JP2016000970A - Internal combustion engine control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To select an appropriate flame-out suppression control according to the cause of flame-out, and to efficiently suppress the flame-out.SOLUTION: An ECU 50 calculates a compression end temperature and a necessary compression end temperature variation that is a variation in the compression end temperature necessary to suppress flame-out. Furthermore, the ECU 50 calculates a cylinder oxygen concentration and a necessary oxygen concentration variation that is a variation in the cylinder oxygen concentration necessary to suppress flame-out. If the necessary oxygen concentration variation is greater than the necessary compression end temperature variation, the ECU 50 executes an EGR feedback control to overcome insufficient oxygen in a cylinder. On the other hand, if the necessary oxygen concentration variation is smaller than the necessary compression end temperature variation, the ECU 50 executes a pilot feedback control to overcome insufficient preheating in the cylinder.

Description

  The present invention relates to a control device for an internal combustion engine applied to an automobile or the like, and more particularly to a control device for an internal combustion engine equipped with an EGR mechanism.

  As a conventional technique, for example, as disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2007-303305), a control device for an internal combustion engine having an EGR mechanism is known. In the prior art, the compression end temperature in the cylinder is detected, and when the detected compression end temperature is lower than a predetermined temperature, the fuel injection amount is corrected to be increased in order to suppress misfire and the like.

JP 2007-303305 A JP 2010-106734 A

  In the prior art described above, the compression end temperature is raised to suppress misfire. However, in this control, even when the oxygen concentration is insufficient as a cause of misfire, the compression end temperature can only be increased, and appropriate control corresponding to the cause of misfire can be executed. There is a problem that you can not.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to select an appropriate misfire suppression control according to the cause of misfire and efficiently suppress misfire. An object of the present invention is to provide a control device for an internal combustion engine.

A first invention comprises a fuel injection valve for injecting fuel into a cylinder,
An EGR mechanism that recirculates a portion of the exhaust gas as EGR gas to the intake system;
First misfire suppression means for suppressing misfire by controlling the recirculation amount of EGR gas by the EGR mechanism;
Second misfire suppression means for suppressing misfire by controlling the fuel injection amount of pilot injection executed before main injection;
Compression end temperature calculating means for calculating the compression end temperature at the compression top dead center;
In-cylinder oxygen concentration calculating means for calculating in-cylinder oxygen concentration;
A temperature change amount calculating means for calculating a change amount of the compression end temperature necessary for suppressing misfire based on a calculated value of the compression end temperature;
A concentration change amount calculating means for calculating a change amount of the in-cylinder oxygen concentration necessary for suppressing misfire based on the calculated value of the in-cylinder oxygen concentration;
When the change amount of the in-cylinder oxygen concentration is larger than the change amount of the compression end temperature, the first misfire suppression means is operated, and the change amount of the in-cylinder oxygen concentration is larger than the change amount of the compression end temperature. Control switching means for activating the second misfire suppression means.

  According to the first invention, it is possible to determine whether the main cause of misfire is oxygen deficiency or preheating deficiency based on the compression end temperature and the in-cylinder oxygen concentration. And when oxygen deficiency is a factor, the recirculation | reflux amount of EGR gas can be controlled by the 1st misfire suppression means, and oxygen deficiency can be eliminated preferentially. In addition, when insufficient preheating is a factor, the fuel injection amount of pilot injection can be controlled by the second misfire suppression means, and preheating can be preferentially resolved. Therefore, appropriate control can be selected according to the cause of misfire, and misfire can be efficiently suppressed.

It is a block diagram for demonstrating the system configuration | structure of the engine by Embodiment 1 of this invention. In Embodiment 1 of this invention, it is a flowchart which shows an example of the control performed by ECU. In Embodiment 1 of this invention, it is a characteristic diagram for demonstrating the calculation process of required compression end temperature variation | change_quantity. FIG. 4 is a characteristic diagram for explaining the calculation process of the required oxygen concentration change amount in the first embodiment of the present invention. In Embodiment 2 of this invention, it is a flowchart which shows an example of the control performed by ECU.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
The first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a configuration diagram for explaining a system configuration of an engine according to Embodiment 1 of the present invention. The system according to the present embodiment includes an engine 10 as an internal combustion engine including a diesel engine. Although FIG. 1 illustrates a four-cylinder engine, the present invention can be applied to an internal combustion engine having an arbitrary number of cylinders. Each cylinder of the engine 10 includes a fuel injection valve 12, an intake valve 14, an exhaust valve 16, and the like that inject fuel into a combustion chamber (inside the cylinder). The engine 10 also includes an intake passage 18 that sucks intake air into each cylinder, and an exhaust passage 20 that discharges exhaust gas from each cylinder. The intake passage 18 is provided with a throttle valve 22 that adjusts the amount of intake air. A catalyst 24 for purifying exhaust gas is provided in the exhaust passage 20.

  The engine 10 includes an EGR mechanism 26 that recirculates a part of the exhaust gas as EGR gas to the intake system. The EGR mechanism 26 includes an EGR passage 28 that connects the intake passage 18 and the exhaust passage 20, and an EGR valve that adjusts the recirculation amount (EGR amount) of EGR gas recirculated from the exhaust system to the intake system via the EGR passage 28. 30. The engine 10 is equipped with a supercharger 32 that supercharges intake air using exhaust pressure. The present invention is also applicable to an internal combustion engine that is not equipped with the supercharger 32.

  The system of the present embodiment includes a sensor system 40 that detects the operating state of the engine 10 and an ECU (Electronic Control Unit) 50 that controls the engine 10 based on the output of the sensor system 40. The sensor system 40 includes a crank angle sensor for detecting the rotation speed (engine rotation speed) and crank angle of the crankshaft, an air flow sensor for detecting the intake air amount, and a water temperature sensor for detecting the coolant temperature of the engine cooling water. An intake pressure sensor that detects intake pressure and an intake air temperature sensor that detects intake air temperature are included. In addition, the sensor system 40 includes various sensors necessary for controlling the engine 10 and the vehicle. The ECU 50 calculates the intake air amount, the engine rotational speed, the engine load, and the like based on the output of the sensor system 40, and drives the actuators such as the fuel injection valve 12, the throttle valve 22, and the EGR valve 30 based on the calculation results. To do.

  The ECU 50 executes pilot injection control and EGR control described below. In the pilot injection control, fuel injection for preheating (pilot injection) is performed before execution of fuel injection (main injection) that contributes to generation of torque. In the pilot injection control, for example, the fuel injection amount (pilot amount) of the pilot injection is set based on the necessity of preheating determined by the warm-up state of the engine 10 or the like. According to this control, the inside of the cylinder is preheated before the main injection to improve the combustibility, and misfires can be suppressed. On the other hand, in the EGR control, the opening degree of the EGR valve 30 is changed according to the operating state of the engine 10 to control the EGR amount.

[Features of Embodiment 1]
In general, as a cause of misfire, lack of preheating in the cylinder, excessive EGR amount, and the like are known. For this reason, in conventional engine control, a misfire index that reflects the presence or absence, frequency, etc. of misfire may be calculated, and EGR control may be performed based on the misfire index. However, depending on the state of the engine, misfire may not be sufficiently suppressed only by EGR control, so it is preferable to use pilot injection control together. However, if the cause of misfire is not specified, it is difficult to determine which of EGR control and pilot injection control is effective.

  For this reason, in this embodiment, the cause of misfire is determined based on the amount of change in the compression end temperature and the amount of change in the in-cylinder oxygen concentration, and the type of misfire suppression control is switched based on the determination result. Hereinafter, this switching control will be described with reference to FIG. FIG. 2 is a flowchart showing an example of control executed by the ECU in the first embodiment of the present invention.

(Calculation of compression end temperature)
First, in step 100 in FIG. 2, the compression end temperature, which is the temperature in the cylinder at the compression top dead center, is calculated based on an example of a calculation model shown in the following equations 1 to 3. More specifically, in Equation 1, the polytropic index n is calculated based on the engine coolant water temperature, intake air temperature, intake pressure, and specific heat ratio. This equation shows an example of a method for calculating the polytropic index n. Also, the coefficients a, b, c, d, e, f, h, i in this equation are constant values set in advance by experiments or the like.

  Next, the compression end pressure is calculated by the following formula 2 using the polytropic index n, and the compression end temperature is calculated by the following formula 3 using the calculated value of the compression end pressure. In addition, Formula 2 is a formula about a polytropic change, and Formula 3 is a formula based on the state equation of gas. In these equations, the TDC (top dead center) cylinder volume and the BDC (bottom dead center) cylinder volume are known values, and the gas constant is a known constant. Further, the cylinder gas amount is calculated based on, for example, the intake air amount, the EGR rate, and the like.

(Calculation of in-cylinder oxygen concentration)
Next, in step 102, the in-cylinder oxygen concentration is approximately calculated by the following equation (4). In this equation, the excess air ratio is calculated based on, for example, the intake air amount, the fuel injection amount, and the like.

(Calculation of combustion reaction rate)
Next, at step 104, the in-cylinder combustion reaction rate is calculated based on the above-mentioned in-cylinder oxygen concentration and compression end temperature. The combustion reaction rate is calculated by the following equation (5) based on the Arrhenius equation.

(Acquisition of misfire suppression reaction temperature)
Next, in step 106, a combustion reaction rate (misfire suppression reaction rate) necessary for suppressing misfire is calculated. The misfire suppression reaction rate is preferably set in advance by experiments or the like. That is, step 106 is a process of reading out the misfire suppression reaction rate stored in advance in the ECU 50.

(Calculation of required compression end temperature change)
Next, in step 108, a change amount of the compression end temperature necessary for realizing the misfire suppression reaction rate (a necessary compression end temperature change amount) is calculated. Here, if the in-cylinder oxygen concentration is a constant value, the above equation 5 is a function of the compression end temperature. Therefore, by substituting the misfire suppression reaction rate into the left side of the equation (5) and solving this equation for the compression end temperature, the compression end temperature (target compression end temperature) necessary for suppression of misfire can be calculated. The target compression end temperature corresponds to the compression end temperature necessary for ignition of the air-fuel mixture. In step 108, the required compression end temperature change amount is calculated by obtaining the difference between the target compression end temperature calculated in this way and the current compression end temperature calculated in step 100.

  FIG. 3 is a characteristic diagram for explaining the calculation process of the required compression end temperature change amount in the first embodiment of the present invention. As shown in this figure, the combustion reaction rate tends to increase as the compression end temperature increases. And if the present compression end temperature rises more than target compression end temperature, since a combustion reaction rate will increase more than a misfire suppression reaction rate, misfire can be suppressed. For this reason, the required compression end temperature change amount ΔT is calculated by subtracting the current compression end temperature from the target compression end temperature.

(Calculation of necessary oxygen concentration change)
Next, in step 110 in FIG. 2, the amount of change in the in-cylinder oxygen concentration (necessary oxygen concentration change) necessary to realize the misfire suppression reaction rate is calculated based on the same idea as in step 108. That is, if the compression end temperature is set to a constant value, the formula 5 is a function of the in-cylinder oxygen concentration. Therefore, by substituting the misfire suppression reaction rate into the left side of the equation 5 and solving this equation for the in-cylinder oxygen concentration, the in-cylinder oxygen concentration (target oxygen concentration) necessary for suppressing misfire can be calculated. Then, by calculating the difference between the current in-cylinder oxygen concentration calculated in step 102 and the target oxygen concentration, the required oxygen concentration change amount is calculated.

  FIG. 4 is a characteristic diagram for explaining the calculation process of the required oxygen concentration change amount in the first embodiment of the present invention. As shown in this figure, the combustion reaction rate tends to increase as the in-cylinder oxygen concentration increases. If the current in-cylinder oxygen concentration rises above the target oxygen concentration, the combustion reaction rate increases above the misfire suppression reaction rate, so misfire can be suppressed. Therefore, the required oxygen concentration change amount ΔO2 is calculated by subtracting the current in-cylinder oxygen concentration from the target oxygen concentration.

(Normalization of calculated values)
Next, in step 112 in FIG. 2, the required compression end temperature change amount and the required oxygen concentration change amount are divided by the reference value corresponding to each change amount, and both are normalized. This makes it possible to compare the required compression end temperature change amount and the required oxygen concentration change amount in the same dimension. As a specific example, as the reference value corresponding to the required compression end temperature change amount, for example, the aforementioned target compression end temperature is adopted. That is, the standardized required compression end temperature change amount is calculated by dividing the required compression end temperature change amount by the target compression end temperature.

  Similarly, for example, the required change in oxygen concentration is calculated by dividing the change in required oxygen concentration by the target oxygen concentration. The reference value used in the present invention is not limited to the target compression end temperature and the target oxygen concentration. Specifically, in the present invention, for example, the compression end temperature and the in-cylinder oxygen concentration in a specific operation state may be adopted as the reference values.

  Next, in step 114, the standardized required compression end temperature change amount and the required oxygen concentration change amount are compared. This makes it possible to determine which of preheating and oxygen concentration is likely to cause a misfire in the current operating state. That is, for example, when the required oxygen concentration change amount is larger than the required compression end temperature change amount, the degree of oxygen shortage with respect to the target oxygen concentration is considered to be relatively larger than the degree of preheating lack with respect to the target compression end temperature.

  Therefore, in this case, the process proceeds to step 116, and EGR feedback control is executed as misfire suppression control. In the EGR feedback control, the EGR amount is feedback-controlled based on a misfire index described later so that the misfire index follows the target value. As a specific example of this control, when it is determined that the misfire frequency is higher than the allowable range based on the misfire index, the EGR amount is decreased to increase the in-cylinder oxygen concentration and suppress misfire.

  On the other hand, when the required compression end temperature change amount is larger than the required oxygen concentration change amount, it is considered that the degree of insufficient preheating is relatively larger than the degree of oxygen shortage. Therefore, in this case, the routine proceeds to step 118, where pilot feedback control is executed as misfire suppression control. In the pilot feedback control, the pilot amount is feedback-controlled so that the misfire index follows the target value. As a specific example of this control, when it is determined that the frequency of misfire is higher than the allowable range, the pilot amount is increased to promote in-cylinder preheating and suppress misfire.

  If misfire is likely to occur, the routine shown in FIG. 2 is repeatedly executed. As a result, at each time point, the control of EGR feedback control and pilot feedback control that is determined to be able to effectively suppress misfire is executed. The misfire index is an index that reflects the presence or absence of misfire, the frequency, and the like. As an example of the misfire index, a variation amount of the crank angular speed is known. The variation amount of the crank angular velocity can be obtained by performing digital filter processing on the crank angular velocity, for example. Specifically, for example, based on the method described in Japanese Patent Laid-Open No. 2001-132532, the presence or absence of misfire and the cylinder in which the misfire has occurred may be determined.

  As described above in detail, according to the present embodiment, it is possible to determine whether the main cause of misfire is oxygen deficiency or preheating deficiency based on the compression end temperature and the in-cylinder oxygen concentration. And when oxygen deficiency is a factor, oxygen deficiency can be eliminated preferentially by EGR feedback control. In addition, when insufficient preheating is a factor, the insufficient preheating can be preferentially resolved by pilot feedback control. Therefore, an appropriate misfire suppression control can be selected according to the cause of misfire, and misfire can be efficiently suppressed.

  In addition, when misfire suppression control is executed without specifying the cause of misfire, a problem may occur due to control incompatibility. That is, for example, when the EGR feedback control is executed even though the in-cylinder oxygen concentration is sufficient, there is a possibility that the NOx emission amount increases unnecessarily and the exhaust emission decreases. In addition, when pilot feedback control is executed in spite of sufficient preheating in the cylinder, there is a possibility that the pilot amount becomes excessive and the smoke performance is deteriorated. On the other hand, in this Embodiment, misfire can be suppressed, avoiding said each problem, by using properly two types of misfire suppression controls.

  In the first embodiment, step 100 in FIG. 2 shows a specific example of the compression end temperature calculating means, and step 102 shows a specific example of the in-cylinder oxygen concentration calculating means. Steps 104, 106, 108, and 112 show specific examples of the temperature change amount calculating means, Steps 104, 106, 110, and 112 show specific examples of the concentration change amount calculating means, and Step 114 shows the control switching. A specific example of the means is shown. Step 116 shows a specific example of the first misfire suppression means, and step 118 shows a specific example of the second misfire suppression means.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIG. The present embodiment is characterized in that the misfire suppression control is switched based only on the compression end temperature. FIG. 5 is a flowchart showing an example of control executed by the ECU in the second embodiment of the present invention. The routine shown in this figure is executed when, for example, a misfire is detected. In the routine shown in FIG. 5, first, at step 200, the compression end temperature is calculated by the above-described method.

  Next, in step 202, it is determined whether the compression end temperature is higher than the ignition required temperature. In general, the required ignition temperature is about 1000 [K]. However, the required ignition temperature varies depending on the fuel properties such as cetane number. For this reason, as long as the fuel property can be detected, the temperature required for ignition may be corrected based on the detection result. Moreover, as the ignition required temperature, the above-described target compression end temperature may be used.

  If the determination in step 202 is established, it is determined that the preheating in the cylinder is sufficient, and the above-described EGR feedback control is executed in step 204. On the other hand, if the determination in step 202 is not satisfied, it is determined that the inside of the cylinder is insufficiently preheated, and the above-described pilot feedback control is executed in step 206.

  In the present embodiment configured as described above, the same effect as in the first embodiment can be obtained. Further, according to the present embodiment, the amount of calculation of ECU 50 may be less than that of the first embodiment, so that the control can be easily implemented and the influence of heat generation of ECU 50 can be suppressed.

  In the first and second embodiments, the case where the compression end temperature is calculated by the calculation model shown in the equations 1 to 3 is exemplified. However, in the present invention, a cylinder pressure sensor that detects the cylinder pressure may be provided, and the compression end temperature may be calculated based on the output of the cylinder pressure sensor.

10 Engine (Internal combustion engine)
12 Fuel Injection Valve 18 Intake Passage 20 Exhaust Passage 26 EGR Mechanism 28 EGR Passage 30 EGR Valve 40 Sensor System 50 ECU

Claims (1)

A fuel injection valve for injecting fuel into the cylinder;
An EGR mechanism that recirculates a portion of the exhaust gas as EGR gas to the intake system;
First misfire suppression means for suppressing misfire by controlling the recirculation amount of EGR gas by the EGR mechanism;
Second misfire suppression means for suppressing misfire by controlling the fuel injection amount of pilot injection executed before main injection;
Compression end temperature calculating means for calculating the compression end temperature at the compression top dead center;
In-cylinder oxygen concentration calculating means for calculating in-cylinder oxygen concentration;
A temperature change amount calculating means for calculating a change amount of the compression end temperature necessary for suppressing misfire based on a calculated value of the compression end temperature;
A concentration change amount calculating means for calculating a change amount of the in-cylinder oxygen concentration necessary for suppressing misfire based on the calculated value of the in-cylinder oxygen concentration;
When the change amount of the in-cylinder oxygen concentration is larger than the change amount of the compression end temperature, the first misfire suppression means is operated, and the change amount of the in-cylinder oxygen concentration is larger than the change amount of the compression end temperature. Control switching means for operating the second misfire suppression means,
The control apparatus of the internal combustion engine provided with.

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