JP3607765B2 - Engine air-fuel ratio control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an air-fuel ratio control device for an engine in which an air-fuel ratio sensor is provided for each exhaust system of a plurality of cylinder banks and feedback control is performed on the air-fuel ratio of each bank independently.
[0002]
[Prior art]
Conventionally, in an engine having a plurality of cylinder banks, such as a horizontally opposed engine or a V-type engine, in order to control the air-fuel ratio for each cylinder bank, an air-fuel ratio sensor is provided in each exhaust system of each cylinder bank. Some perform air-fuel ratio feedback control for each cylinder bank based on the output voltage of the fuel ratio sensor. For example, in Japanese Patent Laid-Open No. 5-44541, a catalyst is interposed in a so-called dual exhaust provided for each of the left and right cylinder banks of a horizontally opposed engine, and an air-fuel ratio sensor is provided upstream of each catalyst. A technique for controlling the air-fuel ratio for each cylinder bank based on the output value of each air-fuel ratio sensor is disclosed.
[0003]
Japanese Patent Application Laid-Open No. 3-26845 discloses the period of the output signal of the air-fuel ratio sensor provided for each of the left and right cylinder banks, and the relative empty of both the air-fuel ratio sensors based on the ratio of the two periods. A technique is disclosed in which an air-fuel ratio of one cylinder bank is matched with an air-fuel ratio of the other cylinder bank by detecting a control deviation of the fuel ratio and correcting the air-fuel ratio of one cylinder bank in accordance with the control deviation. ing.
[0004]
[Problems to be solved by the invention]
However, in the former prior art, since the air-fuel ratio is controlled independently for each cylinder bank, if a deviation occurs in the air-fuel ratio control between the cylinder banks, this control deviation cannot be detected. An air-fuel ratio control error occurs.
[0005]
On the other hand, in the latter prior art, since the relative deviation of the air-fuel ratio control between the cylinder banks is corrected, the air-fuel ratio control error between the cylinder banks is corrected. When the deterioration occurs, the output cycle of the air-fuel ratio sensor becomes longer than the output cycle of the normal air-fuel ratio sensor. Therefore, the ratio of the cycle is one than the normal value (a value close to 1.0). Therefore, if the control of the air-fuel ratio of one cylinder bank is corrected based on the ratio of the output periods of the two air-fuel ratio sensors, the air-fuel ratio control of the cylinder bank is not performed normally, so that Control deviation occurs in the air-fuel ratio of the exhaust gas, and exhaust emission deteriorates.
[0006]
In view of the above circumstances, the present invention provides an air-fuel ratio control apparatus for an engine that can improve exhaust emission by matching air-fuel ratios between a plurality of cylinder banks without being affected by deterioration of an air-fuel ratio sensor. The purpose is to do.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, as shown in the basic configuration diagram of FIG. In the engine air-fuel ratio control apparatus that independently controls the air-fuel ratio of each bank based on the above, one of the air-fuel ratio sensors is a main air-fuel ratio sensor and the other air-fuel ratio sensor is a sub-air-fuel ratio sensor. Main air-fuel ratio control means for controlling the air-fuel ratio of the main air-fuel ratio sensor side cylinder bank based on the output voltage of the main air-fuel ratio sensor; The output voltage width of each air-fuel ratio sensor is detected by the difference between the maximum value and the minimum value of the output voltage of each air-fuel ratio sensor, and the output voltage width and the reference voltage width set for each air-fuel ratio sensor The output voltage of each air-fuel ratio sensor is amplified and normalized according to the ratio Based on the output voltage of the subordinate air-fuel ratio sensor, the reference voltage conversion means for calculating the potential difference between the output voltage of the main air-fuel ratio sensor after the standardization and the output voltage of the subordinate air-fuel ratio sensor, And a sub-air-fuel ratio control means for setting the air-fuel ratio of the sub-air-fuel ratio sensor side cylinder bank and correcting the air-fuel ratio according to the potential difference to control the air-fuel ratio of the sub-air-fuel ratio sensor side cylinder bank. And
[0009]
That is, according to the first aspect of the present invention, the air-fuel ratio of the cylinder bank in which the main air-fuel ratio sensor is disposed in the exhaust system is controlled based on the output voltage of the main air-fuel ratio sensor, and the output voltage of the sub-air-fuel ratio sensor is adjusted. The air-fuel ratio set on the basis of the reference voltage is converted according to the potential difference between the output voltage of the main air-fuel ratio sensor and the output voltage of the sub-air-fuel ratio sensor, and the air-fuel ratio of the sub-air-fuel ratio sensor side cylinder bank is controlled, Correction is made to match the air-fuel ratio of the main air-fuel ratio sensor side cylinder bank.
[0010]
in this case, The standardization of the output voltage of each air-fuel ratio sensor is based on the output voltage width of each air-fuel ratio sensor detected by the difference between the maximum value and the minimum value of the output voltage of each air-fuel ratio sensor and the reference voltage set in the air-fuel ratio sensor. The output voltage of each air-fuel ratio sensor is amplified in accordance with the ratio with the width.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 8 shows an overall schematic diagram of the engine. Reference numeral 1 in FIG. 8 denotes an engine. In the figure, a 4-cycle 6-cylinder horizontally opposed engine is shown. The cylinder block 2 of the engine 1 includes left and right cylinder banks, for example, a cylinder group of # 1, # 3, and # 5 cylinders on the right cylinder bank (left bank in the figure; hereinafter abbreviated as “RH bank”) side. And a cylinder group of # 2, # 4, and # 6 cylinders is arranged on the left cylinder bank (right bank in the figure; hereinafter abbreviated as “LH bank”) side.
[0012]
An intake port 4 is formed in each cylinder head 3 of both banks, and an intake manifold 5 is communicated with each intake port 4. In addition, resonance pipes 6a and 6b communicate with the banks upstream of the intake manifold 5 and a variable intake valve 11e is interposed in a passage 6c connecting the resonance pipes 6a and 6b. The resonance pipes 6a and 6b, the passage 6c, and the variable intake valve 11e constitute a variable resonance supercharging system.
[0013]
Further, the upstream of each resonance pipe 6a, 6b is communicated with the surge tank 7 via the throttle chambers 11a, 11b, and an air cleaner 9 is attached to the upstream side of the surge tank 7 via the intake pipe 8. An intake air amount sensor 10 of a hot wire type or the like is interposed immediately downstream of 9.
[0014]
In addition, throttle valves 11c and 11d (so-called twin throttle valves) are interposed in the throttle chambers 11a and 11b, respectively. One throttle valve 11d is turned on when the throttle opening sensor 12a and the throttle valve are fully closed. A throttle sensor 12 having a switch 12b is provided continuously.
[0015]
Further, the downstream side of the throttle valves 11c and 11d of the throttle chambers 11a and 11b is communicated by a passage 6d. An ISC (idle speed control) valve 13 is interposed.
[0016]
In addition, an injector 14 is disposed immediately upstream of each intake port 4 of each cylinder of the intake manifold 5, and an ignition plug 15 that exposes the tip of each cylinder head 3 to the combustion chamber for each cylinder. Is installed. An ignition coil 15 a is connected to the ignition plug 15, and the ignition coil 15 a is connected to the igniter 16.
[0017]
A cooling water temperature sensor 21 is exposed to a cooling water passage (not shown) formed in the cylinder block 2, and an RH bank knock sensor 22a and an LH bank knock sensor are provided in each bank of the cylinder block 2, respectively. The exhaust pipes 24a and 24b provided for each bank are communicated from the exhaust ports 23 of the cylinder heads 3 respectively.
[0018]
Each of the knock sensors 22a and 22b is, for example, a resonance type knock sensor including a vibrator having substantially the same natural frequency as knock vibration and a piezoelectric element that detects vibration acceleration of the vibrator and converts it into an electric signal. The vibration transmitted to the cylinder block or the like by the combustion pressure wave in the combustion stroke of the engine is detected, and a detection signal corresponding to the vibration waveform is output.
[0019]
Further, main catalyst converters 25a and 25b are interposed in the exhaust pipes 24a and 24b, respectively, and a sub-catalyst converter 26 is interposed in the downstream junction of the exhaust pipes 24a and 24b. Main O2 sensors 27a and LH banks which are examples of main air-fuel ratio sensors for detecting the oxygen concentration in the exhaust gas from the cylinder group of the RH bank upstream of the main catalytic converters 25a and 25b in the exhaust pipes 24a and 24b. A sub O2 sensor 27b, which is an example of a sub air-fuel ratio sensor for detecting the oxygen concentration in the exhaust gas from the cylinder group, is exposed, and an auxiliary O2 sensor 28 is exposed downstream of the sub-catalytic converter 26. The air / fuel ratio of the bank is controlled based on the output voltages of the main O2 sensor 27a and the auxiliary O2 sensor 28, and the air / fuel ratio of the LH bank is controlled based on the output voltages of the sub O2 sensor 27b and the auxiliary O2 sensor 28. It has a so-called dual O2 sensor (DOS) structure for each bank, and the air-fuel ratio of the LH bank depends on the output voltage of the main O2 sensor 27a. The correction is made based on the deviation amount of the output voltage of the O2 sensor 27b, and control is performed so that the air-fuel ratio of the LH bank matches the air-fuel ratio of the RH bank.
[0020]
On the other hand, a crank sprocket 1b (see FIGS. 9 and 10) is pivotally mounted on the crankshaft 1a of the engine 1, and a timing belt (see FIG. 9) around which the rotation of the crankshaft 1a is wound around the crank sprocket 1b. (Not shown) is transmitted to the camshaft 1c, and the camshaft 1c rotates 1/2 with respect to the crankshaft 1a.
[0021]
The crankshaft 1a has a first crank rotor 29 for detecting the crank angle and a group (three groups of # 1, # 2 cylinder, # 3, # 4 cylinder, and # 5, # 6 cylinder) cylinder discrimination. The second crank rotor 30 is mounted at a predetermined interval in the axial direction of the crankshaft 1a, and protrusions that are detected bodies are detected on the outer circumferences of the first and second crank rotors 29 and 30. First and second crank angle sensors 31 and 32 made up of electromagnetic pickups and the like are respectively provided. A cam rotor 33 for cylinder discrimination is mounted on the camshaft 1c, and a cam angle sensor 34 made of an electromagnetic pickup or the like is provided on the outer periphery of the cam rotor 33. As shown in FIG. 9, each of the crank angle sensors 31, 32 has a predetermined opening angle θ0 (for example, 25 °) with respect to the axial center of the crankshaft 1a and is predetermined in the axial direction of the crankshaft 1a. And a predetermined spatial distance is maintained so that noise is not generated by being influenced by a change in magnetic flux generated when the detected object passes through the crank angle sensors 31 and 32.
[0022]
Further, as shown in FIG. 10, the first crank rotor 29 for detecting the crank angle has a protrusion 29a formed on its outer periphery, and the second crank rotor 30 for determining the group cylinder is As shown in FIG. 11, a projection 30a for group cylinder discrimination is formed on the outer periphery. When the crankshaft 1a is rotated by the operation of the engine 1 by the operation of the engine 1, the crankshaft 1a is rotated, and the crank rotors 29 and 30 are rotated to change the magnetic flux when the protrusions 29a and 30a pass. An AC voltage signal train is output from the angle sensors 31 and 32 to the electronic control unit 40 described later, and converted into a crank pulse and a group discrimination pulse, respectively.
[0023]
Specifically, the first crank rotor 29 for detecting the crank angle has protrusions 29a formed at equal intervals at intervals of 30 ° starting from, for example, 10 ° before compression top dead center (BTDC) of each cylinder, Further, one projection 30a of the second crank rotor 30 for group cylinder discrimination is formed, for example, at the position of BTDC 55 ° of the # 1, # 2 cylinder, and from the position of BTDC 55 ° of the # 3, # 4 cylinder. Two are formed every 30 °, and three are formed every 30 ° from the position of BTDC 55 ° of the # 5 and # 6 cylinders. On the other hand, as shown in FIG. 12, in order to determine the compression top dead center of the specific cylinder, the cam rotor 33 has a protrusion at a position of 43.2 ° CA after compression top dead center (ATDC) of the # 1 cylinder, for example. One cylinder 33a is formed, and individual cylinders are discriminated by the cam pulse from the cam angle sensor 34 and the group discrimination pulse.
[0024]
Next, the configuration of the electronic control unit 40 will be described with reference to FIG. The electronic control unit 40 is composed mainly of two computers, a main computer 41 that performs fuel injection control, ignition timing control, and the like, and a sub computer 42 dedicated to knock detection processing, and supplies predetermined stabilized power to each part. A constant voltage circuit 43, a drive circuit 55 connected to the main computer 41, an A / D converter 57, and various peripheral circuits connected to the sub computer 42 are incorporated.
[0025]
The constant voltage circuit 43 is connected to a battery 45 via a relay contact of an ECU relay 44, and a relay coil of the ECU relay 44 is connected to the battery 45 via an ignition switch 46, and the ignition switch 46 Is turned on and the relay contact of the ECU relay 44 is closed, the control power is supplied to the computers 41 and 42. The battery 45 is directly connected to the backup RAM 50a of the main computer 41 via the constant voltage circuit 43.
[0026]
The main computer 41 is a microcomputer in which a CPU 48, a ROM 49, a RAM 50, a backup RAM 50a, a counter / timer group 51, a serial communication interface SCI 52, and an I / O interface 53 are connected via a bus line 54. Regardless of whether the ignition switch 46 is on or off, the backup RAM 50a is always supplied with backup power from the constant voltage circuit 43 directly connected to the battery 45 and holds data.
[0027]
The counter / timer group 51 includes various counters such as a free-run counter, a cam pulse input counting counter, a fuel injection timer, an ignition timer, a periodic interrupt timer for generating a periodic interrupt, and the crank pulse input interval timing. For convenience, various timers such as a timer for monitoring and a watchdog timer for monitoring system abnormality are collectively referred to, and the main computer 41 uses various other software counters and timers.
[0028]
Similarly to the main computer 41, the sub computer 42 is a microcomputer in which a CPU 66, a ROM 67, a RAM 68, a counter / timer group 69, an SCI 70, and an I / O interface 71 are connected via a bus line 72. The main computer 41 and the sub computer 42 are connected to each other by a serial communication line via the SCIs 52 and 70.
[0029]
An idle switch 12b, first and second crank angle sensors 31, 32 and a cam angle sensor 34 are connected to an input port of the I / O interface 53 of the main computer 41, and an intake air amount sensor 10, a throttle The opening sensor 12a, the cooling water temperature sensor 21, the main O2 sensor 27a, the sub O2 sensor 27b, the auxiliary O2 sensor 28, and the atmospheric pressure sensor 35 are connected via the A / D converter 57, and this A / D The voltage VB of the battery 45 is input to the D converter 57 and monitored.
[0030]
The igniter 16 is connected to the output port of the I / O interface 53, and the actuators such as the ISC valve 13 and the injector 14 are connected via a drive circuit 55.
[0031]
On the other hand, the first and second crank angle sensors 31 and 32 and the cam angle sensor 34 are connected to the input port of the I / O interface 71 of the sub-computer 42, and the RH bank knock sensor 22a and the LH bank knock sensor. 22b are connected via an amplifier 73, a frequency filter 74, and an A / D converter 75, respectively, and after the knock detection signals from the knock sensors 22a and 22b are amplified to a predetermined level by the amplifier 73, the frequency A necessary frequency component is extracted by the filter 74, converted into a digital signal by the A / D converter 75, and input.
[0032]
The main computer 41 processes detection signals from the sensors and switches, and performs various engine controls such as fuel injection control, ignition timing control, and idle speed control, while the sub computer 42 performs engine speed control. The sample section of the signal from each knock sensor 22a, 22b is set based on the engine load and the signal from the knock sensor 22a, 22b is A / D converted at high speed in this sample section to faithfully digitalize the vibration waveform. The data is converted to data, and the presence or absence of knocking is determined based on this data.
[0033]
The output port of the I / O interface 71 of the sub computer 42 is connected to the input port of the I / O interface 53 of the main computer 41, and knock determination data in the sub computer 42 is input to the I / O interface 53. Is output. The main computer 41 reads the knock data from the sub computer 42 from the serial communication line via the SCI 52 when the determination result indicating the occurrence of knock is output from the sub computer 42, and immediately applies the corresponding data based on the knock data. Delay the ignition timing of the cylinder to avoid knocking.
[0034]
In such an engine control system, when the ignition switch 46 is turned on, the ECU relay 44 is turned on, and the main computer 41 supplies constant voltages to the respective parts via the constant voltage circuit 43 to execute various controls. . That is, the CPU 48 processes the detection signals from the sensors and switches, the battery voltage and the like input via the I / O interface 53 according to the program stored in the ROM 49, and stores various data stored in the RAM 50. Various control amounts are calculated based on various learning value data stored in the backup RAM 50a, fixed data stored in the ROM 49, and the like. Then, a drive pulse signal corresponding to the calculated fuel injection amount is output to the injector 14 of the corresponding cylinder at a predetermined timing to perform fuel injection control, and an ignition signal is sent to the igniter 16 at a timing corresponding to the calculated ignition timing. The ignition timing control is executed by outputting, and further, the control duty signal is outputted to the ISC valve 13 in accordance with the calculated duty ratio to execute the idle speed control or the like. Since the sub computer 42 is a computer dedicated to knock detection processing, detailed description of its operation is omitted.
[0035]
Here, the main computer 41 has functions as main air-fuel ratio control means, reference voltage conversion means, potential difference calculation means, and sub-air-fuel ratio control means related to air-fuel ratio control. Specifically, the ignition switch 46 When the power is turned on by turning ON the electronic control device 40, the data and flag values stored in the RAM 50 are cleared by system initialization (except for the data and flag values stored in the backup RAM 50a), and after system initialization. 2 to 6 are executed at predetermined intervals, and when the DOS control condition is satisfied in the bank-by-bank air-fuel ratio feedback correction coefficient setting routine, that is, the main O2 sensor 27a, the auxiliary O2 sensor 28, And when it is determined that the catalyst is activated, the DOS shown in FIGS. The bank-by-bank air-fuel ratio feedback correction coefficient setting subroutine is used to set the RH bank-side air-fuel ratio feedback correction coefficient λ1 based on the output voltages VF1O2 and VauxO2 of the main 02 sensor 27a and the auxiliary O2 sensor 28, and Based on the output voltage VF2O2, the LH bank side air-fuel ratio feedback correction coefficient λ2 is set. Further, in the potential difference calculation routine shown in FIG. 2, the output voltages VF1O2 and VF2O2 are converted into reference voltages to obtain reference voltages VSF1O2 and VSF2O2, and the potential difference ΔVSO2 between the two normalized outputs VSF1O2 and VSF2O2, that is, empty in both banks. The deviation amount of the fuel ratio is calculated. In the bank-specific fuel injection amount setting routine shown in FIG. 6, the fuel injection amount set for each bank is corrected by the air-fuel ratio feedback correction coefficients λ1, λ2, and the bank-specific air-fuel ratio matches the target air-fuel ratio. The air-fuel ratio control on the LH bank side is corrected by the air-fuel ratio correction coefficient λ3 set based on the potential difference ΔVSO2, and the air-fuel ratio on the LH bank side is changed to the air-fuel ratio on the RH bank side. To match.
[0036]
The bank-specific air-fuel ratio feedback correction coefficient setting routine shown in FIG. 3, the bank-specific air-fuel ratio feedback correction coefficient setting subroutine based on DOS control shown in FIGS. 4 to 5, and the bank-specific fuel injection amount setting routine shown in FIG. Prior to the description, the potential difference calculation routine shown in FIG. 2 will be described. This potential difference calculation routine is executed every predetermined time (for example, 50 ms). First, in step S1, the output voltage VF1O2 of the main O2 sensor 27a is read, and the output voltage VF1O2 is converted into a reference voltage in steps S2 to S7. .
[0037]
In step S2, the maximum output value VF1O2MAX stored in a predetermined address of the RAM 50 is read and compared with the output voltage VF1O2. If VF1O2> VF1O2MAX, the process proceeds to step S3. If VF1O2 ≦ VF1O2MAX, the process proceeds to step S4. Then, the minimum output value VF1O2MIN stored at a predetermined address in the RAM 50 is read and compared with the output voltage VF1O2. The maximum output value VF1O2MAX indicates the maximum value of the output voltage VF1O2 of the main O2 sensor 27a after the power is turned on by turning on the ignition switch 46, and the minimum output value VF1O2MIN is the output of the main O2 sensor 27a after the power is turned on. The minimum value of the voltage VF1O2 is shown. In addition, when the routine is executed for the first time after the electronic control unit 40 is turned on by turning on the ignition switch 46, the maximum output value VF1O2MAX and the minimum output value VF1O2MIN are set to initial values VF1O2MAX ← VF1O2, VF1O2MIN ← VF1O2, respectively. Is done.
[0038]
Then, when the process proceeds from step S2 to step S3, the output maximum value VF1O2MAX and the current output voltage VF1O2 are averaged based on the following formula to calculate a new output maximum value VF1O2MAX, which is stored at a predetermined address in the RAM 50. Update the output maximum value VF1O2MAX.
VF1O2MAX ← {(VF1O2-VF1O2MAX) / 2 ⁿ } + VF1O2MAX
Here, n is a constant.
[0039]
On the other hand, if it is determined in step S4 that VF1O2 <VF1O2MIN, the process proceeds to step S5. If VF1O2≥VF1O2MIN, that is, VF1O2MAX≥VF1O2≥VF1O2MIN, the process jumps to step S7.
[0040]
Then, when the process proceeds from step S4 to step S5, the output minimum value VF1O2MIN and the current output voltage VF1O2 are averaged based on the following equation to calculate a new output maximum value VF1O2MIN, which is stored at a predetermined address in the RAM 50. Update the output maximum value VF1O2MIN.
VF1O2MIN ← {(VF1O2-VF1O2MIN) / 2 ⁿ } + VF1O2MIN
Here, n is a constant.
[0041]
Then, when the process proceeds from step S3 or step S5 to step S6, the output voltage width VPPMAX1 of the main O2 sensor 27a is calculated from the difference between the output maximum value VF1O2MAX and the output minimum value VF1O2MIN (VPPMAX1 ← VF1O2MAX−VF1O2MIN). The process proceeds to step S7.
[0042]
In step S7, based on the following formula, the output voltage VF1O2 of the main O2 sensor 27a read this time is converted to a reference voltage to calculate a standardized voltage VSF1O2, and the process proceeds to step S8.
VSF1O2 ← VF1O2 × (VPPO / VPPMAX1) −VF1O2MIN
Here, VPPO is a reference voltage width of the main O2 sensor 27a and the sub O2 sensor 27b. For example, if the reference voltage is 0-1V, VPPO = 1000 mV.
[0043]
As shown in FIG. 14 (a), if the output minimum value VF1O2MIN of the output voltage VF1O2 of the main O2 sensor 27a is 0V, VPPMAX1 = VF1O2MAX, and the main O2 detected this time indicated by a broken line in FIG. 14 (b). The output voltage VF1O2 of the sensor 27a is amplified by an amount corresponding to the ratio between the reference voltage width VPPO and the output voltage width VPPMAX1, and becomes a standardized voltage VSF1O2 indicated by a solid line. Note that SL1 in the figure is a slice level for determining whether the air-fuel ratio is lean / rich.
[0044]
Thereafter, when the process proceeds to step S8, the output voltage VF2O2 of the slave O2 sensor 27b is read. In steps S9 to S14, the reference voltage conversion process for the output voltage VF2O2 is performed in the same manner as the reference voltage conversion process for the main O2 sensor output voltage. Do.
[0045]
In step S9, the output voltage VF2O2 is compared with the output maximum value VF2O2MAX read from a predetermined address of the RAM 50. If VF2O2> VF2O2MAX, the process proceeds to step S10. If VF2O2 ≦ VF2O2MAX, the process proceeds to step S11. The output voltage VF2O2 is compared with the output minimum value VF2O2MIN read from a predetermined address of the RAM 50. The maximum output value VF2O2MAX represents the minimum value of the output voltage VF2O2 of the slave O2 sensor 27b after power-on, and the minimum output value VF2O2MIN represents the maximum value of the output voltage VF2O2 of the slave O2 sensor 27b after power-on. As with the above-described maximum output value VF1O2MAX and minimum output value VF1O2MIN of the main O2 sensor 27a, at the time of the first routine execution after the electronic control device 40 is turned on by turning on the ignition switch 46, VF2O2MAX ← VF2O2, VF2O2MIN ← Initial values are respectively set in VF2O2.
[0046]
Then, when the process proceeds from step S9 to step S10, the output maximum value VF2O2MAX and the current output voltage VF2O2 are averaged based on the following formula to calculate a new output maximum value VF2O2MAX, which is stored at a predetermined address in the RAM 50. Update the output maximum value VF2O2MAX.
VF2O2MAX ← {(VF2O2-VF2O2MAX) / 2 ⁿ } + VF2O2MAX
Here, n is a constant.
[0047]
On the other hand, if it is determined in step S11 that VF2O2 <VF2O2MIN, the process proceeds to step S12. If VF2O2≥VF2O2MIN, that is, VF2MAX≥VF2O2≥VF2O2MIN, the process jumps to step S14.
[0048]
When the process proceeds from step S11 to step S12, the output minimum value VF2O2MIN and the current output voltage VF2O2 are averaged based on the following equation to calculate a new output maximum value VF2O2MIN, which is stored in a predetermined address of the RAM 50. Update the output maximum value VF2O2MIN.
VF2O2MIN ← {(VF2O2-VF2O2MIN) / 2 ⁿ } + VF2O2MIN
Here, n is a constant.
[0049]
When the process proceeds from step S10 or step S12 to step S13, the output voltage width VPPMAX2 of the slave O2 sensor 27b is calculated from the difference between the maximum output value VF2O2MAX and the minimum output value VF2O2MIN (VPPMAX2 ← VF2O2MAX−VF2O2MIN). The process proceeds to step S14.
[0050]
In step S14, based on the following equation, the output voltage VF2O2 of the slave O2 sensor 27b read this time is converted to a reference voltage to calculate a normalized voltage VSF2O2, and the process proceeds to step S15.
VSF2O2 ← VF2O2 × (VPPO / VPPMAX2) −VF2O2MIN
Here, VPPO is a reference voltage width.
[0051]
As shown in FIG. 15A, if the output minimum value VF2O2MIN of the output voltage VF2O2 of the slave O2 sensor 27b is 0V, VPPMAX2 = VF2O2MAX, and the slave O2 detected this time indicated by a broken line in FIG. The output voltage VF2O2 of the sensor 27b is amplified by an amount corresponding to the ratio between the reference voltage width VPPO and the output voltage width VPPMAX2, and becomes a reference voltage VSF2O2 indicated by a solid line. Note that SL2 in the figure is a slice level for determining whether the air-fuel ratio is lean / rich.
[0052]
In step S15, the difference between the standardized voltage VSF1O2 of the main 02 sensor 27a and the standardized voltage VSF2O2 of the sub O2 sensor 27b determines the standardized voltage VSF2O2 of the sub O2 sensor 27b relative to the standardized voltage VSF1O2 of the main O2 sensor 27a. The potential difference ΔVSO2 is calculated (ΔVSO2 ← VSF1O2-VSF2O2), and the routine is exited.
[0053]
Here, since both the reference voltages VSF1O2 and VSF2O2 are converted into reference voltages based on the output characteristics of the O2 sensors 27a and 27b, the potential difference ΔVSO2 of the output value of the sub O2 sensor 27b with respect to the main O2 sensor 27a is calculated from the RH bank. The amount of deviation of the air-fuel ratio of the LH bank with respect to can be accurately grasped without being affected by the deterioration of the O2 sensor. The potential difference VSO2 is referred to in the bank-specific fuel injection amount setting routine of FIG. 6, and the fuel injection amount for each cylinder in the LH bank is corrected according to the potential difference VSO2.
[0054]
Next, the bank-by-bank air-fuel ratio feedback correction coefficient setting routine of FIG. 3 will be described. This bank-specific air-fuel ratio feedback correction coefficient setting routine is executed at each set time, sets the air-fuel ratio feedback correction coefficient for each bank, the main O2 sensor 27a and the auxiliary O2 sensor 28 are active, and each catalytic converter. When it is determined that the catalyst is activated, the air-fuel ratio control is shifted to DOS control using the output of the auxiliary O2 sensor 28.
[0055]
First, in step S21, it is determined whether or not a clamping condition such as a throttle full opening increase correction is performed during deceleration fuel cut. If the clamping condition is satisfied, the process branches to step S30 and the average output value of the auxiliary O2 sensor 28 stored in the RAM 50 is determined. VMauxO2 is cleared, the RH bank air-fuel ratio feedback correction coefficient λ1 is set in step S31, the LH bank air-fuel ratio feedback correction coefficient λ2 is set in step S32, and the routine is exited.
[0056]
The RH bank air-fuel ratio feedback correction coefficient λ1 corrects the fuel injection amount for each cylinder (# 1, # 3, # 5 cylinder) of the RH bank by air-fuel ratio, and the LH bank air-fuel ratio feedback correction coefficient λ2 This is for correcting the fuel injection amount for each cylinder (# 2, # 4, # 6 cylinder). Here, the setting of the air / fuel ratio feedback correction coefficients λ1 and λ2 in the above steps S31 and S32 when the clamping condition is satisfied is performed by clamping the air / fuel ratio feedback correction coefficients λ1 and λ2 to values set according to the clamping condition. The fuel ratio control is open loop control.
[0057]
In step S21, when the clamping condition is not established due to normal operation, the process proceeds to step S22, and the output voltage VauxO2 of the auxiliary O2 sensor 28 is detected. In step S23, the value of the auxiliary O2 sensor activation flag F1 is referred to and cleared. If YES in step S24, the flow advances to step S24. If set, the flow jumps to step S26.
[0058]
The initial value of the auxiliary O2 sensor activation flag F1 is 0, and is set to “1” when it is determined that the auxiliary O2 sensor 28 has been activated, as will be described later, and the electronic control unit 40 is turned on. When the first routine is executed and when it is not yet determined that the auxiliary O2 sensor 28 has been activated, the process proceeds to step S24 to determine whether the auxiliary O2 sensor 28 has been activated.
[0059]
Conditions for determining the activation of the auxiliary O2 sensor 28 are as follows.
1) After the main O2 sensor 27a is in an active state and the air-fuel ratio feedback control shifts to closed loop control.
2) VauxO2 ≧ RCLSR or VauxO2 <RCLSL.
Here, RCLSR and RCLSL are preset values.
3) The state satisfying the above 1) and 2) was the engine rotation, and RINLDS was continued continuously.
[0060]
If it is determined in step S24 that the auxiliary O2 sensor 28 is inactive without satisfying the above condition, the process proceeds to step S31 via step S30, and the RH bank air-fuel ratio feedback correction coefficient λ1 is set. In step S32, the LH bank air-fuel ratio feedback correction coefficient λ2 is set and the routine is exited. At this time, the air-fuel ratio feedback correction coefficients λ1 and λ2 are set in steps S31 and S32 without using the output voltage VauxO2 of the auxiliary O2 sensor 28 and the state of the engine and the main O2 sensor 27a or the sub O2 sensor 27b. When the main O2 sensor 27a or the sub O2 sensor 27b is inactive, the air-fuel ratio feedback correction coefficients λ1 and λ2 are clamped at 1.0, respectively, and the air-fuel ratio control is set to open loop control. When each of the O2 sensors 27a and 27b is active and when the above clamping condition is not established, the RH bank air-fuel ratio feedback correction coefficient λ1 is set based on the output voltage VF1O2 of the main O2 sensor 27a in step S31, and is followed in step S32. Based on the output voltage VF2O2 of the O2 sensor 27b, the LH bank air-fuel ratio The feedback correction coefficient λ2 is set, and air-fuel ratio feedback control is performed for each bank. The setting of the air / fuel ratio feedback correction coefficients λ1 and λ2 and the learning values KLR1 and KLR2 and the learning correction coefficients KBLRC1 and KBLRC2 in the air / fuel ratio learning described later are disclosed in JP-A-5-44540 and JP This is described in detail in JP-A-5-44541.
[0061]
If it is determined in step S24 that all the conditions are satisfied and the auxiliary O2 sensor 28 is activated, the process proceeds to step S25, and the auxiliary O2 sensor activation flag F1 is set.
[0062]
Then, the process proceeds to step S26, and the value of the catalyst activation flag F2 is referred to. This catalyst activation flag F2 is set when it is determined that the catalyst of each catalytic converter has been activated, and its initial value is zero.
[0063]
When it is determined in step S26 that F2 = 0 and the process proceeds to step S27, whether or not the catalytic converter 25a has been activated, for example, the elapsed time set based on the cooling water temperature at the time of engine startup has elapsed since the engine startup. It is determined whether the integrated value of the intake air amount after starting has reached a predetermined amount or the catalyst temperature detected by the catalyst temperature sensor facing the catalytic converter 25a, etc., and the catalyst is determined to be inactive. In step S31, the process proceeds to step S31, where the RH bank air-fuel ratio feedback correction coefficient λ1 is set based on the output voltage VF1O2 of the main O2 sensor 27a. In step S32, the output of the sub O2 sensor 27b is set. Based on the voltage VF2O2, the LH bank air-fuel ratio feedback correction coefficient λ2 is set and the routine is exited. When it is determined that the catalyst is activated, the process proceeds to step S28, and the catalyst activation flag F2 is set.
[0064]
Then, in step S27, it is determined that the catalyst is activated. In step S28, the catalyst activation flag F2 is set, and when the process proceeds to step S29, the main O2 sensor 27a, the sub O2 sensor 27b, and the auxiliary O2 sensor 28 are set. The RH bank air-fuel ratio feedback correction coefficient λ1 and the LH bank air-fuel ratio feedback correction coefficient λ2 are set by DOS control using both of the above and the routine is exited.
[0065]
If the auxiliary O2 sensor activation flag F1 and the catalyst activation flag F2 are both set because the clamping condition is not satisfied, the output voltage VauxO2 of the auxiliary O2 sensor 28 is detected in step S22, and then steps S23 and S26 are performed. The process jumps to step S29, and immediately, the air-fuel ratio feedback correction coefficients λ1 and λ2 are set by DOS control.
[0066]
The setting of the air-fuel ratio feedback correction coefficients λ1 and λ2 by the DOS control in step S29 is executed according to the bank-by-bank air-fuel ratio feedback correction coefficient setting subroutine by the DOS control shown in the flowcharts of FIGS. First, in steps S41 to S51, the RH bank air-fuel ratio feedback correction coefficient λ1 is set. In step S41, the output voltage VF1O2 of the main O2 sensor 27a is read. In step S42, the output voltage VauxO2 of the auxiliary O2 sensor 28 is smoothed. That is, the output voltage VauxO2 of the auxiliary O2 sensor 28 read in step S22 of the bank-by-bank air-fuel ratio feedback correction coefficient setting routine and the average output value VMauxO2 calculated at the previous routine execution stored in a predetermined address of the RAM 50. Based on the above, the current average output value VMauxO2 is calculated from the following equation, and the average output value VMauxO2 stored at a predetermined address in the RAM 50 is updated.
VMauxO2 ← {(VauxO2-VMauxO2) / 2 ^na } + VMauxO2
Here, na is a constant.
[0067]
In step S43, based on the average output value VMauxO2 of the auxiliary O2 sensor 28, an integral amount IPHOS and a proportional amount (skip amount) PPHOS are obtained. The integral amount IPHOS and the proportional amount PPHOS are I and P minutes set according to the comparison result between the average output value VMauxO2 and the slice level for air-fuel ratio determination, and the average output value VMauxO2 crosses the slice level. When reversed.
[0068]
Thereafter, in step S44, the integral amount IPHOS and the proportional amount PPHOS are added to the auxiliary O2 sensor correction coefficient PHOS calculated at the previous routine execution stored in the predetermined address of the RAM 50, and a new auxiliary O2 sensor correction coefficient PHOS is obtained. Is set (PHOS ← PHOS + IPHOS + PPHOS).
[0069]
Then, in steps S45 to S48, it is determined whether or not the auxiliary O2 sensor correction coefficient PHOS is within an appropriate range. If the auxiliary O2 sensor correction coefficient PHOS is outside the appropriate range, the auxiliary O2 sensor correction coefficient PHOS is corrected. First, in step S45, it is determined whether the auxiliary O2 sensor correction coefficient PHOS is lower than the lower limit value PHMIN. If PHOS <PHMIN, the process branches to step S46, and the auxiliary O2 sensor correction coefficient PHOS is set at the lower limit value PHMIN. Then, the process proceeds to step S49. If PHOS ≧ PHMIN, the process proceeds to step S47 to determine whether the auxiliary O2 sensor correction coefficient PHOS is higher than the upper limit value PHMAX. If PHOS> PHMAX, the process branches to step S48, the auxiliary O2 sensor correction coefficient PHOS is set at the upper limit value PHMAX, and the process proceeds to step S49. When PHOS ≦ PHMAX, it is determined that the auxiliary O2 sensor correction coefficient PHOS calculated this time is within the appropriate range, and the process directly proceeds to step S49.
[0070]
In step S49, the proportional amount (skip amount) PU1 and the integral amount IU1 are set from the comparison result between the output voltage VF1O2 of the main O2 sensor 27a and the slice level SL1 (see FIG. 14A). When the output voltage VF1O2 crosses the slice level SL1, the proportional amount PU1 and the integral amount IU1 are inverted.
[0071]
Thereafter, in step S50, the auxiliary O2 sensor correction coefficient PHOS is added to the proportional amount PU1 to obtain the current P1 portion (proportional amount). In step S51, the RH bank air-fuel ratio feedback correction calculated at the previous routine execution time. The proportional amount P1 and the integral amount IU1 are added to the coefficient λ1 to set a new RH bank air-fuel ratio feedback correction coefficient λ1 (λ1 ← λ1 + P1 + IU1).
[0072]
Next, in steps S52 to S55, the LH bank air-fuel ratio feedback correction coefficient λ2 is set. In step S52, the output voltage VF2O2 of the slave O2 sensor 27b is read. In step S53, the proportional amount (skip amount) is obtained from the comparison result between the output voltage VF2O2 of the slave O2 sensor 27b and the slice level SL2 (see FIG. 15A). ) PU2 and integration amount IU2 are set. When the output voltage VF2O2 crosses the slice level SL2, the proportional amount PU2 and the integral amount IU2 are inverted.
[0073]
Thereafter, in step S54, the auxiliary O2 sensor correction coefficient PHOS is added to the proportional amount PU2 to obtain the current P2 (proportional amount), and in step S55, the LH bank air-fuel ratio feedback correction calculated at the previous routine execution time. The proportional amount P2 and the integral amount IU2 are added to the coefficient λ2, and a new LH bank air-fuel ratio feedback correction coefficient λ2 is set (λ2 ← λ2 + P2 + IU2), and the routine is exited.
[0074]
Although the air-fuel ratio feedback correction coefficient is not set for each bank, the setting of the air-fuel ratio feedback correction coefficient by DOS control is disclosed in Japanese Patent Application Laid-Open No. 62-29738 and Japanese Patent Application No. 7-52742 by the present applicant. Is described in detail.
[0075]
The air-fuel ratio feedback correction coefficients λ1 and λ2 are used when setting the bank-specific fuel injection pulse widths Ti1 and Ti2 for determining the fuel injection amount for each bank in the bank-specific fuel injection amount setting routine shown in FIG.
[0076]
Next, the bank-specific fuel injection amount setting routine will be described with reference to FIG. First, in step S61, a basic fuel injection pulse width TP corresponding to the basic fuel injection amount is calculated from the following equation based on the intake air amount Q and the engine speed N.
TP ← K × Q / N
Here, K is an injector characteristic correction constant.
[0077]
Next, in step S62, based on the cooling water temperature Tw by the cooling water temperature sensor 21, the throttle opening by the throttle opening sensor 12a, the idle output by the idle switch 12b, etc., the cooling water temperature correction, acceleration / deceleration correction, full opening increase correction, after idling Various kinds of increase correction coefficients COEF related to the increase correction and the like are set, the process proceeds to step S63, and the above-described both air-fuel ratio feedback correction coefficients λ1, λ2 are read.
[0078]
In step S64, the engine speed N and the basic fuel injection pulse width TP representing the engine load are used as parameters and stored in the RH bank air-fuel ratio learning value table of the backup RAM 50a that has learned the air-fuel ratio state on the RH bank side. The RH bank air-fuel ratio learning correction coefficient KBLRC1 is set by searching for the air-fuel ratio learning value KLR1 that is present and performing interpolation calculation.
[0079]
Next, in step S65, as in step S64, the engine speed N and the basic fuel injection pulse width TP are used as parameters to store in the LH bank air-fuel ratio learning value table of the backup RAM 50a that has learned the air-fuel ratio state on the LH bank side. The air-fuel ratio learning value KLR2 that has been set is searched and the LH bank air-fuel ratio learning correction coefficient KBLRC2 is set by interpolation calculation.
[0080]
The air-fuel ratio learning values KLR1 and KLR2 are the values of the intake air amount measuring system such as the intake air amount sensor 10 and the fuel of the injector 14 and the like, as disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 5-44541 by the applicant. This is for correcting variations in the production time of the system or deviations in the air-fuel ratio due to changes over time. When an air-fuel ratio feedback condition is established by O2 sensor activation or the like, the engine rotation divided into a plurality in the air-fuel ratio learning value table When the air-fuel ratio feedback correction coefficients λ1 and λ2 repeat the air-fuel ratio rich / lean by the proportional integral control a predetermined number of times in one operation region among the operation regions with the number N and the basic fuel injection pulse width TP, The learning values KLR1 and KLR2 stored in the corresponding region are updated according to the average value of the fuel ratio feedback correction coefficients λ1 and λ2. Air-fuel ratio feedback correction coefficient .lambda.1, the center value of λ2 is set to be respectively the reference value (= 1.0), and to keep the air-fuel ratio of the both banks to the stoichiometric air-fuel ratio.
[0081]
Next, in step S66, a correction amount Ks for correcting an LH bank air-fuel ratio correction coefficient LSHOS, which will be described later, is set by referring to the table with interpolation calculation using the potential difference ΔVSO2 and the intake air amount Q as parameters. To do. FIG. 7 shows the characteristics of the table. When the potential difference ΔVSO2 is a positive value, the air-fuel ratio of the LH bank detected by the secondary O2 sensor 27b is shifted to the lean side with respect to the air-fuel ratio of the RH bank detected by the main O2 sensor 27a. As the intake air amount Q is larger and the potential difference ΔVSO2 is larger on the plus side and the air-fuel ratio of the LH bank is shifted to the lean side, a larger correction amount Ks is stored on the plus side to increase the fuel increase. . When the potential difference ΔVSO2 is a negative value, the air / fuel ratio of the LH bank detected by the sub O2 sensor 27b is shifted to the rich side with respect to the air / fuel ratio of the RH bank detected by the main O2 sensor 27a. The larger the intake air amount Q, the larger the potential difference ΔVSO2 is on the minus side, and the more the air-fuel ratio of the LH bank is shifted to the rich side, the larger the correction amount Ks on the minus side is stored to increase the fuel reduction amount. Has been.
[0082]
In step S67, the LH bank air-fuel ratio correction coefficient LSHOS set at the previous routine execution is read, and the correction amount Ks is added to the LH bank air-fuel ratio correction coefficient LSHOS, so that the current LH bank air-fuel ratio correction coefficient LSHOS is added. Is calculated.
[0083]
Thereafter, the process proceeds to step S68, where the LH bank air-fuel ratio correction coefficient LSHOS is added to the LH bank air-fuel ratio learning correction coefficient KBLRC2, and the LH bank air-fuel ratio for making the LH bank air-fuel ratio coincide with the RH bank air-fuel ratio. A correction coefficient λ3 is set.
[0084]
Thereafter, in step S69, a voltage correction coefficient Ts for interpolating the invalid injection time of the injector 14 is set based on the terminal VB voltage of the battery 45, and the process proceeds to step S70.
[0085]
In step S70, the final fuel injection pulse width Ti1 for determining the fuel injection amount for the fuel injection target cylinder in the RH bank is set. In step S71, the final fuel injection amount for the fuel injection target cylinder in the LH bank is determined. A typical fuel injection pulse width Ti2 is set.
[0086]
That is, in step S70, the basic fuel injection pulse width TP calculated in step S61 is emptied by the various increase correction coefficients COEF set in step S62 and the RH bank air-fuel ratio feedback correction coefficient λ1 read in step S63. In addition to correcting the fuel ratio, learning correction is performed using the RH bank air-fuel ratio learning correction coefficient KBLRC1 set in step S64, and further, voltage correction is performed using the voltage correction coefficient Ts set in step S69 to obtain the RH bank fuel injection pulse width Ti1. Calculate from the formula.
[0087]
Ti1 ← TP × COEF × λ1 × KBLRC1 + Ts
In step S71, the basic fuel injection pulse width TP is corrected by the air fuel ratio by the various increase correction coefficients COEF and the LH bank air / fuel ratio feedback correction coefficient λ2 read in step S63, and calculated in step S68. The air-fuel ratio is corrected with the LH bank air-fuel ratio correction coefficient λ3, and the voltage is corrected with the voltage correction coefficient Ts set in step S69 to calculate the LH bank fuel injection pulse width Ti2 from the following equation.
[0088]
Ti2 ← TP × COEF × λ2 × λ3 + Ts
In step S72, the fuel injection pulse widths Ti1 and Ti2 set for each bank are set in the injection timer provided for each cylinder, and the routine is exited. Then, the injection timer is started at a predetermined timing, a drive pulse signal of the fuel injection pulse width Ti1, Ti2 is output to the injector 14 of the fuel injection target cylinder, and a predetermined amount of fuel is injected from the injector 14. .
[0089]
As described above, in this embodiment, the output voltage VF1O2 of the main O2 sensor 27a and the output voltage VF2O2 of the sub O2 sensor 27b are temporarily converted into a reference voltage, and the standardized output voltage is calculated. Since the air-fuel ratio is corrected so that the air-fuel ratio of the LH bank matches the air-fuel ratio of the RH bank based on the potential difference ΔVSO2 between the VSF1O2 and VSF2O2, the output voltage of one of the O2 sensors 27a and 27b is deteriorated or the like Even if it decreases, the deviation of the air-fuel ratio of the LH bank relative to the RH bank can be accurately detected without being affected by deterioration or the like. As a result, good air-fuel ratio control performance can be obtained.
[0090]
The present invention is not limited to the above-described embodiment. For example, the air-fuel ratio sensor is not limited to the O2 sensor, but may be a wide-range air-fuel ratio sensor, and may have three or more cylinder banks.
[0091]
【The invention's effect】
According to the first aspect of the present invention, the output voltage of the main air-fuel ratio sensor disposed in the exhaust system of one cylinder bank and the output voltage of the sub-air-fuel ratio sensor disposed in the exhaust system of another cylinder bank are The reference voltage is converted, and based on the potential difference between the standardized voltage of the main air-fuel ratio sensor and the standardized voltage of the sub-air-fuel ratio sensor, the air-fuel ratio of the sub-air-fuel ratio sensor side cylinder bank to the main air-fuel ratio sensor-side cylinder bank is changed. The amount of deviation is calculated, and based on this amount of deviation, the air-fuel ratio of the secondary air-fuel ratio sensor side cylinder bank is corrected to match the air-fuel ratio of the main air-fuel ratio sensor side cylinder bank, so the output voltage of each air-fuel ratio sensor deteriorates Even if it is reduced due to, etc., the deviation of the air-fuel ratio of the sub air-fuel ratio sensor side cylinder bank with respect to the air-fuel ratio of the main air-fuel ratio sensor side cylinder bank without being affected by deterioration The can be detected, this on the basis of the shift amount by matching the air-fuel ratio of the two cylinder banks, good air-fuel ratio control performance is obtained as a whole system, it is possible to improve the exhaust emission.
[0092]
or, By standardizing the output voltage of each air-fuel ratio sensor according to the ratio of the output voltage width detected by the difference between the maximum value and the minimum value of the output voltage of each air-fuel ratio sensor and the reference voltage width, Since the output voltage is relatively standardized corresponding to the eigenvalue of the fuel ratio sensor, the deviation of the air fuel ratio can be detected more accurately.
[Brief description of the drawings]
FIG. 1 is a basic configuration diagram of the present invention.
FIG. 2 is a flowchart showing a potential difference calculation routine.
FIG. 3 is a flowchart showing a bank-specific air-fuel ratio feedback correction coefficient setting routine.
FIG. 4 is a flowchart showing a bank-specific air-fuel ratio feedback correction coefficient setting subroutine by DOS control.
FIG. 5 is a flowchart showing a bank-specific air-fuel ratio feedback correction coefficient setting subroutine by DOS control (continued).
FIG. 6 is a flowchart showing a bank-specific fuel injection amount setting routine;
FIG. 7 is a conceptual diagram of a correction amount setting table.
FIG. 8 is an overall schematic diagram of the engine.
FIG. 9 is a front view of a crank rotor and a crank angle sensor.
FIG. 10 is a front view of a first crank rotor and a first crank angle sensor.
FIG. 11 is a front view of a second crank rotor and a second crank angle sensor.
FIG. 12 is a front view of a cam rotor and a cam angle sensor.
FIG. 13 is a circuit configuration diagram of an electronic control system.
FIG. 14 is a time chart showing the relationship between the output voltage of the main O2 sensor and the standardized voltage.
FIG. 15 is a time chart showing the relationship between the output voltage of the slave O2 sensor and the standardized voltage.
[Explanation of symbols]
1 engine
14 Injector
24a, 24b Exhaust pipe (exhaust system)
27a Main O2 sensor (main air-fuel ratio sensor)
27b Sub O2 sensor (sub air-fuel ratio sensor)
40 Electronic control unit
VF1O2 (Main O2 sensor) output voltage
VF2O2 (sub O2 sensor) output voltage
VF1O2MAX, VF2O2MAX maximum output value
VF1O2MIN, VF2O2MIN output minimum value
VPPMAX1, VPPMAX2 output voltage width
VPPO reference voltage width
VSF1O2, VSF2O2 standardized voltage
ΔVSO2 potential difference
λ3 Air-fuel ratio correction factor

Claims (1)

An air-fuel ratio sensor is provided for each exhaust system of a plurality of cylinder banks,
In an air-fuel ratio control device for an engine that feedback-controls the air-fuel ratio of each bank independently based on the output value of each air-fuel ratio sensor,
One of the air-fuel ratio sensors is a main air-fuel ratio sensor, and the other air-fuel ratio sensor is a slave air-fuel ratio sensor.
Main air-fuel ratio control means for controlling the air-fuel ratio of the main air-fuel ratio sensor side cylinder bank based on the output voltage of the main air-fuel ratio sensor;
The output voltage width of each air-fuel ratio sensor is detected by the difference between the maximum value and the minimum value of the output voltage of each air-fuel ratio sensor, and the output voltage width and the reference voltage width set for each air-fuel ratio sensor Reference voltage conversion means for amplifying and standardizing the output voltage of each air-fuel ratio sensor according to the ratio to
A potential difference calculating means for calculating a potential difference between the output voltage of the main air-fuel ratio sensor after the standardization and the output voltage of the sub-air-fuel ratio sensor;
Based on the output voltage of the sub air / fuel ratio sensor, the air / fuel ratio of the sub air / fuel ratio sensor side cylinder bank is set, and the air / fuel ratio is corrected according to the potential difference to control the air / fuel ratio of the sub air / fuel ratio sensor side cylinder bank. An air-fuel ratio control apparatus for an engine, comprising: a sub-air-fuel ratio control means.

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