JP2623791B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a lean burn system for an internal combustion engine using a torque variation.

[Conventional technology]

2. Description of the Related Art In recent years, a lean burn system (lean burn system) in which an air-fuel ratio of an engine is operated in a lean state has been adopted as a measure against fuel consumption as well as prevention of exhaust pollution. As one of them, there is one in which a lean mixture sensor is provided in an exhaust pipe of an engine, and an air-fuel ratio of the engine is feedback-controlled to an arbitrary lean air-fuel ratio by using an output of the lean mixture sensor. However, in a lean burn system using a lean mixture sensor, the control air-fuel ratio is set to just before a misfire limit (lean limit) in consideration of variations in components such as the lean mixture sensor, the fuel injection valve, etc., aging, or aging. If it is set up to the lean region, a misfire occurs and the drivability deteriorates. Therefore,
Normally, the air-fuel ratio is controlled in a stable region that is richer than the lean limit, and as a result, emission reduction and fuel efficiency improvement are insufficient.

Accordingly, the present applicants have already proposed a lean burn system that does not use a lean mixture sensor (see Japanese Patent Application Laid-Open No. 60-122234). That is, as shown in FIG. 2, when the air-fuel ratio A / F approaches the misfire region becomes lean (hatched portion), exhaust gas components, in particular, NO _x components is reduced, also, the fuel consumption rate FC also Although it decreases, it rapidly increases when it enters the misfire region, and furthermore, the torque fluctuation amount ΔTRQ of the engine.
Also increase sharply. Therefore, it is preferable to set the air-fuel ratio A / F to the lean side in order to prevent exhaust pollution and to reduce fuel consumption.In this case, the torque of the engine must be set so that the air-fuel ratio A / F is not set to the lean side until the misfire region. What is necessary is that the control is performed so that the variation ΔTRQ is within a certain range. In other words, the point at which the torque fluctuation ΔTRQ rises sharply is the lean limit point.
By performing feedback control of the air-fuel ratio of the engine so that Q is always constant, it is possible to operate at the lean limit point which is the best in terms of fuel efficiency. For this reason, the above-mentioned JP-A-60
In JP-A-122234, a combustion pressure fluctuation amount as an engine torque fluctuation amount is detected, and for example, a load region provided for each region of an intake air amount per rotation and a rotation speed of the engine for each load region of the engine. The other learning value is updated so that the combustion pressure fluctuation amount becomes a predetermined value, that is, feedback control is performed. In this case, the predetermined value corresponds to a lean limit point of the air-fuel ratio.

[Problems to be solved by the invention]

However, in a lean burn system based on normal torque fluctuations, if the lean limit point changes due to environmental changes when the engine is stopped and restarted, the air-fuel ratio may exceed the lean limit point until the learning value is updated. is there. For example, the air-fuel ratio that becomes the lean limit point with respect to a change in humidity changes as shown in FIG. That is, in FIG. 3, when the humidity changes from 25% to 90%, the air-fuel ratio becomes rich about 1.0 in terms of air-fuel ratio because the combustion speed is reduced. As a result, if the vehicle is started in a high-humidity state with the learning value in the low-humidity state, the air-fuel ratio may be operated beyond the lean limit point.
There is a problem that drivability is deteriorated due to misfire or deterioration of combustion.

Accordingly, an object of the present invention, the air-fuel ratio can be prevented from exceeding the lean limit point also vary the lean limit point when after the engine stop and restart, thereby misfire or deterioration of combustion, deterioration of the NO _x emissions, An object of the present invention is to provide a lean burn system that uses a torque fluctuation amount that prevents drivability deterioration and the like.

[Means for Solving the Problems] Means for solving the above problems are shown in FIG.
That is, the torque variation calculating means calculates the torque variation ΔTRQ of the internal combustion engine, and the feedback execution condition determining means determines whether the engine satisfies the torque variation feedback execution condition. As a result, when the engine satisfies the torque fluctuation amount feedback execution condition, the learning means sets the region-based learning value K provided for each operation region of the engine.
_ij is updated to torque so that the variation ΔTRQ becomes a predetermined value. The air-fuel ratio adjusting means adjusts the air-fuel ratio of the engine near the lean limit point in accordance with the learning value _Kij for each region, and enriches the air-fuel ratio when the engine satisfies the torque fluctuation amount feedback execution condition for the first time after starting. Side.

(Operation)

According to the above-described means, even if the lean limit point changes after a change in the operating state such as after starting, the air-fuel ratio is set to the rich side while the learning value is being updated, so that the air-fuel ratio does not exceed the lean limit point.

〔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. The pressure sensor 3 directly measures the absolute 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 the A / D converter 101 with built-in multiplexer of the control circuit 10. Distributor 4 has
For example, a crank angle sensor 5 which generates a reference position detecting pulse signal every 720 ° when converted into a crank angle and a crank angle sensor which generates a reference position detecting pulse signal every 30 ° when converted into a crank angle 6 are provided. The pulse signals of the crank angle sensors 5 and 6 are supplied to an input / output interface 102 of the control circuit 10, and the output of the crank angle sensor 6 is supplied to an interrupt terminal of the CPU 103.

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

The water jacket 8 of the cylinder block of the engine body 1 is provided with a water temperature sensor 9 for detecting the temperature of the cooling water. The water temperature sensor 9 detects the temperature TH of the cooling water.
Generates an analog voltage electric signal corresponding 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 for directly measuring the in-cylinder pressure in the cylinder of the engine, for example, the first cylinder, and generates an analog voltage electric signal corresponding to the in-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, a catalytic converter 13 is provided for accommodating the lean NO _x catalyst for purifying harmful components NO _x in the exhaust gas. In addition, harmful components HC, C
The reason why the three-way catalyst for purifying O and NO _x is not used at the same time is not used because it is not necessary to purify HC and CO components for the engine of the lean burn system.

The control circuit 10 is configured as a microcomputer, for example, and includes an A / D converter 101, an input / output interface 102,
Outside of PU 103, RAM 104, RAM 105, backup RAM 10
6. A clock generation circuit 107 and the like are provided.

In the control circuit 10, the down counter 108, the flip-flop 109, and the drive circuit 110
Is to control the That is, when the fuel injection amount TAU is calculated in a routine described later, the fuel injection amount TAU is preset in the down counter 108 and the flip-flop 109 is also set. As a result, the drive circuit 110 starts energizing the fuel injection valve 7. On the other hand, when the down counter 108 counts a clock signal (not shown) and the carry-out terminal finally becomes "1" level, the flip-flop 109 is set and the drive circuit 110 sets the fuel injection valve 7 Stop energizing. That is, the fuel injection valve 7 is energized by the above-described fuel injection amount TAU, so that an amount of fuel corresponding to the fuel injection amount TAU is sent to the combustion chamber of the engine body 1.

The CPU 103 interrupt is generated by the A / D converter 101
At the end of the conversion, after the input / output interface 102 receives the pulse signal of the crank angle sensor 6, the clock generation circuit
For example, when an interrupt signal from 107 is received.

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 fetched by an A / D conversion routine executed every predetermined time and stored in a predetermined area of the RAM 105. That is, the data PM and T in the RAM 105
HW is updated every predetermined time. The rotation speed data Ne is calculated by interruption every 30 ° CA of the crank angle sensor 6 and stored in a predetermined area of the RAM 105.

 Hereinafter, the operation of the control circuit 10 of FIG. 4 will be described.

FIG. 5 is an initial routine executed only once after an ignition switch (not shown) is turned on. That is, in step 501, the initial increase control request flag XIA
Set the F (XIAF = "1") , it clears the initial boost value F _IAF at step 502. Then, the process proceeds to a main routine (idle loop). Thus, to make the initial increase value F _IAF only the initial value F _IAF0 once after the lean limit conditions establishment by the torque fluctuation after the start is set.

FIG. 6 shows an average effective torque calculation routine which is executed at predetermined time intervals. That is, the routine shown in FIG. 6 performs the combustion at four points of a plurality of crank angle positions ATDC 5 CA (5 ° after top dead center), ATDC 20 CA, ATDC 35 CA, and ATDC 50 CA shown in FIG. The average effective combustion pressure obtained by calculating the pressures P ₁ , P ₂ , P ₃ , and P ₄ and adding these instantaneous combustion pressures is used as a torque substitute value TRQ. The present applicant has already proposed this calculation method in JP-A-63-61129.

That is, in steps 601 to 605, the crank angle position
DC 160 ゜ CA (160 ゜ before top dead center), ATDC 5 ゜ CA, ATDC 20 ゜ C
A, Determine whether ATDC 35 CA or ATDC 50 CA. If not at any crank angle position, step 617
Go directly to.

Step 60 if the crank angle position is BTDC 160 ス テ ッ プ CA
Proceed to 6, the combustion pressure of the combustion pressure sensor 11 captures and converts A / D, is stored as V ₀ in RAM 105. The value V ₀ near the intake bottom dead center is used as a reference value of the combustion pressure at another crank position in order to absorb the output drift due to the temperature of the combustion pressure sensor 11, the variation of the offset voltage, and the like. .

Advances the crank angle position in the step 607 if the ATDC 5 ° CA, captures the combustion pressure of the combustion pressure sensor 11 as V ₁ converts A / D. Next, at step 608, a value P ₁ (= V ₁ −V ₀ ) obtained by subtracting the reference value V ₀ is calculated as the combustion pressure at ATDC 5 CA, and stored in the RAM 105.

Advances the crank angle position in the step 609 if the ATDC 20 ° CA, captures the combustion pressure of the combustion pressure sensor 11 as V ₂ converted A / D. Next, at step 610, a value P ₂ (= V ₂ −V ₀ ) obtained by subtracting the reference value V ₀ is calculated as the combustion pressure at ATDC 20 ゜ CA and stored in the RAM 105.

Advances the crank angle position in the step 611 if the ATDC 35 ° CA, captures the combustion pressure of the combustion pressure sensor 11 as V ₃ converts A / D. Next, in step 612, a value P ₃ (= V ₃ −V ₀ ) obtained by subtracting the reference value V ₀ is calculated as the combustion pressure at ATDC 35 ゜ CA, and stored in the RAM 105.

Advances the crank angle position in the step 613 if the ATDC 50 ° CA, captures the combustion pressure of the combustion pressure sensor 11 as V ₄ converts A / D. Next, at step 614, a value P ₄ (= V ₄ −V ₀ ) obtained by subtracting the reference value V ₀ is calculated as the combustion pressure at ATDC 50 ゜ CA and stored in the RAM 105. Then, an average effective torque value TRQ at step 615 calculates the _{TRQ ← 05 · P 1 +2.0 ·} P 2 +3.0 · P 3 +4.0 · P 4, then the torque at step 616 Variation ΔT
Calculate RQ. Step 616 will be described later.

 Then, in step 617, this routine ends.

Although the routine of FIG. 6 is configured to be executed at predetermined time intervals, actually, the routine of the crank angle sensor 6 is performed.
This is performed by a 30 CA interrupt routine that is performed by interrupting the 30 CA signal. In this case, as shown in FIG. 7, an angle counter NA which is cleared according to the 720 ° CA signal and counts up every 30 ° CA interrupt is provided, and the combustion pressure is A / A according to the value of the angle counter NA. For D conversion, the position of ATDC 5 CA, ATDC 35 CA is 30
し な い Does not match the CA interrupt time. Therefore, ATDC 5 ゜
For A / D conversion at CA, ATDC 35 CA, the 15 CA time is calculated at the time of the immediately preceding 30 CA interrupt (NA = "0", "1") and set to the timer. This is done by interrupting.

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

FIG. 8 is a detailed flowchart of the torque variation calculating step 616 in FIG. That is, in step 801, the amount of decrease ΔTRQ from the value TRQ0 one cycle before the average effective torque TRQ is calculated. That is, ΔTRQ ← TRQ0−TRQ. In step 802, TRQ is set to TRQ0 in preparation for the next execution.
And

In step 803, it is determined whether the torque decrease amount ΔTRQ is positive or negative. That is, when the torque decrease amount ΔTRQ is negative, in other words, when the torque increases,
Assuming that the torque value TRQ is changing along with the ideal torque, the value ΔTRQ
Is set to 0. On the other hand, when the torque reduction amount TRQ is positive,
In other words, only when the torque decreases, it is considered that a torque fluctuation has occurred, and the value ΔTRQ is regarded as the torque fluctuation amount.In this case, the torque decreases even during deceleration. Do. That is, at the time of deceleration, it is not possible to distinguish between a decrease in torque due to a decrease in the intake air amount and a decrease in torque due to the deterioration of combustion. Therefore, as described later, control of the engine based on the amount of torque fluctuation, for example, feedback control of the fuel injection amount is stopped. It was done.

In step 806, the calculation of the learned value K _ij based on the amount of torque fluctuation? Trq. Step 806 will be described later.

 Then, in step 807, this routine ends.

FIG. 9 is a detailed flowchart of the deceleration processing step 804 in FIG. That is, in step 901, it is determined whether or not the amount of torque fluctuation (the amount of decrease) ΔTRQ is larger than a predetermined value X ₁ , and in step 902, the number of times CNT in which the state of ΔTRQ> X ₁ appears continuously is counted. As a result, only if? Trq> state of X ₁ lasted more than ₂ times X, the flow of the step 903 proceeds to step 904, sets the deceleration flag FD (FD =
“1”). On the other hand, if? Trq ≦ X _1, the process proceeds to the flow step 905 in step 901, the counter CNT is cleared, further, resets the deceleration flag FD in step 906 (F
D = "0").

 Then, in step 907, this routine ends.

The value X ₂ at step 903 is 3, for example.

FIG. 10 is a detailed flowchart of the learning step 806 in FIG. That is, in step 1001, it is determined whether the lean limit execution condition is satisfied. The lean limit execution conditions are, for example, i) not in the starting state, ii) not in the increasing state after the start, iii) not in the fuel cut state, iv) the engine speed Ne is equal to or less than a predetermined value, v) the cooling water temperature THW is equal to or more than a predetermined value, and the like. .

If the lean limit execution condition is not satisfied, the process directly proceeds to step 1012, and if the lean limit execution condition is satisfied, the process proceeds to step 1002.

In step 1002, it is determined whether or not the initial increase request flag XIAF is “1”. When XIAF = “1”, the process proceeds to step 1003, the flag XIAF is reset, and in step 1004, the initial increase value F _IAF is initialized. Set the value F _IAF0 . Next, when this routine is executed again, the flow of steps 1003, 1004 is switched to the flow of steps 1005, 1006, 1007 because the initial increase request flag XIAF is "0". In step 1005, the initial boost value F _IAF are allowed decreased by [Delta] F (constant value) is gradually decreased initial increase value F _IAF, Step 1006,100
At 7, guard the initial increase value _FIAF with 0.

In step 1008, it is determined whether or not the vehicle is in a deceleration state (FD = “1”). If the vehicle is not decelerating, the process proceeds to step 1009. If the vehicle is in a decelerating condition, the process directly proceeds to step 1012. Then, step
In 1009, the amount of torque fluctuation ΔTRQ determines whether larger than the set value X _3. As a result, the process proceeds to step 1010 when greater than the set value X _3, intake air pressure data P from the RAM 105
The M and the rotation speed data Ne are read, and the learning value K _ij for each load region of the region belonging to PM and Ne is read from the backup RAM 106, and K _ij ← K _ij + 1%. The load area learning value K _ij is, as shown in the table below is given as a two-dimensional map of PM and Ne in delimited each region in equal intervals (or at irregular intervals).

On the other hand, the process proceeds to step 1011 when less than the set value X _3, reads the intake air pressure data PM and speed data Ne from the RAM 105, read out from the backup RAM 106 of the load region learning value K _ij regions belonging to the PM and Ne, _Let K _ij ← K _ij -1%. That is, when greater than the set value X ₃ are setpoint ΔTRQ as rich side by increasing the area learning value K _ij
To be closer to the X _3. On the other hand,? Trq as lean side by reducing the area learning value K _ij when less than the set value X ₃
The so as to approach the set point X _3.

 Then, in step 1012, this routine ends.

Note that the torque fluctuation amount ΔTRQ in step 1009 may use an average value of several cycles to 10 cycles so that the delay does not increase. The setting value X ₃ is the engine operating conditions may be changed by such environmental conditions.

Further, in the above-described routine with decrease in the output torque as the amount of torque fluctuation, other values may be used for example variance S ^2.

FIG. 11 shows an injection amount calculation routine which is executed at every predetermined crank angle, for example, every 360 ° CA. In step 1001, the intake air pressure data PM and the rotation speed data Ne are read from the RAM 105 to calculate the basic injection amount TAUP. In step 1102, the value K is interpolated by the two-dimensional map shown in the above table stored in the backup RAM 106 based on the intake air pressure data PM and the rotation speed data Ne from the RAM 105. When the lean limit execution condition is not satisfied, K is set to 1.0. Then, in step 1103, the final injection amount TAU, computed by _{TAU ← TAUP · K · F IAF} · α + β. Α and β are correction amounts determined by other operating state parameters, for example, a correction amount determined by a signal from a throttle position sensor (not shown), a signal from an intake air temperature sensor, a battery voltage, and the like. Stored at 105. Next, at step 1104, the injection amount TAU is set in the down counter 108 and the flip-flop 109 is set to start fuel injection. Then, in step 1105, this routine ends. As described above, when the time corresponding to the injection amount TAU has elapsed, the flip-flop 109 is reset by the carry-out signal of the down counter 108, and the fuel injection ends.

FIG. 12 is a timing chart showing the operation according to the present invention. First, it is operated in a low humidity state, and the torque fluctuation ΔTR
It is assumed that learning control is performed based on Q. It is assumed that the engine is stopped in this state and the engine is stopped with the ignition switch turned off. At that time, the learning value _Kij is _stored in the backup RAM 1
Stored in 06. Next, the engine is started the next day, and after the warm-up operation, the lean limit control is started when the operating state such as the cooling water temperature satisfies the lean limit execution condition.
At this time, in the present invention, the predetermined value F _{IAF0 is added} to the initial increase value F _IAF.
(For example, A / F = about 1.0 rich amount), and attenuate to become “0” after a predetermined time (time or number of rotations). During this period, the learning control is also performed, so that the learning value K _ij is reduced until a predetermined torque fluctuation level is reached in the same humidity state as the previous day, and thereafter, the learning value K _ij of the initial increase value F _IAF is _calculated . With the decay, the learning value returns to a learning value K _ij substantially equal to the previous day. In this case, the air-fuel ratio is slightly higher than the optimum air-fuel ratio during the period until the desired torque fluctuation is reached (for example, a hatched portion). Conversely, when the humidity is higher than the previous day, the change in the optimum air-fuel ratio due to the humidity change is compensated for by the initial increase value _FIAF. Therefore, when the two are almost equal, the learning value _Kij becomes almost equal to the previous day. Thereafter, the learning value _Kij is updated to the increasing side with the attenuation of the initial increasing value _FIAF .

The influence of the torque fluctuation limit may be not only humidity but also intake air temperature. As means for correcting the air-fuel ratio to the rich side, the learning value K
means for multiplying _ij by a correction coefficient α (<1) to obtain a rich side;
In those having an intake air temperature sensor or humidity sensor, when the intake air temperature or humidity is higher than a certain reference value, a means for correcting the initial increase value _FIAF or the learning value _Kij , the intake air temperature and humidity are stored in the backup RAM, Changes in intake air temperature and humidity at the start of torque fluctuation are detected, and the initial increase F
Means for changing the _IAF or the correction coefficient α may be used.

Further, in the above-described embodiment, the fuel injection amount is calculated according to the intake air pressure and the engine speed, but the fuel injection amount is calculated according to the intake air amount and the engine speed, or the throttle valve opening and the engine speed. The fuel injection amount may be calculated.

Further, in the above-described embodiment, the internal combustion engine in which the fuel injection valve controls the fuel injection amount to the intake system is described. However, the present invention can be applied to a carburetor-type internal combustion engine. For example, one that controls the air-fuel ratio by adjusting the intake air amount of the engine with an electric air control valve (EACV),
Electric bleed air control valve adjusts the air bleed amount of the carburetor to control the air-fuel ratio by introducing air into the main passage and the slow passage, and controls the amount of secondary air sent to the exhaust system of the engine. The present invention can be applied to a device to be adjusted. In this case, the basic fuel injection amount corresponding to the basic injection amount TAUP in step 1101 is determined by the carburetor itself, that is, determined in accordance with the intake pipe negative pressure according to the intake air amount and the engine speed, and step 1103. At the final fuel injection amount TAU
Is calculated.

〔The invention's effect〕

According to the present invention described above, since the air-fuel ratio be lean limit point is changed by a change in the environmental conditions at the time after the engine stop and restart does not exceed the lean limit point, misfire or deterioration of combustion, NO _x Deterioration of emission and drivability can be prevented.

[Brief description of the drawings]

FIG. 1 is an overall block diagram for explaining the configuration of the present invention, FIG. 2 is a graph showing torque fluctuation, fuel consumption and exhaust emission characteristics, and FIG. 3 is a graph showing the relationship between humidity and air-fuel ratio at a lean limit point. FIG. 4 is a general diagram showing an embodiment of an air-fuel ratio control apparatus for an internal combustion engine according to the present invention, FIG. 5, FIG. 6, FIG. 8, FIG. 9, FIG. 11 is a flowchart for explaining the operation of the control circuit of FIG. 4, FIG. 7 is a timing chart for supplementary explanation of the flowchart of FIG. 6, and FIG. 12 is a timing chart showing the operation according to the present invention. It is. 1 ... engine body, 3 ... pressure sensor, 4 ... distributor, 5, 6 ... crank angle sensor, 10 ... control circuit, 11 ... combustion pressure sensor, 13 ... catalytic converter.

Continued on the front page (72) Inventor Yoshihiko Budo 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Co., Ltd. (56) References JP-A-60-122234 (JP, A)

Claims (1)

(57) [Claims] A torque variation calculating means for calculating a torque variation of the internal combustion engine; a feedback execution condition determining means for determining whether the engine satisfies a torque variation feedback execution condition; Learning means for updating a learning value for each area provided for each operating area of the engine such that the torque fluctuation amount becomes a predetermined value when a fluctuation amount feedback execution condition is satisfied; Air-fuel ratio adjustment means for adjusting the air-fuel ratio of the engine to the vicinity of the lean limit point and correcting the air-fuel ratio to the rich side when the engine satisfies the torque fluctuation amount feedback execution condition for the first time after the start of the engine. An air-fuel ratio control device for an internal combustion engine.