JP6705397B2 - Oxygen concentration sensor controller - Google Patents

Description

The present invention relates to an oxygen concentration sensor control device.

In recent years, exhaust gas emission regulations have been strengthened and promoted in the vehicle technical field, and further reduction of harmful substances in exhaust gas has been demanded. The oxygen concentration sensor is provided to detect the excess air ratio in the exhaust gas of the internal combustion engine, but in order to reduce such harmful substances in the exhaust gas, it is necessary to improve the detection accuracy of the oxygen concentration sensor. Is required.

In order to improve the detection accuracy of the oxygen concentration sensor, it is necessary to reach the temperature at which the oxygen concentration sensor is activated at an early stage and maintain the temperature at which the oxygen concentration sensor is activated. Therefore, conventionally, the temperature of the oxygen concentration sensor is detected, and the temperature of the oxygen concentration sensor is kept at the activation temperature by using a heater.

Since there is a correlation between the temperature of the oxygen concentration sensor and the impedance of the elements that make up the oxygen concentration sensor, a method for detecting the temperature of the oxygen concentration sensor in response to detecting the impedance of the oxygen concentration sensor has been developed. (For example, see Patent Document 1). According to the technique described in Patent Document 1, an arbitrary fixed voltage is applied to the oxygen concentration sensor, the current value flowing in the current detection resistor and the voltage between the terminals of the oxygen concentration sensor are measured at this time, and the value is determined according to these values. To calculate the impedance.

JP, 2016-105065, A

When the technique described in the above-mentioned Patent Document 1 is adopted, the upper limit of the voltage that can be applied differs depending on the oxygen concentration sensor used, and thus the power supply voltage requires various variations and is impractical. Is not preferable.

An object of the present invention is to provide an electronic control device capable of calculating the impedance of an oxygen concentration sensor with high accuracy.

According to the invention described in claim 1, the sweep voltage applying section applies a voltage corresponding to any one of the plurality of sweep modes to the sensor element of the oxygen concentration sensor through one power supply voltage source, and impedance calculation is performed. At this time, the section calculates the impedance of the sensor element according to the voltage generated in the sensor element, and the switching section switches the applied voltage by the sweep voltage applying section by switching a plurality of sweep modes. Therefore, the temperature of the sensor element can be controlled by adjusting the voltage applied to the sensor element while the number of power supply voltage sources for driving is one, and the impedance of the oxygen concentration sensor can be calculated with high accuracy. Moreover, it is not necessary to prepare a power supply voltage source for each oxygen concentration sensor. The switching unit controls ON/OFF pulse of a voltage application switch for switching application/stop of voltage to the sensor element of the oxygen concentration sensor by the sweep voltage application unit, and changes the voltage applied to the sensor element of the oxygen concentration sensor. It is configured to be able to switch to the sweep mode.

Electrical configuration diagram schematically showing the oxygen concentration sensor control device of the first embodiment. The flowchart explaining the whole operation|movement in 1st Embodiment. Flowchart for schematically explaining the processing operation of the pre-sweep mode (first sweep mode) in the first embodiment. Timing chart for explaining the flow of processing in the pre-sweep mode in the first embodiment Enlarged view showing a change in the terminal voltage of the sensor element in the pre-sweep mode in the first embodiment (No. 1) An enlarged view showing a change in terminal voltage of the sensor element in the pre-sweep mode in the first embodiment (No. 2) Explanatory drawing which shows the correspondence of the temperature of a sensor element, and a sweep mode in 1st Embodiment. Flowchart for schematically explaining the processing operation of the normal sweep mode (second sweep mode) in the first embodiment. Timing chart for explaining the flow of processing in the normal sweep mode in the first embodiment Enlarged view showing changes in the terminal voltage of the sensor element in the normal sweep mode in the first embodiment. Explanatory drawing which shows the correspondence of the temperature of a sensor element, and a sweep mode in 2nd Embodiment.

Hereinafter, some embodiments of the oxygen concentration sensor control device will be described. In the following embodiments, parts having the same function or similar functions between the embodiments will be described with the same reference numerals, and in the second and subsequent embodiments, the embodiments described before will be described. A configuration having the same or similar function as described above, its operation, description of cooperation operation, and the like will be omitted as necessary.

(First embodiment)
1 to 10 are explanatory views of the first embodiment. FIG. 1 is a schematic block diagram showing the electrical configuration of the electronic control unit 101 of the oxygen concentration sensor.

The electronic control unit 101 shown in FIG. 1 includes a control block of an oxygen concentration sensor 2 for detecting the oxygen concentration in exhaust gas as a gas to be detected. The oxygen concentration sensor 2 has a structure in which the heater 4 is built in the sensor element 3 and is arranged in the exhaust path (not shown) of the internal combustion engine. The oxygen concentration sensor 2 is used as a sensor for realizing feedback control of the combustion injection system. The sensor element 3 includes a solid electrolyte layer made of a material such as the zirconia resistor 5 and produces an electromotive force according to the oxygen concentration in the exhaust gas. Therefore, the electronic control unit 101 can detect the oxygen concentration in the exhaust gas by detecting the electromotive force generated between the terminals of the sensor element 3. The electronic control device 101 includes a microcomputer 6, switches SW1 and SW2, a current detection resistor 7, a capacitor 8 and a resistor 9 for electromotive force detection, and a control switch 10 for controlling energization of the heater 4.

As shown in FIG. 1, the microcomputer 6 of the electronic control unit 101 is composed of a CPU, a ROM, a RAM and the like (not shown), and executes a program stored in the ROM as a non-transitional physical recording medium. The function corresponding to the program is realized by the microcomputer 6 executing the program, and this function is shown as a block in FIG. As shown in FIG. 1, the microcomputer 6 includes a current detection unit 11 as a current acquisition unit, a voltage detection unit 12 as a voltage acquisition unit, an A/D conversion unit 13, an impedance calculation unit 14, a sweep voltage application unit 15, and an estimation. The functions of the unit 16, the heater control unit 17, and the switching unit 18 are provided.

The switches SW1 and SW2 are connected between the supply node of the power supply voltage VCC and the ground node, and each of them is composed of, for example, a digital transistor. The switch SW1 is configured as a voltage application switch for switching the application/stop of the voltage to the sensor element 3 of the oxygen concentration sensor 2. The switch SW2 is configured as a charge discharging switch for discharging the electric charge applied to the sensor element 3.

The microcomputer 6 can be turned on/off by the heater control unit 17 through the control switch 10 to turn on/off the energization of the heater 4. The heater 4 is provided to maintain the element temperature of the sensor element 3 of the oxygen concentration sensor 2 at the activation temperature. It is known that there is a predetermined correlation between the impedance of the sensor element 3 of the oxygen concentration sensor 2 and the temperature of the sensor element 3. For example, when the element temperature of the sensor element 3 increases, the impedance decreases, The impedance rises as the element temperature falls. In other words, if the element temperature of the sensor element 3 changes, the impedance changes.

As shown in FIG. 1, the sensor element 3 of the oxygen concentration sensor 2 is divided into a resistance component of the zirconia resistance 5 that changes according to a temperature change and an interface resistance component 5a between the element of the zirconia resistance 5 and the electrode. Can be described on the equivalent circuit. Further, FIG. 1 also shows the electromotive force 5b generated in the sensor element 3. The oxygen concentration sensor 2 is exposed to exhaust gas and the like as the temperature/humidity environment of its installation location changes, so that its equivalent circuit also changes with time, and the capacitance component of the sensor element 3 changes with time. Will increase.

Now, the sweep voltage applying section 15 inside the microcomputer 6 can drive the switches SW1 and SW2 on and off respectively, and by changing the sweep voltage applied to the sensor element 3 of the oxygen concentration sensor 2, the sensor element 3 It is possible to apply, hold, and discharge electric charges.

The microcomputer 6 can be switched to any one of a plurality of sweep modes by the switching unit 18, and the sweep voltage applying unit 15 can sweep the applied voltage of the sensor element 3 in the plurality of sweep modes. ing. The microcomputer 6 switches to any one of the sweep modes by the switching unit 18, and the sweep voltage applying unit 15 drives the switches SW1 and SW2 on/off in accordance with the sweep mode to apply the sweep voltage. At this time, in each sweep mode, each element value of the internal circuit configuration of the electronic control unit 101 is adjusted so that the applied voltage to the sensor element 3 is saturated under the condition that the applied voltage is not higher than a predetermined voltage (Vz in FIG. 7 described later). Has been adjusted.

In this embodiment, a pre-sweep mode (corresponding to the first sweep mode) and a normal sweep mode (corresponding to the second sweep mode) are prepared as the sweep mode. The pre-sweep mode is a mode in which the voltage applied to the sensor element 3 of the oxygen concentration sensor 2 is changed by performing on/off pulse control of the switch SW1 while holding the switch SW2 off. The normal sweep mode is a mode in which the switch SW1 is turned on while the switch SW2 is held off, and a voltage is applied to the sensor element 3 of the oxygen concentration sensor 2 so as to reach a predetermined voltage. Thereby, the impedance and the temperature T of the sensor element 3 can be adjusted in any mode.

Inside the electronic control unit 101, a capacitor 8 and a resistor 9 are connected in parallel with the sensor element 3, and the voltage applied to the sensor element 3 can be detected by detecting the terminal voltage of the resistor 9. The voltage detection unit 12 in the microcomputer 6 detects the voltage between the terminals of the sensor element 3, waveform-shapes this detection voltage and outputs it to the A/D conversion unit 13, and the A/D conversion unit 13 analogizes this detection voltage. Convert to digital.

On the other hand, a current detection resistor 7 is connected to the energization path between the common connection point of the switches SW1 and SW2 and the sensor element 3. The current detection unit 11 in the microcomputer 6 inputs the voltage between both terminals of the current detection resistor 7, waveform-shapes the voltage between the terminals and outputs the waveform to the A/D conversion unit 13, and the A/D conversion unit 13 This output signal is converted from analog to digital. Thereby, the microcomputer 6 can acquire the detection voltage of the voltage detection unit 12 and the detection current of the current detection unit 11, and can acquire the voltage generated in the oxygen concentration sensor 2 by the detection voltage of the voltage detection unit 12.

In the pre-sweep mode, for example, the microcomputer 6 causes the impedance calculation unit 14 to detect the sensor element 3 of the oxygen concentration sensor 2 in accordance with the voltage generated in the sensor element 3 of the oxygen concentration sensor 2 by the applied voltage swept by the sweep voltage application unit 15. Is configured to calculate the impedance of the.

Further, the microcomputer 6 calculates the impedance according to the voltage generated in the sensor element 3 of the oxygen concentration sensor 2 by the applied voltage swept by the sweep voltage applying unit 15 and the current flowing in the sensor element 3 in the normal sweep mode, for example. The unit 14 is configured to calculate the impedance of the sensor element 3.

The microcomputer 6 is configured so that the estimation unit 16 estimates the temperature T of the sensor element 3 of the oxygen concentration sensor 2 according to the impedance calculated by the impedance calculation unit 14. Further, the microcomputer 6 is configured to adjust and control the temperature T of the sensor element 3 to an appropriate temperature by repeating the sweep mode switching process by the switching unit 18 and the impedance computing process by the impedance computing unit 14. ..

The operation of the above configuration will be described. When a battery power supply voltage for operation is applied to the electronic control unit 101 by turning on a power supply switch such as an ignition key switch, a power supply circuit (not shown) generates a power supply voltage VCC as a voltage for applying to the sensor element 3. It is applied to one terminal of the switch SW1. Further, the microcomputer 6 is activated and processes as shown in FIG.

FIG. 2 schematically shows the whole flow by a flowchart. When the internal combustion engine is cold, the temperature of the internal combustion engine is lower than the predetermined temperature immediately after the power is turned on, and therefore it is assumed that the impedance of the sensor element 3 of the oxygen concentration sensor 2 is higher than the predetermined impedance value. Therefore, the microcomputer 6 determines YES in S1 of FIG. 2 in the first time immediately after the power is turned on when the ignition switch of the vehicle is turned on, and in S2, switches to the pre-sweep mode as the first sweep mode and is set. Operates in pre-sweep mode.

FIG. 3 schematically shows the processing contents in the pre-sweep mode, and FIG. 4 schematically shows the overall flow in the pre-sweep mode by a timing chart.
Note that the fluctuation period of the sensor signal of the oxygen concentration sensor 2 is approximately every several seconds (for example, 4 to 5 seconds), and the sweep cycle (= in each sweep mode (pre-sweep mode, normal sweep mode) described in the present embodiment (= The cycle becomes significantly longer than that of tens of milliseconds. For easier understanding of the explanation, the timing chart of FIG. 4 and the like shows an example of a waveform when the sensor signal is a non-signal.

When the microcomputer 6 starts to operate in the pre-sweep mode, first, in S10 of FIG. 3, the heater control unit 17 controls the heater 4 to be always on. By energizing the heater 4, the temperature of the sensor element 3 can be raised. Then, the microcomputer 6 acquires the initial voltage of the inter-terminal voltage of the sensor element 3 by the A/D converter 13 in S11. The acquired initial voltage indicates the terminal voltage of the sensor element 3 immediately before the sweep voltage applying section 15 applies the voltage to the sensor element 3.

Next, the microcomputer 6 outputs a drive signal to the switches SW1 and SW2, and performs pulse control (for example, PWM control) so that the switch SW1 is repeatedly turned on and off. During this period, the switch SW2 is off controlled (see the pulse control period of SW1 in FIG. 4). As a result, charging between the terminals of the sensor element 3 is started. The microcomputer 6 detects the terminal voltage by the voltage detection unit 12, and inputs information on the terminal voltage of the sensor element 3 of the oxygen concentration sensor 2 through the A/D conversion unit 13.

FIG. 5 is an enlarged view showing a change in the terminal voltage of the sensor element 3 when the switch SW1 is repeatedly turned on and off, and FIG. 6 shows a flow when the information of the terminal voltage of the sensor element 3 is obtained once. Details are shown in the timing chart.

As shown in FIG. 5, the sensor element 3 and the capacitor 8 are charged when the switch SW1 is turned on in the period T1, and these charged charges are discharged through the resistor 9 when the switch SW1 is turned off in the period T2. To be done. Therefore, the terminal voltage of the sensor element 3 rises while fluctuating up and down. This process is repeated for a predetermined on/off period.

Next, the microcomputer 6 determines in S13 of FIG. 3 whether or not the on/off period of the switch SW1 has elapsed. The ON/OFF period of the switch SW1 indicates a period of one cycle in which the switch SW1 is ON/OFF controlled, and a predetermined value is used at the beginning of the control, but thereafter, it is set in S17 described later. The on/off period will be used.

As shown in FIG. 5, the terminal voltage of the sensor element 3 gradually increases as it moves up and down, but as shown in FIG. 6, the maximum value Vmax1 and the minimum value Vmin1 of the vertical movement change stabilize with the passage of time. .. The time for the maximum value Vmax1 and the minimum value Vmin1 of the vertical movement change to stabilize is determined depending on the type of the oxygen concentration sensor 2 and its individual difference. For this reason, the ON/OFF period of the switch SW1 in S13 is set to a predetermined value, for example, by using simulation or experiment, which is supposed to be saturated in advance according to the type of the oxygen concentration sensor 2. Then, the microcomputer 6 may determine whether or not this time has elapsed, for example, by using a built-in timer or the like.

Further, FIGS. 5 and 6 also show the holding timing ta of the terminal voltage of the sensor element 3. When the microcomputer 6 determines in S13 of FIG. 3 that the ON/OFF period has elapsed, it acquires the sampling timing of the A/D conversion unit 13 at the time of ON immediately before the switch SW1 is changed from ON to OFF in S14 of FIG. At timing ta, the terminal voltage of the sensor element 3 at this timing ta is held.

Further, the sampling timing of the A/D conversion unit 13 immediately after the switch SW1 is changed from on to off may be held as the acquisition timing ta. Any timing may be set as the acquisition timing ta as long as the terminal voltage of the sensor element 3 is as close to the maximum value Vmax1 as possible.

Thereafter, the microcomputer 6 discharges the accumulated charge of the capacitor 8 by turning off the switch SW2→on→off in S15 of FIG. 3 while keeping the switch SW1 in the off state (see period T3 of FIG. 6). The ON period T3 of the switch SW2 at this time is set to a time that allows all the charges accumulated in the capacitor 8 to be discharged from the resistor 9 and the like. That is, the microcomputer 6 may set the discharge time to be long if the charge time is long and set the discharge time to be short if the charge time is short, but the discharge time may be appropriately adjusted.

Next, the microcomputer 6 calculates the impedance of the sensor element 3 by the impedance calculation unit 14 in S16 of FIG. Since the resistance value of the current detection resistor 7 is sufficiently smaller than the resistance values of the resistors connected in series to the sensor element 3 and the resistance value of the resistance component of the sensor element 3, it can be ignored here. Therefore, the microcomputer 6 can use the detection voltage of the voltage detection unit 12 to calculate the impedance by the impedance calculation unit 14. Here, in order to calculate the impedance as quickly as possible, it is desirable to use the impedance that is uniquely determined based on the voltage detected by the voltage detection unit 12.

FIG. 7 schematically shows the temperature dependence of the impedance of the sensor element 3. The sensor element 3 of the oxygen concentration sensor 2 has an impedance of, for example, 10 kΩ or more at 400° C. or lower, but 130 Ω at 500° C., 64 Ω at 600° C., 20 Ω at 700° C., 15 Ω at 800° C., 900° C. It becomes about 12Ω.

For example, before starting the internal combustion engine, if the temperature of the sensor element 3 is, for example, normal temperature (for example, 25° C.), the impedance of the zirconia resistor 5 of the sensor element 3 exceeds 10 kΩ. The operating temperature range of the sensor element 3 of the oxygen concentration sensor 2 is a predetermined temperature range Ta (for example, 450° C. to 950° C.), and the target control temperature of the sensor element 3 of the oxygen concentration sensor 2 is the target temperature between them. The range is set to Tb (for example, 530° C. to 720° C.), and the impedance at this time is several Ω to several tens Ω. Therefore, when the temperature of the sensor element 3 becomes lower than the predetermined temperature range Ta (for example, up to 450° C.), the impedance of the sensor element 3 is about several hundred Ω or more. In this case, the impedance is calculated. Precision is not required more than necessary.

In such a case, the impedance calculator 14 of the microcomputer 6 may uniquely calculate the impedance from the voltage detector 12 without using the current detected by the current detector 11. At this time, the impedance calculation unit 14 may calculate the current value as a fixed value and divide the detected voltage of the voltage detection unit 12 by the current fixed value, or uniquely associate it with the voltage value in advance. The obtained impedance may be stored as a table inside the microcomputer 6 and the impedance may be calculated with reference to this table. Further, the microcomputer 6 detects the current from the current detection unit 11 at the same timing as the timing ta when the voltage is acquired by the A/D conversion unit 13, and divides the detection voltage of the voltage detection unit 12 by the detection current of the current detection unit 11. The impedance may be calculated in accordance with this.

When the impedance calculating unit 14 calculates the impedance in S16 of FIG. 3, the estimating unit 16 of the microcomputer 6 can estimate the temperature T according to the impedance. After that, the microcomputer 6 sets the next ON/OFF period of the switch SW1 in S17 of FIG. For example, the microcomputer 6 extends the ON/OFF period as the impedance of the sensor element 3 is estimated to be relatively high and the temperature T is low, and turns on/off as the impedance of the sensor element 3 is relatively low and the temperature T is estimated to be high. The period is set to be short (see FIG. 7 described later). Since the temperature T is lower than the target temperature range Tb while the pre-sweep mode is maintained, the on/off period may be kept constant at a predetermined value.

After that, the microcomputer 6 returns to the processing shown in FIG. 2 and switches the sweep mode according to the impedance of the sensor element 3. As shown in FIG. 2, the microcomputer 6 determines NO in S3 while the impedance is equal to or higher than a predetermined impedance value (in the present embodiment, equal to or higher than the first and second impedance values Ra) in S3. The sweep mode is set, and the above-described processing of S10 to S17 of FIG. 3 is repeated.

That is, the microcomputer 6 controls the ON/OFF pulse of the switch SW1 by the sweep voltage application unit 15 when the impedance value of the sensor element 3 calculated by the impedance calculation unit 14 in S12 is equal to or higher than a predetermined first impedance value (that is, Ra or higher). Then, the applied voltage to the sensor element 3 is changed, and the impedance calculation unit 14 calculates the impedance in S16. These processes are repeated.

Further, for example, when the initial temperature of the sensor element 3 is near room temperature (for example, 25° C.), as described above, when the power switch such as the ignition switch is turned on and the power supply voltage is supplied to the electronic control unit 101, The microcomputer 6 always controls the heater 4 to be turned on by the heater control unit 17 in the pre-sweep mode.

In other words, the microcomputer 6 keeps the heater 4 constantly operating the heater 4 by the heater controller 17 when the impedance value of the sensor element 3 calculated by the impedance calculator 14 in the pre-sweep mode is equal to or higher than a predetermined second impedance value (that is, Ra or higher). ON control.

When the heater 4 is constantly turned on, the temperature T of the sensor element 3 gradually rises. When the temperature T of the sensor element 3 increases, the impedance of the sensor element 3 gradually decreases. As a result, the microcomputer 6 can detect the temperature rise of the sensor element 3 by calculating the impedance by the impedance calculator 14.

Further, when the microcomputer 6 determines in S3 of FIG. 2 that the impedance calculated by the impedance calculation unit 14 becomes lower than the predetermined impedance value Ra (corresponding to the temperature Tra), the microcomputer 6 sets the normal sweep mode as the second sweep mode in S4. Transition.

FIG. 8 schematically shows the processing contents in the normal sweep mode, FIG. 9 schematically shows the whole flow in the normal sweep mode by a timing chart, and FIG. 10 shows an enlarged view of a part thereof. There is. When shifting to the normal sweep mode, the heater control unit 17 of the microcomputer 6 controls the heater 4 to be turned on/off in S20. In other words, the microcomputer 6 controls the heater control unit 17 to turn on/off the heater 4 when the impedance value of the sensor element 3 calculated by the impedance calculation unit 14 is lower than the second impedance value Ra. At this time, on/off control of the heater 4 is performed by, for example, PWM control. At this time, for example, the PWM cycle is set to about several hundred milliseconds.

Then, the microcomputer 6 acquires the initial voltage of the terminal voltage of the sensor element 3 by the A/D conversion unit 13 in S21. This initial voltage indicates the terminal voltage of the sensor element 3 immediately before the voltage is applied by the sweep voltage applying section 15. It may be acquired immediately after the voltage is applied.

Next, the microcomputer 6 outputs a drive signal to each of the switches SW1 and SW2, and controls the switch SW1 to turn on while keeping the switch SW2 off. When the sweep voltage application unit 15 of the microcomputer 6 continuously controls the switch SW1 to be turned on, the terminal voltage of the sensor element 3 of the oxygen concentration sensor 2 increases according to a predetermined time constant as shown in FIGS. 9 and 10.

The microcomputer 6 detects the terminal voltage by the voltage detection unit 12 and acquires the terminal voltage of the sensor element 3 through the A/D conversion unit 13. Then, the microcomputer 6 determines in S23 whether or not the ON period has elapsed. For this on period, a predetermined value is used at the beginning of control, but thereafter, the on period set in S28 described below is used. Although the terminal voltage of the sensor element 3 increases according to a predetermined time constant, the terminal voltage stabilizes over time as shown in FIG.

FIG. 10 also shows the voltage acquisition timing tb. If the microcomputer 6 determines in S23 of FIG. 8 that the ON period has elapsed, it determines YES in S23, and acquires the sampling timing of the A/D conversion unit 13 immediately before the switch SW1 is changed from ON to OFF in S24. Then, the terminal voltage at this timing tb is acquired, and the switch SW1 is turned off in S25.

Note that the acquisition timing tb may be the time immediately after the switch SW1 is changed from on to off. At this time, any timing may be used as the acquisition timing tb as long as the terminal voltage of the sensor element 3 can be maximized. The microcomputer 6 regards the voltage acquired at this timing tb as the maximum value Vmax2.

FIG. 7 shows the maximum value Vmax1 of the terminal voltage of the sensor element 3 in the pre-sweep mode and the maximum value Vmax2 of the terminal voltage of the sensor element 3 in the normal sweep mode in correlation with impedance and temperature. As shown in FIG. 7, in the normal sweep mode, the switch SW1 is continuously turned on while the switch SW2 is kept off, so the maximum value Vmax2 is higher than in the pre-sweep mode.

On the other hand, in the pre-sweep mode, the microcomputer 6 controls the switch SW1 with the on/off pulse while keeping the switch SW2 off, so that the maximum value Vmax1 can be suppressed as compared with the maximum value Vmax in the normal sweep mode. When the temperature T is relatively low, the impedance is relatively high, and therefore the terminal voltage of the sensor element 3 tends to be high. However, as shown in FIG. 7, when the impedance is relatively high, the switch SW1 is set in the pre-sweep mode. Since the on/off pulse control is performed, the maximum value Vmax1 can be suppressed. Therefore, even if the specified range Vz corresponding to the rated voltage of the terminal voltage of the sensor element 3 is predetermined, the maximum values Vmax1 and Vmax2 of the terminal voltage of the sensor element 3 are set to the specified range Vz in any mode. Can be suppressed.

After that, the microcomputer 6 discharges the accumulated charge of the capacitor 8 by turning off the switch SW2→on→off by the sweep voltage applying unit 15 in S26 of FIG. 8 (see the on period T4 of FIG. 10). At this time, the ON period T4 of the switch SW2 is set to a time that allows all the charges accumulated in the capacitor 8 to be discharged. That is, the microcomputer 6 sets the discharge time longer when the charging time of the capacitor 8 is longer, and sets the discharge time shorter when the charging time is short. The discharge time of the capacitor 8 may be adjusted appropriately.

Further, the microcomputer 6 calculates the impedance of the sensor element 3 by the impedance calculation unit 14 in S27 of FIG. Here, as described above, the impedance uniquely determined based on the voltage detected by the voltage detection unit 12 may be used as the calculation result of the impedance calculation unit 14 without using the detection current of the current detection unit 11. In order to improve the calculation accuracy, it is desirable to use the current detected by the current detection unit 11 to divide the detection voltage of the voltage detection unit 12 by the detection current of the current detection unit 11 to perform the calculation as accurately as possible. That is, when it is assumed that the temperature of the sensor element 3 exceeds a threshold temperature (for example, 450° C.), the impedance calculation accuracy is required accordingly.

For example, in order to set a predetermined target temperature (for example, 600° C.) in the target temperature range (for example, 530° C. to 720° C.), several Ω, 0. Unless a change of several Ω unit is accurately detected, the target temperature cannot be controlled to a predetermined target temperature (for example, 600° C.) accurately. In such a case, the current detected by the current detection unit 11 and the voltage detected by the voltage detection unit 12 are controlled. It is desirable to use it to calculate the impedance. This can improve the impedance calculation accuracy and the temperature T estimation accuracy.

Then, the microcomputer 6 sets the ON period of the switch SW1 according to the impedance calculated in S28 of FIG. As shown in FIG. 7, for example, the microcomputer 6 sweeps when the impedance is relatively low and the temperature T of the sensor element 3 is higher than a predetermined value (for example, a predetermined target temperature or an upper limit value Tu) within the target temperature range Tb. The ON period of the switch SW1 by the voltage applying unit 15 is shortened, and when the impedance is relatively high and the temperature T is lower than a predetermined value (for example, a predetermined target temperature or lower limit value Td) in the target temperature range Tb, the ON period of the switch SW1. Set longer.

Further, the microcomputer 6 sets the duty ratio when performing on/off PWM control of the heater 4 by the heater control unit 17 in S29 of FIG. For example, the microcomputer 6 sets the duty ratio low when the temperature T is higher than a predetermined value (for example, the predetermined target temperature or the upper limit value Tu) within the target temperature range Tb, and the temperature T is within the predetermined range within the target temperature range Tb. When it is lower than the value (for example, the predetermined target temperature or the lower limit value Td), the duty ratio is set high.

As shown in FIG. 2, the microcomputer 6 determines that the impedance of the sensor element 3 becomes equal to or higher than a predetermined impedance value (NO in S3) even immediately after the power is turned on (NO in S1). When the temperature of 3 is lower than the predetermined temperature Tra, the process is switched to the pre-sweep mode in S2. That is, the microcomputer 6 can adjust the impedance of the sensor element 3 within the target range by repeating the sweep mode switching processing by the switching section 18 and the impedance calculation processing by the impedance calculation section 14, and the sensor element 3 concerned. It becomes possible to control the temperature T of the target temperature range Tb to a predetermined target temperature within the target temperature range Tb.

<Conceptual summary according to the present embodiment>
The microcomputer 6 applies a voltage from the single power supply voltage VCC to the sensor element 3 through the switch SW1 by the sweep voltage applying section 15, and switches the sweep mode according to the impedance of the sensor element 3 of the oxygen concentration sensor 2. , ON/OFF control and ON control of the switch SW1 are selected to switch the voltage to be swept to the sensor element 3. Therefore, the temperature T of the sensor element 3 can be controlled by adjusting the voltage applied to the sensor element 3 while the number of driving power source voltage VCC is set to one, and the power source voltage source for each oxygen concentration sensor 2 can be controlled. You don't have to prepare. As a result, the impedance can be calculated without requiring various variations in the power supply voltage.

Moreover, the target temperature range Tb for activating the sensor element 3 of the oxygen concentration sensor 2 can be reached early, and after reaching the target temperature range Tb, the target temperature range Tb can be maintained at a constant target temperature range Tb. Further, in the microcomputer 6, the estimation unit 16 can estimate the temperature T of the sensor element 3 of the oxygen concentration sensor 2 according to the impedance calculated by the impedance calculation unit 14.

The microcomputer 6 uses the switching unit 18 to switch to the pre-sweep mode immediately after the power is turned on, and the sweep voltage applying unit 15 controls the on/off pulse of the switch SW1 to change the voltage applied to the sensor element 3. Even if the impedance of the sensor element 3 is extremely high immediately after turning on, the maximum value Vmax1 of the applied voltage of the sensor element 3 can be suppressed, and the applied voltage to the sensor element 3 can be suppressed within the specified range Vz.

Further, since the pre-sweep mode is switched to when the impedance of the sensor element 3 is equal to or higher than the predetermined first impedance value Ra, the maximum value Vmax1 of the applied voltage to the sensor element 3 can be similarly suppressed, and the sensor element 3 The terminal voltage can be suppressed within the specified range Vz.

Since the normal operation mode is switched when the impedance of the sensor element 3 is lower than the predetermined first impedance value Ra, the maximum value Vmax2 of the applied voltage to the sensor element 3 is high even when the normal operation mode is entered. The voltage applied to the sensor element 3 can be suppressed within the specified range Vz. In this way, the voltage applied to the sensor element 3 can be adjusted while using the hardware configuration shown in FIG. 1, and convenience can be improved. Further, even when a sudden change in the environment occurs, the terminal voltage of the sensor element 3 can be suppressed within the specified range Vz by controlling according to the calculated impedance.

When the microcomputer 6 uses the impedance calculator 14 to calculate the impedance according to the detection value of the voltage detector 12, the impedance of the sensor element 3 can be quickly calculated.
When the microcomputer 6 uses the impedance calculator 14 to calculate the impedance according to the detected value of the voltage detector 12 and the detected value of the current detector 11, the impedance can be accurately calculated and the temperature T can be accurately derived.

When the impedance of the sensor element 3 is equal to or higher than a predetermined impedance value (that is, Ra or higher), the microcomputer 6 constantly controls the heater 4 to turn on the heater 4, and when the impedance is lower than the impedance value Ra, the heater control unit 17 controls the heater. On/off pulse control of the power supply to No. 4 is performed. Therefore, the temperature T can be quickly increased when the temperature is lower than the predetermined threshold temperature Tra that corresponds to the impedance value Ra, and the temperature T can be accurately controlled when the temperature is close to the target temperature range Tb.

(Second embodiment)
FIG. 11 shows an additional explanatory diagram of the second embodiment. FIG. 11 shows a timing chart which replaces FIG. 7 of the first embodiment, but the difference from the first embodiment is the control switching condition of the heater 4. The same parts as those in the above-mentioned embodiment are designated by the same reference numerals and the description thereof will be omitted.

In the first embodiment, the heater 4 is constantly turned on in the pre-sweep mode, and the heater 4 is turned on/off in the normal sweep mode. However, the present invention is not limited to this. For example, as shown in FIG. 11, when the lower limit value Td of the target temperature range Tb is crossed, the constant ON control and the ON/OFF control of the heater 4 may be switched.

In particular, when the temperature of the sensor element 3 of the oxygen concentration sensor 2 is lower than the lower limit value Td of the target temperature range Tb, it is desirable that the heater 4 is always on-controlled until it reaches the target temperature range Tb. That is, when the temperature T and the impedance value are described in association with each other, the microcomputer 6 controls the heater when the impedance value of the sensor element 3 calculated by the impedance calculation unit 14 is equal to or higher than a predetermined second impedance value (that is, Raa or higher). It is preferable that the heater 17 always controls the heater 4 to be turned on, and the heater controller 17 controls the heater 4 to turn on/off a pulse (for example, on/off duty) when the heater 4 is lower than the predetermined second impedance value Raa. Here, as shown in FIG. 11, the second impedance value Raa is set to a value smaller than the first impedance value Ra.

On the contrary, when the temperature of the oxygen concentration sensor 2 is higher than the upper limit value Tu of the target temperature range Tb, the heater 4 may be constantly off-controlled until reaching the target temperature range Tb.
Also in the present embodiment, the same operational effects as those of the above-described embodiment are exhibited. Further, since the second impedance value Raa is set smaller than the first impedance value Raa, the temperature T of the sensor element 3 can be quickly targeted by constantly controlling the heater 4 in the range lower than the second impedance value Raa. The temperature range Tb can be adjusted.

(Other embodiments)
The present disclosure is not limited to the above-described embodiments, can be variously modified and implemented, and can be applied to various embodiments without departing from the gist thereof. For example, the following modifications or extensions are possible.

In the above-described embodiment, when the power switch such as the ignition switch is turned on, the temperature of the sensor element 3 rises from an environment in which the temperature is sufficiently lower than the temperature Tra (eg, 400° C.) (eg, 25° C.). However, the present invention is not limited to this. For example, when the ignition switch is turned on and the internal combustion engine starts to operate, and the temperature of the sensor element 3 is sufficiently high (for example, 600° C.), It can also be applied to the operation when the power switch is turned off and then immediately turned on again.

That is, for example, in the light of the processing contents of the first embodiment, the electronic control unit 101 operates as shown in FIG. 2, FIG. 3, and FIG. 8 even when the ignition switch is turned off, turned on again, and turned on again. Processing is performed based on the flowchart. At this time, immediately after the power is turned on, the processing is performed in the pre-sweep mode in S2 of FIG. 2. As a result of the microcomputer 6 calculating the impedance in S15, it is determined that the impedance is sufficiently low and the temperature T is sufficiently high. If so, the microcomputer 6 determines that the impedance is lower than the predetermined impedance value in S3 of FIG. 2 from the second time onward, and the processing is performed in the normal sweep mode. As a result, the same effect as that of the above-described embodiment can be obtained. Although the description is omitted, the same applies to the second embodiment.

As the voltage acquisition unit, the form in which the voltage detection unit 12 that detects the terminal voltage of the sensor element 3 is applied is shown, but the present invention is not limited to this, and for example, the voltage dividing resistance of the terminal voltage of the sensor element 3 (see FIG. The divided voltage may be acquired by (not shown), or any circuit may be configured as long as a certain value (corresponding to the acquired value) can be acquired according to the voltage generated in the sensor element 3.

As the current acquisition unit, the mode in which the current detection unit 11 that detects the current flowing in the current detection resistor 7 is applied is shown, but the present invention is not limited to this, and for example, some value may be set according to the current flowing in the sensor element 3. The circuit may have any configuration as long as (corresponding to the acquired value) can be acquired.

Further, the switching timing of the ON control and ON/OFF control of the heater 4 is made to coincide with the timing of switching the pre-sweep mode and the normal sweep mode in the first embodiment, and in the second embodiment, the target temperature range Tb Although a form is shown in which the timing is made to coincide with the lower limit value Td, it is not necessary to make these coincide with each other. That is, the timing may be determined according to the value of the impedance of the sensor element 3 of the oxygen concentration sensor 2, or a predetermined temperature determined independently of the lower limit value Td of the target temperature range Tb or corresponding thereto. The switching timing may be a timing that crosses the impedance value.

The estimation unit 16 shows the mode in which the temperature T of the sensor element 3 of the oxygen concentration sensor 2 is estimated according to the impedance calculated by the impedance calculation unit 14, but, for example, the impedance of the sensor element 3 and the temperature T , The temperature T need not be estimated, and the estimation unit 16 may be provided as necessary.

The switch SW1, SW2 connected between the supply terminal of the power supply voltage VCC and the ground node is turned on/off to change the voltage applied to the sensor element 3 of the oxygen concentration sensor 2. It is not limited to the circuit configuration of SW2.

A part or all of the functions that configure the microcomputer 6 may be configured by one or a plurality of ICs or the like, and may be configured by a logic circuit other than the microcomputer 6 or the like.
The reference numerals in parentheses in the claims indicate the corresponding relationship with the specific means described in the embodiments as one aspect of the present invention, and limit the technical scope of the present invention. Not a thing. A mode in which a part of the above-described embodiment is omitted as long as the problem can be solved can be regarded as the embodiment. Further, all possible modes can be regarded as the embodiments without departing from the essence of the invention specified by the wording recited in the claims.

Further, although the present invention has been described based on the above-described embodiment, it is understood that the present invention is not limited to the embodiment and the structure. The present invention also includes various modifications and modifications within the equivalent range. In addition, various combinations and forms, and other combinations and forms including one element, more, or less than them are also included in the scope and concept of the present disclosure.

In the drawing, 101 is an electronic control device, 2 is an oxygen concentration sensor, 3 is a sensor element, 4 is a heater, 11 is a current detection unit (current acquisition unit), 12 is a voltage detection unit (voltage acquisition unit), and 14 is impedance calculation. Reference numeral 15 is a sweep voltage application unit, 16 is an estimation unit, 17 is a heater control unit, and 18 is a switching unit.

Claims (11)

A sensor element (3) of an oxygen concentration sensor (2) for detecting an oxygen concentration in exhaust gas of an internal combustion engine with a voltage according to any one of a plurality of sweep modes through one power supply voltage source (VCC). ) And a sweep voltage applying section (15)
An impedance calculation section (14) for calculating the impedance of the sensor element according to the voltage generated in the sensor element of the oxygen concentration sensor by the applied voltage swept by the sweep voltage application section;
A switching unit (18) for switching the applied voltage by the sweep voltage applying unit by switching the plurality of sweep modes ,
The switching unit controls ON/OFF pulse of a voltage application switch (SW1) for switching the voltage application/stop to the sensor element of the oxygen concentration sensor by the sweep voltage application unit, thereby switching the sensor element of the oxygen concentration sensor to the sensor element. An electronic control device configured to be switchable to a first sweep mode in which an applied voltage is changed . The electronic control device according to claim 1, further comprising: an estimation unit (16) that estimates the temperature (T) of the sensor element of the oxygen concentration sensor according to the impedance calculated by the impedance calculation unit. The electronic control device according to claim 1, wherein the switching unit switches to the first sweep mode immediately after power is turned on. The electronic control device according to claim 1, wherein the switching unit switches to the first sweep mode when the impedance calculated by the impedance calculation unit is equal to or higher than a predetermined first impedance value (Ra). The switching unit can switch to a second sweep mode in which a voltage application switch (SW1) for switching application/stop of voltage to the oxygen concentration sensor is turned on to apply a predetermined voltage to a sensor element of the oxygen concentration sensor. The electronic control device according to claim 1 , wherein the electronic control device is configured as described above. The electronic control device according to claim 5 , wherein the switching unit switches to the second sweep mode when the impedance calculated by the impedance calculation unit is lower than a predetermined first impedance value (Ra). A voltage acquisition unit (12) for acquiring a value corresponding to the voltage generated in the sensor element,
The electronic control device according to any one of claims 1 to 6 , wherein the impedance calculation unit calculates the impedance according to the acquired value of the voltage acquisition unit. A current acquisition unit (11) for acquiring a value according to the current flowing through the sensor element,
The electronic control device according to claim 7 , wherein the impedance calculation unit calculates impedance according to an acquired value of the voltage acquisition unit and an acquired value of the current acquisition unit. To any one of the heater control unit (17), from claim 1, further comprising a 8 for controlling the heater (4) for adjusting the temperature of the sensor element of the oxygen concentration sensor in accordance with the plurality of sweep mode Electronic control device as described. A heater controller (17) for controlling the heater (4) for adjusting the temperature of the sensor element of the oxygen concentration sensor,
When the impedance calculated by the impedance calculation unit is equal to or greater than a predetermined second impedance value, the heater control unit constantly controls the heater to be turned on,
When the impedance computed by the impedance computing section is lower than a predetermined second impedance value, the heater control unit according to any one of claims 1 to 8 for turning on and off pulses controlling the energization of the heater Electronic control unit. A heater controller (17) for controlling a heater for adjusting the temperature of the oxygen concentration sensor,
When the impedance calculated by the impedance calculation unit is equal to or higher than a predetermined second impedance value (Ra, Raa), the heater control unit constantly controls the heater to be turned on,
When the impedance calculated by the impedance calculation unit is lower than a predetermined second impedance value, the heater control unit controls ON/OFF pulse of energization of the heater.
7. The electronic control device according to claim 4, wherein the second impedance value is set lower than the first impedance value.

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