JP2006002685A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain accuracy of air-fuel ratio feed back control by correcting slippage of output characteristics of an air-fuel ratio sensor. <P>SOLUTION: In an air-fuel ratio control device 2 for an internal combustion engine provided with an exhaust gas sensor 9 sensing of which output value changes with sensing component of exhaust gas of an engine 1 and changing output value and an air-fuel ratio feed back control means 2 determining air-fuel ratio of air-fuel mixture supplied to the engine 1 with corresponding to output value of the exhaust gas sensor 9 and performing feed back control to make the air-fuel ratio close to target one, an air-fuel ratio changing means 2 changing air-fuel ratio by changing fuel injection quantity at a predetermined increase decrease width and a predetermined changing cycle during engine operation and an exhaust gas sensor output voltage collection means 2 correcting exhaust gas sensor output voltage corresponding to theoretical air-fuel ratio based on output voltage displacement of the exhaust gas sensor 9 while the ratio is changing are provided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to air-fuel ratio control of an internal combustion engine, and more particularly to a technique for maintaining the accuracy of air-fuel ratio feedback control.

  2. Description of the Related Art An internal combustion engine equipped with an electronically controlled fuel injection device is known that includes an oxygen concentration sensor that detects an oxygen concentration in an exhaust passage, and feedback-controls the air-fuel ratio based on the detected oxygen concentration.

Patent Document 1 discloses an air-fuel ratio characteristic map table corresponding to the oxygen sensor output when the output characteristic of the oxygen sensor is shifted to rich / lean due to deterioration or the like, and a function of rich / lean output deviation from the original value. A technique for correcting by subtraction / addition is disclosed.
Japanese Patent Laid-Open No. 7-127505

  However, in the technique described in Patent Document 1, the characteristic map table is corrected only in the lean state or the rich state where the output value of the oxygen sensor is stable, and thus the characteristic deviation in the vicinity of the stoichiometry cannot be corrected.

  Accordingly, an object of the present invention is to make it possible to accurately correct a characteristic deviation in the vicinity of the stoichiometric oxygen sensor.

  An air-fuel ratio control apparatus for an internal combustion engine according to the present invention includes an exhaust sensor whose output value changes in response to a component of the exhaust gas of the engine, and an air-fuel ratio supplied to the engine corresponding to the output value of the exhaust sensor. In an air-fuel ratio control apparatus for an internal combustion engine having an air-fuel ratio feedback control means for obtaining an air-fuel ratio and performing feedback control so that the air-fuel ratio approaches a target air-fuel ratio, the fuel injection amount is increased by a predetermined increase / decrease range during engine operation. And an exhaust gas sensor output voltage corresponding to the stoichiometric air fuel ratio based on the displacement of the output voltage of the exhaust sensor while the air fuel ratio is fluctuating. And an exhaust sensor output voltage correction means for correcting.

  According to the present invention, the air-fuel ratio is changed by increasing or decreasing the fuel injection amount, and the output voltage correction is performed using the fluctuation range of the output voltage of the exhaust sensor detected at this time. A highly accurate correction can be performed, whereby the accuracy of the air-fuel ratio feedback control can be maintained well, and the purification performance of the catalyst can be ensured.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  Reference numeral 1 denotes an engine, 3 denotes an intake passage for supplying air to the engine 1, and 5 denotes an exhaust passage for discharging exhaust of the engine 1.

  The intake passage 3 is provided with an air flow meter (hereinafter referred to as AFM) 10 for measuring the amount of intake air and an atmospheric pressure sensor 8 for detecting the pressure of the intake air, and downstream thereof in conjunction with an accelerator pedal (not shown). A throttle valve 4 for adjusting the amount of intake air is provided. A fuel injection valve 7 that injects fuel into the intake port 11 is installed in the intake port 11 downstream of the intake passage 3.

  In the exhaust passage 5, an air-fuel ratio sensor 9 serving as an exhaust sensor for detecting the air-fuel ratio of the intake air-fuel mixture by detecting the oxygen concentration in the exhaust, and oxidation of CO and HC in the exhaust and reduction of NOx are performed. A three-way catalyst 6 is provided that goes and purifies.

  The output values of the AFM 10, the atmospheric pressure sensor 8, the air-fuel ratio sensor 9 and the accelerator opening sensor (not shown) are sent to an engine control unit (hereinafter referred to as ECU) 2 as air-fuel ratio fluctuation means and exhaust sensor output voltage correction means. Based on these values, the ECU 2 controls the opening of the throttle valve 4, the fuel injection amount, and the like.

  The fuel injection amount is controlled according to the required torque determined from the accelerator opening, the engine speed, etc. At this time, the ECU 2 outputs the output value of the air-fuel ratio sensor 9 so that the air-fuel ratio becomes the stoichiometric air-fuel ratio (stoichiometric). Based on the feedback control. In some cases, the engine is controlled to be richer than stoichiometric during high-load operation such as during acceleration, and leaner than stoichiometric during low-load driving.

  Here, the air-fuel ratio sensor 9 used in the present embodiment will be described.

  The air-fuel ratio sensor 9 generates an electromotive force according to the oxygen concentration in the exhaust gas, and this electromotive force has a characteristic as shown in FIG. 2A with respect to the air-fuel ratio (excess air ratio). .

  2A, the horizontal axis represents the air-fuel ratio (excess air ratio) and the vertical axis represents the sensor output (mV). As shown in the output voltage-actual air-fuel ratio conversion table of FIG. SETABF (n) has a one-to-one correspondence with the output voltage AFSOUT (n). In FIG. 2A, the output voltage at the time of stoichiometry is AFSOUT6, and the actual air-fuel ratio is SETABF6.

  The output of the air-fuel ratio sensor 9 has a characteristic that it increases as the air-fuel ratio becomes leaner than stoichiometric (SETABF6) and decreases as it becomes richer. In addition, the slope of the output characteristic is different between the rich side and the lean side starting from the stoichiometry.

  By the way, the output characteristics of the air-fuel ratio sensor 9 may change due to deterioration, individual differences, circuit variations, variations due to environmental changes, etc., and there may be a deviation in the correspondence relationship between the air-fuel ratio and sensor output described above. The accuracy of control may be deteriorated.

  As a form of change of the output characteristics, although the sensor output at the time of stoichiometry does not change, the gain change that changes the slope of the output characteristics (FIG. 13A), the slope of the output characteristics does not change, but the sensor output at the time of stoichiometry is There is a shift change that shifts (FIG. 13B), and a gain + shift change (FIG. 13C) in which both the slope of the output characteristic and the sensor output at the time of stoichiometry shift.

  Therefore, in the present embodiment, the accuracy of the air-fuel ratio feedback control is maintained by correcting the output voltage of the air-fuel ratio sensor 9.

  Next, a method for correcting the output voltage will be described with reference to the flowchart of FIG.

  FIG. 3 is a flowchart of the control executed by the ECU 2 for correcting the output of the air-fuel ratio sensor 9 and is performed at least once from the engine start to the stop.

  Hereinafter, it demonstrates according to each step of a flowchart.

  In step S1, it is determined whether or not the air-fuel ratio sensor 9 is activated. The determination is made based on, for example, whether a predetermined time has elapsed since the engine was started, whether the sensor output voltage has become a predetermined value or more, and the like.

  When the determination is no, that is, when the air-fuel ratio sensor 9 is not activated, the output voltage of the air-fuel ratio sensor 9 does not become a value corresponding to the air-fuel ratio and is not in a state where correction can be performed, so that it is activated. Wait until.

  If the determination is yes, the process proceeds to step S2, and air-fuel ratio feedback control is started based on the output voltage of the air-fuel ratio sensor 9 using the output characteristic table of FIG.

  Subsequently, in step S3, the fuel injection amount is alternately increased or decreased by a predetermined amount from the lean side to the rich side in a predetermined cycle with the injection amount at the time of stoichiometry as a reference, and the air-fuel ratio is changed actively.

  The fluctuation range of the fuel injection amount at this time is called a fuel injection amount fluctuation range, and the switching cycle in the increase / decrease direction is called a drive cycle.

  Here, the predetermined fuel injection amount fluctuation range and the drive cycle will be described with reference to FIG.

  FIG. 4 is a time chart showing changes in the fuel injection rate based on stoichiometry and changes in the output voltage of the air-fuel ratio sensor 9 based on the output voltage (standard stoichiometric voltage) during stoichiometry.

  As shown in FIG. 4, the fuel injection amount is increased and decreased by a certain amount with a fixed period based on the stoichiometry.

  The fluctuation range of the fuel injection amount means the fluctuation range of the fuel injection amount at this time. The increase or decrease is performed, for example, by changing the injection rate of the fuel injection valve by changing the pulse width for energizing the fuel injection valve.

  Specifically, the fluctuation range of the fuel injection amount is, for example, suppressed to about ± 3% on the basis of stoichiometry during low load operation and to about 6% even during high load operation. This prevents the occurrence of torque change due to air-fuel ratio fluctuations.

  Further, by changing the fuel injection amount, the air-fuel ratio changes from the lean side to the rich side, so the output of the air-fuel ratio sensor 9 also changes from the lean side to the rich side.

  Since the fluctuation range of the fuel injection amount is constant, theoretically, the fluctuation range of the output voltage of the air-fuel ratio sensor 9 is also a constant value. However, in reality, the variation in the system system and the gas exchange in the air-fuel ratio sensor 9 are changed. Due to factors such as sex, some variation occurs as shown in the figure.

  The driving cycle refers to the increase / decrease switching cycle of the fuel injection amount, for example, about 1 Hz. The number of times of switching between increasing / decreasing is called the number of driving times.

  Returning to the flowchart of FIG. In step S4, it is detected whether or not the number of times of driving is equal to or greater than the predetermined number of times. The predetermined number of times is, for example, 10 inversion.

  In step S5, the oxygen sensor 8 output voltage ABFOUTVn (n: number of times of driving) during the number of times of driving is read.

  In step S6, based on the air-fuel ratio sensor 9 output voltage ABFOUTVn read in the above, the difference ΔAFSOUT between the stoichiometric voltage obtained from the measured value from the following equation (1) and the standard stoichiometric voltage (AFSOUT6 in FIG. 2) is calculated. .

ΔAFSOUT = [{(ABFOUTV1 × α + ABFOUTV2 × β) −AFSOUT6} + (ABFOUTV3 × α + ABFOUTV4 × β) −AFSOUT6] +... (ABFOUTVn × α + ABFOUTV (n + 1) × β) −AFSOUT6} / number of inversions (1) )
However,
α: Output correction coefficient from stoichiometric to lean side (AFSOUT6 to AFSOUT16 in FIG. 2) β: Output correction coefficient from stoichiometric to rich side (AFSOUT1 to AFSOUT6 in FIG. 2) Output correction coefficients α and β are specific to the oxygen sensor 8 to be used. It is a numerical value and is obtained in advance through experiments or the like.

  In step S7, the corrected standard stoichiometric voltage is corrected from the following equation (2) using ΔAFSOUT calculated by the equation (1).

Standard stoichiometric voltage after correction = AFSOUT6 + ΔAFSOUT (2)
Then, using the corrected standard stoichiometric voltage set as described above as a reference, the lean side (AFSOUT6 to AFSOUT16 in FIG. 2) and the rich side (AFSOUT1 to AFSOUT6 in FIG. 2) are used using the output correction coefficients α and β. Correct the output characteristics.

  Even when the output characteristics of the air-fuel ratio sensor 9 change due to deterioration or the like by the above control, the output voltage at the time of stoichiometry is corrected, and the output characteristics on the rich side and lean side are also corrected using the output correction coefficients α and β. It can be corrected.

  As described above, in the present embodiment, even when the output characteristic of the air-fuel ratio sensor 9 changes due to deterioration or the like and the output voltage at the time of stoichiometry shifts, the air-fuel ratio is changed richly and leanly and the detected actual The output voltage at the time of stoichiometry is corrected based on the output voltage, and the output characteristics on the rich side and the lean side are also corrected based on the corrected output voltage at the time of stoichiometry, so that air-fuel ratio feedback control can be executed with high accuracy. This makes it possible to maximize the purification performance of the catalyst.

  A second embodiment will be described.

  In the present embodiment, the air-fuel ratio is actively changed as in the first embodiment, and the output voltage at the time of stoichiometry is corrected based on the displacement of the output voltage of the air-fuel ratio sensor 9 at this time. However, in the first embodiment, the fuel injection amount and the driving cycle are constant, but in the present embodiment, the fuel injection amount and the driving cycle are changed according to the operating state. The operating state is determined, for example, by detecting the intake air amount.

  FIG. 5 is a flowchart of control executed by the ECU 2 in the present embodiment.

  Steps S21 and S22 are the same as steps S1 and S2 in FIG.

  In step S23, the detected intake air amount is compared with the intake air amount at the previous correction, and when the detected intake air amount is smaller than the intake air amount at the previous correction, the intake air amount is larger than at the previous correction. Wait until it becomes.

  If it has increased from the time of the previous correction, the process proceeds to step S24, and the air-fuel ratio is actively changed at the fuel injection amount corresponding to the intake air amount and the drive cycle.

  As shown in the table of FIG. 14, the relationship between the intake air amount, the fuel injection rate, and the drive cycle corresponds to the fuel injection amount AFBAND (n) and the drive cycle DRCYCLE (n) with respect to the intake air amount QAVALUE (n). is doing.

  Thereafter, steps S25 to S28 perform the same control as steps S3 to S7 in FIG.

  Here, the reason why the correction is not performed when the intake air amount at the previous correction is smaller in step S23 will be described.

  When the amount of intake air is small, for example during idle operation, if the fuel injection amount is increased or decreased, there is a concern that the drivability deteriorates, such as the generation of a torque step due to the fluctuation of the air-fuel ratio. Therefore, in order not to deteriorate the drivability, the increase / decrease width of the fuel injection amount cannot be increased, and the drive cycle cannot be shortened.

  On the other hand, during high load operation with a large amount of intake air, the torque fluctuation due to fluctuations in the air-fuel ratio has less influence on the drivability than in the idle state. Therefore, it is possible to increase the increase / decrease range of the fuel injection amount, increase the fluctuation of the air-fuel ratio, and shorten the drive cycle.

  In order to correct the output voltage of the air-fuel ratio sensor 9, it is possible to perform accurate correction when the fluctuation range of the output voltage is large. Therefore, it is desirable that the amount of intake air is large as a condition for performing correction. .

  Therefore, in step S23, the intake air amount at this time and the previous correction are compared, and it is determined whether correction with higher accuracy than the previous correction can be performed.

  As described above, in the present embodiment, a condition under which more accurate correction can be performed is detected, and the air-fuel ratio is actively changed by changing the fuel injection amount and the driving cycle according to the engine state. Since the output voltage is corrected based on the actual output voltage of the air-fuel ratio sensor 9, even when the output characteristics of the air-fuel ratio sensor 9 change due to deterioration or the like, the output voltage at the time of stoichiometry is corrected, and further after the correction Since the rich side and lean side output characteristics are also corrected based on the output voltage at the time of stoichiometry, air-fuel ratio feedback control can be executed with high accuracy, and the purification performance of the catalyst can be maximized.

  A third embodiment will be described with reference to FIGS.

  FIG. 6 is a control flowchart for correcting the output voltage of the air-fuel ratio sensor 9 executed by the ECU 2 in the present embodiment. After correcting the output voltage at the time of stoichiometry, further correcting the maximum output voltage and the minimum output voltage. Also do. Hereinafter, it demonstrates according to each step.

  Steps S31 to S38 are the same as steps S21 to S28 in FIG.

  In step S39, it is determined whether or not the atmosphere is currently lean.

  For example, if the accelerator is turned off during traveling and the fuel is cut, the determination method determines that the atmosphere is lean.

  If it is not a lean atmosphere, it waits until a lean atmosphere is reached. If the lean atmosphere is reached, the process proceeds to step S40, and the output voltage in the lean atmosphere is read.

  At this time, since the fuel is cut, the air-fuel ratio becomes the leanest side, and the air-fuel ratio sensor 9 shows the maximum output voltage (AFSOUTMA).

  In step S41, an atmospheric pressure correction value, which is a correction value for variations in atmospheric pressure (oxygen partial pressure), is calculated. Specifically, as shown in FIG. 7, the search is performed by detecting the atmospheric pressure at which the table in which the output correction value (LEVHOSA) is assigned for each atmospheric pressure (ATOMSP) is detected.

  In step S42, an element temperature correction value, which is a correction value for the element temperature variation of the air-fuel ratio sensor 9, is performed. Specifically, as shown in FIG. 8, a table in which an output correction value (LEVHOSR) is assigned for each internal resistance (ELIMPED) of the element is searched by the internal resistance of the detected element. Here, the internal resistance is used because it is possible to estimate the element temperature without providing a sensor or the like for detecting the element temperature by utilizing the fact that the element temperature is proportional to the internal resistance. is there. Note that either step S41 or S42 may be performed first.

  In step S43, first, the corrected lean-side maximum output voltage AFSOUT16H is calculated by the following equation (2) using the correction value calculated above.

AFSOUT16H = AFSOUTMA + LEVHOSR (n) + LEVHOSA (n) (2)
Then, as shown in FIG. 9, the corrected lean maximum output voltage AFSOUT16H becomes the lean maximum output voltage AFSOUT16 in the output characteristic diagram calculated based on the corrected stoichiometric output voltage obtained in step S38. Make corrections. FIG. 9 is an output characteristic diagram calculated using the output correction coefficient α with the corrected stoichiometric output voltage as a starting point, and the corrected lean-side maximum output voltage AFSOUT16H is corrected to be AFSOUT16 on the output characteristic diagram. To do. As a result, the maximum output voltage is corrected.

  Next, in step S44, it is determined whether or not the current atmosphere is a stable rich atmosphere.

  Specifically, the determination is made based on whether or not the fuel increase is being performed, such as during high-load operation such as acceleration or when recovering from a fuel cut.

  If it is not a rich atmosphere, the process proceeds to step S45 until the rich atmosphere is reached.

  In step S45, the rich atmosphere, that is, the minimum output voltage AFSOUTMI during the fuel increase is read.

  In steps S46 and S47, similarly to steps S41 and S42, the atmospheric pressure correction value REVHOSA and the element temperature correction value REVHOSR are obtained using the atmospheric pressure correction table in FIG. 10 and the element temperature correction table in FIG. 11, and are corrected in step S48. The rear rich side minimum output voltage AFSOUT1H is obtained by the following equation (3).

AFSOUT1H = AFSOUTMI + REVHOSR (n) + REVHOSA (n) (3)
Then, the corrected rich side minimum output voltage AFSOUT1H is the minimum on the output characteristic coefficient calculated using the output correction coefficient β starting from the corrected stoichiometric output voltage as shown in FIG. Correction is performed so that the output voltage AFSOUT1 is obtained. As a result, the minimum output voltage is corrected.

  As described above, the control of the present embodiment first corrects the output voltage at the time of stoichiometry, and uses the output correction coefficients α and β obtained in advance from the corrected output voltage at the time of stoichiometry as the starting point. After that, the maximum output voltage is corrected in the lean state, and the minimum output voltage is corrected in the rich state.

  As described above, in the present embodiment, in addition to the same effects as those of the second embodiment, correction is further performed when the fuel is cut on the lean side of the stoichiometry and when the fuel is increased on the rich side. Even if the output voltage and the slope of the output characteristics at the time of stoichiometry are both "gain + shift change", it is possible to perform accurate correction, and it is possible to execute air-fuel ratio feedback control with high accuracy, The purification performance of the catalyst can be maximized.

  In the present embodiment, the case where the air-fuel ratio sensor 9 is used has been described. However, the oxygen sensor can be similarly controlled.

  The present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made within the scope of the technical idea described in the claims.

  The present invention is applicable to output voltage correction of an oxygen sensor used for air-fuel ratio feedback control of an internal combustion engine.

It is a figure showing the structure of the system of this embodiment. (A) is an output characteristic diagram of an air-fuel ratio sensor, and (b) is a conversion table of output voltage and actual air-fuel ratio. It is a control flowchart of a 1st embodiment. (A) is a figure showing the fluctuation range of a fuel injection rate, and a drive period, (b) is a figure showing the change of the output voltage of an air fuel ratio sensor. It is a control flowchart of a 2nd embodiment. It is a control flowchart of a 3rd embodiment. It is a conversion table for the correction of the atmospheric pressure on the lean side. It is a conversion table for lean side element temperature correction. It is a figure for demonstrating lean side output voltage correction | amendment. It is a conversion table for atmospheric pressure correction on the rich side. It is a conversion table for element temperature correction on the rich side. It is a figure for demonstrating rich side output voltage correction | amendment. (A)-(c) is a figure for demonstrating the shift | offset | difference of the output voltage of an air fuel ratio sensor. It is a table showing the relationship between an intake air amount, a fuel injection rate, and a driving cycle.

Explanation of symbols

1 Engine 2 Control unit (ECU)
DESCRIPTION OF SYMBOLS 3 Intake passage 4 Throttle valve 5 Exhaust passage 6 Three way catalyst 7 Fuel injection valve 8 Atmospheric pressure sensor 9 Air fuel ratio sensor 10 Air flow meter (AFM)
11 Intake port

Claims (10)

Equipped with an exhaust sensor whose output value changes in response to the exhaust gas component of the engine,
Finding the air-fuel ratio of the air-fuel mixture supplied to the engine corresponding to the output value of the exhaust sensor,
In an air-fuel ratio control apparatus for an internal combustion engine provided with an air-fuel ratio feedback control means for performing feedback control so that the air-fuel ratio approaches a target air-fuel ratio,
Air-fuel ratio changing means for changing the air-fuel ratio by changing the fuel injection amount at a predetermined increase / decrease range and a predetermined fluctuation period during engine operation;
Exhaust gas sensor output voltage correction means for correcting an exhaust sensor output voltage corresponding to the stoichiometric air-fuel ratio based on the displacement of the output voltage of the exhaust sensor while the air-fuel ratio varies. Engine air-fuel ratio control device.   The richer and leaner output characteristics than the stoichiometric air-fuel ratio are calculated based on the exhaust sensor output voltage at the stoichiometric air-fuel ratio corrected by the exhaust sensor output voltage correcting means and an output correction coefficient unique to the exhaust sensor. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1.   The air-fuel ratio control device for an internal combustion engine according to claim 1 or 2, wherein the air-fuel ratio fluctuation means variably controls the increase / decrease width and fluctuation cycle of the fuel injection amount in accordance with the operating state of the engine. Intake air amount detection means for detecting the intake air amount is provided,
4. The air-fuel ratio control apparatus for an internal combustion engine according to claim 3, wherein the air-fuel ratio fluctuation means controls the increase / decrease width and fluctuation period of the fuel injection amount in accordance with the detection value of the intake air amount detection means.   When the intake air amount is large, the air-fuel ratio changing means increases and decreases the fluctuation range of the fuel injection amount and shortens the fluctuation cycle. When the intake air amount is small, the air-fuel ratio fluctuation means decreases and fluctuates the increase and decrease range of the fuel injection amount. The air-fuel ratio control device for an internal combustion engine according to claim 4, wherein the cycle is lengthened.   6. The internal combustion engine according to claim 4, wherein only when the intake air amount is larger than the intake air amount at the time of previous correction, the air-fuel ratio is changed by the air-fuel ratio changing means and the exhaust sensor output voltage correction means is used for correction. Air-fuel ratio control device. Rich state detection means for detecting an operation state in which the exhaust sensor outputs a stable rich voltage;
7. A rich output voltage correction unit that performs correction so that an exhaust sensor output voltage at that time matches an output characteristic calculated by the output characteristic calculation unit when a rich state is detected. An air-fuel ratio control apparatus for an internal combustion engine according to claim 1.   The lean output voltage correction means for correcting the exhaust sensor output voltage at that time so as to match the output characteristic calculated by the output characteristic calculation means when a lean state is detected. An air-fuel ratio control apparatus for an internal combustion engine according to claim 1.   The air-fuel ratio control apparatus for an internal combustion engine according to claim 7 or 8, further comprising an atmospheric pressure correction unit that corrects the exhaust sensor output voltage in the rich state or the lean state according to atmospheric pressure.   The air-fuel ratio control apparatus for an internal combustion engine according to claim 7 or 9, further comprising element temperature correction means for correcting the exhaust sensor output voltage in the rich state or lean state according to the element temperature of the exhaust sensor.

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