Machine element or mechanism – Gearing – Nonplanetary gearing differential type
Reexamination Certificate
2000-06-09
2002-10-15
Wright, Dirk (Department: 3681)
Machine element or mechanism
Gearing
Nonplanetary gearing differential type
Reexamination Certificate
active
06463830
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a differential apparatus capable of achieving difference in rotation between right and left driving wheels or between front and rear drive shafts of automobiles, and capable of increasing a driving force by generating a differential-limiting torque when one of driving wheels or drive shafts is rotating idle, and a method for producing such a differential apparatus, particularly to a differential apparatus having good durability and a stable differential-limiting torque and a method for producing such a differential apparatus.
PRIOR ART
A differential apparatus of an automobile is an apparatus enabling difference in rotation between right and left driving wheels or between front and rear driving wheels when the automobile turns a curve (in the case of a four-wheel driving vehicle). Widely used as a differential apparatus having such a function for automobiles is conventionally a differential apparatus comprising a pinion gear between a pair of bevel gears connected to output shafts, thereby enabling difference in rotation between output shafts by rotating the pinion gear at the time of differential rotation, in a case where a rotation force is applied to a shaft of the pinion gear from outside.
However, when one of the driving wheels is trapped in snow, sand, etc. or falls in a ditch, one wheel runs idle by differential rotation, resulting in total loss of a driving force, etc., which leads to failure to escape from the trapping. In the case of turning a curve, a wheel runs idle when a load applied to wheels on the radial inside at turn extremely decreases, thereby losing a driving force for running on a curve at a high speed.
Proposed as a differential apparatus for overcoming such a problem is, for instance, a differential apparatus having a differential limitation mechanism of a clutch disc pressure fit-type. Because a clutch disc is given biasing pressure in advance to obtain a driving force even when one of the driving wheels is not in contact with a road in this type of the differential apparatus, each of the driving wheels is constrained even when no driving force is given from the engine. Accordingly, it is disadvantageous in combination with an apparatus required to have independence from the rotation of each wheel, such as an anti-lock brake system.
A differential apparatus equipped with a viscous coupling-type, torque-sensing, differential limitation mechanism has also been proposed and put into practical use. Because a viscous coupling transmits a torque by utilizing a shear resistance of a viscous liquid such as a silicone oil, etc., it can provide smooth differential limitation effects responsive to difference in rotation between driving wheels. However, because an initial resistance is given by a viscous liquid, it still suffers from the disadvantage that the driving wheels are constraining each other.
In view of such circumstances, a differential apparatus smaller than the above differential apparatuses and having a differential limitation function without containing a particular mechanism was proposed (Japanese Patent Laid-Open No. 8-170705). This differential apparatus comprises (a) a pair of disc plates fixed to driving wheels and coaxially disposed opposite to each other in an axial direction, each of which has on an opposing surface a circumferential, continuous groove winding such that a radial position varies at a constant period; (b) a ball holder disposed between a pair of disc plates and having a plurality of radially extending guide grooves circumferentially at an equal interval; (c) balls rolling along the circumferential, continuous grooves of a pair of the opposing disc plates, one ball radially reciprocally movable in each guide groove; (d) a casing containing rotatable disc plates and a stationary ball holder; and (e) thrust washers disposed in contact with the outer surfaces of the disc plates. Because balls move back and forth in a radial direction in the guide grooves while they move circumferentially in the continuous groove, a driving force from the engine is transmitted to each of the driving wheels via each disc plate, thereby enabling differential rotation when difference in rotation occurs in the driving wheels. When one of the driving wheels runs idle, a sliding friction force is generated between the outer surfaces of the disc plates and thrust washers by a thrust force generated in the disc plates connected to the driving wheels, thereby obtaining differential limitation effects.
FIG. 18
shows one example of the differential apparatus disclosed by Japanese Patent Laid-Open No. 8-170705, and
FIG. 19
shows an assembly of one disc plate, a ball holder and balls. As shown in
FIG. 18
, the differential apparatus of Japanese Patent Laid-Open No. 8-170705 comprises a case
1
having an open end and a coaxial annual projection
11
at the other end, a case cover
2
having an open end of the same size as that of the open end of the case
1
and a coaxial annual projection
21
at the other end, a pair of disc plates
3
,
4
disposed coaxially opposite to each other, a ball holder
5
disposed between a pair of disc plates
3
,
4
, a plurality of balls
6
rotatably held by the ball holder
5
, and a pair of thrust washers
7
,
7
positioned outside the disc plates
3
,
4
.
The annual projection
11
coaxial with the case
1
functions as a bearing supporting one disc plate
3
. The ball holder
5
engages the case
1
via a plurality of engaging members
10
positioning between an outer surface of the ball holder
5
and an inner wall of the case
1
. The case
1
is provided with a plurality of apertures
14
in a side wall, such that a lubricating oil can flow into the case
1
. A flange
15
formed around the open end of the case
1
is provided with a large number of apertures
15
a for bolts.
The case cover
1
is in the shape of a shallow dish, whose coaxial annual projection
21
functions as a bearing rotatably supporting the other disc plate
4
. The side wall of the case cover
2
is provided with a plurality of apertures
24
for permitting a lubricating oil to flow thereinto. A flange formed around the open end of the case cover
2
is provided with a large number of apertures
25
a
at positions corresponding to those of the apertures
15
a
of the case
1
. The case
1
is fixed to the case cover
2
by bolts (not shown) penetrating both apertures
15
a,
25
a.
The other end of each disc plate
3
,
4
is provided with annual projections
32
,
42
for connecting the drive shaft (not shown) of the wheel. Also, an inner surface of each annual projection
32
,
42
is provided with an axially extending groove
32
a,
42
a
for fixing the drive shaft.
Thrust washers
7
,
7
are disposed between the case
1
and the disc plate
3
, and between the case cover
2
and the disc plate
4
, in contact with outer surfaces of the disc plates
3
,
4
. When there is no difference in rotation between both driving wheels (not shown), or when one of the driving wheels does not run idle, a thrust force is not applied to the disc plate
3
or
4
, resulting in substantially no friction force between the disc plates
3
,
4
and the thrust washers
7
,
7
.
Because the winding continuous grooves of the disc plates
3
and
4
extend in opposite rotational directions with the same variations, only one of the disc plates
3
will be explained below. It should be noted that the same explanation is applicable to the other disc plate
4
.
As shown in
FIG. 19
, an opposing surface of the disc plate
3
is provided with a circumferential, continuous groove winding such that a radial position varies at a constant period, and each winding continuous groove has an arcuate cross section such that balls can roll through the groove. The ball holder
5
is provided with a large number of elongated guide holes
51
each having such a width as to receive a ball
6
, in which a ball
6
can move back and forth in a radial direction. A radial length of each guide hole
51
determining a range of t
Hara Masanori
Ito Yoshitaka
Kurakake Kazuyuki
Maruyama Naoki
Mikami Akira
Hitachi Metals Ltd.
Wright Dirk
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