JPH0612104B2 - Piezoelectric fuel injection valve - Google Patents

Description

The present invention relates to a fuel injection device for an internal combustion engine, and more particularly to a fuel injection valve using a piezoelectric element.

[Conventional technology]

In the conventional device, as described in Japanese Patent Application Laid-Open No. 50-60630, a piezoelectric element that causes a mechanical displacement corresponding to its polarity by applying a voltage, and a voltage is constantly applied to this piezoelectric element. Since the application means for performing polarity reversal of the voltage and the valve that opens and closes in conjunction with the mechanical displacement in the opposite direction accompanying the polarity reversal to intermittently inject high-pressure fluid, without using a return spring, The mechanical displacement in the opposite direction can be directly applied to the opening and closing to accelerate the valve opening and closing responses, and the structure is simple.

[Problems to be Solved by the Invention]

The above-mentioned prior art has a simple configuration in which a return valve is not used and a needle valve, a piezoelectric element, a fixture and the like are housed in a series in a valve casing, but each member except the piezoelectric element is a rigid body made of a metal material. When the valve has an appropriate closing force and is assembled and fixed, the repulsive force acting on each member is absorbed by the piezoelectric element made of a relatively soft material. In addition, since the respective members are displaced from each other in concentricity, parallelism, etc. in manufacturing, mechanical force such as bending force or shearing force acts on the piezoelectric element. Therefore, there is concern that the reliability of the piezoelectric element during driving is extremely poor and that stable reciprocating operation cannot be obtained due to eccentricity and inclination of the members.

An object of the present invention is to provide a piezoelectric fuel injection valve capable of driving a piezoelectric element with high reliability, obtaining a stable variation amount, and performing accurate fuel injection control.

[Means for Solving the Problems]

The above-mentioned object is to use a piezoelectric element capable of high-speed operation as an actuator, and to open and close an injection hole by mechanical displacement of the piezoelectric element to inject and supply fuel to an engine. A coil-shaped spring having a spherical valve integrally connected to one surface and a guide member connected to the other surface, for applying a force in a direction in which the spherical valve closes the injection hole, and the coil-shaped spring. With a spring adjuster for adjusting the spring force of a spring, via the guide member, the piezoelectric element is slidably arranged in the axial direction within the valve casing, and when a negative voltage is applied to the piezoelectric element, This is achieved by opening the injection hole by contraction of the piezoelectric element and injecting and supplying fuel.

[Action]

The piezoelectric element has its eccentricity and inclination corrected by the spherical portion of the spherical valve integrally connected, and slides in the valve casing with high precision and coaxially by the guide member. or,
The piezoelectric element makes a stable reciprocating motion due to the restoring force of the coiled spring that gives the closing force of the spherical valve.

Therefore, the piezoelectric element is driven with high reliability without applying a local load, and furthermore, it obtains an appropriate amount of displacement and slides in the valve casing to open and close the fuel injection hole to reduce the injection amount. Control can be performed with high accuracy.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 is a vertical sectional view showing an embodiment of the present invention, and FIG.
The figure is a sectional view taken along the line AA of FIG. In the figure, 1 is a cylindrical valve casing, 1a is a fuel injection hole provided at the tip of the valve casing 1, b is a conical valve seat inclined toward the injection hole 1a, 2 is a columnar piezoelectric element, and 3 is A spherical valve 4 integrally connected to the piezoelectric element 2 is a guide member having a guide portion 4a for coaxially sliding in a slide hole 1c in the valve casing 1, and 4b is a guide member 4 surrounding the guide member 4. Notched fuel passage holes, 5 are coil-shaped springs that apply a force in the direction of closing the injection hole 1a, 6 is a spring adjuster that adjusts the restoring force of the coil-shaped spring 5, and 6a is provided in the spring adjuster 6. The fuel introduction hole 7 is a lead wire terminal of the piezoelectric element 2. Here, the piezoelectric element 2 may be a multi-layered one. The stacked ones are electrically parallel and mechanically series, and the total displacement is the sum of each element. By laminating in this way, a large force and displacement can be obtained.

With such a configuration, the piezoelectric element 2, the spherical valve 3 integrally connected to the piezoelectric element 2, and the guide member 4 are held in the valve guide 1 so as to be slidable in the axial direction. The spherical valve 3 is seated on the valve seat 1b so as to close the injection hole 1a by the restoring force of the leaf spring 5. The restoring force of the coiled spring 5 is adjusted by changing the axial position of the spring adjuster 6 as described above. The seating force (seat force) is adjusted here.

On the other hand, when a negative voltage is applied to the piezoelectric element 2 by a control circuit (not shown), the piezoelectric element 2 is instantly contracted (moves upward in the figure), and the spherical valve 3 causes the valve seat 1b of the valve casing 1 to move. Leave more.

On the other hand, when the voltage is released, the piezoelectric element 2 stops contracting and returns to the original position. At this time, the spherical valve 3 collides with the valve seat 1b, and vibration called "bounce" is generated. However, due to the restoring force of the coiled spring 5, the piezoelectric element 2 and the spherical valve 3 and the guide member 4 which are integrally connected to the piezoelectric element 2. Is pushed downward in the figure, and this is suppressed, and the spherical valve 3 is immediately seated.
Sit on 1b.

To describe the disclosed operation of the injection hole 1a, the injection hole 1a is opened by the instantaneous contraction of the piezoelectric element 2, and the piezoelectric element 2 movable in the valve casing 1 is restored by the restoring force of the coil spring 5. And the injection hole 1a is closed. Therefore, the piezoelectric element 2 integrally connecting the guide member 4 coaxially housed in the valve casing 1 with high precision and the spherical valve 3 for correcting the eccentricity and the inclination by the spherical portion is locally attached to the piezoelectric element 2. It is driven with high reliability without any load being applied. Further, it is possible to perform accurate displacement control by a stable reciprocating operation.

Here, the high-pressure fuel supplied from a fuel pump (not shown) passes from the fuel introduction hole 6a burned in the spring adjuster 6 through the fuel passage hole 4b provided in the guide member 4 to the piezoelectric element 2
To reach the injection hole 1a. Here, the gas is injected and supplied to the outside of the valve from the injection hole 1a through a gap (a gap between the spherical valve 3 and the valve seat 1b) which is opened in advance.

The injection flow rate can be widely varied by exciting the piezoelectric element 2 with a valve and controlling the pulse frequency, or by controlling the opening time by keeping the frequency constant, and the injection flow rate per pulse is finely adjusted to obtain the total flow rate. It is held within the target accuracy range in the area. This fine adjustment method is carried out by the method described below, but in any case, appropriate flow rate control is performed.

As one of the fine adjustment methods, a displacement amount determined by applying a voltage is controlled by varying the voltage, and a lift amount of a spherical valve 3 integrally coupled to the piezoelectric element 2 is adjusted. Is.

Two fine adjustment methods are to control the charging / discharging time of the piezoelectric element 2 to vary the rising and falling speeds of the displacement, and to set the rising and falling speeds of the spherical valve 3 integrally connected thereto. It is a fine adjustment. That is, the opening time interval of the injection hole 1a is finely adjusted.

The three fine adjustment methods are to adjust the restoring force of the coil spring 5 to finely adjust the return speed of the spherical valve 3 to control the bounce suppression time. That is, the opening time interval of the injection hole 1a is finely adjusted.

The flow rate can be reliably adjusted by using the above methods alone or in combination.

[Advantages of the Invention] According to the present invention, the piezoelectric element can be driven with high reliability without applying a local load, and the stable reciprocating operation allows the injection hole to be opened and closed, and an appropriate displacement. The fuel injection control can be performed with high accuracy by the amount control.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a piezoelectric fuel injection valve showing an embodiment of the present invention, and FIG. 2 is a sectional view taken along the line AA of FIG. . 1 ... Valve casing, 1a ... Injection hole, 1b ... Valve seat,
2 ... Columnar piezoelectric element, 3 ... Spherical bulb, 4 ... Guide member, 5 ... Coil spring, 6 ... Spring adjuster.

Claims (1)

[Claims] 1. A piezoelectric fuel injection valve which uses a piezoelectric element capable of high-speed operation as an actuator and opens and closes an injection hole by mechanical displacement of the piezoelectric element to inject and supply fuel to an engine. A coiled spring having a spherical valve integrally connected to one surface and a guide member connected to the other surface, the spherical valve applying a force in a direction to close the injection hole, and the coil When the piezoelectric element is slidably arranged in the axial direction within the valve casing via the guide member and a spring adjuster that adjusts the spring force of the spiral spring, and a negative voltage is applied to the piezoelectric element. A piezoelectric fuel injection valve, characterized in that the injection hole is opened by contraction of the piezoelectric element to supply and inject fuel.