JP3596011B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an air-fuel ratio control device for an internal combustion engine, and in particular, linearly detects an air-fuel ratio corresponding to an output value of an oxygen sensor whose output value changes in response to the oxygen concentration in exhaust gas, and based on the detected value. The present invention relates to a technique for stabilizing the control accuracy of a device that performs feedback control so that the air-fuel ratio approaches a target air-fuel ratio.
[0002]
[Prior art]
In an internal combustion engine equipped with an electronic control fuel injection device, it is common to provide an oxygen sensor for detecting an air-fuel ratio in an exhaust passage, and to feedback-control the air-fuel ratio based on the detected air-fuel ratio under predetermined operating conditions. (See JP-A-58-10644).
[0003]
In normal air-fuel ratio feedback control, the output of the oxygen sensor is compared with the slice level. If the output is higher than the slice level, the air-fuel ratio is detected to be rich and lean when the output is lower than the slice level, and the air-fuel ratio is made lean and rich, respectively. The direction is controlled. Specifically, when the air-fuel ratio is determined to be rich (lean), the air-fuel ratio is first made large (rich) by the proportional component P or the like, and then gradually increased by the integral component I or the like. The amount of fuel supply is controlled to increase or decrease.
[0004]
In response to such control, a normal oxygen sensor is formed so as to relatively rapidly reverse its value from the target air-fuel ratio.
However, in the above-described control method in which only the rich / lean determination with respect to the target air-fuel ratio is performed based on the output of the air-fuel ratio sensor, even if the PI control as described above is performed, the air that can cope with the change in the air-fuel ratio well. It could not be said that fuel ratio control was performed, and there was room for improvement in exhaust emission performance and driving performance.
[0005]
Therefore, the air-fuel ratio corresponding to the output that changes in the ordinary oxygen sensor as described above is obtained in advance, and the control constants such as the proportional component P and the integral component I are varied according to the air-fuel ratio obtained from the output value. It has been proposed that the deviation of the air-fuel ratio be reduced as much as possible to further improve the exhaust gas purification performance and the driving performance by performing fine-grained feedback control corresponding to the actual air-fuel ratio.
[0006]
[Problems to be solved by the invention]
However, in this type of oxygen sensor, the correspondence between the output value and the air-fuel ratio may be deviated due to deterioration or product variation, and the accuracy of the air-fuel ratio feedback control may be reduced.
The present invention has been made in view of such a conventional problem, and maintains the correspondence between the output value of the oxygen sensor and the air-fuel ratio in a correct relationship at all times, so that the air-fuel ratio feedback control accuracy can be maintained satisfactorily. It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine, which is described above.
[0007]
[Means for Solving the Problems]
Therefore, the present invention, as shown in FIG.
An oxygen sensor A whose output value changes in response to the oxygen concentration in the exhaust gas of the engine is provided. A map table B in which 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 An air-fuel ratio control device for an internal combustion engine including an air-fuel ratio feedback control unit C that detects an air-fuel ratio based on the air-fuel ratio and performs feedback control so that the air-fuel ratio approaches the target air-fuel ratio.
A specific operating state means D for detecting a specific operating state of the engine in which the output value of the oxygen sensor A is stable;
In the rich control state, the set value of the map table is decreased and corrected based on the output value of the oxygen sensor in the rich control state so that the decreasing value gradually increases on the side where the output value is large. At the time , there is provided a set value correcting means E for increasing and correcting the output value based on the output value of the oxygen sensor in the lean control state so that the output value increases gradually on the smaller side .
Is provided.
[0008]
[Action]
If the oxygen sensor is deteriorated or product variation occurs, the output value when the air-fuel ratio is stable in the rich or lean state with respect to the target air-fuel ratio (stoichiometric air-fuel ratio) will deviate from the reference value. Accordingly, the correspondence between the output value and the air-fuel ratio also deviates from the initially set characteristics.
[0009]
Therefore, the specific operation state detecting means detects a specific operation state in which the operation state is stabilized in the rich state or the lean state, and corrects the set value of the map table based on the output value of the oxygen sensor in the operation state. The correction by the means can maintain the correspondence between the output value of the oxygen sensor and the air-fuel ratio well, and thus can maintain the air-fuel ratio feedback control accuracy well.
[0010]
【Example】
An embodiment of the present invention will be described below with reference to the drawings.
In FIG. 2 showing a configuration of one embodiment, an intake passage 12 of an engine 11 is provided with an air flow meter 13 for detecting an intake air flow rate Q and a throttle valve 14 for controlling the intake air flow rate Q in conjunction with an accelerator pedal. An electromagnetic fuel injection valve 15 as fuel supply means is provided for each cylinder in the downstream manifold portion.
[0011]
The fuel injection valve 15 is driven to open by an injection pulse signal from a control unit 16 containing a microcomputer, and injects fuel supplied from a fuel pump (not shown) under pressure and controlled to a predetermined pressure by a pressure regulator. Further, a water temperature sensor 17 for detecting a cooling water temperature Tw in the cooling jacket of the engine 11 is provided.
[0012]
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 gathering portion. the three-way catalyst 20 as an exhaust gas purifying catalyst for purifying performing the reduction of oxidation and NO _X are provided. 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 to the oxygen concentration in the exhaust gas, and has an 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.
[0013]
A distributor (not shown in FIG. 2) has a built-in crank angle sensor 21 that counts a crank unit angle signal output from the crank angle sensor 21 in synchronization with the engine rotation for a certain period of time. The cycle of the reference angle signal is measured to detect the engine speed N.
Next, a routine for controlling the air-fuel ratio by controlling the fuel injection amount by the control unit 16 will be described with reference to the flowchart of FIG.
[0014]
In step (denoted by S in the figure) 1, the amount of intake air per unit rotation is determined based on the intake air flow rate Q detected by the air flow meter 13 and the engine speed N calculated based on a signal from the crank angle sensor 22. the basic fuel injection quantity T _P corresponding to operation by the following equation.
T _P = K × Q / N (K is a constant)
In step 2, various correction coefficients COEF are set based on the coolant temperature Tw and the like detected by the coolant temperature sensor 17.
[0015]
In step 3, the output value (voltage) _V02 of the oxygen sensor 19 is read.
In step 4, the air-fuel ratio corresponding to the output value _VO2 is obtained by searching the map table. Here, the map table is set in the 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. .
[0016]
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 where the air-fuel ratio correction amount is set by PID control will be described. The proportional component 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 described below. Set by adding an integral I set proportionally to the integrated value and a differential D set proportional to the amount of change in deviation, that is, the difference between the present value and the previous value. Is done.
[0017]
In step 5, a voltage correction amount T _S is set based on the battery voltage value. This is for correcting a change in the injection flow rate of the fuel injection valve 15 due to a change in the battery voltage.
In step 6, the final fuel injection amount T _I calculated according to the following equation, is set in the output register of the fuel injection amount T _I which is said computed.
[0018]
T _I = T _P × COEF × α + T _S
Consequently, when a fuel injection timing of a predetermined engine rotation synchronization, fuel injection is performed a drive pulse signal having a pulse width of the calculated fuel injection amount T _I is given to the fuel injection valve 15.
Next, a basic characteristic change due to deterioration of the oxygen sensor will be described.
[0019]
Deterioration of the oxygen sensor can be roughly classified into the following two patterns.
{Circle around (1)} Rich shift Due to deterioration due to high temperature and poisoning with lead (Pb), the rich output decreases as shown in FIG. 5A, and the air-fuel ratio control point shifts to the rich side.
(2) Lean shift When poisoned by silicon (Si) or phosphorus (P), the lean output increases as shown in FIG. 5B, and the control point of the air-fuel ratio shifts to the lean side.
[0020]
A routine according to the present invention for correcting the set values 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, it is not a condition that can be modified, so that the routine is terminated after resetting the values n and m described later in step 28 without modification, and if it is activated, go to step 12 if activated. move on.
[0021]
In step 12, it is determined whether or not the fuel injection amount is being increased.
Step 12 is under increasing correction, that is, if it is determined that the rich control state, the routine advances to a step 13, to read store the output value V _R of the oxygen sensor 19. Here, the output value (voltage) V _R of the oxygen sensor 19 is maximum because of the rich control state.
[0022]
Next, the routine proceeds to step 14, in which the number of readings n in the step 13 is incremented. In step 15, it is determined whether or not the number n has reached a predetermined value N.
In step 16, the n with reset to zero, similarly to the obtained n times the output in the average value and the V _RAV previous rich control state of the output value V _R of the n times of the oxygen sensor 19 in the rich control state It calculates a deviation [Delta] V _R between the average value _{V RAV0} value.
[0023]
In step 17, it is determined whether the deviation [Delta] V _R reaches the set value A.
When the set value A has not been reached, the process returns to step 11, but when the set value A has been reached, the process proceeds to step 18, where the set value λ _{T (V) of} the air-fuel ratio corresponding to the output value V of the map table is used. the modifying updated with the value obtained by reducing the function f ([Delta] V _R) of the deviation [Delta] V _R from the current value. Here, the function f ([Delta] V _R) is set to increasing in accordance with increase of the output value V as shown in FIG. 7 (A), for example, proportionally with respect to time deviation [Delta] V _R set to _{{f (ΔV R) = a} · ΔV R · f '(V)} by can be modified to the characteristic commensurate with the amount of decrease in the output value.
[0024]
In step 19, for the next calculation, the average value V _RAV of the current output value is set as the average value V _RAV0 of the previous output value.
On the other hand, if it is determined in step 12 that the fuel is not being increased, the process proceeds to step 20, in which it is determined whether the fuel is being cut or the secondary air is being supplied (the air pump is ON), that is, whether or not the lean control is being performed.
[0025]
When the vehicle is not in the lean control state, the routine is terminated because there is no condition for correcting the map table. However, when it is determined that the vehicle is in the lean control state, the process proceeds to step 21.
In step 21, the output value _VL of the oxygen sensor 19 is read and stored. Here, the output value _VL is minimum because it is in the lean control state.
[0026]
Thereafter, in the same manner as in the case of 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. At the same time as resetting, a deviation ΔV _L between the average value V _{LAV of the} current m output values _VL and the previous average value V _LAVO is calculated, and in step 25, the deviation ΔV _L is compared with the set value B, and ΔV _L ≧ the deviation [Delta] V _L to the function g ([Delta] V _L) by a value obtained by adding a correction update setting value of the air-fuel ratio corresponding to the output value V of the map table in step 25 lambda _{T (V) is} the current value when the B . Here, the function g ([Delta] V _L) is set to increasing in response to a decrease of the output value V as shown in FIG. 7 (B), for example, proportionally with respect to time deviation [Delta] V _L By setting {g (ΔV _L ) = b · ΔV _L · g ′ (V)}, the characteristic can be corrected to a value corresponding to the amount of decrease in the output value. In step 26, the current average value V _LAV is set as the average value V _LAV0 of the previous output value.
[0027]
As described above, when the output characteristics of the oxygen sensor 19 deviate from the reference characteristics due to deterioration or product variation, the deviation of the maximum output in the rich control state or the minimum output in the lean control state from the reference value becomes large. Since the set value of the map table in which the air-fuel ratio is set for the output value is corrected according to the air-fuel ratio, the air-fuel ratio can always be detected with high accuracy, and the air-fuel ratio can be accurately adjusted to the target air-fuel ratio. Feedback control can be performed, and exhaust purification performance _and operation performance can be maintained as good as possible.
[0028]
Note that the present invention can be applied to an oxygen sensor of a type that originally detects rich / lean with respect to a target air-fuel ratio, but a type formed so that the slope of the output value with respect to the air-fuel ratio becomes smoother. Needless to say, the same sensor element is used, but oxygen is supplied from the exhaust gas through the sensor element so that the sensor element is energized and the oxygen concentration in a predetermined empty room is set to a reference value. Can be applied to a so-called wide-range air-fuel ratio sensor that linearly determines the air-fuel ratio from the current value (limit current) at that time. 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, a map table of the air-fuel ratio set corresponding to the current value according to the change amount. Should be corrected.
[0029]
【The invention's effect】
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 in the rich control state or the lean control state of the oxygen sensor. Even if the correspondence between the output value and the air-fuel ratio is deviated due to deterioration or product variation, the output value and the air-fuel ratio are corrected appropriately, so feedback control to a good target air-fuel ratio can be performed at all times, and exhaust purification performance and operation performance can be improved as much as possible. Can be maintained well.
[Brief description of the drawings]
FIG. 1 is a block diagram showing the configuration and functions of the present invention.
FIG. 2 is a diagram showing a configuration of one embodiment of the present invention.
FIG. 3 is a diagram showing output characteristics of the oxygen sensor used in the embodiment.
FIG. 4 is a flowchart showing an air-fuel ratio control routine of the embodiment.
FIG. 5 is a diagram showing a characteristic change due to deterioration of an oxygen sensor.
FIG. 6 is a flowchart showing a map table correction routine of the embodiment.
FIG. 7 is a diagram showing correction of a map table during a rich shift and a lean shift in the 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)

An oxygen sensor whose output value changes in response to the oxygen concentration in the exhaust gas of the engine is provided. Based on a map table in which 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. In an air-fuel ratio control device for an internal combustion engine having an air-fuel ratio feedback control unit that detects a fuel ratio and performs feedback control so that the air-fuel ratio approaches the target air-fuel ratio,
A specific operation state detection unit that detects a rich control state or a lean control state of the engine in which the output value of the oxygen sensor is stable;
In the rich control state, the set value of the map table is decreased and corrected based on the output value of the oxygen sensor in the rich control state so that the decreasing value gradually increases on the side where the output value is large. An air-fuel ratio of the internal combustion engine, wherein a set value correction means for increasing and increasing the increase value sequentially on the side where the output value is smaller is provided based on the output value of the oxygen sensor in the lean control state. Control device.

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