JP2004316553A - Control device for air-fuel ratio sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the generation of an excessive sensor current in an air-fuel ratio sensor in the case where gas similar to atmospheric air flows in an exhaust passage in a control device for the air-fuel ratio sensor disposed in the exhaust passage in an internal combustion engine. <P>SOLUTION: In the exhaust passage in the internal combustion engine, the air-fuel ratio sensor that generates sensor current in accordance with an exhaust air-furl ratio as prescribed voltage is applied is disposed. While a vehicle system is actuated, voltage of 0.4V is added to the air-fuel ratio sensor (steps 104 and 106) except for F/C or during operation with the internal combustion engine stopped (in the case of an H/V vehicle or an economy running vehicle). Even while the vehicle system is actuated, in a situation in which atmospheric air is introduced to around the air-fuel ratio sensor 32 as in cases during the F/C or operation with the internal combustion engine stopped, applied voltage to the air-fuel ratio sensor is set to be 0V (steps 104 and 114). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a control device for an air-fuel ratio sensor, and more particularly to a control device for an air-fuel ratio sensor suitable for controlling an air-fuel ratio sensor disposed in an exhaust passage for detecting an exhaust air-fuel ratio of an internal combustion engine.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as disclosed in, for example, JP-A-2000-258387, there is known a system including an air-fuel ratio sensor for detecting an exhaust air-fuel ratio in an exhaust passage of an internal combustion engine. The air-fuel ratio sensor has a first electrode exposed to exhaust gas and a second electrode exposed to the atmosphere. The first electrode and the second electrode are provided on both sides of a solid electrolyte such as zirconia. When a voltage is applied between the two so that an electric field is generated from the second electrode to the first electrode, the first electrode and the second electrode are connected to the air-fuel ratio sensor. Flows through the sensor current according to the amount of oxygen in the exhaust gas. Since the oxygen amount in the exhaust gas is a characteristic value of the exhaust air-fuel ratio, the exhaust air-fuel ratio can be detected according to the above sensor current. The conventional system always applies a predetermined applied voltage to the air-fuel ratio sensor during the operation of the vehicle system in order to detect the exhaust air-fuel ratio based on such a principle.
[0003]
[Patent Document 1]
JP-A-2000-258387
[Patent Document 2]
JP-A-9-101285
[Patent Document 3]
JP 2001-323837 A
[Patent Document 4]
JP-A-2002-243694
[0004]
[Problems to be solved by the invention]
In a vehicle, when the accelerator pedal is depressed in a region where the engine speed is sufficiently high, in order to prevent unnecessary fuel consumption, a process of stopping the supply of fuel to the internal combustion engine, that is, a fuel cut ( Hereinafter, “F / C” may be performed. During the execution of F / C, only air flows through the inside of the internal combustion engine, and a gas containing a large amount of oxygen flows around the air-fuel ratio sensor disposed in the exhaust passage, similarly to the atmosphere.
[0005]
As described above, the air-fuel ratio sensor is a sensor that generates a sensor current according to the oxygen concentration in the exhaust gas. Therefore, if a gas similar to the atmosphere flows inside the exhaust passage with the execution of F / C, the air-fuel ratio sensor may generate an excessive sensor current. Such an excessive sensor current promotes oxidation of the sensor electrode and the inside of the sensor, and causes early deterioration of the air-fuel ratio sensor. For this reason, in the above-mentioned conventional system, the situation where the deterioration of the air-fuel ratio sensor is promoted by repeating the execution of the F / C occurs.
[0006]
SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an air-fuel ratio sensor that does not generate an excessive sensor current in an air-fuel ratio sensor when a gas similar to the atmosphere flows in an exhaust passage. It is an object of the present invention to provide a control device.
[0007]
[Means for Solving the Problems]
A first invention is an air-fuel ratio sensor control device that is disposed in an exhaust passage of an internal combustion engine and receives a predetermined voltage to generate a sensor current corresponding to the exhaust air-fuel ratio in order to achieve the above object. So,
Voltage application means for applying a predetermined voltage to the air-fuel ratio sensor during operation of the vehicle system,
During operation of the vehicle system, when fuel injection to the internal combustion engine is stopped, applied voltage limiting means for limiting the applied voltage to the air-fuel ratio sensor so that its absolute value is equal to or less than a predetermined threshold,
It is characterized by having.
[0008]
According to a second aspect, in the first aspect, the applied voltage limiting means starts limiting the applied voltage after a predetermined delay time after fuel injection to the internal combustion engine is stopped. And
[0009]
In a third aspect based on the first or second aspect, the voltage applying means reduces the applied voltage limited to the threshold value or less after the fuel injection to the internal combustion engine is restarted, by an increase rate thereof. Is increased toward the predetermined voltage within a range not exceeding the limit value.
[0010]
In a fourth aspect, in the first to third aspects,
The voltage applying means, after fuel injection to the internal combustion engine is restarted, comprises an applied voltage return means for returning the applied voltage limited to the threshold or less to the predetermined voltage,
Control execution means for performing predetermined control based on the sensor current,
A predetermined mask period after fuel injection to the internal combustion engine is restarted, a sensor current reflection inhibiting means for inhibiting the sensor current from being based on the control,
It is characterized by having.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. Elements common to the drawings are denoted by the same reference numerals, and redundant description will be omitted.
[0012]
Embodiment 1 FIG.
[Description of system configuration]
FIG. 1 shows the configuration of the first embodiment of the present invention. The configuration shown in FIG. 1 includes an internal combustion engine 10. An intake passage 12 and an exhaust passage 14 communicate with the internal combustion engine 10. An air filter 16 is arranged at an end of the intake passage 12. Downstream of the air filter 16, an air flow meter 18 for detecting the amount of air flowing through the intake passage 12, that is, the amount of intake air Ga is arranged.
[0013]
A throttle valve 20 is provided downstream of the air flow meter 18. Near the throttle valve 20, a throttle sensor 22 for detecting the throttle opening TA and an idle switch 24 that is turned on when the throttle valve 20 is fully closed are arranged. The intake passage 12 is further provided with a fuel injection valve 26 for injecting fuel to an intake port of the internal combustion engine 10.
[0014]
In the exhaust passage 14, an upstream catalyst 28 and a downstream catalyst 30 are arranged in series. These catalysts can exhibit a function of purifying exhaust gas by reaching a predetermined activation temperature after the internal combustion engine 10 is started. The upstream catalyst 28 and the downstream catalyst 30 each have an oxygen storage capacity (OSC: O ₂ Storage Capacitor) and can store oxygen within its capacity range. When unburned components such as HC and CO are contained in the exhaust gas, these catalysts 28 and 30 oxidize the unburned components by releasing the occluded oxygen. If the gas contains a large amount of oxygen, NOx, or the like, the atmosphere inside the catalyst can be maintained at the stoichiometric air-fuel ratio by storing excess oxygen. The upstream catalyst 28 and the downstream catalyst 30 purify the exhaust gas according to the above principle.
[0015]
An air-fuel ratio sensor 32 is arranged upstream of the upstream catalyst 28. The air-fuel ratio sensor 32 is a sensor that outputs an output according to the oxygen concentration in the exhaust gas. The oxygen concentration in the exhaust gas has a correlation with the exhaust air-fuel ratio. Therefore, the air-fuel ratio sensor 32 can detect the air-fuel ratio of the exhaust gas flowing into the upstream catalyst 28, that is, the exhaust gas immediately after being discharged from the internal combustion engine 10.
[0016]
A downstream oxygen sensor 34 is arranged downstream of the upstream catalyst 28, that is, upstream of the downstream catalyst 30. The downstream oxygen sensor 34 is a sensor that largely changes its output depending on whether or not oxygen exists in the exhaust gas. Oxygen does not remain in the exhaust gas when the exhaust air-fuel ratio is rich. On the other hand, when the exhaust air-fuel ratio is lean, oxygen in the exhaust gas remains. Therefore, the downstream oxygen sensor 34 can accurately detect whether the exhaust gas flowing out of the upstream catalyst 28 is rich or lean.
[0017]
The system shown in FIG. 1 includes an ECU (Electronic Control Unit) 40. The ECU 40 is supplied with sensor outputs from the various sensors described above. Further, the ECU 40 can calculate a fuel amount to be supplied to the internal combustion engine 10 based on the sensor outputs, and control the fuel injection valve 26 so that the fuel amount is injected.
[0018]
[Description of configuration of control device for air-fuel ratio sensor]
FIG. 2 is a circuit diagram of a control device of the air-fuel ratio sensor 32 configured inside the ECU 40. The air-fuel ratio sensor 32 includes a first electrode exposed to the internal space of the exhaust passage 14, a second electrode exposed to the atmosphere, and a solid electrolyte layer such as zirconia sandwiched between the two electrodes. In the circuit diagram shown in FIG. 2, the air-fuel ratio sensor 32 is equivalently represented by setting the terminal on the first electrode side to “AF−” and setting the terminal on the second electrode side to “AF +”.
[0019]
A potential switching point 46 is connected to the AF-terminal 42 of the air-fuel ratio sensor 32 via a buffer circuit 44. The potential switching point 46 is grounded via a resistor 48 and connected to a power supply potential via both a main power supply path 50 and a sub power supply path 52. Main power path 50 includes resistors 54 and 56, while sub power path 52 includes switch 58 and resistor 60. The main power supply path 50 can generate a potential of 3.3 V between the resistors 54 and 56 and generate a potential of 2.9 V at the potential switching point 46 when the switch 58 is off. . The sub power supply path 52 can generate a 3.3 V potential at the potential switching point 46 when the switch 58 is turned on.
[0020]
A pulse application circuit 68 is connected to the AF + terminal 62 of the air-fuel ratio sensor 32 via a buffer circuit 66. The pulse applying circuit 68 is connected to the 3.3 V point of the main power supply path 50 via the buffer circuit 70. According to the buffer circuit 70, the 3.3 V potential generated in the main power supply path 50 can be supplied to the pulse applying circuit 68 as it is. The pulse applying circuit 68 is a circuit for sequentially changing the output potential in a pulse-wise manner by 0.2 V on both the positive side and the negative side centering on the input potential (3.3 V) at predetermined intervals. Therefore, in the buffer circuit 66, the voltage of the AF + terminal 62 of the air-fuel ratio sensor 32 periodically changes from 3.3V to 3.5V to 3.1V to 3.3V around 3.3V. An electric potential is supplied.
[0021]
The buffer circuit 66 includes a sensor current detection resistor 72 connected in series with the air-fuel ratio sensor 32. An amplifier circuit 74 is connected to both sides of the sensor current detection resistor 72. Further, an analog-to-digital converter (ADC) 76 for detecting a sensor current is connected to the amplifier circuit 74. The amplification circuit 74 is provided with an amplification factor of, for example, about eight times. The buffer circuit 66 and the amplification circuit 74 supply a current flowing through the air-fuel ratio sensor 32, that is, a sensor current generated by the air-fuel ratio sensor 32 to the ADC 76. It is configured to be able to detect.
[0022]
[Description of operation of control device for air-fuel ratio sensor]
According to the control device illustrated in FIG. 2, by setting the switch 58 of the sub power supply path 52 to the off state, a potential of 2.9 V can be applied to the AF-terminal 42 of the air-fuel ratio sensor 32. In this case, a voltage of 0.4 V is applied between both terminals of the air-fuel ratio sensor 32 except when the pulse application circuit 68 is changing the output potential.
[0023]
FIG. 3 is a diagram for explaining the sensor characteristics of the air-fuel ratio sensor 32. In this figure, the horizontal axis is the applied voltage to the air-fuel ratio sensor 32, and the vertical axis is the sensor current of the air-fuel ratio sensor 32. In FIG. 3, curves indicated by reference signs (1), (2), (3), and (4) represent sensor currents and applied voltages, respectively, which are established under different exhaust gas air-fuel ratios. The relationship is The characteristics of the air-fuel ratio sensor 32 indicate a change from the curve (1) to the curve (4) as the air-fuel ratio of the exhaust gas increases, that is, as the oxygen content in the exhaust gas increases.
[0024]
As shown in FIG. 3, when a voltage of 0.4 V is applied to the air-fuel ratio sensor 32, the sensor current has a value representing the air-fuel ratio of the exhaust gas. For this reason, according to the control circuit shown in FIG. 2, the exhaust air-fuel ratio can be detected by detecting the sensor current with the ADC 76. The ECU 40 can execute air-fuel ratio feedback control for maintaining the exhaust air-fuel ratio near the stoichiometric air-fuel ratio based on the exhaust air-fuel ratio detected in this manner.
[0025]
Further, according to the control circuit shown in FIG. 2, the voltage applied to the air-fuel ratio sensor 32 can be periodically changed by the function of the pulse application circuit 68. The control circuit can detect the internal impedance of the air-fuel ratio sensor 32 by checking the amount of change in the sensor current caused by the change in the applied voltage. The ECU 40 can perform impedance control or the like for keeping the temperature of the air-fuel ratio sensor 32 constant based on the impedance of the air-fuel ratio sensor 32 detected in this way.
[0026]
[Description of characteristic operation in the present embodiment]
In the system of the present embodiment, when the idle switch 24 is turned on in an environment where the engine speed is sufficiently high, the F / C is executed to stop the injection of the fuel to the internal combustion engine 10. During the execution of the F / C, the gas flowing through the exhaust passage 14 contains a large amount of oxygen as in the atmosphere. In this case, the first electrode (the electrode on the exhaust passage side) of the air-fuel ratio sensor 32 is exposed to the atmosphere, even during the operation of the vehicle system (the IG switch of the vehicle is turned on). .
[0027]
The system of the present embodiment may be mounted on a hybrid (H / V) vehicle or an eco-run vehicle. In an H / V vehicle or an eco-run vehicle, the internal combustion engine 10 may be stopped even when the vehicle system is operating (the key switch of the vehicle is turned on) (hereinafter, such driving is performed). The state is referred to as “internal combustion engine stop operation”). During the internal combustion engine stop operation, the first electrode of the air-fuel ratio sensor 32 is exposed to the atmosphere. As described above, in a situation where the air-fuel ratio sensor 32 is mounted on a vehicle and is actually used, the air-fuel ratio sensor 32 is not limited to when the vehicle system is not operating (IG off or key switch off), and is also available during the operation of the vehicle system. May be exposed to
[0028]
In FIG. 3 described above, the curves (1) to (3) respectively show the relationship corresponding to the exhaust air-fuel ratio that normally occurs with the execution of the air-fuel ratio feedback control. On the other hand, the curve {circle over (4)} shows the relationship realized when the gas in the exhaust passage 14 becomes atmospheric, such as during F / C. These four curves (1) to (4) indicate that when a sufficient applied voltage is applied to the air-fuel ratio sensor 32 during F / C, the sensor current is extremely large as compared to during execution of the air-fuel ratio feedback control. Value. That is, the four curves (1) to (4) shown in FIG. 3 indicate that when the applied voltage of 0.4 V is maintained during the F / C in the system of the present embodiment, the air-fuel ratio sensor 32 has an excessively large value. This indicates that the sensor current flows. Such an excessive sensor current promotes the oxidation of the electrodes and the solid electrolyte of the air-fuel ratio sensor 32, and promotes the deterioration thereof. Therefore, in order to ensure the durability and reliability of the air-fuel ratio sensor 32, it is desirable to prevent the generation of such an excessive sensor current.
[0029]
As described above, the control device illustrated in FIG. 2 turns on the switch 58 of the sub power supply path 52 to set the potential of the potential switching point 46 to 3.3 V, that is, the AF- of the air-fuel ratio sensor 32. The potential applied to the terminal 42 can be 3.3 V. When a potential of 3.3 V is applied to the AF-terminal 42, the voltage applied between both terminals of the air-fuel ratio sensor 32 becomes 0 V in principle. Therefore, according to the control device of the present embodiment, by turning on the switch 58, the voltage applied to the air-fuel ratio sensor 32 can be set to 0 V in principle.
[0030]
If the applied voltage is 0 V, the air-fuel ratio sensor 32 will not generate a sensor current, no matter how much oxygen is present inside the exhaust passage 14. In addition, during F / C or when the internal combustion engine is stopped (in case of H / V or eco-run vehicle), it is not necessary to execute the air-fuel ratio feedback control. Not causing any problem does not cause any control disadvantage. Therefore, in the present embodiment, when a situation occurs in which the atmosphere flows through the exhaust passage 14 during operation of the vehicle system, the ECU 40 in other words, injects fuel to the internal combustion engine 10 during operation of the vehicle system. When the operation is stopped (during F / C, the internal combustion engine is stopped), the switch 58 of the sub power supply path 52 is turned on, and the voltage applied to the air-fuel ratio sensor 32 is set to zero.
[0031]
FIG. 4 shows a flowchart of a control routine executed by the ECU 40 to realize the above functions.
In the routine shown in FIG. 4, first, it is determined whether or not the air-fuel ratio sensor 32 is active (step 100).
The air-fuel ratio sensor 32 exhibits normal output characteristics when heated to a predetermined activation temperature. Therefore, a heater is incorporated in the air-fuel ratio sensor 32, and the ECU 40 controls the sensor element temperature using the heater after the operation of the vehicle system is started. In step 100, the element temperature is estimated based on the impedance of the air-fuel ratio sensor 32, and it is determined whether the element temperature has reached the activation temperature.
[0032]
If it is determined in step 100 that the air-fuel ratio sensor 32 is not active, it can be determined that the sensor output cannot be used as a basis for the air-fuel ratio feedback control. In this case, thereafter, after the open control of the air-fuel ratio is executed (step 102), the current processing cycle is ended.
[0033]
On the other hand, if the activation of the air-fuel ratio sensor 32 is recognized in step 100, then, it is determined that the F / C is being performed, or the internal combustion engine of the H / V vehicle or the eco-run vehicle is being stopped (the vehicle system is operating). Is determined. That is, it is determined whether or not a situation occurs in which the atmosphere is guided around the air-fuel ratio sensor 32 in an environment where the ECU 40 is in a normal operation state (step 104).
[0034]
If it is determined in step 104 that neither the F / C nor the internal combustion engine is stopped, the normal exhaust gas around the air-fuel ratio sensor 32, that is, the air-fuel ratio that does not greatly deviate from the stoichiometric air-fuel ratio is set. It can be determined that the exhaust gas contained is guided. In this case, the switch 58 of the control circuit (FIG. 2) is turned off, and the voltage applied to the air-fuel ratio sensor 32 is set to 0.4 V (step 106).
[0035]
In the routine shown in FIG. 4, next, after a voltage applied to the air-fuel ratio sensor 32 is switched from 0 V to 0.4 V, a predetermined time (appropriate time of about 0.5 to 1.0 sec) has elapsed. It is determined whether or not it is (step 108).
As a result, when it is determined that the predetermined time has not yet elapsed, the process of the above-described step 102 is thereafter executed to perform the open control of the air-fuel ratio. On the other hand, if it is determined that the predetermined time has elapsed, then the air-fuel ratio feedback control based on the output of the air-fuel ratio sensor 32 is executed (step 110), and the current processing cycle is ended. .
[0036]
FIG. 5 is a diagram showing a temporal change in the sensor current of the air-fuel ratio sensor 32 after the voltage applied to the air-fuel ratio sensor 32 is switched from 0 V to 0.4 V. Immediately after the applied voltage changes from 0 V to 0.4 V, the same state as when an AC voltage is applied to the air-fuel ratio sensor 32 instantaneously occurs. Therefore, even if the air-fuel ratio of the gas surrounding the air-fuel ratio sensor 32 is the same, the sensor current temporarily shows a large value after the applied voltage is switched as shown in FIG.
[0037]
During a period in which the sensor current of the air-fuel ratio sensor 32 indicates an excessive value, it is desirable that the sensor current is not reflected in the air-fuel ratio feedback control. Therefore, in the present embodiment, a period during which the sensor current of the air-fuel ratio sensor 32 temporarily becomes large due to the switching of the applied voltage is experimentally detected in advance, and the period (“signal mask” shown in FIG. ) Is the predetermined time in step 108.
[0038]
According to the processing of steps 108, 102, and 110, the open control of the air-fuel ratio is performed without depending on the output of the air-fuel ratio sensor 32 until a predetermined time (a signal mask period) elapses after the applied voltage is switched. Is executed. Then, after a predetermined time has elapsed, the feedback control using the output of the air-fuel ratio sensor 32 is started. Therefore, according to the system of the present embodiment, it is possible to reliably prevent improper air-fuel ratio feedback control based on a sensor current including an error immediately after switching of the applied voltage.
[0039]
In the routine shown in FIG. 4, if it is determined in the above step 104 that the F / C or the internal combustion engine stop operation is being performed, then, after the F / C or the internal combustion engine stop operation is started, It is determined whether a predetermined delay time has elapsed (step 112).
The atmosphere is led around the air-fuel ratio sensor 32 after a certain period of time has elapsed after the start of the F / C or the internal combustion engine stop operation. Therefore, even if a voltage of 0.4 V is applied to the air-fuel ratio sensor 32, no excessive sensor current is generated until that time has elapsed.
The delay time used in step 112 is a time set assuming a time until the atmosphere is led around the air-fuel ratio sensor 32. Therefore, when it is determined that the above-described delay time has elapsed, it can be determined that the air is guided around the air-fuel ratio sensor 32, while it is determined that the above-described delay time has not elapsed. In this case, it can be determined that the air has not been guided around the air-fuel ratio sensor 32 yet.
[0040]
In the routine shown in FIG. 4, when it is determined in step 104 that the delay time has already elapsed, the switch 58 of the control circuit (see FIG. 2) is turned on, and the voltage applied to the air-fuel ratio sensor 32 is changed. Is set to 0 V (step 114).
When the applied voltage is set to 0 V, the air-fuel ratio sensor 32 does not generate an excessive sensor current even if the atmosphere is guided around the first electrode. For this reason, according to the above-described processing, it is possible to reliably prevent the deterioration of the air-fuel ratio sensor 32 from being promoted due to the execution of the F / C or the internal combustion engine stop operation.
[0041]
On the other hand, if it is determined in step 104 that the delay time has not yet elapsed, the processes in and after step 106 are executed without switching the applied voltage to 0V. As a result, the air-fuel ratio feedback control based on the sensor current of the air-fuel ratio sensor 32 is continued.
The applied voltage of the air-fuel ratio sensor 32 may be set to 0 V immediately after the start of the F / C or the internal combustion engine stop operation. However, the F / C and the internal combustion engine stop operation may be immediately stopped after being started. When the applied voltage once set to 0 V is returned to 0.4 V, the sensor current temporarily becomes excessive (see FIG. 5). Therefore, as described above, a signal mask period is provided for a certain period. It is necessary to open control the air-fuel ratio. For this reason, when the method of setting the applied voltage to 0 V immediately after the start of the F / C or the internal combustion engine stop operation is employed, unnecessary return control is required when the operation is returned to the normal operation after a short time. Occurs.
[0042]
On the other hand, according to the routine shown in FIG. 4, the applied voltage can be maintained at 0.4 V until the air is actually led around the air-fuel ratio sensor 32. Since the period in which the applied voltage is maintained at 0.4 V is a period in which excessive oxygen is not guided around the air-fuel ratio sensor 32, even if such a method is employed, an excessive sensor current may be generated. It does not occur. Further, according to the above method, when the F / C or the internal combustion engine stop operation is immediately stopped, the voltage applied to the air-fuel ratio sensor 32 is continuously maintained at 0.4 V, and the air-fuel ratio There is no need to open-control the. Therefore, according to the system of the present embodiment, the execution period of the air-fuel ratio feedback control can be ensured as long as possible while reliably preventing the sensor current of the air-fuel ratio sensor 32 from becoming excessive.
[0043]
In the first embodiment, the voltage applied to the air-fuel ratio sensor 32 is set to 0 V during the execution of the F / C or the internal combustion engine stop operation. However, the voltage is not necessarily required to be 0 V. Absent. In other words, the F / C or the applied voltage during the internal combustion engine stop operation only needs to be a voltage at which the air-fuel ratio sensor 32 does not generate an excessive sensor current, and the absolute value of the applied voltage satisfies such a condition. It only has to be kept within the range.
[0044]
Further, in the first embodiment described above, the circuit shown in FIG. 2 is used as the control circuit of the air-fuel ratio sensor 32, but the circuit that can be used as the control circuit is not limited to this.
FIG. 6 is a circuit diagram of another control circuit applicable to the system according to the first embodiment. In FIG. 6, the same components as those shown in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted or simplified.
The circuit shown in FIG. 6 is the same as the control circuit shown in FIG. 2 except that the switch 58 is inserted between the buffer circuit 44 and the AF- terminal 42 instead of removing the sub power supply path 52. It is. According to the circuit shown in FIG. 6, by turning on the switch 58, a potential of 2.9 V can be supplied to the AF- terminal 42, and an applied voltage of 0.4 V can be applied to the air-fuel ratio sensor 32. . When the switch 58 is turned off in this circuit, the AF- terminal 42 is in an electrically floating state. In this case, the potential of the AF- terminal becomes equal to the potential of the AF + terminal 62, and the voltage applied to the air-fuel ratio sensor 32 becomes substantially 0V.
In this way, the control circuit shown in FIG. 6 also switches the voltage applied to the air-fuel ratio sensor 32 between 0.4 V and 0 V by turning on and off the switch 58, similarly to the control circuit shown in FIG. be able to. Therefore, even when the control circuit shown in FIG. 6 is used, similarly to the case where the control circuit shown in FIG. 2 is used, it is possible to surely prevent an excessive sensor current from being generated during the fuel cut and the internal combustion engine stop operation. it can.
[0045]
In the first embodiment, the ECU 40 executes the processing of step 106, and the “voltage applying means” in the first invention executes the processing of step 114 to execute the first processing. The "applied voltage limiting means" in the invention is realized.
In the first embodiment described above, the “applied voltage limiting means” in the second aspect of the present invention is realized by the ECU 40 executing the processing of step 114 following the processing of step 112.
Further, in the first embodiment described above, the ECU 40 executes the processing of step 106 after the end of the F / C or the internal combustion engine stop operation, whereby the “applied voltage return means” in the fourth aspect of the present invention performs By executing the processing of step 110, the "control execution means" of the fourth invention is realized, and by executing the processing of step 108, "sensor current reflection inhibition means" of the fourth invention is realized. ing.
[0046]
Embodiment 2 FIG.
Next, a second embodiment of the present invention will be described with reference to FIGS.
The system of the present embodiment can be realized by mounting the control circuit shown in FIG. 7 on the ECU 40 and executing a routine shown in FIG. 8 described later in the configuration shown in FIG.
[0047]
FIG. 7 is a circuit diagram of a control circuit of the air-fuel ratio sensor 32 used in the present embodiment. 7, the same components as those shown in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted or simplified.
The control circuit shown in FIG. 7 is the same as the circuit shown in FIG. 2 except that an RC circuit, that is, a resistor 80 and a capacitor 82 is provided between the potential switching point 46 and the buffer circuit 44. In this circuit, when the potential of the potential switching point 46 changes with the switching of the switch 58, the RC circuit functions as a smoothing circuit that makes the change gradual and transmits the change to the buffer circuit 44.
[0048]
In the first embodiment described above, the voltage applied to the air-fuel ratio sensor 32 changes stepwise with the switching of the switch 58. When the applied voltage shows such a stepwise change, the same state as when the AC voltage is applied is formed, and the sensor current of the air-fuel ratio sensor 32 temporarily becomes a value that does not correspond to the exhaust air-fuel ratio. It becomes. Therefore, in the system of the first embodiment, after the applied voltage to the air-fuel ratio sensor 32 is switched from 0 V to 0.4 V, a mask period for prohibiting the use of the sensor current for a predetermined period is provided.
[0049]
On the other hand, if the potential transmitted to the buffer circuit 44 changes gently, the change in the applied voltage to the air-fuel ratio sensor 32 becomes gradual, similar to the case where the AC voltage is applied to the air-fuel ratio sensor 32. State formation can be prevented. In this case, the air-fuel ratio sensor 32 exhibits the characteristic shown in FIG. 3, and immediately after the switch 58 is switched (strictly, immediately after the applied voltage has risen to about 0.1 V), the exhaust air-fuel ratio Generates a sensor current corresponding to. Therefore, in the system of the present embodiment, it is possible to immediately restart the air-fuel ratio feedback control after the end of the F / C or the internal combustion engine stop operation.
[0050]
FIG. 8 shows a flowchart of a control routine executed by the ECU 40 in the present embodiment. The routine shown in FIG. 8 is the same as the routine shown in FIG. 4 except that the process of step 108 is deleted. According to the routine shown in FIG. 8, when the condition of step 104 is not satisfied, the applied voltage of 0.4 V is always set, and the air-fuel ratio feedback control is executed. In this case, it is assumed that the sensor current of the air-fuel ratio sensor 32 substantially corresponds to the actual exhaust air-fuel ratio in a situation where the applied voltage of 0.4 V is set (the switch 58 is turned off). Can be. Therefore, according to the system of the present embodiment, it is possible to quickly restart the highly accurate air-fuel ratio feedback control after the termination of the F / C or the internal combustion engine stop operation.
[0051]
By the way, in Embodiment 2 described above, the air-fuel ratio feedback control is always performed when the applied voltage is set to 0.4 V, but the present invention is not limited to this. That is, until the voltage applied to both ends of the air-fuel ratio sensor 32 actually rises to about 0.1 V after the applied voltage is switched from 0 V to 0.4 V, strictly speaking, the sensor current and the exhaust air-fuel ratio Do not correspond to each other (see FIG. 3). Therefore, the sensor current may be masked and the air-fuel ratio may be open-controlled for a short period until the voltage applied to both ends of the air-fuel ratio sensor 32 rises to about 0.1 V.
[0052]
Further, in the above-described second embodiment, the control circuit is a circuit in which an RC circuit is incorporated in the circuit shown in FIG. 2 (see FIG. 7). However, the control circuit that can be used in the present embodiment is not limited to this. Not something.
FIG. 9 is a circuit diagram of another control circuit applicable to the system according to the first embodiment. In FIG. 9, the same components as those shown in FIG. 6 or 7 are denoted by the same reference numerals, and the description thereof will be omitted or simplified.
The control circuit shown in FIG. 9 is the same as the circuit shown in FIG. 6 except that an RC circuit is inserted between the switch 58 and the AF-terminal 42. The RC circuit includes a resistor 80 and a capacitor 82, as in the RC circuit shown in FIG. In the circuit shown in FIG. 9, when the potential of the AF-terminal 42 changes with the switching of the switch 58, the RC circuit functions as a smoothing circuit that makes the change gentle. For this reason, the circuit shown in FIG. 9 can also prevent the applied voltage to the air-fuel ratio sensor 32 from changing abruptly with the switching of the switch 58 similarly to the circuit shown in FIG. Can realize the same function as the circuit shown in FIG.
[0053]
In the above-described second embodiment, the resistor 80 and the capacitor 82 constituting the RC circuit are set so that the rate of change of the applied voltage caused by the switching of the switch 58 does not exceed a predetermined limit value. . Here, the limit value is a limit value of a change rate that does not cause the air-fuel ratio sensor 32 to generate a sensor current that does not correspond to the exhaust air-fuel ratio, and is specifically determined experimentally in advance. It is assumed that In the present embodiment, the “voltage applying means” in the third aspect of the present invention is realized by the ECU 40 executing the process of step 106 on the premise that the control circuit of the air-fuel ratio sensor 32 is configured as described above. Have been.
[0054]
Embodiment 3 FIG.
Next, a third embodiment of the present invention will be described with reference to FIGS.
The system of the present embodiment can be realized by mounting the control circuit shown in FIG. 10 on the ECU 40 and executing a routine shown in FIG. 11 described later in the configuration shown in FIG.
[0055]
FIG. 10 is a circuit diagram of a control circuit of the air-fuel ratio sensor 32 used in the present embodiment. In FIG. 10, the same components as those shown in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted or simplified.
The control circuit shown in FIG. 10 is the same as the circuit shown in FIG. 2 except that a digital / analog converter (DA converter) 90 is provided instead of main power supply path 50 and sub power supply path 52. In this circuit, a control potential (a potential such as 3.3 V or 2.9 V) required to generate a voltage applied to the air-fuel ratio sensor 32 is generated by the DA converter 90. According to the DA converter 90, the voltage applied to the air-fuel ratio sensor 32 can be gradually changed between 0V and 0.4V. Therefore, according to the control circuit shown in FIG. 10, the same function as the control circuit in the second embodiment can be realized without using the RC circuit.
[0056]
FIG. 11 shows a flowchart of a control routine executed by the ECU 40 in the present embodiment. The routine shown in FIG. 11 is the same as the routine shown in FIG. 8 except that the processing in step 106 is replaced with the processing in steps 120 and 122. That is, in the routine shown in FIG. 8, when the condition of step 104 is not satisfied or when the condition of step 112 is not satisfied, first, it is determined whether or not the voltage applied to the air-fuel ratio sensor 32 has reached 0.4 V. Is determined (step 120).
In the present step 120, more specifically, it is determined whether or not the potential supplied from the DA converter 90 to the buffer 44 is 2.9 V or less.
[0057]
As a result, when it is determined that the applied voltage has reached 0.4 V, the process of step 110 (air-fuel ratio feedback control) is immediately executed. On the other hand, when it is determined that the applied voltage has not reached 0.4 V, the applied voltage is slightly increased by a predetermined step width (step 122), and then the process of step 110 is executed.
[0058]
According to the above processing, when the applied voltage to the air-fuel ratio sensor 32 is lower than 0.4 V, the value is gradually increased, and after the applied voltage reaches 0.4 V, the value is maintained. Can be. Therefore, according to the routine shown in FIG. 11, the applied voltage that was set to 0 V after the end of the F / C or the internal combustion engine stop operation can be gradually increased with 0.4 V as the upper limit. As described above, according to the combination of the control circuit shown in FIG. 10 and the routine shown in FIG. 11, the same functions as those of the control circuit (see FIGS. 7 to 9) in the second embodiment can be realized. For this reason, the same effects as in the second embodiment can be obtained by the system of the present embodiment.
[0059]
In the third embodiment, the processing in step 122 is designed so that the rate of change of the applied voltage caused by the repetition of the processing does not exceed a predetermined limit value. Here, the limit value is a limit value of a change rate that does not cause the air-fuel ratio sensor 32 to generate a sensor current that does not correspond to the exhaust air-fuel ratio, and is specifically determined experimentally in advance. It is assumed that In the present embodiment, the “voltage applying means” in the third aspect of the present invention is realized by the ECU 40 executing the processes of steps 120 and 122 described above.
[0060]
【The invention's effect】
Since the present invention is configured as described above, it has the following effects.
According to the first aspect, even when the vehicle system is operating, when the fuel injection to the internal combustion engine is stopped, the voltage applied to the air-fuel ratio sensor is suppressed to a sufficiently small value. Therefore, according to the present invention, it is possible to reliably prevent the air-fuel ratio sensor from generating an excessive sensor current when a gas similar to the atmosphere flows in the exhaust passage.
[0061]
According to the second aspect, after the fuel injection to the internal combustion engine is stopped, the limitation of the applied voltage can be started after a predetermined delay time. Therefore, according to the present invention, it is possible to effectively prevent the applied voltage from being uselessly limited before the gas containing a large amount of oxygen actually reaches around the air-fuel ratio sensor.
[0062]
According to the third aspect, after the fuel injection to the internal combustion engine is restarted, the voltage applied to the air-fuel ratio sensor can be slowly returned. Therefore, according to the present invention, it is possible to effectively prevent an error due to a sudden change in the applied voltage from being superimposed on the sensor current at the time of the return.
[0063]
According to the fourth aspect, it is possible to prevent the output of the air-fuel ratio sensor from being reflected in the control during a predetermined mask period after the fuel injection into the internal combustion engine is restarted. Therefore, according to the present invention, it is possible to effectively prevent inaccurate control based on the sensor current on which an error is superimposed from being performed when the applied voltage is restored.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining a configuration of a first embodiment of the present invention.
FIG. 2 is a circuit diagram of a control device for an air-fuel ratio sensor configured inside the ECU shown in FIG. 1;
FIG. 3 is a diagram for explaining sensor characteristics of the air-fuel ratio sensor shown in FIG.
FIG. 4 is a flowchart of a control routine executed in the first embodiment of the present embodiment.
FIG. 5 is a diagram showing a temporal change occurring in a sensor current after an applied voltage to the air-fuel ratio sensor shown in FIG. 1 is switched.
FIG. 6 is a circuit diagram of another control device that can be used in the first embodiment of the present invention.
FIG. 7 is a circuit diagram of a control device used in Embodiment 2 of the present invention.
FIG. 8 is a flowchart of a control routine executed in a second embodiment of the present invention.
FIG. 9 is a circuit diagram of another control device used in the second embodiment of the present invention.
FIG. 10 is a circuit diagram of a control device used in Embodiment 3 of the present invention.
FIG. 11 is a flowchart of a control routine executed in Embodiment 3 of the present embodiment.
[Explanation of symbols]
10 Internal combustion engine
12 Intake passage
14 Exhaust passage
28 Upstream catalyst
30 Downstream catalyst
32 air-fuel ratio sensor
50 Main power path
52 Sub power path
46 Potential switching point
58 switch
80 Resistance
82 capacitor
90 Digital-to-analog converter (DA converter)

Claims (4)

An air-fuel ratio sensor control device that is arranged in an exhaust passage of an internal combustion engine and receives a predetermined voltage to generate a sensor current according to an exhaust air-fuel ratio.
Voltage application means for applying a predetermined voltage to the air-fuel ratio sensor during operation of the vehicle system,
During operation of the vehicle system, when fuel injection to the internal combustion engine is stopped, applied voltage limiting means for limiting the applied voltage to the air-fuel ratio sensor so that its absolute value is equal to or less than a predetermined threshold,
A control device for an air-fuel ratio sensor, comprising: 2. The control device for an air-fuel ratio sensor according to claim 1, wherein the applied voltage limiting unit starts limiting the applied voltage after a predetermined delay time after fuel injection to the internal combustion engine is stopped. 3. After the fuel injection to the internal combustion engine is restarted, the voltage application unit increases the applied voltage, which has been limited to the threshold or less, toward the predetermined voltage within a range where the rate of increase does not exceed the limit value. The control device for an air-fuel ratio sensor according to claim 1 or 2, wherein: The voltage applying means, after fuel injection to the internal combustion engine is restarted, comprises an applied voltage return means for returning the applied voltage limited to the threshold or less to the predetermined voltage,
Control execution means for performing predetermined control based on the sensor current,
A predetermined mask period after fuel injection to the internal combustion engine is restarted, a sensor current reflection inhibiting means for inhibiting the sensor current from being based on the control,
The control device for an air-fuel ratio sensor according to any one of claims 1 to 3, further comprising:

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