JP2005227013A - Control unit of oxygen concentration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the control unit of an oxygen concentration sensor capable of pricisely detecting the impedance of the oxygen concentration sensor. <P>SOLUTION: In the control unit 100 of the oxygen concentration sensor for detecting the concentration of oxygen, the impedance RS of the oxygen concentration sensor 5 is calculated on the basis of the voltage (ADC1-ADC2) between first and second nodes A and B when voltage is applied to the control unit 100 of the oxygen concentration sensor 5. When the impedance of the oxygen concentration sensor is relatively large, the applying time T<SB>ON</SB>of voltage to the control unit of the oxygen concentration sensor is set relatively large and the reading timing T<SB>AD</SB>of the voltage between the first and second nodes is set relatively slow. The applying time of the voltage to the control unit of the oxygen concentration sensor and the reading timing of the voltage between the first and second nodes are determined on the basis of the calculated impedance. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an oxygen concentration sensor control device that detects an oxygen concentration, and more particularly to an oxygen concentration sensor control device that can accurately detect the impedance of an oxygen concentration sensor for a vehicle.

In vehicles such as automobiles, the oxygen concentration in the exhaust gas discharged from the engine is detected by an oxygen concentration sensor or the like, and the fuel injection amount and the exhaust purification catalyst are controlled based on the detected value. . As a characteristic of this oxygen concentration sensor, it is known that the temperature dependence of the output voltage is high (functions as an O ₂ sensor at a predetermined temperature or higher). This is because when the temperature rises, the active state of the zirconia element in the oxygen concentration sensor is improved, and an electromotive force is generated when a predetermined oxygen concentration difference occurs. Therefore, it is necessary to perform control for maintaining the oxygen concentration sensor at a temperature at which the oxygen concentration can be optimally detected (hereinafter, this temperature is referred to as “activation temperature”). Generally, a heater is attached to the oxygen concentration sensor, and the oxygen concentration sensor is maintained near the activation temperature by controlling the heater.

  Here, in order to maintain the oxygen concentration sensor at the activation temperature with the heater as described above, it is necessary to detect the temperature of the oxygen concentration sensor. However, if the temperature sensor is directly disposed on the oxygen concentration sensor, the oxygen concentration sensor This increases the size and cost of the sensor. Accordingly, paying attention to the fact that the element impedance of the oxygen concentration sensor changes according to the element temperature, the element impedance is detected, and the element temperature is calculated from the detected value.

  There is a conversion error in the AD converter used when calculating the impedance of the oxygen concentration sensor, and there is a limit to reducing this. This is because the AD converter for a vehicle has limitations such as cost and mounting on a printed circuit board, and a highly accurate one cannot be used. Due to the conversion error of the AD converter, the impedance range in which the impedance of the oxygen concentration sensor can be detected with high accuracy is limited, and the impedance detection accuracy decreases with deviation from the range.

Japanese Patent Laid-Open No. 9-292364 Japanese Patent Laid-Open No. 9-229901

  An object of the present invention is to provide a control device for an oxygen concentration sensor that can accurately detect the impedance of the oxygen concentration sensor.

  The oxygen concentration sensor control device according to the present invention is an oxygen concentration sensor control device that detects an oxygen concentration, and includes a first node and a second node when a voltage is applied to the oxygen concentration sensor control device. When the impedance of the oxygen concentration sensor is calculated based on the voltage and the impedance of the oxygen concentration sensor is relatively large, the time during which the voltage is applied to the control device of the oxygen concentration sensor is set to be relatively large. In addition, the voltage reading timing between the first and second nodes is set relatively late.

  The oxygen concentration sensor control device according to the present invention is an oxygen concentration sensor control device that detects an oxygen concentration, and includes a first node and a second node when a voltage is applied to the oxygen concentration sensor control device. The impedance of the oxygen concentration sensor is calculated based on the voltage, and when the voltage between the first and second nodes detected at the first reading timing is smaller than a set value, the first reading is performed. The impedance of the oxygen concentration sensor is calculated based on the voltage between the first and second nodes detected at a second reading timing that is later than the timing.

  The oxygen concentration sensor control device according to the present invention is an oxygen concentration sensor control device that detects an oxygen concentration, and includes a first node and a second node when a voltage is applied to the oxygen concentration sensor control device. Based on the voltage, the impedance of the oxygen concentration sensor is calculated, and based on the calculated impedance, the time during which the voltage is applied to the control device of the oxygen concentration sensor, and between the first and second nodes The voltage reading timing is determined.

  The oxygen concentration sensor control device according to the present invention is an oxygen concentration sensor control device that detects an oxygen concentration, and includes a first node and a second node when a voltage is applied to the oxygen concentration sensor control device. The impedance of the oxygen concentration sensor is calculated based on a voltage, has a plurality of circuit constants, and is switched to the circuit constant that relatively increases the voltage between the first and second nodes. .

  The oxygen concentration sensor control device according to the present invention is an oxygen concentration sensor control device that detects an oxygen concentration, and includes a first node and a second node when a voltage is applied to the oxygen concentration sensor control device. The impedance of the oxygen concentration sensor is calculated based on the voltage, and has a plurality of circuit constants, and is switched to the circuit constant that relatively increases the voltage of the first node.

  In the oxygen concentration sensor control device of the present invention, the circuit constant is switched based on the impedance.

  The control device for an oxygen concentration sensor according to the present invention includes an RC circuit including a resistor and a capacitor, and the resistance component of the RC circuit is switched as the circuit constant.

  In the control device for an oxygen concentration sensor according to the present invention, an input unit to which a voltage for driving the oxygen concentration sensor is applied, a first resistor connected to the input unit, and the input of the first resistor A second resistor connected at the first node to the second node and the oxygen concentration sensor on the opposite side of the unit, and a first voltage detecting means for detecting a voltage at the second node; And a second voltage detecting means for detecting the voltage of the first node, wherein the impedance is calculated based on the voltage of the first node and the voltage of the second node. .

  In the control device for an oxygen concentration sensor of the present invention, when the calculated impedance is relatively large, a resistance value of the second resistor is relatively small, and the calculated impedance is relatively small. In this case, the resistance value of the first resistor is relatively small.

  In the control device for an oxygen concentration sensor according to the present invention, the resistors are switched to a parallel arrangement.

  In the oxygen concentration sensor control device of the present invention, the constants of the resistor and the capacitor are determined so that the RC circuit maintains a predetermined time constant before and after the switching of the circuit constant. .

  According to the control device for an oxygen concentration sensor of the present invention, the impedance of the oxygen concentration sensor can be detected with high accuracy.

  Hereinafter, an embodiment of a control device for an oxygen concentration sensor of the present invention will be described in detail with reference to the drawings.

(First embodiment)
First, an outline of the present embodiment will be described.

  As a method for obtaining the element impedance of the oxygen concentration sensor, there is a method of obtaining a pulse width voltage that does not affect the control at a frequency that is not easily affected by the electrode impedance, and is obtained by applying a pulse width voltage to the sensor. The impedance of the detection circuit is calculated after reading the voltage of the detection circuit. However, if the sensor impedance is large, the voltage is not sufficiently saturated at the timing after a predetermined time, so that a voltage difference between both ends of the shunt resistor for current detection hardly occurs. In some cases, the voltage difference is within the range of variation in AD conversion. In some cases, impedance cannot be measured accurately. In order to solve this problem, the accuracy of sensor impedance calculation is ensured by making the pulse voltage width to be applied variable according to the sensor impedance value and making the predetermined time for reading the voltage value variable as well.

  Next, in order to facilitate understanding of the present embodiment, the basic principle of impedance calculation by the oxygen concentration sensor control device will be described.

  An oxygen concentration sensor (hereinafter also referred to as “air-fuel ratio sensor”) is attached to an exhaust pipe extending from an engine of a vehicle, and a current proportional to the oxygen concentration in the exhaust gas flows with the application of voltage. As the oxygen concentration sensor, a device in which platinum is coated on the inner and outer surfaces of a zirconia element is usually used. This oxygen concentration sensor uses a mechanism in which electric power is generated by the difference in oxygen concentration between the inner and outer surfaces of the sensor. In other words, when the oxygen concentration difference between the atmosphere introduced into the sensor (which contains a lot of oxygen) and the exhaust gas outside the sensor (which does not contain so much oxygen) is larger, the voltage difference is larger and there is no difference in oxygen concentration. There is no voltage difference. An electrical signal such as a voltage value corresponding to the current flowing through the oxygen concentration sensor is supplied to an ECU (Engine Control Unit) in the vehicle, and the ECU controls the fuel injection amount based on the detection result.

  Here, the relationship between the element temperature and the element impedance of the oxygen concentration sensor will be described with reference to FIG. In FIG. 8, the horizontal axis indicates the element temperature of the oxygen concentration sensor, and the vertical axis indicates the element impedance. As shown by the characteristic N, the oxygen concentration sensor has a characteristic that the element impedance changes remarkably according to the element temperature. Further, the output voltage of the oxygen concentration sensor starts to be generated at a predetermined temperature or higher, and the electromotive force slightly changes depending on the element temperature. Therefore, it is necessary to maintain the element temperature at an appropriate temperature (that is, the activation temperature). In FIG. 8, the temperature indicated by T1 is the temperature at which the oxygen concentration sensor starts to be activated (eg, 400 ° C.), and the temperature indicated by T2 is the activation temperature of the oxygen concentration sensor (eg, 700 ° C.). Generally, a heater is attached to the oxygen concentration sensor, and the heater is controlled so that the oxygen concentration sensor is maintained near the activation temperature T2. At this time, instead of directly detecting the temperature of the oxygen temperature sensor, the element impedance is detected by noting that the element impedance of the oxygen concentration sensor changes according to the element temperature as shown in FIG. The element temperature is calculated from the value.

  When the element impedance is remarkably large (area indicated by x1 in FIG. 8) and when the element impedance is remarkably small (area indicated by x2 in FIG. 8), the disconnection of the oxygen concentration sensor or the like using the element impedance value. Or short circuit can be determined. However, in that case, it is necessary to calculate the element impedance of the oxygen concentration sensor with high accuracy even in regions such as x1 and x2.

  Next, the electrical configuration employed in the control device for the oxygen concentration sensor will be described with reference to FIG. Hereinafter, a method for detecting the impedance of the oxygen concentration sensor will be mainly described.

  The oxygen concentration sensor control device 100 shown in FIG. 1 mainly includes an in-vehicle ECU (Engine Control Unit) 10 and an oxygen concentration sensor 5 driven by the ECU 10. The oxygen concentration sensor 5 is driven by the power supply voltage Vc. A PNP transistor Tp functioning as a switch is connected immediately below the input portion of the power supply voltage Vc. The transistor Tp is turned on when the impedance RS of the oxygen concentration sensor 5 is measured, and applies a voltage to the oxygen concentration sensor 5 and the like. The transistor Tp is controlled by the ECU 10.

  A resistor R1 is connected to the transistor Tp, and a resistor R2 is connected via the resistor R1. The oxygen concentration sensor 5 is connected to the resistor R2, and the oxygen concentration sensor 5 is connected to the ground. The element impedance of the oxygen concentration sensor 5 is expressed as RS. The AD converter 1 and the AD converter 2 are connected to both ends of the resistor R2, and these output values are taken into the ECU 10. The ECU 10 calculates the impedance RS in the oxygen concentration sensor 5 based on these output values.

  On the other hand, a capacitor C1 is connected to a connection portion between the resistor R1 and the resistor R2, and the capacitor C1 is connected to the ground. The capacitor C1 is used to apply a voltage generated by turning on the transistor Tp to the oxygen concentration sensor 5 with a predetermined time constant delay. This time constant delay corresponds to the AC frequency of the applied voltage, and corresponds to a frequency that is not easily affected by the electrode impedance. Further, an NPN transistor Tn is connected to the connection portion of the resistors R1 and R2 via the resistor RD, and is connected from the transistor Tn to the ground. The transistor Tn is turned on at the end of the measurement of the impedance of the oxygen concentration sensor 5 or immediately after the start, and is used to discharge the charges accumulated in the capacitor C1 and the oxygen concentration sensor 5. This transistor Tn is also controlled by the ECU 10.

  The ECU 10 calculates the impedance RS of the oxygen concentration sensor 5 based on the output values from the AD converter 1 and the AD converter 2 as described above. Further, the element temperature of the oxygen concentration sensor 5 is calculated from the impedance RS, and a heater (not shown) attached to the oxygen concentration sensor 5 is controlled. The ECU 10 also detects the oxygen concentration in the exhaust gas from the output voltage of the oxygen concentration sensor 5, and performs air-fuel ratio feedback control and the like. In addition, the ECU 10 can perform overall control of the transistors Tp and Tn and various controls of the entire vehicle.

  Here, the voltage value of the power supply voltage Vc is Vc, the output voltage value of the AD converter 1 is ADC1, the output voltage value of the AD converter 2 is ADC2, the resistance value of the resistor R1 is R1, the resistance value of the resistor R2 is R2, and the oxygen concentration An equation used to calculate the impedance value RS of the oxygen concentration sensor 5 in the ECU 10 will be described, where the impedance value of the sensor 5 is expressed as RS and the electric capacity of the capacitor C1 is expressed as C1.

When the transistor Tp is turned on, the voltage applied to the oxygen concentration sensor 5 is ADC2, and the current flowing through the oxygen concentration sensor 5 is (ADC1-ADC2) / R2. Therefore, the impedance value RS of the oxygen concentration sensor 5 is obtained by the following equation 1.
RS = ADC2 / ((ADC1−ADC2) / R2) Equation 1

  From the above equation 1, it can be seen that the calculated RS is affected by ADC2 when it is input to the ECU 10 (ADC1-ADC2). Therefore, when the difference between ADC1 and ADC2 is very small, or when ADC2 is small, it becomes particularly susceptible to circuit tolerances and AD conversion variations caused by AD converters 1 and 2, and RS The calculation accuracy of is reduced.

  As described with reference to FIG. 1, in order to obtain the impedance RS of the oxygen concentration sensor 5, the pulse voltage Vc is applied to the oxygen concentration sensor 5 from the outside by turning on the transistor Tp, and applied to the impedance RS. There is a method of calculating the impedance RS from the voltage ADC2 and the flowing current value ((ADC1-ADC2) / R2). In order to obtain the impedance RS, the time for forcibly applying the voltage Vc from the outside to the oxygen concentration sensor 5 (the time for turning on the transistor Tp) is preferably shorter in consideration of the influence on the sensor voltage used in normal control. . If the time for applying the voltage Vc is long, more charges are accumulated in the capacitance components of the capacitor C1 and the oxygen concentration sensor 5. Even if the transistor Tn is turned on and the accumulated charge is discharged, the transistor Tn is not completely discharged but a part of the charge remains. This is because the voltage difference (resistance value between nodes A and B) at both ends of the current detection shunt resistor drifts and causes a detection error of the oxygen concentration sensor 5.

  However, if the time during which the voltage Vc is applied to the oxygen concentration sensor 5 is set to a short time, and the impedance RS of the oxygen concentration sensor 5 is large, the AD read timing of the AD converter 1 and AD converter 2 when the transistor Tp is ON. Therefore, if the difference between the two is not enough and the AD converters 1 and 2 fall within the range of the AD reading error, accurate impedance measurement cannot be performed.

That is, when the impedance RS of the oxygen concentration sensor 5 is not large, the voltage rise time constant when the voltage is applied by turning on the transistor Tp is not large, so that the voltage Vc is set to the oxygen concentration as shown in FIG. Even when the time applied to the sensor 5 (time for turning on the transistor Tp) is short T1, ADC1 and ADC2 are saturated, and there is a sufficient difference between ADC1 and ADC2, so that detection is possible with high accuracy. is there.
On the other hand, when the impedance RS of the oxygen concentration sensor 5 is large, the voltage rise time constant when a voltage is applied by turning on the transistor Tp is large, and the voltage Vc is reduced to oxygen as shown in FIG. If the time applied to the concentration sensor 5 (time for turning on the transistor Tp) is short, the reading is performed before ADC1 and ADC2 are saturated, and the difference between ADC1 and ADC2 is not sufficiently high. Detection cannot be performed with high accuracy. In other words, when the impedance RS of the oxygen concentration sensor 5 is large, the voltage is read at the timing (T1) before the voltage change to be read is saturated, so that the difference between the target read voltage signals ADC1 and ADC2 is sufficiently large. If the difference falls within the reading error of the AD converter, accurate impedance cannot be measured depending on the AD converter.

  In order to avoid this, when the impedance RS of the oxygen concentration sensor 5 is large, the AD reading timing is delayed (= the time for applying the voltage Vc to the oxygen concentration sensor 5 is lengthened) (T2 in FIG. 2-2). ), The difference between ADC1 and ADC2 is detected with high accuracy, and when the impedance RS of the oxygen concentration sensor 5 is not large, the reading timing is advanced (= the time for applying the voltage Vc to the oxygen concentration sensor 5 is shortened). ) (Timing of T1 in FIG. 2-1), while reducing the influence on the sensor voltage other than the voltage application time (such as the problem of resistance drift between the nodes A and B), the sensor impedance Calculation accuracy can also be improved.

  The above concept can be expressed by the flowchart of FIG. That is, after the voltage Vc is applied to the oxygen concentration sensor 5 (step S1), when the time T1 (see FIGS. 2-1 and 2-2) has elapsed (step S2-Y), ADC1 and ADC2 are read (step S2-Y). Step S3). The difference between the read voltages ADC1 and ADC2 is obtained, and when the difference is larger than the set value a (step S4-Y), the application of the voltage Vc is terminated (step S7), and based on the read voltages ADC1 and ADC2. The impedance RS is calculated (step S8). On the other hand, when the difference is not larger than the set value a (step S4-N), the impedance RS is large in view of the voltage division ratio, so that the time T2 (T2> T1, FIGS. 2-1 and 2- 2) (step S5-Y), ADC1 and ADC2 are read (step S6), and then the application of the voltage Vc is terminated (step S7). Based on the read voltages ADC1 and ADC2, Impedance RS is calculated (step S8).

  In FIG. 3, when the difference between ADC1 and ADC2 is large at an early timing, the application of the voltage Vc to the oxygen concentration sensor 5 is terminated at that time, and the difference between ADC1 and ADC2 is not large at the early timing. First, the application of the voltage Vc to the oxygen concentration sensor 5 is continued, and after the voltage values of the ADC1 and ADC2 are read at a relatively late timing, the application of the voltage Vc to the oxygen concentration sensor 5 is terminated. Thereby, both the request to suppress the time for applying the voltage from the outside to the sensor in a short time and the request to calculate the impedance RS of the oxygen concentration sensor 5 with high accuracy in terms of the influence on the sensor voltage used in the normal control. Can be made.

  Next, a method (program) for specifically realizing the concept of the present embodiment will be described. FIG. 4 is a flowchart showing the operation of the present embodiment, corresponding to the contents programmed in the present embodiment. Each time the engine is started, the flow of FIG. 4 is repeated.

[Step S1]
First, as shown in step S1, it is determined whether or not the impedance RS of the oxygen concentration sensor 5 has been calculated. If the impedance RS is calculated, the process proceeds to step S3, and if not, the process proceeds to step S2. At the first stage when this flow is executed, the impedance RS has not been calculated, so the process proceeds to step S2.

[Step S2]
In step S2, T _ON0 that is the initial value of the ON time of the transistor Tp and T _AD0 that is the initial value of the reading timing of ADC1 and ADC2 are read from the memory, and the ON time T _ON and the reading timing T _AD are respectively read. Set. Following step S2, step S4 is performed.

[Step S3]
In step S3, the set ON time T _ON and the set read timing T _AD are read. In step S3, the ON time T _ON set in step S6 of the previous flow, the read timing T _AD , that is, the ON time T _ON ′ determined based on the impedance RS calculated in the previous flow, Read timing T _AD 'is read. After step S3, step S4 is performed.

[Step S4]
In step S4, only during the ON time T _ON which is set, the transistor Tp is the ON, the voltage value of the ADC1 and ADC2 at read timing T _AD which is set is read, the read-in ADC1, ADC2 Based on the above, impedance RS (Z) is calculated. At the initial stage when this flow is executed, the ON time T _ON and the read timing T _AD that have been set are initial values (step S2), so that the transistor Tp is turned on under the initial value conditions, The impedance RS is calculated by reading the voltage values of the ADC1 and ADC2. Following step S4, step S5 is performed.

[Step S5]
In step S5, the ON time T _ON ′ of the transistor Tp and the reading timing T _AD ′ of ADC1 and ADC2 are obtained based on the calculated impedance RS (Z). Following step S5, step S6 is performed.

[Step S6]
In step S6, T _ON 'and T _AD ' obtained in step S5 are set to the ON time T _ON and the read timing T _AD , respectively.

When the temperature of the oxygen concentration sensor 5 in a state immediately after engine startup and before warm-up is low, the value of the impedance RS is large, and the value of the impedance RS increases as the temperature of the oxygen concentration sensor 5 rises due to warm-up. Gradually becomes smaller. From this, when calculating the impedance RS for the first time before warming up (first time, step S1-N), the reading timing T _AD and the transistors of ADC 1 and ADC 2 correspond to the large value of the impedance RS. The initial value (T _AD0 , T _ON0 ) of the ON time T _ON of Tp is set to a large value (step S2). Thereby, even if the rising time constants of ADC1 and ADC2 are large, the voltage is prevented from being read before the voltage is saturated, and a sufficiently large value can be detected as the difference between ADC1 and ADC2.

When the initial impedance RS is calculated under the conditions of the initial value reading timing T _AD0 and the ON time T _ON0 (step S4), the reading timing T _{AD ′} and the initial value RS are calculated based on the calculated impedance RS value. The ON time T _{ON ′} is obtained (step S5), and in the second time following the first time, the impedance RS is calculated under the conditions of the obtained read timing T _{AD ′} and the ON time T _{ON ′} (step S5). S6 → step S1-Y → step S3 → step S4). In step S5, a map prepared in advance is used so that the reading timing T _{AD ′} and ON time T _{ON ′} large enough to saturate ADC 1 and ADC 2 are obtained according to the value of impedance RS.

Based on the value of the impedance RS calculated for the second time, the reading timing T _{AD ′} for the third measurement and the ON time T _{ON ′} are obtained (step S5), and the reading for the third measurement is performed. The third impedance RS is calculated under the conditions of the timing T _{AD ′} and the ON time T _{ON ′} .

Similarly, based on the value of the impedance RS calculated at the third time, the reading timing T _{AD ′} for the fourth measurement and the ON time T _{ON ′} are obtained, and the reading for the fourth measurement is performed. The fourth impedance RS is calculated under the conditions of the timing T _{AD ′} and the ON time T _{ON ′} . Here, since the warm-up proceeds with time, the impedance RS calculated at the third time is smaller than the impedance RS calculated at the second time. Accordingly, if the reading timing T _{AD ′} and the ON time T _{ON ′} for the third measurement are obtained based on the value of the impedance RS calculated for the second time, the reading is performed when the impedance RS is calculated for the third time. The timing T _AD and the ON time T _ON are not too short (the voltages ADC1 and ADC2 are read in a state before the voltages ADC1 and ADC2 are saturated).

  According to the first embodiment described above, from the viewpoint of the influence on the sensor voltage used in the normal control, the request to apply the voltage from the outside to the sensor in a short time and the impedance RS of the oxygen concentration sensor 5 are increased. It is possible to satisfy both demands for calculation with high accuracy.

  Next, a second embodiment will be described with reference to FIG.

  A method for calculating the impedance RS of the oxygen concentration sensor 5 will be described using the electrical configuration diagram according to the second embodiment shown in FIG. The control device 200 for the oxygen concentration sensor shown in FIG. 5 switches the circuit constant of the electric circuit for calculating the impedance RS based on the calculated impedance RS of the oxygen concentration sensor 5, thereby improving the calculation accuracy of the impedance RS. We are trying to improve.

  A specific method for calculating the impedance RS of the oxygen concentration sensor 5 will be described. The oxygen concentration sensor 5 in the oxygen concentration sensor control device 200 is driven by the power supply voltage Vc. A PNP transistor Tp is connected immediately below the input portion of the power supply voltage Vc. The transistor Tp is turned on when the impedance RS of the oxygen concentration sensor 5 is measured, and applies a voltage to the oxygen concentration sensor 5. The transistor Tp is controlled by the ECU 10.

  A resistor R1, a switch SW1, and a resistor R11 are connected to the transistor Tp through the switch SW1. When the switch SW1 is turned on, a parallel circuit of the resistors R1 and R11 is formed. In addition, the resistor R1, the resistor R11, the resistor R2, the switch SW2, and the resistor R22 are connected through the switch SW2. When the switch SW2 is turned on, a parallel circuit of the resistor R2 and the resistor R22 is formed. The switches SW1 and SW2 are controlled by the ECU 10.

  Thus, the electric circuit for calculating the impedance RS of the oxygen concentration sensor 5 according to the present embodiment employs a configuration in which the resistance value can be switched by the switch. This makes it possible to switch circuit constants. In addition, control of said switch SW1 and switch SW2 is performed based on impedance RS of the oxygen concentration sensor 5 calculated in ECU10. The specific control will be described later.

  In FIG. 5, an oxygen concentration sensor 5 is connected immediately below the resistor R2 or R22, and the oxygen concentration sensor 5 is connected to the ground. The oxygen concentration sensor 5 is the same as that described above. Further, the AD converter 1 and the AD converter 2 are connected to both ends of the resistor R2 or the resistor R22. The output values of these AD converters 1 and 2 are taken into the ECU 10. The ECU 10 calculates the impedance RS in the oxygen concentration sensor 5 based on these output values.

  On the other hand, a capacitor C1 and a resistor RD are connected to a connection portion between the resistors R1 and R11 and the resistors R2 and R22. The capacitor C1 is used to apply a voltage generated by turning on the transistor Tp to the oxygen concentration sensor 5 with a predetermined time constant delay. An NPN transistor Tn is connected from the resistor RD. The transistor Tn is turned on at the end of the measurement of the impedance RS of the oxygen concentration sensor 5 or immediately after the start, and is used to discharge the charge accumulated in the capacitor C1 and the like. This transistor Tn is also controlled by the ECU 10. The capacitor C1 and the transistor Tn are connected to the ground.

  The ECU 10 calculates the impedance RS of the oxygen concentration sensor 5 based on the output values from the AD converter 1 and the AD converter 2 described above. Further, the element temperature of the oxygen concentration sensor 5 is calculated from the impedance RS, and a heater (not shown) attached to the oxygen concentration sensor 5 is controlled. The ECU 10 also detects the oxygen concentration in the exhaust gas from the output voltage of the oxygen concentration sensor 5, and performs air-fuel ratio feedback control and the like. In addition, the ECU 10 can perform overall control of the transistors Tp and Tn and various controls of the entire vehicle.

  Here, the output voltage of the AD converter 1 is ADC1, the output voltage of the AD converter 2 is ADC2, the resistance value of the resistor R1 is R1, the resistance value of the resistor R2 is R2, the impedance value of the oxygen concentration sensor 5 is RS, and the capacitor C1 The electrical resistance is C1, the combined resistance value of the resistor R1 and the resistor R11 when the switch SW1 is turned on is R1 ′ (1 / R ′ = 1 / R1 + 1 / R11), and the resistor R2 and the resistor R22 when the switch SW2 is turned on The combined resistance value is expressed as R2 ′ (1 / R2 ′ = 1 / R2 + 1 / R22). At this time, the time constant τ of the resistor R1, resistor R11, resistor R2, resistor R22, and capacitor C1 is set to a value that satisfies the following Expression 2.

τ = (R1 ′ × (R2 ′ + RS)) / (R1 ′ + R2 ′ + RS) × C1 (Equation 2)
This is because the impedance RS calculated when the resistance value is changed by switching the switch ON / OFF does not deviate in the vicinity of the temperature (eg, 700 ° C.) used during normal driving of the vehicle. It is for doing so. For R1 and R2, the time constant τ to be satisfied when R1 is substituted for R1 ′ and R2 ′ is substituted for R2 ′ in Expression 2.

  Next, the relationship between the output voltage ADC1 of the AD converter 1 and the output voltage ADC2 of the AD converter 2 and the impedance RS of the oxygen concentration sensor 5 when the switch SW1 or the switch SW2 is turned on will be described.

  FIG. 6 shows the relationship between the impedance RS and ADC1 and ADC2 when only the switch SW1 is turned on. The horizontal axis represents the impedance RS of the oxygen concentration sensor 5, and the vertical axis represents ADC1 and ADC2. On the horizontal axis, the value of RS increases as it goes to the right, and the value of RS decreases as it goes to the left. When the switch SW1 is turned on, a parallel circuit of R1 and R11 is formed, so that the resistance value (R1 ') immediately before the AD converter 1 is reduced. Therefore, the output voltage ADC1 of the AD converter 1 becomes large (that is, becomes larger than the increment of ADC2), and the difference from the output voltage ADC2 of the AD converter 2 becomes remarkable. Therefore, even when the value of the impedance RS calculated by the ECU 10 is large, the value of (ADC1-ADC2) can be ensured (the region indicated by reference sign b1 in FIG. 6). Therefore, even when the RS value is large, the calculated impedance RS is hardly affected by variation by turning on the switch SW1.

  FIG. 7 shows the relationship between the impedance RS and ADC1 and ADC2 when only the switch SW2 is turned on. The horizontal and vertical axes take the same values as in FIG. When the switch SW2 is turned on, a parallel circuit of R2 and R22 is formed, so that the resistance value (R2 ') immediately before the AD converter 2 is reduced. Here, when Equation 1 is modified and ADC2 is described, Equation 3 is obtained.

ADC2 = ADC1 × RS / (R2 ′ + RS) Equation 3
From Equation 3, it can be seen that since R2 ′ is a small value, the value of ADC2 can be ensured even when the impedance RS is small (the region indicated by reference sign b2 in FIG. 7). Therefore, even when the RS value is small, the calculated RS is less affected by the variation by turning on the switch SW2.

From the above, it is optimal to turn on only the switch SW1 when the calculated impedance RS of the oxygen concentration sensor 5 is large, and to turn on only the switch SW2 when the calculated impedance RS is small. Thereby, the impedance of the oxygen concentration sensor 5 can be calculated with high accuracy (see the above formula 1). Thus, in the second embodiment, the impedance RS can be calculated with high accuracy without adjusting the ON time T _ON of the transistor Tp and the reading timing T _{AD of the} ADC 1 and ADC 2 as in the first embodiment. Is possible.

In the second embodiment, the circuit constant is switched to a parallel circuit and the resistance value is made variable. However, as another embodiment, the capacitance value of the capacitor can be changed (for example, the circuit constant can be switched). Etc.) may be adopted in which the time constants are aligned. That is, in the first embodiment, the time constant changes according to the magnitude of the impedance RS, and the ON time T _ON of the transistor Tp and the ADC 1 and ADC 2 correspond to the difference in the rise of the voltage of the ADC 1 and ADC 2. whereas the a configuration for adjusting the read timing T _AD, as other embodiments, by adjusting the value of the electrical capacitance of the capacitor in accordance with the magnitude of the impedance RS, regardless of the magnitude of the impedance RS, It is also possible to keep a constant time constant so that there is no difference in the rise of the voltages of ADC1 and ADC2.

It is a figure which shows the structure of the control apparatus of the oxygen concentration sensor for demonstrating the basic principle of the impedance calculation of an oxygen concentration sensor. It is a figure which shows the relationship between the voltage rise of an AD converter, and voltage reading timing when the impedance of an oxygen concentration sensor is small. It is a figure which shows the relationship between the voltage rise of an AD converter, and voltage reading timing when the impedance of an oxygen concentration sensor is large. It is a flowchart which shows the view of 1st Embodiment of the control apparatus of the oxygen concentration sensor of this invention. It is a flowchart which shows the operation | movement in 1st Embodiment of the control apparatus of the oxygen concentration sensor of this invention. It is a figure which shows the structure of 2nd Embodiment of the control apparatus of the oxygen concentration sensor of this invention. It is a figure which shows one of the effects of 2nd Embodiment of the control apparatus of the oxygen concentration sensor of this invention. It is a figure which shows another one of the effect of 2nd Embodiment of the control apparatus of the oxygen concentration sensor of this invention. It is a figure which shows the relationship between the element temperature of an oxygen concentration sensor, and an impedance.

Explanation of symbols

1, 2 AD converter 5 Oxygen concentration sensor 10 ECU
100, 200 Oxygen sensor control device R1, R11, R2, R22, RD Resistance C1 Capacitor Tp, Tn Transistor SW1, SW2 Switch

Claims (11)

A control device for an oxygen concentration sensor for detecting oxygen concentration,
The impedance of the oxygen concentration sensor is calculated based on the voltage between the first and second nodes when a voltage is applied to the control device of the oxygen concentration sensor,
When the impedance of the oxygen concentration sensor is relatively large, the time during which the voltage is applied to the control device of the oxygen concentration sensor is set to be relatively large, and the voltage between the first and second nodes is set. The oxygen concentration sensor control device is characterized in that the reading timing of is set relatively late. A control device for an oxygen concentration sensor for detecting oxygen concentration,
The impedance of the oxygen concentration sensor is calculated based on the voltage between the first and second nodes when a voltage is applied to the control device of the oxygen concentration sensor,
When the voltage between the first and second nodes detected at the first reading timing is smaller than a set value, it is detected at the second reading timing that is later than the first reading timing. The oxygen concentration sensor control device, wherein an impedance of the oxygen concentration sensor is calculated based on a voltage between the first and second nodes. A control device for an oxygen concentration sensor for detecting oxygen concentration,
The impedance of the oxygen concentration sensor is calculated based on the voltage between the first and second nodes when a voltage is applied to the control device of the oxygen concentration sensor,
Based on the calculated impedance, a time during which the voltage is applied to the control device of the oxygen concentration sensor and a reading timing of the voltage between the first and second nodes are determined. Concentration sensor control device. A control device for an oxygen concentration sensor for detecting oxygen concentration,
The impedance of the oxygen concentration sensor is calculated based on the voltage between the first and second nodes when a voltage is applied to the control device of the oxygen concentration sensor,
Has multiple circuit constants,
The control device for the oxygen concentration sensor, wherein the circuit constant is switched so that the voltage between the first and second nodes becomes relatively large. A control device for an oxygen concentration sensor for detecting oxygen concentration,
The impedance of the oxygen concentration sensor is calculated based on the voltage between the first and second nodes when a voltage is applied to the control device of the oxygen concentration sensor,
Has multiple circuit constants,
The control device for an oxygen concentration sensor, wherein the circuit constant is switched so that the voltage at the first node is relatively large. In the control apparatus of the oxygen concentration sensor according to claim 4 or 5,
The control device for an oxygen concentration sensor, wherein the circuit constant is switched based on the impedance. In the control device of the oxygen concentration sensor according to any one of claims 4 to 6,
An RC circuit composed of a resistor and a capacitor is provided.
The oxygen concentration sensor control device, wherein the resistance component of the RC circuit is switched as the circuit constant. In the control apparatus of the oxygen concentration sensor according to claim 7,
An input unit to which a voltage for driving the oxygen concentration sensor is applied;
A first resistor connected to the input unit;
A second resistor connected at the first node to the second node on the opposite side of the input portion of the first resistor and the oxygen concentration sensor;
First voltage detecting means for detecting a voltage of the second node;
Second voltage detecting means for detecting the voltage of the first node;
The control device for an oxygen concentration sensor, wherein the impedance is calculated based on the voltage of the first node and the voltage of the second node. In the control apparatus of the oxygen concentration sensor according to claim 8,
If the calculated impedance is relatively large, the resistance value of the second resistor is relatively small,
When the calculated impedance is relatively small, the resistance value of the first resistor is relatively small. The control device for an oxygen concentration sensor. In the control device of the oxygen concentration sensor according to any one of claims 7 to 9,
The resistance is switched to a parallel arrangement. An oxygen concentration sensor control device. In the control apparatus of the oxygen concentration sensor according to any one of claims 7 to 10,
The controller of the oxygen concentration sensor, wherein the constants of the resistor and the capacitor are determined so that the RC circuit maintains a predetermined time constant before and after switching of the circuit constants.

Images