Planetary gear transmission systems or components – Fluid drive or control of planetary gearing – Pump and motor in series with planetary gearing
Reexamination Certificate
2001-08-29
2003-02-25
Wright, Dirk (Department: 3681)
Planetary gear transmission systems or components
Fluid drive or control of planetary gearing
Pump and motor in series with planetary gearing
Reexamination Certificate
active
06524206
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a driving unit used to reduce rotation speed of a hydraulic motor and output the reduced rotation speed, which is used as a driving device for a traveling apparatus.
2. Description of the Prior Art
A driving unit is used as a driving device of a construction machine traveled by a crawler as typified particularly by a driving device of a hydraulic shovel among construction machines. In the driving unit, a hydraulic motor is disposed in an interior of a fixed casing fixed to a vehicle body, so that the rotation as output is transmitted to a rotating casing concentrically fitted to the fixed casing to freely rotate through a planetary gear mechanism, so as to drive the crawler by means of a sprocket disposed around a periphery of the rotating casing. Because of the constraint that the driving unit is located in the interior of the crawler, there is a restriction on the entire inner configuration space, for the reason of which the driving unit is required to have small size and high power.
The driving units of this type are known by publications such as Japanese Laid-open (Unexamined) Patent Publications No. Hei 4-140538, No. Hei 6-249297, Hei 8-247223 and No. Hei 9-240525.
However, the driving units of this conventional type are all being demanded to be further downsized.
It is the object of the present invention to provide a driving unit structurally optimized for every principal part, to provide downsizing and improved durability.
SUMMARY OF THE INVENTION
In accordance with a 1st aspect of the invention, there is provided a driving unit comprising a fixed casing having a hydraulic motor therein; a rotating casing rotatably supported around a periphery of the fixed casing via a bearing inserted from one end portion of the fixed casing and having an internal gear around an inside thereof; a sun gear mounted on an output shaft projected from the hydraulic motor toward the one end portion of the fixed casing; a planetary gear train disposed between the sun gear and the internal gear to reduce speed in two or more stages; a trunnion boss, integrally projected from the one end portion of the fixed casing, for rotatably supporting the planetary gear train of a final stage engaging with the internal gear; a holder in which a front end portion of the trunnion boss is inserted; support pillars projecting from the holder toward the fixed casing; and fastening means for fixing the support pillars and the fixed casing.
Known as a conventional driving unit is the one disclosed by Japanese Laid-open (Unexamined) Patent Publication No. Hei 4(1992)-140538, for example. A typical conventional driving unit
101
is shown in FIG.
25
. The driving unit
101
has a cylindrical fixed casing
102
in which a hydraulic motor
103
is disposed. An output shaft
104
a
of the hydraulic motor
103
is coupled with an input shaft
104
b
via a spline coupling
117
, and a sun gear
105
is mounted on a front end portion of the input shaft
104
b.
A rotating casing
107
is rotatably supported around a periphery of the fixed casing
102
via a bearing
106
, and an internal gear
108
is formed around an inside of the rotating casing
107
. The rotation of the sun gear
105
is transmitted to the internal gear
108
through a planetary gear
109
, a second sun gear
111
engaged with a planetary gear frame
110
of the planetary gear
109
, and a second planetary gear
113
supported on a trunnion boss
112
projected from the front end portion of the fixed casing
102
, to rotate the rotating casing
107
at a reduced speed. A flange
114
of the fixed casing
102
is bolted to the body (not shown), and a flange
115
of the rotating casing
107
is bolted to a crawler sprocket (not shown).
The driving torque of the hydraulic motor
103
fixedly mounted in the fixed casing
102
is reduced via a planetary gear train of the first stage comprising the sun gear
105
and the planetary gears
109
and a planetary gear train of the second stage comprising a second sun gear
111
and second planetary gears
113
and is transmitted to the rotation of the rotating casing
107
.
However, since the trunnion boss
112
for rotatably supporting the second planetary gears
113
is projected from the end of the fixed casing
102
in a cantilever fashion, a bending stress is generated at the basal end of the trunnion boss
112
when a load is applied thereto through the second planetary gears
113
. For this reason, the trunnion boss
112
is required to have a large thickness. As a result of this, the bearing
106
and the floating seal
116
inserted from the trunnion boss
116
side of the fixed casing
102
are increased in size, which causes the rotating casing
107
to increase in size and in turn causes the entire driving unit
101
to increase in radial dimension.
According to the construction of the 1st aspect of the invention, the trunnion boss is allowed to be supported at opposite ends thereof by the holder fixed to the fixed casing through the support pillars. This enables the load applied to the trunnion boss to be dispersed to the holder and the fixed casing, and as such can allow the trannion boss to be reduced in diameter or can allow the fixed casing to be reduced in circumferential dimension. This produces the result that the rotating casing supported around the periphery of the fixed casing by the bearing inserted thereon is also reduced in outer diameter. Also, the support pillars projected from the holder have thickness such that even when the holder body is small in thickness, the fastening means to be fixed to the fixed casing applies a sufficient fastening force at the support pillars. This enables the support of the planetary gear train for rotation, without any axial elongation and with good durability. Thus, the downsizing of the driving unit can be achieved and improved durability can also be provided.
In accordance with a 2nd aspect of the invention, there is provided a driving unit according to 1st aspect of the invention, wherein the support pillars are in abutment with support pillars projected from the fixed casing at their abutment surfaces, which are located within a width of the planetary gear of the final stage.
This construction enables the abutment surfaces to be away from the basal ends of the support pillars to which a maximum bending moment is applied, by projecting the support pillars from the fixed casing side as well.
In accordance with a 3rd aspect of the invention, there is provided a driving unit according to 1st aspect of the invention, wherein the trunnion boss is projected along a periphery of the fixed casing and a rounded portion is formed at a basal end of the trunnion boss except an area close to the periphery of the fixed casing.
According to this construction, since the direction of the load acting on the trunnion boss is a tangent direction to the fixed casing, the fixed casing can be reduced in circumferential diameter by forming no rounded portion for relaxing the bending stress at the basal end of the trunnion boss located around the periphery of the fixed casing.
In accordance with a 4th aspect of the invention, there is provided a driving unit according to 1st aspect of the invention, wherein the abutment surfaces are located at an approximately widthwise center portion of the planetary gear of the final stage.
This construction can allow the abutment surfaces to be located at an approximately axial center of the support pillar at which a bending moment is minimized. Also, this construction can ensure a dimension from underhead of the bolt used as the fastening means to the abutment surfaces.
In accordance with a 5th aspect of the invention, there is provided a driving unit comprising a fixed casing having a hydraulic motor therein; a rotating casing rotatably supported around a periphery of the fixed casing via a bearing inserted from one end portion of the fixed casing and having an internal gear around an inside thereof; a sun gear mounted on an output shaf
Okufuji Hidekazu
Tsunemi Masahiro
Nabco Ltd.
Rosenthal & Osha L.L.P.
Wright Dirk
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