Valves and valve actuation – Heat or buoyancy motor actuated
Patent
1995-11-20
1997-10-28
Chambers, A. Michael
Valves and valve actuation
Heat or buoyancy motor actuated
251368, F16K 3170
Patent
active
056810245
DESCRIPTION:
BRIEF SUMMARY
FIELD OF TECHNOLOGY
The present invention relates to a microvalve which may be used in pneumatic applications, for instance.
Pneumatic controls are widely used in many fields of technology, for they are characterized by high longevity, operational safety, and large forces. An electro-mechanical transducer (actuating element) actuated by an electrical signal, acts directly or by way of several pressure stages on the actual valve stage (control element) which, in turn, manipulates a predetermined parameter (pressure, rate of flow) in a desired manner.
STATE OF THE ART
In pneumatics, the major control elements used for main or master stages are primarily cylindrical sluice or slide gate valves and, for directly actuated valves or pilot valves, cylindrical seat valves. The solenoid has found wide acceptance as an actuator, for its kind of drive is characterized by high operative efficiency and simple structure. The dimensions of a conventional solenoid valve made of plastic components are about 25.times.25.times.40 mm; such a valve operates at pressures up to 8 bar and, when energized, requires about 2.5 W.
For reasons of reducing costs, lower materials consumption, increased flexibility and improved switching characteristics, the trend towards miniaturization may also be observed for certain applications in the field of pneumatics. The size of pneumatic microvalves is increasingly determined by the dimensions of the solenoid, the size of the coil of which may only be reduced at significant increases in costs at unavoidably lower efficiency. Miniature solenoid valves (10.times.10.times.15 mm.sup.1) made by precision engineering techniques are at least five times more expensive than conventional miniature valves.
A silicon valve made by micro-structure technology for controlling the flow rate of a liquid is known from European Patent 208,386. The valve consists of a first planar portion having an outlet opening and a second portion having a planar surface which, for opening and closing the outlet opening, is moveable relative thereto. For moving the closure member, an external force is applied to it, for instance by a plunger. The entire structure required for this valve is very complex.
Other actuators for moving a diaphragm closure member in microvalves are known from German Patent 39 19 876. In this context, piezo-electrically and thermo-electrically operating coatings of the diaphragm and electro-static and thermo-fluidic actuation are to be especially mentioned. Particularly during the opening phase of a valve against abutting pressure, a greater force is initially necessary than during the ensuing opening operation. This is a requirement which cannot be met by the actuators mentioned supra.
Furthermore, piezo-electric and electro-static microvalves cannot satisfy the operational conditions demanded by pneumatics. In order to switch at the high pressures (1-7 bar) prevalent in pneumatics, very high control voltages would be required. Since the strokes attainable with such valves are small, the valve openings would have to be large to provide the requisite flow rate (1-30 l/min). Problems would arise with contaminations (oil, water) by the operating medium (oil-contaminated moist pressurized air). Furthermore, icing may occur. This is less critical with thermal valves as their closure diaphragm becomes very hot. The attainable stroke is larger.
Thermo-fluidic actuation is disadvantageous in that, without additional annoying means, the cooling process proceeds very slowly (low dynamics).
From European Patent 0,512,521 a microvalve is known which is made of a micro-structurable material and consists of a first part positioned at the pressure side and having, as a closure member, a diaphragm structure, and of a second part connected to the first part and provided with at least one output opening and at least one valve seat, at least one of the two parts being provided with one or more recesses of defined depth. At one surface, the diaphragm structure is coated in such a manner with a material having an elo
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Lisec Thomas
Quenzer Hans-Joachim
Wagner Bernd
Chambers A. Michael
Fraunhofer-Gesellschaft zur Forderung der angerwanden Forschung
Hormann Karl
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