Planet-pinion carrier assembly for planetary gear system

A planet-pinion carrier assembly for a planetary gear system includes a planet-pinion carrier having first and second radially extending sections, planet pinions each rotatably mounted onto a pinion shaft through a bearing, a first thrust washer disposed between one axial end of each planet pinion and the first section, and a second thrust washer disposed between the other axial end of each planet pinion and the second section. The first and second thrust washers each have a surface hardness large enough to ensure an improved durability and reliability.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to a planet-pinion carrier assembly for a 
planetary gear system to be used in an automatic transmission and, more 
specifically, to the planet-pinion carrier assembly, wherein thrust 
washers disposed between axial ends of each planet pinion and a 
planet-pinion carrier rotatably supporting the planet pinions have a 
surface hardness large enough to ensure improved durability and 
reliability. 
2. Description of the Background Art 
There is known a planet-pinion carrier assembly for a planetary gear system 
to be used in an automatic transmission, such as disclosed in Japanese 
First (Unexamined) Utility Model Publication No. 62-40346. 
In this known structure, the carrier assembly includes a planet-pinion 
carrier having a rotation axis, planet pinions each rotatably mounted on a 
pinion shaft which is fixed to the pinion carrier, a needle roller bearing 
disposed between the pinion shaft and the planet pinion for rotatably 
supporting the planet pinion, and thrust washers. Specifically, the pinion 
carrier has first and second sections extending radially with respect to 
the rotation axis and axially spaced apart by a predetermined distance 
from each other for receiving the planet pinions therebetween. The first 
and second sections are fixedly connected to each other and fixedly 
support each of the pinion shafts therebetween. The planet pinion is 
rotatably mounted on each pinion shaft through the needle roller bearing. 
Further, a pair of the thrust washers are disposed in slidable contact 
with each other between one axial end surface of each planet pinion and 
the first section, and another pair of the thrust washers are disposed in 
slidable contact with each other between the other axial end surface of 
each planet pinion and the second section, for supporting axial loads 
applied thereto from the planet pinion and the needle roller bearing. By 
utilizing two thrust washers arranged in slidable contact with each other, 
a relative rotational speed between the two thrust washers, when the 
planet pinions are rotated, can be reduced so as to improve the durability 
of the thrust washers. 
In this known planet-pinion carrier assembly, however, a problem exists 
that the durability of the thrust washers is insufficient when the applied 
load is large, i.e. when the planet pinions are rotated at a high speed 
and with a large torque. Specifically, in the known structure, each thrust 
washer is formed by applying a soft nitriding process to a high carbon 
tool steel to have a surface hardness of about Hv (Vickers hardness) 400. 
Accordingly, the thrust washers, particularly those which face the axial 
end surfaces of each planet pinion are subject to abrasion when the 
applied load is large, due to the contact with axial ends of the needle 
roller bearing and due to the load applied unevenly to the thrust washers 
which is caused by inclination of each mounted planet pinion. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide 
a-planet-pinion carrier assembly for a planetary gear system that can 
eliminate the above-noted defects inherent in the known structure. 
It is another object of the present invention to provide a planet-pinion 
carrier assembly for a planetary gear system, wherein thrust washers 
disposed between axial end surfaces of each planet pinion and radially 
extending sections of a planet-pinion carrier are formed hard enough not 
to be subject to the abrasion so as to ensure improved durability and 
reliability of the thrust washers. 
To accomplish the above-mentioned and other objects, according to one 
aspect of the present invention, a planet-pinion carrier assembly for a 
planetary gear system comprises a planet-pinion carrier having a rotation 
axis and including a first section extending radially with respect to the 
rotation axis and a second section radially extending and axially spacing 
a predetermined distance from the first section, and planet pinions each 
rotatably mounted onto a pinion shaft through bearing means, the pinion 
shaft extending between the first and second sections with its one axial 
end fixed to the first section and with its other axial end fixed to the 
second section, the planet pinions each having a first axial end facing 
the first section and a second axial end facing the second section. 
The planet-pinion carrier assembly further includes a first thrust washer 
disposed between the first axial end of each planet pinion and the first 
section, and a second thrust washer disposed between the second axial end 
of each planet pinion and the second section. 
The first and second thrust washers each are designed to have a surface 
hardness of no less than Hv 700. 
According to another aspect of the present invention, in a planet-pinion 
carrier assembly for a planetary gear system, the planet-pinion carrier 
assembly including a planet-pinion carrier which has a rotation axis and 
includes a first section extending radially with respect to the rotation 
axis and a second section radially extending and axially spacing a 
predetermined distance from the first section, planet pinions each 
rotatably mounted onto a pinion shaft through bearing means, the pinion 
shaft extending between the first and second sections with its one axial 
end fixed to the first section and with its other axial end fixed to the 
second section, the planet pinions each having a first axial end facing 
the first section and a second axial end facing the second section, a 
first thrust washer disposed between the first axial end of each planet 
pinion and the first section, and a second thrust washer disposed between 
the second axial end of each planet pinion and the second section, a 
method of forming each of the first and second thrust washers comprises 
applying a boron dipping process to a base material to provide each of the 
first and second thrust washers, the first and second thrust washers each 
having a surface hardness of no less than Hv 700.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A preferred embodiment of a planet-pinion carrier assembly for a planetary 
gear system to be used in an automatic transmission according to the 
present invention will be described with reference to FIG. 1. 
In FIG. 1, a planet-pinion carrier assembly generally designated by a 
reference numeral 10 includes a planet-pinion carrier which is also 
generally designated by a reference numeral 12. The pinion carrier 12 has 
a rotation axis Rx and includes a first section 12a extending radially 
with respect to the rotation axis Rx and a second section 12b extending 
radially and spacing a predetermined distance from the first section 12a 
in the axial direction for receiving planetary pinions 14 therebetween. 
The first and second sections of the pinion carrier 12 are fixedly 
connected to each other and fixedly support each of pinion shafts 16 
therebetween. Each pinion 14 is rotatably mounted onto the corresponding 
pinion shaft 16 through a needle roller bearing 18. A pair of thrust 
washers 20 and 21 are arranged axially in slidable contact with each other 
between one axial end surface of the pinion 14 and the first section 12a, 
and another pair of thrust washers 22 and 23 are also arranged axially in 
slidable contact with each other between the other axial end surface of 
the pinion 14 and the second section 12b, for supporting axial load 
applied thereto. The thrust washers 20 and 22 are the same members each 
facing the corresponding axial end surface of the pinion 14 and each being 
formed by applying the boron dipping process to a high carbon tool steel 
to provide a surface hardness of no less than Hv 700, preferably Hv 700 to 
1500, and an internal or inside hardness of no more than Hv 350, 
preferably Hv 200 to 350. The surface hardness of no less than Hv 700 
extends across a maximum thickness of 60 .mu.m from surfaces of each of 
the thrust washers 20 and 22. On the other hand, the thrust washers 21 and 
23 are the same members each facing the corresponding first or second 
section 12a or 12b and each being formed of a copper alloy material. The 
thrust washer 21 has a pawl 21a at its outer periphery which is fitted 
into a recess 12c formed at a corresponding portion of the first section 
12a for preventing rotation of the thrust washer 21. Similarly, the thrust 
washer 23 has a pawl 23a at its outer periphery which is fitted into a 
recess 12d formed at a corresponding portion of the second section 12b for 
preventing rotation of the thrust washer 23. 
An annular groove 24 is formed on the inner periphery of the first section 
12a and a lubricant passage 26 is further formed in the first section 12a. 
The lubricant passage 26 extends radially outward from the annular groove 
24 to communicate with a lubricant passage 28 formed through the pinion 
shaft 16. The lubricant passage 28, in turn, opens to rolling contact 
surfaces of rolling elements of the needle bearing 18. 
A sun gear 30 has a center bore section 32 which receives a rotation shaft 
therein to be firmly connected thereto, and meshes with the planet pinions 
14. A ring gear 34 is further provided encircling the planet pinions 14 
and meshes therewith, while the pinion carrier 12 has a hub section 36 for 
receiving a rotation shaft to be firmly connected thereto. In this 
embodiment, the sun gear 30, the planet pinions 14 and the ring gear 34 
are all helical gears. The sun gear 30 is formed with a lubricant passage 
38 for conducting the lubricant supplied through a lubricant circuit 
formed in the associated rotation shaft to the annular groove 24. 
An annular bearing race 40 is provided at a left side of the first section 
12a in FIG. 1. The bearing race 40 receives thereon rolling elements of a 
thrust bearing 42 which is supported by a radial extension 44 of the sun 
gear 30. 
Now, the operation of the foregoing preferred embodiment will be described 
hereinbelow. 
When the planet pinions 14 are rotated, since the helical gears are used as 
mentioned above, a thrust load is applied to the thrust washers 20, 21 or 
the thrust washers 22, 23 depending on a direction of the rotation of the 
planet pinions 14. Further, the needle bearing 18 is also rotated to exert 
a load to the thrust washers 20 and 22 due to the interference between the 
axial ends of the needle bearing 18 and the associated thrust washers 20 
and 22. However, since the thrust washers 20 and 22 each have a surface 
hardness of not less than Hv 700 which is large enough to prevent the 
abrasion, even when a substantially large load is applied to the thrust 
washers 20 and 22, the thrust washers 20 and 22 are not subject to the 
substantial abrasion so that the highly reliable durability is ensured. On 
the other hand, though relative rotation is generated between the thrust 
washers 20 and 21 and between the thrust washers 22 and 23, since the 
thrust washers 21 and 23 each are formed of the copper alloy material 
which has a high lubricity, the thrust washers 21 and 23 are not subject 
to the abrasion due to the sliding interference with the thrust washers 20 
and 22. 
The lubricant is supplied to the thrust washers 20 to 23 for lubricating 
same. Specifically, the lubricant introduced through the lubricant circuit 
formed in the rotation shaft of the sun gear 30 is introduced into the 
annular groove 24 through the lubricant passage 38. The lubricant is, in 
turn, introduced to the rolling surfaces of the needle bearing 18 through 
the lubricant passages 26 and 28. After lubricating the needle bearing 18, 
the lubricant is supplied to the thrust washers 20 to 23 through the axial 
ends of the needle bearing 18. 
It is to be appreciated that the thrust washers 21 and 23 may be designed 
to have a hardness of no less than Hv 700 as the thrust washers 20 and 22. 
In this case, the pawls 21a and 23a can be eliminated to allow the 
rotation of the thrust washers 21 and 23. Further, it is also possible to 
use only the thrust washers 20 and 22 and eliminate the thrust washers 21 
end 23. 
It is to be understood that this invention is not to be limited to the 
embodiment described above, and that various changes and modifications may 
be made without departing from the spirit and scope of the invention as 
defined in the appended claims.