JP2004100557A - Fuel injection control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control to appropriate values a fuel injection timing and a fuel injection amount of each injection in a multiple fuel injection. <P>SOLUTION: Cylinder pressure sensors 29a to 29d for detecting pressure inside a combustion chamber are respectively provided on cylinders of a diesel engine 1 for performing the multiple fuel injection a plurality of times per one cylinder cycle. An electronic control unit (ECU) 20 of the engine calculates a primary change rate and a secondary change rate with respect to a crank angle of the pressure inside the combustion chamber based on the detected pressure inside the combustion chamber by the cylinder pressure sensors. By comparing the calculated primary and secondary change rates with a previously determined reference value, the electronic control unit 20 controls the fuel injection timing and the fuel injection amount for each injection in a multiple fuel injection to the appropriate values. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel injection control device for an internal combustion engine, and more particularly, to a fuel injection control device that optimizes combustion of a diesel engine.
[0002]
[Prior art]
In recent years, demands for stricter exhaust gas regulations and requirements for noise reduction have increased demands for diesel engines to optimize combustion in a combustion chamber. In order to optimize combustion, it is necessary to accurately control the fuel injection amount, fuel injection timing, injection period, and the like even in a diesel engine.
[0003]
However, in diesel engines, combustion is performed in a lean air-fuel ratio region that is considerably higher than the stoichiometric air-fuel ratio, and it was not necessary to maintain the air-fuel ratio exactly at the target air-fuel ratio, unlike gasoline engines. Fuel injection parameters such as quantity and fuel injection timing are not as precisely controlled as gasoline engines. Conventionally, in a diesel engine, target values such as a fuel injection amount, an injection timing, an injection pressure, an EGR gas amount, and the like are determined from engine operating conditions (rotational speed, accelerator opening, etc.), and a fuel injection valve is determined in accordance with the target value. Although the open loop control does not prevent the actual fuel injection amount from producing an error with respect to the target injection amount, it is not possible to accurately control the combustion state to the target state. It was difficult.
[0004]
Furthermore, in order to improve exhaust gas properties and reduce noise, it is effective to use multiple fuel injections that perform multiple fuel injections before and after the main fuel injection during one cycle of each cylinder to adjust the combustion state optimally. It is. However, in order to perform multi-fuel injection, it is necessary to precisely control the fuel injection amount and the injection timing of each of the multiple fuel injections.
[0005]
In addition, the common-rail high-pressure fuel injection system, which has recently been used in diesel engines to improve the combustion state, has a short fuel injection time and changes the fuel injection pressure during injection. There is a problem that an error easily occurs. For this reason, in the common rail type high-pressure fuel injection device, measures such as setting the tolerance of the fuel injection valve to be small to improve the fuel injection accuracy are taken. In both cases, since the fuel injection characteristics change, it is difficult to always accurately match the fuel injection amount to the target value.
[0006]
As described above, in a diesel engine, an error easily occurs in the fuel injection amount and the like, so that even if a target value for obtaining an optimum combustion state can be set, it is difficult to actually match the fuel injection amount to the target value. .
In order to match the combustion state to the target combustion state, the actual combustion state is detected in some form, and the fuel injection amount and fuel injection timing are adjusted so that the actual combustion state matches the target combustion state. It is effective to feedback control the fuel injection parameters.
[0007]
As described above, an example of a combustion control apparatus for an internal combustion engine that detects a combustion state and performs feedback control of a fuel injection parameter is described in Patent Document 1.
[0008]
The device of Patent Document 1 measures combustion noise of a diesel engine, determines whether the pilot injection amount is too large or too small based on the measured combustion noise, and corrects the pilot injection amount based on this. . In addition, by using a differential value or a second-order differential value of the in-cylinder pressure detected by the in-cylinder pressure sensor that detects the pressure in the combustion chamber, the accuracy of detecting the combustion noise can be improved by eliminating the influence of mechanical vibration. I have to.
[0009]
That is, the apparatus of Patent Document 1 always controls the combustion noise to a target level or less by performing feedback control of the pilot injection amount based on the actually measured combustion noise.
[0010]
[Patent Document 1]
JP 2001-123881 A
[0011]
[Problems to be solved by the invention]
In the device disclosed in Patent Document 1, since the pilot injection amount is feedback-controlled based on the actually measured combustion noise, the combustion noise can always be suppressed to a target level or less. However, in the device of Patent Document 1, although the combustion noise is suppressed to a target value or less, a good combustion state is not always obtained, and the exhaust characteristics may deteriorate.
[0012]
That is, in order to obtain good exhaust properties, it is necessary to appropriately control not only the pilot injection amount but also the injection timing. However, in the device of Patent Document 1, the pilot injection amount is determined based on combustion noise. Since only the control is performed, there is a problem that even if the combustion noise is reduced, the exhaust property is not always improved.
[0013]
Further, since the device of Patent Document 1 is intended only for pilot injection, which is an operation in which pilot injection is performed only once, a multi-fuel system that performs multiple pilot injections or after-injection after main fuel injection may be used. In the injection, the injection amount and the injection timing of each fuel injection cannot be appropriately controlled.
[0014]
SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems of the related art, and has been made in consideration of the above-described problems. It is intended to provide.
[0015]
[Means for Solving the Problems]
According to the first aspect of the present invention, there is provided an internal combustion engine that performs multi-fuel injection in which fuel is injected into an engine combustion chamber before or after main fuel injection or both before and after main fuel injection in addition to main fuel injection. A fuel injection control device, comprising: an in-cylinder pressure sensor that detects a pressure in an engine combustion chamber, and calculating a primary change rate and a secondary change rate of a combustion chamber pressure detected by the in-cylinder pressure sensor with respect to a crank angle or time. It is determined whether the injection amount of each fuel injection in the multiple fuel injection is an appropriate value based on the calculated temporary change rate, and the combustion start timing in the combustion chamber is determined based on the calculated secondary change rate. A fuel injection control device for an internal combustion engine is provided that determines whether or not the fuel injection is appropriate and controls an injection amount and an injection timing of each fuel injection of the multi-fuel injection according to the determination result.
[0016]
That is, in the first aspect of the present invention, the change rate of the combustion chamber pressure P detected by the in-cylinder pressure sensor (the change rate (dP / dθ) and (d2P / dθ2) with respect to the crank angle θ, or the change rate (dP / dt) with respect to time t. ) And (d2P / dt2)), the injection amount and the injection timing of each fuel injection in the multiple fuel injection are controlled. Hereinafter, the case of the change rate with respect to the crank angle will be described. However, the case where the change rate with respect to time is used is the same as the following description.
[0017]
When the fuel injected into the combustion chamber burns, the pressure in the combustion chamber increases. For this reason, the value of the pressure change rate (dP / dθ) in the combustion chamber increases every time each fuel injection of the multiple fuel injection is performed, and a peak corresponding to each injection (dP / dθ) is generated.
It has been found that the magnitude of this peak has a correlation with the fuel injection amount.
[0018]
When multiple fuel injection is performed, a plurality of fuel injections are performed for one stroke cycle. However, when the fuel injected by each fuel injection burns, the combustion pressure increases. There should be a peak corresponding to the combustion of the fuel injected by the fuel injection. However, in actuality, especially in the case of a short interval between fuel injections in multi-fuel injection, the pressure rise in the combustion chamber is caused by each injection, and the pressure peak corresponding to each fuel injection is increased. Is difficult to separate.
[0019]
On the other hand, the pressure change rate (dP / dθ) has a distinct peak value for each fuel injection. For this reason, even when multiple fuel injections are performed using (dP / dθ), it is possible to individually determine the injection amount of each injection, so that accurate feedback control of the injection amount can be performed.
[0020]
Further, the secondary change rate (d2P / dθ2) of the pressure in the combustion chamber also exists for each fuel injection similarly to the primary change rate. Further, since the secondary change rate of the pressure in the combustion chamber has a peak corresponding to the time when the pressure at the start of combustion starts to increase, it is difficult to determine the pressure in the combustion chamber itself or the pressure change rate (dP / dθ). The combustion start timing corresponding to each fuel injection can also be clearly determined. Therefore, even when multiple fuel injection is performed, the combustion start timing corresponding to each injection can be individually determined using the secondary pressure change rate (d2P / dθ2). Feedback control can be performed.
[0021]
According to the second aspect of the present invention, a point in time at which the secondary change rate exceeds a predetermined reference value is determined as a combustion start timing of the fuel injected by each fuel injection, and the combustion start timing is determined as the engine operation time. 2. The fuel injection control device for an internal combustion engine according to claim 1, wherein an injection amount and an injection timing of each fuel injection of the multi-fuel injection are controlled so as to coincide with a predetermined timing according to a condition.
[0022]
That is, according to the second aspect of the present invention, the time when the secondary change rate of the pressure in the combustion chamber exceeds a predetermined reference value is determined as the combustion start timing in the combustion chamber. Although the peak of the secondary change rate of the pressure corresponds to the combustion start time, in the present invention, the time when the secondary change rate increases and becomes equal to or more than the reference value instead of detecting the local maximum value is defined as the combustion start time. Judgment is made, and the injection timing of each fuel injection is feedback-controlled so that the detected combustion start timing coincides with the optimum combustion timing obtained in advance through experiments or the like. As described above, since it is not necessary to perform the peak detection (maximum value detection) of the secondary change rate by determining whether the secondary pressure change rate is equal to or more than the reference value, the combustion start timing can be easily determined. Therefore, the calculation load on the control device can be reduced.
[0023]
According to the invention described in claim 3, the injection amount in each fuel injection is set so that all of the values of the calculated primary rate of change corresponding to each fuel injection in the multi-fuel injection fall within a predetermined reference range. According to a first aspect of the present invention, there is provided a fuel injection control device for an internal combustion engine which controls the fuel injection.
[0024]
That is, in claim 3, the injection amount of each fuel injection is controlled such that all the values of the primary change rate of the pressure in the combustion chamber corresponding to each injection of the multi-fuel injection fall within the respective reference ranges. As described above, the primary change rate of the pressure corresponding to each fuel injection has a correlation with the injection amount in each fuel injection, but the primary change rate of the pressure corresponding to each fuel injection alone indicates the injection amount of the corresponding fuel injection. There is a case where it is not always determined whether or not is appropriate. For example, even if the pressure secondary change rate corresponding to the pilot injection exceeds the reference value, if the amount of the pilot injection is small, the pressure increase rate due to the combustion of the fuel in the main fuel injection increases, and the primary pressure increases. The peak value of the change rate becomes excessive. Therefore, in order to make the injection amount of the pilot injection appropriate, it is necessary to reduce the injection amount of the pilot injection until the primary change rate of the pressure corresponding to the main fuel injection becomes equal to or less than a certain upper limit.
[0025]
In the present invention, when the injection amount of all fuel injections becomes appropriate, the reference range of the primary change rate of the pressure corresponding to each fuel injection is determined in advance by experiments or the like, and the reference range corresponding to each fuel injection during engine operation is set. The injection amount of each fuel injection is controlled so that the primary change rate of the applied pressure falls within this reference range. As a result, the fuel injection amount of all the fuel injections is controlled to an appropriate value.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a diagram showing a schematic configuration of an embodiment when the fuel injection device of the present invention is applied to a diesel engine for an automobile.
[0027]
In FIG. 1, reference numeral 1 denotes an internal combustion engine (in this embodiment, a four-cylinder four-cycle diesel engine having four cylinders # 1 to # 4 is used), and 10a to 10d denote the internal combustion engines # 1 to # 4 of the engine 1. 2 shows a fuel injection valve for directly injecting fuel into each cylinder combustion chamber. The fuel injection valves 10a to 10d are connected to a common accumulator (common rail) 3 via fuel passages (high-pressure fuel pipes). The common rail 3 has a function of storing pressurized fuel supplied from the high-pressure fuel injection pump 5 and distributing the stored high-pressure fuel to the fuel injection valves 10a to 10d via a high-pressure fuel pipe.
[0028]
In FIG. 1, reference numeral 20 denotes an electronic control unit (ECU) that controls the engine. The ECU 20 is configured as a microcomputer having a known configuration in which a read-only memory (ROM), a random access memory (RAM), a microprocessor (CPU), and an input / output port are connected by a bidirectional bus. In the present embodiment, the ECU 20 controls the discharge amount of the fuel pump 5 to control the pressure of the common rail 3 to a target value determined according to the engine operating conditions, and also controls the fuel pressure according to the engine operating state. In addition to setting the injection timing and injection amount of the injection, the fuel injection amount, the injection timing, and the like are feedback-controlled using the primary change rate and the secondary change rate of the combustion chamber pressure obtained based on the in-cylinder pressure sensor output described later. Performs basic engine control such as fuel injection control.
[0029]
In order to perform these controls, in the present embodiment, the common rail 3 is provided with a fuel pressure sensor 27 for detecting the fuel pressure in the common rail, and an accelerator opening degree near the accelerator pedal (not shown) of the engine 1. An accelerator opening sensor 21 for detecting (a driver's accelerator pedal depression amount) is provided. In FIG. 1, reference numeral 23 denotes a cam angle sensor for detecting the rotational phase of the camshaft of the engine 1, and reference numeral 25 denotes a crank angle sensor for detecting the rotational phase of the crankshaft. The cam angle sensor 23 is disposed near the camshaft of the engine 1 and outputs a reference pulse every 720 degrees in terms of a crank rotation angle. The crank angle sensor 25 is disposed near the crankshaft of the engine 1 and generates a crank angle pulse at every predetermined crank rotation angle (for example, every 15 degrees).
[0030]
The ECU 20 calculates the engine speed from the frequency of the crank rotation angle pulse signal input from the crank angle sensor 25, and based on the accelerator opening signal input from the accelerator opening sensor 21 and the engine speed, the fuel injection valve 10a The fuel injection timing and the fuel injection amount of 10d are calculated from the above.
[0031]
In FIG. 1, reference numerals 29a to 29d denote in-cylinder pressure sensors of a known type which are disposed in the respective cylinders 10a to 10d and detect the pressure in the cylinder combustion chamber. Each combustion chamber pressure detected by the in-cylinder pressure sensors 29a to 29d is supplied to the ECU 20 via the AD converter 30.
[0032]
In the present embodiment, the fuel pressure of the common rail 3 is controlled by the ECU 20 to a pressure corresponding to the engine operating state, and is high, for example, from about 10 MPa to about 150 MPa, and varies over a wide range. In this embodiment, the engine 1 performs multi-fuel injection in which fuel is injected into the cylinder a plurality of times during one cycle of each cylinder stroke.
[0033]
FIG. 2 is a diagram illustrating each fuel injection constituting the multi-fuel injection according to the present embodiment.
[0034]
In FIG. 2, the horizontal axis represents the crank angle (CA), and the TDC on the horizontal axis represents the compression top dead center. The vertical axis in FIG. 2 represents the injection rate of each fuel injection, and the area of each peak roughly indicates the relative fuel injection amount of each fuel injection. As shown in the figure, in the multiple fuel injection, all or a part of the early pilot injection, the proximity pilot injection, the main injection (main fuel injection), the after injection, the post injection, and the like are performed.
[0035]
Hereinafter, each fuel injection other than the main injection will be briefly described.
(1) Early pilot injection
The early pilot injection is pilot injection performed at a considerably earlier timing than the main injection (for example, at a timing earlier than the start of the main injection by a crank angle of 20 degrees (20 ° CA) or more). The fuel injected by the early pilot injection forms a premixed gas, and is compressed and ignited. _X By performing early pilot injection with little generation of particulates or particulates, exhaust properties can be improved. In addition, the early pilot injection raises the temperature and pressure in the combustion chamber and shortens the ignition delay period of the proximity pilot injection and the main injection, which will be described later. _X Generation can be suppressed.
[0036]
Since the early pilot injection is performed at a time when the temperature and pressure in the combustion chamber are relatively low, when the injection amount is large, the injected fuel reaches the cylinder wall in a liquid state and causes problems such as lubrication oil dilution. . For this reason, in the early pilot injection, when the injection amount is large, the required injection amount is divided into a plurality of injections and the small amount is injected little by little to prevent the liquid fuel from reaching the cylinder wall.
[0037]
(2) Proximity pilot injection
Proximity pilot injection is pilot injection performed immediately before main injection (for example, within 20 ° CA from the start of main injection). Proximity pilot injection generates less hydrocarbons as compared to early pilot injection, and similarly to early pilot injection, shortens the ignition delay period of main injection and reduces noise and NO of main injection. _X Generation can be suppressed.
[0038]
(3) After injection
The after-injection is an injection started immediately after the end of the main injection or at a relatively short interval (for example, within 15 ° CA after the end of the main injection).
The after-injection is performed for the purpose of improving the combustion by increasing the temperature, pressure, turbulence, and the like in the combustion chamber again at a later stage of the combustion of the fuel of the main injection, and reducing the injection amount of the main injection.
[0039]
That is, in the later stage of the main injection combustion, the temperature and pressure in the combustion chamber are reduced, and the turbulence in the cylinder is reduced. By performing the after-injection in this state, the turbulence due to the fuel injection increases and the temperature and pressure increase due to the combustion of the injected fuel, so that the atmosphere in the combustion chamber is improved to promote the combustion. Further, since the injection amount of the main injection can be reduced by the injection amount of the after injection, the generation of a locally rich region generated by the main injection fuel is suppressed. Also, by appropriately setting the amount and timing of the after-injection, the main injection amount can be reduced and the maximum in-cylinder temperature due to combustion can be reduced. _X Has the effect of suppressing generation of
[0040]
(4) Post injection
Post-injection is fuel injection that is started at a relatively long interval after the end of the main injection (for example, 15 ° CA or more after the end of the main injection). The main purpose of post-injection is to increase exhaust temperature and pressure.
[0041]
For example, in the case where the temperature of the exhaust gas purification catalyst disposed in the exhaust system is low and does not reach the activation temperature and the exhaust gas purification action cannot be obtained, the exhaust temperature is increased by performing post-injection, and the catalyst is quickly reduced. The temperature can be raised to the activation temperature. In addition, since post-injection increases the temperature and pressure of exhaust gas, engines with a turbocharger increase the work of the turbine to improve the acceleration performance by increasing the supercharging pressure and to suppress the effects of smoke during acceleration. Obtainable.
Further, as an exhaust gas purifying catalyst, NO in exhaust gas using HC components is used. _X When a selective reduction catalyst for purifying NO is used, HC is supplied to the catalyst by performing post injection to make NO _X Purification rate can be improved.
[0042]
By performing the multi-fuel injection as described above, it is possible to significantly improve the exhaust characteristics and noise of the diesel engine. It is necessary to precisely control the injection timing. For example, in the proximity pilot injection in which the accuracy of the injection amount and the injection timing is required most, the amount of one fuel injection is 1.5 to 2.5 mm. ³ It is necessary to control the injection timing within about ± 2 ° CA.
As described above, since the fuel injection valve has variations among individuals due to tolerances and changes in fuel injection characteristics depending on the service period, the accuracy of fuel injection cannot be improved by ordinary open loop control.
[0043]
Further, for example, even if the fuel injection is controlled based on the combustion noise as in the above-mentioned Patent Document 1, the injection amount of a part of the pilot injection can be controlled, but the injection amount of each fuel injection is individually controlled. However, there is a problem that the injection timing cannot be controlled at all.
In particular, in the multi-fuel injection, the above-described fuel injection of the proximity pilot injection, the main injection, and the after-injection may be performed consecutively when the injection interval is extremely short. There is a problem that the injection amounts of these three injections cannot be separated and determined even by only the above.
[0044]
In the present embodiment, each fuel injection is performed using a primary change rate (differential value) and a secondary change rate (second-order differential value) of the pressure in the combustion chamber detected with the in-cylinder pressure sensors 29a to 29d with respect to the crank angle or time. By controlling the injection amount and the injection timing of each of these, it is possible to accurately control each fuel injection.
[0045]
In the following description, an example is described in which fuel injection is controlled using the primary change rate and the secondary change rate ((dP / dθ) and (d2P / dθ2)) of the pressure P in the combustion chamber with respect to the crank angle θ. However, exactly the same control is possible when the primary change rate and the secondary change rate of the pressure in the combustion chamber with respect to time are used.
[0046]
FIGS. 3 (A) to 3 (D) show cranks of the pressure in the combustion chamber detected by the in-cylinder pressure sensors 29a to 29d and the rate of change thereof in the case of performing the multi-fuel injection including the close pilot injection, the main injection, and the after injection. FIG. 7 is a timing chart showing a change with respect to an angle (horizontal axis).
[0047]
In FIG. 3, FIG. 3 (A) shows the valve lift of the fuel injection valve (substantially equal to the fuel injection rate), I in FIG. 3 (A) shows the proximity pilot injection, II shows the main injection, and III shows the after injection. ing.
[0048]
FIG. 3B shows a change in the pressure P in the combustion chamber detected by the in-cylinder pressure sensor. As shown in FIG. 3 (B), the pressure changes due to the proximity pilot injection, the main injection, and the after-injection overlap with each other and interfere with each other when viewed simply from the pressure P in the combustion chamber. It is not possible to determine the peak that occurs.
[0049]
FIG. 3C is a diagram showing a primary change rate (dP / dθ) with respect to the crank angle of the combustion chamber pressure P in FIG. 3B. As can be seen from FIG. 3 (C), by taking the primary rate of change (dP / dθ) of the pressure P, the peaks (I, II, III) for the proximity pilot injection, the main injection, and the after injection are clearly separated and determined. It is possible. The primary rate of change (dP / dθ) of the pressure P is the rate of increase of the pressure, and it has been found that the maximum value (peak value) has a correlation with the injection amount in each injection. Therefore, the actual injection amount of each injection can be individually determined from the peak value of the primary change rate of the pressure P.
[0050]
Next, FIG. 3D is a diagram showing a secondary change rate (d2P / dθ2) of the pressure P with respect to the crank angle. As shown in FIG. 3 (D), the secondary change rate (d2P / dθ2) of the pressure P also has a clear peak (FIG. 3 (D) I to III) corresponding to each injection.
[0051]
The peak value of the secondary change rate of the pressure P indicates the primary change rate of the pressure P, that is, the maximum value of the change of the pressure rise rate, that is, the change rate of the pressure rise rate at the start of fuel combustion in each injection. Therefore, when (d2P / dθ2) exceeds a certain reference value, it can be determined that a rapid pressure increase has started, that is, combustion has started.
In the present embodiment, it is determined that the combustion has started when the secondary change rate of the pressure P exceeds a certain reference value P0 ″ shown in FIG.
[0052]
The primary change rate (dP / dθ) of the pressure P also shows a clear peak corresponding to each injection as shown in FIG. 3 (C), and (dP / dθ) represents the pressure rise rate in the combustion chamber. Therefore, it is theoretically possible to determine that the combustion has started when the pressure rise rate (dP / dθ) of the pressure P exceeds a predetermined reference value.
[0053]
However, since the peak value of the primary change rate (dP / dθ) of the pressure P is significantly different between the proximity pilot injection, the main injection, and the after injection, the presence or absence of the start of each fuel injection is determined using (dP / dθ). To make the determination, it is necessary to provide a reference value for determining the start of combustion for each injection.
[0054]
On the other hand, when the secondary change rate of the pressure P (d2P / dθ2) is used, the peak value corresponding to each injection becomes substantially the same value, and therefore, the reference value common to all the injections (FIG. 3) (D) P0 ″) has the advantage that the determination of the start of combustion can be made. FIGS. 3A to 3D show the case where only the proximity pilot injection, the main injection, and the after injection are performed. However, the presence / absence of the start of combustion can be determined with the same determination value (P0 ″ in FIG. 3 (D)) even when there are other early pilot injections and post injections.
[0055]
Next, feedback control of the fuel injection amount and the injection timing in the present embodiment will be described.
In the present embodiment, the injection amount and the injection timing of each fuel injection are controlled by the following procedure.
(1) Setting of basic fuel injection amount and injection timing
In the present embodiment, the ECU 20 determines the basics of each of the multiple fuel injections based on a predetermined relationship from the engine speed calculated from the output of the crank angle sensor 25 and the accelerator opening detected by the accelerator opening sensor 21. The injection amount and the basic injection timing are set. The basic (target) injection amount and the basic (target) injection timing of each injection are stored in advance in the ROM of the ECU 20 as a two-dimensional numerical table using the engine speed and the accelerator opening. As a method of setting the basic injection amount and the injection timing, any known method can be used, and therefore a detailed description is omitted here.
[0056]
(2) Confirmation of combustion of each fuel injection and adjustment of fuel injection amount
When each fuel injection is performed with the basic injection amount and the basic injection timing, it is determined whether or not combustion is occurring by determining whether the secondary change rate (d2P / dθ2) of the combustion chamber pressure P exceeds the reference value P0 ″. The determination is made based on whether or not the fuel injection amount is not larger than the reference value, and the fuel injection amount of the corresponding injection is increased.
[0057]
For example, in the example of FIG. 3, if there is no peak corresponding to I of (d2P / dθ2) in FIG. 3D, that is, (d2P / dθ2) is the reference value from the start of the proximity pilot injection to the start of the main injection. Does not exceed, it means that the proximity pilot injection has not been performed or the injection amount is insufficient. Therefore, in this case, the injection amount of the proximity pilot injection is increased until (d2P / dθ2) exceeds the reference value P0 ″ in the portion corresponding to I.
[0058]
If there is no peak corresponding to III (after-injection) in FIG. 3D, that is, if (d2P / dθ2) does not exceed the reference value after the end of main injection, it is determined whether after-injection has been performed. Alternatively, it is determined that the injection amount is insufficient, and the injection amount of the after injection is increased until (d2P / dθ2) exceeds the reference value after the main injection.
By performing the above operation until the value of the secondary change rate (d2P / dθ2) of the pressure corresponding to each injection exceeds the reference value P0 ″, the fuel injected by each injection is surely burned.
[0059]
(3) Adjustment of injection timing
By the above operation, when all the secondary change rates (d2P / dθ2) of the pressures corresponding to the respective injections exceed the reference value P0 ″, then the crank angle at which (d2P / dθ2) exceeds the reference value P0 ″ However, the injection timing of each injection is adjusted so as to match the basic injection timing set in (1). Thus, the injection timing of each injection is feedback-controlled to the target injection timing (the basic injection timing in the present embodiment).
[0060]
(4) Final adjustment of injection amount
After the above operation, the injection amount of each injection adjusted in (2) is adjusted by comparing the primary change rate (dP / dθ) of the pressure corresponding to each injection with the reference value of each injection.
[0061]
In the present embodiment, an upper limit is set in advance as a reference value for each injection, and (dP / dθ) corresponding to each fuel injection does not exceed the respective upper limit, that is, in the combustion corresponding to each fuel injection. The injection amount is adjusted so that the pressure rise rate does not become excessive. Here, the reference value (upper limit value) corresponding to each injection is the upper limit value (dP / dθ) at which optimal combustion is obtained in advance by experiments or the like under each operating condition (combination of engine speed and accelerator opening). And stored in the ROM of the ECU 20 as a numerical table using the engine speed and the accelerator opening for each multi-fuel injection.
[0062]
In this case, the adjustment of the injection amount is not necessarily performed only for the injection in which (dP / dθ) exceeds the upper limit, but is also performed for other injections and finally corresponds to each injection (dP / dθ). The injection amounts are adjusted so that the values of the above ()) are all equal to or less than the respective upper limit values.
[0063]
For example, in the example of FIG. 3, if the value of (dP / dθ) for pilot injection (FIG. 3 (C) I) exceeds the upper limit (FIG. 3, P1 ′), the pilot injection amount Is determined to be excessive, the pilot injection amount itself is reduced so that (dP / dθ) becomes equal to or less than the upper limit value P1 ′.
[0064]
When the value of (dP / dθ) (FIG. 3 (C) III) with respect to the after-injection exceeds the upper limit (FIG. 3, P3 ′), the after-injection injection amount is similarly reduced ( dP / dθ) is not more than the upper limit value P3 ′.
[0065]
However, if the value of (dP / dθ) for the main injection (II in FIG. 3 (C)) exceeds the upper limit P2 ′, the injection amount of the main injection itself is not adjusted but the pilot injection is performed. Increase volume. This means that (dP / dθ) corresponding to the main injection has exceeded the upper limit value P2 ′, which means that the ignition delay of the fuel for the main injection becomes large due to the insufficient pilot injection amount, and therefore the pressure rise This is because the speed is considered to be excessive.
[0066]
By performing the above operation, the injection amount of each fuel injection is adjusted so that the value of the primary change rate of the pressure for each fuel injection is all within the respective reference ranges (in the present embodiment, not more than the upper limit value). The injection amount of each fuel injection is feedback-controlled to an optimal value.
[0067]
FIG. 4 is a flowchart showing a control operation corresponding to the above (2) to (4). This operation is executed by the ECU 20 at regular intervals (constant crank angle).
[0068]
In FIG. 4, steps 401 and 403 indicate the calculation operation of (dP / dθ) and (d2P / dθ2), respectively.
[0069]
In the present embodiment, the primary change rate (dP / dθ) and the secondary change rate (d2P / dθ2) of the pressure P in the combustion chamber are calculated by the following equations.
[0070]
(DP / dθ) = Pn-P (n-1)
(D2P / dθ2) = (P (n) −2P (n−1) + P (n−2))
Here, Pn indicates the pressure in the combustion chamber detected by the in-cylinder pressure sensors 29a to 29d. In this embodiment, the ECU 20 samples the output of the in-cylinder pressure sensor at every constant crank angle, Pn represents the pressure in the combustion chamber sampled this time, P (n-1) represents the pressure in the combustion chamber sampled last time, and P (n-2). ) Is the pressure in the combustion chamber sampled two times before.
[0071]
Next, in steps 405 and 407, the combustion confirmation of each fuel injection and the adjustment of the fuel injection amount described in the above (2) are performed. That is, in step 405, the secondary pressure change rate (d2P / dθ2) corresponding to each fuel injection is compared with the common reference value P0 ″, and if the reference value is not reached, the response is performed until the reference value is reached. The injection amount of the injection to be performed is increased (step 407).
[0072]
Step 409 is the adjustment operation of the injection timing described in the above (3). That is, in step 409, each crank angle at which the secondary change rate (d2P / dθ2) corresponding to each injection becomes larger than the reference value P0 ″ matches the basic injection timing determined by the engine speed and the accelerator opening. The injection timing of the injection is adjusted.
[0073]
After the adjustment of the injection timing is completed in step 409, the final adjustment of the injection amount described in the above (4) is performed in step 411, and the values of (dP / dθ) corresponding to each injection are all set in the respective reference ranges (upper limit values). The injection amount of each injection is adjusted so as to satisfy the following.
[0074]
In the above-described embodiment, the case of performing only the close pilot injection, the main injection, and the after injection in FIG. 3 has been described. However, the same applies to the case of performing the early pilot injection (including a plurality of times) and the post injection. Control is possible.
[0075]
When the early pilot injection is performed and the injection amount of the early pilot injection is small, the peak of (dP / dθ) or (d2P / dθ2) for the early pilot injection may not clearly appear. In such a case, despite the fact that (dP / dθ) corresponding to the normal pilot injection exceeds the upper limit value P1 ′ and it is determined that the injection amount of the close pilot injection is too large, it corresponds to the main injection. (DP / dθ) exceeds the upper limit value P2 ′, and it is determined that the pilot injection amount is insufficient. In such a case, it can be determined that the injection amount of the early pilot injection is insufficient. Therefore, by increasing the injection amount of the early pilot injection, (dP / dθ) corresponding to each fuel injection can be determined. All are adjusted to be less than the upper limit.
[0076]
In addition, as described above, in the operation of FIG. 4, the injection amount and the injection timing are adjusted using the primary change rate and the secondary change rate of the pressure that can be calculated by a simple calculation (difference calculation), and The injection amount and the injection timing can be adjusted only by determining whether the calculated primary change rate and secondary change rate exceed a predetermined reference value, and a complicated operation can be performed to achieve the maximum value of these values or There is no need to find a local minimum. For this reason, the calculation load of the ECU 20 is prevented from increasing, and the injection amount and injection timing of each injection can be accurately adjusted simply and reliably.
Further, in the present embodiment, since the injection amount and the injection timing of the multi-fuel injection are feedback-controlled, for example, when the variation between individual fuel injection characteristics due to the tolerance of the fuel injection valve is relatively large, Even when the characteristics change, each fuel injection can be accurately controlled. For this reason, even in the common rail type fuel injection device, variations in the characteristics of the fuel injectors can be tolerated to some extent, and it is not necessary to strictly manage the variations in the characteristics of the fuel injectors as in the related art. Costs can be reduced.
[0077]
【The invention's effect】
According to the invention described in each of the claims, there is a common effect that the injection amount and the injection timing of each fuel injection can be feedback-controlled to appropriate values even in an engine that performs multi-fuel injection.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of an embodiment in which the present invention is applied to a four-cylinder diesel engine for an automobile.
FIG. 2 is a diagram for explaining each fuel injection constituting multi-fuel injection.
FIG. 3 is a diagram illustrating the principle of adjusting the injection amount and the injection timing of each fuel injection according to the present invention.
FIG. 4 is a flowchart illustrating an example of a fuel injection control operation.
[Explanation of symbols]
1. Diesel engine
3… Common rail
10a to 10d: In-cylinder fuel injection valve
20 ... Electronic control unit (ECU)
21 ... Accelerator opening sensor
25 ... Crank angle sensor
29a-29d ... in-cylinder pressure sensor

Claims (3)

In addition to the main fuel injection, before or after the main fuel injection, or both before and after the fuel injection control device of the internal combustion engine performing multi-fuel injection to inject fuel into the engine combustion chamber,
Equipped with an in-cylinder pressure sensor that detects the pressure in the engine combustion chamber,
A primary change rate and a secondary change rate with respect to the crank angle or time of the pressure in the combustion chamber detected by the in-cylinder pressure sensor are calculated, and the injection amount of each fuel injection in the multi-fuel injection based on the calculated temporary change rate Is determined to be an appropriate value, and whether the combustion start timing in the combustion chamber is appropriate is determined based on the calculated secondary change rate, and each fuel of the multi-fuel injection is determined according to the determination result. A fuel injection control device for an internal combustion engine that controls an injection amount and an injection timing of an injection. The time when the secondary change rate exceeds a predetermined reference value is determined as the combustion start time of the fuel injected in each fuel injection, and the combustion start time matches a predetermined time according to the engine operating conditions. The fuel injection control device for an internal combustion engine according to claim 1, wherein the injection amount and the injection timing of each fuel injection of the multi-fuel injection are controlled as described above. 2. The internal combustion engine according to claim 1, wherein the injection amount in each fuel injection is controlled such that all of the values corresponding to each of the fuel injections in the multi-fuel injection of the calculated primary change rate are within a predetermined reference range. Fuel injection control device.

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