JP5903992B2 - Oxygen sensor control device - Google Patents

Description

  The present invention relates to an oxygen sensor control device used for air-fuel ratio control of an internal combustion engine.

  A control device and a control method for an oxygen sensor used for air-fuel ratio control of an internal combustion engine are disclosed in Japanese Patent Application Laid-Open No. 2004-177178 (Patent Document 1) and Japanese Patent Application Laid-Open No. 61-26853 (Patent Document 2). .

  In an automobile air-fuel ratio control system, the oxygen concentration in exhaust gas is detected by an oxygen sensor, and the air-fuel ratio of the air-fuel mixture sucked into the engine is feedback-controlled based on the detected value, thereby improving the exhaust gas purification performance by the catalyst. I try to increase it. Since the oxygen sensor generally has a large temperature dependency of the output voltage, it is necessary to keep the element temperature of the oxygen sensor at an appropriate temperature (active temperature) in order to maintain good detection accuracy of the oxygen concentration. For this reason, some oxygen sensors are provided with a heater, and the element temperature is controlled to be kept at the activation temperature (for example, about 600 ° C. or higher) by the heat generated by the heater. In addition, it is necessary to detect the element temperature in order to perform feedback control of energization to the heater. However, if a temperature sensor is arranged in the oxygen sensor, it becomes a factor of increase in size and cost. For this reason, focusing on the fact that the impedance (element resistance) of the oxygen sensor changes according to the element temperature, a method for detecting the impedance and calculating the element temperature has been proposed.

  Patent Document 1 describes an example of an impedance detection apparatus for the oxygen sensor described above. FIG. 14A is a diagram showing an example of the relationship between the element temperature and impedance of the oxygen sensor described above, and FIG. 14B shows the impedance detection period of the oxygen sensor and the air-fuel ratio control period of the oxygen sensor. It is the figure which showed an example of this flow.

  FIG. 15A is a diagram illustrating a circuit configuration of a main part of a conventional oxygen sensor control device 90 similar to that of Patent Document 1. In FIG. FIG. 15B is a timing chart of the two transistors SW1 and SW2 constituting the impedance measurement switching circuit 20 in the oxygen sensor control device 90 of FIG.

  An oxygen sensor control device 90 shown in FIG. 15A is a control device for the oxygen sensor 10 used for air-fuel ratio control of an internal combustion engine.

  The oxygen sensor control device 90 of FIG. 15A has a shunt resistor Rs connected in series to the oxygen sensor 10 in order to detect the impedance Z of the oxygen sensor 10 and control the temperature. Further, the oxygen sensor control device 90 receives a signal from the electronic control unit (ECU) 30, and in series between the impedance detection period of the oxygen sensor 10 and the air-fuel ratio control period of the oxygen sensor 10 shown in FIG. An impedance measurement switching circuit 20 that switches between the connected shunt resistor Rs and the value of the current flowing through the oxygen sensor 10 is provided. The impedance measurement switching circuit 20 shown in FIG. 15 (a) includes two transistors SW1 and SW2 connected in series between the power supply potential VCC and the ground potential. In the oxygen sensor control device 90, the shunt resistor Rs and the oxygen sensor 10 connected in series at the connection point P1 are inserted between the connection point P2 of the two transistors SW1 and SW2 and the ground potential. The impedance Z of the oxygen sensor 10 is detected by the calculation formula shown in FIG. 15A by sweeping the voltage applied to the oxygen sensor 10 during the sweep period of FIG. Further, resistors R1 and R2 for dividing and reading the electromotive force of the oxygen sensor 10 in the air-fuel ratio control period of FIG. 15B are connected between the connection point P2 and the shunt resistor Rs.

  Exhaust gas discharged from an internal combustion engine such as an automobile is generally purified by a three-way catalyst. In the oxygen sensor 10, the electromotive force changes greatly around the oxygen concentration (air ratio λ = 1) corresponding to the theoretical air-fuel ratio (14.7: 1). The ECU 30 reads the electromotive force change of the oxygen sensor 10 and determines the fuel injection time of the injector so that the optimum air-fuel ratio is obtained.

JP 2004-177178 A JP-A 61-26853

  On the other hand, exhaust gas contains various gas components such as hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NOx). Of these gas components contained in the exhaust gas, the purification rate of HC and CO decreases when the air-fuel ratio is richer than the stoichiometric air-fuel ratio (λ <1), and NOx is leaner than the stoichiometric air-fuel ratio (λ When it becomes> 1), the purification rate decreases. For this reason, in order to maximize the purification rate for each gas component of HC, CO, and NOx, precise control of the air-fuel ratio is required. In order to precisely perform the air-fuel ratio control by the oxygen sensor, for example, as disclosed in Patent Document 2, an electric current is drawn from the oxygen sensor or a current is supplied to the oxygen sensor, so that the electromotive force greatly changes. A method of shifting the fuel ratio to a predetermined control target can be used.

  FIG. 16 shows the relationship between the above-described air ratio λ (air-fuel ratio) and the purification rates of HC, CO, and NOx, and air when current is drawn from the oxygen sensor (−) or current is flowed to the oxygen sensor (+). It is the figure which showed collectively about the electromotive force change of the oxygen sensor with respect to ratio (lambda) (air fuel ratio). For example, in order to stably remove NOx, as shown by the left-pointing white arrow in FIG. 16, a current of 300 μA is drawn from the oxygen sensor, and the air-fuel ratio at which the electromotive force of the oxygen sensor changes greatly is λ = 0. The air-fuel ratio is controlled in the vicinity of 9705.

  In order to maintain the detection accuracy of the oxygen concentration by the oxygen sensor, it is necessary to accurately detect the impedance of the oxygen sensor and maintain the temperature of the oxygen sensor at an appropriate temperature as described above. In addition, as described above, in order to maximize the purification rate for each gas component contained in the exhaust gas, precise control of the air-fuel ratio by the oxygen sensor is necessary, and current is drawn from the oxygen sensor or supplied to the oxygen sensor. Thus, it is necessary to accurately shift the air-fuel ratio at which the electromotive force greatly changes to a predetermined control target.

  As described above, individual technical proposals have been made for maintaining the detection accuracy of the oxygen concentration by the oxygen sensor and refining the air-fuel ratio control by the oxygen sensor. However, a specific combination of these two technologies has not yet been studied. Both of the above-mentioned two techniques require control of the current flowing through the oxygen sensor, and depending on the combination, mutual interference occurs, which hinders the detection accuracy of the oxygen concentration and the control accuracy of the air-fuel ratio.

  Therefore, the present invention is an oxygen sensor control device used for air-fuel ratio control of an internal combustion engine, which enables both accurate impedance detection of the oxygen sensor and precise air-fuel ratio control by the oxygen sensor with a simple configuration, It aims at providing the control apparatus of the oxygen sensor which can contribute to maintenance of a high purification rate about each gas component.

An oxygen sensor control apparatus according to the present invention is an oxygen sensor control apparatus used for air-fuel ratio control of an internal combustion engine, and is connected in series to the oxygen sensor in order to detect the impedance of the oxygen sensor and control the temperature. A shunt resistor, an impedance measurement switching circuit that is connected to the high potential side of the shunt resistor and switches the current flowing through the shunt resistor between the impedance detection period of the oxygen sensor and the air-fuel ratio control period of the oxygen sensor, and the temperature of the oxygen sensor is predetermined. In an activated state in which the temperature is higher than the temperature of the current, the current that is drawn in or flows into the oxygen sensor to control the air-fuel ratio at which the electromotive force of the oxygen sensor suddenly changes from the theoretical air-fuel ratio to the rich side or lean side is controlled. And a constant current circuit for setting the value to a predetermined value. The impedance measurement switching circuit is connected to the oxygen sensor without a switch, and the constant current circuit is connected between the high potential side of the oxygen sensor and the impedance measurement switching circuit.

  The oxygen sensor control device has a shunt resistor connected in series to the oxygen sensor. The oxygen sensor generally has a large temperature dependency of the output voltage, and it is necessary to maintain the element temperature at an appropriate temperature (active temperature, for example, about 600 ° C. or more) in order to maintain good detection accuracy of the oxygen concentration. is there. The element temperature is normally controlled by detecting the element temperature and performing feedback control of energization to the heater attached to the oxygen sensor.

  The shunt resistor detects the element temperature of the oxygen sensor in order to perform the feedback control described above, and utilizes the fact that the impedance (resistance) of the oxygen sensor varies with the element temperature. The shunt resistor is connected in series to the oxygen sensor, and by measuring the potential across the shunt resistor, the current flowing through the shunt resistor (and hence the oxygen sensor) can be calculated. In addition, the impedance can be detected. The element temperature of the oxygen sensor is calculated from the detected impedance.

  Further, the oxygen sensor control device has an impedance measurement switching circuit connected to the high potential side of the shunt resistor. The impedance measurement switching circuit switches the current flowing through the shunt resistor between the impedance detection period of the oxygen sensor and the air-fuel ratio control period of the oxygen sensor.

  In the impedance detection period of the oxygen sensor, as described above, the element temperature of the oxygen sensor can be detected by passing a current through the shunt resistor and the oxygen sensor connected in series. On the other hand, in the oxygen sensor, the electromotive force greatly changes around the oxygen concentration corresponding to the theoretical air-fuel ratio (14.7: 1, the air ratio λ = 1 of the supplied air amount to the air amount required for the theoretical air-fuel ratio) The ECU reads the change in electromotive force of the oxygen sensor, and determines the fuel injection time of the injector so that the optimum air-fuel ratio is obtained. Therefore, in the air-fuel ratio control period by the oxygen sensor, basically, it is not necessary to pass a current through the oxygen sensor (and the shunt resistor connected in series).

  However, in order to individually increase the purification rate for each gas component contained in the exhaust gas, as described above, an electric current is passed through the oxygen sensor, and the air-fuel ratio at which the electromotive force changes greatly is set to a predetermined value on the fuel rich side or the lean side. It is necessary to make an accurate transition to the control target. In this case, it is necessary to flow a predetermined current through the oxygen sensor not only in the impedance detection period but also in the air-fuel ratio control period.

  In addition to the shunt resistance and impedance measurement switching circuit described above, the oxygen sensor control device has a constant current circuit for shifting the air-fuel ratio at which the electromotive force of the oxygen sensor suddenly changes from the stoichiometric air-fuel ratio to the rich side or lean side. doing. The constant current circuit shifts the air-fuel ratio at which the electromotive force suddenly changes by drawing a current set to a predetermined value from the oxygen sensor to the rich side, or flows a current set to a predetermined value to the oxygen sensor. As a result, the air-fuel ratio at which the electromotive force changes suddenly is shifted to the lean side. For example, hydrocarbons (HC) and carbon monoxide (CO) contained in the exhaust gas have a reduction rate of purification by a three-way catalyst when the air-fuel ratio is richer than the theoretical air-fuel ratio (λ <1). Control is performed by flowing an electric current and shifting the air-fuel ratio at which the electromotive force changes suddenly to the lean side (λ> 1). On the other hand, since the purification rate of nitrogen oxide (NOx) decreases when the air-fuel ratio becomes leaner than the stoichiometric air-fuel ratio, by drawing current from the oxygen sensor, the air-fuel ratio at which the electromotive force changes suddenly shifts to the lean side. Control.

  As described above, in order to individually increase the purification rate for each gas component contained in the exhaust gas, a current is supplied to the oxygen sensor not only during the oxygen sensor impedance detection period but also during the air-fuel ratio control period of the oxygen sensor. is necessary. On the other hand, the current required for the oxygen sensor impedance detection and the current required for shifting the air-fuel ratio to the rich side or lean side differ greatly, and the latter requires control of a current value several orders of magnitude smaller. Become.

  As described in the background art, individual technical proposals have been made to maintain the detection accuracy of the oxygen sensor by detecting the impedance (element temperature) described above and to refine the air-fuel ratio control by the oxygen sensor. Yes. However, the combination of these two techniques has not been studied so far. Both of the above-mentioned two techniques require control of the current flowing through the oxygen sensor, and depending on the combination, mutual interference occurs, which hinders the detection accuracy of the oxygen concentration and the control accuracy of the air-fuel ratio.

  Therefore, in the oxygen sensor control device, a constant current for shifting the air-fuel ratio to the rich side or the lean side in order to achieve both accurate impedance detection of the oxygen sensor and precise air-fuel ratio control by the oxygen sensor with a simple configuration. The circuit is configured to be connected between the high potential side of the oxygen sensor and the impedance measurement switching circuit.

  The current that flows through the oxygen sensor during the impedance detection period and the current that flows through the oxygen sensor during the air-fuel ratio control period may be independently ON-OFF controlled in a necessary period. However, the oxygen sensor control device adopts the above-described constant current circuit connection configuration so that the impedance measurement switching circuit simultaneously switches the value of the current flowing through the oxygen sensor during the impedance detection period and the air-fuel ratio control period. I have to. This makes it possible to achieve both impedance detection of the oxygen sensor and air-fuel ratio control by the oxygen sensor with a simple circuit configuration.

  In particular, the oxygen sensor control device preferably has a configuration in which a constant current circuit is connected between the shunt resistor and the oxygen sensor.

  According to this, since the current of the constant current circuit does not flow through the shunt resistor during the air-fuel ratio control period, the voltage across the shunt resistor due to the current of the constant current circuit is taken into account when detecting the electromotive force of the oxygen sensor. This is unnecessary, and the measurement accuracy of electromotive force can be increased.

  On the other hand, the oxygen sensor control device can take a configuration in which, for example, a constant current circuit is connected between an impedance measurement switching circuit and a shunt resistor.

  In this case, since the current of the constant current circuit flows through the shunt resistor during the air-fuel ratio control period, it is necessary to subtract the voltage across the shunt resistor due to the current of the constant current circuit when detecting the electromotive force of the oxygen sensor. is there. However, when impedance is detected, the same current flows through the shunt resistor and the oxygen sensor and is not easily affected by the constant current circuit. Therefore, the impedance measurement accuracy of the oxygen sensor is improved, and the oxygen sensor can be temperature controlled more accurately. it can.

  In the oxygen sensor control device, the constant current circuit has a constant current source and the constant current source in a current input line, draws current from the oxygen sensor connected to the current output line, or feeds current to the oxygen sensor. And a current mirror circuit. According to the above circuit configuration using the current mirror circuit, current drawing from the oxygen sensor and current flow into the oxygen sensor can be realized by various circuit patterns.

  When the configuration of the constant current circuit is adopted, it is preferable that the current value of the constant current source is configured to be changeable. According to this, the air-fuel ratio at which the electromotive force of the oxygen sensor suddenly changes can be precisely controlled by appropriately changing the current drawn from the oxygen sensor and the value of the current drawn into the oxygen sensor.

  Moreover, it is preferable that the oxygen sensor control device is configured to be able to change the current draw from the oxygen sensor or the current flow to the oxygen sensor so as to cope with any gas component contained in the exhaust gas.

  Further, the oxygen sensor control device preferably has a stop circuit for stopping the current draw from the oxygen sensor or the current flow to the oxygen sensor by the constant current circuit during the impedance detection period of the oxygen sensor. .

  According to this, even when the constant current circuit is connected between the shunt resistor and the oxygen sensor, the current flowing through the shunt resistor becomes the current flowing through the oxygen sensor connected in series as it is during the impedance detection period. For this reason, it is not necessary to consider the current drawn from the oxygen sensor by the constant current circuit or the current drawn into the oxygen sensor, and the measurement accuracy of the impedance of the oxygen sensor can be improved.

  The stop circuit includes, for example, a gate transistor inserted between a gate of a transistor constituting a current mirror circuit and a power supply potential or a ground potential, and the gate transistor is turned on during an impedance detection period of the oxygen sensor. In addition, by fixing the potential of the gate of the transistor constituting the current mirror circuit to the power supply potential or the ground potential, the current drawing from the oxygen sensor or the current feeding to the oxygen sensor can be stopped.

  In addition, a diode is inserted between the current output line of the current mirror circuit and the oxygen sensor, and an output control transistor is inserted into the current output line, and the output control transistor is turned on or off during the impedance detection period of the oxygen sensor. By doing so, it can also be set as the structure which stops drawing of the electric current from an oxygen sensor, or the flow of an electric current to an oxygen sensor via the said diode.

  In this case, it is possible to immediately stop the drawing of the current from the oxygen sensor or the flowing of the current to the oxygen sensor without using the gate transistor that requires a predetermined rise time.

  In addition, the current output lines of the two current mirror circuits are connected in series, and the connection point and the oxygen sensor are connected by a single wire and flow to one current input line of the current mirror circuit. The current value is configured to be changeable, and the current flowing through the current output lines of the two current mirror circuits is equalized during the impedance detection period of the oxygen sensor, so that the current can be drawn from the oxygen sensor or supplied to the oxygen sensor. It may be configured to stop the flow of current. This also makes it possible to immediately stop drawing current from the oxygen sensor or flowing current to the oxygen sensor.

  In the oxygen sensor control device, for example, the impedance measurement switching circuit is composed of two transistors in series between a power supply potential and a ground potential, and the shunt resistor and the oxygen sensor connected in series are the two transistors. It is possible to adopt a configuration in which the connection point is inserted between the connection point and the ground potential.

  The impedance measurement switching circuit is composed of an amplifier that outputs an AC voltage and a changeover switch that turns on and off the output of the amplifier. A shunt resistor and an oxygen sensor connected in series are connected to the output line of the amplifier. The structure formed by connecting to may be sufficient.

  As described above, each of the oxygen sensor control devices described above is a control device for an oxygen sensor used for air-fuel ratio control of an internal combustion engine. Therefore, it is possible to achieve an oxygen sensor control apparatus that can contribute to maintaining a high purification rate for each gas component of the exhaust gas.

(A), (b) is the figure which showed the structural example of the principal part of the oxygen sensor control apparatus which concerns on this invention, and is a block diagram of the oxygen sensor control apparatuses 100 and 110, respectively. (A), (b) is the example which actualized the oxygen sensor control apparatuses 100 and 110 of FIG. 1 (a), (b), respectively, and is the figure which showed the circuit structure of the oxygen sensor control apparatuses 101 and 111. is there. It is a figure which shows another structural example of an impedance measurement switching circuit, (a) is a circuit diagram of the oxygen sensor control apparatus 102 which has the impedance measurement switching circuit 21 of another structure, (b) is an equivalent circuit schematic of (a). It is a figure which shows the calculation formula of the impedance Z of the oxygen sensor 10. (A) is the modification of the oxygen sensor control apparatus 100 shown to Fig.1 (a), and is a block diagram of the oxygen sensor control apparatus 100a. (B) is a specific example of the oxygen sensor control device 100a of (a), and is a diagram showing a circuit configuration of the oxygen sensor control device 103. 5 is a diagram illustrating an example of a flow of an impedance detection period of the oxygen sensor 10 and an air-fuel ratio control period of the oxygen sensor 10 with respect to the oxygen sensor control devices 100a and 103 illustrated in FIG. In another example, the circuit configuration of the oxygen sensor control device 104 is shown. (A), (b) is the figure which showed the example of a preferable structure about each constant current source J1-J3 which comprises the constant current circuit 40a of FIG. 6, The circuit block diagram of constant current source Ja, Jb, respectively It is. FIG. 7 is a diagram showing a circuit configuration of an oxygen sensor control device 105 as a modification of the oxygen sensor control device 104 shown in FIG. 6. In another example, the oxygen sensor control device 106 is a circuit configuration. In another example, the oxygen sensor control device 107 is a circuit configuration. In another example, the oxygen sensor control device 108 is a circuit configuration. FIG. 10 is a diagram showing a circuit configuration of an oxygen sensor control device 109 as a modification of the oxygen sensor control device 106 shown in FIG. 9. FIG. 7 is a diagram showing a circuit configuration of an oxygen sensor control device 112 as a modification of the oxygen sensor control device 104 shown in FIG. 6. (A) is the figure which showed an example of the relationship between the element temperature of an oxygen sensor, and an impedance, (b) is the figure which showed an example of the flow of the impedance detection period of an oxygen sensor, and the air-fuel ratio control period by an oxygen sensor It is. (A) is the figure which showed the circuit structure of the principal part in the conventional oxygen sensor control apparatus 90. FIG. (B) is the figure which showed the timing chart of two transistor SW1, SW2 which comprises the impedance measurement switching circuit 20 in the oxygen sensor control apparatus 90 of (a). The relationship between the air ratio λ (air-fuel ratio) and the purification rates of HC, CO, and NOx, and the air ratio λ (air-fuel ratio) when current is drawn from the oxygen sensor (-) or current is sent to the oxygen sensor (+) It is the figure which showed collectively about the electromotive force change of the oxygen sensor with respect to.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

  FIGS. 1A and 1B are diagrams showing a configuration example of a main part of the oxygen sensor control device according to the present invention, and are block diagrams of the oxygen sensor control devices 100 and 110, respectively. FIGS. 2A and 2B are examples of the oxygen sensor control devices 100 and 110 shown in FIGS. 1A and 1B, respectively. The circuit configurations of the oxygen sensor control devices 101 and 111 are shown in FIGS. FIG. In addition, in each oxygen sensor control apparatus 100,110,101,111 shown in FIG. 1 and FIG. 2, the same code | symbol is attached | subjected about the part similar to the oxygen sensor control apparatus 90 shown to Fig.15 (a).

  The flowchart of the impedance detection period and the air-fuel ratio control period by the oxygen sensor control devices 100, 110, 101, and 111 is the same as that in FIG. In the oxygen sensor control devices 101 and 111 shown in FIG. 2, the timing chart of the two transistors SW1 and SW2 constituting the impedance measurement switching circuit 20 is the same as FIG. Accordingly, the operation of each oxygen sensor control device 100, 110, 101, 111 will be described below with reference to the flowchart shown in FIG. 14B and the timing chart shown in FIG.

  The oxygen sensor control devices 100, 110, 101, and 111 shown in FIGS. 1 and 2 are all control devices for the oxygen sensor 10 used for air-fuel ratio control of an internal combustion engine, and include a shunt resistance Rs and an impedance measurement switching circuit. 20 and a constant current circuit 40.

  The shunt resistor Rs is connected in series to the oxygen sensor 10 at the connection point P1 in order to detect the impedance of the oxygen sensor 10 and control the temperature. The impedance measurement switching circuit 20 is connected to the high potential side of the shunt resistor Rs at the connection point P2, and the impedance detection period of the oxygen sensor 10 and the air-fuel ratio by the oxygen sensor 10 shown in FIGS. 14 (b) and 15 (b). The current flowing through the shunt resistor Rs is switched according to the control period. Further, as shown in FIG. 16, the constant current circuit 40 shifts the air-fuel ratio (air ratio λ) at which the electromotive force of the oxygen sensor 10 changes suddenly from the theoretical air-fuel ratio (λ = 1) to the rich side or the lean side. Therefore, the current drawn from the oxygen sensor 10 or flowing into the oxygen sensor 10 is set to a predetermined value.

  The oxygen sensor control devices 100 and 101 in FIGS. 1A and 2A and the oxygen sensor control devices 101 and 111 in FIGS. 1B and 2B have the constant current circuit 40 of FIG. The connection position is different. The oxygen sensor control devices 100 and 101 in FIGS. 1 (a) and 2 (a) have a configuration in which a constant current circuit 40 is connected to a connection point P1 between the shunt resistor Rs and the oxygen sensor 10. The oxygen sensor control devices 110 and 111 in FIG. 1B and FIG. 2B have a configuration in which the constant current circuit 40 is connected to a connection point P2 between the impedance measurement switching circuit 20 and the shunt resistor Rs.

  Each of the oxygen sensor control devices 100, 110, 101, and 111 shown in FIGS. 1 and 2 has a shunt resistor Rs connected in series to the oxygen sensor 10. The oxygen sensor 10 generally has a large temperature dependency of the output voltage, and it is necessary to maintain the element temperature at an appropriate temperature (the active temperature, for example, about 600 ° C. or higher) in order to maintain good detection accuracy of the oxygen concentration. There is. The element temperature is usually controlled by feedback control of energization to a heater (not shown) provided by detecting the element temperature of the oxygen sensor 10.

  The shunt resistor Rs detects the element temperature of the oxygen sensor 10 in order to perform the above-described feedback control. As illustrated in FIG. 14A, the impedance (resistance) Z of the oxygen sensor 10 varies depending on the element temperature. You are taking advantage of that. The shunt resistor Rs is connected in series to the oxygen sensor 10 at the connection point P1, and as shown in FIG. 2, the both-end potential (AD signal 1 and AD signal 2) of the shunt resistor Rs is measured. As a result, the current flowing through the shunt resistor Rs (accordingly, the oxygen sensor 10) can be calculated, and the impedance Z can be detected together with the potentials at both ends of the oxygen sensor 10 (AD signal 1 and GND). From the detected impedance Z, the element temperature of the oxygen sensor 10 can be calculated according to the relationship illustrated in FIG.

  Further, each of the oxygen sensor control devices 100, 110, 101, and 111 shown in FIGS. 1 and 2 has an impedance measurement switching circuit 20 connected to the high potential side of the shunt resistor Rs. The impedance measurement switching circuit 20 switches the current flowing through the shunt resistor Rs between the impedance detection period of the oxygen sensor 10 and the air-fuel ratio control period of the oxygen sensor 10 shown in FIGS. 14 (b) and 15 (b). is there.

  In the impedance detection period, the element temperature of the oxygen sensor 10 can be detected by passing a current through the shunt resistor Rs and the oxygen sensor 10 connected in series as described above. On the other hand, as illustrated in FIG. 16, the oxygen sensor 10 has an oxygen concentration in the vicinity of the theoretical air-fuel ratio (14.7: 1, the air ratio λ = 1 of the supplied air amount to the air amount required for the theoretical air-fuel ratio). The electromotive force changes greatly at the boundary, and the ECU 30 reads this electromotive force change, and determines the fuel injection time of the injector (not shown) so as to obtain an optimum air-fuel ratio. Therefore, in the air-fuel ratio control period, basically, it is not necessary to pass a current through the oxygen sensor 10 (and the shunt resistor Rs connected in series).

  However, in order to individually increase the purification rate for each gas component contained in the exhaust gas, as illustrated in FIG. 16, an electric current is passed through the oxygen sensor 10 to change the air-fuel ratio at which the electromotive force changes greatly to the fuel rich side or It is necessary to accurately shift to a predetermined control target on the lean side. In this case, it is necessary to flow a predetermined current through the oxygen sensor 10 not only in the impedance detection period but also in the air-fuel ratio control period.

  Each of the oxygen sensor control devices 100, 110, 101, and 111 shown in FIGS. 1 and 2 has an air-fuel ratio at which the electromotive force of the oxygen sensor 10 changes suddenly in addition to the shunt resistance Rs and the impedance measurement switching circuit 20 described above. A constant current circuit 40 for shifting from the stoichiometric air-fuel ratio to the rich side or the lean side is provided. The constant current circuit 40 shifts the air-fuel ratio at which the electromotive force suddenly changes by drawing a current set to a predetermined value from the oxygen sensor 10 to the rich side, or the current set to a predetermined value to the oxygen sensor 10. The air-fuel ratio at which the electromotive force changes abruptly by flowing in is shifted to the lean side.

  For example, as shown in FIG. 16, the hydrocarbon (HC) and carbon monoxide (CO) contained in the exhaust gas are purified by the three-way catalyst when the air-fuel ratio is richer than the stoichiometric air-fuel ratio (λ <1). Therefore, an electric current is supplied to the oxygen sensor 10 (+), and the air-fuel ratio at which the electromotive force changes suddenly is shifted to the lean side (λ> 1) for control. On the other hand, since the purification rate of nitrogen oxide (NOx) decreases when the air-fuel ratio becomes leaner than the stoichiometric air-fuel ratio, the air-fuel ratio at which the electromotive force changes suddenly is reduced by drawing current from the oxygen sensor 10 (−). Control by shifting to. Note that the oxygen sensor control devices 101 and 111 shown in FIGS. 2A and 2B are predetermined from the oxygen sensor 10 as indicated by arrows in the drawing in order to increase the purification rate of nitrogen oxides (NOx). The current I1 set to the value is drawn.

  As described above, in order to individually increase the purification rate for each gas component contained in the exhaust gas, it is necessary to flow current to the oxygen sensor 10 not only in the impedance detection period but also in the air-fuel ratio control period. On the other hand, the current value differs greatly between the current required for impedance detection of the oxygen sensor 10 and the current required for shifting the air-fuel ratio to the rich side or the lean side, and in the latter, control of a current value several orders of magnitude smaller is required. Become.

  Regarding the maintenance of the detection accuracy of the oxygen sensor 10 based on the impedance (element temperature) detection described above and the refinement of the air-fuel ratio control by the oxygen sensor 10, as described in the background art, individual technical proposals have been made so far. Yes. However, the combination of these two techniques has not been studied so far. Both of the above-described two techniques require control of the current flowing through the oxygen sensor 10, and depending on the combination, mutual interference occurs, which hinders oxygen concentration detection accuracy and air-fuel ratio control accuracy. .

  Therefore, in the oxygen sensor control devices 100, 110, 101, and 111 shown in FIGS. 1 and 2, in order to achieve both accurate impedance detection of the oxygen sensor 10 and precise air-fuel ratio control by the oxygen sensor 10 with a simple circuit, The following circuit configuration is adopted. That is, in the oxygen sensor control devices 100, 110, 101, and 111, the constant current circuit 40 for shifting the air-fuel ratio to the rich side or the lean side is between the high potential side of the oxygen sensor 10 and the impedance measurement switching circuit 20. It has a connected circuit configuration. More specifically, in the oxygen sensor control devices 100 and 101 of FIGS. 1A and 2A, the constant current circuit 40 is connected to the connection point P1 between the shunt resistor Rs and the oxygen sensor 10. 1 (b) and 2 (b), the constant current circuit 40 is connected to a connection point P2 between the impedance measurement switching circuit 20 and the shunt resistor Rs. It has become.

  The current that flows to the oxygen sensor 10 during the impedance detection period and the current that flows to the oxygen sensor 10 during the air-fuel ratio control period may be independently ON-OFF controlled in a necessary period. However, in the oxygen sensor control devices 100 and 101 in FIGS. 1A and 2A and the oxygen sensor control devices 101 and 111 in FIGS. 1B and 2B, the constant current circuit 40 described above is used. Thus, the impedance measurement switching circuit 20 simultaneously switches the value of the current flowing through the oxygen sensor 10 during the impedance detection period and the air-fuel ratio control period. Thereby, it is possible to achieve both impedance detection of the oxygen sensor 10 and air-fuel ratio control by the oxygen sensor 10 with a simple circuit configuration.

  Next, the difference between the oxygen sensor control devices 100 and 101 shown in FIGS. 1 (a) and 2 (a) and the oxygen sensor control devices 110 and 111 shown in FIGS. 1 (b) and 2 (b) will be described.

  As described above, if the constant current circuit 40 is connected between the high potential side of the oxygen sensor 10 and the impedance measurement switching circuit 20, accurate impedance detection of the oxygen sensor 10 and oxygen sensor 10 can be performed with a simple circuit configuration. The air-fuel ratio control by can be compatible. However, in order to increase the measurement accuracy of the electromotive force of the oxygen sensor 10, as in the oxygen sensor control devices 100 and 101 of FIGS. 1 (a) and 2 (a), the constant current circuit 40 is connected to the shunt resistor Rs and oxygen. It is preferable to adopt a configuration in which the sensor 10 is connected. According to this, since the current of the constant current circuit 40 does not flow through the shunt resistor Rs during the air-fuel ratio control period, the shunt resistor Rs due to the current of the constant current circuit 40 is detected when detecting the electromotive force of the oxygen sensor 10. There is no need to consider the voltage between both ends, and the electromotive force measurement accuracy can be increased.

  On the other hand, in order to increase the measurement accuracy of the impedance Z of the oxygen sensor 10, the constant current circuit 40 is connected to the impedance measurement switching circuit 20 as in the oxygen sensor control devices 110 and 111 of FIGS. 1B and 2B. It is also possible to adopt a configuration in which the connection is made between the shunt resistors Rs. In this case, since the current of the constant current circuit 40 flows through the shunt resistor Rs during the air-fuel ratio control period, the voltage across the shunt resistor Rs due to the current of the constant current circuit 40 is detected when detecting the electromotive force of the oxygen sensor 10. It is necessary to deduct. However, when the impedance of the oxygen sensor 10 is detected, since the same current flows through the shunt resistor Rs and the oxygen sensor 10 and is not easily affected by the constant current circuit 40, the measurement accuracy of the impedance Z is improved, and the oxygen sensor 10 is more accurately detected. The temperature can be controlled.

  Next, details of the oxygen sensor control devices 101 and 111 shown in FIGS. 2A and 2B will be described.

  In the oxygen sensor control devices 101 and 111 of FIG. 2, the constant current circuit 40 has a constant current source 41 and a constant current source 41 in the current input line, and supplies current from the oxygen sensor 10 connected to the current output line. The current mirror circuit C1 is pulled in. In each oxygen sensor control device exemplified below, the constant current circuit has a constant current source and the constant current source in the current input line, and draws current from the oxygen sensor connected to the current output line. In this example, a current mirror circuit for supplying current to the oxygen sensor is used. According to the above circuit configuration using the current mirror circuit, it is possible to realize the current drawing from the oxygen sensor 10 and the current flow to the oxygen sensor 10 with various circuit patterns.

  2 is similar to the oxygen sensor control device 90 of FIG. 15 in that the impedance measurement switching circuit 20 includes two transistors SW1, SW1 in series between the power supply potential VCC and the ground potential. It is composed of SW2. The shunt resistor Rs and the oxygen sensor 10 connected in series are inserted between the connection point P2 of the two transistors SW1 and SW2 and the ground potential. As described above, the impedance Z of the oxygen sensor 10 is detected by the calculation formula shown in FIG. 15A by sweeping the voltage applied to the oxygen sensor 10 in the sweep period of FIG.

  As in the oxygen sensor control device 90 of FIG. 15, the oxygen sensor control devices 101 and 111 of FIG. 2 have resistances R1 and R2 for dividing and reading the electromotive force of the oxygen sensor 10 as a connection point P2 and a shunt resistance Rs. Connected between. In the air-fuel ratio control period of FIG. 15B, the electromotive force of the oxygen sensor 10 is read through the resistors R1 and R2, and the fuel injection time of the injector is determined by the ECU 30 so that the optimal air-fuel ratio is obtained. .

  The impedance measurement switching circuit 20 of the oxygen sensor control devices 101 and 111 shown in FIG. 2 may have another configuration. FIG. 3 is a diagram illustrating another configuration example of the impedance measurement switching circuit. FIG. 3A is a circuit diagram of the oxygen sensor control device 102 having the impedance measurement switching circuit 21 having another configuration, and FIG. FIG. 5 is a diagram showing an equivalent circuit diagram of FIG. 5 and a calculation formula for impedance Z of the oxygen sensor 10. In addition, in the oxygen sensor control apparatus 102 shown in FIG. 3, the same code | symbol was attached | subjected about the part similar to the oxygen sensor control apparatuses 100 and 101 of FIG. 1 (a) and FIG. 2 (a).

  The impedance measurement switching circuit 21 shown in FIG. 3A includes an amplifier A1 that outputs an alternating voltage and a changeover switch SW3 that turns on and off the output of the amplifier A1. The shunt resistor Rs and the oxygen sensor 10 connected in series are connected to the output line of the amplifier A1 at the connection point P2. In the oxygen sensor control device 102, the change-over switch SW3 is turned on during the impedance detection period, an impedance detection AC signal is output from the amplifier A1, and the potential of the connection point P1 between the shunt resistor Rs and the oxygen sensor 10 is monitored. Then, the impedance Z of the oxygen sensor 10 is detected by the calculation formula shown in FIG.

  Next, modifications of the oxygen sensor control devices 100, 110, 101, and 111 shown in FIGS. 1 and 2 will be described.

  FIG. 4A is a block diagram of the oxygen sensor control device 100a, which is a modification of the oxygen sensor control device 100 shown in FIG. FIG. 4B is an example in which the oxygen sensor control device 100a of FIG. 4A is embodied, and is a diagram showing a circuit configuration of the oxygen sensor control device 103. FIG. 5 is a diagram showing an example of the flow of the impedance detection period of the oxygen sensor 10 and the air-fuel ratio control period of the oxygen sensor 10 for the oxygen sensor control devices 100a and 103 shown in FIG.

  The oxygen sensor control device 100a shown in FIG. 4A has a circuit configuration having a stop circuit 50 in addition to the circuit configuration of the oxygen sensor control device 100 shown in FIG. The stop circuit 50 stops the drawing of current from the oxygen sensor 10 or the flow of current into the oxygen sensor 10 by the constant current circuit 40 during the impedance detection period of the oxygen sensor 10. For example, as shown in the flowchart of FIG. 5, the stop circuit 50 is turned on before starting impedance measurement in the impedance detection period, and the current is drawn from the oxygen sensor 10 by the constant current circuit 40 or to the oxygen sensor 10. Stop the flow of current. Then, before starting the air-fuel ratio measurement in the air-fuel ratio control by the oxygen sensor 10, the stop circuit 50 is turned off, and the current value drawn from the oxygen sensor 10 by the constant current circuit 40 or flowing into the oxygen sensor 10 is set.

  In the example of the oxygen sensor control device 103 shown in FIG. 4B, the stop circuit 51 includes an OR element 51a and an N-channel gate transistor 51b. The OR element 51a receives the same signal as the gate input of the transistors SW1 and SW2 constituting the impedance measurement switching circuit 20, and in the impedance detection period of FIG. Output a signal. The gate transistor 51b receives the H signal from the OR element 51a, fixes the gate of the transistor constituting the current mirror circuit C1 to GND, and stops the current I1 from the oxygen sensor 10 from being drawn by the constant current circuit 40. .

  In the case where the stop circuits 50 and 51 are provided as in the oxygen sensor control devices 100a and 103 shown in FIG. 4, even if the constant current circuit 40 is connected between the shunt resistor Rs and the oxygen sensor 10, the impedance is reduced. In the detection period, the current flowing through the shunt resistor Rs becomes the current flowing through the oxygen sensor 10 connected in series as it is. For this reason, it is not necessary to consider the current drawn from the oxygen sensor 10 or the current drawn into the oxygen sensor 10 by the constant current circuit 40, and the measurement accuracy of the impedance Z of the oxygen sensor 10 can be improved.

  FIG. 6 is a diagram showing a circuit configuration of the oxygen sensor control device 104 as another example.

  The oxygen sensor control device 104 shown in FIG. 6 includes a constant current source 41a and a constant current circuit 40a including current mirror circuits Ca1 to Ca5 configured in five stages. The constant current circuit 40a allows the oxygen sensor control device 104 to generate currents from the oxygen sensor 10 corresponding to the respective nitrogen oxide (NOx) and carbon monoxide (CO) gas components contained in the exhaust gas. The drawing or current flow into the oxygen sensor 10 can be changed.

  That is, the oxygen sensor control device 104 shown in FIG. 6 switches between control of the air-fuel ratio suitable for NOx removal and control of the air-fuel ratio suitable for CO removal by the control gas switching circuits S1, S2. The control gas switching circuit S1 includes an N-channel transistor S1b connected to the inverter element S1a and the gate of the current mirror circuit Ca3. The control gas switching circuit S2 is connected to the inverter element S2a and the gate of the current mirror circuit Ca5. P-channel transistor S2b. In order to control at an air-fuel ratio suitable for NOx removal, the L signal inverted by the inverter element S1a is applied to the gate of the transistor S1b of the control gas switching circuit S1 while the H signal is output from the terminal NOx_SW of the ECU 30. Is applied. Therefore, the current I1 indicated by the arrow pointing rightward is drawn from the oxygen sensor 10 by the current mirror circuits Ca1 and Ca3 without the gate potential of the current mirror circuit Ca3 being fixed to GND. Further, in order to control at an air-fuel ratio suitable for CO removal, the L signal inverted by the inverter element S2a is applied to the gate of the transistor S2b of the control gas switching circuit S2 while the H signal is output from the terminal CO_SW of the ECU 30. Is applied. Therefore, the current mirror circuit Ca5 does not fix the gate potential to VCC, and the current mirror circuit Ca2, Ca4, Ca5 causes the current I2 indicated by the left arrow to flow into the oxygen sensor 10.

  In the example of the oxygen sensor control device 104 shown in FIG. 6, the stop circuit 52 includes a NOR element 52a and a P-channel gate transistor 52b. The NOR element 52a outputs an L signal during the impedance detection period. The gate transistor 52b receives the L signal from the NOR element 52a, fixes the gates of the transistors constituting the current mirror circuits Ca1 and Ca2 to VCC, and draws the current I1 from the oxygen sensor 10 by the constant current circuit 40a. The flow of the current I2 into the oxygen sensor 10 is stopped.

  In the oxygen sensor control device 104 of FIG. 6, the constant current source 41a constituting the constant current circuit 40a is composed of three constant current sources J1 to J3 connected in parallel, and the current of the constant current source 41a is The value can be changed by a signal from the ECU 30. Therefore, in the oxygen sensor control device 104, the air-fuel ratio suitable for NOx removal by the switching circuit S1 and the air-fuel ratio suitable for CO removal by the switching circuit S2 and the air-fuel ratio suitable for HC removal are controlled respectively. A suitable current value can be set.

  As described above, the oxygen sensor control device 104 shown in FIG. 6 can change the current draw from the oxygen sensor 10 or the current flow to the oxygen sensor 10 so as to cope with any gas component contained in the exhaust gas. It is configured. Further, the value of the current I1 drawn from the oxygen sensor 10 and the value of the current I2 drawn into the oxygen sensor 10 can be appropriately changed, and the air-fuel ratio at which the electromotive force of the oxygen sensor 10 changes suddenly can be precisely controlled.

  FIGS. 7A and 7B are diagrams showing a preferred configuration example for each of the constant current sources J1 to J3 constituting the constant current circuit 40a of FIG. 6, and the circuits of the constant current sources Ja and Jb, respectively. It is a block diagram.

A constant current source Ja shown in FIG. 7A has a configuration using an amplifier A2 and a band gap reference potential (BGR), and V1 = BGR in the figure. The constant current source Jb shown in FIG.
By using both the PNP transistor T1 and the NPN transistor T2, the Vf temperature characteristics of the PNP transistor T1 and the NPN transistor T2 are canceled, and V2≈BGR in the figure. In addition, the constant current sources Ja and Jb shown in FIGS. 7A and 7B use resistance chrome-silicon (Cr-Si) resistance or polysilicon resistance having low temperature characteristics as the resistances Rv and Rw in the figure. Thus, the temperature characteristic becomes small.

  FIG. 8 shows a circuit configuration of the oxygen sensor control device 105 as a modification of the oxygen sensor control device 104 shown in FIG. In the oxygen sensor control device 105 of FIG. 8, the same parts as those of the oxygen sensor control device 104 shown in FIG.

  In the oxygen sensor control device 105 of FIG. 8, the control gas switching circuits S1 and S2 and the stop circuit 52 in the oxygen sensor control device 104 of FIG. That is, the stop circuit 53 in the oxygen sensor control device 105 of FIG. 8 includes an NOR element 52a and two NAND elements 53a and 53b connected as shown in the figure, and an N-channel gate transistor connected to the gate of the current mirror circuit Ca3. 53d and a P-channel gate transistor 53c connected to the gate of the current mirror circuit Ca5. Thus, similar to the oxygen sensor control device 104 shown in FIG. 6, the switching function between the air-fuel ratio control suitable for NOx removal and the air-fuel ratio control suitable for CO removal, and the constant current circuit 40b in the impedance detection period. A function of stopping the drawing of the current I1 from the oxygen sensor 10 or the flowing of the current I2 into the oxygen sensor 10 can be provided.

  Further, in the oxygen sensor control device 104 of FIG. 6, the low potential side of the oxygen sensor 10 is at the GND potential. On the other hand, in the oxygen sensor control device 105 of FIG. 8, the low potential side of the oxygen sensor 10 is connected to the output of the amplifier A3 and raised to a predetermined potential. Thus, in each oxygen sensor control device described above, the low potential side of the oxygen sensor 10 may be lifted from the GND potential by a predetermined potential.

  FIG. 9 is a diagram showing a circuit configuration of the oxygen sensor control device 106 as another example.

  The constant current circuit 40c in the oxygen sensor control device 106 of FIG. 9 includes a constant current source 42, current mirror circuits Cb1 to Cb5, and switches Sb1 to Sb3, which are connected as follows. That is, the current mirror circuits Cb1 to Cb4 are connected in parallel, and their connection configuration is switched by the switches Sb1 to Sb3. The current output lines of the current mirror circuit Cb4 and the current mirror circuit Cb5 are connected in series. The connection point P3 and the high potential side of the oxygen sensor 10 (connection point P1 between the oxygen sensor 10 and the shunt resistor Rs) Are connected by a single wire.

  The configuration of the stop circuit 52 in the oxygen sensor control device 106 of FIG. 9 is the same as that of the oxygen sensor control device 104 shown in FIG.

  In each of the oxygen sensor control devices described above, the current I1 is drawn from the oxygen sensor 10 or the current I2 is fed to the oxygen sensor 10 through separate wires connected to the high potential side of the oxygen sensor 10. It was. On the other hand, in the oxygen sensor control device 106 shown in FIG. 9, the connection configuration of the current mirror circuits Cb1 to Cb5 is switched by the switches Sb1 to Sb3, and the current I1 is drawn from the oxygen sensor 10 or the current to the oxygen sensor 10 is switched. The flow of I2 is performed as follows through the same single wiring connected to the high potential side of the oxygen sensor 10.

  For example, when all of the switches Sb1 to Sb3 are open, the current I0 that is the same as the input line flows through the current output line of the current mirror circuit Cb4, and no current flows through the current mirror circuit Cb5. All the current I0 of the current output line flows into the oxygen sensor 10 (I2 = I0). For example, when all of the switches Sb1 to Sb3 are closed, a current of 3 × I0 flows through the current input line of the current mirror circuit Cb5, and the current from the current mirror circuit Cb4 flows through the current output line of the current mirror circuit Cb5. Since I0 flows, the insufficient current 2 × I0 is drawn from the oxygen sensor 10 (I1 = 2 × I0).

  In general, the following relationship holds between the current flowing through the transistor M1 in the current input line of the current mirror circuit Cb5 and the current flowing through the transistor M2 in the current output line of the current mirror circuit Cb4. By setting the current flowing in M <b> 1 <the current flowing in M <b> 2, the difference current I <b> 2 is flowed into the oxygen sensor 10. Further, by setting the current flowing in M <b> 1> the current flowing in M <b> 2, the difference current I <b> 1 is drawn from the oxygen sensor 10.

  FIG. 10 is a diagram showing a circuit configuration of the oxygen sensor control device 107 as another example.

  The constant current circuit 40d in the oxygen sensor control device 107 in FIG. 10 includes a constant current source 41a and current mirror circuits Cc1 to Cc3. Between the current output lines of the current mirror circuits Cc3 and Cc2 and the oxygen sensor 10, Diodes D1 and D2 are inserted in the direction shown in the figure. In addition, the stop circuit 54 of the oxygen sensor control device 107 includes an output control inserted into the NOR element 52a, the AND element 54a, the NAND element 54b, and the current output lines of the current mirror circuits Cc2 and Cc3 connected as shown in the figure. It is composed of transistors 54c and 54d.

  Each of the stop circuits of the oxygen sensor control device described above has a gate transistor inserted between the gate of the transistor constituting the current mirror circuit and the power supply potential or the ground potential. Then, during the impedance detection period of the oxygen sensor 10, the gate transistor is turned on, and the potential of the gate of the transistor constituting the current mirror circuit is fixed to the power supply potential or the ground potential, thereby drawing current from the oxygen sensor 10. Alternatively, the current flow to the oxygen sensor 10 is stopped. In the case of the stop circuit using the gate transistor, a predetermined rise time is required until the gate transistor is turned on. For this reason, in the stop circuit using a gate transistor, current drawing from the oxygen sensor 10 or current flow into the oxygen sensor 10 cannot be stopped immediately.

  On the other hand, in the oxygen sensor control apparatus 107 shown in FIG. 10, the output control transistors 54d and 54c are turned on or off in the impedance detection period of the oxygen sensor, respectively, and thereby the oxygen sensor 10 is connected via the diodes D1 and D2. The current I1 is drawn from the current sensor or the current I2 is flown into the oxygen sensor 10 is stopped.

  For example, when controlling at an air-fuel ratio suitable for NOx removal, an H signal is input to one input terminal of the AND element 54a. The other input terminal of the AND element 54 a receives an H signal during the air-fuel ratio control period of the oxygen sensor 10 and an L signal during the impedance detection period of the oxygen sensor 10. Therefore, the P-channel output control transistor 54c inserted in the current output line of the current mirror circuit Cc3 is turned on during the air-fuel ratio control period, and the current output line from above in the figure is cut off, and the current I1 = I0 Is drawn from the oxygen sensor 10 via the diode D1. On the other hand, during the impedance detection period, the output control transistor 54c is turned OFF, and the current output line of the current mirror circuit Cc3 is short-circuited to the power supply potential VCC. For this reason, the current I1 = I0 drawn from the oxygen sensor 10 via the diode D1 in the air-fuel ratio control period stops, and the same current I0 flows from VCC to GND.

  In addition, when control is performed with an air-fuel ratio suitable for CO removal, an H signal is input to one input terminal of the NAND element 54b. The other input terminal of the NAND element 54 b receives an H signal during the air-fuel ratio control period of the oxygen sensor 10 and an L signal during the impedance detection period of the oxygen sensor 10. Accordingly, the N-channel output control transistor 54d inserted in the current output line of the current mirror circuit Cc2 is turned off during the air-fuel ratio control period, and a current of I2 = I0 flows into the oxygen sensor 10 via the diode D2. It is. On the other hand, during the impedance detection period, the output control transistor 54d is turned ON, and the current output line of the current mirror circuit Cc2 is short-circuited to GND. For this reason, the current of I2 = I0 that has flowed into the oxygen sensor 10 via the diode D2 during the air-fuel ratio control period stops, and the same current of I0 flows from VCC to GND.

  As described above, the oxygen sensor control device 107 in FIG. 10 combines the output control transistors 54c and 54d and the diodes D1 and D2, and switches the current flow path to change the current flowing through the oxygen sensor 10 during the air-fuel ratio control period. I1 and I2 are stopped. According to this, the drawing of the current I1 from the oxygen sensor 10 or the flowing of the current I2 into the oxygen sensor 10 can be stopped immediately without using the gate transistor that requires a predetermined rise time.

  FIG. 11 is a diagram showing a circuit configuration of the oxygen sensor control device 108 as another example.

  The constant current circuit 40e in the oxygen sensor control device 108 of FIG. 11 includes a constant current source 42, current mirror circuits Cd1 to Cd7 and switches Sb1 to Sb3 connected as shown in the figure, and currents of the current mirror circuits Cd6 and Cd7. Between the output line and the oxygen sensor 10, diodes D1 and D2 are inserted in the direction shown in the drawing. Further, the stop circuit 55 of the oxygen sensor control device 108 includes an NOR circuit 52a, an inverter element 55a, and output control transistors 55b connected in parallel to the output side transistors of the current mirror circuits Cd7 and Cd4, respectively. 55c.

  An oxygen sensor control device 108 shown in FIG. 11 is configured by combining the oxygen sensor control device 106 shown in FIG. 9 and the oxygen sensor control device 107 shown in FIG. In the oxygen sensor control device 108 shown in FIG. 11, the connection configuration of the current mirror circuits Cd1 to Cd7 is switched by the switches Sb1 to Sb3, and the current I1 is drawn from the oxygen sensor 10 or the current I2 is flown into the oxygen sensor 10. The currents I1 and I2 are stopped through the diodes D1 and D2 as follows.

  In the oxygen sensor control device 108 of FIG. 11, the output control transistor 55b is turned off and the output control transistor 55c is turned on during the air-fuel ratio control period. Conversely, during the impedance detection period, the output control transistor 55b is turned on and the output control transistor 55c is turned off. For example, when all the switches Sb1 to Sb3 are open, no current flows through the current mirror circuits Cd6 and Cd7, and the current I2 is supplied to the oxygen sensor 10 via the diode D2 during the air-fuel ratio control period. In the impedance detection period, since the current output line of the current mirror circuit Cd5 is short-circuited to GND by the output control transistor 55b, the flow of the current I2 to the oxygen sensor 10 via the diode D2 is immediately stopped.

  FIG. 12 is a diagram showing a circuit configuration of the oxygen sensor control device 109 as a modification of the oxygen sensor control device 106 shown in FIG.

  The stop circuit 52 of the oxygen sensor control device 106 shown in FIG. 9 includes a NOR element 52a and a P-channel gate transistor 52b, similar to the oxygen sensor control device 104 shown in FIG. In the oxygen sensor control device 106 of FIG. 9, the gates of the transistors constituting the current mirror circuits Cb1 to Cb4 are fixed to VCC using the gate transistor 52b, and the currents I1 and I2 flowing through the oxygen sensor 10 are stopped. Let

  On the other hand, the stop circuit 56 in the oxygen sensor control device 109 of FIG. 12 includes a NOR element 52a, AND elements 56a and 56b and a NAND element 56c connected as shown in the diagram for switching the switches Sb1 to Sb3. ing.

  In the oxygen sensor control device 109 of FIG. 12, for example, all the switches Sb1 to Sb3 are closed during the air-fuel ratio control period, and a current of I1 = 2 × I0 is drawn from the oxygen sensor 10. In the impedance detection period, only the switch Sb3 is closed, and the current flowing through the transistor M3 in the current output line of the current mirror circuit Cb5 and the current flowing through the transistor M2 in the current output line of the current mirror circuit Cb4 are both I0 and Then, the current drawing from the oxygen sensor 10 is stopped.

  As illustrated in the oxygen sensor control device 109 of FIG. 12, generally, the current output lines of two current mirror circuits are connected in series, and the connection point and the oxygen sensor are connected by a single wire. Thus, the value of the current flowing in one current input line of the current mirror circuit can be changed, and the current flowing in the current output lines of the two current mirror circuits is made equal in the impedance detection period of the oxygen sensor. Thus, current drawing from the oxygen sensor or current flow into the oxygen sensor can be stopped. This also makes it possible to immediately stop drawing current from the oxygen sensor or flowing current to the oxygen sensor.

  FIG. 13 is a diagram showing a circuit configuration of the oxygen sensor control device 112 as a modification of the oxygen sensor control device 104 shown in FIG.

  The constant current circuit 40f in the oxygen sensor control device 112 of FIG. 13 has the same configuration as the constant current circuit 40a of the oxygen sensor control device 104 shown in FIG. 6, but the connection position to the oxygen sensor 10 is different. Yes. In the oxygen sensor control device 104 of FIG. 6, the constant current circuit 40a is connected between the shunt resistor Rs and the oxygen sensor 10 (connection point P1). On the other hand, in the oxygen sensor control device 112 of FIG. 13, like the oxygen sensor control device 111 shown in FIG. 2B, the constant current circuit 40f is connected between the impedance measurement switching circuit 20 and the shunt resistor Rs ( It is connected to the connection point P2). Therefore, the oxygen sensor control device 104 of FIG. 6 can increase the measurement accuracy of the electromotive force of the oxygen sensor 10, and the oxygen sensor control device 112 of FIG. 13 can increase the measurement accuracy of the impedance Z of the oxygen sensor 10. it can.

  13 has a circuit configuration in which the stop circuit 52 in the oxygen sensor control device 104 of FIG. 6 is omitted. When the constant current circuit 40f is connected between the impedance measurement switching circuit 20 and the shunt resistor Rs as in the oxygen sensor control device 112 of FIG. 13, all the current flowing through the shunt resistor Rs is oxygen connected in series. The sensor 10 flows. Therefore, even if the stop circuit 52 of FIG. 6 is omitted and the current of the constant current circuit 40f is always flowing, the impedance measurement accuracy of the oxygen sensor 10 does not deteriorate.

  As described above, each of the oxygen sensor control devices described above is a control device for an oxygen sensor used for air-fuel ratio control of an internal combustion engine. Therefore, the control device for the oxygen sensor can contribute to the maintenance of a high purification rate for each gas component of the exhaust gas.

90, 100 to 109, 110 to 112 Oxygen sensor control device 10 Oxygen sensor Rs Shunt resistance 20, 21 Impedance measurement switching circuit 30 ECU
40, 40a-40f Constant current circuit 50-56 Stop circuit

Claims (12)

A control device for an oxygen sensor used for air-fuel ratio control of an internal combustion engine,
In order to detect the impedance of the oxygen sensor and control the temperature, a shunt resistor connected in series to the oxygen sensor;
An impedance measurement switching circuit that is connected to the high potential side of the shunt resistor and switches the current flowing through the shunt resistor between an impedance detection period of the oxygen sensor and an air-fuel ratio control period of the oxygen sensor;
In the activated state where the temperature of the oxygen sensor is higher than a predetermined temperature, the oxygen sensor is controlled by shifting the air-fuel ratio at which the electromotive force of the oxygen sensor suddenly changes from the stoichiometric air-fuel ratio to the rich side or the lean side. A constant current circuit for setting the current drawn from or into the oxygen sensor to a predetermined value,
The impedance measurement switching circuit is connected to the oxygen sensor without a switch,
The oxygen sensor control device, wherein the constant current circuit is connected between a high potential side of the oxygen sensor and the impedance measurement switching circuit.   The oxygen sensor control device according to claim 1, wherein the constant current circuit is connected between the shunt resistor and the oxygen sensor.   The oxygen sensor control device according to claim 1, wherein the constant current circuit is connected between the impedance measurement switching circuit and the shunt resistor. The constant current circuit is
A constant current source;
A current mirror circuit having the constant current source in a current input line and drawing current from the oxygen sensor connected to the current output line or flowing current into the oxygen sensor. Item 4. The oxygen sensor control device according to any one of Items 1 to 3.   The oxygen sensor control device according to claim 4, wherein the current value of the constant current source is configured to be changeable.   6. The oxygen sensor control device according to claim 4, wherein drawing of current from the oxygen sensor or flowing of current into the oxygen sensor is configured to be changeable. 6.   5. The apparatus according to claim 4, further comprising a stop circuit that stops drawing of current from the oxygen sensor or flowing of current to the oxygen sensor by the constant current circuit during an impedance detection period of the oxygen sensor. The oxygen sensor control device according to any one of claims 1 to 6. The stop circuit includes a gate transistor inserted between a gate of a transistor constituting the current mirror circuit and a power supply potential or a ground potential;
In the impedance detection period of the oxygen sensor, the gate transistor is turned on, and the potential of the gate of the transistor constituting the current mirror circuit is fixed to the power supply potential or the ground potential, thereby drawing current from the oxygen sensor or The oxygen sensor control device according to claim 7, wherein the flow of current into the oxygen sensor is stopped. A diode is inserted between the current output line of the current mirror circuit and the oxygen sensor, and an output control transistor is inserted in the current output line,
In the impedance detection period of the oxygen sensor, when the output control transistor is turned on or off, current drawing from the oxygen sensor or current feeding to the oxygen sensor is stopped via the diode. The oxygen sensor control device according to claim 7. The current output lines of the two current mirror circuits are connected in series, and the connection point and the oxygen sensor are connected by a single wire,
The value of the current flowing in one current input line of the current mirror circuit is configured to be changeable,
In the impedance detection period of the oxygen sensor, the current flowing through the current output lines of the two current mirror circuits is made equal to stop the current draw from the oxygen sensor or the current flow to the oxygen sensor. 8. The oxygen sensor control device according to claim 7, wherein The impedance measurement switching circuit is composed of two transistors in series between a power supply potential and a ground potential,
The oxygen sensor according to any one of claims 1 to 10, wherein the shunt resistor and the oxygen sensor connected in series are inserted between a connection point of the two transistors and a ground potential. Control device. The impedance measurement switching circuit is composed of an amplifier that outputs an alternating voltage, and a changeover switch that turns on and off the output of the amplifier.
11. The oxygen sensor control device according to claim 1, wherein the shunt resistor and the oxygen sensor connected in series are connected to an output line of the amplifier.

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