In an electromagnetic relay of a relatively small size, for example 32.times.35.times.32 mm, an armature holding structure is used in order to support an armature rotatably on one end portion of the yoke of the electromagnet.
Examples of the prior art armature holding structure in an electromagnetic relay are illustrated in FIGS. 1A, 1B, 2A and 2B. In the structures of FIGS. 1A, 1B, 2A and 2B, the armature 2', having a rectangular aperture 23' and a groove 22', rides on one end of the yoke 13', having a rectangular aperture 132', of the electromagnet 1'. In order to maintain the pivot relationship between the armature 2' and the yoke 13', a hinge plate spring 3' having the ends partly rolled under (FIGS. 1A, 1B) or a hinge plate spring 3" having several bent portions (FIGS. 2A, 2B) bridges the groove 22' in the armature 2' and the rectangular aperture 132' of the yoke 13'. Such hinge plate spring 3' or 3" is manufactured by the process of punching a planar plate having a predetermined size from a sheet and then working such punched planar plate to give either a shape in which the ends are partly rolled under (FIGS. 1A, 1B) or a shape having several bent portions (FIGS. 2A, 2B).
However, there are problems in the structure and the manufacturing process of the devices of FIGS. 1A, 1B, 2A and 2B. First, the provision of the rectangular apertures 23' and 132' in the armature 2' and the yoke 13' causes each of the magnetic flux paths through the armature 2' and through the yoke 13' to become narrow, and hence the magnetic reluctances of the armature 2' and the yoke 13' are increased, and hence the magnetic efficiency of the magnetic path of the electromagnet 1' is deteriorated. If such deterioration of the magnetic efficiency is not desirable, the entire size of the electromagnet must be increased, which does not comply with the requirement for the reduction of the size of the electromagnetic relay.
Second, the process of attaching the hinge plate spring 3' or 3" to the groove 22' and the rectangular aperture 132' requires specially skillful work, without which the preliminarily given shape and the preliminarily stored resilient force of the hinge plate spring 3' or 3" are apt to be deviated so that uniformity of the operating characteristics of the produced electromagnetic relays cannot be achieved.
Third, in the case where the hinge plate spring 3' or 3" is manufactured by the process of punching a planar plate from a sheet having a large size in the longitudinal direction, which sheet has been manufactured by the rolling process, the degree of utilization of the sheet as a material for such punched planar plate cannot be increased. This is because the punching of the planar plate should be carried out so that the longitudinal direction of the hinge plate spring coincides with the longitudinal direction of the sheet in order to ensure the metallurgical strength of the hinge plate spring.
The structure of FIGS. 2A, 2B is disclosed in Japanese utility model application laid-open No. 53-89541.