JPH0742904B2 - Piezoelectric actuator for fuel injector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a piezoelectric actuator in which a piston is driven by a piezoelectric element laminate as an actuator used in a fuel injection device.

[Conventional technology]

In a fuel injection device of a diesel engine that supplies fuel supplied from a fuel injection pump to an engine through an injection nozzle, a fuel passage connecting the fuel injection pump and the injection nozzle, a fuel pressurizing chamber including a pump chamber, etc. An actuator is connected to control the fuel pressure.

For example, in a distributed fuel injection pump, it is applied to reduce noise and vibration during idling operation by causing the actuator to pressurize the fuel in the pump chamber that is pressurized by the plunger to perform pilot injection. Has been done.

In such an engine injection system, the operating performance of the actuator, that is, the responsiveness becomes a problem.

As an actuator excellent in responsiveness, an electromagnetic drive type actuator is conventionally known. This type operates a piston by applying a voltage to a solenoid coil, and has an advantage that the operating speed is faster than that of a pneumatic or hydraulic drive type.

However, even an electromagnetic actuator has a problem that the control speed becomes slow when the engine rotates at high speed. For example, when trying to perform pilot injection when the engine rotates at high speed, it is necessary to turn the actuator on and off within 1 msec (10 ^-3 sec).
Such high speed operation is not possible with an electromagnetic actuator.

Also, the electromagnetic actuator has a relatively small pressing force,
There is also a problem that it becomes large when trying to increase it.

In order to solve such a problem, the use of a piezoelectric element laminate as a drive source for an actuator has been studied.

It is known that a piezoelectric element laminated body is formed by alternately laminating several tens of PZT elements and electrode plates, and has a piezoelectric effect and an inverse piezoelectric effect. When used as a drive source
^It is responsive to the order of ^-6 sec) and has the advantage that a large pressing force can be obtained, which is convenient for the actuator of the fuel injection system.

[Problems to be solved by the invention]

By the way, when trying to use the above piezoelectric element laminate as a drive source for an actuator, there are various problems in its implementation.

That is, the piezoelectric actuator is composed of a cylinder, a piston housed in the cylinder, and a piezoelectric element laminated body that drives the piston. However, if the piston and the piezoelectric element laminated body are separated, a large space is required. Since the size of the piston is large, it is desirable that the piston has a cylindrical shape with the piston head side closed, and the piezoelectric element stack is housed in this cylindrical piston.

However, in such a case, the piezoelectric element laminate has a dimensional variation among the ceramic element solids in the axial length thereof, and it is very difficult to eliminate this dimensional variation. With such a piston, the position of its piston head tends to vary. If the piston head position is not constant, the characteristics will be affected. Therefore, a means of adjusting the piston head position is required.

On the other hand, in the piezoelectric element laminate, the pressing load varies due to the dimensional variation among the ceramic element solids as described above, which affects the characteristics.

Furthermore, since a high voltage is applied to the piezoelectric element laminate and a high voltage is generated, there is a risk of leakage. In order to prevent this, applying silicon oil improves the withstand voltage. However, there is a concern that silicone oil may dissolve in the fuel and be washed away, so a seal structure is required.

Therefore, the present invention is intended to provide a piezoelectric actuator for a fuel injection device that can adjust the position and load of the piston head, can adjust the variation in characteristics, and can maintain a reliable sealing property. .

[Means for solving problems]

The present invention relates to a piezoelectric actuator of a fuel injection device, wherein the piston has a tubular shape in which the piston head side is closed, and the tubular piston has a structure in which the piezoelectric element stack is housed in the piston. A seal structure for isolating the piezoelectric element laminate from the fuel is formed, a coil spring for urging the piston in the backward direction is installed between the cylinder and the piston, and the position of the piston head is adjusted for the cylinder. It is characterized by screwing an adjustment bolt.

[Action]

With such a configuration, the position of the piston head and the load of the coil spring can be adjusted by the adjusting bolt, so that the variation in the characteristics can be corrected and the piezoelectric element laminate is separated from the fuel by the seal structure. Silicone oil does not elute, and it is possible to maintain high voltage resistance and long life.

Example of Invention

Hereinafter, the present invention will be described based on an embodiment shown in the drawings.

This embodiment shows an example in which a piezoelectric actuator for pilot injection is installed in the pump chamber of a distribution type fuel injection pump. In the figure, 1 is a distribution type fuel injection pump and 2 is a piezoelectric type actuator.

The distribution type fuel injection pump 1 is a well-known one, so a detailed description thereof will be omitted. However, as shown in FIG.
The plunger 3 sucks fuel into the pump chamber 4, pressurizes the fuel, and sends the fuel to the fuel injection nozzle 5 under pressure. That is, the plunger 3 is rotated by an engine (not shown) in synchronism with the engine, and is provided with a face cam 6, and the plunger 3 is provided with the same number of cam rollers 7 as the number of cylinders rolling on the face cam 6.
During the one rotation, it is reciprocated according to the number of cylinders of the engine. During the suction stroke of the plunger 3, one of the suction grooves 8 ...
The fuel in the fuel chamber 10 is sucked into the pump chamber 4 through the introduction passage 11. During the compression stroke of the plunger 3, the fuel in the pump chamber 4 is pressurized, and this pressurized fuel is vertically vented.
When the supply port 14 is pushed out to 13 and communicates with one of the plurality of discharge ports 15, it is supplied to the fuel injection nozzle 5 via the delivery passage 16 and the delivery valve 17.

When fuel is being supplied to the fuel injection nozzle 5 through the injection passage 16, the spill port 19 communicating with the vertical hole 13 extends from the end surface of the spill ring 18 provided in the plunger 3 to the fuel chamber.
The fuel in the vertical hole 13 is released to the fuel chamber 10 through the spill port 19 to the fuel chamber 10. As a result, the fuel supply to the fuel injection nozzle 5 is stopped. Therefore, by controlling the movement of the spill ring 18 in the axial direction of the plunger 3, the fuel injection amount and the fuel injection timing can be controlled.

A piezoelectric actuator 2 for pilot injection is connected to the pump chamber 4. The piezoelectric actuator 2 is shown in FIG. 1, and 20 is a cylinder whose both ends are open. One end of the cylinder 20 is screwed to the pump head 21 forming the pump chamber 4, and the O-rings 22 and 23 are attached.
Liquid tightness is maintained by the sealing material such as. A cylinder chamber 24 that communicates with the pump chamber 4 through the one end is formed in the cylinder 20.

A piston 25 is slidably accommodated in the cylinder 20. The piston 25 has a cylindrical shape with one end facing the cylinder chamber 24 being closed, and this closed end has a piston head 26.
Has become.

A piezoelectric element stack 27 is housed in the piston 25.
Although not shown in detail, this piezoelectric element laminate 27 is composed of several tens of PZT
The element is constructed by alternately laminating the electrode plates, and such a laminated body 27 is coated with silicone oil in order to increase the withstand voltage. The piezoelectric element laminate 27 and the piston 25 are insulated by a resin tube (not shown).

A cover head 28 is slidably capped on the other end of the piston 25. O between the cover head 28 and the piston 25
Liquid tightness is maintained by a sealant such as the ring 29, and therefore the piezoelectric element laminate 27 is liquid tightly isolated from the fuel around the piston 25.

The cover head 28 is fixed to the detent block 30. The detent block 30 is fitted into the other end of the cylinder 20 so as to be movable in the axial direction of the cylinder 20, and is kept liquid-tight with respect to the cylinder 20 by a sealing material such as an O-ring 31.

A locking groove 32 along the axial direction is formed at one location on the peripheral surface of the rotation preventing block 30, and the locking groove 32 has
A rotation stop screw 33 screwed into the side wall of the cylinder 20 is inserted.

Therefore, the detent block 30 is supported so as to be movable in the axial direction but not circumferentially, that is, not rotatable.

An adjusting bolt 34 is screwed into the other end of the cylinder 20. The adjusting bolt 34 has a cylindrical shape and has a cylinder on the outer peripheral surface.
It is screwed onto the inner surface of 20. The adjustment bolt 34 is in contact with the rotation stop block 30, and when the adjustment bolt 34 is screwed back and forth, the rotation stop block 30 moves in the axial direction, and the piston head is passed through the cover head 28 and the piezoelectric element laminate 27. 26 positions can be adjusted. In this case, the adjustment bolt 34 is rotated, but the detent block 30 does not rotate, so the cover head 28 also does not rotate, and the piezoelectric element laminate
Does not transfer rotational force to 27.

Lead wires 35, 35 for supplying electric power to the piezoelectric element laminate 27 are inserted into the cover head 28 and the rotation-stop block 30, and these lead wires 35, 35 pass through the adjustment bolt 34 to the outside. It has been derived. Note that the lead wires 35,35
The derived root is bonded to the whirl-stop block 30 while maintaining gas-liquid tightness with an adhesive 36.

A step portion 37 is formed on the cylinder 20 and a flange 38 is formed on the piston 25.

A compression coil spring 39 having a small spring constant is inserted between the step portion 37 and the flange 38. The compression coil spring 39 constantly urges the piston 25 in the direction of retracting, whereby a compressive load is applied to the piezoelectric element laminate 27.

The operation of the embodiment having such a configuration will be described.

As described above, the distributed fuel injection pump 1 pressurizes the fuel in the pump chamber 4 by the compression operation of the plunger 3,
This pressurized fuel is pushed out into the vertical hole 13 and the supply port 14
Is supplied to the fuel injection nozzle 5 when it communicates with one of the plurality of discharge ports 15. At this time, a voltage is applied to the piezoelectric element laminate 27 in advance to extend the piezoelectric element laminate 27. Leave. Then, the fuel in the pump chamber 4 is pressurized by the plunger 3 and the supply port 14 becomes the discharge port.
At the initial stage of communicating with 15, the voltage stored in the piezoelectric element laminate 27 is removed through the lead wires 35, 35. Then, the piezoelectric element laminate 27 instantly contracts and deforms, which causes the piston 25 to move backward, that is, to move to the right side in the drawing.

Therefore, the piston 25 reduces the fuel pressure in the cylinder chamber 24, and thus the fuel pressure in the pump chamber 4 also decreases. Therefore, at the stage when the fuel pressure in the pump chamber 4 is increased to a predetermined pressure by the original plunger 3, the pressure is momentarily reduced by the piezoelectric actuator 2, so that the supply port 14 communicates with the discharge port 15 at the initial stage. The injection of fuel is separated at the injection nozzle 5, and so-called pilot injection is performed.

In the piezoelectric type actuator 2 having such an action, when the adjusting bolt 34 screwed to the other end of the cylinder 20 is screwed back and forth, the detent block 30 moves in the axial direction, and the cover head 28 and the piezoelectric element laminate 27. The position of the piston head 26 can be adjusted via. Piezoelectric element stack
In No. 27, the variation in the axial length easily occurs due to the variation between solids, and it is very difficult to eliminate this variation in the axial length.
The position of the piston head 26 can be set to a constant position by the 34, and therefore the total internal volume of the cylinder chamber 24 and the pump chamber 4 communicating with this can be made constant, so that the pump performance can be made constant. .

In this case, when the adjusting bolt 34 is rotated, the rotational force can be transmitted to the detent block 30 that is in contact with the adjusting bolt 34, but in the locking groove 32 formed on the peripheral surface of the detent block 30,
Since the detent screw 33 that is screwed into the side wall of the cylinder 20 is inserted, the detent block 30 is movable in the axial direction, but is prevented from rotating in the circumferential direction, that is, rotating. Therefore, the cover head 28 also does not rotate and the rotational force is not transmitted to the piezoelectric element laminate 27. As a result, the piezoelectric element laminate 27 constituted by alternately stacking several tens of PZT elements and electrode plates was coated without causing rotational deviation between these PZT elements and electrode plates. Problems such as peeling of the silicon oil and damage to the resin tube interposed between the piezoelectric element laminate 27 and the piston 25 for insulation are prevented. Further, twisting of the lead wires 35, 35 is prevented.

Further, a cover head 28 is capped on the other end of the cylindrical piston 25 whose one end is closed.
Since the oil-tightness is maintained by a sealing material such as an O-ring 29 between the two, the piezoelectric element laminate 27 accommodated is
It is oil-tightly isolated from the fuel around 25. Therefore, the applied silicon oil is not soaked in the fuel, the withstand voltage performance is maintained, and the leak is prevented.

By the way, when the piezoelectric element laminate 27 of this type is compressed in advance by applying a predetermined load by the coil spring 39,
When the voltage is removed, the compression recovery operation characteristics are good and the pump performance is improved.

FIG. 3 and FIG. 4 are characteristic diagrams of measurement results regarding the injection amount and the injection delay of the pump with respect to the spring load applied to the piezoelectric element laminate.

From these characteristic diagrams, the larger the set load of the coil spring 39, the larger the injection amount can be secured and the injection delay can be reduced. That is, the pump performance can be improved.

Further, if the set load of the coil spring 39 is increased, it is possible to prevent the piston 25 and the laminated body 27 from dancing, that is, swinging, which is caused by a sudden change in the hydraulic pressure applied to the piezoelectric element laminated body 27.

However, since it is preferable to quickly expand and contract the piezoelectric element laminate 27 for pilot injection,
Rather, the smaller the set load of the coil spring 39, the better.

In order to satisfy these requirements and eliminate variations, it is necessary to make the set load of the coil spring 39 constant. For that purpose, a coil spring 39 having a large stroke, that is, a small spring constant is desirable.

Moreover, when a coil spring 39 having a small spring constant is used, the variation in the axial length of the piezoelectric element laminate 27 is corrected, so that even if the position of the piston head 26 is adjusted by the adjusting nut 34, a substantially constant load is applied. Will be able to be added.

The present invention is not limited to the above embodiment.

That is, the piezoelectric actuator 2 of the above embodiment is connected to the pump chamber 4 of the distribution type fuel injection pump 1 and applied to pilot injection. However, the present invention uses the conventional electromagnetic type actuator in various fuel injection systems. However, it can be used in place of this electromagnetic actuator, for example, it can be used in place of the electromagnetic unit in JP-A-59-65992.

Further, in the above embodiment, the detent block 30 and the cover head 28 are separately configured to facilitate the processing, but they may be integrally configured.
Although the rotation stopper screw 33 is screwed into the side wall of the cylinder 20 to prevent the rotation of the cylinder 30, the rotation of the cylinder 30 may be blocked by a key or a split pin.

Also, in the above embodiment, the piston 25 and the cover head
Although an O-ring 29 between 28 is interposed to form a seal structure,
A packing or the like may be used as long as it can seal without hindering the movement of the piston 25.

Further, in order to isolate the piezoelectric element laminate 27 from the fuel, a means such as attaching a piston ring to the sliding portion between the piston 25 and the cylinder 20 may be used. With such a seal structure, the cover head 28 Can be omitted, and other measures can be taken.

〔The invention's effect〕

As described above, according to the present invention, a seal structure for separating the fuel from the fuel is formed in the piezoelectric element stack housed in the piston, and a coil spring for urging the piston in the backward direction is provided between the cylinder and the piston. In addition, since the adjustment bolt for adjusting the position of the piston head is screwed to the cylinder, the piezoelectric element laminate is isolated from the fuel by the seal structure, thus preventing the elution of silicon oil and increasing the withstand voltage. And can maintain a long life,
Further, since the position of the piston head and the load of the coil spring can be adjusted by the adjusting bolt, the characteristic variation can be corrected. If a coil spring having a small spring constant is used, for example, the pump load can be made constant without a large change in the set load, and the set load can be kept substantially constant even when adjusted by the adjusting bolt. it can.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention. FIG. 1 is an enlarged sectional view showing a main part of FIG. 2, and FIG. 2 is a distribution type fuel injection pump provided with a piezoelectric actuator for pilot injection. A cross-sectional view showing an example, FIGS. 3 and 4 are characteristic diagrams of the injection amount and the injection delay of the pump with respect to the spring load. 1 ... Distribution type fuel injection pump, 2 ... Piezoelectric actuator, 3 ... Plunger, 4 ... Pump chamber, 5 ... Fuel injection nozzle, 20 ... Cylinder, 24 ... Cylinder chamber, 25 ...
… Piston, 26 …… Piston head, 27 …… Piezoelectric element stack, 28 …… Cover head, 29 …… O-ring, 30 …… Rotating block, 33 …… Rotating screw, 34 …… Adjusting bolt, 39 ...... Compression coil spring.

Claims (2)

[Claims] 1. A fuel injection device in which an actuator for controlling fuel pressure is connected to a fuel passage connecting a fuel injection pump and an injection nozzle or to a fuel pressurizing chamber including a pump chamber, the actuator comprising a cylinder and a cylinder. In a piezoelectric actuator composed of a piston housed in a cylinder and a piezoelectric element laminated body for driving the piston, the piston has a cylindrical shape in which the piston head side is closed, and the cylindrical piston has the piezoelectric element laminated body. And forming a seal structure for isolating the piezoelectric element laminate housed in the piston from the fuel, and installing a coil spring for urging the piston in the backward direction between the cylinder and the piston. An adjustment bolt for adjusting the position of the piston head is screwed into the cylinder. The piezoelectric actuator of the fuel injector. 2. A detent member is provided between the adjusting bolt and the rear end surface of the piezoelectric element laminate to prevent the rotational force of the adjusting bolt from being transmitted to the piezoelectric element laminate. A piezoelectric actuator for a fuel injection device according to claim 1.