Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02490679 2004-12-22
- 1 -
BOOT FOR CONSTANT VELOCITY UNIVERSAL JOINT
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to boots for
protecting constant velocity universal joints disposed, for
example, on a driving shaft (power transmission shaft) or
the like which transmits a power to an axle hub from a
differential gear of an automobile, particularly to a seal
between an outer peripheral surface of an outer housing of
a constant velocity universal joint and an inner peripheral
surface of a large-diameter-side end portion of a boot
fixed to the outer peripheral surface.
Description of the Related Art
Constant velocity universal joints have been used,
for example, in opposite end portions of a driving shaft
for an automobile. Moreover, flexible boots which cover
bent portions of the constant velocity universal joints are
attached in order to seal grease for lubricating the
constant velocity universal joints and prevent invasion of
foreign matters such as dust and water from the outside.
Large-diameter-side and small-diameter-side end portions of
the boot are usually fastened and fixed to an outer
peripheral surface of an outer housing (casing) of the
constant velocity universal joint on a differential gear
(differential) side or a hub side, and an outer peripheral
surface of a drive shaft portion by bands, respectively.
CA 02490679 2004-12-22
- 2 -
In general, the casing whose outer peripheral
surface has a simple cylindrical shape is used in the
constant velocity universal joint on the hub side (outboard
side).
In this case, the inner peripheral surface of the
boot for the constant velocity universal joint, and the
outer peripheral surface of the casing of the constant
velocity universal joint are prevented from being shifted
from each other, and are sealed, for example, by engagement
of a protrusion protruded/disposed on the inner peripheral
surface of the large-diameter-side end portion of the boot
for the constant velocity universal joint with a peripheral
groove disposed in the outer peripheral surface of the
casing over a peripheral direction.
On the other hand, in the constant velocity
universal joint on the differential side (inboard side), it
is general to use a tripod joint (triport joint)
constituted by axially slidably disposing, for example,
three sets of rollers on a shaft portion of the driving
shaft in a trifurcated manner.
In order to achieve thinning and lightening, for
example, three axial-direction grooves disposed in an axial
direction of the outer peripheral surface are formed in the
casing of the tripod joint in a scattered manner in the
peripheral direction. In this case, for example, a thick
portion whose shape viewed in the axial direction protrudes
in a circular shape is formed in the inner peripheral
CA 02490679 2004-12-22
- 3 -
surface of the large-diameter-side end portion of the boot
for the constant velocity universal joint in such a manner
as to be adapted to the groove surface of the axial-
direction groove of the casing.
When the tripod joint is used in this manner, it
is also considered that the outer peripheral surface of the
casing and the inner peripheral surface of the boot are
prevented from being shifted, and sealed by the engagement
of the peripheral groove formed in the casing with the
protrusion formed on the boot side in the same manner as in
the outboard side.
However, when the groove of the peripheral
direction is formed in the groove surface of the axial-
direction groove in the casing outer peripheral surface,
there is a problem that machining at the time of
preparation of the casing becomes remarkably complicated
and this increases costs.
To solve the problem, the following technical
means for preventing the shifting and achieving the sealing
on the differential side (inboard side) are known.
That is, a concave groove for fastening a band is
disposed in the outer periphery of the large-diameter-side
end portion, a plurality of circumferential seal lips are
disposed on the large-diameter-side end portion inner
periphery positioned right under the concave groove, the
large-diameter-side end portion is fastened via fastening
means such as a band from the outer peripheral side, and
CA 02490679 2004-12-22
- 4 -
protruding end portions of the seal lips are pressed onto
the outer peripheral surface of the casing to thereby
achieve the sealing. Moreover, a shift preventive concave
portion is disposed in a circumferential direction inside
portions in which the seal lips are arranged in the axial
direction of the boot, and a protruding portion to engage
with the shift preventive portion is disposed on the outer
peripheral surface end portion of the casing of the tripod
joint to thereby prevent the shifting (e. g., FIG. 4, etc.
of Japanese Utility Model Laid-Open No. 62-16541, FIG. 1,
etc. of Japanese Patent Application Laid-Open No. 2003-
202034).
However, these prior techniques have the following
disadvantages.
0 Since the seal lips are disposed in positions
deviating from the shift preventive portion in the axial
direction, a boot volume is large, materials are wasted,
and costs are raised. Moreover, an insertion property of
the boot into the casing has been unsatisfactory.
2~ Since the shift preventive portion is
consciously disposed in a position deviating from a band
fastening position in the axial direction, the shift toward
the small-diameter-side end portion of the boot can be
regulated, but a force for regulating the shift toward the
large-diameter-side end portion is remarkably small.
Furthermore, the technique described in Patent
Document 2 also has the following disadvantages.
CA 02490679 2004-12-22
- 5 -
~3 In a structure in which the bead (protruding
portion) is disposed in the axial-direction groove of the
outer peripheral surface of the casing of the tripod joint,
and the concave portion to engage with the bead is disposed
in the inner periphery of the large-diameter-side end
portion of the boot, the insertion property of the boot
into the casing is further deteriorated by the presence of
the bead.
~ After forging, lathe working is not performed.
Therefore, concentricity of a core of the attached boot
with the driving shaft present in the casing is
deteriorated, and boot lifetime is shortened in many cases.
05 Since the concave portion to engage with the
bead is also disposed in the thick portion of the large-
diameter-side end portion, the concave portion constitutes
an undercut at a forming time, mold releasing has been
difficult, and forming properties have been unsatisfactory.
~ Since the bead remains to be formed by forging,
dimensional precision fluctuation is larger than that in
the lathe working. Unless the concave portion on the boot
side is provided with backlash, the portion falls on the
bead. Even when the bands are fastened, seal does not work
in some case.
The present invention has been developed in
consideration of the problem of the conventional technique,
and an object thereof is to prevent shifting and enhance
sealing properties between a boot for a constant velocity
CA 02490679 2004-12-22
- 6 -
universal joint, having a thick portion formed to protrude
from the inner peripheral surface of a large-diameter-side
end portion, and the outer peripheral surface of a tripod
joint casing, further enhance insertion properties of the
boot into the casing, and reduce costs of boot materials,
so that cost reduction, casing preparing cost reduction,
and manufacturing facilitation are achieved.
SUMMARY OF THE INVENTION
As technical means for achieving the above-
described object, according to the present invention, there
is provided a boot for a tripod joint constituted by
forming a plurality of axial-direction grooves in a casing
outer peripheral surface, the boot comprising: a large-
diameter-side end portion into which a casing of the tripod
joint is inserted; a small-diameter-side end portion into
which a shaft portion connected to the tripod joint is
inserted; and a bellows portion formed between the large-
diameter-side end portion and the small-diameter-side end
portion, the large-diameter-side end portion being
fastened/fixed to the tripod joint casing from an outer
peripheral surface side via a band, the large-diameter-side
end portion comprising: a thick portion formed facing the
axial-direction groove of the casing and protruding from
the inner peripheral surface; one or a plurality of seal
lips disposed in the form of a protrusion over the whole
periphery in a peripheral direction of the inner peripheral
CA 02490679 2004-12-22
_ 7 _
surface of the large-diameter-side end portion; and shift
preventive walls which are disposed on opposite sides of
the axial direction via the seal lip and whose inner
diameters are formed to be smaller than those of base
portions of the seal lips, and the shift preventive walls
and the seal lips are disposed right under a band fastening
portion.
According to the present invention, since the seal
lips are disposed between the front and back shift
preventive walls in the axial direction, a boot volume o~
the large-diameter-side end portion can be reduced, and
materials are not wasted.
Moreover, since the volume is reduced, the
thickness is reduced, and an insertion property into the
casing is also satisfactory. According to the present
invention, unlike the conventional technique, since any
bead is not disposed in the axial-direction groove of the
casing outer peripheral surface of the tripod joint, the
insertion property into the casing is not impaired. In the
present invention, since the front/back shift preventive
walls and the seal lips are disposed right under the band
fastening portion, the fastening force by the band acts on
both the front/back shift preventive walls and the seal
lips. Therefore, there is not any shift, and a sealing
property is superior. According to the present invention,
since the large-diameter-side end portion is thin, and has
flexibility, the shift preventive wall, which is an
CA 02490679 2004-12-22
undercut, does not impair a forming property.
Furthermore, machining (lathe working) to be
performed with respect to the outer peripheral surface
formed by forging the casing of the tripod joint is
performed with respect to a peripheral-direction groove
having the surface which engages with the shift preventive
wall of the boot and a tapered surface of an edge on an
opening end portion side only, and is accordingly minimized.
The surface portion which abuts on the seal lip does not
have to be formed by cutting during the machining, or is
worked to the minimum. Therefore, a cutting allowance at a
machining time is reduced, and the working of the casing
can be simplified.
Additionally, both edges along the axial-direction
groove formed in the outside of the casing are usually R-
chamfered, and rounded/finished, but the above-described
seal lip is disposed across this chamfered portion. In
this case, for example, the peripheral-direction groove is
formed in the portion other than the axial-direction groove
in the outer surface of the casing. As compared with a
case where the seal lip is allowed to abut on the groove
bottom, a bend angle of the seal lip in the chamfered
portion can be reduced, and accordingly a sealing
performance is enhanced.
Moreover, in the above-described case, the base
portion of the seal lip may be disposed on a surface
portion in which the inner diameter of the inner peripheral
CA 02490679 2004-12-22
- 9 -
surface of the large-diameter-side end portion is maximized.
Furthermore, the shift preventive wall may be
constituted in such a manner that a protrusion formed on at
least the portion other than the axial-direction groove in
the casing of the constant velocity universal joint is
engaged in such a manner as to be held from the front/back
in the axial direction.
Additionally, at least two seal lips are disposed
in parallel, and these two seal lips are formed in such a
manner as to protrude from the surface portion whose inner
diameter is substantially constant over a cylinder axial
direction of the large-diameter-side end portion.
Moreover, the shift preventive wall may comprise a
tapered surface formed in such a manner that the inner
diameter is reduced as a distance from the seal lip
Increases.
According to the present invention, shift
prevention and sealing performance between the boot for the
constant velocity universal joint, having the thick portion
formed in such a manner as to protrude from the inner
peripheral surface of the large-diameter-side end portion,
and the outer peripheral surface of the casing of the
tripod joint are enhanced, and further the insertion
property of the boot into the casing is enhanced. Moreover,
cost reduction by reduction of costs of boot materials,
reduction of costs for preparing the casing, and
facilitation of the manufacturing can be achieved.
CA 02490679 2004-12-22
- 10 -
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a transverse sectional view of a casing
of a tripod joint attached to one embodiment of a boot for
a constant velocity universal joint, to which the present
invention is applied;
FIG. 2 is a sectional view along line II-II of FIG.
1;
FIG. 3 is a vertical sectional view of a first
embodiment of the boot for the constant velocity universal
joint, to which the present invention is applied;
FIG. 4 is a diagram of the boot viewed from an end
face side of a large-diameter-side end portion;
FIG. 5 is a sectional view along line V-V of FIG.
4;
FIG. 6 is a sectional view along line VI-VI of FIG.
4;
FIG. 7A is a sectional view showing a state in
which the boot of the present embodiment is attached/fixed
to the casing of the tripod joint;
FIG. 7B is a diagram showing a relation between a
conventional boot and the casing of the tripod joint;
FIG. 8A is an enlarged sectional view of a main
part of FIG. 7A;
FIG. 8B is an enlarged sectional view of a main
part of FIG. 7B;
FIG. 8C is a diagram showing a state in which the
CA 02490679 2004-12-22
- 11 -
casing (portion shown by a solid line) of the tripod joint
for use in the present embodiment is superimposed on the
casing (portion shown by a two-point chain line) of the
tripod joint for use in a conventional mode to compare
cutting allowances; and
FIG. 9 is a diagram showing a shape of an outer
peripheral surface (surface formed by forging) of a mother
material of the casing in the present embodiment, an axial-
direction view shape of a surface portion formed by
machining the mother material, and an axial-direction view
shape of a groove bottom surface.
DESCRIPTION OF THE PREFERRED EMBODIMENT
An embodiment of a boot for a constant velocity
universal joint, to which the present invention is applied,
will be described hereinafter. It is to be noted that the
present embodiment is simply one embodiment of the present
invention, is not interpreted as limited to this embodiment,
and can be changed in design within the scope of the
present invention.
First, a shape of a casing of a tripod joint to
which the boot for the constant velocity universal joint of
the present embodiment is attached will be described. FIG.
1 is a main part sectional view of the casing of the tripod
joint. As shown in FIG. l, a casing 1 of the tripod joint
is entirely formed into a cylindrical shape, and the boot
for the constant velocity universal joint is attached to
CA 02490679 2004-12-22
- 12 -
one opening end portion 3. FIG. 2 is a II-II line
sectional view of the casing 1 of the tripod joint shown in
FIG. 1. For example, grooves 5 which contain three sets of
rollers attached to a shaft portion of a driving shaft in a
trifurcated manner are formed in three positions apart from
one another by 120° in a peripheral direction in the inner
peripheral surface of the casing 1. The groove 5 has a
substantially constant section shape in an axial direction,
and comprises a groove bottom portion 7 whose section is
formed in a circular concave surface, and groove side
surface portions 9 formed on opposite sides of the
peripheral direction. Moreover, a surface portion 11 whose
inner diameter from an axial center is smallest in the
inner peripheral surface of the casing 1 and which is
disposed in such a manner as to be directed toward the
axial center of the casing 1 is formed between the adjacent
groove side surface portions 9 of the adjacent grooves 5.
Moreover, in an outer peripheral surface 13 of the
casing 1 corresponding to the backside of the groove bottom
portion 7, cylindrical surfaces 13a formed into cylindrical
surface shapes substantially concentric with the axial
center of the casing 1, and axial-direction grooves 13b
dented into circular sectional shapes from opposite sides
of the cylindrical surfaces 13a are formed. That is, the
outer peripheral surface 13 of the casing 1 is constituted
of three cylindrical surfaces 13a displaced every 120° in
the peripheral direction, and three axial-direction grooves
CA 02490679 2004-'12-22
- 13 -
13b disposed between the respective cylindrical surfaces
13a. As shown in FIG. 2, boundaries 17 between the
cylindrical surfaces 13a and the axial-direction grooves
13b are R-chamfered, rounded, and finished.
Furthermore, as shown in FIG. 1, a peripheral-
direction groove 19 is formed in the cylindrical surface
13a of the outer peripheral surface 13 in the vicinity of
the opening end portion 3 of the casing 1, and a surface
portion (protrusion) 23 is formed in a desired range
between the peripheral-direction groove 19 and the opening
end portion 3.
This peripheral-direction groove 19 has a
trapezoidal sectional shape, for example, as shown in FIG.
1, and its width is formed to be narrower as depth
increases. Moreover, a tapered face 21 is formed on an
edge on the side of the opening end portion 3.
Shift preventive walls (tapered surfaces 51, 53)
of a boot 1 described later engage with a tapered surface
19a and the tapered face 21 in the vicinity of the end
portion 3 of the peripheral-direction groove 19.
It is to be noted that the peripheral-direction
groove 19 or the tapered face 21 is not formed in the
above-described axial-direction groove 13b even in the
outer surface of the casing 1.
Next, FIG. 3 is an elevation view showing an
appearance of the boot for the constant velocity universal
joint of the present embodiment. As shown in FIG. 3, a
I I
CA 02490679 2004-12-22
- 14 -
boot 25 is entirely formed into a cylindrical shape, and
has a large-diameter-side end portion 27 fixed to the side
of the casing 1 of the constant velocity universal joint,
and a small-diameter-side end portion 29 fixed to a shaft
portion side (not shown) of the driving shaft. Moreover,
bellows 31 having flexibility and constituted to be
bendable are formed between the large-diameter-side end
portion 27 and the small-diameter-side end portion 29. It
is to be noted that in the present embodiment, the boot 25
is formed of a resin having elasticity, such as
thermoplastic polyester-based elastomer, and a grommet 33
disposed on an inner peripheral side of the large-diameter-
side end portion is formed of a resin having hardness lower
than or equal to that of a portion other than the boot 25,
such as an outer peripheral side of the large-diameter-side
end portion. However, the present invention is not limited
to this example. For example, a boot 25 main body
including an outer peripheral portion of the large-
diameter-side end portion, and the grommet may be
integrally formed of the same resin material, for example,
by injection forming or the like. The grommet 33 may be
formed of rubber.
The bellows 31 are constituted in such a manner
that convex portions 31a and concave portions 31b extending
in the peripheral direction are repeatedly arranged in a
cylinder axial direction of the boot 25, that is, a
vertical direction in FIG. 3. That is, sections of the
CA 02490679 2004-12-22
- 15 -
bellows 31 are convex on the outer peripheral side in the
convex portions 31a, and sections of the bellows 31 are
convex on the inner peripheral side in the concave portions
31b. In the present embodiment, for example, five convex
portions 31a are disposed, and the corresponding concave
portions 31b are disposed on a large-diameter-side end
portion 27 side of each convex portion 31a. Moreover, the
diameters of the convex portions 31a and the concave
portions 31b are set to be large toward the large-diameter-
side end portion 27 from the small-diameter-side end
portion 29. As a result, the bellows 31 are entirely
formed into a substantially conical shape.
A surface portion 35 formed into a substantially
constant outer diameter over the axial direction is
disposed in the outer peripheral surface of the large-
diameter-side end portion 27.
The surface portion 35 is used as a band fastening
portion to which a band 63 (shown in FIGS. 7, 8) for
fastening the boot 25 with respect to the surface portion
23 of the casing 1 of the tripod joint and the groove
surfaces of the axial-direction grooves 13b is attached.
This surface portion will be described as the band
fastening portion 35.
Stepped portions 37, 39 for preventing the band
from shifting in the axial direction are formed on opposite
ends of the band fastening portion 35 in the cylinder axial
direction of the boot 25.
CA 024906719 2004-12-22
- 16 -
Moreover, FIG. 4 is a diagram of the boot 25
viewed from an end face side of the large-diameter-side end
portion 27. As shown in FIG. 4, on the inner peripheral
surface of the large-diameter-side end portion 27, thick
portions 41 protruded in circular shapes are formed in such
a manner as to be adapted to the groove surfaces of the
axial-direction grooves 13b formed in the outer surface of
the casing 1. It is to be noted that regions other than
the thick portions 41 on the inner surface of this large-
diameter-side end portion 27 will be hereinafter referred
to as thin portions 43 for the sake of convenience.
FIG. 5 is a sectional view along arrows V-V of FIG.
4, and is an enlarged sectional view of the boot 25 in the
thin portion 43 of the large-diameter-side end portion 27.
As shown in FIG. 5, in the thin portion 43, the inner
peripheral surface of the large-diameter-side end portion
27 is formed in such a manner as to be dented into a
substantially trapezoidal sectional shape, and a surface
portion 45 corresponding to an upper base of this
trapezoidal shape and having a maximum inner diameter is
formed in such a manner that its inner diameter is
substantially constant over the axial direction.
Moreover, protruding seal lips (sealing lips) 47,
49 are formed on opposite end portions of the surface
portion 45 in the axial direction.
The sectional shapes of the seal lips 47, 49 are
triangular shapes whose protruding end portions (vertex
CA 02490679 2004-12-22
- 17 -
portions) are rounded, for example, as shown in FIG. 5, but
the present invention is not limited to this example.
Moreover, the protruding end portions of the respective
seal lips 47, 49 in the axial direction (width direction of
the seal lips 47, 49) of the boot 25 are positioned
substantially in middle portions of the seal lips.
Moreover, tapered surfaces 51, 53 are formed on
the opposite sides of the boot 25 in the axial direction
with respect to the surface portion 45 on which the above-
described seal lips 47, 49 are disposed. When the boot 25
for the constant velocity universal joint of the present
embodiment is inserted into the casing 1 of the above-
described tripod joint, these tapered surfaces 51, 53 abut
on the tapered face 21 formed on the edge of the opening
end portion 3 of the casing l, and the tapered surface 19a
of the peripheral-direction groove 19 of the outer
peripheral surface 13 of the casing 1, respectively. These
abutting tapered surfaces 51, 53 function as shift
preventive walls which prevent the boot 25 from shifting in
the axial direction with respect to the casing 1. These
tapered surfaces 51, 53 are formed in such a manner that
their inner diameters decrease as distances from the seal
lips 47, 49 increase.
It is to be noted that in the present embodiment,
the tapered surfaces 51, 53 are disposed in consideration
of the insertion property at an attaching time, but these
surfaces may be vertically disposed in a diametric
CA 02490679 2004-'12-22
- 18 -
direction of the large-diameter-side end portion 27, and
the design can be changed in the scope of the present
invention.
These tapered surfaces 51, 53 will be described
hereinafter as the shift preventive walls 51, 53.
Moreover, the seal lips 47, 49 and the shift
preventive walls (tapered surfaces) 51, 53 are disposed
right under the band fastening portion 35.
Moreover, FIG. 6 is a sectional view along arrows
VI-VI of FIG. 4, and is an enlarged sectional view of the
boot 25 in the thick portion 41 of the large-diameter-side
end portion 27.
As shown in FIG. 6, in the present embodiment, the
shift preventive walls (tapered surfaces) 51, 53 like the
thin portions are not disposed on the thick portion 41, but
the seal lips 47, 49 are also formed on the surface 55 of
the thick portion 41.
That is, the seal lips 47, 49 are formed over the
whole periphery of the inner peripheral surface of the
large-diameter-side end portion 27 regardless of the thick
portion 41 or the thin portion 43. It is to be noted that
regions in which these seal lips 47, 49 are disposed are
formed into substantially the same sectional shapes over
the axial direction of the boot 25 on the surface 55 of the
thick portion 41.
FIGS. 7A and 7B show a state in which the boot is
attachedlfixed to the casing 1 of the tripod joint, FIG. 7A
CA 02490679 2004-I12-22
- 19 -
shows a relation between the boot for the constant velocity
universal joint according to the present embodiment and the
casing of the tripod joint, and FIG. 7B shows a relation
between the conventional boot and the casing of the tripod
joint. FIG. 8A is an enlarged sectional view of a main
part of FIG. 7A, and FIG. 8B is an enlarged sectional view
of a main part of FIG. 7B.
Accordingly, the present embodiment (FIGS. 7A and
8A) are compared with a conventional mode (FIGS. 7B and 8B)
as follows.
In the present embodiment, the seal lips 47, 49
are disposed between the shift preventive walls 51 and 53.
On the other hand, in the conventional mode, as confirmable
from FIG. 8B, a shift preventive concave portion 301 is
disposed in a position shifting inwards from a position in
which a seal lip 302 is disposed in the axial direction of
a boot 300. Moreover, a protrusion 201 which engages with
the shift preventive concave portion 301 is disposed on an
end portion of an outer peripheral surface of a casing 200
of the tripod joint. In this constitution, a size of a
boot volume is obvious in the conventional technique,
materials are wasted, and an insertion property into the
casing is unsatisfactory. On the other hand, according to
the present embodiment, the thickness is small, the volume
is also small, the materials are not wasted, and the
insertion property into the casing is also superior.
Moreover, in the conventional technique, the
CA 02490679 2004-12-22
- 20 -
above-described shift preventive structure (201 and 301)
are consciously shifted from a band fastening portion 400
(500 denotes a band in the figure). Therefore, even when
the shift of the boot 300 toward the small-diameter-side
end portion (shift in an L direction in the figure) can be
regulated, a force for regulating the shift toward the
large-diameter-side end portion (shift in an R direction in
the figure). On the other hand, in the present embodiment,
since the shift preventive walls 53, 51 and the seal lips
49, 47 are disposed right under the band fastening portion
35, a fastening force of the band 63 acts on the front/back
shift preventive walls 53, 51 and the seal lips 49, 47.
Therefore, the shift in any direction before/after the
axial direction can also be regulated, and a sealing
performance is also remarkably superior.
As described above, according to the present
embodiment, it is sufficient to perform the machining on
the outer peripheral surface 13 of the casing 1 of the
constant velocity universal joint only with respect to the
peripheral-direction groove 19 and the tapered face 21
excluding unavoidably performed surface finishing with a
micro cutting allowance with respect to a forged surface.
Therefore, there is an effect that the working at the time
of preparation of the casing 1 of the constant velocity
universal joint can be simplified.
FIG. 8C shows a state in which the casing 1
(portion shown by a solid line) of the tripod joint for use
CA 02490679 2004-I12-22
- 21 -
in the present embodiment is superimposed on the lathe-
worked casing 200 (portion shown by a two-point chain line)
of the tripod joint for use in the conventional mode to
compare the cutting allowance. Since a portion shown by
slant lines A in the figure does not have to be cut in the
present embodiment, great rationalization can be expected.
Moreover, the seal lips 47, 49 are allowed to abut
on the surface portion (protrusion) 23 of the casing 1 of
the tripod joint, having a large diameter. Therefore, the
bend angle in the boundary 17 between the portion
contacting the surface portion (protrusion) 23 and the
portion contacting the axial-direction groove 13b is
reduced in each of the seal lips 47, 49. Accordingly, the
sealing performance is enhanced. This principle will be
described with reference to FIG. 9. FIG. 9 is a diagram
showing a shape of an outer peripheral surface (surface
formed by forging) of a mother material of the casing 1 in
the present embodiment, an axial-direction view shape of
the surface portion 23 (surface formed by machining the
mother material), an axial-direction view shape of the
bottom surface of the peripheral-direction groove 19, and
an axial-direction view shape of the groove surface of the
axial-direction groove 13b. The outer peripheral surface
shape of the mother material of the casing 1 formed by the
forging is shown by a solid line 101. The surface shape of
the surface portion 23 of the casing 1 contacting the seal
lips 47, 49 is shown by a broken line 103. Furthermore,
CA 02490679 2004112-22
- 22 -
the surface shape of the groove bottom surface of the
peripheral-direction groove 19 is shown by one-dot chain
line 105. Moreover, for example, the seal lips 47, 49 are
constituted in such a manner as to abut on the peripheral-
s direction groove 19 whose outer diameter is formed to be
small by cutting the surface of the casing 1. In this
constitution, the seal lips 47, 49 are bent at a
comparatively large angle (3 in a point 107 at which the
groove bottom surface of the peripheral-direction groove 19
contacts the surface of the axial-direction groove 13b.
When the seal lips 47, 49 are bent at the comparatively
large angle in this manner, the sealing performance is
supposed to drop in this bent portion. On the other hand,
in the present embodiment, the seal lips 47, 49 are bent in
a point 109 in which the surface of the surface portion 23
contacts the surface of the axial-direction groove 13b, but
a bend angle a is comparatively smaller than that in the
point 107, and therefore it is considered that the sealing
performance can be enhanced.
Furthermore, according to the present embodiment,
the thin portion 43 of the large-diameter-side end portion
27 between the surface portion 45 on the inner peripheral
side and the band fastening portion 35 on the outer
peripheral side which is the backside can be formed to be
thin. Accordingly, the boot 25 can be lightened, and the
materials for use can be reduced. Moreover, rigidity of
the large-diameter-side end portion 27 drops, the portion
i n I.
CA 02490679 2004-12-22
- 23 -
becomes flexible, and therefore an attaching operation to
the casing 1 is facilitated.
Additionally, the boot 25 comprising the small-
diameter-side end portion 29, bellows 31, and large-
diameter-side end portion 27 is mostly formed of a resin,
but the grommet 33 is formed of a material having a
hardness smaller than that of the resin forming the boot 25,
and the seal lips 47, 49 are formed of the same material as
that of the grommet 33. Therefore, the hardness of the
seal lips 47, 49 can be lowered, accordingly a sufficient
elastic deformation amount can be secured, and therefore
the sealing performance can be remarkably enhanced.
It is to be noted that the present invention is
not limited to the above-described embodiment, and can be
appropriately changed in the scope of the present invention.
For example, the protrusion which functions as the seal lip
may be formed into another shape. The number of the
protrusions is not limited to two as in the present
embodiment, and may be smaller or larger. In this case,
when the number of the protrusions is increased, the
sealing performance can further be enhanced. Furthermore,
the grommet may be formed of a rubber, another portion may
be formed of a resin, and the whole boot may be formed of
the rubber or the resin alone.
