Power plants – Motor operated by expansion and/or contraction of a unit of... – Mass is a solid
Patent
1990-09-25
1991-12-10
Ostrager, Allen M.
Power plants
Motor operated by expansion and/or contraction of a unit of...
Mass is a solid
188299, 188313, F03G 706
Patent
active
050706977
DESCRIPTION:
BRIEF SUMMARY
INTRODUCTION
The invention relates to an actuator comprising a cylindrical housing with an elongated actuating element movably supported therein, and an element of memory metal engaging said acuating element, the housing and the actuating element being movable relative to one another by activation of the element of memory metal and the housing being provided at one end with at least one opening through which the actuating element protrudes longitudinally upon said relative movement.
BACKGROUND OF THE INVENTION
An actuator of this type is known from Japanese Patent 59,206,682.
The term memory metal is used to define a metal alloy or a group of metal alloys which have the characteristic that after the metal has acquired a certain shape at a suitable temperature it always returns spontaneously to this shape on heating above a certain transition temperature, the so-called shape recovery behaviour. Below this transition temperature, the memory metal is apparently plastically deformable. The transition temperature and a hysteresis region around the transition temperature are determined by the composition of the alloy. As a consequence of the good controllability and the unlimited repeatability of the shape recovery behaviour and because of the relatively sharply restricted transition temperature, these alloys are used for thermal transducers and for converters of thermal energy to mechanical energy. The alloy for which there is most interest are CuZnAl, CuAlNi and TiNi, the latter alloy also being termed Nitinol.
In the actuator disclosed in JP-A-59,206,682 the distance over which the housing and the actuating element can be moved relative to one another can be predetermined via an assembly of two compression springs and an adjusting screw. When this known actuator is used in hydraulic or pneumatic devices, the fluid flow in a system of channels in these devices can be influenced only in a predetermined manner, in accordance with the on/off principle. The set fluid control can be changed only by changing the relative distance of movement of the housing and the actuating element by means of the adjusting screw, for example manually. The assembly of the two compression springs acting on the actuating element also has an adverse influence on the response speed of the actuator.
As a consequence of the spontaneous shape recovery behaviour, the memory metal in itself possesses only the characteristics of an on/off control. In practice, however, there is also need for electrically operated actuators with which proportionally the magnitude of the fluid flow in one or more channels of such a system of channels can be controlled.
BRIEF DESCRIPTION OF THE INVENTION
The aim of the invention is to provide an actuator of the type mentioned in the preamble which is universally applicable for influencing fluid or gas flows in a hydraulic and/or pneumatic system proportionally and with a desired response speed while maintaining the advantages of the use of memory metal.
For the purpose the invention is characterized in that the actuator is provided with locking means engaging the actuating element for mutually locking the actuating element and the housing in one or more positions, in particular for proportionally influencing the fluid flow in hydraulic and/or pneumatic devices.
Compared with the known actuator, in the embodiment according to the invention the distance over which the housing and the actuating element can be moved relative to one another can be set with the aid of the locking means without influencing the response speed. Consequently, for example, in the case of a fixed housing the actuating element can thus be moved under the influence of the element of memory metal to a position outside the housing and, by means of the locking means engaging this element, locked proportionally and discontinuously in one or more positions, the actuator being able, for example, to operate a flap or shut-off valve with which the fluid flow in a system of channels is controlled. On the other hand, the actuating element can be
REFERENCES:
patent: 4187683 (1980-02-01), Northrop et al.
Koni
Lewis J. Gordon
Ostrager Allen M.
Seitter Robert P.
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