JPS6350641A - Air-fuel ratio control system for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent a torque shock at the time of selection from occurring, by controlling an air quantity in a throttle valve bypass passage with an air quantity to be related to an accelerator manipulated variable and a correction factor corresponding to a desired air-fuel ratio at the time of selecting it to the desired air-fuel ratio at the lean side according to the running state. CONSTITUTION:A control unit 50 operates a fundamental fuel injection quantity on the basis of a suction air quantity out of an air flow meter 22 and an engine speed out of a crank angle sensor 32. And, it performs water temperature correction based on the detected value of a water temperature sensor 31 and feedback correction to the desired air-fuel ratio based on a pump current of an oxygen sensor 33, etc. And, the control unit 50 sets the desired air-fuel ratio conformed to the suction air quantity and the engine speed, turning the value to the lean side at the specified driving area. And, at the time of selecting it to the lean side, an air correction factor is operated according to the desired air-fuel ratio, and with this correction factor and an air flow rate to be related to an accelerator manipulated variable, it operates and controls opening of an idle control valve 21.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an air-fuel ratio control device for an internal combustion engine such as an automobile that performs lean combustion.

(Prior art) In recent years, demands on automobile engines have become more sophisticated.
There is a tendency for the achievement of mutually contradictory issues such as reduced exhaust gas, high output, and low fuel consumption to a high level.

To address these issues, nine combustion control systems have been developed under ultra-lean air-fuel ratios, and unlike the characteristic of a constant stoichiometric air-fuel ratio during steady driving, the aim is to maintain a lean air-fuel ratio even in some acceleration regions. value.

A conventional air-fuel ratio control device that performs such lean burn is described in, for example, Japanese Patent Laid-Open No. 60-45742. In this device, when all of the following conditions are met, feedback control to the stoichiometric air-fuel ratio is stopped, and the air-fuel ratio is controlled to the lean side.

b) Cooling water temperature is 80℃ or higher; (c) Throttle valve opening is below a specified value (partial range); c) Vehicle speed change is below a specified value.

(Problems to be Solved by the Invention) However, in such conventional air-fuel ratio control devices, engine generated torque changes significantly when switching between a lean air-fuel ratio and a normal air-fuel ratio such as a stoichiometric air-fuel ratio. As a result, there was a problem in that the shock at the time of switching was large, causing jerky vibrations.

On the other hand, in order to solve this problem, it has also been proposed to take measures such as smoothly changing the air-fuel ratio when switching the target air-fuel ratio (see Japanese Patent Laid-Open No. 7741/1983). When switching the air-fuel ratio, this system gradually decreases or increases the fuel injection amount to smoothly change the current air-fuel ratio, and is intended to reduce shock during switching. However, even if such measures are taken, the generated torque changes regardless of the movement of the accelerator, resulting in an unnatural feeling.

Further, since it takes some time to shift to a lean air-fuel ratio, new problems arise such as an increase in exhaust emissions such as NOx and a reduction in the extent of fuel efficiency improvement due to lean burn.

(Objective of the Invention) Therefore, the present invention calculates a correction factor for the air flow rate based on the value of the target air-fuel ratio, and also calculates a passage that bypasses the throttle valve based on a parameter related to the accelerator operation amount (e.g. throttle valve opening degree). By controlling the air flow rate according to the above-mentioned correction factor, the purpose is to suppress torque fluctuations at the time of air-fuel ratio switching and improve drivability (drive feeling).

(Means for Solving the Problems) Air-fuel compression of an internal combustion engine according to the present invention? In order to achieve the above-mentioned purpose, the device No. 11, as shown in the basic conceptual diagram in FIG. The target value setting means sets a target air-fuel ratio based on the stoichiometric air-fuel ratio and selects the target air-fuel ratio to be leaner than the stoichiometric air-fuel ratio during at least a part of steady driving. a fuel amount calculation means C that calculates the amount of fuel; a fuel supply means d that supplies fuel to the intake passage based on the output of the fuel amount calculation means C; and a fuel supply means d that supplies fuel to the intake passage based on the output of the fuel amount calculation means C; a correction factor calculation means e for calculating an air correction factor to be corrected; a calculation means f for calculating the auxiliary air flow rate based on the air flow rate etc. related to the accelerator operation amount and the air correction factor; and a calculation means f for calculating the auxiliary air flow rate based on the output of the calculation means f. and an auxiliary air valve g for controlling the air flow rate of the passage that bypasses the throttle valve.

(Function) In the present invention, in addition to calculating the fuel amount as in the conventional method, an air flow rate correction factor for correcting the air-fuel ratio is calculated according to the value of the target air-fuel ratio, and a parameter related to the accelerator operation amount is calculated. For example, the air flow rate in the passage bypassing the throttle valve is controlled based on the air flow rate or the opening degree of the throttle valve at that time, in accordance with the correction factor. Therefore, when shifting to the target air-fuel ratio, engine torque changes smoothly in relation to the amount of accelerator operation, improving drivability.

(Example) Hereinafter, the present invention will be explained based on the drawings.

2 to 7 are diagrams showing one embodiment of the present invention, and the present invention is referred to as SP i (Single Point Inj
This is an example in which the present invention is applied to an engine of the 3.

First, the configuration will be explained. In Fig. 2, 1 is an engine, and intake air passes from an air cleaner 2 to a throttle chamber 3, and is turned 0N10FF by a heater control signal S.
After being heated by the PTC heater 4, the fuel is supplied to each cylinder from each branch of the intake manifold 5, and the fuel is supplied to a single injector (fuel supply means) provided upstream of the throttle valve 6 based on injection signals S and i. )7.

An ignition plug 10 is attached to each cylinder, and a high-voltage pulse PULSE from an ignition coil 12 is supplied to the ignition plug 10 via a distributor 11. The air-fuel mixture in the cylinder is heated by the spark plug 10 by high-pressure pulse PULSE.
It ignites and explodes due to the discharge of
Through the catalytic converter 15, harmful components (Co
, HC, NOx) are purified by the conversion action (oxidation and reduction) of the three-way catalyst and are discharged from the muffler 16.

Here, the flow of intake air is controlled by a throttle valve 6 in the throttle chamber 3 which is interlocked with the accelerator pedal, and the throttle valve 6 is almost closed during idling. Air flow during idling is by bypass passage 20
through the opening signal SAA. AAC valve (A
uxiliary Air Control Valv
e: Idle control valve) (auxiliary air valve) 21 ensures appropriate air.

The intake air flow rate Qa is detected by the air flow meter 22 of the hot wire 2, and the opening degree α of the throttle valve 6 is detected by the throttle sensor 30.

Further, the coolant temperature Tw is detected by the water temperature sensor 31, and the engine crank angle Ca is detected by the distributor 1.
The moxibustion is carried out by the crank angle sensor 32 built in 1. Note that the engine rotation speed N can be determined by counting pulses representing the crank angle Ca. An oxygen sensor 33 is attached to the exhaust pipe 14, and the oxygen sensor 33 is connected to an air-fuel ratio detection circuit 34. The air-fuel ratio detection circuit 34 supplies the pump current 1p to the oxygen sensor 33, detects the oxygen concentration in the exhaust gas from the value of the pump current 1p, and outputs it as an air-fuel ratio signal Vip.

On the other hand, the operating position of the transmission is detected by a position sensor 36, and the speed svsp of the vehicle is detected by a vehicle speed sensor 37. In addition, the operation of the air conditioner is controlled by the air conditioner switch 38.
The operation of the power steering is detected by the power steering detection switch 39.

Each of the above sensors 22.30.31.32.34.36.3
The signals from 7.38 and 39 are input to the control unit 5o, and the control unit 5o performs engine combustion control (ignition timing control, fuel injection control, etc.) based on the sensor information from these.

That is, the control unit 50 has a function as an operating state detection means together with the air flow meter 22 and the crank angle sensor 32, and also functions as a target value setting means, a fuel amount calculation means, a correction factor calculation means, and a calculation means by itself. CPU51, ROM52, RA
It is composed of M53 and I10 ports 54.

The CPU 51 reads necessary external data from the I10 boat 54 according to the program written in the ROM 52, and calculates processing values necessary for engine combustion control while exchanging data with the RAM 53. , and outputs the processed data to the I10 port 54 as necessary. Each of the above sensors 2 is connected to the I10 port 54.
Signals from 2.30.31.32.34.36.37.38 and 39 are input, and I10 port 5
From 4 onwards, each of the signals STi, Sl, 5AAC% 5s
cv and S are output. ROM52 is cPU
51 is stored, and RAM5
3 stores data used in calculations in the form of a map or the like. Note that a part of the RAM 53 is made up of a non-volatile memory, and retains its stored contents even after the engine 1 is stopped.

Next, the effect will be explained.

FIG. 3 is a flowchart showing a program for controlling the air flow rate, and this program is executed in synchronization with the rotation of the engine. Note that this embodiment is an example in which an AAC valve 21 is used as an auxiliary air valve, which is an actuator for air flow rate control, and also performs idle speed control, air amount control during deceleration, and the like.

The above actuator does not necessarily have to be an AA like this.
In addition to the C valve 21, other valves may be used.

First, the basic opening degree AACTW of the AAC valve 21 is calculated using P. This basic opening degree AACTw is determined using the cooling water temperature Tw or the state of auxiliary equipment load such as an air conditioner as a parameter, and may be obtained by, for example, table lookup.

Next, in P2, a deceleration air-fuel ratio correction value A CAIV is calculated. The deceleration air-fuel ratio correction value AAC□9 is calculated based on the air flow rate Qa, the cooling water temperature TW, etc., and has a characteristic that it gradually decreases during deceleration. Next, in P3, it is determined whether or not the vehicle is idling. This determination is made based on information from the throttle sensor 30. When the engine is in idle operation, the feed bank control amount A A CF B is calculated in P4 and the process proceeds to P. Feedback control ill A A CF e is increased or decreased according to the difference between the target engine speed (idle target value) Ni and the actual engine speed during idling, and Ni
The rotation speed is feedback-corrected so that On the other hand, if the idle operation is not performed in step P3, P
Jump to 4 and proceed to P. At P, a correction value Bα0 is calculated according to the following equation (2) based on each of the above calculated values.

BαO=AA CTw +AA CAB+/ +A
A CFI...■ Next, at P, look up the air correction factor KBA corresponding to the target air-fuel ratio KMR from the table map shown in FIG. FIG. 4 shows a characteristic in which the value of the air correction factor KB increases as the target air-fuel ratio KMR shifts to the lean side.

Note that in this example, the air correction factor KBA is determined based only on the value of the target air-fuel ratio KMR, but since the map characteristics shown in Fig. 4 change slightly depending on the operating conditions (load, etc.), higher If accuracy is to be achieved, it is preferable to make corrections based on engine load and cooling water temperature, for example. However, even if the method of determination is as in this embodiment, there is almost no problem in practice, and it is sufficient to set the KBA characteristics to an average value.

Therefore, the air flow rate taken into the engine 1 is corrected to increase or decrease according to the value of KBA determined in this step.

Next, at P7, the throttle opening area Aα corresponding to the throttle opening degree α is looked up from the table map shown in FIG. 5, and at P[l, the AAC valve opening area corresponding to the correction value Bα0 is looked up from the table map shown in FIG. Area ABα
Look up 0.

Next, the corrected aperture area ABα1 with the air-fuel ratio corrected by P is calculated according to the following equation (2).

ABα1-(Aα+ABα0)XKBA+ABα0
・・・・・・■ Next, P. Then, from the table map shown in FIG. 6, the AAC valve opening degree Bα corresponding to the corrected opening area ABα1 is determined.
Look up 1. This can be done by reading the horizontal axis against the vertical axis of human power from the map characteristics shown in FIG. Then, at P, battery voltage correction etc. are added to this AAC valve opening degree Bα1, and a control signal S for the AAC valve opening degree is generated.
Determine the final duty value AACDuty of AAC.

In this way, in this embodiment, in addition to the conventional air flow rate operation when performing feedback control to the idle target rotation speed Ni, the air correction factor K is adjusted according to the value of the target air-fuel ratio KMR.
In addition to calculating BA, A is calculated based on a parameter related to the amount of accelerator operation, that is, the throttle opening degree α.
A duty value AAC Duty of the AC valve 21 is calculated. Therefore, when the target air-fuel ratio is switched, the air flow rate is appropriately corrected according to the value of the air-fuel ratio at the time of switching, taking into consideration the amount of operation of the accelerator, without requiring any operation of the accelerator. In other words, the air-fuel ratio (A/F
) is varied. Therefore, the torque change when switching the air-fuel ratio becomes extremely smooth and natural, and it is possible to significantly improve the drive feeling while preventing shock during switching. Further, it is possible to avoid a large amount of time for switching the air-fuel ratio, avoid an increase in exhaust emissions, and increase the range of improvement in fuel efficiency.

FIG. 7 is a flowchart showing a program for fuel injection amount control that is performed in parallel with the air flow rate control as described above, and the calculation of the target air-fuel ratio described above is also performed by this program.

First, at PH1, based on the air flow meter 22 output Qa and the engine rotation speed N, the cylinder inflow air amount QcyL per unit rotation is calculated according to the following equation (2).

Next, the cooling water temperature Tw is compared with a predetermined value TWO at P2°. When TW≧TwO, it is determined in pz3 whether the cylinder inflow air FjlQcvL is within a predetermined range.

When QCYL is within the predetermined range, it is determined in P24 whether the engine speed N is within the predetermined range. When the engine speed N is within the predetermined range, the process advances to P2S. Therefore, when proceeding to PX3, engine 1 is warmed up,
Since the conditions that QcYL is in the partial range and the rotational speed N is within a predetermined range are satisfied, it is determined that the engine is in the lean burn operation range.

On the other hand, when P2□ to P24 deviate from such an AND condition, it is determined that the vehicle is within the normal operating range, and the process proceeds to P26. pzs looks up the lean target air-fuel ratio KMR2 from a predetermined table map and stores this value as the new target value NKMR. In addition, KMR2 is the engine rotation speed N and the cylinder inflow air ffl Q cv L
It is determined from a three-dimensional table map in which parameters are assigned. In this case, the optimum value of KMR2 is determined experimentally in advance for each operating condition, taking into account fuel efficiency, engine stability, etc., and is stored in the map. At P26, the normal target air-fuel ratio KMR1 is look-amplified and this value is also stored as the new target value NKMR.

Next, in P2□, the water temperature increase correction coefficient K T w corresponding to the cooling water temperature Tw is looked up from the table map as in the conventional case. Note that the water temperature increase correction coefficient KTw is used to lynch the air-fuel ratio when the engine is cold. Then,
pzs calculates the final target air-fuel ratio KMR according to the following equation (2).

...■ However, n: smoothing coefficient Here, the smoothing coefficient n is a coefficient for eliminating sudden changes in KMR, and is a coefficient for smoothly changing the target air-fuel ratio (ie, smoothing). Then, at pzz, basic injection MTp is calculated according to the following equation (2), and at P3°, the final injection amount Ti is calculated according to the following equation (2).

T i = T p X L A M B D A X
K A CC + T s...■ However, KACC: Transient correction coefficient Ts: Invalid pulse width LAMBDA is a feedback correction coefficient for performing feedback control of the air-fuel ratio based on the output from the air-fuel ratio detection circuit 34 It is.

The following routine determines the partial operating range from the operating conditions, appropriately calculates the fuel injection iTi that achieves lean burn in the partial range, and injects the fuel from the injector 7 at a predetermined injection timing. At this time, in addition to calculating the injection amount Ti corresponding to the change in the target air-fuel ratio KMR, as mentioned above, the shock at the time of air-fuel ratio switching is suppressed while the air flow rate is appropriately corrected. It is.

Therefore, as shown in FIG. 9, which will be described later, problems such as shocks and fluctuations in generated torque occurring when switching between the normal air-fuel ratio and the normal air-fuel ratio regardless of the accelerator pedal are reduced, and drivability is improved.

FIG. 8 is a diagram showing a second embodiment of the present invention, and this embodiment improves the calculation of the air correction factor KBA.

In the air correction factor calculation subprogram shown in FIG. 8, a new air correction factor NKBA is calculated in P41. N.K.
Since BA is the same as the air correction factor KBA corresponding to the target air-fuel ratio KMR as shown in the table map of FIG. 5, the same value is looked up. Next, in P4□, the current air correction factor NKBA and the air correction factor KBA in the previous routine are calculated.
The absolute value of the difference (INKBA-KBA' l) is compared with the smoothing determination comparison level L'H. l NKBA-KB
When A'l>LH, the final air correction factor KBA is calculated in Pd2 according to the following equation (2), and is delayed with respect to NKBA.

KBA=NKBAx 1/n, 1 +KAB 'Xn1
-1/nl...■ However, nl: smoothing coefficient On the other hand, when INKBA-KBA' l≦LH in P4□, the target air correction factor KBA is calculated in p4a according to the following formula ( (varying the degree of smoothing).

KB A = N KB A X 1 / n 2
+ K B A 'Xn2-1/n2...
・■ However, by executing a program with n2: smoothing coefficient or more, in this embodiment, in addition to the effect of the first embodiment, the actual air-fuel ratio is equal to the target air-fuel ratio K.
Due to a phenomenon that has a delay compared to MR, the target air-fuel ratio KMR
However, if the air amount is increased too quickly for the air-fuel ratio, this prevents the generated torque from changing due to the difference. That is, FIG. 9(a)
As shown in the figure, the actual air-fuel ratio lags behind the target air-fuel ratio KMR because the wall flow rate of fuel in the intake pipe changes in response to changes in the air-fuel ratio. This is because the air-fuel ratio lags due to the amount of fuel being consumed. However, if the air amount is increased based on the target air-fuel ratio KMR, the air amount will be increased too quickly relative to the change in the air-fuel ratio, and the generated torque will vary depending on the difference.

Therefore, in this embodiment, in consideration of the fact that when the target air-fuel ratio KMR suddenly changes, the change in the actual air-fuel ratio does not become a delayed waveform with a constant time constant, but instead changes quickly in the early stage and slows down in the latter stage. , +NKBA-KBA' By changing the degree of smoothing according to the value of l (see FIG. 9(b)),
Figure 9 (
c)), more natural driving becomes possible. In addition, it is possible to cope with sudden changes in the air-fuel ratio target value.

In addition, in each of the above embodiments, since the smoothing process is performed in synchronization with the engine rotation, even if the engine rotation speed is low, higher accuracy of smoothing can be ensured.

However, in the case of time synchronization, for example, it is preferable to change the values of nl and n2 depending on the engine speed.

(Effects) According to the present invention, when the air-fuel ratio is switched, in addition to calculating the fuel amount as in the conventional method, an air flow rate correction factor is calculated for correcting the air-fuel ratio according to the value of the target air-fuel ratio, Since the air flow rate in the passage that bypasses the throttle valve is controlled according to the parameter related to the amount of accelerator operation, such as the air flow rate or throttle valve opening at that time, according to the above correction factor, engine torque can be changed smoothly, further improving drivability.

[Brief explanation of drawings]

Figure 1 is a basic conceptual diagram of the present invention, Figures 2 to 7 are diagrams showing the first embodiment of the present invention, Figure 2 is its overall configuration diagram, and Figure 3 is the calculation of the AAC valve control value AAC Duty. 4 is a table map of the air correction factor KBA, FIG. 5 is a table map of the throttle opening area Aα, FIG. 6 is a table map of the AAC valve opening area ABα, and FIG. 7 is a table map of the AAC valve opening area ABα. is a flowchart showing a program for calculating the fuel injection signal Ti,
8 and 9 are diagrams showing a second embodiment of the present invention, and FIG.
The figure is a flowchart showing a subprogram for calculating the air correction factor KBA, and FIG. 9 is a diagram showing the relationship among the air fuel ratio (a), the air correction factor KBA (b), and the generated torque (C). 7... Injector (fuel supply means), 21.
...AAC valve (auxiliary air valve), 22.32.
50... (operating state detection means), 50...
...Control unit (target (a B foot means, fuel amount calculation means, correction factor calculation means, calculation means).

Claims (1)

[Scope of Claims] a) Operating state detection means for detecting the operating state of the engine using intake air amount, rotation speed, etc. as parameters, and b) Setting a target air-fuel ratio based on the operating state of the engine, and at least steady running. c) target value setting means for selecting the target air-fuel ratio to be leaner than the stoichiometric air-fuel ratio in a part of the system; a fuel supply means that supplies fuel to the intake passage based on the output of the quantity calculation means; and e) a correction factor calculation that calculates an air correction factor that corrects the flow rate of auxiliary air that bypasses the throttle valve according to the target air-fuel ratio. f) a calculation means for calculating the auxiliary air flow rate based on an air flow rate, etc. related to the accelerator operation amount and an air correction factor; g) an air flow rate in a passage that bypasses the throttle valve based on the output of the calculation means; An air-fuel ratio control device for an internal combustion engine, comprising: an auxiliary air valve for operating an auxiliary air valve;