JP3817826B2 - Engine fuel injection valve - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an engine fuel injection valve that drives a needle valve by changing the fuel pressure before and after the needle valve via an actuator such as a piezoelectric element or a magnetostrictive element.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a fuel injection valve provided in an automobile engine has a needle valve (valve element) opened by an actuator including a piezoelectric element that changes in volume according to an applied voltage and a magnetostrictive element that changes in volume according to a change in a magnetic field. It is known that the valve operates, and by driving the needle valve with these actuators, the responsiveness of the fuel injection valve can be improved, the injectable range can be expanded and the engine output can be increased. The fuel can be stably injected, and the fuel consumption of the engine can be reduced.
[0003]
As such a fuel injection valve, for example, one disclosed in Japanese Patent Laid-Open No. 5-180113 is known, and a piezoelectric actuator made of a piezoelectric element is used as an actuator, and the opening and closing of a needle valve is controlled by a differential pressure across the front and back. It is based on this.
[0004]
To explain this, a fuel pressure chamber and a differential pressure chamber are defined before and after the needle valve, fuel is introduced into the fuel pressure chamber at a predetermined pressure, and the differential pressure chamber is communicated with the fuel pressure chamber by an orifice. . A piezo actuator provided with a piston is provided in the differential pressure chamber behind the needle valve, and the opening and closing operation of the needle valve is controlled by the expansion and contraction of the piezo actuator. On the outer periphery of the piston, an O-ring that is in sliding contact with the inner periphery of the casing is provided to define a differential pressure chamber and a space for housing the piezoelectric actuator.
[0005]
The pressure in the fuel pressure chamber and the differential pressure chamber before and after the needle valve is equalized through the orifice in a state where a preset voltage is applied to the piezo actuator and the piezoelectric actuator is extended.
[0006]
At this time, the needle valve is held closed by the urging force of the return spring. When the voltage applied to the piezo actuator is changed to a predetermined valve opening voltage from this state and the piezo actuator is instantaneously contracted, the volume of the differential pressure chamber behind the needle valve increases.
[0007]
At the same time, since the differential pressure chamber communicates with the fuel pressure chamber in front of the needle valve via an orifice, the internal pressure of the differential pressure chamber temporarily decreases and a pressure difference in the valve opening direction occurs before and after the needle valve. To do. As a result, the needle valve is opened against the return spring, and the nozzle is opened to inject fuel.
[0008]
[Problems to be solved by the invention]
However, in the above-described conventional example, an O-ring is provided on the outer periphery of the piston that slides on the inner periphery of the casing to define a differential pressure chamber and a space on the atmospheric pressure side that houses the piezoelectric actuator. When the piezo actuator is driven to extend, the piston is displaced in the direction of reducing the volume of the differential pressure chamber, and the pressure in the differential pressure chamber increases. At this time, the end of the O-ring that is in sliding contact with the inner periphery of the casing is As the pressure in the differential pressure chamber increases, it deforms to the atmospheric pressure side, so the volume in the differential pressure chamber increases, and the pressure in the differential pressure chamber cannot be increased according to the displacement of the piston, resulting in pressure loss. On the contrary, when the valve is opened to retract the piezo actuator from the extended state, the O-ring causes the piston and piezo to move due to a sudden pressure drop in the differential pressure chamber. Since the piston is deformed in the direction in which the piston is pulled with respect to the displacement direction of the actuator, there is a problem that the pressure in the differential pressure chamber cannot be reduced quickly, causing pressure loss on the decompression side and driving efficiency of the piezo actuator lowering. .
[0009]
Therefore, the present invention has been made in view of the above problems, and improves the driving efficiency by suppressing the pressure loss of the fuel injection valve using the piezoelectric element or the magnetostrictive element due to the deformation of the O-ring of the piston. For the purpose.
[0010]
[Means for Solving the Problems]
A first invention includes a fuel pressure chamber through which pressurized fuel is guided, a needle valve that is displaced according to a differential pressure between the fuel pressure chamber and the differential pressure chamber, a nozzle that is opened and closed by the needle valve and injects fuel in the fuel pressure chamber, An elastic member for urging the needle valve in the valve closing direction, an actuator composed of a piezoelectric element or a magnetostrictive element, a piston for increasing / decreasing the pressure in the differential pressure chamber according to the expansion / contraction of the actuator, and attached to this piston In a fuel injection valve of an engine provided with a seal member that defines a differential pressure chamber side and a space for housing an actuator, the differential pressure chamber includes a first differential pressure chamber facing a needle valve, and the piston. Consists of an enclosed second differential pressure chamber and a communication path that connects the first and second differential pressure chambers, and the second differential pressure chamber can be in close contact with a wall surface facing the end surface of the piston. And a plate-like member having a through hole facing the communication path, and a pin Is defined from the disposed a cylindrical bellows between the end faces of tons and the plate-like member, said plate-like member has a cylindrical portion which fits within the periphery the communication path.
[0011]
In a second aspect based on the first aspect, an inner diameter of the through hole provided in the plate member is smaller than an inner diameter of the communication path.
[0012]
In a third aspect based on the first aspect, the bellows is formed of a flexible member that urges the actuator toward the contraction direction.
[0014]
【The invention's effect】
In the first invention, since the second differential pressure chamber for housing the piston is defined by a cylindrical bellows provided between the piston end surface and the plate-like member provided with the through hole, the penetrating surface facing the communication path is provided. Through the hole, the first and second differential pressure chambers have the same internal pressure, and the internal pressure of the first and second differential pressure chambers fluctuates when the valve is opened and closed. Therefore, the fuel is prevented from leaking to the outer periphery of the bellows from between the wall surface and the plate-like member, and the pressure fluctuation of these differential pressure chambers is directly applied to the seal member provided on the outer periphery of the piston. As a result, the deformation of the seal member due to the pressure fluctuation of the differential pressure chamber as in the conventional example can be prevented, and the pressure loss due to the deformation can be prevented, and the drive efficiency of the actuator can be improved. And that much of the piezo actuator Making it possible to mold reduction, can promote the reduction of the production cost, also the sealing member because there is not deformed by the pressure, as in the prior example, it is possible to improve the durability. Further, since the plate-like member has a cylindrical portion that fits to the inner periphery of the communication path, the first differential pressure chamber and the second differential pressure chamber communicate with each other through a through hole in the inner periphery of the cylindrical portion, and the cylindrical portion is in the through hole. Since it is fitted to the circumference, the position of the through hole and the communication path is not displaced, and fuel can be reliably prevented from leaking from between the plate member and the wall surface to the outer periphery of the bellows, and the seal member provided on the piston is deformed. Can be more reliably prevented.
[0015]
In the second invention, since the inner diameter of the through hole provided in the plate-like member is set smaller than the inner diameter of the communication path, the wall surface faces the second differential pressure chamber even when the plate-like member is displaced. This prevents the fuel from leaking to the outer periphery of the bellows from between the plate-like member pressed against the wall surface and the wall surface.
[0016]
In the third aspect of the invention, since the cylindrical bellows is composed of a flexible member and constantly urges the actuator in the contraction direction, a member for providing the actuator with a preload in the contraction direction is separately provided. There is no need, the increase in the number of parts can be suppressed, and the plate-like member can be securely adhered to the wall surface.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which the present invention is applied to a fuel injection valve of an engine disposed in a direct injection spark ignition engine will be described with reference to the accompanying drawings.
[0019]
1 and 2, a nozzle body 1 that faces a combustion chamber of an engine (not shown) is provided at the tip of a casing 9 of the fuel injection valve. The nozzle body 1 is connected to a fuel spray from a nozzle 1a that opens at the tip. Is configured to be injected into the combustion chamber.
[0020]
A needle valve 2 having a valve body 2a formed on the nozzle hole 1a side and a piston portion 2c formed on the other end is slidably housed inside the nozzle body 1. A fuel pressure chamber 3 is defined so as to surround 2, and the nozzle 1 a is opened and closed by the needle valve 2.
[0021]
Supply of the pressurized fuel to the fuel pressure chamber 3 is performed from a fuel inlet 6 opened on the side surface of the casing 9, and the fuel inlet 6 communicates with a fuel supply means (not shown).
[0022]
The needle valve 2 forms a valve body 2a that contacts and separates from the seat portion of the nozzle body 1 on the nozzle hole 1a side, and slides the inner periphery of the nozzle body 1 on the base end (right side in the figure) of the casing 9 on the partition wall 9a side. A moving piston portion 2c is formed, and a rod-shaped rod portion 2b is formed between the valve body 2a and the piston portion 2c.
[0023]
A differential pressure chamber 8 serving as a first differential pressure chamber is defined between the piston portion 2c and the partition wall 9a on the back surface of the piston portion 2c, that is, on the side of the casing 9 facing the partition wall 9a. 8, a return spring 4 is interposed as an elastic member for biasing the needle valve 2 in the valve closing direction via the piston portion 2c.
[0024]
A throttle passage 20 having a predetermined gap or the like is formed between the end face of the piston portion 2c and the partition wall 9a, and fuel is transferred between the fuel pressure chamber 3 and the differential pressure chamber 8 via the throttle passage 20. Can be done gradually.
[0025]
On the other hand, the base end side (right side in the figure) of the casing 9 is formed in a cylindrical shape, and a piezo actuator 10 made of a piezoelectric element is extendable in the axial direction (left and right direction in the figure) on the inner periphery. The sealing member 16 is disposed at the open end (base end) of the casing 9.
[0026]
The piezo actuator 10 is formed by laminating a number of members in which piezoelectric elements made of PZT (lead zirconate titanate) ceramic, PMN (lead magnesium niobate) ceramic, etc. are formed in a disk shape. Electrodes (not shown) are interposed between and at both ends, and the piezo actuator 10 expands and contracts in the axial direction in response to an applied voltage from a controller (not shown).
[0027]
A space 90 for accommodating the piezo actuator 10 is defined between the sealing member 16 provided on the opening end side of the casing 9 and the partition wall 9a. The space 90 has, for example, a circular cross section, and supports a piston 11 (to be described later) freely slidable in the axial direction on the inner periphery 9d.
[0028]
A plate-like spacer 14 is fixed on the proximal end side of the piezo actuator 10 facing the sealing member 16, and a ball 15 is interposed between the spacer 14 and the sealing member 16. Since 10 is supported on the proximal end side via the spacer 14, when the piezoelectric actuator 10 is driven to extend, the distal end side is displaced in the axial direction toward the partition wall 9a.
[0029]
The ball 15 interposed between the spacer 14 and the sealing member 16 is provided on the axis of the piezo actuator 10 to allow relative rotation of the piezo actuator 10 with respect to the sealing member 16. This prevents the piezo actuator 10 from being twisted about its axis.
[0030]
On the other hand, a piston 11 that slides along the axis C on the inner periphery 9d of the casing 9 is fixed to the tip of the piezoelectric actuator 10 facing the partition wall 9a. The end surface 11a of the piston 11 faces the wall surface 9c of the partition wall 9a, and a second differential pressure chamber is formed between the end surface 11a and the wall surface 9c via an defining plate 7 and a bellows 5 as plate-like members. The pressure chamber 13 is defined as will be described later, and the pressure chamber 13 communicates with the differential pressure chamber 8 through a through hole 9b having a circular cross section as a communication passage provided in the partition wall 9a.
[0031]
The bellows 5 is formed of a flexible member, and is formed in a cylindrical shape, for example, a cylindrical shape from the peripheral edge 11b of the end surface 11a of the piston 11 toward the wall surface 9c, and has a base end fixed to the peripheral edge 11b. The tip is fixed to the defining plate 7 which can be in close contact with the wall surface 9c.
[0032]
The defining plate 7 is composed of a predetermined plate-like member, for example, a disc-like member, and forms a circular through-hole 7a coaxially at a position facing the through-hole 9b. The inner diameter of the through hole of the defining plate 7 is set smaller than the inner diameter of the through hole 9b of the partition wall 9a.
[0033]
The partition plate 7 is pressed toward the partition wall 9a by the elasticity of the bellows 5, and is always in close contact with the wall surface 9c, and the space surrounded by the bellows 5, the partition plate 7 and the end surface 11a of the piston 11 serves as a second differential pressure chamber. A pressure chamber 13 is defined and communicates with the differential pressure chamber 8 through the through holes 7a and 9a.
[0034]
An O-ring 12 as a seal member that is in sliding contact with the inner periphery 9 d of the casing 9 is provided on the outer periphery of the piston 11, and prevents fuel leaking from the outer periphery of the bellows 5 from entering the space 90.
[0035]
Note that the spring constant k of the return spring 4 is that the pressure receiving area of the piston 11 is A, the differential pressure applied to the piston portion 2c of the needle valve 2 is ΔP, the force applied to the piston 11 is F, and the force generated by the return spring 4 is Assuming Fk, in a state where the piezo actuator 10 is driven to contract and the needle valve 2 is opened,
| F | = | ΔP × A | >> | Fk | (1)
The spring constant of the return spring 4 is set so that
[0036]
Next, the operation of the fuel injection valve will be described.
[0037]
FIG. 1 shows a closed state of a fuel injection valve. A controller (not shown) applies a predetermined valve closing voltage to drive the piezo actuator 10 to extend, while a fuel pressure supply circuit (not shown) supplies a predetermined pressure Pf (hereinafter referred to as a fuel pressure supply circuit). , Fuel pressure) is supplied to the fuel pressure chamber 3 through the fuel inlet 6.
[0038]
The piezo actuator 10 extends toward the partition wall 9a in accordance with the applied valve closing voltage, and is driven to the maximum extension position against the elasticity of the bellows 5. As the piezo actuator 10 extends, the piston 11 moves to the pressure chamber 13. The pressure in the pressure chamber 13 rises to move in the direction of reducing the volume of the partition wall (side of the partition wall 9a), and the difference between the pressure chamber 13 communicates with the pressure chamber 13 through the through hole 7a of the defining plate 7 and the through hole 9b of the partition wall 9a. The pressure in the pressure chamber 8 increases.
[0039]
Due to the pressure increase in the differential pressure chamber 8 and the urging force of the return spring 4, the piston 2c is pressed against the fuel pressure Pf in the fuel pressure chamber 3 toward the nozzle 1a, and the valve body 2a closes the nozzle 1a and closes it. The valve state can be maintained.
[0040]
Since the inner diameter of the through hole 7a of the defining plate 7 is set smaller than the inner diameter of the through hole 9b of the partition wall 9a, the wall surface 9c is prevented from facing the pressure chamber 13 even when the defining plate 7 is displaced in the radial direction. Thus, it is possible to reliably prevent fuel from leaking to the outer periphery of the bellows 5 from between the defining plate 7 pressed against the wall surface 9c and the wall surface 9c, and an O-ring provided on the outer periphery of the piston 11 even if fuel leaks. 12, the fuel can be prevented from entering the space 90.
[0041]
And when the period which maintains this valve closing state extends for a long period of time, the fuel pressure chamber 3, the differential pressure chamber 8, and the pressure chamber 13 via the throttle part 20 of the inner periphery of the piston part 2c and the nozzle body 1 are shown. The pressure is equalized.
[0042]
On the other hand, the valve opening drive of the fuel injection valve is performed by switching the drive voltage applied to the piezo actuator 10 from the valve close voltage to the valve open voltage by a controller (not shown). Shrink to.
[0043]
The piezoelectric actuator 10 contracts with the valve opening voltage applied from the controller, and is biased toward the most contracted position by the elasticity of the bellows 5.
[0044]
In this valve open state, since the piezo actuator 10 is in a contracted state, the piston 11 is displaced toward the sealing member 16 and the volume of the pressure chamber 13 increases rapidly.
[0045]
The internal pressure of the pressure chamber 13 is suddenly reduced as the volume rapidly increases, and the pressure in the differential pressure chamber 8 is also rapidly reduced along with this sudden pressure reduction. While the differential pressure chamber 8 is suddenly depressurized, a predetermined fuel pressure Pf is always applied to the fuel pressure chamber 3, so that the differential pressure applied to the piston portion 2 c of the needle valve 2 increases, and the needle valve 2 has a return spring 4. Displaces in the valve opening direction (partition wall 9a side) against the urging force.
[0046]
With the displacement of the needle valve 2, the valve body 2a is opened to open the injection port 1a, and the pressurized fuel in the fuel pressure chamber 3 supplied from the fuel inlet 6 is injected into a combustion chamber (not shown).
[0047]
When the valve is opened from the closed state, the bellows 5 constituting the side wall of the pressure chamber 13 is pulled in the axial direction (axis C direction) by the piston 11, and the pressure in the pressure chamber 13 and the differential pressure chamber 8 decreases. The bellows 5 supports the pressure from the outer peripheral side to the inner peripheral side, and the defining plate 7 is urged and brought into close contact with the wall surface 9c by the elasticity of the bellows 5 as described above. Can be held.
[0048]
At the time of this valve opening, as shown in FIG. 2, the O-ring 12 only defines a space 90 in which the piezo actuator 10 is accommodated. That is, the effect of sudden pressure reduction is not applied, and only a pressure substantially equal to the atmospheric pressure in the space 90 is applied. Therefore, the O-ring 12 contracts the piston 11 and the piezoelectric actuator 10 due to the sudden decrease in pressure as in the conventional example. It is possible to prevent deformation against the direction and suppress the occurrence of pressure loss, quickly reduce the internal pressure of the pressure chamber 13 and quickly open the fuel injection valve. Responsiveness can be improved.
[0049]
In order to stop the fuel injection, the valve closing voltage is again applied to the piezo actuator 10 to drive it to extend rapidly, and the piston 11 increases the pressure in the pressure chamber 13 and the differential pressure chamber 8 while compressing the bellows 5. Then, similarly to the valve closing state, the urging force of the return spring 4 is applied to close the needle valve 2.
[0050]
When the valve is closed from the open state, the bellows 5 constituting the side wall of the pressure chamber 13 is compressed in the axial direction (axis C direction) by the piston 11, and the pressure in the pressure chamber 13 and the differential pressure chamber 8 is increased. Along with this, the pressure from the inner peripheral side toward the outer peripheral side is supported, and similarly, the pressure is also applied to the defining plate 7 toward the wall surface 9c, so that the inner diameter of the through hole 7a is changed to the inner diameter of the through hole 9a as described above. Therefore, the fuel in the pressure chamber 13 can be prevented from leaking to the outer periphery of the bellows 5.
[0051]
At this time, as shown in FIG. 2, the O-ring 12 only defines a space 90 in which the piezo actuator 10 is accommodated, and the pressure from the pressure chamber 13 is not directly applied, and the bellows Since only a pressure substantially equal to the atmospheric pressure of the space 90 is applied to the outer circumference of the space 5, the O-ring 12 is deformed against the extending direction of the piston 11 and the piezo actuator 10 due to a sudden increase in pressure as in the conventional example. It is possible to prevent the occurrence of pressure loss and to quickly increase the internal pressure of the pressure chamber 13 and quickly close the valve, thereby improving the responsiveness of the fuel injection valve. .
[0052]
Thus, since the pressure chamber 13 is defined by the bellows 5 and the separating plate 7 provided on the piston end surface 11a, it is possible to prevent deformation of the O-ring 12 due to pressure fluctuations in the pressure chamber 13 both when the valve is opened and when the valve is closed. The pressure loss due to the deformation of the O-ring as in the conventional example can be prevented, and the driving efficiency of the piezo actuator 10 can be improved. Accordingly, the piezo actuator 10 can be downsized and the manufacturing cost can be reduced. In addition, since the O-ring 12 is not deformed as in the conventional example, it is possible to improve the durability as compared with the conventional example. Since it is composed of a member having flexibility, it is not necessary to separately provide a member for applying a preload in the contraction direction to the piezo actuator 10, and an increase in the number of parts can be suppressed. It is. The reason why the preload is applied in the contraction direction is that the piezo actuator 10 needs to be used in a compression environment, and thereby the durability of the piezo actuator 10 is improved.
[0053]
FIG. 3 shows a second embodiment in which a cylinder portion 7b that fits into the through hole 9b is formed on the defining plate 7 of the first embodiment, and the other configurations are the same as those of the first embodiment. It is.
[0054]
A cylindrical portion 7b is formed at a predetermined position of the defining plate 7 corresponding to the through hole 9b of the partition wall 9a toward the differential pressure chamber 8, and the differential pressure is passed through the through hole 7a on the inner periphery of the cylindrical portion 7b. The chamber 8 and the pressure chamber 13 communicate with each other.
[0055]
In this case, since the cylindrical portion 7b is fitted into the through hole 9b, the positions of the through hole 7a and the through hole 9b are not shifted, and the wall surface 9c is not exposed to the pressure chamber 13, and the separating plate 7 and It is possible to reliably prevent the fuel from leaking from the space between the wall surface 9c of the partition wall 9a to the outer periphery of the bellows 5 and further reliably prevent the O-ring 12 provided on the piston 11 from being deformed.
[0056]
In the above embodiment, the piezoelectric actuator 10 made of a piezoelectric element is used as the actuator for driving the piston 11. However, although not shown, magnetostriction using a magnetostrictive element that expands and contracts according to the strength of the magnetic field is shown. The same applies when an actuator or a giant magnetostrictive actuator is employed.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a fuel injection valve showing an embodiment of the present invention.
FIG. 2 is an enlarged cross-sectional view showing the relationship between a piston, a bellows, and an defining plate.
FIG. 3 is a schematic sectional view of a fuel injection valve showing a second embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Nozzle body 1a Injection hole 2 Needle valve 2a Valve body 2c Piston part 3 Fuel pressure chamber 4 Return spring 5 Bellows 6 Fuel inlet 7 Definition plate (plate-shaped member)
7a Through-hole 7b Cylindrical part 8 Differential pressure chamber (first differential pressure chamber)
9 Casing 9a Partition wall 9b Through hole (communication path)
9c Wall surface 9d Inner circumference 10 Piezo actuator 11 Piston 11a End face 11b Perimeter 12 O-ring 13 Pressure chamber (second differential pressure chamber)

Claims (3)

A fuel pressure chamber through which pressurized fuel is guided;
A needle valve that is displaced according to the differential pressure between the fuel pressure chamber and the differential pressure chamber;
A nozzle that is opened and closed by a needle valve to inject fuel in the fuel pressure chamber;
An elastic member for urging the needle valve in the valve closing direction;
An actuator composed of a piezoelectric element or a magnetostrictive element;
A piston that increases and decreases the pressure in the differential pressure chamber according to the expansion and contraction of the actuator;
In a fuel injection valve of an engine provided with a seal member attached to the piston and defining a differential pressure chamber side and a space for housing an actuator,
The differential pressure chamber is composed of a first differential pressure chamber facing the needle valve, a second differential pressure chamber housing the piston, and a communication path communicating the first and second differential pressure chambers. And
The second differential pressure chamber has a plate-like member that can be in close contact with a wall surface facing the end surface of the piston and that has a through-hole facing the communication path, and between the end surface of the piston and the plate-like member. It is defined by the arranged cylindrical bellows ,
The engine fuel injection valve according to claim 1, wherein the plate-like member has a cylindrical portion fitted to the inner periphery of the communication path .   2. The fuel injection valve for an engine according to claim 1, wherein an inner diameter of the through hole provided in the plate-like member is smaller than an inner diameter of the communication path.   The engine fuel injection valve according to claim 1, wherein the bellows is formed of a flexible member that urges the actuator toward a contraction direction.

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