Valves and valve actuation – Electrically actuated valve – Having element dimensionally responsive to field
Reexamination Certificate
2000-04-20
2001-11-06
Shaver, Kevin (Department: 3754)
Valves and valve actuation
Electrically actuated valve
Having element dimensionally responsive to field
C251S282000, C251S335300, C251S337000
Reexamination Certificate
active
06311950
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a fluid metering device that employs a sealing element in which a pressurized fluid, such as, a liquid or a gas, can be delivered or injected in a metered dose amount by the controlled and guided movement of a valve needle.
2. Description of the Prior Art
Various sealing elements or leadthrough elements are generally known in the art. However, in the case of the application of metering fuels that are under pressure of up to 300 bar, for example, and a work temperature range of −40° C. up to +150° C., special requirements have to be met by a product that is suitable for mass production. Generally, requirements have to be met concerning brittleness, wear and reliability.
The fatigue strength or wear over time of the known O-ring seals does not meet the above requirements. Instead of O-rings, membrane seals, such as, metal beads or other like membrane seals, can also be used. However, these have the disadvantage of having a highly pressure-loaded surface that effects the movement of the valve needle. Taking a 1 mm
2
large pressure-loaded surface into consideration given a one-sided excess pressure of 300 bar, for example, a force of already 30 N results. Therefore, the utilization of membranes as a leadthrough or sealing element of the valve needle through a pressurized chamber cannot meet the requirements regarding a high axial elasticity or resilience and a sufficient resistance to pressure at the same time. Although a high resistance to pressure can be accounted for by a correspondingly dimensioned membrane, the increased membrane thickness results in a high axial rigidity. A pressure-independent function of the fluid metering device is not possible due to the large membrane surface and the extremely high pressure forces acting on the valve needle as a result thereof. However, a compensating member, such as, a mechanical spring, can be utilized in combination with the membrane seal to compensate or dampen the force that is directed to the valve needle via the membrane seal. Yet, the compensating member has limited use where it operates best in a single operating point.
It is also generally known that the valve needle leadthrough or sealing element can also be constructed of a clearance fit of the needle by way a cylindrical housing borehole. However, disadvantages result due to the unavoidable leakage along the needle leadthrough, so that a return line to the tank or to the low-pressure connection of the fuel feed pump is required. In addition, the overall efficiency of the motor is reduced as a result of the greater hydraulic losses.
SUMMARY OF THE INVENTION
The invention is based on the object of providing a fluid metering device that employs a sealing element which sealingly guides a valve needle through a chamber filled with a pressurized fluid while directing or exerting negligible, if any, pressure induced force which would effect the movement of the valve needle.
Many existing problems can be solved by utilizing a sealing element, such as, a metal bellows sealing element, for a valve needle that moves axially through a chamber for delivering a metered dose of a pressurized fluid that is contained within the chamber. The invention is based on the exact understanding of the behavior of the metal bellows sealing element, including its number of corrugated elements, that is subject to pressure induced forces due to a difference in pressure between the fluids that contact an external and internal surface of the metal bellows sealing element when the metal bellows sealing element is utilized to seal off a high pressurized fluid chamber from another lower pressurized fluid chamber. As a result of the metal bellows construction and operation, the amount of force that acts on the valve needle due to the metal bellows sealing element is essentially negligible, that is, it has little, if any, effect on the axial movement of the valve needle as it moves to deliver the metered dose of fluid.
A particularly advantageous embodiment provides the radial attachment of the valve needle by way of firmly connecting the metal bellows sealing element to the valve needle and the housing.
In another embodiment of the invention, the utilization of a pressure spring between the housing and the valve needle ensures a reliable closing force, which acts on the valve.
In addition to the great stability or wear of the metal bellows or metal bellows sealing element, a sealing enclosure can be employed to further protect the metal bellows. The sealing enclosure has a cylindrical construction that encloses the metal bellows so as to act as a guide for the metal bellows in order to reduced the risk of buckling.
The particular advantages of the metal bellows are achieved not only with respect to internal pressurization, that is, pressure that acts on the internal surface of the metal bellows, but also with respect to external pressurization, that is, pressure that acts on the external surface of the metal bellows.
In an embodiment, the wall thickness of the metal bellows ranges from 25 to 500 &mgr;m so as to withstand high pressures, such as, 300 bar.
Tests have indicated that it is particularly advantageous to construct the metal bellows in the form of semi-circular segments that are successively attached in a longitudinal direction. These semi-circular segments can be respectively attached by straight sections lying in between.
Advantageously, the metal bellows sealing element is firmly connected to the valve needle and the housing. For purposes of installing the valve needle and the metal bellows in the housing, for example, with respect to an injection valve with a plurality of elements interlaced in one another, the connecting points, that is, the location where the metal bellows seal element is attached to the valve needle and housing, must be optimally sized so as to minimize the amount of space for each connecting point. Weld joints, such as, laser welds, can be advantageously utilized for such purpose.
In order to be able to purposefully influence the pressure forces acting on the pressurized surfaces given high adjacent fluid pressures, a specific equilibrium, with regard to the valve needle, of the fluid pressure-conditioned forces acting in opposite directions should be present. Overall, it is desired to achieve a compensation of these forces, so that the valve needle is approximately free of forces with respect to the cited forces or so that a closing force is adjacent that increases proportionally to the pressure. This means that the pressure-effective forces are slightly larger in closing direction than the ones that are directed against the closing force. In addition, the force of a closing spring can be advantageous.
On principle, the fluid metering device can be constructed with a valve needle that can be opened to the inside or to the outside of the housing. The construction of the metal bellows sealing element must be correspondingly adapted relative to the other elements, in particular, relative to the primary drive or actuator that operates to move the valve needle. An electromagnetic mechanism or other like mechanism can be utilized as the actuator. For example, it is advantageous to utilize piezoactuators that include a biased tube spring.
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Chemisky Eric
Fischer Bernhard
Gottlieb Bernhard
Kappel Andreas
Meixner Hans
Bonderer David A.
Schiff & Hardin & Waite
Shaver Kevin
Siemens Aktiengesellschaft
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