JPH0674130A - Fuel injection valve - Google Patents

Abstract

PURPOSE:To prevent the occurrence of secondary injection by retarding the valve opening speed of a needle at the time of fuel injection stop by providing a relief valve which opens when the fuel pressure in a back pressure chamber formed on the top surface of the needle has become higher than a fixed value, and relieves the fuel in the back pressure chamber into a fuel pool. CONSTITUTION:A back pressure chamber 20 is formed on a needle top surface 19 and connected to a pressure control chamber through a fuel hole 22 extending to the upper part. An enlarged head portion 23 is integrally formed at a needle top portion, and a needle lift regulating surface 21 is formed at the inner wall of a needle insertion hole into which the enlarged head portion 23 is inserted slidably. In addition, a compression spring 26 to energize the needle in a valve opening direction is provided inside the back pressure chamber 20. In this constitution, a relief valve 24 that opens when the fuel pressure in the back pressure chamber 20 has become higher than a fixed value, and relieves the fuel into a fuel pool 16, is provided at the inside of the enlarged head portion 23. The relief valve 24 connects a valve body guide hole 27 that is inserted with a valve body 28 slidably, to the fuel pool 16 by means of a return passage 31.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a fuel injection valve.

[0002]

2. Description of the Related Art A back pressure chamber is formed on the top surface of a needle, the back pressure chamber is connected to a pressure control chamber, and the volume of the pressure control chamber filled with fuel is controlled by an actuator to control the volume of the pressure control chamber. When the needle is increased, the needle rises to open the nozzle port and at this time the top surface of the needle abuts the needle lift restriction surface formed on the inner wall of the needle insertion hole to restrict the maximum lift amount of the needle, A fuel injection valve is known in which the needle is biased in the valve closing direction to close the nozzle port when the volume of the pressure control chamber is reduced (see JP-A-60-1369).

In this fuel injection valve, when the volume of the pressure control chamber is increased and the fuel pressure acting on the top surface of the needle is decreased, the needle rises, and as a result, the needle opens the nozzle opening, so that fuel injection is performed. Be started. Then, when the volume of the pressure control chamber is decreased, the fuel pressure acting on the top surface of the needle, that is, the fuel pressure in the back pressure chamber is increased. As a result, the needle is urged in the valve closing direction to close the nozzle opening, so that the fuel injection is stopped.

[0004]

By the way, in this fuel injection valve, the needle does not immediately descend even if the volume of the pressure control chamber is reduced in order to stop fuel injection, and therefore the fuel pressure in the back pressure chamber rises rapidly. To do. As a result, the fuel pressure in the back pressure chamber becomes high, so that the needle is urged at a high speed in the valve closing direction. However, when the needle is urged in the valve closing direction at a high speed in this way, the needle collides with the valve seat at a high speed, so that the reaction force of the collision action causes the needle to close and then open again. There is no so-called secondary injection phenomenon.

[0005]

In order to solve the above problems, according to the present invention, a back pressure chamber is formed on the top surface of the needle, and the back pressure chamber is connected to the pressure control chamber and filled with fuel. When the volume of the pressure control chamber is controlled by an actuator to increase the volume of the pressure control chamber, the needle rises to open the nozzle port, and at this time, the top surface of the needle is formed on the inner wall of the needle insertion hole. When the maximum lift amount of the needle is regulated by abutting the needle lift regulation surface and the volume of the pressure control chamber is reduced, the needle is urged in the valve closing direction to close the nozzle opening. A relief valve is provided which opens when the fuel pressure in the pressure chamber becomes higher than the fuel pressure in the fuel reservoir by a predetermined value or more and allows the fuel in the back pressure chamber to escape into the fuel reservoir.

[0006]

In the present invention, the volume of the pressure control chamber is reduced and the fuel pressure in the pressure control chamber rises. Therefore, when the fuel pressure in the back pressure chamber rises, the needle starts to descend. At this time, when the fuel pressure in the back pressure chamber becomes higher than the fuel pressure in the fuel pool by a predetermined value or more, the relief valve opens to let the fuel in the back pressure chamber escape into the fuel pool, and as a result, the needle The downward force acting on the top surface is reduced, and the closing speed of the needle is reduced.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, 1 is a fuel injection valve housing, 2 is a nozzle holder having a nozzle port 3 at its tip, 4 is a needle arranged in the nozzle holder 2, and 5 is a housing 1. The piston holder is fitted, 6 is a piston slidably inserted in the piston insertion hole 7 of the piston holder 5, 8 is a piezoelectric element made of a laminated body of disk-shaped piezoelectric element plates, and 9 is a guide for the piezoelectric element 8. Sleeves 10 and 10 are piezoelectric element holders, respectively.

Piston holder 5 and piezoelectric element holder 1
0 is fixed to a regular position in the housing 1 by a retainer 11 screwed to the housing 1, and the nozzle holder 2
Is fixed to a regular position in the housing 1 by a retainer 12 screwed to the housing 1. A pressure control chamber 13 defined by the lower end surface of the piston 6 is formed in the piston insertion hole 7 formed in the piston holder 5.
A fuel reservoir 16 is formed around the conical pressure receiving surface 15 of the needle 4. The fuel reservoir 16 is connected to the nozzle port 3 on the one hand, and is connected to the fuel supply port 18 via the fuel supply pipe 18a on the other hand.

As shown in FIG. 2, a back pressure chamber 20 is formed on the top surface 19 of the needle 4. A fuel hole 22 extending upward is formed from the central portion of the top surface of the back pressure chamber 20, and the back pressure chamber 20 is connected to the pressure control chamber 13 via the fuel hole 22. A cylindrical enlarged head portion 23 is integrally formed on the top of the needle 4, and the enlarged head portion 23 serves as the nozzle holder 2
It is slidably inserted into the needle insertion hole 2a formed therein. Further, a needle lift restricting surface 21 is formed on the inner wall of the needle insertion hole 2a, and the needle 4 contacts the needle lift restricting surface 21 to restrict the maximum lift amount of the needle 4.

A compression spring 26 is arranged in the back pressure chamber 20 between the top surface of the back pressure chamber 20 and the top surface of the needle 4. The compression spring 26 urges the needle 4 in the valve closing direction by its spring force, and particularly prevents the nozzle port 3 from being opened by accident when the valve is closed.

Still referring to FIG. 2, in the present embodiment,
A relief valve 24 is provided in the enlarged head 23 of the needle 4. The relief valve 24 covers the valve body guide hole 27 formed in the enlarged head 23, the valve body 28 slidably inserted in the valve body guide hole 27, and the top of the valve body guide hole 27. It is composed of an end plate 30 having an orifice hole 29 and a compression spring that biases the valve body 28 toward the orifice hole 29, and the bottom of the valve body guide hole 27 is connected to the fuel reservoir 16 via a return passage 31. .

The valve body 28 is biased by the spring force of the compression spring 32 to close the orifice hole 29, and therefore the relief valve 24 is normally closed. However, the downward force acting on the valve body 28 due to the increase of the fuel pressure in the back pressure chamber 20 is the resultant upward force acting on the valve body 28 due to the fuel pressure in the fuel pool 16 and the spring force of the compression spring 32. At a larger size, the valve body 28 is urged downwards and thus the relief valve 24 opens.

Further, a communication hole 33 is formed in the valve body 28. Therefore, when the relief valve 24 opens, the back pressure chamber 20
The fuel inside flows out to the valve body guide hole 27 through the orifice hole 29, and flows to the fuel pool 16 through the communication hole 33 and the return passage 31.

When the electric charge charged in the piezoelectric element 8 is discharged and the piezoelectric element 8 contracts in the axial direction, the piston 6 is raised. Even if the piston 6 is raised, the needle 4 does not immediately rise, and at this time, the fuel pressure in the pressure control chamber 13 and the fuel hole 22 sharply drops.
Therefore, the fuel pressure in the back pressure chamber 20 drops sharply. As a result, the fuel pressure applied to the top surface of the enlarged head 23 is reduced, and the needle 4 is raised by the fuel pressure applied to the pressure receiving surface 15. As a result, the needle 4 opens the nozzle port 3 to start fuel injection.

When the needle 4 starts rising, the back pressure chamber 20
The fuel pressure inside rises slightly. At this time, the fuel pressure in the back pressure chamber 20 is lower than the fuel pressure in the fuel pool 16. Therefore, the spring force of the compression spring 32 and the fuel pool 16
Since the upward force acting on the valve element 28 due to the internal fuel pressure becomes larger than the downward force acting on the valve element 28 due to the fuel pressure inside the back pressure chamber 20, the relief valve 24 does not open and the relief valve 24 does not open. The same operation as a general needle without 24 is performed, and the needle 4 moves up. Next, the needle 4 comes into contact with the needle lift restricting surface 21 to restrict the lift, so that the rising of the needle 4 is stopped.

On the other hand, when the piezoelectric element 8 is charged with electric charge and the piezoelectric element 8 expands in the axial direction, the piston 6 is lowered, and as a result, the volume of the pressure control chamber 13 is reduced. Even if the volume of the pressure control chamber 13 is reduced, the needle 4 does not immediately descend, and therefore the pressure control chamber 13
And the fuel pressure in the fuel hole 22 rises. Therefore, the fuel pressure in the back pressure chamber 20 rapidly increases. As a result, the needle 4 is biased in the valve closing direction, so that the needle 4 starts descending.

At this time, the fuel pressure in the back pressure chamber 20 rises and the downward force acting on the valve body 28 acts on the valve body 28 by the fuel pressure in the fuel pool 16 and the spring force of the compression spring 32. When it becomes larger than the resultant force in the upward direction, the valve body 28 is urged downwardly, so that the relief valve 24 opens. As a result, the high-pressure fuel in the back pressure chamber 20 flows out into the valve body guide hole 27 through the orifice hole 29, and the communication hole 3
3 and further to the fuel reservoir 16 via the return passage 31. Therefore, the fuel pressure in the back pressure chamber 20 decreases, and the pressure acting on the top surface 19 of the needle 4 decreases. Therefore, the descending speed of the needle 4 is reduced. As a result, the speed at which the needle 4 comes into contact with the valve seat becomes slower, so that the needle 4 does not bounce at the valve seat, and thus it is possible to prevent the secondary injection phenomenon from occurring.

Due to the outflow of the fuel, the fuel pressure in the back pressure chamber 20 decreases and the downward force acting on the valve body 28 is reduced by the fuel pressure in the fuel pool 16 and the spring force of the compression spring 32. If it is smaller than the upward resultant force acting on
The valve body 28 is urged in the valve closing direction to close the orifice hole 29, so that the outflow of fuel from the back pressure chamber 20 to the fuel reservoir 16 is stopped.

Further, in this embodiment, the relief valve 24 is opened / closed so that the difference between the fuel pressure in the back pressure chamber 20 and the fuel pressure in the fuel pool 16 becomes constant regardless of the fuel pressure in the fuel pool 16. Therefore, the valve closing speed becomes constant regardless of the fuel pressure in the fuel reservoir 16. Therefore, even if the fuel pressure in the fuel pool 16 changes depending on the change in the valve closing timing, a constant valve closing time can be obtained. As a result, even when it is considered that the fuel pressure in the fuel pool 16 changes depending on the difference in valve closing timing, a constant valve closing time is obtained, and therefore the accuracy of the injection amount is improved.

However, when it is considered that the fuel pressure in the fuel reservoir 16 does not depend on the fluctuation of the valve closing timing, the relief valve 24 can be provided as shown in FIG. In this embodiment, the relief valve 24 is formed in the piston holder 5. In the relief valve 24, the valve body guide hole 27 formed in the piston holder 5, the valve body 28 slidably inserted in the valve body guide hole 27, and the back pressure chamber 2 through the communication hole 29a.
0, the restraining end plate 30 having the return passage 31, and the compression spring 32 that biases the valve body 28 toward the orifice hole 29. The side facing the plate 30 is connected via a return passage 31 to a chamber 34 that connects the fuel supply port 18 and the fuel supply pipe 18a.

The valve body 28 is biased by the spring force of the compression spring 32 to close the orifice hole 29, and therefore the relief valve 24 is normally closed. However, the fuel pressure in the back pressure chamber 20 rises and the force in the valve opening direction acting on the valve body 28 acts on the valve body 28 due to the fuel pressure in the fuel pool 16 and the spring force of the compression spring 32. When it becomes larger than the resultant force in the valve direction, the valve body 28 is urged in the valve opening direction, so that the relief valve 24 opens.

Further, a communication hole 33 is formed in the valve body 28. Therefore, when the relief valve 24 opens, the back pressure chamber 20
The fuel inside flows into the valve body guide hole 27 through the communication hole 29a, the orifice hole 29, and the chamber 34 through the communication hole 33 and the return passage 31. Further, this outflow fuel flows into the fuel pool 16 from the chamber 34 through the fuel supply pipe 18a.

When the piston 6 is raised to start fuel injection and thus the needle 4 starts to rise,
The fuel pressure in the back pressure chamber 20 is lower than the fuel pressure in the fuel pool 16. Therefore, the resultant force in the valve closing direction acting on the valve element 28 by the spring force of the compression spring 32 and the fuel pressure in the fuel reservoir 16 becomes larger than the force in the valve opening direction acting on the valve element 28, so that the relief valve 24 opens. Without the relief valve 24, the needle 4 has the same action as a general needle without the relief valve 24.
Rises. Next, the needle 4 comes into contact with the needle lift restricting surface 21 to restrict the lift, so that the rising of the needle 4 is stopped.

On the other hand, the piston 6 is lowered to stop the fuel injection, and thus the needle 4 starts to descend. At this time, when the force in the valve opening direction acting on the valve body 28 becomes larger than the resultant force in the valve closing direction acting on the valve body 28 due to the fuel pressure in the fuel reservoir 16 and the spring force of the compression spring 32, the valve body 28 is Since the relief valve 24 is biased in the valve opening direction, the relief valve 24 opens. As a result, the high-pressure fuel in the back pressure chamber 20 flows into the valve body guide hole 27 through the communication hole 29a and the orifice hole 29, and also flows into the chamber 34 through the communication hole 33 and the return passage 31. . Further, this outflow fuel flows into the fuel pool 16 from the chamber 34 through the fuel supply pipe 18a. Therefore, the fuel pressure in the back pressure chamber 20 decreases, and the pressure acting on the top surface 19 of the needle 4 decreases. Therefore, the descending speed of the needle 4 is reduced. As a result, the speed at which the needle 4 comes into contact with the valve seat becomes slower, so that the needle 4 does not bounce at the valve seat, and thus it is possible to prevent the secondary injection phenomenon from occurring.

Due to this fuel outflow, the fuel pressure in the back pressure chamber 20 decreases and the force in the valve opening direction acting on the valve body 28 is valved by the fuel pressure in the fuel reservoir 16 and the spring force of the compression spring 32. When it becomes smaller than the resultant force in the valve closing direction acting on the body 28, the valve body 28 is urged in the valve closing direction to close the orifice hole 29, and thus the outflow of fuel from the back pressure chamber 20 to the fuel reservoir 16 is stopped.

[0026]

[Effect of the Invention] When the fuel injection is stopped, the valve closing speed of the needle can be slowed to prevent the secondary injection phenomenon from occurring.

[Brief description of drawings]

FIG. 1 is a side sectional view of a fuel injection valve.

FIG. 2 is an enlarged side sectional view of a portion A of the fuel injection valve shown in FIG.

FIG. 3 is an enlarged side sectional view of a part of a fuel injection valve showing another embodiment.

[Explanation of symbols]

 4 ... Needle 6 ... Piston 8 ... Piezoelectric element 13 ... Pressure control chamber 20 ... Back pressure chamber 24 ... Relief valve

Claims (1)

[Claims] 1. A back pressure chamber is formed on the top surface of a needle, the back pressure chamber is connected to the pressure control chamber, and the volume of the pressure control chamber filled with fuel is controlled by an actuator to control the volume of the pressure control chamber. When the needle is increased, the needle rises to open the nozzle port and at this time the top surface of the needle abuts the needle lift restriction surface formed on the inner wall of the needle insertion hole to restrict the maximum lift amount of the needle, In the fuel injection valve in which the needle is biased in the valve closing direction to close the nozzle port when the volume of the pressure control chamber is reduced, the fuel pressure in the back pressure chamber is set to a predetermined value higher than the fuel pressure in the fuel reservoir. A fuel injection valve equipped with a relief valve that opens when the pressure rises above a certain value to allow the fuel in the back pressure chamber to escape into the fuel reservoir.