Spring devices – Coil – Including end thrust member
Reexamination Certificate
2001-12-13
2003-04-08
Lavinder, Jack (Department: 3613)
Spring devices
Coil
Including end thrust member
C267S180000, C267S248000
Reexamination Certificate
active
06543757
ABSTRACT:
This application claims priority under 35 U.S.C. Sec.119 to a patent application No.2000-379738 filed in Japan on Dec. 14, 2000, the entire content of which is herein incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a helical compression spring for use in a strut type vehicle suspension, and relates to a strut type vehicle suspension having a helical compression spring.
2. Description of the Related Arts
In general, a vehicle suspension is provided with a helical compression spring, which is generally designed to provide a coil axis that coincides with a direction of reaction force of the spring. Various types of vehicle suspension system have been known heretofore. Among them, a strut type suspension with a shock absorber employed as a strut for positioning a wheel is popular. According to the strut type suspension, however, due to a displacement between its load input axis and strut axis, a bending moment is exerted on the strut, with side force acting on a guide and a piston of the strut. This side force prevents the piston from sliding smoothly in the guide to act as the shock absorber. In order to compensate the bending moment, it has been known to arrange a coil axis of a cylindrical helical compression spring to be offset to the strut axis.
Since the arrangement between the coil axis of the helical compression spring and the strut axis of the shock absorber is determined geometrically, it has been required that the helical compression spring should be designed to coincide its coil axis with the direction of reaction force of the spring. In order to meet such requirement, various studies have been made, including the article “Approaches to Minimizing Side Force of Helical Coil Springs in Suspension Design”, presented by engineers including the inventor of the present application, and received by Japan Society for Spring Research on Aug. 28, 1995, wherein it was proposed to minimize the side force of the helical compression spring.
In contrast, on pages 56 and 57 of “Automotive Engineering” issued on September 1997, there are disclosed two kinds of spring having a coil axis inclined to an axis of a shock absorber so as to minimize a friction of the shock absorber for a strut type suspension. One spring is so constituted that one end coil is formed into a pig tail coil, and an axis for connecting the center of the pig tail coil and the center of the other end coil is served as the axis of the shock absorber, and that the axis and a spring force direction (reaction force direction) are arranged to provide a certain angle so that they are intersected at the center of the other end coil. The other spring is so constituted that both end coils are formed into the pig tail coils, and an axis for connecting the centers of those end coils is served as the axis of the shock absorber, and that the axis and the spring force direction are arranged to provide a certain angle so that they are intersected at a longitudinal center of the spring.
With respect to the vehicle suspension, further reduction in size is required now. By means of mere improvement made to a supporting mechanism of the strut having a conventional cylindrical helical compression spring, therefore, it is difficult to compensate the bending moment exerted on the strut due to load from a road. Rather, it is necessary to positively increase a side force applied by the helical compression spring to the strut type suspension, especially widthwise of the vehicle. However, it is not easy to apply a desired side force to the suspension by the conventional helical compression spring. By means of the helical spring disclosed in the aforementioned publication of the Automotive Engineering, sufficient side force necessary for the strut type suspension can not be obtained. Namely, it is impossible to apply the side force to the guide portion and piston portion of the strut enough to compensate the side force exerted thereon.
Therefore, the applicant proposed a helical compression spring for a strut type suspension with a simple structure to apply a desired side force to the strut when mounted on the strut type suspension, in a Japanese patent application No.11-163652 filed on Jul. 10, 1999, which was published under Japanese Patent Publication No.2000-351311 on Dec. 19, 2000 in Japan. According to the helical compression spring as proposed above, by simply installing the helical compression spring as described hereinafter in the suspension without making a specific change to the prior suspension, the spring is properly mounted on the strut so that a reaction force axis of the spring lies approximately on the center of an upper seat, and that the desired side force is applied to the strut, whereby a smooth absorbing operation can be ensured. In the helical compression spring for the vehicle suspension to be compressed between an upper seat and a lower seat, the spring is formed to provide an end coil center line connecting the centers of an upper end coil and a lower end coil of the spring to be offset to a coil axis of a body portion of the spring, and a pitch of the lower end coil is set to tilt a lower end plane of the spring seated on the lower seat at a predetermined angle to the lower seat in the direction for shortening the longitudinal length of one side of the spring with the end coil center line thereof offset to the coil axis, in an unloaded state of the spring, and/or a pitch of the upper end coil is set to tilt an upper end plane of the spring seated on the upper seat, at a predetermined angle in the direction for shortening the longitudinal length of the other side of the spring opposite to the one side of the spring with the end coil center line thereof offset to the coil axis, in the unloaded state of the spring.
According to the helical compression spring as constituted above, if a position of coiling end of a lower end coil can not be changed, for example, it will be necessary to limit the total number of coils (turns) to 4.55 coils, for example, so as to direct the side force in a predetermined direction. This limitation of the number of coils requires a change of the total number of coils by a unit of one coil. As a result, change in diameter of a coil wire will be necessitated, so that it will be difficult to reduce a total weight of the spring, as explained with referenced to
FIGS. 9
,
10
and
11
, hereinafter.
FIG. 9
shows a model helical compression spring
5
x
having an end coil center line for connecting the centers of the lower end coil and upper end coil, which coincides with a coil axis of a body portion of the spring, on the z-axis as shown in FIG.
9
. In general, the reaction force, which is caused when the helical compression spring is compressed, does not coincide with the coil axis. As shown in
FIG. 9
, its component projected on the x-y plane is called as a side force (SF), and an angle (&thgr;) rotated clockwise from the y-axis indicative of its direction is called as a side force direction. The value and direction of the side force are varied periodically in response to the total number of coils of the helical compression spring, as shown in FIG.
10
and
FIG. 11
, respectively.
Accordingly, when the helical compression spring as proposed in the above-described Japanese patent application No.11-163652 is installed in the vehicle, it is desirable to adjust the side force not only widthwise of the vehicle, but also lengthwise of the vehicle. In this case, however, different countermeasures will have to be made, in the case where it is possible to change a position of a coiling end of a lower end coil (or upper end coil), or it is possible to change a design of the lower end coil (or upper end coil), and the case where it is impossible to change the position of the coiling end of the lower end coil (or upper end coil), or it is impossible to change the design of the lower end coil (or upper end coil), as explained hereinafter.
In the case where it is possible to change the position of the coiling end of the lower end coil (o
Burns Doane , Swecker, Mathis LLP
Chuo Hatsujo Kabushiki Kaisha
Lavinder Jack
Pezzlo Benjamin A.
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