JP3057874B2 - Fuel injection valve for internal combustion engine - 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 for an internal combustion engine.

[0002]

2. Description of the Related Art A back pressure chamber filled with fuel is formed on the top surface of a needle valve, and the fuel pressure in the back pressure chamber is controlled by using expansion and contraction of a piezoelectric element. When the needle valve is raised, the needle valve is lowered and the needle valve is closed, and when the fuel pressure in the back pressure chamber is reduced, the needle valve is raised and the needle valve is opened and the top surface of the needle valve is raised. 2. Description of the Related Art A fuel injection valve is known in which a valve collides with a top inner wall surface of a back pressure chamber to restrict a lift amount of a needle valve (see Japanese Utility Model Laid-Open No. 1-1114975).

[0003]

However, particularly when the fuel pressure in the back pressure chamber is controlled by utilizing the expansion and contraction action of the piezoelectric element, the fuel in the back pressure chamber has good response to expansion and contraction. The pressure increases or decreases rapidly. Therefore,
The top surface of the needle valve collides at a high speed in top inner wall surface of the back pressure chamber when the fuel pressure in the back pressure chamber has been made to decrease to the needle valve increases rapidly, resulting needle valve is the back pressure chamber It rebounds on the inner wall surface of the top and descends greatly in the valve closing direction. However, in the small injection amount region where the period during which the needle valve is opened is short, the time when the needle valve rebounds on the top inner wall surface of the back pressure chamber and descends in the valve closing direction, and the time when the piezoelectric element is extended to complete injection Doo is will overlap, resulting in a problem that the result originally intended to have optimum injection quantity metering accuracy for the needle valve resulting in faster closing valve than the time deteriorates. Also, after a short time after the needle valve rebounds on the inner wall surface at the top of the back pressure chamber and descends in the valve closing direction, the needle valve starts to rise this time.
As described above, the time when the needle valve is rising and the time when the piezoelectric element is extended to complete the injection are overlapped, and the closing timing of the needle valve is later than the originally intended optimum time. Thus, also in this case, there arises a problem that the adjustment accuracy of the injection amount deteriorates.

[0004]

According to the present invention, there is provided a piston which is driven by a piezoelectric element.
Can be moved in the axial direction of the needle between the needle and the top surface of the needle
A stopper member, and the lower end face of the stopper member
Together with the formation of a fuel-filled backpressure chamber between the tops of the dollars
Between the upper end surface of the stopper member and the piston is filled with fuel
Pressure control chamber, and these back pressure chambers and pressure control chamber
Stopper for fuel in the pressure control chamber, communicating with each other
Stopper member for the fuel in the back pressure chamber with the pressure receiving area of the member
To be larger than the pressure receiving area of
Need when the fuel pressure in the pressure control chamber is reduced
Of the stopper collides with the lower end surface of the stopper member.
As the topper rises away from the top of the needle
The needle is held at the position where it nearly collided, and the fuel
The fuel pressure in the pressure control chamber was increased to stop
The stopper pressure and the needle
, A force in the needle valve closing direction is applied .

[0005]

When the needle valve collides with the stopper member at the start of fuel injection, the kinetic energy of the needle valve is converted into the kinetic energy of the stopper member.
As the needle rises away from the top of the needle,
It is held at the position at the time of collision. Therefore, the needle valve can be prevented from descending in the closing direction immediately after the needle valve is opened, and the needle valve can be closed at the originally intended optimum time in the small injection amount region where the injection period is short. Can be. On the other hand, the stopper part raised
When the fuel injection is stopped, the material is kneeed by the fuel pressure in the pressure control chamber.
The stopper member is urged in the dollar closing direction, so that the stopper member
It is surely returned to the original position before the fuel injection is started.

[0006]

1 and 2, reference numeral 1 denotes a fuel injection valve housing, 2 denotes a nozzle holder having a nozzle port 3 at the tip thereof, 4 denotes a needle valve disposed in the nozzle holder 2, and 5 denotes a housing. Reference numeral 6 denotes a piezoelectric element formed of a laminate of disk-shaped piezoelectric element plates, 7 denotes a sleeve for guiding the piezoelectric element 6, and 8 denotes a piezoelectric element holder.

The holder 5 and the piezoelectric element holder 8 are fixed in a proper position in the housing 1 by a retainer 9 screwed to the housing 1, and the nozzle holder 2 is fixed in the housing 1 by a retainer 10 screwed to the housing 1. It is fixed at the regular position. Needle valve 4 in holder 5
A large-diameter hole 11, a small-diameter hole 12, and a medium-diameter hole 13 located between the large-diameter hole 11 and the small-diameter hole 12 are formed coaxially with the axis of Is the annular step 14
However, between the small-diameter hole 12 and the medium-diameter hole 13, annular step portions 15 are respectively formed. A piston 16 is slidably inserted into the large-diameter hole 11, and a cylindrical groove 17 is formed at the center of the lower end surface of the piston 16. The upper end of the piston 16 is connected to the lower end of the piezoelectric element 6, and the upper end of the piezoelectric element 6 is supported by the piezoelectric element holder 8.

On the other hand, an upper small-diameter portion 18 is provided in the holder 5,
A stopper member 21 having a lower small diameter portion 19 and a central large diameter portion 20 is disposed. The central large-diameter portion 20 of the stopper member 21 is hermetically slidably inserted into the medium-diameter hole 13, and the lower small-diameter portion 19 of the stopper member 21 is also substantially slidably slidably inserted in the small-diameter hole 12. Is inserted into. On the other hand, the upper small diameter portion 18 of the stopper member 21 is inserted into the cylindrical groove 17 of the piston 16 with a small play.
Accordingly, the annular chamber 22 formed between the lower end surface of the piston 16 and the central large-diameter portion 20 of the stopper member 21, and between the bottom surface of the concave cylindrical groove 17 of the piston 16 and the top surface of the upper small-diameter portion 18 of the stopper member 21. The small chamber 23 is formed with the upper small diameter portion 18 of the stopper member 21 and the cylindrical groove 1 of the piston 16.
The annular chamber 22 and the small chamber 23 are communicated with each other through a gap formed between the pressure control chambers 7, and the pressure control chamber whose volume changes when the piston 16 is moved by the expansion and contraction of the piezoelectric element 6. 22 and 23 are formed. A disc spring 24 for pressing the piston 16 upward is inserted between the piston 16 and the annular step portion 14 in the annular chamber 22 which is a part of the pressure control chambers 22 and 23.
A first compression spring 25 that presses the stopper member 21 downward is inserted into the small chamber 23 that is a part of the third member 3.

On the other hand, a fuel reservoir 27 is formed around the conical pressure receiving surface 26 of the needle valve 4. The fuel reservoir 27 is connected on one hand to the nozzle port 3 and on the other hand to a fuel supply port 28. Further, a back pressure chamber 2 is provided between the lower end surface of the lower small diameter portion 19 of the stopper member 21 and the top surface of the needle 4.
9 is formed, and a second compression spring 30 that presses the needle 4 downward is inserted between the stopper member 21 and the top surface of the needle 4. The second compression spring 30 is formed to have a lower spring force than the first compression spring 25.

The back pressure chamber 29 communicates with a small chamber 23 forming a part of the pressure control chambers 22 and 23 through a fuel passage 31 formed in the stopper member 21. Fuel pool 2
An annular gap 32 is formed between the enlarged portion of the needle valve 4 located between the nozzle 7 and the back pressure chamber 29 and the nozzle holder 2, and the gap 32 communicates the fuel reservoir 27 with the back pressure chamber 29. A throttle passage is formed. Therefore, the fuel supply port 28
A part of the high-pressure fuel supplied from the fuel supply into the fuel reservoir 27 is supplied into the back pressure chamber 29 through the throttle passage 32 and further supplied into the pressure control chambers 22 and 23 through the fuel passage 31. Accordingly, the pressure control chambers 22, 23 and the back pressure chamber 29 are filled with high-pressure fuel.

As described above, the first compression spring 25 is
The spring force is formed stronger than that of the compression spring 30, and the pressure receiving area of the stopper member 21 is smaller than that of the pressure control chambers 22,2.
Since the pressure receiving area for 3 is larger than the pressure receiving area for the back pressure chamber 29, the stopper member 21 normally stops at the position where the central large diameter portion 20 of the stopper member 21 abuts against the annular step portion 15. FIGS. 1 and 2 show a needle valve 4.
Shows a state in which the needle 4 closes the nozzle port 3 most, and at this time, a gap g (see FIG. 4) is formed between the lower end surface of the lower small diameter portion 19 of the stopper member 21 and the top surface of the needle valve 4. 1) is formed. This gap g corresponds to the maximum lift of the needle valve 4.

The piezoelectric element 6 extends in the axial direction when the electric charge is charged in the piezoelectric element 6, and contracts in the axial direction when the electric charge charged in the piezoelectric element 6 is discharged. When the piezoelectric element 6 is charged with electric charge and the piezoelectric element 6 extends in the axial direction, the piston 16 is lowered, and as a result, the pressure control chambers 22, 23
Is reduced. Even if the volumes of the pressure control chambers 22 and 23 are reduced, the needle valve 4 does not immediately descend, and thus the fuel pressure in the pressure control chambers 22 and 23 and the back pressure chamber 29 increases. When the fuel pressure in the back pressure chamber 29 rises, the needle valve 4 rapidly drops downward, and as a result, the fuel injection is stopped because the needle valve 4 closes the nozzle port 3.

On the other hand, when the electric charge charged in the piezoelectric element 6 is discharged and the piezoelectric element 6 contracts in the axial direction, the piston 16
Is raised, and as a result, the volumes of the pressure control chambers 22 and 23 are increased. Even if the volumes of the pressure control chambers 22 and 23 are increased, the needle valve 4 does not immediately rise,
Thus, the fuel pressure in the pressure control chambers 22, 23 and the back pressure chamber 29 decreases. When the fuel pressure in the back pressure chamber 29 decreases, the needle valve 4 is rapidly increased by the fuel pressure applied to the pressure receiving surface 26, and as a result, the fuel injection is started because the needle valve 4 opens the nozzle port 3. Next, the top surface of the needle valve 4 collides with the lower end surface of the stopper member 21.

When the top surface of the needle valve 4 collides with the lower end surface of the stopper member 21, the stopper member 21 moves upward by the collision force of the needle valve 4. That is, the kinetic energy of the needle valve 4 is converted into the kinetic energy of the stopper member 21, so that the stopper member 21 moves upward. At this time, the needle valve 4 loses the kinetic energy and is stopped at the position where the collision occurred. . Accordingly, when the needle valve 4 is opened to the maximum lift amount, the needle valve 4 does not rebound and does not move in the valve closing direction, so that the fuel injection rate does not greatly decrease, and thus good injection characteristics can be obtained. . Note that theoretically, when the mass of the needle valve 4 and the mass of the stopper member 21 are equal, the kinetic energy of the needle valve 4 is completely converted into the kinetic energy of the stopper member 21 at the time of collision, so that the mass of the needle 4 and the stopper When the masses of the members 21 are equal, the needle valve 4 will stop at that position at the moment of collision. However, even if the needle valve 4 slightly moves in the valve opening direction or slightly moves in the valve closing direction immediately after the needle valve 4 collides with the stopper member 21, the fuel injection rate is not significantly affected. Accordingly, even if the mass of the needle 4 and the mass of the stopper member 21 are slightly different, no particular problem occurs.

On the other hand, when the stopper member 21 moves upward due to the collision action of the needle valve 4 and is temporarily stopped, the stopper member 21 is moved by the spring force of the first compression spring 25 so that the central large-diameter portion 20 of the stopper member 21 becomes an annular stepped portion. It descends until it touches 15. While the stopper member 21 moves upward and separates from the top surface of the needle valve 4, the needle valve 4 slightly rises, so that when the stopper member 21 is lowered, the central large-diameter portion 20 of the stopper member 21 becomes the annular step portion 15. Before contact, the stopper member 21 again contacts the top surface of the needle valve 4.
When the stopper member 21 collides with the top surface of the needle valve 4, the needle valve 4 descends. However, the needle valve 4 descends after a relatively long time has elapsed since the needle valve 4 was opened. is there. Therefore, when the injection period is long, the time when the needle valve 4 descends and the time when the piezoelectric element is extended to complete the injection may overlap. However, even if they overlap, the injection amount is originally large, so the total injection amount is large. The error of the injection amount relative to the injection amount is extremely small and is therefore not particularly problematic.

[0016]

As described above, since the needle valve does not rebound immediately after the needle valve opens and does not largely move again in the valve closing direction, the accuracy of adjusting the injection amount in a region where the injection amount is small can be improved.

[Brief description of the drawings]

FIG. 1 is a partially enlarged side sectional view of the fuel injection valve shown in FIG. 2;

FIG. 2 is a side sectional view of the fuel injection valve.

[Explanation of symbols]

 4 ... Needle valve 6 ... Piezoelectric element 16 ... Piston 21 ... Stopper member 22,23 ... Pressure control chamber 29 ... Back pressure chamber

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F02M 51/06

Claims (1)

(57) [Claims] A piston and a piston driven by a piezoelectric element;
Needle that can move in the axial direction of the needle between the top surfaces of the needles.
The stopper member is arranged, and the lower end surface of the stopper member and the needle
A fuel-filled back pressure chamber is formed between the top surfaces and
Pressure filled with fuel between the upper end surface of the wrapper member and the piston
A control chamber is formed and these back pressure chambers and pressure control chamber
Communication between the stopper member and the fuel in the pressure control chamber.
The pressure receiving area is the pressure of the stopper member against the fuel in the back pressure chamber.
Pressure control to start fuel injection
When the fuel pressure in the cabin drops, the needle
The surface collides with the lower end surface of the stopper member.
Needle as member rises away from top of needle
Is held at the position where it nearly collided, stopping fuel injection.
When the fuel pressure in the pressure control chamber is increased to stop
This fuel pressure causes the stopper member and needle to
A fuel injection valve for an internal combustion engine to which a force in a needle closing direction is applied .