JP3838288B2 - Fuel injection valve - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel injection valve that directly performs needle lift by an electrostrictive actuator.
[0002]
[Prior art]
As a prior art of a fuel injection valve using an electrostrictive actuator, one that opens and closes a needle valve via a hydraulic pressure shown in Japanese Patent Publication No. 4-67026 is known. However, since this fuel injection valve performs ON-OFF control via hydraulic pressure, there is a response delay and the valve opening amount of the needle cannot be controlled continuously.
[0003]
In recent years, as a fuel injection valve, it has been desired to control the injection rate from the start to the end of the injection freely in a short time and with good response, and direct control of the needle valve is required.
However, the problem of the direct acting valve that directly controls the needle valve is that the electrostrictive actuator and the housing have different thermal expansion, so that the usable temperature range is narrow. As a technique, as disclosed in Japanese Patent Application Laid-Open No. 60-129481, it is common to provide a thermal displacement adjusting member so that the sum of the thermal displacement amount with the electrostrictive actuator matches the thermal displacement amount of the housing. However, such an injection valve can cope with a uniform temperature change, but has a problem that it cannot respond when the temperature inside and outside the housing differs due to a sudden temperature change.
[0004]
[Problems to be solved by the invention]
The present invention solves the difference in thermal expansion which is a problem of a direct acting valve by controlling the valve opening amount in a short time and continuously with good response even when the temperature of each part is uneven. With the goal.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, the present invention uses the configuration described in claim 1 . According to the first aspect of the present invention, since each member to which the extension force of the electrostrictive actuator is abutted by the contact spring without any gap, it is possible to compensate for a change over time such as a difference in thermal expansion and a sag and the needle. There is an effect that the valve opening amount can be continuously controlled.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a cross-sectional view taken along the central axis of the fuel injection valve according to the first embodiment of the present invention.
This fuel injection valve is used to inject fuel into the combustion chamber of a direct injection type engine, and is installed in each cylinder, for example, four in the case of four cylinders. Fuel pumped from a known pump (not shown) flows into the fuel injection valve from the fuel inlet 22, passes through the fuel passage 21, and is injected through the seat 17 by opening the needle valve 16.
[0007]
The main part of the fuel injection valve is composed of a control part 1 of the needle valve 16, an operation part constituted by an end fixing part 2 for positioning the control part 1, and a nozzle part 3, and the nozzle part 3 is operated by a retainer 7. It is fastened to the housing 4 of the part.
The housing 4 has a bottomed stepped cylindrical shape, in which the control unit 1, the end fixing unit 2, the contact spring 6, and the plate 23 are interposed via the control unit 1 and the end fixing unit 2 and the connecting rod 5. The screw 24 is fixed so as to keep contact with the needle valve 16 constantly. In the control unit 1, a control electrostrictive actuator 8, a piston 9, a disc spring 10, and a sleeve 12 are assembled in a case 11 and fixed with a cap 13. Here, the connecting rod 5 and the piston 9 form an intermediate member. The piston 9 can slide within the case 11 following the expansion and contraction of the electrostrictive actuator 8 for control. At that time, the disc spring 10 urges the piston 9 upward to contact the electrostrictive actuator 8 for control. As a result, a preset load of about 50 kgf is applied to the control electrostrictive actuator 8.
[0008]
The end fixing portion 2 is composed of a press member 15 and a fixing actuator 14 which is composed of an electrostrictive actuator and whose central axis is disposed in a direction perpendicular to the central axis of the control electrostrictive actuator 8. A cylinder having a surface width and a hole through which the lead wire 26 passes in the center, the upper and lower surfaces are in contact with the control unit 1 and the contact spring 6, and the end portion of the fixing actuator 14 is fixed to the two surface width portions. Yes.
[0009]
The clearance between the fixing actuator 14 and the large-diameter portion of the housing 4 expands when the fixing actuator 14 is energized, abuts against the large-diameter portion of the inner peripheral surface of the housing 4 and is pressed and fixed by contact force. Is not moved even if it receives a force from below, and is attached with a clearance that contracts when it is not energized and can move vertically. Further, the lead wire 25 of the fixing actuator 14 extends to the outside from the hole of the plate 23 and is connected to a drive circuit (not shown).
[0010]
The electrostrictive actuator 8 for control used here is a cylindrical PZT element having a diameter of 20 mm and a thickness of 0.5 mm and a stainless steel plate having a diameter of 18 mm and a thickness of 0.02 mm alternately stacked. The side electrodes and the stainless steel plate are coupled so that a voltage can be applied in parallel in the thickness direction of each PZT element. The side electrode and the lead wire 26 are electrically connected and extend from the hole of the plate 23 to the outside, and are electrically coupled to a drive circuit (not shown).
[0011]
A PZT element is a ferroelectric ceramic sintered with lead zirconate titanate as a main component, and is a typical element having a piezoelectric effect. As for the physical properties, when a voltage of 500 V is applied in the thickness direction, the thickness increases by 0.5 μm, and conversely, when a voltage of 500 V is applied and short-circuited, the thickness decreases by 0.5 μm.
The electrostrictive actuator 8 for control according to the first embodiment has 200 PZT elements coupled mechanically in series and electrically in parallel. Therefore, by applying a voltage of 500 V, the expansion and contraction is 100 μm. Is obtained. More specifically, it is known that this type of ferroelectric ceramic is linearly displaced with respect to the injected charge amount when a voltage is applied. In the first embodiment, a charge amount control type driving circuit is used. Yes.
[0012]
The nozzle unit 3 includes a nozzle body 28, a needle valve 16, a valve closing spring 18, a spring plate 27, and a stopper 19, and is closed by the valve closing spring 18.
FIG. 2 is a time chart showing the operating state of the fuel injection valve of the first embodiment.
[0013]
At the initial stage of operation, the fixing actuator 14 and the control actuator 8 are short-circuited, and the contact spring 6 is used to stop the end fixing portion 2, the control portion 1, the connecting rod 5, and the upper end of the needle valve 16 of the nozzle portion 3. 19 is in contact.
At time t1, the upper end of the controller 1 is fixed by energizing the actuator 14 for fixing the end fixing portion 2 and the force transmission between the contact spring 6 and the needle valve 16 is cut off.
[0014]
Thereafter, the control electrostrictive actuator 8 is energized at time t2, and the control electrostrictive actuator 8 is expanded and contracted by arbitrarily controlling the injected charge amount. Then, since the upper end is fixed at the end fixing portion 2, the control electrostrictive actuator 8 pushes down the needle valve 16 to open the needle valve 16, and the expansion / contraction amount of the control electrostrictive actuator 8 is changed to the needle valve 16. Therefore, it is possible to arbitrarily control the fuel injection amount.
[0015]
At time t4 after the end of injection at time t3, the fixing actuator 14 of the end fixing portion 2 is short-circuited, so that the fixing actuator 14 contracts to have a clearance and can be moved in the vertical direction. Therefore, the urging force of the contact spring 6 is transmitted again in the direction of the control unit 1, and the end fixing unit 2, the control unit 1, the connecting rod 5, and the stopper 19 at the upper end of the needle valve 16 of the nozzle unit 3 are Keep in touch.
[0016]
At time t5, the fixing actuator 14 of the end fixing portion 2 is energized again, and the same is repeated thereafter, and one cycle is from time t1 to time t5.
Here, it is necessary to fix the end fixing portion 2 while the control portion 1 is operating, but it is not necessary to fix the end portion fixing portion during the rest. Therefore, even if a dimensional change between the control unit 1 and the housing 4 occurs due to a difference in thermal expansion or a sag due to a temperature change, the end fixing unit 2, the control unit 1, the connecting rod 5, and the nozzle are constantly applied by the contact spring 6 during the pause. The stopper 19 at the upper end of the needle valve 16 of the part 3 can be brought into contact, and the control unit 1 can continuously control the opening amount of the needle valve 16.
[0017]
In addition, since the difference in thermal expansion or sag due to temperature change does not occur every cycle, the short circuit of the end fixing portion 2 may be intermittent, for example, every 10 cycles.
FIG. 3 is a cross-sectional view along the central axis of a fuel injection valve according to a second embodiment in which the present invention is applied to an inner valve.
The difference from the first embodiment in FIG. 1 is that the control unit 1 and the needle valve 16 are contacted with a lever 32 having a substantially disc shape and having a ring-shaped protrusion at the bottom, and a bottomed cylindrical shape. By using the connecting portion 29 that contacts the outer periphery of the lever portion 32, it becomes possible to transmit the displacement in the direction opposite to the displacement direction of the control portion 1 to the needle valve 16, and urge the needle valve 16 in the valve closing direction. The position of the valve closing spring 18 is coupled to the housing 4, and is connected to the upper end surface of the needle valve 16 and the plate 35 inserted so as not to contact the coupling portion 29 from the side surface side of the coupling portion 29. This is provided between the stoppers 19. Here, the piston 9, the connecting portion 29, and the lever portion 32 form an intermediate member.
[0018]
With this configuration, it is possible to compensate for a dimensional change due to a difference in thermal expansion from the housing 4 due to heat generation of the PZT element, a sag, etc., and the valve opening amount of the inner valve can be controlled continuously and precisely.
In addition to the electrostrictive actuator used in the control unit 1, the fixing actuator 14 of the present embodiment has a magnetostrictive actuator (for example, manufactured by Moritex Co., Ltd.) or the hydraulic pressure shown in FIG. It is possible to replace it with a valve-controlled type.
[0019]
FIG. 4 is a cross-sectional view along the central axis of the fuel injection valve of the third embodiment in which the fixing actuator 14 is replaced with a hydraulic type using an electromagnetic two-way valve.
In the third embodiment, a stepped piston 42 is installed at the upper end of the control unit 1 so as to be vertically movable and oil-tight, and the pressing force is urged by the contact spring 6 so that the stepped piston 42 The contact of each part up to the needle valve 16 of the nozzle part 3 is maintained, and the dimensional change due to a difference in thermal expansion or a sag is compensated.
[0020]
Further, the valve needle 45 for shutting off the pressure chamber 51 is connected to the armature 47 and is normally connected to the drain 48 from the fuel inlet 40 by the valve needle spring 46 at a seat 49 provided substantially at the center of the separator plate 44. It is biased to seal the passage. Here, the piston 9, the connecting portion 29, and the lever portion 32 form an intermediate member.
[0021]
The operation will be described. The fuel inlet 40 is connected to a pump (not shown), and the pressure-fed fuel passes through the check valve 41 and is filled into the pressure chamber 51.
Since the pressure chamber 51 is sealed, the fuel injection is performed by energizing the control electrostrictive actuator 8 so that the control electrostrictive actuator extends toward the nozzle side and the needle valve 16 is opened.
[0022]
The control electrostrictive actuator 8 is short-circuited and becomes non-energized. After the control electrostrictive actuator 8 contracts and the fuel injection is completed, the solenoid 50 is energized, whereby the armature 47 is sucked and coupled. The valve needle 45 moves away from the seat 49, opens a passage to the drain 48, the fuel in the pressure chamber 51 is discharged from the drain 48, and is returned to a fuel tank (not shown).
[0023]
Before energizing the fuel the next time, the solenoid 50 is de-energized, and the valve needle spring 46 again seals the passage from the fuel inlet 40 to the drain 48 at the seat 49 to prepare for fuel filling and fuel injection into the pressure chamber 51. Thus, it is possible to compensate for a dimensional change due to a difference in thermal expansion from the housing 4 due to heat generation of the PZT element, a sag, etc., and the valve opening amount of the inner valve can be controlled continuously and precisely.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view along a central axis of a fuel injection valve according to a first embodiment of the present invention.
FIG. 2 is a time chart showing the operating state of the fuel injection valve of the first embodiment.
FIG. 3 is a cross-sectional view along the central axis of a fuel injection valve according to a second embodiment in which the present invention is applied to an inner valve.
FIG. 4 is a cross-sectional view along the central axis of a fuel injection valve according to a third embodiment in which the fixing actuator 14 is replaced with a hydraulic type using an electromagnetic two-way valve.
[Explanation of symbols]
4 Housing 6 Contact spring 8 Control electrostrictive actuator 14 Fixing actuator 15 Press member 16 Needle valve 41 Check valve 42 Stepped piston 45 Valve needle 46 Valve needle spring 47 Armature 48 Drain 49 Seat 50 Solenoid 51 Pressure chamber

Claims (1)

A control electrostrictive actuator is disposed along the central axis of the housing so that the central axes thereof coincide with each other, and one end surface of a stepped piston forming an oil-tight movable member is brought into contact with one end of the control electrostrictive actuator. ,
The other end face of the stepped piston is brought into contact with a compression biased contact spring and the hydraulic pressure in the pressure chamber is applied,
The pressure chamber communicates with a check valve that allows only the inflow of oil into the pressure chamber and an electromagnetic two-way valve that controls the outflow and stop of the oil from the pressure chamber,
When the solenoid of the electromagnetic two-way valve is not energized, the valve needle spring seals the communication with the pressure chamber between the valve needle and the seat, and oil flows into the pressure chamber through the check valve. When energizing to, the armature is sucked and the valve needle coupled to the armature is separated from the seat to open the passage to the drain, and the oil in the pressure chamber flows out,
Further, a needle valve is brought into contact with the other end of the electrostrictive actuator for control via an intermediate member,
When the electrostrictive actuator for control is contracted without energizing the electrostrictive actuator for control, the solenoid of the electromagnetic two-way valve is energized to flow out the oil in the pressure chamber, and the compression-biased contact Pressing the stepped piston, the electrostrictive actuator for control, the intermediate member, and the needle valve by the pressing force of a spring to bring them into contact with no gaps,
When the electrostrictive actuator for control is energized and the electrostrictive actuator for control is extended, the solenoid of the electromagnetic two-way valve is de-energized to seal the pressure chamber in an oil-tight manner and pass through the check valve. A fuel injection valve characterized in that oil is flowed into a pressure chamber to maintain the pressure chamber at a predetermined pressure so that the stepped piston is hydraulically supported to support the extension force of the control electrostrictive actuator.

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