JP2007092645A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately calculate cylinder filling air quantity while considering intake air cooling effect by evaporation latent heat of injected fuel, in a cylinder injection engine. <P>SOLUTION: This control device calculates base intake air quantity according to engine rotation speed and intake air pressure or the like, and temperature correction coefficient according to intake air temperature and cooling water temperature. Moreover, intake air cooling effect correction coefficient is calculated according to fuel injection start timing in intake stroke. Since a cylinder injection engine has characteristics that cooling effect of intake air by evaporation latent heat of injected fuel gets larger and cylinder filling air quantity increases as fuel injection timing in intake stroke is retarded, establishment is done to make intake air cooling effect collection coefficient gets larger as fuel injection start timing in intake stroke is retarded. Cylinder filling air quantity corrected according to intake air cooling effect by evaporation latent heat of injected fuel by multiplying the base intake air quantity by the temperature correction coefficient and the intake air cooling effect correction coefficient. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine in which injected fuel injected from a fuel injection valve is mixed with intake air and burned.

In general, in a control system for an internal combustion engine, an in-cylinder charged air amount (the amount of air charged in the cylinder) is calculated based on the operating state of the internal combustion engine, and a fuel injection amount or an ignition is calculated based on the in-cylinder charged air amount. Control parameters such as timing are calculated. For example, as described in Patent Document 1 (Japanese Patent Laid-Open No. 9-303242), the intake air amount per rotation is calculated based on the output of the air flow meter and the rotation speed of the internal combustion engine at a predetermined cycle, For each intake stroke of each cylinder, the average value of the intake air amount at the intake valve opening timing and the intake valve closing timing (or the intake air amount at the midpoint of the intake valve opening period) is the representative value of the intake air amount of each cylinder ( In some cases, the ignition timing of each cylinder is calculated based on the representative value of the intake air amount.
JP-A-9-303242 (pages 5 to 6 etc.)

  In general, in an internal combustion engine, fuel injected from a fuel injection valve is mixed with intake air and burned. When the injected fuel evaporates (vaporizes) in the intake air, the intake air is cooled by the latent heat of vaporization of the injected fuel. As a result, the density of the intake air increases. According to the research results of the present inventors, it has been confirmed that the amount of air charged in the cylinder is increased due to the cooling effect of the intake air generated by the latent heat of vaporization of the injected fuel, and the air-fuel ratio is changed. In a direct injection internal combustion engine that directly injects fuel, the influence of the intake air cooling effect due to the latent heat of vaporization of the injected fuel on the control parameters of the internal combustion engine tends to be greater than that of the intake port injection internal combustion engine.

  However, in the technique of Patent Document 1 described above, the intake air cooling effect due to the latent heat of vaporization of the injected fuel is not taken into consideration at all, and therefore, the in-cylinder charged air amount tends to be calculated smaller than the actual amount. For this reason, the control parameters such as the fuel injection amount and the ignition timing calculated based on the calculated value of the in-cylinder charged air amount are deviated from appropriate values, and the internal combustion engine cannot be accurately controlled.

  The present invention has been made in consideration of such circumstances. Therefore, the object of the present invention is to reflect the intake air cooling effect due to the latent heat of vaporization of the injected fuel in the control parameters of the internal combustion engine. It is an object of the present invention to provide a control device for an internal combustion engine that can improve the calculation accuracy and consequently the control accuracy of the internal combustion engine.

  In order to achieve the above object, according to a first aspect of the present invention, there is provided a control apparatus for an internal combustion engine in which the injected fuel injected from the fuel injection valve is mixed with the intake air and burned. The control parameters of the internal combustion engine are corrected according to the intake air cooling effect due to latent heat.

  In this way, the fuel injection amount calculated based on the in-cylinder charged air amount corresponding to the substantial change in the in-cylinder charged air amount according to the intake air cooling effect due to the latent heat of vaporization of the injected fuel. Control parameters such as ignition timing and the like can be corrected, so that the calculation accuracy of the control parameters and thus the control accuracy of the internal combustion engine can be improved.

  In this case, in the system for calculating the in-cylinder charged air amount filled in the cylinder of the internal combustion engine as in claim 2, the in-cylinder charged air amount is corrected according to the intake air cooling effect due to the latent heat of vaporization of the injected fuel. You may do it. In this way, the calculated value of the in-cylinder charged intake air amount can be corrected in response to the substantial change in the in-cylinder charged air amount according to the intake air cooling effect due to the latent heat of vaporization of the injected fuel, The in-cylinder charged intake air amount can be calculated with high accuracy. In addition, if the in-cylinder charged air amount is corrected, it is not necessary to individually correct the control parameters such as the fuel injection amount and ignition timing calculated based on the in-cylinder charged air amount, thereby simplifying the calculation process. There is also an advantage that can be.

  Further, as in claim 3, the control parameter may be corrected in consideration of the fuel injection timing in addition to the intake air cooling effect due to the latent heat of vaporization of the injected fuel. When the fuel injection timing changes, the so-called wet amount (the amount of fuel adhering to the wall surface) changes and the amount of injected fuel that evaporates in the intake air changes, and the intake cooling effect due to the latent heat of vaporization of the injected fuel changes. If the control parameter (for example, the control parameter calculated based on the in-cylinder charged air amount or the in-cylinder charged air amount) is corrected in accordance with Can be corrected.

  According to the research results of the present inventors, as shown in FIG. 2, in the cylinder injection internal combustion engine, when the fuel injection timing in the intake stroke is early, the fuel is injected at the timing when the piston is positioned above the cylinder. Since the amount of fuel adhering to the piston increases and the amount of injected fuel that evaporates in the intake air decreases accordingly, the intake air cooling effect due to the latent heat of vaporization of the injected fuel is reduced, and the amount of air charged in the cylinder is substantially reduced. Decrease. On the other hand, if the fuel injection timing in the intake stroke is delayed, the fuel is injected when the piston is positioned below the cylinder, so the amount of fuel adhering to the piston decreases, and the injected fuel that evaporates in the intake air accordingly. Since the amount increases, the intake air cooling effect due to the latent heat of vaporization of the injected fuel increases, and the in-cylinder charged air amount substantially increases. That is, it has been found that in a cylinder injection internal combustion engine, as the fuel injection timing in the intake stroke is delayed, the intake air cooling effect due to the latent heat of vaporization of the injected fuel tends to increase, and the amount of cylinder charge air tends to increase.

  In consideration of such circumstances, when the present invention is applied to a direct injection internal combustion engine as in claim 4, the control parameter becomes longer as the fuel injection timing in the intake stroke of the direct injection internal combustion engine is delayed. It is good to correct so that the amount of correction becomes larger. In this way, as the fuel injection timing in the intake stroke of the in-cylinder internal combustion engine is delayed, the intake air cooling effect due to the latent heat of vaporization of the injected fuel increases, and the increase in the in-cylinder charged air amount increases. Thus, the correction amount of the control parameter can be increased.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
First, a schematic configuration of the entire engine control system will be described with reference to FIG. An air cleaner 13 is provided at the most upstream portion of the intake pipe 12 of the cylinder injection engine 11 which is a cylinder injection internal combustion engine, and a throttle valve whose opening degree is adjusted by a motor 14 on the downstream side of the air cleaner 13. 15 is provided. Further, a surge tank 16 is provided on the downstream side of the throttle valve 15, and an intake pipe pressure sensor 17 for detecting the intake pipe pressure is provided in the surge tank 16. The surge tank 16 is provided with an intake manifold 18 that introduces air into each cylinder of the engine 11.

  A fuel injection valve 19 for directly injecting fuel into the cylinder is attached to the upper part of each cylinder of the engine 11. The fuel discharged from the high-pressure fuel pump 21 is sent to the delivery pipe 23 through the high-pressure fuel pipe 22, and the high-pressure fuel is distributed from the delivery pipe 23 to the fuel injection valve 19 of each cylinder. The delivery pipe 23 is provided with a fuel pressure sensor 24 that detects the pressure of the fuel supplied to the fuel injection valve 19.

  Further, a spark plug 20 is attached to each cylinder of the cylinder head of the engine 11, and the air-fuel mixture in the cylinder is ignited by spark discharge of each spark plug 20. Furthermore, the intake valve and the exhaust valve of the engine 11 are each provided with a variable valve timing device (not shown) that varies the opening / closing timing.

  On the other hand, the exhaust pipe 25 of the engine 11 is provided with an exhaust gas sensor 26 (an air-fuel ratio sensor, an oxygen sensor, etc.) that detects the air-fuel ratio or rich / lean of the exhaust gas. Between the upstream side of the exhaust gas sensor 26 in the exhaust pipe 25 and the surge tank 16 on the downstream side of the throttle valve 15 in the intake pipe 12, an EGR pipe 27 for returning a part of the exhaust gas to the intake side. And an EGR valve 28 for controlling the exhaust gas recirculation amount (EGR amount) is provided in the middle of the EGR pipe 27.

  A cooling water temperature sensor 29 that detects the cooling water temperature and a crank angle sensor 30 that outputs a crank angle signal (pulse signal) each time the crankshaft of the engine 11 rotates a predetermined crank angle are attached to the cylinder block of the engine 11. It has been. Based on the crank angle signal of the crank angle sensor 30, the crank angle and the engine speed are detected. Further, the accelerator sensor 31 detects the amount of depression of the accelerator pedal (accelerator opening).

  Outputs of these various sensors are input to an engine control circuit (hereinafter referred to as “ECU”) 32. The ECU 32 is mainly composed of a microcomputer, and executes various engine control programs stored in a built-in ROM (storage medium) to thereby determine the fuel injection amount of the fuel injection valve 19 according to the engine operating state. The ignition timing of the spark plug 20 is controlled.

At that time, the ECU 32 calculates the in-cylinder charged air amount (the amount of air charged in the cylinder) as follows by executing a later-described in-cylinder charged air amount calculation program in FIG.
As shown in FIG. 3, first, the basic intake air amount is calculated by a map or a mathematical formula according to the engine speed, the intake pipe pressure, the intake valve closing timing, the exhaust valve closing timing, and the like.

  Further, a temperature correction coefficient is calculated by a map or a mathematical expression according to the intake air temperature and the cooling water temperature. Generally, the lower the intake air temperature and the cooling water temperature, the higher the density of intake air and the greater the amount of in-cylinder charged air. Therefore, the temperature correction coefficient is set so as to increase as the intake air temperature or the cooling water temperature decreases.

  Further, an intake cooling effect correction coefficient is calculated by a map or a mathematical expression according to the fuel injection start timing in the intake stroke. As shown in FIG. 2, in the in-cylinder injection engine 11, when the fuel injection start timing in the intake stroke is early, the fuel is injected at a timing when the piston is located at the upper part of the cylinder, so that the amount of fuel adhering to the piston increases. Accordingly, the amount of injected fuel that evaporates in the intake air is reduced, so that the intake air cooling effect due to the latent heat of vaporization of the injected fuel is reduced, and the in-cylinder charged air amount is substantially reduced. On the other hand, when the fuel injection timing in the intake stroke is delayed, the fuel is injected when the piston is located at the lower part of the cylinder, so the amount of fuel adhering to the piston decreases, and the injected fuel that evaporates in the intake air accordingly. Since the amount increases, the intake air cooling effect due to the latent heat of vaporization of the injected fuel increases, and the in-cylinder charged air amount substantially increases. In other words, in the in-cylinder injection engine 11, as the fuel injection start timing in the intake stroke is delayed, the intake air cooling effect due to the latent heat of vaporization of the injected fuel tends to increase and the amount of in-cylinder charged air tends to increase. In consideration of such circumstances, the intake air cooling effect correction coefficient for correcting the in-cylinder charged air amount according to the intake air cooling effect due to the latent heat of vaporization of the injected fuel becomes larger as the fuel injection start timing in the intake stroke is delayed. It is set as follows.

After calculating the temperature correction coefficient and the intake air cooling effect correction coefficient in this way, as shown in FIG. 3, the basic air intake air amount is multiplied by the temperature correction coefficient and the intake air cooling effect correction coefficient to obtain the temperature correction coefficient and An in-cylinder charged air amount corrected using the intake air cooling effect correction coefficient is obtained.
In-cylinder charged air amount = basic intake air amount x temperature correction coefficient x intake air cooling effect correction coefficient

  The ECU 32 calculates control parameters such as the fuel injection amount, the ignition timing, and the EGR amount based on the in-cylinder charged air amount calculated as described above, the engine rotation speed, and the like by using a map or a mathematical expression.

  Hereinafter, processing contents of the cylinder charge air amount calculation program of FIG. 4 executed by the ECU 32 will be described. The in-cylinder charged air amount calculation program shown in FIG. 4 is executed at a predetermined cycle while the ECU 32 is turned on, and serves as the in-cylinder charged air amount calculation means in the claims. When this program is started, first, at step 101, the engine speed detected by the crank angle sensor 30 is read. Thereafter, the process proceeds to step 102, and the intake pipe pressure detected by the intake pipe pressure sensor 17 is read. Then, the process proceeds to step 103, and the closing timing of the intake valve and the closing timing of the exhaust valve are read.

  Thereafter, the routine proceeds to step 104, where the basic intake air amount is calculated according to the engine speed, intake pipe pressure, intake valve closing timing, and exhaust valve closing timing with reference to the basic intake air amount map. To do. The basic intake air amount map is set in advance based on test data, design data, and the like, and is stored in the ROM of the ECU 32.

  Thereafter, the process proceeds to step 105, the intake air temperature detected by an intake air temperature sensor (not shown) is read, and then the process proceeds to step 106, where the cooling water temperature detected by the cooling water temperature sensor 29 is read.

  Thereafter, the process proceeds to step 107, and a temperature correction coefficient corresponding to the intake air temperature and the cooling water temperature is calculated with reference to the temperature correction coefficient map. In general, the lower the intake air temperature or the cooling water temperature, the higher the intake air density and the larger the amount of air charged in the cylinder. Therefore, the temperature correction coefficient map increases as the intake air temperature or the cooling water temperature decreases. Is set to The temperature correction coefficient map is set in advance based on test data, design data, and the like, and is stored in the ROM of the ECU 32.

  Thereafter, the routine proceeds to step 108, and after reading the fuel injection start timing of the intake stroke, the routine proceeds to step 109, where the intake cooling effect correction coefficient corresponding to the fuel injection start timing is determined with reference to the map of the intake cooling effect correction coefficient. calculate.

  As described above, in the in-cylinder injection engine 11, as the fuel injection start timing in the intake stroke is delayed, the intake air cooling effect due to the latent heat of vaporization of the injected fuel tends to increase and the amount of in-cylinder charged air tends to increase. The map of the cooling effect correction coefficient is set so that the intake air cooling effect correction coefficient increases as the fuel injection start timing is delayed. The cooling effect correction coefficient map is set in advance based on test data, design data, and the like, and is stored in the ROM of the ECU 32.

  Thereafter, the routine proceeds to step 110, where the basic intake air amount is multiplied by the temperature correction coefficient and the intake air cooling effect correction coefficient to obtain the in-cylinder charged air amount corrected using the temperature correction coefficient and the intake air cooling effect correction coefficient. Ask. The processing of these steps 109 and 110 serves as an intake air cooling effect correction means in the claims.

  In the present embodiment described above, attention is paid to the characteristic that as the fuel injection timing in the intake stroke of the in-cylinder injection engine 11 is delayed, the intake air cooling effect due to the latent heat of vaporization of the injected fuel increases and the in-cylinder charged air amount increases. Thus, an intake air cooling effect correction coefficient is obtained according to the fuel injection start timing in the intake stroke of the in-cylinder injection engine 11, and the basic intake air amount is corrected using the intake air cooling effect correction coefficient to obtain the in-cylinder charged air amount. Since it is calculated, the calculated value of the in-cylinder charged intake air amount can be corrected in response to the change in the in-cylinder charged air amount in accordance with the intake air cooling effect due to the latent heat of vaporization of the injected fuel. The charged intake air amount can be accurately calculated. As a result, even if the intake air cooling effect due to the latent heat of vaporization of the injected fuel changes, it is possible to accurately calculate control parameters such as the fuel injection amount, ignition timing, and EGR amount that are calculated based on the in-cylinder charged air amount. The control accuracy of the engine 11 can be improved. Moreover, in order to correct the in-cylinder charged air amount, it is not necessary to individually correct control parameters such as the fuel injection amount, ignition timing, and EGR amount calculated based on the in-cylinder charged air amount, thereby simplifying the calculation process. There is also an advantage that can be realized.

In the above embodiment, the intake air cooling effect correction coefficient is obtained according to the fuel injection start timing. However, the intake air cooling effect correction coefficient may be obtained according to the fuel injection end time.
In the above embodiment, the in-cylinder charged air amount is corrected using the intake cooling effect correction coefficient. However, the fuel injection amount, ignition timing, EGR amount, etc. calculated based on the in-cylinder charged air amount The control parameter may be corrected using an intake air cooling effect correction coefficient. In this way, the fuel injection amount calculated based on the in-cylinder charged air amount and the ignition timing corresponding to the change in the in-cylinder charged air amount according to the intake air cooling effect due to the latent heat of vaporization of the injected fuel. The control parameters such as the EGR amount can be corrected, and the control parameters such as the fuel injection amount, the ignition timing, and the EGR amount can be accurately calculated even if the intake air cooling effect due to the latent heat of vaporization of the injected fuel changes. The control accuracy of the engine 11 can be improved.

  In the above embodiment, the present invention is applied to a direct injection engine, but may be applied to an intake port injection engine. In an intake port injection type engine, for example, an intake cooling effect correction coefficient is obtained in accordance with the fuel injection timing or the wet amount, and control parameters (in-cylinder charged air amount and in-cylinder charged air amount are calculated using the intake cooling effect correction coefficient). If the control parameters such as the fuel injection amount, ignition timing, and EGR amount calculated based on the above are corrected, the control parameters can be corrected according to the intake air cooling effect due to the latent heat of vaporization of the injected fuel.

  In the above embodiment, the intake air cooling effect correction coefficient is calculated according to the fuel injection timing. However, other information related to the intake air cooling effect due to the latent heat of vaporization of the injected fuel (for example, fuel pressure, fuel injection amount, etc.) The intake cooling effect correction coefficient may be calculated based on the fuel injection time, the number of fuel injections, the in-cylinder pressure, and the like.

  The control parameters to be corrected according to the intake air cooling effect due to the evaporation latent heat of the injected fuel are not limited to the in-cylinder charged air amount, the fuel injection amount, the ignition timing, and the EGR amount. Other control parameters that are affected (for example, valve timing, valve lift amount, purge amount, etc.) may be corrected according to the intake air cooling effect due to the latent heat of vaporization of the injected fuel.

It is a schematic block diagram of the whole engine control system in one Example of this invention. It is a characteristic view explaining the relationship between the fuel injection start timing and the cylinder air charge amount. It is a block diagram which shows roughly the calculation function of the cylinder air charge amount. It is a flowchart which shows the flow of a process of the cylinder air charge amount calculation program.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Cylinder-injection engine (cylinder-injection internal combustion engine), 12 ... Intake pipe, 15 ... Throttle valve, 17 ... Intake pipe pressure sensor, 19 ... Fuel injection valve, 20 ... Spark plug, 25 ... Exhaust pipe, 29 ... Cooling water temperature sensor, 30 ... Crank angle sensor, 32 ... ECU (in-cylinder charged air amount calculating means, intake air cooling effect correcting means)

Claims (4)

In a control device for an internal combustion engine that burns fuel injected from a fuel injection valve by mixing with intake air,
A control apparatus for an internal combustion engine, comprising: an intake air cooling effect correcting means for correcting a control parameter of the internal combustion engine in accordance with an intake air cooling effect due to latent heat of vaporization of the injected fuel. In-cylinder charged air amount calculating means for calculating an in-cylinder charged air amount to be filled in the cylinder of the internal combustion engine,
2. The control device for an internal combustion engine according to claim 1, wherein the intake air cooling effect correction unit corrects the in-cylinder charged air amount in accordance with an intake air cooling effect caused by latent heat of vaporization of the injected fuel.   3. The internal combustion engine according to claim 1, wherein the intake air cooling effect correcting unit corrects the control parameter in consideration of a fuel injection timing in addition to an intake air cooling effect due to latent heat of vaporization of the injected fuel. Control device. The internal combustion engine is a cylinder injection internal combustion engine that directly injects fuel into a cylinder.
4. The control device for an internal combustion engine according to claim 3, wherein the intake air cooling effect correcting means corrects the control parameter so that the correction amount of the control parameter increases as the fuel injection timing in the intake stroke is delayed.

Images