Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2002-01-18
2002-10-08
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06462463
ABSTRACT:
The present invention relates to an actuator having an active piston.
A particularly advantageous application of the invention lies in brake actuators, in particular in the field of aviation.
Generally, presently-known brake actuators are hydraulic type actuators that enable very large forces to be applied, while nevertheless presenting good ability to take up slack due to wear, changes in temperature, etc. . . . .
Nevertheless, those actuators present drawbacks associated with the use of a hydraulic fluid: risks of leakage, the need for a pressure generator, etc. . . . .
An object of the invention is to propose an actuator that does not present the drawbacks of hydraulic actuators.
Actuators have already been proposed that comprise a piston constituted by a plurality of successive magneto-strictive segments suitable for being controlled independently of one another.
In this context, reference can be made to the various following patents: U.S. Pat. No. 5,281,875, U.S. Pat. No. 5,317,223, U.S. Pat. No. 5,039,894.
Such actuators require magnetic field generator means to be provided around the piston, which means are complex and particularly bulky.
In particular, for identical volume, they do not enable the same forces to be generated as a hydraulic actuator.
Piezoelectric actuators are also known comprising a guide jacket and a piston suitable for moving axially in said jacket, said piston comprising a plurality of successive segments of multilayer piezoelectric material, said actuator including control means suitable for applying control voltages to said segments to cause the segments to expand in such a manner that they become blocked relative to the guide jacket and to lengthen other segments inside said jacket, these expansions and lengthenings being controlled by said control means in sequences that displace the piston in said jacket.
Such actuators are already described in particular in FR 2 702 895 and in the abstract of Japanese patent JP 60 148 389. They are conventionally constituted by segments, some of which are for expanding perpendicularly to the travel direction of the piston, while the others are for expanding in the travel direction, these various segments being arranged in H-shaped structures.
It will be understood that such structures remain a form of embodiment that is very expensive and complicated.
The invention proposes a piezoelectric actuator structure that is particularly simple.
In particular, the control means of the actuator of the invention are suitable for applying a voltage to each of the segments to shorten said segment and block it in the guide jacket and an opposite voltage which releases said segment relative to said jacket and lengthens it therein, these two voltages being applied in succession to said segment during a piston-displacement sequence, each segment thus being used for blocking purposes and for lengthening purposes during such a sequence.
Such an actuator structure is capable of generating very high pressures (in the range 50 megaPascals (MPa) to 100 MPa) that are of the same order of magnitude as the highest pressures that exist in present-day hydraulic circuits. For equivalent diameters, a piezoelectric piston is capable of generating the same forces as a hydraulic piston.
Such an actuator is advantageously associated with the various following characteristics taken singly or in any technically feasible combination:
a segment presents a plurality of electrodes which extend transversely relative to the axis of the piston, at least one piece of electrical control metallization extending over at least a portion of the height of the piston to a setback in which the metallization is in contact with every other electrode of the segment, the electrodes of the segments being offset in alternation relative to said setback, the metallization in register with segments that it does not feed being offset relative to the setback so that it does not come into contact with the electrodes of said segments;
the piston has a metal case in which the segments are received, control metallization being received in a groove which extends in the height of the piston;
the guide jacket comprises an inner cylinder, an outer cylinder, and an intermediate cylinder, the material of the intermediate cylinder having a coefficient of expansion greater than the coefficients of the inner and outer cylinders;
the intermediate cylinder presents slots extending radially from its inner surface towards its outer surface; and
the control means comprise means for causing the segments to deform in a sequence such that initially the piston advances so as to take up the slack which separates it from the surface against which it is to bear, and subsequently it applies a force against said surface.
REFERENCES:
patent: 3551764 (1970-12-01), Evans
patent: 4623044 (1986-11-01), Ohta et al.
patent: 4971106 (1990-11-01), Tsutsui et al.
patent: 5281875 (1994-01-01), Kiesewetter et al.
patent: 5327041 (1994-07-01), Culp
patent: 0 518 262 (1992-12-01), None
patent: 0 908 961 (1999-04-01), None
patent: 2 702 895 (1994-09-01), None
patent: 63-3664 (1988-01-01), None
patent: 2001-298970 (2001-10-01), None
Patent Abstracts of Japan; vol. 017, No. 083 (M-1369), Feb. 18, 1993 & JP 04 282035 A (Aisin Seiki Co. Ltd), Oct. 7, 1992; abstract.
Blakely & Sokoloff, Taylor & Zafman
Dougherty Thomas M.
Sagem S.A.
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