JPH0364662A - Fuel injection valve - Google Patents

Abstract

PURPOSE:To control high-precise control of injection of fuel through simple structure by a method wherein a piezoelectric element is nipped between a fixing part with which a resilient body is formed and a flexible part arranged facing the fixing part, and along with displacement of the piezoelectric element, the valve body of a fuel injection valve is operated through the flexible part. CONSTITUTION:A displacement enlarging member 47 is contained in a space 25 of a housing body 21 having a fuel inlet 27 and a fuel outlet 29. The displacement enlarg ing member 47 is provided with a fixing part 49 fixed to a bottom wall 21a of a housing body 21, a flexible part 51 arranged facing the fixing part 49 and on the base end side of a valve body 41 and having a relatively thin section and extended to the central part of a fuel injection part, and a coupling part 53 for intercoupling the end parts of the fixing part 49 and the flexible part 51. The displacement enlarging member is formed approximately in a U-shape in cross section and has a lamination type piezoelectric body 57 nipped on the coupling part 53 side between the fixing part 49 and the flexible part 51. The piezoelectric body 57 is energized, displacement is transmitted to the flexible part 51, and through upward enlarging displacement of the tip part thereof, the valve body 41 is opened to inject fuel through a fuel injec tion hole 31.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a fuel injection valve that injects fuel by reciprocating a valve body using a piezoelectric element.

<Prior art> A fuel injection valve used in an internal combustion engine is one in which a valve body is pressed against a seat around a fuel injection hole by a return spring, and is lifted by a solenoid, thereby injecting fuel. is well known. However, with this solenoid type, the response when opening and closing the valve body is poor due to the large electrical time constant of the solenoid and the relatively large mass of the valve body, which is a moving part, relative to the thrust of the solenoid. The problem is that it's bad.

Therefore, in order to improve responsiveness, in recent years, a method using a piezoelectric element has been proposed (see Japanese Patent Application Laid-open No. 59-206671).While fuel injection valves using a piezoelectric element operate at high speed, they do not cause distortion. Since it is on the order of microns, it is difficult to put it into practical use in order to ensure a sufficient injection amount, and a displacement amplification mechanism is required to amplify the displacement amount of the piezoelectric element.

For example, JP-A-62-134983 uses displacement expansion tuI. There is one described in Japanese Utility Model Application Publication No. 63-52968.

Figures 4 and 5 are shown in the above-mentioned JP-A-62-1
This is quoted from Publication No. 34983, which includes a valve body 1 that can open and close a fuel injection hole 2 by a spherical portion 1a on the tip side.
A coupling member 3 made of a magnetic material attached to the proximal end side of the
In this case, the central part of a plate-shaped flexible member 5 is fixed, and both ends of the flexible member 5 are fixed to a lever member 7, and a pulse is applied to a piezoelectric element 9 provided on the base end side of the lever member 7. By applying an electric field of , the lever member 7 expands outward, thereby displacing the flexible member 5 between the solid line position and the broken line position shown in FIG. 4, thereby opening and closing the valve body 1.

A magnetic flange 11 is formed on the side of the valve body 1, and a permanent magnet 13.15 provided on the side of the valve body 1 acts on this flange 11 to bring the valve body 1 into the closed state. The open state is maintained stably.

Further, as shown in FIG. 5, a gap sensor 17 is provided close to the coupling member 3, and this determines the open/closed state of the valve body 1. For example, when the valve body 1 is in the open state when the engine is stopped, , and then apply a pulsed current to return it to the closed position.

(Problem to be Solved by the Invention) However, in a fuel injection valve equipped with such a conventional displacement amplifying mechanism, the flexible member 5 is located between the solid line position and the broken line position in FIG. Since the structure is such that the fuel injection amount can only be displaced between two states, an open state and a closed state, it is not possible to precisely control the fuel injection amount, and the structure is also complex, resulting in poor productivity. This is also disadvantageous in terms of cost.

Therefore, an object of the present invention is to enable precise control of the fuel injection amount with a relatively simple structure even in a fuel injection valve in which a displacement magnifying device f1 is added to a piezoelectric element.

[Configuration of the Invention (Means for Solving the Problems)] In order to solve the above-mentioned problems, the present invention provides a fixed part fixed to a housing, a flexible part disposed opposite to the fixed part, and a fixed part. and a connecting portion that connects the ends of the flexible portions to each other. An elastic body is housed in the housing, and a valve body that reciprocates and controls fuel injection as the flexible portion bends is provided. The piezoelectric element is sandwiched between the fixed part and the fixed part.

(Function) When a voltage is applied to the piezoelectric element and distortion occurs, the flexible portion is expanded and displaced to cause the valve body to reciprocate, thereby controlling fuel injection. The amount of flexure of the flexure portion changes depending on the magnitude of the applied voltage, so the amount of lift of the valve body can be precisely controlled.

The fuel injection amount will be controlled with high precision.

(Example) Hereinafter, an example of the present invention will be described based on FIGS. 1 to 3.

FIG. 1 shows a fuel injection valve according to a first embodiment of the invention. The housing of this fuel injection valve has a housing body 21 and a nozzle housing 23. The housing body 21 has a space 25 formed therein, and a fuel inlet 27 and a fuel outlet 29 communicating with the space 25. has been done. The nozzle housing 23 has a fuel injection hole 31 formed on the tip side, and a flange portion 33 formed on the opposite side to the fuel injection hole 31 is connected to the caulking portion 35 of the housing body 21.
Both are fixed by caulking.

36 is an O-ring for sealing.

Nozzle housing 23 side bottom wall 21 of housing body 21
A and the nozzle housing 23 are formed with a through hole 37 and a through hole 39, respectively. This through hole 37.
Approximately half of the distal end of the valve body 41 is inserted into the valve body 39 , while the proximal end is disposed within the space 25 of the housing body 21 . A fuel passage 43 communicating with the space 25 is formed between the valve body 41 and the through hole 37.39, and a fuel reservoir 45 is further provided between the fuel passage 43 and the fuel injection hole 31.

In the space 25 of the housing body 21, a displacement magnifying member 47 serving as an elastic body constituting a displacement magnifying mechanism is housed at a position facing the fuel inlet 27. Displacement magnifying member 47
consists of four short and thick fixing parts fixed to the bottom wall 21a of the housing main body 21, and a relatively thin fuel injection valve with a relatively thin tip disposed on the proximal end side of the valve body 41 facing the fixing parts 49. The flexible part 51 extends to the center of the fuel tank 27, and the connecting part 53 which is arranged to face the fuel tank 27 and connects the four fixing parts and the ends of the flexible part 51, and has a substantially U-shaped cross section. A notch 55 is formed on the inner surface of the end of the flexible portion 51 on the coupling portion 53 side to improve the flexibility of the flexible portion 51.

A laminated piezoelectric body 57 as a piezoelectric element made of laminated piezoelectric ceramic thin plates such as PZT is sandwiched on the joint portion 53 side between the fixed portion 49 and the flexible portion 51 of the displacement magnifying member 47. Five lead wires are connected to the laminated piezoelectric body 57, and the lead wires 59 are connected to the flexible member 51 and the seal member 6.
1 through the housing body 21 having an electrode terminal 63
It is taken out as an external device.

A mounting hole 65 is formed on the distal end side of the flexible portion 51 of the displacement magnifying member 47, and the small diameter portion 67 of the valve body 41 is slidably connected thereto. A large diameter portion 69 is formed on the distal end side of the valve body 41 of the small diameter portion 67, while a flange 71 is formed on the proximal end side of the valve body 41. A spacer 73 is fitted into the small diameter portion 67 between the flexible portion 51 and the large diameter portion 69 with a slight gap formed on the flexible portion 51 side. On the other hand, the flexible portion 51
A ring 75 made of a highly wear-resistant material is fitted into the small diameter portion 67 between the flange 71 and the flange 71 . Seven return springs fitted into protrusions 77 formed at the center of the inner wall surface are interposed between the end surface of the flange 71 and the upper inner wall surface of the housing body 21. Valve body 41
The fuel injection hole 31 is always closed by the return spring 79.
This allows the spherical portion 41a at the tip of the valve body 1 to come into close contact with the seat portion 81 inside the fuel injection hole 31.

Next, the operation of the fuel injection valve configured as described above will be explained.

In order to inject fuel with the fuel injection valve, first, a step voltage Va as shown in FIG. By applying a step voltage, the laminated piezoelectric body 57 is displaced, and this displacement causes the flexible portion 51 to be displaced.
As a result, the tip portion is expanded upward in the figure against the return spring 79, and accordingly, the valve body 41 moves upward and fuel is injected from the fuel injection hole 31.

On the other hand, by applying the high frequency voltage ΔV, the bending portion 51 resonates and bending vibration occurs. This bending vibration causes the valve body 41
When the voltage vo is applied to fuel injection, the valve body 41 vibrates ultrasonically and this causes the fuel injection hole 31 to vibrate.
Atomizes nearby fuel. By changing the magnitude of the step voltage vo, the lift amount of the valve body 41 can be arbitrarily changed. Therefore, high accuracy can be achieved from a large flow rate area during high engine load to a minute flow rate area such as during warm-up. The fuel injection amount can be controlled by IIJ, and combustion efficiency can be significantly improved by promoting atomization of the fuel by ultrasonic vibration.

In order to cause bending vibration by applying a high frequency voltage of 20 KHz to the bending part 51 as described above, the length and thickness of the bending part 51 are set so that the resonance frequency of the bending vibration by the bending part 51 is 20 KHz. do. Since the notch 55 is not formed for m-unit, the fixing part 49 and the connecting part 53
is sufficiently thicker than the thickness of the flexible portion 51, the above-mentioned resonant frequency can be determined by regarding the flexible portion 51 as a cantilever beam. r! A. For example, if the thickness of the flexible portion 51 is t and the length thereof is 1, then the resonant frequency f is f=(α, 2/4
π3172 ) (L/n 2)×(E/ρ〉1/2).

However, E and ρ are the Young's modulus and density of the material of the displacement magnifying member 47 constituting the flexible portion 51, and α is a constant.

Therefore, by setting the thickness and length of the flexible portion 51 so that the resonance frequency r becomes 20 KHz using the above equation, the flexible portion 51 can be caused to resonate by applying the high frequency voltage ΔV as shown in FIG. can be done.

Also, between the flexible portion 51 and the spacer 73 and the valve body 41
A small gap is provided between the flange 71 and the ring 75, but this gap may be caused by variations in the dimensions of the components during manufacturing or by temperature rise when the fuel injector is operated. This is to absorb variations due to differences in thermal expansion of the component parts, and there is no problem even if this is not provided.

The laminated piezoelectric body 57 generates heat when the fuel injection valve is driven, and its characteristics may change due to the influence of the heat. However, since new fuel is constantly circulating in the space 25, the characteristics may change depending on the temperature. Characteristic changes are prevented.

FIG. 3 shows a second embodiment of the invention.

In this embodiment, the present invention is applied to an outward-opening valve type fuel injection valve. This fuel injection valve has a fuel inlet 8
3 and a fuel outlet 85; and a nozzle housing 9 having eight fuel injection holes formed at its tip.
1. Spaces 93 and 95 that communicate with each other are formed within the housing body 87 and the nozzle housing 91, and the space 93 has the fuel inlet 83 and the fuel outlet 8.
5 and 5 respectively, and the space 95 has the fuel injection hole 8.
9 can be communicated. The housing body 87 and the nozzle housing 91 are fixed by a mounting flange 97 of the nozzle housing 91 being caulked to nine caulking portions of the housing body 87, and an O ring 101 is fitted between the two.

The valve body 103 has a flange 107 formed in the space 95 while a spherical part 105 at the tip is exposed to the outside.
A return spring 109 interposed between the nozzle housing 91 and the nozzle housing 91 urges it upward in the figure.

This allows the spherical portion 105 to come into close contact with the seat portion 111 formed on the outside of the fuel injection hole 89 . The base end side of the valve body 103 reaches near the inner step 119 of the space 93 on the extension of the fuel population 83, and its end 103a is formed into a spherical shape.

A displacement enlarging member 113 as an elastic body constituting a displacement enlarging mechanism is disposed at a position facing the fuel inlet 83 in the housing body 87. The displacement enlarging member 113 is a lid that closes the upper opening of the housing main body 87. A fixed part 117 attached to the lower surface of the body 115, a flexible part 121 opposite to the fixed part 117 and thinner and longer than the fixed part 117, and ends of the fixed part 117 and the flexible part 121 are connected to each other. It consists of a connecting part 123. A notch 125 is formed on the inner surface of the flexible portion 121 on the coupling portion 123 side, while the tip side reaches the center of the fuel injection valve and the surface facing the valve body 103 is formed in a spherical shape, and this spherical portion 121a and A gap 127 is formed between the valve body 103 and the end portion 103a to absorb dimensional variations during manufacturing of each component.
A laminated piezoelectric body 129 as a piezoelectric element formed by laminating piezoelectric ceramic thin plates such as PZT is interposed between the fixed part 117 and the flexible part 121. Laminated piezoelectric body 12
Lead wire 131 is connected to lead wire 1.
31 penetrates through the fixing portion 117 and the sealing material 133 fitted into the lid 115 and is taken out as an electrode terminal 135 to the outside.

Similarly to the first embodiment, the fuel injection valve of the second embodiment configured in this way also has a step voltage Vo as shown in FIG.
Hz>voltage is applied in a superimposed manner. By applying a step voltage, the laminated piezoelectric body 129 is displaced, and this amount of displacement is transmitted to the bending portion 129, causing its tip portion to expand and displace downward in the figure, and the spherical portion 121a at its tip becomes a valve. body 1
The end 103a of the valve 03 is pressed to open the valve and fuel is injected. On the other hand, by applying the high frequency voltage ΔV, the bending portion 121 resonates and bending vibration is generated, and this bending vibration is transmitted to the valve body 103, thereby atomizing the fuel. Therefore, in this embodiment as well, the voltage V is stepped in the same manner as in the first embodiment. By changing the size of valve body 1
The lift amount of 03 can be changed arbitrarily, and the fuel injection amount can be controlled with high precision from the large flow rate area when the engine is under high load to the minute flow rate area such as during warm-up. By promoting this process, combustion efficiency can be significantly improved.

In the second embodiment as well, the resonance frequency of the bending portion 117 can be calculated using the formula for calculating the resonance frequency f used in the first embodiment, and bending vibration can be generated in the bending portion 117.

[Effects of the Invention] As explained above, according to the present invention, a piezoelectric element is sandwiched between a fixed part that constitutes an elastic body and a flexible part arranged opposite to the fixed part, and the displacement of the piezoelectric element is controlled. Since the valve body is actuated by the flexible part that expands and displaces as the fuel injects fuel, the opening/closing operation of the valve body can be controlled according to the amount of displacement of the flexible part, without complicating the structure. Highly accurate fuel injection control becomes possible.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a first embodiment of the invention, FIG. 2 is an explanatory diagram showing the voltage applied to the laminated piezoelectric body in the above embodiment, and FIG. 3 is a second embodiment of the invention. 4 is a plan sectional view showing a conventional example, and FIG. 5 is a longitudinal sectional view of the same portion. 21.87... Housing body 23.91... Nozzle housing 41.103... Valve body 47.113... Displacement magnifying member (elastic body) 49.11
7...Fixed part 51.121...Flexible part 53.123...Joining part

Claims (1)

[Claims] An elastic body having a fixed part fixed to the housing, a flexible part disposed opposite to the fixed part, and a coupling part that couples ends of the fixed part and the flexible part to each other is housed in the housing,
A fuel injection valve characterized in that a valve body is provided which reciprocates to control fuel injection as the flexible portion bends, and a piezoelectric element is sandwiched between the flexible portion and the fixed portion.