JPH07332200A - Fuel injection device for diesel engine - Google Patents

Abstract

PURPOSE:To effectively stop the injection of fuel upon completion of the fuel injection and to prevent generation of smoke or deterioration of fuel consumption. CONSTITUTION:A fuel injection device comprises a needle valve 3 moving in a direction to open a fuel injection hole 2 depending on the pressure of high pressure fuel, a piston 7 provided in a pressure chamber 6 and moving the needle valve 3 in a direction to close against the pressure of the high pressure fuel so as to close the fuel injection hole 2, when the high pressure fuel is fed in the pressure chamber 6, a control valve 11 for feeding the high pressure fuel to a control chamber 10 and discharging it therefrom and an orifice 22 provided between the control chamber 10 and the pressure chamber 6 and having a section larger on the control chamber 10 side and gradually reduced toward the pressure chamber 6 side. Thus, the high pressure fuel rapidly enters the pressure chamber 6 from the control chamber 10 and the needle valve 3 quickly closes the fuel injection hole 2.

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 a diesel engine.

[0002]

2. Description of the Related Art An example of a conventional diesel engine fuel injection device will be described with reference to FIG.
A fuel injection hole 2 is provided at the lower end of the fuel injection device main body 1, and a needle valve 3 is accommodated on the fuel injection hole 2 so as to be vertically movable. A step portion 4 is formed on the outer periphery of the middle portion of the needle valve 3, and a portion above the step portion 4 is a large diameter portion 5.

A pressure chamber 6 is formed above the needle valve 3 of the fuel injection device main body 1, and a piston 7 is provided in the pressure chamber 6 so as to slide vertically. A stem 8 is provided on the lower surface of the piston 7, and the lower end of the stem 8 is brought into contact with the upper end of the large diameter portion 5 of the needle valve 3. An orifice 9 is attached to the upper part of the pressure chamber 6, and a control chamber 10 is formed above the orifice 9.

A tubular control valve 11 is provided above the control chamber 10 of the fuel injection device main body 1 so as to slide vertically, and the control valve 11 is urged downward by a spring 12. The lower end outer periphery of the control valve 11 is normally brought into contact with the upper edge of the control chamber 10. Further, a through hole 13 is formed at one location on the outer circumference near the lower end of the control valve 11.

A solenoid 14 is provided above the control valve 11. When the switch 15 is closed and the solenoid 14 is energized, the control valve 11 is attracted by the solenoid 14 and the control valve 11 resists the force of the spring 12. Rise and control valve 1
The outer periphery of the lower end of 1 is separated from the upper edge of the control chamber 10.

A high-pressure fuel supply pipe 16 is provided outside the fuel injection device main body 1 so that high-pressure fuel is always supplied. The high-pressure fuel supply pipe 16 is branched and connected to the control high-pressure fuel supply passage 17 and the high-pressure fuel supply passage 18 of the fuel injection device main body 1. The control high-pressure fuel supply passage 17 opens at the position of the through hole 13 when the control valve 11 is descending, and the high-pressure fuel supply passage 18 opens just below the step portion 4 of the needle valve 3.

A high-pressure fuel discharge passage 19 is provided immediately above the control chamber 10 and the high-pressure fuel discharge passage 19 is provided.
Communicates with the high pressure fuel outlet 20.

Next, the operation of the above-described conventional diesel engine fuel injection device will be described.

As shown in FIG. 5, when the switch 15 is opened and the current to the solenoid 14 is cut off, the control valve 11 is lowered by the urging force of the spring 12, and the control valve 1
At the same time that the outer periphery of the lower end of 1 comes into contact with the upper edge of the control chamber 10,
The through hole 13 of the control valve 11 is in communication with the high pressure control fuel supply passage 17.

Therefore, the high-pressure fuel that has entered the control high-pressure fuel supply passage 17 from the high-pressure fuel supply pipe 16 enters the inside of the cylindrical control valve 11 through the through hole 13 and passes through the opening 21 at the lower end of the control valve 11. It is supplied to the control room 10 through the same.

At this time, the outer periphery of the lower end of the control valve 11 is the control chamber 1
Since the control chamber 10 is in contact with the upper edge of 0, the control chamber 10 is in the cutoff state with respect to the high-pressure fuel discharge passage 19, so that the high-pressure fuel supplied to the control chamber 10 is discharged from the high-pressure fuel outlet 20. Without flowing through, it flows into the pressure chamber 6 while being throttled by the orifice 9.

The pressure in the pressure chamber 6 gradually increases due to the high pressure fuel flowing in through the orifice 9, and the piston 7
Is pushed down toward the needle valve 3.

On the other hand, the high pressure fuel in the high pressure fuel supply pipe 16 is
Always pass through the high pressure fuel supply passage 18 and the step portion 4 of the needle valve 3.
It is supplied immediately below and applies a pushing force to the needle valve 3.

As described above, when the high pressure fuel flows into the pressure chamber 6 and the pressure gradually increases, the pressure of the pressure chamber 6 finally becomes the same as that of the high pressure fuel supply passage 18. However, since the effective pressure receiving area on which the pushing-down force acts on the piston 7 is much larger than the effective pressure receiving area on which the pushing-up force acts on the needle valve 3, the piston 7 moves toward the stem 8
The needle valve 3 is pushed down via the, and the lower end of the needle valve 3 closes the fuel injection hole 2.

As described above, FIG. 5 shows a non-injection state in which the high pressure fuel in the high pressure fuel supply passage 18 is cut off.

Next, as shown in FIG. 6, when the switch 15 is closed and the solenoid 14 is energized, the control valve 11 is attracted to the solenoid 14 so that it rises against the force of the spring 12 and the lower end of the control valve 11 is lifted. The outer periphery is separated from the upper edge of the control chamber 10, and the control chamber 10 communicates with the high-pressure fuel discharge passage 19. At the same time, the upper end of the opening 21 of the control valve 11 abuts the needle 24, and the through hole 13 of the control valve 11 has a high pressure for control. Fuel supply path 1
7, the control high-pressure fuel supply passage 17 is closed by the control valve 11.

Therefore, the high-pressure fuel that has entered the high-pressure fuel supply passage 17 for control from the high-pressure fuel supply pipe 16 is no longer supplied to the control chamber 10, and the high-pressure fuel that has been in the control chamber 10 until now is discharged into the high-pressure fuel discharge passage 19. Through the high pressure fuel outlet 20 to the outside of the fuel injection device body 1.

When the high-pressure fuel contained in the control chamber 10 is discharged, the high-pressure fuel in the pressure chamber 6 flows into the control chamber 10 while being throttled by the orifice 9 and passes through the high-pressure fuel discharge passage 19 to the high-pressure fuel outlet. It is discharged from the outside of the fuel injection device main body 1 from 20.

For this reason, the pressure in the pressure chamber 6 gradually decreases, and the force for pushing down the piston 7 toward the needle valve 3 disappears, and the pressure is supplied through the high pressure fuel supply passage 18 to just below the step portion 4 of the needle valve 3. The needle valve 3 is pushed up by the pressure of the high-pressure fuel, the lower end of the needle valve 3 is separated from the fuel injection hole 2, and the high-pressure fuel in the high-pressure fuel supply passage 18 is injected from the fuel injection hole 2.

As described above, FIG. 6 shows the state at the time of fuel injection.

When the fuel injection from the fuel injection hole 2 is terminated, if the switch 15 is opened and the current to the solenoid 14 is cut off as shown in FIG. 7, the solenoid 14 does not adsorb the control valve 11, so the control valve 11 is not adsorbed. 11 is lowered by the urging force of the spring 12, and the outer periphery of the lower end of the control valve 11 comes into contact with the upper edge of the control chamber 10, and at the same time, the through hole 13 of the control valve 11 is in communication with the high pressure fuel supply passage 17 for control. Become.

As a result, the high-pressure fuel in the control high-pressure fuel supply path 17 enters the inside of the cylindrical control valve 11 through the through hole 13 and is supplied to the control chamber 10. Then, while being throttled by the orifice 9, it flows into the pressure chamber 6 to gradually increase the pressure in the pressure chamber 6, pushes down the needle valve 3 via the piston 7 and the stem 8, and closes the fuel injection hole 2 at the lower end of the needle valve 3. Then, the fuel injection from the fuel injection hole 2 is stopped.

As described above, FIG. 7 shows the state at the end of fuel injection, which is the same as the state shown in FIG.

As described above, the fuel injection device for the diesel engine is provided with the orifice 9 between the pressure chamber 6 and the control chamber 10. The reason for providing the orifice 9 is to suppress the injection rate at the initial stage of fuel injection to be low.

At the beginning of fuel injection, the supply of high pressure fuel to the control chamber 10 is stopped by the control valve 11 as shown in FIG. 6, and the high pressure fuel in the pressure chamber 6 is discharged from the high pressure fuel outlet 20. However, when the high-pressure fuel in the pressure chamber 6 is rapidly discharged without the orifice 9, the lower end of the needle valve 3 suddenly separates from the fuel injection hole 2 and a large amount of fuel is injected into the fuel injection hole 2.
Will start to be jetted from.

In the case of a diesel engine, abrupt combustion of a large amount of fuel causes deterioration of exhaust gas such as generation of NOx. Therefore, an orifice 9 is provided to suppress such deterioration of exhaust gas.

On the other hand, at the end of the fuel injection shown in FIG. 7, it is necessary to quickly close the fuel injection hole 2 at the lower end of the needle valve 3 to quickly stop the fuel injection to prevent smoke generation and fuel consumption deterioration.

[0028]

However, as shown in FIGS. 5 to 7, the orifice 9 conventionally provided in the fuel injection device of a diesel engine has a straight shape with a constant diameter. There is.

Therefore, even when the fuel injection is completed, the orifice 9
As a result, the high pressure fuel flows into the pressure chamber 6 while being throttled, so that as shown by the broken line in the graph of FIG.
There is a problem that the increase in the pressure becomes slow, and accordingly, the needle valve 3 also slows down, so that the fuel injection is poor, the smoke is generated, and the fuel consumption is deteriorated.

The present invention solves these conventional problems,
It is an object of the present invention to provide a fuel injection device for a diesel engine, which is capable of improving the fuel shortage at the end of fuel injection and preventing smoke generation and fuel consumption deterioration.

[0031]

SUMMARY OF THE INVENTION The present invention is directed to a needle valve that moves in the direction of opening a fuel injection hole by the pressure of high-pressure fuel and injects high-pressure fuel from the fuel injection hole, and the pressure chamber provided in the pressure chamber. And a control valve for supplying and discharging high-pressure fuel to the control chamber, and a piston for moving the needle valve in the closing direction against the pressure of the high-pressure fuel to close the fuel injection hole when the high-pressure fuel is supplied to the control chamber. And a orifice provided between the control chamber and the pressure chamber, the cross-section on the control chamber side being large and the cross-section gradually shrinking toward the pressure chamber side, the fuel injection device for a diesel engine, It is related.

[0032]

The high-pressure fuel flows from the control chamber into the pressure chamber at a high speed, and the pressure in the pressure chamber rises sharply. As a result, the needle valve quickly closes the fuel injection hole.

[0033]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 2 shows an orifice 2 according to an embodiment of the present invention.
2 is an enlarged cross-sectional view of FIG. 2, in which the orifice 22 has a wide upper end and a large cross section, and the lower part of the orifice 22 has a rounded cross section and is gradually reduced, and the lower end of the orifice 22 has a small cross section.

When the fluid flows from the lower side to the upper side of the orifice 22, the loss coefficient is large and the flow of the fluid is strongly narrowed and difficult to flow.
When the fluid flows from the upper side to the lower side of the, the loss coefficient becomes small, the throttling phenomenon against the flow of the fluid becomes weak, and the fluid easily flows.

FIG. 1 shows such an orifice 22 of FIG.
FIG. 3 is a vertical cross-sectional view of an embodiment of the present invention in which the control chamber 10 has a large cross-section end of the orifice 22 as the control chamber 10 side and a small cross-section end of the orifice 22 as the pressure chamber 6 side. Since the configuration other than the orifice 22 is the same as that of the conventional device shown in FIG. 5, the same parts are designated by the same reference numerals as those in FIG. Is omitted.

Next, the operation of the apparatus shown in FIG. 1 will be described.

When the switch 15 is opened and the current to the solenoid 14 is cut off, the control valve 11 descends due to the urging force of the spring 12, and the high pressure from the high pressure fuel supply pipe 16 into the control high pressure fuel supply passage 17 is reached. Fuel is through hole 1
3 into the inside of the cylindrical control valve 11, and the control valve 11
It is supplied to the control chamber 10 through the opening 21 at the lower end.

The high pressure fuel supplied to the control chamber 10 flows into the pressure chamber 6 through the orifice 22,
At this time, since the loss coefficient due to the orifice 22 is small, the throttling phenomenon with respect to the flow of the fluid is weak, the pressure in the pressure chamber 6 rapidly rises, and the piston 7 pushes down the needle valve 3 rapidly. Quickly closes the fuel injection hole 2.

Then, the switch 15 is closed and the solenoid 14 is closed.
When the valve is energized, the control valve 11 rises against the force of the spring 12, the high-pressure fuel in the control high-pressure fuel supply passage 17 is no longer supplied to the control chamber 10, and the high-pressure fuel previously contained in the control chamber 10 is The fuel is discharged from the high-pressure fuel outlet 20 to the outside of the fuel injection device body 1 through the high-pressure fuel discharge passage 19.

When the high-pressure fuel contained in the control chamber 10 is discharged, the high-pressure fuel in the pressure chamber 6 flows into the control chamber 10 through the orifice 22 and passes through the high-pressure fuel discharge passage 19 to the high-pressure fuel outlet 20. Is discharged to the outside of the fuel injection device main body 1. At this time, since the loss coefficient due to the orifice 22 is large, the throttling phenomenon with respect to the fluid flow is strong, and the pressure in the pressure chamber 6 gradually decreases as in the conventional device, so that the force for pushing the piston 7 toward the needle valve 3 disappears and the high pressure is increased. The needle valve 3 is pushed up by the pressure of the high-pressure fuel supplied directly below the step portion 4 of the needle valve 3 through the fuel supply passage 18, and the lower end of the needle valve 3 is separated from the fuel injection hole 2 and
The high-pressure fuel in the high-pressure fuel supply passage 18 is injected from the fuel injection hole 2.

When the switch 15 is opened to cut off the current to the solenoid 14 in order to terminate the fuel injection from the fuel injection hole 2, the control valve 11 is lowered by the urging force of the spring 12, and the control high pressure fuel supply passage 17 is provided. The high-pressure fuel of 1 enters the inside of the cylindrical control valve 11 through the through hole 13 and is supplied to the control chamber 10. Then, it flows into the pressure chamber 6 through the orifice 22. At this time, since the loss coefficient due to the orifice 22 is small, the throttling phenomenon against the flow of the fluid is weak, the pressure in the pressure chamber 6 rapidly increases, and the piston 7
Causes the needle valve 3 to be pushed down rapidly, so that the lower end of the needle valve 3 quickly closes the fuel injection hole 2.

The changes in the pressure of the pressure chamber 6 and the lift of the needle valve 3 in the present invention having the orifice 22 of FIG. 1 described above are shown by the solid line in the graph of FIG.

That is, when the fuel injection is started, the pressure in the pressure chamber 6 is gradually lowered, the needle valve 3 is gently pushed up, and the injection rate at the initial stage of the fuel injection is low.
Exhaust deterioration such as generation of x can be suppressed.

At the end of fuel injection, the pressure in the pressure chamber 6 rapidly rises, the piston 7 rapidly pushes down the needle valve 3, and the lower end of the needle valve 3 closes the fuel injection hole 2 quickly. The fuel injection of
It is possible to prevent smoke generation and deterioration of fuel efficiency.

FIG. 3 is an enlarged cross-sectional view of an orifice 23 according to another embodiment of the present invention. The orifice 23 has a wide upper end and a large cross-section, and the cross-section gradually linearly decreases toward the bottom. However, the lower end of the orifice 23 has a small cross section.

When the fluid flows from the lower side to the upper side of the orifice 23, separation of the flow occurs and vortices are generated around the orifice, so that the loss coefficient is large and the fluid does not flow easily. When the fluid flows from the upper side to the lower side, separation of the flow does not occur, the distribution approaches an almost uniform distribution over the orifice cross section, the loss coefficient becomes small, and the fluid easily flows.

When such an orifice 23 of FIG. 3 is provided between the control chamber 10 and the pressure chamber 6 with a large cross-section end on the control chamber 10 side and a small cross-section end on the pressure chamber 6. However, similarly to the above-described embodiment of FIG. 1, when the fuel injection is started, the pressure of the pressure chamber 6 gradually decreases, the needle valve 3 is gently pushed up, and the injection rate at the initial stage of fuel injection is low. Exhaust emission deterioration such as NOx generation can be suppressed.
At the end of fuel injection, the pressure in the pressure chamber 6 rapidly rises, the piston 7 rapidly pushes down the needle valve 3, and the lower end of the needle valve 3 closes the fuel injection hole 2 quickly. It is possible to prevent the generation of smoke and the deterioration of fuel efficiency.

[0049]

According to the present invention, since the needle valve gently opens the fuel injection hole at the initial stage of fuel injection, the injection rate is low and NOx is low.
It is possible to suppress the deterioration of exhaust gas such as the occurrence of fuel injection, and the needle valve closes the fuel injection hole at the end of fuel injection, so the fuel injection is well cut off at the end of fuel injection, and smoke generation and fuel consumption deterioration can be prevented. effective.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an embodiment of the present invention.

FIG. 2 is an enlarged sectional view of an orifice according to an embodiment of the present invention.

FIG. 3 is an enlarged sectional view of an orifice according to another embodiment of the present invention.

FIG. 4 is a graph showing pressure in a pressure chamber and needle lift.

FIG. 5 is a vertical sectional view of an example of a conventional fuel injection device for a diesel engine.

FIG. 6 is a vertical cross-sectional view showing an operating state of a fuel injection device for a conventional diesel engine.

FIG. 7 is a vertical cross-sectional view showing an operating state of a fuel injection device for a conventional diesel engine.

[Explanation of symbols]

 2 Fuel injection hole 3 Needle valve 6 Pressure chamber 7 Piston 10 Control chamber 11 Control valve 22 Orifice 23 Orifice

Claims (1)

[Claims] 1. A needle valve for moving a fuel injection hole by a pressure of the high pressure fuel to open the fuel injection hole to inject the high pressure fuel from the fuel injection hole; and a high pressure fuel provided in the pressure chamber when the high pressure fuel is supplied to the pressure chamber. A piston for moving the needle valve in the closing direction against the pressure of the high-pressure fuel to close the fuel injection hole, a control valve for supplying and discharging high-pressure fuel to the control chamber, the control chamber and the pressure chamber A fuel injection device for a diesel engine, comprising: an orifice having a large cross section on the control chamber side and a cross section that gradually decreases toward the pressure chamber side.