JP2004308478A - Injector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent generation of pressure decrease caused by a flow of contraction in a high-pressure side seat part, and to ensure stable operation of a three-way valve. <P>SOLUTION: In a injector, the three-way valve 4 is driven by extending/contracting a piezostack 1, and is selectively seated on a low-pressure seat 45 leading to a low-pressure passage 12 or a high-pressure seat 46 leading to a high-pressure passage 11, and pressure in a control chamber 5 applying back pressure to a nozzle needle 51 is increased/decreased. The three-way valve 4 is comprised of a valve part 41 with a large diameter and a sliding part 42, and pressure is balanced. The overlapping width of the high-pressure seat 46 and a valve face 41a of the three-way valve 4 opposing to the high pressure seat 46 is set to be small, for example below 50 μm, and 2° or more of taper angle difference are secured. A flow passage is rapidly expanded in a downstream side of the seat position, and flow speed is reduced. Accordingly, the pressure decrease due to the flow of the contraction is suppressed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

例えば、状態１は容積が大きい場合、４０ｃｃ／ｓ程度の流量であれば、ｖ_１ ≒０と考えてよい（図４の構成にも適合する）。この条件で、図４の構成においては、状態２ではｖ_２ ＝２０４ｍ／ｓ程度の流速が生じるために、式１が成り立つためには、
Ｐ_１ ＝１８０ＭＰａ
ρ＝８３０ｋｇ／ｃｍ^３
とすると、
Ｐ_２ ＝１０．７ＭＰａ
となる。状態２より下流部では、再度、容積が拡大しているため、状態１と同様に圧力が高くなる。従って、状態２では、周囲より圧力が低くなるために、弁部４１’に下向きの力が作用し、三方弁４の挙動が安定しないおそれがある。
【００４３】
そこで、本発明では図１（ｂ）のように、高圧側シート部（Ａ部）において縮流流れが生じないように、弁部４１の下側の弁面４１ａと高圧シート４６面との重なり幅を小さくする。図５は、縮流部の長さ（重なり幅）と、縮流流れによる圧力降下に伴う発生力低下の関係を示すもので、図示するように、概ね、縮流部長さが５０μｍを超えると油圧による発生力が大きく低下することがわかっている。従って、好ましくは、重なり幅を５０μｍ以下とするのがよく、高圧側シート部を通過する燃料の流速を小さくして、縮流流れによる圧力降下を抑制することができる。
【００４４】
また、高圧側シート部を構成する弁面４１ａと高圧シート４６面のテーパ角度の差を大きくしても、燃料流れを減速させることができる。本発明者等の実験によれば、具体的には、図６において、三方弁４のテーパ角度と高圧シート４６のテーパ角度との差を、概ね２°以上確保すると縮流流れによる圧力降下を抑制する効果が得られることがわかった。
【００４５】
このように、縮流流れを回避するには、弁部４１の弁面４１ａと高圧シート４６面との重なり幅を小さくし、角度差を大きくするのがよい。例えば、重なりを小さくすると、高圧の燃料流れが速やかに弁室４４に流出して減速する。また、角度差を２倍にすると流路面積は約２倍になるため、流速は半減することになり、縮流による圧力低下は１／√２になる。これにより、油圧力の影響を小さくでき、特に三方弁４が低圧シート４５を閉鎖する燃料噴射停止時に安定した作動が可能になる。
【００４６】
さらに、図２のように、本発明では三方弁４の低圧側シート部（Ｂ部）を構成する弁部４１の上側の弁面４１ｂを傾斜させて、弁面４１ｂの外周端縁部がフラットな面からなる低圧シート４５面に当接するようにしている。このように、弁面４１ｂにわずかな逃がしを設けると、シート位置が安定しシート径を正確に設定できるので、開弁力の設定を厳密に行うことができ、誤開弁等を防止できる。この逃がしの角度は、シート部近傍で、例えば１〜５°程度とするのがよい。これにより、常に安定した三方弁４の動作が可能となる。
【００４７】
図７に本発明の第２の実施形態を示す。本実施形態では、三方弁４の高圧側シート部において、弁部４１が当接する高圧シート４６をテーパ面とせず、エッジを有する形状として、該エッジ部に弁部４１の弁面４１ａがシートする構成としている。その他の基本構成および作動は上記第１の実施形態と同様である。本実施形態のシート部構成によれば、シート位置下流で流路が急拡大する同様の効果が得られ、加工が容易で、シート位置が容易に設定可能である。
【００４８】
図８に本発明の第３の実施形態を示す。本実施形態では、三方弁４の高圧側シート部において、弁部４１の弁面４１ａを、略球面状としてある。その他の基本構成および作動は上記第１の実施形態と同様である。本実施形態のシート部構成によれば、シート位置下流で流路が急拡大する同様の効果が得られ、また、弁面４１ａが略球面であるため、三方弁４が傾いた場合でもシートが可能である。
【００４９】
以上のように、本発明によれば、バランス三方弁を用いたインジェクタにおいて、シート部構成を最適化することにより、三方弁の作動を安定にし、アクチュエータの特性を有効に活用して、効率よい燃料噴射を実現することができる。
【図面の簡単な説明】
【図１】本発明のインジェクタの第１の実施形態を示し、（ａ）はバランス三方弁構成を示す拡大断面図、（ｂ）は（ａ）のＡ部拡大断面図である。
【図２】第１の実施形態におけるバランス三方弁近傍の構成を示す要部拡大断面図である。
【図３】本発明のインジェクタの概略構成を示す全体断面図である。
【図４】（ａ）は従来のインジェクタにおけるバランス三方弁構成を示す拡大断面図、（ｂ）は（ａ）のＡ部拡大断面図である。
【図５】縮流部長さと発生力の関係を示す図である。
【図６】第１の実施形態におけるバランス三方弁の低圧側シート部の構成を示す要部拡大断面図である。
【図７】本発明の第２の実施形態におけるインジェクタの全体概略断面図である。
【図８】本発明の第３の実施形態におけるインジェクタの全体概略断面図である。
【符号の説明】
Ｉ インジェクタ
１ ピエゾスタック（アクチュエータ）
１０ ボディ
１１ 高圧通路
１２ 低圧通路
２ ピエゾピストン
２１ スプリングピエゾ
２２ 変位拡大室
３ バルブピストン
３１ スピル通路
３２ 通路
４ バランス三方弁（三方弁）
４１ 弁部
４２ 摺動部
４３ 細径部
４４ 弁室
４５ 低圧シート
４６ 高圧シート
５ 制御室
５１ ノズルニードル
５２ スプリングニードル
６１ メインオリフィス
６２ サブオリフィス[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an injector used for a common rail fuel injection device of a diesel engine, for example.
[0002]
[Prior art]
In a diesel engine, a common rail fuel injection system that accumulates high-pressure fuel in a common rail common to each cylinder is known. An injector for a common rail fuel injection system, for example, is provided with a control chamber that is pressure-controlled by a control valve on the back of a nozzle needle that opens and closes an injection hole, and drives the control valve by an actuator to raise and lower the nozzle needle. I have. In this configuration, while the fuel from the common rail is introduced into the fuel passage of the injector and supplied to the injection hole, the fuel is introduced into the control chamber having the rear end face of the nozzle needle as a chamber wall, and the nozzle needle is closed in the valve closing direction. Used as a control oil to exert pressure.
[0003]
A piezo actuator having good responsiveness can be used as the actuator (for example, Patent Document 1). In addition, since the piezo actuator has a very small displacement, a large-diameter piston that moves up and down as the piezo actuator expands and contracts and a small-diameter piston that drives the control valve are provided, and hydraulic oil is filled between the large and small pistons. There has been proposed a displacement magnifying mechanism including a displacement magnifying chamber. Using this displacement magnifying mechanism, the displacement caused by the extension of the piezo actuator is converted into hydraulic pressure and then amplified according to the diameter difference between the large and small pistons, so that the displacement required to drive the control valve can be efficiently reduced. Obtainable.
[0004]
[Patent Document 1]
JP 2001-140727 A
As the control valve, a control valve having a three-way valve structure is preferably used. The three-way valve described in Patent Literature 1 includes a valve body capable of sitting on a low-pressure seat reaching a low-pressure passage or a high-pressure seat reaching a common rail, and switches communication between the control chamber and the low-pressure passage or the high-pressure passage depending on a seating position. I have. When a three-way valve is used, the control chamber communicates with the low-pressure seat during fuel injection, and the high-pressure seat is closed, so that fuel leakage from the high-pressure seat can be limited. .
[0006]
[Problems to be solved by the invention]
In the injector having the above configuration, in order to inject fuel, the piezo actuator is driven to separate the three-way valve from the low-pressure seat, the pressure in the control chamber is released, and the nozzle needle is opened. In order to terminate the injection, the drive of the actuator is terminated, the three-way valve is separated from the high-pressure seat, and the control chamber pressure is restored. However, at this time, since the high-pressure fuel flows out of the three-way valve and the high-pressure sheet at a very high speed, the flow around the seat part becomes a contracted flow, and the pressure around the seat part may decrease, which may hinder the operation of the three-way valve. Was.
[0007]
The present invention has been made in view of the above circumstances, and suppresses a pressure drop due to a contraction flow in a high-pressure side seat portion of a three-way valve at the end of injection, thereby improving the stability of operation of the three-way valve, thereby improving energy efficiency. It is an object of the present invention to provide a highly reliable, high performance, and highly reliable injector.
[0008]
[Means for Solving the Problems]
The injector according to the first aspect of the present invention includes a control chamber for applying a pressure in the valve closing direction to the nozzle needle, and a three-way valve for switching communication between the control chamber and the high-pressure passage and the low-pressure passage. When the actuator drives the three-way valve to separate from the low-pressure seat leading to the low-pressure passage and seat on the high-pressure seat leading to the high-pressure passage, the pressure in the control chamber is released, and the nozzle needle is opened. Fuel is injected. The injector has means for applying the pressure of the high-pressure passage in a direction to separate the three-way valve from the high-pressure seat, and includes a high-pressure side including the high-pressure seat and a valve surface of the three-way valve opposed thereto. The sheet portion has a shape in which the flow path rapidly expands downstream of the sheet position.
[0009]
In the conventional configuration, at the end of injection, high-pressure fuel is ejected from the high-pressure side seat at a high speed, so that the pressure in the vicinity of the seat decreases and the operation of the three-way valve may become unstable. In this configuration, the high-pressure side sheet portion has a shape in which the flow path suddenly expands downstream of the sheet position, so that the flow is immediately decelerated and the pressure drop due to the contracted flow can be suppressed. Therefore, stable operation of the three-way valve is ensured, and an injector with good energy efficiency and excellent controllability is realized.
[0010]
According to the second aspect of the present invention, the radial overlapping width of the valve surface of the high-pressure sheet and the three-way valve opposed thereto is 50 μm or less.
[0011]
Specifically, when the width of the sheet overlapping portion is reduced to 50 μm or less, the flow path downstream of the sheet rapidly expands and the flow velocity decreases, so that the effect of suppressing the pressure drop due to the contracted flow can be obtained.
[0012]
According to the third aspect of the present invention, the difference between the inclination angle of the high-pressure seat and the inclination angle of the valve face of the three-way valve opposed thereto is 2 ° or more.
[0013]
Alternatively, by increasing the angle difference between the high-pressure sheet and the valve surface of the three-way valve to 2 ° or more, the downstream flow path is rapidly expanded to reduce the flow velocity, and the pressure decrease due to the contraction flow is suppressed. The effect is obtained.
[0014]
In the invention according to claim 4, the low-pressure seat is a flat surface, and the valve surface of the opposed three-way valve is a surface that inclines inward from the outer peripheral edge so that the outer peripheral edge of the valve surface is in the seated state. It is configured to contact the low-pressure sheet.
[0015]
If one of the two seats has a flat surface, an axial deviation can be tolerated, but the seat position becomes unstable. Therefore, it is preferable to provide a relief with the valve surface of the three-way valve abutting on the inclined surface. As a result, the seat position is stabilized, and the seat diameter can be accurately set, so that the setting of the valve opening force is facilitated.
[0016]
In the invention described in claim 5, the downward inclination angle of the valve surface of the three-way valve seated on the low-pressure seat is in the range of 1 ° to 5 °.
[0017]
Preferably, the downward inclination angle of the valve face of the three-way valve is set in the range of 1 ° to 5 °, and an effect of stabilizing the seat position is obtained.
[0018]
In the invention according to claim 6, the three-way valve has a valve portion that moves between the low-pressure seat and the high-pressure seat, and a sliding portion slidably disposed on the body, The diameter, the high-pressure sheet diameter, and the sliding portion diameter are substantially equal.
[0019]
The three-way valve is provided with a valve part for opening and closing the low-pressure seat and the high-pressure seat, and a sliding part. If the diameters of the respective parts are substantially equal, the hydraulic pressure acting on the three-way valve is canceled to balance the pressure. be able to.
[0020]
In the invention according to claim 7, the actuator is a piezo actuator.
[0021]
Since the piezo actuator has good responsiveness and excellent controllability, by applying the present invention to the present invention, it is possible to achieve both stable operation and energy efficiency.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a schematic configuration diagram of an injector I of the present invention, and FIGS. The injector I of the present invention is used, for example, for a common rail fuel injection system of a diesel engine, is provided corresponding to each cylinder of the engine, and receives supply of fuel from a common common rail. The fuel pumped by the high-pressure supply pump is stored in the common rail at a predetermined high pressure corresponding to the injection pressure.
[0023]
In FIG. 3, the injector I has a body 10 attached to a combustion chamber wall (not shown). The body 10 accommodates components of each part of the injector and has a high-pressure passage 11 communicating with a common rail (not shown). A passage such as a low-pressure passage 12 communicating with a fuel tank (not shown) is formed.
[0024]
The injector I slidably holds a stepped nozzle needle 51 in a vertical hole 53 formed in the lower end of the body 10. An annular oil reservoir 13 is formed on the outer periphery of the lower half-diameter portion of the nozzle needle 51, and high-pressure fuel is constantly supplied to the oil reservoir 13 from the common rail through the high-pressure passage 11. Below the vertical hole 53, a sack portion 15 is formed so as to be continuous with the vertical hole 53, and an injection hole 14 for fuel injection is formed through the sack portion 15 forming wall.
[0025]
When the nozzle needle 51 is at the lower end position, the tip of the conical shape is seated on a seat provided at the boundary between the sack portion 15 and the vertical hole 53, the sack portion 15 is closed, and the fuel from the oil reservoir chamber 13 to the injection hole 14 is discharged. Shut off supply. When the nozzle needle 51 rises and separates from the seat and the sack portion 15 is opened, fuel is injected.
[0026]
The space defined by the upper end surface of the nozzle needle 51 and the wall surface of the vertical hole 53 is a control chamber 5 for applying a back pressure to the nozzle needle 51. Fuel as control oil is introduced into the control chamber 5 through the balance three-way valve 4 and the main orifice 61 and from the high-pressure passage 11 through the sub-orifice 62 to generate a back pressure of the nozzle needle 51. are doing. This back pressure acts downward on the nozzle needle 51 to urge the nozzle needle 51 in the seating direction together with the spring needle 52 housed in the control chamber 5. On the other hand, the high-pressure fuel in the oil reservoir chamber 13 acts on the step surface of the nozzle needle 51 upward to urge the nozzle needle 51 in the unseating direction.
[0027]
A piezo stack 1 as a piezo actuator, a large-diameter piezo piston 2, and a small-diameter valve piston 3 are coaxially arranged in the vertical hole formed in the upper half portion of the body 10 in this order from the upper side. The piezo stack 1 is a general one having a capacitor structure in which piezoelectric ceramic layers such as PZT and electrode layers are alternately laminated, and has a laminating direction, that is, a vertical direction, which is an expansion and contraction direction, and is charged and discharged by a drive circuit (not shown). It has become. A constant initial load is applied to the piezo stack 1 by a spring piezo 21 provided on the outer periphery of the upper end of the piezo piston 2. Accordingly, the piezo piston 2 moves up and down as the piezo stack 1 expands and contracts.
[0028]
The piezo piston 2 and the valve piston 3 are slidably held in a cylinder provided in a vertical hole. The valve piston 3 has a small-diameter lower end abutting on the upper end of the three-way valve 4, and a space between the piezo piston 2 and the valve piston 4 is filled with fuel to form a displacement expansion chamber 22. Therefore, when the piezo stack 1 is extended and presses the piezo piston 2, the pressing force is transmitted to the valve piston 3 via the fuel in the displacement expansion chamber 22, and the valve piston 3 is urged downward to operate the three-way valve 4. It is designed to be pressed.
[0029]
Here, since the diameter of the valve piston 3 is smaller than that of the piezo piston 2, the amount of extension of the piezo stack 1 is expanded and converted into the vertical displacement of the valve piston 3. Thus, the two large and small pistons 2 and 3 and the displacement expansion chamber 22 function as a hydraulic displacement expansion mechanism.
[0030]
The balance three-way valve 4 (hereinafter referred to as the three-way valve 4) is selectively seated on a low-pressure seat 45 opening on the ceiling surface of the valve chamber 44 or on a high-pressure seat 46 opening on the bottom surface. The pressure in the control chamber 5 which is always in communication with the chamber 44 is increased or decreased. The low-pressure seat 45 and the high-pressure seat 46 are provided at opposing positions at the center of the ceiling surface and the center of the bottom surface of the valve chamber 44. The low-pressure seat 45 communicates with the low-pressure passage 12 through the spill passage 31, and the high-pressure seat 46 communicates with the passage 32. Through the high pressure passage 11.
[0031]
As shown in FIG. 1A in an enlarged manner, the three-way valve 4 has a pressure-balanced structure having a large-diameter valve portion 41 and a sliding portion 42, and the upper end serving as the valve portion 41 is provided in the valve chamber 44. The sliding portion 42 located at the lower end is slid in the cylinder following the high-pressure sheet 46. The valve portion 41 and the sliding portion 42 are connected by a small diameter portion 43, and a passage 32 leading to the high pressure passage 11 is opened in an annular space formed on the outer periphery of the small diameter portion 43.
[0032]
When the valve portion 41 of the three-way valve 4 is at the upper end position where it is seated on the low-pressure seat 45 (the state shown in the figure), the high-pressure seat 46 is opened, and the 5 control chamber 5 and the high-pressure passage 11 communicate with each other. When the valve portion 41 is at the lower end position in which the high-pressure seat 46 is seated, the low-pressure seat 45 is opened, and the control chamber 5 and the low-pressure passage 12 communicate with each other. As the operating state of the three-way valve 4 switches, the pressure in the control chamber 5 communicating with the valve chamber 44, that is, the back pressure of the nozzle needle 51 increases and decreases.
[0033]
The three-way valve 4 has a low-pressure seat 45, a high-pressure seat 46, and a sliding portion 42 having substantially the same diameter, and a hydraulic pressure acting upward on the valve portion 41 (in a direction of separating from the high-pressure seat 46) and downward acting on the sliding portion 42. The hydraulic pressure acting in the direction (separating from the low-pressure seat 45) is substantially balanced. Thereby, the driving energy required for the piezo stack 1 when the piezo stack 1 is extended to displace the three-way valve 4 downward can be reduced. In addition, if the diameter of both the low-pressure seat 45 and the high-pressure seat 46 is slightly larger than the diameter of the sliding portion 42 and the upward hydraulic pressure acts on the three-way valve 4, the three-way valve 4 may operate unintentionally when the injection is stopped. The three-way valve 4 can be quickly separated from the high-pressure seat 46 at the end of the injection without opening the low-pressure seat 45, and the three-way valve 4 can operate more stably.
[0034]
In the present invention, the high-pressure side seat portion (A portion) of the three-way valve 4 has a shape in which the flow path rapidly expands downstream of the seat position as shown in an enlarged view in FIG. Specifically, the lower valve surface 41a of the valve portion 41 and the high-pressure sheet 46 surface facing the lower surface are tapered surfaces that increase in diameter upward, and the overlapping width of the valve surface 41a and the high-pressure sheet 46 surface is reduced. The taper angle is set to be very small and the difference in taper angle is increased. Thereby, the effect of suppressing the pressure drop due to the contracted flow in the downstream portion of the seat and stabilizing the operation of the three-way valve 4 can be obtained.
[0035]
As shown in FIG. 2, the low-pressure side seat portion (B portion) of the three-way valve 4 is configured such that the outer peripheral portion of the upper valve surface 41 b of the valve portion 41 facing the low-pressure seat 45 having a flat surface is moved from the outer peripheral edge portion. A relief is provided as an inclined surface that inclines slightly inward. Thereby, the effect of stabilizing the seat position is obtained, and the setting of the valve opening force is facilitated. The three-way valve 4 has a central portion of the upper valve surface 41b protruding upward, and an end surface of the three-way valve 4 having a substantially spherical shape, and is brought into contact with the valve piston 3. Thereby, the displacement of the shaft is absorbed, and the driving force can be efficiently transmitted to the three-way valve 4.
[0036]
The structures of the low-pressure side seat portion (portion A) and the high-pressure side seat portion (portion B in FIG. 1B) of the three-way valve 4 are characteristic portions of the present invention, and will be described later in detail.
[0037]
A spring chamber 71 for housing the spring valve 7 is provided below the sliding portion 42 of the three-way valve 4, and the three-way valve 4 is urged upward by the spring valve 7. The spring chamber 71 communicates with the drain passage 12 via the communication passage 72 so as to prevent the spring chamber 71 from becoming a closed chamber and generating a damper force (see FIG. 3). In this manner, the downward movement of the three-way valve 4 is not suppressed, and the valve portion 41 quickly separates from the low-pressure seat 15 at the start of injection.
[0038]
The operation of the injector I having the above configuration will be described. In FIG. 3, when the piezo stack 1 is charged from a state in which the piezo stack 1 is contracted in a discharged state, the piezo stack 1 expands and pushes down the piezo piston 2 to increase the pressure in the displacement expansion chamber 22. When the valve piston 3 moves downward by this oil pressure and pushes down the three-way valve 4, the valve portion 41 is separated from the low-pressure seat 45, further displaced downward and seated on the high-pressure seat 46. As a result, the low-pressure seat 45 communicating with the low-pressure passage 12 is opened, and the fuel in the control chamber 5 flows out through the main orifice 61 and the valve chamber 44, so that the pressure in the control chamber 5 decreases. When the downward urging force of the nozzle needle 51 falls below the upward urging force, the nozzle needle 51 is disengaged and fuel injection is started.
[0039]
On the other hand, when the piezo stack 1 is discharged again, the piezo stack 1 contracts, the piezo piston 2 moves upward, the pressure in the displacement expansion chamber 22 drops, and the pushing force of the three-way valve 4 is released. As a result, the high-pressure sheet 46 communicating with the high-pressure passage 11 is opened, and control is performed by the high-pressure fuel flowing into the control chamber 5 through the valve chamber 44 and the main orifice 61 and the high-pressure fuel flowing through the sub-orifice 62. The chamber 5 pressure increases again. Then, when the downward urging force of the nozzle needle 51 exceeds the upward urging, the nozzle needle 51 is seated and the injection ends.
[0040]
The sub-orifice 62 functions to alleviate the pressure drop in the control chamber 5 at the start of injection, to promote the pressure rise in the control chamber 5 at the time of injection stop, to slowly open the nozzle needle 51, and quickly close it. Having. A configuration without the sub-orifice 62 may be adopted.
[0041]
Next, features of the present invention will be described. As described above, in the three-way valve 4 of the pressure balance type, since the force generated by the hydraulic pressure is always canceled, the driving energy of the piezo stack 1 can be reduced, while the three-way valve 4 opens and closes with a slight force. The structure of the seat portion greatly affects the operation of the three-way valve 4. 4 (a) and 4 (b) are views showing the structure of a conventional balance three-way valve 4 ', in which a high pressure is applied to a valve chamber 44 from a gap between a valve surface 41a' of a valve portion 41 'and a high pressure seat 46'. When the fuel flows out, it tends to be a contracted flow. From the viewpoint of fluid engineering, it is well known that the energy of the fluid satisfies the following equation 1 in state 1 (upstream of the high-pressure sheet 46 ') and state 2 (high-pressure side sheet) in FIG. 4B. ing.
[0042]
(Equation 1)

For example, in the state 1, when the volume is large, if the flow rate is about 40 cc / s, it may be considered that v ₁ ≒ 0 (also applicable to the configuration of FIG. 4). Under these conditions, in the configuration of FIG. 4, a flow velocity of about v ₂ = 204 m / s occurs in the state 2, and therefore, in order for the expression 1 to be satisfied,
P ₁ = 180 MPa
ρ = 830 kg / cm ³
Then
P ₂ = 10.7 MPa
It becomes. In the downstream part of the state 2, the volume is increased again, so that the pressure increases as in the state 1. Therefore, in state 2, since the pressure is lower than the surroundings, a downward force acts on the valve portion 41 ', and the behavior of the three-way valve 4 may not be stable.
[0043]
Therefore, in the present invention, as shown in FIG. 1B, the lower valve surface 41a and the high pressure sheet 46 overlap with each other so that a contracted flow does not occur in the high pressure side seat portion (A portion). Reduce the width. FIG. 5 shows the relationship between the length of the contraction portion (overlap width) and the reduction in the generated force due to the pressure drop due to the contraction flow. As shown in the drawing, when the length of the contraction portion exceeds approximately 50 μm. It has been found that the power generated by hydraulic pressure is greatly reduced. Therefore, the overlap width is preferably set to 50 μm or less, and the flow velocity of the fuel passing through the high-pressure side sheet portion can be reduced to suppress the pressure drop due to the contracted flow.
[0044]
Further, even if the difference between the taper angles of the valve surface 41a and the high-pressure seat 46 constituting the high-pressure side seat portion is increased, the fuel flow can be reduced. According to the experiments conducted by the present inventors, specifically, in FIG. 6, when the difference between the taper angle of the three-way valve 4 and the taper angle of the high-pressure sheet 46 is approximately 2 ° or more, the pressure drop due to the contracted flow is reduced. It turned out that the effect of suppressing is obtained.
[0045]
As described above, in order to avoid the contraction flow, it is preferable to reduce the overlapping width between the valve surface 41a of the valve portion 41 and the high-pressure sheet 46 and increase the angle difference. For example, when the overlap is reduced, the high-pressure fuel flow quickly flows into the valve chamber 44 and decelerates. Further, if the angle difference is doubled, the flow path area is approximately doubled, so that the flow velocity is halved, and the pressure drop due to the contraction becomes 1 / √2. As a result, the influence of the oil pressure can be reduced, and a stable operation can be achieved especially when the three-way valve 4 closes the low-pressure seat 45 and stops fuel injection.
[0046]
Further, as shown in FIG. 2, in the present invention, the upper valve surface 41b of the valve portion 41 constituting the low pressure side seat portion (portion B) of the three-way valve 4 is inclined so that the outer peripheral edge of the valve surface 41b is flat. The low-pressure sheet 45 is formed in such a manner as to contact the low-pressure sheet 45. When a slight relief is provided on the valve surface 41b in this manner, the seat position is stabilized and the seat diameter can be accurately set, so that the valve opening force can be set strictly and erroneous valve opening and the like can be prevented. It is preferable that the angle of this escape is, for example, about 1 to 5 ° near the seat portion. As a result, the operation of the three-way valve 4 can be always stabilized.
[0047]
FIG. 7 shows a second embodiment of the present invention. In the present embodiment, in the high-pressure side seat portion of the three-way valve 4, the high-pressure seat 46 with which the valve portion 41 abuts is not formed into a tapered surface, but has a shape having an edge, and the valve surface 41a of the valve portion 41 is seated at the edge portion. It has a configuration. Other basic configurations and operations are the same as those in the first embodiment. According to the configuration of the seat portion of the present embodiment, the same effect that the flow path rapidly expands downstream of the seat position is obtained, processing is easy, and the seat position can be easily set.
[0048]
FIG. 8 shows a third embodiment of the present invention. In the present embodiment, the valve surface 41a of the valve portion 41 in the high-pressure side seat portion of the three-way valve 4 has a substantially spherical shape. Other basic configurations and operations are the same as those in the first embodiment. According to the configuration of the seat portion of the present embodiment, the same effect that the flow path rapidly expands downstream of the seat position is obtained, and since the valve surface 41a is substantially spherical, even if the three-way valve 4 is inclined, the seat can be moved. It is possible.
[0049]
As described above, according to the present invention, in the injector using the balanced three-way valve, by optimizing the seat configuration, the operation of the three-way valve is stabilized, and the characteristics of the actuator are effectively used to improve the efficiency. Fuel injection can be realized.
[Brief description of the drawings]
FIGS. 1A and 1B show an injector according to a first embodiment of the present invention, wherein FIG. 1A is an enlarged sectional view showing a configuration of a balanced three-way valve, and FIG. 1B is an enlarged sectional view of a portion A of FIG.
FIG. 2 is an enlarged sectional view of a main part showing a configuration near a balance three-way valve according to the first embodiment.
FIG. 3 is an overall sectional view showing a schematic configuration of an injector of the present invention.
FIG. 4A is an enlarged sectional view showing a configuration of a three-way balance valve in a conventional injector, and FIG. 4B is an enlarged sectional view of a portion A in FIG.
FIG. 5 is a diagram illustrating a relationship between a length of a contraction portion and a generated force.
FIG. 6 is an enlarged sectional view of a main part showing a configuration of a low pressure side seat portion of the balance three-way valve in the first embodiment.
FIG. 7 is an overall schematic sectional view of an injector according to a second embodiment of the present invention.
FIG. 8 is an overall schematic sectional view of an injector according to a third embodiment of the present invention.
[Explanation of symbols]
I Injector 1 Piezo stack (actuator)
DESCRIPTION OF SYMBOLS 10 Body 11 High pressure passage 12 Low pressure passage 2 Piezo piston 21 Spring piezo 22 Displacement expansion chamber 3 Valve piston 31 Spill passage 32 Passage 4 Balanced three-way valve (Three-way valve)
41 Valve part 42 Sliding part 43 Small diameter part 44 Valve chamber 45 Low pressure seat 46 High pressure seat 5 Control room 51 Nozzle needle 52 Spring needle 61 Main orifice 62 Sub orifice

Claims (7)

A control chamber for applying pressure in the valve closing direction to the nozzle needle, and a three-way valve for switching the communication between the control chamber and the high-pressure passage and the low-pressure passage are provided. The actuator drives the three-way valve to reach the low-pressure passage. An injector for releasing the pressure in the control chamber by opening the nozzle needle by releasing from the low-pressure seat and seating on the high-pressure seat reaching the high-pressure passage, wherein the three-way valve separates from the high-pressure seat. A means for applying the pressure of the high-pressure passage in the direction in which the high-pressure sheet is formed, and a high-pressure side seat portion formed of the high-pressure sheet and the valve surface of the three-way valve opposed thereto has a flow path downstream of the seat position. An injector characterized by a shape that expands rapidly. 2. The injector according to claim 1, wherein a radial overlapping width between the high-pressure sheet and a valve face of the three-way valve opposed thereto is 50 μm or less. 3. The injector according to claim 1, wherein a difference between an inclination angle of the high-pressure sheet and an inclination angle of a valve surface of the three-way valve opposed thereto is 2 ° or more. The low-pressure seat is a flat surface, and the valve surface of the three-way valve opposed to the low-pressure seat is a surface that inclines inward from the outer peripheral edge, and the outer peripheral edge of the valve surface contacts the low-pressure seat when seated. The injector according to any one of claims 1 to 3, wherein the injector is configured. The injector according to claim 4, wherein a downward inclination angle of a valve surface of the three-way valve seated on the low-pressure seat is in a range of 1 ° to 5 °. The three-way valve has a valve portion that moves between the low-pressure seat and the high-pressure seat, and a sliding portion slidably disposed on the body. The injector according to any one of claims 1 to 5, wherein the diameters of the sliding portions are substantially equal. 7. The injector according to claim 1, wherein the actuator is a piezo actuator.

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