JP2001074693A - Heater control device for gas concentration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a heater control device, for a gas concentration sensor, which saves electric power when a heater is used and which ensures a proper sensor output. SOLUTION: A cup-shaped A/F sensor 30 which is composed of a limiting current-type air-fuel ratio sensor is arranged and installed at an engine exhaust pipe 13. A microcomputer 20, for air-fuel ratio detection, inside and ECU 15 controls a heater control circuit 25 and a bus control circuit 40 according to a prescribed control program. For example, when a voltage is applied, a current value flowing in the A/F sensor 30 is measured, the measured current value is converted into an air-fuel ratio (A/F), and its A/F value is output to a microcomputer 16 for engine control. In addition, the microcomputer 20 for air-fuel ratio detection judges whether the execution condition of an air-fuel ratio F/B control operation is established or not, and it changes the target temperature of a sensor element so as to be set according to whether the execution condition is established or not. In addition, the target temperature is changed so as to be set according to whether a sensor output is used or not.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a heater control device for a gas concentration sensor.

[0002]

2. Description of the Related Art As a conventional technique of this kind, for example, as disclosed in Japanese Patent Application Laid-Open No. 61-132851, the internal resistance of a limiting current type oxygen sensor and the resistance value of a heater vary according to temperature. The power required to activate the oxygen sensor is determined by the operating conditions of the internal combustion engine and supplied to the heater, and the power supplied to the heater is corrected according to the internal resistance of the oxygen sensor and the resistance value of the heater. There is something to do.

Further, as disclosed in Japanese Patent Application Laid-Open No. 63-249046, the internal resistance of the oxygen sensor and the resistance value of the heater become a predetermined value corresponding to a predetermined temperature after the energization of the heater is started. Until then, the entire power is supplied from the power supply to the heater, and thereafter, the power supplied to the heater is controlled so that the internal resistance value of the sensor becomes a predetermined value corresponding to a predetermined temperature.

Further, as disclosed in Japanese Patent Application Laid-Open No. 8-278279, full power is supplied to the heater from a power source until the heater temperature reaches a predetermined initial heating temperature. There is an apparatus that controls the energization of the heater in accordance with the detected element temperature when the element temperature reaches a predetermined value.

[0005]

However, in each of the above-mentioned prior arts, electric power is supplied to the heater so that the sensor element can be maintained at a predetermined activation temperature (about 700 ° C.) irrespective of various conditions such as the operating state of the internal combustion engine. Has been supplied. for that reason,
In recent automobile technology, power saving of various electric devices has been demanded, and supplying large power to the heater cannot meet this demand.

For example, since the electric power used in an automobile also affects the fuel efficiency, it is considered necessary to reduce the power consumption of various electric systems in order to improve the fuel economy of the automobile. In particular, in a vehicle using an electric motor such as a hybrid vehicle, the effect of the power consumption on fuel efficiency is further increased as compared to a gasoline-powered vehicle.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to reduce the power consumption when using a heater while ensuring a gas concentration capable of ensuring an appropriate sensor output. The object is to provide a heater control device for the sensor.

[0008]

For example, in an apparatus for detecting the concentration of oxygen in exhaust gas discharged from an internal combustion engine, there are cases where an accurate sensor output is required according to the engine operating state and an accurate sensor output. Sometimes it is not always required. Actually, accuracy requirements for the sensor output differ depending on conditions such as whether the sensor output is used for controlling the internal combustion engine and whether the air-fuel ratio feedback control is performed. Further, the temperature condition for ensuring the accuracy of the gas concentration sensor differs according to the sensor output value. Therefore, the temperature range in which the sensor temperature should be maintained differs depending on the condition such as the range in which the sensor output value is located.

According to the first aspect of the present invention, a setting means for variably setting a target temperature of a sensor element or a heater in accordance with a use environment and an application of a gas concentration sensor, and a heater in accordance with the set target temperature are provided. Heater control means for supplying current.

According to the above configuration, when the sensor output is not used, when the air-fuel ratio feedback control is not performed, or when the desired output accuracy can be ensured under relatively low temperature conditions, the target temperature of the sensor element or the heater is set. By setting the temperature downward, power saving can be achieved when using the heater. In addition, by setting the target temperature of the sensor element or the heater in accordance with the use environment or use, the gas concentration sensor can be maintained in a desired active state, and an appropriate sensor output can be secured. Further, since power saving can be realized, improvement in fuel efficiency of the internal combustion engine can be realized at the same time.

In this specification, "the heater is energized by variably setting the target temperature of the sensor element or the heater".
The term “directly” includes not only controlling the temperature of the sensor element or the heater directly but also controlling the temperature indirectly by a factor such as a resistance related to the temperature.

According to the invention described in claim 2, the setting means changes the target temperature of the sensor element or the heater depending on whether the signal output of the gas concentration sensor is used or not. In this case, particularly when the signal output of the gas concentration sensor is not used, the target temperature of the sensor element or the heater may be set lower than when it is used.

According to a fourth aspect of the present invention, there is provided a condition judging means for judging an execution condition such as whether or not the air-fuel ratio feedback control is executed, and the setting means is provided when the execution condition of the air-fuel ratio feedback control is satisfied. The target temperature of the sensor element or the heater is changed and set depending on whether or not the condition is satisfied. The gas concentration sensor described in claim 4 includes an oxygen sensor (air-fuel ratio sensor) for detecting oxygen concentration, a NOx sensor for detecting NOx concentration, and the like.

That is, in the air-fuel ratio feedback control, when the sensor output signal is used for the feedback control, it is necessary to maintain the gas concentration sensor at the activation temperature, and the sensor element needs to correspond to the sensor activation temperature. Alternatively, a target temperature of the heater is set. On the other hand, when the sensor output signal is not used for the air-fuel ratio feedback control, there is no problem even if the sensor becomes lower than the activation temperature. Therefore, in order to save power, the target temperature of the sensor element or the heater is set to a relatively low temperature, and the power consumption of the heater is reduced. Actually, it may be set to about −100 ° C. with respect to the target temperature during the feedback control.

As shown in FIGS. 13 and 17, even when the air-fuel ratio (oxygen concentration) of the exhaust gas is the same, the sensor output differs according to the temperature of the sensor element. in this case,
The temperature gradient of the sensor output differs depending on the air-fuel ratio to be detected, and the sensor output does not become an appropriate value unless the element temperature exceeds a predetermined temperature for each air-fuel ratio. Therefore, in order to ensure an appropriate sensor output, it is desirable to set the target temperature of the sensor element or the heater according to the air-fuel ratio level at each time. Also, at this time, if the required minimum target temperature is set within the temperature range for obtaining an appropriate sensor output,
Power saving can also be realized.

Therefore, in the invention according to claim 5, the setting means changes and sets the target temperature of the sensor element or the heater in accordance with the air-fuel ratio detected by the gas concentration sensor. Actually, it is preferable that the setting unit is configured as in claims 6 and 7. That is, in the invention according to claim 6, if the air-fuel ratio detected by the gas concentration sensor is leaner than the stoichiometric air-fuel ratio, the target temperature of the sensor element or the heater is set higher than when the stoichiometric air-fuel ratio is detected. . In the invention described in claim 7, if the air-fuel ratio detected by the gas concentration sensor is richer than the stoichiometric air-fuel ratio, the target temperature of the sensor element or the heater is set higher than when the stoichiometric air-fuel ratio is detected.

According to the sixth and seventh aspects, the target temperature of the sensor element or the heater is increased during the lean control or the rich control so that the air-fuel ratio can be detected within a wide range based on the stoichiometric air-fuel ratio. And a highly accurate sensor output can be obtained. As a result, the air-fuel ratio detection range can be extended. In addition, when the stoichiometric air-fuel ratio is detected, the target temperature is set lower than the others, so that the heater power is reduced and power saving can be realized.

Further, as set forth in claim 8, the target temperature of the sensor element or the heater may be changed and set according to the control range of the air-fuel ratio. Also in such a case, excellent effects such as obtaining a highly accurate sensor output within a wide range of the air-fuel ratio can be obtained. In this case, if the air-fuel ratio control region is lean, or if the air-fuel ratio control region is rich,
It is preferable that the target temperature of the sensor element or the heater is higher than that at the time of detecting the stoichiometric air-fuel ratio.

On the other hand, as an output signal of the gas concentration sensor,
In a gas concentration detection device for selectively outputting an electromotive force signal corresponding to an oxygen concentration in a detected gas based on a stoichiometric air-fuel ratio and a limit current signal for linearly detecting an air-fuel ratio of the detected gas, In the invention described in Item 9, the target temperature of the sensor element or the heater is set differently when the sensor output is an electromotive force signal and when the sensor output is a limit current signal. According to the tenth aspect, when the air-fuel ratio control is performed using the electromotive force signal in a relatively narrow air-fuel ratio range, and when the air-fuel ratio range using the electromotive force signal is wider than the relatively narrow air-fuel ratio range. The target temperature of the sensor element or the heater is changed and set when the air-fuel ratio control is performed using the limit current signal in the air-fuel ratio range.

In short, when the electromotive force signal is output,
Compared with the case where the limiting current signal is output, the former has a lower activation temperature of the gas concentration sensor for obtaining an appropriate sensor output. Therefore, according to the ninth or tenth aspect of the present invention, by setting the target temperature of the sensor element or the heater by changing the target temperature as described above, it is possible to secure an appropriate sensor output while saving power when the heater is used. Can be. Further, the air-fuel ratio control can be optimized.

According to the eleventh aspect of the present invention, the gas concentration sensor is constituted by a compound gas sensor capable of outputting a signal corresponding to each gas concentration from a plurality of types of gas components in the detected gas. Includes output determination means for determining what kind of signal output is to be performed, and the setting means variably sets a target temperature of the sensor element or the heater according to the determination result.

In this case, even if the activation temperature for obtaining an appropriate sensor output differs depending on the type of signal output from the gas concentration sensor (composite gas sensor), the sensor element does not change depending on the sensor output. Alternatively, by changing and setting the target temperature of the heater, it is possible to secure an appropriate sensor output while saving power when the heater is used.

According to a twelfth aspect of the present invention, the present invention is applied to a hybrid vehicle that travels using both the output of an internal combustion engine and the output of a motor. The setting means stops the operation of the internal combustion engine and drives only the motor. The target temperature of the sensor element or the heater is lowered. As described above, an appropriate sensor output can be secured while saving power when using the heater. In particular, in the case of a hybrid vehicle, the effect of power consumption on fuel efficiency is further increased, but fuel efficiency can be improved with power saving.

According to a thirteenth aspect of the present invention, there is provided a deterioration detecting means for detecting the degree of deterioration of the gas concentration sensor, and the sensor element set by the setting means according to the detected degree of deterioration of the gas concentration sensor. Alternatively, the target temperature of the heater is corrected.

That is, when the solid electrolyte, the electrode, and the heater are deteriorated, or the porous diffusion layer constituting the sensor element is clogged and the gas concentration sensor is deteriorated, for example, the internal resistance of the sensor element increases. It is conceivable that the sensor output decreases due to this, but by correcting the target temperature of the sensor element or the heater to the rising side, an appropriate sensor output can be secured. Conversely, it is conceivable that the gas concentration sensor deteriorates in the direction in which the sensor output increases.However, by correcting the target temperature of the sensor element or the heater to the descending side, the electric power supplied to the heater is minimized. Power can be saved.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment of the present invention embodied in a vehicle air-fuel ratio control system will be described below with reference to the drawings. In the air-fuel ratio control system according to the present embodiment, a fuel injection amount to the engine is feedback-controlled (F / B) to a desired air-fuel ratio based on a detection result of an air-fuel ratio sensor provided in an exhaust pipe of the engine. In the following description, the air-fuel ratio (A
/ F), the procedure for detecting the internal resistance of the sensor element, and the procedure for controlling the energization of the heater provided in the sensor will be described in detail.

FIG. 1 is a configuration diagram showing an outline of an air-fuel ratio control system according to the present embodiment. In FIG. 1, an engine 10 is configured as a multi-cylinder four-cycle internal combustion engine. An intake pipe 11 is provided with an injector 12 for injecting and supplying fuel to each cylinder of the engine 10. The exhaust pipe 13 is provided with a cup-type A / F sensor 30 composed of a limiting current type air-fuel ratio sensor. The sensor 30 is provided with an oxygen concentration in exhaust gas (or carbon monoxide in unburned gas). And outputs a linear and wide air-fuel ratio signal in proportion to the air-fuel ratio.

The A / F sensor 30 includes a solid electrolyte 31 and a diffusion resistance layer 32 constituting a sensor element, and a solid electrolyte 3
Electrodes 33 provided inside and outside (atmosphere side and exhaust side)
34, and a heater 35 for heating the sensor element. Here, the solid electrolyte 31 is made of an oxygen ion conductive oxide sintered body, and the diffusion resistance layer 32 is made of a heat-resistant inorganic substance. The electrodes 33 and 34 are both made of a noble metal having a high catalytic activity such as platinum, and the surfaces thereof are subjected to porous chemical plating or the like.

On the other hand, an electronic control unit (hereinafter referred to as an ECU) 15 includes an engine control microcomputer 16 for optimally controlling the fuel injection amount of the injector 12. The engine control microcomputer 16 fetches various types of engine operation information from a sensor group (not shown), and detects an engine operation state such as an engine speed, an intake pressure, a water temperature, and a throttle opening from the sensor detection results.

An air-fuel ratio detecting microcomputer 20 is connected to the engine controlling microcomputer 16 so that they can communicate with each other.
The air-fuel ratio detecting microcomputer 20 operates the heater control circuit 25 and the bias control circuit 40 according to a predetermined control program. For example, a current value flowing through the A / F sensor 30 with the application of a voltage is measured, and the measured current value is converted into an air-fuel ratio (A / F) using the relationship shown in FIG. Output to the microcomputer 16. Further, the air-fuel ratio detecting microcomputer 20 operates the heater control circuit 25 so that the A / F sensor 30 is maintained in the active state, and energizes the heater 35 as necessary.

Here, the bias command signal Vr for applying a voltage to the A / F sensor 30 is input from the air-fuel ratio detecting microcomputer 20 to the D / A converter 21, and the D / A converter 21 converts the signal into an analog signal. After being converted into a signal Vb, the signal is input to an LPF (low-pass filter) 22. In addition, LPF22
The output voltage Vc from which the high-frequency component of the analog signal Vb has been removed is input to the bias control circuit 40. The bias control circuit 40 applies a voltage for detecting the air-fuel ratio or for detecting the element resistance to the A / F sensor 30. In this case, when the air-fuel ratio is detected, a predetermined applied voltage corresponding to the air-fuel ratio at each time is set. On the other hand, when the element resistance is detected, a single-shot voltage consisting of a predetermined frequency signal and having a predetermined time constant is used. Is applied.

The limit current output of the A / F sensor 30 corresponding to the air-fuel ratio (oxygen concentration) at that time is detected by a current detection circuit 50 in the bias control circuit 40. A /
When the F sensor 30 outputs a different electromotive force depending on whether it is rich or lean at the stoichiometric air-fuel ratio, the electromotive force is detected by the electromotive force detection circuit 55. The detection values of the current detection circuit 50 and the electromotive force detection circuit 55 are input to the air-fuel ratio detection microcomputer 20 via the A / D converter 23. Heater control circuit 2
Reference numeral 5 denotes duty control of the amount of power to the heater 35 in accordance with the element temperature of the A / F sensor 30, the heater temperature, and the like.
The heating control of No. 5 is performed.

Since the air-fuel ratio F / B control by the engine control microcomputer 16 is not the gist of the present invention and the details of the control are well-known, the detailed description thereof will be omitted here. The engine control microcomputer 16 takes in the detection result of the air-fuel ratio by the A / F sensor 30 and the detection results of various other sensors, and based on the detection results, according to a control algorithm such as modern control or PI control. The air-fuel ratio F / B control is performed in a wide air-fuel ratio detection range including the region. Alternatively, F / B control is performed on the actual air-fuel ratio with respect to the target value using stoichiometric (theoretical air-fuel ratio) as the target value. In short, the amount of fuel injected and supplied from the injector 12 to each cylinder of the engine 10 is controlled so that the air-fuel ratio at that time matches the target air-fuel ratio.

The A / F sensor 30 having the above-described structure is similar to that shown in FIG.
When the air-fuel ratio F / B control is performed over a wide range including the air-fuel ratio lean region having the output characteristics of (a) and (b), FIG.
A limit current signal Ip corresponding to the characteristic (a) is output. Further, when the air-fuel ratio F / B control near the stoichiometric (λ = 1) is performed, an electromotive force voltage signal VOX2 corresponding to the characteristic of FIG. 2B is output.

That is, when a predetermined voltage is applied to the A / F sensor 30, as shown in FIG.
Is a limiting current signal I that linearly changes in accordance with the air-fuel ratio λ.
p [mA] is output. The increase / decrease of the limit current signal Ip corresponds to the increase / decrease of the air-fuel ratio (that is, the degree of lean / rich). The limit current increases as the air-fuel ratio becomes leaner, and the limit current decreases as the air-fuel ratio becomes richer. I do.
Also, as shown in FIG. 2B, the A / F sensor 30
Outputs a voltage signal VOX2 [V] that greatly changes at the stoichiometric air-fuel ratio λ = 1. At this time, the voltage signal VOX
Numeral 2 corresponds to an electromotive force corresponding to the difference between the oxygen concentration in the atmosphere and the oxygen concentration in the exhaust gas, and the value is about 1 V on the rich side and about 0 V on the lean side.

Next, the operation of the air-fuel ratio control system configured as described above will be described. First, a main routine executed by the air-fuel ratio detecting microcomputer 20 will be described with reference to the flowchart of FIG. In this embodiment, when detecting the element resistance value, the “AC element impedance Zac” is obtained by using the sweep method.

In FIG. 4, first, in step 100,
It is determined whether or not a predetermined time Ta has elapsed since the previous detection of the air-fuel ratio. The predetermined time Ta is a time corresponding to an air-fuel ratio detection cycle, and is set to, for example, about Ta = 4 ms. If the predetermined time Ta has elapsed since the previous detection of the air-fuel ratio (YES in step 100), the process proceeds to step 110 to execute the air-fuel ratio detection process. Step 100 is NO
If so, this routine is once ended as it is.

At the time of detecting the air-fuel ratio in step 110, the air-fuel ratio detecting microcomputer 20 outputs the current value flowing through the solid electrolyte 31 due to the application of the voltage, that is, the sensor output (limit current signal Ip) detected by the current detecting circuit 50. After the reading, the voltage corresponding to the sensor output at that time is applied to both electrodes 33 and 34 of the A / F sensor 30 in order to detect the next air-fuel ratio. Further, using the current-A / F conversion map shown in FIG. 3, the sensor output at each time (limit current signal Ip)
Is converted to an A / F value, and the A / F value is output to the engine control microcomputer 16.

Thereafter, in step 120, it is determined whether or not a predetermined time Tb has elapsed since the previous detection of the element impedance. The predetermined time Tb is equal to the element impedance Z.
This is a time corresponding to the detection cycle of ac, and is selectively set according to, for example, an engine operating state. In this embodiment, in the normal state (the engine 1
0 at the time of steady operation), and Tb = 2s (second) at the time of a rapid change of the air-fuel ratio (at the time of starting the engine 10 or at the time of transient operation).
The predetermined time Tb is variably set to 128 ms (millisecond).

If YES in step 120, the element impedance Zac is detected in step 130, and the energization control of the heater 35 is performed in step 140. The processing of steps 130 and 140 is
This is performed according to FIGS. 5 and 6 described later. Step 1 above
If NO is determined, the routine is temporarily terminated.

Next, the procedure for detecting the element impedance Zac in step 130 in FIG. 4 (detection procedure by the sweep method) will be described with reference to FIG. In FIG. 5, in step 131, the bias command signal Vr is manipulated to change the applied voltage Vp (the voltage for detecting the air-fuel ratio) up to that point in a one-time change to the positive side. The application time of the element impedance detection voltage is set to about several tens to 100 μs in consideration of the frequency characteristics of the A / F sensor 30. Thereafter, in step 132, the voltage change amount ΔV at that time and the sensor output change amount ΔI detected by the current detection circuit 50 are read. In step 133, the element impedance Zac is calculated from the above ΔV and ΔI (Zac = ΔV
/ ΔI).

In the following step 134, the calculated element impedance Zac is converted into the element temperature Ts, and thereafter the present routine is terminated and the flow returns to the original routine of FIG. Here, the element impedance Zac obtained as described above
Has a relationship shown in FIG. 9 with respect to the element temperature Ts. That is, as the element temperature Ts is lower, the element impedance Za
c increases dramatically.

According to the above processing, the LPF 2 shown in FIG.
A voltage having a predetermined time constant is applied to the A / F sensor 30 one by one via the bias control circuit 40. As a result, as shown in FIG. 8, a peak current ΔI (current change amount) is detected after a lapse of t time from the application of the voltage, and an element impedance Zac is detected from the voltage change amount ΔV and the peak current ΔI at that time. (Zac = Δ
V / ΔI). In such a case, by applying a one-shot voltage to the A / F sensor 30 via the LPF 22, the occurrence of an excessive peak current is suppressed, and the element impedance Za
The detection accuracy of c is improved.

Next, the procedure for controlling the energization of the heater in step 140 of FIG. 4 will be described with reference to FIG. In FIG. 6, in a step 141, it is determined whether or not the current time is in the process of raising the temperature during a cold start of the engine or the like. Then, the process proceeds to step 142 on condition that the temperature is being raised.

In step 142, the element temperature Ts calculated in FIG. 5 is a predetermined judgment value (Z in this embodiment) for judging the semi-active state of the solid electrolyte 31 (sensor element).
(ac = value corresponding to 200Ω) or more. For example, when the engine 10 is started at a low temperature, step 14 is executed.
2 is NO, the routine proceeds to step 143, where "100% energization control" of the heater 35 is performed. In the 100% energization control, the duty ratio control signal Duty to the heater 35 is 1
It is maintained at 00%.

Next, at step 146, Duty = 10
The heater is energized by the control signal of 0%, and thereafter, the present routine is terminated and the process returns to the original routine of FIG. Such one
In the 00% energization control, the element temperature Ts rises and the
The operation is continuously performed until the determination of 2 is affirmative.

Then, the element temperature rises due to the heating action of the heater 35, and if the determination in step 142 is affirmative, the routine proceeds to step 144, where the element temperature Ts is a predetermined determination value for starting the element temperature F / B control. (In the present embodiment, Zac =
It is determined whether the value is equal to or more than 40Ω.

If the determination in step 144 is negative before the sensor is activated, the flow advances to step 145 to execute "power control".
The energization control of the heater 35 is performed by the
After the heater is energized at 46, the present routine is terminated and the routine returns to the original routine of FIG. In this power control, the element temperature T
A larger power command value is determined as s is smaller (as Zac is larger), and a duty ratio control signal Duty is calculated according to the power command value.

When the activation of the sensor is completed, the step 144 is completed.
Is affirmatively determined, the routine proceeds to step 200, where "element temperature F / B control" is performed. Details of the element temperature F / B control will be described later with reference to FIG. Then, step 146
Then, the heater is energized based on the duty ratio control signal Duty calculated in the processing of the element temperature F / B control, and thereafter, the present routine ends and returns to the original routine of FIG.

After starting the engine, step 141 is executed.
Is negatively determined each time, and the determination in steps 142 and 144 is not performed. Therefore, 100% energization control and power control (steps 143 and 145) are not executed after the warm-up is completed.

The detailed procedure of the element temperature F / B control will be described with reference to the flowchart of FIG. In FIG. 7, first, in step 201, it is determined whether or not the output of the A / F sensor 30 is used. For example, when the engine is stopped, or when an abnormality occurs in the air-fuel ratio control system and the F / B control is interrupted, for example, step 201 is negatively determined and the process proceeds to step 202. Then, in step 202, the duty ratio control signal Duty for energizing the heater is forcibly set to "0%", and thereafter, the present routine ends, and the routine returns to the original routine of FIG. However, in the process of step 202, the duty is not set to Duty = 0%, but is set to a minute Duty.
May be set to continue the heater energization with low power.

If the determination in step 201 is affirmative, the routine proceeds to step 203, where it is determined whether or not the conditions for implementing the air-fuel ratio F / B control are satisfied. The implementation conditions are, for example: (1) The temperature condition of the engine cooling water is satisfied (for example, water temperature ≧ 40 ° C.). (2) Not in a high load / high rotation state. (3) Fuel cut is not in progress. And all or at least one of the conditions. If the condition is satisfied, the process proceeds to step 204, and if not, the process proceeds to step 205. The determination as to whether the condition is appropriate is made based on the engine operation information transmitted from the engine control microcomputer 16.

In step 204, the element temperature target value Tsre
f is set to a normal target value of “700 ° C.”, and in step 205, the element temperature target value Tsref is set to “600 ° C.” lower than the normal target value. That is, when the sensor output is used for the air-fuel ratio F / B control, the A / F sensor 3
An element temperature target value Tsref is set based on a temperature for maintaining 0 in a predetermined active state. On the other hand, when the sensor output is not used for the air-fuel ratio F / B control, there is no problem even if the sensor becomes lower than the activation temperature. Therefore, the element target temperature is set to a relatively low temperature in order to save power. .

Thereafter, in step 206, a deterioration correction coefficient Ks according to the degree of deterioration of the A / F sensor 30 is obtained, and in step 207, the set element temperature target value Tsref is corrected using the deterioration correction coefficient Ks. (Tsre
f = Ks.Tsref). The deterioration correction coefficient Ks is obtained using, for example, the relationship shown in FIG. In this case, if the output of the A / F sensor 30 has deteriorated so as to be larger than the standard value, a deterioration correction coefficient Ks of Ks <1 is set, and thereby the element temperature target value Tsref is reduced. A /
If the output of the F sensor 30 has deteriorated so as to be smaller than the standard value, a deterioration correction coefficient Ks of Ks> 1 is set, thereby increasing the element temperature target value Tsref.

Thereafter, in step 208, a duty ratio control signal Duty for performing F / B control of the element temperature Ts to the target value Tsref is calculated according to the following procedure. In the present embodiment, a PID control procedure is used as an example.

That is, the proportional term Gp, the integral term Gi, and the differential term Gd are calculated by the following equations. Gp = Kp · (Ts−Tsref) Gi = Gi + Ki · (Ts−Tsref) Gd = Kd · (Ts−Ts0) where Kp is a proportional constant, Ki is an integral constant,
Kd indicates the differential constant, and Ts0 indicates the element temperature during the previous processing.

Thereafter, in step 209, the element temperature Ts at that time is stored as the previous value Ts0, and the subsequent step 2
In step 10, the duty ratio control signal Duty is calculated by adding the proportional term Gp, the integral term Gi, and the differential term Gd (D
uty = Gp + Gi + Gd).

Further, at step 211, the calculated duty ratio control signal Duty is corrected according to the battery voltage, and thereafter, the present routine is terminated and the routine returns to the original routine of FIG. In step 211, for example, FIG.
Using the relationship of 1, the correction is performed according to the change from the standard value of the battery voltage (+ B). The heater control procedure described above
The control is not limited to the PID control described above, and another control such as PI control or P control may be performed.

In this embodiment, the microcomputer 20 for detecting the air-fuel ratio constitutes the setting means, the heater control means, the condition determining means and the deterioration detecting means. According to the present embodiment described in detail above, the following effects can be obtained.

(A) It is determined whether or not the execution condition of the air-fuel ratio F / B control is satisfied, and the element temperature target value Tsref is changed depending on whether the execution condition of the air-fuel ratio F / B control is satisfied or not. It is set (steps 203 to 205 in FIG. 7).
According to the above configuration, an appropriate sensor output can be ensured by maintaining the A / F sensor 30 in a desired active state as needed while achieving power saving when the heater is used. In addition, since power saving can be realized, improvement in engine fuel efficiency can also be realized.

Incidentally, the target element temperature Tsref is set to 700
When the temperature is set to ° C., about 14.5 W of electric power is required, whereas when the element temperature target value Tsref is set to 600 ° C., about 8.5 W of electric power is required. In this case, about 6
W power reduction can be realized.

(B) It is determined whether or not the sensor output is used. If not, the duty ratio control signal Du is used.
ty is forcibly set to “0%” (step 20 in FIG. 7).
1,202). Therefore, unnecessary power can be reduced, and further power saving can be achieved.

(C) The element temperature target value Tsref is corrected according to the degree of deterioration of the A / F sensor 30 (FIG. 7).
Steps 206 and 207). In this case, for example, even if the sensor output is degraded in a decreasing direction, the element temperature target value Tsre
By correcting f to the rising side, an appropriate sensor output can be secured. Conversely, even if the sensor output deteriorates in the increasing direction, by correcting the element temperature target value Tsref to the descending side, the power supplied to the heater 35 can be minimized and power saving can be achieved. it can.

(D) The duty ratio control signal Duty is increased or decreased according to the battery voltage (step 21 in FIG. 7).
1). Therefore, appropriate heater energization control can always be performed irrespective of fluctuations in the battery voltage.

(E) Cup-shaped A as in the present embodiment
When the / F sensor 30 is applied, a larger amount of power is supplied to the heater than in the case of a stacked A / F sensor having excellent thermal conductivity. However, according to the above configuration, the absolute amount of power can be reduced. Therefore, it is particularly effective in a cup type A / F sensor.

Next, second to sixth embodiments of the present invention will be described. However, in the configurations of the following embodiments, the same components as those of the above-described first embodiment are denoted by the same reference numerals in the drawings, and the description is simplified. The following description focuses on differences from the first embodiment.

(Second Embodiment) Incidentally, the element temperature and the A / F detection range have a relationship as shown in FIG. 12, and the A / F detection range changes according to the element temperature. Actually, when the element temperature is low, the air-fuel ratio on the lean side and the rich side can hardly be detected, but when the element temperature rises, the A / F detection range is extended.

As shown in the relationship of FIG. 13, even with the same air-fuel ratio, the sensor output (mA) differs depending on the element temperature at each time. For example, when A / F = 18, the sensor output does not reach the original current value (approximately 7 mA in the figure) unless the element temperature rises to about 650 ° C., and an accurate lean is obtained in the element temperature <650 ° C. region. Air-fuel ratio (A / F = 1
8) cannot be detected. When A / F = 13,
If the element temperature does not rise to about 630 ° C., the sensor output does not reach the original current value (about −6 mA in the figure), and the element temperature <
In the region of 630 ° C., an accurate rich air-fuel ratio (A / F = 1
3) cannot be detected.

From this, it can be seen that for each air-fuel ratio (A / F = 1
3 and 18), it can be seen that the element temperature required for obtaining a normal output is different. Incidentally, the stoichiometric air-fuel ratio (A / F =
In 14.7), since the sensor output is originally 0 mA, a normal sensor output can be obtained even at an element temperature of about 600 ° C.
Therefore, in the present embodiment, the element temperature target value Tsref is changed according to whether the output range of the A / F sensor 30 is a stoichiometric value, a lean value, or a rich value.

In addition, the A / F sensor 30 includes a linear limit current signal (A / F output) corresponding to a wide range of air-fuel ratio and an electromotive force signal (O2 output) corresponding to whether the air-fuel ratio is rich or lean. ) Can be selectively output, and when the electromotive force signal is used, the appropriate sensor activation temperature is lower than when the limit current signal is used, and the element temperature may be maintained at about 350 ° C. Then, the engine control microcomputer 16 performs the air-fuel ratio F / B control in a relatively wide air-fuel ratio range including the lean and rich regions by using the former limit current signal, and by using the latter electromotive force signal. The air-fuel ratio F / B control is performed in a relatively narrow air-fuel ratio range near the stoichiometric ratio. That is,
The above-described limit current signal is a sensor output generated by applying a predetermined voltage to the A / F sensor 30 when performing air-fuel ratio F / B control over a relatively wide range. On the other hand, the electromotive force signal is a voltage output generated by the electromotive force without applying a voltage to the A / F sensor 30 when performing the air-fuel ratio F / B control in the vicinity of the stoichiometric range. Actually, the limit current signal (A / F output) is the limit current signal Ip in FIG.
And the electromotive force signal (O2 output) corresponds to the voltage signal VOX2 in FIG.

Therefore, in the present embodiment, the engine control microcomputer 16 determines an appropriate sensor activation temperature in accordance with the type of air-fuel ratio control to be performed, and determines the element temperature target value Ts
Change ref.

FIG. 14 shows the element temperature F in this embodiment.
15 is a flowchart showing a / B control subroutine, and the process of FIG. 14 is executed in place of the process of FIG. 14, first, at step 301, the air-fuel ratio control data transmitted from the engine control microcomputer 16 is read, and the microcomputer 16 reads the air-fuel ratio F over a relatively wide range.
It is determined whether / B control is to be performed. For example, when the engine control microcomputer 16 performs the air-fuel ratio F / B control in a comparatively narrow range near stoichiometry, step 301
And the process proceeds to step 302. Step 302
Here, the output of the A / F sensor 30 is regarded as "O2 output", and the element temperature target value Tsref is set to "350 ° C".

If the engine control microcomputer 16 performs the air-fuel ratio F / B control over a relatively wide range, the routine proceeds to step 303. In step 303, based on the air-fuel ratio control data of the engine control microcomputer 16, the air-fuel ratio F / B
It is determined whether the control is performed in the stoichiometric, lean, or rich control range. If the stoichiometric air-fuel ratio control is to be performed, the element temperature target value Tsref is set to “650 ° C.” in step 304. If the air-fuel ratio control in the lean region is performed, the element temperature is controlled in step 305. If the temperature target value Tsref is set to “720 ° C.” and the air-fuel ratio control in the rich region is performed, step 306 is executed.
To set the element temperature target value Tsref to “700 ° C.”.

Note that Tsre in steps 304 to 306
The f value is set based on the relationship in FIG. Actually, the element temperature target value Tsref has some allowance in a temperature range where a normal sensor output can be obtained at each air-fuel ratio.
Is set.

Thereafter, in steps 307 to 309, a duty ratio control signal Duty is obtained from the sum of the proportional term Gp, the integral term Gi, and the differential term Gd. Steps 307 to 309
Is similar to steps 208 to 210 in FIG. 7 and the description is omitted here. However, step 3
When Tsref = 350 ° C. is set in 02, since the element impedance cannot be detected because the element temperature is low, constant power control is performed in this state.

Although not shown, in the process of FIG. 14, similarly to the process of FIG. 7, the correction of the element temperature target value reflecting the degree of deterioration of the A / F sensor 30 (steps 206 and 206 in FIG. 7). 207) or correction of the element temperature target value according to the battery voltage (step 211 in FIG. 7) may be appropriately performed.

According to the present embodiment, as in the first embodiment, the A / F sensor 30 is maintained in a desired active state as needed while achieving power saving when using the heater. By doing so, it is possible to obtain an excellent effect that an appropriate sensor output can be secured.

In addition, the target element temperature Tsref is changed and set according to the control range of the air-fuel ratio (steps 303 to 306 in FIG. 14). Actually, at the time of the air-fuel ratio control in the lean region or the rich region, the element temperature target value Tsref is set higher than that in the stoichiometric control. According to this configuration, a highly accurate sensor output is obtained in any air-fuel ratio control, and the control accuracy is improved. In addition, at the time of the stoichiometric control, the element temperature target value Tsref is set lower than the others, so that the heater power is reduced and power saving can be realized. Further, at this time, by setting a minimum necessary target temperature within a temperature range for obtaining an appropriate sensor output, further power saving can be realized.

Further, when the air-fuel ratio control is realized in a relatively narrow air-fuel ratio range using the electromotive force signal, and when the air-fuel ratio control is performed in a relatively wide air-fuel ratio range using the limit current signal. Thus, the target element temperature Tsref is changed and set (steps 301 to 306 in FIG. 14). Therefore,
When the activation temperature for obtaining an appropriate sensor output is different between the O2 output and the A / F output, it is possible to reduce the power consumption when using the heater while securing the appropriate sensor output at each time. it can. Further, the air-fuel ratio control can be optimized.

In step 301 of FIG. 14, the sensor output signal is monitored to determine whether the output signal is an O2 output or an A / F output, and the target element temperature Tsref is changed according to the result. You may comprise. In step 303, it is determined whether the current A / F output is a stoichiometric value, a lean value, or a rich value.
The device temperature target value Tsref may be changed according to the result. Actually, when the sensor output is “O2 output”, Tsref = 350 ° C. When the sensor output is “A / F output”, Tsref = 650 if A / F output = stoichiometric value
℃, ・ If A / F output = lean value, Tsref = 720 ℃
・ If A / F output = rich value, Tsref = 700 ° C.
And

Also in this configuration, excellent effects such as high-precision sensor output can be obtained within a wide range of air-fuel ratio detection, heater power can be reduced and power saving can be realized, and so on can be obtained.

(Third Embodiment) FIG. 15 is a flowchart showing an element temperature F / B control subroutine in a third embodiment. In FIG.
The common parts with the B control subroutine (FIGS. 7 and 14) are omitted, and only the changed parts are shown. Steps 401 to 401 in FIG.
403 is, for example, steps 303 to 306 in FIG.
The processing is executed in place of the above processing. Note that the processing in FIG. 15 is based on the lean air-fuel ratio control, and the air-fuel ratio control in the rich region is omitted.

In FIG. 15, in step 401, A
The A / F output range of the / F sensor 30 is determined. A / F
When the air-fuel ratio F / B control is performed in the vicinity of the stoichiometric range based on the output, the process proceeds to step 402, where the target element temperature Tsref is set to “700 ° C.”. A / F
When the lean F / B control in the lean region is performed based on the output, the process proceeds to step 403 and sets the element temperature target value Tsref to “720 ° C.”.

According to the third embodiment, similarly to the above-described embodiments, the A / F sensor 30 can be set in a desired active state as necessary while achieving power saving when using the heater. By maintaining the temperature, an excellent effect such as an appropriate sensor output can be obtained.

(Fourth Embodiment) In the second embodiment, when air-fuel ratio control is performed using the A / F output from the A / F sensor 30, the element temperature is controlled in accordance with the control range. Although the target value Tsref was set to be variable,
An extremely lean state at the time of fuel cut (F / C) may be detected from the / F output. In that case also F / C
To obtain the original sensor output at the time, it is necessary to set a target element temperature value corresponding to the state.

That is, as shown in FIG.
At the time of detecting the atmospheric state, the sensor output cannot be obtained unless the element temperature is raised to a predetermined temperature higher than the target temperature in the normal lean region (A / F = around 18 to 23). In other words, at the time of atmospheric detection, the degree of leanness of the exhaust gas component is extremely large, so that the target temperature for obtaining a normal output needs to be set to a relatively high temperature.

FIG. 16 shows the element temperature F / in this embodiment.
FIG. 16 is a flowchart showing a B control subroutine. FIG. 16 omits parts common to the above-described element temperature F / B control subroutine (FIGS. 7 and 14) and shows only changed parts. Steps 501 to 504 in FIG. 16 are executed in place of, for example, the processing of steps 303 to 306 in FIG.

In FIG. 16, in step 501, A
The form of the output signal of the / F sensor 30 is determined. In this case, based on the air-fuel ratio control data, the F / C control data, and the like transmitted from the engine control microcomputer 16, the sensor output is set to “A / F detection state”, “F / C detection state”, or “F / C detection state”.
Which state corresponds to “C non-detection state” is determined. In the A / F detection state, the element temperature target value Tsref is set to “700 ° C.” in step 502, and in the F / C detection state, the element temperature target value Tsref is set to “750 ° C.” in step 503. If the F / C is not detected, the target element temperature Tsref is set to “600 ° C.” in step 504.

The F / C non-detection state refers to a state that is not the A / F detection state and is not the F / C detection state. More specifically, the A / F sensor 30 is controlled by the F / C control or the like.
When the output current of the A / F increases, the voltage applied to the A / F sensor 30 is suppressed to stop the F / C detection, and the output current is set to a current value between the A / F output and the F / C output. Say to control. As a result, this current signal is
For a long time, the internal circuit generates heat, or the signal from the A / F sensor 30 exceeds the detection range of the voltage detection circuit 50.

According to the fourth embodiment, as in the above embodiments, the A / F sensor 30 is activated in a desired active state as necessary while achieving power saving when using the heater. By maintaining the temperature, an excellent effect such as an appropriate sensor output can be obtained. Further, the air-fuel ratio at the time of F / C can be accurately detected.

(Fifth Embodiment) In this embodiment,
A gas concentration sensor (NO as a so-called composite gas sensor) capable of detecting the oxygen concentration simultaneously with the detection of the NOx concentration
An example of application to (x sensor) will be described.

First, the structure of the gas concentration sensor will be described with reference to FIG. The gas concentration sensor 100 in FIG. 18 has a pump cell 110 for detecting the oxygen concentration and a sensor cell 120 for detecting the NOx concentration, and has a two-cell structure.

In FIG. 18, the gas concentration sensor 100
Requires a pump cell 110, a porous diffusion layer 101, a sensor cell 120, an air duct 102, and a heater 103, and these members are laminated. The sensor 1
00 is attached to the engine exhaust pipe at the right end of the figure,
The upper and lower surfaces and the left surface are exposed to exhaust gas.

More specifically, the pump cell 110 is provided between the porous diffusion layer 101 and the exhaust gas space. A pump first electrode 111 is provided on the exhaust gas side (upper side in the figure) of the pump cell 110, and is located on the porous diffusion layer 101 side (lower side in the figure).
Is provided with a pump second electrode 112. The sensor cell 120 is provided between the porous diffusion layer 101 and the air duct 102. Porous diffusion layer 1 of sensor cell 120
A sensor first electrode 121 is provided on the 01 side (upper side in the figure), and a sensor second electrode 122 is provided on the atmosphere duct 102 side (lower side in the figure). Then, exhaust gas is introduced into the porous diffusion layer 101 from the left side of the figure and flows to the right side of the figure.

The pump cell 110 and the sensor cell 120 have solid electrolytes formed by lamination, and these solid electrolytes are converted to ZrO2, HfO2, ThO2, Bi2O3, etc.
It is composed of an oxygen ion conductive oxide fired body in which aO, MgO, Y2 O3, Yb2 O3, etc. are dissolved as a stabilizer. Further, the porous diffusion layer 101 is made of a heat-resistant inorganic substance such as alumina, magnesia, quartzite, spinel, and mullite.

The first pump on the exhaust gas side of the pump cell 110
The electrode 111 and the sensor first and second electrodes 121 and 122 of the sensor cell 120 are made of a noble metal having high catalytic activity such as platinum Pt. On the other hand, the pump second electrode 112 on the porous diffusion layer 101 side of the pump cell 110 is made of a noble metal such as Au-Pt which is inert to the NOx gas (it is difficult to decompose the NOx gas).

The heater 103 is embedded in the insulating layer 104,
An air duct 102 is formed between the insulating layer 104 and the sensor cell 120. Atmosphere is introduced into the air duct 102 constituting the reference gas chamber from the outside, and the air is used as a reference gas serving as a reference for the oxygen concentration. Insulation layer 1
04 is made of alumina or the like, and the heater 103 is made of cermet of platinum and alumina. Heater 103
Generates thermal energy by external power supply in order to activate the entire sensor (including electrodes) including the pump cell 110 and the sensor cell 120.

In the gas concentration sensor 100 having the above structure, an exhaust gas component is introduced into the porous diffusion layer 101 from the left side of the figure, and when the exhaust gas passes near the pump cell 110, a voltage is applied to the pump cell 110. A decomposition reaction occurs. At this time, as described above, the pump cell 110
Is formed by a NOx inert electrode (electrode that hardly decomposes NOx gas), only oxygen in the exhaust gas is decomposed by the pump cell 110 and discharged from the pump first electrode 111 into the exhaust gas. . Then, the current flowing through the pump cell 110 is detected as the concentration of oxygen contained in the exhaust gas, and the detected value is input to, for example, the ECU 15 (the air-fuel ratio detecting microcomputer 20).

The oxygen in the exhaust gas is pump
And a part thereof flows as it is to the vicinity of the sensor cell. Then, by applying a voltage to the sensor cell 120, the residual oxygen and NOx react with each other,
x is decomposed. That is, NOx is decomposed by the sensor first electrode 121 of the sensor cell 120 and is discharged from the sensor second electrode 122 to the atmosphere of the atmosphere duct 102 via the sensor cell 120. At this time, the current flowing through the sensor cell 120 is detected as the concentration of NOx contained in the exhaust gas, and the detected value is input to, for example, the ECU 15 (the air-fuel ratio detection microcomputer 20).

In the gas concentration detecting device provided with the sensor 100 having the above-described configuration, the ECU 15 (the air-fuel ratio detecting microcomputer 20) controls the energization of the heater as follows. FIG. 19 is a flowchart showing an element temperature F / B control subroutine according to the present embodiment. In FIG. 19, common parts with the element temperature F / B control subroutine (FIGS. 7, 14 and the like) are omitted. , Only the changed part is shown. Steps 601 to 604 in FIG. 19 are performed, for example, in step 301 in FIG.
306.

In FIG. 19, at step 601, the form of the output signal of the gas concentration sensor 100 is determined. In this case, based on the air-fuel ratio control data transmitted from the engine control microcomputer 16 or the like, “O2 output” or “A2
/ F output ”or“ NOx output ”. And if the sensor output is “O2 output”,
Proceeding to step 602, the element temperature target value Tsref is set to "3
50 ° C ”and if the sensor output is“ A / F output ”,
Proceeding to step 603, the element temperature target value Tsref is set to "7
00 ° C. ”and if the sensor output is“ NOx output ”,
Proceeding to step 604, the element temperature target value Tsref is set to "7
80 ° C ”. However, if the A / F output and the NOx output can be simultaneously obtained from the sensor, the higher element temperature target value Tsref (that is, 780 ° C.) is used.

According to the fifth embodiment, even if the activation temperature for obtaining an appropriate sensor output differs depending on the type of the signal output from the gas concentration sensor 100, the sensor output is determined. By appropriately setting the element temperature target value Tsref accordingly, it is possible to secure an appropriate sensor output while saving power when using the heater. In the present embodiment, an output determination unit is configured by the ECU 15 (the air-fuel ratio detection microcomputer 20).

On the other hand, the gas concentration sensor (NO
The x sensor 100 has a two-cell structure, but may of course be a three-cell sensor. A gas concentration sensor (NOx sensor) 200 having a three-cell structure will be described with reference to FIG.
In the gas concentration sensor 200 of FIG. 20, the oxygen pump cell 210 includes a solid electrolyte SEA and a pair of electrodes 2 on both surfaces thereof.
11 and 212. Solid electrolyte SEA and electrode 2
A pinhole 213 having a predetermined size is formed in each of the holes 11 and 212. Reference numeral 214 denotes a porous protective layer.

The oxygen sensing cell 220 includes a solid electrolyte SEB and a pair of electrodes 221 and 222 on both surfaces thereof. Electrode 2
Reference numeral 21 denotes, for example, a porous Pt electrode, and the electrode activity of the electrode 222 is adjusted so as to be inactive for reduction of NOx and active for reduction of oxygen, similarly to the electrode 212 of the oxygen pump cell 210. . The NOx detection cell 230 is a solid electrolyte S common with the oxygen detection cell 220.
EB and a pair of electrodes 231 and 232 on both sides thereof.
The electrode 231 is made of, for example, a porous Pt electrode.
Numeral 2 is composed of, for example, a porous Pt electrode active for reduction of NOx.

The first internal space 241 and the second internal space 241 adjacent to each other between the solid electrolytes SEA and SEB via the communication holes 243 are connected.
An internal space 242 is formed. An air passage 244 is formed on the back surface side of the solid electrolyte SEB, and a heater 245 for heating each cell is further laminated.

In the gas concentration sensor 200 having the above-described structure, the exhaust gas passes through the pinhole 213 and passes through the first internal space 2.
41 is introduced. In the oxygen sensing cell 220, the electrode 22
An electromotive force is generated based on the oxygen concentration difference between the two sides of the first and second sides. By measuring the magnitude of the electromotive force, the oxygen concentration in the first internal space 241 is detected.

In the oxygen pump cell 210, the electrodes 211 and 211
The voltage is applied between the first internal space 241 and the second internal space 241.
Oxygen inside is taken in and out, and the oxygen concentration in the internal space 241 is controlled to a predetermined low concentration. Oxygen pump cell 210
The amount of current supplied to the electrodes 221 and 22 of the oxygen sensing cell 220
Feedback control is performed so that the electromotive force generated between the two becomes a predetermined constant value. Here, since the electrodes 212 and 222 facing the first internal space 241 are inactive for reduction of NOx, NOx is not decomposed in the first internal space 241 and NOx in the first internal space 241 The amount does not change.

Oxygen pump cell 210 and oxygen detection cell 2
The exhaust gas having a constant low oxygen concentration due to 20 is introduced into the second internal space 242 through the communication hole 243. The NOx detection cell 230 facing the second internal space 242 is N
Since it is active against Ox, when a predetermined voltage is applied between the electrodes 231 and 232, NOx is reduced and decomposed on the electrode 232, and an oxygen ion current flows. By measuring this current value, the concentration of NOx contained in the exhaust gas is detected.

The gas concentration sensor 200 having the structure shown in FIG.
Also, by executing the processing as shown in FIG. 19, the excellent effects as described above can be obtained. That is, even if the activation temperature for obtaining an appropriate sensor output differs according to the type of sensor output, an appropriate sensor output can be ensured while saving power when using the heater.

(Sixth Embodiment) The gas concentration detecting device of the present invention is applied to a hybrid vehicle. The hybrid vehicle includes, for example, an engine and a motor that are driven and connected in a parallel system or a serial system, and is configured so that the vehicle travels by using both outputs thereof. The above-described A / F sensor 30 is disposed in the exhaust pipe of the engine, and the output of the A / F sensor 30 is taken into the controller and the air-fuel ratio F / F
B control is performed.

FIG. 21 shows the element temperature F / in this embodiment.
FIG. 21 is a flowchart showing a B control subroutine. FIG. 21 omits parts common to the above-described element temperature F / B control subroutine (FIGS. 7, 14 and the like) and shows only changed parts. Steps 701 to 703 in FIG. 21 are executed in place of, for example, the processing in steps 303 to 306 in FIG.

In FIG. 21, in step 701, the operating state of the hybrid vehicle is determined. If both the engine and the motor are operated, step 702
And the target element temperature Tsref is set to “700 ° C.”. If the engine is stopped and only the motor is driven, the routine proceeds to step 703, where the element temperature target value Ts
ref is set to “600 ° C.”.

As described above, according to the sixth embodiment, it is possible to secure an appropriate sensor output while saving power when the heater is used, as in the above-described embodiments.
In particular, in the case of a hybrid vehicle, the effect of power consumption on fuel efficiency is further increased, but fuel efficiency can be improved with power saving. Incidentally, when the engine is stopped, the element temperature target value Ts
In addition to the configuration for reducing the ref, when the air-fuel ratio F / B control is not performed, such as during idling, the element temperature target value T
The sref may be reduced or the heater energization may be stopped (duty = 0%).

The present invention can be embodied in the following modes other than the above. In each of the above embodiments, the A / F sensor 3
0 (or gas concentration sensor 100, 200) element temperature T
Although the F / B control of the heater was performed according to s, this is changed as follows.

(A) F / B control of the heater is performed according to the internal resistance of the sensor element. In this case, for example, the air-fuel ratio F
When / B is performed, the target value of the internal resistance is relatively low to secure an appropriate sensor output. When the air-fuel ratio F / B is not performed, the target value of the internal resistance is relatively high to save power. Alternatively, the target value of the internal resistance is made relatively low during the lean control or the rich control, and the target value of the internal resistance is made relatively high during the stoichiometric control.

(B) F / B control of the heater is performed according to the temperature or resistance value of the heater. In this case, for example, when the air-fuel ratio F / B is performed, the target value of the heater temperature or the resistance value is set relatively high to secure an appropriate sensor output, and the air-fuel ratio F / B
Is not performed, the target value of the heater temperature or the resistance value is set relatively low to save power. Alternatively, the target value of the heater temperature or the resistance value is made relatively high during the lean control or the rich control, and the target value of the heater temperature or the resistance value is made relatively low during the stoichiometric control. Incidentally, the heater generally has a characteristic that the resistance value increases as the temperature increases.

(C) F / B control of the heater is performed according to the power supplied to the heater. In this case, for example, the air-fuel ratio F / B
In this case, the target value of the heater power is set relatively high to secure an appropriate sensor output, and when the air-fuel ratio F / B is not performed, the target value of the heater power is set relatively low to save power. Alternatively, the target value of the heater power is made relatively high during the lean control or the rich control, and the target value of the heater power is made relatively low during the stoichiometric control.

(D) The duty ratio control signal Duty is variably set in accordance with conditions such as whether the air-fuel ratio F / B is performed or whether stoichiometric control is performed. The heater control is performed based on the control.

In any of the above configurations (a) to (d), by changing the operating temperature of the sensor, it is possible to secure an appropriate sensor output while saving power while using the heater.

In the above-described embodiment, the AC element impedance Zac is detected by using the sweep method, but this configuration is changed. For example, the DC element resistance Ri may be detected instead of the AC element impedance Zac, and the F / B control of the heater may be performed according to the Ri value.

When the target temperature of the sensor element or the heater is variably set according to whether the output (limit current signal) of the A / F sensor or the control range of the air-fuel ratio is stoichiometric, lean, or rich, for example, as shown in FIG. The target temperature is determined by searching the map using the relationship of No. 22. According to FIG. 22, the target temperature is lowest in the vicinity of the stoichiometry, and the target temperature increases as the distance from the stoichiometry increases toward the lean side or the rich side. Even in such a configuration, the excellent effects as described above can be obtained.

In each of the first to sixth embodiments, the method of variably setting the target temperature of the sensor element or the heater in accordance with the use environment and application of the gas concentration sensor is as follows: (1) Air-fuel ratio F / B The target temperature is set differently when the control condition is satisfied and when it is not satisfied. (2) The target temperature is changed and set depending on whether or not the sensor output is used. (3) The target temperature is corrected according to the degree of sensor deterioration. (4) The target temperature (Duty) is corrected according to the battery voltage. (5) The target temperature is changed and set according to the air-fuel ratio (detection range) corresponding to the sensor output. (6) The target temperature is changed and set depending on whether the sensor output is O2 output, A / F output or NOx output. (7) In a hybrid vehicle, the air-fuel ratio of the engine F /
The target temperature is changed and set depending on whether the B control is useful. The above-described methods are appropriately combined and implemented, but the combination is arbitrary and the above-described configurations (1) to (7) may be implemented by combining them as needed. In any case, according to the present invention, an appropriate sensor output can be secured by maintaining the gas concentration sensor in a desired active state as needed while achieving power saving when the heater is used. In addition, since power saving can be realized, improvement in engine fuel efficiency can also be realized.

In addition, it is determined whether or not sensor output is required from the beginning of warm-up at the time of cold start of the engine. If sensor output is required from the beginning of warm-up, the target temperature of the sensor element or heater is determined. It is also possible to increase the temperature rising rate by increasing the temperature, otherwise lower the target temperature of the sensor element or the heater and decrease the temperature rising rate (using heating by the exhaust gas temperature).

In the first embodiment, the duty ratio control signal Duty depends on the state of deterioration of the A / F sensor 30.
Is corrected (steps 206 and 207 in FIG. 7, FIG. 10) according to whether the sensor output is increasing or decreasing from the standard value, but this is changed. For example, the deterioration degree of the A / F sensor 30 is determined from the relationship between the element internal resistance and the heater supply power at a time when the exhaust gas temperature is stable. When the sensor deteriorates such that the element internal resistance becomes excessive for the same heater supply power, the duty ratio control signal Duty at that time is corrected to the increasing side.

Of course, the element temperature target value Tsref is not limited to the above specific value, but may be changed and set each time.
In the first to fourth embodiments, a one-cell limiting current type oxygen concentration sensor is used as the A / F sensor 30.
The present invention is not limited to this, and a two-cell oxygen concentration sensor may be used.
Further, the present invention is not limited to the cup type oxygen concentration sensor, and may be a stacked type oxygen concentration sensor.

The air-fuel ratio may be feedback-controlled based on the NOx concentration detected by the NOx sensor. That is, the current air-fuel ratio is monitored based on the signal output of the NOx sensor, and feedback control is performed so that the air-fuel ratio matches the target value. In this case, similarly, the target temperature of the sensor element or the heater may be variably set depending on whether or not to perform the feedback control.

In the above-described air-fuel ratio control system, an A / F sensor is provided in the exhaust pipe of the engine, and the oxygen concentration in the exhaust gas is detected by the A / F sensor, but this configuration is changed. An A / F sensor is provided in the intake pipe of the engine instead of or in addition to the A / F sensor on the exhaust side.
The oxygen concentration in the intake gas is detected by the / F sensor. Then, the air-fuel ratio is feedback-controlled based on the oxygen concentration in the intake gas.

More specifically, an exhaust gas recirculation system (EG
R device), the A provided on the intake side
The EGR device is controlled based on the detection result of the / F sensor, and the air-fuel ratio is controlled by reflecting the control result. In this case, A /
The target temperature of the sensor element or the heater is changed when the signal output of the F sensor is used (when EGR control is performed) and when it is not used (when EGR control is not performed). In the latter case, the sensor element is changed. Alternatively, the target temperature of the heater is set lower. In particular, in a hybrid vehicle, since the EGR control is not required when the engine is stopped and only the motor is driven, the target temperature of the sensor element or the heater is lowered in that case. Alternatively, when the EGR control is not performed, the heater energization itself may be stopped.

In a device for performing a so-called evaporation purge control, in which fuel vapor (evaporation gas) in a fuel tank is temporarily stored in a canister and then discharged to an intake pipe of an engine, an evaporation gas is provided by an A / F sensor provided in the intake pipe. Is monitored, and the fuel injection amount is corrected accordingly. In such an apparatus, when performing the evaporative purge, the heater of the A / F sensor is controlled at a relatively high temperature, and when not performing the evaporative purge, the heater of the A / F sensor is controlled at a low temperature, or the energization of the heater is stopped. In any case, it is possible to secure an appropriate sensor output while saving power when the heater is used.

As gas concentration sensors used in the gas concentration detecting device, an A / F sensor 30 for detecting oxygen concentration and a gas concentration sensor 10 for detecting nitrogen oxide (NOx) concentration
0, 200, but the present invention is not limited to these, and the gas concentration using a gas concentration sensor for detecting the gas concentration of hydrocarbons (HC), carbon monoxide (CO), etc. The same can be applied to the detection device.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an outline of an air-fuel ratio detection device according to an embodiment of the invention.

FIG. 2 is a diagram showing output characteristics of an A / F sensor.

FIG. 3 is a diagram showing a relationship between a sensor current and A / F.

FIG. 4 is a flowchart showing a main routine.

FIG. 5 is a flowchart illustrating an element impedance detection routine.

FIG. 6 is a flowchart showing a heater control routine.

FIG. 7 is a flowchart showing an element temperature F / B control subroutine.

FIG. 8 is a waveform diagram showing changes in voltage and current when impedance is detected.

FIG. 9 is a diagram showing a relationship between element temperature and element impedance.

FIG. 10 is a diagram for setting a deterioration correction coefficient.

FIG. 11 is a diagram for setting a + B correction gain.

FIG. 12 is a diagram showing a relationship between an element temperature and an A / F detection range.

FIG. 13 is a diagram showing a relationship between an element temperature and a sensor output corresponding to a predetermined A / F.

FIG. 14 is a flowchart illustrating an element temperature F / B control subroutine according to the second embodiment.

FIG. 15 is a flowchart illustrating a part of an element temperature F / B control subroutine according to the third embodiment.

FIG. 16 is a flowchart showing a part of an element temperature F / B control subroutine in a fourth embodiment.

FIG. 17 is a diagram showing a relationship between an element temperature and a sensor output corresponding to a predetermined A / F.

FIG. 18 is a cross-sectional view of a main part showing a configuration of a gas concentration sensor having a two-cell structure in a fifth embodiment.

FIG. 19 is a flowchart showing a part of an element temperature F / B control subroutine in the fifth embodiment.

FIG. 20 is a cross-sectional view of a main part showing a configuration of a gas concentration sensor having a three-cell structure.

FIG. 21 is a flowchart showing a part of an element temperature F / B control subroutine in a sixth embodiment.

FIG. 22 is a diagram showing a relationship between an A / F and a target temperature of a sensor element or a heater.

[Explanation of symbols]

10 engine as combustion engine, 13 exhaust pipe, 15
.. ECU, 20... Air-fuel ratio detecting microcomputer constituting setting means, heater control means, condition determining means, output determining means, deterioration detecting means, 30... A / F sensor as gas concentration sensor (oxygen sensor), 31. Solid electrolyte, 35: heater, 100, 200: gas concentration sensor (composite gas sensor), 103, 245: heater.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yukihiro Yamashita 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture Inside Denso Co., Ltd. (72) Inventor Tetsushi Haseda 1-1-1, Showa-cho, Kariya-shi, Aichi Co., Ltd. Inside DENSO

Claims (13)

[Claims] The present invention is applied to a gas concentration sensor having a sensor element using a solid electrolyte and a heater for heating the sensor element to a predetermined activation temperature, and detecting a concentration of a specific component in a gas to be detected. A setting means for variably setting a target temperature of a sensor element or a heater according to a use environment or an application of a gas concentration sensor; anda heater control means for energizing a heater according to the set target temperature. Control device for the gas concentration sensor. 2. The heater control of a gas concentration sensor according to claim 1, wherein the setting means changes the target temperature of the sensor element or the heater when the signal output of the gas concentration sensor is used and when it is not used. apparatus. 3. The heater control device for a gas concentration sensor according to claim 2, wherein said setting means lowers the target temperature of the sensor element or the heater when not using the signal output of the gas concentration sensor than when using the signal output. Control device for the gas concentration sensor. 4. A gas concentration sensor for detecting the concentration of a specific component in exhaust gas discharged from a combustion engine or in intake gas sucked into the combustion engine. A condition determining unit that determines an execution condition such as whether or not the air-fuel ratio feedback control is performed, wherein the setting unit is configured to execute the air-fuel ratio feedback control when the execution condition of the air-fuel ratio feedback control is satisfied. 2. The heater control device for a gas concentration sensor according to claim 1, wherein the target temperature of the sensor element or the heater is changed and set depending on whether the temperature is not satisfied. 5. A gas concentration sensor for detecting an air-fuel ratio from a specific component in exhaust gas discharged from the combustion engine or in intake gas sucked into the combustion engine. The gas concentration according to claim 1, wherein the gas concentration is applied to an air-fuel ratio control device that performs feedback control of a fuel ratio, wherein the setting unit changes and sets a target temperature of a sensor element or a heater according to an air-fuel ratio detected by a gas concentration sensor. Sensor heater control device. 6. The heater control device for a gas concentration sensor according to claim 5, wherein the setting means detects the stoichiometric air-fuel ratio if the air-fuel ratio detected by the gas concentration sensor is leaner than the stoichiometric air-fuel ratio. A heater control device for a gas concentration sensor that raises a target temperature of a sensor element or a heater as compared with a case. 7. The heater control device for a gas concentration sensor according to claim 5, wherein the setting means is configured to output a stoichiometric air-fuel ratio if the air-fuel ratio detected by the gas concentration sensor is richer than the stoichiometric air-fuel ratio. A heater control device for a gas concentration sensor that raises the target temperature of the sensor element or the heater as compared with the time of detection of the temperature. 8. A gas concentration sensor for detecting an air-fuel ratio from a specific component in exhaust gas discharged from a combustion engine or in intake gas sucked into the combustion engine. 2. The heater control of the gas concentration sensor according to claim 1, wherein the control unit is applied to an air-fuel ratio control device that performs feedback control of a fuel ratio, and wherein the setting unit changes and sets a target temperature of a sensor element or a heater according to an air-fuel ratio control region. apparatus. 9. An output signal of the gas concentration sensor, comprising: an electromotive force signal corresponding to an oxygen concentration in the gas to be detected based on a stoichiometric air-fuel ratio; and a limit current signal for linearly detecting the air-fuel ratio of the gas to be detected. Is applied to the gas concentration detection device that selectively outputs, when the sensor output is an electromotive force signal,
2. The heater control device for a gas concentration sensor according to claim 1, wherein the target temperature of the sensor element or the heater is changed and set when the sensor output is a limit current signal. 10. An output signal of a gas concentration sensor, comprising: an electromotive force signal corresponding to an oxygen concentration in a gas to be detected based on a stoichiometric air-fuel ratio; and a limit current signal for linearly detecting an air-fuel ratio of the gas to be detected. Is applied to the gas concentration detection device that selectively outputs the air-fuel ratio control, and the setting unit compares the air-fuel ratio control when the air-fuel ratio control is performed using the electromotive force signal in a relatively narrow air-fuel ratio range. The target temperature of the sensor element or the heater is set differently when the air-fuel ratio control is performed using the limit current signal in the air-fuel ratio range wider than the narrow air-fuel ratio range.
3. The heater control device for a gas concentration sensor according to claim 1. 11. A gas concentration sensor comprising a compound gas sensor capable of outputting a signal corresponding to each gas concentration from a plurality of types of gas components in a gas to be detected, and what kind of signal output the sensor performs. 2. The heater control device for a gas concentration sensor according to claim 1, further comprising an output determination unit configured to determine the target temperature of the sensor element or the heater according to the determination result. 3. 12. A hybrid vehicle that travels using both the output of an internal combustion engine and the output of a motor, wherein the setting means includes a sensor element or a heater when the operation of the internal combustion engine is stopped and only the motor is driven. 2. The heater control device for a gas concentration sensor according to claim 1, wherein the target temperature is lowered. 13. A method for detecting a degree of deterioration of a gas concentration sensor, comprising the steps of: correcting a target temperature of a sensor element or a heater set by said setting means in accordance with the detected degree of deterioration of the gas concentration sensor; The heater control device for a gas concentration sensor according to claim 1.