Machine element or mechanism – Gearing – Directly cooperating gears
Reexamination Certificate
1999-11-12
2001-08-21
Herrmann, Allan D. (Department: 3682)
Machine element or mechanism
Gearing
Directly cooperating gears
C277S354000
Reexamination Certificate
active
06276225
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a ball screw assembly provided with a nut having an axial end portion to which a seal member is provided.
A nut of a ball screw assembly is provided with a seal device for preventing foreign matters from invading and for preventing a lubricant filled in the nut from leaking. Various kinds of such seal devices have been proposed, including one example of a ring-shaded seal member having a spiral projection. The seal member is fitted to a ball rolling groove formed on a screw shaft and is mounted on an axial end portion of the nut, and such example has been applied widely to the commercial use. However, there is a possibility of often causing dimensional errors between the screw shaft or the ball rolling groove and the seal members when assembled, and hence, it is difficult to make a complete tight-contact between the inner peripheral surface of the ring-shaped seal member and the screw shaft.
In order to overcome such problem mentioned above, there is provided a seal device as shown in
FIGS. 12A and 12B
(for example, as disclosed in Japanese Utility Model Laid-open Publication No. HEI 6-6795). With reference to
FIGS. 12A and 12B
, a portion of a ring-shaped seal member
1
is divided into a plurality of blocks
1
a
,
1
a
, - - - ,
1
a
in its circumferential direction. The respective blocks
1
a
are pushed into a screw shaft
2
so that projections
1
b
of the blocks
1
a
can closely contact a ball rolling groove
2
a
. Opposing divided surfaces
1
c
and
1
d
of the adjacent divided blocks
1
a
,
1
a
are inclined with respect to the radial direction of the screw shaft
2
and also inclined with respect to the axial direction of the screw shaft
2
in a twisted (spiral) direction of the ball rolling groove
2
a.
According to such seal device, since the respective blocks
1
a
can be displaced or shifted in the radial direction of the screw shaft
2
, the respective blocks
1
a
can surely contact the screw shaft
2
even in the presence of the dimensional error. Moreover, when the screw shaft
2
is screwed into the nut
3
, foreign matters sticking on the screw shaft
2
can be scraped by the divided surface
1
c
of the block
1
a
directed to the rotational direction of the nut
3
with respect to the screw shaft
2
. The scraped foreign matters can be removed outside the outer periphery of the nut
3
and outward in the axial direction in accordance with the inclination of the divided surface
1
c.
Incidentally, in the seal member
1
mentioned above, the two divided surfaces
1
c
and
1
d
of the adjacent blocks
1
a
,
1
a
are substantially parallel to each other and, hence, widths of slits formed between these divided surfaces
1
c
and
1
d
of the respective blocks
1
a
are also substantially constant. Accordingly, the divided surface
1
d
has a so-called overhang shape in which the divided surface
1
d
gradually projects in the circumferential direction as being displaced from the inner peripheral side of the seal member
1
towards the outer peripheral side thereof, and hence, the respective blocks
1
a
have a shape such that a parallelogram is curved along the screw shaft
2
as viewed from the axial direction of the nut
3
.
Therefore, when a pushing force is applied, as shown by an arrow A in
FIG. 12A
, to a portion near the divided surface
1
d
towards the screw shaft
2
side, it is difficult to receive such pushing force by a portion between the inner periphery of the block
1
a
and the screw shaft
2
, and such pushing force acts to displace the divided surface
1
d
towards the radial central portion so that the portion near the divided surface
1
d
makes the width of the slit
4
narrow.
Accordingly, a force acting on the other side of the block a, i.e. the divided surface
1
c
as shown by an arrow B in
FIG. 12A
, acting in a direction apart from the screw shaft
2
, arises and this force raises the inner peripheral edge
1
e
of the divided surface
1
c
from the screw shaft
2
. In such a state, when the screw shaft
2
is screwed into the nut
3
, the foreign matters sticking on the screw shaft
2
may be caught into the inner peripheral side of the seal member
1
.
The divided surface
1
c
functions as mentioned above when the screw shaft
2
is screwed into the nut
3
, however, the foreign matters will be pushed towards the radially central side and axially inside of the nut
3
by the opposing divided surface
1
d
if the foreign matters are kept in the slit
4
when the screw shaft
2
is screwed out of the nut
3
. For this reason, there is a possibility of the foreign matters being caught between the seal member
1
and the screw shaft
2
.
SUMMARY OF THE INVENTION
An object of the present invention is to substantially eliminate defects or drawbacks encountered in the prior art mentioned above and to provide a ball screw assembly which improves sealing performance, compared with the conventional structure, of the structure in which a portion of the seal member is divided into a plurality of blocks.
This and other objects can be achieved according to the present invention by providing a ball screw assembly comprising:
a screw shaft formed, at an outer periphery thereof, with a ball rolling groove in shape of spiral;
a number of balls rolling along the ball rolling groove of the screw shaft;
a nut screwed with the screw shaft to be relatively rotatable with the balls being interposed therebetween; and
a seal device including seal members mounted on both axial end portions of the nut, the seal member being formed in shape of ring having inner periphery to which a spiral projection to be fitted to the ball rolling groove is formed,
wherein a portion of each of the seal members is divided into a plurality of blocks in a circumferential direction thereof by a plurality of slits formed to the seal member so as to extend from one end surface directing outward in an axial direction of the nut to an axial intermediate portion of the seal member, each of the blocks having a pair of end faces in the circumferential direction, the end faces including one end face directed to a rotational direction of the nut with respect to the screw shaft when the screw shaft is screwed into the nut and another one end face opposing to the above-mentioned one end face, this one end face being inclined so as to be gradually displaced, towards an outer peripheral side from an inner peripheral side of the seal member, in a direction reverse to the rotational direction with respect to a radial direction of the nut, and the another one end face extending in this radial direction of the nut or in a direction inclined to a side reverse to the one end face with respect to the radial direction of the nut.
In a preferred embodiment, the above-mentioned one end face may be inclined in the same direction as a twisted (spiral) direction of the ball rolling groove with respect to the axial direction of the nut at an inclination angle equal to or greater than a lead angle of the ball rolling groove, and the another one end face extends ir a direction perpendicular to a center line of the ball rolling groove or in a direction inclined on a side reverse to the twisted direction of the ball rolling groove from the perpendicular direction.
Some of the plural blocks may contact only the ball rolling grove at intersecting portions between inner peripheral edges of the above-mentioned one end faces and the projections of the seal member and some of other plural blocks contact only an outer peripheral surface of the screw shaft at the inner peripheral edges of the one end faces.
The seal device may comprise wiper rings mounted on both axial end portions of the nut, each of the wiper rings comprising the ring-shaped seal member having an outer periphery in which grooves are formed and spring rings fitted in the grooves for clamping the seal member in the central side thereof.
According to the ball screw assembly of the structures mentioned above, since each of the blocks is formed in a substantially trapezoidal sh
Honma Mitsuaki
Nishide Tetsuhiro
Niwa Hiroshi
Takeda Ryuji
Herrmann Allan D.
THK Co. Ltd.
Young & Thompson
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