JP3006103B2 - Heater control device for oxygen concentration detection sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heater control device for an oxygen concentration detecting sensor, and more particularly to a heater control device for controlling the heater supply power so that the resistance value of a heater installed in an oxide semiconductor type oxygen concentration detecting sensor becomes a target resistance value. The present invention relates to a heater control device that performs variable control.

[0002]

2. Description of the Related Art In an electronically controlled fuel injection system, intake air
Basic calculated from the amount (or intake pipe negative pressure) and engine speed
The fuel injection time is controlled by the oxygen concentration provided in the exhaust passage of the internal combustion engine.
Degree detection sensor (hereinafter referred to as O_TwoSensor output)
By making corrections based on the signal,
The supplied air-fuel mixture is adjusted to a predetermined target air-fuel ratio (for example,
Air-fuel ratio feedback control
This will improve drivability and improve fuel efficiency.
Above, it is purifying exhaust gas. Perform such control
Oxygen concentration sensor as an oxygen concentration detection sensor
Conductor (eg TiO _Two) Changes depending on the oxygen concentration.
So-called oxide semiconductor type oxygen concentration detection utilizing changing characteristics
Oxygen concentration difference between both surfaces of sensor and zirconia element
And the zirconia element has the property of generating voltage.
A so-called concentration cell type oxygen concentration detection sensor used is known.
You.

Here, as shown in FIG. 13, when the oxygen concentration is low, that is, when the air-fuel ratio is rich, the resistance value R _T of the oxide semiconductor type oxygen concentration detection sensor exhibits a low resistance characteristic like I, In addition, when the air-fuel ratio is lean, a high resistance characteristic such as II is exhibited. And, as an example of a method for detecting changes in the resistance value, as shown in an equivalent circuit diagram of FIG. 4 which will be described later, instead of detecting the change in the R _T resistor of the oxide semiconductor directly the constant resistance R ₀ It is detected as a change in partial pressure. When the air-fuel ratio is rich, the detection voltage V is higher than when the air-fuel ratio is lean.
There is a configuration that takes out _OX .

In this case, the sensor output voltage V _OX is expressed by the following equation. V _OX = V _B · R ₀ / (R ₀ + R _T )
(1) Therefore, when the air-fuel ratio is rich, V _OX = V _B (H level) because R _T ≪R ₀ , and conversely, when the air-fuel ratio is lean, V _OX because R _T ≫R _0. = 0 _(V) (L level).

[0005] Of the above two types of O ₂ sensors, the latter type O ₂ sensor detects the oxygen concentration difference between both surfaces of the zirconia element, and thus fixes the oxygen concentration on one side of the element. For this purpose, an atmosphere introducing section is provided in the O ₂ sensor.

[0006] On the other hand, the former type O ₂ sensor does not require such an air introduction part, and therefore has the advantage of low cost. On the other hand, the resistance value of the oxide semiconductor is not only the oxygen concentration but also the oxygen concentration. As can be seen from FIG. 13 described above, it has a characteristic that it changes depending on its own temperature (sensor temperature), so it is necessary to control the sensor temperature appropriately and accurately. Therefore, a heater for heating the oxide semiconductor is usually provided inside the O ₂ sensor, and the heater resistance value is set to a predetermined target resistance value by utilizing the fact that the resistance value of the heater has a paired relationship with the heater temperature. The sensor temperature is controlled to a desired temperature by controlling the power supplied to the heater such that

However, in such heater control, even if the heater resistance value reaches the target resistance value, the heater temperature at the time when the heater resistance value reaches the target resistance value differs for each heater due to individual differences in heater resistance. There's a problem.

For this reason, the present applicant detects the heater supply power when the heater resistance value matches the target resistance value in the predetermined operation state, and determines the temperature of the heater resistance value based on the difference in the heater supply power. We have proposed a heater control device that learns and controls the target resistance value so as to grasp the variation in the characteristics and eliminate the deviation of the sensor temperature from the target value due to the variation. -88227
issue).

[0009]

However, in the heater control device proposed by the applicant of the present invention, for example, after the target resistance value is learned, if the battery is once removed by battery replacement or the like, the target resistance learning value is stored. Since the stored contents of the memory are destroyed, during the learning period after the battery is installed and until the learning in the predetermined operation state is completed, the target value of the sensor temperature due to the variation in the temperature characteristics of the heater resistance value or the like is not obtained. Extreme deviation occurs, the air-fuel ratio deviates from the target air-fuel ratio, and the emission deteriorates.

[0010] The present invention has been made in view of the above points,
When the contents stored in the memory are destroyed, the control for keeping the heater supply power constant is performed until a predetermined operating condition is satisfied, and the value based on the smoothed processing value of the heater resistance value calculated during the period is set to the target resistance value. It is an object of the present invention to provide a heater control device for an oxygen concentration detection sensor that solves the above-described problem by starting constant resistance control of a heater resistance as an initial value of.

[0011]

In order to achieve the above-mentioned object, the present invention provides an oxygen sensor for detecting an oxygen concentration in exhaust gas, which is installed in an exhaust passage 12 of an internal combustion engine 11 as shown in FIG. An oxygen concentration detection sensor 13 including a detection element 13a and a heater 13b for heating the oxygen detection element 13a.
A heater control means 14 for variably controlling the power supplied to the heater 13b so that the detected resistance value of the heater 13b becomes the target resistance value; a readable / writable memory 15 storing the target resistance value; In the heater control device having learning means 16 for learning and updating the target resistance value in the memory 15 according to the value of the heater supply power by the control means 14, it is detected whether or not the storage contents of the memory 15 are destroyed. This is configured to include a detection unit 17, a power fixing unit 18, a calculation unit 19, and a control unit 20.

When the detection means 17 detects that the contents stored in the memory 15 are destroyed, the power fixing means 18 supplies the power from the heater control means 14 to the heater 13b until a predetermined operation state is reached. Fix the power.
The calculating means 19 calculates a smoothed processing value of the heater resistance value when the heater supply power is fixed. Further, the control means 20 starts the constant resistance control of the heater control means 14 with the value based on the smoothing processing value as the initial value of the target resistance value when the predetermined operation state is detected.

[0013]

When the learning value of the target resistance value stored in the memory 15 has disappeared, the detection means 17 notifies the control means 18 of the destruction of the stored contents of the memory 15 and thereby fixes the power. Until the means 18 enters the predetermined operation state, the operation of the heater control means 14 is stopped to output fixed heater supply power. As described above, when the learning value for compensating for the variation in the heater resistance value has disappeared, the control based on the heater resistance value is stopped until the predetermined operation state is reached. Variations in temperature can be prevented.

Further, in the present invention, when the normal operation of the heater control means 14 is started by entering the predetermined operation state, the value obtained by forming the heater resistance value when the heater supply power is fixed is set to the target resistance value. Since the initial resistance is used as the initial value, it is possible to prevent a large learning value from being suddenly adopted as the initial value of the target resistance when controlling the power so that the heater resistance becomes the target resistance. In addition, the occurrence of overshoot of the heater supply power can be prevented.

[0015]

FIG. 2 is a block diagram showing one embodiment of the present invention. This embodiment is an example in which an internal combustion engine 11 is applied to an automobile engine.
Controls the operation of each unit. Further, the heater control means 14 shown in FIG. 1 is controlled by software operation of the heater control circuit 22 and the electronic control device 21 as described later, and the learning means 16, the detection means 17 and the control means 18 are controlled by software of the electronic control device 21 described later. It is realized by operation.

In FIG. 2, a surge tank 2 is provided downstream of an air flow meter 23 through a throttle valve 24.
5 are provided. Throttle position sensor 39
Is attached to the throttle body and the throttle valve 2
It has a structure to detect the movement of 4 by various contact points,
When the throttle valve 24 is fully closed (idle position), its IDL contact is turned on.

The surge tank 25 is connected to a combustion chamber 27 of the engine via an intake manifold 26.
The combustion chamber 27 is provided with an intake valve 28 and an exhaust valve 29, and the combustion chamber 27 communicates with an exhaust manifold 30 (corresponding to the exhaust passage 12). Reference numeral 31 denotes a fuel injection valve which injects fuel into the air flow passing through the intake manifold 26 for a time specified by the electronic control unit 21. 32 is a spark plug whose plug gap is
It is provided so as to protrude inside. A piston 33 reciprocates vertically in the figure.

The engine having such a schematic configuration is provided with a rotation angle sensor 34, a water temperature sensor 35, an intake air temperature sensor 36, an oxygen concentration detection sensor 37 with a heater, a vehicle speed sensor 38, and various other sensors. Each is supplied to the control device 21.

The rotation angle sensor 34 detects the rotation speed of the distributor shaft to detect the engine rotation speed. Further, the water temperature sensor 35 is provided so as to penetrate the engine block and partially protrude into the water jacket, and detects the temperature of the engine cooling water.

The intake air temperature sensor 36 is connected to the air flow meter 23.
Measure the intake air temperature on the upstream side of. The vehicle speed sensor 38 outputs a pulse signal according to the vehicle speed in conjunction with the axle. Further, an oxygen concentration detection sensor (O ₂ sensor) 37 with a heater, which will be described later, is arranged so that a part thereof protrudes through the exhaust manifold 30, and a three-way catalyst device (not shown)
The oxygen concentration in the exhaust gas before entering is detected.

The hardware configuration of the electronic control unit 21 is the same as the conventional one, and is configured as shown in FIG. 2, the same components as those of FIG. 2 are denoted by the same reference numerals, and the description thereof will be omitted. In FIG. 3, the electronic control unit 21 has a central processing unit (CPU) 40, a read only memory (ROM) 41 storing a processing program, and a random access memory (RAM) used as a work area. 42), a backup RAM 43 for retaining data even after the engine is stopped, and an input / output interface circuit 45
And an A / D converter 46 are connected via a bidirectional bus line 47.

The above backup RAM (B-RAM)
43 constitutes the memory 15 described above. This BR
The AM 43 is a volatile memory, but since the power supply voltage is constantly applied from the battery regardless of whether the ignition switch is on or off, the CPU 40, the ROM 41, and the RAM 42 are turned off by turning off the ignition switch.
For example, the stored data is retained even when the engine is stopped where no power supply voltage is applied. However, due to battery replacement etc.
Once the battery is removed, the power supply voltage to the B-RAM 43 is no longer applied.
The stored contents of the AM 43 are lost.

Each detection signal from the water temperature sensor 35, the intake air temperature sensor 36, the O ₂ sensor 37 with heater, the air flow meter 23 and the throttle position sensor 39 is supplied via an input interface circuit 44 to an A / D with multiplexer.
The data is supplied to a converter 46, where the data is converted into digital data, and is sequentially supplied to a bus line 47.

On the other hand, an engine speed detection signal from the rotation angle sensor 34, a vehicle speed signal from the vehicle speed sensor 38, and a heater resistance detection voltage from an A / D converter 51, which will be described later, are transmitted via a bus via an input / output interface circuit 45. Sent to line 47. Further, the fuel injection valve 31 is transmitted from the CPU 40 via the bus line 47 and the input / output interface circuit 45.
A control signal is sent to each of the switching transistors 52 described later.

Next, the oxygen concentration detection sensor (O ₂ sensor) 37 with heater shown in FIGS. 2 and 3 will be described. The heater-equipped O ₂ sensor 37 includes, for example, an oxide semiconductor (corresponding to the oxygen sensing element 13a in FIG. 1) made of titania (titanium oxide; TiO ₂ ) formed in a film shape on the surface of an insulating substrate made of alumina. , Heater 37 for heating titania
b (corresponding to the heater 13b in FIG. 1). Since the electrical resistance value of titania changes according to the oxygen concentration in the exhaust gas that comes into contact with titania, the oxygen concentration can be detected using the change in the electrical resistance value of titania.

That is, when the oxygen concentration in the exhaust gas is low and the air-fuel ratio is rich, the O ₂ molecules of titania, which is an oxide semiconductor, are released to the outside, and the free electrons inside the titania increase. As shown by I, the resistance value of titania becomes small, and conversely, when the air-fuel ratio is lean, FIG.
As shown by II, the resistance value of titania becomes large.

FIG. 4 is an equivalent circuit diagram of the titania O ₂ sensor 37. _RT is the resistance value of the titania, and the resistance value changes according to the oxygen concentration. The resistance value R of the above titania
_T is configured to supply voltage V _B is applied through a constant resistance R ₀ in series, thereby, oxygen concentration sensing signal represented by the equation (1) from both ends of the constant resistor R ₀ (voltage) V
_OX is taken out.

The power supplied to the heater of the O ₂ sensor 37 with heater is controlled by a pulse signal from the heater control circuit 22.

FIG. 5 is a circuit diagram of one embodiment of the heater control circuit 22. In the figure, 50 is a battery, applies the output voltage V _B is applied with the one end of the heater 37b of the heater with the O ₂ sensor 37, as an operating power supply voltage to the electronic control device 21 via an A / D converter 51 I do.

The resistance value Rh of the heater 37b changes according to the heater temperature. The other end of the heater 37b is connected to one end of a resistor 53 via a collector and an emitter of the switching transistor 52. The other end of the resistor 53 is grounded and has a predetermined resistance R _C.
Is set to 54 is an amplifier, amplifies the voltage V _C generated in the resistor 53, and supplies to the A / D converter 51.

In the heater control circuit 22 having such a configuration, a pulse signal is supplied from the electronic control unit 21 to the base of the switching transistor 52, and the switching of the switching transistor 52 is controlled, whereby the power supplied to the heater 37b is controlled.

Next, O ₂ with a heater is controlled by the electronic control unit 21.
The heater control operation of the sensor 37 will be described. 6 to 8 show a flowchart of one embodiment of the main routine of the heater resistance control. In FIG. 6, first, Step 6
It is determined in step 1 whether the heater 37b is on. If the heater 37b is off, the process proceeds to step 78 described later.
The battery voltage V _B from the A / D converter 51 and the emitter voltage V _C of the switching transistor 52 in FIG.
5 and the known resistance value R _C , as can be seen from FIG. 5, Rh = _RC · {(V _B / V _C ) −1}.
(2) The heater resistance value Rh is calculated according to the following equation.

Next, in step 63, it is determined whether or not a predetermined operating state (for example, an idle operating state) of the internal combustion engine has continued for 2 seconds. If the predetermined operating state has continued for 2 seconds, step 64 is performed. To heater supply power Ph
Is calculated according to the following equation. Ph = ｛V _C · (V _B −V
_C ) / R _C ｝ · {a / (a + b)} (3) In the above equation, the battery voltage V _B and the resistance value R _C are respectively constant, but the duty ratio of the pulse signal shown in FIG. a
/ (A + b) changes. Here, (a +
b) is a fixed period of 512 ms, and a is a time from when a value C of a flow counter described below reaches 0 to a value D of a duty counter, which varies according to the correction amount. This heater supply power Ph is added to the previous value Phn to update the heater supply power integrated value Phn. Note that Phn has been reset to zero before starting the control routine.

Subsequently, this heater resistance control routine is performed in two steps.
It is determined whether it has been started 56 times (step 65), 256
When the heater has been activated twice, the heater supply power integrated value P at that time
hn by "256" to obtain the average value P of the heater supply power.
hm is calculated (step 66), and ΔRt is calculated from the average value Phm with reference to the map indicated by the solid line in FIG. 11 and stored in the ROM 41 (step 67). This △
Rt is a correction value of the heater resistance value to the target resistance value Rt, which is obtained from the deviation of the heater supply power average value Phm corresponding to a predetermined internal combustion engine operating state.

As described above, as Phm becomes larger than Pho, ΔRt becomes a larger negative value. This is heater 3
The target value Rt of the heater resistance is decreased as the power supplied to the heater 7b becomes larger than the standard value, thereby canceling the excessive power supply to the heater.

The rate of change of ΔRt with respect to Phm is
As shown in FIG. 11, the rate may be relatively low only in the vicinity of Pho as indicated by the solid line, and may be modified so as to increase as shown by the broken line in the figure when Phm is farther than Pho. In this case, in particular, it is preferable that the rate of change in a region where Phm is smaller than Pho is even greater than that in a region where Phm is larger than Pho so that insufficient heating of the heater does not occur.

Next, at step 68 in FIG. 6, the correction value ΔRt is added to the previous heater target resistance value Rt _n−1 to update the current heater target resistance value Rt _n . The heater target resistance Rt _n is stored in the B-RAM 43. The above steps 66 to 68 correspond to the learning means 16.

Subsequently, the CPU 40 determines whether or not the contents stored in the B-RAM 43 have been destroyed (step 69). Here, in the B-RAM 43, data of the upper byte or lower byte of the output data of 2 bytes is used as, for example, data indicating a target resistance value, and the remaining 1 byte of data that is not used as data is used as data. 1-byte data and a value obtained by inverting each bit at all times. Therefore, when the B-RAM 43 is outputting normal data, the 1-byte data used as the above data and the remaining 1-byte data not used as the data are added to be "FF" in hexadecimal. Is obtained. Then, in the above step 69, when the addition of the upper byte and the lower byte is performed and the addition result of "FF" is not obtained, it is determined that the storage content of the B-RAM 43 is destroyed. Judge that it is not destroyed.

When it is determined that the stored content of the B-RAM 43 has not been destroyed, the constant resistance control routine from step 70 in FIG. 7 is executed. On the other hand, when it is determined that the stored content has been destroyed. The fixed duty ratio control routine after step 84 in FIG. 8 is executed. This step 69 corresponds to the detection means 17. When it is determined in step 63 that the predetermined operating state does not continue for 2 seconds, and when it is determined in step 65 that the predetermined operation state is less than 256 times, the process jumps to step 69. Constant resistance control routine of FIG. 7, to realize the heater control unit 14 with steps 61 through 65 in FIG. 6, as the heater resistance value Rh is equal to the target resistance value Rt _n, varies the electric power supplied to the heater 37b Variable control is performed based on the duty ratio pulse.

That is, assuming that the storage contents of the B-RAM 43 have not been destroyed, step 7 in FIG.
Comparison between the heater target resistance Rt _n and the current heater resistance Rh after the update is performed by 0,71. R
When h> Rt, the duty counter value D is subtracted by "1" (step 72), and when Rh <Rt, the duty counter value D is added by "1" (step 73), and Rh = R
In the case of t, the process proceeds to step 78 described later.

After the duty counter value D is added or subtracted in steps 72 and 73, the upper limit value is set to "256" if the duty counter value D is larger than "256" (steps 74 and 75), and the lower limit value is set if it is smaller than "8". “8”
(Steps 76 and 77).

As indicated by the dashed line in FIG. 10A, the duty counter value D is compared with the flow counter value C in step 79, which will be described later, to determine the magnitude of the duty counter value D.
Is a value that determines the duty ratio of the pulse signal (shown in FIG. 10 (B)) supplied thereto, and since the maximum value of the flow counter value C is “256”, the upper limit value is limited to “256”. The lower limit is limited to "8" for the purpose of practical heater control.

Next, the process proceeds to step 78, where the value of the flow counter value C is increased by "8", and is compared with the duty counter value D in step 79. If C <D, the heater 37b is turned on. A level signal is transmitted (step 80). When C ≧ D, a low level signal for turning off the heater 37b is transmitted (step 81).

Thereafter, it is determined whether or not the flow counter value C has reached the maximum value "256" (step 82). When the value has reached "256", the flow counter value C is returned to zero (step 83). If it is less than 256 ", the heater resistance control routine ends (step 90). In this way, the flow counter value C is incremented by "8" every time the control routine is started every 16 ms, and the value is increased by "25".
It changes periodically (every 512 ms) as shown by the solid line in FIG. 10A so that it returns to zero when it reaches 6 ".
A pulse signal shown in FIG. 10B is taken out according to the magnitude comparison between the duty counter value D and the flow counter value C, and applied to the base of the switching transistor 52 in FIG.

[0045] As duty counter value D above as described in Step 70 to 73, as measured heater resistance Rh approaches the heater target resistance Rt _n, increase or decrease being controlled result according to their difference, FIG. As can be seen from FIGS. 10 (A) and (B), the duty ratio a / (a + b) of the pulse signal
Is small when Rh> Rt, large when Rh <Rt,
When Rh = Rt, the heater supply power is controlled to the same value as the previous time, and the heater supply power is controlled based on the above equation (3) (the element temperature of the O ₂ sensor 37 during the normal heater constant resistance control is, for example, About 700 ° C.).

In the heater control in this embodiment, since the electric resistance of a metal generally changes depending on the temperature of the metal, controlling the electric resistance to be constant is equivalent to controlling the temperature of the metal to be constant. In view of this, the control is performed by controlling the heater supply power so that the heater resistance value becomes the target resistance value.

In this embodiment, the B-RAM
When it is determined in step 69 that the storage contents of 43 have been destroyed, the heater supply power is fixedly controlled by the processing of steps 84 to 89 in FIG. The above means 18 to 20 can be realized by the routine of FIG.

In step 84, the CPU 40 determines whether or not the engine cooling water temperature THW is 70 ° C. or higher based on the engine cooling water temperature detection signal from the water temperature sensor 35. When the engine cooling water temperature THW is warmed up at 70 ° C. or higher, the routine proceeds to step 85, where it is determined whether the value of the learning permission counter value CIDLTMP is equal to or higher than a predetermined value K. This learning permission counter value CIDL
TMP is calculated by the interrupt routine shown in FIG.

The interrupt routine will be described. When the interrupt routine is started, for example, every 2.62 seconds, first, according to the value QC based on the intake air amount detected by the air flow meter 23, FIG. 2 shown in
A correction value △ CIDLTMP is calculated from the dimensional map (step 91). This correction value △ CIDLTMP is shown in FIG.
As can be seen from FIG. 2, the value of QC is negative or zero at the time of a small light load operation where QC is less than 4.76 l / sec or at the time of a large high load operation where QC is 14.00 l / sec or more. During intermediate load operation between them, the value is set to a relatively large positive value.

Then, the process proceeds to a step 92, wherein the calculated correction value △ CIDLTMP is replaced by the previous learning permission counter value C.
IDLTMP is added to the learning permission counter value CIDL
The TMP is updated, and the process ends. Therefore, in the magnitude comparison at step 85 in FIG. 8, when the high-load operation continues and the exhaust temperature is high, or when the low-load operation continues and the exhaust temperature is low, the learning permission counter value CIDLTMP is equal to or more than the predetermined value K. However, only when the middle load operation has continued to some extent and the exhaust gas temperature has reached an appropriate temperature, CIDLTMP becomes equal to or higher than the predetermined value K. This is because the sensor temperature of the O ₂ sensor 37 is affected by the exhaust gas temperature, and therefore, the smoothed value of the heater resistance value Rt _n is calculated only during the medium load operation in which the exhaust gas temperature is appropriate and stable.

When either one of the operation conditions in steps 84 and 85 in FIG. 8 is not satisfied, the routine proceeds to step 86, where the duty ratio of the pulse signal shown in FIG. 10B is mapped by the power supply voltage at that time. And fixed at the duty ratio. The fixed duty ratio is set so that the sensor temperature of the O ₂ sensor 37 becomes close to a predetermined value (for example, 700 ° C.). For example, when the power supply voltage is about 14 to 15 V, the duty ratio is set to 60%. You. At this time, the resistance value of the heater currently used is considered to be the center value of the manufacturing tolerance, and the heater central to such manufacturing tolerance is set to a predetermined temperature (for example, 700 ° C.).
C.) is set in the B-RAM 43 as the target resistance value Rt.

By fixing the duty ratio, the power supplied to the heater 37b becomes constant. Smoothing process value of the heater resistance (average value) RhAV _n is calculated using the following equation Subsequently (step 87).

[0053]

(Equation 1) Here, RhAV _n-1 in the above equation is the previously calculated annealing value, and the initial value is the heater resistance value Rh calculated in step 62. The above smoothing process value RhAV _n After calculating,
This routine ends (step 90).

Thus, after the stored contents of the B-RAM 43 are destroyed, the fixed duty ratio control for supplying a constant power to the heater 37b continues to be performed, and during that period, the smoothing processing value RhAV _{n is} obtained in step 87. Is continuously calculated.

Here, the vehicle continues to run under the fixed duty ratio control.
When driving, O for some reason while driving _TwoSensor 37
If the air temperature changes, the air-fuel ratio is adjusted to the optimal value
Exhaust emissions and catalyst emissions
Bad odor may occur. The sensor temperature is
It is easily affected by exhaust gas temperature. Therefore, the exhaust temperature is stable.
After changing to the fixed duty ratio control,
Switch to control to eliminate deviation of sensor temperature from target value
It is desirable.

[0056] Therefore, if in this example the operating condition of step 84 and 85 are satisfied both the target resistance moderation process value RhAV _n calculated in step 87 just before the routine proceeds to step 88 in FIG. 8 B-RA as the value Rt _n
M43, and then step 8 for control stability.
After a delay time of 2 seconds is obtained in step 9, step 70 in FIG.
Then, the process proceeds to the constant resistance control of the heater resistance.

As described above, according to the present embodiment, the B-RA
When the stored content of M43 is destroyed, the heater control is performed by the so-called fixed duty ratio control in step 86. Therefore, a large fluctuation of the heater supply power due to the fact that the learned target resistance value is not stored in the B-RAM 43 is detected. Can be suppressed.

When switching from the fixed duty ratio control to the constant resistance control of the heater resistance, if the heater resistance is at the tolerance limit (upper limit or lower limit), the learning value of the target resistance value greatly changes, and the pulse value becomes higher. The duty ratio of the signal changes abruptly, whereby the heater supply power changes abruptly, causing an overshoot or undershoot of the sensor temperature,
The air-fuel ratio may also be affected.

[0059] However, the initial value of the target resistance Rt _n at the time of transition from the fixed duty ratio control in the constant resistance control of the heater resistor in the present embodiment, is said smoothing processing value RhAV _n, the heater resistance value Rh Since the value is set in consideration of the variation, it is possible to prevent the target resistance value from abruptly changing. As a result, even if the heater supply power is controlled so that the heater resistance value becomes the target resistance value, the heater supply power is reduced. Will not overshoot.

Here, the averaging processing value generally indicates a value calculated by the following equation. RhAV _n ←
((M−a) × RhAV _n−1 + a × Rh) / m (5)
Such processing is called a / m smoothing (where m>
a) Therefore, regarding the values of m and a, m = 4 in the equation (4),
The value is not limited to a = 1 and can be set to various values.

The present invention is not limited to the above-described embodiment. For example, the load state may be obtained from the intake pipe pressure instead of the intake air amount.

[0062]

As described above, according to the present invention, when it is detected that the storage content of the memory storing the target resistance value is destroyed, the constant resistance control of the heater resistance is stopped. Perform heater control with fixed heater supply power,
By suppressing large fluctuations in the target resistance value, it is possible to eliminate extreme variations in the temperature of the O ₂ sensor even when the memory contents are destroyed. Since the initial value of the target resistance value when shifting to control can be set to a value that takes into account the variation in the heater resistance, it is possible to suppress a rapid change in the heater supply power, thereby preventing the sensor temperature from overshooting or undershooting. It has features such as prevention.

[Brief description of the drawings]

FIG. 1 is a principle configuration diagram of the present invention.

FIG. 2 is a configuration diagram of one embodiment of the present invention.

FIG. 3 is a diagram illustrating a hardware configuration of an electronic control device in FIG. 2;

FIG. 4 is an equivalent circuit diagram of the oxide semiconductor type oxygen concentration detection sensor.

FIG. 5 is a circuit diagram of an example of a heater control circuit in FIG. 2;

FIG. 6 is a flowchart (part 1) illustrating an embodiment of a heater resistance control routine that is a main part of the present invention.

FIG. 7 is a flowchart (part 2) showing one embodiment of a heater resistance control routine which is a main part of the present invention.

FIG. 8 is a flowchart (part 3) illustrating an embodiment of a heater resistance control routine that is a main part of the present invention.

FIG. 9 is a flowchart showing an interrupt routine for calculating a counter value in the flowchart of FIG. 8;

FIG. 10 is a time chart for explaining the operation of the flowchart in FIG. 7;

FIG. 11 is an explanatory diagram of a map used in the flowchart of FIG. 6;

FIG. 12 is an explanatory diagram of a map used in the flowchart of FIG. 9;

FIG. 13 is a characteristic diagram showing a relationship between a sensor temperature and a sensor resistance of the oxide semiconductor type oxygen concentration detection sensor.

[Explanation of symbols]

Reference Signs List 11 internal combustion engine 12 exhaust passage 13 oxygen concentration detection sensor 13a oxygen detection element 13b heater 14 heater control means 15 memory 16 learning means 17 detection means 18
Power fixing means 19 Calculation means 20 Control means 21 Electronic control unit 22 Heater control circuit 37 Titania O ₂ sensor 40 Central processing unit (CPU) 43 Backup random access memory (B-RAM)

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshio Suematsu 1 Toyota Town, Toyota City, Aichi Prefecture Within Toyota Motor Corporation (72) Inventor Noriaki Kurita 1-1-1 Showacho, Kariya City, Aichi Prefecture Japan Denso Co., Ltd. (56) reference Patent flat 2-285245 (JP, a) JP flat 4-242161 (JP, a) JP flat 3-185350 (JP, a) (58 ) investigated the field (Int.Cl. ⁷ G01N 27/12 G01N 27/409 G01N 27/419

Claims (1)

(57) [Claims] 1. An oxygen concentration detection sensor provided in an exhaust passage of an internal combustion engine and configured to detect an oxygen concentration in exhaust gas, a heater for heating the detection element, and a target resistance value are stored. A readable and writable memory, and heater control means for detecting the resistance value of the heater and variably controlling the power supplied to the heater so that the detected heater resistance value becomes the target resistance value read from the memory. Learning means for learning and updating a target resistance value in the memory in accordance with a value of heater supply power by the heater control means, wherein whether the storage content of the memory is destroyed or not is determined. Detecting means for detecting, and when the destruction is detected by the detecting means, an electric power for fixing power supplied to the heater taken out from the heater control means until a predetermined operating state is attained. Force fixing means, and calculating means for calculating a smoothing value of a heater resistance value detected by the heater control means when the supply power to the heater is fixed,
Control means for starting constant resistance control of the heater control means with an initial value of the target resistance value as the smoothing processing value when the predetermined operation state is detected. apparatus.