Piezoelectrically actuated fuel injection valve

Details Piezoelectrically actuated fuel injection valve Piezoelectrically actuated fuel injection valve

1999-06-02

2001-01-02

Shaver, Kevin (Department: 3754)

Valves and valve actuation

Fluid actuated or retarded

Fluid link or column actuator

C251S030020, C251S129060, C251S129070

Utility Patent

active

06168133

ABSTRACT:

PRIOR ART
The invention relates to a valve for controlling liquids One such valve is known from European Patent Disclosure EP 0 477 700. There, the actuating piston of the valve member is disposed, tightly displaceably, in a smaller-diameter portion of a stepped bore, while conversely a larger-diameter piston which is moved by the piezoelectric actuator is disposed in a larger-diameter portion of the stepped bore. A hydraulic chamber is defined between the two pistons, in such a way that whenever the larger piston is moved a certain distance by the actuator, the actuator piston of the valve member is moved by an increased distance, the increase being due to the step-up ratio of the cross-sectional areas of the stepped bore. The valve member, the actuator piston, the larger-diameter piston and the piezoelectric actuator are located in line with one another along a common axis.
In such valves, there is the problem of compensating for changes in length of the piezoelectric actuator, the valve, the enclosed pressure chamber liquid, or the valve housing by means of the hydraulic coupling chamber. Since, to open the valve, the piezoelectric actuator generates a pressure in the pressure chamber, this pressure also leads to a loss of pressure chamber liquid. To prevent the coupling chamber from being pumped dry, refilling is necessary. A device which is supposed to effect such refilling is indeed already known from the prior art defined at the outset, but it has the disadvantage that a constantly open communication in both of the possible flow directions between the coupling chamber and a closed supply container, the latter being equipped with a certain constant volume, has a substantial influence on the operating performance of the piezoelectric actuator. In particular, a thus-increased volume leads to a compressibility that lessens the transfer rigidity of the hydraulic column formed by the coupling chamber. Yet the known device essentially contemplates leakage from the coupling chamber, in order to compensate for tolerances in the working stroke. To counteract the attendant increase in compressibility, provision is made for adding stabilizing material, which has a compressibility-reducing effect, to the liquid in the coupling chamber. This purpose is served for instance by rubber or metal elements that are added to the liquid.
ADVANTAGES OF THE INVENTION
The valve of the invention has the advantage over the prior art that the coupling chamber always remains adequately well filled, because replenishing coupling liquid can flow toward the coupling chamber from the adjoining low-pressure chambers in the periods between the working strokes of the piezoelectric actuator. Any change in length of the overall device that may occur is thus corrected on an ongoing basis. The refilling or replenishment of the coupling chamber is accomplished without problems via the piston guides. This is true even if the piezoelectric actuator, the valve, the enclosed pressure chamber liquid, or the housing should change its length, for instance from warming up, because such a change in length in the coupling chamber is compensated for by leakage. It is also advantageous that the device functions securely and reliably, is simple in design, and assures secure, reliable sealing.
In an advantageous refinement set forth herein, the filling is promoted by the volumetric increase in the return stroke of the actuator piston, along with the piezoelectric actuator and the resultant pressure drop.
This pressure drop is advantageously also reinforced according to claim
4
, by a spring that urges the actuator piston toward the piezoelectric actuator. The invention is substantially improved by the provision gaps of defined size, which are designed for their task of refilling the coupling chamber. The dimensioning rule recited herein promotes this sizing very substantially.
The planning of the construction of the piston that actuates the valve and of the actuator piston can be done on this basis, which says that only part of the length of the pistons determines the criteria that define the communication between the low-pressure chamber and the coupling chamber, while a remaining part of the piston in each case furnishes the length that is required to assure exact guidance of the pistons. This is improved still further in which only a short gap length near the coupling chamber is provided for the pistons, and where the liquid can be brought, unthrottled, out of the low-pressure chamber to quite near the gap l
w
via the pressure fluid conduit.
A substantial improvement in the refilling according to the invention is obtained by setting a certain pressure, which is raised above the ambient pressure, in the low-pressure chambers. This increases the pressure drop toward the coupling chamber, which promotes the refilling of the coupling chamber; this pressure is furnished as recited hereinafter.


REFERENCES:
patent: 4728074 (1988-03-01), Igashira et al.
patent: 5660368 (1997-08-01), De Matthaeis et al.
patent: 5697554 (1997-12-01), Auwaerter et al.
patent: 5779149 (1998-07-01), Hayes, Jr.
patent: 5803370 (1998-09-01), Heinz et al.
patent: 5810255 (1998-09-01), Itoh et al.

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