JP4725481B2 - Air-fuel ratio control device - Google Patents

Description

  The present invention relates to an air-fuel ratio control device. More preferably, the present invention relates to an air-fuel ratio control apparatus for an internal combustion engine that can use an alternative fuel other than gasoline.

  Japanese Patent Application Laid-Open No. 2000-170581 discloses an internal combustion engine that uses fuel other than gasoline as fuel. As described in this prior art, the composition of each gas in the fuel used in such an internal combustion engine differs for each fuel. Even if the fuel is the same, for example, the composition may differ depending on the manufacturer of the gas fuel. Thus, when using fuel other than gasoline, the theoretical air-fuel ratio of the internal combustion engine has a value different from that of gasoline, and further, the theoretical air-fuel ratio differs depending on the fuel used. Specifically, the stoichiometric air-fuel ratio varies widely in the vicinity of 17.0.

  Such variations in the theoretical air-fuel ratio are measured by measuring the oxygen concentration of the exhaust gas, obtaining an air-fuel ratio feedback correction value from the measured value, and correcting the fuel injection amount, and storing the correction value. When feedback learning control for learning is performed, the control is absorbed to a certain extent. However, if the variation in the stoichiometric air-fuel ratio becomes so large that it cannot be absorbed by these controls, it may cause extreme combustion failure or knocking.

  Therefore, in the above prior art, it is determined whether or not a combustion failure has occurred when the internal combustion engine is started. As a result of this determination, if it is determined that the combustion is in a poor state, the fuel property is different from the fuel that has been used so far. There is. Therefore, the feedback learning value related to the fuel injection amount based on the fuel properties so far is deleted. At the same time, the air-fuel ratio correction value is once set to a correction correction value for correcting the air-fuel ratio to the rich side when an excessively lean state is assumed. From this state, the correction correction value is gradually returned to the original air-fuel ratio correction value. In this recovery process, the feedback learning value is calculated and stored. As a result, an air-fuel ratio correction value and feedback learning value that match the fuel properties can be set, and even when the fuel properties used in the internal combustion engine change, the fuel injection amount can be controlled in accordance with the fuel properties. It is supposed to be.

JP 2000-170581 A Japanese Patent Laid-Open No. 2000-220482

  According to the above prior art, when the internal combustion engine is started, the air-fuel ratio control that matches the fuel property can be performed by recalculating the feedback correction value and the learning value for the fuel injection amount. However, during the recalculation performed when a change in fuel properties is recognized, normal air-fuel ratio control cannot be performed, and a correction correction value is forcibly set and the correction value is gradually corrected from that correction value. Control to change the value is required. Therefore, it is difficult to suppress fuel variation and drivability deterioration during recalculation.

  Further, from the output of the air-fuel ratio sensor, usually the air-fuel ratio when the fuel is gasoline is detected. Therefore, when fuel other than gasoline is used, the air-fuel ratio calculated from the output of the air-fuel ratio sensor is different from the actual air-fuel ratio, and an air-fuel ratio calculation error occurs. However, in order to perform more accurate air-fuel ratio control, it is preferable that the air-fuel ratio can be accurately detected according to the fuel properties.

  The present invention has been made to solve the above-described problems. Even when the fuel property changes, the air-fuel ratio is detected according to the fuel property while performing the air-fuel ratio control at an earlier stage. It is an object of the present invention to provide an air-fuel ratio control apparatus improved so as to be able to achieve the above.

In order to achieve the above object, a first invention is an air-fuel ratio control apparatus that controls the air-fuel ratio of an internal combustion engine according to the output of an air-fuel ratio sensor that can use fuel other than gasoline as fuel,
Fuel property determining means for determining the fuel property of the fuel used in the internal combustion engine;
Completion determination means for determining whether or not the fuel property determination is completed;
When the completion of the fuel property determination is not recognized, an electromotive force generated between both electrodes of the air-fuel ratio sensor without applying a voltage between the air-side electrode and the exhaust-side electrode of the air-fuel ratio sensor. Electromotive force detection means for detecting;
Positive voltage application that applies a positive voltage between both electrodes of the air-fuel ratio sensor so that the potential of the atmosphere side electrode is higher than the potential of the exhaust side electrode when the fuel property determination is completed Means,
Sensor current detection means for detecting a sensor current flowing between both electrodes of the air-fuel ratio sensor;
When the completion of the fuel property determination is not recognized, air-fuel ratio control is performed according to the electromotive force. When the completion of the fuel property determination is confirmed, the fuel property determination is performed according to the sensor current detected when the positive voltage is applied. Air-fuel ratio control means for performing air-fuel ratio control,
It is characterized by providing.

According to a second invention, in the first invention,
Map selection means for selecting a map that defines a relationship between a sensor current and an air-fuel ratio detected when the positive voltage is applied, in accordance with the determined fuel property, when the fuel property is determined;
Air-fuel ratio detecting means for detecting an air-fuel ratio according to the selected map in accordance with a sensor current detected when the positive voltage is applied;
The air-fuel ratio control means performs air-fuel ratio control according to the air-fuel ratio when completion of the fuel property determination is recognized.

According to a third invention, in the first or second invention,
Impedance detection voltage application means for applying an impedance detection voltage for detecting an element impedance of a sensor element of the air / fuel ratio sensor to the air / fuel ratio sensor;
An element impedance calculation means for calculating the element impedance according to a sensor current detected during application of the impedance detection voltage;
Is further provided.

According to a fourth invention, in the third invention,
First element temperature determining means for determining whether the temperature of the sensor element of the air-fuel ratio sensor has reached a first activation temperature according to the element impedance when the completion of the fuel property determination is not recognized; ,
Second element temperature determining means for determining whether or not the temperature of the sensor element has reached a second activation temperature according to the element impedance when completion of the fuel property determination is recognized;
Further comprising
The electromotive force detection means detects the electromotive force when it is recognized that the temperature of the sensor element has reached the first activation temperature,
The positive voltage applying means applies the positive voltage when it is recognized that the temperature of the sensor element has reached the second activation temperature.

  According to the first invention, when the completion of the fuel property determination is not recognized, the air-fuel ratio control is performed according to the electromotive force detected in a state where no voltage is applied to the air-fuel ratio sensor, and the completion of the fuel property determination is completed. If it is recognized, air-fuel ratio control is performed in accordance with the sensor current detected with a positive voltage applied. Here, when the electromotive force is detected in a state where no voltage is applied to the air-fuel ratio sensor, the electromotive force has the same characteristics as the oxygen sensor. That is, the electromotive force changes abruptly in the vicinity of the stoichiometric air-fuel ratio regardless of the fuel properties, and shows a substantially constant low value when the oxygen is excessive with respect to the stoichiometric air-fuel ratio. Shows an almost constant high value. Therefore, based on the electromotive force, it is possible to detect whether at least the current air-fuel ratio is excessive or insufficient. Therefore, the air-fuel ratio can be controlled at least in the vicinity of the theoretical air-fuel ratio until the fuel property determination is completed. Therefore, even when the fuel property changes, it is possible to suppress a decrease in drivability and variations in combustion while suppressing an increase in emissions in the exhaust gas during the fuel property determination.

  According to the second invention, a map that defines the relationship between the sensor current and the air-fuel ratio during application of a positive voltage is selected according to the determined fuel property, and the air-fuel ratio can be detected according to this map. . Therefore, even if the fuel property changes, the air-fuel ratio corresponding to the fuel can be detected, and the air-fuel ratio control can be realized with higher accuracy.

  According to the third aspect of the invention, the element impedance can be calculated based on the sensor current detected during application of the impedance detection voltage. Therefore, even when the electromotive force is detected without applying a voltage to the air-fuel ratio sensor, the element impedance can be easily detected by switching to the impedance detection voltage application.

  According to the fourth aspect of the invention, the sensor element temperature is determined according to the element impedance, and the electromotive force is detected when the sensor element temperature is found to have reached the first activation temperature. When it is recognized that the temperature has reached the second activation temperature, a positive voltage is applied. Thus, the air-fuel ratio sensor is reliably controlled by the activation temperature corresponding to each use state, and a more accurate air-fuel ratio sensor output can be obtained.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof is simplified or omitted.

Embodiment.
[Configuration of Air-Fuel Ratio Sensor of Embodiment]
FIG. 1 is a schematic diagram for explaining the structure of a system in which an air-fuel ratio control apparatus according to an embodiment of the present invention is mounted. The system shown in FIG. 1 includes an internal combustion engine 10. The internal combustion engine 10 can use gasoline, ethanol, or a mixture of gasoline and ethanol as the fuel. The internal combustion engine 10 includes a plurality of cylinders, and each cylinder includes an injector (not shown) that supplies fuel into the cylinder. Necessary fuel is supplied from the fuel tank 12 to the injector of each cylinder. A fuel property sensor 14 is attached to the fuel tank 12. Based on the output of the fuel sensor 14, it is possible to detect the property of the fuel filled in the fuel tank 12.

  An exhaust passage 16 is provided in the exhaust system of the internal combustion engine 10. A catalyst 18 is installed in the exhaust passage 16. An air-fuel ratio sensor 20 is attached upstream of the catalyst 18 in the exhaust passage 16. An oxygen sensor 22 is attached downstream of the catalyst 18 in the exhaust passage 16.

  This system includes an ECU (Electronic Control Unit) 24 as an air-fuel ratio control device. A fuel property sensor 14, an air-fuel ratio sensor 20, and an oxygen sensor 22 are connected to the input side of the ECU 24, and outputs from these sensors are taken into the ECU 24 to detect information on the fuel property, air-fuel ratio, and the like. Further, a necessary control signal is issued from the output side of the ECU 24, thereby performing control necessary for the operation of the internal combustion engine 10.

[Air-fuel ratio sensor drive circuit]
FIG. 2 is a circuit diagram for driving the air-fuel ratio sensor 20 connected to the air-fuel ratio sensor 20 in the embodiment of the present invention. The drive circuit 30 shown in FIG. 2 includes an anode terminal 32 connected to the atmosphere side electrode (not shown) of the air-fuel ratio sensor 20 and a negative electrode terminal 34 connected to the exhaust side electrode (not shown). Yes. A switching circuit 36 is connected to the anode terminal 32. Connected to the switching circuit 36 is a feedback circuit for controlling the voltage supplied from the applied voltage operation unit to be constant and supplying the voltage to the anode terminal. A switching circuit 38 is connected to the negative terminal 34. The switching circuit 38 is connected to a feedback circuit for controlling the voltage supplied from the applied voltage operation unit to be constant and supplying the voltage to the negative terminal 34.

  The switching circuits 36 and 38 are connected to an output port (not shown) of the ECU 24. The ECU 24 switches connection of the switches SW1 and SW2 of the switching circuits 36 and 38 by a control signal for switching ON / OFF of SW1 and ON / OFF of SW2. When the switches of the switching circuits 36 and 38 are switched to SW1, the potential of the anode terminal 32 and the potential of the negative terminal 34 are maintained at the potential supplied from the applied voltage operation unit.

  Specifically, during normal air-fuel ratio detection, an anode reference voltage (for example, 3.3 V) is supplied to the anode terminal 32, and the potential is maintained at the anode reference voltage. A negative reference voltage (for example, 2.9V) is supplied to the negative terminal 34, and the potential thereof is maintained at the negative reference voltage (2.9V). As a result, an air-fuel ratio detection voltage (positive voltage) is applied between the anode terminal 32 and the negative electrode terminal 34. That is, a positive voltage is applied to the air-fuel ratio sensor 20 in a state where the electrodes of the air-fuel ratio sensor 20 are connected to the terminals 32 and 34. The potential of the anode terminal 32 at this time is guided to AD1. The ECU 24 can detect the sensor current that flows when a positive voltage is applied to the air-fuel ratio sensor 20 by taking in the potential guided to AD1. Hereinafter, in this embodiment, such a use state of the air-fuel ratio sensor 20 is referred to as an “air-fuel ratio detection mode”.

  Further, when an AC voltage for detecting element impedance is supplied in addition to the positive voltage from the applied voltage operation unit, an impedance detection voltage is applied between the electrodes of the air-fuel ratio sensor 20. The ECU 24 can detect a sensor current based on the potential of AD1, and further detect an element impedance based on the sensor current. Hereinafter, in this embodiment, such a use state of the air-fuel ratio sensor 20 is referred to as an “impedance detection mode”. The element impedance has a correlation with the sensor element temperature (element temperature) of the air-fuel ratio sensor 20. Therefore, the element temperature can be detected based on the element impedance, or the element temperature can be controlled according to the element impedance.

  On the other hand, when the switching circuits 36 and 38 are in the SW2 state, the voltage applied between the anode terminal 32 and the negative electrode terminal 34, that is, the voltage applied to the air-fuel ratio sensor 20, becomes zero. In this voltage application OFF state, the negative terminal 34 is grounded, and the positive terminal is connected to AD2 of the ECU 24. The electromotive force from the air-fuel ratio sensor 20 is guided to AD2. The ECU 24 can detect the electromotive force when the voltage application of the air-fuel ratio sensor 20 is OFF by taking in the output of AD2. Hereinafter, in this embodiment, such a use state of the air-fuel ratio sensor 20 is referred to as an “oxygen sensor mode”.

[Detecting air-fuel ratio according to fuel properties]
By the way, in this system, as described above, gasoline, ethanol, or a mixture of these can be used as the fuel. Further, the fuel is not always the same, and different fuels can be used when the mixing ratio of ethanol is between 0 and 100%. However, when the fuel property (mixing ratio) of the fuel used in this way changes, the value of the theoretical air-fuel ratio changes according to the fuel, and the correspondence between the sensor current when a positive voltage is applied and the air-fuel ratio of the exhaust gas Will be different. Therefore, in this embodiment, the detection of the air-fuel ratio according to the fuel property is realized by the following method.

  FIG. 3 is a diagram showing the output of the air-fuel ratio sensor 20 when the air-fuel ratio sensor 20 is used in the air-fuel ratio detection mode in the embodiment of the present invention. In FIG. 3, the horizontal axis represents the air-fuel ratio, and the vertical axis represents the sensor current. Also, the solid line (a) in FIG. 3 represents the sensor current when gasoline is used as the fuel for the internal combustion engine 10, and the dotted line (b) is the sensor current when 100% ethanol fuel is used as the fuel for the internal combustion engine 10. Represents.

  When a positive voltage is applied between both electrodes of the air-fuel ratio sensor 20, a sensor current corresponding to the oxygen concentration in the exhaust gas flows between the electrodes. The normal ECU 24 stores a map that defines the relationship between the sensor current and the air-fuel ratio when gasoline is used as fuel, as shown by the solid line (a). When gasoline is used as the fuel, the air-fuel ratio is detected according to this map according to the output (sensor current) of the air-fuel ratio sensor 20 taken into the ECU 24.

  Here, the sensor current detected in the air-fuel ratio detection mode corresponds to the oxygen concentration in the exhaust gas regardless of the fuel property. However, the air-fuel ratio with respect to the oxygen concentration in the exhaust gas differs for each fuel property. That is, when the fuel properties are different, the relationship between the sensor current and the exhaust gas air-fuel ratio is different.

  Specifically, for example, as shown by the dotted line (b) in FIG. 3, the air-fuel ratio corresponding to the sensor current in the case of 100% ethanol is different from the air-fuel ratio in the case of gasoline (solid line (a)). . Specifically, in the case of 100% ethanol, the theoretical air-fuel ratio A / F = 9. Therefore, the air-fuel ratio (dotted line (b)) with respect to the sensor current at 100% ethanol shown in FIG. 3 is calculated as the air-fuel ratio (solid line (a)) in the case of gasoline, and the air-fuel ratio calculated when the sensor current is zero. It becomes a value approximated to a value shifted to a position where the fuel ratio becomes 9. However, particularly in the region richer than the stoichiometric air-fuel ratio, the inclination of the output characteristics shown in FIG. 3 tends to be different between gasoline and ethanol.

  The characteristics of the air-fuel ratio with respect to such a sensor current are different for each fuel property. For example, in a fuel in which gasoline and ethanol are mixed, the air-fuel ratio corresponding to the sensor current tends to decrease as the mixing ratio of ethanol increases.

  Therefore, the ECU 24 stores a map that defines the relationship between the sensor current and the air-fuel ratio for each fuel property. When the ethanol content in the fuel is different, the map can be switched to a map that defines the relationship between the sensor current and the air-fuel ratio in accordance with the fuel properties. By switching to the map corresponding to the fuel property in this way, the air-fuel ratio can be calculated based on the sensor current of the air-fuel ratio sensor 20.

[Air-fuel ratio control until map switching]
FIG. 4 is a diagram illustrating an electromotive force in the oxygen sensor mode of the air-fuel ratio sensor 20. In FIG. 4, the horizontal axis represents the air-fuel ratio, and the vertical axis represents the sensor output [V]. In FIG. 4, the solid line (a) represents the electromotive force when the fuel is gasoline, and the dotted line (b) represents the electromotive force when the fuel is 100% ethanol.

  As shown in FIG. 4, in the case of gasoline fuel (solid line (a)) or in the case of 100% ethanol fuel (dotted line (b)), voltage application to the air-fuel ratio sensor 20 is turned off. There is no significant difference in the characteristics of the sensor output (electromotive force) detected in (1). That is, the electromotive force is about 1 [V] when the exhaust gas is leaner than the stoichiometric air-fuel ratio (excess oxygen), regardless of the fuel properties, and 0 [V] when the exhaust gas is rich (oxygen deficient) It becomes a low value close to, and rapidly reverses in the vicinity of the theoretical air-fuel ratio. This is because when the air-fuel ratio sensor 20 is used as an oxygen sensor, the electromotive force thereof corresponds to the oxygen partial pressure in the exhaust gas. In other words, even if the stoichiometric air-fuel ratio varies depending on the fuel properties, the amount of oxygen in the exhaust gas in the vicinity of the stoichiometric air-fuel ratio does not change depending on the fuel properties, so the output changes abruptly at the stoichiometric air-fuel ratio. The output characteristics are almost the same regardless of the fuel properties. Therefore, when the air-fuel ratio sensor 20 is used in the oxygen sensor mode, it can be used as it is even when the fuel properties are different.

  By the way, as described above, even when fuel other than gasoline is used, if the fuel property is determined, the air-fuel ratio sensor 10 switches the map according to the fuel property, and based on the sensor current. The air-fuel ratio can be detected. However, in order to switch maps in this way, it is necessary to determine the fuel property of the internal combustion engine 10 every time the fuel property changes.

  The fuel property can be detected by a fuel sensor 14 attached to the fuel tank 12. However, it is difficult to instantly detect the fuel property accurately by the fuel sensor 14, and a certain amount of time is required. Until the fuel property is detected, the air-fuel ratio cannot be detected by the air-fuel ratio sensor 20. Accordingly, it is conceivable that various deviations occur in the air-fuel ratio control, such as a deviation in the target value of the fuel injection amount during this period.

  Therefore, in the system of the embodiment, the air-fuel ratio sensor 20 is used in the oxygen sensor mode until the fuel property is correctly detected after the fuel property is changed. As a result, it is possible to detect whether the exhaust gas is richer or leaner than the stoichiometric air-fuel ratio by the electromotive force detected from the air-fuel ratio sensor 20. Thereby, it is possible to control at least the exhaust gas air-fuel ratio to be close to the stoichiometric air-fuel ratio until the fuel property is determined. After the fuel property is detected, the map is switched to a map corresponding to the fuel property, and then application of a positive voltage to the air-fuel ratio sensor 20 is started. Thereby, the air-fuel ratio can be detected correctly according to the fuel property.

  As described above, the air-fuel ratio sensor 20 is switched between the oxygen sensor mode and the air-fuel ratio detection mode before and after the detection of the fuel property. As a result, the variation in air-fuel ratio control until the fuel property is determined can be reduced, and after the fuel property determination, the air-fuel ratio corresponding to the fuel can be detected, and the air-fuel ratio control can be performed with higher accuracy. Can be realized.

[Control of element temperature]
Here, in the case of the above use, in the oxygen sensor mode, it is preferable to use the oxygen sensor in a state where the activation temperature (first activation temperature) as an oxygen sensor of about 550 ° C. has been reached. On the other hand, in the case of use in the air-fuel ratio detection mode, it is preferably used in a state where the activation temperature (second activation temperature) of a normal air-fuel ratio sensor of about 650 ° C. has been reached. Therefore, in this embodiment, the element temperature is controlled to an appropriate temperature in each of the oxygen sensor mode and the air-fuel ratio detection mode. Specifically, since the element temperature has a correlation with the element impedance as described above, the element impedance can be detected in the impedance detection mode and controlled based on this.

[Specific Control Routine of this Embodiment]
FIG. 5 is a flowchart for illustrating a control routine executed by the system in the embodiment of the present invention. In the routine of FIG. 5, it is first determined whether or not the internal combustion engine 10 is currently being started (S100). Since it is considered that the addition of fuel is normally performed in a state in which the internal combustion engine 10 is stopped, there is a low possibility that a change in the fuel property will occur at a time other than when the internal combustion engine 10 is started. Therefore, if it is not recognized that the internal combustion engine 10 is being started, the current process ends.

  On the other hand, if it is determined in step S100 that the internal combustion engine 10 is being started, the fuel property is then determined (S110). The fuel property is determined in the ECU 24 by taking the output of the fuel property sensor 14 installed in the fuel tank 12.

  Next, it is determined whether or not the fuel property determination is completed (S120). If the completion of the fuel property determination is not recognized in step S120, it is next determined whether or not the element temperature of the air-fuel ratio sensor 20 has reached the activation temperature in the oxygen sensor mode (here, about 550 ° C.). (S130). Specifically, the air-fuel ratio sensor 20 is set to the impedance detection mode, and the element impedance is calculated according to the sensor current. Thereafter, it is determined whether or not the calculated element impedance is smaller than an impedance corresponding to 550 ° C.

  In step S130, when it is not recognized that the element temperature is 550 ° C. or higher, the element temperature is determined in step S130 while the air-fuel ratio sensor 20 is warmed up until the element temperature reaches the activation temperature. . On the other hand, when it is recognized that the element temperature is 550 ° C. or higher, the air-fuel ratio sensor 20 is switched to the oxygen sensor mode (S132). That is, the switching circuits 36 and 38 are controlled by the control signal from the ECU 24, whereby the switches of both circuits are connected to the SW2 side. As a result, the negative electrode terminal 34 side is connected to the ground, and the anode terminal 32 is connected to AD2 of the ECU 24. As a result, the electromotive force of the air-fuel ratio sensor 20 is guided to AD2 and detected by the ECU 24. As a result, it is detected by this electromotive force whether or not the current air-fuel ratio is shifted to the rich side or the lean side, and in accordance with this, control close to the theoretical air-fuel ratio becomes possible.

  On the other hand, when the completion of the fuel property determination is recognized in step S120, the map of the air-fuel ratio and the sensor current is switched according to the fuel property (S140). Specifically, a map corresponding to the fuel property determined in S110 is read, and this map is set as a map that defines the relationship between the sensor current and the air-fuel ratio. A map corresponding to the fuel property is stored in the ECU 24 in advance.

  Next, it is determined whether or not the element temperature of the air-fuel ratio sensor 20 has reached the activation temperature in the air-fuel ratio detection mode (here, about 650 ° C.) (S142). Here, as in the case of step S130, the impedance detection mode is switched to detect the element impedance, and the element temperature is determined based on this. If it is not recognized that the element temperature is 650 ° C. or higher, the element temperature determination in step S142 is repeatedly performed while the sensor element is warmed up.

  On the other hand, if it is recognized that the element temperature has reached 650 ° C. or higher, then the air-fuel ratio sensor 20 is set to the air-fuel ratio detection mode (S144). Specifically, the switching circuits 36 and 38 are controlled by a control signal from the ECU 24, whereby the switches of both circuits are switched to the SW1 side and connected. As a result, the anode terminal 32 and the negative electrode terminal 34 are maintained at the respective reference potentials, and a positive voltage is applied between both electrodes of the air-fuel ratio sensor 20. As a result, a sensor current corresponding to the oxygen concentration of the exhaust gas flows through the air-fuel ratio sensor 20. This current is calculated based on the anode potential taken into the ECU 24 from AD1. Thereafter, the air-fuel ratio is obtained according to the map set in step S140. Thereby, air-fuel ratio control according to the target air-fuel ratio can be executed.

  As described above, according to this embodiment, in the stage before the fuel property determination, the air-fuel ratio sensor 20 is used as an oxygen sensor so that air-fuel ratio control at least near the stoichiometric air-fuel ratio can be executed. ing. Further, after the fuel property determination is completed, the air-fuel ratio can be detected according to the fuel property by switching the map. Therefore, air-fuel ratio control can be performed with higher accuracy.

  In this embodiment, the case where the fuel property is determined every time the internal combustion engine 10 is started has been described. However, the present invention is not limited to this. For example, it is possible to detect that the fuel has been actually replenished and to perform the control of the embodiment only when the fuel is replenished.

  Further, in the embodiment, a case has been described in which the internal combustion engine 10 can use a mixed fuel of gasoline and ethanol containing ethanol at different contents of 0 to 100%. However, the fuel to be used is not limited to gasoline, ethanol and a mixed fuel thereof, but may be another fuel or a mixture of other fuel and gasoline. Even in such a case, the air-fuel ratio using the air-fuel ratio sensor 20 is stored in advance in the ECU 24 by storing a map of the sensor current and the air-fuel ratio in the same manner as described above for each fuel property assumed to be used. Detection can be performed. Even when the fuel properties are different, the characteristics of the electromotive force detected in the oxygen sensor mode are almost the same. Therefore, until the fuel property determination is completed, at least the vicinity of the theoretical air-fuel ratio can be controlled by using the oxygen sensor mode regardless of the fuel property.

  Further, in the embodiment, the case has been described in which the ECU 24 stores a map corresponding to the fuel property. However, for example, in the case of a fuel containing gasoline and ethanol, the value of the air-fuel ratio with respect to the sensor current corresponding to the fuel properties is the air-fuel ratio in the case of gasoline, and the air-fuel ratio when the sensor current is zero is the theory of the fuel. The air-fuel ratio is approximated to a parallel shift. Therefore, instead of a map for each fuel property, for example, based on the relationship as described above, a correction value corresponding to the fuel content of ethanol or the like is obtained by a map or calculation. By correcting the air-fuel ratio calculated from the above, the air-fuel ratio corresponding to the fuel property can be obtained.

  In the embodiment, the element temperature in the oxygen sensor mode is about 550 ° C. or higher, and the element temperature in the air-fuel ratio detection mode is about 650 ° C. or higher. However, the element temperature is not limited to this in the present invention. For example, when it is necessary to start air-fuel ratio control sooner, use in the oxygen sensor mode may be started even when the element temperature is 550 ° C. or lower. In this case, however, the sensor element temperature is preferably controlled to about 350 ° C. or higher.

  In the embodiment, the case where the element temperature is controlled based on the element impedance detected has been described. However, the control of the element temperature is not limited to such a method, and may be performed by another method.

  Further, in the embodiment, the case where the determination of the fuel property is performed based on the output of the fuel property sensor 14 attached to the fuel tank 12 has been described. However, the present invention is not limited to this, and the fuel property sensor 14 may be attached to another position. Further, the fuel property determination is not limited to the fuel property sensor 14, and the fuel property determination may be performed by another method.

  In the above embodiment, when referring to the number of each element, quantity, quantity, range, etc., unless otherwise specified or clearly specified in principle, the number referred to It is not limited. Further, the structures described in the embodiments, steps in the method, and the like are not necessarily essential to the present invention unless otherwise specified or clearly specified in principle.

  For example, in FIG. 5, by executing step S110, the “fuel property determining means” of the present invention is realized, and by executing step S120, the “completion determining means” is realized, and step S132 is executed. The “electromotive force detection means” is realized by being executed, and the “sensor current detection means” is realized by executing step S144. Further, the “air-fuel ratio control means” is realized by controlling the air-fuel ratio based on the detected electromotive force or sensor current based on the determination in step S120.

  Further, for example, the “map selection unit” of the present invention is realized by executing step S140, and the “air-fuel ratio detection unit” is realized by detecting the air-fuel ratio in step S144. Further, the impedance detection voltage is supplied by the applied voltage operation means, thereby realizing the “impedance detection voltage application means” of the present invention, the sensor current at this time is detected, and the element impedance is calculated in the ECU 24. Thus, an “impedance calculation means” is realized. Further, for example, the “first element temperature determination unit” is realized by executing step S130, and the “second element temperature determination unit” is realized by executing step S142.

It is a schematic diagram for demonstrating the structure of the system in embodiment of this invention. It is a schematic diagram for demonstrating the drive circuit of the air fuel ratio sensor in embodiment of this invention. It is a figure for demonstrating the relationship between the sensor electric current and an air fuel ratio of the air fuel ratio sensor in embodiment of this invention. It is a figure for demonstrating the relationship between an electromotive force and an air fuel ratio of the air fuel ratio sensor in embodiment of this invention. It is a flowchart for demonstrating the routine of control which ECU performs in embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Fuel tank 14 Fuel property sensor 16 Exhaust passage 18 Catalyst 20 Air-fuel ratio sensor 22 Oxygen sensor 24 ECU
30 Driving Circuit 32 Anode Terminal 34 Negative Terminal 36, 38 Switching Circuit

Claims (4)

An air-fuel ratio control device for controlling the air-fuel ratio of an internal combustion engine that can use fuel other than gasoline as fuel according to the output of the air-fuel ratio sensor,
Fuel property determining means for determining the fuel property of the fuel used in the internal combustion engine;
Completion determination means for determining whether or not the fuel property determination is completed;
When the completion of the fuel property determination is not recognized, an electromotive force generated between both electrodes of the air-fuel ratio sensor without applying a voltage between the air-side electrode and the exhaust-side electrode of the air-fuel ratio sensor. Electromotive force detection means for detecting;
First air-fuel ratio control means for controlling the air-fuel ratio to the vicinity of the theoretical air-fuel ratio in accordance with the electromotive force until the completion of the fuel property determination is recognized;
A positive voltage applying means for applying a positive voltage between the electrodes of the air-fuel ratio sensor so that the potential of the atmosphere side electrode is higher than the potential of the exhaust side electrode after the completion of the fuel property determination is recognized. When,
Sensor current detection means for detecting a sensor current flowing between both electrodes of the air-fuel ratio sensor;
Air-fuel ratio detecting means for detecting an air-fuel ratio of the internal combustion engine according to the fuel property and the sensor current;
Second air-fuel ratio control means for performing air-fuel ratio control in accordance with the air-fuel ratio detected by the air-fuel ratio detection means after completion of the fuel property determination is recognized;
An air-fuel ratio control apparatus comprising: Map selection means for selecting a map that defines a relationship between a sensor current and an air-fuel ratio detected when the positive voltage is applied, in accordance with the determined fuel property, when the fuel property is determined;
Air-fuel ratio detecting means for detecting an air-fuel ratio according to the selected map in accordance with a sensor current detected when the positive voltage is applied;
2. The air-fuel ratio control apparatus according to claim 1, wherein the air-fuel ratio control means performs air-fuel ratio control according to the air-fuel ratio when completion of the fuel property determination is recognized. Impedance detection voltage application means for applying an impedance detection voltage for detecting an element impedance of a sensor element of the air / fuel ratio sensor to the air / fuel ratio sensor;
An element impedance calculation means for calculating the element impedance according to a sensor current detected during application of the impedance detection voltage;
The air-fuel ratio control apparatus according to claim 1, further comprising: First element temperature determining means for determining whether the temperature of the sensor element of the air-fuel ratio sensor has reached a first activation temperature according to the element impedance when the completion of the fuel property determination is not recognized; ,
Second element temperature determining means for determining whether or not the temperature of the sensor element has reached a second activation temperature according to the element impedance when completion of the fuel property determination is recognized;
Further comprising
The electromotive force detection means detects the electromotive force when it is recognized that the temperature of the sensor element has reached the first activation temperature,
4. The air-fuel ratio control apparatus according to claim 3, wherein the positive voltage applying unit applies the positive voltage when it is recognized that the temperature of the sensor element has reached the second activation temperature. 5. .

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