JP2006307716A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct a sensor output characteristic depending on temperatures of a sub-O<SB>2</SB>sensor, and to control to keep a constant air-fuel ratio of an internal combustion engine. <P>SOLUTION: An air-fuel ratio control device has a linear air-fuel ratio sensor disposed upstream of a catalyst and the sub-O<SB>2</SB>sensor disposed downstream of the catalyst, and performs a main feedback control combined with a sub-feedback control. In the sub-feedback control (Yes in a step S10), when a calculated integrated intake air amount exceeds a predetermined value and a housing part temperature of the sub-O<SB>2</SB>sensor is stabilized (Yes in steps S11, S12), a supply amount of heat is calculated to calculate a temperature of the housing part (steps S13, S14). Then a sub-feedback control target voltage is calculated based on the temperature (a step S15). At this time, if the temperature is low, the target voltage is set to be higher. If the temperature is high, the target voltage is set to be low. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention includes a linear air-fuel ratio sensor provided on the upstream side of the catalyst and a sub oxygen sensor (hereinafter referred to as a sub O ₂ sensor) provided on the downstream side of the catalyst, and includes main feedback control and sub feedback control. More specifically, the sensor output characteristic can be corrected according to the temperature of the sub O ₂ sensor, and the internal combustion engine can be controlled to an equal air-fuel ratio. The present invention relates to an air-fuel ratio control device for an internal combustion engine.

2. Description of the Related Art Conventionally, an air-fuel ratio control apparatus for an internal combustion engine provided with a plurality of oxygen sensors in an exhaust passage in order to control the air-fuel ratio of the internal combustion engine is known. That is, the air-fuel ratio control apparatus for an internal combustion engine includes a linear air-fuel ratio sensor that detects an oxygen concentration in exhaust gas that is provided upstream of a catalyst disposed in an exhaust passage, and a catalyst that is provided downstream of the catalyst. And a sub-O ₂ sensor for detecting the oxygen concentration of the exhaust gas that has passed through the main feedback control for setting the air-fuel ratio of the exhaust gas flowing into the catalyst to the target air-fuel ratio based on the output of the linear air-fuel ratio sensor. On the other hand, based on the output of the sub O ₂ sensor, sub feedback control is performed to set the air-fuel ratio of the exhaust gas that has passed through the catalyst to the stoichiometric air-fuel ratio.

  Thus, in an internal combustion engine that executes a combination of main feedback control and sub feedback control, when main feedback control is ideally performed, rich or lean exhaust gas flows out downstream of the catalyst. There is nothing. The sub-feedback control is a control for correcting the control parameter of the main feedback control so that the deviation is corrected when the exhaust gas flowing out downstream of the catalyst is rich or lean.

For example, the control device calculates a predetermined corrected air-fuel ratio output based on the output of the linear air-fuel ratio sensor or the output of the sub O ₂ sensor, and the corrected air-fuel ratio output becomes a value corresponding to the target air-fuel ratio. A process for controlling the fuel injection amount is executed. The sub O ₂ sensor is a sensor that suddenly changes the output depending on whether the exhaust gas flowing out from the catalyst is rich or lean with respect to the stoichiometric air-fuel ratio. If the deviation between the output voltage of the sub O ₂ sensor and the target value of the output voltage (hereinafter referred to as the sub feedback control target voltage) can be made as small as possible, the rich or lean exhaust gas flows out downstream of the catalyst. This makes it possible to realize ideal feedback control without any problem.

Therefore, accurately setting the sub feedback control target voltage in accordance with the output characteristics of the sub O ₂ sensor is important in performing control to bring the air-fuel ratio of the exhaust gas closer to the stoichiometric air-fuel ratio. Therefore, a configuration example of a conventional sub O ₂ sensor will be specifically described.

FIG. 11 is a cross-sectional view showing a state in which the conventional sub O ₂ sensor is attached to the exhaust pipe. As shown in FIG. 11, the sub O ₂ sensor 24 is provided in the exhaust pipe 20 downstream of the catalyst (not shown). In the sub O ₂ sensor 24, a sensor element 24a is supported by a protective cover 24b, and the protective cover 24b is held by the housing portion 24c via a talc sealing portion 24d, a sealing member 24k, and the like.

  The housing portion 24c includes an inner cover 24f that covers the tip of the protective cover 24b, and an outer cover 24h. The inner cover 24f is provided with a plurality of vent holes 24g, and the outer cover 24h is also provided with a plurality of vent holes 24j. The housing portion 24c is fixed to the exhaust pipe 20 via a washer 24e so that the outer cover 24h protrudes into the exhaust pipe 20.

  As a related prior art, a technique for setting a high target voltage when the temperature is high in an oxygen sensor using a relationship between internal resistance and temperature has been proposed (for example, see Patent Document 1).

  In addition, a technology has been proposed for detecting the concentration of a component to be detected in exhaust gas with high accuracy by performing temperature control and temperature correction of the concentration cell element in consideration of the relationship between the internal resistance of the concentration cell element and the temperature. (For example, see Patent Document 2).

JP-A-9-49448 JP-A-10-260158

Since the conventional sub O ₂ sensor 24 is configured as described above, as shown by a circle in FIG. 11, an airtight leak may occur at an engagement portion between the protective cover 24b and the housing portion 24c. On the other hand, it is difficult to completely eliminate this airtight leakage.

When an airtight leak occurs at such a location, for example, as shown in FIG. 12, air from the outside enters the gap between the protective cover 24b and the inner cover 24f and mixes with the exhaust gas that has entered through the vent holes 24j and 24g. For this reason, the oxygen concentration of the exhaust gas becomes high, and the output characteristic of the sub O ₂ sensor 24 with respect to the exhaust gas air-fuel ratio changes. Here, FIG. 12 is a cross-sectional view schematically showing the flow of exhaust gas and airtight leakage with respect to the sub O ₂ sensor.

Further, as shown in FIG. 13, the airtight leakage amount changes depending on the temperature of the housing portion 24c of the sub O ₂ sensor 24, and the change in the airtight leakage amount increases as the temperature increases. Alternatively, air leakage quantity, the temperature and the sensor element 24a of the sub O ₂ sensor 24, varies with the temperature of the sub-O ₂ sensor 24 near the exhaust pipe 20, these changes significantly as the temperature becomes higher. Here, FIG. 13 is a graph showing the relationship between the temperature of the housing portion of the sub O ₂ sensor and the amount of airtight leakage.

Further, as shown in FIG. 14, the λ (excess air ratio) characteristic changes due to the change in the amount of airtight leakage due to the influence of the temperature of the housing portion 24c. That is, when the temperature of the housing part 24c is high, it is indicated by a solid line, and when it is low, it is indicated by a one-dot chain line. When the temperature of the housing part 24c is high (see point A) and low (see point B) The output of the sub O ₂ sensor 24 is lower than Here, FIG. 14 is a graph showing the influence of the temperature of the housing portion on the output characteristics of the sub O ₂ sensor.

  In addition, as shown in FIG. 15, when the above-mentioned sub feedback (in the figure, indicated as sub F / B) control target voltage is set to be almost constant regardless of the temperature of the housing portion 24c (see the two-dot chain line), When the temperature of the housing portion 24c becomes high and low, a large deviation as indicated by an arrow occurs with respect to the sub feedback control target voltage to be actually set (see the solid line). Here, FIG. 15 is a graph showing the relationship between the estimated temperature of the housing portion and the sub feedback control target voltage.

For example, when a vehicle equipped with the internal combustion engine is left in idle operation, the sub O ₂ sensor 24 exposed to the exhaust gas is at a relatively low temperature, but decelerates after high load traveling and performs idle operation. In this case, since the sub O ₂ sensor 24 becomes high temperature, the temperature change of the sub O ₂ sensor 24 also becomes large. When this temperature change becomes large, the amount of airtight leakage of the sub O ₂ sensor 24 also changes greatly, and the output characteristics with respect to the exhaust gas air-fuel ratio tend to change.

Accordingly, the output characteristics of the sub O ₂ sensor 24 by a change in air leakage amount due to a temperature change of the sub-O ₂ sensor 24 Te to vary, it is difficult to control the internal combustion engine to equal air. As a result, the internal combustion engine emission may be deteriorated.

The present invention has been made in view of the above, and it is possible to correct the output characteristics according to the temperature of the sub O ₂ sensor, and to control the internal combustion engine to an equal air-fuel ratio. An object of the present invention is to provide a fuel ratio control device.

  In order to solve the above-described problems and achieve the object, an air-fuel ratio control apparatus for an internal combustion engine according to claim 1 of the present invention is provided upstream of a catalyst disposed in an exhaust passage, and has an oxygen concentration in exhaust gas. And a sub-oxygen sensor that is provided downstream of the catalyst and detects the oxygen concentration of the exhaust gas that has passed through the catalyst, and based on the output of the linear air-fuel ratio sensor Main feedback control is performed to set the air-fuel ratio of the exhaust gas flowing into the engine to a target air-fuel ratio, while the air-fuel ratio of the exhaust gas that has passed through the catalyst is set to the stoichiometric air-fuel ratio based on the output of the sub oxygen sensor In an air-fuel ratio control apparatus for an internal combustion engine that performs sub-feedback control, the temperature of the sub oxygen sensor or the temperature of the exhaust passage in the vicinity of the sub oxygen sensor is detected or estimated When the sub-feedback control is performed and the temperature detected or estimated by the temperature detection unit is low, a target output of the sub oxygen sensor is set high, and the temperature detection unit And a target output setting means for setting a target output of the sub oxygen sensor low when the detected or estimated temperature is high.

  Therefore, according to the present invention, when performing the sub-feedback control, if the temperature of the sub oxygen sensor detected or estimated by the temperature detecting means or the temperature of the exhaust passage near the sub oxygen sensor is low, the sub oxygen sensor On the other hand, when the temperature is high, the target output of the sub oxygen sensor is set low. Thereby, the output characteristic is corrected according to the temperature of the sub oxygen sensor or the temperature of the exhaust passage in the vicinity of the sub oxygen sensor.

  An air-fuel ratio control apparatus for an internal combustion engine according to a second aspect of the present invention provides the air-fuel ratio control apparatus according to the first aspect of the present invention by the temperature detection means when the integrated value of the intake air amount of the internal combustion engine exceeds a predetermined value. The temperature of the sub oxygen sensor or the temperature of the exhaust passage in the vicinity of the sub oxygen sensor is detected or estimated.

  Therefore, according to the present invention, after the difference between the temperature of the exhaust gas and the temperature of the sub oxygen sensor or the exhaust passage in the vicinity of the sub oxygen sensor is reduced and the temperature of the sub oxygen sensor is stabilized, the sub oxygen sensor or the like The temperature is detected or estimated. Thus, the target output of the sub oxygen sensor can be set with high accuracy by the target output setting means based on the stable temperature information.

  According to a third aspect of the present invention, there is provided an air-fuel ratio control apparatus for an internal combustion engine according to the first or second aspect, wherein the sub oxygen sensor is disposed in the sub oxygen sensor or an exhaust passage near the sub oxygen sensor. A cooling means for cooling is provided.

  When a vehicle equipped with an internal combustion engine is left in idle operation, the sub oxygen sensor exposed to the exhaust gas is at a relatively low temperature, but when the vehicle is decelerated after high load driving and idle operation is performed, The oxygen sensor becomes hot. As described above, when the temperature of the sub oxygen sensor is changed, the airtight leakage amount of the sub oxygen sensor is also changed, and the output characteristic with respect to the exhaust gas air-fuel ratio is easily changed.

  Therefore, for example, the sub oxygen sensor is directly cooled by cooling the casing of the sub oxygen sensor by the cooling means, or the sub oxygen sensor is indirectly cooled by cooling the exhaust passage near the sub oxygen sensor by the cooling means. Cool down.

  Thus, by cooling the sub oxygen sensor and maintaining a stable temperature state, the air leak rate of the sub oxygen sensor becomes constant, and the λ (excess air ratio) characteristic due to the air leak rate difference is stabilized. The engine can be controlled with an equal air fuel ratio. Thereby, it is possible to suppress the deterioration of the emission due to the deviation of the control air-fuel ratio of the internal combustion engine.

  According to the air-fuel ratio control apparatus for an internal combustion engine according to the present invention (claim 1), the output characteristics can be corrected in accordance with the temperature of the sub oxygen sensor or the temperature of the exhaust passage in the vicinity of the sub oxygen sensor. The engine can be controlled to an equal air fuel ratio. Accordingly, it is possible to suppress the deterioration of the emission of the internal combustion engine.

  According to the air-fuel ratio control apparatus for an internal combustion engine according to the present invention (Claim 2), the difference between the temperature of the exhaust gas and the temperature of the sub oxygen sensor or the exhaust passage in the vicinity of the sub oxygen sensor is reduced. Since the temperature of the sub oxygen sensor or the like is detected or estimated after the temperature of the oxygen sensor is stabilized, the target output of the sub oxygen sensor can be set with high accuracy.

  Further, according to the air-fuel ratio control apparatus for an internal combustion engine according to the present invention (Claim 3), by cooling the sub oxygen sensor and maintaining a stable temperature state, the amount of airtight leakage of the sub oxygen sensor becomes constant, Since the λ characteristic due to the difference in the airtight leakage amount is stabilized, the internal combustion engine can be controlled with an equal air-fuel ratio. Thereby, it is possible to suppress the deterioration of the emission due to the deviation of the control air-fuel ratio of the internal combustion engine.

  Embodiments of an air-fuel ratio control apparatus for an internal combustion engine according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

  FIG. 2 is a schematic diagram illustrating the air-fuel ratio control apparatus for the internal combustion engine according to the first embodiment. In the following description, members that are the same as or correspond to those already described are denoted by the same reference numerals, and redundant description is omitted or simplified.

  As shown in FIG. 2, an internal combustion engine (hereinafter, appropriately referred to as an engine) 10 is provided with an intake pipe 30 and an exhaust pipe (exhaust passage) 20. In order to purify the exhaust gas, for example, an upstream catalyst (catalyst) 21 and a downstream catalyst 22 which are three-way catalysts are arranged in series in the exhaust pipe 20.

  That is, exhaust gas discharged from the internal combustion engine 10 is first purified by the upstream catalyst 21, and exhaust gas that could not be purified by the upstream catalyst 21 is purified by the downstream catalyst 22.

  These catalysts 21 and 22 can store a predetermined amount of oxygen, and store unburned components such as hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas. If the exhaust gas contains oxidizing components such as nitrogen oxides (NOx), they can be reduced and occluded oxygen can be stored. It is configured to be able to.

  A linear air-fuel ratio sensor 23 that detects the oxygen concentration in the exhaust gas is provided upstream of the upstream catalyst 21. That is, the linear air-fuel ratio sensor 23 detects the air-fuel ratio of the air-fuel mixture burned in the internal combustion engine 10 based on the oxygen concentration of the exhaust gas flowing into the upstream side catalyst 21.

Further, a sub O ₂ sensor 24 serving as a means for detecting the oxygen concentration in the exhaust gas is provided downstream of the upstream catalyst 21. That is, the sub O ₂ sensor 24 is a fuel-rich exhaust gas (an exhaust gas containing HC and CO) or a fuel-lean exhaust gas based on the oxygen concentration of the exhaust gas flowing out of the upstream catalyst 21. Whether or not (exhaust gas containing NOx) is detected. The upstream catalyst 21 is also provided with a temperature sensor (not shown) for detecting the exhaust gas temperature.

Further, details of the structure of the sub O ₂ sensor 24 and its mounting structure are as shown in FIG. Temperature sensor 25 serves to detect the temperature of the exhaust pipe 20 of the temperature or sub-O ₂ sensor 24 near the housing portion 24c of the sub-O ₂ sensor 24.

The temperature sensor 25 is not necessarily required as long as the temperature of the sub O ₂ sensor 24 can be estimated as shown in steps S13 and S14 of FIG.

  The intake pipe 30 includes an air filter 31, an intake air temperature sensor 32 that detects the intake air temperature, an air flow meter 33 that detects the intake air amount, a throttle valve 34, a throttle sensor 35 that detects the throttle opening, and a fully closed state of the throttle valve 34. An idle switch 36, a surge tank 37, a fuel injection valve 38, and the like are provided.

The electronic control unit (hereinafter referred to as ECU) 41 is connected to various sensors such as the linear air-fuel ratio sensor 23, the sub O ₂ sensor 24, the vehicle speed sensor 39, and the cooling water temperature sensor 40, and outputs the sensor output values. Based on this, the air-fuel ratio of the internal combustion engine 10 is controlled and operated.

  In addition, the ECU 41 executes a combination of main feedback control and sub feedback control in the same manner as the above-described conventional control.

Further, the ECU 41 functions as a temperature detecting means for detecting or estimating the temperature of the sub O ₂ sensor 24.

Further, when performing the sub-feedback control, the ECU 41 sets the sub-feedback control target voltage of the sub O ₂ sensor 24 high when the estimated temperature is low, and sub-feedback when the estimated temperature is high. It functions as target output setting means for setting the control target voltage low.

  The control operation according to the first embodiment will be described below with reference to FIG. Here, FIG. 1 is a flowchart showing a control operation according to Embodiment 1 of the present invention. The following control is executed by the ECU 41.

  As shown in FIG. 1, first, it is determined whether or not an execution condition for sub feedback control (referred to as sub F / B control in FIG. 1) is satisfied (step S10). If the execution condition is not satisfied (No at Step S10), the control ends because it is out of the scope of this control. On the other hand, if the execution condition is satisfied (Yes at Step S10), the process proceeds to the next Step S11.

  In step S11, the integrated intake air amount is calculated by integrating the intake air amount detected by the air flow meter 33. Then, it is determined whether or not the integrated intake air amount exceeds a predetermined value (step S12).

This predetermined value is such that, when the internal combustion engine 10 is operated for a predetermined time, the difference between the temperature of the exhaust gas and the temperature of the sub O ₂ sensor 24 or the housing portion 24c becomes small, and the temperature of the sub O ₂ sensor 24 is stabilized. This is a threshold value for determining whether or not it has been obtained, and is obtained in advance by experiments or the like.

By determining in this way, it is possible to estimate the stable temperature of the housing portion 24c in the next steps S13 to S14. Accordingly, in step S15 described later, the sub O ₂ sensor is based on the stable temperature information. The 24 sub-feedback control target voltages can be set with high accuracy.

If the integrated intake air amount exceeds the predetermined value (Yes at Step S12), it can be determined that the temperature of the sub O ₂ sensor 24 is stable, and the process proceeds to the next Step S13. In step S13, the engine speed, the engine load factor, the engine coolant temperature, the ignition timing, the fuel injection amount, etc. are read based on the sensor information and the like, and the amount of heat supplied to the internal combustion engine 10 is calculated.

Next, based on the supplied heat quantity calculated in step S13, the temperature of the housing portion 24c of the sub O ₂ sensor 24 is calculated and estimated (step S14). The relationship between the amount of heat supplied and the temperature of the housing portion 24c can be created in advance as a map by experiments or the like, and the temperature of the housing portion 24c can be estimated by referring to this map.

  In step S15, the sub feedback control target voltage is calculated using the estimated temperature of the housing portion 24c calculated in step S14. That is, since the relationship between the estimated temperature of the housing portion 24c and the sub feedback control target voltage can be prepared in advance by experiments or the like as shown in FIG. The feedback control target voltage can be calculated.

Here, FIG. 3 is a map for correcting the sub-feedback control target voltage based on the estimated temperature of the housing portion 24c. In the map shown in FIG. 3, when the estimated temperature of the housing portion 24c is low, the sub feedback control target voltage of the sub O ₂ sensor 24 is set high, and when the estimated temperature is high, the sub feedback control target voltage is set. It is designed to be set low.

By performing the control as described above, the deviation of the sub feedback control target voltage shown in FIG. 15 is corrected according to the temperature of the housing portion 24c of the sub O ₂ sensor 24, and the sub feedback control is executed with high accuracy. Therefore, the internal combustion engine 10 can be controlled to an equal air fuel ratio. As a result, the deterioration of the emission of the internal combustion engine 10 can be suppressed.

In the first embodiment, the temperature of the housing portion 24c of the sub O ₂ sensor 24 is estimated in step S14 shown in FIG. 1. However, the present invention is not limited to this. For example, the temperature of the housing portion 24c is set. You may measure and detect directly with the temperature sensor 25. FIG.

Further, the temperature of the exhaust pipe 20 in the vicinity of the sub O ₂ sensor 24 may be directly measured and detected by the temperature sensor 25, or the temperature may be estimated.

4 is a cross-sectional view showing a water-cooled pipe provided in the exhaust pipe 20 near the sub O ₂ sensor 24 according to Embodiment 2 of the present invention, and FIG. 5 is a plan view showing the water-cooled pipe.

As shown in FIGS. 4 and 5, the water cooling pipe (cooling means) 50 is provided in the exhaust pipe 20 so as to surround the vicinity of the sub O ₂ sensor 24 in an arc shape. For example, the engine cooling water of the internal combustion engine 10 can be used as the cooling water to the water cooling pipe 50, but a cooling system independent of this can also be provided.

By flowing cooling water through the water cooling pipe 50 configured in this way, the exhaust pipe 20 provided with the water cooling pipe 50 is cooled, and as a result, the housing portion 24c of the sub O ₂ sensor 24 is cooled.

  When the housing portion 24c is cooled by water cooling, the temperature change region of the housing portion 24c is reduced, so that the change range of the conventional airtight leakage amount is large as shown in FIG. The change range of can be considerably reduced. Here, FIG. 6 is a graph showing the effect of reducing the temperature change region of the housing portion 24c and the change region of the airtight leakage amount.

As described above, according to the second embodiment, since the change range of the airtight leakage amount can be reduced, the output characteristics of the sub O ₂ sensor 24 can be stabilized.

  The second embodiment can be implemented independently of the first embodiment, but by adding the configuration of the second embodiment to the configuration of the first embodiment, the sub-feedback control can be executed with higher accuracy. it can.

In the second embodiment, the water cooling pipe 50 is described as being provided in the exhaust pipe 20 so as to surround the vicinity of the sub O ₂ sensor 24 in an arc shape. However, the present invention is not limited to this. For example, FIG. As shown, the vicinity of the sub O ₂ sensor 24 may be provided in the exhaust pipe 20 so as to surround the U-shape. Here, FIG. 7 is a plan view showing another water-cooled pipe 50. Further, the shape of the water cooling pipe 50 may be other than the square.

FIG. 8 is a sectional view showing air cooling fins provided in the exhaust pipe 20 near the sub O ₂ sensor 24 according to Embodiment 3 of the present invention, and FIG. 9 is a plan view showing the air cooling fins.

As shown in FIGS. 8 and 9, the air cooling fins (cooling means) 55 are provided in the exhaust pipe 20 so as to concentrically surround the vicinity of the sub O ₂ sensor 24. When the running wind hits the air cooling fin 55 configured as described above, the exhaust pipe 20 is cooled, and as a result, the housing portion 24c of the sub O ₂ sensor 24 is cooled.

  When the housing portion 24c is cooled by air cooling, although not as much as in the case of the water cooling according to the second embodiment, the temperature change region of the housing portion 24c is reduced, so that as shown in FIG. While the change range of the quantity is large, the change range can be reduced.

As described above, according to the third embodiment, the change range of the airtight leakage amount can be reduced, so that the output characteristics of the sub O ₂ sensor 24 can be stabilized.

  The third embodiment can be implemented independently of the first embodiment, but by adding the configuration of the third embodiment to the configuration of the first embodiment, the sub-feedback control can be executed with higher accuracy. it can.

In the third embodiment, the air cooling fin 55 is described as being provided in the exhaust pipe 20 so as to be concentrically surrounded in the vicinity of the sub O ₂ sensor 24. However, the present invention is not limited to this. For example, FIG. Thus, it may be provided in parallel along the outer periphery of the exhaust pipe 20 in the vicinity of the sub O ₂ sensor 24. Here, FIG. 10 is a plan view showing another air cooling fin 55.

Although not shown in the figure, the air cooling fins 55 may be provided spirally along the outer periphery of the exhaust pipe 20 near the sub O ₂ sensor 24.

As described above, the air-fuel ratio control apparatus for an internal combustion engine according to the present invention includes the linear air-fuel ratio sensor provided on the upstream side of the catalyst and the sub O ₂ sensor provided on the downstream side of the catalyst, and the main feedback This is useful for an internal combustion engine that executes a combination of control and sub-feedback control. In particular, the sensor output characteristic can be corrected in accordance with the temperature of the sub O ₂ sensor, and the internal combustion engine is controlled to an equal air-fuel ratio. Suitable for control devices aiming for.

It is a flowchart which shows the control action which concerns on Example 1 of this invention. It is a schematic diagram which shows the air fuel ratio control apparatus of an internal combustion engine. It is a map for correct | amending a sub feedback control target voltage based on the estimated temperature of a housing part. Is a sectional view showing a water cooling pipe provided in an exhaust pipe of the sub O ₂ sensor vicinity according to a second embodiment of the present invention. It is a top view which shows water cooling piping. It is a graph which shows the effect in which the temperature change area of a housing part and the change area of an airtight leak amount become small. It is a top view which shows other water cooling piping. Is a sectional view showing a cooling fin provided in an exhaust pipe of the sub O ₂ sensor vicinity according to a third embodiment of the present invention. It is a top view which shows an air cooling fin. It is a top view which shows another air cooling fin. It is a sectional view showing a mounting state to the exhaust pipe of the conventional sub O ₂ sensor. The state of the sub-O flow of exhaust gas to ₂ sensor and air leakage is a cross-sectional view schematically showing. A graph showing the relationship between the temperature and the air leakage amount of the housing portion of the sub O ₂ sensor. The temperature of the housing unit is a graph showing the effect on the output characteristics of the sub O ₂ sensor. It is a graph which shows the relationship between the estimated temperature of a housing part, and a sub feedback control target voltage.

Explanation of symbols

10 Internal combustion engine 20 Exhaust pipe (exhaust passage)
21 Upstream catalyst (catalyst)
22 downstream catalyst 23 linear air-fuel ratio sensor 24 sub O ₂ sensor (sub oxygen sensor)
41 ECU (air-fuel ratio control device, temperature detection means, target output setting means)
50 Water-cooled piping (cooling means)
55 Air cooling fin (cooling means)

Claims (3)

A linear air-fuel ratio sensor which is provided upstream of the catalyst disposed in the exhaust passage and detects the oxygen concentration in the exhaust gas;
A sub oxygen sensor that is provided downstream of the catalyst and detects an oxygen concentration of the exhaust gas that has passed through the catalyst;
With
While performing a main feedback control for setting the air-fuel ratio of the exhaust gas flowing into the catalyst to the target air-fuel ratio based on the output of the linear air-fuel ratio sensor,
In the air-fuel ratio control apparatus for an internal combustion engine that performs sub-feedback control for setting the air-fuel ratio of the exhaust gas that has passed through the catalyst to the stoichiometric air-fuel ratio based on the output of the sub-oxygen sensor,
Temperature detecting means for detecting or estimating the temperature of the sub oxygen sensor or the temperature of the exhaust passage in the vicinity of the sub oxygen sensor;
When the sub-feedback control is performed, if the temperature detected or estimated by the temperature detection means is low, the target output of the sub oxygen sensor is set high,
When the temperature detected or estimated by the temperature detection means is high, target output setting means for setting the target output of the sub oxygen sensor low;
An air-fuel ratio control apparatus for an internal combustion engine, comprising:   2. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein when the integrated value of the intake air amount of the internal combustion engine exceeds a predetermined value, the temperature detection means detects or estimates the temperature.   The air-fuel ratio control of the internal combustion engine according to claim 1 or 2, wherein the exhaust passage in the vicinity of the sub oxygen sensor or the sub oxygen sensor is provided with a cooling means for cooling the sub oxygen sensor. apparatus.

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