1. Field of the Invention
The present invention relates to a method for producing an inclined helical spring, and more particularly to the method for producing the inclined helical spring for use in a strut type vehicle suspension.
2. Description of the Related Arts
Various types of helical compression spring have been known heretofore. Among them, a compression spring having an inclined coil axis has been known. In British Patent No. 1192766 for example, proposed are improvements in or relating to vehicle wheel suspension assemblies. The British Patent discloses a helical spring which is coiled in the untensioned state with transverse relative displacement of the turns, and when mounted is stressed by lateral relative displacement of the turns of the spring out of the unstressed position thereof to apply a bending moment to the shock absorber in opposition to the bending moment applied by a wheel support.
In the British Patent, with respect to the compression helical spring having an inclined coil axis, i.e., inclined helical spring, its structure and a method for producing it have not been described. If the inclined helical spring is produced by a cold working according to a conventional process for producing a substantially cylindrical helical spring, it is assumed that the spring is produced by changing the pitch of its coil end portion. According to the produced compression spring, however, its neighboring coils are likely to contact each other, so that it is almost impossible to obtain a desired spring characteristic. On the other hand, as for another conventional method for producing a spring, a hot working has been known heretofore, whereby it is possible to produce the inclined helical spring without changing the pitch.
When the inclined helical spring is produced by the hot working, the coil wire may be wound according to the processes as shown in FIGS. 10-12. That is, by holding one end of a coil wire HW, which was heated up to a certain temperature to be deformed thermally, on an end of a mandrel 202 by a pressing member 201, and drawing the coil wire HW by a lead roller 203 in a predetermined direction so as to wind it around the mandrel 202, the inclined helical spring 50 as shown in FIG. 12 can be formed. In this case, the lead roller 203 is set to provide a larger inclined angle xcex81 for a half of a coil as shown in FIG. 10, and provide a smaller inclined angle xcex82 for a half of a coil followed by the half coil as shown in FIG. 11. Therefore, the diameter D1 of the half coil as shown in FIG. 10 is larger than the diameter D2 of the half coil as shown in FIG. 11. Therefore, by repeating the processes as shown in FIGS. 10 and 11 according to a half coil cycle, can be produced the inclined spring 50 having the coil axis inclined at the angle xcex1 to the opposite end faces, as shown in FIG. 12.
According to the method for producing the inclined helical spring by the hot working as described above, however, not only a large plant including a heating apparatus is needed, but also the angles xcex81 and xcex82 are likely to be varied, thereby requiring a time for checking its characteristic. Also, it is not easy to obtain a desired side force, because its shape is varied by spring-back. In the mean time, there exists a helical spring that is formed to vary a diameter of each coil along the coil axis, such as a truncated cone-shaped helical spring, a barrel-shaped helical spring, or the like. However, it is hardly considered that someone will employ a helical spring having a varying diameter of each coil, with its coil axis inclined, for the helical compression spring as disclosed in the British patent.
Accordingly, it is an object of the present invention to provide a method for producing an inclined helical spring easily by cold working, without a heating process required for forming the spring.
In accomplishing the above and other objects, a method for producing an inclined substantially cylindrical helical spring having a plurality of substantially circular coils along an inclined coil axis, includes the steps of forming each substantially circular coil constituting a predetermined portion of the substantially cylindrical helical spring between one end and the other one end of the spring to be increased and decreased in diameter successively along the longitudinal axis of the spring, with a half section of the coil increased or decreased in diameter compared with a diameter of a preceding or subsequent half section of the coil; and forming the longitudinal axis of the spring in a free state of the of the spring to be inclined substantially at a predetermined angle to an axis to be mounted with the spring.
Or, the method for producing the substantially cylindrical inclined helical spring may include the steps of forming each substantially circular coil constituting a substantially circular helical spring of the whole length thereof between one end and the other end of the spring to be increased and decreased in diameter successively along the longitudinal axis of the spring, with a half section of the coil increased or decreased in diameter compared with a diameter of a preceding or subsequent half section of the coil; and forming the longitudinal axis of the spring to be inclined substantially at a predetermined angle to an axis to be mounted with the spring.
In the methods as defined above, preferably each coil is formed with one section having approximately a half of the circumference of each coil divided by a plane including the coil axis is formed to be increased or decreased in diameter, and the other one section followed by the one section having approximately a half of the circumference of each coil is formed to be decreased or increased in diameter.