system to the intake boat for each cylinder.

Further, a water temperature sensor 9 for detecting the temperature of cooling water is provided in the water jacket 8 of the cylinder block of the engine body l. Water temperature sensor 9 indicates cooling water temperature TH
Generates an analog voltage electrical signal according to W. This output is also supplied to the A/D converter 101 of the control circuit 10.

Reference numeral 11 denotes a heat-resistant piezoelectric combustion pressure sensor that directly measures the cylinder pressure in the cylinder of the engine, for example, the first cylinder, and generates an analog voltage electrical signal corresponding to the cylinder pressure. This output is also supplied to the A/D converter 101 of the control circuit 10.

The exhaust system downstream of the exhaust manifold 12 is provided with a catalytic converter 13 that accommodates a lean NOx catalyst that purifies the harmful component NOx in the exhaust gas. The reason why a three-way catalyst that simultaneously purifies harmful components 1 (C, CO, and NOX) is not used is because the engine is a lean burn system, so there is little need to purify HC and Co components.

The control circuit 10 is configured as a microcomputer, for example, and includes an A/D converter 101, an input/output interface 102, a CPU 103, and a ROM 104, R
An AM 105, a backup RAM 106, a clock generation circuit 107, and the like are provided.

Further, in the control circuit 10, a down counter 108,
Flip-flop 109 and drive circuit 110 are for controlling fuel injection valve 7.

That is, in the routine described later, the fuel injection amount TAU
is calculated, fuel injection 1JTAU is preset to the down counter 108 and the flip-flop 10
9 is also given cents. As a result, the drive circuit 110 starts energizing the fuel injection valve 7. On the other hand, the down counter 108
counts a clock signal (not shown) and when its carrier terminal becomes "1" level, the flip-flop 109 is turned on and the drive circuit 110 stops energizing the fuel injector 7. . In other words, the above-mentioned fuel injection IT
The fuel injection valve 7 is energized by AU, and therefore, an amount of fuel corresponding to the fuel injection amount TAU is sent into the combustion chamber of the engine body l.

Note that the interrupt generation of the CPU 103 is caused by the A/D converter 1.
At the end of A/D conversion of 01, human output interface 10
2 receives a pulse signal from the crank angle sensor 6, receives an interrupt signal from the clock generation circuit 107, etc.

The intake air pressure data PM of the pressure sensor 3 and the cooling water temperature data THW of the water temperature sensor 9 are collected at predetermined time intervals A.
/D conversion routine and stored in a predetermined area of RAM 105. That is, data PM and THW in RAM 105 are updated at predetermined intervals. Further, the rotational speed data Ne is calculated by interrupt every 30° CA of the crank angle sensor 6 and stored in the RAM 10.
5 is stored in a predetermined area.

The operation of the control circuit 10 shown in FIG. 4 will be explained below.

FIG. 5 shows an average effective torque calculation routine, which is executed at predetermined intervals. That is, the routine in FIG.
Multiple crank angle positions shown in the figure: ATDc5°C^ (5° after top dead center), ATDC20” CA, ATDC35°
The average effective combustion pressure obtained by calculating the combustion pressures PI+Pz, P3.Pa at the four points of CA, ATDC50'' CA and adding these instantaneous combustion pressures is used as the torque substitute value PTRQ. This calculation method has already been disclosed by the applicant in Japanese Patent Application Laid-Open No. 63-63.
This is proposed in Publication No. 1129.

That is, in steps 501 to 505, the crank angle position is BTOC 160° CA (160° before top dead center), A
TDC5°CA, ATDC20°C^, ATDC3
Determine whether it is 5' CA or ATDC50'' CA. If it is not at any crank angle position, proceed to step 5.
Proceed directly to step 20.

Crank angle (if the vertical BTDC is 160°CA, proceed to step 506, and check the combustion pressure of the combustion pressure sensor 11 with A/D
Convert it, import it, and store it in 174M 105 as Vo. In addition, the value near the bottom dead center of intake ■. is the combustion pressure sensor 11
This is used as a reference value for combustion pressure at other crank positions in order to absorb output drift due to temperature, etc., variations in offset voltage, etc.

If the crank angle position is ATDC5°C^, step 5
Proceeding to step 07, the combustion pressure of the combustion pressure sensor 11 is A/D converted and taken in as ■1. Next, in step 508, the value P+ (-V+ -Vo) obtained by subtracting the reference value V0 is set to ATDC.
The combustion pressure at 5° CA is calculated and stored in the RAM 105.

If the crank angle position is ATDC 20° CA, the process proceeds to step 509, where the combustion pressure of the combustion pressure sensor 11 is A/D converted and taken in as V2. Next, in step 510, the reference value ■. The value obtained by subtracting P! (=V, -V.) to ATDC
Calculated as combustion pressure at 20°CA: 174M 105
Store in.

If the crank angle position is ATDC 35° CA, the process proceeds to step 511, where the combustion pressure of the combustion pressure sensor 11 is A/D converted and taken in as 3. Next, in step 512, the reference value ■. The value obtained by subtracting P, (=ViI-V.) is 8TD
RAM 105 calculated as combustion pressure at C35°CA
Store in.

If the crank angle position is ATDC50°-, step 5
Proceeding to step 13, the combustion pressure of the combustion pressure sensor 11 is A/D converted and taken in as 4. Next, in step 514, the reference value ■. The value obtained by subtracting P4. (=V4-V.) to ATDC
The combustion pressure at 50° CA is calculated and stored in the RAM 105. Next, in step 515, the average effective torque value PTRQn is calculated as follows: TRQn -0,5·P, +2.0·P! + 3.0・P:l+
4.0.P4, and then, in step 515, the counter n is incremented by +1. Note that the counter n is the average effective torque value PTRQn (n = 0
This is to determine whether or not 15) is obtained.

Only when 16 average effective torque values PTRQn are obtained, the flow of step 517 is changed to steps 518 and 519.
Proceed to. That is, in step 518, a learning routine to be described later is executed, and in step 519, a counter n is cleared in preparation for the next execution.

The routine then ends at step 520.

Although the routine shown in FIG. 5 is configured to be executed at predetermined intervals, in reality, three of the crank angle sensors 6
This is performed by the 30° CA interrupt routine which is performed by the 0° CA signal interrupt.

In this case, as shown in Fig. 6, an angle counter NA is provided which is cleared in response to the 720° CA signal and counts and amplifies every 30° CA interrupt, and the combustion pressure is adjusted to A/A according to the value of the angle counter NA. Although it is for D conversion, the positions of ATDC5°CA and ATDC35°CA do not match the 30'CA interrupt time. Therefore, ATD
C5' CA, 8TDC A/D conversion at 35°CA is performed at the immediately preceding 30°CA interrupt time (NA="0", "1"
”), calculates the 15° CA time, sets it in a timer, and causes the CPU 103 to interrupt the timer.

Further, although combustion pressure is used as the average effective torque value, it can also be directly obtained by providing a torque sensor.

FIG. 7 is a detailed flowchart of the learning step 518 of FIG. That is, in step 701, the variance S2 of the 16 average effective torque values PTRQn (n = O to 15) is calculated as the amount of torque fluctuation. In other words, .

Next, in step 702, it is determined whether the variance S2 is larger than a set value. As a result, if the fuel correction amount ΔG is larger than the set value, the fuel correction amount ΔG is set to 1% in step 703, and the variance S1 is made closer to the set value. On the other hand, if it is smaller than the set value, the fuel correction amount ΔG is set to 11% in step 704 to make the variance S2 closer to the set value.

Next, in step 705, the cooling water temperature data THW is read from 174M 105, and it is determined whether TIIW<80°C. That is, it is determined whether the engine is warming up or after warming up is completed. If it is being warmed up (TIIW < 80° C.), the process proceeds to step 706, where the learned value Wl for each water temperature region of the region to which the cooling water temperature T HW belongs is read out from the backup RAM 106 and set as W,←Wi+ΔG. Note that the learning value W for each water temperature range is, for example, the cooling water temperature THW (for example, from 0°C to
A one-dimensional map is provided for each region divided at equal intervals (irregular intervals are also acceptable).

A two-dimensional map is provided for each area divided according to Table 1 (irregular intervals may be used).

Table 2 And the updated learning value W is again the back amplifier RA
It is stored in the same area of M106. On the other hand, if the warm-up is completed (THW≧80°C), the intake air pressure data PM and rotational speed data Ne are read from the RAM 105, and the learned value KJ for each load region of the region belonging to PM and Ne is read out.
Read k from the backup RAM 106 and set K←Kjk+ΔG. As shown in Table 2, the load area-specific learned values Kjk are calculated by setting PM and Ne at equal intervals, and the routine ends at step 708.

In addition, in the routine shown in Fig. 7, the variance 3 is used as the amount of torque fluctuation.
2 is used, but other values such as the amount of decrease in output torque may be used.

FIG. 8 shows an injection amount calculation routine, which is executed at every predetermined crank angle, for example, every 360'' CA.Step 80
1, the RAM 105 reads the intake air pressure data PM and the rotational speed data Ne, and sets the basic injection amount TAUP.
Calculate. In step 802, the cooling water temperature data THW is read from the RAM 105 and stored in the bank-up RAM 1.
The value W is determined by the one-dimensional map shown in Table 1 stored in 06.
Calculate by interpolation. Furthermore, in step 803, the RAM
The intake air pressure data PM and the rotational speed data Ne are read out from 105 and a value K is calculated by interpolation using the two-dimensional map shown in Table 2 stored in the bank-up RAM 106. Then, in step 804, the final injection amount TAU is calculated by TAU4-TAUP.ni.匈.alpha.+.beta. Note that α and β are correction amounts determined by other operating state parameters, such as a signal from a throttle position sensor (not shown), a signal from an intake air temperature sensor,
These are correction amounts determined by battery voltage and the like, and these are also stored in the RAM 105. Next, in step 805, the injection ITAU is set in the down counter 108 and the flip-flop 109 is turned on to start fuel injection. The routine then ends at step 806. Furthermore, as mentioned above, the injection fTA
When the time corresponding to U has elapsed, the down counter 108
The flip-flop 109 is reset by the carrier signal, and the fuel injection ends.

Furthermore, in the above-mentioned embodiment, fuel injection ■ is calculated according to the intake air pressure and the engine rotation speed, but it is calculated according to the intake air amount and the engine rotation speed, or the throttle valve opening and the engine rotation speed. The fuel injection amount may also be calculated.

Further, in the above embodiment, an internal combustion engine is shown in which the amount of fuel injected into the intake system is controlled by a fuel injection valve, but the present invention can also be applied to a carburetor type internal combustion engine. For example, an electric air control valve (EACV) is used to control the air-fuel ratio by adjusting the intake air amount of the engine, and an electric bleed air control valve is used to adjust the amount of air bleed from the carburetor to control the main system passage and slow air. The present invention can be applied to devices that control the air-fuel ratio by introducing atmospheric air into system passages, devices that adjust the amount of secondary air sent to the exhaust system of an engine, and the like. In this case, the basic fuel injection amount corresponding to the basic injection withstand amount TAUP in step 801 is determined by the carburetor itself,
That is, it is determined according to the intake pipe negative pressure corresponding to the intake air amount and the rotational speed of the engine, and the supplied air amount corresponding to the final fuel injection 11 TAU is calculated in step 804.

〔Effect of the invention〕

As explained above, according to the present invention, during warm-up, the learned value W, which is different from the learned value KJk after warm-up, is updated, so the air-fuel ratio after warm-up is stabilized, and therefore ,HC,CO,N
Deterioration of oX emission, drivability, fuel efficiency, etc. can be prevented.

[Brief explanation of the drawing]

Fig. 1 is an overall block diagram for explaining the present invention in detail, Fig. 2 is a graph showing torque fluctuation amount, fuel consumption, and exhaust emission characteristics, and Fig. 3 is a graph showing the relationship between cooling water temperature and lean limit air-fuel ratio. 4 is an overall schematic diagram showing an embodiment of the air-fuel ratio control device for an internal combustion engine according to the present invention, and FIGS. 5, 7, and 8 explain the operation of the control circuit shown in FIG. 4. FIG. 6 is a timing diagram for supplementary explanation of the flowchart in FIG. 5. 1... Engine body, 3... Pressure sensor, 4
... Distributor, 5.6... Crank angle sensor, 10... Control circuit, 11... Combustion pressure sensor, 13... Catalytic converter.

Claims (1)

[Claims] 1. Torque fluctuation calculation means for calculating the torque fluctuation of an internal combustion engine; warm-up state determination means for determining whether the engine is warmed up; learning means for updating a temperature range-specific learning value provided for each temperature range of the engine at a certain time so that the torque fluctuation amount becomes a predetermined value; An air-fuel ratio control device for an internal combustion engine, comprising: an air-fuel ratio adjusting means for adjusting the air-fuel ratio of the engine according to a learned value.