JP6274690B2 - Fuel injection control method and common rail fuel injection control device - Google Patents

Description

  The present invention relates to fuel injection control, and more particularly to correction of pilot injection and further stabilization of fuel injection and the like.

How to perform fuel injection control in an internal combustion engine is an important problem because it greatly affects the operation performance of the internal combustion engine, and various control methods have been proposed and put into practical use.
For example, various techniques related to so-called multistage injection control in which a plurality of fuel injections are performed during one engine cycle from the viewpoint of improving fuel efficiency and exhaust gas purification in a diesel engine have been proposed and put into practical use (for example, Patent Document 1). reference).

  By the way, in such multi-stage injection control, the time interval between pilot injection and main injection (hereinafter referred to as “interval time” for convenience of explanation) is, for example, based on the timing of each injection start or pilot injection. It is determined based on the end time and the start time of main injection.

JP 2011-122479 A (page 5-11, FIGS. 1 to 7)

The above-mentioned interval time is determined based on the characteristics of the standard injector. However, the actual individual injector characteristics vary within an allowable range, and are not necessarily appropriate for the actual individual injector. Not necessarily.
Further, even if the actual injector characteristics are the same as those of the standard injector, there is a problem that the deterioration of the fuel injection characteristics is caused due to the deterioration of the nozzle as the usage time elapses. For example, as the usage time of the injector elapses, the seat portion on which the nozzle needle sits wears, leading to an increase in the seat diameter, resulting in an increase in nozzle opening pressure, resulting in an injection delay and an injection amount. It is well known that it leads to a decrease in.

For this reason, in order to compensate for such a decrease in the injection amount due to the deterioration of the nozzle and obtain the original injection amount, the fuel injection amount correction has been conventionally performed by various methods. Basically, the energization time is further extended from the original timing in accordance with the correction amount.
In other words, since the timing at the end of injection is delayed more than originally, the interval time area described above is eroded, and it becomes impossible to secure an appropriate interval time as the correction amount increases. Invite.

  The present invention has been made in view of the above circumstances, and can maintain a desired interval time between the pilot injection and the main injection regardless of variations in individual characteristics of the injectors and deterioration of characteristics due to use. A fuel injection control method and a common rail fuel injection control device capable of realizing more reliable fuel injection are provided.

In order to achieve the above object of the present invention, a fuel injection control method according to the present invention comprises:
A fuel injection control method in a common rail fuel injection control device configured to be able to execute pilot fuel injection amount correction control for correcting a deviation in pilot fuel injection amount due to a deviation in injection characteristics of an injector,
When the pilot fuel injection amount is corrected and pilot injection is performed with the corrected pilot fuel injection amount, a valve closing timing of a solenoid valve provided in the injector that occurs after the pilot injection ends is acquired, A valve closing time deviation, which is a time difference from the previously acquired valve closing timing of the solenoid valve before correction of the pilot fuel injection amount, is calculated, and thereafter, when the injector starts energization in pilot injection, the valve closing time is calculated. It is configured to be preceded by the deviation.
In order to achieve the above object of the present invention, a common rail fuel injection control device according to the present invention includes:
An electronic control unit that performs operation control of an internal combustion engine, and is configured to execute pilot fuel injection amount correction control that corrects a deviation in pilot fuel injection amount caused by a deviation in injection characteristics of an injector A common rail fuel injection control device comprising:
The electronic control unit is
When the pilot fuel injection amount is corrected and pilot injection is performed with the corrected pilot fuel injection amount, a valve closing timing of a solenoid valve provided in the injector that occurs after the pilot injection ends is acquired, A valve closing time deviation, which is a time difference from the previously acquired valve closing timing of the solenoid valve before correction of the pilot fuel injection amount, is calculated, and thereafter, when the injector starts energization in pilot injection, the valve closing time is calculated. It is configured to be preceded by the deviation.

  According to the present invention, the desired interval between the pilot injection and the main injection is performed while performing the necessary pilot fuel injection amount correction without being affected as much as possible by variations in individual characteristics of the injector and deterioration in characteristics due to use. As a result, it is possible to achieve more reliable fuel injection than in the prior art.

It is a block diagram which shows the structural example of the common rail type fuel injection control apparatus to which the fuel injection control method in embodiment of this invention is applied. 2 is a subroutine flowchart showing a procedure of fuel injection control processing in the embodiment of the present invention executed in the common rail fuel injection control device shown in FIG. 1. FIG. 3 is a schematic diagram schematically showing the timing of pilot fuel injection by execution of fuel injection control processing in the embodiment of the present invention, and FIG. 3 (A) is an energization of the injector before pilot fuel injection amount correction is performed. FIG. 3B is a schematic diagram schematically showing the waveform of the injector and the energization waveform after the pilot fuel injection amount correction is performed. FIG. 3B is a case where the energization start time is corrected after the pilot fuel injection amount correction is performed. It is the schematic diagram which showed typically the electricity supply waveform of this injector.

Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 3.
The members and arrangements described below do not limit the present invention and can be variously modified within the scope of the gist of the present invention.
First, a configuration example of a fuel injection control apparatus to which a fuel injection control method according to an embodiment of the present invention is applied will be described with reference to FIG.

The fuel injection control device according to the embodiment of the present invention is a so-called common rail fuel injection control device. The common rail fuel injection control device includes a high pressure pump device 50 that pumps high pressure fuel, and the high pressure pump device 50. A plurality of injectors 2-1 to 2-n that inject the high-pressure fuel supplied from the common rail 1 into cylinders of a diesel engine (hereinafter referred to as “engine”) 3; An electronic control unit (denoted as “ECU” in FIG. 1) 4 that executes operation control of the engine 3 and fuel injection control processing to be described later is configured as a main component.
Such a configuration itself is the same as the basic configuration of this type of fuel injection control apparatus that has been well known.

The high-pressure pump device 50 has a known and well-known configuration with the supply pump 5, the metering valve 6, and the high-pressure pump 7 as main components.
In this configuration, the fuel in the fuel tank 9 is pumped up by the supply pump 5 and supplied to the high-pressure pump 7 through the metering valve 6. As the metering valve 6, an electromagnetic proportional control valve is used, and the amount of energization is controlled by the electronic control unit 4, so that the flow rate of fuel supplied to the high-pressure pump 7, in other words, the discharge of the high-pressure pump 7. The amount is to be adjusted.

A return valve 8 is provided between the output side of the supply pump 5 and the fuel tank 9 so that surplus fuel on the output side of the supply pump 5 can be returned to the fuel tank 9. .
The supply pump 5 may be provided separately from the high-pressure pump device 50 on the upstream side of the high-pressure pump device 50 or may be provided in the fuel tank 9.

The injectors 2-1 to 2-n are provided for each cylinder of the engine 3, are supplied with high-pressure fuel from the common rail 1, and perform fuel injection by injection control by the electronic control unit 4. As the injectors 2-1 to 2-n in the embodiment of the present invention, what is called a solenoid type is used.
As is well known, this solenoid type injector is connected to a fuel pool called a control chamber formed on the side opposite to the tip side of the nozzle needles (not shown) of the injectors 2-1 to 2-n. By driving a solenoid valve (not shown) that controls the inflow and outflow of fuel, the seating and separation of the nozzle needle (not shown) on the seat can be controlled.

  The electronic control unit 4 has, for example, a microcomputer having a known and well-known configuration, a storage element (not shown) such as a RAM and a ROM, and energizes the injectors 2-1 to 2-n. A circuit (not shown) for driving and a circuit (not shown) for energizing and driving the metering valve 6 and the like are configured as main components. In the embodiment of the present invention, a current monitor circuit ("I-MONI" in FIG. 1) for detecting a counter electromotive current generated in solenoids (not shown) of injectors 2-1 to 2-n. (Notation) 12 is provided, and its detection output is supplied to a microcomputer (not shown) and used for obtaining the closing timing of solenoid valves (not shown) provided in the injectors 2-1 to 2-n. (Details will be described later).

  In addition to the detection signal of the pressure sensor 11 that detects the pressure of the common rail 1 being input to the electronic control unit 4, various detection signals such as the engine speed, the accelerator opening, the outside air temperature, and the atmospheric pressure are input. It is used for operation control of the engine 3 and fuel injection control in the embodiment of the present invention.

Next, the fuel injection control process in the embodiment of the present invention executed by the electronic control unit 4 will be described with reference to FIGS.
First, the common rail fuel injection control apparatus according to the embodiment of the present invention is premised on what is called multi-stage injection control. As an example, pilot injection and main injection are performed one stage at a time. It is assumed that there is.

Furthermore, the common rail fuel injection control apparatus according to the embodiment of the present invention is configured such that the basic pilot fuel injection amount correction control as described below is executed by the electronic control unit 4. It is assumed.
The pilot fuel injection amount correction control that is assumed in the embodiment of the present invention is also performed in the conventional device, and particularly due to deterioration or failure of the injectors 2-1 to 2-n, The deviation of the fuel injection amount in the pilot injection from the original fuel injection amount is corrected.
As typical examples of the deterioration phenomenon of the injectors 2-1 to 2-n, there are wear due to use of the seat portion on which the nozzle needle is seated and an increase in the armature lift of a solenoid valve (not shown). it can.
The wear of the seat portion causes an increase in the valve opening pressure due to an increase in the seat diameter, which causes a delay in injection timing and a decrease in the fuel injection amount.
Further, the increase in the armature lift of the solenoid valve (not shown) is caused by a phenomenon similar to the above-described wear of the seat portion occurring in the front end portion of the armature. The increase in the armature lift is caused by the injector 2. It will cause a delay in the time from the end of energization of -1 to 2-n until the amateur is seated.
The pilot fuel injection amount correction control that is assumed in the embodiment of the present invention corrects the deviation from the original fuel injection amount due to the increase in seat diameter and the increase in amateur lift as described above.

That is, the pilot fuel injection amount correction control will be outlined. First, when the engine 3 is in the overrun state (non-injection state), a minute fuel injection amount corresponding to the rail pressure is set, and the minute injection is performed. Fuel injection by quantity, that is, micro injection is executed about several tens of times, and the frequency component of fluctuations in engine speed occurring at that time is extracted as an average value. Such processing is performed for each of the injectors 2-1 to 2-n.
Next, based on the fluctuation frequency component, an estimated value (estimated injection amount) of the fuel amount that would be actually injected at that time is calculated.

  When the estimated injection amount calculated for the first time exceeds a predetermined threshold value determined for each rail pressure, the estimated injection amount decreases toward the predetermined threshold value so as to almost converge to the predetermined threshold value. In addition, when the estimated injection amount is repeatedly acquired while the minute injection amount in the minute injection is reduced, and the estimated injection amount calculated for the first time is less than a predetermined threshold set for each rail pressure, the estimated injection amount The estimated injection amount is repeatedly acquired while the micro injection amount in the micro injection is increased so that the amount rises toward the predetermined threshold value and almost converges to the predetermined threshold value, and the estimation is made when it converges to the predetermined threshold value. The difference ΔET between the energization time ET required to obtain the injection amount and the reference energization time is stored in the energization time learning value map as a difference energization time learning value.

  Here, the reference energization time is the energization time at the start of use of each of the injectors 2-1 to 2-n. In other words, the reference energization time is an energization time measured immediately before the start of use of the injectors 2-1 to 2-n, and corresponds to the rail pressure and the fuel injection amount for each of the injectors 2-1 to 2-n. The energization time is mapped (hereinafter referred to as “reference energization time map” for convenience) and stored in advance in the electronic control unit 4.

Thus, when fuel is injected at the fuel injection amount when the differential energization time learning value ΔET is acquired, the time corrected by the differential energization time learning value ΔET is used as the energization time, and fuel injection is performed. The difference between the amount and the energization time can be corrected.
Such pilot fuel injection amount correction control is a technique that has already been publicly known, for example, based on a proposal by the applicant of the present application (Japanese Patent Laid-Open No. 2013-15076).
The method for obtaining the correction amount in the pilot fuel injection amount correction control is not necessarily limited to the above-described method, and as a result, the energization time of the injectors 2-1 to 2-n is extended according to the correction amount, or If shortened, the present invention can be similarly applied.

Under such a premise, the fuel injection control process in the present invention shown in FIG. 2 determines the timing at which the above-described pilot fuel injection amount correction process is executed, that is, the vehicle is in a non-injection state, and the pilot fuel injection When the amount correction process is executed, it is executed subsequently.
Hereinafter, specifically, referring to FIG. 2, first, the electronic control unit 4 executes the pilot fuel injection amount correction process under the predetermined driving state of the vehicle as described above ( (See step S102 in FIG. 2).

Next, pilot injection with the corrected pilot injection amount is performed, and the valve closing times of the injectors 2-1 to 2-n at that time are acquired (see step S104 in FIG. 2).
That is, the pilot injection is performed at the pilot injection amount that has been subjected to the pilot fuel injection amount correction based on the processing of step S102, and the solenoid valves (not shown) configured in the injectors 2-1 to 2-n at that time are executed. The valve closing timing is measured and acquired by the electronic control unit 4 as described below.

First, referring to the schematic diagram of the energization waveform of the injectors 2-1 to 2-n shown in FIG. 3, the energization time of each of the injectors 2-1 to 2-n before and after correction of the pilot injection amount The energization timing will be described.
In FIG. 3A, the waveform represented by a two-dot chain line is the energization waveform of the injectors 2-1 to 2-n at the time of pilot injection before the pilot fuel injection amount correction, and the waveforms of the injectors 2-1 to 2-n. 2 schematically shows a back electromotive current waveform generated when a solenoid valve (not shown) is closed. In the figure, time tp1 is the start of energization of the injectors 2-1 to 2-n, and time tp2 is the end of energization of the injectors 2-1 to 2-n.
The times tp1 and tp2 described above are determined based on the timing at which the piston (not shown) in the engine 3 is at the top dead center (TDC), and the same applies to other times in FIG. .

  The energization waveforms of the injectors 2-1 to 2-n rise rapidly with the lapse of time from the start of energization at time tp1, temporarily decrease after reaching a certain peak value, and then become a substantially constant current until the end of energization. The change decreases toward zero with the passage of time from the end of energization at time tp2. Then, after the energization waveforms of the injectors 2-1 to 2-n reach zero, a two-dot chain line that peaks in a relatively short time after some time has elapsed and then becomes zero in a relatively short time. The waveform of the current is represented by the closing of solenoid valves (not shown) of the injectors 2-1 to 2-n.

That is, as is well known, this is a counter electromotive current due to the counter electromotive force generated by the inductance component of the solenoid valve (not shown), and the peak thereof is the closing of the solenoid valve (not shown). Conventionally, it corresponds to the timing of the valve, and in the example of FIG. 3, it is the time ta1.
In FIG. 3, the time interval between the time tp2 at the end of energization and the time ta1 at the valve closing timing is denoted as “W1”.
In the embodiment of the present invention, the above-described back electromotive current is detected by the current monitor circuit 12 and the detected signal is input to a microcomputer (not shown) constituting the electronic control unit 4, whereby the injector It is possible to acquire valve closing times of 2-1 to 2-n.

The energization time of pilot injection after correction of the pilot fuel injection amount (indicated as “corrected ET” in FIG. 3) is between time tp1 and time tp3 in FIG. Due to the correction, the energization time between the time tp2 and the time tp3 is extended from that before the correction, and in FIG. 3A, the energization current waveform in the extended section is represented by a dotted line. ing.
With the extension of the energization time, the valve closing time (valve closing timing) also becomes later than before the pilot fuel injection amount correction, and is at the time ta2 (see FIG. 3A).
Note that the valve closing timing is not only delayed by the amount corresponding to the extension of the energization time, but as described above, a delay occurs as the amateur lift increases due to the deterioration of the injector. Therefore, the time interval W2 (see FIG. 3) between the time tp3 at the end of energization after the correction of the pilot fuel injection amount and the time ta2 of the valve closing timing is generally W2 as compared with the time interval W1 before the correction. > W1.
The data at the time ta2 of the valve closing time is acquired by the electronic control unit 4 via the current monitor circuit 12 as described above.

Thus, after the valve closing time after the pilot fuel injection amount correction is acquired as described above, the time difference from the valve closing time before the pilot fuel injection amount correction, that is, the valve closing time deviation ΔT is the electronic control unit. 4 (see step S106 in FIG. 2).
That is, the valve closing time deviation ΔT is calculated in the electronic control unit 4 as Δt = ta2−ta1. The valve closing time ta1 before the correction of the pilot fuel injection amount is acquired as measured data at the start of use of the apparatus, and is stored in advance in an appropriate storage area of the electronic control unit 4, and is used for the above-described arithmetic processing. It has come to be.

Next, the energization start time is corrected (see step S108 in FIG. 2).
That is, thereafter, the energization start time of pilot injection is advanced by the valve closing time deviation ΔT obtained in the process of the previous step S106. In FIG. 3B, the energization waveform of the injectors 2-1 to 2-n and the solenoid valve (not shown) are closed when the energization start time of pilot injection is advanced by the valve closing time deviation ΔT. The back electromotive force waveform is schematically shown, and the time tc1 is the start of energization, and this energization starts when the time tp1 before the pilot fuel injection amount correction is preceded by the valve closing time deviation ΔT. It has become.
On the other hand, the end of energization is the time when the corrected energization time (see “after-correction ET” in FIG. 3A) has elapsed since time tc1.

The reason why the energization start after the correction of the pilot fuel injection amount is advanced by the valve closing time deviation ΔT is as follows.
First, in the common rail fuel injection control apparatus according to the embodiment of the present invention, as described above, main injection is performed after pilot injection as in the prior art.
In this case, the time interval (interval time) between the pilot injection and the main injection is based on the standard injection characteristics of the injector, as the time interval between the start of pilot injection and the start of main injection, or It is determined as the time interval between the end of pilot injection and the start of main injection. For convenience of the following description, the interval time determined as described above is particularly referred to as “reference interval time”.

However, the actual injection characteristics of the injectors 2-1 to 2-n are not necessarily the same as the injection characteristics of the standard injectors, and those having a deviation in an allowable range are usually selected and used. It has become.
Therefore, the actual interval time does not necessarily coincide with the reference interval time. However, as long as the injection characteristics are within the allowable range, the difference between the actual interval time and the reference interval time is not much in fuel injection. There is no impact.

  However, the deterioration of the injection characteristics and the like accompanying the physical deterioration of the injectors 2-1 to 2-n occurs with the passage of the years of use. Typical examples of the deterioration phenomenon of the injector that greatly affects the injection characteristics include wear of a seat portion on which a nozzle needle is seated and an increase in an armature lift of a solenoid valve (not shown). Normally, wear of the seat part causes a decrease in the pilot fuel injection amount, and an increase in the amateur lift causes an increase in the pilot fuel injection amount, resulting in a deviation from the original fuel injection amount. The injection amount needs to be corrected. Therefore, as described above, in this apparatus as well, in order to compensate for the change from the original value of the pilot fuel injection amount due to wear of the seat portions of the injectors 2-1 to 2-n, etc., as in the past. As described above, the pilot fuel injection amount correction process (see step S102 in FIG. 2) is executed.

  In such pilot fuel injection amount correction processing, the required pilot fuel injection amount is ensured by extending the pilot fuel injection end time according to the correction amount of the pilot fuel injection amount. As the deterioration of −1 to 2-n progresses and the correction amount increases, the end of injection becomes slower than the end of original injection. This means erosion of the previous interval time. That is, the originally required interval time is not ensured, and the fluctuation of the interval time causes deterioration of the main injection characteristics.

In the case of multistage injection in which pilot injection is performed before main injection, pressure fluctuations occur in the injectors 2-1 to 2-n due to pilot injection and remain after the pilot injection ends, so the fuel injection amount after the pilot injection ends It has long been known to pulsate and affect the main injection.
Therefore, the interval time for determining the interval between the pilot injection and the main injection is usually determined so that the influence of the pressure fluctuation in the injector as described above and the fluctuation of the fuel injection amount resulting therefrom is minimized. It is difficult to sufficiently reduce the influence on these main injections only by time. Therefore, in order to correct the fluctuation of the fuel injection amount in the main injection caused by the pilot injection, the fuel injection amount correction process of the main injection is normally performed, but it is assumed that the interval time is as set. The correction amount is calculated and set.
The fuel injection amount correction control for the main injection described above is a technique that has already been publicly known, for example, based on a proposal by the applicant of the present application (Japanese Patent Application Laid-Open No. 2011-122479).

However, if the energization time is extended by the previous pilot fuel injection correction control and the original interval time cannot be ensured, the correction amount by the fuel injection amount correction processing for the main injection as described above becomes inaccurate. There is a risk that proper main injection cannot be secured.
Therefore, in the embodiment of the present invention, while ensuring the correction of the pilot fuel injection amount by executing the pilot fuel injection correction control, it is necessary to ensure the required interval time without affecting the interval time. As described above, the valve closing time of the solenoid valves (not shown) of the injectors 2-1 to 2-n is set to be subject to the correction of the pilot fuel injection amount by making the energization start earlier by the valve closing time difference ΔT. Regardless, they are matched.

  It is suitable for a common rail fuel injection control device in which it is desired to maintain an interval time between pilot injection and main injection regardless of deterioration of injector characteristics.

DESCRIPTION OF SYMBOLS 1 ... Common rail 2-1 to 2-n ... Injector 3 ... Engine 4 ... Electronic control unit 12 ... Current monitor circuit

Claims (2)

A fuel injection control method in a common rail fuel injection control device configured to be able to execute pilot fuel injection amount correction control for correcting a deviation in pilot fuel injection amount due to a deviation in injection characteristics of an injector,
When the pilot fuel injection amount is corrected and pilot injection is performed with the corrected pilot fuel injection amount, a valve closing timing of a solenoid valve provided in the injector that occurs after the pilot injection ends is acquired, A valve closing time deviation, which is a time difference from the previously acquired valve closing timing of the solenoid valve before correction of the pilot fuel injection amount, is calculated, and thereafter, when the injector starts energization in pilot injection, the valve closing time is calculated. Preceding by the amount of deviation keeps the interval between the solenoid valve closing timing after pilot injection and the energization start timing of main injection performed after pilot injection before and after correction of the pilot fuel injection amount. A fuel injection control method. An electronic control unit that performs operation control of an internal combustion engine, and is configured to execute pilot fuel injection amount correction control that corrects a deviation in pilot fuel injection amount caused by a deviation in injection characteristics of an injector A common rail fuel injection control device comprising:
The electronic control unit is
When the pilot fuel injection amount is corrected and pilot injection is performed with the corrected pilot fuel injection amount, a valve closing timing of a solenoid valve provided in the injector that occurs after the pilot injection ends is acquired, A valve closing time deviation, which is a time difference from the previously acquired valve closing timing of the solenoid valve before correction of the pilot fuel injection amount, is calculated, and thereafter, when the injector starts energization in pilot injection, the valve closing time is calculated. By leading the deviation , the interval between the solenoid valve closing timing after pilot injection and the energization start timing of main injection performed after the pilot injection before and after correction of the pilot fuel injection amount is kept constant. Common rail characterized by comprising Fuel injection control device.

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