JPS61272432A - Method of feedback-controlling air-fuel ratio of internal-combustion engine - Google Patents

Abstract

PURPOSE:To decrease an amount of CO and HC discharged, by a method wherein a correction value, applicable to proportional control, is set to a low value according to a specified condition of an exhaust gas concentration detection value, and is set according to the load condition of an engine. CONSTITUTION:An O2 sensor 15, inserted in an exhaust pipe, detects oxygen concentration in exhaust gas to feed the result to an ECU 5. In the ECU 5, a first correction value, applicable to proportional control, is set to a low value when an exhaust gas concentration detection value is varied from the rich side to the lean side in relation to a reference value, and is set depending upon the load condition of an engine. This enables reduction of an amount of a CO and an HC component discharged.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to an air-fuel ratio control method for an internal combustion engine, and more particularly to an air-fuel ratio control method for an internal combustion engine that improves the purification efficiency of an exhaust gas purification device and improves the exhaust purification performance of the engine. Regarding the method.

(Technical background of the invention and its problems) Generally, in order to improve the exhaust purification performance of internal combustion engines,
The engine is equipped with an exhaust gas purification device to reduce the amount of harmful substances emitted from the engine.

For example, a three-way catalyst device is used as an exhaust gas purification device, and in order to simultaneously purify the three components of Co, HC, and NOx in the exhaust gas, feedback changes according to the output value of an exhaust concentration detector placed in the engine exhaust system. The air-fuel ratio of the air-fuel mixture supplied to the engine is feedback-controlled using the control signal so that it reaches the stoichiometric air-fuel ratio. In order to carry out such control, for example, the concentration value detected by the exhaust gas concentration detector is compared with a predetermined reference value, and a lean signal and a rich signal are generated, respectively, which indicate that the air-fuel mixture is on the lean side and rich side of the stoichiometric mixture ratio. A signal is obtained, and when a change from a lean signal to a rich signal or the opposite change occurs due to a change in the detection value of the detector, a predetermined correction value is applied to increase or decrease the feedback control signal (proportional correction). control) and obtain the required feedback control signal.

On the other hand, in a three-way catalyst device, the purification rate of CO and HC components is when the mixture is leaner than the stoichiometric mixture ratio;
The purification rate of NOx components increases on the rich side. Further, the air-fuel ratio at which the purification ability of the catalyst device constituting the exhaust gas purification device is maximized differs depending on the type of catalyst device. Therefore, in order to improve the purification efficiency of exhaust gas purification equipment,
It is necessary to control the air-fuel ratio of the air-fuel mixture to a predetermined (target) air-fuel ratio depending on the components of the harmful substances to be purified and the type of exhaust gas purification device.

To achieve this goal, for example, the exhaust concentration detected by an exhaust concentration detector installed in the exhaust system of an internal combustion engine is compared with a predetermined reference value, and the air-fuel mixture supplied to the engine is determined. Proportional control for increasing or decreasing the air-fuel ratio by a first correction value when the detected exhaust gas concentration value changes from a rich side to a lean side or from a lean side to a rich side with respect to the predetermined reference value; When the detected exhaust gas concentration value is on the lean side or the rich side with respect to the predetermined reference value, the air-fuel ratio is fed back to the target air-fuel ratio by at least one of integral control that increases or decreases the air-fuel ratio at predetermined intervals using second correction values. An air-fuel ratio control method has been proposed by the applicant (Japanese Patent Application No. 58-243491).
.

By the way, in a high-load operating state, compared to operating states other than high-load, the amount of fuel supplied to the engine due to acceleration and the like increases more than the amount of fuel for the stoichiometric air-fuel ratio. Further, when a gear change is performed in an acceleration state, which is a high load state, the throttle valve is fully closed at this time, which increases the amount of HC components discharged due to incomplete combustion of the air-fuel mixture.

For this reason, there has been a problem in that the purification rate of CO and HC components in the three-way catalyst device decreases, and in particular, the amount of HC components discharged increases.

(Object of the Invention) The present invention has been made in view of the above points, and provides air-fuel ratio feedback for an internal combustion engine that improves the exhaust purification performance of the engine during high-load operation and reduces CO and HC emissions. The purpose is to provide a control method.

(Structure of the Invention) In order to achieve such an object, according to the present invention, when the detected exhaust gas concentration value changes from the rich side to the lean side or from the lean side to the rich side, the air-fuel ratio is adjusted to the first level. At least one of proportional control that increases or decreases the air-fuel ratio by a second correction value, and integral control that increases or decreases the air-fuel ratio at predetermined intervals when the detected exhaust gas concentration value is on the lean side or rich side. In the air-fuel ratio feedback control method for an internal combustion engine that performs feedback control to a target air-fuel ratio, the first correction value used in the proportional control is such that the detected exhaust concentration value changes from a rich side to a lean side with respect to the predetermined reference value. Provided is an air-fuel ratio feedback control method for an internal combustion engine, characterized in that when the change occurs from a lean side to a rich side, the first correction value is set smaller than when the change changes from a lean side to a rich side, and the first correction value is set depending on the load state of the engine. .

(Example of the invention) Embodiments of the present invention will be described below based on the drawings.

FIG. 1 illustrates an air-fuel ratio control device to which the method of the present invention is applied, in which an intake pipe 2 is connected to a four-cylinder internal combustion engine 1,
A throttle body 3 having a throttle valve disposed inside is provided in the middle of the intake pipe 2. A throttle valve opening sensor 4 is connected to the throttle valve to convert the opening of the throttle valve into an electrical signal and send it to an electronic control unit (hereinafter referred to as rECUJ) 5.

A fuel metering device (fuel injection valve 6 in the illustrated example) is provided between the engine 1 and the throttle body 3 in the intake pipe 2, and is connected to a fuel pump (not shown) and electrically connected to the ECU 3. The valve opening time of fuel injection is controlled by a signal from the ECU 3.

On the other hand, an absolute pressure sensor 8 is provided immediately downstream of the throttle valve of the throttle body 3, and an absolute pressure signal converted into an electrical signal by the absolute pressure sensor 8 is sent to the ECU 3.

The main body of the engine 1 is provided with an engine water temperature sensor 10. This sensor 10 is made of a thermistor, etc., and is installed in the circumferential wall of the engine cylinder filled with cooling water, and supplies its detected water temperature signal to the ECU 3.

An engine rotation angle position sensor 11 and a cylinder discrimination sensor 12 are attached around a camshaft (not shown) or a crankshaft of the engine, and the former 11 receives a TDC signal, that is, a predetermined crank angle position every 180° rotation of the engine crankshaft. The latter 12 outputs one pulse at each predetermined crank angle position of a specific cylinder, and these pulses are sent to the ECU 3.

A three-way catalyst 14 is disposed in the exhaust pipe 13 of the engine 1 to purify HC, Co, and NOx components in the exhaust gas. An 02 sensor 15 is inserted into the exhaust pipe 13 on the upstream side of the three-way catalyst 14, and this sensor 15 detects the oxygen concentration in the exhaust gas, and compares the detected value with a predetermined reference value Vr (Fig. 3). A deviation signal of is supplied to the ECU 3.

The ECU 3 adjusts the TDC based on the various parameter signals mentioned above.
The fuel injection time TOUT given by the following equation during which the injection valve is opened in synchronization with the signal is calculated.

Touv=Ti XK2 XKO2+2- (1) Here, Ti indicates the basic fuel injection time of the fuel injection valve 6,
This basic injection time is read out from a memory device in the ECUS based on, for example, the intake pipe absolute pressure PBA and the engine speed Ne. Ko2 is 0 according to the present invention, which will be detailed later.
2 is a feedback correction coefficient, and K1 and 2 are correction coefficients and correction variables respectively calculated according to various engine parameter signals, and are used to optimize engine characteristics such as fuel consumption characteristics and engine acceleration characteristics according to engine operating conditions. The predetermined value is determined so that the

ECU3 calculates the fuel injection time TOU as described above.
Based on T, a drive signal for opening the fuel injection valve 6 is output.

FIG. 2 is a diagram showing the circuit configuration inside the ECU 3 shown in FIG.
It is supplied as a TDC signal to a central processing unit (hereinafter referred to as CPU) 22, and also to an engine rotation speed measurement counter (hereinafter referred to as Me counter) 24. The Me counter 24 is the engine rotation angle position sensor 1
It counts the time interval from the input of the previous TDC signal from 1 to the input of the current TDC signal, and the counted value M
e is proportional to the reciprocal of the engine speed Ne. The Me counter 24 transfers this count value Me to C via the data bus 26.
It is supplied to PU22.

On the other hand, a throttle valve opening sensor 4, an absolute pressure sensor 8, an engine water temperature sensor 10, an engine rotation angle position sensor 1
The output signals of the 1 and 02 sensors 15 are respectively applied to a level correction circuit 28, corrected to a predetermined voltage level in the circuit 28, and then sequentially sent to an analog-to-digital converter 32 by a multiplexer 30 operating based on a command from the CPU 22. supplied to The converter 32 converts the output signals of the aforementioned sensors into digital signals, and supplies the digital signals to the CPU 22 via the data bus 26.

This CPU 22 is further connected to a read-only memory (hereinafter referred to as ROM) 34 and a random access memory (hereinafter referred to as RAM) 36 via a data bus 26.
and is connected to the drive circuit 38. The ROM 34 stores a control program executed by the CPU 22 and various data such as correction coefficient values. Further, the RAM 36 is
It temporarily stores the calculation results etc. in the PU22.

Then, the CPU 22 reads coefficient values or variable values corresponding to the output signals of the respective sensors described above from the ROM 34 according to the control program stored in the ROM 34, and calculates the valve opening time of the fuel injection valve 6 based on the above calculation formula (1). TOUT is calculated, and the value obtained by this calculation is supplied to the drive circuit 38 via the data bus 26. The drive circuit 38 supplies the fuel injection valve 6 with a control signal to open the fuel injection valve 6 over the calculated valve opening time TOUT.

FIG. 3 is a diagram showing an air-fuel ratio feedback control method according to an embodiment of the present invention. As shown in (a) of the same figure, 0
The output of the two-sensor 15 fluctuates during engine operation, and the fluctuation period T changes depending on the engine rotation speed Ne, becoming shorter at high rotation speeds.

The sensor 15 outputs a rich signal when the detected concentration value exceeds the reference value Vr, and outputs a lean signal when the detected concentration value falls below the reference value Vr. Both signals represent the mixture being richer and leaner than the stoichiometric mixture, respectively.

In this embodiment, the air-fuel ratio of the air-fuel mixture is controlled to a predetermined air-fuel ratio that is lower than the stoichiometric mixture ratio in order to reduce the amount of nitrogen oxide NOx emitted from the engine 1 equipped with the three-way catalyst 14 shown in FIG. do. Therefore, as shown in Figure 3(b),
When the 02 sensor output changes from a rich signal to a lean signal, the correction value PR is applied as the first correction value at a cycle twice the fluctuation cycle T of the 02 sensor output, and the 02 feedback correction coefficient value Ko2 is increased. are doing. Further, when the 02 sensor output changes from a rich signal to a lean signal and from a lean signal to a rich signal other than the correction value PR application base, a predetermined correction value P smaller than the correction value PR is applied to respectively set the coefficient value KO2. The required coefficient value Ko2 is obtained by gradually increasing and decreasing the KO2 value using a second correction value using integral control, which will be described later, except when there is a change. As a result,
An average value of the correction coefficient value Ko2 of 1 below is a value larger than the average value Ko2° when only the correction value P is used as in the conventional method. Therefore, when such coefficient value KO2 is used as a feedback control signal, the air-fuel ratio of the air-fuel mixture is biased (riched) to a value smaller than the stoichiometric air-fuel ratio due to the contribution of the increase in the above-mentioned average value. The magnitude of this deviation, and therefore the air-fuel ratio of the air-fuel mixture, is controlled to a required value by appropriately setting the magnitude of the correction values PR, P and the application cycle of the PR value.

In addition, during high-load feedback operation such as during acceleration (region ■" in Figure 4), the air-fuel ratio of the mixed tank air is lower than the stoichiometric mixture ratio in order to reduce the emissions of -carbon oxide CO and unburned fuel HC. It is necessary to control the air-fuel ratio to a large predetermined air-fuel ratio (lean side). Therefore, when the 02 sensor output changes from a rich signal to a lean signal, the first correction value is Correction value P smaller than correction value PR
R2 is applied to increase the 02 feedback correction coefficient value Ko2. The correction value PR2 at this time is a value smaller than the correction value P2 applied when the 02 sensor output changes from a rich signal to a lean signal or from a lean signal to a rich signal in the feedback operation region ■ or V' in Fig. 4. Set to .

As a result, the average value of the correction coefficient value KO2 during high-load operation is 02''', which is the average value K when only the correction value P2 is applied.
o2 “is a smaller value. Therefore, such a coefficient value K
When o2 is used as a feedback control signal, the air-fuel ratio of the air-fuel mixture is biased (leaned) to a value larger than the stoichiometric air-fuel ratio due to the contribution of the decrease in the average value. The magnitude of such deviation, and therefore the air-fuel ratio of the mixture, is determined by the correction value PR2,P
By appropriately setting the magnitude of PH1 value and the application period of the PH1 value, it is controlled to a desired value.

FIG. 5 shows a flowchart of a subroutine for calculating the 02 feedback correction coefficient Ko2 according to the embodiment of FIG.

First, it is determined whether activation of the 02 sensor is completed (step 1). That is, due to the internal resistance detection method of the 02 sensor, the output voltage of the 02 sensor reaches the activation starting point Vx (
For example, it is detected whether or not the voltage reaches Vx (Q, 6V), and it is determined that the voltage is activated when the voltage reaches Vx. The answer is negative (N
O), set Ko2 to 1 (step 2
) On the other hand, if the answer is affirmative (Yes), it is determined whether the engine is being operated in an open loop control region (step 3). The open loop control ranges are the full load range I, the low rotational speed range (2), the high rotational speed range (2), and the lean mixture range (2) of the internal combustion engine shown in FIG.

If the determination result in step 3 is affirmative (Yes), KO2 is set to 1 in the same manner as described above (step 2), and 1 is set to the correction coefficient value of the front bottom (1) as is known in the art. Set the value according to the value and use this to perform open loop control.

On the other hand, if the answer to step 3 is negative (No), it is determined that the operating state of the engine is in the feedback operating region (2) or V' shown by diagonal lines in FIG. 4, and feedback control is performed. That is, it is determined whether the output level of the 02 sensor has been reversed or not (Step 4), and the answer is affirmative (Yes).
In this case, it is determined whether the output level of the 02 sensor 15 is a low level (lean signal) in order to perform proportional control (P-term control) (step 5), and the answer is affirmative (Yes).
), the process moves to step 6, and the predetermined period tpR(
Figure 6) is calculated. This predetermined period tpR is a parameter for applying the correction value PR at a period twice as many times as the fluctuation period T of the 02 sensor output. For example, the predetermined period tpR is set to a value that is 1.25 times the fluctuation period t.

Since the fluctuation period t becomes shorter as the engine speed Ne increases, the predetermined period tpR is set to a smaller value as the engine speed Ne increases, as shown in FIG. 6, and the correction value PR is set over the entire engine speed range. The application period of is constant (=
2 T). The predetermined period tpR is, for example, when the engine speed Ne is 1100 as shown in FIG.
Orp to the value tpR1, 11000rp to 40
At 00 rpm, the value tpR2 (ktpRl) is 4000.
If it exceeds the rpm, it is set to the value tpR3 (<tpR2).

Following step 6, it is determined whether a predetermined period tpR has passed since the previous application of the correction value PR (step 7), and if the answer is affirmative (Yes), the correction value PR should be applied (step 7).
A correction value PR is determined based on the Ne-PaA-PR table stored in the OM 34 and the engine speed Ne and the intake pipe absolute pressure PBA (step 8). The correction value PR is, for example, as shown in FIG.
Irrespective of the A value, the value PR+ (for example, 0.025 >
For example, when the engine operating state is greater than 340 mmHg), it is determined that the engine operating state is in the high load, high rotation range within the feedback operating region shown in Fig. 4, and the correction value PR is set to the value PR.
2 (for example, 0.030).

Further, when the engine rotation speed Ne exceeds the predetermined rotation speed NFB and the PaA value is smaller than the predetermined value PBAO2, it is determined that the engine operating state is in the low load region ■ in the feedback operation region shown in FIG. , correction value PR
is set to the value PR3 (eg 0.041).

On the other hand, the answer to step 7 is negative (No), that is, the correction value P
If it is determined that the predetermined period tpR has not elapsed since the previous application of R, the process moves to step 9 and a correction value P corresponding to the engine speed Ne is determined from the Ne-P table stored in the ROM 34. As shown in FIG. 8, the correction value P takes a value P1 (for example, 0.020) when the engine speed Ne is below a predetermined speed NFB, and a value P2 (for example, 0.034') when it exceeds the engine speed NFB. are set respectively.

Next, in step lO, from step 8 to step 10
If the transition is made to the correction value Pi, the correction value PR+~PR3
If any of the above is transferred from step 9, the correction value P
1 or P2 to calculate the current KO2 value by adding this Pi value to the previous Ko2 value.

If the answer to step 5 is negative (No), step 1
1, calculate the correction value P1 or P2 according to the engine speed Ne from the above-mentioned Ne-P table, and then subtract the correction value P1 or P2 thus calculated from the previous Ko2 value to obtain the current Ko2. Find the value (step 12).

In steps 11 and 12, the correction value Pi (Pl or P2) is determined when the output of the 02 sensor 15 is at a high level (lean side), and in steps 6 to 10, the output of the 02 sensor 15 is at a low level (lean side). correction value pi (PRI or PR2 or PR3 or P
l or P2) is determined. In this case, each correction value Pi has the following relationships (2) to (4).

PRI >P+...(2
)PR3>P2...(3)
PR2<P2...(4) When the engine operating condition is in the region ■ of Fig. 4, the formula (2) is applied.
, (3), the correction value Pi (=PRt or PI') when the detected exhaust gas concentration value is on the rich side is set larger than the correction value Pi (=P1 or P2>) when the detected exhaust gas concentration value is on the rich side. Therefore, as shown in FIG. 3(b), the average value 77 of the correction coefficient value Ko2 shifts to the rich side, and as a result, the air-fuel mixture becomes rich (the air-fuel ratio becomes small). When the operating condition is in the region V° of Fig. 4, the correction value Pi (=PR2) when the detected exhaust gas concentration value is on the lean side is the correction value Pi (=P2) when the detected exhaust gas concentration value is on the rich side, according to equation (4). Therefore, during high-load operation such as during acceleration within the feedback operation region, the average value Ko21T of the correction coefficient values Ko2 shifts to the lean side as shown in FIG. 3(b), and as a result, the mixture The air becomes leaner (the air-fuel ratio increases).

As a result, the amount of CO and HC discharged during high load operation (region v') within the feedback operation region is reduced.

If the answer to step 4 is negative (No), that is, 0
If the two sensor output levels remain the same, integral control (one-term control) is performed. That is, first, it is determined whether the output level of the 02 sensor is Low or not (step 13),
If the answer is affirmative (Yes), 1 is added to the previous count number NxL to count the number of pulses of the TDC signal (Step 14), and the count number N is set to a predetermined value N.
Determine whether or not x (for example, 30 pulses) has been reached (step 15), and if it has not yet reached it, maintain Ko2 at the value just before that (step 16).
When the value reaches Ko2, a predetermined value Δk (for example, about 0.3% of Ko2) is added to Ko2 (step 17). At the same time, the number of pulses Nx counted so far is set to O (step 18), and a predetermined value Δk is added to Ko2 every time Nx reaches Nx.

On the other hand, if the answer is negative (No) in step 13, the number of pulses of the TDC signal is counted (step 19), and it is determined whether the counted number N has reached a predetermined value Nx. Step 20), the answer is negative (NO)
In this case, the value of Ko2 is maintained at the previous value (step 21), and if the answer is affirmative (Yes), a predetermined value Δk is subtracted from KO2 (step 22), and the counted number of pulses NxH is set to O. In the reset step 23), the predetermined value Δk is subtracted from Ko2 every time the N-work H reaches Nx, as described above.

(Effects of the Invention) As detailed above, according to the air-fuel ratio feedback control method for an internal combustion engine of the present invention, the detected exhaust gas concentration value detected by the detected exhaust gas concentration value arranged in the exhaust system of the internal combustion engine and the predetermined standard When the detected exhaust gas concentration value changes from the rich side to the lean side or from the lean side to the rich side with respect to the predetermined reference value, the air-fuel ratio of the air-fuel mixture supplied to the engine is Proportional control that increases or decreases correction using a first correction value, and when the detected exhaust gas concentration value is on the lean side or rich side with respect to the predetermined reference value, increases or decreases the air-fuel ratio at predetermined intervals using second correction values. In an air-fuel ratio feedback control method for an internal combustion engine that performs feedback control to a target air-fuel ratio by at least one of integral control, the first ? The +ti positive value is set smaller when the detected exhaust gas concentration value changes from the rich side to the lean side with respect to the predetermined reference value than when it changes from the lean side to the lean side,
In addition, since the first correction value is set according to the engine load condition, the air-fuel ratio can be unified during high loads such as during acceleration within the feedback operation region, and the CO and HC components can be reduced. emissions can be reduced,
Particularly, this has the effect of reducing the amount of HC components discharged when changing gears during acceleration.

[Brief explanation of drawings]

Fig. 1 is an overall configuration diagram illustrating an air-fuel ratio control device to which the method of the present invention is applied, Fig. 2 is a block circuit diagram showing the electronic control unit of Fig. 1, and Fig. 3 is an embodiment of the present invention. Figure 4 is a diagram showing the operating range of the engine.
The figures are a flowchart of a subroutine for calculating the 02 feedback correction coefficient Ko2 according to the embodiment of Fig. 3, Fig. 6 is a graph showing an example of setting the predetermined period tpR, and Figs.
The figures are graphs showing examples of setting the correction values PR and P, respectively. DESCRIPTION OF SYMBOLS 1... Internal combustion engine, 5... Electronic control unit, 6... Fuel injection valve, 11... Engine rotation angle position sensor, 13... Exhaust pipe, 14... Three-way catalyst, 15...02 sensor. Applicant Honda Motor Co., Ltd. Agent Patent attorney Satoshi Watanabe Onma Kanji Nagato

Claims (1)

[Claims] 1. Compare the detected exhaust concentration value detected by the exhaust concentration detector placed in the exhaust system of the internal combustion engine with a predetermined reference value, and determine the air-fuel ratio of the air-fuel mixture supplied to the engine when the detected exhaust concentration value is Proportional control that increases or decreases the air-fuel ratio by a first correction value when the air-fuel ratio changes from a rich side to a lean side or from a lean side to a rich side with respect to a predetermined reference value, and the detected exhaust concentration value is changed with respect to the predetermined reference value. In an air-fuel ratio feedback control method for an internal combustion engine, the air-fuel ratio is feedback-controlled to a target air-fuel ratio by at least one of integral control that increases or decreases the air-fuel ratio at predetermined intervals using second correction values when the air-fuel ratio is on the lean side or the rich side. , the first correction value applied to the proportional control is set smaller when the detected exhaust gas concentration value changes from a rich side to a lean side with respect to the predetermined reference value than when it changes from a lean side to a rich side. , and the first correction value is set according to a load condition of the engine.