JPH07127505A - Air-fuel ratio controller for internal combustion engine - Google Patents

Abstract

PURPOSE:To favorably maintain air-fuel ratio feedback control accuracy by correcting a map table in which an air-fuel ratio is set according to the output value of an oxygen sensor based on the output value under the specified operational condition of the oxygen sensor. CONSTITUTION:An oxygen sensor A, 19 whose output value is varied in response to oxygen concentration in the exhaust gas of an internal combustion engine 11 is provided and an air-fuel ratio feedback control means C, 16 is provided for detecting the air-fuel ratio based on a map table B in which the air-fuel ratio of air-fuel mixture supplied to the engine 11 in response to the output value of the oxygen sensor A, 19, and making the air-fuel ratio to approach a target air-fuel ratio. Especially, a specified operational condition detection means D, 21 for detecting the specified operational condition of the engine 11 in which the output value of the oxygen sensor A, 19 becomes stable, and a set value corrective means E for correcting the set value of the map table B based on the output value of the oxygen sensor A, 19 under the specified operational condition, are provided. Consequently, air-fuel ratio flow chart control accuracy can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control system for an internal combustion engine, and more particularly to linearly detecting the air-fuel ratio corresponding to the output value of an oxygen sensor whose output value changes in response to the oxygen concentration in exhaust gas. However, the present invention relates to a technique for stabilizing the control accuracy of an apparatus that performs feedback control so that the air-fuel ratio approaches the target air-fuel ratio based on the detected value.

[0002]

2. Description of the Related Art In an internal combustion engine equipped with an electronically controlled fuel injection device, an oxygen sensor for detecting an air-fuel ratio is provided in an exhaust passage, and the air-fuel ratio is feedback-controlled on the basis of the detected air-fuel ratio under a predetermined operating condition. This is generally done (see Japanese Patent Laid-Open No. 58-10644).

In the normal air-fuel ratio feedback control, the output of the oxygen sensor is compared with the slice level, and if the output is higher than the slice level, it is detected that the air-fuel ratio is rich or lean, and the air-fuel ratio is made lean respectively. , It is controlling in the direction of enrichment. Specifically, when the air-fuel ratio is determined to be rich (lean), the proportional-fuel ratio P is first used to greatly increase the air-fuel ratio (rich), and then the integral I is used to gradually increase the air-fuel ratio to lean (rich). The fuel supply amount is controlled to increase or decrease so that

In response to such control, a normal oxygen sensor is formed so as to relatively rapidly reverse the value with the target air-fuel ratio as a boundary. However, as described above, in the control method in which only the rich / lean determination with respect to the target air-fuel ratio is performed from the output of the air-fuel ratio sensor, even if the PI control as described above is performed, the air-fuel ratio that responds well to the change in the air-fuel ratio is used. It cannot be said that fuel ratio control is being performed, and there was room for improvement in exhaust emission performance and operating performance.

Therefore, the air-fuel ratio corresponding to the changing output of the normal oxygen sensor as described above is obtained in advance, and the proportional component P and the integral component I are calculated according to the air-fuel ratio obtained from the output value.
It has been proposed to variably set the control constants such as, and perform fine feedback control in accordance with the actual air-fuel ratio to minimize the deviation of the air-fuel ratio and improve the exhaust purification performance and operation performance. .

[0006]

However, in this type of oxygen sensor, the correspondence between the output value and the air-fuel ratio may deviate due to deterioration or product variation, which reduces the air-fuel ratio feedback control accuracy. There were times when it happened. The present invention has been made in view of such conventional problems, and by always maintaining a correct relationship between the output value of the oxygen sensor and the air-fuel ratio, it is possible to maintain good air-fuel ratio feedback control accuracy. It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine.

[0007]

Therefore, the present invention is based on FIG.
As shown in, an oxygen sensor A whose output value changes in response to the oxygen concentration in the exhaust gas of the engine is provided, and the air-fuel ratio of the air-fuel mixture supplied to the engine is set in accordance with the output value of the oxygen sensor A. In the air-fuel ratio control device for an internal combustion engine, which includes an air-fuel ratio feedback control means C for detecting an air-fuel ratio based on the map table B and performing feedback control so that the air-fuel ratio approaches the target air-fuel ratio, the output of the oxygen sensor A Specific operating state means D for detecting a specific operating state of the engine whose value is stable, and set value correcting means E for correcting the set value of the map table based on the output value of the oxygen sensor A in the specific operating state. , Are provided.

[0008]

[Function] When the oxygen sensor deteriorates or product variations occur, the output value when the air-fuel ratio is stable in the rich state or lean state with respect to the target air-fuel ratio (theoretical air-fuel ratio) becomes the reference value. However, the correspondence relationship between the output value and the air-fuel ratio also deviates from the initially set characteristic.

Therefore, the specific operating state detecting means detects a specific operating state in which the operating state is stable in a rich state or a lean state, and the set value of the map table is set based on the output value of the oxygen sensor in the operating state. By correcting with the set value correction means, the correspondence relationship between the output value of the oxygen sensor and the air-fuel ratio can be kept good, and thus the air-fuel ratio feedback control accuracy can be kept good.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 2 showing the configuration of one embodiment, an air flow meter for detecting an intake air flow rate Q is provided in an intake passage 12 of an engine 11.
A throttle valve 14 that controls the intake air flow rate Q in association with 13 and the accelerator pedal is provided, and an electromagnetic fuel injection valve 15 as fuel supply means is provided for each cylinder in the downstream manifold portion.

The fuel injection valve 15 is driven to open by an injection pulse signal from a control unit 16 having a built-in microcomputer, and is fuel-fed from a fuel pump (not shown) to be injected under control to a predetermined pressure by a pressure regulator. . Further, a water temperature sensor 17 for detecting the cooling water temperature Tw in the cooling jacket of the engine 11 is provided.

On the other hand, the exhaust passage 18 is provided with an oxygen sensor 19 for detecting the air-fuel ratio of the intake air-fuel mixture by detecting the oxygen concentration in the exhaust gas at the manifold collecting portion, and the CO in the exhaust gas is provided in the exhaust pipe downstream thereof. , A three-way catalyst 20 is provided as an exhaust gas purification catalyst that purifies by oxidizing HC and reducing NO _x . The oxygen sensor 19 is, for example, a known zirconia oxygen sensor that generates an electromotive force according to the ratio of the oxygen concentration in the atmosphere as the reference gas and the oxygen concentration in the exhaust gas, and the air-fuel ratio (excess air ratio λ) On the other hand, it has a static output characteristic as shown in FIG. However, the oxygen sensor 19 is not limited to the zirconia oxygen sensor.

A crank angle sensor 21 is built in a distributor (not shown in FIG. 2), and a crank unit angle signal output from the crank angle sensor 21 in synchronization with engine rotation is counted for a certain period of time. Alternatively, the engine rotation speed N is detected by measuring the cycle of the crank reference angle signal. Next, a routine for controlling the air-fuel ratio by controlling the fuel injection amount by the control unit 16 is shown in FIG.
It will be described according to the flowchart of

In step (denoted as S in the figure) 1, the amount of intake air per unit rotation based on the intake air flow rate Q detected by the air flow meter 13 and the engine speed N calculated based on the signal from the crank angle sensor 22. The basic fuel injection amount T _P corresponding to the intake air amount is calculated by the following equation. T _P = K × Q / N (K is a constant) In step 2, various correction factors COEF are set based on the cooling water temperature Tw detected by the water temperature sensor 17.

In step 3, the output value of the oxygen sensor 19
(Voltage) _Read V _O2 . In step 4, the air-fuel ratio corresponding to the output value V _O2 is obtained by searching the map table. Here, the map table is set in a rewritable RAM as the value of the air-fuel ratio corresponding to the output value of the oxygen sensor 19, and is corrected according to the deterioration of the oxygen sensor 19 and the product variation by a routine described later. .

In step 5, the air-fuel ratio correction amount α in the air-fuel ratio feedback control is set based on the air-fuel ratio obtained in step 4. As a specific example, the case of setting the air-fuel ratio correction amount by PID control will be described. The proportional amount P set proportionally to the deviation between the obtained air-fuel ratio and the target air-fuel ratio, and the deviation obtained each time are shown. It is set by adding the integral I set proportionally to the integrated value and the differential D set proportionally to the variation of the deviation, that is, the difference between the current value and the previous value. To be done.

In step 5, the voltage correction component T _S is set based on the battery voltage value. This is for correcting the change in the injection flow rate of the fuel injection valve 15 due to the battery voltage change. In step 6, the final fuel injection amount T _I
Is calculated according to the following equation, and the calculated fuel injection amount T _I is set in the output register.

T _I = T _P × COEF × α + T _S As a result, when the predetermined fuel injection timing of engine rotation synchronization is reached, a drive pulse signal having a pulse width of the calculated fuel injection amount T _I is given to the fuel injection valve 15 And fuel injection is performed. Next, a basic characteristic change due to deterioration of the oxygen sensor will be described.

The deterioration of the oxygen sensor can be roughly classified into the following two patterns. Rich shift Due to deterioration due to high temperature and poisoning by lead (Pb),
As shown in (A), the rich output decreases and the air-fuel ratio control point shifts to the rich side. Lean shift When poisoned by silicon (Si) or phosphorus (P),
As shown in FIG. 5B, the lean output rises and the air-fuel ratio control point shifts to the lean side.

A routine according to the present invention for correcting the set value of the map table in order to cope with the characteristic change due to the deterioration of the oxygen sensor and the product variation will be described with reference to the flowchart of FIG. In step 11, it is determined whether or not the oxygen sensor 19 is activated. If it is not activated, the condition is not such that the correction can be made. Therefore, without making any correction, the values n and m, which will be described later, are reset to 0 in step 28, and this routine is terminated.
Go to 12.

In step 12, it is determined whether or not the fuel injection amount is being increased and corrected. If it is determined in step 12 that the amount is being increased, that is, if the rich control state is in effect, step
Advances to 13, Reads stores the output value V _R of the oxygen sensor 19. Here, the output value of the oxygen sensor 19 since it is rich control state (voltage) V _R is maximum.

Then, the process proceeds to step 14 and step 13
Increment the reading count n in
In step 15, it is judged whether or not the number of times n reaches a predetermined value N, and when it reaches, the process proceeds to step 16. In step 16, n is reset to 0 and the oxygen sensor in the rich control state is
Calculates a deviation [Delta] V _R between the average value V _RAV0 of the output value of n times that obtained in the same manner at 19 the average value and the V _RAV previous rich control state of the output value V _R of the n times of.

In step 17, it is judged whether or not the deviation ΔV _R has reached the set value A. Then, when the set value A is not reached, the process returns to step 11, but when the set value A is reached, the process proceeds to step 18, and the set value λ _{T (V) of} the air-fuel ratio corresponding to the output value V of the map table. Is corrected and updated with a value obtained by reducing the function f (ΔV _R ) of the deviation ΔV _R from the current value. Here, the function f (ΔV _R ) is set so as to increase in accordance with the increase of the output value V as shown in FIG. 7 (A). For example, at the same time, the function f (ΔV _R ) is proportional to the deviation ΔV _R. By setting {f (ΔV _R ) = a · ΔV _R · f ′ (V)}, it is possible to correct the characteristics in accordance with the decrease amount of the output value.

In step 19, for the next calculation, the average value V _RAV of the current output values is changed to the average value V _RAV of the previous output values.
_Set as _RAV0 . On the other hand, when it is determined in step 12 that the fuel amount is not being increased, the process proceeds to step 20, and the fuel is being cut or the secondary air is being supplied (air pump O
N), that is, whether or not it is in the lean control state.

If it is not in the lean control state, it is not a condition for correcting the map table, so this routine is ended, but if it is determined that it is in the lean control state, the routine proceeds to step 21. In step 21, the output value V _L of the oxygen sensor 19 is read and stored. Here, the output value V _L
Is the minimum because it is a lean control state.

In the same manner as in the rich control state, the number of readings m in step 21 is incremented in step 22, and the number of readings m is compared with a predetermined value M in step 23, and when M is reached, in step 24. the m calculates a deviation [Delta] V _L between the current m times the mean value V _LAV and the last average value V _Lavo output value V _L with reset to zero, the deviation Δ in step 25
The V _L is compared with a set value B, step when the [Delta] V _L ≧ B
25 by the setting value of the air-fuel ratio corresponding to the output value V of the map table lambda _{T (V) is} the current value deviation [Delta] V _L of the function g (delta
_VL ) is added and corrected and updated. Here, the function g (ΔV _L ) is set so as to increase in accordance with the decrease of the output value V as shown in FIG. 7 (B). For example, at the same time, the function g (ΔV _L ) is proportional to the deviation ΔV _L. set {g (ΔV _L)
= BΔV _L g '(V)}, it is possible to correct the characteristics to match the decrease amount of the output value. In step 26, the current average value V _LAV is set to the average value V _{LAV0 of the} previous output values.
Set as.

In this way, when the output characteristic of the oxygen sensor 19 deviates from the reference characteristic due to deterioration or product variation, the maximum output in the rich control state and the minimum output in the lean control state are compared with the reference value. Since the set value of the map table that sets the air-fuel ratio for the output value is modified according to the size of the deviation, the air-fuel ratio can always be detected accurately, and the air-fuel ratio can be set to the target air-fuel ratio. Feedback control with high accuracy,
Exhaust gas purification performance _and operation performance can be maintained as good as possible.

The present invention is originally applicable to an oxygen sensor of the type that detects rich / lean with respect to the target air-fuel ratio, but is formed so that the slope of the output value with respect to the air-fuel ratio becomes smoother. Of course, it can be applied to the type, and the same sensor element is used,
Oxygen is transported from the exhaust gas through the sensor element so that the sensor element is energized so that the oxygen concentration in a predetermined chamber becomes the reference value, and the air-fuel ratio is linearly calculated from the current value (limit current) at that time. It is also applicable to a so-called wide area type air-fuel ratio sensor required for. In this case, the current value in the rich control state or the lean control state changes according to the deterioration of the sensor or the product variation.Therefore, the map table of the air-fuel ratio set corresponding to the current value according to the change amount. Should be corrected.

[0029]

As described above, according to the present invention, the map table in which the air-fuel ratio is set for the output value of the oxygen sensor is modified based on the output value of the oxygen sensor in a specific operating state. Therefore, even if the output value and the air-fuel ratio are misaligned due to deterioration or product variation, the output value and the air-fuel ratio can be corrected as appropriate, so feedback control to a target air-fuel ratio that is always good can be performed, and exhaust purification performance _and operating performance can be maximized. Can be maintained in good condition.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration and functions of the present invention.

FIG. 2 is a diagram showing the configuration of an embodiment of the present invention.

FIG. 3 is a diagram showing the output characteristics of the oxygen sensor used in the above-mentioned embodiment.

FIG. 4 is a flowchart showing an air-fuel ratio control routine of the above embodiment.

FIG. 5 is a diagram showing characteristic changes due to deterioration of the oxygen sensor.

FIG. 6 is a flowchart showing a map table correction routine of the above embodiment.

FIG. 7 is a diagram showing correction of the map table at the time of rich shift and at the time of lean shift in the same embodiment.

[Explanation of symbols]

 11 Internal combustion engine 13 Air flow meter 15 Fuel injection valve 16 Control unit 19 Oxygen sensor 21 Crank angle sensor

Claims (1)

[Claims] 1. A map provided with an oxygen sensor whose output value changes in response to the oxygen concentration in the exhaust gas of the engine, and in which the air-fuel ratio of the air-fuel mixture supplied to the engine is set corresponding to the output value of the oxygen sensor. In an air-fuel ratio control device for an internal combustion engine, which detects an air-fuel ratio based on a table, and performs feedback control so that the air-fuel ratio approaches the target air-fuel ratio, an engine in which the output value of the oxygen sensor is stable A specific operating state means for detecting a specific operating state of the internal combustion engine, and a set value correcting means for correcting the set value of the map table based on the output value of the oxygen sensor in the specific operating state. Air-fuel ratio control system for engines.