JPH0716744B2 - Shape memory alloy coil spring - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an improvement of a coil spring made of a shape memory alloy, and more particularly to preventing the hook portions provided at both ends of the coil portion from sagging.

Shape memory alloys memorize a certain shape at a temperature above the martensitic transformation point, and after deforming this at a temperature below the transformation point and then raising the temperature, the characteristic that the shape remembered at the transformation point is restored to the certain shape. As shown, it is hard at temperatures above the martensite transformation point and soft at temperatures below the transformation point, so it is used in combination with a bias spring, or in combination with two shape memory alloy coil springs for actuators, etc. ing. There is a limit to the amount of deformation that a shape memory alloy can recover by heating, that is, the amount of deformation that can be recovered, and if the amount of deformation exceeds a certain amount, it will not return to the completely remembered shape even if the temperature rises above the transformation point. Absent. This recoverable strain amount is
The Ni-Ti-based shape memory alloy is 8% and the Cu-Zn-Al-based shape memory alloy is 2%.

Therefore, in order to obtain a large amount of deformation using a shape memory alloy, as shown in FIG. 1, a coil spring having hook portions (2) formed at both ends of the coil portion (1) parallel to the coil axis (A). Is used. The method of forming the shape memory alloy wire into a coil spring varies depending on the type of alloy and the purpose of use, but is generally adjusted so that the entire coil spring exhibits uniform shape memory characteristics. Therefore, since the entire coil spring has the same transformation temperature, the entire coil spring is in a soft state at a temperature below the transformation point.

When such a coil spring is stretched at a temperature below the transformation point,
As shown in FIG. 2, the base portion (3) of the hook portion (2) is strongly deformed, so that the hook portion (2) itself is also subjected to bending deformation. Such non-uniform deformation increases as the deflection of the coil spring increases, and in particular, the shape memory alloy coil spring is used with a large deformation strain of one digit or more compared to general coil springs. The abnormal deformation of No. 2 becomes large, changes the effective number of turns of the coil spring, adversely affects the operating characteristics, and is not preferable from the viewpoint of repeated life, and its improvement has been strongly desired.

As a result of various studies in view of the above, the present invention has found that the hook portion can be prevented from sagging by strengthening the hook portion by work hardening, and a coil spring made of a shape memory alloy with less deformation of the hook portion is provided. In the developed one, in a shape memory alloy coil spring in which hook portions parallel to the coil axis are provided at both ends of the coil portion, the coil portion is still subjected to shape memory heat treatment, and the hook portion is further work hardened. It is characterized by that.

This will be described in detail with reference to the drawings.

FIG. 3 shows an embodiment of the coil spring of the present invention.
In the figure, (1) shows a coil portion, and (2) shows a hook portion formed at one end thereof. A shape memory alloy wire is formed into a tightly wound coil at a temperature equal to or higher than a transformation point, and both ends thereof are fixed to fix the entire coil. Shape memory heat treatment is performed at a temperature equal to or higher than the transformation point. Next, at a temperature below the transformation point, a hook forming machine is formed on both ends of the coil portion (1) in a direction opposite to the bending direction of the coil portion (1) to form hook portions (2) parallel to the axial direction (A). To do. In this hook forming, the coil portion (1) is stretched at a temperature below the transformation point, and when the shape of the coil portion (1) is recovered, a deformation amount equal to or more than the amount of strain capable of completely recovering the shape is added to the hook portion (2) for work hardening. . That is, the hook portion (2) is deformed until it is work hardened. For example, in Ni-Ti shape memory wire,
After the shape memory heat treatment, deformation processing of 12% or more is further applied to the hook portion (2) to work-harden the hook portion (2).

The coil spring of the present invention has the above-mentioned structure, and when the coil is stretched at a temperature below the transformation point, the base portion (3) of the hook portion (2) is hardly deformed as shown in FIG. Also in (2), there is almost no deformation.

Specific examples of the coil spring of the present invention will be described below.

A shape memory alloy wire rod (transformation point: 45 ° C) consisting of Ni55wt% and the balance Ti with a diameter of 1.0mm was formed into a tightly wound coil with a winding diameter of 7.5mm at room temperature, then both ends were fixed and the entire coil temperature was 500 ° C. The shape memory was heat-treated for 30 minutes. Next, both ends of this coil were rolled at a room temperature (20 ° C.) in a direction opposite to the coil winding direction by a hook forming machine, and 15% deformation processing was applied to work-harden the hook portion.

When the coil spring of the present invention thus obtained was mounted on a device and used, it was found to be in a good mounted state, and when it was actually operated as an element, even after a number of repetitions, the hook portion after operation was completely flat. Was not recognized.

As described above, according to the present invention, it is possible to prevent the hook portion of the shape memory alloy coil spring from sagging, and to exert a remarkable effect that the life thereof can be remarkably improved.

[Brief description of drawings]

FIG. 1 is a side view showing an example of a conventional shape memory alloy coil spring, FIG. 2 is an explanatory view showing a deformed state when the coil shown in FIG. 1 is stretched, and FIG. 3 is a shape memory alloy of the present invention. FIG. 4 is a side view showing an embodiment of the coil spring, and FIG. 4 is an explanatory view showing a deformed state when the coil shown in FIG. 3 is stretched. 1 ... Coil part, 2 ... Hook part, 3 ... Hook base part.

Claims (1)

[Claims] 1. A coil spring made of a shape memory alloy in which hook portions parallel to the coil axis are provided at both ends of the coil portion, the coil portion is still subjected to shape memory heat treatment, and the hook portion is further work hardened. A coil spring made of a shape memory alloy, which is characterized in that