JP3141683B2 - Fuel injection valve - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection valve.

[0002]

2. Description of the Related Art Conventionally, a so-called inner-open type fuel injection valve in which a nozzle port formed at the tip of a fuel injection valve body is controlled to open and close from the inside of the nozzle port by a needle arranged in the fuel injection valve body. And a valve portion is formed at the protruding tip of the needle while projecting the tip of the needle from the tip of the fuel injection valve body, and the needle valve controls opening and closing of the nozzle port from outside the nozzle port. Externally opened fuel injection valves are known. In this case, for example
As described in JP-A-62-67276,
The needle is usually kept closed by a strong compression spring.
Be held.

[0003]

[0004]

[0005]

However, if the needle is to be kept closed by such a strong compression spring, a large-sized compression spring is required, which increases the size of the fuel injection valve. There's a problem. Further, when the needle is opened, the needle must be opened against the strong compression spring, so that a strong actuator is required for the needle. When such a strong compression spring is used, a response delay occurs in the valve opening operation of the needle, and the needle is closed only by the spring force of the compression spring as in the fuel injection valve described in the above-mentioned publication. Then, there is a problem that a response delay occurs in the valve closing operation of the needle.

[0006]

According to the present invention, there is provided a fuel injection valve comprising:
Protrude the needle from the tip of the body and the needle
A valve is formed at the tip, and the needle is inserted inside the fuel injection valve body.
The valve closes the nozzle port when it is moved in the
When the needle is moved outward, the valve
In the fuel injection valve having an opening, the fuel injection valve
For intermittently supplying fuel into the fuel inlet passage of the vehicle
Equipped with a feeding device, fixed the piston on the needle,
Pressure control filled with fuel on one side of the piston on the spill port
The other side of the piston opposite the nozzle port, forming a chamber
Fuel to discharge fuel leaked from the pressure control chamber
A fuel discharge chamber, and replace the leaked fuel discharge chamber with the leaked fuel discharge chamber.
Through a check valve that can only flow to the fuel inlet passage
It is connected to the fuel inlet passage and the pressure is
Control the fuel pressure in the control room to increase the pressure in the pressure control room
The needle is driven by the fuel pressure acting on the piston when
To close the nozzle port and
Fuel acting on the needle valve when pressure is reduced
Move the needle by pressure to open the nozzle port
I have to.

[0007]

[0008]

[0009]

[0010]

[0011]

1 and 2 show a four-stroke compression ignition type internal combustion engine using a fuel injection valve according to the present invention.
1 and 2, reference numeral 1 denotes an engine body, 2 denotes a cylinder block, 3 denotes a cylinder head, 4 denotes a piston, 5
Is a combustion chamber, 6 is a pair of intake valves, 7 is a pair of intake ports,
Reference numeral 8 denotes a pair of exhaust valves, 9 denotes a pair of exhaust ports, 10 denotes a fuel injection valve arranged at the center of the top of the combustion chamber 5, and 11 denotes an engine-driven injection pump. Each intake port 7 consists of a straight port extending almost straight, and
In the compression ignition type internal combustion engine shown in FIG.
No swirl is generated in the combustion chamber 5 due to the airflow flowing into the combustion chamber 5 from the inside.

FIG. 3 is a side sectional view of the injection pump 11. Referring to FIG. 3, reference numeral 20 denotes an injection pump main body, 21 denotes a fuel supply pump, and the fuel supply pump 21 is rotated by 90 degrees so that the structure can be easily understood. The fuel supply pump 21 has a rotor 23 mounted on a drive shaft 22 driven by an engine. Fuel sucked from a fuel supply port 24 passes through a rotor 23 and is discharged from a fuel discharge port 25 to a pump inside the injection pump body 20. The fuel is discharged into the pressurized fuel chamber 26. The inner end of the drive shaft 22 projects into the pressurized fuel chamber 26, and a gear 27 is attached to the inner end of the drive shaft 22.

On the other hand, one end of a plunger 29 is inserted into a cylinder 28 formed in the fuel pump body 20, and the other end of the plunger 29 has the same number of cam lobes 3 as the number of cylinders.
0a is connected to the cam plate 30 formed. The inner end of the drive shaft 22 is connected to the cam plate 30 via a coupling 31 capable of transmitting a rotational force.
Is pressed onto the roller 33 by the spring force of the compression spring 32. When the drive shaft 22 rotates, the cam peak 3 of the cam plate 30
When 0a engages with the roller 33, the plunger 29 moves in the axial direction. Therefore, the plunger 29 is reciprocated while rotating.

A pressurizing chamber 34 is formed at the tip of the plunger 29, and a fuel discharge port 35 and a fuel overflow hole 36 communicating with the pressurizing chamber 34 are formed in the plunger 29. Around the plunger 29, the same number of fuel discharge passages 37 as the number of cylinders that can be aligned with the fuel discharge port 35 are formed at equal angular intervals, and each fuel discharge passage 37 is connected to a corresponding fuel via a check valve 38. It is connected to the injection valve 10. On the other hand, a spill ring 39 for controlling opening and closing of the fuel overflow hole 36 is inserted on the plunger 29, and the position of the spill ring 39 is controlled by a control link mechanism 41 rotatably supported around a pivot pin 40. Is done.

The upper end of the control link mechanism 41 has a rotating shaft 42
The rotation shaft 42 is connected to the accelerator pedal 12 (FIG. 1) and is rotated by the accelerator pedal 12.
In the pressurized fuel chamber 26, there is provided a governor mechanism 45 which is rotated by the gear 27 and urges the control ring mechanism 41 clockwise as the number of rotations increases. The pressurized fuel in the pressurized fuel chamber 26 is supplied from the fuel supply port 26 a into the pressurized chamber 34, and the fuel in the pressurized chamber 34 is supplied to the plunger 2.
As 9 moves to the right, it is compressed. Next, the fuel discharge port 35 formed in the plunger 29
Ejection out when communicating with the passage 37 the pressurized fuel in the pressure chamber 34 is supplied to the fuel injection valve 10 corresponding via a check valve 38.

Next, when the plunger 29 moves further rightward and the fuel overflow hole 36 opens into the pressurized fuel chamber 26, the supply of fuel to the fuel injection valve 10 is stopped. The timing at which the fuel overflow hole 36 opens into the pressurized fuel chamber 26 varies depending on the position of the spill valve 39, and therefore the amount of fuel supplied to the fuel injection valve 10 is controlled by the position of the spill valve 39. The position of the spill valve 39 is controlled by the control link mechanism 41 and the governor mechanism 45. As the depression amount of the accelerator pedal 12 (FIG. 1) increases, the amount of fuel supplied to the fuel injection valve 10 increases, and as the engine speed increases, the fuel injection increases. Control is performed such that the amount of fuel supplied to the valve 10 decreases.

As shown in FIG. 3, the fuel pump main body 11
Is provided with an injection pressure control valve 46. The injection pressure control valve 46 has a fuel overflow port 47 communicating with the pressurizing chamber 34.
A valve body 49 for closing the fuel overflow port 47 by the spring force of a normal compression spring 48, and a back pressure chamber 5 of the valve body 49.
And the back pressure chamber 50 is connected to the pressurized fuel chamber 26 via a conduit 51. Pressurizing chamber 34 by plunger 29
When the fuel pressure in the pressurizing chamber 34 becomes higher than the valve opening pressure of the valve element 49 when the fuel in the inside is compressed, the fuel in the pressurizing chamber 34 overflows through the fuel overflow port 47, and then The spilled fuel is returned to the pressurized fuel chamber 26 via the conduit 52. Therefore, the maximum fuel pressure in the pressurizing chamber 34 is determined by the valve opening pressure of the valve body 49, and the maximum pressure of the fuel supplied to the fuel injection valve 10 is also determined by the valve opening pressure of the valve body 49.

The higher the engine speed, the higher the discharge rate of the fuel supply pump 21. Therefore, the higher the engine speed, the higher the fuel pressure in the pressurized fuel chamber 26. When the fuel pressure in the pressurized fuel chamber 26 rises, the fuel pressure in the back pressure chamber 50 rises with it. As the engine speed increases, the valve opening pressure of the valve element 49 increases. The higher the number, the higher the maximum pressure of the fuel supplied to the fuel injection valve 10.

The above-described injection pump 11 is an improved version of a conventional distribution type fuel injection pump, and includes a fuel metering mechanism including a spill ring 39, a governor mechanism 45, and the like. However, as will be described later, in the embodiment according to the present invention, the fuel injection valve 10 comprises a fuel injection valve of a type having a fuel storage chamber for storing fuel therein, and the opening time of the fuel injection valve 10 or the fuel injection time Therefore, the fuel injection amount can be controlled by controlling the fuel injection pressure. Therefore, only the fuel pressure adjusting means such as the injection pressure control valve 46 is provided without the spill ring 39 and the governor mechanism 45. A fuel injection pump can also be used.

FIG. 4 is a side sectional view of the fuel injection valve 10. Referring to FIG. 4, reference numeral 60 denotes a fuel injection valve main body;
Reference numeral 1 denotes a needle slidable within the fuel injection valve main body 60, 62 denotes a valve portion integrally formed at the tip of the needle 61, 63 denotes a fuel reservoir formed around the conical pressure receiving surface 61a of the needle 61, and 64 denotes a fuel reservoir. A fuel storage chamber having a volume several tens of times the fuel injection amount at the time of the maximum injection amount, 65 is a fuel supply port, 66 is a piezoelectric element obtained by laminating a ring-shaped thin piezoelectric element plate. Shown respectively. As shown in FIG. 4, the lower end of the piezoelectric element 66 is supported by the fuel injector main body 60, and an end plate 67 is fixed to the upper end of the piezoelectric element 66. The upper end of the needle 61 is located inside the piezoelectric element 66 and the end plate 67.
The end plate 67 is screwed to the upper end of the needle 61. The end plate 67 is firmly fixed to the needle 61 by, for example, a locking nut 68.

The fuel supply port 65 is connected to a corresponding fuel discharge passage 37 (FIG. 3) of the injection pump 11, so that the fuel discharged from the injection pump 11 is supplied to the fuel supply port 65. The fuel supplied to the fuel supply port 65 is supplied to the fuel storage chamber 64 via a check valve 69 that can only flow from the fuel supply port 65 to the fuel storage chamber 64, and the fuel is supplied to the fuel storage chamber 6.
The fuel supplied into 4 is supplied around the distal end of needle 61 through fuel reservoir 63 and fuel passage 70.

FIG. 5 shows the tip of the needle 61. As shown in FIG. 5, the valve portion 62 of the needle 61 has a conical injection fuel guide surface 71, which is normally seated on a seat surface 72. At this time, the fuel injection from the fuel injection valve 10 is stopped. When fuel is to be injected from the fuel injection valve 10, electric charges are discharged from the piezoelectric element 66. When the electric charge is discharged from the piezoelectric element 66, the piezoelectric element 66 contracts in the axial direction.
1 is lowered. As a result, the valve portion 62 separates from the seat surface 72, and thus the fuel in the fuel storage chamber 64 is injected from the nozzle port 73 formed between the valve portion 62 and the seat surface 71.

Next, when electric charge is charged in the piezoelectric element 66, the piezoelectric element 66 extends in the axial direction. As a result, the needle 61 is raised, and the injected fuel guide surface 71 of the valve portion 62 is seated on the seat surface 72 again. In this manner, the fuel injection operation is stopped. Thus, the fuel injection valve 10 shown in FIG. 4 does not have any spring for urging the needle 61 in the axial direction.
1 controls the opening and closing of the nozzle port 73 by the piezoelectric element 66
This is performed by the stretching action. The expansion and contraction time of the piezoelectric element 66 is very short, and thus the needle 61
Is directly driven by the piezoelectric element 61, the needle 6
1, the opening and closing time of the nozzle port 73 can be made extremely short.

As shown in FIG. 5, at the time of fuel injection, the injected fuel F is guided by the injected fuel guide surface 71 of the valve portion 62 and spreads out from the nozzle port 73 into a thin film cone. In the embodiment shown in FIG. 1, the fuel injection valve 10 is arranged at the center of the top of the combustion chamber 5. Therefore, in the embodiment shown in FIG. 1, the fuel F is supplied from the center of the top of the combustion chamber 5 to the center of the combustion chamber 5. It is sprayed so as to spread in the shape of a thin film cone toward the periphery.

The piezoelectric element 66 of the fuel injection valve 10 is controlled based on the output signal of the electronic control unit 80 shown in FIG. The electronic control unit 80 is comprised of a digital computer, which are connected to each other via a bidirectional bus 81 ROM (read only memory) 82, R AM (random access memory) 83, CPU (microprocessor) 84, input port 85 and an output port 86. A load sensor 90 that generates an output voltage proportional to the amount of depression of the accelerator pedal 12 is provided to the accelerator pedal 12.
The output voltage is input to an input port 85 via an AD converter 87. The input port 85 is connected to a crank angle sensor 91 that generates an output pulse every time the engine rotates at a constant crank angle. From the output pulse of the crank angle sensor 91, the current crank angle and the engine speed are calculated. You. On the other hand, the output port 86 is connected to the piezoelectric element 66 of the fuel injection valve 10 via the drive circuit 88.

[0026] Next, while referring to substantially innovative new combustion method capable of the zero generation of soot and NO _X which is performed using the fuel injection valve 10 shown in FIG. 4 to FIGS. 6-9 explain. Note that this new combustion method will be described with focus on the most soot and NO _X are high-load operation which tends to occur. In a conventional compression ignition type internal combustion engine conventionally used, fuel having an average particle size of about 20 μm to 50 μm or less is supplied into the combustion chamber about 30 ° before compression top dead center. However simultaneous average particle size soot also matter how setting the fuel injection pressure also try to how set the injection timing as long as the fuel so as to 50μm or less so as to inject atomized and NO _X in this way fuel particles it is difficult to reduce, let alone it is impossible to substantially zero amount of generation of soot and NO _X. This is because the conventional combustion method has an essential problem. That is, a major factor simultaneous reduction is difficult soot and NO _X in the conventional combustion method is considered two there. One is that as soon as the fuel is injected, some of the fuel is vaporized immediately, and the vaporized fuel starts rapid combustion at an early stage. The other is that even if an attempt is made to distribute the fuel uniformly throughout the combustion chamber, the fuel is not actually uniformly dispersed throughout the combustion chamber, and the fuel collects in a limited area within the combustion chamber, or Even if the fuel is dispersed almost entirely in the combustion chamber, the rich region and the lean region are mixed.

That is, if the combustion is started early after the start of the injection as described above, the following injected fuel jumps into the combustion flame, so that these injected fuels are burned in a state of insufficient air. Comb soot will occur. Further, when an over-enriched mixture is formed in the combustion chamber, soot is generated by the combustion of the over-enriched mixture. On the other hand, when the injected fuel is collected in a limited area in the combustion chamber and the collected fuel is burned, the combustion temperature in this area becomes higher than the combustion temperature when the fuel is dispersed in the combustion chamber, Thus, NO _X will be generated. Also the injected fuel combustion temperature and the combustion pressure rapidly burned early rises rapidly becomes even higher, further NO _X will occur to thus.

The inventor of the present invention removes the above two factors, that is, prevents the injected fuel from evaporating early after the injection and disperses the injected fuel uniformly in the combustion chamber.
Simultaneous reduction of O _X is the thought to be a possible. As a result of repeated experiments, the average particle size of the injected fuel was set to be much larger than the average particle size used in the conventional combustion method, and the injection timing was generally used in the conventional combustion method. considerably accelerate and soot and NO _X than
Has been found to be able to reduce the amount of generation to substantially zero. Next, this will be described.

The curve in FIG. 6 shows a change in the pressure P in the combustion chamber 5 due to only the compression action of the piston 4. As can be seen from FIG. 6, the pressure P in the combustion chamber 5 is almost equal to B before the compression top dead center.
It rises rapidly above TDC 60 degrees. This is independent of the closing timing of the intake valve 6, and the pressure P in the combustion chamber 5 changes as shown in FIG. 6 in any reciprocating internal combustion engine.

The curve shown by the solid line in FIG. 7 shows the boiling temperature of the fuel at each crank angle, that is, the boiling point T. If the pressure P in the combustion chamber 5 rises, the boiling point T of the fuel also rises with it, so that the boiling point T of the fuel rises rapidly when it exceeds almost 60 degrees before the compression top dead center. On the other hand, the broken line in FIG. 7 shows the difference in the temperature change of the fuel particles due to the difference in diameter of the fuel particles when the fuel is injected in the compression top dead center BTDC theta ₀ degrees. The temperature of the fuel particles immediately after the injection is lower than the boiling point T determined by the pressure at that time, and then the fuel particles receive heat from the surroundings and rise in temperature. At this time, the temperature rise speed of the fuel particles increases as the particle size decreases.

That is, the particle size of the fuel particles is from 20 μm to 50 μm.
If it is about μm, the temperature of the fuel particles rapidly rises after the injection and reaches the boiling point T at a crank angle far before the compression top dead center TDC, and a rapid vaporization of fuel due to boiling from the fuel particles starts. Is done. Also, as can be seen from FIG. 7, even when the particle size of the fuel particles is 200 μm, the temperature of the fuel particles reaches the boiling point T before reaching the compression top dead center TDC, and the rapid vaporization of fuel due to boiling starts. If the rapid evaporation of fuel due to boiling is started before reaching the compression top dead center TDC, explosive combustion occurs at this time due to the evaporated fuel, and thus a large amount of soot and NO _X will occur.

On the other hand, when the diameter of the fuel particle is larger than about 500 μm, the temperature rise rate of the fuel particle becomes slow, so that the temperature of the fuel particle becomes almost equal to the compression top dead center TDC. Do not reach. Therefore, if the diameter of the fuel particles is made larger than about 500 μm, the fuel will not evaporate rapidly due to boiling before it reaches the compression top dead center TDC, but will be substantially boiling at the compression top dead center TDC or after the compression top dead center TDC. A rapid fuel vaporization action is started.

In practice, the fuel contains various components having different boiling points, and the boiling point of the fuel means that there are many boiling points. Therefore, when considering the boiling point of the fuel, it is preferable to consider the boiling point of the main fuel component.
Further, since the particle size of the injected fuel cannot be completely uniform, it is preferable to consider the average particle size of the injected fuel when considering the particle size of the injected fuel. Considering the above, the average particle diameter of the injected fuel is defined as the particle diameter at which the temperature of the fuel particle having the average particle diameter reaches the boiling point T of the main fuel component determined by the pressure at the time after the compression top dead center TDC or the compression top dead center TDC. With the above, rapid fuel evaporation due to boiling from the fuel particles does not occur until almost reaching the compression top dead center TDC after the injection, but rapid evaporation due to the boiling from the fuel particles occurs almost after the compression top dead center TDC. become.

In this case, a rapid fuel vaporization action starts by boiling in all the fuel particles almost simultaneously,
The fuel evaporated from all the fuel particles ignites and starts burning. At this time, as shown in FIG. 8A, if the fuel particles are concentrated in a part of the combustion chamber 5, the amount of air around each fuel particle is insufficient, and each fuel particle is in a state of insufficient air. And soot is generated, so that soot is generated. In order to prevent the generation of soot, the fuel particles are separated from each other by a sufficient distance so that there is sufficient air around each fuel particle when the fuel is ignited, as shown in FIG. It is preferable that each fuel particle is dispersed throughout the combustion chamber 5 as shown in FIG.

As shown in FIG. 8B, in order for the fuel particles to be dispersed throughout the combustion chamber 5 at the time of ignition, the fuel must be injected from the fuel injection valve 10 when the pressure P in the combustion chamber 5 is low. Must. That is, when the pressure P in the combustion chamber 5 increases, the air resistance increases, so that the flight distance of the injected fuel becomes short. Thus, at this time, as shown in FIG. Cannot spread throughout the interior. As described above, the pressure P in the combustion chamber 5 rapidly rises and rises when the pressure exceeds BTDC 60 degrees before compression top dead center, and in fact fuel injection is performed after the pressure P almost exceeds BTDC 60 degrees before compression top dead center. As shown in FIG. 8A, the fuel particles do not sufficiently spread in the combustion chamber 5. On the other hand, the pressure P in the combustion chamber 5 is low before the BTDC 60 degrees before the compression top dead center, and therefore, when the fuel injection is performed almost before the BTDC 60 degrees before the compression top dead center, the ignition timing is as shown in FIG. The fuel particles are dispersed throughout the combustion chamber 5 as shown in FIG. This has been confirmed by experiment.
In this case, the fuel injection timing is almost equal to the compression top dead center TD.
If the BTDC before C is 60 degrees or less, it may be during the compression stroke or during the intake stroke.

Thus, the BTDC 6 almost before the compression top dead center is obtained.
The fuel is injected before 0 degree, and the average particle diameter of the injected fuel at this time is approximately equal to the compression top dead center TDC
Alternatively, if the particle diameter reaches the boiling point T of the main fuel component determined by the pressure at the time after the compression top dead center TDC or more, the fuel rapidly evaporates due to the boiling from the fuel particles until it almost reaches the compression top dead center TDC after the injection. Does not occur and the compression top dead center T
After DC, rapid evaporation of fuel due to boiling from the fuel particles starts, and at this time, each fuel particle is dispersed throughout the combustion chamber 5 as shown in FIG. 8B.

When the evaporation of the fuel from each fuel particle is started, the fuel evaporated from each fuel particle is ignited and burned together. In this case there is no sufficient air soot is generated because there is around the fuel particles and the combustion is performed throughout the combustion chamber 5 the combustion temperature is lowered, thus to NO _X occurs Nothing to do. Further, the fuel particles tend NO _X occurs higher combustion gas temperature in the combustion gases of the burning fuel is heated later by heat of combustion of fuel burned before the resulting time difference in the start of combustion . However, since the fuel evaporated from the fuel particles, as described above at about the same time combustion is initiated NO _X In this sense does not occur.

FIG. 9 shows that the compression ratio is 18 and the fuel injection pressure is 2
The experimental results of the soot, that is, the amount of smoke and the amount of NO _X generated when the injection timing was changed with 0 MPa, the engine speed set to 1000 rpm, and the fuel injection amount set to 15 mm ³ . BTDC 6 before compression top dead center
Surprisingly smoke and N when set before 0 degrees
O _X it can be seen that does not occur at all.

As can be seen from the above description, the new combustion method established by the present inventor is substantially a compression top dead center TDC.
The fuel injection is started before the previous 60 degrees, and the average particle diameter of the injected fuel at this time is determined by the pressure at which the temperature of the fuel particles having the average particle diameter is substantially equal to the compression top dead center TDC or the pressure after the compression top dead center TDC. The particle diameter is set to be equal to or larger than the particle diameter reaching the boiling point T of the fuel component. Then the amount of generation of soot and NO _X can be substantially zero using this new combustion method.

An important point in carrying out this new combustion method is to disperse the fuel having a relatively large particle size throughout the combustion chamber 5 while keeping an interval between the fuel particles.
Therefore, from a hardware standpoint, the fuel injection device, particularly the fuel injection valve 10, plays an important role in executing a new combustion method. FIG. 4 shows an example of a fuel injection valve 10 suitable for executing such a new combustion method.
On the other hand, FIG. 10 shows a time chart of the fuel injection control. Therefore, a method of forming the fuel spray by the fuel injection valve 10 will be described next with reference to FIG.

As described above, when the driving signal of the piezoelectric element 66 is generated and the electric charge is discharged from the piezoelectric element 66, the fuel injection is started. As shown in FIG. 10, in the embodiment according to the present invention, for example, 18
The pressurized fuel discharged from the injection pump 11 about 0 degrees before is supplied into the fuel storage chamber 64 of the fuel injection valve 10. As a result, the fuel pressure in the fuel storage chamber 64 is increased. At this time, the fuel pressure in the fuel storage chamber 64 is about 20 MPa. Next, a little before the BTDC 60 degrees before the compression top dead center, a drive signal for the piezoelectric element 66 is issued, and the electric charge is discharged from the piezoelectric element 66 accordingly. When the electric charge is discharged from the piezoelectric element 66, the needle 61 descends and the fuel in the fuel storage chamber 64 is jetted into the combustion chamber 5.

The fuel pressure in the fuel storage chamber 64 is about 20 MPa, which is quite low, while the lift amount of the needle 61 is set larger than that of a general fuel injection valve.
Therefore, when the needle 61 descends, fuel having a large particle diameter is injected from the nozzle port 73 at once. At this time, the pressure in the combustion chamber 5 is low, so that the injected fuel satisfactorily scatters to the periphery of the combustion chamber 5. When fuel injection is started, FIG.
As shown in (2), the pressure in the fuel storage chamber 64 decreases, and thus the fuel injection rate becomes highest at the start of the injection, and then gradually decreases. When the pressure in the fuel storage chamber 64 decreases, the ejection speed of the fuel from the nozzle port 73 decreases. Therefore, the fuel injected later does not overtake the fuel injected earlier, so that the fuel particles are uniformly dispersed in the combustion chamber 5. Next, as shown in FIG. 10, fuel injection is completed before the BTDC reaches 60 degrees before the compression top dead center.

As described above, the valve opening pressure of the valve element 49 of the injection pressure control valve 46 attached to the injection pump 11 increases as the engine speed increases, so that the fuel discharged from the fuel pump 11 stores the fuel. As shown in FIG. 11A, the fuel pressure in the fuel storage chamber 64 when supplied into the chamber 64 increases as the engine speed N increases. That is, it takes time for the injected fuel to spread to the periphery of the combustion chamber 5,
On the other hand, the time from injection to ignition is shorter as the engine speed N is higher. Therefore, the higher the engine speed N, the higher the fuel pressure in the fuel storage chamber 64, and the higher the engine speed N, the faster the injected fuel spreads in the combustion chamber 5, so that at the time of ignition, regardless of the engine speed N, Instead, the fuel particles are evenly spread in the combustion chamber 5 as shown in FIG. 8 (B). In this case, instead of controlling the fuel injection pressure, the injection start timing may be advanced as the engine speed N increases.

In the embodiment according to the present invention, FIG.
As shown in (B), the fuel injection start timing θS is advanced as the depression amount L of the accelerator pedal 12 increases, that is, as the engine load increases. The injection period θT is stored in advance in the ROM 82 in the form of a map shown in FIG. 11C as a function of the depression amount L of the accelerator pedal 12 and the engine speed N.

The control of fuel injection from the fuel injection valve 10 is shown in FIG.
This is executed by the routine shown in FIG. This routine is executed by interruption every fixed crank angle. Referring to FIG. 12, first, at step 100, the injection start timing θS is calculated from the relationship shown in FIG. 11 (B). Next, at step 101, the injection period θT is calculated from the relationship shown in FIG. Then step 102
Then, the injection completion timing θE is calculated from the injection start timing θS and the injection period θT. Next, at step 103, a drive signal is generated for the piezoelectric element 66 to discharge the electric charge from the piezoelectric element 66 at the injection start timing θS and to charge the piezoelectric element 66 at the injection completion timing θE.

FIG. 13 shows another embodiment of the fuel injection valve 10. In this embodiment, the same components as those in FIG. 4 are denoted by the same reference numerals. Referring to FIG. 13, in this embodiment, a cylinder 110 is formed coaxially with the needle 61 in the fuel injection valve main body 60 around the upper end of the needle 61, and a piston 111 fixed to the upper end of the needle 61 is connected to the cylinder 110. It is slidably inserted into the inside. A pressure control chamber 112 is formed on one side of the piston 111 on the nozzle port 73 side, and a compression spring 113 having a weak spring force for urging the piston 111 upward is disposed in the pressure control chamber 112. On the other hand, on the other side of the piston 111 opposite to the nozzle port 73, a leaked fuel discharge chamber 114 for discharging fuel leaked from the pressure control chamber 112 to the outside is formed. The fuel in the leaked fuel discharge chamber 114 is guided around the piezoelectric element 66 through the discharge passage 115, and is discharged from the discharge port 117 after cooling the piezoelectric element 66. Therefore, the pressure in the leaked fuel discharge chamber 114 is low.

On the other hand, a piston 118 slidable in the axial direction of the needle 61 is disposed in the fuel injection valve main body 60, and a piezoelectric element 66 is inserted between the top surface of the piston 118 and the fuel injection valve main body 60. . This piston 118 is urged toward the piezoelectric element 66 by a disc spring 119. On the other hand, below the piston 118 is the piston 11
A variable volume chamber 120 defined by the lower end surface of the chamber 8 is formed. The variable volume chamber 120 has a fuel passage 121 on the one hand.
Is connected to the pressure control chamber 112 via the fuel passage 122, and is connected to the fuel storage chamber 64 via the fuel passage 122 on the other hand. In the fuel passage 122, a check valve 123 that can flow only from the variable volume chamber 120 to the fuel storage chamber 64 is disposed. Further, the fuel supply port 65 is connected to the pressure control chamber 112 via a fuel inlet passage 124 and a check valve 125 that can only flow from the fuel inlet passage 124 to the pressure control chamber 112.

As described above, the fuel is supplied to the fuel supply port 65 approximately 180 ° crank angle before the fuel is injected from the injection pump 11. This fuel is supplied to the pressure control chamber 112 and the variable volume chamber 120 via the check valve 125, and further supplied to the fuel storage chamber 64 via the check valve 123. At this time, the pressure control chamber 112 and the variable volume chamber 12
0 and the inside of the fuel storage chamber 64 have substantially the same high pressure. Therefore, at this time, the needle 61 is urged upward by the fuel pressure in the pressure control chamber 112 acting on the piston 111, and the nozzle port 73 is opened by the valve portion 62. It is closed. As described above, the closing operation of the nozzle port 73 by the needle 61 is performed by the fuel pressure in the pressure control chamber 112.

When the fuel injection is to be started, the electric charge is discharged from the piezoelectric element 66. When the electric charge is discharged from the piezoelectric element 66, the piezoelectric element 66 contracts, and as a result, the piston 118 rises, so that the fuel pressure in the variable volume chamber 120 decreases. When the fuel pressure in the variable volume chamber 120 decreases, the fuel pressure in the pressure control chamber 112 also decreases. Thus, the fuel pressure acting on the back surface of the valve portion 62 of the needle 61 lowers the needle 61 to start fuel injection. Is done. Next, when the piezoelectric element 66 is charged with electric charge and the piezoelectric element 66 expands, the piston 118 descends and the fuel pressure in the pressure control chamber 112 rises. Thus, the needle 61 is raised, so that the fuel injection is performed. Stopped.

In this embodiment, the diameter of the piston 111 is considerably smaller than the diameter of the piston 118. When the diameter of the piston 111 is smaller than the diameter of the piston 118 in this way, even if the movement amount of the piston 118 is small, the piston 1
11 can be increased. In other words, the lift amount of the needle 61 can be increased. In this embodiment, the valve closing action of the needle 61 is not performed by the spring force of the compression spring 113.
As for the spring force of No. 3, a small spring force is sufficient, and in some cases, the compression spring 113 may not be provided.

FIG. 14 shows still another embodiment of the fuel injection valve 10. In FIG. 14, the same components as those in FIG. 13 are indicated by the same reference numerals. Referring to FIG. 14, in this embodiment, a leaked fuel discharge chamber 114 is connected to a fuel inlet passage 124 upstream of a check valve 125 via a discharge passage 130, and the leaked fuel discharge chamber 114 is connected to the fuel inlet passage 124 in the discharge passage 130. A check valve 131 that can flow only toward the inside 124 is arranged. Also in this embodiment, the fuel is supplied to the fuel supply port 65 approximately 180 ° crank angle before the fuel is injected from the injection pump 11, and the fuel supply operation from the injection pump 11 is not performed. When the fuel pressure in the passage 124 is low, the fuel in the leaked fuel discharge chamber 114 is returned to the fuel inlet passage 124 via the check valve 131. In this embodiment, since there is no need to arrange a discharge conduit for discharging fuel from the leaked fuel discharge chamber 114 outside the fuel injection valve, the entire fuel injection system can be simplified.

[0052]

As described above, the responsiveness of the opening / closing control of the nozzle port by the needle can be improved, and the entire fuel injection system can be simplified.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a compression ignition type internal combustion engine.

FIG. 2 is a bottom view of the cylinder head of FIG. 1;

FIG. 3 is a side sectional view of the injection pump.

FIG. 4 is a side sectional view of the fuel injection valve.

FIG. 5 is an enlarged side sectional view of a front end portion of the fuel injection valve.

FIG. 6 is a diagram showing a pressure change in a combustion chamber caused only by a compression action of a piston.

FIG. 7 is a diagram showing a boiling point and a change in temperature of fuel particles.

FIG. 8 is a diagram showing a distribution of fuel particles.

FIG. 9 is a diagram showing the amounts of smoke and NO _X generated.

FIG. 10 is a time chart of fuel injection control.

FIG. 11 is a diagram showing a fuel pressure and the like in a fuel storage chamber.

FIG. 12 is a flowchart for performing injection control.

FIG. 13 is a side sectional view of another embodiment of the fuel injection valve.

FIG. 14 is a side sectional view of still another embodiment of the fuel injection valve.

[Explanation of symbols]

 5 Combustion chamber 6 Intake valve 8 Exhaust valve 10 Fuel injection valve 61 Needle 62 Valve section 64 Fuel storage chamber 65 Fuel supply port 66 Piezoelectric element 69, 123, 125, 131 Check valve 73 ... Nozzle port 111,118 ... Piston 112 ... Pressure control chamber 114 ... Leaked fuel discharge chamber 120 ... Variable volume chamber

Claims (1)

(57) [Claims] 1. A tip of a needle is attached to a tip of a fuel injection valve body.
Protruding tip of needle while projecting from the end to the outside
The needle is formed in the direction of the fuel injection valve body
The valve closes the nozzle port when moved to
When the valve is moved outward, the valve opens the nozzle port.
In the fuel injection valve, the fuel of the fuel injection valve is
Fuel supply device for intermittently supplying fuel into the inlet passage
The piston is fixed on the needle, and the nozzle
A pressure control chamber filled with fuel is formed on one side of the side piston.
Pressure on the other side of the piston opposite the nozzle port
Leakage fuel discharge to discharge fuel leaked from the control room
A chamber is formed and the leaked fuel discharge chamber is raised above the leaked fuel discharge chamber.
Via a check valve that can only flow to the fuel inlet passage
It is connected to the fuel inlet passage and the pressure is
Control the fuel pressure in the control room to increase the pressure in the pressure control room
The needle is driven by the fuel pressure acting on the piston when
To close the nozzle port and
Fuel acting on the needle valve when pressure is reduced
Move the needle by pressure to open the nozzle port
Fuel injection valve that was.