Outer mirror for motor vehicle

An outer mirror for use in a motor vehicle is designed to prevent or attenuate chattering vibrations which a mirror holder holding a mirror produces against a mirror visor. This outer mirror assembly is provided with a first vibration-preventive member which is used in the mirror holder and with a second vibration-preventive member which is housed in a mirror visor and held in slidable contact with the first vibration-preventive member. The slidable surface of the first vibration-preventive member forms a curve which satisfies a condition that the inclination .alpha.' of the tangential line at each contact point of the two vibration-preventive members is always larger than the angle of friction .lambda. between the two vibration-preventive members. According to this structure, the first vibration-preventive member or the mirror holder is always given an outwardly acting force by the second vibration-preventive member which is provided with a spring. The force acting only in one direction assuredly prevents a mirror holder from producing chattering vibrations.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention generally relates to an outer mirror assembly, such 
as a door mirror assembly and a fender mirror assembly, for a motor 
vehicle and, more particularly, to an outer mirror assembly wherein the 
vibration of the mirror holder that occurs against the mirror visor during 
driving is prevented or attenuated. 
2. Prior Art 
For the prevention of such a vibration there have been proposed various 
means, one of which, officially disclosed under Japanese first Utility 
Model Publication No. 37857/1985, comprises a first vibration-preventive 
member provided to a mirror holder and a second vibration-preventive 
member in a mirror visor, each member placed in slidable contact with each 
other, as shown in FIG. 6. 
In said means illustrated in FIG. 6, a mirror 1 is provided, as well as a 
mirror holder 2 which holds the back of the mirror 1, and a 
mirror-positioning unit 4 which tilts the mirror upwardly and downwardly 
as well as laterally. This mirror-positioning unit 4 is fixedly housed in 
a space interiorly defined by the mirror visor which is not shown in the 
drawings. 
The mirror holder 2 has a coupling means 2a at its center and a case 4b of 
the mirror-positioning unit 4 also has a coupling means 4a. The coupling 
means 2a fitted with the coupling means 4a in such a manner as to be 
movable in a upwardly and downwardly and laterally tilting movement. 
The mirror-positioning unit 4 has at least one mirror-driving rod 5, one 
end of which is relatively movably connected to the mirror holder 2. This 
rod 5 is generally threaded. A motor and a motive power transmission 
mechanism therefor are provided in the case 4b of the mirror-positioning 
unit. The motive power transmission mechanism includes a nut member (not 
shown) which is fitted over the rod 5. By rotation of this nut, the rod 5 
is moved in axial directions in such a manner as to move said mirror 
holder 2 and to change the attitude of the mirror 1. 
Both the mirror holder 2 and case 4b have at least two vibration-preventive 
members 3 or 4d. The two vibration-preventive members 3 and 4d face each 
other and come into contact with each other at their respective slidable 
contact surfaces 3a and 4c. Therefore, if a vibration occurs in a motor 
vehicle during driving, the occurrence of the relative chattering 
vibration which the mirror 1 (the mirror visor) produces against the case 
4b is, the mirror visor, is effectively prevented. 
In these vibration-preventive members 3 and 4d, each of the respective 
slidable contact surfaces 3a and 4c forms an arc having as the center a 
point O around which the mirror holder 2 is moved for changing the 
attitude of the mirror 1. 
However, problems are involved in the practices where arcs are formed as 
stated above. Once a chattering vibration starts, caused by, for example, 
resonance in the mirror holder assembly, friction loses its effect. 
Therefore, chattering vibrations cannot be effectively prevented. 
SUMMARY OF THE INVENTION 
Accordingly, an essential object of the present invention is to 
structurally improve the vibration-preventive member on the mirror holder 
and on the mirror visor, with respect to each facing pair, so as to 
effectively prevent chattering vibrations of the mirror and the mirror 
holder. 
In accomplishing this and other objects, an embodiment is provided 
according to the present invention wherein: 
a second vibration-preventive member formed on the side of the mirror 
visor, relative to a first vibration-preventive member formed on the side 
of the mirror holder, is positioned at an outer side in the direction of a 
radius extending form a point on which the mirror holder is pivotally 
moved; 
said first vibration-prevention member has a slidable surface which faces 
said second vibration-preventive member, whereas said second 
vibration-prevention member is formed of a spring as material and has a 
contacting member which is pressed against said slidable surface of said 
first vibration-preventive member; and 
said slidable surface of said first vibration-preventive member is required 
to be a curved surface which satisfies the condition that, 
given .alpha.' as the inclination of a tangential line at each contact 
point of both vibration-preventive members and given .lambda. as the angle 
of friction between said two vibration-preventive members, 
.alpha.'&gt;.lambda. must be satisfied by whatever position the mirror holder 
takes with respect to its attitude. 
Since, in this structure and the relative positions, the inclination 
.alpha.' of the tangential line at each contact point of both 
vibration-preventive members is always larger than the angle of friction 
.lambda. between said two vibration-preventive members, the contacting 
member of said second vibration-preventive member is always under pressure 
to fall along the slidable surface of said first vibration-preventive 
member. In other words, said first-vibration preventive member, that is, 
the mirror holder, is always under pressure to act outwardly by the 
pressure of said second vibration-preventive member acting as a spring. By 
virtue of pressure only in one direction as stated above, a mirror holder 
is assuredly prevented from chattering vibration. 
In the structure as stated above, it is preferable for the slidable curved 
surface of said first vibration-preventive member to be a curved surface 
consisting of a logarithmic spiral or a curve similar to it in cross 
section taken in the sliding direction. Since, in this structure, the 
inclination of the tangential line at each contacting point between the 
two vibration-prevention members is always maintained constant 
irrespective of the position of the mirror holder, the resistance to the 
pivotal movement becomes a constant value, and consequently, it becomes 
possible to pivotally smoothly move the mirror holder. 
Further scope of applicability of the present invention will become 
apparent from the detailed description given hereinafter. However, it 
should be understood that the detailed description and specific examples, 
while indicating preferred embodiments of the invention, are given by way 
of illustration only, since various changes and modifications within the 
spirit and scope of the invention will become apparent to those skilled in 
the art from this detailed description.

DETAILED DESCRIPTION OF THE INVENTION 
Before the description of the present invention proceeds, it is to be noted 
that like parts are designated by like reference numerals and symbols 
throughout the several views of the accompanying drawings. 
Referring now to FIGS. 1 through 5, a preferred embodiment of the present 
invention will now be described. 
In this embodiment, in a manner similar to a conventional example as shown 
in FIG. 6, a mirror-positioning unit 14 is fixed in position in a space 
interiorly defined by a mirror case 15. 
In FIG. 1, a mirror-positioning unit 14 housed in a space interiorly 
defined by a mirror visor 15, and a mirror holder 12 to hold a mirror are 
shown as seen from the front of a motor vehicle toward the back thereof. 
In this embodiment, in a manner similar to a conventional example as shown 
in FIG. 6, the mirror-positioning unit 14 is fixed in position with the 
mirror visor 15, and a coupling means provided for the case 14a of the 
mirror-positioning unit is connected with coupling means provided to the 
mirror holder 12 in such a manner as to be pivotally movable. More 
specifically, the mirror holder 12, is movable relative to the 
mirror-positioning unit 14 and to the mirror visor 15 along the Y-Y axis 
and along the X-X axis. 
A pair of claw type vibration-preventive members 13 (first 
vibration-preventive members) are provided for the mirror holder 12 at 
predetermined positions on the back thereof. The pair of first 
vibration-preventive members 13 are provided at positions a little to the 
right of the center O of the pivotal movement of the mirror holder and 
substantially in symmetry on both sides of the X-X axis. 
The case 14a of the mirror-positioning unit 14 has a peculiar shape. A pair 
of protruded vibration preventive members 14d (second vibration-preventive 
members) are provided on the case 14a in correspondence to the pair of 
first vibration-preventive members 13, referred to above. 
In FIG. 2, contact between a first vibration-preventive member 13 and a 
second vibration-prevention member 14d is shown whereby the two jointly 
perform their functions. As shown in FIGS. 1 and 2, each of the second 
vibration-preventive members 14d is positioned relative to a first 
vibration-preventive member 13 at an outer side in the direction of a 
radius extending from a point O on which the mirror is pivotally moved. 
The contacting point 14c formed at the tip of a second 
vibration-preventive member 14d is pressed against the sliding surface 13a 
of a first vibration-preventive member 13. The second vibration-preventive 
member 14d is formed of a spring material and pliably movable on the base 
as a fulcrum. The spring of said second vibration-preventive member 14d 
has its force substantially toward the center of the pivotal movement of 
the mirror. 
The slidable contact surface 13a of the first vibration-preventive member 
13, in a cross-sectional view taken in the sliding directions, has a 
logarithmic spiral which has the center O on which the mirror holder is 
pivotally moved. The slidable contact surface may also be a curve which 
closely resembles said logarithmic spiral. 
As shown in FIG. 3, a logarithmic spiral is a curve wherein, as is known, 
angles formed by the tangential lines at arbitrary points a and b and the 
straight lines connecting said points "a" and "b" with the center O, 
expressed as .sigma..sub.0, are constant. 
When the slidable surface 13a of a first vibration-preventive member 13 
thus assumes a logarithmic spiral or a curve closely resembling it, 
whatever position the mirror holder is pivotally moved to on the Y-Y axis, 
as shown in FIG. 5, the tangential line at a contact point of the two 
vibration-preventive members forms substantially a constant angle with the 
straight line connecting the contact point with the center O. Whatever 
position a mirror holder, or the first vibration-preventive member 13, may 
take on the solid line, or on the one dot-chain line, or on the two 
dot-chain line, the condition of contact of the two vibration-preventive 
members is substantially constant, the second vibration-preventive member 
14d receiving a constant force from the first vibration-preventive member 
13. The mirror holder can thus be pivotally moved under stabilized 
resistance and, can therefore be smoothly moved. Since, as shown in FIG. 
5, the position of the tip of the second vibration-preventive member 
changes depending on the position of the first vibration-preventive 
member, there may occur a change in the force which the second 
vibration-preventive member 14d applies to the first vibration-preventive 
member 13, but the change occurs in only a negligible degree. 
The logarithmic spiral is preferred to be such that the undermentioned 
condition can be satisfied. 
In FIG. 4, the center on which a mirror holder is pivotably moved is 
denoted as O, the pressure which the second vibration-preventive member 
has upon a first vibration-preventive member is shown as m, and the 
resistance which the first vibration-preventive member has upon the second 
vibration-preventive member is shown as R. Whereas a line P is drawn at a 
right angle to the pressure m and the resistance R, the tangential line at 
the contact point between the two vibration-preventive members is given by 
S, the inclination formed by said tangential line S against the line P is 
given by .alpha., the normal against the tangential line S is given by H, 
and the angle of friction is given by .lambda.t. The relation between the 
two vibration-preventive members is then studied as a problem of sliding 
friction. 
If the second vibration-preventive member is stationary against the first 
vibration-preventive member at the tangential line S, .alpha.&lt;.lambda. 
results. 
If the second vibration-preventive member exhibits sliding against the 
first vibration-preventive member, .alpha.&gt;.lambda. must be satisfied. In 
this embodiment, the inclination formed by the tangent line S' is set at 
an angle .alpha.' which is sufficiently larger than .alpha.. In other 
words, .alpha.'&gt;.lambda. is given (H' is a normal for the line S'). When 
an inclination is set as above, the second vibration-preventive member is 
always under pressure to slide against the first vibration-preventive 
member. In other words, the first vibration-preventive member, or the 
mirror holder, is always pressurized by the second vibration-preventive 
member to move in the direction of the arrow A with O as the center of the 
pivotal movement. Therefore, even if there is a little looseness between 
the outer thread of the mirror-driving rod and the inner thread of the nut 
which drives it, the looseness is absorbed by a pushing pressure exerted 
by a turn of the mirror holder. In the state as described above, it is not 
mere frictional force that puts one vibration-preventive member in firm 
contact with the other, but they are in tight contact by the pressure of 
the second vibration-preventive member acting on the first 
vibration-preventive member. A chattering vibration that occurs during 
driving of a motor vehicle can, therefore, be effectively prevented. 
Although the present invention has been fully described by way of example 
with reference to the accompanying drawings, it is to be noted, here, that 
various changes and modifications will be apparent to those skilled in the 
art. Therefore, unless such changes and modifications depart from the 
scope of the present invention, they should be construed as included 
therein.