JP2572620B2 - Fuel injection valve for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fuel injection valve used for an internal combustion engine such as a diesel engine, and more particularly, to a fuel injection valve having improved fuel injection characteristics and needle valve movement characteristics. It is intended for.

[Prior Art] Generally, in this type of fuel injection valve, it is desirable to increase the fuel injection pressure in order to enhance the combustion performance of the engine, and for that purpose, it is necessary to set the valve opening pressure to be high. On the other hand, to increase the durability of needle valves and valve seats,
It is necessary to set a low valve closing pressure to reduce the impact when the needle valve is seated on the valve seat.

Techniques that satisfy such conditions include:
There is a structure described in No. 8. In such a structure, a hydraulic damper is configured using a spring receiver of a nozzle spring, and the force applied to the needle valve in the valve closing operation is limited by a hydraulic damper.

[Problems to be Solved by the Invention] However, in this structure, it is necessary to provide a large-capacity part in the middle of the fuel passage as a hydraulic chamber for the hydraulic damper, and this part exerts a pressure accumulating action on the fuel. As a result, a time lag occurs between a change in the pressure of the fuel supplied to the fuel injection valve (a change in the inlet pressure) and the actual injection operation at the injection port, and it is difficult to accurately control the injection operation. There are cases.

As a technique satisfying the above-mentioned conditions, Japanese Patent Application Laid-Open No.
There is also a structure described in No. 2269. In this structure, a differential piston (plunger) biased by fuel oil pressure is provided,
Mainly only in the valve opening operation, a force in the closing direction from the differential piston (ie, a force for increasing the valve opening start pressure) is effectively exerted on the needle valve.

However, in the structure described in Japanese Patent Application Laid-Open No. 60-122269, a differential piston body portion (casing portion) that houses a differential piston is formed integrally with a valve body that houses a spring receiving extension. The inlet fitting connected to the high-pressure fuel pipe is also formed integrally with the valve body.

On the other hand, in the differential piston body portion, it is necessary to sufficiently improve the processing accuracy of the inner peripheral surface on which the differential piston slides. However, in the above structure, since the differential piston body is integral with the valve body and the inlet fitting and is formed as a part of a large-diameter and long part as a whole, its processing and finishing (machining, quenching, inner diameter Polishing, etc.).

In order to solve the above problem, the following inlet fitting mounting structure can be used. In its conventional structure,
A screw hole is provided at the end of the valve body, and the end of the inlet fitting is screwed into the screw hole. Therefore, when utilizing this conventional structure, the differential piston may be accommodated in the bottom of the screw hole of the valve body, and the inlet fitting may be screwed into the opening side of the screw hole.

However, in such a structure, in order to secure the sealing performance at the contact surface between the differential piston body and the valve body, it is necessary to machine both contact surfaces with sufficiently high precision. Therefore, it is necessary to finish the bottom surface of the screw hole with high precision for the valve body, and there is a problem that the processing is difficult to perform.

Further, in the structure in which the inlet fitting and the differential piston are attached to the hole of the valve body as described above, the dimension (particularly, the dimension in the diameter direction) of the valve body increases. Therefore, when the dimensions of the valve body are limited as in a small engine, there is a problem that such a structure cannot be adopted.

When the structure of the above-mentioned Japanese Patent Application Laid-Open No. 60-122269 is examined from another point of view, the injection rate sharply increases simultaneously with the opening of the valve. It is not designed to perform a low injection operation. Therefore, the combustion characteristics of the engine cannot be sufficiently improved.

Further, in this structure, in order to rapidly increase the injection rate simultaneously with the start of the valve opening as described above, in the valve opening operation, the increase in the volume of the fuel passage due to the rise of the needle valve is caused by the protrusion of the differential piston into the fuel passage. It is configured to offset by the decrease in the volume of the passage (Publication No. 477, lower right column, lines 16 to 20).
line).

However, according to this structure, in order to effectively realize the above-described canceling action, it is necessary to increase the volume of the fuel passage as described in detail below.

That is, even in the above-mentioned conventional structure, a nozzle spring is provided as a main closing force applying means, and the differential piston is a so-called auxiliary closing force applying means. It must be sufficiently smaller than the area (for example, about 1/2 or less), and if the cross-sectional area of the differential piston is set to a value close to the cross-sectional area of the needle valve, it will not be possible to separate the needle valve from the valve seat. Will be possible. As described above, it is inevitable that a difference occurs in the pressure receiving area between the needle valve and the differential piston, and a difference also occurs in the moving volumes of the two. Despite such a large volume difference, in order to obtain the volume change canceling effect as described above, generally, the volume of the entire fuel passage is increased, and the volume change rate of the entire passage (to the volume of the entire fuel passage). It is necessary to minimize the volume difference).

When the structure described in JP-A-60-122269 is examined in consideration of this point, it is not clearly described in the specification,
The drawing describes a structure in which a fuel passage portion, which is much wider than other passage portions, is formed over a long range in the vicinity of a working piston (central plunger).

From the description of the drawing and the above description, it is clear that this prior art also employs a structure in which the passage volume is expanded, in other words, in order to obtain the operation and effect described in this publication. Obviously, it is essential to set the passage volume much larger than the volume required for the original transport function of the passage. Therefore, also in the structure described in this publication, similarly to the structure described in JP-B-53-648, it is difficult to accurately control the injection operation because the fuel passage having a large volume exerts a pressure accumulating action on the fuel. It may be.

An object of the present invention is to provide a structure that solves the above-mentioned problem, and more specifically, to reduce the size of the entire fuel injection valve and simplify the processing and finishing of the valve body and the differential piston body. The purpose is to provide a structure that can be used.

Also, the present invention uses a differential piston,
It is an object of the present invention to provide a fuel injection valve that can perform an injection operation at a low injection rate in an initial stage of the injection operation and that can minimize the volume of a fuel passage.

Means for Solving the Problems In order to achieve the above object, the present invention provides a generally cylindrical valve body assembly having a nozzle body at the tip, and opens and closes a nozzle body nozzle inside the valve body assembly. Needle valve, a nozzle spring for urging the needle valve in the closing direction, a differential piston connected to the needle valve, a fuel passage extending from the outlet of the external high-pressure oil supply passage to the injection port, and an opening direction for the needle valve. A hydraulic chamber for applying hydraulic pressure to the differential piston and a hydraulic chamber for applying hydraulic pressure in the direction of closing the needle valve to the differential piston are provided, and the operating chamber and the hydraulic chamber are communicated with the fuel passage. The above-mentioned nozzle body, a valve body having the nozzle body fixed at one end, a differential piston body seated on the other end of the valve body in surface contact, and a differential contact with the end face of the differential piston body opposite to the valve body. Entrance fitting to sit down And a case nut located around and around the differential piston body, one end of the case nut is screwed into a threaded portion on the outer periphery of the valve body, and the other end of the case nut is attached to the outer periphery of the inlet fitting. Engaging, thereby integrally fixing the valve body, the differential piston body and the inlet fitting, the auxiliary spring is disposed between the inlet fitting and the differential piston, and the differential piston is moved in the closing direction of the needle valve. It is characterized by being biased.

Further, in the embodiment of the present invention, in the initial stage of the needle valve opening operation, the needle valve moves from the fully closed position to the fully opened position while exerting a throttle action on the fuel. Each component is configured such that, when the fuel injection rate reaches the initial stage, the fuel injection rate increases to a maximum value at an increase rate higher than the increase rate of the fuel injection rate in the initial stage.

[Operation] In the structure of the above embodiment, in the initial stage of the needle valve opening operation, the needle valve moves from the fully closed position to the fully opened position while exerting a throttle action on the fuel. There is a time delay before the hydraulic pressure that reaches the hydraulic chamber reaches the working chamber of the needle valve, and the hydraulic pressure in the hydraulic chamber becomes higher than the working chamber. In addition, the working chamber is close to the injection port from which fuel is ejected, and the opening degree of the needle valve gradually increases (that is, the flow area of the nozzle portion and the flow coefficient change in a direction to promote the flow of fuel). Therefore, the pressure rise rate of the working chamber (the pressure rise value per unit time) is lower than the pressure rise rate of the hydraulic chamber.

For these reasons, the opening operation of the needle valve is restricted, and the needle valve moves at a relatively low speed. As a result, a small amount of fuel is injected at a low fuel injection rate (injection amount per unit time) in the initial stage, that is, until a certain time has elapsed from the start of opening of the needle valve.

When the needle valve reaches the fully open position after the initial stage,
The fuel injection rate rises to a maximum value at an increase rate (that is, abruptly) higher than the increase rate of the injection rate in the initial stage.
Such an operation occurs as a result of the operation at the initial stage. That is, when the initial stage is completed, the opening degree of the needle valve does not increase (that is, the flow path area and the flow coefficient of the nozzle portion do not change in a direction to promote the flow of fuel), and the needle valve is supplied to the fuel passage. The oil pressure and quantity of fuel will increase after the end of the initial phase. Moreover, at the stage where the initial stage has been completed, as a result of the throttling operation with the needle valve up to that time, the oil pressure upstream of the valve seat is increased. As a result, when the initial stage ends, high-pressure fuel flows to the injection port through the working chamber, and the fuel injection pressure and the fuel injection rate (injection amount per unit time) at the injection port rapidly increase to a predetermined maximum value. .

The fuel injection pressure and the fuel injection rate thus increased to the maximum value are maintained for a predetermined time, and this operation stage is the main injection stage.

The main injection stage ends when the supply pressure to the fuel injection valve decreases. The stage at which the injection rate drops from the maximum value to zero is referred to as the late injection stage. In this late injection stage, the needle valve is quickly moved in the closing direction by the hydraulic pressure of the hydraulic chamber and the elasticity of the nozzle spring, and as a result,
After the end of the main injection, the fuel injection operation is suddenly stopped. That is, the injection operation can be completed in a state where nobody is left behind. However,
At the time when the needle valve has moved to just before the closed position, the oil pressure in the hydraulic chamber of the differential piston has also significantly decreased, so that the needle valve is generally seated on the valve seat only by the force of the nozzle spring. Therefore, the force with which the needle valve collides with the valve seat is small, and as a result, wear and breakage of the needle valve and the valve seat are effectively prevented.

[Embodiment] In FIG. 1, a valve body assembly 5 of a fuel injection valve is fitted and fixed in a fuel injection valve mounting hole of a cylinder head 1 via a sleeve (not shown). The valve body assembly 5 has a substantially cylindrical shape as a whole, and is arranged so that its center line OO is parallel to, for example, the cylinder center line.

In the valve body assembly 5, a nozzle body 8 is provided at the tip of the valve body 6 with an interpiece 7 (spacer) interposed therebetween.
Are seated, and they are integrally fixed by a case nut 9.

A differential piston body 11 (casing) and an inlet fitting 12 are concentrically arranged at the end opposite to the nozzle body 8 of the valve body 6 and fixed by a case nut 10 as follows.

The above-mentioned end of the valve body 6 has a substantially simple cylindrical shape, and one end of a differential piston body 11 is seated on the annular front end face 15 in a surface contact state, and an inlet fitting 12 is provided at the other end of the differential piston body 11. Sitting in surface contact.

The case nut 10 is located around the differential piston body 11 and around the ends of the valve body 6 and the inlet fitting 12 adjacent thereto. One end of the case nut 10 is screwed into a male screw provided on the outer periphery of the end of the valve body 6, and the intermediate portion is fitted in close contact with the outer periphery of the differential piston body 11. Case nut
An annular inward flange portion 16 is provided integrally with the inner periphery of the other end of the flange 10, and this flange portion 16 is different from an annular outward flange portion 17 provided at the end of the inlet fitting 12. The piston body 11 is engaged from the opposite side. Also, flange
The outer periphery of 17 is fitted to the inner periphery of case nut 10. Further, positioning pins 18 are driven into contact surfaces between the valve body 6 and the differential piston body 11 and between the differential piston body 11 and the inlet fitting 12.

With the above structure, the valve body 6 and the differential piston body 11
Are joined to each other in a liquid-tight state, and the differential piston body 11 and the inlet fitting 12 are also joined to each other in a liquid-tight state.

An outlet of a fuel high-pressure pipe 13 (only a center line is shown) is connected to an end of the inlet fitting 12 opposite to the differential piston body 11. The inlet of the fuel high-pressure pipe 13 is connected to a fuel injection pump (not shown). Further, although not shown, the inlet fitting 12 also serves as an outlet fitting, and an oil leakage pipe is also connected thereto.

Each of the above parts constituting the valve body assembly 5 is a cylindrical body extending concentrically or in parallel with the center line OO. And
A needle valve 20 is housed inside the nozzle body 8, and the valve body 6
Accommodates a spring receiver 21 and an extension 22 thereof, and a differential piston 23 is accommodated inside the differential piston body 11. The needle valve 20, the spring receiver 21 (and the extension 22 integral therewith), and the differential piston 23 are formed as separate components, and their ends are connected to each other.
These connecting portions may have an uneven fitting structure, in which case at least the extension 22 and the working piston
A gap is formed in the concave-convex fitting portion with 23 so that the relative movement of the two in the radial direction is slightly permitted.

The needle valve 20 has a conical tip end seated on an annular and tapered valve seat 24 formed on the inner periphery of the nozzle body 8. In order to control the opening and closing operation of the needle valve 20 with respect to the valve seat 24, the nozzle spring 25, the working chamber 26 and the hydraulic chamber 27
Is provided.

The nozzle spring 25 is provided around the spring receiving extension 22, one end of which is seated on the spring receiving 21, and the other end of which is seated on an annular step provided on the inner peripheral surface of the valve body 6. The working chamber 26 is formed by an annular concave portion on the inner peripheral surface of the nozzle body 8, and surrounds an intermediate portion in the longitudinal direction of the needle valve 20. The needle valve 20 has a smaller diameter at the distal end portion than at the proximal end portion, and a tapered outer peripheral surface formed between both portions faces the working chamber 26. Hydraulic chamber
Reference numeral 27 denotes a recess having a shallow (short length in the direction of the center line OO) circular section formed on the end face of the differential piston body 11 on the side of the inlet port 12.

The elasticity of the nozzle spring 25 and the hydraulic pressure inside the hydraulic chamber 27 with respect to the differential piston 23 act in a direction to close the needle valve 20. Further, the oil pressure in the working chamber 26 acts on the tapered outer peripheral surface of the needle valve 20 in a direction to open the needle valve 20.

The fuel passage 30 has an inlet connected to the internal passage of the high-pressure fuel pipe 13 and an outlet formed at the nozzle 31 formed at the tip of the nozzle body 8.
Connected to The fuel passage 30 is specifically configured as follows.

The center hole of the inlet fitting 12 extends from the outlet of the high-pressure fuel pipe 13 to the hydraulic chamber.
A fuel passage portion extending to 27 is formed. A passage hole extending from the hydraulic chamber 27 to the joint surface with the valve body 6 is formed in the end face of the differential piston body 11 and a portion near the outer periphery. A series of passage holes connected to the passages in the differential piston body 11 and extending to the working chamber 26 are formed in portions of the valve body 6, the interpiece 7, and the nozzle body 8 near the outer periphery. Further, the passage portion downstream of the hydraulic chamber 27 is
Formed by an annular gap between the inner periphery of the nozzle body 8 and the small diameter portion of the needle valve 20, a gap between the valve seat 24 and the needle valve 20, and an internal space (suck portion 32) at the tip of the nozzle body 8. Have been.

According to the above structure, as shown in FIG. 2 showing the relationship between the time and the injection rate, in the initial stage T1 (time section), the fuel injection is performed at a relatively low injection rate. Subsequent main injection stage
At T2, the injection rate rises sharply and reaches a predetermined maximum,
That state continues. In the late injection stage T3, the injection rate drops sharply and the injection stops.

In order to perform the injection with such characteristics, each part in FIG. 1 is configured to operate as follows.

In the initial stage T1 of the needle valve opening operation, the needle valve 20 exerts a throttle action on the fuel while the needle valve 20 fully closes (the tip is the valve seat 24).
The needle valve 20 moves from the fully seated position (the position where the large-diameter base end of the needle valve 20 contacts the end face of the interpiece 7). In this operation, the hydraulic pressure in the hydraulic chamber 27 near the fuel high-pressure pipe 13 rises earlier in time than the hydraulic pressure in the working chamber 26,
At the same time, the hydraulic pressure in the hydraulic chamber 27 becomes higher than the hydraulic pressure in the working chamber 26. The working chamber 26 is close to the injection port 31. In addition, since the opening of the needle valve 20 gradually increases, the pressure increase rate of the working chamber 26 (the pressure increase value per unit time) is lower than the pressure increase rate of the hydraulic chamber 27.

For these reasons, etc., the opening operation of the needle valve 20 is regulated,
Move relatively slowly. As a result, the injection is performed at a low injection rate in the initial stage. However, since the injection pressure corresponds to the sum of the resilience of the nozzle spring 25 and the hydraulic load applied to the differential piston 2, as in the prior art, a device without the differential piston 23, that is, a needle valve using only the nozzle spring In general, the pressure of the fuel supplied to the injection port 31 at the start of the injection is higher than that of the structure in which the injection is started, and the fuel is injected at a high pressure.

When the needle valve 20 reaches the fully open position after the initial stage T1 is completed, the opening degree of the needle valve 20 does not increase (that is, the flow path area and the flow coefficient of the nozzle portion change in a direction to promote the flow of fuel). No), and the oil pressure and amount of the fuel supplied from the fuel high-pressure pipe 13 also increase thereafter. Moreover, at the stage where the initial stage T1 is completed, as a result of the throttle operation with the needle valve 20 up to that time,
The hydraulic pressure on the upstream side of the needle valve 20 is increased. As a result, when the initial stage T1 ends, high-pressure fuel flows to the injection port 31, and the fuel injection pressure and the fuel injection rate at the injection port 31 rapidly increase to a predetermined maximum value and are maintained for a predetermined time.

The main injection stage T2 ends when the supply pressure to the fuel injection valve decreases. At this stage, the needle valve 20 is quickly moved in the closing direction by the hydraulic pressure of the hydraulic chamber 27 and the elasticity of the nozzle spring 25, and as a result, the fuel injection operation is suddenly stopped after the main injection ends. That is, the injection operation can be completed in a state where nobody is left behind. However, when the needle valve 20 has moved to just before the closing position, the oil pressure in the hydraulic chamber of the hydraulic chamber 27 has also been significantly reduced, so that the needle valve 20 is generally seated on the valve seat 24 only by the force of the nozzle spring 25. . Therefore, the force with which the needle valve 20 collides with the valve seat 24 is small, and as a result, the needle valve 20 and the valve seat
Wear and breakage of 24 are effectively prevented.

Further, in the above-described series of operations, the differential piston 23 can move slightly in the radial direction with respect to the spring receiving extension 22. Therefore, the differential piston 23 alone is capable of sliding resistance with the differential piston body 11. Can be moved in the radial direction to the least position. Therefore, the differential piston 23 operates smoothly.

In the above structure, the needle valve opening / closing direction (center line OO
The extension 22 and the differential piston 23 extending in the direction (parallel to) are formed as separate components. Both are connected by an abutting portion (or an uneven fitting portion), and the differential piston 23 is in a state where it can be separated from the extension portion 22 in the needle valve opening and closing direction. The differential piston 24 is located on the opposite side of the needle valve 20 with the spring receiver 21 and its extension 22 interposed therebetween. If such a structure is adopted in the overflow type injection device, the following inconvenience may occur with respect to the responsiveness of the injection operation.

That is, in the overflow type injection device, there is necessarily a suction stroke. Therefore, if the structure shown in FIG. 1 is used as it is, the hydraulic chamber 27 is in a negative pressure state in the suction / retraction stroke, and the differential piston 23 floats up to the inlet fitting 12 alone, and in that state, the next fuel injection cycle Is started. As a result, even if the pressure wave of the fuel reaches the hydraulic chamber 27, immediately after that, the differential piston 23 only idles toward the extension 22 side, and after the differential piston 23 is connected to the extension 22, Otherwise, the differential piston 23 does not start a substantial fuel-fuel control operation. Therefore, the needle valve for the fuel supply operation from the outside
A delay occurs in the opening operation of the motor 20, and such a delay is a problem particularly in a high-speed operation state.

In order to solve such a problem, the structure shown in FIG. 1a is adopted.

In FIG. 1a, the inlet fitting 12 facing the differential piston 23
An annular cutout 28 is provided at the center of the end surface of the, and an auxiliary spring 29 (compression coil spring) is provided between the cutout 28 and the hydraulic chamber 27. The auxiliary spring 29 is a weak compression coil spring. Both ends are seated on the end face of the differential piston 23 and the annular bottom (step) of the notch 28, respectively, and the differential piston 23 is separated from the extension 22 as described above. To prevent floating. Therefore, in the structure shown in FIG. 1a, the needle valve 20 does not respond to the fuel supply operation from the fuel injection pump.
Can be prevented from being delayed.

[Effects of the Invention] As described above, in the present invention, the valve body 6, the differential piston body 11, and the inlet fitting 12 are joined together and fixed by the case nut 10, so that the valve body assembly near the differential piston 11 is provided. The dimension (particularly, the dimension in the diameter direction) of the solid 5 can be reduced.

Further, since the differential piston body 11 is formed of only one member, the processing is simple.

Further, the seating surface (15) of the valve body 6 on which the differential piston body 11 is seated is formed by the distal end surface 15 of the cylindrical end of the valve body 6, so that the processing is simple.

Moreover, in the structure of the illustrated embodiment, the above-described injection rate change characteristics shown in FIG. 2 can be obtained, and the injection pressure can be increased. Moreover, the collision force between the needle valve 20 and the valve seat 24 in the valve closing operation can be set small. Therefore, it is possible to improve the operating performance of the engine and to obtain a fuel injection valve having excellent durability.

Also, since the fuel injection at a low injection rate is performed in the initial stage of the fuel injection operation, the injection rate sharply increases simultaneously with the start of the injection operation as in the structure described in Japanese Patent Application No. 60-122269. Therefore, a structure for increasing the volume of the entire passage to obtain a volume canceling effect is not required. As a result, in the present invention, the volume of the entire fuel passage is adversely affected by the passage resistance and the like. As far as possible, the pressure accumulating effect of the passage is eliminated by minimizing the injection operation, and the injection operation can be accurately controlled.

[Brief description of the drawings]

1 is a sectional view of an embodiment of the present invention, FIG. 1a is a partial sectional view of another embodiment of the present invention, and FIG. 2 schematically shows the injection characteristics of the fuel injection valve of the embodiment of FIG. It is a graph shown. 5 ... valve body assembly, 6 ... valve body, 8 ... nozzle body, 10 ... case nut, 11 ... differential piston body,
12 ... Inlet fitting, 20 ... Needle valve, 21 ... Spring receiver, 22 ...
Spring receiving extension, 23… Differential piston, 25… Nozzle spring, 26 …… Working chamber, 27 …… Hydraulic chamber, 29 …… Auxiliary spring, 30 …… Fuel passage, 31 …… Nozzle

Claims (1)

(57) [Claims] 1. A substantially cylindrical valve body assembly having a nozzle body at a tip thereof, a needle valve for opening and closing a nozzle port of the nozzle body, and a nozzle spring for urging the needle valve in a closing direction inside the valve body assembly. And a differential piston connected to the needle valve,
A fuel passage extending from the outlet of the external high-pressure oil supply passage to the injection port, an operating chamber for applying oil pressure in the opening direction to the needle valve, and a hydraulic chamber for applying oil pressure in the closing direction of the needle valve to the differential piston. The working chamber and the hydraulic chamber communicate with the fuel passage, the valve body assembly, the nozzle body,
A valve body having a nozzle body fixed at one end, a differential piston body seated in surface contact with the other end of the valve body, and an inlet fitting seated in surface contact with the end face of the differential piston body opposite to the valve body. A case nut is provided around and around the differential piston body, one end of the case nut is screwed into a threaded portion on the outer periphery of the valve body, and the other end of the case nut is engaged with the outer periphery of the inlet fitting. So that
The valve body, the differential piston body and the inlet fitting are integrally fixed, the auxiliary spring is arranged between the inlet fitting and the differential piston, and the differential piston is urged in the closing direction of the needle valve. The fuel injection valve of the internal combustion engine.