1. Field of the Invention
The present invention relates to a device for transmitting, without vibrations, the up-down and left-right movements from an electrical control to a mirror-holder plate of a rearview mirror, particularly of an automobile vehicle.
2. Description of the Prior Art
A rearview mirror of the type illustrated in U.S. Patent No. 4,598,605 is described hereinafter with reference to the part reproduced in the invention, as shown in FIGS. 1 through 3 of the accompanying drawings.
The known rearview mirror has a casing made of plastic material, which includes a body 1 and a cover 2. It also includes a plate 3 on which a mirror is fixed. A cross presents two perpendicular pivot pins 4 and 5, clipped in a fork joint 6 on the plate and in a fork joint 7 on the cover, respectively.
The body 1 of the casing contains two electric motors 8 and 9 coupled to tangent screws 10 and 11 meshing with tangent wheels 12 and 13 integral with nuts 14 and 15 which cooperate with screws 16 and 17.
The screw 16 is provided with a ball joint 18 clipped in a bearing 19 of the plate 3 and, similarly, the screw 17 is provided with a ball joint clipped in another bearing (neither of which are shown in the drawing) of the plate. The mean geometrical axes 20 and 21 of the screws 16 and 17 are substantially perpendicular to the plate and disposed at 90.degree. with respect to the center 22 where the pivot pins 4 and 5 cross.
Each of the nuts 14 and 15 is fixed against a bottom 23 of the body of the casing by means of a screw blocked in the tapped hole of a central boss in each nut. The head of the screw applies a washer against the outer face of the bottom and presses the nut against the inner face of the bottom.
This type of assembly does not enable the axis of each pinion to be permanently aligned with the axis of the corresponding control ball joint 18. This results in a considerable solidity and the necessity of providing an axial clearance which, even if very small, generates vibrations of the mirror and produces shaky images.
In U.S. Pat. No. 4,598,605, another type of connection is proposed in an attempt to overcome the drawback set forth hereinabove. Each of the nuts 14 and 15 is provided with a ball joint clipped in a bearing integrally made in the bottom 23 of the casing body. Its center of rotation lies very close to the bottom and towards the outside. In addition, its seat defined by the clip is disposed between the ball joint and the cover, a stop being opposite this eat in order to render the ball joint captive.
A first drawback of this known transmission device resides in the fact that, during pivoting of the mirror, through a maximum angle "a" in one direction or in the other, each of the geometrical axes 20 and 21 of the nuts 14 and 15 pivots through an angular amplitude such that their end ball joints rub against the walls of their housing and wear them out. Due to such wear, which occurs relatively quickly since the parts are made of plastic material and are small, the mirror vibrates, as in the prior art, when the vehicle is moving and the image that it reflects is shaky. This results in the driver's vision of the environment being disturbed and imperils safe driving conditions.
A second drawback is that manouevring of the mirror is not as smooth as might be desired, to the detriment of the precision and fidelity of the adjustments.
A third drawback is that, as the casing is made of molded plastic material and is of relatively small dimensions, serious difficulties are encountered when making the housings for the ball joints, resulting in imperfect guiding and holding of the ball joints.
In the device disclosed in U.S. Pat. No. 4,598,605, each nut is integral with the corresponding tangent wheel, with the result that transmission of the rotation from one to the other is effected in homokinetic manner, i.e. with a very high precision, and without clearance, i.e. without risk of vibrations at that level.
Another known rearview mirror of the same type is described in European Patent No. 112,140. In this rearview mirror, the pinion cooperating with a driving screw is separate from the nut cooperating with a driven screw. This arrangement makes it possible to place the center of pivoting of the nut inside the pinion so that the axis of the nut is always aligned with the axis of the ball joint actuating the mirror, when the motor driving the driving screw/pinion pair is controlled. In fact, the nut forms a sphere pivotally guided about its center in a spherical bushing of the pinion, the sphere being maintained in place by clipping by utilization of a deformable retaining lip.
For pivotally coupling the nut with the pinion, the means employed are constituted by two diametrically opposite, longitudinal flutes or ribs projecting into the spherical bushing and by two grooves made in the sphere. The grooves are divergent at their two ends in order to allow both the transmission of the rotation from the pinion to the nut and the freedom of pivoting of the sphere of the nut about is center.
Finally, a corrugated washer is interposed between the pinion and the casing to form an elastic stop.
European Patent No. 112,140, therefore, teaches that the center of pivoting of the nut may be brought closer to the ball joint actuating the mirror, which might make it possible to overcome the drawbacks set forth hereinabove of the rearview mirror according to U.S. Pat. No. 4,598,605.
However, this teaching cannot be retained within the scope of the latter Patent as, according to the European Patent, it necessitates that the nut be separate from the pinion, while, in U.S. Pat. No. 4,598,605, they are integral with each other. Now, the separation of the nut and pinion leads to serious drawbacks. The pivoting coupling of the sphere with the pinion generates, on the one hand, a non-homokenetic transmission of rotation, detrimental to the fidelity and precision of the adjustment, and, on the other hand, clearances promoting vibrations of the mirror. Clipping of the ball joint in the pinion does not ensure perfect hold of the ball joint, with the result that wear and clearance may occur. Finally, the corrugated washer opposes perfect positioning of the pinion, since it serves as support for the pinion and is deformable.