JPH0693937A - Fuel injection valve - Google Patents

Abstract

PURPOSE:To obstruct deterioration in accuracy of an injection amount by reduc ing pressure acted to the downward annular surface of a needle in the case where the capacity of an annular chamber is increased in association with rising of the needle. CONSTITUTION:A back pressure chamber 20 is formed on the top surface of a needle 4, and also it is connected to a pressure control chamber 13. An annular chamber 24 is formed especially between a downward annular surface 27 formed on the outer circumferential surface of the needle 4 and an upward annular surface 26 formed on the inner circumferential surface of a needle inserting hole 2a. When a piezoelectric element 8 is contracted, and a piston 6 is raised so as to reduce fuel pressure in a pressure control chamber 13, the needle 4 is raised. At this time, large negative pressure is generated in the annular chamber 24 temporarily, and downward force is acted to the downward annular surface 27 of the outer circumferential surface of the needle 4 by its negative pressure, so that downward force is acted to the needle 4. As a result, rising speed of the needle 4 is reduced. It is thus possible to obstruct deterioration of accuracy of an injection amount by delaying opening speed of the needle 4 at the time of fuel injection.

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 pressure control chamber. When the volume is increased, the needle rises to open the nozzle opening, and at this time, the needle abuts the needle lift regulation surface formed on the inner wall surface of the needle insertion hole to regulate 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 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]

However, in this fuel injection valve, the needle does not immediately rise even if the volume of the pressure control chamber is increased in order to start fuel injection, and therefore the fuel pressure in the back pressure chamber drops sharply. To do. As a result, the fuel pressure in the back pressure chamber becomes high, so that the needle is urged in the valve opening direction at a high speed. However, when the needle is urged in the valve opening direction at a high speed in this way, the needle collides with the needle lift regulation surface at a high speed, so that the reaction force of the collision action causes the needle to rebound on the needle lift regulation surface. Become. However, when the needle bounces like this, the valve closing operation of the needle is started while the needle bounces, especially when the injection period is short. In this case, if the valve closing operation of the needle is started while the needle is descending due to rebound, the needle closing time will be earlier than the scheduled time, while the needle will rebound and then rise again. If the needle closing operation is started during the start, the needle closing timing becomes later than the scheduled timing.
In other words, if the needle rebounds, the closing time of the needle will shift from the scheduled time,
Therefore, there is a problem that the injection amount deviates from the regular injection amount.

[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, so that When the volume of the filled pressure control chamber is controlled by the actuator and the volume of the pressure control chamber is increased, the needle rises to open the nozzle port and at this time the needle is formed on the inner wall surface of the needle insertion hole. When the maximum lift amount of the needle is regulated by contacting 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. An annular chamber is formed between the downward annular surface formed on the outer peripheral surface and the upward annular surface formed on the inner peripheral surface of the needle insertion hole, and the volume of the annular chamber increases as the needle rises. And it is adapted to reduce the pressure on the downward annular surface of the needle.

According to the present invention, in order to solve the above problems, a first annular surface is formed between the downward annular surface formed on the outer peripheral surface of the needle and the upward annular surface formed on the inner peripheral surface of the needle insertion hole. An annular chamber is formed to reduce the pressure acting on the downward annular surface of the needle when the volume of the first annular chamber increases as the needle rises, and the upward direction formed on the outer peripheral surface of the needle A second annular chamber is formed between the annular surface of the needle and the downwardly facing annular surface formed on the inner peripheral surface of the needle insertion hole, and when the volume of the second annular chamber increases as the needle descends, The pressure acting on the annular surface is reduced.

[0007]

According to the first aspect of the invention, when the volume of the pressure control chamber is increased and the fuel pressure in the pressure control chamber decreases, the needle moves up. At this time, a large negative pressure is temporarily generated in the annular chamber, and due to the negative pressure, a downward force acts on the downward annular surface of the outer peripheral surface of the needle, and thus a downward force acts on the needle. As a result, the rising speed of the needle is reduced.

According to the second aspect of the invention, as described above, in addition to the fact that the rising speed of the needle is reduced due to the negative pressure generated in the first annular chamber when the needle is lifted, At the time of descending, a large negative pressure is temporarily generated in the second annular chamber, and due to this negative pressure, an upward force acts on the upward annular surface of the needle inner peripheral surface, and thus an upward force acts on the needle, As a result, the descending speed of the needle is reduced.

[0009]

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 sump 16 is connected to the nozzle port 3 on the one hand and to the fuel supply port 18 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. In this example,
A fuel hole 22 extending upward from the central portion of the top surface of the back pressure chamber 20.
Is formed, and the back pressure chamber 20 is connected to the pressure control chamber 13 via the fuel hole 22. A cylindrical enlarged head 23 is integrally formed on the top of the needle 4, and the enlarged head 23 is slidably inserted into a needle insertion hole 2 a formed in the nozzle holder 2. 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.

An upward annular surface 26 is formed on the inner peripheral surface of the needle insertion hole 2a, and a downward annular surface 27 facing the upward annular surface 26 is formed on the outer peripheral surface of the enlarged head 23. Thus, between the upwardly facing annular surface 26 and the downwardly facing annular surface 27, an annular chamber 24 is formed which is adapted to reduce the pressure acting on the downwardly facing annular surface 27 when the needle is raised.

On the other hand, between the needle 4 and the needle insertion hole 2a located between the fuel reservoir 16 and the annular chamber 24, and between the annular chamber 2
4 and the fuel hole 22 between the enlarged head 23 and the needle insertion hole 2a, annular gaps 25a and 25b are formed, respectively. The gap 25a is formed by the fuel pool 16 and the annular chamber 2.
4 forms a throttle passage that communicates with the fuel cell 4, and the gap 25b forms a throttle passage that connects the annular chamber 24 and the fuel hole 22. Therefore, part of the high-pressure fuel supplied from the fuel supply port 18 into the fuel reservoir 16 is supplied into the annular chamber 24 via the throttle passage 25a, and part of the fuel supplied to the annular chamber 24 is contained in the throttle passage 25b. Is supplied to the fuel hole 22 and the pressure control chamber 13 via the.

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.
Further, at this time, the fuel pressure applied to the top surface of the enlarged head 23 is lowered, 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 to rise, the annular chamber 24
Greatly increases the volume of. While the needle 4 is rising, almost no fuel flows into the annular chamber 24, and the volume of the annular chamber 24 is greatly increased as described above, so that the inside of the annular chamber 24 becomes a negative pressure. As a result, this negative pressure exerts a downward force on the downward annular surface 27 of the outer peripheral surface of the needle, and thus a downward force on the needle 4. The fuel pressure in the pressure control chamber 13 and the fuel hole 22 slightly increases as the needle 4 rises, and the negative pressure in the annular chamber 24 increases as the needle 4 rises, so that the valve opening speed of the needle 4 decreases. To be Next, as shown in FIG. 2B, the needle 4 comes into contact with the needle lift restricting surface 21 to restrict the lift of the needle 4, but the speed of the needle 4 at this time is slow, and therefore the needle lift restricting surface 21 It can prevent the collision and the bounce. As a result, deterioration of the accuracy of the injection amount can be prevented.

When the needle 4 comes into contact with the needle lift restricting surface 21, the fuel in the fuel reservoir 16 gradually flows out into the annular chamber 24 through the throttle passage 25a, and thus the annular chamber 2
The fuel pressure in 4 is almost equal to the fuel pressure in the fuel pool 16. Further, at this time, the fuel in the annular surface 24 has the throttle passage 2
5b, the fuel pressure in the pressure control chamber 13 and the fuel hole 22 is gradually discharged to the annular chamber 24.
Is almost equal to the fuel pressure inside.

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 as shown in FIG. 2 (A), and as a result, the volume of the pressure control chamber 13 is increased. Is reduced. Even if the volume of the pressure control chamber 13 is reduced, the needle 4 does not immediately descend, so that the fuel pressure in the pressure control chamber 13 and the fuel hole 22 increases. As a result, the needle 4 is biased in the valve closing direction, so that the needle 4 starts descending.

When the needle 4 descends, the fuel in the annular chamber 24 is compressed and the internal pressure of the annular chamber 24 becomes high. As a result, when the needle 4 descends, the fuel in the annular chamber 24 exerts an upward force on the annular surface 27 of the outer peripheral surface of the needle, and thus the upward force is applied to the needle 4. Next, the fuel in the annular chamber 24 passes through the throttle passage 25a and the fuel pool 16
It flows out inside, and the needle 4 descends accordingly. 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,
Therefore, it is possible to prevent the undesirable so-called secondary injection phenomenon from occurring.

FIG. 3 shows another embodiment. Note that FIG.
3A shows the valve closed, and FIG. 3B shows the valve open. In this embodiment, the intermediate member 17 is inserted between the nozzle holder 2 and the piston holder 5, and the needle insertion hole 2a is formed between the inner peripheral surface of the intermediate member 17 and the inner peripheral surface of the nozzle holder 2.
Is formed.

With reference to FIG. 3, in this embodiment, a downward annular surface 28 is formed on the inner peripheral surface of the needle insertion hole 2a together with an upward annular surface 26, and a downward annular surface 27 is formed on the outer peripheral surface of the needle 4. An upwardly facing annular surface 29 is formed. Therefore, between the upward annular surface 26 of the needle insertion hole 2a and the downward annular surface 27 of the needle 4, the pressure acting on the downward annular surface 27 when the needle is raised is reduced. The annular chamber 24 is formed, and the pressure acting on the upward annular surface 29 when the needle descends is reduced between the downward annular surface 28 of the needle insertion hole 2a and the upward annular surface 29 of the needle 4. A second annular chamber 30 is formed which is adapted to allow.

On the other hand, an annular gap 25c is formed between the needle 4 and the needle insertion hole 2a located between the second annular chamber 30 and the fuel hole 22. The gap 25c forms a throttle passage that connects the second annular chamber 30 and the fuel hole 22.
Therefore, part of the high-pressure fuel supplied from the first annular chamber 24 into the second annular chamber 30 is supplied into the fuel hole 22 via the throttle passage 25c.

When the piston 6 is raised to start the fuel injection and thus the needle 4 is raised, the volume of the first annular chamber 24 is greatly increased and the second annular chamber 3 is increased.
The volume of 0 is greatly reduced. As a result, the first annular chamber 2
Negative pressure is generated in the needle 4 and a downward force is applied to the needle 4, and the inside of the second annular chamber 30 becomes high pressure and the needle 4
A downward force is exerted on the upwardly facing annular surface 29 and thus a further downward force is exerted on the needle 4. Next, the fuel in the second annular chamber 30 flows into the throttle passage 25c.
And flows out into the fuel hole 22 through which the needle 4 rises. Therefore, the rising speed of the needle 4 is reduced. As a result, the speed of the needle 4 when the needle 4 comes into contact with the top surface of the back pressure chamber 20 is reduced, and therefore, at this time, the needle 4 can be prevented from bouncing on the needle lift limiting surface 21. Therefore, it is possible to prevent the accuracy of the injection amount from deteriorating.

On the other hand, when the piston 6 is lowered to stop the fuel injection and thus the needle 4 is lowered, the volume of the first annular chamber 24 is greatly reduced and the volume of the second annular chamber 30 is greatly increased. To do. As a result, the pressure in the first annular chamber 24 becomes high and an upward force is applied to the needle 4, and a negative pressure is generated in the second annular chamber 27 so that the downward annular surface 29 of the needle 4 is directed upward. A force will thus be exerted and thus a further upward force on the needle 4. Next, the fuel in the first annular chamber 24 flows into the throttle passage 2
It flows out into the fuel hole 22 through 5a, and the needle 4 descends accordingly. 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.

FIG. 4 shows still another embodiment. It should be noted that FIG. 4A shows the valve closed and FIG. 4B shows the valve open.

In this embodiment, a downward annular surface 28 is formed together with an upward annular surface 26 on the inner peripheral surface of the needle insertion hole 2a, and a downward annular surface 2 is formed on the outer peripheral surface of the needle 4.
Together with 7, an upwardly facing annular surface 29 is formed. Therefore, between the upward annular surface 26 of the needle insertion hole 2a and the downward annular surface 27 of the needle 4, the pressure acting on the downward annular surface 27 when the needle is raised is reduced. The annular chamber 24 is formed, and the pressure acting on the upward annular surface 29 when the needle descends is reduced between the downward annular surface 28 of the needle insertion hole 2a and the upward annular surface 29 of the needle 4. A second annular chamber 30 is formed which is adapted to allow.

On the other hand, an annular gap 25c is formed between the needle 4 and the needle insertion hole 2a located between the second annular chamber 30 and the fuel hole 22 forming the back pressure chamber. Gap 2
5 c forms a throttle passage that connects the second annular chamber 30 and the fuel hole 22. Therefore, from the first annular chamber 24 to the second
Part of the high-pressure fuel supplied into the annular chamber 30 is supplied into the fuel hole 22 through the throttle passage 25c.

However, in this embodiment, the downward annular surface 28 of the needle insertion hole 2a forms a needle lift limiting surface, and the upward annular surface 29 of the needle 4 is formed.
Comes into contact with the downward annular surface 28 of the needle insertion hole 2a to regulate the maximum lift amount of the needle 4. At this time,
When the needle 4 rises and therefore the upwardly facing annular surface 29 of the needle 4 abuts the downwardly facing annular surface 28 of the needle insertion hole 2a, the volume of the second annular chamber 30 is exhausted, so that the needle 4 in this embodiment is The movement is slightly different from the movement of the needle 4 in the embodiment shown in FIG. The other operation of the needle 4 is the same as that of the embodiment shown in FIG.

[0028]

[Effect of the Invention] When the fuel is injected, the valve opening speed of the needle can be slowed to prevent the accuracy of the injection amount from deteriorating.

[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.

FIG. 4 is an enlarged side sectional view of a part of a fuel injection valve showing still another embodiment.

[Explanation of symbols]

 2a ... Needle insertion hole 4 ... Needle 6 ... Piston 8 ... Piezoelectric element 13 ... Pressure control chamber 20 ... Back pressure chamber 23 ... Expanding head 24 ... First annular chamber 26 ... Upward annular surface of needle insertion hole 27 ... Needle Downward annular surface 28 ... downward annular surface of the needle insertion hole 29 ... upward needle annular surface 30 ... second annular chamber

Claims (2)

[Claims] 1. 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 pressure control chamber. When the volume is increased, the needle rises to open the nozzle opening, and at this time, the needle abuts the needle lift regulation surface formed on the inner wall surface of the needle insertion hole to regulate the maximum lift amount of the needle, In a fuel injection valve in which the needle is biased in the valve closing direction to close the nozzle port when the volume of the control chamber is reduced, a downward annular surface formed on the outer peripheral surface of the needle and the inner peripheral surface of the needle insertion hole are formed. An annular chamber is formed between the upwardly facing annular surfaces of the needle to reduce the pressure acting on the downwardly facing annular surface of the needle when the volume of the annular chamber increases as the needle rises. Fuel injection valve. 2. A back pressure chamber is formed on the top surface of the 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 pressure control chamber. When the volume is increased, the needle rises to open the nozzle opening, and at this time, the needle abuts the needle lift regulation surface formed on the inner wall surface of the needle insertion hole to regulate the maximum lift amount of the needle, In a fuel injection valve in which the needle is biased in the valve closing direction to close the nozzle port when the volume of the control chamber is reduced, a downward annular surface formed on the outer peripheral surface of the needle and the inner peripheral surface of the needle insertion hole are formed. The first annular chamber is formed between the upwardly facing annular surfaces formed on the needle, and the pressure acting on the downwardly facing annular surface of the needle is increased when the volume of the first annular chamber increases as the needle rises. Along with the lowering of the needle, a second annular chamber is formed between the upward annular surface formed on the outer peripheral surface of the needle and the downward annular surface formed on the inner peripheral surface of the needle insertion hole. A fuel injection valve adapted to reduce the pressure acting on the upward annular surface of the needle when the volume of the second annular chamber increases.