U.S. patent application number 13/970765 was filed with the patent office on 2013-12-26 for slide rail device for vehicle seat.
This patent application is currently assigned to SHIROKI CORPORATION. The applicant listed for this patent is SHIROKI CORPORATION. Invention is credited to Akihiro KIMURA.
Application Number | 20130341983 13/970765 |
Document ID | / |
Family ID | 46198359 |
Filed Date | 2013-12-26 |
United States Patent
Application |
20130341983 |
Kind Code |
A1 |
KIMURA; Akihiro |
December 26, 2013 |
SLIDE RAIL DEVICE FOR VEHICLE SEAT
Abstract
A slide rail device which includes a lower rail, an upper rail
which is freely slidably engaged with the lower rail, and balls
which are installed between the lower and upper rails. The lower
rail includes a lower-rail bottom wall, a pair of lower-rail side
walls, a pair of lower-rail upper wails, a pair of lower-rail
lower-ball contact R-portions, and a pair of lower-rail upper-ball
contact R-portions. The upper rail includes an upper-rail top wall,
a pair of upper-rail side walls, and a pair of upper-rail
ball-bearing walls. Each upper-rail ball-bearing wall includes an
upper-rail lower-ball contact portion and an upper-rail upper-ball
contact portion. A radius of curvature of the lower-rail lower-ball
contact R-portion of the lower rail is greater than that of the
lower ball, and a radius of curvature of the lower-rail upper-ball
contact R-portion of the lower rail is greater than that of the
upper ball.
Inventors: |
KIMURA; Akihiro;
(Fujisawa-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SHIROKI CORPORATION |
Fujisawa-Shi |
|
JP |
|
|
Assignee: |
SHIROKI CORPORATION
Fujisawa-Shi
JP
|
Family ID: |
46198359 |
Appl. No.: |
13/970765 |
Filed: |
August 20, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13410732 |
Mar 2, 2012 |
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13970765 |
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13316679 |
Dec 12, 2011 |
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13410732 |
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Current U.S.
Class: |
297/344.1 |
Current CPC
Class: |
B60N 2/0722 20130101;
B60N 2/072 20130101; F16C 29/048 20130101; B60N 2/0705
20130101 |
Class at
Publication: |
297/344.1 |
International
Class: |
B60N 2/07 20060101
B60N002/07 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 13, 2010 |
JP |
2010277512 |
Claims
1. A slide rail device which includes a lower rail having a uniform
cross section, an upper rail having a uniform cross section which
is freely slidably engaged with said lower rail, and balls which
are installed between said lower rail and said upper rail, wherein
said lower rail comprises: a lower-rail bottom wall; a pair of
lower-rail side walls which extend upward from both ends of said
lower-rail bottom wall, with respect to a lateral direction,
respectively; a pair of lower-rail upper walls which extend toward
a center of said lower rail in the lateral direction from upper
ends of said pair of lower-rail, side walls, respectively; and a
pair of lower-rail lower-ball contact R-portions via which said
pair of lower-rail side walls are connected to said lower-rail
bottom wall, respectively; and a pair of lower-rail upper-ball
contact R-portions via which said pair of lower-rail upper walls
are connected to said pair of lower-rail side walls, respectively,
wherein said upper rail comprises: an upper-rail top wall; a pair
of upper-rail side walls which are continuous with said upper-rail
top wall and extend downward between said pair of lower-rail upper
walls into said lower rail from both sides of said upper-rail top
wall with respect to said lateral direction, respectively; and a
pair of upper-rail ball-bearing walls winch extend outwardly
upwards from lower ends of said pair of upper-rail side walls,
respectively, wherein each of said pair of upper-rail ball-bearing
walls includes an upper-rail lower-ball contact portion which is
formed to face an adjacent lower-rail lower-ball contact R-portion
of said pair of lower-rail lower-ball contact R-portions of said
lower rail wherein said balls include a pair of lower balls which
are installed between said pair of lower-rail lower-ball contact
R-portions of said lower rail and said upper-rail lower-ball
contact portions of said pair of upper-rail ball-bearing walls of
said upper rail, respectively, and wherein a radius of curvature of
said lower-rail lower-ball contact R-portion of said lower rail is
greater than a radius of said lower ball.
2-3. (canceled)
4. The slide rail device according to claim 2, wherein said
upper-rail lower-ball contact portion of each of said pair of
upper-rail ball-bearing walls of said upper rail is formed as an
upper-rail lower-ball contact R-portion that is formed into a
circular arc shape with a specific curvature in cross section, a
radius of curvature of said upper-rail lower-ball contact R-portion
being greater than said radius of said lower ball.
5. The slide rail device according to claim 1, wherein the
following conditions are satisfied: R1.gtoreq.1.1r1, and wherein r1
designates said radius of said lower ball, and R1 designates said
radius of curvature of said lower-rail lower-ball contact
R-portion
6. (canceled)
7. The slide rail device according to claim 1, wherein said lower
rail further comprises a pair of lower-rail inner side walls which
are positioned between said pair of lower-rail side walls and
extend downward from inner ends of said pair of lower-rail upper
walls, respectively.
8. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a slide rail device for
[0003] making an adjustment to the position of a vehicle seat, in
the forward/rearward direction.
[0004] 2. Description of Related Art
[0005] A typical slide rail device (slide rail assembly) is
configured of a lower rail that, is fixed to a vehicle floor, an
upper rail that is fixed to a vehicle seat and engaged with the
lower rail to be freely slidable thereon, and balls (steel balls)
for reducing frictional resistance that are installed between the
upper rail and the lower rail. The upper rail and the lower rail
are each made of a metallic material (usually an iron-based
material) having a uniform cross section. Such a slide rail device
is disclosed, in Japanese Patent Publication No 4,230,945.
[0006] In this known slide rail device, application of a force on
the upper rail and the lower raid, therebetween that is produced by
the weight of someone (a driver or a passenger) sitting in the
vehicle seat causes relatively large forces that exert, on the
rails at points of contact with the balls. As a consequence;
sometimes indentations are made on the rails via the balls. Since
such indentations obviously deteriorate the reliability of the
balls, it Is desirable that the rails be formed into a shape
preventing such indentations from being made on the rails as much
as possible. For this reason, the radius of the balls has been set
to be identical to the radius of curvature of the ball contact
portions of each rail in conventional slide rail devices. Namely,
if the radius of the balls is identical to the radius of curvature
of the ball contact portions of each rail, the surface pressure
exerted on the rails is at a geometric minimum, so that the
possibility of indentations being made on the rails via the balls
is low. However, the inventor of the present invention has found
that, if the radius of the balls is made to be identical in design
to the radius of curvature of the ball contact portions of each
rail, the rollability of the balls sometimes deteriorates
regardless of the presence
[0007] or absence of indentations on the rails (aside from the
problem of indentations), to thereby make the sliding operation of
the upper rail with respect to the lower rail unstable.
SUMMARY OF THE INVENTION
[0008] As a result of having pursued the cause of the lack of
stability of the sliding operation of the slide rail, device, the
inventor of the present, invention has completed the present
invention after coming to the conclusion that if the radius of the
balls is made to be identical to the radius of curvature of the
ball contact portion of each rail, there is a possibility of a
combination of a ball and a rail being unintentionally produced in
which the radius of curvature of the ball contact portion of the
rail is smaller than the radius of the balls due to manufacturing
error, thus causing the ball and the rail to be in contact with
each other at two points to thereby deteriorate the reliability of
the balls. The balls (steel balls) are extremely high in
dimensional accuracy and hardness, as is known in the art, so that
there is little possibility of an error in the dimensional accuracy
of the balls affecting the reliability thereof. The length (angle)
of the circular arc in each ball contact R-portion of the lower
rail is usually greater than that of the upper rail, so that the
shapes of the basil contact R-portions of the lower rail greatly
affect the reliability of the balls.
[0009] According to an aspect of the present invention, a slide
rail device is provided, which includes a lower rail having a
uniform cross section, an upper rail having a uniform cross section
which is freely slidably engaged with the lower rail, and balls
which are installed between the lower rail and the upper rail, The
lower rail includes a lower-rail bottom wall; a pair of lower-rail
side walls which extend upward from both ends of the lower-rail
bottom wall, with respect to a lateral direction, respectively; a
pair of lower-rail upper walls which extend toward a center of the
lower rail in the lateral direction from upper ends of the pair of
lower-rail side walls, respectively; a pair of lower-rail
lower-ball contact R-portions via which the pair of lower-rail side
walls are connected to the lower-rail bottom wall, respectively;
and a pair of lower-rail upper-ball contact R-portions via which
the pair of lower-rail upper wails are connected to the pair of
lower-rail side walls, respectively. The upper rail includes an
upper-rail top wall; a pair of upper-rail side walls which are
continuous with the upper-rail top wall and extend downward between
the pair of lower-rail upper walls into the lower rail from both
ends of the upper-rail top wall, with respect to a lateral
direction, respectively; and a pair of upper-rail ball-bearing
walls which extend outwardly upwards from lower ends of the pair of
upper-rail side walls, respectively. Each of the pair of upper-rail
ball-bearing wails includes an upper-rail lower-ball contact
portion which is formed to face an adjacent lower-rail lower-ball
contact R-portion of the pair of lower-rail lower-ball contact
R-portions of the lower rail, and an upper-rail upper-ball contact
portion which is formed to face an adjacent lower-rail upper-ball
contact R-portion of the pair of lower-rail upper-ball contact
R-portions of the lower rail. The balls include a pair of upper
balls which are installed between the pair of lower-rail upper-ball
contact R-portions of the lower rail and the upper-rail upper-ball
contact portions of the pair of upper-rail ball-bearing wails of
the upper rail, respectively; and a pair of lower balls which are
installed between the pair of lower-rail lower-ball contact
R-portions of the lower rail and the upper-rail lower-ball contact
portions of the pair of upper-rail ball-bearing wails of the upper
rail, respectively. A radius of curvature of the lower-rail
lower-ball contact E-portion of the lower rail is
[0010] greater than a radius of the lower ball, and a radius of
curvature of the lower-rail upper-ball contact R-portion of the
lower rail is greater than a radius of the upper ball.
[0011] Note that the term "R-portion" denotes a portion of the
lower or upper rail which is formed into a circular arc shape with
a specific: curvature in cross section. This curvature can be
circular or elliptical. In addition, the term "lateral" denotes a
lateral direction in a vehicle widthwise direction, and the term
"outward" denotes an outward direction from, a cross sectional
center of the rail,
[0012] Although both the upper-rail upper-ball contact portion and
the upper-rail lower-ball contact portion of each of the pair of
upper-rail ball-bearing wails can be formed as flat surfaces, it is
desirable that at least the upper-rail upper-ball contact portion
of each of the pair of upper-rail ball-bearing walls of the upper
rail be formed as an upper-rail upper-ball contact R-portion that
is formed into a circular arc shape with a specific curvature in
cross section. This is because the ratio between the force that
acts on the pair of upper-rail ball-bearing walls via the upper
balls and the associated reaction force caused by deformation, of
the rails (the pair of upper-rail ball-bearing walls) is greater
than the ratio between the force that acts on the pair of
upper-rail ball-bearing walls via the lower balls and the
associated reaction force caused by deformation of the rails (the
pair of upper-rail ball-bearing walls), and accordingly, it is
desirable that the upper-rail upper-ball contact portion of each
upper-rail ball-bearing wall be formed as the aforementioned
upper-rail upper-ball contact R-portion that is smaller in surface
pressure than a fiat surface. In addition, the radius of curvature
of the upper-rail upper-ball contact R-portion is desirably set to
be greater than the radius of the upper ball due to the same reason
as that of the radius of curvature of the lower-rail lower-ball
contact R-portion being greater than the radius of the lower
ball.
[0013] It is desirable that the upper-rail lower-ball contact
portion of each upper-rail ball-bearing wall of the upper rail be
also formed as an upper-rail lower-ball contact R-portion (that is
formed into a circular arc shape with a specific curvature in cross
section) rather than a fiat surface. In this case, it is desirable
that the radius of curvature of the upper-rail lower-ball contact
R-portion be also set to be greater than the radius of the lower
ball.
[0014] It is desirable for the following conditions to be
satisfied;
R1.gtoreq..1 and R2.gtoreq.1.1r2,
more desirably R1.gtoreq.1.2r1 and R2.gtoreq.1.2r2,
[0015] wherein r1 designates the radius of the lower ball, r2
designates the radius of the upper ball, R1 designates the radius
of curvature of the lower-rail lower-ball contact R-portion, and R2
designates the radius of curvature of the lower-rail upper-ball
contact R-portion, Considering dimensional errors of the rails in
manufacturing, if R1 and R2 are smaller than 1.11r and 1.11r2,
respectively, it has been confirmed that the reliability of the
balls deteriorates (a combination of a ball and a rail in which the
radius of curvature of the ball contact portion of the rail is
smaller than the radius of the ball is unintentionally produced),
though the surface pressure exerted on the rails is reduced.
[0016] On the other hand, the upper limit of the radius of
curvature (R1 or R2) of each ball contact R-portion is determined
so that the surface pressure at the ball contact. R-portion, with
which the balls are in contact, becomes equal to or smaller than an
allowable surface pressure in consideration of the material of the
rails.
[0017] In the slide rail device according to the present invention,
it is conceivable that each of inner surfaces of the two connecting
corners between the upper wall of the upper rail and the pair of
upper-rail side walls of the upper rail, respectively, serves as an
assumed deformation rotational center when the upper rail is
resiliently deformed upon a normal load being applied thereto. In
an embodiment of the slide rail device according to the present
invention, each inner surface of two connecting corners between the
upper-rail top wall of the upper rail and the pair of upper-rail
side walls of the upper rail serves as an assumed deformation
rotational center when the upper rail is resiliently deformed upon
a normal load being applied thereto, and a cross sectional shape of
the upper rail is determined so as to define an outward crossing
angle between a line segment, which connects the assumed
deformation rotational center and a center of associated one of the
pair of lower balls and a line segment which is tangent to both the
associated, one of the pair of lower balls and the upper-rail,
lower-ball contact R-portion at an angle in a range from 80 degrees
to less than 30 degrees, desirably in the range from 80 to 88
degrees.
[0018] By setting the outward crossing angle in this manner, the
pair of upper-rail side walls can be securely made to be
resiliently deformable inwardly (i.e., in directions toward each
other) via the lower balls. It has been confirmed that deformation
of the pair of upper-rail side walls outwardly in opposite
directions away from each other may deteriorate the slidability of
the slide rail device.
[0019] If the aforementioned outward crossing angle is set at an
angle of 90 degrees, the load carrying capacity of the upper rail
30 becomes maximum in theory. However, if the outward crossing
angle is set at an angle of 90 degrees, a combination of a ball and
a rail in which the outward, crossing angle exceeds 90 degrees may
be unintentionally produced due to manufacturing error, which may
cause the pair of upper-rail side walls to be deformed outwardly in
opposite directions away from each other.
[0020] According to the present invention, the radius of curvature
of each ball contact R-portion of at least the lower rail is set to
be greater than the radius of the associated balls, which makes it
possible to obtain a slide rail device in which the indentation
prevention performance and the reliability of the ball are
well-balanced.
[0021] It is desirable for the lower rail to include a pair of
lower-rail inner side wails which are positioned between the
[0022] pair of lower-rail side wails and extend downward from inner
ends of the pair of lower-rail upper walls, respectively.
[0023] It is desirable for each of the pair of upper-rail
ball-bearing wails to include a vertical connecting wall via which
the upper-rail lower-ball contact portion and the upper-rail
upper-ball contact portion are connected.
[0024] The present disclosure relates to subject matter contained
in Japanese Patent Application No. 2010-277512 (filed on Dec. 13,
2010) which is expressly incorporated herein by reference in its
entirety.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The present invention will be discussed below in detail with
reference to the accompanying drawings, in which;
[0026] FIG. 1 is a longitudinal sectional view of an embodiment of
a slide rail device according to the present invention;
[0027] FIG. 2 is a sectional view of part of the upper rail shown
in FIG. 1, showing the detailed shape thereof; and
[0028] FIG. 3 is a graph showing experimental data on the
relationship between the contact-surface pressure and the radius of
curvature (R) of a ball contact R-portion divided by the radius (r)
of the ball.
DESCRIPTION OF THE EMBODIMENT
[0029] FIG. 1 shows an embodiment of a slide rail device 10
according to the present invention. The slide rail device 10 is
provided with a lower rail 20 and an upper rail 30 which are fixed
to a vehicle floor (not shown) and a vehicle seat (not shown),
respectively, and is provided between the lower rail 20 and the
upper rail 30 that are engaged with each other to be relatively
slidable, with two types of steel balls, i.e., lower balls 40 and
upper balls 50, which are installed between the lower rail 20 and
the upper rail 30. The slide rail device is bilaterally symmetrical
in shape in a cross section taken along a plane normal to the
extension direction (lengthwise direction) of the rails 20 and 30.
The lower balls 40 are greater in diameter than the upper balls 50.
As known in the art, two of the slide rail devices 10 are used as a
pair (left and right slide rail devices) in a state of being fixed
to a vehicle, and a lock mechanism and other components are
installed to this pair of slide rail devices. However, since the
main concept of the present embodiment is centered, around the
uniform cross-sectional shapes of the lower rail 20 and the upper
rail 30, only such cross sectional shapes of the lower rail 20 and
the upper rail 30 will be discussed in the following descriptions.
Additionally, in the following descriptions, the terms "lateral"
denote a lateral direction in a vehicle widthwise direction,
respectively, the term "outward" denotes an outward direction from
a cross sectional center of the lower rail 20 or the upper rail 30,
and the term "R-portion" denotes a portion of the lower rail 20 or
the upper rail 30 which is formed into a circular arc shape with a
specific curvature in cross section.
[0030] The lower rail 20 is provided with a lower-rail bottom wall
21, a pair of lower-rail outer side walls 22, a pair of lower-rail,
upper wails 23 and a pair of lower-rail inner side wails 24, The
horizontal, lower-rail bottom wall 21 is fixed to a vehicle floor;
the pair of lower-rail outer side walls 22 extend upward from both
ends (sides) of the lower-rail bottom wall 21, with respect to the
lateral direction, respectively; the pair of lower-rail upper walls
23 extend in the lateral direction toward the longitudinal center
of the lower rail 20 from upper ends of the pair of lower-rail
outer side wails 22, respectively; and the pair of lower-rail inner
side walls 24 extend downward front inner ends of the pair of
lower-rail upper walls 23, respectively, and are positioned between
the pair of lower-rail outer side walls 22.
[0031] The lower-rail bottom wall 21 and the pair of lower-rail
outer side walls 22 are connected via a pair of lower-rail
lower-ball contact R-portions 25, respectively, and the pair of
lower-rail outer side wails 22 and the pair of lower-rail upper
wails 23 are connected via a pair of lower-rail upper-ball contact
R-portions 26, respectively.
[0032] The upper rail 30 is provided with an upper-rail top wall
31, a pair of upper-rail side wails 32 and a pair of upper-rail
ball-bearing wails 33, The horizontal upper-rail top wall 31 is
fixed to a vehicle seat. The pair of upper-rail side walls 32 are
continuous with the upper-rail top wall 31 and extend downward
between the pair of lower-rail inner side walls 24 into the lower
rail 20 from both ends (sides) of the upper-rail top wall 31, with
respect to the lateral direction, respectively. The pair of
upper-rail ball-bearing walls 33 extend outwardly upwards, toward
the pair of lower-rail upper walls 23, from
[0033] the lower ends of the pair of upper-rail side walls 32,
respectively.
[0034] Each, upper-rail ball-bearing wall 33 is provided at a lower
part thereof with an upper-rail lower-ball contact R-portion 34
which is formed to face the adjacent lower-rail lower-ball contact
R-portion 25 of the lower rail 20, and is provided above the
upper-rail lower-ball contact R-portion 34 with an upper-rail
upper-ball contact R-portion 35 which is formed to face the
adjacent lower-rail upper-ball contact R-portion 26 of the lower
rail 20, Each upper-rail ball-bearing wall 33 is further provided
between the upper-rail lower-ball contact R-portion 34 and the
upper-rail upper-ball contact R-portion 35 with a vertical,
connecting wall 36 via which the upper-rail lower-ball contact
R-portion 34 and the upper-rail upper-ball contact R-portion 35 are
connected.
[0035] The upper-rail, lower-ball contact R-portion 34 and the
upper-rail, upper-ball contact R-portion 35 of each upper-rail
ball-bearing wall 33 each have a curvature so as to hold (insert)
the lower balls 40 between the upper-rail lower-ball contact
R-portion 34 and the adjacent lower-rail lower-ball contact
[0036] R-portion 25 and to hold (insert) the upper balls 50 between
the upper-rail upper-ball contact R-portion 35 and the adjacent
lower-rail upper-ball contact R-portion 26, However, the upper-rail
lower-ball contact R-portion 34 and the upper-rail upper-ball
contact R-portion 35 of each upper-rail ball-bearing wall 33 are
smaller in area (angle) at which a curvature is formed than the
adjacent lower-rail lower-ball contact R-portion 25 and the
adjacent lower-rail upper-ball contact R-portion 26, respectively.
Each adjacent lower-rail lower-ball contact R-portion 25 and each
adjacent lower-rail upper-ball contact R-portion 26 are formed to
extend, by an angle of 90 degrees, whereas the curved area (angle)
of the upper-rail lower-ball contact R-portion 34 of each
upper-rail ball-bearing wall 33 in particular is small, (can be
reduced) , thus capable of being replaced by a flat surface (flat
surface area).
[0037] The radius of curvature R1 of the lower-rail lower-ball
contact R-portions 25 and the radius of curvature R1' of the
upper-rail lower-ball contact R-portions 34 are each defined
greater than the radius r1 of the lower balls 40. Likewise, the
radius of curvature R2 of the lower-rail upper-ball contact
[0038] R-portions 26 and the radius of curvature R2' of the
upper-rail upper-ball contact R-portions 35 are each defined
greater than the radius r2 of the upper balls 50. The radius of
curvature R1 and the radius of curvature R1' can be mutually
identical or slightly different from each other. Likewise, the
radius of curvature R2 and the radius of curvature R2' can be
mutually identical or slightly different from each other.
[0039] FIG. 3 is a graph showing experimental data indicating
variations of the contact-surface pressure at a ball contact
R-portion (25, 26, 34 or 35) when the ratio between the radius r
(r1 or r2) of the lower balls 40 or the upper balls 50 and the
radius of curvature R (R1, R2, R1' or R2') of the ball contact
R-portion (25, 26, 34 or 35) is changed. As can be understood from
the graph of FIG. 3, a boundary at which the contact-surface
pressure drastically changes exists (is defined) between a point
where the value R/r (the radius of curvature R divided by the
radius r) is equal to 1.1 and a point where the value R/r is equal
to 1.2. Considering this fact and variations in radius of curvature
of the ball contact E-portions of the lower rail 20 and the upper
rail 30 due to manufacturing error, reliable reliability of the
lower balls 40 and the upper balls 50 can be ensured regardless of
variations in radius of curvature R of the ball contact R-portion
25, 26, 34 or 35, by setting the radius of curvature R so as to be
equal to or greater than approximately 1.1 times of the radius r
(i.e., R 1.1r); more desirably equal to or greater than
approximately 1.2 times of the radius r (i.e.,.gtoreq.R 1.2r), On
the other hand, the upper limit of the radius of curvature R (R1
and R2) of each ball contact R-portion (25 and 26) is set so that
the surface pressure at the ball contact R-portion, with which the
balls (40 or 50) are in contact, becomes equal to or smaller than
an allowable surface pressure in consideration of the material of
the rails.
[0040] In addition to each lower-rail lower-ball contact R-portion
25 and each lower-rail upper-ball contact R-portion 25, each
upper-rail lower-ball contact R-portion 34 and each upper-rail
upper-ball contact R-portion 35 are also each formed as an
R-portion in the above illustrated embodiment; however, each
upper-rail lower-ball contact R-portion 34 in particular among each
upper-rail lower-ball contact R-portion 34 and each upper-rail
upper-ball contact R-portion 35 can be made as a flat portion. On
the other hand, it is desirable that each upper-rail upper-ball
contact R-portion 35 be formed as an R-portion which is smaller in
surface pressure than a fiat surface like the above described
embodiment because each upper-rail upper-ball contact R-portion 35
plays a role in providing flexibility to the associated upper-rail
ball-bearing wall 33 via the associated lower ball 40.
[0041] FIG. 2 is a diagram for illustrating a desirable shape of
the upper rail 30 in its free state. In each of left and right
halves of the upper rail 30 (only a left half of the upper rail 30
is shown in FIG. 2), an inner surface of the connecting corner
between the upper wall 31 and the upper-rail side wall 32 becomes
an assumed deformation rotational center X when the upper rail 30
is resiliently deformed upon a normal load being applied thereto.
The cross sectional, shape of the upper rail in its free state is
determined so as to define an outward crossing angle between a line
segment Y, which connects the assumed deformation rotational center
X and the center of the associated lower ball 40, and a line
segment Z which is tangent to both the associated lower ball 40 and
the upper-rail lower-ball contact R-portion 34, at an angle in the
range from 80 degrees to less than 90 degrees, more desirably in
the range from 80 to 88 degrees. By setting the outward crossing
angle .alpha. in this manner, the pair of upper-rail side walls 32
can be securely made to be resiliently deformable inwardly (i.e.,
in directions toward each other) via the lower balls 40,
Conversely, deformation of the pair of upper-rail side walls 32
outwardly in opposite directions away from each other may
deteriorate the slidability of the slide rail device 10.
[0042] In other words, the load carrying capacity of the upper rail
30 becomes maximum in theory when the line segment Y and the line
segment Z intersect each other at right angles (at an angle of 90
degrees). However, if the upper rail 30 is designed so that the
line segment Y and the line segment Z intersect each other at
right, angles, the outward crossing angle may become greater than
90 degrees when the shape of the upper rail 30 varies due to
manufacturing error, and consequently, the pair of upper-rail side
walls 32 become easy to deform outwardly, thus having an adverse
effect on the slidability of the slide rail device 10. In the
present embodiment of the slide rail device 10, the shape of the
slide rail device 10 is defined so that the outward crossing angle
is always less than 90 degrees even with the presence of
manufacturing error. This definition of the shape of the upper rail
30 in its free state is independent from the aforementioned
features of the radius of curvature R1 of the lower-rail lower-ball
contact R-portions and the radius of curvature R1' of the
upper-rail lower-ball contact R-portions 34 (being each defined
greater than the radius r1 of the lower balls 40) and of the radius
of curvature R2 of the lower-rail upper-ball contact R-portions 26
and the radius of curvature R2' of the upper-rail upper-ball
contact R-portions 35 (being each defined greater than the radius
r2 of the upper balls 50).
[0043] Obvious changes may be made in the specific embodiment of
the present invention described herein, such modifications
[0044] being within the spirit and. scope of the invention claimed.
It is indicated that all matter contained herein is illustrative
said does not limit the scope of the present invention.
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