JP2005076571A - Injector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure stable actuation by reducing dynamic pressure generated at a return passage at the time of injection, and reducing force acting to a valve piston in a valve closing direction. <P>SOLUTION: This injector comprises a control chamber 5 to apply pressure to a nozzle needle 51 in a valve closing direction, and a three-way valve 4 to switch connection/disconnection between a high pressure fuel passage 11 and the return passage 12. The valve piston 3 is driven by a piezo stack 20 to push down the three-way valve 4, when dynamic pressure generated at the return passage 12 is absorbed by a dynamic pressure reducing means 8 having a volume-changeable chamber 81 having a movable wall 82 for a chamber wall. Application of the dynamic pressure to the valve piston 3 is thus restricted. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an injector that is used in, for example, a common rail fuel injection device of a diesel engine and injects fuel at a high pressure.

  In a diesel engine, a common rail fuel injection system that accumulates high-pressure fuel on a common rail common to each cylinder is known. In the injector for the common rail fuel injection system, for example, a control chamber whose pressure is controlled by a control valve is provided on the back of the nozzle needle that opens and closes the nozzle hole, and the nozzle is moved up and down by driving the control valve by an actuator. Yes. In this configuration, the fuel from the common rail is introduced into the fuel passage of the injector and supplied to the nozzle hole, while it is introduced into the control chamber having the rear end surface of the nozzle needle as the chamber wall, and the nozzle needle is closed in the valve closing direction. Used as control oil to apply pressure.

As the actuator, a piezo actuator having good response can be used (for example, Patent Document 1). Since the piezo actuator has a very small displacement, a large-diameter piezo piston that moves up and down as the piezo actuator expands and contracts and a small-diameter valve piston that drives the control valve are provided. A displacement magnifying mechanism has been proposed that is provided with a displacement magnifying chamber filled with hydraulic oil. When this displacement magnifying mechanism is used, the displacement due to the expansion of the piezo actuator is converted into hydraulic pressure and then amplified according to the diameter difference between the large and small pistons, so that the amount of displacement necessary to drive the control valve can be efficiently obtained. Can be obtained.
JP 2001-140727 A

  A control valve having a three-way valve structure is preferably used as the control valve. The three-way valve described in Patent Document 1 includes valve bodies that can be respectively seated on a low-pressure seat leading to a low-pressure passage or a high-pressure seat leading to a common rail, and the communication between the control chamber and the low-pressure passage or the high-pressure passage is switched depending on the seating position. Yes. In addition, if common rail pressure is introduced into the displacement expansion chamber and the pressure receiving areas of the small-diameter piston and the three-way valve seat are made equal, the force generated by the hydraulic pressure is always canceled, and the three-way valve can be operated with a small driving force even at high pressures. It can be activated.

  In the injector configured as described above, when the piezo actuator is driven, the three-way valve is separated from the low-pressure seat by being pushed by the valve piston. As a result, the control chamber communicates with the return passage, the control chamber pressure decreases, the nozzle needle rises, and fuel is injected from the nozzle. In order to end the injection, the drive of the actuator is stopped and the three-way valve is seated on the low pressure seat to restore the control chamber pressure.

  However, when the three-way valve is separated from the low-pressure seat at the start of fuel injection, high-pressure fuel flows out from the control chamber to the return passage at a very high speed, so that a large dynamic pressure is generated in the return passage. Due to this dynamic pressure, a force in the three-way valve closing direction acts on the valve piston, and the three-way valve may fail to open and injection may become unstable. In addition, the piezo injector has a problem that since the lift speed of the valve piston is high, overshoot vibration occurs after full lift, and the injection amount cannot be obtained linearly with respect to the command value in a region where the injection command value is short. .

  The present invention reduces the dynamic pressure generated in the return passage during injection, reduces the force acting on the valve piston in the valve closing direction, ensures stable operation, and suppresses overshoot vibration and the like. The purpose is to provide a high performance and reliable injector.

  The injector according to claim 1 of the present invention is driven by an actuator, a control chamber for applying pressure in the valve closing direction to the nozzle needle, a three-way valve for switching communication / blocking between the control chamber and the high pressure passage and the low pressure passage. A piston member that separates the three-way valve from the low-pressure seat surface that reaches the low-pressure passage, and the nozzle needle is opened when the control chamber and the low-pressure passage communicate with each other. And it is provided in the middle of the low pressure passage, and comprises a dynamic pressure reducing means for reducing the dynamic pressure generated in the low pressure passage by changing the volume according to the pressure of the fluid flowing out from the control chamber to the low pressure passage. Is.

  If dynamic pressure is generated in the low-pressure passage by the fluid flowing out from the control chamber to the low-pressure passage at high speed, the piston member may receive a force in the valve closing direction and the operation may become unstable. Accordingly, the dynamic pressure reducing means can be installed to absorb the dynamic pressure, and the dynamic pressure can be prevented from acting on the piston member. Therefore, the operation of the piston member is stable, and a highly reliable injector having stable injection performance can be realized.

  According to a second aspect of the present invention, the dynamic pressure reducing means has a variable volume chamber communicating with the low pressure passage, and the fluid flowing out from the control chamber when the three-way valve is separated from the low pressure seat surface. The volume is changed according to the pressure.

  Specifically, the above effect can be obtained by providing a variable volume chamber communicating with the low pressure passage and changing the volume according to the pressure of the fluid flowing out of the control chamber.

  According to a third aspect of the present invention, the dynamic pressure reducing means includes a variable volume chamber communicating with the low pressure passage and a movable wall constituting a part of the chamber wall.

  In the above-described configuration, when dynamic pressure is generated in the low-pressure passage, the movable wall moves to expand the volume of the variable volume chamber and reduce the dynamic pressure.

  According to a fourth aspect of the present invention, the variable volume chamber and the air chamber are provided adjacent to each other inside the screw member screwed into the end face of the injector body, and the chamber wall that divides both chambers is provided. Is the movable wall.

  More specifically, the dynamic pressure reducing means can be provided inside a screw member that is separate from the injector body, which is advantageous because the injector body can be made smaller.

  According to a fifth aspect of the present invention, the piston member is hollow, the interior thereof is partitioned into the volume-variable chamber and the air chamber communicating with the low-pressure passage, and the chamber wall that divides both chambers is defined as the movable wall. To do.

  If the dynamic pressure reducing means is provided inside the piston member, the dynamic pressure can be quickly reduced and the injector body can be downsized.

  According to a sixth aspect of the present invention, a spring that urges the movable wall in a direction of reducing the volume of the variable volume chamber is housed in the air chamber.

  Specifically, the movable wall is configured to be supported by a spring, and the spring force is appropriately set, whereby the movable wall can be moved according to the return pressure, and the dynamic pressure can be effectively reduced.

  According to a seventh aspect of the present invention, the dynamic pressure reducing means is composed of a variable volume chamber communicating with the low pressure passage and a diaphragm constituting a part of the chamber wall.

  Alternatively, a chamber having a deformable chamber wall such as a diaphragm may be provided to provide the above-described variable volume chamber. Also in this case, the dynamic pressure can be effectively reduced by deforming the diaphragm in the direction of expanding the volume in accordance with the return pressure.

  According to an eighth aspect of the present invention, the three-way valve is provided with a chamber for applying a pressure in the direction of seating on the low pressure seat surface, and a communication hole is provided for communicating the chamber with the upstream portion of the low pressure passage.

  If it does in this way, the dynamic pressure of the above-mentioned low-pressure passage will act in the direction which applies a brake to the above-mentioned three-way valve in a lift, and it can control overshoot and can reduce injection quantity fluctuation.

  In the invention according to claim 9, the actuator is a piezo actuator.

  Piezo actuators have good responsiveness and excellent controllability, so a higher performance injector can be realized.

Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an injector according to the present invention. The injector of the present invention is used, for example, for a common rail fuel injection system of a diesel engine, is provided corresponding to each cylinder of the engine, and is supplied with fuel from a common rail. The common rail stores fuel (light oil) pumped by a high-pressure supply pump at a predetermined high pressure corresponding to the injection pressure.

  In FIG. 1, an injector has a body 1 attached to a combustion chamber wall (not shown). In the body 1, components of each part of the injector are housed, and a high-pressure fuel passage 11 communicating with a common rail (not shown), A passage such as a return passage 12 is formed as a low pressure passage communicating with a fuel tank (not shown).

  The injector slidably holds a stepped nozzle needle 51 in a vertical hole 53 formed in the lower end portion of the body 1. An annular oil reservoir chamber 13 is formed on the outer periphery of the lower half small diameter portion of the nozzle needle 51, and high-pressure fuel from the common rail is always supplied to the oil reservoir chamber 13 through the high-pressure fuel passage 11. Below the vertical hole 53, a sack portion is formed continuously therewith, and a nozzle 14 for fuel injection is formed through the sack portion forming wall.

  When the nozzle needle 51 is at the lower end position, the conical tip is seated on the seat surface 15 provided at the boundary between the sack portion and the vertical hole 53, and the fuel supply from the oil reservoir 13 to the nozzle 14 is shut off. The nozzle needle 51 rises and separates from the seat surface 15, and fuel is injected.

  A space defined by the upper end surface of the nozzle needle 51 and the wall surface of the vertical hole 53 is a control chamber 5 that applies back pressure to the nozzle needle 51. Fuel as control oil is introduced into the control chamber 5 through the balance three-way valve 4 and the main orifice 61 and from the high-pressure fuel passage 11 through the sub-orifice 62, and the back pressure of the nozzle needle 51 is reduced. It has occurred. This back pressure acts downward on the nozzle needle 51 to urge the nozzle needle 51 in the seating direction together with the spring needle 52 housed in the control chamber 5. On the other hand, the high-pressure fuel in the oil sump chamber 13 acts upward on the outer peripheral portion from the seat surface 15 of the nozzle needle 51 to urge the nozzle needle 51 in the seating direction.

  In a vertical hole formed in the upper half of the body 1, a piezo stack 20 as a piezo actuator, a large-diameter piezo piston 2, and a small-diameter valve piston 3 are coaxially arranged in order from the top. The piezo stack 20 is a typical capacitor structure in which piezoelectric ceramic layers such as PZT and electrode layers are alternately stacked to form a capacitor structure. The stacking direction, that is, the vertical direction, is an expansion / contraction direction, and is charged / discharged by a drive circuit (not shown). It is like that. A constant initial load is applied to the piezo stack 20 by a spring piezo 21 provided on the outer periphery of the upper end of the piezo piston 2. As a result, the piezo piston 2 moves up and down as the piezo stack 20 expands and contracts.

  The large-diameter piezo piston 2 and the small-diameter valve piston 3 are slidably held in a cylinder provided in a vertical hole. The valve piston 3 is in contact with the upper end of the three-way valve 4 at the lower end of the small diameter, and is filled with fuel between the piezo piston 2 and the valve piston 3 to form a displacement expansion chamber 22. Accordingly, when the piezo stack 20 extends and presses the piezo piston 2, the pressing force is transmitted to the valve piston 3 through the fuel in the displacement expansion chamber 22, and the valve piston 3 is urged downward to cause the three-way valve 4 to move. It comes to press.

  Here, since the valve piston 3 has a smaller diameter than the piezo piston 2, the extension amount of the piezo stack 20 is expanded and converted into a vertical displacement of the valve piston 3. Thus, the two large and small pistons 2 and 3 and the displacement expansion chamber 22 function as a hydraulic displacement expansion mechanism.

  The balance three-way valve 4 (hereinafter referred to as the three-way valve 4) is selectively seated on the low-pressure seat surface 41 that opens to the ceiling surface of the valve chamber 44 or the high-pressure seat surface 42 that opens to the bottom surface. The pressure in the control chamber 5 that is always in communication with the valve chamber 44 is increased or decreased. The low-pressure seat surface 41 and the high-pressure seat surface 42 are provided at positions opposed to the center portion of the ceiling surface and the bottom portion of the valve chamber 44, and the low-pressure seat surface 41 communicates with the return passage 12 following the spill passage 31. Communicates with the high pressure fuel passage 11 following the passage 32.

  The three-way valve 4 is a pressure balance type structure having a sliding portion below the large-diameter valve portion 43, the upper end portion serving as the valve portion 43 is located in the valve chamber 44, and the lower end sliding portion 42 is a high pressure. It slides in the cylinder following the seat surface 42. A passage 32 leading to the high-pressure fuel passage 11 is opened in an annular space around the small diameter portion connecting the valve portion 43 and the sliding portion.

  When the valve portion 43 of the three-way valve 4 is at the upper end position where the valve portion 43 is seated on the low pressure seat surface 41, the high pressure fuel passage 11 following the high pressure seat surface 42 communicates with the control chamber 5. When the valve portion 43 is at the lower end position where the valve portion 43 is seated on the high pressure seat surface 42, the return passage 12 following the low pressure seat surface 41 communicates with the control chamber 5. As the operating state of the three-way valve 4 is switched in this way, the pressure in the control chamber 5 communicating with the valve chamber 44, that is, the back pressure of the nozzle needle 51 increases or decreases.

  The three-way valve 4 has substantially the same sliding portion diameter as that of the low pressure seat surface 41 and the high pressure seat surface 42, and acts on the hydraulic pressure and the sliding portion acting upward on the valve portion 43 (in the direction away from the high pressure seat surface 42). The hydraulic pressure acting downward (in the direction of separating from the low-pressure seat surface 41) is substantially balanced. As a result, the drive energy required for the piezo stack 20 when the piezo stack 20 is extended to displace the three-way valve 4 downward can be reduced. In addition, if the upper end surface outer peripheral portion of the three-way valve 4 is not a flat surface but an inclined surface, the seat position is stabilized. Further, if the center of the upper end surface is made to be substantially spherical and brought into contact with the valve piston 3, the shaft deviation can be absorbed.

  A spring chamber 7 that houses a spring valve 71 is provided below the three-way valve 4, and the three-way valve 4 is biased upward by the spring valve 71. The spring chamber 7 communicates with the return passage 12 immediately after the spill passage 31 via the communication passage 72. In this manner, the downward movement of the three-way valve 4 is not suppressed at the start of injection, the valve portion 43 is quickly separated from the low-pressure seat surface 41, and the three-way valve 4 is introduced by introducing the return pressure. The effect of suppressing the vibration of the piezo piston 2 can be obtained during full lift.

  In the present embodiment, dynamic pressure reducing means 8 for reducing the dynamic pressure generated in the return passage 12 is provided in a holo screw type member 85 as a screw member screwed to the upper end surface of the body 1. The dynamic pressure reducing means 8 has a variable volume chamber 81 connected to the upper end portion of the return passage 12, an air chamber 83 adjacent to the chamber 81, and a movable wall 82 partitioning both chambers. The spring 84 accommodated in the air chamber 83 is urged toward the variable volume chamber 81. The low-pressure passage 121 branched from the connection portion between the return passage 12 and the variable volume chamber 81 extends through the side of the hollow screw type member 85 to the outside. In the normal state shown in the drawing, the movable wall 82 is pressed against a stepped portion provided in the inner periphery of the hollow screw type member 85. When the pressure in the return passage 12 rises, the movable wall 82 is compressed upward. It moves to expand the volume of the variable volume chamber 81 and absorb the dynamic pressure.

  The operation of the injector having the above configuration will be described. In FIG. 1, when the piezo stack 20 is energized, the piezo stack 20 extends and pushes down the piezo piston 2 to increase the pressure in the displacement expansion chamber 22. When the valve piston 3 is moved downward by this oil pressure and the three-way valve 4 is pushed down, the valve portion 41 is separated from the low-pressure seat surface 41 and further displaced downward to be seated on the high-pressure seat surface 42. As a result, the low-pressure seat surface 41 communicating with the return passage 12 is opened, and the fuel in the control chamber 5 flows out through the main orifice 61 and the valve chamber 44, so that the pressure in the control chamber 5 drops. When the downward urging force of the nozzle needle 51 falls below the upward urging force, the nozzle needle 51 is separated from the seat surface 15 and fuel injection is started.

  On the other hand, when the piezo stack 20 is discharged, the piezo piston 2 moves upward as the piezo stack 20 contracts, the pressure in the displacement expansion chamber 22 drops, and the push-down force of the three-way valve 4 is released. As a result, the high-pressure seat surface 42 communicating with the high-pressure fuel passage 11 is opened, and the high-pressure fuel flowing into the control chamber 5 via the valve chamber 44 and the main orifice 61 and the high-pressure fuel flowing through the sub-orifice 62 are used. The control chamber 5 pressure rises again. When the downward urging force of the nozzle needle 51 exceeds the upward urging force, the nozzle needle 51 is seated and the injection ends.

  Here, as shown in FIG. 2 (a), in the conventional structure without the dynamic pressure reducing means 8, after the small-diameter valve piston 3 is displaced downward and pushes down the three-way valve 4 during fuel injection, the control chamber Since high-pressure fuel flows out of the return passage 12 at a high speed from 5, dynamic pressure is generated in the return passage 12. Further, the action of the dynamic pressure causes a return that causes the valve piston 3 to be displaced upward again, and the operation of the three-way valve 4 becomes unstable. On the other hand, in the present embodiment shown in FIG. 2B, the dynamic pressure can be absorbed by providing the dynamic pressure reducing means 8. That is, when the pressure in the return passage 12 rises, the movable wall 82 moves upward against the spring force of the spring 84 to enlarge the volume of the variable volume chamber 81 and reduce the generated dynamic pressure. As a result, it is possible to suppress the return of the valve piston 3 due to the action of the dynamic pressure, always ensure a stable operation regardless of the injection conditions, and stabilize the injection.

  Moreover, there is an advantage that the injector main body can be reduced in size by providing the dynamic pressure reducing means 8 separately from the body 1 as in the present embodiment. Further, the dynamic pressure reducing means 8 has a simple structure of a hollow screw integrated type, and is installed directly connected to the outlet of the return passage 12 from the body 1, so that the dynamic pressure is quickly reduced and stable operation is achieved. Can be realized.

  3A and 3B are diagrams showing the effect of the communication hole 72. FIG. In the conventional piezo injector structure, since the lift speed of the valve piston 3 is fast, overshoot vibration is likely to occur in the large-diameter piezo piston 2 during full lift as shown in FIG. On the other hand, as in the present embodiment shown in FIG. 3B, the spring chamber 7 below the three-way valve 4 and the upstream portion of the return passage 12 are connected by the communication hole 72 so that the return pressure is introduced into the spring chamber 7. By doing so, it is possible to apply a brake to the three-way valve 4 that is being lifted to moderate vibration during a full lift. As a result, the overshoot vibration of the piezo piston 2 can be suppressed. For example, the piston behavior during multi-injection with a short injection interval can be stabilized, and the variation in the injection amount due to the change of the injection interval can be reduced.

  FIG. 4 shows a second embodiment of the present invention. In the present embodiment, the valve piston 3 is hollow and the dynamic pressure reducing means 9 is provided. The dynamic pressure reducing means 9 includes a movable wall 93 that vertically divides the hollow portion of the valve piston 3, an air chamber 91 formed above the movable wall 93, and a variable volume oil chamber formed below the movable wall. The oil chamber 94 communicates with the return passage 12 through the communication hole 95. The movable wall 93 is biased toward the oil chamber 94 by a spring 92 accommodated in the air chamber 91.

  Even with the configuration of the present embodiment, the dynamic pressure generated in the return passage 12 during fuel injection moves the movable wall 93 upward against the spring force of the spring 92, thereby expanding the volume of the oil chamber 94. Can be reduced. As a result, it is possible to obtain the same effect that suppresses the return of the valve piston 3 due to the action of dynamic pressure and ensures a stable operation. Moreover, since the dynamic pressure reducing means 9 is provided in the valve piston 3, it is generated by opening the communication hole 95 at the upstream end of the return passage 12 following the spill passage 31 and causing high-pressure fuel to flow out during injection. The dynamic pressure can be reduced quickly. Further, since the dynamic pressure reducing means 9 does not need to be provided separately, the injector can be made smaller.

  FIG. 5 shows a third embodiment of the present invention. This embodiment is a modification of the second embodiment shown in FIG. 4, and a diaphragm 96 is installed as a chamber wall that divides the air chamber 91 and the oil chamber 94 in place of the movable wall 93 supported by the spring 92. Thus, the dynamic pressure reducing means 9 is provided. Also according to the present embodiment, the diaphragm 96 is elastically deformed and the volume of the oil chamber 94 is expanded as the pressure in the return passage 12 increases, so that the same effect can be obtained for reducing the dynamic pressure.

  As described above, according to the present invention, by providing the dynamic pressure reducing means having the variable volume chamber, the dynamic pressure generated in the return passage 12 can be reduced and stable fuel injection can be realized.

1 is an overall cross-sectional view of an injector showing a first embodiment of the present invention. (A) is a figure which shows the time change of the return pressure and small diameter piston displacement in a conventional structure, (b) is a figure which shows the time change of the return pressure and valve piston (small diameter piston) displacement in 1st Embodiment structure. (A) is a figure which shows the time change of the three-way valve lower part pressure and piezo piston (large diameter piston) displacement in a conventional structure, (b) is the three-way valve lower part pressure and piezo piston (large diameter piston) in 1st Embodiment structure. It is a figure which shows the time change of a displacement. It is a whole sectional view of an injector showing a 2nd embodiment of the present invention. It is a principal part expanded sectional view of the injector which shows the 3rd Embodiment of this invention.

Explanation of symbols

1 Body (Injector body)
11 High-pressure fuel passage (high-pressure passage)
12 Return passage (low pressure passage)
2 Piezo piston 20 Piezo stack (actuator)
21 Spring piezo 22 Displacement expansion chamber 3 Valve piston (piston member)
31 Spill passage 32 Passage 4 Balance three-way valve (three-way valve)
41 Low-pressure seat surface 42 High-pressure seat surface 43 Valve section 44 Valve chamber 5 Control chamber 51 Nozzle needle 52 Spring needle 61 Main orifice 62 Sub-orifice 7 Spring chamber 71 Spring valve 72 Communication hole 8 Dynamic pressure reducing means 81 Volume variable chamber 82 Movable Wall 83 Air chamber 84 Spring 85 Hollow screw type member (screw member)
9 Dynamic pressure reducing means 91 Air chamber 92 Spring 93 Movable wall 94 Oil chamber (variable volume chamber)
95 Communication hole 96 Diaphragm

Claims (9)

A control chamber that applies a pressure in the valve closing direction to the nozzle needle, a three-way valve that switches communication between the control chamber and the high-pressure passage and the low-pressure passage, and a low pressure that is driven by an actuator to bring the three-way valve into the low-pressure passage An injector that opens the nozzle needle when the control chamber and the low-pressure passage communicate with each other.
Dynamic pressure reducing means is provided in the middle of the low pressure passage and reduces the dynamic pressure generated in the low pressure passage by changing the volume according to the pressure of the fluid flowing out from the control chamber to the low pressure passage. Characteristic injector.   The dynamic pressure reducing means has a variable volume chamber communicating with the low pressure passage, and changes the volume according to the pressure of the fluid flowing out from the control chamber when the three-way valve is separated from the low pressure seat surface. The injector according to claim 1, wherein   3. The injector according to claim 2, wherein the dynamic pressure reducing means has a variable volume chamber communicating with the low pressure passage and a movable wall constituting a part of the chamber wall.   The variable volume chamber communicating with the low pressure passage and an air chamber are provided adjacent to each other inside a screw member screwed into an end face of the injector body, and a chamber wall that divides both chambers is the movable wall. Item 4. The injector according to Item 3.   4. The injector according to claim 3, wherein the piston member is hollow, the inside thereof is divided into the volume-variable chamber communicating with the low-pressure passage and an air chamber, and the chamber wall that divides both chambers is the movable wall. .   The injector according to claim 4 or 5, wherein a spring that urges the movable wall in a direction to reduce the volume of the variable volume chamber is accommodated in the air chamber.   The injector according to claim 2, wherein the dynamic pressure reducing means comprises a variable volume chamber communicating with the low pressure passage and a diaphragm constituting a part of the chamber wall.   The injector according to any one of claims 1 to 7, wherein a chamber for applying pressure in the seating direction of the low-pressure seat surface is provided in the three-way valve, and a communication hole is provided for communicating the chamber and the upstream portion of the low-pressure passage.   The injector according to any one of claims 1 to 8, wherein the actuator is a piezo actuator.

Images