JP2001020796A - Fuel injection control system of common rail type - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimize pilot injection timing at a start of an engine, which performs pilot injection and main injection according to engine operating conditions, by correcting the pilot injection timing according to value obtained by comparison between target value of common rail pressure and actual value. SOLUTION: Under control by an ECU 2 during engine operation, target value of a total injection volume is determined based on output from an engine speed sensor 7 and accelerator opening sensor 8 with reference to a total injection volume map. Then target values of a pilot injection volume and main injection volume are determined by using respective maps, and energizing durations for pilot injection and main injection is calculated. Further, target value of common rail pressure, main injection timing, and pilot injection time interval are determined with reference to a common rail pressure map, main injection timing map and pilot injection interval map, respectively. The target value of pilot injection time interval is corrected according to the target common rail pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a common rail fuel injection control device applied to a diesel engine or the like.

[0002]

2. Description of the Related Art In general, in a common rail type direct injection diesel engine, the common rail pressure is controlled to a predetermined target value in accordance with the operating state of the engine, and it is assumed that the actual common rail pressure is equal to the target value. The injection amount and the injection timing are determined from a predetermined map. In order to improve the startability, a two-stage injection using a small amount of pilot injection and a large amount of main injection is known. According to this, even at the time of the low temperature start, the main combustion by the main injection can be executed based on the type of the fire generated by the pilot injection, the combustion can be made good, and the startability can be improved.

[0003]

As shown in FIG. 5, the actual common rail pressure at the start of the engine rapidly rises from the initial value cp ₀ at the start of the engine and reaches the target value cp.
_It gradually decreases toward the target value cp _i while fluctuating near _i . This means that the actual value is not equal to the target value for a predetermined time. Therefore, the above-described method for determining the injection timing on the premise that they are equal does not always provide the optimum injection timing. In particular, at the moment when the overshoot p + and the undershoot p- occur, the actual value deviates most from the target value, and the deviation of the injection timing becomes the largest.

[0004] This is a particular problem in pilot injection. That is, the pilot injection produces the first kind of ignition, and since there is a relatively long ignition delay period, the injection timing must be strictly controlled in relation to this. On the other hand, in the case of the main injection, since a fire has already been generated, the ignition delay period is extremely short, and is hardly affected by the common rail pressure. Therefore, the above is not so problematic.

As described above, it is a main object of the present invention to optimize the pilot injection timing at the time of starting the engine.

[0006]

According to the present invention, a common rail pressure is controlled to a predetermined target value according to an engine operating state, and a pilot injection is performed at a predetermined injection amount and injection timing according to the engine operating state. In a common rail fuel injection control device for executing main injection, a pilot injection timing is corrected according to a comparison value between a target value and an actual value of the common rail pressure.

According to this, since the pilot injection timing can be corrected in consideration of the actual value of the common rail pressure, the pilot injection timing can be optimized.

Here, the correction of the pilot injection timing advances the pilot injection timing when the actual value of the common rail pressure is smaller than the target value, and sets the pilot injection timing when the actual value of the common rail pressure is larger than the target value. Preferably, it retards.

Further, the comparison value is a difference between the target value and the actual value, and the pilot injection timing is corrected indirectly by correcting a pilot interval according to the difference. Is preferred.

[0010]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 6 shows a fuel injection control device of a common rail type direct injection diesel engine to which the present invention is applied. As shown in the figure, an injector 1 is provided for each cylinder of an engine (here, four cylinders), and an electromagnetic valve provided in the injector 1 is turned on / off by an electronic control unit (hereinafter referred to as ECU) 2 as a control device. Thus, the fuel injection is controlled. The injector 1 is constantly supplied with high-pressure fuel of about several tens to several hundreds of MPa stored in the common rail 3. The high-pressure pump 4 sucks the fuel in the fuel tank 5, increases the pressure, and discharges the fuel to the common rail 3. The common rail 3 is provided with a common rail pressure sensor 6 for detecting the actual common rail pressure. The pressure signal of the common rail pressure sensor 6 is sent to the ECU 2, and based on this, the ECU 2 adjusts the discharge pressure of the high-pressure pump 4 and performs feedback control of the common rail pressure as described later.

The ECU 2 is connected to an engine speed sensor 7 and an accelerator opening sensor 8. The engine rotation speed sensor 7 includes a magnetic sensor, and is disposed to face a crank gear 9 attached to an engine crank shaft. A plurality of teeth are provided along the outer circumference of the crank gear 9, and each time the teeth pass, the engine speed sensor 7 generates a rotation pulse. The ECU 2 detects the crank phase based on the pulse and calculates the engine speed. The accelerator opening sensor 8 outputs an output corresponding to the actual accelerator opening to the ECU 2.
To send to. The value of the accelerator opening is a value corresponding to the engine load.

In addition, various sensors such as a water temperature sensor and an intake pressure sensor are connected to the ECU 2. The ECU 2 controls the injection system based on information from these sensors.

Next, the details of the fuel injection control by the present device will be described.

FIG. 4 shows a specific state of the pilot injection and the main injection executed by the present apparatus at the time of starting the engine. The pilot injection amount is indicated by Qp, and the main injection amount is indicated by Qm. The total Qp + Qm of these is the total injection amount Qt. The pilot injection amount Qp and the main injection amount Qm are replaced by energizing periods (ON times) Δtp and Δtm to the injector 1, and the control of each injection amount is actually performed by controlling each energizing period. Start timing of pilot injection is ITp
, The start timing of the main injection is ITm. There is a predetermined non-injection period, ie, a pilot interval, between the pilot injection and the main injection. The pilot interval here is defined by a period ITV from the end of the pilot injection to the start of the main injection. The unit of each timing and period is a crank angle (° CA), and the ECU 2 determines the arrival of each timing and the like based on a rotation pulse (crank angle) obtained from the engine rotation speed sensor 7. Here, the retard direction (the direction in which the crank angle increases) is positive.

The contents of the start control by the present apparatus are shown in the flowchart of FIG. This flow is repeatedly executed by the ECU 2 for each fuel injection cycle.

In a first step 101, the ECU 2 determines a target value Qt of the total injection amount (hereinafter referred to as "target total injection amount") from the total injection amount map M1. This map M1 is a three-dimensional map, and the actual engine speed RPM and accelerator opening Ac
The target total injection amount Qt is determined based on c. The engine speed RPM is detected by an engine speed sensor 7, and the accelerator opening Acc is detected by an accelerator opening sensor 8.

Next, at step 102, a target value Qp of the pilot injection amount (hereinafter referred to as "target pilot injection amount") is determined from the pilot injection amount map M2. The map M2 is also a three-dimensional map, and determines the target pilot injection amount Qp based on the engine rotation speed RPM and the previously calculated target total injection amount Qt. After determining the target pilot injection amount Qp in this way, this value is immediately replaced with the pilot energizing period Δtp.

Thereafter, at step 103, a target value Qm of the main injection amount (hereinafter referred to as "target main injection amount") is determined. The target main injection amount Qm is calculated by the following equation.

Qm = Qt-Qp After the target main injection amount Qm is determined in this way, this value is immediately replaced with the main energizing period Δtm.

Next, at step 104, a target value CP of the common rail pressure (hereinafter referred to as "target common rail pressure") is determined from the common rail pressure map M3. The map M3 is also a three-dimensional map, and determines the target common rail pressure CP based on the engine rotation speed RPM and the previously calculated target total injection amount Qt.

Thereafter, at step 105, a target value ITm of the main injection timing (hereinafter referred to as "target main injection timing") is determined from the main injection timing map M4. The map M4 is also a three-dimensional map, and determines the target main injection timing ITm based on the engine rotation speed RPM and the previously obtained target main injection amount Qm.

As shown in FIG. 4, the "main injection timing" here means the start timing of the main injection.
However, there is no limitation on how to determine the timing. For example, an intermediate timing of the main injection period Δtm is defined as “main injection timing”, and the center of gravity of the actual injection rate is defined as “main injection timing”.
It can also be. The same is true for pilot injection.

Next, at step 106, the target value IT of the pilot interval is obtained from the pilot interval map M5.
V (hereinafter referred to as “target pilot interval”). Map M5 is also a three-dimensional map with engine speed
The target pilot interval ITV is determined based on the RPM and the target pilot injection amount Qp obtained earlier.

As shown in FIG. 4, the "pilot interval" here means a period ITV from the end of the pilot injection to the start of the main injection. However, there is no limitation on how to determine this period. For example, as described above, the period may be a period between the “pilot injection timing” and the “main injection timing” which are intermediate timings of each injection period.
The period from the start of the pilot injection to the start of the main injection can also be set. In short, the period can be broadly set between the pilot injection and the main injection.

Next, at step 107, the target pilot interval ITV determined in this way is corrected by the following method to obtain a corrected target pilot interval ITVfnl as a final value.

FIG. 2 shows the corrected target pilot interval.
A flowchart for determining ITVfnl, and FIG. 3 shows a correction value map M6 used for the determination.

As shown in FIG. 2, the ECU 2 determines the target pilot interval ITV determined in step 201 earlier.
And the target common rail pressure CP are read. Then, in step 202, the actual value CPr of the common rail pressure is read from the output of the common rail pressure sensor 6. Next, step 203
Then, using the correction value map M6, the interval correction value ΔITV
Is calculated.

The correction value map M6 is a three-dimensional map, and determines the interval correction value ΔITV from the engine speed RPM and the difference ΔCP = CP−CPr between the target value and the actual value of the common rail pressure. The correction value map M6 indicates that the interval correction value ΔITV = 0 when the difference ΔCP is 0 in all engine rotation ranges.
So that the greater the difference ΔCP is in the (+) direction, the greater the interval correction value ΔITV in the (+) direction, and the greater the difference ΔCP in the (−) direction, the greater the interval correction value ΔITV in the (−) direction. Has become.

The difference ΔCP is the “comparison value” of the present invention. However, the example of the comparison value is not limited to this. For example, the ratio CPr / CP of the target value and the actual value may be set as the “comparison value”.

When the interval correction value ΔITV is obtained in this way, in step 204, the corrected target pilot interval ITVfnl is calculated by the following equation.

ITVfnl = ITV + ΔITV Next, returning to the flow of FIG. 1, at step 108, the target pilot injection timing ITp is determined by the following equation.

ITp = ITm-ITVfnl-.DELTA.tp When the target values are determined as described above, the energization control of the injector 1 is performed according to these values. Thus, predetermined pilot injection and main injection are executed. Further, the discharge pressure of the high-pressure pump 4 is adjusted so that the actual common rail pressure CPr becomes the target common rail pressure CP.
As a result, feedback control of the common rail pressure is performed.

According to the above control, when the actual value CPr of the common rail pressure is smaller than the target value CP (ΔCP> 0), ΔIT
V> 0, and the target pilot interval ITV is corrected to the long-term side. As a result, the pilot injection timing ITp
Is corrected to the advance side as compared with the case where the actual value CPr of the common rail pressure is equal to the target value CP.

On the other hand, when the actual value CPr of the common rail pressure is larger than the target value CP (ΔCP <0), ΔITV <0, and the target pilot interval ITV is corrected to the short-term side. As a result, the pilot injection timing ITp is corrected to the retard side as compared with the case where the actual value CPr of the common rail pressure is equal to the target value CP.

As described above, in this control, the target pilot injection timing ITp is indirectly corrected by correcting the target pilot interval ITV.

When the actual value CPr of the common rail pressure is smaller than the target value CP, the target pilot injection timing ITp is corrected to the advance side for the following reason. In other words, the common rail pressure corresponds to the injection pressure. If the injection pressure is low, the spray diameter increases and the reach of the spray decreases. Accordingly, the diffusion and mixing of the spray are deteriorated, and the ignitability in the cylinder is deteriorated. That is, the ignition delay period becomes longer. For this reason,
The pilot injection is executed early, so that the time required for ignition is obtained and the ignition is reliably performed before the main injection.

Conversely, when the actual value CPr of the common rail pressure is larger than the target value CP, the target pilot injection timing ITp is corrected to the retard side for the following reason. If the common rail pressure, that is, the injection pressure is large, the spray diameter becomes smaller and the reach of the spray becomes longer. As a result, the diffusion and mixing of the spray become good. At this time, if the pilot injection is executed at the same time when the actual value CPr of the common rail pressure is equal to the target value CP, the pilot injection is too early, and the in-cylinder pressure and the in-cylinder temperature decrease due to excessive evaporation and mixing. And the ignitability deteriorates. Therefore, when the actual value CPr of the common rail pressure is larger than the target value CP, the pilot injection timing ITp is delayed as compared with the case where they are equal to prevent the deterioration of the ignitability.

As described above, the actual value of the common rail pressure CP
By taking into account r, the pilot injection timing at the start of the engine is optimized, and good pilot combustion can be obtained even during the common rail pressure rise period and fluctuation period immediately after the engine start, especially during the overshoot and undershoot. , Improved startability, white smoke at startup
Noise can be reduced.

As described above, various other embodiments of the present invention can be considered. For example, the correction of the pilot injection timing may not be performed indirectly by correcting the pilot interval, but may be a correction of the pilot injection timing directly. The engine of the present invention is not limited to four cylinders, direct injection, and diesel, but can be any type of engine with any number of cylinders and injection systems, and a direct injection gasoline engine is also possible. In the present embodiment, only the two-stage injection at the time of starting the engine is shown, but the present invention is not limited to this, and can be applied to the two-stage injection in all situations.

[0041]

In summary, according to the present invention, an excellent effect that the pilot injection timing at the time of starting the engine is optimized and the startability is improved can be exhibited.

[Brief description of the drawings]

FIG. 1 is a flowchart showing control contents of the embodiment.

FIG. 2 is a flowchart for determining a corrected target pilot interval.

FIG. 3 shows a correction value map.

FIG. 4 is a time chart showing a state of pilot injection and main injection.

FIG. 5 is a time chart showing how the actual common rail pressure changes when the engine is started.

FIG. 6 is a system diagram of the embodiment.

[Explanation of symbols]

 1 Injector 2 Electronic control unit (ECU) 3 Common rail 4 High pressure pump 7 Engine speed sensor 8 Accelerator opening sensor CP Target common rail pressure CPr Actual common rail pressure ITm Target main injection timing ITp Target pilot injection timing ITV Target pilot interval ITVfnl After correction Target pilot interval Qm Target main injection amount Qp Target pilot injection amount Qt Target total injection amount RPM Engine speed ΔCP Difference between target value and actual value of common rail pressure ΔITV Interval correction value

Claims (3)

[Claims] 1. A common rail system that controls a common rail pressure to a predetermined target value according to an engine operating state and executes pilot injection and main injection at a predetermined injection amount and injection timing according to the engine operating state. A fuel injection control device, wherein a pilot injection timing is corrected according to a comparison value between a target value and an actual value of a common rail pressure. 2. The correction of the pilot injection timing advances the pilot injection timing when the actual value of the common rail pressure is smaller than the target value, and delays the pilot injection timing when the actual value of the common rail pressure is larger than the target value. 2. The common rail fuel injection control device according to claim 1, wherein the fuel injection control device is angled. 3. The comparison value is a difference between the target value and the actual value, and the correction of the pilot injection timing is indirectly performed by correcting a pilot interval according to the difference. The common rail fuel injection control device according to claim 1.