JPH0227132A - Device for controlling air-fuel ratio of internal combustion engine - Google Patents

Abstract

PURPOSE:To continuously carry out the optimum lean burn control with a low-cost structure by feedback controlling an air-fuel ratio to be on a lean side so as to estimatingly bring the level of a surge torque to the limit of stability. CONSTITUTION:In a control unit 8, engine speed variations per unit time are operated according to the input of the reference signal of a crank angle sensor 13 and the largest one among these is defined as the variation level of engine speed. The level of a surge torque corresponding to the engine-speed variation level is obtained by retrieving a map. Further, by obtaining the deviation between the surge-torque level and the stability-limit level of the surge torque, and by using a fuzzy quantity obtained by grasping same by human feeling and rewriting same, the lean burn control of air-fuel ratio is carried out. Thereby, it is possible to further lean combustion while keeping the stable condition of surge torque without being affected by the dispersion of parts, based on only the signal of an ordinarily provided O2 sensor.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an air-fuel ratio control device for an internal combustion engine, and particularly to a device for controlling the air-fuel ratio to a lean state.

<Conventional technology> Conventionally, in order to improve fuel efficiency as much as possible, there are systems that burn a mixture that is set to be leaner than the stoichiometric air-fuel ratio (hereinafter referred to as lean burn control), and exhaust purification measures are also simple. It has the advantage that it can be performed with a simple configuration.

<Problems to be Solved by the Invention> By the way, the normal type 02 sensor used for so-called air-fuel ratio feed bank control has a characteristic that the output level is reversed around the stoichiometric air-fuel ratio, and whether it is richer or leaner than the stoichiometric air-fuel ratio. It is difficult to perform highly accurate lean burn control using the 02 sensor because only an ON/OFF determination can be made.

If feedback control is performed using a wide range air fuel ratio sensor whose output level changes linearly with changes in the air fuel ratio, it is possible to perform highly accurate lean burn control, but wide range air fuel ratio sensors are expensive. There are high drawbacks. Incidentally, as a prior art using a wide range air-fuel ratio sensor, there is, for example, the one shown in Japanese Utility Model Application Laid-Open No. 63-51137.

Therefore, open-loop control is performed in which the air-fuel ratio is set to a desired value on the lean side without detecting the air-fuel ratio.

However, with such open-loop control, due to variations in the characteristics of the fuel injection valves and air flow meters, changes over time, etc., the desired air-fuel ratio cannot be obtained and the surge torque shifts to the lean side, exceeding the stability limit, or shifts to the rich side. Therefore, a sufficient fuel efficiency reduction effect may not be obtained, and it is also difficult to suppress the amount of NOx generated to an appropriate level.

In addition, due to changes in internal EGR due to mechanical changes in the engine over time, the surge torque may exceed the stability limit at the desired air-fuel ratio in the initial state. The air-fuel ratio may change, and we were unable to deal with this. Note that this problem similarly occurs even when the wide-range air-fuel ratio sensor is used, as long as the air-fuel ratio is controlled to be constant.

The present invention was made in view of these conventional problems, and provides optimal lean burn control with an inexpensive configuration by performing lean burn feedback control of the air-fuel ratio based on the detection of operating conditions other than the air-fuel ratio. An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine that can continuously perform the following steps.

<Means for Solving the Problems> Therefore, as shown in FIG. 1, the present invention includes a rotational speed fluctuation level detection means for detecting the fluctuation level of the engine rotational speed;
surge torque estimating means for estimating the level of surge torque generated in the engine based on the detected level of variation in engine rotational speed; and an air-fuel mixture supplied to the engine so as to bring the estimated level of surge torque close to a stable limit level. and a lean air-fuel ratio feedback control means for feedback controlling the air-fuel ratio to lean side.

Further, the lean air-fuel ratio feedback control means may perform feedback control of the air-fuel ratio based on a value set by reconsidering the deviation between the estimated surge torque level and the stability limit level using a human sense. .

Furthermore, by stopping the operation of the acceleration/deceleration detection means for detecting acceleration/deceleration of the engine, and the rotational speed fluctuation level detection means or the lean air-fuel ratio feedback control means when acceleration/deceleration is detected, a A lean air-fuel ratio feedback control stopping means may be provided to stop feedback control of the air-fuel ratio. Also, in this product, you can turn on whether the air-fuel ratio is richer or leaner than the stoichiometric air-fuel ratio.
.

The air-fuel ratio detection means may be provided with an air-fuel ratio detection means that detects the off-state, and a stoichiometric air-fuel ratio feedback control means that feedback-controls the air-fuel ratio to the stoichiometric air-fuel ratio based on the detected value from the air-fuel ratio detection means when detecting acceleration/deceleration. .

Effect> The level of variation in engine speed, that is, the amount of change per unit time, has a deep correlation with the level of surge torque.
Therefore, based on the fluctuation level detected by the rotational speed fluctuation level detection means, the surge torque estimation means
The surge torque level can be estimated.

The lean air-fuel ratio feedback control means feedback-controls the air-fuel ratio toward the lean side so that the surge torque level estimated as described above approaches the stability limit level.

As a result, the air-fuel ratio is made lean to the point where the surge torque is maintained near the stability limit level.

Furthermore, in the lean air-fuel ratio feedback control means,
In the system, the air-fuel ratio is feedback-controlled based on a set value based on a human-like understanding of the deviation between the estimated surge torque level and the stability limit level.
Control is performed such that the air-fuel ratio is hardly changed for level deviations that are not perceivable to the human senses, and the feedback correction amount of the air-fuel ratio is increased as the level deviation becomes more noticeable.

Furthermore, it is provided with an acceleration/deceleration detection means and a lean air-fuel ratio feedback control stop means, and when the engine is decelerating, the rotation speed is stopped by stopping the operation of the rotation speed fluctuation level detection means or the lean air-fuel ratio feedback control means. By stopping feed bank control of the air-fuel ratio according to the fluctuation level, lean burn control will not be performed due to erroneously detecting rotational fluctuations during acceleration and deceleration as surges. Further, if an air-fuel ratio detection means and a stoichiometric air-fuel ratio feedback control means are added to this, and feedback control is performed to the stoichiometric air-fuel ratio during acceleration and deceleration, acceleration and deceleration performance becomes stable.

<Example> Embodiments of the present invention will be described below based on the drawings.

In FIG. 2 showing the configuration of one embodiment, an air flow meter 3 for detecting the intake air flow rate is installed in the intake passage 2 of the engine 1.
and a throttle sensor 5 that detects the opening degree of the throttle valve 4.
and is provided.

Further, the intake manifold 6 is provided with an electromagnetic fuel injection valve 7 for each cylinder, which is driven to open by an injection pulse signal from a control unit 8 containing a microcomputer, which will be described later. Fuel is injected into the intake manifold 6 and is controlled to a predetermined pressure by a pressure regulator.

Further, a water temperature sensor 10 is provided to detect the cooling water temperatures T and A in the cooling jacket 9 of the engine, and the air-fuel ratio of the intake air-fuel mixture corresponding to the oxygen concentration in the exhaust gas in the exhaust passage 11 is determined according to the theoretical value. A 0□ sensor 12 is provided as an air-fuel ratio detecting means for detecting ON/OFF whether the air-fuel ratio is on the lean side or on the lean side.

In addition, a crank angle sensor 13 outputs a unit angle signal for each minute unit crank angle in synchronization with the engine rotation, and also outputs a reference signal for each stroke crank angle period for each cylinder.
is built into the distributor or the like.

Then, the control unit 8 calculates the fuel injection amount from the fuel injection valve 7 according to the detection signals from the various sensors, and outputs an injection pulse signal having a pulse width corresponding to the amount of fuel injected from the fuel injection valve 7. Controls fuel ratio.

Below, various calculation routines for performing the air-fuel ratio control will be explained according to the flowcharts shown in FIGS. 3 to 8.

FIG. 3 shows an engine rotational speed calculation routine, in which each time the reference signal is input from the crank angle sensor 13 (for example, 4
In a cylinder internal combustion engine, the process is performed every 1/4 revolution of the engine.

In step (denoted as S in the figure) (2), the period for each reference signal input is calculated.

In step 2, the engine rotational speed N is calculated based on the calculated period using the following equation.

N-(1/reference signal period) Xi/2
Executed every m5.

In step 11, the latest data of the engine rotational speed N obtained in the routine shown in FIG.
100.150.200.30050 based on a predetermined portion of the past 20 data stored last time.
Engine rotational speed fluctuation value ΔN1)Iz(=IN-Nm
l) and store it.

In step 12, the engine rotation speed N detected this time is set to 5.
The data is updated as data from 0 m5 ec ago, and the data sampled every 5 Q msec up to 1 sec before is sequentially shifted, and the latest 20 engine rotational speed N data are always stored.

In step 13, the maximum value is detected from among the fluctuation values ΔN1Hz stored in step 11, and the maximum value is determined as maxΔN.
be memorized as . This corresponds to the fluctuation level of the engine rotational speed N.

Therefore, the routines shown in FIGS. 3 and 4 correspond to the rotational speed fluctuation level detection means.

FIG. 5 shows the routine performed in the background job (B G J ).

In step 21, based on the current engine rotational speed N and the basic fuel injection amount TP (representative of the engine load (direct), which will be described later), the target lean air-fuel ratio at all 4'1tll is Lean degree TA
Find F (-%) by searching from a map, etc.

In step 22, the surge torque STkg corresponding to the rotational speed fluctuation level maxΔN obtained in the routine of FIG.
The level of m is found by searching from a map, etc. The function of step 22 corresponds to surge torque estimating means.

In step 23, the estimated surge torque level STkgm and the surge torque stability limit level, for example, 0
．． The deviation ΔS T kg m from 0.07 kgm is calculated.

In step 24, the calculated deviation ΔSTkgm is replaced with an amount (fuzzy amount) that can be sensed by humans.

FIG. 6 shows a routine for detecting acceleration/deceleration of the engine, which is executed, for example, every 101 Ilsec.

In step 31, a throttle valve opening TVO signal is input from the throttle sensor 5.

In step 32, the human-powered throttle valve opening degree TV
The deviation between the latest value and the previous value of O, that is, the throttle valve opening change rate ΔTVO is calculated.

In step 33, the throttle valve opening change rate ΔTV
The absolute value of O is compared with a predetermined value (for example, 1°/10 m5ec), and if it exceeds the predetermined value, it is determined that acceleration/deceleration is occurring, and the process proceeds to step 34, where an acceleration/deceleration flag Ftr is set.

Next, the process proceeds to step 35, where the timer Tmacc for measuring the elapsed time after the end of acceleration/deceleration is reset.

Also, in step 33, the throttle valve opening change rate ΔTVO
When it is determined that T_macc is less than a predetermined value, the process advances to step 36 and the timer T_macc is incremented.

Next, the process proceeds to step 37, where the timer T maceO value is compared with a time set as the time until the large fluctuation level of ΔN converges after acceleration and deceleration, for example, 1 sec.
When the set time is reached, the process proceeds to step 38 and the acceleration/deceleration flag Ftr is reset.

In this way, lean burn control is stopped as described later when the acceleration/deceleration flag Ftr is set.

This routine corresponds to acceleration/deceleration detection means.

FIG. 7 shows the air-fuel ratio feed hack correction coefficient LAMBDA for variably controlling the air-fuel ratio according to the engine operating state.
This shows a routine for setting the engine speed, and is executed, for example, every revolution of the engine.

In step 41, it is determined whether the acceleration/deceleration flag Ftr is set.

In the steady operating state in which it is determined that the engine speed is not set, the process proceeds to step 42, where it is determined whether the current engine rotational speed N is within a set range, for example, 11,000 rpm to 3,000 rpm.

When it is determined that the value is within the set range, the latest data of the basic fuel injection amount T+' (injection pulse width) corresponding to the stoichiometric air-fuel ratio is within the set range (for example, 1.3 m5ec to 3.5 m5ec).
5ec).

When it is determined that the temperature is within the set range, the process proceeds to step 44, where the cooling water temperature T detected by the water temperature sensor 10 is
8 is a predetermined value, for example, 70° C. or higher, and it is determined whether or not the warm-up is completed.

If it is determined that the value is greater than or equal to the predetermined value, it is determined that the operating conditions for performing lean burn control are satisfied, and step 45
Then, the target air-fuel ratio mLAMBDA (set with the stoichiometric air-fuel ratio as 1) for lean burn control in the operating state is set using the lean degree TAF obtained in step 21 of FIG. 5 using the following equation.

mLAMBDA=1.0 + T A F1a Next, the process proceeds to step 46, where the air-fuel ratio feedback correction coefficient LAMBDA is set by the following equation using the fuzzy amount U obtained in step 24 of FIG.

1, AMBDA=mL8MBDAX (1+u/M)
However, the weighting of M is a constant.

On the other hand, if it is determined in steps 41 to 44 that the lean burn control conditions are not met, step 4
Proceed to 7, rich from 0□ sensor 12.

Enter the lean detection value.

Next, the process proceeds to step 48, where it is determined whether the conditions for feedback control to the stoichiometric air-fuel ratio using the 02 sensor 12 are satisfied. This means, for example, that the water temperature T11 is above a predetermined value (for example, 20°C), the engine rotation speed N, and the basic fuel injection amount T.
, 0□sensor 1 is in the predetermined operating range determined by
The establishment condition is when all the conditions such as the output value of No. 2 is within the normal functioning range are satisfied.

Then, if it is determined that the condition is set, step 49
Then, the output value of the 0□ sensor 12 is compared with the reference value to determine whether it is rich or lean.

When it is determined that the engine is lean, the process proceeds to step 50, and it is determined whether the rich state has just been reversed or not, depending on whether the rich/lean flag FR is set to 1-.

When it is determined that the air-fuel ratio is set, the previous state was rich and the air-fuel ratio has just changed to lean. Feedback correction coefficient LA? IBDA is updated with a value obtained by adding a predetermined proportional rich amount PR to the previous value.

If it is determined in step 50 that it has not been set, since this is the second or subsequent time after the inversion, the process proceeds to step 53, where the air-fuel ratio feedback correction coefficient LAMBDA is set by a predetermined integral rich I with respect to the previous value.

Update with the added value.

If it is determined to be rich in step 49, step 5
4, the rich/lean flag FR is determined in the same way, and immediately after the reversal to the rich state, which is not set, the process proceeds to step 55, where the rich/lean flag FR is set, and then the process proceeds to step 56, where LAMBDA is proportionally set. It is updated with a value obtained by subtracting the lean portion PL, and then proceeds to step 57, where it is updated with a value obtained by subtracting the integral lean portion.

Further, when it is determined in step 48 that the feedback control condition for the stoichiometric air-fuel ratio is not satisfied, the process proceeds to step 58 and LAMBDA is fixed at the reference value 1.0.

As a result, open-loop control is performed, and the air-fuel ratio is controlled to a value richer than the stoichiometric air-fuel ratio by various corrections to be described later.

FIG. 8 shows a fuel injection amount setting routine, for example 1
Executed every 0m5ec.

In step 61, the intake air flow rate Q signal from the air flow meter 3 is input.

In step 62, a basic fuel injection amount T corresponding to the stoichiometric air-fuel ratio is calculated based on the intake air flow rate Q and the engine rotational speed N obtained in the routine shown in FIG. 3 using the following equation.

TP-K -Q/N In step 63, various correction coefficients C according to water temperature T8, etc.
0EF and correction numerator depending on battery voltage.

Calculate.

In step 64, based on these correction amounts and the air-fuel ratio feedback correction coefficient LAMBDA obtained in FIG.
Final fuel injection amount T from the fuel injection valve 7.

(Injection pulse width) is set using the following formula.

T, =T, ・ C0EF ・ AMBT
I80T.

In lean control, when the lean burn control condition is satisfied, the surge torque estimated in step 22 of FIG. 5 based on the rotational fluctuation level of the engine rotation speed N is corrected by feedback correction of LAMBDA in step 46 of FIG. It is possible to approach the stability limit value. That is, the fifth
The functions of step 21 in the figure and steps 45 and 46 in FIG. 7, and the function of the fuel injection amount setting routine in FIG. 8 constitute a lean air-fuel ratio feedback control means.

Further, the function of stopping the air-fuel ratio feedback control toward the lean side during acceleration/deceleration based on the determination in step 41 corresponds to the lean air-fuel ratio feedback control stopping means, and the functions of steps 47 to 57 correspond to the stoichiometric air-fuel ratio feedback control means. Equivalent to.

According to such control, surge torque can be maintained in a stable state without being affected by component variations, based only on signals from normally installed sensors, without using expensive wide-range air-fuel ratio sensors. At the same time, by promoting a lean engine, fuel efficiency can be improved as much as possible, and an optimal operating state can be obtained in which the level of NOx generation can be kept low.

Furthermore, even if the desired air-fuel ratio in the initial state is no longer able to satisfy the surge torque level due to changes in the internal ECR due to mechanical changes in the engine over time, the present invention allows the air-fuel ratio itself to be set to the optimum value. Feedback control can be performed to bring the surge torque level closer to the stability limit while making appropriate corrections.

Furthermore, in this embodiment, in step 24 of FIG. 5, the deviation of the surge torque level from the stability limit level is replaced with a "fuzzy quantity" that is perceived by human senses, and this quantity is used to perform lean burn control of the air-fuel ratio. Therefore, even if there is a certain degree of deviation from the stability limit level, when it is not noticeable to humans, the air-fuel ratio is hardly corrected, and only after reaching a certain degree of deviation is the deviation large enough to be sensed. The air-fuel ratio can be modified accordingly.

Therefore, even though the surge torque level is sufficiently comfortable, the air-fuel ratio is not needlessly enriched.
Furthermore, when the surge torque increases, it is corrected in a responsive manner, so that a comfortable ride is always ensured and fuel efficiency etc. can be improved as much as possible.

Further, in this embodiment, acceleration/deceleration is detected by the routine shown in FIG. 6, lean burn control is stopped during acceleration/deceleration, and,
When special predetermined conditions with a small degree of acceleration/deceleration are met, feedback control is performed to the stoichiometric air-fuel ratio based on the signal from the 02 sensor 12, so fuel efficiency, exhaust emissions, etc. are minimized as much as possible during acceleration/deceleration. It is possible to maintain good acceleration/deceleration performance while satisfying the above requirements.

<Effects of the Invention> As explained above, according to the present invention, the configuration is such that the air-fuel ratio is feedback-controlled to the lean side so as to approach the stability limit while estimating the surge torque level, so that the configuration can be implemented at low cost. Despite this, excellent lean burn control is always performed without being affected by variations in the characteristics of parts or changes in the engine over time, etc., and it is possible to improve fuel efficiency as much as possible while maintaining a comfortable ride and NOx generation level. be.

In addition, in air-fuel ratio feedback control, the control is performed using values perceived by human senses.
This allows efficient and rational control that prioritizes ride comfort.

Furthermore, when acceleration/deceleration is detected, acceleration/deceleration performance can be stabilized by stopping the above-mentioned combustion control.
Furthermore, if feedback control is performed to the stoichiometric air-fuel ratio under predetermined acceleration/deceleration conditions, acceleration/deceleration performance can be maintained satisfactorily while satisfying fuel efficiency, exhaust emissions, etc. as much as possible during acceleration/deceleration.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of the present invention, and FIG. 2 is a block diagram showing the configuration of the present invention.
Figures 3 to 8, which are diagrams showing the configuration of an embodiment of the present invention, are flowcharts 1 showing various routines for controlling the embodiment. 1... Engine 7... Fuel injection valve 8... Control unit 12... 0□ Sensor 13.
・・Crank angle sensor

Claims (4)

[Claims] (1) A rotational speed fluctuation level detection means for detecting a fluctuation level of the engine rotational speed, a surge torque estimating means for estimating the level of surge torque generated in the engine based on the detected fluctuation level of the engine rotational speed, an internal combustion engine comprising: lean air-fuel ratio feedback control means for feedback-controlling the air-fuel ratio of the air-fuel mixture supplied to the engine toward a lean side so that the level of surge torque approaches a stable limit level; air-fuel ratio control device. (2) A claim in which the lean air-fuel ratio feedback control means performs feedback control of the air-fuel ratio based on a value set by reconsidering the deviation between the estimated surge torque level and the stability limit level using a human sense. 1. The air-fuel ratio control device for an internal combustion engine according to 1. (3) Acceleration/deceleration detection means for detecting acceleration/deceleration of the engine, and when acceleration/deceleration is detected, stopping the operation of the rotation speed fluctuation level detection means or the lean air-fuel ratio feedback control means, so as to control the rotation speed according to the rotation speed fluctuation level. 3. The air-fuel ratio control device for an internal combustion engine according to claim 1, further comprising lean air-fuel ratio feedback control stopping means for stopping feedback control of the air-fuel ratio toward the lean side. (4) Turn on whether the air-fuel ratio is richer or leaner than the stoichiometric air-fuel ratio
, comprising an air-fuel ratio detection means for detecting an OFF state, and a stoichiometric air-fuel ratio feedback control means for feedback-controlling the air-fuel ratio to the stoichiometric air-fuel ratio based on a detected value from the air-fuel ratio detection means when acceleration/deceleration is detected. Claim 3 characterized by
An air-fuel ratio control device for an internal combustion engine according to.