JP6241385B2 - Air-fuel ratio sensor control device - Google Patents

Description

  The present invention relates to an air-fuel ratio sensor control device that controls a two-cell type air-fuel ratio sensor.

  As an air-fuel ratio sensor, there is a two-cell type sensor having an electromotive force cell (also called a Nernst cell) which is an oxygen concentration cell and an oxygen pump cell. In the two-cell type air-fuel ratio sensor, the pump current flowing through the oxygen pump cell is controlled so that the output voltage (Nernst voltage) of the electromotive force cell becomes a target value. Then, the air-fuel ratio and oxygen concentration are calculated from the pump current. The air-fuel ratio sensor also includes a heater for heating the electromotive force cell and the oxygen pump cell (see, for example, Patent Document 1).

An apparatus for controlling this type of air-fuel ratio sensor includes a sensor driving IC and a microcomputer.
The sensor driving IC detects the output voltage of the electromotive force cell, determines a pump current for setting the detected value to a target value, and passes the determined pump current to the oxygen pump cell. Control for detecting the output voltage of the electromotive force cell and determining the pump current from the detected value is called precision control. Then, the sensor driving IC notifies the microcomputer of the value of the pump current passed through the oxygen pump cell, for example, by communication.

  The microcomputer calculates the air-fuel ratio from the pump current value notified from the sensor driving IC. The calculated air-fuel ratio and oxygen concentration are used to correct the fuel injection amount for the internal combustion engine. The calculated oxygen concentration is used to correct an EGR (Exhaust Gas Recirculation) valve opening.

Further, the microcomputer outputs a drive signal in the form of a PWM (pulse width modulation) signal to the heater, and controls the amount of heat generated by the heater according to the duty ratio of the drive signal.
By the way, the state of the sensor driving IC is alternately switched between a state in which precise control is performed and a state in which precise control is not performed. If the microcomputer inverts the drive signal to the heater during the period in which the sensor drive IC performs the precision control (hereinafter referred to as the precision control period), the output voltage of the electromotive force cell in the sensor drive IC. Is not detected correctly, and as a result, the detection accuracy of the air-fuel ratio deteriorates. The inversion of the drive signal includes both inversion from the inactive level that does not energize the heater to the active level that energizes the heater and inversion from the active level to the inactive level.

  Therefore, in the conventional air-fuel ratio sensor control device, an inversion permission signal indicating permission / inhibition of inversion of the drive signal to the heater is output from the sensor driving IC to the microcomputer. The inversion permission signal is a high or low binary signal, and if it is not a precise control period, it becomes a level indicating permission of inversion of the drive signal (hereinafter referred to as inversion permission level). On the contrary, in the fine control period, the inversion permission signal is at a level indicating that the driving signal is not inverted (hereinafter referred to as an inversion prohibiting level).

  The microcomputer constantly monitors the inversion permission signal from the sensor driving IC, and does not invert the drive signal when the inversion permission signal is at the inversion prohibition level. Specifically, the microcomputer allows the inversion permission signal to change to the inversion permission level when the inversion permission signal is at the inversion prohibition level when the off timing for inverting the drive signal at the active level to the inactive level has arrived. Until the inversion of the drive signal to the inactive level is postponed. Similarly, if the inversion permission signal is the inversion prohibition level when the on timing for inverting the drive signal set to the inactive level to the active level has arrived, the microcomputer until the inversion permission signal changes to the inversion permission level. Postpones the inversion of the drive signal to the active level.

Special table 2013-528810 gazette

  In the above conventional air-fuel ratio sensor control device, the microcomputer has no choice but to delay the off timing at which the drive signal to the heater is inverted to the inactive level and the on timing at which the drive signal is inverted to the active level.

  When the drive signal OFF timing is delayed, the time during which the drive signal is at an active level in one cycle of the drive signal (that is, the energization time in one cycle, hereinafter also referred to as the ON time) controls the heater. It will be longer than the required value. Therefore, the cell is excessively heated (heated too much) by the heater. In addition, when the on timing of the drive signal is delayed, the cycle of the drive signal becomes longer. And if the period of a drive signal becomes longer than the tolerance | permissible_range of the period, the followability of the actual temperature with respect to target temperature will deteriorate.

  Therefore, the present invention achieves both the control performance of the heater and the non-inversion of the drive signal to the heater during the precision control period in the air-fuel ratio sensor control device that controls the two-cell type air-fuel ratio sensor. The purpose is that.

  The air-fuel ratio sensor to be controlled is a two-cell type air-fuel ratio sensor having an electromotive force cell and an oxygen pump cell, and a heater for heating the two cells. The air-fuel ratio sensor control device according to the first aspect of the present invention includes a sensor drive unit and a heater control unit.

  The sensor driving unit detects the output voltage of the electromotive force cell, performs precise control for determining the pump current to the oxygen pump cell for setting the detected value to the target value, and determines the pump current determined by the precise control. Flow in oxygen pump cell. And the state of a sensor drive part switches alternately with the state which implements precise control, and the state which does not implement precise control.

The heater control unit outputs a drive signal in the form of a PWM signal to the heater, and includes storage means, timing determination means, and signal output means.
The storage means stores schedule information indicating the respective times of a precision control period in which the sensor drive unit performs precise control and a non-precision control period in which the sensor drive unit does not perform precise control. Has been.

  The timing determining means determines the on timing and the off timing of the drive signal so as to be out of the precise control period (in other words, within the non-precision control period) based on the schedule information in the storage means. To do. The ON timing of the drive signal is a timing at which the drive signal is inverted from the inactive level that does not energize the heater to the active level that energizes the heater. The off timing of the drive signal is a timing at which the drive signal is inverted from the active level to the inactive level.

  The signal output means is instructed by the on timing and the off timing determined by the timing determining means. The signal output means inverts the output level of the drive signal to the active level when the instructed on timing arrives, and inverts the output level of the drive signal to the inactive level when the instructed off timing arrives. In the following description, inverting the drive signal from the inactive level to the active level is also referred to as “turning on”, and inverting the drive signal from the active level to the inactive level is also referred to as “turning off”.

In the air-fuel ratio sensor control device according to the first aspect of the invention, the heater control unit has schedule information indicating what time the precise control period and the non-precision control period in the sensor drive unit are.
For this reason, before turning off the drive signal, the heater control unit deviates the off timing from the precise control period, and the on time of the drive signal is not longer than the required value for controlling the heater. Can be determined. Therefore, it is possible to prevent overheating as in the conventional apparatus. Similarly, before turning on the drive signal, the heater control unit makes the on-timing deviate from the precise control period, and the cycle of the drive signal does not exceed the allowable range of the cycle (more preferably To be within the tolerance range). Therefore, it is possible to prevent the temperature follow-up deterioration as in the conventional apparatus.

Therefore, according to the air-fuel ratio sensor control apparatus of the first aspect of the invention, it is possible to achieve both the control performance of the heater and the inversion of the drive signal to the heater during the precision control period.
In addition, the code | symbol in the parenthesis described in the claim shows the correspondence with the specific means as described in embodiment mentioned later as one aspect, Comprising: The technical scope of this invention is limited is not.

It is a block diagram showing the electronic controller (ECU) of embodiment. It is explanatory drawing explaining control (precision control) of the pump current based on a Nernst voltage. It is explanatory drawing explaining a heater control mode. It is the 1st explanatory view explaining a period table. It is the 2nd explanatory view explaining a period table. It is explanatory drawing of a request | requirement on period-instruction | indication on period conversion table. It is explanatory drawing explaining the determination conditions of an on timing. It is a flowchart showing a heater control process. It is explanatory drawing explaining an effect | action of an electronic control apparatus.

An electronic control device according to an embodiment to which the present invention is applied will be described.
An electronic control device (hereinafter referred to as an ECU) 1 of the present embodiment is a device that controls, for example, an engine of a vehicle. Here, a part related to an air-fuel ratio sensor will be described.

As shown in FIG. 1, an ECU 1 is connected to an air-fuel ratio sensor 3 for detecting the air-fuel ratio.
The air-fuel ratio sensor 3 is a two-cell type air-fuel ratio sensor having two cells 3a and 3b, an electromotive force cell 3a which is an oxygen concentration cell and an oxygen pump cell 3b. The air-fuel ratio sensor 3 supplies the oxygen pump cell 3b with an output voltage (Nernst voltage) of the electromotive force cell 3a corresponding to the oxygen concentration difference between the measurement gas space into which the exhaust gas is introduced and the reference gas space. This is a sensor in which the flowing pump current is controlled and the pump current represents the air-fuel ratio.

  Furthermore, the air-fuel ratio sensor 3 also includes a heater 3c. The heater 3c heats the cells 3a and 3b by being energized by a drive signal in the form of a PWM signal output from the ECU 1 (hereinafter also referred to as a heater drive signal).

  The ECU 1 includes a sensor driving IC 5 as a sensor driving unit that drives the air-fuel ratio sensor 3, and a heater control unit 7 that outputs the heater driving signal to the heater 3c. Then, the heater control unit 7 performs the various processes including the control process of the heater 3c, and the heater drive signal as an energization current to the heater 3c in accordance with a drive instruction signal in the form of a PWM signal output from the microcomputer 8. Output circuit 9.

  As shown in FIG. 2, the sensor driving IC 5 detects the Nernst voltage, which is the output voltage of the electromotive force cell 3a, and sets the detected value to a target value (in this example, the reference potential (= 0 V)). The precision control for determining the pump current is performed, and the pump current determined by the precision control is supplied to the oxygen pump cell 3b. That is, the pump current is adjusted so that the Nernst voltage becomes the reference potential.

  The sensor driving IC 5 is alternately switched between a state in which precise control is performed and a state in which precise control is not performed. A period during which the sensor driving IC 5 performs the precision control is referred to as a precision control period, and a period during which the sensor driving IC 5 does not perform the precision control is referred to as a non-precision control period.

  As illustrated in the first stage in FIG. 7, the precise control period and the non-precise control period appear alternately. In the first stage of FIG. 7, the low period is the precise control period, and the high period is the non-precise control period. The same applies to FIG. 9 described later.

  From the sensor driving IC 5 to the microcomputer 8, a pump current value, which is a pump current value flowing through the oxygen pump cell 3b, is output by serial communication, for example. The microcomputer 8 converts the pump current value acquired from the sensor driving IC 5 into an air-fuel ratio and an oxygen concentration. The calculated air-fuel ratio is used to correct the fuel injection amount to the engine. The calculated oxygen concentration is used to correct the EGR valve opening.

  The sensor driving IC 5 performs processing for detecting the impedance of the electromotive force cell 3a in the non-precision control period. For example, an impedance measurement current is applied to the electromotive force cell 3a, and the impedance of the electromotive force cell 3a is calculated from the difference between both end voltages of the electromotive force cell 3a measured before and after the application of the current. Then, the sensor driving IC 5 also outputs the calculated impedance value to the microcomputer 8 by, for example, serial communication.

Since the impedance of the electromotive force cell 3a has a correlation with the temperature of the electromotive force cell 3a, the microcomputer 8 is used to control the heater 3c.
As shown in FIG. 3, the control mode of the heater 3c (hereinafter referred to as heater control mode or simply mode) includes condensation drying control, rapid temperature rise control, and feedback (F / B) control. The “heater driving duty” on the vertical axis in FIG. 3 is the duty ratio of the heater driving signal output to the heater 3c.

  Condensation drying control is control for preventing the air-fuel ratio sensor 3 from cracking due to condensation, and is a control for energizing the heater 3c by setting the duty ratio of the heater drive signal to a minute value by open control.

  The rapid temperature increase control is a control for rapidly increasing the temperature of the cells 3a and 3b to an activation temperature suitable for detecting the air-fuel ratio (oxygen concentration), and the duty ratio of the heater drive signal is adjusted by open control. Control.

  The feedback control is control for maintaining the temperature of the cells 3a and 3b at the activation temperature, so that the impedance of the electromotive force cell 3a becomes a target value (that is, the temperature of the cells 3a and 3b becomes the target temperature). 2) Control for adjusting the duty ratio of the heater drive signal. The impedance value output from the sensor driving IC 5 to the microcomputer 8 is used for this feedback control.

  A mode information signal instructing the heater control mode is output from the sensor driving IC 5 to the microcomputer 8 through a dedicated signal line or serial communication. Then, the microcomputer 8 controls the mode indicated by the mode information signal regarding the control of the heater 3c. As shown in FIG. 3, the heater control mode transitions in the order of “condensation drying control → rapid temperature rise control → feedback control”. The switching timing of each mode is a multiple of the heater drive signal cycle.

  The microcomputer 8 includes a CPU 11, a ROM 13 in which a program 12 executed by the CPU 11 is stored, a RAM 14, and a PWM circuit 15. The ROM 13 also stores a period table 17 described later.

The PWM circuit 15 is a timer circuit that outputs a drive instruction signal that is a PWM signal to the output circuit 9.
The PWM circuit 15 is instructed by the CPU 11 by setting the on timing and the off timing of the drive instruction signal. The ON timing of the drive instruction signal is a timing at which the drive instruction signal is inverted from an inactive level (low in this example) that does not energize the heater 3c to an active level (high in this example) that energizes the heater 3c. is there. The off timing of the drive instruction signal is a timing at which the drive instruction signal is inverted from high to low.

  When the ON timing set by the CPU 11 (in other words, instructed) arrives, the PWM circuit 15 sets the output level of the drive instruction signal to high. After that, when the OFF timing set (in other words, instructed) by the CPU 11 arrives, the PWM circuit 15 sets the output level of the drive instruction signal to low. In the PWM circuit 15, for example, an elapsed time from the on timing is set as the off timing.

  The output circuit 9 energizes the heater 3c if the drive instruction signal from the microcomputer 8 is high, and stops energizing the heater 3c if the drive instruction signal is low. Energizing the heater 3c corresponds to setting the heater driving signal to an active level (high in this example), and stopping energizing the heater 3c causes the heater driving signal to be inactive (low in this example). ).

Next, the period table 17 stored in the ROM 13 will be described.
The period table 17 is schedule information indicating the respective times of the precision control period and the non-precision control period in the sensor driving IC 5.

  In the period table 17 of the present embodiment, as shown in FIG. 4, for each heater control mode, the transition time (start time) to the mode is set as the start (0 μs) as the reference time, and the elapsed time from the start. Defines a precision control period and a non-precision control period. In each mode, “non-precision control period → precision control period → non-precision control period →...” Is repeated, and the period table 17 records the time of each repeated period.

The period table 17 in the example of FIG. 4 represents the contents of FIG.
That is, in the condensation drying control mode, the time T1 (= 6310 μs) elapses from the start (start) of the mode, and then the time T2 (= 1400 μs) elapses. Until is the precision control period. After that, the time until the time T3 (= 640 μs) elapses is the non-precision control period, and then the time T4 (= 1640 μs) elapses is the precision control period. Thereafter, this is repeated. In the rapid temperature increase control mode, the time T5 (= 253 μs) elapses from the start of the mode is the non-precision control period, and thereafter the time T6 (= 413 μs) elapses. The precision control period. Thereafter, this is repeated. Similarly, in the feedback control mode, the time T7 (= 253 μs) elapses from the start of the mode is a non-precise control period, and then the time T8 (= 413 μs) elapses. It is a precision control period. Thereafter, this is repeated.

  If the microcomputer 8 inverts the heater drive signal to the heater 3c during the precision control period in which the sensor drive IC 5 performs the precision control, the sensor drive IC 5 correctly detects the Nernst voltage of the electromotive force cell 3a. As a result, the air-fuel ratio detection accuracy deteriorates. Signal inversion is both low to high inversion and high to low inversion. That is, the precise control period is a period in which the inversion of the heater drive signal is prohibited, and the non-precision control period is a period in which the inversion of the heater control signal is permitted.

  For this reason, the microcomputer 8 uses the period table 17 to deviate the on timing for inverting the heater drive signal from low to high and the off timing for inverting the heater drive signal from high to low. (In other words, within the non-precision control period).

  Then, next, the processing content which the microcomputer 8 performs in order to control the heater 3c is demonstrated. Note that the processing performed by the microcomputer 8 is realized by the CPU 11 executing the program 12 in the ROM 13, and therefore the CPU 11 will be mainly described.

[Processing content 1: Calculation of request on time]
The CPU 11 calculates the ON time from when the heater drive signal is set to high until it is set to low based on the control logic of the heater 3c. The control logic of the heater 3 c is stored in the ROM 13 as the program 12. The on-time is a high time in one cycle of the heater drive signal (that is, energization time in one cycle). The ratio of the on time to one cycle of the heater drive signal (PWM signal) is the duty ratio. Since the on-time calculated based on the control logic of the heater 3c is an on-time required for controlling the heater 3c, it is called a requested on-time.

  For example, the required on-time is calculated to a constant value in the condensation drying control mode, and is calculated to a value corresponding to the elapsed time from the start of the mode in the rapid temperature increase control mode (see FIG. 3). ). In the feedback control mode, the required on-time is calculated as a value for setting the impedance to a target value according to the impedance of the electromotive force cell 3a.

[Processing content 2: Creation of request on period-instruction on period conversion table]
For each heater control mode, the CPU 11 uses the period table 17 to create a request on period-instruction on period conversion table (hereinafter simply referred to as an on period conversion table) as shown in FIG. The required on period is a period from when the heater driving signal is turned on until the required on time elapses. The instruction on period is a period from the on timing to the PWM circuit 15 to the off timing.

  As shown in FIG. 6, when an arbitrary time starting from the start of the mode (specifically, the time from the start of the mode) is input to the on-period conversion table, the time does not enter the precise control period. Is a data table obtained as an output time.

  Specifically, in the on-period conversion table, if the input time is not in the precise control period (in other words, if it is in the non-precision control period), the input time is the output time. If the input time is in the precise control period, the output timing is the end timing of the non-precision control period that exists immediately before the precise control period in which the input time is entered. The end timing of the non-precise control period is the final time among the times at the minimum resolution included in the non-precise control period in the table.

  If the horizontal axis in FIG. 6 is the input time and the vertical axis in FIG. 6 is the output time, for example, when the time t1 within the non-precision control period is input to the on-period conversion table, the time t1 is the output time. Become. Further, for example, when the time t3 within the precise control period is input to the on-period conversion table, the end timing of the non-precise control period existing immediately before the precise control period in which the time t3 is included (in this example, the time t2 ) Is the output time.

  In this example, it is assumed that the on-timing of the heater drive signal is time t1, and the off-timing after the requested on-time from the on-timing is time t3. That is, as shown in part (1) in FIG. 6, it is assumed that the period from time t1 to time t3 is the request on period.

  In this case, if two times t1 and t3 are input to the on-period conversion table as request on-periods, it is a period from time t1 to time t2, and both the on-timing and off-timing are from the precise control period. An out-of-period is output. As shown in part (2) in FIG. 6, the period from time t1 to time t2 is a period from the on timing to the off timing instructed to the PWM circuit 15 (that is, the designated on period). Can do. From this, the on-period conversion table in FIG. 6 is named “request on-period-instruction on-period conversion table” in the full name. The on-period conversion table is a graph that is stepped in the precise control period between the precise control period and the non-precise control period when the requested on-period is on the horizontal axis and the instruction on-period is on the vertical axis. The “instruction on time” described in the portion (2) in FIG. 6 is the length of the instruction on period, and is the time from the on timing to the off timing instructed to the PWM circuit 15. .

[Processing content 3: Determination of heater drive signal ON timing]
The CPU 11 determines the ON timing of the heater driving signal based on the above-described period table 17 so that the following conditions <1> to <3> are satisfied every time the heater driving signal is inverted to high. In addition, every time before the output circuit 9 inverts the heater drive signal to high, in other words, every time before the PWM circuit 15 inverts the drive instruction signal to the output circuit 9 to high. Further, in the processing, the CPU 11 determines the on timing of the drive instruction signal instructed to the PWM circuit 15 as the on timing of the heater drive signal.

<1> As shown in the dotted ellipse in FIG. 7, the current on-timing, which is the on-timing determined this time, deviates from the precise control period.
<2> As shown in the dotted ellipse in FIG. 7, the interval T0 between the current on-timing and the previous on-timing that is the previously determined on-timing is within the allowable range (TCmin to TCmax) of the cycle of the heater drive signal Range, which is hereinafter referred to as a cycle tolerance). “TCmin” is an allowable minimum value of the cycle, and “TCmax” is an allowable maximum value of the cycle.

  <3> As shown in the dashed-dotted ellipse in FIG. 7, N times (N is an integer of 1 or more) after the time within the period allowable range (T1, T2 in this example) starting from the current on-timing In this example, the timing of N = 2) deviates from the precise control period.

  Based on the above-described period table 17, the CPU 11 determines the precise control period and the non-precise control period with respect to the time based on the start time of each heater control mode (or the start time of the condensation drying control which is the first mode). Can be determined. Therefore, the CPU 11 can determine the current on-timing based on the period table 17 so that the conditions <1> to <3> are satisfied.

  Further, for example, the CPU 11 determines the first on-timing from the start of each heater control mode only by the condition <1> among the above conditions <1> to <3>. For example, the timing within the first non-precision control period from the start of the heater control mode is determined as the first on-timing.

  Note that the N timings that satisfy the above condition <3> are timings that can be adopted as the next on timing. That is, the condition <3> is a condition for satisfying the conditions <1> and <2> also for N on-timings after the next time.

  It is also possible to remove the above condition <3> from the condition for determining the on-timing this time. However, if the current on-timing is configured to be determined only by the above conditions <1> and <2>, the selection margin for the current on-time is widened. As a result, for example, as illustrated in the stage of “Comparative Example” in FIG. 7, when determining the on timing after the next time, there is no timing that satisfies the conditions <1> and <2>. there is a possibility. On the other hand, if the condition <3> is included as a condition for determining the current on-timing, the timing satisfying the conditions <1> and <2> is determined when determining the on-timing after the next time. It can be prevented from disappearing.

[Processing content 4: Determination of heater drive signal off timing]
The CPU 11 sets the timing (time) after the requested on-time calculated in the “processing content 1” from the on-timing determined in the “processing content 3” (current on-timing) to the above-described on-period conversion table (FIG. By substituting 6) as the input time, the heater drive signal OFF timing is determined. In the processing, the CPU 11 determines the off timing of the drive instruction signal that instructs the PWM circuit 15 as the off timing of the heater drive signal.

  For this reason, if the timing after the requested on-time from the on-timing is not within the precise control period, the timing after the requested on-time is determined as the off timing. Further, as exemplified in the part (1) in FIG. 6, it is assumed that the timing (time t3 in the example of FIG. 6) after the requested on-time has entered the precise control period. At that time, as illustrated in the part (2) in FIG. 6, the end of the non-precision control period existing immediately before the precision control period including the timing (t3) after the requested on-time from the on-timing. The timing (time t2 in the example of FIG. 6) is determined as the off timing.

Note that the requested on time for determining the off timing may be increased and corrected by correcting “processing content 5” described later.
[Processing content 5: Correction of requested on-time]
When the CPU 11 determines the end timing of the non-precision control period as the off timing when determining the previous off timing, the CPU 11 adds the correction value ΔT to the requested on time used to determine the current off timing. To do. The correction value ΔT includes a request on time used to determine the previous off timing (hereinafter referred to as a request on time used last time) and a time from the previous on timing to the previous off timing (that is, the previous time). Is the difference between the previous on-time and the previous actual on-time).

  In other words, if the timing after the requested on-time from the determined on-timing is in the precise control period and the end timing of the non-precision control period is determined as the off-timing, the actual on-time is requested on Shorter than time. For this reason, the correction value ΔT, which is the shortened time, is added to the required on time for determining the next off timing.

[Processing content 6: Delay correction]
The output circuit 9 has an operation delay. That is, there is a delay between the inversion of the drive instruction signal from the microcomputer 8 to the output circuit 9 and the inversion of the output level of the heater drive signal. There is also a signal propagation delay in the signal path from the PWM circuit 15 to the output circuit 9 in the microcomputer 8.

  Therefore, the portion corresponding to the signal output means for outputting the heater drive signal (in this example, the PWM circuit 15 and the output circuit 9) increases the output level of the heater drive signal after the ON timing instructed by the CPU 11 has arrived. Until the first delay time Td1. Similarly, the portion corresponding to the signal output means has a second delay time Td2 from when the OFF timing instructed by the CPU 11 arrives until the output level of the heater drive signal is inverted to low. Note that the first delay time Td1 and the second delay time Td2 may be the same or different. In general, the signal propagation delay of the signal path is negligibly small compared to the operation delay of the output circuit 9, so that the delay times Td 1 and Td 2 can be said to be the delay time of the operation of the output circuit 9.

  For this reason, the CPU 11 shifts the on-timing determined in the “processing content 3” by the first delay time Td1 and the off-timing determined in the “processing content 4” by the second delay time Td2. The delay correction is performed. Then, the CPU 11 instructs the PWM circuit 15 of the on timing and off-off timing after the delay correction. If the delay times Td1 and Td2 are so small that they can be ignored, such delay correction can be omitted.

Next, a heater control process performed by the CPU 11 for controlling the heater 3c will be described again with reference to FIG.
The CPU 11 executes the heater control process of FIG. 8 when the operation is started as the ECU 1 is powered on.

  In the heater control process, first, in step S110, the CPU 11 uses the period table 17 in the ROM 13 as described in “Processing content 2”, and uses an on period conversion table (requested on period−instruction for each heater control mode). Create an on-period conversion table). The on-period conversion table may be created first corresponding to the mode of condensation drying control, and then created corresponding to the switched mode every time the heater control mode is switched.

In step S120, the CPU 11 determines the current on-timing (current on-timing) of the heater drive signal as described in “Processing content 3”.
In the next S130, the CPU 11 calculates the correction value ΔT for the requested on-time described in “Processing content 5”. As described above, the correction value ΔT is a value obtained by subtracting the previous instruction on-time from the previous request on-time.

  In the next S140, the CPU 11 calculates the required on-time based on the control logic of the heater 3c, as described in “Processing content 1”. Note that the requested on-time may be calculated by a process different from that in FIG.

  In the next S150, the CPU 11 calculates a value obtained by adding the correction value ΔT calculated in S130 to the current required on-time calculated in S140 as the required on-time for determining the off timing. This process corresponds to the correction of the requested on-time described in “Processing content 5”, but the correction is substantially performed when the correction value ΔT is not zero.

  In the next S160, the CPU 11 determines the current off timing of the heater drive signal by the processing described in “Processing content 4”. Specifically, the CPU 11 substitutes the timing after the requested on-time calculated in S150 from the current on-timing determined in S120 as the input time in the above-described on-period conversion table. To decide. The time from the current on-timing determined in S120 to the current off-timing determined in S150 is the current instruction on-time.

  If the timing assigned to the on-period conversion table in the previous S160 (that is, the timing after the previous on-timing required on-time) is not within the precise control period, the timing is the off-timing. As determined. In that case, the request on time of the previous use and the previous instruction on time are the same. Therefore, the correction value ΔT is 0 in the current S130, and the current request on time calculated in S140 is the request on time for determining the off timing as it is in S150. That is, the required on-time increase correction is not performed.

  On the other hand, if the timing assigned to the on-period conversion table is in the precise control period in the previous S160, the end timing of the non-precise control period existing immediately before the precise control period in which the timing is entered is the off timing. As determined. In that case, the previous instruction on time is shorter than the request on time of the previous use, and the correction value ΔT calculated in S130 of this time becomes a value larger than zero. Therefore, in this S150, the required on-time increase correction is performed. That is, a value obtained by adding the correction value ΔT to the current required on-time based on the control logic of the heater 3c becomes the required on-time for determining the off timing.

  In the next S170, the CPU 11 shifts the current on-timing determined in S120 by the first delay time Td1 and the current off-timing determined in S160 as described in “Processing content 6”. Delay correction is performed to shift the second delay time Td2 forward. Then, in the next S180, the CPU 11 instructs the PWM circuit 15 on timing and off timing after correction in S170.

  Then, the PWM circuit 15 inverts the drive instruction signal to the output circuit 9 to high when the on-timing of the on-timing and off-timing instructed by the CPU 11 arrives, and then drives when the off-timing arrives. Invert the indication signal low.

  In the next S190, the CPU 11 determines whether or not the drive instruction signal from the PWM circuit 15 is high. If it is high (that is, if the off timing instructed to the PWM circuit 15 in S180 has not yet arrived). , Return to S140. The OFF timing can be changed by performing the processing of S140 to S180 during the period from the arrival of the ON timing instructed to the PWM circuit 15 to the arrival of the OFF timing. Note that even if the PWM circuit 15 is instructed at S180 in S180, the output of the drive instruction signal is not affected.

  If the CPU 11 determines in S190 that the drive instruction signal is not high (that is, low), the CPU 11 proceeds to S200 and determines whether or not the heater drive stop condition is satisfied. The heater drive stop condition is satisfied, for example, when the engine is stopped.

  If the CPU 11 determines in S200 that the heater drive stop condition is not satisfied, the process returns to S120. Therefore, the CPU 11 performs the processing of S120 to S180 while the drive instruction signal from the PWM circuit 15 is low (in other words, every time the heater drive signal is inverted to high).

If the CPU 11 determines in S200 that the heater drive stop condition is satisfied, the CPU 11 ends the heater control process.
Next, the operation of the ECU 1 will be described using the example of FIG.

  In the stage (2) of FIG. 9, the “request cycle” is a standard value of the cycle of the heater drive signal required for controlling the heater 3c, and is the center value of the cycle allowable range (TCmin to TCmax). . In the stage (2) of FIG. 9, the “requested on time” is the requested on time calculated in S140 of FIG. 8 (the on time of the heater driving signal required for controlling the heater 3c). . Further, in the stage (2) of FIG. 9, the “required on-time after correction” is the requested on-time for determining the off timing to which the correction value ΔT is added in S150 of FIG.

  The stage (3) in FIG. 9 represents the on timing and the off timing calculated in steps S120 and S160 in FIG. 8, and the stage (4) in FIG. 9 performs delay correction in step S170 in FIG. The on-timing and off-timing after being performed are shown. In each stage of (3) and (4) in FIG. 9, the rising timing of the rectangular wave is the on timing, and the falling timing of the rectangular wave is the off timing. In the stage (3) of FIG. 9, the “instruction cycle” is the on-timing interval calculated in S120 of FIG. 8, and the “instruction cycle” is the actual cycle of the heater drive signal. Further, in the stage (3) of FIG. 9, the “instruction on time” is the time from the on timing to the off timing instructed to the PWM circuit 15 as described above, and the “instruction on time” is the heater. This is the actual on-time of the drive signal.

  As shown in FIG. 9, it is assumed that the time t11 within the non-precision control period is determined as the on timing by S120 in FIG. Then, it is assumed that the correction value ΔT calculated in S130 of FIG. 8 is 0, and the requested on-time calculated in S140 of FIG. 8 is “Tron1”.

  In this case, in S150 of FIG. 8, “Tron1” is calculated as the requested on-time for determining the off timing (because ΔT = 0). In S160 of FIG. 8, a time t13 that is “Tron1” after the time t11 that is the on timing is substituted into the on period conversion table. In this example, since the time t13 is in the precise control period, the end timing of the non-precise control period (time t12 in this example) existing immediately before the precise control period in which the time t13 is entered is the off timing. Will be determined. Therefore, the time from time t11 to time t12 (= Tson1 <Tron1) is the current instruction on time.

  Then, as shown in the stage (4) of FIG. 9, the timing when the time t11 is shifted by the delay time Td1 and the timing when the time t12 is shifted by the delay time Td2 by S170 and S180 of FIG. Is instructed to the PWM circuit 15 as the on timing and the off timing, respectively.

  Then, as shown in the stage (5) of FIG. 9, the actual heater drive signal becomes high at time t11 and becomes low at time t12. That is, the heater drive signal is inverted between the on timing and the off timing before delay correction.

The operation for determining the next on-timing and off-timing will be described.
In FIG. 9, the time t <b> 14 after the “request period” from the time t <b> 11 should be the next on-timing. However, in this example, time t14 is in the precise control period. Therefore, it is assumed that the time t15 within the non-control period closest to the time t14 is determined as the next on-timing of the time t11 by S120 in FIG. The time from time t11 to time t15 is the above-described “instruction cycle”, which is the actual cycle of the heater drive signal, but at time t15, the actual cycle is determined to be within the cycle allowable range. Is done.

In this case, since the previous instruction on time (= Tson1) is shorter than the previous request on time (= Tron1), the correction value ΔT calculated in S130 of FIG.
Therefore, assuming that the request on-time calculated in S140 of FIG. 8 is “Tron2”, in S150 of FIG. 8, “Tron2 + ΔT” is used as the request on-time for determining the off timing (requested on-time after correction). Calculated.

  Then, in S160 of FIG. 8, a time t16 that is “Tron2 + ΔT” after the time t15, which is the current on-timing, is substituted into the on-period conversion table. In this example, since the time t16 does not enter the precise control period (enters the non-precision control period), the time t16 is determined as the off timing. Therefore, the time from time t15 to time t16 (= Tson2 = Tron2 + ΔT) is the current instruction on time.

  Then, as shown in the stage (4) of FIG. 9, the timing at which the time t15 is shifted forward by the delay time Td1 and the timing at which the time t16 is shifted forward by the delay time Td2 by S170 and S180 in FIG. Is instructed to the PWM circuit 15 as the on timing and the off timing, respectively.

  Then, as shown in the stage (5) of FIG. 9, the actual heater drive signal becomes high at time t15 and becomes low at time t16. The heater drive signal is inverted between the on timing and the off timing before delay correction.

  In the ECU 1 as described above, the microcomputer 8 constituting the heater control unit 7 has a period table 17 indicating what time the precision control period and the non-precision control period in the sensor driving IC 5 are.

  Therefore, before turning off the heater drive signal (reversing to low), the microcomputer 8 (specifically, the CPU 11) sets the off timing to be out of the precise control period, and the actual on time is the required on time. It can be decided not to be longer. Therefore, it is possible to prevent overheating as in the conventional apparatus. Similarly, the microcomputer 8 turns on the heater drive signal before turning it on (reverses to high) so that the on-timing is out of the precision control period, and the cycle of the heater drive signal falls within the allowable range. Can be determined. Therefore, it is possible to prevent the temperature follow-up deterioration as in the conventional apparatus.

According to such an ECU 1, it is possible to achieve both the inversion of the heater drive signal during the precision control period and the control performance of the heater 3c.
Also, as described in “Processing content 4”, the CPU 11 of the microcomputer 8 determines that the timing after the requested on-time from the determined on-timing is not within the precise control period, the timing after the requested on-time. Is determined as an off timing. On the other hand, if the timing after the requested on-time has entered the precise control period from the on-timing, the end timing of the non-precision control period that exists immediately before the precise control period with the timing after the requested on-time Determined as the off timing.

  For this reason, it is possible to make the actual on-time not more than the requested on-time and closest to the requested on-time while removing the off timing from the precise control period. Therefore, in the control of the heater 3c, the temperature tracking performance with respect to the target temperature is good.

  Further, as described in “Processing content 5”, when the CPU 11 determines the end timing of the non-precision control period as the off timing when the previous off timing is determined, the CPU 11 determines the current off timing. The above-described correction value ΔT is added to the required on-time for this. For this reason, the actual on-time can be matched with the requested on-time when viewed in a plurality of cycles. Therefore, in the control of the heater 3c, the temperature followability with respect to the target temperature can be further improved.

  Further, the CPU 11 determines the ON timing so that the conditions <1> and <2> described in “Processing content 3” are satisfied. For this reason, the on-timing can be determined so that the on-timing interval falls within the cycle allowable range of the heater drive signal while the on-timing is excluded from the precise control period. Therefore, the actual cycle of the heater drive signal can be within the cycle allowable range.

  Furthermore, the CPU 11 determines the ON timing so that the condition <3> described in “Processing content 3” is also satisfied. For this reason, the period allowable range of a heater drive signal can be protected more reliably.

  Further, as described in “Processing content 6”, the CPU 11 instructs the PWM circuit 15 as the on-timing at the timing when the determined on-timing is shifted forward by the delay time Td1. Similarly, the CPU 11 instructs the PWM circuit 15 as an off timing at a timing at which the determined off timing is shifted forward by the delay time Td2.

  For this reason, it is possible to prevent the actual inversion timing of the heater drive signal from entering the precise control period after the determined on timing and off timing. That is, the heater drive signal can be reliably inverted at the on timing and the off timing determined while avoiding the precise control period.

As mentioned above, although embodiment of this invention was described, this invention can take a various form, without being limited to the said embodiment. The above-mentioned numerical values are also examples, and other values may be used.
For example, the detection result of the air-fuel ratio may be sent from the microcomputer 8 of the ECU 1 to another ECU, and the ECU may control the fuel injection. That is, the ECU 1 may be a dedicated device for detecting the air-fuel ratio.

  In addition, the functions of one component in the above embodiment may be distributed as a plurality of components, or the functions of a plurality of components may be integrated into one component. Further, at least a part of the configuration of the above embodiment may be replaced with a known configuration having the same function. Moreover, you may abbreviate | omit a part of structure of the said embodiment. In addition, all the aspects included in the technical idea specified by the wording described in the claims are embodiments of the present invention. In addition to the ECU described above, the present invention can be implemented in various forms such as a system including the ECU as a constituent element, a program for causing a computer to function as the ECU, a medium storing the program, and a control method for the air-fuel ratio sensor. It can also be realized.

  DESCRIPTION OF SYMBOLS 3 ... Air-fuel ratio sensor, 3a ... Electromotive force cell, 3b ... Oxygen pump cell, 3c ... Heater, 5 ... Sensor drive IC (sensor drive part), 7 ... Heater control part, 8 ... Microcomputer, 9 ... Output circuit, 11 ... CPU, 13 ROM, 15 PWM circuit, 17 period table (schedule information)

Claims (7)

An air-fuel ratio sensor control device for controlling an air-fuel ratio sensor (3) having an electromotive force cell (3a) and an oxygen pump cell (3b) and a heater (3c) for heating them,
A precise control for detecting an output voltage of the electromotive force cell and determining a pump current to the oxygen pump cell for setting the detected value to a target value is performed, and the pump current determined by the precise control is used as the oxygen pump cell. A sensor driving unit (5) to be passed through,
A heater control unit (7 (8, 9)) that outputs a drive signal in the form of a PWM signal to the heater;
The state of the sensor drive unit is alternately switched between a state in which the precise control is performed and a state in which the precise control is not performed.
The heater control unit
Schedule information (17) indicating respective times of a precise control period in which the sensor drive unit performs the precise control and a non-precise control period in which the sensor drive unit does not perform the precise control Storage means (13) in which is stored,
An on timing for inverting the drive signal from an inactive level that does not energize the heater to an active level that energizes the heater, and an off timing that inverts the drive signal from the active level to the inactive level. Timing determining means (11, S120, S160) for determining so as to be out of the precise control period based on the schedule information;
The on timing and the off timing determined by the timing determining means are instructed, and when the instructed on timing arrives, the output level of the drive signal is inverted to the active level, and the instructed off timing is Signal output means (9, 15) for inverting the output level of the drive signal to the inactive level when it arrives;
An air-fuel ratio sensor control device. In the air-fuel ratio sensor control device according to claim 1,
The heater control unit
An on-time calculating means (11, S140) for calculating an on-time from when the drive signal is set to the active level to when the drive signal is set to the inactive level, based on the control logic of the heater;
The timing determining means includes
First determination means (11, S120) for determining the on-timing of the drive signal so as to be out of the precise control period based on the schedule information;
Based on the on-timing determined by the first determining unit, the on-time calculated by the on-time calculating unit, and the schedule information, the off timing of the drive signal is changed to the precise control period. Second determining means (11, S160) for determining so as to deviate from
The second determining means includes
If the timing after the ON time after the ON timing determined by the first determining means is not within the precise control period, the timing after the ON time is determined as the OFF timing, If the timing after the ON time is in the precise control period, the end timing of the non-precision control period existing immediately before the precise control period after the ON time is set as the OFF timing. To decide as,
An air-fuel ratio sensor control device. The air-fuel ratio sensor control device according to claim 2,
When the second determining means determines the end timing of the non-precision control period as the off timing when the previous off timing is determined, it is used to determine the previous off timing. A difference between the ON time and the time from the previous ON timing to the previous OFF timing is added to the ON time used by the second determining means to determine the current OFF timing. Time correction means (11, S130, S150),
An air-fuel ratio sensor control device. In the air-fuel ratio sensor control device according to claim 2 or 3,
The first determining means determines the on-timing so that the on-timing interval falls within an allowable range of a period of the driving signal;
An air-fuel ratio sensor control device. In the air-fuel ratio sensor control device according to claim 4,
The first determining means sets the ON timing so that the following conditions <1> and <2> are satisfied before the signal output means inverts the output level of the drive signal to the active level. To decide,
An air-fuel ratio sensor control device.
<1> The current on timing, which is the on timing determined this time, deviates from the precise control period.
<2> An interval between the current on-timing and the previously determined on-timing is within the allowable range. In the air-fuel ratio sensor control device according to claim 5,
The first determining means determines the on-timing so that the following condition <3> is satisfied;
An air-fuel ratio sensor control device.
<3> N timings (N is an integer of 1 or more) after the time within the allowable range starting from the current on-timing deviate from the precise control period. The air-fuel ratio sensor control device according to any one of claims 1 to 6,
The signal output means includes
It has a first delay time from when the instructed on-timing arrives until the output level of the drive signal is inverted to the active level, and after the instructed off-timing has arrived, A second delay time until the output level is inverted to the inactive level;
The air-fuel ratio sensor control device
A delay for correcting the shift of the on-timing determined by the timing determination unit by the first delay time and the off-timing determined by the timing determination unit by the second delay time. Correction means (11, S170);
Instructing means (11, S180) for instructing the signal output means of the on timing and the off timing after being corrected by the delay correcting means,
An air-fuel ratio sensor control device.

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