JPH0633810A - Exhaust system protection control method for engine and device thereof - Google Patents

Abstract

PURPOSE:To control the temperature of an exhaust system properly with no waste without deteriorating reliability of the exhaust system by estimating the temperature of the exhaust system, and not carrying out reduction control of the exhaust system temperature till the estimated value exceeds a set value. CONSTITUTION:An exhaust gas temperature is estimated on the basis of various kinds of parameters showing various engine data is and operating condition thereof (Step 60 and Step 80), and the wall temperature of an exhaust manifold is estimated on the basis of the estimated exhaust gas temperature and heat transfer element information of an exhaust manifold (Step 170). It is judged whether the estimated wall temperature of the exhaust manifold exceeds a prescribed allowable limit value or not (Step 200), and when it does not exceed, the limit valve an engine is F/B operated (Step 210), and when it exceeds the limit value the engine is operated in enrich condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine exhaust system protection control method and apparatus. More specifically, it relates to a novel control method and apparatus for preventing overheating of an exhaust system of an engine.

[0002]

2. Description of the Related Art FIG. 8 is a schematic block diagram of an electronic control unit for an automobile engine that has been generally adopted conventionally. As shown in the figure, the amount of fuel injected and supplied from the injector 6 provided in the intake system 4 of the engine 2 is controlled by the controller 8 which is a microcomputer. As is well known, the controller 8 is the intake air amount detected by the air flow meter 10 and the rotation sensor 1.
The basic value of the fuel supply amount is calculated based on the engine speed detected in 2 and the water temperature sensor 14, knock sensor 16, throttle opening sensor 18, intake air temperature sensor 2
0, throttle fully open sensor 22, air-fuel ratio sensor 26, and the like based on information signals from various sensors, warm-up increase correction, post-start increase correction, acceleration increase correction, high load increase correction,
Various corrections such as intake air temperature correction and air-fuel ratio feedback correction are appropriately executed according to the operating state of the engine 2 to determine the final fuel supply amount.

Here, the feedback (F
/ B) correction is provided in the exhaust system 24 when the execution conditions such as the engine speed and the load are within a predetermined F / B zone as shown in the air-fuel ratio control map of FIG. 6 are satisfied. Based on the output of the air-fuel ratio sensor 26 such as the O ₂ sensor 26a, the fuel supply amount is corrected so that the air-fuel ratio value detected by the air-fuel ratio sensor 26 converges near the theoretical air-fuel ratio value 14.7.

Further, the engine speed and the load are F above.
When the exhaust gas temperature goes out of the / B zone and enters the enriched zone where the exhaust gas temperature becomes high, as shown in the time chart of FIG. 7, the temperature of the exhaust system 24 such as the exhaust manifold 24a falls below the allowable limit value T _a . The exhaust gas temperature is lowered by, for example, correcting the fuel supply amount by increasing the high load so that the air-fuel ratio is made richer than the theoretical air-fuel ratio value of 14.7 so as not to overheat.

However, as described above, if the engine speed and the load of the engine 2 enter the predetermined enriched zone and the exhaust gas temperature lowering control is started at the same time, the wall temperature of the exhaust system 24 is actually reduced. since still it will initiate the reduction control of the previous from prematurely exhaust gas temperature reaching the allowable limit value T _a in, while the wall temperature of the exhaust system 24 is increased to the allowable limit value T _a (time t _{1 to} t ₃ ), the engine performance is unnecessarily impaired, and this is one of the causes of deteriorating the fuel economy, especially when the exhaust gas temperature is lowered by increasing the fuel amount as described above.

In order to solve this problem, therefore, the exhaust temperature lowering control is started by increasing the fuel amount after a lapse of a predetermined delay time from the time when the engine speed and the load enter the predetermined enrichment zone. In addition, by changing the delay time according to the level of the exhaust gas temperature, the exhaust system 24 can be prevented while preventing deterioration of fuel efficiency.
Japanese Patent Laid-Open No. 60-
It is proposed in Japanese Patent No. 43144.

[0007]

However, since the actual exhaust system temperature to be protected always causes a delay in response to changes in the exhaust gas temperature, even in the case of the proposal,
As long as the setting of the delay time that determines the start timing of the exhaust gas temperature lowering control by increasing the fuel amount is changed according to the height of the exhaust gas temperature, appropriate control in accordance with the actual change of the exhaust system temperature We couldn't do it enough and there was room for improvement.

In the method of directly detecting the temperature of the exhaust system to be protected and controlling the decrease of the exhaust gas temperature when the exhaust system temperature exceeds the allowable limit value, there is a detection delay of the sensor, so the exhaust gas temperature is In order to deal with the occurrence of overheat when the temperature of the exhaust system is extremely high and suddenly rises, it is unavoidable to set the allowable limit temperature low.However, if the allowable limit temperature is set low in this way, exhaust gas will be adversely affected. If the system temperature rises slowly, unnecessary exhaust gas temperature reduction control will be performed.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to ensure thermal protection of an exhaust system and ensure its reliability, while minimizing waste. (EN) An exhaust system protection control method for an engine and a device therefor capable of controlling exhaust gas temperature reduction.

[0010]

In order to achieve the above object, an engine exhaust system protection control method of the present invention predicts an exhaust gas temperature based on various parameters indicating engine specifications and operating conditions. Then, the exhaust system temperature is predicted based on the predicted exhaust gas temperature and the exhaust system heat transfer element information, and when the predicted exhaust system temperature is equal to or higher than a predetermined allowable limit value, the exhaust gas temperature decreases. It is characterized by controlling to.

Further, in order to achieve the above object, the exhaust system protection control device for an engine according to the present invention predicts the exhaust gas temperature based on various parameters indicating engine specifications and operating conditions. Prediction means, an exhaust system temperature prediction means for predicting the exhaust system temperature based on the predicted exhaust gas temperature and the exhaust system heat transfer element information, and when the predicted exhaust system temperature is equal to or higher than the allowable limit value, the exhaust gas An exhaust gas temperature decrease control means for controlling the gas temperature in a decreasing direction is provided.

Here, it is desirable to adopt a fuel increasing means as the exhaust gas temperature decrease control means.

Further, in order to achieve the above-mentioned object, as another constitution, an exhaust system protection control device of the present invention comprises a different fuel judging means, an output value from the different fuel judging means, an engine specification and its operating condition. Exhaust gas temperature predicting means for predicting exhaust gas temperature based on various parameters indicating, and exhaust system temperature predicting means for predicting exhaust system temperature based on predicted exhaust gas temperature and exhaust system heat transfer element information, An exhaust gas temperature decrease control means for controlling the exhaust gas temperature in a decreasing direction when the predicted exhaust system temperature is equal to or higher than an allowable limit value.

[0014]

According to the present invention having the above-described structure, various parameters (engine speed, empty speed, etc.) indicating the specifications of the engine (compression ratio, S / B ratio (cylinder diameter / bore diameter), overlap, etc.) and their operating states are provided. The exhaust gas temperature predicting means predicts the exhaust gas temperature based on the fuel ratio, volume efficiency, ignition timing, etc., and the predicted exhaust gas temperature and exhaust system heat transfer element information (heat capacity, thermal resistance, exhaust pipe surface area, etc.) The exhaust system temperature predicting means further predicts the exhaust system temperature based on the above, and when the predicted value of the exhaust system temperature exceeds a predetermined allowable limit value, the exhaust gas temperature decrease control means decreases the exhaust gas temperature. Since the exhaust system can be reliably protected, the exhaust gas temperature reduction control is not unnecessarily executed before the exhaust system reaches a temperature high enough to cause overheating.
The engine performance will not be wasted.

Further, when the fuel amount increase control means is adopted as the exhaust gas temperature decrease control means, the exhaust gas temperature decrease control by the fuel increase is not unnecessarily performed, so that the fuel consumption can be reduced as much as possible. It is possible to reliably protect the exhaust system while suppressing the above.

Further, if a means for determining different types of fuel is added to determine the type of fuel used, and the exhaust gas temperature is predicted by taking into consideration the information of this determination result, for example, a high-octane engine will be mistaken. Even if regular gasoline is mixed in, appropriate temperature control can be performed.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings. The basic structure of the engine exhaust system temperature control device of the present invention is the same as that of the conventional electronic control device of FIG. 8 described above, and a detailed description thereof will be omitted.

The difference between this embodiment and the conventional example is as follows.

In the prior art, the exhaust temperature lowering control by the high load increase correction of the fuel is started after the elapse of a predetermined delay time from the time when the engine speed and the load enter the predetermined enriched zone, and the delay is performed. The time was changed according to the level of the exhaust gas temperature.

On the other hand, in the present embodiment, the specifications (compression ratio, S) of the engine 2 stored in the ROM of the controller in advance.
/ B ratio, overlap, etc.) and various sensors 10-22,
The exhaust gas temperature is predicted based on various parameters (engine speed, air-fuel ratio, volumetric efficiency, ignition timing, etc.) indicating the operating state of the engine 2 detected by 26, and is used from the number of knocking occurrences detected by the knock sensor 16. It is determined whether the fuel is regular gasoline or high-octane gasoline, and the predicted value of the exhaust gas temperature is corrected based on this determination result. Then, based on the corrected predicted value of the exhaust gas temperature and the exhaust system heat transfer element information (heat capacity, thermal resistance, exhaust pipe surface area, etc.) also stored in advance in the ROM,
It predicts further wall temperature of the exhaust manifold 24a which forms an exhaust system, until the wall temperature of the predicted exhaust manifold 24a exceeds the allowable limit value T _a, the air-fuel ratio is the stoichiometric air-fuel ratio value 1
F / B correction control is performed on the fuel supply amount to the engine 2 so as to converge to the vicinity of 4.7, and when the allowable limit value T _a is exceeded, the F / B correction control is stopped to perform high load increase correction. Starting, the engine 2 is made to perform an enriched operation to lower the exhaust gas temperature.

That is, FIG. 1 is a control conceptual diagram of the exhaust system protection control device according to the present invention. In FIG. 1, 30 is an exhaust gas temperature predicting means, and this exhaust gas temperature predicting means 30 is detected by a knock sensor 16. Fuel type information such as high-octane gasoline or regular gasoline, which is determined from the number of times knocking has occurred, specification information of the engine 2 (compression ratio, S / B ratio, intake / exhaust valve overlap, etc.), and operating state of the engine 2. Parameters (volumetric efficiency,
The exhaust gas temperature is predicted based on the engine speed, air-fuel ratio, ignition timing, etc.). Further, in the figure, numeral 32 is an exhaust system temperature predicting means for predicting the wall temperature of the exhaust manifold 24a based on the predicted exhaust gas temperature. Further, in the figure, the exhaust gas temperature decrease control means 34 comprises a comparison means 36 and a judgment means 38, and the comparison means 36 is the above-mentioned predicted wall temperature of the exhaust manifold 24a and a preset allowable limit value of the wall temperature. Compare with. Further, the judging means 38 judges, based on the comparison result of the comparing means 36, whether the air-fuel ratio of the engine 2 should be F / B controlled or enriched.

FIG. 2 is a flow chart showing the control contents of this embodiment. When the control routine is started, the first calculation flag which indicates that the calculation of the control routine is the first time is set to 1 (S10). Next, it is determined whether the engine water temperature is higher than a predetermined value. If the engine water temperature is lower than the predetermined value (S20, NO), this determination is repeated until the engine water temperature is equal to or higher than the predetermined value (S20), and the engine water temperature is predetermined. When it becomes higher than the value (Warm-up completion, S20, YES), the F / B operation execution condition of the air-fuel ratio determined by the engine speed of the engine 2, load shape, etc. is determined (S30).

If the F / B operation execution condition is satisfied (S30, YES), the target air-fuel ratio is set to 14.7 and F / B correction control is performed. On the other hand, if the F / B operation condition is not satisfied (S30, NO), the air-fuel ratio value is set to a predetermined enrichment target value and the enrichment operation is performed.

Next, the exhaust gas predicted temperature T _g is calculated based on the exhaust gas temperature prediction model when using high-octane gasoline (S60). Here, in the calculation formula of the exhaust gas temperature prediction model, various parameters (S / B ratio, compression ratio, overlap, exhaust pipe surface area, volumetric efficiency, engine speed, etc.) indicating the specification information and operating state of the engine are used. ), The following equation obtained by performing multivariate analysis is adopted.

T _g = a1 + (a2 + a3 * [volumetric efficiency]
+ A4 * [Air consumption]) * [Engine speed] + a5 *
[Volume efficiency] + a6 * [Air fuel economy] (1) (where a1 to a6 are constants determined from the S / B ratio, compression ratio, overlap, exhaust pipe surface area, volume efficiency, air-fuel ratio, etc. It should be noted that the above equation (1) can be specifically modified and expressed as the following equation from the data obtained by the experiment. However, this example is M
BT (Minimum Spark Advance)
for Best Torque) This is an exhaust gas temperature prediction formula when the lead angle is advanced.

T _g = (-79.917-0.02289)
4 * N) * [S / B ratio] + (3.097-0.0002
88 * N) * [Volume efficiency] + (32.04-0.000
76 * N) * [air-fuel ratio] + (− 97.617 + 0.01
4526 * N) * [compression ratio] + (5.564-0.00
0476 * N) * [overlap] + (0.0000
4614-1.1 * 10 ^-10 * N) * [Exhaust pipe surface area]
+ (867.17-0.03376 * N) ... (1)
′ (Here, N is the engine speed.) Next, based on the knocking occurrence frequency of the engine 2 detected by the knock sensor 16, it is determined whether or not the different fuel determination condition is satisfied (S70). ). That is, the fuel determination is made as to whether or not the gasoline fuel is regular.
Then, if the different fuel determination condition is satisfied (S70,
YES), the exhaust gas temperature predicted value when using high-octane fuel obtained in S60 is corrected, and an appropriate exhaust gas predicted temperature is recalculated. This correction method uses the term [volumetric efficiency] and the constant term (867.17-0.0) in the exhaust gas temperature prediction equation.
3376 * N) and the value is reduced.

Next, it is judged whether or not the different fuel judgment is the first judgment (S90), and if the different fuel judgment is the first judgment (S90, YES), the different fuel judgment first flag is set to 1.
(S100). If the different fuel determination is not the first time (S90, NO), the different fuel determination first time flag is left as it is.

Next, it is judged whether or not the initial operation flag is 1 (S110). If the initial operation flag is 1 (S110, YES), the value of the wall temperature of the exhaust manifold 24a is set to the exhaust gas temperature. (S120), and the initial operation flag is set to 0 (S130). On the other hand, the initial operation flag is 1
If not (S110, NO), it is determined whether or not the different fuel determination initial flag is 1 (S140).

If the different fuel determination initial flag is 1 (S140, YES), from the number of knocking occurrences,
A predicted value of the wall temperature of the exhaust manifold 24a is calculated (S1
50), the different fuel determination initial flag is set to 0 (S16).
0). If the different fuel determination initial flag is not 1 (S140, NO), the exhaust gas is exhausted based on the predicted exhaust gas temperature and the heat transfer element information (heat capacity, thermal resistance, exhaust pipe surface area, etc.) of the exhaust manifold 24a. Manifold 24a
The predicted value of the wall temperature is calculated (S160). At this time, the calculation formula of the wall temperature prediction model of the exhaust manifold 24a is T _x = (1− (τ / R _t * C)) * X + (K / C) * τ * T _g ... (2) Has been given. Here, R _t , C, and K are constants obtained from the heat capacity and heat resistance of the exhaust manifold, T _g
Is the exhaust gas temperature, and τ is the calculation cycle. Note that R _t ,
C and K are obtained by the same parameters. That is,
R _t (constant equivalent to heat capacity), C (constant equivalent to thermal resistance), and K (constant) are calculated so that the sum of squares of the difference between the predicted value and the measured value of the exhaust manifold wall temperature is minimized.

Next, it is determined whether the throttle valve 28 is fully opened (S180). If the throttle valve 28 is fully opened (S180, YES), the F / B operation is switched to the enriched operation (S190). On the other hand, if the throttle valve 28 is not fully opened (S180, NO),
It is determined whether the predicted wall temperature of the exhaust manifold 24a exceeds the allowable limit value T _a (S200).

If the predicted wall temperature of the exhaust manifold 24a exceeds the allowable limit value T _a (S200, YE
S), the air-fuel ratio F / B operation is stopped, and the operation is switched to the enriched operation (S190). Then, the process returns to S20.

If the predicted wall temperature of the exhaust manifold 24a does not exceed the allowable limit value T _a (S200, N
O), F / B operation is continued (S210). And S
When 210 ends, the routine of returning to S20 is repeated.

Therefore, as is apparent from the above description, in this embodiment, the exhaust gas is exhausted based on the specification information of the engine 2 and the various parameters output from the various sensors 10 to 22 and 26 according to the operating state thereof. Since the gas temperature is predicted, the exhaust gas temperature can be appropriately predicted even if the operating state of the engine 2 changes.

Here, FIG. 3 is a graph in which the predicted value data of the exhaust gas temperature calculated by the above-mentioned prediction formula (1) 'and the actually measured exhaust gas temperature data are plotted on the horizontal axis and the vertical axis, respectively. As is clear from this graph, the predicted value is within the error range of ± 25 degrees, and the prediction can be performed with considerably high accuracy. In addition,
This test condition is that the engine speed is 4500-600.
0 rpm, cooling water temperature 88 degrees Celsius, air-fuel ratio 10-1
5, The intake negative pressure is 0 to -250 mmHg, and the ignition timing is MBT.

Then, the exhaust manifold temperature is further predicted from the predicted value of the exhaust gas temperature, and the decrease control of the exhaust gas temperature by the fuel increase is not performed until the exhaust manifold temperature becomes equal to or higher than the allowable limit value T _a. The F / B operation can be performed with the air-fuel ratio as long as possible except when the throttle valve is fully opened as shown in the map of FIG.

That is, as shown in the time chart of FIG. 5, even if the engine 2 is operated in the high load and high rotation range and the exhaust gas temperature rises (time t1), the air-fuel ratio A / F is the theoretical air-fuel ratio. The F / B correction control is continued as it is, and when the predicted wall temperature of the exhaust manifold 24a reaches the allowable limit value T _a (time t2), the exhaust gas temperature lowering control by the fuel increase is started for the first time and the air-fuel ratio of Enriched driving,
As a result, the exhaust gas temperature is lowered and the wall temperature of the exhaust manifold 24a is reliably suppressed from rising above the allowable limit value T _a . And, no matter how high the exhaust gas temperature is, until the temperature of the exhaust manifold 24a reaches the allowable limit value T _a , the exhaust gas temperature is not unnecessarily controlled to decrease by increasing the fuel amount, so that the fuel is wasted. It can be prevented as much as possible, and the improvement of fuel efficiency can be promoted.

The present invention is not limited to the above-described embodiment, but the exhaust gas temperature prediction model and the exhaust system temperature prediction model are changed to perform the exhaust system temperature protection control corresponding to the specifications of various engines. You can Further, the exhaust gas temperature decrease control means is replaced with the fuel increase control means, and other means, for example, secondary air supply control means is used to supply secondary air to the exhaust system to reduce the exhaust gas temperature. You may plan. Even if the secondary air supply control means or the like is replaced in this way, the exhaust gas temperature reduction control is performed in a state urged to the extent of the exhaust system temperature increase as much as possible, and wasteful reduction control is executed. Is removed as much as possible, so that engine performance is not unnecessarily impaired.

Further, it is desirable that the prediction point of the exhaust system temperature is a heat point at which the wall temperature becomes the highest, for example, a curved portion having a large curvature of the exhaust manifold.

[0039]

As described above in detail in the embodiments,
According to the present invention, engine specifications (compression ratio, S / B ratio,
The exhaust gas temperature is predicted by the exhaust gas temperature predicting means based on various parameters (engine speed, air-fuel ratio, volumetric efficiency, ignition timing, etc.) that indicate the operating conditions and the predicted exhaust gas temperature. And the exhaust system heat transfer element information (heat capacity, thermal resistance, exhaust pipe surface area, etc.), the exhaust system temperature predicting means further predicts the exhaust system temperature, and the predicted value of the exhaust system temperature is a predetermined allowable limit value. If it exceeds,
Since the exhaust gas temperature decrease control means controls the exhaust gas temperature in the decreasing direction, it is possible to control the decrease of the exhaust gas temperature as much as possible to the situation of the exhaust system temperature increase, and thus to reduce it unnecessarily. It is possible to prevent the control from being executed as much as possible and prevent the engine performance from being unnecessarily impaired.

Further, when the fuel amount increase control means is adopted as the exhaust gas temperature decrease control means, the exhaust gas temperature decrease control by the fuel increase is not performed unnecessarily, so that the fuel consumption can be reduced as much as possible. It is possible to reliably protect the exhaust system while suppressing the above.

Further, if different fuel determining means is added to determine the type of fuel used, and the exhaust gas temperature is predicted by taking into consideration the information of this determination result, for example, a high-octane engine will be mistaken. Even if regular gasoline is mixed in, appropriate temperature control can be performed.

[Brief description of drawings]

FIG. 1 is a control conceptual diagram of an exhaust pipe temperature control device according to the present invention.

FIG. 2 is a flowchart showing the control contents of one embodiment of the present invention.

FIG. 3 is a graph showing the validity of an exhaust gas temperature predicted value according to the present invention.

FIG. 4 is a map showing an air-fuel ratio zone setting according to the present invention.

FIG. 5 is a time chart explaining the operation of the control according to the present invention.

FIG. 6 is a map showing a conventional air-fuel ratio zone setting.

FIG. 7 is a time chart illustrating the operation of conventional control.

FIG. 8 is a schematic configuration diagram showing a conventional electronic control device for an engine, which is common to an exhaust system protection control device for an engine according to the present invention.

[Explanation of symbols]

 2 Engine 4 Intake System 6 Injector 8 Controller 10 Air Flow Meter 12 Rotation Sensor 14 Water Temperature Sensor 16 Knock Sensor (Different Fuel Judgment Means) 18 Throttle Opening Sensor 20 Intake Temperature Sensor 22 Throttle Full Open Sensor 24 Exhaust System 24a Exhaust Manifold 26 Empty Fuel ratio sensor 28 Throttle valve 30 Exhaust gas temperature prediction means 32 Exhaust system temperature prediction means 34 Exhaust gas temperature decrease control means 36 Comparison means 38 Judgment means

Claims (5)

[Claims] 1. An exhaust gas temperature is predicted based on various information indicating engine specifications and various operating conditions, and the exhaust system temperature is calculated based on the predicted exhaust gas temperature and exhaust system heat transfer element information. An exhaust system protection control method comprising: predicting and controlling the exhaust gas temperature in a decreasing direction when the predicted exhaust system temperature is equal to or higher than an allowable limit value. 2. An exhaust gas temperature predicting means for predicting an exhaust gas temperature on the basis of various parameters indicating engine specification information and its operating state, and based on the predicted exhaust gas temperature and exhaust system heat transfer element information. An exhaust system temperature predicting means for predicting the exhaust system temperature, and an exhaust gas temperature lowering controlling means for controlling the exhaust gas temperature in a decreasing direction when the predicted exhaust system temperature is equal to or higher than an allowable limit value. A characteristic engine exhaust system protection control device. 3. The engine exhaust system protection control device according to claim 2, wherein the exhaust gas temperature decrease control means is a fuel increase control means. 4. The engine exhaust system protection according to claim 2, wherein the parameter is at least one of intake air amount, engine speed, air-fuel ratio, and ignition timing. Control device. 5. A different fuel judging means, an exhaust gas temperature predicting means for predicting an exhaust gas temperature based on an output from the different fuel judging means, engine specification information, and various parameters indicating its operating state, Exhaust system temperature predicting means that predicts the exhaust system temperature based on the exhaust gas temperature and the exhaust system heat transfer element information, and controls the exhaust gas temperature in the decreasing direction when the predicted exhaust system temperature is equal to or higher than the set value. An exhaust gas system protection control device for an engine, comprising: