JPH11141432A - Fuel injection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the injection quantity of insufficiently atomized fuel just after or before the fuel injection of an injector by changing the pressure of the fuel supplied from an accumulating chamber during the injection period of the fuel SOLUTION: The pressure of a common rail 3 is once reduced up to just before fuel injection by driving an electromagnetic relief valve 5 by the control signal from an ECU 8. Therefore, the injection pressure is in a relatively low state in injection start with a low injection ratio, so that generation of insufficiently atomized fuel spray can be minimized. The pressure of the common rail 3 is reduced by the electromagnetic relief valve 5 just before injection end. Since the fuel injection ratio is reduced by this pressure reduction, the quantity of insufficiently atomized fuel spray in short choke area can be reduced. Particularly, the fuel spray in the end of fuel injection is important since it has an influence on the black smoke generation in the latter period of combustion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection device for injecting high-pressure fuel supplied from a common rail.

[0002]

2. Description of the Related Art Conventionally, as disclosed in Japanese Unexamined Patent Publication No. Hei 5-71438, fuel in a fuel tank is stored in a high-pressure state by a fuel pump in a pressure storage chamber common to each injector called a common rail. 2. Description of the Related Art There is known an apparatus that supplies high-pressure fuel to an injector corresponding to a cylinder and performs fuel injection in a high-pressure state.

In the fuel injection device described in the above publication, the back pressure of the needle nozzle provided in the injector is switched in two stages during fuel injection, and the fuel injection at a low injection rate and a high injection rate is performed by one fuel injection. I can do it.

[0004]

As a nozzle structure employed in a conventional injector, a VCO shown in FIG.
A (valve covered orifice) nozzle is known.

In the VCO nozzle structure shown in FIG. 7, a nozzle hole 14 is formed in a seat portion 16 which is a contact portion between a nozzle body 12 and a needle 13, and a sack 15 seen in a general nozzle shown in FIG. No fuel remains in the sack 15 after one fuel injection, and the fuel remaining in the sack 15 is sucked into the combustion space in the next intake stroke of the engine, and the emission increases when the engine burns.
It is difficult for the phenomenon that the particulates generated due to HC increases to occur, and a VCO nozzle has recently been used.

However, since the VCO nozzle shown in FIG. 7 has a region called a choke region of the nozzle immediately after the valve is opened and immediately before the needle 13 is closed, atomization of the spray becomes extremely worse when passing through this region. Would. In the nozzle of the type shown in FIG. 6, when the interval between the seat portions 16 immediately after opening and immediately before closing the valve is small, when the high-pressure fuel on the upstream side once passes through the seat portion 16, the injection holes 14 Since it is located on the sack 15 downstream of the part 16 and can secure a distance necessary to recover the pressure, the fuel actually injected from the nozzle returns to the high pressure state.

On the other hand, since the VCO nozzle has the nozzle injection holes 17 in the sheet portion, the possible pressure recovery is not sufficient in the nozzle of the type shown in FIG. 6 and the atomization is deteriorated. More specifically, the atomization becomes better when the injection speed of the fuel from the injection hole 17 is higher, and therefore the atomization becomes better when the fuel pressure at the injection hole is higher. In the VCO nozzle, the speed at which the fuel pressure becomes the same on the upstream side and the downstream side across the seat portion at the stage where the interval between the seat portions immediately after opening or closing the valve is narrow, as compared with the nozzle of FIG. Say slow.

In a fuel injection system having a common rail, the fuel pressure supplied to the injector is 100
Since the pressure is considerably high in the order of MPa, the needle 13
The injection amount per unit time in the choke region immediately after opening and immediately before closing the valve, that is, the fuel injection rate becomes considerably large. Therefore, there is a possibility that the amount of the insufficiently atomized fuel injected as described above is considerably increased, and it is difficult to obtain a good air-fuel mixture.

SUMMARY OF THE INVENTION In view of the above problems, it is a technical object of the present invention to reduce the amount of insufficiently atomized fuel immediately after or immediately before fuel injection by an injector.

[0010]

In order to achieve the above-mentioned object, according to the first aspect of the present invention, the fuel stored in the pressure accumulating chamber is supplied, and the fuel is injected into the accumulating chamber. During the injection period, the pressure of the fuel supplied from the accumulator is changed.

According to a second aspect of the present invention, in the fuel injection device having a common rail, the fuel pressure of the common rail is reduced at least before the start of fuel injection, and then the common rail fuel pressure is increased. The fuel injection is started at the ascending stage.

According to a third aspect of the present invention, in the fuel injection device having a common rail, the common rail fuel pressure is reduced at least before the end of the fuel injection.
The fuel injection is terminated after the start of the reduction of the common rail fuel pressure.

According to a fourth aspect of the present invention, in the fuel injection device having a common rail, the fuel injection is started at the stage of increasing the fuel pressure of the common rail, and thereafter, the common rail fuel pressure is started to decrease. The fuel injection is terminated after the fuel pressure starts to decrease.

According to the first aspect of the present invention, the pressure of the fuel supplied from the accumulator is changed during the fuel injection, so that the fuel is injected during the nozzle choke period immediately after the start or immediately before the end of the fuel injection. Injection amount of insufficiently atomized fuel can be suppressed.

According to the second aspect, it is possible to suppress a large amount of insufficiently atomized fuel immediately after the start of injection.

According to the third aspect, it is possible to suppress a large amount of insufficiently atomized fuel immediately before the end of the injection.

In the fuel injection device according to the fourth aspect, it is possible to suppress a large amount of insufficiently atomized fuel from being released both immediately after the start of injection and immediately before the end of injection.

[0018]

Embodiments of the present invention will be described below. When the present invention is applied to a fuel injection device with a common rail provided with an injector having the above-described VCO nozzle structure, the intended effect can be obtained particularly well. Therefore, a fuel injection device with a common rail having an injector having a VCO nozzle structure is provided. It will be described on the assumption.

FIG. 1 is an overall configuration diagram showing a fuel injection device with a common rail according to the present invention. In FIG.
Reference numeral 1 denotes an injector, which is provided corresponding to a combustion chamber of each cylinder of the engine. FIG. 1 shows one of them.
Only one is shown and the rest are omitted. The injection hole of the injector 1 is opened and closed by the vertical movement of the needle 13 as shown in FIG. In the present embodiment, since the injector tip has a VCO nozzle structure, problems associated with remaining fuel after fuel injection are prevented. The injector 1 is provided with a pipe for returning a part of the fuel leaked or supplied from the common rail 3 to the fuel tank. FIG.
The middle 2 is a fuel supply pump for supplying the fuel in the fuel tank 6 to the common rail 3 through the high pressure pipe 7 in a high pressure state. Reference numeral 11 denotes a pump control valve, which is a means for adjusting the amount of fuel supplied to the common rail according to a control signal from an ECU (Electronic Control Unit) 8. In FIG. 1, fuel is directly supplied from the fuel pump to the fuel supply pump 6, but a feed pump for fuel feed may be provided between the fuel tank 6 and the fuel supply pump 2.

Reference numeral 3 denotes a common rail for accumulating high-pressure fuel supplied from a fuel supply pump, and each injector is connected via a high-pressure fuel pipe 4. Reference numeral 10 denotes a pressure sensor for detecting the pressure in the common rail 3, and a pressure signal is input to the ECU 8. Reference numeral 5 denotes an electromagnetic relief valve, which is a valve for returning a part of the fuel in the common rail 3 to the fuel pump 6. The pressure in the common rail 3 can be adjusted by adjusting the electromagnetic relief valve 5. The electromagnetic relief valve 5 is an electromagnetically driven valve driven by a control signal from the ECU 8.

Reference numeral 8 denotes an ECU to which output signals of various sensors including the pressure sensor 10, for example, an engine speed sensor and an accelerator opening sensor are input. E
The CU 8 includes a well-known electronic circuit unit including a CPU, a bus, a ROM, a RAM, and an interface circuit. The ECU 8 outputs a control signal for driving the valve to the electromagnetic relief valve 5 at an appropriate timing based on information from various sensors, and the electromagnetic relief valve 5 operates based on the drive control signal. Also,
Since the injector 1 has an electromagnetic valve (not shown) for causing the needle 13 to move up and down, the ECU 8 turns on and off the electromagnetic valve based on information from various sensors to drive the injector 1. Is also output. Further, the ECU 8 outputs a control signal to a pump control valve 11 for controlling the amount of fuel supplied to the common rail 3 of the fuel supply pump 2. 9 is ED
U (Electronic Driving Unit), which is a drive circuit for driving the solenoid valve of the injector 1. Arrows in FIG. 1 represent various signal lines.

Next, the manner of controlling fuel injection in the fuel injection device of FIG. 1 will be described with reference to FIGS. 2 to 5 show the time course of the common rail pressure signal, the injector 1 control command signal, the control signal of the electromagnetic relief valve 5, and the injection pressure signal in the injection cycle, respectively. Common rail pressure signal is pressure sensor 1
0, and the injector 1 control command signal and the electromagnetic relief valve control signal are ON-OFF signals output from the ECU 8.

FIG. 2 shows an example in which fuel injection with insufficient atomization immediately after the start of fuel injection is reduced. The electromagnetic relief valve 5 is driven by a control signal from the ECU 8 to control the common rail 3 pressure immediately before the start of fuel injection. Reduce the pressure once. Therefore, at the start of injection, the injection pressure is relatively low,
Since the injection rate at the start of injection is low, which corresponds to the period in the short choke region at the early stage of valve opening in the VCO nozzle, the generation of insufficiently atomized spray can be minimized. After the pressure of the common rail 3 is once reduced by the electromagnetic relief valve 5, the fuel supply pump 2 rapidly increases the pressure to the pressure required for the injection during the injection. Due to the rapid increase of the common rail pressure, after the VCO nozzle passes through the short choke region, a spray with good atomization is generated by the original high-pressure injection.

FIG. 3 shows an example in which the spray state immediately before the end of the injection is improved. Until immediately before the end of the injection, the pressure of the common rail 3 is kept high to maintain a good state of atomization by high-pressure injection. Then, immediately before the end of the injection, the pressure of the common rail 3 is reduced by the electromagnetic relief valve 5. In the VCO nozzle, the short choke region immediately before closing the valve is a short choke region, and the spray state at this time deteriorates. However, since the fuel injection rate decreases due to the decrease in the common rail 3 pressure, the amount of the atomized atomization in the short choke region is reduced. Can be reduced. In particular, spraying at the end of fuel injection is important because it affects the generation of black smoke in the latter stage of combustion. After the fuel injection is completed, the fuel supply pump 2 increases the common rail 3 pressure until it reaches a predetermined pressure in preparation for the next injection.

FIG. 4 shows an example in which the fuel injection pressure is changed both immediately after the start and immediately before the end of the fuel injection, and can be achieved by a combination of the control shown in FIGS.

FIG. 5 is also an example in which the injection rate in the short choke region of the VCO nozzle at the start and end of the injection is reduced. However, unlike FIGS. 2 to 4, the pressure of the common rail 3 before the start of the injection is in the middle of the injection, that is, It is set lower than the high pressure fuel pressure required at the time of injection. At this time, the pressure of the common rail 3 may be controlled by the fuel supply pump 2 or may be controlled by the electromagnetic relief valve 5 at the end of the injection in the previous cycle.
May be the result of the above control. Since the injection rate at the start of injection is low, the adverse effect of spraying in the short choke region of the VCO nozzle can be minimized. Immediately after the start of the injection, the pressure of the common rail 3 is increased by the fuel supply pump 2, whereby high-pressure injection is achieved in the middle stage of the injection, and good spray is obtained. Immediately before the end of injection, the pressure is reduced by the pressure electromagnetic relief valve 5 of the common rail 3. Since the injection rate is reduced by the reduction of the common rail 3 pressure by the electromagnetic relief valve 5, the amount of spray that is not well atomized in the short choke region can be suppressed. After the injection, the common rail 3 pressure is maintained at the initial low pressure.

As described above, according to the embodiment of the present invention, the injection rate pattern can be changed by controlling the electromagnetic relief valve 5 during the injection period, so that the exhaust gas can be improved and the combustion noise can be reduced. The fuel injection control patterns shown in FIGS. 2 to 5 may be appropriately changed according to the operating state of the internal combustion engine, that is, during low load operation, medium load operation, and high load operation. In the embodiment of the present invention, the VCO
Although the description has been made on the assumption that the fuel injection device has a nozzle structure, the present invention may be applied to a fuel injection device having a nozzle with a sack 15 as shown in FIG.

[Brief description of the drawings]

FIG. 1 is an overall view of a fuel injection device with a common rail according to the present invention.

FIG. 2 is a diagram illustrating control of fuel injection. (Control at the start of injection)

FIG. 3 is a diagram illustrating control of fuel injection. (Control at the end of injection)

FIG. 4 is a diagram illustrating control of fuel injection. (Control at the start and end of injection)

FIG. 5 is a diagram illustrating control of fuel injection. (Control at the start and end of injection)

FIG. 6 is a sectional view showing a nozzle structure at the tip of the injector.
(With sack)

FIG. 7 is a cross-sectional view showing the nozzle structure at the tip of the injector.
(VCO nozzle)

[Explanation of symbols]

Reference Signs List 1 injector 2 fuel supply pump 3 common rail 4 high-pressure fuel pipe 5 electromagnetic relief valve 6 fuel tank 7 high-pressure pipe 8 ECU (electronic control unit) 9 EDU (electronic driving unit) 10 pressure sensor 11 pump control valve 12 nozzle body 13 needle 14 injection Hole 15 Sack 16 Seat

Claims (4)

[Claims] 1. A fuel injection device for supplying fuel stored in a pressure storage chamber and injecting the fuel, wherein the pressure of the fuel supplied from the pressure storage chamber is changed at least during a fuel injection period. Characteristic fuel injection device. 2. A fuel injection device having a common rail, wherein at least before the start of fuel injection, the fuel pressure of the common rail is reduced, and thereafter the common rail fuel pressure is increased, and the fuel injection is started at the fuel pressure rising stage. A fuel injection device characterized in that: 3. A fuel injection device having a common rail, wherein the fuel pressure of the common rail is reduced at least before the end of the fuel injection, and the fuel injection is terminated after the reduction of the common rail fuel pressure is started. Fuel injector. 4. In a fuel injection device having a common rail, fuel injection is started at a stage of increasing the fuel pressure of the common rail, and thereafter, a decrease of the common rail fuel pressure is started. A fuel injection device, which is terminated.