JPS6153456A - Fuel injection valve - Google Patents

Abstract

PURPOSE:To reduce a degree of unevenness in a fuel injection quantity among tubes as well as to improve drivability ever so better, by constituting a volumetrical variation in a nozzle spring chamber to vary according to the lift of a needle valve so as to make it reducible in time of lifting the needle valve with which one end of a central plunger is made contact. CONSTITUTION:A nozzle body 3 is attached to the lower end of a nozzle holder 1 with a retaining nut 4 via a spacer 2, and a needle valve 5 is inserted into the nozzle body 3 free of slide motion in an axial direction. An upper end face 5a of this needle valve 5 is installed in an opposite end face of the spacer 2 so as to separate away as far as a main injection lift value l. In addition, a pin 8 is projectingly installed in the upper end face 5a, while a lower part of a movable spring seat 7 housed in a spring chamber 6 is fitted in this pin 8, and the needle valve 5 is energized in the closing direction by the spring force of the nozzle spring 9 housed in the spring chamber 6. A lower end of a central plunger 12 is made contact with the top of the movable spring seat whereby fuel pressure is made to operate downward on an end face 12d of a large diametral upper part 12a of the plunger 12.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a fuel injection valve, and particularly to a fuel injection valve that reduces variation in injection amount.

(Technical Background of the Invention) In a diesel engine, in order to reduce nitrogen oxide emissions, it is necessary to make the spray particle size as small as possible, and to quickly vaporize the fuel and mix it with air after injection. For this purpose, it is necessary to set the opening pressure of the fuel injection valve to a high level and inject fuel at a high injection pressure. Japanese Patent Application Laid-Open No. 151058/1984 has proposed such a fuel injection valve.

However, when the injected fuel pressure is made high, the amount of leakage increases, and the variation in the amount of injection between various parts increases, making it difficult to operate the engine properly.

This variation in the injection amount between each part can be reduced by sealing the spring chamber housing the nozzle spring to eliminate fuel leakage. However, if the spring chamber is simply sealed to eliminate fuel leakage, so-called leak-free, the needle valve will be closed.

When the needle valve is lifted, the volume of the spring chamber changes and the fuel in the spring chamber is compressed, generating pressure in the direction of closing the needle valve. This pressure varies due to the influence of temperature, clearance between the needle valve and the nozzle body, etc., and as a result, variation occurs in the injection material between each part.

(Object of the Invention) The present invention has been made in view of the above-mentioned points, and it reduces the change in volume of the spring chamber that changes when the needle valve lifts, reduces the generated pressure, and reduces the effect on the injection amount. The purpose is to make it smaller.

(Summary of the invention) In order to achieve the above object, the present invention provides.

A fuel injection valve equipped with a central plunger has a spring chamber that accommodates a nozzle spring that causes one end of the central plunger to come into contact with an opposite end surface of the needle valve to operate integrally with the needle valve and close the needle valve. The central plunger and the needle valve are liquid-tightly sealed to eliminate fuel leakage, and when the needle valve is lifted, the change in volume of the spring chamber due to the needle valve is offset by the change in volume due to the lift of the central plunger. The present invention also provides a fuel injection valve in which the volume change of the spring chamber is substantially reduced, and variations in the injected fuel pressure caused by the temperature of the fuel and the clearance between the needle valve and the nozzle body are reduced. be.

(Example of the invention) An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

In FIG. 1, a nozzle body 3 is supported by a retaining nut 4 at the lower end of the nozzle holder 1 via a spacer 2, and a needle valve 5 is axially inserted into a hole 3a formed in the nozzle body 3 in the axial direction. The spacer 2 is slidably inserted, and the end surface 5a and the opposing end surface of the spacer 2 are opposed to each other with a distance of the main injection lift flQ.

Holes 1a, lb, and lc are formed concentrically and in communication with each other in the axis of the nozzle holder 1, and a spring chamber 6 is defined by the hole 1c and the spacer 2. This spring chamber 6 has a movable spring seat 7.
The lower part of the valve seat 7 is loosely fitted into the hole 2a of the spacer 2, and is also fitted into a pin 8 protruding from the axis of the end surface 5a of the needle valve 5.

A nozzle spring 9 is housed in the spring chamber 6, and one end of the nozzle spring 9 is pressed against the upper end surface of the spring seat 7, and the other end is pressed against a fixed spring seat 10 disposed at the upper end of the spring chamber 6.

This nozzle spring 9 connects the tip 5b of the needle valve 5 to the nozzle body 3.
is pressed against the valve seat 3b with a predetermined load. The pressurized chamber 11 provided at the tip of the nozzle body 3 is connected to the nozzle hole 3 through the valve hole 3c.
b.

The upper part 12a of the central plunger 12 is fitted into the hole 1b of the nozzle holder 1 in an oil-tight manner and slidable in the axial direction.
The shaft portion 12b is inserted through the hole 10a of the fixed spring seat 1o and located in the spring chamber 6, and its end surface abuts the upper surface of the movable spring seat 7. The return spring 13 is interposed between the fixed spring seat 10 and a flange 12c provided on the shaft portion 12b of the central plunger 12, and has one end in pressure contact with the fixed spring seat 10 and the other end in pressure contact with the flange 12c. The end surface of the shaft portion 12b is pressed against the upper surface of the movable spring seat 7. As a result, the needle valve 5, movable spring seat 7, and central plunger 12 always operate as one unit.

And, the spring chamber 6 is not provided with a leak passage,
The spring chamber 6 is liquid-tightly sealed by the needle valve 5 and the central plunger 12. The hole 1a (fuel inflow passage) of the nozzle holder 1 and the pressurizing chamber 11 of the nozzle body 3 are communicated through passages 15, 16, and 17 provided in the nozzle holder 1, spacer 2, and nozzle body 3, respectively.

The diameter d of the end portion 12a of the central plunger 12 is set to a predetermined value smaller than the diameter of the needle valve 5 (d<D), and the diameter Ds of the valve hole 3c of the nozzle body 3 is also set to be smaller than the diameter of the needle valve 5. (Ds<D) is set to a predetermined value.

Next, the operation of the fuel injection valve having the above configuration will be explained.

Fuel pumped under pressure from a fuel injection pump (not shown) flows into the passage 1a of the nozzle holder 1 through an injection pipe (not shown), and further flows into the pressurizing chamber 11 through passages 15 to 17. As the fuel flows into the pressurizing chamber 11, the pressure P inside the injection pipe increases, and this pressure P acts on the needle valve 5 and the end surface 12d of the end 12a of the central plunger 12.

and.

The fuel pressure received by the needle valve 5 in the pressurizing chamber 11 is determined by the spring force Fs of the nozzle spring 9 and the pressure receiving surface 1 of the central plunger 12.
2d exceeds the resultant force of the pressure inside the injection pipe, the needle valve 5 lifts and fuel is injected from the minute hole 3d. The load (spring force) on the nozzle spring 9 at this time is expressed by the following equation.

F s = P x 7 (D ” D s 2d 2
) (1) Therefore, if the valve opening pressure is the same, the load Fs on the nozzle spring 9 can be set smaller than in the case without the central plunger 12. By the way, the nozzle splash 12 without the central plunger 12
The set load Fs' is expressed by the following formula.

Fs'=:PX'-(D''-Ds2) -(2)
The volume of the spring chamber 6 changes according to the lift of the needle valve 5, and decreases by the lift amount of the needle valve 5. On the other hand, the central plunger 12 lifts in response to the lift of the needle valve 5, and the volume of the spring chamber 6 increases by the lift amount of the end portion 12a of the plunger 12. As a result.

The volume of the spring chamber 6 changes by a difference ΔV due to the offset between the decrease due to the lift of the needle valve 5 and the increase due to the lift of the central plunger 12. The change ΔV in the substantial volume of the spring chamber 6 is expressed by the following equation.

ΔV=QX engineering (D"-d")...(3)
That is, the volume of the spring chamber 6 is reduced by this change Δ■.

Incidentally, the change (decrease) ΔV' in the volume of the spring chamber 6 when there is no central plunger is expressed by the following formula (%). Therefore, as is clear from the above equations (3)' and (4), the change (decrease) in the volume of the spring chamber 6 when the needle valve is lifted is The volume change ΔV of No. 6 becomes smaller. Since the actual amount of change ΔV in the volume of the spring chamber 6 is small, the pressure due to liquid compression in the spring chamber 6 is also small, and as a result, the spring chamber pressure due to variations in temperature and clearance between the needle valve 5 and the nozzle body 3 The variation ΔP of Pa is also second
It becomes smaller as shown in the figure. As a result, variations in fuel injection amount between cylinders are reduced.

Note that when the injected fuel pressure is constant, the pressure receiving surface 12d of the central plunger 12 is increased (however, d < D).
The smaller the difference between the diameter d of the pressure receiving surface 12d and the diameter of the needle valve 5, that is, the difference in pressure receiving area, the smaller the volume change ΔV of the spring chamber 6 that changes when the needle valve 5 lifts. Therefore, the pressure change in the spring chamber 6 also becomes smaller. Accordingly, the set load of the nozzle spring 9 can also be reduced, which is advantageous in terms of design.

At the end of injection, the pressure receiving surface 12 of the central plunger 12
Since the pressure inside the injection pipe applied to d is lower than the pressure in the pressurizing chamber 11, the force that suppresses the needle valve 5 through the central plunger 12 becomes smaller, and the force applied to the needle valve 5 is smaller than when the valve is opened. It remains stationary and performs the valve closing action.

(Effects of the Invention) As explained above, according to the present invention, one end of the central plunger of a fuel injection valve equipped with a central plunger is brought into contact with the opposite end surface of the needle valve to operate integrally with the needle valve. , a spring chamber housing a nozzle spring that closes the needle valve is liquid-tightly sealed by the central plunger and the needle valve to eliminate fuel leakage, and when the needle valve is lifted, the spring chamber is closed by the needle valve. By offsetting the change in volume due to the lift of the central plunger and substantially reducing the change in volume of the spring chamber, the temperature of the fuel and the difference between the needle valve and the nozzle body are reduced. Variations in the spring chamber pressure due to clearance are reduced, and variations in the fuel injection amount are reduced, and as a result, the engine can be operated satisfactorily. In addition, by sealing the spring chamber to eliminate fuel leakage, a leak pipe of the nozzle holder is no longer required, which has excellent effects such as simplifying the structure and reducing costs. be.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing an embodiment of the fuel injection valve according to the present invention, and FIG. 2 is a characteristic diagram showing fuel pressure changes of the fuel injection valve shown in FIG. 1. 1... Nozzle holder, 3... Nozzle body, 5...
・Total 1 valve, 6...Spring chamber, 9...Nozzle spring, 12
...Central plunger. Fig. 1 Cf1A angle) e -32'.

Claims (1)

[Claims] 1. A fuel injection valve equipped with a central plunger has a spring chamber that accommodates a nozzle spring that causes one end of the central plunger to come into contact with an opposite end surface of the needle valve to operate integrally with the needle valve and close the needle valve. The central plunger and the needle valve are liquid-tightly sealed to eliminate fuel leakage, and when the needle valve is lifted, the change in volume of the spring chamber due to the needle valve is offset by the change in volume due to the lift of the central plunger. The fuel injection valve is characterized in that a change in volume of the spring chamber is substantially reduced.