Valve for controlling fluids

Details Valve for controlling fluids Valve for controlling fluids

2000-02-14

2001-12-25

Sircus, Brian (Department: 2837)

Electrical generator or motor structure

Non-dynamoelectric

Piezoelectric elements and devices

C310S346000

Reexamination Certificate

active

06333586

ABSTRACT:

PRIOR ART
The invention is based on a valve for controlling fluids as generically defined hereinafter. In one such valve, known from European Patent Disclosure EP A 0 371 469, the actuation of the valve member is accomplished by a piezoelectric actuator, by the provision of a hydraulic chamber between the piezoelectric actuator and the valve member, by way of which chamber tolerances can be to compensated for. Such valves have the disadvantage that care must be taken to assure that the hydraulic chamber is always adequately filled with adjusting fluid. Furnishing a hydraulic chamber also means major expense for sealing the chamber off. If conversely the valve for controlling fluids is to be actuated directly by a piezoelectric actuator, then problems arise from the fact that the work of a piezoelectric actuator, because of a supply of current to it, produces considerable heat. The heat leads to changes in a length of the piezoelectric actuator itself and to thermal expansions of the housing that surrounds the piezoelectric actuator and heats the piezoelectric acuator. Over the course of operation of such a valve, it can thus happen that because of the different thermal expansions, the valve can no longer reach its closing position or a defined position.
ADVANTAGES OF THE INVENTION
The valve according to the invention for controlling fluids has an advantage over the prior art that a simple valve can be furnished which is actuated directly by the piezoelectric actuator; by the compensating elements provided, temperature-dictated changes in length of the piezoelectric actuator are substantially compensated for compared to those of the housing receiving the piezoelectric actuator. Advantageously, this is achieved by incorporating a Peltier element, which is triggered by an electric control unit in such a way that temperature-dictated changes in length of the piezoelectric actuator are at least partly compensated for compared with those changes in the housing that receives the piezoelectric actuator, into the heat flow from the piezoelectric actuator to a heat-dissipating part of the housing. Depending upon how electrical current is supplied, such a Peltier element can effect either cooling or heating in a known manner at the intended installation location and can thus counteract undesired changes of length, especially those in the actuating direction of the piezoelectric actuator, because either heat is supplied or heat is dissipated, depending on the state of operation or the construction specifications.
Advantageously, compensation is accomplished by using compensating elements whose material has a different coefficient of thermal expansion from that of the surrounding materials. A material with a high coefficient of thermal expansion has the advantage that by means of heating and/or cooling by the Peltier element, relatively large compensating changes in length in the actuating direction of the piezoelectric actuator are attained, which can absorb the large changes in length resulting in the region of heat development of the piezoelectric stack that is in operation, and thus a compensation for these changes in length is achieved compared to the lesser changes in length in the surrounding housing because of the lesser heat flow density there.
The heating or cooling of the compensating elements can be done by means of an axially or radially adjoining Peltier element. In the latter version, the advantages are a smaller axial installation space required and a larger contacting surface area between the compensating elements and Peltier element and the heat-absorbing housing that furnishes a heat sink. The heat outflow from the piezoelectric element to the heat sink can advantageously be improved by interposing the cup-shaped housing as set forth hereinafter, so as to achieve the least possible temperature dependency of the actuating stroke of the piezoelectric actuator.


REFERENCES:
patent: 4933591 (1990-06-01), Stahlhuth
patent: 5402159 (1995-03-01), Takahashi et al.
patent: 2417450A1 (1975-10-01), None
Derwent english abstract of admitted art DE 196 19 319 (Ufermann).*
Derwent english abstract of DT 2417450A1 (Hamburger).

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