JP2844742B2 - Diesel engine fuel injection nozzle - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection nozzle for a diesel engine, and more particularly to an improvement in a fuel injection nozzle that suppresses a needle valve lift at an initial stage of injection to a predetermined value.

2. Description of the Related Art In a diesel engine, it is effective to reduce the injection rate (injection amount per unit time or unit crank angle) at an early stage of injection in order to reduce exhaust emissions and noise.

For this reason, a fuel injection nozzle of a central plunger type in which the needle valve lift amount at the beginning of injection is regulated to a relatively small predetermined value has been proposed in, for example, JP-A-62-225761.

FIG. 4 shows this conventional fuel injection nozzle.
The needle valve 31 is slidably fitted in the nozzle body 32, and the needle valve 31 is
Presses in the closing direction via the spring receiving member 34. Further, a central plunger 35 is disposed to face the back side of the spring receiving member 34. The central plunger 35 has a base end slidably fitted to the nozzle holder 36, and a fuel pressure is applied to the base end surface 35a thereof. Is stipulated. Reference numeral 38 denotes a coil spring that biases the central plunger 35 relatively weakly in the protruding direction. A predetermined gap Δl is provided between the tip of the central plunger 35 and the spring receiving member 34.

In the above configuration, when the urging force in the lift direction generated by the fuel pressure acting on the pressure receiving surface 31a of the needle valve 31 exceeds the set load of the nozzle spring 33, the needle valve 31
Lift starts. When the needle valve 31 is lifted by the gap Δl, the spring receiving member 34 comes into contact with the central plunger 35,
Since the fuel pressure also acts in the closing direction via 35, the lift of the needle valve 31 is once regulated at that position. When the fuel pressure further rises and the sum of the urging forces acting in the lift direction exceeds the urging force acting in the closing direction, the needle valve 31 further lifts together with the central plunger 35.

In the above-described conventional configuration, the position of the spring receiving member 34 is defined by the seating surface between the tip of the needle valve 31 and the nozzle body 32, and the position of the tip of the central plunger 35 is located on the nozzle holder 36 side. As defined by the Shim 37. Therefore, the influence of the dimensional error of many components is reflected on the gap Δl, and as a result, the gap Δl, that is, the initial lift amount is likely to be non-uniform. In addition, the gap Δl tends to change due to the tightening force at the time of attachment to the internal combustion engine, and the influence of the temperature change is large. Further, since the shim 37 is held by the nozzle spring 33, the central plunger 35 may move toward the needle valve 31 at the moment when the fuel pressure acts on the base end surface 35a of the central plunger 35, and the intended lift amount may be reduced. There is a risk of contraction.

Means for Solving the Problems A fuel injection nozzle for a diesel engine according to the present invention comprises:
A nozzle body having a nozzle hole at a tip thereof and held by a nozzle holder via a distance piece; a nozzle body slidably accommodated in the nozzle body; A needle valve for receiving a force in the opening direction by the fuel pressure in the portion, a nozzle spring for constantly urging the needle valve in the closing direction, a large-diameter portion recessed on the end face of the distance piece on the nozzle body side, and the large-diameter portion. A plunger fitting portion comprising a small diameter portion recessed on the bottom surface of the diameter portion, and a large diameter portion and a small diameter portion slidably fitted to the large diameter portion and the small diameter portion of the plunger fitting portion, respectively. At a predetermined position in contact with the base end surface of the nozzle body, which is a boundary with the distance piece, the base end faces the base end surface of the needle valve via a predetermined gap. A plunger lift also with the needle valve when the large needle valve is lifted Ri,
An oil chamber formed annularly between the large-diameter portion rear surface of the plunger and the plunger fitting portion, and through which fuel pressure is guided so as to urge the plunger in the closing direction of the needle valve; The maximum lift amount of the needle valve is defined by the contact between the small-diameter portion end face of the plunger and the small-diameter portion bottom surface of the plunger fitting portion, so that the oil chamber to which the fuel pressure is guided always remains.

When the fuel pressure increases, the plunger is pressed against the base end face of the nozzle body by the fuel pressure guided into the oil chamber. When the urging force due to the fuel pressure exceeds the set load of the nozzle spring, the needle valve lifts,
Since the needle valve comes into contact with the plunger when lifted by the gap, the initial lift amount is regulated to the gap equivalent amount. And when the fuel pressure increases further,
The needle valve lifts with the plunger.

Here, the gap is determined only by the positional relationship between the base end face of the needle valve and the base end face of the nozzle body, and it is easy to ensure the accuracy.

Hereinafter, an embodiment of the present invention will be described in detail with reference to FIG.

This fuel injection nozzle has a nozzle body 1 provided with a plurality of injection holes 2 at its tip, a nozzle holder 3 having a high-pressure fuel inlet 4 and a return fuel outlet 5, and a nozzle holder 3 between the nozzle body 1 and the nozzle holder 3. An interposed distance piece 6 and a nozzle nut 7 for fastening the nozzle body 1 to the nozzle holder 3 together with the distance piece 6
And a needle valve 8 slidably housed in the nozzle body 1.

The needle valve 8 has a tapered seat surface 8a at the tip end for closing the injection hole 2, and a pressure receiving surface 8b at an intermediate portion. An oil reservoir 9 formed in the nozzle body 1 to surround the pressure receiving surface 8b
It communicates with the high pressure fuel inlet 4 of the nozzle holder 3 via 0,11,12.

A small diameter rod portion 8d is provided at the center of the base end face 8c of the needle valve 8.
Is formed to extend, and receives a tip of the nozzle spring 13 housed in the nozzle holder 3.
14 is fitted to the tip of the rod portion 8d. The needle spring 8 is normally urged in the closing direction by the nozzle spring 13. Reference numeral 15 denotes a shim for adjusting the set load of the nozzle spring 13. Here, the base end face 8c of the needle valve 8 has a gap Δ corresponding to a predetermined initial lift amount between the base end face 1a of the nozzle body 1 and the base end face 1a of the nozzle body 1 when the needle valve 8 is seated at the tip end of the nozzle body 1.
It is formed at a position where l occurs.

On the other hand, a plunger fitting portion 16 is recessed at the center of the distance piece 6 on the nozzle body 1 side where the base end surface 8c of the needle valve 8 faces, and a plunger 17 is slidably fitted therein. ing. The plunger fitting section 16
A large diameter portion 16a having a larger diameter D ₁ than the diameter D ₃ of the needle valve 8 proximal surface 8c, the diameter D ₂ which is further recessed at the center thereof
(D ₂ <D ₃ ), and the rod portion 8d of the needle valve 8 penetrates the center hole.

The plunger 17 has a large-diameter portion 17a and a small-diameter portion 17b that respectively fit into the large-diameter portion 16a and the small-diameter portion 16b of the plunger fitting portion 16, and the central hole is formed by the rod portion 8d of the needle valve 8. Penetrates. Further, the distal end surface of the large diameter portion 17a is formed as a flat surface. The height of the large-diameter portion 17a is set to be smaller than the depth of the large-diameter portion 16a of the plunger fitting portion 16, and thereby, between the rear surface of the large-diameter portion 17a and the plunger fitting portion 16. An annular oil chamber 18 is defined. The oil chamber 18 communicates with the high-pressure fuel passage 11 through a communication hole 19. Even when the plunger 17 is in contact with the base end surface 1a of the nozzle body 1, the small-diameter portions 16b and 17b maintain the fitted state, and the oil chamber 18 is not opened.

In the above configuration, the fuel pressure supplied from the fuel injection pump (not shown) through the high-pressure fuel inlet 4 is also guided to the oil chamber 18 through the communication hole 19, so that the plunger 17 is pressed toward the nozzle body 1. Then, the nozzle body 1 is positioned in contact with the base end surface 1a. Since the tip of the plunger 17 is a flat surface, in this state,
A predetermined gap Δl is maintained between the needle valve 8 and the base end face 8c.

On the other hand, the needle valve 8, to the pressure receiving area of the outer peripheral side than the diameter D ₄ of the tip seat, opening direction is exerted by the fuel pressure. When the urging force in the opening direction due to the fuel pressure exceeds the set load of the nozzle spring 13, the needle valve 8 starts lifting. When the base end face 8c of the needle valve 8 comes into contact with the plunger 17 after being lifted by the gap Δl, the urging force in the closing direction by the oil chamber 18 is applied to the needle valve 8 via the plunger 17. The needle valve 8 once stops at that position. That is, the initial lift amount of the needle valve 8 is regulated to a predetermined value Δl, and as a result, the initial injection rate decreases (see FIGS. 2 and 3).

Further, when the fuel pressure becomes higher, the needle valve 8 lifts further together with the plunger 17. The maximum lift amount of the needle valve 8 is determined by the end face of the small diameter portion 17b of the plunger 17 abutting against the bottom surface of the plunger fitting portion 16, and the needle valve 8 remains in the oil chamber 18 even in the state of the maximum lift. The urging force in the valve closing direction is received by the introduced fuel pressure. Accordingly, the lift characteristics are as shown in FIG. 2, and the injection rate is as shown in FIG. The broken lines in FIGS. 2 and 3 show a comparative example in which such initial lift amount regulation is not performed.

As described above, in the above configuration, the initial lift amount can be regulated in the same manner as in the conventional central plunger system, but the gap Δl corresponding to the initial lift amount is formed between the base end face 8c of the needle valve 8 and the nozzle body. Since the gap Δl is defined by the base end face 1a, the gap Δl can be obtained very accurately as long as the processing accuracy of the nozzle body 1 and the needle valve 8 is ensured. In other words, without being affected by dimensional errors of the distance piece 6, the nozzle holder 3, etc.
In addition, there is no change due to the tightening force when the engine is mounted. Further, the influence of the temperature change is very small.

Moreover, since the plunger 17 is firmly positioned by the base end surface 1a of the nozzle body 1, even if the fuel pressure guided to the oil chamber 18 rises rapidly, the plunger 17 does not move, and the gap Δl is securely maintained. Dripping. Therefore, desired characteristics can be stably obtained.

As is apparent from the above description, in the fuel injection nozzle of the diesel engine according to the present invention, the plunger positioned in contact with the base end face of the nozzle body is provided, and the plunger is positioned between the plunger and the needle base end face. Because the initial lift amount of the needle valve is defined by the gap, the initial lift amount can be stably obtained without being affected by the dimensional accuracy of the nozzle holder or the like or the tightening force when the engine is mounted. . Further, the influence of the temperature change is reduced, and the plunger can be prevented from moving when the fuel pressure acts rapidly.

[Brief description of the drawings]

FIG. 1 is a sectional view of a fuel injection nozzle according to the present invention, and FIG.
FIG. 3 is a lift characteristic diagram of the needle valve of this embodiment, FIG. 3 is an injection rate characteristic diagram thereof, and FIG. 4 is a sectional view of a conventional fuel injection nozzle. 1 ... Nozzle body, 6 ... Distance piece, 8 ...
... Needle valve, 13 ... Nozzle spring, 16 ... Plunger fitting part, 17 ... Plunger, 18 ... Oil chamber.

Claims (1)

(57) [Claims] A nozzle body having an injection hole at a tip thereof and held by a nozzle holder via a distance piece;
A needle valve that is slidably housed in the nozzle body and has a tip portion that closes the injection hole and receives a force in an opening direction by fuel pressure in an oil reservoir, and a needle valve that is always closed. An energizing nozzle spring, a plunger fitting portion comprising a large-diameter portion recessed in the end face of the distance piece on the nozzle body side and a small-diameter portion recessed in the bottom surface of the large-diameter portion; The needle has a large-diameter portion and a small-diameter portion slidably fitted to the large-diameter portion and the small-diameter portion, respectively, and at a predetermined position in contact with a base end surface of the nozzle body which is a boundary with the distance piece. A plunger that opposes the base end surface of the valve via a predetermined gap and lifts together with the needle valve when the needle valve lifts larger than the gap; An oil chamber formed annularly between the back surface of the large diameter portion of the lancer and the plunger fitting portion, and adapted to guide a fuel pressure so as to urge the plunger in the closing direction of the needle valve; The maximum lift amount of the valve is defined by the contact between the small-diameter portion end surface of the plunger and the small-diameter portion bottom surface of the plunger fitting portion, and the oil chamber to which the fuel pressure is guided always remains. Features a diesel engine fuel injection nozzle.