JPH07269401A - Air-fuel ratio control device for engine - Google Patents

Abstract

PURPOSE:To compute a heat receiving quantity of an air-fuel ratio sensor based on a parameter relative to an exhaust temperature, determine a heat radiation quantity of the air-fuel ratio sensor by using a specified heat radiation coefficient, and estimate a detection element temperature of the air-fuel ratio sensor from a value obtained by subtracting the heat radiation quantity from the heat receiving quantity so as to enhance air-fuel ratio control accuracy. CONSTITUTION:Signals of an engine speed, intake air quantity, throttle valve opening, O2 concentration and the like are read into an ECU 15, first a basic injection quantity is computed, and at the time of judging air-fuel ratio feedback a feedback correction quantity is computed based on output of an O2 sensor 10. At the time of idling, a chip temperature is estimatedly computed from a heat receiving quantity based on fuel injection quantity and a heat radiation quantity based on heat radiation coefficient, and a reversing period of normal O2 sensor output in this idling is measured as an ordinary value. In the case where the idling is continued for a long time, an exhaust temperature is decreased, and the chip temperature is lower than a specified value, a correction quantity corresponding to the ordinary value as the sensor reversing period is determined in place of the feedback correction quantity so as to find a final injection quantity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine equipped with feedback control means for feedback-controlling the air-fuel ratio of an air-fuel mixture drawn into a combustion chamber to a target air-fuel ratio based on the output of an air-fuel ratio sensor provided in an exhaust system. Relates to the air-fuel ratio control device.

[0002]

2. Description of the Related Art As an air-fuel ratio control device for an engine, an air-fuel ratio sensor such as an oxygen concentration sensor (O ₂ sensor) is provided in an exhaust system, and a basic fuel injection amount calculated from an engine speed and an intake air amount is described above. It is conventionally known that an air-fuel ratio feedback control means for feedback-controlling an air-fuel ratio of an air-fuel mixture sucked into a combustion chamber to a target air-fuel ratio by performing a correction with a feedback correction value based on the output of an air-fuel ratio sensor is known. There is.

In the air-fuel ratio control of the engine by the air-fuel ratio control device, a normal sensor output cannot be obtained unless the exhaust gas temperature rises to some extent and the detection element of the air-fuel ratio sensor reaches the activation temperature. If the feedback control is performed based on such an abnormal sensor output, the air-fuel ratio does not converge to the target value, the fluctuation becomes large, and the exhaust gas purification performance deteriorates.
For example, if the engine is left in an idle state for a long time, the exhaust gas temperature may drop, and as a result, the O ₂ sensor or the like may not be able to maintain the activation temperature of 300 ° C., for example. Then, the inversion cycle of the sensor output becomes long and the amplitude becomes small, so that the air-fuel ratio sensor does not function normally. Therefore, in the conventional air-fuel ratio control device, generally, a heater is incorporated in the O ₂ sensor so that the detection element temperature (hereinafter referred to as the chip temperature) always maintains the activation temperature.

Further, as described in, for example, Japanese Unexamined Patent Publication No. 5-125978, the inversion cycle of the output of the O ₂ sensor during the air-fuel ratio feedback control is observed, and the deterioration of the sensor is detected from the cycle change, It is known that the deterioration of the sensor is detected from the change of the response time by looking at the time interval (response time) at which the O ₂ sensor output crosses the reference value.

[0005]

An air-fuel ratio sensor such as an O ₂ sensor cannot obtain a normal sensor output unless the chip temperature reaches the activation temperature. However, if a heater is built into the air-fuel ratio sensor as in the conventional case, high cost cannot be avoided.

Further, the air-fuel ratio control device is configured to detect the chip temperature of the sensor and, when the chip temperature does not reach the activation temperature, modify the air-fuel ratio control to reduce the fluctuation of the air-fuel ratio. There is also a possibility that
As described above, it is conceivable to estimate the chip temperature from the periodic change or response time of the sensor output by looking at the periodic change or response time. However, such periodic changes in sensor output and response time have individual differences, and it is difficult to distinguish them from variations due to individual differences at the level of whether the activation temperature is reached or not. Also,
It is not possible to directly detect the chip temperature of the air-fuel ratio sensor.

The present invention is intended to solve such a problem, and an object of the present invention is to make it possible to accurately detect the detection element temperature without being affected by variations due to individual differences in air-fuel ratio sensors. To do.

[0008]

An engine air-fuel ratio control system according to the present invention sets an air-fuel ratio of an air-fuel mixture sucked into a combustion chamber to a target air-fuel ratio based on an output of an air-fuel ratio sensor provided in an exhaust system. In an engine air-fuel ratio control device having feedback control means for feedback control, a sensor heat-receiving amount calculation means for calculating the heat-receiving amount of an air-fuel ratio sensor based on a parameter related to exhaust gas temperature, and a heat-radiation amount of the air-fuel ratio sensor Is set by using a predetermined heat dissipation coefficient, and sensor detection for estimating the detection element temperature of the air-fuel ratio sensor based on a value obtained by subtracting the set value of the heat dissipation amount from the calculated value of the heat reception amount. An element temperature estimating means is provided.

The parameter is preferably a set fuel injection amount.

Further, since it is necessary to estimate the temperature of the detecting element mainly when it is left in an idle state, the heat radiation amount is calculated by using a heat radiation coefficient corresponding to the idle state of the engine. It is preferable to set it, and the heat radiation amount is set by using the heat radiation coefficient corresponding to the idle state in this way, and the detection element temperature estimation means estimates the detection element temperature at the time of idling. Is good. Even at the same idle time, when the intake air amount is increasing to idle-up with an external load such as a vehicle air conditioner, the exhaust gas temperature is higher than that during normal idling due to the large air amount. Since the amount of heat received may change due to a change in the intake air amount, such as a higher value, it is preferable to use the intake air amount together with the set fuel injection amount as the parameter.

As means for performing processing when the estimated detection element temperature of the air-fuel ratio sensor does not reach a temperature at which the normal sensor function can be exerted, for example, the detection element temperature is higher than the set temperature. When the inversion cycle storage means for storing the inversion cycle of the output of the air-fuel ratio sensor at the time, and the detection element temperature estimated by the sensor detection element temperature estimation means is less than or equal to the set temperature, the feedback control means is used. The feedback control based on the actual output of the air-fuel ratio sensor is stopped, and the air-fuel mixture is sucked into the combustion chamber based on the fixed inversion cycle fixed to the inversion cycle stored by the normal time inversion cycle storage means. It is preferable to provide pseudo feedback control means for performing feedback control of the fuel ratio to the target air-fuel ratio.

Further, when the detection element temperature estimated by the sensor detection element temperature estimation means is equal to or lower than the preset temperature, feedback stop means for stopping the feedback control by the air-fuel ratio feedback control means is provided, and the estimated air-fuel ratio sensor is provided. If the detection element temperature does not reach the temperature at which the normal sensor function can be achieved, the feedback may not be performed.

If the detection element temperature estimated by the sensor detection element temperature estimation means is equal to or lower than the preset temperature, a failure display means may be provided for failing the judgment.

Since the amount of heat released increases as the outside air temperature decreases, it is preferable to set the heat dissipation coefficient according to the outside air temperature. Preferably, the lower the outside air temperature, the greater the set value of the amount of heat released. Set to such a value.

Further, since the amount of heat released increases due to the traveling wind as the vehicle speed increases, it is preferable to set the heat dissipation coefficient according to the vehicle speed. Preferably, the higher the vehicle speed, the larger the set value of the amount of heat released. Set to a value like this.

Further, the heat dissipation coefficient may be a constant value.

Further, the air-fuel ratio sensor is assumed to detect the oxygen concentration in the exhaust gas, for example.

The set temperature is preferably an activation temperature at which the detection element normally functions.

FIG. 1 is an overall configuration diagram of the present invention showing the above configuration.

[0020]

According to the engine air-fuel ratio control apparatus of the first aspect of the present invention, the air-fuel ratio of the air-fuel mixture sucked into the combustion chamber becomes the target air-fuel ratio based on the output of the air-fuel ratio sensor provided in the exhaust system. Feedback controlled. Further, the amount of heat received by the air-fuel ratio sensor is calculated based on the parameter related to the exhaust gas temperature, and the amount of heat released by the air-fuel ratio sensor is set using a predetermined heat dissipation coefficient. Then, the detection element temperature of the air-fuel ratio sensor is estimated based on a value obtained by subtracting the set value of the heat radiation amount from the calculated value of the heat receiving amount. The detection element temperature thus estimated is not affected by the individual difference of the air-fuel ratio sensor and has high accuracy.

Further, according to the second aspect of the present invention, the amount of heat received by the air-fuel ratio sensor is calculated based on the fuel injection amount that is directly related to the exhaust gas temperature, and the air-fuel ratio sensor is calculated using a predetermined heat dissipation coefficient. The heat radiation amount is set, and the detection element temperature of the air-fuel ratio sensor is estimated based on the value obtained by subtracting the heat radiation amount setting value from the calculated heat receiving amount. In this way, when the fuel injection amount is used as the parameter, the accuracy of the detection element temperature estimation becomes particularly high.

According to the third aspect of the present invention, the heat radiation amount is set by using the heat radiation coefficient corresponding to the idling state of the engine, so that the detection element temperature is detected in the idling state. The element temperature can be estimated more accurately.

Further, according to the structure of claim 4, the heat radiation amount is set by using the heat radiation coefficient corresponding to the idle state, and then the detection element temperature is estimated at the idle time. As a result, the estimation accuracy of the detection element temperature during idling is further improved.

According to the fifth aspect of the present invention, the detection element temperature is estimated based on the calculation of the amount of heat received by using the measured value of the intake air amount together with the set value of the fuel injection amount as the parameter during idling. By doing so, it is possible to perform accurate estimation corresponding to idle-up and the like.

According to the structure of claim 6, the inversion cycle of the output of the air-fuel ratio sensor when the detection element temperature is higher than the set temperature is stored, and when the estimated detection element temperature is equal to or lower than the set temperature, Feedback control based on the actual output of the air-fuel ratio sensor is stopped, and the air-fuel ratio of the air-fuel mixture sucked into the combustion chamber is set to the target air-fuel ratio based on the fixed inversion cycle fixed to the stored inversion cycle during normal operation. Pseudo feedback control for feedback control is performed. This reduces fluctuations in the air-fuel ratio when the detection element temperature does not reach the temperature at which the normal sensor function can be exerted.

Further, according to the structure of claim 7, the feedback control is stopped when the estimated detection element temperature is equal to or lower than the set temperature, whereby the feedback control is performed based on the output of the air-fuel ratio sensor which does not function normally. The fluctuation of the air-fuel ratio becomes smaller than that of

According to the eighth aspect of the present invention, when the estimated detection element temperature is equal to or lower than the set temperature, it is judged as a failure and a fail display is made.

Further, according to the structure of claim 9, the heat radiation coefficient is set according to the outside air temperature, so that it is possible to accurately set the heat radiation amount which changes depending on the outside air temperature.

According to the structure of claim 10, the heat dissipation coefficient is set such that the lower the outside air temperature, the larger the set value of the heat dissipation amount, and the lower the outside air temperature, the larger the heat dissipation amount becomes. The setting will be in line with high accuracy.

According to the eleventh aspect of the invention, since the heat radiation coefficient is set according to the vehicle speed, the heat radiation amount that changes depending on the vehicle speed can be set with high accuracy.

According to the twelfth aspect of the invention, the heat radiation coefficient is set to a value such that the set value of the heat radiation increases as the vehicle speed increases, and the heat radiation characteristic is such that the heat radiation increases as the vehicle speed increases. The setting will be in line with high accuracy.

According to the thirteenth aspect, the heat radiation coefficient is set to a constant value, which simplifies the process of estimating the detection element temperature.

According to the fourteenth aspect of the invention, the amount of heat received by the acidity concentration sensor is calculated based on parameters such as the fuel injection amount related to the exhaust gas temperature, and the air-fuel ratio sensor of the air-fuel ratio sensor is calculated using a predetermined heat dissipation coefficient. The amount of heat radiation is set. Then, the detection element temperature of the oxygen concentration sensor is estimated based on a value obtained by subtracting the set value of the heat radiation amount from the calculated value of the heat receiving amount.

Further, according to the structure of the fifteenth aspect, since the set temperature is set to an activation temperature at which the detection element normally functions, the functions of the sixth, seventh and eighth aspects become more objective. It becomes a thing.

[0035]

FIG. 2 is an overall system diagram of Embodiment 1 of the present invention. In this embodiment, the engine 1 has, for example, four cylinders, and the intake passage 2 has an air flow sensor 3 for detecting the intake air amount and an throttle for adjusting the intake air amount in order from the upstream side to the upstream side of the surge tank 2a. A valve 4 is provided, and an injector 5 for fuel injection is provided for each cylinder in an independent intake passage portion downstream of the surge tank 2a. Further, a bypass passage 6 that bypasses the throttle valve 4 is formed in the intake passage 2, and an ISC (idle speed control) valve 7 composed of an electromagnetic valve is arranged in the bypass passage 6. Further, a catalyst device 9 for purifying the exhaust gas is provided in the exhaust passage 8 of the engine 1, and O ₂ for detecting the oxygen concentration in the exhaust gas for air-fuel ratio feedback control is provided upstream of the catalyst device 9. A sensor 10 is provided. An ignition plug 12 is arranged in the combustion chamber 11 of the engine, and the ignition plug 12 is connected to an igniter 14 via a distributor 13.

In the engine 1, the control unit 15 composed of a microcomputer controls the air-fuel ratio, ignition timing, idle speed, and the like. Therefore, the control unit 15 receives the intake air amount signal from the air flow sensor 3 from the distributor 13.
A crank angle signal and a rotation signal are input as information from a crank angle sensor and a rotation sensor attached to the engine 1, an engine water temperature signal is input from a water temperature sensor 16 attached to the engine 1, and a throttle sensor attached to the throttle valve 4 is input. A throttle opening signal is input, an air-fuel ratio signal is input from the O ₂ sensor 10, and various other signals such as a vehicle speed signal are input.

The control unit 15 calculates the fuel injection amount, the ignition timing, the ISC control amount, etc. based on these input information, and the injector 5, igniter 14 and I
Each control signal is output to the SC valve 7.

In the control of the air-fuel ratio, when the engine water temperature is equal to or higher than a predetermined value, the fuel injection amount is corrected based on the output of the O ₂ sensor 10 so as to converge to the target air-fuel ratio preset as a map value. Air-fuel ratio feedback control is performed. Specifically, the basic injection amount is calculated from the engine speed and the intake air amount, various corrections such as water temperature correction are added thereto, and further feedback correction based on the output of the O ₂ sensor 10 is added to finally make a final correction. The fuel injection amount is set. Then, an injection pulse having a pulse width corresponding to the set injection amount is applied to the injector 5,
As a result, fuel is injected from the injector 5.

In the control of the ignition timing, the ignition timing is set by the map using the engine speed and the intake charge amount as parameters, and the ignition signal is output to the igniter 14. Further, in the ISC control, the amount of bypass air is set by the map using the engine water temperature as a parameter.
The C valve 7 is controlled.

At the time of idling, the detection element temperature (chip temperature) of the O ₂ sensor 10 is estimated from the fuel injection amount, and when the chip temperature becomes lower than a predetermined temperature (for example, 300 ° C.), the sensor output is The chip temperature is higher than a predetermined temperature, and the inversion cycle is set to a normal value when a normal sensor output is obtained. Then, pseudo feedback control is performed based on the fixed inversion period.

The estimation of the chip temperature is performed in real time by the following approximate expression using the fuel injection amount for each time. Tn = Tn _-1 + AB Here, Tn is the chip temperature and Tn _-1 is the previous value. A is the amount of heat received by the O ₂ sensor 10, and B is the amount of heat released.

The amount of heat received A is calculated, for example, as A = Q.a. (900- _Tn-1 ). Here, Q is the total heat quantity obtained from the fuel injection quantity, and is calculated by, for example, Q = 1.6 · Ti. 1.6 is the processing cycle (seconds), and Ti is 1
It is the fuel injection amount per second.

Further, a is a calorific value conversion coefficient, and
(900-T _n-1 ) corresponds to the transfer rate.

The heat radiation amount B is set as B = b.Tn _-1 . Here, b is a heat dissipation coefficient. As shown in FIG. 3, this heat dissipation coefficient b is set to a smaller value as the outside air temperature is lower.

Next, the air-fuel ratio control of this embodiment will be specifically described with reference to the flow chart shown in FIG.

When the flowchart of FIG. 4 starts, first, in step S1, various signals such as engine speed, intake air amount, throttle valve opening, and O ₂ sensor output are read. Then, in S2, the basic injection amount is calculated from the engine speed and the intake air amount, and the process proceeds to S3.

In S3, it is determined whether or not the engine operating condition is in a predetermined feedback zone of low rotation and medium load. And when in the feedback zone, S4
Then, the feedback correction amount is calculated based on the output of the O ₂ sensor, and the process proceeds to S5.

At S5, it is determined whether or not the engine is idling based on the engine speed and the throttle valve opening. If it is in the idle state, the process proceeds to S6, the tip temperature Tn is predicted and calculated by the above approximate expression, and in S7, the normal O at the idle time is calculated.
₂ Measure the inversion cycle of the sensor output as a normal value.

Next, in S8, it is checked whether or not the idle has continued for a predetermined period. Then, if the exhaust temperature continues to drop for a long time as long as there is idle, it is checked in S9 whether the chip temperature is below the predetermined temperature α, and if it is below the predetermined temperature α, in S10, the feedback correction amount is replaced with the normal value. A correction amount corresponding to the above-mentioned normal value which is the inversion cycle at temperature is set. Then, in S11, the correction amount is added to the basic injection amount to obtain the final injection amount, and the injection signal corresponding to the final injection amount is output to the injector 5 in S12.

Even when the idle continues for a predetermined period, if the chip temperature does not fall below α, S
In step 11, the final injection amount is calculated using the feedback correction amount calculated in S4 as it is. In addition, even when the predetermined period has not elapsed after the idling, the process also proceeds to S11 and the final injection amount is calculated using the feedback correction amount.

When not in the feedback zone,
The process proceeds to S13, and the feedback correction amount is set to 0 (zero).

In the above embodiment, the amount of heat received by the air-fuel ratio sensor is calculated based on the fuel injection amount at the time of idling. However, even at the time of idling, the idling is performed while an external load such as a vehicle air conditioner is applied. When the intake air amount is increased to increase, the exhaust gas temperature becomes higher than that during normal idling because the air amount is large, so the amount of heat received may change as the intake air amount changes. In such a case, the amount of heat received may be calculated using the measured value of the intake air amount together with the set value of the fuel injection amount.

Further, in the above embodiment, when the chip temperature is lower than the set temperature, the pseudo feedback correction is performed based on the fixed inversion period fixed to the inversion period in the normal state, instead of the feedback correction based on the actual sensor output. Although it is performed, an embodiment is also possible in which the feedback control itself is not performed when the chip temperature is low.

Further, when the chip temperature is lower than the set temperature, fail display may be performed.

In the above embodiment, the lower the outside air temperature,
Although the heat dissipation coefficient in the approximate expression is increased, an embodiment in which this heat dissipation coefficient is fixed to a constant value is also possible, and since the amount of heat dissipation increases due to traveling wind as the vehicle speed increases, The coefficient may be set according to the vehicle speed.In that case, the heat dissipation coefficient is generally increased as the vehicle speed increases, but other settings may be possible in some cases, and a setting considering parameters other than the vehicle speed may also be used. It is possible.

The air-fuel ratio sensor is not limited to the O ₂ sensor.

[0057]

According to the air-fuel ratio control system for an engine of the first aspect of the present invention, the amount of heat received by the air-fuel ratio sensor is calculated based on the parameter related to the exhaust gas temperature, and
A heat radiation amount of the air-fuel ratio sensor is set using a predetermined heat radiation coefficient, and the detection element temperature of the air-fuel ratio sensor is estimated based on a value obtained by subtracting the set value of the heat radiation amount from the calculated value of the heat receiving amount. As a result, the detection element temperature can be accurately grasped without being affected by variations due to individual differences in the air-fuel ratio sensor.

Further, according to the second aspect of the present invention, the amount of heat received by the air-fuel ratio sensor is calculated based on the fuel injection amount which is directly related to the exhaust gas temperature, and the air-fuel ratio sensor is calculated using a predetermined heat dissipation coefficient. Since the amount of heat radiation is set and the detection element temperature of the air-fuel ratio sensor is estimated based on the value obtained by subtracting the set value of the amount of heat radiation from the calculated value of the amount of heat received, the accuracy of estimation of the detection element temperature can be improved. it can.

According to the third aspect of the present invention, the heat radiation amount is set by using the heat radiation coefficient corresponding to the idling state of the engine, so that the detection element temperature can be estimated in the idling state. The temperature can be estimated more accurately.

Further, according to the structure of claim 4, the heat radiation amount is set by using the heat radiation coefficient corresponding to the idle state, and then the detection element temperature is estimated during the idle state, so that The estimation accuracy of the detection element temperature can be further improved.

According to the fifth aspect of the invention, the detection element temperature is estimated based on the calculation of the heat receiving amount using the measured value of the intake air amount together with the set value of the fuel injection amount during idling. Accurate estimation can be performed even at idle-up.

According to the structure of claim 6, the inversion cycle of the output of the air-fuel ratio sensor when the detection element temperature is higher than the set temperature is stored, and when the estimated detection element temperature is equal to or lower than the set temperature, Feedback control based on the actual output of the air-fuel ratio sensor is stopped, and the air-fuel ratio of the air-fuel mixture sucked into the combustion chamber is set to the target air-fuel ratio based on the fixed inversion cycle fixed to the stored inversion cycle during normal operation. By performing the pseudo feedback control for performing the feedback control, it is possible to reduce the fluctuation of the air-fuel ratio when the detection element temperature does not reach the temperature at which the normal sensor function can be exhibited.

Further, according to the structure of claim 7, when the estimated detection element temperature is equal to or lower than the set temperature, the feedback control is stopped, so that the fluctuation of the air-fuel ratio can be reduced.

Further, according to the structure of claim 8, when the estimated detection element temperature is equal to or lower than the set temperature, it can be judged as a failure and fail display can be performed.

According to the ninth aspect of the invention, since the heat radiation coefficient is set according to the outside air temperature, it is possible to accurately set the heat radiation amount that changes depending on the outside air temperature.

Further, according to the structure of claim 10, the heat dissipation coefficient is set to a value such that the lower the outside air temperature, the larger the set value of the heat dissipation amount, and thus the heat dissipation amount increases as the outside air temperature lowers. It is possible to make highly accurate settings according to the characteristics.

According to the eleventh aspect of the invention, since the heat dissipation coefficient is set according to the vehicle speed, the amount of heat dissipation that changes depending on the vehicle speed can be set with high accuracy.

According to the twelfth aspect of the present invention, the heat dissipation coefficient is set to a value such that the greater the vehicle speed, the larger the set value of the heat radiation amount, so that the running wind increases the heat radiation amount as the vehicle speed increases. It is possible to set with high accuracy in accordance with the heat radiation characteristics.

According to the thirteenth aspect, since the heat radiation coefficient is set to a constant value, the detection element temperature estimation processing can be simplified.

According to the fourteenth aspect of the invention, the amount of heat received by the acidity concentration sensor is calculated based on the parameters such as the fuel injection amount related to the exhaust gas temperature, and the air-fuel ratio sensor of the air-fuel ratio sensor is calculated using a predetermined heat dissipation coefficient. A heat radiation amount is set, and the detection element temperature of the oxygen concentration sensor is estimated based on a value obtained by subtracting the set value of the heat radiation amount from the calculated value of the heat receiving amount, so that an approximate calculation can be accurately performed. .

Further, according to the structure of the fifteenth aspect, the initial purpose can be more surely achieved by setting the set temperature to an activation temperature at which the detection element normally functions.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of the present invention.

FIG. 2 is an overall system diagram of an embodiment of the present invention.

FIG. 3 is a characteristic diagram of a heat dissipation coefficient in the embodiment of FIG.

FIG. 4 is a flowchart for executing air-fuel ratio control of the embodiment shown in FIG.

[Explanation of symbols]

1 Engine 5 Injector 10 O ₂ Sensor 15 Control Unit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display area F02D 45/00 N

Claims (15)

[Claims] 1. An air-fuel ratio control device for an engine, comprising: feedback control means for feedback-controlling an air-fuel ratio of an air-fuel mixture drawn into a combustion chamber to a target air-fuel ratio based on an output of an air-fuel ratio sensor provided in an exhaust system. A sensor heat receiving amount calculating means for calculating a heat receiving amount of the air-fuel ratio sensor based on a parameter related to the exhaust gas temperature; and a sensor heat releasing amount setting means for setting a heat releasing amount of the air-fuel ratio sensor using a predetermined heat releasing coefficient. A sensor detection element temperature estimating means for estimating the detection element temperature of the air-fuel ratio sensor based on a value obtained by subtracting the set value of the heat radiation amount from the calculated value of the heat reception amount. Fuel ratio control device. 2. The air-fuel ratio control apparatus for an engine according to claim 1, wherein the parameter is a set fuel injection amount. 3. The air-fuel ratio control device for an engine according to claim 1, wherein the heat radiation amount is set by using a heat radiation coefficient corresponding to an idle state of the engine. 4. The engine air-fuel ratio control apparatus according to claim 3, wherein the sensor detection element temperature estimation means estimates the detection element temperature during idling. 5. The engine air-fuel ratio control device according to claim 4, wherein the parameters are a set fuel injection amount and an intake air amount. 6. A normal time reversal cycle storage means for storing a reversal cycle of the output of the air-fuel ratio sensor when the detection element temperature is higher than a set temperature, and a detection element temperature estimated by the sensor detection element temperature estimation means. Is equal to or lower than the preset temperature, the feedback control based on the actual output of the air-fuel ratio sensor by the feedback control means is stopped, and the fixed inversion fixed to the inversion cycle stored in the normal time inversion cycle storage means is stopped. 3. The engine air-fuel ratio control device according to claim 1, further comprising pseudo feedback control means for performing feedback control of the air-fuel ratio of the air-fuel mixture sucked into the combustion chamber to the target air-fuel ratio based on the cycle. 7. The feedback stop means for stopping the feedback control by the air-fuel ratio feedback control means when the detection element temperature estimated by the sensor detection element temperature estimation means is equal to or lower than the set temperature.
Alternatively, the air-fuel ratio control device for the engine according to item 2. 8. The engine according to claim 1, further comprising fail display means for displaying a fail indication when the detection element temperature estimated by the sensor detection element temperature estimation means is equal to or lower than the set temperature and is judged as a failure. Air-fuel ratio controller. 9. The air-fuel ratio control apparatus for an engine according to claim 1, wherein the heat dissipation coefficient is set according to the outside air temperature. 10. The air-fuel ratio control apparatus for an engine according to claim 9, wherein the heat dissipation coefficient is set to a value such that the set value of the heat dissipation increases as the outside air temperature decreases. 11. The air-fuel ratio control apparatus for an engine according to claim 1, wherein the heat dissipation coefficient is set according to the vehicle speed. 12. The air-fuel ratio control apparatus for an engine according to claim 11, wherein the heat dissipation coefficient is set such that the set value of the heat dissipation increases as the vehicle speed increases. 13. The heat dissipation coefficient is a constant value.
Alternatively, the air-fuel ratio control device for the engine according to item 2. 14. The engine air-fuel ratio control device according to claim 1, wherein the air-fuel ratio sensor detects the oxygen concentration in the exhaust gas. 15. The air-fuel ratio control device for an engine according to claim 6, 7 or 8, wherein the set temperature is an activation temperature at which the detection element normally functions.