The present invention relates to a seat sliding device for sliding a seat of a vehicle.
A kind of seat sliding device for sliding a seat of a vehicle as shown in FIGS. 1 and 2 has been disclosed. A pair of these kind of seat sliding devices are provided for a seat and arranged in parallel with each other in a back-and-forward direction of the seat. The seat sliding device has a pair of rails, a lower rail and an upper rail. The lower rail is fixedly mounted on a vehicle body and the upper rail is fixedly mounted on the seat and slidably engaged with the lower rail by rolling members.
A horizontally settled seat sliding device is shown in FIG. 1, and a longitudinally settled seat sliding device is shown in FIG. 2.
In the horizontally settled seat sliding device, a lower rail 1 mounted on a vehicle body is provided with a lower base 1a which has a somewhat U shaped cross section and a pair of lower flanges 1b which are provided on both upper ends of the lower base 1a and extend toward the outside thereof. The upper rail 2 is directly mounted on a bottom face of the seat, or it can be indirectly mounted on the bottom face of the seat through a supporting member. Further, the upper rail 2 comprises an upper body 2a (which covers an open end of the lower rail 1) and a pair of upper flanges 2b. These upper flanges 2b are provided on both side ends of the upper body 2a, extend downwards, and are engaged with the pair of lower flanges 1b, as shown in FIG. 1. The upper rail 2 is supported by a roller 3 which is provided inside the lower rail 1. A pair of balls 4 are provided in a pair of spaces which are formed by the lower flanges lb and the engaged upper flanges 2b. These balls receive a pulling force applied to the upper rail 2 in order to slide the upper rail 2 smoothly along the lower rail 1. Further, the balls 4 and roller 3 are retained by a retainer so that all these rolling members are moved together inside a seat sliding body M which is formed by the upper rail 2 and lower rail 1.
FIG. 2 shows a longitudinally settled seat sliding device in which a lower rail 6 and an upper rail 7 are longitudinally settled. In direct contrast to the above described horizontally settled seat sliding device, the lower rail 6 has a structure identical to that of the upper rail 2, and the upper rail 7 has a structure identical to that of the lower rail 1. The other members such as the roller 3, the balls 4, and the retainer 5 in FIG. 2 correspond to those shown in FIG. 1 which have the same reference numbers. An N depicts a seat sliding body of the longitudinally settled seat sliding device.
In the above-described horizontally settled seat sliding device, since the cross section of the upper rail 2 has a somewhat rectangular shape as shown in FIG. 1 and the longitudinal length of the upper rail 2 is much shorter than the horizontal length thereof, a longitudinal flexural strength of the upper rail 2 is insufficient. Therefore, when the plate thickness of the upper rail 2 is thickened in order to strengthen the flexural strength thereof, the upper rail 2 becomes heavy and results in a high cost.
In the case of the longitudinally settled seat sliding device, the longitudinal length of the upper rail 7 is wide enough to create a sufficient longitudinal flexural strength in the upper rail 2. However, since the horizontal width of the upper rail 7 cannot be made large enough and the upper rail 7 does not have any support means which work to support the upper rail 7 in a horizontal direction, the horizontal strength of the upper rail 7 may not be sufficient thereby leading to a possible rattly condition in which the upper rail 7 cannot slide smoothly along the lower rail 6.
Moreover, since the structure of the lower rail 1 is not similar to that of the upper rail 2 and the structure of the lower rail 6 is not similar to that of upper rail 7, errors when forming the lower rail 1 or 6 and the upper rail 2 or 7 may occur resulting in a misfitting of the lower rail 1 in the upper rail 2 or of the upper rail 7 in the lower rail 6. In this situation, the upper rail 2 or 7 cannot slide smoothly along the lower rail 1 or 6, respectively.