JP2005282441A - Fuel injection control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately determine whether or not a pilot injection amount should be corrected before correcting the pilot injection amount and thereby to reduce combustion noise. <P>SOLUTION: The fuel injection control device is employed in an engine, in which fuel injection is divided into pilot injection and main injection to inject the fuel into a combustion chamber 17 of each cylinder 12, and the pilot injection amount is adjusted to suppress the combustion noise. An electronic control unit 35 calculates the maximum value of change rate in combustion pressure for each of the pilot injection and the main injection based on a detection value of cylinder pressure sensor 27. Only when the sum of each maximum value is larger than a determination value corresponding to an upper limit value of a tolerance with regard to the combustion noise, the pilot injection amount is corrected. In the correction, the maximum value of the change rate with regard to the pilot injection is compared to a predetermined target value. As a result of comparison, when the maximum value is larger than the target value, the correction of the the pilot injection amount is performed to reduce the amount. When the maximum value is the target value or less, the correction of the pilot injection amount is performed to increase the amount. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel injection control device for an internal combustion engine that executes pilot injection prior to main injection.

  In the initial stage of the combustion process in a diesel engine, the fuel injected into the combustion chamber for each cylinder starts to burn rapidly due to self-ignition, so the rate of change in combustion pressure tends to increase. Therefore, in order to reduce combustion noise, it is effective to suppress a sudden change in combustion pressure in the initial stage of the combustion process.

  Therefore, conventionally, “split injection” in which a required amount of fuel is injected into “pilot injection” and “main injection” has been put into practical use. In this divided injection, after a part of the fuel to be injected into the combustion chamber is injected (pilot injection), the injection is temporarily interrupted. Then, after the fuel injected at the time of pilot injection is self-ignited, the remaining fuel is injected again into the combustion gas (main injection). The fuel injected at the time of main injection is burned as if it were the fuel injected at the time of pilot injection, so the ignition delay period is shortened, the rise in combustion pressure in the initial stage of the combustion process becomes slow, and combustion noise is reduced. Increase is suppressed.

  In such divided injection, there is an optimum pilot injection amount (optimum value) that can most suppress the combustion noise. If the pilot injection amount is less than the optimum value, the ignition delay period of the main injection becomes long and the combustion noise increases. Conversely, if the pilot injection amount is greater than the optimum value, the injected fuel at the time of pilot injection burns rapidly, which can cause combustion noise.

Thus, for example, Patent Document 1 describes a technique for effectively reducing combustion noise by controlling the pilot injection amount to be an optimum value. In this technique, the vibration of the engine is detected by an acceleration sensor attached to the cylinder block. The pilot injection amount is sequentially increased by a set amount until the detected engine vibration falls below the threshold value. When the detected engine vibration falls below the threshold value, the pilot injection amount immediately before that is held.
Japanese Patent Laid-Open No. 7-12002 (page 4, FIG. 1)

  However, in the technique described in Patent Document 1, since the acceleration sensor is attached to the cylinder block, not only the vibration based on the combustion pressure is detected but also other vibrations, for example, the piston hits the wall surface of the cylinder bore. In addition, vibration generated when the camshaft cam depresses the valve or valve lifter is also detected. Therefore, in the above technique using the detection value including vibration other than vibration based on the combustion pressure, the accuracy of determination as to whether or not to correct the pilot injection amount is low. As a result, the pilot injection amount is maintained even though large combustion noise is generated, and the combustion noise cannot be suppressed, or the pilot injection amount is unnecessary even though the combustion noise is sufficiently low. There is a risk of increasing the amount of correction.

  The present invention has been made in view of such circumstances, and its purpose is to accurately grasp the necessity of correcting the pilot injection amount and then correct the pilot injection amount to reduce combustion noise. It is an object of the present invention to provide a fuel injection control device for an internal combustion engine.

  In general, the in-cylinder pressure of an internal combustion engine mainly includes a pressure (compression pressure) that changes with the reciprocation of a piston, and a pressure (combustion pressure) that changes with the combustion of fuel. These compression pressures and combustion pressures serve as excitation forces for pistons, cylinder heads and the like. These pressures vibrate pistons, cylinder heads, and the like, and the vibrations are transmitted to the wall surface of the cylinder block through the various parts of the engine. These vibrations may be transmitted as air vibrations (sound waves) and cause noise.

  On the other hand, in an internal combustion engine that performs split injection in which the required amount of fuel is divided into pilot injection and main injection, the combustion noise is effectively suppressed by correcting the pilot injection amount to an optimum value. I know I can.

  The inventors of the present invention have examined various guidelines for determining whether or not to correct the pilot injection amount, and further, in which direction of increase or decrease should be corrected when correction is necessary. Obtained knowledge.

  (I) When calculating the rate of change, which is the time differential value, from the combustion pressure, for each of the pilot injection and the main injection, is there a strong correlation between the maximum value of the rate of change and the combustion noise? Or there is almost no correlation. On the other hand, for the pilot injection and the main injection, a strong correlation is found between the sum of the maximum values of both change rates and the combustion noise.

Therefore, if the sum of the maximum values of both change rates is used as a substitute value for the combustion noise, it is possible to determine whether or not the pilot injection amount needs to be corrected.
(Ii) When the maximum value of the change rate of the combustion pressure at the time of pilot injection is large, it is considered that the combustion pressure is changing rapidly because the pilot injection amount is larger than the appropriate value. On the contrary, when the maximum value of the change rate of the combustion pressure at the time of pilot injection is small, it is considered that the change of the combustion pressure is moderate because the pilot injection amount is smaller than the appropriate value.

  Therefore, if it is determined in the above (i) that the pilot injection amount needs to be corrected, the maximum value of the change rate of the combustion pressure during pilot injection is compared with the target value set based on the combustion noise. Thus, it is possible to determine whether to increase or decrease.

  By the way, it is difficult to directly detect only the combustion pressure during operation of the internal combustion engine. This is because not only the combustion pressure but also the compression pressure changes simultaneously. Therefore, it is conceivable to detect the in-cylinder pressure. However, as described above, the in-cylinder pressure includes the compression pressure. Therefore, if the rate of change of the in-cylinder pressure is simply calculated, only the rate of change of pressure in the form in which the combustion pressure is superimposed on the compression pressure can be obtained. However, the compression pressure can be obtained separately by calculation. Therefore, the change rate of only the combustion pressure can be obtained by subtracting the change rate of the compression pressure from the change rate of the in-cylinder pressure.

  Based on the above knowledge, in the first aspect of the invention, fuel is divided into pilot injection and main injection and injected into the combustion chamber of each cylinder of the internal combustion engine, and combustion noise is suppressed by adjusting the pilot injection amount. In the internal combustion engine fuel injection control apparatus configured as described above, for each of the pilot injection and the main injection, a maximum value calculating means for calculating the maximum value of the change rate of the combustion pressure, and both maximum values by the maximum value calculating means Pilot injection amount correcting means for calculating the sum and correcting the pilot injection amount only when the sum is larger than a determination value corresponding to the upper limit value of the allowable range for the combustion noise is provided.

  According to the above configuration, the maximum value calculation means calculates the maximum value of the change rate of the combustion pressure for each of the pilot injection and the main injection. The pilot injection amount correcting means calculates the sum of the maximum values of the change rate of the combustion pressure by the maximum value calculating means for both the pilot injection and the main injection. Then, the sum is compared with a determination value corresponding to an upper limit value allowable for combustion noise. When the sum is less than or equal to the determination value, the combustion noise is at an acceptable level, and when the sum is greater than the determination value, it can be said that the combustion noise exceeds the allowable level. For these reasons, the pilot injection amount correction means does not need to correct the pilot injection amount when the sum of both maximum values is equal to or smaller than the determination value, and corrects the pilot injection amount when the sum is larger than the determination value. It is judged necessary. Based on this determination result, correction is not performed in the former case, and correction is performed in the latter case, so that the pilot injection amount can be set to an appropriate value and combustion noise can be suppressed.

  The invention according to claim 2 further comprises in-cylinder pressure detecting means for detecting the pressure in the cylinder in the invention according to claim 1, wherein the maximum value calculating means is configured to detect the in-cylinder pressure. It is assumed that the change rate of the combustion pressure is calculated by subtracting the maximum value of the change rate of the compression pressure that changes as the piston reciprocates from the maximum value of the change rate of the in-cylinder pressure by the means.

  According to said structure, the cylinder pressure of an internal combustion engine is detected by the cylinder pressure detection means. As described above, the in-cylinder pressure includes the compression pressure in addition to the combustion pressure. The compression pressure in the pilot injection and the main injection can be calculated separately even when the engine is not operating. From this, the maximum value calculating means calculates the maximum value of the rate of change of the in-cylinder pressure detected by the in-cylinder pressure detecting means for each of the pilot injection and the main injection. Then, the maximum value of the change rate of the compression pressure in the pilot injection and the main injection is subtracted from this maximum value. By these subtractions, the maximum value of the change rate of the combustion pressure in the pilot injection and the main injection can be obtained with high accuracy.

  Furthermore, in the invention of claim 3, in the invention of claim 1 or 2, the maximum value of the rate of change for the pilot injection by the maximum value calculation means and the pilot for making the combustion noise an appropriate value. Comparing means for comparing with a target value corresponding to the injection amount is further provided, and the pilot injection amount correcting means reduces the pilot injection amount when the maximum value of the change rate is larger than the target value by the comparing means. When the maximum value of the change rate is equal to or less than the target value, the pilot injection amount is corrected to be increased.

  According to the above configuration, when the pilot injection amount correcting means determines that the sum of both maximum values is larger than the determination value, the combustion noise is large, and thus the pilot injection amount needs to be corrected. In this case, the comparison means compares the maximum value of the change rate for the pilot injection by the maximum value calculation means with the target value corresponding to the pilot injection amount for making the combustion noise an appropriate value. As a result of comparison, if it is determined that the maximum value of the rate of change is larger than the target value, the pilot injection amount will deviate more than the appropriate value due to, for example, variations among individual combustion injectors or changes over time. Therefore, it is considered that the injected fuel at the time of pilot injection burns rapidly and combustion noise may be generated. On the other hand, when it is determined that the maximum value of the change rate is equal to or less than the target value, the pilot injection amount shifts to a smaller side than the appropriate value, and the ignition delay period of the main injection becomes longer and the combustion noise increases. It is thought that there is a risk. Therefore, the pilot injection amount correction means corrects the pilot injection amount when the maximum value of the change rate is larger than the target value, and reduces the pilot injection amount when the maximum value is less than the target value. The increase is corrected. These corrections make it possible to bring the pilot injection amount close to an appropriate value and reduce the combustion noise.

Hereinafter, an embodiment embodying the present invention will be described.
FIG. 1 shows a schematic configuration of a diesel engine (hereinafter simply referred to as an engine) 11 mounted on a vehicle. The engine 11 includes a cylinder block 13 having a plurality of cylinders 12 and a cylinder head 14 disposed thereon. A piston 15 is accommodated in each cylinder 12 so as to be able to reciprocate. Each piston 15 is connected via a connecting rod 16 to a crankshaft (not shown) that is an output shaft of the engine 11. The reciprocating motion of each piston 15 is converted into rotational motion by the connecting rod 16 and then transmitted to the crankshaft.

The engine 11 is provided with a combustion chamber 17 for each cylinder 12. An intake passage 18 and an exhaust passage 19 are connected to each combustion chamber 17.
A fuel injection valve 21 that injects fuel into the combustion chamber 17 of each cylinder 12 is attached to the cylinder head 14. Each fuel injection valve 21 is provided with an electromagnetic valve and a needle valve (both not shown), and the fuel injection from the fuel injection valve 21 to each combustion chamber 17 is controlled by controlling the energization of the electromagnetic valve. . The fuel injection valve 21 for each cylinder 12 is connected to a common rail 22 that is a common stock pressure pipe. While the needle valve is lifted and the fuel injection valve 21 is opened, the fuel in the common rail 22 is The fuel is injected from the injection hole of the fuel injection valve 21 into the corresponding combustion chamber 17. A relatively high pressure corresponding to the fuel injection pressure is accumulated in the common rail 22. In order to realize this stock pressure, the common rail 22 is connected to a supply pump (both not shown) via a supply pipe. The supply pump sucks fuel from the fuel tank and reciprocates the plunger by a cam synchronized with the rotation of the engine 11 to increase the fuel to a predetermined pressure and supply the fuel to the common rail 22.

  Then, fuel is injected from the fuel injection valve 21 into the high-temperature and high-pressure intake air introduced into the cylinder 12 through the intake passage 18 and compressed by the piston 15. The injected fuel self-ignites and burns. The piston 15 is reciprocated by the combustion gas generated at this time, the crankshaft is rotated, and the driving force (output torque) of the engine 11 is obtained.

  The combustion process in the engine 11 is roughly divided into a premixed combustion period and a subsequent diffusion combustion period. In the premixed combustion period, the fuel injected into the combustion chamber 17 becomes a combustible air-fuel mixture and self-ignites, so that the fuel combustion proceeds rapidly. In the diffusion combustion period, the fuel is injected into the combustion gas generated in the combustion chamber 17 during the premixed combustion period, so that the fuel is continuously burned.

  By the way, in the premixed combustion period, since the combustion proceeds rapidly as described above, the change rate (increase rate) of the combustion pressure in the combustion chamber 17 tends to increase. Therefore, if this premixed combustion period becomes long, that is, if the proportion of fuel that burns rapidly by self-ignition increases, combustion noise increases.

  In order to suppress such an increase in combustion noise, in the engine 11 of this embodiment, in the fuel injection, in addition to “normal injection” in which a required amount of fuel is injected at a time, the required amount of fuel is “pilot injection” and “ “Split injection” is performed in which the fuel is divided into “main injection”. In the split injection, after a part of the fuel to be injected into the combustion chamber 17 is injected (pilot injection), the fuel injection is temporarily interrupted. Then, when the fuel injected by the pilot injection is ignited, the remaining fuel is injected again (main injection). By executing such pilot injection, the premixed combustion period is shortened, and the proportion of fuel that burns rapidly by self-ignition decreases. Therefore, the increase in combustion pressure becomes slow, and the increase in combustion noise is suppressed. In the figure, pilot injection may be expressed as “P injection” and main injection may be expressed as “M injection”.

  The vehicle is provided with various sensors for detecting various state quantities related to the operation of the engine 11. For example, a crank angle sensor 26 that outputs a pulse signal every time the shaft rotates by a predetermined angle is disposed near the crankshaft. This pulse signal is used to calculate a crank angle that is the rotation angle of the crankshaft, an engine speed that is the number of rotations of the shaft per time, and the like. An in-cylinder pressure sensor 27 is attached to the cylinder head 14 as in-cylinder pressure detection means for detecting the in-cylinder pressure P. A water temperature sensor 28 that detects the temperature of the cooling water that is the temperature of the cooling water flowing in the engine 11 is attached to the cylinder block 13.

  An intake air amount sensor 29 that detects an intake air amount that is the amount of air flowing through the passage 18 and an intake pressure sensor 30 that detects an intake pressure that is the pressure of the intake air are respectively attached to the intake passage 18. It has been. The common rail 22 is provided with a rail pressure sensor 31 that detects a rail pressure that is a pressure of fuel accumulated in the common rail 22.

Further, an accelerator sensor 32 is provided in the vicinity of an accelerator pedal (not shown) for detecting an accelerator depression amount that is a depression amount of the pedal by the driver.
In order to control each part of the engine 11 based on the detection values of the various sensors 26 to 32, an electronic control device 35 is provided in the vehicle. The electronic control unit 35 is configured around a microcomputer, and a central processing unit (CPU) performs arithmetic processing according to a control program, initial data, a control map, etc. stored in a read-only memory (ROM). Various controls are executed based on the calculation result. The calculation result by the CPU is temporarily stored in a random access memory (RAM).

  One of various controls by the electronic control unit 35 is fuel injection control of the fuel injection valve 21. In this fuel injection control, as described above, in addition to “normal injection” in which a required amount of fuel is injected at a time, “divided injection” in which a required amount of fuel is divided into pilot injection and main injection is performed.

  In the fuel injection control in the normal injection, the electronic control unit 35 calculates the basic fuel injection amount and the injection timing according to the operating conditions of the engine 11. Further, the target injection amount is calculated by performing necessary corrections on the calculated basic injection amount. Furthermore, the injection time required for the injection of the amount corresponding to the target injection amount is calculated according to the engine speed and the rail pressure at that time.

  When the injection timing comes, the electronic control unit 35 opens the fuel injection valve 21 by controlling energization to the electromagnetic valve to lift the needle valve, and each cylinder 12 of high-pressure fuel supplied from the common rail 22 is opened. Start injection into Thereafter, the fuel injection valve 21 is held open for the calculated injection time to perform a required amount of fuel injection, and then the fuel injection valve 21 is closed to terminate the fuel injection.

  On the other hand, in the fuel injection control at the time of split injection, the electronic control unit 35 distributes the basic injection amount into the basic pilot injection amount and the basic main injection amount. Further, the target pilot injection amount and the target main injection amount are respectively calculated by performing necessary corrections on both the basic injection amounts. Furthermore, the injection time in both injections according to the engine speed and the rail pressure at that time, that is, the pilot injection time and the main injection time are calculated.

  Then, at the fuel injection timing, the electronic control unit 35 opens the fuel injection valve 21 by lifting the needle valve through the energization control of the solenoid valve over the pilot injection time, and makes the minute amount corresponding to the target pilot injection amount. After injecting a small amount of fuel into each cylinder 12, the fuel injection valve 21 is once closed. Then, after a predetermined period, the fuel injection valve 21 is opened again to resume fuel injection. Thereafter, the fuel injection valve 21 is opened over the main injection time to inject fuel for the target main injection amount, and then the fuel injection is terminated.

  Here, the in-cylinder pressure P of the engine 11 includes a pressure (compression pressure) that changes as the piston 15 reciprocates and a pressure (combustion pressure) that changes as the fuel burns. These compression pressure and combustion pressure serve as an excitation force to the piston 15 and the cylinder head 14. Due to these pressures, the piston 15, the cylinder head 14, and the like vibrate, and the vibrations are transmitted to the wall surface of the cylinder block 13 through each component of the engine 11. This vibration may be transmitted as air vibration (sound wave) and cause noise.

  On the other hand, in the engine 11 of the present embodiment that performs the divided injection in which a required amount of fuel is divided into pilot injection and main injection, combustion noise is corrected by correcting the pilot injection amount to an optimum value. It has been found that can be effectively suppressed.

  The inventors of the present invention have examined various guidelines for determining whether or not to correct the pilot injection amount, and further, in which direction of increase or decrease should be corrected when correction is necessary. Obtained knowledge.

  (I) When the rate of change, which is a time differential value, is calculated from the combustion pressure, there is no strong correlation between the maximum value of the rate of change and the combustion noise for each of the pilot injection and the main injection, or There is almost no correlation. On the other hand, for the pilot injection and the main injection, a strong correlation is found between the sum of the maximum values of the change rates and the combustion noise. Therefore, if the sum of the maximum values of these change rates is used as a substitute value for the combustion noise, it is possible to determine whether or not it is necessary to correct the pilot injection amount.

  By the way, during operation of the engine 11, not only the combustion pressure but also the compression pressure changes at the same time, so it is difficult to directly detect only the combustion pressure. Therefore, in this embodiment, the in-cylinder pressure P is detected by the in-cylinder pressure sensor 27. However, as described above, the in-cylinder pressure P includes the compression pressure. Therefore, if the rate of change of the in-cylinder pressure P is simply calculated, only the rate of change of pressure in the form in which the combustion pressure is superimposed on the compression pressure can be obtained. However, the compression pressure can be obtained by calculation. Therefore, the change rate of the combustion pressure is obtained by subtracting the change rate of the compression pressure from the change rate of the in-cylinder pressure P.

  FIGS. 2A to 2D show the process for obtaining the rate of change of the combustion pressure. Specifically, FIG. 2A shows a change in the lift amount of the needle valve in the fuel injection valve 21 at the time of split injection. The period during which the lift amount changes corresponds to the pilot injection and the main injection. The solid line in FIG. 2B indicates the in-cylinder pressure P that varies with the lift of the needle valve, and the two-dot chain line indicates the compression pressure that varies with the reciprocation of the piston 15. The compression pressure changes more slowly than the combustion pressure. Therefore, the combustion pressure changes at a high frequency of about 1 KHz to 3 KHz, while the compression pressure changes at a low frequency of several hundred Hz. The in-cylinder pressure P is a value measured by the in-cylinder pressure sensor 27, and the compression pressure is obtained by calculation.

  The solid line in FIG. 2 (C) shows the rate of change (time differential value) of the in-cylinder pressure P in FIG. 2 (B), and the two-dot chain line in FIG. ) Shows the rate of change (time differential value) of the compression pressure. In FIG. 2C, the change rate of the in-cylinder pressure P is the sum of the change rate of the compression pressure and the change rate of the combustion pressure.

  FIG. 2 (D) shows the deviation between the rate of change of in-cylinder pressure P and the rate of change of compression pressure in FIG. 2 (C), that is, the rate of change of combustion pressure. In FIG. 2D, the maximum value during pilot injection is ΔdPp, and the maximum value during main injection is ΔdPm.

  FIG. 3 shows the result of measuring the combustion noise when the maximum value ΔdPp of the change rate of the combustion pressure during pilot injection is variously changed. It can be seen from FIG. 3 that there is no strong correlation between the two. FIG. 4 shows the result of measuring the combustion noise when the maximum value ΔdPm of the change rate of the combustion pressure during main injection is variously changed. It can be seen from FIG. 4 that there is almost no correlation between the two.

  On the other hand, FIG. 5 shows the measurement result of the combustion noise when the sum ΔdP of the maximum values ΔdPp and ΔdPm is variously changed. From this figure, it can be seen that when the sum ΔdP (= ΔdPp + ΔdPm) is small, the combustion noise is small, and as the sum ΔdP increases, the combustion noise increases, that is, a positive proportional relationship is observed between the two.

  (Ii) When the maximum value ΔdPp of the change rate of combustion pressure at the time of pilot injection is large, the combustion pressure changes rapidly because the pilot injection amount is larger than the appropriate value, and the maximum value ΔdPp of the same change rate When is small, it is considered that the change in the combustion pressure is moderate because the pilot injection amount is smaller than the appropriate value.

  Therefore, if it is determined in (i) that the pilot injection amount needs to be corrected, the maximum value ΔdPp of the change rate of the combustion pressure at the time of pilot injection and the pilot injection amount for setting the combustion noise to an appropriate value are set. By comparing with a corresponding value (hereinafter referred to as a target value), it is possible to determine the direction of correction such as whether to increase correction or decrease correction.

  Based on the above knowledge, the electronic control unit 35 corrects the pilot injection amount in order to suppress combustion noise. The flowchart of FIG. 6 shows a routine for correcting the pilot injection amount. This pilot injection amount correction routine is performed when a predetermined execution condition is satisfied. The predetermined execution condition is, for example, a so-called steady state in which the operating state of the engine 11 is stable, such as during idling.

  The electronic control unit 35 first reads in-cylinder pressure P from the in-cylinder pressure sensor 27 in step 110. As described above, this in-cylinder pressure P includes not only the combustion pressure but also the compression pressure. Subsequently, in step 120, a change rate that is a time differential value of the in-cylinder pressure P in step 110 is calculated.

  Next, in step 130, a change rate that is a time differential value of the combustion pressure is calculated. Specifically, the rate of change of the compression pressure calculated based on the position of the piston 15, the compression ratio, the supercharging pressure, the EGR rate, etc. is subtracted from the rate of change of the in-cylinder pressure P in step 120. The subtraction result is the change rate of the combustion pressure.

  In step 140, based on the rate of change in combustion pressure in step 130, the maximum value ΔdPp of the rate of change in combustion pressure during pilot injection is calculated. In step 150, the maximum value ΔdPm of the change rate of the combustion pressure at the time of main injection is calculated. Next, in step 160, the sum ΔdP (= ΔdPp + ΔdPm) of the maximum value ΔdPp in step 140 and the maximum value ΔdPm in step 150 is calculated. As described above, there is a strong positive correlation between the sum ΔdP and the combustion noise.

  Next, in step 170, it is determined whether the sum ΔdP obtained in step 160 is larger than a determination value ΔdPmax corresponding to the upper limit value of the allowable range for combustion noise. If this determination condition is not satisfied (ΔdPmax ≧ ΔdP), the combustion noise is suppressed to an appropriate level, and correction of the pilot injection amount for suppressing the combustion noise is unnecessary. Thus, the pilot injection amount correction routine is terminated without performing subsequent processing.

  On the other hand, if the determination condition of step 170 is satisfied (ΔdPmax <ΔdP), the combustion noise is larger than the appropriate level, and it is necessary to correct the pilot injection amount and lower the combustion noise to the appropriate level. However, only the determination process in step 170 cannot grasp the direction of the correction, ie, the increase correction or the decrease correction. Therefore, in step 180, processing for determining the direction of correction is performed. Specifically, in step 180, it is determined whether or not the maximum value ΔdPp in step 140 is larger than the target value. Here, the target value corresponds to the pilot injection amount for setting the combustion noise to an appropriate value, and varies depending on the operating state of the engine 11, for example, the engine speed, the engine load, and the like.

  As a situation where the determination condition of step 180 is satisfied, for example, the pilot injection amount is deviated more than the command value due to variations among individual fuel injection valves 21, changes with time, etc., and the fuel was injected at the time of pilot injection. It is conceivable that the fuel is burning rapidly. This rapid increase in combustion pressure accompanying combustion can contribute to an increase in combustion noise. Therefore, if the determination condition of step 180 is satisfied, the pilot injection amount is corrected to decrease in step 190 to approach the target value. For example, a predetermined value is subtracted from the pilot injection amount at that time, and the subtraction result is set as a new pilot injection amount.

  On the other hand, if the determination condition of step 180 is not satisfied, the pilot injection amount is shifted to a direction smaller than the command value, and it is considered that the ignition delay period of main injection becomes longer and combustion noise may increase. For this reason, in step 200, the pilot injection amount is corrected to be increased to approach the target value. For example, a predetermined constant value is added to the pilot injection amount at that time, and the addition result is set as a new pilot injection amount. Then, after the processing of step 190 or 200, the pilot injection amount correction routine is terminated.

  The pilot injection amount corrected in steps 190 and 200 as described above is used as a pilot injection amount when the operating state of the engine 11 is stable, such as at the next idle.

  In the pilot injection amount correction routine described above, the processing of steps 140 and 150 by the electronic control unit 35 corresponds to the maximum value calculation means, the processing of steps 160 to 200 corresponds to the pilot injection amount correction means, and the processing of step 180 is performed. It corresponds to the comparison means.

According to the embodiment described in detail above, the following effects can be obtained.
(1) The in-cylinder pressure P detected by the in-cylinder pressure sensor 27 is read (step 110), and the combustion pressure is calculated based on the in-cylinder pressure P. For each of the pilot injection and the main injection, the maximum values ΔdPp and ΔdPm of the change rate of the combustion pressure are calculated (steps 140 and 150), and the sum ΔdP of both maximum values ΔdPp and ΔdPm is calculated (step 160). It is determined whether the sum ΔdP is larger than a determination value ΔdPmax corresponding to the upper limit value of the allowable range for combustion noise (step 170). As a result of the determination, the pilot injection amount is not corrected when the sum ΔdP is equal to or smaller than the determination value ΔdPmax, and the pilot injection amount is corrected when the sum is larger than the determination value ΔdPmax (steps 180 to 200). For this reason, unlike the patent document 1 in which the pilot injection amount is corrected to be increased when the engine vibration detected by the acceleration sensor is equal to or greater than the threshold value, the present embodiment accurately grasps whether or not the pilot injection amount needs to be corrected. In addition, the pilot injection amount can be corrected to an appropriate value, and combustion noise can be suppressed.

  (2) The in-cylinder pressure P detected by the in-cylinder pressure sensor 27 includes the compression pressure in addition to the combustion pressure. The compression pressure in the pilot injection and the main injection can be calculated separately even when the engine is not operating. From this, the maximum value of the change rate of the in-cylinder pressure P detected by the in-cylinder pressure sensor 27 is calculated for each of the pilot injection and the main injection, and the change of the compression pressure in the pilot injection and the main injection is calculated from this maximum value. The maximum rate is subtracted. Therefore, by these subtractions, the maximum values ΔdPp and ΔdPm of the change rate of the combustion pressure in the pilot injection and the main injection can be obtained with high accuracy.

  (3) When it is determined that the sum ΔdP of both maximum values ΔdPp and ΔdPm is larger than the determination value ΔdPmax and the pilot injection amount needs to be corrected (step 170: YES), the change rate of the pilot injection The maximum value ΔdPp is compared with a target value corresponding to the pilot injection amount for setting the combustion noise to an appropriate value (step 180). As a result of comparison, if the maximum value ΔdPp is larger than the target value, the pilot injection amount is corrected to decrease, and if the maximum value ΔdPp is less than the target value, the pilot injection amount is corrected to increase. In this way, the pilot injection amount is corrected after the direction of correction of the pilot injection amount is reliably grasped, whereby the pilot injection amount can be brought close to an appropriate value and combustion noise can be reliably suppressed.

Note that the present invention can be embodied in another embodiment described below.
The value that is subtracted from the pilot injection amount when the decrease correction is performed in step 190 in FIG. 6 and the value that is added to the pilot injection amount when the increase correction is performed in step 200 are made different depending on the operating state of the engine 11. May be.

  The present invention can also be applied to a fuel injection control device for an internal combustion engine in which pilot injection is performed twice or more prior to main injection.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows the structure about one Embodiment of the fuel-injection control apparatus of the internal combustion engine of this invention. (A) is a change mode of the lift amount of the needle valve in the fuel injection valve, (B) is a change mode of the in-cylinder pressure and the compression pressure, and (C) is a change mode of each change rate of the in-cylinder pressure and the compression pressure. (D) is a timing chart showing the change mode of the change rate of the combustion pressure. The characteristic view which shows the relationship between maximum value (DELTA) dPp and combustion noise. The characteristic view which shows the relationship between maximum value (DELTA) dPm and combustion noise. The characteristic view which shows the relationship of the sum (DELTA) dP (= (DELTA) dPp + (DELTA) dPm) of maximum value, and combustion noise. The flowchart which shows a pilot injection amount correction | amendment routine.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Diesel engine (internal combustion engine), 12 ... Cylinder, 15 ... Piston, 17 ... Combustion chamber, 27 ... Cylinder pressure sensor (cylinder pressure detection means), P ... Cylinder pressure, (DELTA) dPp, (DELTA) dPm ... Maximum value, (DELTA) dP ... Sum, ΔdPmax: judgment value.

Claims (3)

In a fuel injection control device for an internal combustion engine in which fuel is divided into pilot injection and main injection and injected into a combustion chamber for each cylinder of the internal combustion engine, and the combustion noise is suppressed by adjusting the pilot injection amount.
Maximum value calculating means for calculating the maximum value of the change rate of the combustion pressure for each of the pilot injection and the main injection,
A pilot injection amount correcting unit that calculates a sum of both maximum values by the maximum value calculating unit and corrects the pilot injection amount only when the sum is larger than a determination value corresponding to an upper limit value of an allowable range for combustion noise; A fuel injection control device for an internal combustion engine, comprising: In-cylinder pressure detecting means for detecting the pressure in the cylinder further comprises
The maximum value calculating means subtracts the maximum value of the change rate of the compression pressure that changes with the reciprocation of the piston from the maximum value of the change rate of the in-cylinder pressure by the in-cylinder pressure detection means. The fuel injection control device for an internal combustion engine according to claim 1, wherein the change rate of the engine is calculated. Comparing means for comparing the maximum value of the rate of change for the pilot injection by the maximum value calculating means with a target value corresponding to the pilot injection amount for making the combustion noise an appropriate value;
The pilot injection amount correction means corrects the pilot injection amount by decreasing when the maximum value of the change rate is larger than the target value by the comparing means, and the maximum value of the change rate is equal to or less than the target value. 3. The fuel injection control device for an internal combustion engine according to claim 1, wherein the pilot injection amount is corrected to be increased.

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