FORM 2
THE PATENT ACT 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. TITLE OF THE INVENTION PLANETARY GEAR ASSEMBLY
2. APPLICANT
MAHINDRA & MAHINDRA LTD.
GATEWAY BUILDING, APOLLO BUNDER, MUMBAI - 400001.AN
INDIAN COMPANY.
The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION:
The present invention relates to planetary gear transmission, and more particularly, to a planetary gear assembly having planetary gear and planetary shaft integrated together to form a single unit and supported with carrier plate for low weight and a low-cost planetary transmission.
BACKGROUND OF THE INVENTION:
Generally a planetary gear transmission comprises essential components such as a sun gear, an outer ring gear, plurality of planet gears and a planet carrier for holding the plurality of planetary gears between the sun gear and outer ring gear, in which, sun gear, ring gear and planetary carrier are independently disposed for determining input-output ratio by keeping either of these components stationary and using the other two components as input or output as per the requirement. This particular type of construction ensures unique advantages over the conventional parallel axis transmission, such as high power density, possibility of multiple combinations of input-output ratio, large reduction in gear ratio and unique combination of compactness and efficiency. Another important advantage is sharing of load distribution and torque capability due to plurality of planet gears.
Hence, to have a planetary gear arrangement of better torque capability and even distribution of load, planet gear has to be uniquely designed and supported with planet carrier. In conventional practice, planet gear is supported with a connecting device which in turn is supported with planetary carrier and the planet gear rotates about the axis of connecting device. Broadly, there are two types of construction in which one type involves robust construction having integrated planetary carrier support and precise engagement among the gears such as sun gear, planet gears and ring gear,

and another type is split type carrier support and loose engagement of gears. Each type of construction has its own pros and cons such as, even though the former gives better performance, it involves high cost in development of the system, high product cost and complexity in design, whereas the later construction even though very cost effective and simple in design, gives more noise and vibration. There have been many inventions in the field of planetary gear assembly for providing a reliable and robust planetary gear arrangement at low cost considering aforementioned shortcomings.
US patent 20060293142 discloses a compact planetary gear assembly for a final drive wherein planet gears are assembled in an integrated planetary gear carrier in which the external surface of the final derive forms a part of the carrier. There are no holes in the external surface associated with the connection of the planetary gears to the integrated planetary gear carrier. The integrated planetary gear carrier having an inner carrier structure and an outer carrier structure and planetary pinion gear, planetary pinion shaft and bearing together form planetary gear assembly which is being assembled between inner structure carrier and outer structure carrier. Robust construction of integrated planetary gear carrier may lead to high product cost and also the invention involves more number of parts which may lead to complexity in design the system.
US Patent 4901602 discloses a planetary gear assembly for a planetary gear transmission comprises a unitary sun gear having an inner sun gear portion and two outer sun gear boss portion and planetary gear assembly comprises a planetary gear ring meshed with said sun gear, two unitary planetary discs having an outer thrust projections, a planetary gear shaft for supporting planetary gear ring and planetary discs, a carrier assembly for receiving said planetary shaft and rotatably supporting said planetary gear assembly, an outer inner-toothed unitary ring gear. This particular invention involves more number of parts which will lead to increase in weight and cost of the entire

system, also necessitates complex design of parts and may take more time for assembly of the system.
US Patent 7448980 discloses a planetary gear assembly comprises a carrier, a planet shaft coupled to the carrier, a planet gear rotatable about the planet shaft, a plurality of rollers between the planet gear and the plane shaft to facilitate rotation of the planet gear about the planet shaft and a sleeve that surrounds the planet shaft such that plurality of rollers roll on the sleeve. This invention describes or improves only the bearing assembly of planetary gear assembly.
Hence, there has been a need for a planetary gear assembly having plurality of planetary pinion gears integrated with planetary pinion shaft and supported with planetary carrier via bearings, further supported with the help of a supporting pin and a bolt thereby to provide a planetary gear assembly with reduced weight and low cost.
OBJECTIVE OF THE INVENTION:
The present invention overcomes the shortcomings associated with the background art and achieves other advantages not realized by the background art.
The main object of the present invention is to provide a low weight planetary gear assembly by providing an integrated unit of planetary pinion gear and planetary pinion shaft.
Another object of the present invention is to provide a robust construction of planetary gear assembly by supporting the integrated planetary unit with planetary carrier via connecting device.

Yet another object of the present invention is to provide a planetary gear assembly in which bearing assembly of low dynamic rating can be used without compromising on reliability of the planetary system.
Yet another object of the present invention is to provide a planetary gear assembly in which bearing means can be assembled onto the planetary system either with press-fitting method or sliding method.
Yet another object of the present invention is to provide a planetary gear assembly having minimum number of parts and simple design.
Yet another object of the present invention is to provide a planetary gear assembly taking less time to assemble the entire system. In accordance with one aspect of the present invention, planetary gear assembly comprises a planetary gear with extended circular portion on either side along the central axis thereof, a pair of planetary carrier plate with a single diameter for rotatably supporting planetary gear with the extended portion via bearing means, a connecting device for supporting the planetary gear with the carrier plate with help of a projection provided on one end of connecting device and a thrust plate along with bolting arrangement on another end of the connecting device.
In another aspect of the present invention, the connecting device is provided with a through hole adapted to receive a bolt for constraining axial movement of the planetary gear.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and

scope of the invention will become apparent to those skilled in the art from this detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS:
The invention will be better understood and objects other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein:
FIG. 1 is section view of planetary gear assembly according to one
embodiment of the present invention; and FIG. 2 is section view of another embodiment with reference to FIG.1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT:
The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its applications or uses.
Referring to FIG.1 & FIG.2, planetary gear assembly of the present invention is being designated by numeral 1 which comprises a pair of planet carrier 2, at least one planet gear 3, and at least one connecting device 4 and at least a thrust plate 5. The planetary gear 3 is constantly meshed with a sun gear and a ring gear (not shown).
The planet carrier 2 is provided with a single diameter bore 8. The planet gear 3 has a circular extended portion 6 on either side along the central axis thereof and provided with a through bore 7 throughout the width of planet gear with extended portion 6 thereby forming a planetary unit. The planet

gear extended portion 6 is disposed in the single diameter bore 8. Planet gear extended portion 6 is made without any step or geometrical variation for taking advantage of cheaper manufacturing processes.
The connecting device 4 comprises a shank 17 and a head portion 16. Free end of the shank 17 is provided with a bore along with internal threads 14. The head portion 16 and shank 17 is provided with relief groove (not shown) for reducing stress concentration. Sufficient gap needs to be provided between shank 17 and inner diameter of planetary gear bore 7 for efficient performance of the planetary gear assembly according to the present invention. Inner face of the head portion 16 of the connecting device 4 has projection 15 for centering said connecting device 4 with the bore 8 of carrier plate 2. Thrust plate projection 12 and carrier bore 8 forms a spigot and recess joint.
The Planetary gear is rotatably supported with carrier plate 2 via bearing means 9. Length of planet gear extended portion 6 is in accordance with the length of bearing means 9. Bearing means 9 is inserted in the extended portion 6 with press fit method. Bearing means 9 may be with or without inner or outer race. Bearing means 9 is constrained axially by projection 12 of thrust plate 5 on one side and projection 15 on connecting device 4 on other side.
Thrust plate 5 has bore 11. Diameter of the bore 11 depends on fastening option selected. Thrust plate 5 has a projection 12 for centering thrust plate 5 with the center of the planet carrier bore 8. Thrust plate projection 12 and planet carrier bore 8 form a spigot and recess joint. The whole system is packed with bolt 13 to prevent undesired axial movement.
It is desirable to either restrain carrier plate 2 from rotation or to secure it to a rotating member for simultaneous rotation therewith. Carrier assembly 1 therefore, includes spline disposed on carrier plate which may be connected

with a conventional friction clutch brake member or with a toothed member which in turn would be secured to another element within the planetary transmission or any output device.
In alternate construction, the connecting device 4 can be made with bore 18 throughout the length thereof. A longer bolt 19 and nut 20 are used for constraining the whole system. Welding, bolting, riveting or any other means can be used for constraining planet gear, axle and the thrust plate in axial direction.
It will be readily appreciated by those skilled in the art that modifications may be made to the invention without departing from the concepts disclosed in the foregoing description. Accordingly, the particular embodiments described in detail herein are illustrative only and are not limiting to the scope of the invention, which is to be given the full breadth of the appended claims and any all equivalents thereof.

We claim:
1) A planetary gear assembly comprising:
at least one planet gear provided with an extension having circular cross section substantially extended from either side along central axis thereof;
a pair of planet carrier for rotatably supporting said planet gear, wherein parts of said pair of planet carrier is individually assembled in the planetary gear assembly; and
at least one connecting device adapted to integrate said planet gear with said pair of planet carrier
2) The planetary gear assembly according to claim 1 wherein said extension has a diameter less than outer diameter of said planet gear and is adapted to receive a bearing means thereon.
3) The planetary gear assembly according to claim 1 wherein said planet gear is provided with a through bore along the central axis for receiving said connecting device therein.
4) The planetary gear assembly according to claim 1 wherein said pair of planet carrier is provided with bore adapted to receive the bearing means along with said planet gear.

5) The planetary gear assembly according to claim 1 wherein said pair of planet carrier is having thickness sufficiently more than thickness of the bearing means.
6) The planetary gear assembly according to claim 1 wherein said connecting device has a head portion and & shank.
7) The planetary gear assembly according to claim 6 wherein inner face of said head portion is provided with a projection having diameter equal to the diameter of the bore provided on the planet carrier so as to ensure axis of said connecting device and said planet gear is coaxial in assembling the planetary gear assembly.
8) The planetary gear assembly according to claim 6 wherein free end of said shank is provided with a bore longitudinally for threadingly receiving a fastening means.
9) The planetary gear assembly according to claim 1 wherein the planetary gear assembly further comprises a thrust plate having provided with a bore axially for receiving said fastening means and is provided with a projection having diameter equal to the diameter of the bore provided on the planet carrier so as to restrict axial movement of said planet gear and misalignment of said connecting device and the mounting of the fastening means.

10) The planetary gear assembly according to claim 6 wherein said
connecting device is provided with a bore throughout the length thereof to receive a longer bolt from free end of said shaft and fasten with a nut at said head portion thereby to ensure robust assembly of planetary gear assembly.