JP2008223698A - Injector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an injector providing improved accuracy of the amount of fuel injected. <P>SOLUTION: This injector includes: a needle 10 opening/closing a nozzle port by being moved up and down; a booster chamber 21 and a back pressure chamber 22 into which fuel is introduced and also which apply pressure to the needle 10 in the opening/closing directions of the nozzle port 24; a control chamber 32 which varies differential pressure between the booster chamber 21 and the back pressure chamber 22 by the inflow/outflow of the fuel into/from the booster chamber 21 or the back pressure chamber 22 in conjunction with the expansion and contraction of a piezo actuator 30; and an orifice 51 which suppresses a fuel flow when applied in the opening direction to the needle 10 by the control chamber 32. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an injector, and more particularly to an injector used in a diesel engine.

  Conventionally, an injector using a piezoelectric actuator has been proposed (see Patent Documents 1 and 2). The piezo actuator expands and contracts when a voltage is applied, and such an injector is configured to move the needle up and down in conjunction with the expansion and contraction of the piezo actuator. Since the piezo actuator has better response than the solenoid actuator, there is an advantage that the fuel injection can be precisely controlled by adopting the piezo actuator in the injector. In particular, this is effective for diesel engines in which highly viscous light oil is used as the fuel.

JP 2000-104644 A Japanese Patent Laid-Open No. 11-200981

  FIG. 4A is a graph simply showing the characteristics of a piezo actuator employed in such an injector, with the ordinate indicating the piezo-generating force and the abscissa indicating the piezo lift amount. FIG. 4B is a graph simply showing the force required for the needle to lift in the opening direction. The vertical axis shows the force required to push up the needle, and the horizontal axis shows the lift amount of the needle.

  In order for the needle to open and reach the full lift position while suppressing an increase in size of the piezoelectric actuator when a constant voltage is applied to the piezoelectric actuator, It is necessary to set so as to form a straight line as shown in 4 (a).

On the other hand, the relationship between the force required to push up the needle and the lift amount of the needle decreases as the needle opens, as shown in FIG.
In this way, when a voltage is applied to the piezo actuator until the needle opens, while suppressing an increase in size of the piezo actuator, the full lift position is reached as soon as the needle opens. Therefore, it is difficult to realize a small amount of fuel injection by controlling the needle to the half lift position.

  Accordingly, an object of the present invention is to provide an injector with improved fuel injection amount accuracy.

The above-described object includes a needle that opens and closes a nozzle hole by raising and lowering, a pressure chamber and a back pressure chamber that introduce a fluid and act on the needle in an opening direction and a closing direction that open the nozzle hole, respectively. A differential pressure changing mechanism that changes the differential pressure between the pressurizing chamber and the back pressure chamber by the flow of the fluid into and out of the pressurizing chamber or the back pressure chamber in conjunction with expansion and contraction of the piezo actuator, and the differential pressure changing mechanism This can be achieved by an injector characterized by comprising suppression means for suppressing the flow of the fluid when acting in the opening direction with respect to the needle.
With this configuration, since the flow of the fluid acting in the opening direction with respect to the needle is suppressed, it is possible to prevent the needle from reaching the full lift immediately. Thereby, a small amount of fuel injection can be realized by controlling the needle to the half lift position.

Further, in the above configuration, the differential pressure changing mechanism includes a communication path communicating with one of the pressure increasing chamber and the back pressure chamber, a control chamber communicating with the communication path and changing in volume in conjunction with expansion and contraction of the piezoelectric actuator. The suppression means can employ a configuration including an orifice formed in the communication path.
With this configuration, the differential pressure between the pressure increasing chamber and the back pressure chamber is changed in conjunction with the volume change of the control chamber, and the flow of fluid acting in the opening direction with respect to the needle is suppressed by the orifice formed in the communication path. be able to. Therefore, a small amount of fuel can be injected with a simple mechanism.

In the above configuration, the orifice may have a configuration in which the shapes of the openings at both ends are different from each other so as to promote the flow of the fluid acting in the closing direction rather than the flow of the fluid acting in the opening direction. .
With this configuration, it is possible to suppress a decrease in the speed of the needle that shifts from the open state to the closed state. Therefore, a smaller amount of fuel injection can be realized.

Further, in the above configuration, the control chamber includes an auxiliary passage that communicates with the control chamber and one of the boost chamber and the back pressure chamber that communicates with the control chamber via the communication passage. A configuration including a check valve that allows only the flow of fluid acting in the direction can be employed.
Also with this configuration, it is possible to improve the flow of the fluid acting in the closing direction, and it is possible to suppress a decrease in the speed of the needle that shifts from the open state to the closed state.

  ADVANTAGE OF THE INVENTION According to this invention, the injector which the precision of the fuel injection quantity improved can be provided.

  Embodiments according to the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram illustrating a configuration of an injector according to an embodiment, which will be described as an application example to a common rail fuel injection device of a diesel engine.
One of the injectors provided for each cylinder of the engine is shown, and fuel (light oil) is supplied from the common rail. In the common rail, fuel pumped by the high-pressure supply pump is stored at a predetermined high pressure corresponding to the injection pressure.

  As shown in FIG. 1, the injector according to the embodiment includes a needle 10, an oil sump chamber 20, a boost chamber 21, a back pressure chamber 22, a sack portion 23, a nozzle hole 24, a piezo actuator 30, a piston 31, a control chamber 32, It comprises a supply passage 40, a communication passage 50, an orifice 51, a return passage 60, a check valve 61, and the like. Although not shown, these are integrally formed in the housing.

The needle 10 is supported so as to be movable up and down, and opens and closes the nozzle hole 24. Further, the needle 10 moves up and down by the pressure difference between the pressure increasing chamber 21 and the back pressure chamber 22.
An annular oil reservoir chamber 20 is formed on the outer periphery of the lower portion of the needle 10. The oil reservoir chamber 20 is always supplied with high-pressure fuel from the common rail 90 via the supply passage 40. A sac portion 23 is formed below the oil reservoir chamber 20, and an injection hole 24 is formed in the sac portion 23.

  A back pressure chamber 22 is formed on the upper end surface of the needle 10. The back pressure chamber 22 applies a back pressure to the needle 10. That is, the back pressure chamber 22 applies pressure to the needle 10 in the closing direction that closes the nozzle hole 24. In FIG. 1, the back pressure chamber 22 applies pressure to the needle 10 in the downward direction.

In addition, a boost chamber 21 is formed between the oil reservoir chamber 20 and the boost chamber 21. The pressurizing chamber 21 applies a pressure for raising the needle 10. That is, pressure is applied to the needle 10 in the opening direction that opens the nozzle hole 24. In FIG. 1, the pressurizing chamber 21 applies pressure to the needle 10 in the upward direction. High pressure fuel is supplied to the booster chamber 21 from the common rail 90 through the back pressure chamber 22 and the return passage 60.
The needle 10 moves up and down by changing the differential pressure between the back pressure chamber 22 and the pressure increasing chamber 21.

The piezo actuator 30 has a structure in which piezoelectric ceramic layers and electrode layers are alternately stacked, and expands and contracts in the vertical direction when a voltage is applied.
The piston 31 is arranged at the lower end of the piezo actuator 30 and moves up and down in conjunction with the expansion and contraction of the piezo actuator 30.

  The control chamber 32 is supplied with high-pressure fuel from the common rail 90 through the back pressure chamber 22, the return passage 60, and the communication passage 50. The control chamber 32 communicates with the booster chamber 21 via the communication passage 50.

  The communication passage 50 communicates with the control chamber 32 and the pressure increasing chamber 21, and the return passage 60 communicates with the back pressure chamber 22 and the communication passage 50. A check valve 61 is provided in the return passage 60. The check valve 61 allows fuel flow in the direction from the back pressure chamber 22 to the pressure increasing chamber 21 or the control chamber 32, but prevents flow in the reverse direction.

Next, the raising / lowering operation | movement of the needle 10 is demonstrated.
When the needle 10 is in the lower end position, that is, in the position shown in FIG. 1, the conical tip of the needle 10 is seated on a seat provided in the vicinity of the sack portion 23, and the sack portion 23 is closed. The supply of fuel from the oil reservoir chamber 20 to the nozzle hole 24 is shut off.

  From the state shown in FIG. 1, the piezo actuator 30 extends downward and pushes down the piston 31, whereby high-pressure fuel in the control chamber 32 is supplied into the boost chamber 21 through the communication path 50. . Further, the fuel in the back pressure chamber 22 flows into the pressure increasing chamber 21 through the return passage 60, and the volume of the back pressure chamber 22 is reduced. High pressure fuel from the back pressure chamber 22 and the control chamber 32 is supplied into the pressure increasing chamber 21.

As a result, the volume of the pressurizing chamber 21 increases, the pressure in the pressurizing chamber 21 becomes larger than the back pressure in the back pressure chamber 22, and the needle 10 moves upward. As a result, the needle 10 is separated from the seat, the sack portion 23 is opened, and the high-pressure fuel in the oil reservoir chamber 20 is ejected through the nozzle hole 24.
In addition, since the check valve 61 is formed in the return passage 60, the high-pressure fuel sent from the control chamber 32 does not return to the back pressure chamber 22.

  Next, the piezoelectric actuator 30 contracts upward, and the piston 31 receives the upward pressure of the fuel in the control chamber 32 and moves upward in conjunction with the piezoelectric actuator 30. As the piston 31 moves upward, the fuel in the pressure increasing chamber 21 flows out and flows into the control chamber 32 through the communication passage 50.

  As a result, the pressure that causes the needle 10 to act in the opening direction decreases, and the needle 10 moves in the closing direction due to the back pressure from the back pressure chamber 22. Thereby, the needle 10 is seated on the seat and the sack portion 23 is closed.

As described above, the control chamber 32 acts to change the pressure difference between the boost chamber 21 and the back pressure chamber 22 by controlling the pressure in the boost chamber 21.
Although not shown in FIG. 1, a discharge passage for discharging unnecessary fuel to the drain is provided.

Next, the orifice 51 will be described in detail.
The orifice 51 is formed in the communication path 50.
The orifice 51 suppresses the flow of fuel when acting on the needle 10 in the opening direction. That is, the flow of fuel flowing from the control chamber 32 into the pressure increasing chamber 21 is suppressed. Thereby, when the needle 10 shifts from the state in which the nozzle hole 24 is closed to the state in which the nozzle hole 24 is opened, the high-pressure fuel in the control chamber 32 flows into the pressure-increasing chamber 21, and the needle 10 is in the full lift position (upper end position) in a short time. ) Can be suppressed.

  Therefore, the needle 10 can be controlled to the half lift position (intermediate position between the upper end position and the lower end position). Thereby, the fuel ejected from the nozzle hole 24 can be reduced by a simple mechanism, and the accuracy of the fuel ejection amount is improved.

Next, the structure of the orifice 51 will be described in detail.
FIG. 2 is an explanatory diagram of the orifice 51.
As shown in FIG. 2, the orifice 51 is formed so that the opening end 51b on the boosting chamber 21 side is larger than the opening end 51a on the piezoelectric actuator 30 side.

This is because the flow of fuel that causes the needle 10 to act in the opening direction, that is, the flow rate of fuel from the control chamber 32 to the boosting chamber 21 is reduced, and the flow of fuel that causes the needle 10 to act in the closing direction, that is, the boosting chamber 21. It acts to increase the flow rate of the fuel from the engine to the control chamber 32. Thereby, the fall of the speed which moves the needle 10 in the closing direction can be prevented.
As described above, the time for moving the needle 10 in the closing direction can be made relatively earlier than the time for moving the needle 10 in the opening direction. As a result, the needle 10 can be raised to the half lift position and lowered again to the lower end position in a short time. Therefore, a small amount of fuel can be injected with a simple mechanism.

  Next, a modification of the injector will be described. In addition, about the injector which concerns on a modification, the overlapping description is abbreviate | omitted by attaching | subjecting the same code | symbol to the part same as the injector mentioned above.

FIG. 2 is a schematic diagram illustrating a configuration of an injector according to a modification.
An auxiliary passage 70 is provided in the injector according to the modification.
The auxiliary passage 70 is formed so as to communicate the control chamber 32 and the booster chamber 21. The auxiliary passage 70 also communicates with the communication passage 50 and the return passage 60.

  A check valve 71 is provided in the auxiliary passage 70. The check valve 71 allows only the flow of fuel from the boost chamber 21 to the control chamber 32 and prevents the fuel from flowing from the control chamber 32 to the boost chamber 21. Thereby, the flow of fuel when acting on the needle 10 in the opening direction, that is, the flow of fuel flowing out from the control chamber 32 and flowing into the pressurizing chamber 21 can be suppressed, and the needle 10 acts in the closing direction. The flow of fuel at the time of fuel flow, that is, the flow of fuel flowing out from the pressure increasing chamber 21 and flowing into the control chamber 32 can be increased.

  Thereby, since the flow of the fuel which acts on the needle 10 in the closing direction can be improved, a decrease in the speed of the needle 10 that shifts from the open state to the closed state can be suppressed, and a smaller amount of fuel injection can be realized. .

  Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

  In the above embodiment, the needle 10 is moved in the opening direction by increasing the pressure on the needle 10 in the pressurizing chamber 21. However, the present invention is not limited to such a configuration. Thus, the pressure in the back pressure chamber may be reduced. That is, the needle may be moved up and down by lowering the pressure of the back pressure chamber that applies pressure to the needle in the closing direction.

  Moreover, in the said Example, the opening edge parts 51a and 51b of the orifice 51 are not limited to the shape shown in FIG. In other words, the opening shapes at both ends are different, and it is sufficient that the flow rate flowing into the control chamber 32 is larger than the flow rate flowing out from the control chamber 32.

It is the schematic diagram which showed the structure of the injector. It is explanatory drawing of an orifice. It is the schematic diagram which showed the structure of the injector which concerns on a modification. FIG. 4A is a graph simply showing the characteristics of the piezo actuator employed in such an injector, and FIG. 4B simply shows the force required for the needle to lift in the opening direction. It is a graph.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Needle 20 Oil sump chamber 21 Booster chamber 22 Back pressure chamber 23 Suck part 24 Injection hole 30 Piezo actuator 31 Piston 32 Control chamber 40 Supply passage 50 Communication passage 51 Orifice 60 Return passage 61, 71 Check valve 70 Auxiliary passage

Claims (4)

A needle that opens and closes the nozzle hole by ascending and descending;
A pressurizing chamber and a back pressure chamber that apply pressure in the opening direction and the closing direction in which the fluid is introduced and the nozzle hole is opened with respect to the needle, respectively;
A differential pressure changing mechanism that changes the differential pressure between the boost chamber and the back pressure chamber by the flow of the fluid into and out of the boost chamber or the back pressure chamber in conjunction with expansion and contraction of the piezo actuator,
An injector comprising: suppression means for suppressing flow of the fluid when the differential pressure changing mechanism acts on the needle in the opening direction. The differential pressure changing mechanism includes a communication path that communicates with one of the boost chamber and the back pressure chamber, and a control chamber that communicates with the communication path and changes in volume in conjunction with expansion and contraction of the piezoelectric actuator,
2. The injector for a diesel engine according to claim 1, wherein the suppressing means includes an orifice formed in the communication path.   The opening of both ends of the orifice is different from the flow of the fluid acting in the opening direction so as to promote the flow of the fluid acting in the closing direction. For diesel engines. An auxiliary passage communicating the control chamber and one of the boost chamber and the back pressure chamber communicated with the control chamber via the communication passage;
The injector for a diesel engine according to claim 2 or 3, wherein the auxiliary passage includes a check valve that allows only a flow of fluid acting in the closing direction.

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