JPS59206668A - Electrostrictive-strain operation type fuel injection valve - Google Patents

Abstract

PURPOSE:To obtain the proper response speed and the valve opening lift by executing the actual opening and closing of an injection valve and preservation of said state by a hydraulic pressure only by using an electric-strain type actuator as a trigger for opening and closing the valve. CONSTITUTION:A little negative voltage is applied onto an electric-strain type actuator 2 when fuel injection is started, and a voltage of 500V is removed, then said electric-strain type actuator 2 contracts, and a pump piston 12 is raised by a belleville spring 13, and a pump chamber 28 is enlarged, and a negative pressure is generated, and the pressure acting onto the upper edge surface of a nozzle needle 3 through a discharge hole 27 is reduced. Therefore, the nozzle needle 3 is pushed-up by the fuel pressure (200atm) in a fuel sump 23, and the upper edge surface is closely attached with the lower edge surface of a distant piece 14. In this state, the nozzle needle 3 is stopped at the position of the upper edge, and an injection port 26 communicates to the fuel sump 23, and fuel injection is permitted.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of a fuel injection valve in which the fuel injection valve is opened and closed by an electrostrictive actuator.

The shorter the time required for opening and closing the fuel injection valve, that is, the better the response to opening and closing, the better the control accuracy and the better the performance of the engine. Conventionally, solenoids have been used as actuators to open and close valves, but the response time in this case is 1
It requires more than m5ec. Electrostrictive actuators are known as quick-response actuators, but they have the problem of not being able to provide a large lift.

An object of the present invention is to achieve both response speed and valve opening lift by using an electrostrictive actuator as a trigger for opening and closing a valve, and actually opening and closing the valve and maintaining the valve opening and closing state using hydraulic pressure.

The present invention will be explained below with reference to Examples.

FIG. 1 shows a cross-sectional view along the central axis of a first embodiment of the invention. The fuel injection valve 1 of the present invention is similar in appearance and components to a fuel injection valve that is a combination of a commercially available diesel engine hole nozzle and its nozzle holder. The functional difference is that the commercially available one is an automatic valve, whereas the fuel injection valve 1 of the present invention is a control valve driven by an electrostrictive actuator 2.
The difference in the components is that the nozzle needle 3 is different from the nozzle body 4.
There is no pressure spring to press the valve to close it, and there is no overflow mechanism. The casing 5 of the fuel injection valve 1 consists of a nozzle holder 6 and a retaining nut 7. The nozzle holder 6 has a cylindrical space 8 formed therein, and the retaining nut 7 has a cylindrical space 8 formed therein. The two are connected by the male thread 10 of the nozzle holder 6 and the female thread 11 of the retaining nut 70, forming a stepped cylindrical space inside. In this space, from the top of FIG. Distance piece 14. A nozzle body 4 is housed therein.

The nozzle body 4 has a stepped cylindrical shape, and its narrow cylindrical portion 1
5 protrudes below the lower end of the retaining nut 7. A nozzle needle 3 is housed in a stepped cylindrical space inside the nozzle body 4. The nozzle needle 3 also has a stepped cylindrical shape, and its small diameter portion 16 is connected to the nozzle body 4.
The large diameter portion 18 is housed in the small diameter portion 17 of the nozzle body 4 and is slidable in the axial direction. The movable range of the nozzle needle 3 is about 50 μm, and the lower end is limited by a valve seat 20 provided on the nozzle body 4, and the upper end is limited by a distance piece 14.

The clearance 22 between the small diameter portions 16 and 17 is approximately 1 in diameter.
mm, and the clearance 2] between the large diameter portions 18 and 19 is approximately 20 μm in diameter. The connecting portion between the large diameter portion 19 and the small diameter portion 17 of the stepped cylindrical space of the nozzle body 4 is an annularly enlarged space forming a fuel reservoir 23 . The fuel reservoir 23 is located in the nozzle body 4. distance piece 1
4. A fuel passage 24 communicates with the nozzle holder 6, and the fuel passage 21 opens into an inlet boat 25 at the upper end of the nozzle holder 6. The fuel in the fuel reservoir 23 should pass through the clearance 22 and be injected and supplied to the internal combustion engine from the nozzle 26 provided at the lower end of the nozzle body 4. When the nozzle needle 3 is located at the lowest end, the valve The seat 20 is closed and no fuel reaches the nozzle 26. The upper end surface of the nozzle needle 3 is polished and has a smooth surface, and can be brought into close contact with the lower surface of the distance piece 14, which is also polished and has a smooth surface. Due to the close contact between the two, the discharge hole 27 passing through the disc-shaped distance piece 14 in the axial direction is closed.

The upper end surface of the distance piece 14 and the pump piston I2
It faces the lower end surface of the pump with a gear, and a pump chamber 28 is formed by this gap. A discharge hole 27 passing through the distance piece 14 is connected to this pump chamber 2.
8 is conductive.

Also, within the pump chamber 28 is a disc spring 13 that urges the pump piston 12 upward. The pump piston 12 is driven by the expansion and contraction of the electrostrictive actuator 2 above it,
The pumping action is housed in the pump chamber 28, and an O-ring 29 is used for sealing. The electrostrictive actuator 2 is made into a cylindrical shape by laminating about 50 thin disc-shaped electrostrictive elements.

The electrostrictive element is a ceramic called PZT, which has lead zirconate titanate as its main component, and has a thickness of 5 mm in the thickness direction.
When a voltage of 00■ is applied, it extends 18 m. If 50 of these elements are stacked and 500V is applied in the thickness direction of each element, a total elongation of 50 μm can be obtained. If this voltage is removed or a slight negative voltage is applied, the film will shrink by 50 μm and return to its original length. Apply and release voltage using lead wire 30
This is done by an external controller via the .

Note that a knock bottle 31 is used to regulate the relative positions of the nozzle holder 6, distance piece 14, and nozzle body 4 to secure the fuel passage 24.

Further, an accumulator 32 is used to supply fuel to the fuel injection valve 1. Fuel pressure of 200 atmospheres is stored in the accumulator 32 by a pump, a pressure setting valve, etc. (not shown), and this pressure is continuously maintained.

The operation in the above configuration will be explained. When a voltage of 500V is applied to the electrostrictive actuator 2 at the time when fuel injection should be stopped, the electrostrictive actuator 2 expands by about 50 μm and lowers the pump piston 12, so that the fuel in the pump chamber 28 is compressed. The high pressure acts on the upper end surface of the nozzle needle 3 through the discharge hole 27 and lowers it.
The lower end of the nozzle needle 3 is pressed against the valve seat 2o to close it and cut off the fuel supply to the nozzle 26. The high pressure fuel acting on the upper end of the nozzle needle 3 has a clearance of 19
However, the fuel pressure in the fuel reservoir 23, that is, the fuel pressure in the accumulator 32, does not drop below that of the accumulator 32, and a fuel pressure of at least 200 atmospheres acts on the entire upper end surface of the nozzle needle 3. continue.

The area corresponding to the difference in cross-sectional area between the large diameter portion 18 and the small diameter portion 16 of the nozzle needle 3 is the fuel pressure of the fuel reservoir 23, 2°O.
Although the atmospheric pressure acts upward, it cannot match the downward force and the force difference continues to press the lower end of the nozzle needle 3 against the valve seat 20. That is, the fuel injection valve 1 continues to be closed.

Electrostrictive actuator 2 at the time when fuel injection should start.
When a slight negative voltage is applied to and the voltage of 500V is released, the electrostrictive actuator 2 contracts by about 50 μm, the pump piston 12 is raised by the disc spring 13, and the pump chamber 28+;! It expands and generates negative pressure, and the discharge hole 2
7, the pressure acting on the upper end surface of the nozzle needle 3 is reduced.

Therefore, the nozzle needle 3 has a fuel pressure of 200 in the fuel reservoir 23.
It is pushed up by the atmospheric pressure, and its upper end surface comes into close contact with the lower end surface of the distance piece 14. In this state, there is no downward force acting on the nozzle needle 3, the nozzle needle 3 remains at the upper end position, and the nozzle 26 is in communication with the fuel reservoir 23 to continue fuel injection. That is, fuel injection valve 1
Continue to open the door.

The operation when stopping fuel injection thereafter is as described above, and fuel can be injected at any time and for any period according to the request of the internal combustion engine.

Here, the clearance 19 is set to 20 μm, but since this value has an influence on the response time as shown in FIG. 2, it needs to be smaller than 40 μm.

If it is too small, the fuel in the pump chamber 28 will remain trapped, causing problems such as deterioration of the fuel oil and inclusion of air bubbles, so it is better to have a diameter of 10 μm or more.

In any case, it can be said that the accuracy of the clearance between the nozzle needle and the nozzle body is reduced by nearly an order of magnitude compared to a general diesel engine injection valve that has a pressure spring and an overflow mechanism.

Further, the ratio of the stroke volume of the pump piston 12 to the stroke volume of the nozzle needle large diameter portion 18 has an influence on the response time as shown in FIG. 3. Although it is better to have a large stroke volume ratio from the viewpoint of responsiveness, a ratio of 1.5 to 2.5 should be selected from the viewpoint of downsizing the fuel injection valve 1. If this is less than 1, it will not function when the valve is opened.

A second embodiment is shown in FIG. The difference from the first embodiment is that there are two small holes 33 and 34 in the large diameter part 18 of the nozzle needle 3.
This is because we have established the following. The small hole 33 passes through the large diameter portion 18 in the diametrical direction, and both ends thereof are open to the clearance 21. The small hole 34 opens at the upper end surface of the large diameter portion 18, is coaxial with the discharge hole 27, and is in communication with the small hole 33 so as to be orthogonal thereto.

By doing this, even when the upper end surface of the nozzle needle 3 is in close contact with the lower end surface of the distance piece 14,
The fuel in the fuel reservoir 23 has a clearance of 21. Small hole 33.
Small hole 34. The fuel enters the pump chamber 28 through the discharge hole 27 and brings the pressure inside the pump chamber 28 close to the same as the pressure in the fuel reservoir 23. Even if they are the same, the opening area of the discharge port 27 is sufficiently smaller than the difference between the cross-sectional area of the large diameter part 18 and the cross-sectional area of the small diameter part 16, so the nozzle needle 3 directs the upward force to the upper end. continue to be located. Thereafter, when a voltage of 500 V is applied to the electrostrictive actuator 2 and the pump piston 12 starts to descend, the pressure in the pump chamber 28 can rise more quickly than if the small holes 33, 34 were not present.

In the embodiment, the fuel injection valve 1 was described as being applied to a diesel engine, but there is no problem even if the present invention is used for intake pipe injection in a gasoline engine.

At this time, the set pressure of the accumulator 32 may be 2 to 10 atmospheres, and a reservoir may be used instead of the accumulator.

As explained in detail above, according to the present invention, the actual opening/closing and maintenance of the valve opening/closing state can be performed simply by using the electrostrictive actuator as a trigger for opening/closing the valve, resulting in fast response speed and controllability with large valve opening lift. An excellent electrostrictive fuel injection valve can be obtained.

[Brief explanation of drawings]

Fig. 1 is a sectional view along the central axis of the first embodiment of the present invention, Figs. 2 and 3 are characteristic diagrams showing changes in response time with respect to the ratio of clearance and stroke volume, and Fig. 4 is a cross-sectional view of the second embodiment of the present invention. A cross-sectional view along the central axis of the example is shown in each case. 2... Electrostrictive actuator, 3... Nozzle needle, 4... Nozzle body, 12... Pump piston, 13... Belleville spring, 14... Distance piece,
21... Throttle passage, 23... Fuel reservoir, 26...
- Nozzle, 28...pump room. Representative Patent Attorney Takashi Okabe Figure 1 Figure 2 Figure 3

Claims (1)

[Scope of Claims] (A nozzle body (4) having 11 orifices (26), and a nozzle needle (3) housed in the nozzle body (4).
), an electrostrictive actuator (2), and a pump chamber (2B) facing the end face of the electrostrictive actuator (2) and the end face of the nozzle needle (3), The nozzle needle (3) is reciprocated in the axial direction by expanding and contracting the type actuator (2) to change the pressure in the pump chamber (28), thereby opening and closing the spout (26). Electrostrictive actuation type%
Formula % (2) The electrostrictive operation according to claim 1, wherein fuel oil pressure is applied to the end face of the nozzle needle (3) through the throttle passage (21) when the valve is closed to maintain the valve closed. type fuel injection valve. (3) By providing a distance piece (14) between the pump chamber (28) and the end face of the nozzle needle (3), and bringing the end face of the nozzle needle (3) into close contact with the distance piece (14) when the valve is opened. Nozzle needle (
3) The electrostrictive fuel injection valve according to claim 2, which maintains the valve open. (4) The pump chamber (28) is always connected via the throttle passage (21).
The electrostrictive fuel injection valve according to claim 3, wherein the fuel injection valve is electrically connected to the fuel reservoir (23).