Planetary gear transmission systems or components – Differential planetary gearing – Spur gear differential
Reexamination Certificate
2002-04-26
2003-09-16
Wright, Dirk (Department: 3681)
Planetary gear transmission systems or components
Differential planetary gearing
Spur gear differential
C475S345000, C475S902000, C074SDIG001
Reexamination Certificate
active
06620074
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a center differential unit including a planetary gear, and particularly to a center differential unit containing a planetary gear used for effectively transmitting power from an engine to driving wheels of a vehicle, which can produce a sufficient differential toque and has an excellent durability.
2. Discussion of the Related Art
In a four wheel drive, power from an engine is transmitted to front and rear wheels usually by a center differential unit. In other words, power from the engine is first transmitted to a transmission by way of a clutch. The transmission output is divided by a center differential unit and transmitted to a front differential unit and a rear differential unit. Torque decelerated by the front and rear differential units is conveyed respectively to the front and rear wheels.
The center differential unit of a planetary gear type is widely used since it is relatively compact and changes in torque delivery to front and rear wheels is easily controlled.
Japanese Patent 2652715 discloses a four wheel drive with a center differential unit having a planetary gear. The center differential unit will now be explained by referring to a schematic cross section of a center differential unit shown in
FIG. 5 and a
schematic diagram in FIG.
6
.
An output shaft
101
is connected with a rear drive shaft
102
, which transmits power to a rear differential unit by way of a propeller shaft. The output shaft
101
and the rear drive shaft
102
are provided to rotate coaxially via bushings
103
and thrust bearings
104
. A reduction gear
105
is supported by the output shaft
101
via the bushings
103
and rotates on the output shaft
101
. The reduction gear
105
and the output shaft
101
are supported on a gearbox casing
100
by ball bearings
106
. A center differential unit
110
is provided over the output shaft
101
, the rear drive shaft
102
and the reduction gear
105
coaxially therewith. The reduction gear
105
meshes with a reduction gear
108
provided on a front drive shaft
107
. Here, the front drive shaft
107
functions to transmit power to a front differential unit.
The center differential unit
110
includes a large diameter sun gear
111
on the output shaft
101
of a transmission on the input side, a small diameter sun gear
112
on the rear drive shaft
102
on the output side, a small diameter pinion
113
meshed with the large diameter sun gear
111
, and a large diameter pinion
114
meshed with the small diameter sun gear
112
. The small diameter pinion
113
and the large diameter pinion
114
are provided on a single pinion member
115
.
Moreover, a supporting plate
117
for a carrier
116
is attached to the rear drive shaft
102
by way of a ball bearing
118
. The supporting plate
117
and the reduction gear
105
are united as an integral body, and a pinion shaft
119
extends over the supporting plate
117
and the reduction gear
105
. The pinion member
115
is supported by the pinion shaft
119
having needle bearings
120
therebetween. Both ends of the pinion member
115
are supported on the reduction gear
105
and the supporting plate
117
by a thrust washer
122
interposed therebetween. An oil supply hole
121
is perforated on the pinion shaft for supplying oil to the needle bearings
120
. For the pinion shaft
119
, high-carbon steel or case-hardened steel which has been subjected to a thermal treatment for hardening the surface.
In the above-mentioned center differential unit
110
containing a planetary gear of a compound type without a ring gear, differential function is attained by using the large diameter sun gear
111
and the small diameter sun gear
112
with an appropriate number of teeth. A disproportional torque ratio on the rear wheels is provided by appropriately distributing the output torque of the transmission. This is achieved by appropriately setting the distance from the meshing point of the large diameter sun gear
111
and the small diameter pinion
113
to the center of the large diameter sun gear
111
, and the distance from the meshing point of the small diameter sun gear
112
and the large diameter pinion
114
to the center of the small diameter sun gear
112
.
Alternatively, it is possible to use helical gears for the large diameter sun gear
111
, small diameter sun gear
112
, small diameter pinion
113
and large diameter pinion
114
so as to generate a thrust load. The thrust load causes friction between the edges of the thrust washer
122
and the pinion member
115
. In addition, force resulting from a separation load and a tangential load is applied to the small diameter pinion
113
, large diameter pinion
114
and a contacting face between the pinion member
115
and the pinion shaft
119
(needle bearings
120
). Accordingly, frictional force is generated on the needle bearings
120
. Thus, a differential control mechanism is provided.
In Japanese Patent 2652715, a radial load is applied to the pinion member
115
depending upon an input torque. In order to eliminate a seizure of the pinion shaft
119
with the pinion member
115
, and the galling of these, the needle bearings
120
are provided as bearings for the pinion member
115
. The needle bearings
120
can be replaced by bushings.
The needle bearing
120
is durable against a large load, but has a small frictional resistance, since it is a rolling bearing. On the other hand, the bushings contact with the pinion member
115
by sliding therebetween. Therefore, the bushing has a large frictional resistance, but a seizure will occur when lubricating oil is in sufficiently supplied. Accordingly, it is difficult to take an appropriate countermeasure when large torque for reducing differential action is required based on a load when traveling for instance on a muddy road or a road with a bad surface condition.
Usually, metal materials are employed for the pinion member
115
and the pinion shaft
119
in order to attain a sufficient strength. When large torque for reducing differential action is necessary, it is possible to increase friction between the pinion member
115
and the pinion shaft
119
by supporting the pinion member directly on the pinion shaft
119
without providing the needle bearing
120
or the bushing. In this case, however, it is impossible for the pinion shaft
119
and the pinion member to endure such a large stress, which causes seizure. Alternatively, if forced lubrication is carried out so as to prevent the seizure, the frictional resistance between the pinion shaft
119
and the pinion member
115
is decreased.
In order to obtain sufficient friction, it is effective to use a paper material, which is usually used as a friction material for a multi-plate clutch for an automatic transmission, by interposing the paper material between the pinion shaft
119
and the pinion member
115
. However, the paper material is not suitable for practical use when lubricating oil containing an additive of a mineral material is used for the differential gear. This is because the durability of the paper friction material is largely decreased due to absorption of such oil.
In this way, it is difficult to obtain both sufficient friction and torque for reducing differential action.
OBJECT AND SUMMARY OF THE INVENTION
It is therefore a first object of the present invention to provide a center differential unit of a planetary gear type which provides torque for reducing differential action corresponding to an input torque in addition to maintaining a stable function of a planetary gear contained therein by obtaining a sufficient frictional force between a pinion shaft and a pinion member without interposing a bearing or a bushing therebetween and efficiently eliminating a seizure therebetween, comprising a carrier; a first sun gear for receiving an output from a transmission and positioned interiorly of the carrier; a second sun gear provided on an output side with respect to the first sun gear and positioned interiorly of the carr
Ishihara Hiroshi
Kanazawa Kazuo
Kurosaki Shin
Nakagawa Takao
Sato Hirotaka
Fuji Jukogyo Kabushiki Kaisha
Smith , Gambrell & Russell, LLP
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