JP2591203B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device for an internal combustion engine, and more particularly to an air-fuel ratio control for richly controlling the air-fuel ratio when the exhaust temperature of the internal combustion engine is equal to or higher than a predetermined temperature. Related to the device.

[Conventional technology]

A catalytic device for purifying exhaust gas of an internal combustion engine can reduce harmful components in the exhaust gas by operating in a predetermined temperature range. When the temperature becomes higher than the predetermined allowable temperature range, the catalyst device is overheated, and the catalyst is deteriorated or damaged.

Therefore, in order to reduce the exhaust gas temperature at a high temperature exceeding the allowable temperature range, the temperature of the exhaust gas flowing into the turbine casing of the turbocharger is directly detected by an exhaust gas temperature sensor, and the detected exhaust gas temperature is reduced. There is known an air-fuel ratio control device that controls the air-fuel ratio to be a predetermined value to thereby prevent thermal destruction of a supercharger and exhaust system components (Japanese Patent Application Laid-Open No. 56-81235).

However, in this conventional device, an exhaust gas temperature, that is, an exhaust gas temperature sensor that detects an exhaust gas temperature is directly exposed to an extremely high exhaust gas temperature, so that expensive materials with excellent heat resistance must be used. However, it is expensive and has a problem in durability. Moreover, since the temperature of the flowing exhaust gas is measured, the detection temperature changes depending on how the exhaust gas hits the exhaust gas temperature sensor, and it is difficult to accurately detect the exhaust gas temperature.

Therefore, instead of directly detecting the exhaust gas temperature, instead of detecting the exhaust gas temperature, the ratio of the intake air amount to the engine speed and the throttle opening are detected, and the exhaust gas temperature is measured based on this, and the air-fuel ratio control is performed. An air-fuel ratio control device has been proposed.
JP-A-58-51241, JP-A-60-53645, JP-A-62-876
No. 35).

However, in this conventional device, since the state of the internal combustion engine is not directly grasped, the exhaust gas temperature control corresponding to changes in the temperature inside the engine (for example, the temperature of the engine cooling water) and the temperature outside the engine (for example, the temperature in the engine room). Can not be exactly.

Therefore, conventionally, the combustion heat (the amount of heat generated by combustion) is roughly estimated from the engine operating state, the exhaust gas temperature is estimated based on the combustion heat, and the air-fuel ratio is controlled to be rich when the exhaust gas temperature is equal to or higher than a predetermined temperature. An apparatus has been proposed (see
No. 62-203965).

[Problems to be solved by the invention]

However, the exhaust gas temperature is not determined by the combustion heat, but is also affected by the cooling loss. For this reason, the conventional air-fuel ratio control device that estimates the exhaust gas temperature from the above estimated combustion heat cannot accurately grasp the exhaust gas temperature, and therefore controls the air-fuel ratio so that the exhaust gas temperature falls within a predetermined temperature range. However, the temperature may exceed the allowable temperature range.

The present invention has been made in view of the above points, and an object of the present invention is to provide an air-fuel ratio control device that solves the above-described problem by estimating an exhaust gas temperature from an engine operating state and a heat flux of a head unit. I do.

[Means for solving the problem]

FIG. 1 is a principle structural diagram of an air-fuel ratio control device according to the present invention. The present invention relates to an air-fuel ratio control device that changes the air-fuel ratio to a rich side in accordance with the exhaust gas temperature when the temperature of the exhaust gas of the internal combustion engine 11 exceeds a predetermined temperature. 13, Exhaust temperature calculation means 14, Comparison means 1
5 and control means 16 are provided.

The heat flux detecting means 12 measures the heat flux of the gas flowing through a part of the cylinder head of the internal combustion engine 11, and the operating state detecting means 13 detects the operating state of the internal combustion engine 11. Also,
The exhaust gas temperature calculating means 14 calculates the exhaust gas temperature based on the detected values of the heat flux detecting means 12 and the operating state detecting means 13.

The comparing means 15 compares the exhaust gas temperature with a preset allowable value of the exhaust gas temperature, and based on the comparison result, the control means 16
Controls the air-fuel ratio to be richer than at the time of the previous air-fuel ratio control when at least the exhaust gas temperature exceeds the allowable value.

[Action]

In view of the fact that the temperature of the exhaust gas, that is, the exhaust gas temperature is affected by the cooling loss, and the cooling loss can be grasped by the heat flux, the present invention detects the engine operating state by the operating state detecting means 13 and detects the cooling loss by the heat flux detecting means. Estimate from the heat flux measured by 12. That is, the heat flux detecting means 12 directly measures the calorific value of the gas flowing in the cylinder head of the internal combustion engine 11, and estimates the cooling loss from the calorific value.

As a result, the exhaust gas temperature calculating means 14 calculates and calculates an estimated value of the exhaust gas temperature in consideration of the cooling loss.

As a result, when the comparison means 15 and the control means 16 control the air-fuel ratio in accordance with the calculated exhaust gas temperature, the air-fuel ratio can be controlled in consideration of the cooling loss.

〔Example〕

FIG. 2 shows a configuration diagram of an embodiment of the apparatus of the present invention. The present embodiment is an example in which the present invention is applied to a supercharged six-cylinder spark ignition type internal combustion engine (engine) as an internal combustion engine, and is controlled by a microcomputer 20 described later.

In FIG. 2, the downstream side of the air cleaner 21 burns an engine body 28 (corresponding to the internal combustion engine 11) via an air flow meter 22, an intake passage 23, a throttle valve 24, a surge tank 25, an intake manifold 26, and an intake valve 27. It is connected to room 29.

The engine body 28 includes a cylinder block 30 and a cylinder head 31, and a piston 32 is provided in the cylinder block 30.
Are housed in the cylinder head 29 and the combustion chamber 29
An ignition plug 32 is provided for each cylinder so that a part thereof protrudes. The intake manifold 26 is provided with a fuel injection valve 33 for each cylinder so that a tip portion protrudes into the intake manifold 26. The igniter 34 generates a high voltage based on an ignition instruction signal from the microcomputer 20, and supplies the high voltage to the ignition plug 32 via the distributor 35.

The combustion chamber 29 of the engine body 28 is connected to an exhaust passage 38 via an exhaust valve 36 and an exhaust manifold 37. The intake passage 23 on the upstream side of the throttle valve 24
A compressor 39 is provided therein, and a turbine 40 is mounted on the exhaust passage 38 coaxially with the compressor 39. In addition, a waste gate valve 42 is provided at a suction port on the exhaust manifold 37 side of the bypass passage 41 that connects the upstream side and the downstream side of the turbine 40 and bypasses the turbine 40, and closes or opens the suction port. It is configured to be controlled by an actuator 44 via a link mechanism 43. The actuator 44 is connected to the intake passage
The operation is controlled by the air pressure introduced through a passage 45 communicating with 23.

Here, when the exhaust gas flowing through the exhaust manifold 37 flows into the turbine 40 and rotates the turbine 40, the compressor 39 also rotates accordingly, and the air flow meter 22
The intake air that has passed through is compressed by the compressor 39,
The high-density air is sent to the combustion chamber 29 via the surge tank 25 and the intake manifold 26 to increase the output. At this time, when the supercharging pressure is equal to or lower than the set value, the actuator 44 does not operate and the waste gate valve 42 is closed, so that the exhaust gas flows into the turbine 40 in its entirety.
However, when the supercharging pressure rises due to the high engine speed, and becomes higher than a set value, the actuator 44 is operated by air pressure higher than a predetermined value inputted through the passage 45, and the link mechanism is operated.
The waste gate valve 42 is moved to the left in the drawing via 43 to open the intake port of the exhaust manifold 37. As a result, a part of the exhaust gas flowing into the turbine 40 is bypassed through the bypass passage 41, so that the rotation speed of the turbine 40 is reduced. In this way, the supercharging pressure is controlled to be constant.

In this embodiment, various sensor groups are provided. That is, an intake air temperature sensor 47 for measuring the temperature of air taken out of the air cleaner 21 and taken into the air flow meter 22 is provided so as to partially pass through the engine block 30 and protrude into the water jacket. Temperature sensor 48, an idle switch 49 that is turned on when the opening of the throttle valve 24 is fully closed, and a rotation angle sensor that outputs a pulse at predetermined crank angles in synchronization with the rotation of the shaft of the distributor 35 (fourth sensor). 50 in the figure
, A cylinder discrimination sensor (shown by 51 in FIG. 4) that outputs a crank position detection signal from the rotation of the distributor 35, a part of which is provided protruding from the exhaust passage 38, and is input to the catalyst device 46. An enzyme temperature detection sensor (O ₂ sensor) 52 for detecting the oxygen concentration in the previous exhaust gas is provided.

In such a configuration, in the present embodiment, a heat flux sensor 19 corresponding to the above-described heat flux detecting means 12 is provided at a predetermined position of the engine main body 28. Next, the arrangement and structure of the heat flux sensor 19 will be described with reference to FIG. It is explained together with. Fig. 3 (A)
Is a schematic view of the combustion chamber 29 as viewed from the side of the ignition plug 32. The intake valves 27a and 27b and the exhaust valves 36a and 36b (the intake valves 27 and the exhaust valves 36 in FIG. 2 are 27a and 36a or 27b and 36b). A heat flux sensor 19 for measuring the amount of heat flowing therethrough is provided at a desired portion of the combustion chamber 29 which communicates with the intake manifold 26 and the exhaust manifold 37 via a).

As shown in FIG. 3B, the heat flux sensor 19 is provided with a first temperature sensing element 56a and a second temperature sensing element 56b along the longitudinal direction of the sensor main body 55, and the first and second temperature sensing elements 56b are provided. This is a configuration that generates a heat flux signal indicating a difference between the temperatures of the gases detected by the two temperature sensing elements 56a and 56b (that is, a temperature difference between two points of the temperature sensing elements 56a and 56b). As a result, carbon adheres to the wall surface of the combustion chamber 29 due to aging and solid differences, and the heat transfer coefficient of the wall surface decreases, and the exhaust gas temperature rises despite the relatively low head wall temperature. However, the heat flux sensor 19 can provide a heat flux signal corresponding to the exhaust gas temperature.

Next, the microcomputer 20 for controlling the apparatus of this embodiment
Will be described with reference to FIG. 4, the same components as those in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted. In FIG. 4, a microcomputer 20 includes a central processing unit (CPU) 60, a read only memory (ROM) 61 storing a processing program, a random access memory (RAM) 62 used as a work area, and an engine stop. Backup RAM 63 and CPU 6 that retain data afterwards
Clock generator 64 supplying its master clock to 0
These are connected to each other via a bidirectional bus line 65, and are connected to an input / output port 66, an input port 67, and an output interface circuit 68, respectively.

Further, the microcomputer 20 detects the detection signal from the air flow meter 22 taken out through the buffer 69, the intake temperature detection signal from the intake temperature sensor 47 taken out through the buffer 70, and the water temperature sensor taken out through the buffer 71.
A multiplexer 73 selects a water temperature sensor signal (THW) from 48 and a heat flux signal from the heat flux sensor 19 extracted via the buffer 72.

As a result, each input detection signal of the multiplexer 73 becomes CP
After being selectively output from the multiplexer 73 under the control of U60, the signal is converted into a digital signal by the A / D converter 74, and then stored in the RAM 62 via the input / output port 66.

The microcomputer 20 receives the oxygen temperature detection signal from the O ₂ sensor 52 through a buffer
A signal obtained by shaping the waveform here and supplying it to the input port 67, and also shaping the waveform of each detection signal from the rotation angle sensor 50 and the cylinder discrimination sensor 51 by the waveform shaping circuit 77;
The output signal of the idle switch 49 that has passed through a buffer (not shown) is supplied to the input port 67, respectively.

Further, the microcomputer 20 outputs each control signal for controlling the fuel injection valve 33 and the igniter 34 via the output interface circuit 68 based on the output data of the CPU 60.

The microcomputer 20 having such a hardware configuration
Constitute the exhaust gas temperature calculation means 14, the comparison means 15, and the control means 16 shown in FIG. The present invention calculates the exhaust gas temperature by focusing on the fact that the amount of heat (combustion heat) 71 generated by combustion is the sum of the effective work 72, the cooling loss 73, and the exhaust loss 74 as shown in FIG. It is. Here, the heat of combustion 71
Is regarded as the sum of the internal energy of the intake air and the calorific value,
Since the internal energy of the intake air is the product of the specific heat of the air, the intake air amount, and the intake air temperature, the internal energy of the intake air is detected from the air flow meter 22 and the intake air temperature sensor 47, and the calorific value is obtained as shown in FIG. ) Is calculated from a map of the calorific value. Air-fuel ratio is calculated on the basis of the output detection signal of the O ₂ sensor 52.

In this embodiment, the effective work 72 is detected by a two-dimensional map of the output rotation speed signal of the rotation angle sensor 50 and the amount of intake air from the air flow meter 22. However, when the ignition advance is retarded due to knocking, the map value is corrected. The effective work 72 may use a shaft torque measuring device (using distortion) or a combustion pressure (in-cylinder pressure) sensor provided for the crankshaft.

Further, the cooling loss 73 is detected by the heat flux sensor 19, and the gas flow rate in the exhaust loss 74 is detected by the air flow meter 22. Further, the specific heat during the exhaust loss 74 is set to a predetermined value in advance. Therefore, the above-mentioned operating state detecting means 13 includes the air flow meter 22, the intake air temperature sensor 47, the rotation angle sensor 50, and the O ₂ sensor 5.
2 and so on.

Next, the operation of air-fuel ratio control by the microcomputer 20, which is a main part of the present invention, will be described with reference to FIGS. 7 and 8. FIG. FIG. 7 is a flowchart for explaining the operation of one embodiment of the main part of the present invention, and shows the above-described air-fuel ratio control routine. When this control routine is started by interruption at a predetermined timing, calculation of the exhaust gas temperature is performed in step 81. That is, this step 81 is a means for realizing the exhaust temperature calculating means 14 described above, and based on the heat flux detection signal from the heat flux sensor 19 and the detection signals from the air flow meter 22, the intake air temperature sensor 47, the rotation angle sensor 50, and the like. The exhaust gas temperature is calculated from the heat quantity (combustion heat) 71 generated by combustion and the exhaust gas loss 74 as follows. Here, combustion heat = (effective work) + (cooling loss) + (exhaust loss) (1) where the combustion heat is the sum of the internal energy of the intake air and the calorific value.

The exhaust loss indicated by 74 in FIG. 5 is represented by the following equation.

Exhaust loss = (Specific heat) × (Gas flow rate) × (Exhaust temperature) (2) Therefore, rearranging the equations (1) and (2), the exhaust temperature is expressed by the following equation.

Exhaust gas temperature = {(combustion heat) − (effective work) − (cooling loss)} / {(specific heat) × (gas flow rate)} (3) Thus, in step 81, the calculation based on the above formula (3) To calculate the exhaust gas temperature. Although the calculation of the exhaust gas temperature in step 81 is as described above, the outline of the calculation will be described again.

In the above equation (3), (heat of combustion) is calculated by the method described on page 14, lines 4 to 12. Specifically, (a) intake air obtained by multiplying the intake air amount detected by the air flow meter 22, the intake air temperature detected by the intake air temperature sensor 47, and the specific heat of air stored in advance. 6 and the amount of heat generated per unit air amount obtained by referring to the map shown in FIG. 6 based on the air-fuel ratio (A / F) detected by the O ₂ sensor 47, and the amount of heat detected by the air flow meter 22. Is calculated as the sum (a) + (b) of (b) the calorific value obtained by multiplying by the intake air amount.

(Effective work) in the above equation (3) is calculated by the method described on page 14, lines 13 to 20. Specifically, based on the output rotation speed detected by the rotation angle sensor 50 and the intake air amount detected by the air flow meter 22, the calculation is performed by referring to a two-dimensional map relating to the effective work. Note that the effective work may be obtained by another method as described above.

In the above equation (3), (cooling loss) and (gas flow rate)
As described on page 15, lines 1 to 3, based on the amount of moving heat detected by the heat flux sensor 19, or
It is obtained based on the detection value of the air flow meter 22. In the above formula (3), (specific heat) is set to a predetermined value in advance as described on page 15, lines 3-4. In step 81, the exhaust gas temperature is calculated by substituting the calculated value, the detected value, and the like into the above equation (3).

Here, in the heat balance relationship diagram in the engine steady state shown in FIG. 8, the cooling loss b in the heat balance relationship diagram per unit time in FIG. 8A represents the head temperature, and FIG. Exhaust loss f in the heat balance relationship diagram per unit air amount represents exhaust temperature. Also,
In FIG. 8 (A), a is the exhaust loss per unit time, c is the total work, and d is the total calorific value, which increases according to each throttle opening. e and j in FIG. 8 (B) are air-fuel ratios. In this case, when the throttle opening reaches 70%, the exhaust gas temperature reaches an allowable value, so that the throttle opening is between 70% and 100%. Shows an example in which the air-fuel ratio is controlled in a tight manner to keep the exhaust gas temperature within an allowable value.

Further, in FIG. 8 (B), g is a cooling loss per unit air amount, and becomes smaller in substantially proportion to the throttle opening. h is the work per unit air amount and is constant irrespective of the degree of opening of the smell, and i is the amount of heat generated per unit air amount, which changes according to the air-fuel ratio.

As described above, when the calculation of the exhaust gas temperature represented by the exhaust gas loss f per unit air amount in FIG. 8 (B) is calculated in step 81 in FIG. A magnitude comparison between the determined exhaust temperature and a preset allowable value of the exhaust temperature is performed. That is, this step 82 is a processing step for realizing the comparison means 15 described above. In this step 82, when the exhaust gas temperature is larger than the allowable value,
Proceeding to 83, the fuel injection time by the fuel injection valve 33 is calculated to be longer than the previous time so that the air-fuel ratio (A / F) is made richer than the previous time, and the calculated fuel injection time,
Perform fuel injection. Note that the air-fuel ratio due to this fuel injection is calculated based on the detection signal of the O ₂ sensor 52 and is stored in the RAM 62.
Is stored in

On the other hand, if it is determined in step 82 that the exhaust gas temperature is equal to or lower than the allowable value, the process proceeds to step 85 to determine whether or not the previous air-fuel ratio is stoichiometric (stoichiometric air-fuel ratio).
Is determined on the basis of the previous air-fuel ratio data stored in the storage device. If the stoichiometric condition is reached, the fuel injection time is made equal to the previous value in step 86, and fuel injection is performed in step 84.

If it is determined in step 85 that the air-fuel ratio is not stoichiometric, the process proceeds to step 87, and the fuel injection time is calculated to be shorter than the previous time so that the air-fuel ratio is leaner than the previous time. Its fuel injection time at 84,
The fuel injection is performed by the fuel injection valve 33. As described above, the above steps 83 to 87 are processing for realizing the control means 16 described above.

Next, a more specific operation of the present embodiment will be described with reference to FIGS. 7 and 9. FIG. As an example, as shown in FIG. 9 (G), the opening of the throttle valve 24 is changed at time t _1.
And rapidly opened over the ~t ₂ 10% ~100%, holds the state of 100% opening until time t _5, the opening until the subsequent time t ₆ 100
% From closed sharply to 10%, will be described when the time t ₆ after returning to the steady state of 10% opening.

Until time t ₁ is smaller than the allowable value (exhaust temperature tolerance limit) exhaust gas temperature is as shown in Figure No. 9 (A), and the air-fuel ratio is stoichiometric, as shown in FIG. (F) (the stoichiometric air-fuel ratio) There is. Therefore, in this case, until the time t ₁ is the same time the fuel injection and the last is performed through the steps 81,82,85,86 in Figure 7.

Next, in reach time to t ₂ from time t _1, the quick opening of the throttle opening, the amount of heat per unit time that flows from the combustion chamber 29 to the cylinder head 31 increases rapidly as shown in FIG. 9 (C), torque The amount of heat generated per unit time also rises sharply as shown in FIGS. However, FIG. 9 (B)
(A), the amount of heat (cooling loss) flowing from the combustion chamber 29 to the cylinder block 31 is large, so that the exhaust gas temperature does not rise as shown by the solid line I in FIG. Accordingly, in this embodiment, since the exhaust gas temperature is lower than the allowable value and the air-fuel ratio is the stoichiometric air-fuel ratio, the air-fuel ratio is maintained at the stoichiometric air-fuel ratio as shown by the solid line III in FIG. 9 (F).

On the other hand, in the conventional air-fuel ratio control device, when the throttle opening reaches a predetermined value (for example, 70%) according to the map created based on the steady-state conditions shown in FIG. In order to perform the rich control as shown in FIG. 9, the exhaust gas temperature rises more gently than the change I in the exhaust gas temperature of this embodiment as shown by a broken line II in FIG. 4), the temperature rise is slower than the change shown by the solid line V in the present embodiment as shown by the broken line VI.

Since the exhaust temperature at time t ₃ in the present embodiment reaches the allowable value as indicated by the solid line I in FIG. 9 (A), of Figure 7 as indicated by a solid line III in FIG. (F) Step 82 The air-fuel ratio is controlled to the rich side by the processing of. If the exhaust temperature still exceeds the allowable value at the time of the next fuel injection, control is performed to a richer side than the previous time, but if the exhaust temperature falls below the allowable value by the previous rich control, the step of FIG. 8
By the control of 2,85,87, the air-fuel ratio is controlled to be leaner than that at the time of the previous fuel injection (which does not mean leaner than the stoichiometric air-fuel ratio). As described above, the control is performed. On the whole, the rich control is increased more than the lean control, and the air-fuel ratio gradually becomes rich. Consequently, until time t ₅ the throttle opening is 100% exhaust gas temperature is FIG. 9 (A)
Is controlled within an allowable value as shown by the solid line.

In latest time t ₄ than the time t ₃ in the above-described conventional apparatus, the exhaust gas temperature reaches the allowable value as shown by the broken line II in FIG. 9 (A). As described above, in this embodiment, the exhaust gas temperature is estimated by calculation, and the rich control is performed only when the exhaust gas temperature exceeds the allowable value. On the other hand, in the conventional device, as shown by the broken line IV in FIG. 9 (F). Since the rich control is performed when the throttle opening reaches a predetermined value, the present embodiment improves the partial fuel efficiency indicated by a in FIG. In addition, since the exhaust gas temperature obtained by the above calculation takes into account the cooling loss, more accurate air-fuel ratio control can be performed.

Next, 100 the throttle opening from time t ₅ toward t ₆
%, The air-fuel ratio control is performed by comparing the exhaust temperature calculated by the calculation with the allowable value. In this case, the air-fuel ratio is not the stoichiometric air-fuel ratio. As the air becomes gradually lean, it finally reaches the stoichiometric air-fuel ratio as shown in FIG. 9 (F). Therefore, according to this embodiment, the exhaust gas temperature is allowed as shown by the solid line VII in FIG. 9 (A). It rarely exceeds the value.

In contrast, since the conventional apparatus does not consider the cooling loss, when leaner so that the air-fuel ratio to the stoichiometric air-fuel ratio by rapid closing of the throttle opening after time t _5, the head temperature than the steady state compliance High cooling loss is reduced,
The exhaust loss increases, and the exhaust gas temperature exceeds the allowable value as shown by the broken line VIII and in FIG. 9 (A).

The time t ₆ after air-fuel ratio is the stoichiometric air-fuel ratio, and exhaust gas temperature returns to the steady state than the allowable value. According to the present embodiment, since the cooling loss is obtained based on the directly detected heat flux, it is also possible to correct a difference in cooling loss due to a change with time or an individual difference.

The present invention is not limited to the above embodiment, and two or more heat flux sensors 19 may be provided. Further, the present invention is suitable to be applied to the supercharged internal combustion engine shown in FIG. 2 having a high heat load, but it is needless to say that the present invention can also be applied to a naturally aspirated internal combustion engine.

〔The invention's effect〕

As described above, according to the present invention, the cooling loss is grasped by detecting the heat flux, and the exhaust gas temperature is estimated in consideration of the cooling loss. It can be performed accurately, and has such features that the exhaust gas temperature does not exceed an allowable value.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of the present invention, FIG. 2 is a diagram illustrating the configuration of an embodiment of the device of the present invention, FIG. 2 is an explanatory diagram of the hardware configuration of the microcomputer in FIG. 2, FIG. 5 is an explanatory diagram of the amount of heat generated by combustion, FIG. 6 is an explanatory diagram of a map for calculating a calorific value in the present invention, and FIG. FIG. 8 is an explanatory diagram of a heat balance relation, and FIG. 9 is a view showing an excessive behavior in one embodiment of the present invention. 11 internal combustion engine 12 heat flux detecting means 13 operating state detecting means 14 exhaust temperature calculating means 15 comparing means
16 control means, 19 heat flux sensor, 20 microcomputer, 56a, 56b temperature-sensitive element.

Claims (1)

(57) [Claims] 1. An air-fuel ratio control device for an internal combustion engine, wherein the air-fuel ratio is changed to a rich side in accordance with the exhaust gas temperature when the temperature of the exhaust gas of the internal combustion engine is equal to or higher than a predetermined temperature. Heat flux detecting means for detecting a heat flux of a gas flowing in a part of the inside; operating state detecting means for detecting an operating state of the internal combustion engine; based on each detected value of the operating state detecting means and the heat flux detecting means. Exhaust temperature calculating means for calculating the exhaust gas temperature, comparing means for comparing the exhaust gas temperature obtained by the exhaust gas temperature calculating means with a preset allowable value of the exhaust gas temperature, and comparing results of the comparing means. And control means for controlling the air-fuel ratio to be richer than at the time of the previous air-fuel ratio control at least when the exhaust gas temperature exceeds the allowable value.