JP2016050564A - Fuel injection valve - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such the problem that in the conventional injector, since an out-orifice is arranged on the downstream side of a control valve of a three-way valve structure and the control valve is arranged in a hydraulic control chamber, the volume of the hydraulic control chamber is increased to increase pressure pulsation of fuel, and controllability of a needle is deteriorated.SOLUTION: In an injector, since an out-orifice hole 52 is provided in a control plate 6 located on a more upstream side of a control valve chamber 13 and further, the control plate 6 is arranged in a pressure control chamber 14, the volume of a hydraulic control chamber is made small, and thus the pressure pulsation in the pressure control chamber 14 can be reduced. Moreover, even when an out-orifice flow amount is increased for the purpose of reducing a fuel pressure in the pressure control chamber 14 at high speed to improve valve opening responsiveness of a needle 1, the pressure pulsation in the pressure control chamber 14 can be reduced. Accordingly, a deterioration in controllability of the needle 1 can be suppressed during the valve opening operation of the needle.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a fuel injection valve for an internal combustion engine.

[Conventional technology]
Conventionally, as an example of a fuel injection valve that injects fuel into a cylinder of an internal combustion engine (engine), the control valve is switched using an actuator displacement to adjust the fuel pressure (control chamber pressure) in the control chamber. A fuel injection valve (hereinafter, a conventional injector) that controls the opening and closing operation of the needle has been proposed (see, for example, Patent Document 1).
This conventional injector includes a needle that opens and closes a nozzle hole, a control chamber that stores fuel pressure acting on the needle in a valve closing direction, a control valve that controls increase and decrease of the fuel pressure in the control chamber, and this control And an actuator that generates a driving force for switching the valve body (hereinafter referred to as a control valve) of the valve.

This conventional injector employs a configuration in which a control valve is switched using a piezoelectric actuator mainly composed of a piezoelectric element stack as an actuator.
Further, as the control valve, a control valve that selectively communicates a communication port that is in constant communication with the control chamber via a common flow path to a low pressure port that communicates with the low pressure fuel passage and a high pressure port that communicates with the high pressure fuel passage, A control valve having a three-way valve structure having a valve spring that urges the control valve to open the high-pressure port and close the low-pressure port is used. The wall surface of the control valve chamber is provided with a low-pressure sheet that is a low-pressure port opening peripheral part and a high-pressure sheet that is a high-pressure port opening peripheral part. The control valve is housed in the control valve chamber together with the valve spring.

  In this case, when the actuator is energized (ON) based on the injector valve opening command from the electronic control unit (ECU), the actuator is extended and displaced, the control valve is pushed down, and the low pressure seal state is switched to the high pressure seal state. As a result, the control valve is seated on the high-pressure seat and the communication between the high-pressure port and the communication port is blocked, so that the high-pressure fuel does not flow into the control chamber from the high-pressure fuel passage through the control valve chamber. Further, since the control valve is detached from the low pressure seat and the low pressure port and the communication port communicate with each other, the fuel flows out from the control chamber to the low pressure fuel passage through the control valve chamber. As a result, the fuel pressure in the control chamber is quickly reduced, and the valve opening response of the needle is improved.

  On the other hand, when energization to the actuator is stopped (OFF) based on an injector valve closing command from the ECU, the actuator is contracted and displaced, and the control valve is switched from the high pressure seal state to the low pressure seal state by the urging force of the valve spring. As a result, the control valve is seated on the low-pressure seat and the communication between the low-pressure port and the communication port is blocked, so that fuel does not flow out from the control chamber to the low-pressure fuel passage via the control valve chamber. Further, since the control valve is detached from the high-pressure seat and the high-pressure port and the communication port communicate with each other, the high-pressure fuel flows from the high-pressure fuel passage into the control chamber through the control valve chamber. As a result, the fuel pressure in the control chamber rises quickly, and the valve closing response of the needle is improved.

By the way, in the conventional injector, for the purpose of independently controlling the opening / closing valve speed of the needle, the orifice is not set in the common flow path, and the in-orifice is set in the high-pressure fuel passage upstream of the control valve chamber. In addition, an out-orifice is set in the low-pressure fuel passage on the downstream side of the control valve chamber.
In this case, the needle opening speed can be set by the out-orifice flow rate (throttle diameter), and the needle closing speed can be set by the in-orifice flow rate (throttle diameter), so the needle opening and closing valve speed can be set independently. can do. As a result, the degree of freedom in designing the needle opening / closing valve speed is improved.

[Conventional technical problems]
However, the conventional injector has a three-way valve structure in the hydraulic control chamber (including the control chamber, common flow channel, control valve chamber, upstream end of the low pressure fuel passage, etc.) from the pressure receiving surface of the needle to the out orifice. Since the control valves (control valve, valve spring, etc.) are accommodated, the volume of the hydraulic control chamber is increased.
When the volume of the hydraulic control chamber increases, when the injection start command for the injector is used, the fuel pressure in the hydraulic control chamber is changed to the fuel injection pressure when the control valve is pushed down using the displacement of the actuator and the control valve is seated on the high pressure seat. The volume elastic modulus of the fuel greatly fluctuates due to a rapid drop from a high pressure equivalent to. Along with this, the fuel volume pulsation is generated in the hydraulic control chamber as the volume of the fuel repeatedly expands and contracts.

In particular, when the out-orifice flow rate is increased for the purpose of reducing the fuel pressure in the hydraulic control chamber at a high speed and improving the valve opening response of the needle, the amplitude of the pressure pulsation in the hydraulic control chamber becomes larger, When the needle starts to lift, the needle may lift while wobbling. Thereby, since the controllability of the needle is deteriorated, there is a problem that the control accuracy of the injection amount with respect to the injection amount command value (energization length) is deteriorated.
As a result, it is difficult to increase the valve opening speed of the needle, and the valve opening response of the needle cannot be improved. In order to open the needle at a high speed, it is necessary to quickly reduce the fuel pressure in the hydraulic control chamber.
In particular, in the case of an injector that switches the control valve by utilizing the extension displacement of the piezo actuator, the above problem becomes significant.

JP 2006-046323 A

  An object of the present invention is to provide a fuel injection valve that can prevent deterioration of the controllability of the needle and that can independently set the needle opening speed and the needle closing speed.

According to the first aspect of the present invention (fuel injection valve), a switching state in which the low pressure port and the communication port are communicated and the communication between the high pressure port and the communication port is blocked by the switching operation of the control valve (for example, a high pressure seal state) ), The fuel flows out from the control chamber to the low pressure side of the fuel system via the common flow path, the control valve chamber, and the low pressure fuel passage, and the fuel pressure in the control chamber decreases. When the fuel flows out from the control chamber to the control valve chamber via the common flow path, when the switching valve switches the fuel path to the first path, the fuel flowing out from the control chamber to the common flow path side Go to the shared channel side via. Thereby, the fuel flowing out from the control chamber to the control valve chamber via the common flow path passes through the out orifice, so that the valve opening speed of the needle is set by the fuel flow rate defined by the out orifice.
When the fuel pressure in the control chamber, that is, the fuel pressure acting on the needle in the valve closing direction is reduced to the needle opening pressure, the needle is opened (lifted) and fuel injection into the cylinder of the internal combustion engine is started. The

Here, the volume of the control chamber that stores the fuel pressure acting in the valve closing direction on the needle becomes a volume from the pressure receiving surface of the needle to the out orifice, and becomes smaller. That is, since the volume of the control chamber is reduced, the control valve switching operation causes the high pressure port and the communication port to communicate with each other, and the low pressure port and the communication port to communicate with each other. Pressure pulsation in the control chamber that occurs when switching to a switching state (for example, a high-pressure seal state) that connects the port and the communication port and blocks communication between the high-pressure port and the communication port can be reduced. Further, even when the out-orifice flow rate is increased for the purpose of reducing the fuel pressure in the control chamber at a high speed and improving the valve opening response of the needle, the pressure pulsation in the control chamber can be reduced.
Therefore, it is possible to suppress the needle from lifting while undulating. Thereby, since the valve opening operation of the needle is stabilized from the start of the lift to the full lift, the deterioration of the controllability of the needle and the deterioration of the control accuracy of the injection amount can be suppressed.

On the other hand, when the control valve is switched to a switching state (for example, a low pressure seal state) that connects the high pressure port and the communication port and blocks the communication between the low pressure port and the communication port by the switching operation of the control valve, the control valve chamber and the control valve chamber High-pressure fuel is introduced into the control chamber via the common flow path, and the fuel pressure in the control chamber increases. When fuel is introduced from the control valve chamber into the control chamber via the common flow path, when the switching valve switches the fuel path to the second path, the control valve chamber passes through the common flow path to the control chamber. The introduced high-pressure fuel bypasses the out orifice and is introduced into the control chamber.
As a result, the fuel introduced from the control valve chamber into the control chamber via the common flow path does not pass through the out orifice, so that the valve closing speed of the needle is the fuel flowing through the high pressure fuel passage, the control valve chamber, and the common flow path. Set by flow rate.
When the fuel pressure in the control chamber, that is, the fuel pressure acting on the needle in the valve closing direction rises (recovers) to the needle closing pressure, the needle closes (seats) and fuel is injected into the cylinder of the internal combustion engine. Ends.
Therefore, the valve opening speed of the needle and the valve closing speed of the needle can be set independently.

FIG. 1 is a cross-sectional view showing a piezo injector (Example 1). (Example 1) which is sectional drawing which showed the low-pressure seal | sticker state by a control valve. It is sectional drawing which showed the high pressure seal state by a control valve (Example 1). (Example 2) which is sectional drawing which showed the low-pressure seal | sticker state by a control valve. It is sectional drawing which showed the high pressure seal state by a control valve (Example 2). (Example 3) which is sectional drawing which showed the low pressure seal state by a control valve. (Example 3) which is sectional drawing which showed the high pressure seal state by a control valve. (A) is sectional drawing which showed the low pressure seal state by a control valve, (b) is sectional drawing which showed the high pressure seal state by a control valve (Example 4). (A) is sectional drawing which showed the low pressure sealing state by a control valve, (b) is sectional drawing which showed the high pressure sealing state by a control valve (Example 5).

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Configuration of Example 1]
1 to 3 show an injector (Embodiment 1) used in a fuel injection system to which the present invention is applied.

The fuel injection valve of the internal combustion engine of the present embodiment is a direct injection type that injects fuel spray in the form of a mist into a combustion chamber formed in a cylinder of an internal combustion engine (hereinafter referred to as an engine) such as a diesel engine for driving a vehicle such as an automobile. Piezo injector (hereinafter abbreviated as injector). This injector is used as a fuel injection valve of a common rail type fuel injection system (accumulation type fuel injection device) known as a fuel injection system for an internal combustion engine (engine).
The injector has a plurality of nozzle holes (described later) communicating with the combustion chambers of the cylinders of the engine, a bottomed cylindrical nozzle body 2 containing a needle 1 and the like for opening and closing these nozzle holes, and the needle 1. On the other hand, a control valve having a three-way two-position switching valve (hereinafter referred to as a three-way valve) structure for increasing / decreasing the fuel pressure acting in the valve closing direction, and an actuator for generating a driving force for switching the control valve using its own displacement And a cylindrical injector body 4 containing 3 or the like.

  On the central axis of the nozzle body 2 of the injector, a bag hole-like needle accommodation hole is formed which opens at the contact surface of the nozzle body 2 and extends straight from the opening side to the back side in the nozzle axis direction. Inside the needle housing hole, a needle 1 that can reciprocate in the axial direction, a needle spring 5 that urges the needle 1 in the valve closing direction, a control plate 6 that is a floating valve, and the control plate 6 Is housed in a control plate spring 7 that urges the valve 1 in the valve closing direction, and a cylindrical nozzle cylinder 8 that supports the sliding portion of the needle 1 in a reciprocating manner and supports the control plate 6 in a reciprocating manner. Has been.

A valve body 9 and an orifice plate 10 are installed between the nozzle body 2 and the injector body 4. A control valve chamber 13 for accommodating control valves (control valve 11 and valve spring 12) is formed between the valve body 9 and the orifice plate 10.
Here, the control valve is a pressure control valve that causes fuel to flow out from the pressure control chamber 14 to the low pressure side of the fuel system via a fuel discharge passage (described later) when the control valve 11 is opened.
Details of the control valve of this embodiment will be described later.

On the wall surface (bottom surface) of the control valve chamber 13 of the valve body 9, a low-pressure seat surface having a planar ring shape (or a truncated cone (taper) cylinder shape) on which a low pressure side valve portion (described later) of the control valve 11 can be seated ( A low pressure side valve seat) 15 is formed. In the central portion of the low-pressure seat surface 15, a low-pressure port 16 that connects the control valve chamber 13 and a low-pressure fuel passage (described later) is opened.
An annular high pressure seat surface (high pressure side valve seat) 17 is formed on the upper end surface of the orifice plate 10 in the figure so as to face the control valve chamber 13 and on which a high pressure side valve portion (described later) of the control valve 11 can be seated. ing. In the central portion of the high pressure seat surface 17, a high pressure port 18 that opens a high pressure fuel passage (described later) and the control valve chamber 13 is opened.
A communication port 19 that is always in communication with the pressure control chamber 14 is formed in the wall surface of the control valve chamber 13 of the valve body 9.
An annular valve seat surface (described later) on which the valve portion of the control plate 6 can be seated is formed on the lower end surface of the orifice plate 10 in the figure.

In the state where the valve body 9 and the orifice plate 10 are sandwiched between the contact surface of the nozzle body 2 and the contact surface of the injector body 4, the injector body 4 is screwed to the tip end side in the axial direction of the injector body 4. A retaining nut 20 is provided for fixing.
A piezo-accommodating hole that extends straight in the axial direction is formed at a position that is eccentric (offset) by a predetermined radial distance from the central axis of the injector body 4. Inside the piezo-accommodating hole, there is an actuator 3 for switching and driving the valve body (control valve 11) of the control valve, and an oil-tight chamber 23 between the piezo piston 21 and the valve piston 22, and the actuator 3 is extended and displaced. And a displacement enlarging mechanism for enlarging and transmitting it to the valve piston 22. A valve piston spring 24 is also accommodated inside the piezoelectric accommodation hole.

A base end side end (anti-injection hole side end) of the injector body 4 of the injector is connected to a high pressure generating part such as a supply pump or a common rail provided on the high pressure side of the fuel system via a high pressure pipe. And an outlet port connected to a fuel tank provided on the low pressure side of the fuel system or a low pressure portion of the fuel supply path through a low pressure pipe. Further, an external connection connector for connecting the piezoelectric lead terminal of the actuator 3 and an external circuit (external power supply or external control circuit: ECU) is provided on the side opposite to the injection hole of the injector body 4.
The injector controls the opening / closing operation of the needle 1 by adjusting (increasing / decreasing) the fuel pressure in the pressure control chamber 14 by switching and driving the control valve 11 by using the expansion / contraction displacement of the actuator 3. Thus, the fuel injection amount, the injection timing, and the injection pattern (injection rate) injected into the combustion chamber of the engine cylinder are controlled.

Further, the needle accommodation hole of the nozzle body 2 has a fuel reservoir chamber 26 whose hole diameter is larger than the guide diameter of the needle 1 on the downstream side of the fuel flow from the spring accommodation chamber 25 that accommodates the needle spring 5. Yes. In addition, a plurality of injection holes 27 communicating with a concave sac chamber provided at the downstream side of the fuel flow from the fuel reservoir chamber 26 are provided at the tip of the nozzle body 2.
Here, the fuel reservoir chamber 26 is provided in an intermediate portion of the needle accommodation hole. The fuel pressure introduced into the fuel reservoir chamber 26 is a valve opening direction oil pressure (FO) that acts as a biasing force that biases the needle 1 in the valve opening direction.
The plurality of injection holes 27 are provided on the downstream side in the fuel flow direction with respect to the seat portion (valve seat) on which the valve portion of the needle 1 can be seated, and communicate with the inside and outside of the needle accommodation hole. That is, the plurality of nozzle holes 27 communicate the combustion chamber of the engine cylinder with the inside of the nozzle body 2.

  The needle 1 is a valve member of a fuel injection valve, and is accommodated in the needle accommodation hole so as to be reciprocally movable. On the tip end side in the axial direction of the needle 1, a valve portion is provided that closes and opens the plurality of injection holes 27 in contact with and away from the needle seat surface of the nozzle body 2. Further, on the proximal end side in the axial direction of the needle 1, there is provided a sliding portion (small diameter portion: hereinafter referred to as piston portion) 28 that can reciprocate with respect to the hole wall surface of the guide hole (cylinder hole) of the nozzle cylinder 8. ing. On the end surface of the piston portion 28 is provided a housing recess that houses a part of the control plate spring 7 and forms a part of the pressure control chamber 14.

An annular step is provided between the piston portion 28 of the needle 1 and the needle axial direction portion (medium diameter portion).
The needle spring 5 is a needle biasing means (elastic member) that generates a biasing force (elastic force, spring set load: Fsp) that biases the needle 1 in the valve closing direction. The needle spring 5 is disposed in a compressed state in the nozzle axial direction between an annular spring seat 29 fixed to the outer periphery of the middle diameter portion of the needle 1 and an annular end surface (spring seat portion) of the nozzle cylinder 8. It is a compression coil spring.

Here, the pressure control chamber 14 is surrounded by the upper end surface (base end side end surface) of the needle 1 in the axial direction, the bottom surface of the recess on the base end side of the needle 1, the inner peripheral surface of the nozzle cylinder 8, and the control plate 6. It is space. The fuel pressure introduced into the pressure control chamber 14 is a valve closing direction hydraulic pressure (FC) that acts on the needle 1 as a biasing force that biases the needle 1 in the valve closing direction.
The pressure control chamber 14 is a variable volume space formed between the valve-closing pressure receiving surface of the control plate 6 and the pressure receiving surface of the piston portion 28 of the needle 1. The fuel pressure introduced into the pressure control chamber 14 is a valve closing direction hydraulic pressure (FC) that acts on the control plate 6 as a biasing force that biases the control plate 6 in the valve closing direction.

Next, the high-pressure introduction passage and the fuel discharge passage of the injector will be briefly described with reference to FIGS.
The high pressure introduction flow path includes a first high pressure introduction flow path for supplying high pressure fuel introduced from the inlet port of the injector body 4 to the plurality of injection holes 27 via the fuel reservoir chamber 26, and the first high pressure introduction flow. A second high-pressure introduction flow path that branches from the passage and introduces high-pressure fuel into the pressure control chamber 14 via the control valve chamber 13 is provided.

The first high pressure introduction flow path is a high pressure flow path hole 31 to 33 communicating with the inlet port and the needle accommodation hole, a fuel flow path formed between the outer peripheral surface of the nozzle cylinder 8 and the hole wall surface of the needle accommodation hole ( Clearance) 34, a fuel flow path 35 that communicates the fuel flow path 34 and the fuel reservoir chamber 26, a fuel flow path 36 that communicates the fuel reservoir chamber 26 and the plurality of nozzle holes 27, and the like.
The fuel flow path 35 is an annular flow path formed between the outer peripheral surface of the needle 1 and the hole wall surface of the needle accommodation hole. The fuel flow path 36 is formed in the needle housing hole, and an annular fuel flow path formed between the needle seat surface of the nozzle body 2 and the valve portion of the needle 1 when the injector is opened, A sac chamber that communicates the fuel flow path and the plurality of nozzle holes 27 is included.

The second high pressure introduction flow path includes a high pressure fuel passage capable of introducing high pressure fuel from the outside of the injector to the pressure control chamber 14 via the control valve chamber 13, a common flow path communicating with the control valve chamber 13, and the common flow path And a pressure control chamber 14 are provided, and a non-throttle flow path that does not restrict the flow rate of the flowing fuel is provided.
The high-pressure fuel passage includes high-pressure passage holes 31 to 33, an annular high-pressure communication passage 41 communicating with the high-pressure passage holes 31 to 33 and the fuel passage 34, and a high-pressure passage hole 42 communicating with the high-pressure communication passage 41. The in-orifice hole 43 communicates with the high-pressure channel hole 42.

The in-orifice hole 43 is an inlet-side throttle hole that regulates the flow rate of high-pressure fuel introduced into the pressure control chamber 14 via the control valve chamber 13. The in-orifice hole 43 is provided upstream of the control valve chamber 13, the pressure control chamber 14 and the flow passage gap 48 in the fuel flow direction. The in-orifice hole 43 is arranged in series with the control valve chamber 13 and the common flow path hole 45.
The control valve chamber 13 is introduced into the pressure control chamber 14 on the wall surface of the control valve chamber 13, and the low pressure port 16 communicating the control valve chamber 13 with the low pressure fuel passage through which fuel flows from the pressure control chamber 14 to the low pressure side of the fuel system. A high-pressure port 18 that communicates with the high-pressure fuel passage through which the high-pressure fuel flows and the control valve chamber 13 and a communication port 19 that always communicates with the pressure control chamber 14 through the common flow path hole 45 are formed.

The shared flow path has a shared flow path hole 45 and the like that communicates the communication port 19 opened at the wall surface of the control valve chamber 13 and the flow path without restriction. The common flow path hole 45 is a common flow path for allowing fuel to flow into and out of the pressure control chamber 14, and is always in communication with the control valve chamber 13. That is, the common flow path hole 45 is a flow path hole through which high-pressure fuel introduced from the control valve chamber 13 to the pressure control chamber 14 flows during low-pressure sealing of the control valve. The common channel hole 45 is a channel hole through which the fuel flowing out from the pressure control chamber 14 to the control valve chamber 13 flows when the control valve is sealed at high pressure.
The non-throttle flow path is an introduction flow path that introduces high-pressure fuel from the common flow path hole 45 to the pressure control chamber 14, bypassing a flow path with a throttle that will be described later, and a flow path gap 48 that communicates with the common flow path hole 45. , And a communication channel 49 that communicates the channel gap 48 with the pressure control chamber 14.
The channel gap 48 includes an annular groove formed (recessed) on the valve seat surface of the orifice plate 10.

The fuel discharge channel includes a throttled channel, a common channel hole 45, a control valve chamber 13, a low-pressure fuel channel, and an outlet port that throttle the flow rate of the fuel that passes through the high-pressure fuel introduced into the pressure control chamber 14. This is a fuel return path for flowing out to the low pressure side of the fuel system.
The throttled flow path of the fuel discharge flow path has a flow path hole 51 communicating with the pressure control chamber 14, an out-orifice hole 52 communicating with the flow path hole 51, and the like.

The low-pressure fuel passage includes a low-pressure passage hole 54 communicating with the low-pressure port 16, a spring accommodating chamber 55 communicating with the low-pressure passage hole 54, a plurality of radial communication holes 56 communicating with the spring accommodating chamber 55, and these A low-pressure flow path 57 that communicates the radial communication hole 56 and the outlet port is provided.
The out-orifice hole 52 is an outlet-side throttle hole that is installed upstream of the control valve chamber 13 in the fuel flow direction and regulates the flow rate of fuel flowing out from the pressure control chamber 14 to the common flow path hole 45. is there. The out orifice hole 52 is formed on the central axis of the control plate 6. The upstream end of the low-pressure port 16 opens at the bottom surface (top surface) of the concave control valve chamber 13.

The nozzle cylinder 8 has an inner peripheral wall surface that forms a communication channel 49 (such as a communication groove extending in the nozzle axis direction) that communicates the common channel hole 45 and the pressure control chamber 14 with the outer periphery of the control plate 6. Have. The inner peripheral wall surface of the nozzle cylinder 8 is provided with a guide hole for supporting the piston portion 28 of the needle 1 so as to be reciprocally slidable and supporting the control plate 6 so as to be reciprocally movable.
The nozzle cylinder 8 is connected to the joint portion of the orifice plate 10 by welding. The nozzle cylinder 8 is disposed so as to protrude from the coupling portion of the orifice plate 10 into the needle accommodation hole.

  The nozzle cylinder 8 is integrally provided with an annular step which is opposed to the annular step on the outer periphery of the needle 1 with a predetermined axial distance (needle maximum lift amount) therebetween. This annular step constitutes a needle stopper for restricting further movement when the needle 1 is fully lifted. The nozzle cylinder 8 is integrally provided with an annular step which is opposed to the valve seat surface of the orifice plate 10 with a predetermined axial distance (plate accommodation chamber) therebetween. This annular step constitutes a valve stopper for restricting further movement when the control plate 6 is fully lifted.

The valve body 9 is sandwiched between the contact surface of the nozzle body 2 and the contact surface of the injector body 4 together with the orifice plate 10.
The valve body 9 is formed with a high-pressure channel hole 32 that communicates the high-pressure channel hole 31 of the injector body 4 with the high-pressure channel hole 33 of the orifice plate 10. The valve body 9 is formed with a control valve chamber 13 that movably accommodates the control valve 11 and the valve spring 12. Further, the valve body 9 is formed with a through hole 58 that communicates with the spring accommodating chamber 55 of the injector body 4 and the control valve chamber 13 through the low pressure port 16 and extends straight in the plate thickness direction of the valve body 9. ing.
The control valve chamber 13 is a concave groove that opens from the lower end surface of the valve body 9 and extends from the opening side to the back side.

The orifice plate 10 is formed with a valve seat surface (valve seat) 59 that faces the flow passage gap 48 and on which the control plate 6 can be seated.
The orifice plate 10 is formed with a high-pressure channel hole 33 that communicates the high-pressure channel hole 32 of the valve body 9 and the fuel channel 34 of the nozzle body 2. Further, a common flow path hole 45 extending straight in the thickness direction of the orifice plate 10 is formed through the central axis of the orifice plate 10. The orifice plate 10 is formed with a high-pressure flow path hole 42, an in-orifice hole 43, and a high-pressure port 18 that communicate the high-pressure communication path 41 and the control valve chamber 13.

  The upstream end of the high-pressure channel hole 42 opens at the lower end surface of the orifice plate 10 shown in the figure. The downstream end of the high-pressure port 18 opens at the upper end surface of the orifice plate 10 shown in the figure. Further, the upstream end or the downstream end of the common flow path hole 45 opens at the upper end surface of the orifice plate 10 shown in the figure, and communicates with the control valve chamber 13. Further, the downstream end or the upstream end of the common channel hole 45 opens at the lower end surface (valve seat surface 59) of the orifice plate 10 and communicates with the channel gap 48 or the out-orifice hole 52.

Next, details of the actuator 3 will be briefly described with reference to FIGS. 1 to 3.
The actuator 3 includes a piezoelectric element laminate formed by laminating a large number of piezoelectric elements extending and contracting in the axial direction by charge and discharge of electric charges, a cylindrical insulating sleeve (case) for protecting the piezoelectric element laminated body, And insulating substrates provided at both ends in the axial direction of the piezoelectric element laminate. The actuator 3 is configured such that a piezo drive signal (piezo applied voltage or piezo drive current) is applied between a pair of piezo lead terminals from a piezo drive circuit (EDU: not shown).

  When a voltage is applied from the EDU to the piezoelectric element stack in response to an injector valve opening drive command (injection start command) given from the ECU to the EDU, the actuator 3 charges the piezoelectric element stack. Is charged. In response to an injector valve closing drive command (injection end command) given from the ECU to the EDU, the actuator 3 stops the piezo element stack when the voltage application from the EDU to the piezo element stack is stopped (energization stop OFF). Charges are discharged from the body.

Here, in the injector provided with the piezoelectric element laminate, the actuator 3 and the control valve 11 are provided for the purpose of compensating for the shortage of the displacement amount (extension amount) with respect to the magnitude of the driving force, which is a feature of the piezoelectric element laminate. A displacement enlarging mechanism is provided between the piezoelectric piston 21 and the valve piston 22 so that the extension displacement of the actuator 3 is enlarged and transmitted to the valve piston 22 in accordance with the pressure receiving area ratio between the piezoelectric piston 21 and the valve piston 22.
The displacement enlarging mechanism includes a piezo piston (large diameter piston) 21 that moves integrally with the actuator 3 in response to expansion / contraction displacement (extension / contraction) of the actuator 3, and a valve piston (small diameter piston) that is connected to the control valve 11 so as to be able to reciprocate integrally. ) 22 and an oil tight chamber 23 filled with hydraulic oil (fuel). The displacement enlarging mechanism is configured such that the valve piston 22 indirectly drives the control valve 11 in the substantially same direction as the displacement direction of the actuator 3.

The displacement enlarging mechanism includes drive transmission members 61 and 62 that transmit the extension displacement of the actuator 3 to the piezo piston 21, a piezo spring 63 in which a thin metal plate having a large number of slit holes is formed into a cylindrical shape, the piezo piston 21 and the valve piston 22. And a displacement transmitting member that transmits the displacement of the valve piston 22 to the control valve 11 and switches the control valve 11 from the low pressure seat (state) side to the high pressure seat (state) side. (Hereinafter referred to as a displacement transmission pin) 65.
The displacement enlarging mechanism increases the displacement of the actuator 3 and the piezo piston 21 (reducing the driving force) and increases the displacement of the actuator 3 and the piezo piston 21 by increasing the fuel pressure (oil pressure) in the oil-tight chamber 23 due to the extension displacement of the actuator 3. The control valve 11 is switched and driven by the displacement of the valve piston 22.

  The piezo piston 21 is driven together with the drive transmission members 61 and 62 toward one side (tip side) in the axial direction of the piezo accommodation hole when the actuator 3 is energized (ON). The piezo piston 21 has a piston sliding portion that can reciprocate with respect to the hole wall surface of the guide hole (large diameter cylinder hole) of the piston cylinder 64. The illustrated lower end surface of the piston sliding portion is an annular piezo-side pressure receiving surface that receives the oil pressure in the oil tight chamber 23.

The valve piston 22 is driven toward the distal end side in the axial direction of the piezoelectric housing hole when the actuator 3 is energized (ON). The valve piston 22 includes a piston sliding portion that can reciprocate with respect to a hole wall surface of a guide hole (small diameter cylinder hole) of the piston cylinder 64, a piston shaft portion that extends from the piston sliding portion to one end side, and An annular flange 66 is provided on the outer periphery of the tip of the piston shaft. The illustrated upper end surface of the piston sliding portion is an annular valve side pressure receiving surface that receives the oil pressure in the oil tight chamber 23.
The pressure receiving area of the valve piston 22 is smaller than the pressure receiving area of the piezo piston 21.

The oil tight chamber 23 is an annular space surrounded by the piezoelectric side pressure receiving surface of the piezoelectric piston 21, the valve side pressure receiving surface of the valve piston 22, and the inner peripheral surface of the piston cylinder 64.
The valve piston spring 24 is a coil spring that generates a biasing force (Fsp) that biases the valve piston 22 in the valve opening direction of the control valve 11. The valve piston spring 24 is a compression coil spring disposed in a state of being compressed in the axial direction between a spring seat portion on the back side of the spring accommodating chamber 55 and a flange portion 66 (spring seat portion) of the valve piston 22. is there.

The piezo spring 63 is a slit spring that is installed between the outer peripheral protrusion 67 of the piezo piston 21 and an annular ring member 68 fixed to the piston cylinder 64 and applies a preset load to the piezo element stack. The piezo spring 63 is installed in the low pressure flow path 57 of the injector body 4.
In order to prevent the piston cylinder 64 from sticking due to the volume change (breathing action) of the lower end side of the valve piston 22 and the spring accommodating chamber 55 that accommodates the valve piston spring 24 when the actuator 3 is expanded and contracted, For the purpose of securing a hydraulic oil supply path in the spring accommodating chamber 55 from the outside of the cylindrical peripheral wall of the piezo piston 21, a plurality of radial communication holes 56 communicating with the inside and the outside of the cylindrical peripheral wall are formed. That is, the plurality of radial communication holes 56 communicate with the low-pressure channel 57. Note that the low-pressure channel 57 communicates with the outlet port of the injector body 4.

The displacement transmission pin 65 has a substantially cylindrical shape and is installed so as to penetrate the through hole 58 of the valve body 9. The upper end side of the displacement transmission pin 65 in the figure protrudes into the spring accommodating chamber 55 from the upper end face in the figure of the valve body 9, and the upper end face in the figure is in direct contact with the distal end surface of the flange 66 of the valve piston 22. In contact. Further, the lower end side of the displacement transmission pin 65 in the figure protrudes into the control valve chamber 13 of the valve body 9, and the lower end face in the figure directly contacts or contacts the bottom surface of the concave groove of the control valve 11 of the control valve. ing.
The displacement transmission pin 65 transmits the displacement of the valve piston 22 in the valve opening direction, that is, the driving force to the one side in the axial direction by the displacement enlarging mechanism to the control valve 11 of the control valve, and the flange 66 of the valve piston 22. The urging force of the valve piston spring 24 applied to the control valve 11 is transmitted to the control valve 11. That is, the valve piston 22 forcibly opens the control valve 11 via the displacement transmission pin 65.

Next, the details of the control valve of the three-way valve structure of this embodiment will be briefly described with reference to FIGS.
The control valve includes a control valve 11 that is forcibly opened by the valve piston 22 via a displacement transmission pin 65, a valve spring 12 that urges the control valve 11 in the valve closing direction, and the like. The body 9 is accommodated in the control valve chamber 13 so as to be reciprocally movable.
The control valve 11 communicates the high pressure port 18 with the communication port 19 and blocks the communication between the low pressure port 16 and the communication port 19, communicates the low pressure port 16 with the communication port 19, and communicates with the high pressure port 18. It is a valve body that selectively switches between a high-pressure seal state that blocks communication of the communication port 19.

The control valve 11 is in contact with and separated from the low pressure seat surface 15 of the valve body 9 to open and close the low pressure port 16, and the high pressure port 18 is in contact with and separated from the high pressure seat surface 17 of the orifice plate 10. A high pressure side valve portion (second valve body) 72 that opens and closes, a flange portion (large diameter portion) 74 that is provided on the back side (the lower side in the drawing) of the low pressure side valve portion 71 and serves as a working surface of the valve spring 12, Further, it has a valve shaft portion (small diameter portion) 75 or the like that protrudes from the back side (the lower side in the drawing) of the flange portion 74 and has an outer diameter smaller than that of the flange portion 74.
A sliding portion (surface) that can slide back and forth with respect to the hole wall surface of the guide hole (cylinder hole) of the valve body 9 may be provided on the outer periphery of the flange portion 74. In this case, a guide hole is provided in the hole wall surface of the valve body 9 to support the sliding portion of the flange portion 74 so as to be able to reciprocate.

The low-pressure side valve portion 71 has a low-pressure seal surface having a planar shape (or a convex curved surface shape (partial spherical surface)) seated on the low-pressure seat surface 15. The low pressure side valve portion 71 protrudes upward in the figure from the center portion of the flange portion 74.
The high-pressure side valve portion 72 has a planar high-pressure seal surface that is seated on the high-pressure seat surface 17. The high-pressure side valve portion 72 is provided on the lower end surface of the valve shaft portion 75 in the axial direction.
The low-pressure seat surface 15 is disposed opposite to the high-pressure seat surface 17 with a predetermined axial distance (height dimension of the control valve chamber 13). Further, the low pressure side valve portion 71 and the high pressure side valve portion 72 are respectively provided at both ends of the control valve 11 in the axial direction (reciprocating direction).

The valve spring 12 is accommodated in the control valve chamber 13 so as to be reciprocally movable. This valve spring 12 generates a biasing force (Fsp) that biases the control valve 11 in a direction to switch the control valve 11 from the high pressure seat (state) side to the low pressure seat (state) side. Means (elastic member).
Further, the valve spring 12 is disposed in a state compressed in the axial direction between the spring seat portion on the back side of the control valve chamber 13 of the valve body 9 and the flange portion 74 (spring seat portion) of the control valve 11. It is a compression coil spring.

Here, the control valve is forcibly switched from the low-pressure seat side to the high-pressure seat side (valve opening drive) by the valve piston 22 that receives the extension displacement of the actuator 3 when the actuator 3 is energized (the valve spring 12 of the valve spring 12). Pushed down against the force).
As a result, the low pressure side valve portion 71 is separated (lifted) from the low pressure seat surface 15 to open the low pressure port 16, and the high pressure side valve portion 72 is seated (seat) on the high pressure seat surface 17 to close the high pressure port 18. As a result, the fuel in the pressure control chamber 14 passes through the flow path hole 51, the out orifice hole 52, the common flow path hole 45, the control valve chamber 13, and the fuel system via the low pressure fuel passage such as the low pressure port 16. Allow to flow to the low pressure side. As a result, the fuel pressure in the pressure control chamber 14 quickly decreases, and when the fuel pressure in the pressure control chamber 14 decreases to the needle valve opening pressure (Po), the needle 1 starts the valve opening operation and the cylinder of the engine High pressure fuel is injected into the combustion chamber.

The control valve is switched from the high-pressure seat side to the low-pressure seat side (valve-closing drive) by the urging force of the valve spring 12 when the energization of the actuator 3 is stopped.
As a result, the low pressure side valve portion 71 is seated (seat) on the low pressure seat surface 15 to close the low pressure port 16, and the high pressure side valve portion 72 is separated (lifted) from the high pressure seat surface 17 to open the high pressure port 18. As a result, the high-pressure fuel is introduced into the pressure control chamber 14 from the high-pressure port 18 through the control valve chamber 13, the common channel hole 45, the channel gap 48 and the communication channel 49. As a result, the fuel pressure in the pressure control chamber 14 rises quickly, and when the fuel pressure in the pressure control chamber 14 recovers to the needle valve closing pressure (Pc), the needle 1 starts the valve closing operation, and the engine cylinder The fuel injection into the combustion chamber ends.

  Next, details of the control plate 6 of this embodiment will be briefly described with reference to FIGS. Here, the injector of the present embodiment includes a first fuel path (FL1) through which fuel flows out from the pressure control chamber 14 to the common flow path hole 45 via the flow path hole 51 and the out orifice hole 52, and the common flow path. A second fuel path (FL2) for introducing high-pressure fuel from the hole 45 to the pressure control chamber 14 via the flow path gap 48 and the communication flow path 49 and bypassing the flow path hole 51 and the out-orifice hole 52; When fuel flows out from the control chamber 14 to the common flow path hole 45, the fuel path in the injector is switched to the first fuel path (FL1), and when high pressure fuel is introduced from the common flow path hole 45 into the pressure control chamber 14 And a pressure-actuated control plate 6 for switching the fuel path in the injector to the second fuel path (FL2).

  The control plate 6 corresponds to a “switching valve” in the claims. The control plate 6 is a flat plate valve having a predetermined thickness, and is formed above the pressure control chamber 14 (between the valve seat surface 59 of the orifice plate 10 and the annular step of the nozzle cylinder 8). It is accommodated in a space (plate accommodation chamber) so as to be reciprocally movable. Further, the control plate 6 has a difference in vertical pressure received by the control plate 6, that is, a fuel pressure (upper pressure) in the common flow path hole 45 (or flow path gap 48) and a fuel pressure (lower part) in the pressure control chamber 14. This is a floating valve (plate) that reciprocates in the axial direction of the injector (the vertical direction in the figure) in accordance with the pressure difference from the pressure.

The upper end surface of the control plate 6 shown in the figure is in close contact with the valve seat surface 59 of the orifice plate 10 or opposed with a predetermined flow passage gap 48 therebetween, and the fuel pressure in the common flow passage hole 45 (or the flow passage gap 48) is controlled. A valve-opening pressure receiving surface for receiving pressure is provided. A valve-side pressure receiving surface that faces the pressure control chamber 14 and receives the fuel pressure in the pressure control chamber 14 is provided on the lower end surface of the control plate 6 in the figure. In addition, a flow path hole 51 and an out orifice hole 52 are formed through the central axis of the control plate 6.
The channel hole 51 is opened at the lower end surface of the control plate 6 shown in the figure. Further, the out-orifice hole 52 is opened at the upper end surface of the control plate 6 in the figure.
The flow path gap 48 is a variable volume space formed between the valve-opening pressure receiving surface of the control plate 6 and the valve seat surface 59 of the orifice plate 10. The fuel pressure introduced into the flow path gap 48 is a valve opening direction oil pressure (FO) that acts on the control plate 6 as a biasing force that biases the control plate 6 in the valve opening direction.

The control plate spring 7 is accommodated in the pressure control chamber 14 together with the control plate 6. The control plate spring 7 is an elastic member that generates a biasing force (elastic force, spring set load) that biases the control plate 6 in the valve closing direction of the control plate 6.
The control plate spring 7 is compressed in the axial direction between the valve-closing pressure receiving surface (spring seat portion) of the control plate 6 and the bottom surface (spring seat portion) on the back side of the accommodation recess of the needle 1. It is a compression coil spring arranged.

  In the injector of the present embodiment, the valve opening direction oil pressure (FU) received by the valve opening side pressure receiving surface of the control plate 6 is the valve closing direction oil pressure (FL) received by the valve closing side pressure receiving surface of the control plate 6. When the resultant force is larger than the resultant force of the control plate spring 7 in the valve closing direction (Fsp), the control plate 6 is detached from the valve seat surface 59 of the orifice plate 10. At this time, a flow passage gap 48 through which the high-pressure fuel introduced from the common flow passage hole 45 can flow is formed between the upper end surface of the control plate 6 and the valve seat surface 59 of the orifice plate 10.

  Further, in the injector, the valve opening direction oil pressure (FU) received by the valve opening side pressure receiving surface of the control plate 6 is the valve closing direction oil pressure (FL) received by the valve closing side pressure receiving surface of the control plate 6 and the control plate. When the resultant force is smaller than the resultant force with the biasing force (Fsp) in the valve closing direction of the spring 7, the illustrated upper end surface (valve portion) of the control plate 6 is seated (contacted) on the valve seat surface 59 of the orifice plate 10. At this time, the pressure control chamber 14 and the common flow path hole 45 communicate with each other through the flow path hole 51 and the out orifice hole 52.

[Operation of Example 1]
Next, the operation of the injector of this embodiment will be briefly described with reference to FIGS.

  Here, in the injector of this embodiment, the throttle diameter is set so that the flow rate of the in-orifice hole 43 (in-orifice flow rate) is larger than the flow rate of the out-orifice hole 52 (out-orifice flow rate). Yes. As a result, the rate of increase of the fuel pressure in the pressure control chamber 14 at the time of the low pressure seat of the control valve is higher than the rate of decrease of the fuel pressure in the pressure control chamber 14 at the time of the control valve high pressure seat (control chamber pressure The slope of the waveform and injection rate waveform is steep).

When the engine is started, high pressure is applied from the high pressure part of the fuel system such as a supply pump or common rail to the inside of the injector (high pressure fuel passage) via the high pressure pipe (high pressure fuel supply pipe) and the inlet port of the injector body 4. The fuel is introduced.
A part of the high-pressure fuel introduced into the injector passes from the inlet port of the injector body 4 to the fuel reservoir chamber 26 and the fuel channel 36 through the high-pressure channel holes 31 to 33 and the fuel channels 34 and 35. To reach.

Here, when no voltage is applied to the piezoelectric element laminate of the actuator 3 and the control valve 11 is urged toward the low-pressure seat by the urging force of the valve spring 12 and the high-pressure port 18 is opened, the high-pressure port 18 is opened. The remainder of the fuel branches off from the branch portion (high-pressure communication passage 41) between the high-pressure passage holes 32 and 33, and the high-pressure passage hole 42, the in-orifice hole 43, the high-pressure port 18, the control valve chamber 13, and the common passage hole. 45, reaching the channel gap 48.
At this time, since the control valve 11 closes the low pressure port 16, the outflow of fuel from the pressure control chamber 14 to the low pressure side of the fuel system via the low pressure fuel passage is stopped. As a result, the fuel pressure (valve opening direction oil pressure: FO) in the common channel hole 45 and the channel gap 48 is changed between the fuel pressure in the pressure control chamber 14 (valve closing direction oil pressure: FC) and the control plate spring 7. And the resultant force (valve closing direction biasing force: Fsp).

As a result, the control plate 6 is lifted (detached) from the valve seat surface 59 of the orifice plate 10, and a predetermined flow path gap 48 is formed between the control plate 6 and the illustrated upper end surface. That is, the control plate 6 opens, and the fuel path in the injector is switched to the first fuel path (FL1).
At this time, the high-pressure fuel that has reached the common channel hole 45 is introduced into the channel gap 48 from the common channel hole 45. Since the high-pressure fuel introduced into the flow passage gap 48 is introduced into the pressure control chamber 14 through the flow passage gap 48 and the communication flow passage 49, the fuel pressure in the pressure control chamber 14 (valve closing direction). Oil pressure (FC) increases.

Further, the needle 1 has a fuel pressure in the fuel reservoir chamber (valve opening direction oil pressure: FO), a fuel pressure in the pressure control chamber 14 (valve closing direction oil pressure: FC), and a spring set of the needle spring 5. A load (valve closing direction urging force: Fsp) is acting, and FO <FC + Fsp is established.
As a result, no voltage is applied to the piezoelectric element laminate of the actuator 3, and the control valve 11 is urged toward the low pressure seat by the urging force of the valve spring 12 to close the low pressure port 16 and open the high pressure port 18. Since the valve portion of the needle 1 is seated (seat) on the needle seat surface of the nozzle body 2 during the low pressure seat state, the cylinder that communicates the fuel reservoir chamber 26 with the plurality of injection holes 27 The fuel flow path 36 is cut off.

Therefore, in the injector, since the needle 1 maintains the valve closed state, fuel injection into the combustion chamber of the cylinder of the engine is not performed.
The fuel pressure (valve opening oil pressure: FO) in the common channel hole 45 and the channel gap 48 and the fuel pressure (valve closing oil pressure: FC) in the pressure control chamber 14 are balanced. Regardless of the presence or absence of the control plate spring 7, the control plate 6 moves in the valve closing direction while being guided by the guide hole of the nozzle cylinder 8 and is seated (seat) on the valve seat surface 59 of the orifice plate 10. Thereby, the flow path gap 48 between the illustrated upper end surface of the control plate 6 and the valve seat surface 59 is eliminated (or narrowest). That is, the control plate 6 is closed, and the fuel path in the injector is switched to the second fuel path (FL2).

When it becomes the injection timing of the injector of the cylinder of the engine and the application of voltage to the piezo element stack of the actuator 3 is started by the injector valve opening drive command from the ECU, the piezo element stack is charged. When the piezo charging energy reaches a predetermined value, the piezo element stack starts to be extended and displaced to one side in the axial direction. Accordingly, the piezo piston 21 is driven to one side in the axial direction via the drive transmission members 61 and 62.
As described above, when the piezoelectric element stack of the actuator 3 is extended and displaced, the volume of the oil-tight chamber 23 is reduced and the fuel pressure (oil pressure) in the oil-tight chamber 23 is increased as the piezo piston 21 moves (displaces). To do. When the oil pressure in the oil tight chamber 23 rises, the valve piston 22 is assisted by the urging force of the valve piston spring 24 while being substantially in the same direction as the displacement direction of the actuator 3, that is, the control valve 11 is opened. Driven in the valve direction.

And since the displacement transmission pin 65 is contact | abutting at the front-end | tip of the valve piston 22, according to the movement (displacement) of the valve piston 22, the displacement transmission pin 65 pushes down the control valve 11 of a control valve.
For this reason, since the control valve 11 is forcibly opened by the valve piston 22, the low pressure side valve portion 71 of the control valve 11 separates (lifts) from the low pressure seat surface 15, and the high pressure side valve of the control valve 11 The part 72 is seated (seat) on the high-pressure seat surface 17. As a result, the low pressure port 16 is opened and the high pressure port 18 is closed.

On the other hand, since the control plate 6 maintains the valve closed state, the fuel in the pressure control chamber 14 passes through the flow path hole 51 and the out-orifice hole 52 provided on the central axis of the control plate 6, and the orifice. It flows into the common channel hole 45 of the plate 10.
The fuel that has flowed into the common channel hole 45 flows into the control valve chamber 13 of the valve body 9. The fuel that has flowed into the control valve chamber 13 flows into the low pressure passage hole 54 from the low pressure port 16.
Then, the fuel that has flowed into the low pressure passage hole 54 flows out of the injector from the outlet port through the spring accommodating chamber 55, the plurality of radial communication holes 56, and the low pressure passage 57 to the low pressure side of the fuel system. Discharged.

Thereafter, if FO> FC + Fsp is established, the fuel pressure in the fuel reservoir chamber 26 (valve opening direction oil pressure: FO) is changed between the fuel pressure in the pressure control chamber 14 (valve closing direction oil pressure: FC) and the needle spring 5. It exceeds the resultant force with the spring set load (valve closing direction biasing force: Fsp). That is, when the fuel pressure in the pressure control chamber 14 decreases to the needle valve opening pressure (Po), the needle 1 starts to rise (lift) by the fuel pressure in the fuel reservoir chamber 26.
As a result, since the needle 1 is separated (lifted) from the needle seat surface, the needle 1 is opened, and fuel injection from the plurality of injection holes 27 into the combustion chamber of the engine cylinder is started.

Thereafter, when an injector valve opening period (a command injection period calculated from the fuel injection amount and the command injection pressure in the ECU, which corresponds to the energization period for the actuator 3) elapses from the injection timing, the injection end timing is reached. Outputs an injector valve closing drive command.
When the voltage application from the EDU to the piezo element stack is stopped (energization stop OFF) in response to the injector valve closing drive command, the electric charge is discharged from the piezo element stack. Along with this, the piezoelectric element stack is contracted and displaced, and the piezoelectric piston 21 and the drive transmission members 61 and 62 are pushed back by the urging force of the piezoelectric spring 63.

Further, in the injector, when the actuator 3 is contracted and displaced, the piezo piston 21 is returned to the initial position, so that the volume of the oil-tight chamber 23 is expanded and the oil pressure in the oil-tight chamber 23 is reduced (dropped). When the oil pressure in the oil tight chamber 23 decreases, the valve piston 22 resists the urging force of the valve piston spring 24 and is substantially in the same direction as the displacement direction of the actuator 3, that is, the control valve 11 is closed. Driven in the direction. That is, as the oil pressure in the oil tight chamber 23 decreases, the control valve 11, the valve piston 22 and the displacement transmission pin 65 are pushed back (pushed up) by the urging force of the valve spring 12.
Accordingly, the low pressure side valve portion 71 of the control valve 11 is seated (seat) on the low pressure seat surface 15, and the high pressure side valve portion 72 of the control valve 11 is separated (lifted) from the high pressure seat surface 17. Thereby, the low pressure port 16 is closed and the high pressure port 18 is opened.

As described above, when the low pressure side valve portion 71 of the control valve 11 closes the low pressure port 16, the outflow of fuel from the pressure control chamber 14 to the low pressure side of the fuel system via the control valve chamber 13. Stops.
On the other hand, since the high-pressure side valve portion 72 of the control valve 11 opens the high-pressure port 18, the high-pressure fuel introduced into the high-pressure flow path holes 31 to 33 from the outside of the injector flows into the high-pressure communication path 41, the high-pressure flow. The upper end surface of the control plate 6 is reached from the passage hole 42, the in-orifice hole 43, the high-pressure port 18, the control valve chamber 13, and the common flow path hole 45.
As a result, the fuel pressure (valve opening direction oil pressure: FO) in the common channel hole 45 and the channel gap 48 is changed between the fuel pressure in the pressure control chamber 14 (valve closing direction oil pressure: FC) and the control plate spring 7. And the resultant force (valve closing direction biasing force: Fsp).

As a result, the control plate 6 is lifted (detached) from the valve seat surface 59 of the orifice plate 10, and a predetermined flow path gap 48 is formed between the control plate 6 and the illustrated upper end surface. That is, the control plate 6 opens, and the fuel path in the injector is switched to the first fuel path (FL1).
At this time, the high-pressure fuel that has reached the common channel hole 45 is introduced into the channel gap 48 from the common channel hole 45. Since the high-pressure fuel introduced into the flow passage gap 48 is introduced into the pressure control chamber 14 through the flow passage gap 48 and the communication flow passage 49, the fuel pressure in the pressure control chamber 14 (valve closing direction). Oil pressure (FC) recovers rapidly.

Then, the vertical pressure difference of the needle 1 decreases, and FO <FC + Fsp is established. That is, when the fuel pressure in the pressure control chamber 14 recovers to the needle valve closing pressure (Pc), the needle 1 moves in the valve closing direction and the valve portion of the needle 1 is seated on the needle seat surface of the nozzle body 2 (seat). To do.
Therefore, the cylindrical fuel flow path 36 that communicates the fuel reservoir chamber 26 and the plurality of injection holes 27 is blocked, so that the fuel injection from the injection holes 27 of the injector into the combustion chamber of the engine cylinder ends.

[Effect of Example 1]
As described above, in the injector of the present embodiment, the control valve having a three-way valve structure for increasing / decreasing the fuel pressure in the pressure control chamber 14 and the control plate 6 that opens / closes (switches) according to the vertical pressure difference. And.
The control valve includes a control valve 11 that is driven by using the expansion and contraction displacement of the actuator 3, and a valve spring 12 that biases the control valve 11 toward the low-pressure seal side, closes the low-pressure port 16, and high-pressure port. The low-pressure seal state in which 18 is opened and the high-pressure seal state in which the low-pressure port 16 is opened and the high-pressure port 18 is closed are selectively switched.

The control plate 6 bypasses the out-orifice hole 52 from the pressure control chamber 14 and the first fuel path (FL1) through which the fuel flows out from the pressure control chamber 14 through the out-orifice hole 52 to the common flow path hole 45. The second fuel path (FL2) through which fuel flows out to the common flow path hole 45 is switched.
When a voltage is applied (energized ON) to the piezoelectric element laminate of the actuator 3, the control valve 11 is detached from the low pressure seat surface 15 to open the low pressure port 16, and the control valve 11 is seated on the high pressure seat surface 17. The high pressure port 18 is closed (high pressure sealed state).
When the control valve 11 of the control valve is switched to the high-pressure seal state in this way, the fuel passes from the pressure control chamber 14 via the common flow path hole 45, the control valve chamber 13, the low-pressure fuel passage (53 to 56), and the outlet port. The fuel flows out to the low pressure side of the system, and the fuel pressure in the pressure control chamber 14 decreases.

When fuel flows from the pressure control chamber 14 to the control valve chamber 13 through the common flow path hole 45, the control plate 6 is seated on the valve seat surface 59 of the orifice plate 10 and the control plate 6 is closed. Therefore, the fuel path in the injector is switched to the first fuel path (FL1). Then, the fuel flowing out from the pressure control chamber 14 to the common flow path hole 45 side goes to the common flow path hole 45 side via the flow path hole 51 and the out orifice hole 52 of the control plate 6. As a result, the fuel flowing out from the pressure control chamber 14 to the control valve chamber 13 via the common flow path hole 45 passes through the out orifice hole 52, so that the valve opening speed of the needle 1 is defined by the out orifice hole 52. Set by the fuel flow rate.
When the fuel pressure in the pressure control chamber 14, that is, the fuel pressure acting on the needle 1 in the valve closing direction, drops to the needle opening pressure (Po), the needle 1 opens (lifts) and the cylinder of the engine Fuel injection into the combustion chamber is started.

Here, in the injector of the present embodiment, the out orifice hole 52 is provided in the control plate 6 located on the upstream side of the control valve chamber 13, and the control plate 6 is disposed in the pressure control chamber 14. The hydraulic control chamber volume for storing fuel pressure acting in the valve closing direction on the needle 1 is from the upper end surface of the sliding portion 28 of the needle 1 and the bottom surface of the accommodating recess (the pressure receiving surface of the needle 1) to the out-orifice hole 52. It becomes a volume and becomes much smaller than the conventional injector.
That is, since the hydraulic control chamber volume is reduced, the pressure pulsation in the pressure control chamber 14 that occurs when the control valve 11 of the control valve is switched from the low pressure seal state to the high pressure seal state can be reduced. Moreover, even if the out-orifice flow rate is increased, the pressure pulsation in the pressure control chamber 14 is reduced for the purpose of improving the valve opening response of the needle 1 by reducing the fuel pressure in the pressure control chamber 14 at high speed. be able to.
Therefore, it is possible to suppress the needle 1 from lifting while undulating during the needle valve opening operation. Thereby, since the valve opening operation of the needle 1 is stabilized from the start of the lift to the full lift, the deterioration of the controllability of the needle 1 and the deterioration of the control accuracy of the injection amount can be suppressed.

On the other hand, when voltage application to the piezoelectric element laminate of the actuator 3 is stopped (energization stop OFF), the control valve 11 is seated on the low pressure seat surface 15 to close the low pressure port 16 and the control valve 11 is closed to the high pressure seat. The high pressure port 18 is released from the surface 17 (low pressure sealed state).
When the control valve is switched to the low pressure seal state in this way, the high pressure fuel is introduced from the high pressure port 18 to the pressure control chamber 14 via the control valve chamber 13 and the common flow path hole 45, and the fuel in the pressure control chamber 14. Pressure rises (recovers).

When the fuel is introduced from the control valve chamber 13 into the pressure control chamber 14 via the common flow path hole 45, the control plate 6 is pushed down by the fuel pressure in the common flow path hole 45. That is, since the control plate 6 is detached from the valve seat surface 59 of the orifice plate 10 and the control plate 6 is opened, the fuel path in the injector is switched to the second fuel path (FL2). Then, the high-pressure fuel introduced from the control valve chamber 13 into the pressure control chamber 14 via the common flow path hole 45 bypasses the out orifice hole 52 and is introduced into the pressure control chamber 14.
As a result, the fuel introduced from the control valve chamber 13 into the pressure control chamber 14 via the common flow path hole 45 does not pass through the out-orifice hole 52, so that the valve closing speed of the needle 1 is controlled by the high-pressure port 18. The fuel flow rate (the fuel flow rate defined by the in-orifice hole 43) flowing through the valve chamber 13 and the common flow path hole 45 is set.
Therefore, the valve opening speed of the needle 1 and the valve closing speed of the needle 1 can be set independently.

[Configuration of Example 2]
4 and 5 show a piezo injector (Embodiment 2) to which the fuel injection valve of the present invention is applied.
Here, the same reference numerals as those in the first embodiment indicate the same configuration or function, and the description thereof is omitted.

The injector of the present embodiment includes out-orifice holes 52 and 53 that regulate the flow rate of fuel flowing out from the pressure control chamber 14 to the low-pressure fuel passages (53 to 57) through the common flow path hole 45 and the control valve chamber 13. ing.
The out-orifice hole 52 is a first outlet-side throttle hole (located upstream of the communication port 19 of the control valve chamber 13 in the fuel flow direction and between the flow path hole 51 and the common flow path hole 45 ( Main out orifice hole, first out orifice). The out-orifice hole 52 communicates the flow path hole 51 and the shared flow path hole 45. Further, the out-orifice hole 52 is formed on the central axis of the control plate 6.

The out-orifice hole 53 is a second outlet-side throttle hole (sub-portion) installed downstream of the low-pressure port 16 of the control valve chamber 13 in the fuel flow direction and between the low-pressure port 16 and the low-pressure channel hole 54. Out orifice hole, second out orifice). The out orifice hole 53 communicates the low pressure port 16 and the low pressure flow path hole 54.
Here, in the injector of this embodiment, the throttle diameter is set so that the flow rate of the out-orifice hole 53 (sub-out orifice flow rate) is larger than the flow rate of the out-orifice hole 52 (main out-orifice flow rate). Has been.

  Further, in the injector of this embodiment, since the out-orifice hole 53 is provided between the low pressure port 16 of the control valve chamber 13 and the low pressure passage hole 54 of the low pressure fuel passage, the control valve is opened and controlled. When the valve 11 is switched from the low-pressure seal state to the high-pressure seal state, at the moment when the low-pressure side valve portion 71 of the control valve 11 is separated (lifted) from the low-pressure seat surface 15 of the valve body 9, High pressure fuel flows into the low pressure port 16 located through an annular clearance between the outside surface of the control valve 11 and the wall surface of the control valve chamber 13. In this way, a constant pressure can be maintained in the low pressure port 16 immediately above the low pressure side valve portion 71 of the control valve 11, so that the control valve 11 is biased in the direction of the high pressure port 18 (high pressure seal state) ( (Assistance: assist), and the high-pressure seat load on the control valve 11 of the control valve can be reduced.

As a result, the switching operation from the low-pressure seal state to the high-pressure seal state in the control valve 11 of the control valve is accelerated, so that the valve opening timing of the needle 1 is accelerated.
On the other hand, since a constant pressure can be maintained in the low pressure port 16 immediately above the low pressure side valve portion 71 of the control valve 11, a rapid pressure drop in the control valve chamber 13 at the initial stage of fuel injection can be suppressed. Thereby, an effect of suppressing pressure pulsation in the pressure control chamber 14 is provided.
As described above, the injector of the present embodiment has the same effects as those of the first embodiment.

[Configuration of Example 3]
6 and 7 show a piezo injector (Embodiment 3) to which the fuel injection valve of the present invention is applied.
Here, the same reference numerals as those in the first and second embodiments indicate the same configuration or function, and the description thereof will be omitted.

The injector of the present embodiment eliminates the in-orifice hole 43 of the first and second embodiments. The common flow path of the injector includes a common flow path hole 45 communicating with the communication port 19 opened at the wall surface of the control valve chamber 13, and an in (common) orifice hole (hereinafter referred to as an orifice hole) communicating with the common flow path hole 45. 46, and a common channel hole 47 that communicates the orifice hole 46 with a channel without throttle or a channel with throttle.
The orifice hole 46 is connected to the control valve chamber 13, the communication port 19, the common channel hole 45, the orifice hole 46, the common channel hole 47, the channel gap 48, and the communication channel 49 from the high pressure port 18. This is an inlet-side throttle hole that regulates the flow rate of high-pressure fuel introduced into the control chamber 14. The orifice hole 46 is a second outlet that regulates the flow rate of fuel flowing out from the pressure control chamber 14 to the low pressure side of the fuel system through the common flow path hole 45, the control valve chamber 13, and the low pressure fuel passages (54 to 57). It is a side throttle hole. In this case, the out-orifice hole 52 is a first outlet-side throttle hole.

  Here, in the injector of this embodiment, the throttle diameter is set so that the passage flow rate (in (common) orifice flow rate) of the orifice hole 46 is larger than the passage flow rate (out orifice flow rate) of the out orifice hole 52. Has been. As a result, the rate of increase of the fuel pressure in the pressure control chamber 14 at the time of the low pressure seat of the control valve is higher than the rate of decrease of the fuel pressure in the pressure control chamber 14 at the time of the control valve high pressure seat (control chamber pressure The slope of the waveform and injection rate waveform is steep).

When the control valve is a high pressure seat, the fuel flows out from the pressure control chamber 14 through the out orifice hole 52 and the orifice hole 46 to the low pressure side of the fuel system. For this reason, since the double restriction is made when the control valve is at a high pressure, the fuel pressure in the pressure control chamber 14 on the upstream side of the out orifice hole 52 and the common flow path hole 47 on the downstream side of the out orifice hole 52 are reduced. The amount of pressure change between fuel pressure (amount of decrease, pressure difference) is smaller than that in the first embodiment. Further, by providing the out-orifice hole 52 between the pressure control chamber 14 and the orifice hole 46, the volume of the fuel discharge flow path from the pressure control chamber 14 to the orifice hole 46 is divided into two. As a result, the hydraulic control chamber volume that stores the fuel pressure acting in the valve closing direction on the needle 1 is changed from the upper end surface of the sliding portion 28 of the needle 1 and the bottom surface of the accommodating recess (the pressure receiving surface of the needle 1) to the out orifice hole. It becomes a volume up to 52 and becomes very small. Therefore, the pressure pulsation in the pressure control chamber 14 generated when the control valve 11 of the control valve is switched from the low pressure seal state to the high pressure seal state can be further reduced.
As described above, the injector of the present embodiment has the same effects as those of the first and second embodiments.

[Configuration of Example 4]
FIG. 8 shows a piezo injector (Embodiment 4) to which the fuel injection valve of the present invention is applied.
Here, the same reference numerals as in the first to third embodiments indicate the same configuration or function, and the description thereof is omitted.

The injector of the present embodiment includes a control valve having a three-way valve structure movably accommodated in a control valve chamber 13 formed between the concave groove of the valve body 9 and the upper end surface of the orifice plate 10 in the figure. Yes.
The wall surface of the valve body 9 is formed with a truncated cone (taper) cylindrical low pressure seat surface 15 on which the low pressure side valve portion 71 of the control valve 11 of the control valve can be seated (seat). A low-pressure port 16 communicating with the low-pressure channel hole 54 through the out-orifice hole 53 is formed in the concave groove extending from the back side of the low-pressure seat surface 15, that is, from the ceiling surface of the control valve chamber 13. Yes.
A planar high pressure seat surface 17 on which the high pressure side valve portion 72 of the control valve 11 can be seated (seat) is formed on the upper end surface of the orifice plate 10 in the figure. A high-pressure port 18 that communicates with the high-pressure channel hole 42 through the in-orifice hole 43 is formed at the center of the high-pressure sheet surface 17.

The control valve includes a control valve 11 that is forcibly opened by the valve piston 22 via a displacement transmission pin 65, a valve spring 12 that urges the control valve 11 in the valve closing direction, and the like. The body 9 is accommodated in the control valve chamber 13 so as to be reciprocally movable.
The control valve 11 includes a low pressure side valve portion 71, a high pressure side valve portion 72, a flange portion 74, a valve shaft portion 75, and the like.
The low pressure side valve portion 71 has a low pressure sealing surface having a convex curved surface (partial spherical surface) that is seated on the low pressure seat surface 15.
The high-pressure side valve portion 72 has a planar high-pressure seal surface that is seated on the high-pressure seat surface 17.
As described above, the injector of the present embodiment has the same effects as those of the first to third embodiments.
The structure of the control valve 11 of the control valve of this embodiment and the structure of the low pressure seat surface 15 of the control valve chamber 13 may be incorporated in the first to third embodiments.

[Configuration of Example 5]
FIG. 9 shows a piezo injector (Embodiment 5) to which the fuel injection valve of the present invention is applied.
Here, the same reference numerals as in the first to fourth embodiments indicate the same configuration or function, and the description thereof is omitted.

The injector according to the present embodiment transmits the displacement of the valve piston 22 to the control valve 11 as a displacement transmission member for switching the control valve 11 from the low pressure seat (state) side to the high pressure seat (state) side. An integrated displacement transmission pin 81 is provided.
The displacement transmission pin 81 includes a cylindrical shaft portion having a smaller outer diameter than the piston shaft portion (large shaft portion) and the flange portion 66 of the valve piston 22, and a columnar small shaft portion having a smaller outer diameter than the middle shaft portion. And a frustoconical connecting portion that gradually decreases in outer diameter from the middle shaft portion toward the small shaft portion. The displacement transmission pin 81 has a truncated cone-shaped low-pressure passage hole 54 that communicates the low-pressure port 16 of the control valve chamber 13 of the valve body 9 and the low-pressure port 16 and the spring accommodating chamber 55 that accommodates the valve piston spring 24. It is housed so that it can reciprocate inside.

In the case of the injector of the present embodiment, the low pressure passage hole 54 of the low pressure fuel passage has the same function as in the first to fourth embodiments (inside the pressure control chamber 14), although it has a simple shape compared to the first to fourth embodiments. A fuel discharge function for allowing the introduced high-pressure fuel to flow out to the low-pressure side of the fuel system through the common flow path hole 45, the control valve chamber 13, and the low-pressure fuel passage can be achieved, so that the cost of the injector can be reduced. be able to.
As described above, the injector of the present embodiment has the same effects as those of the first to fourth embodiments.
Note that the structure of the valve piston 22 and the structure of the fuel outflow passage of this embodiment may be incorporated in the first to fourth embodiments.

[Modification]
In this embodiment, a control valve that opens and closes (switches) the control plate 6 in accordance with the vertical pressure difference is employed as the switching valve of the present invention. However, the control plate 6 is switched as the switching valve of the present invention. An actuator to be operated may be provided, and the switching valve may be switched by a driving force of the actuator in accordance with a switching command from an engine control unit (electronic control unit: ECU) at a predetermined switching timing.

  In the present embodiment, a piezo-stacked body that expands and contracts in the axial direction by charge and discharge is assumed as the actuator 3 that opens and drives the control valve 11 that is a valve body of a control valve that controls increase and decrease of the fuel pressure in the pressure control chamber 14. However, an actuator that uses a solenoid actuator, an electric actuator, a magnetostrictive element, or the like as a drive source may be used as the actuator that opens or closes the valve body of the control valve.

  In this embodiment, as the fuel injection valve of the present invention, a fuel injection valve (injector) of a type in which a plurality of injection holes 27 are opened and closed by the needle 1 accommodated in the nozzle body 2 so as to be able to reciprocate is adopted. As a fuel injection valve of the present invention, a variable injection hole type fuel injection in which a plurality of first and second injection holes are opened and closed in stages by two first and second needles accommodated in a nozzle body 2 so as to be reciprocally movable. A valve (injector) may be employed.

Further, as the internal combustion engine (engine), a gasoline engine may be used instead of the diesel engine.
Further, the fuel supply path for supplying the fuel stored in the fuel tank to the fuel injection valve (injector) of the internal combustion engine via the supply pump is the fuel supply upstream of the pressurizing chamber of the supply pump. Refers to the route.
The fuel injection valve of the present invention may be applied to a fuel injector that injects fuel into a cylinder of an internal combustion engine (engine) such as a gasoline engine or an intake port communicating with the cylinder.

1 Needle 6 Control plate (switching valve)
7 Control plate spring (switching valve)
11 Control valve (control valve)
12 Valve spring (control valve)
13 Control valve chamber 14 Pressure control chamber 16 Low pressure port (low pressure fuel passage)
18 High pressure port (High pressure fuel passage)
45 Common channel hole

Claims (12)

(A) a needle (1) for opening and closing a nozzle hole (27) for injecting fuel into a cylinder of the internal combustion engine;
(B) a control chamber (14) for storing fuel pressure acting in a valve closing direction on the needle (1);
(C) a common flow path (45 to 47) through which fuel flows into and out of the control chamber (14);
(D) A communication port (19) that always communicates with the control chamber (14) via the shared flow path (45-47), and a high-pressure fuel passage (31) through which high-pressure fuel introduced into the control chamber (14) flows. To 34, 41 to 43), and a low pressure port (16) communicating with the low pressure fuel passage (53 to 57) through which fuel flows out from the control chamber (14) to the low pressure side of the fuel system. A control valve chamber (13) having:
(E) A control valve (11) which is accommodated in the control valve chamber (13) and selectively switches between communication and blocking between the high pressure port (18) or the low pressure port (16) and the communication port (19). 12)
In the fuel injection valve for controlling the opening and closing operation of the needle (1) by adjusting the fuel pressure in the control chamber (14) by switching the control valve (11, 12),
The fuel injection valve is installed upstream of the control valve chamber (13) in the fuel flow direction, communicates the control chamber (14) and the shared flow path (45-47), and An out-orifice (52) for regulating the flow rate of fuel flowing out from the control chamber (14) to the common flow path (45-47);
A first path (FL1) for allowing fuel to flow out from the control chamber (14) to the shared flow path (45-47) via the out orifice (52);
A second path (FL2) for introducing fuel from the common flow path (45-47) to the control valve chamber (13) by bypassing the out orifice (52);
A fuel injection valve comprising a switching valve (6, 7) for switching between the first path (FL1) and the second path (FL2). The fuel injection valve according to claim 1, wherein
The fuel injection valve is installed upstream of the control valve chamber (13) in the fuel flow direction, and controls the flow rate of fuel flowing through the high-pressure fuel passages (31-34, 41-43). A fuel injection valve comprising an orifice (43). The fuel injection valve according to claim 2,
The fuel injection valve is characterized in that a throttle diameter is set so that the in-orifice (43) is larger than the flow rate through the out-orifice (52). In the fuel injection valve according to any one of claims 1 to 3,
The fuel injection valve, wherein the switching valve (6, 7) is installed in the control chamber (14) so as to be capable of switching operation. In the fuel injection valve according to any one of claims 1 to 4,
The fuel injection valve, wherein the out orifice (52) is installed in the switching valve (6, 7). In the fuel injection valve according to any one of claims 1 to 5,
The switching valve is configured to introduce fuel from the control valve chamber (13) into the control chamber (14) via the shared flow path (45 to 47) and to transfer the shared flow from the control chamber (14). A fuel injection valve comprising a pressure-actuated control plate (6) for switching and controlling the discharge of fuel to the control valve chamber (13) via a passage (45-47). The fuel injection valve according to any one of claims 1 to 6,
The fuel injection valve is installed on the downstream side in the fuel flow direction with respect to the first out orifice (52) as the out orifice and the control valve chamber (13), and the low pressure fuel passages (53 to 57). And a second out orifice (53) for regulating the flow rate of the fuel flowing through the fuel injection valve. The fuel injection valve according to claim 7,
The fuel injection valve is characterized in that the throttle diameter is set so that the passage flow rate of the second out orifice (53) is larger than the passage flow rate of the first out orifice (52). Fuel injection valve. The fuel injection valve according to any one of claims 1 to 8,
The control valve communicates the high-pressure port (18) and the communication port (19) and shuts off the communication between the low-pressure port (16) and the communication port (19), and the low-pressure port ( 16) and a valve body (11) that selectively switches between a high-pressure seal state that communicates with the communication port (19) and blocks the communication between the high-pressure port (18) and the communication port (19). A fuel injection valve characterized by comprising: The fuel injection valve according to any one of claims 1 to 9,
The fuel injection valve communicates the valve body (11) of the control valve with the high pressure port (18) and the communication port (19), and communication between the low pressure port (16) and the communication port (19). Is switched from a low pressure seal state that shuts off the high pressure port (16) to the communication port (19) and a high pressure seal state that shuts off the communication between the high pressure port (18) and the communication port (19). A fuel injection valve comprising an actuator (3) for generating a driving force to be driven. The fuel injection valve according to claim 10, wherein
The fuel injection valve according to claim 1, wherein the control valve includes an elastic member (12) that urges the valve body (11) to a side for switching from the high-pressure seal state to the low-pressure seal state. The fuel injection valve according to claim 10 or 11,
The actuator (3) has a piezo element laminate that expands and contracts due to charge and discharge of electric charge.

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