GB2167232A - Variable capacitor - Google Patents

Abstract

A small-sized variable capacitor has poles (18a to 18d) mounted to the baseplate (18) of the capacitor. The poles have protrusions (18f) upstanding on the surfaces of the poles on which the stator plates (1) rest. The stator plates (1) bear on, and are retained by, the inner walls of these protrusions (18f). <IMAGE>

Description

SPECIFICATION Variable capacitors FIELD OF THE INVENTION The present invention relates to variable capacitors and, more particularly, to a smallsized variable capacitor adapted for small-sized radio receivers, radio cassette recorders, and other similar devices.

BACKGROUND OR THE INVENTION A conventional variable capacitor of this kind is shown in Figs. 3, 4, and 5. This device has stator plates 1 that are coated with dielectric 1 A. Washers 2 are disposed alternately with the stator plates 1. These plates 1 and washers 2 form one group 3 of stators.

Other groups 4, 5, 6 of stators have the same structure as the stator group 3. Rotor plates 7 are disposed alternately with the washers 8. A rotor shaft 9 is provided with a threaded portion 9A at its front end. The plates 7 extend through the shaft 9, and a nut 10 is meshed with the threaded portion 9A such that the plates 7 are firmly held. Rotor sections 11, 12, 13, 14 correspond to the stator groups 3, 4, 5, 6, respectively.

The conventional device further includes a front baseplate 15 that has poles 15a, 15b, 15c, 15d, for separately supporting the stator groups 3, 4, 5, 6 and a bearing 15e through which the rotor shaft 9 extends. A rear baseplate 16 has poles 16a, 16b, 16c, 16d corresponding to the poles of the front baseplate 15, and is provided with a hole 16e for the support of the shaft 9. The shaft 9 is held between the baseplates 15 and 16, and is made rotatable by the bearing 15e and the hole 16e formed in the front baseplate 15 and the rear baseplate 16, respectively. The stator groups 3, 4, 5, 6 are held between the poles 15a, 15b, 15c, 15d mounted to the front baseplate 15 and the poles 16a, 16b, 16c, 16d mounted to the rear baseplate 16. Metal terminals 17 extend through the poles 16a, 16b, 16c, 16d mounted to the rear baseplate 16 and fitly engage with the stator groups 3-6.

In mounting the terminals 17, they are urged into the poles 15a, 15b, 15c, 15d mounted to the front baseplate 15.

In the prior art device described above, the stator groups are held between the poles mounted to the baseplates. When the terminals are mounted, they are inserted, fitted, and urged into the poles. Therefore, the terminals must be inserted after hole A in the rear baseplate, hole B in the front baseplate, and holes C in the stator groups have been brought into register with each other. Thus, jigs D have heretofore been used for the assembly operation. Each individual pole requires a separate jig. In addition, the jigs are required to have a horizontal slide mechanism. Furthermore, accuracy is needed for them, because if the stator groups were located at various positions, the variation among the electrostatic capacitances of small-sized variable capacitors would be directly affected thereby.

However, it is difficult to manufacture such ideal jigs. Accordingly, the actual situation is that variation among capacitances due to the locating of the stator is allowed to some extent, and it is corrected by fine adjustment that is made later at a capacitance adjustment step. That is, for the prior art structure, the stator groups are not sufficiently accurately located, necessitating special jigs during assembling operation. Even if such jigs are used, a sufficient locating accuracy is not yet obtained. This needs much labor at the subsequent capacitance adjustment step.

SUMMARY OF THE INVENTION It is the main object of the present invention to provide a small-sized variable capacitor which is free of the foregoing disadvantages with the prior art device and which is especially adapted for small-sized radio receivers, radio cassette recorders, and other similar devices.

The aforementioned object is achieved in accordance with the teachings of the invention by a small-sized variable capacitor having a pair of baseplates disposed opposite to each other, a rotor shaft disposed so as to be rotatable, rotor plates firmly secured to the shaft and each made of a metal sheet, and stator plates each made of a metal sheet and coated with dielectric, the stator plates being opposite to, and slightly spaced from, the rotor plates, the stator plates being held between poles mounted to the baseplates, the capacitor being characterized in that at least one of the poles has a protrusion on the surface on which the stator plates are held between the poles, and that the stator plates bear on, and are retained by, the inner wall of the protrusion.

Other objects and features of the invention will become more readily apparent from the ensuing specification and claims when taken with the drawings.

BRIEF DESCRIPTION OF THE DRA WINGS Figure 1 is an exploded perspective view of main portions of a small-sized variable capacitor according to the present invention; Figure 2 is a top view of the capacitor shown in Fig. 1, and in which the rear baseplate has been omitted; Figure 3 is a longitudinal cross section of a conventional small-sized variable capacitor; Figure 4 is an exploded perspective view of main portions of the capacitor shown in Fig.

3; Figure 5 is a top view of the capacitor shown in Fig. 3, and in which the rear baseplate has been omitted; Figures 6 and 7 are top views of other small-sized variable capacitors according to the invention, and in which the rear baseplate has been omitted.

DETAILED DESCRIPTION OF THE INVENTION Referring to Figs. 1 and 2, there is shown a small-sized variable capacitor embodying the concept of the present invention. It is to be noted that like components are denoted by like reference numerals throughout all the figures. Therefore, those components which have already been described will not be described in detail below. The novel capacitor shown in Figs 1 and 2 includes a front baseplate 18 that has poles 18a, 18b, 18c, 18d which support stator groups. The baseplate 18 is provided with a bearing hole 1 8e through which the rotor shaft 9 extends. Protrusions 1 8f are formed on the surfaces of the poles 18a, 18b, 18c, 18d to which the stators are held. The stators bear on, and are retained by, the inner walls of the protrusions 18f.

In the same manner as in the prior art device, the rotor shaft 9 is rotatably held between the front baseplate 18 and the rear baseplate 16. The stator groups 3-6 are held between the poles 18a, 18b, 18c, 18d mounted to the front baseplate 18 and the poles 16a, 16b, 16c, 16d mounted to the rear baseplate 16. The stator groups 3-6 bear on, and are retained by, the inner walls of the protrusions 1 8f formed on the poles 18a, 18b, 1 8c, 18d mounted to the front baseplate 18.

Metal terminals 17 extend through the poles 16a, 16b, 16c, 16d mounted to the rear baseplate 16 and fitly engage with the stator groups 3-6 . In mounting the terminals 17, they are urged into the poles 18a, 18b, 18c, 18d mounted to the front baseplate 18.

Figs. 6 and 7 show other examples of the shape of the protrusions 18f. In the example of Fig. 6, the protrusions 18f formed at the corners have inner surfaces extending along the outer peripheries of the stator groups 3-6. In the example of Fig. 7, the protrusions 18f are disposed substantially perpendicularly to each other with a given gap therebetween.

Since the novel variable capacitor is constructed as described above, it does not need special jigs for placing stator groups in position, unlike the conventional device already mentioned. Further, it permits positioning that is as accurate as metal molds. This can greatly enhance the efficiency of operation during the subsequent capacitance adjustment step. Hence, the small-sized variable capacitor can be manufactured at lower cost. Consequently, a small-sized variable capacitor can be provided which is cheaper than conventional devices and especially adapted for small-sized radio receivers, radio cassette recorders, and other similar devices.

In the above example, the protrusions are formed on the poles mounted to the front baseplate, but exactly the same advantage can also be had by forming protrusions on the rear baseplate.

Claims (4)

1. In a variable capacitor having a pair of baseplates disposed opposite to each other, a rotor shaft disposed between the baseplates so as to be rotatable, rotor plates firmly secured to the shaft and each made of a metal sheet, and stator plates each made of a metal sheet and coated with dielectric, the stator plates being opposite to, and slightly spaced from, the rotor plates, the stator plates being held between poles mounted to the baseplates, the improvement wherein at least one of the poles has a protrusion on the surface on which the stator plates are held between the poles, and wherein the stator plates bear on, and are retained by, the inner wall of the protrusion.

2. In a variable capacitor as set forth in claim 1, the further improvement wherein the poles have protrusions at the corners, the protrusions having arc-shaped inner surfaces extending along the outer peripheries of the stator groups.

3. In a variable capacitor as set forth in claim 1, the further improvement wherein each of the poles has two protrusions which are disposed substantially perpendicularly to each other at a given gap therebetween at each corner.

4. A variable capacitor substantially as hereinbefore described, with reference to Figs.

1, 2 and 6 of the accompanying drawings.