CLIAMS:We claim:
1. A method for loading a coupling assembly (100) to a predetermined load, said method comprising:
providing a first coupling member (101) and a second coupling member (102) having an aligned opening (103) to receive a fastening member (104); and
fastening said fastening member (104) to said first coupling member (101) and said second coupling member (102) through the openings (103) to prevent relative movement between the coupling assembly (100),
wherein
said fastening member (104) imparts a predetermined amount of force to said first coupling member (101).
2. The method as claimed in claim 1, wherein said fastening member (104) includes a head and a shank having a first threaded portion on its outer surface.
3. The method as claimed in claim 1, wherein said opening (103) includes a second threaded portion formed on internal surface of the first coupling member (101).
4. The method as claimed in claim 1, wherein said first coupling member (101) and said second coupling member (102) are mechanical components designed for transmitting motion.
5. The method as claimed in claim 1, wherein said fastening member (104) is fastened to the first coupling member (101) by an actuating means.
6. The method as claimed in claim 6, wherein a standard torque is applied to the fastening member depending upon the diameter of the fastening member.

Date: 28th March 2013 Signature:
Vikram Pratap Singh Thakur ,TagSPECI:FORM 2
The Patent Act 1970
(39 of 1970)
&
The Patent Rules, 2005
COMPLETE SPECIFICATION
(SEE MEMBER 10 AND RULE 13)
TITLE OF THE INVENTION
“IMPROVING COMPONENT LIFE WITH PRE INDUCED COMPRESSIVE STRESS”

APPLICANT:
Name : Mahindra & Mahindra Ltd.

Nationality : Indian

Address :Mahindra Research Valley, Mahindra World
City Plot No. 41/1, Anjur P.O. Chengalpattu
Kancheepuram Dist, Tamilnadu.- 603204

The following specification particularly describes and ascertains the nature of this invention and the manner in which it is to be performed

FIELD OF INVENTION
[001] The embodiments herein generally relate to preloading a coupling assembly/member, and more particularly relates to assembling a bolt, a stud or similar member to a coupling assembly for applying predetermined tension.
BACKGROUND OF INVENTION
[002] Components subjected to dynamic loading often fail due to fluctuating load. It is a well-known fact that strength of a component is weaker in tension than in compression. Failure of a component when subjected to bending, pull or torsion loads is due to high tensile stresses that exceed the tensile strength of the component material.

[003] More often, the remedy applied to prevent such tensile failure is to increase the geometry i.e., size and shape of the component. Another option to prevent tensile failure of a component is to use a material having higher strength. However both options normally lead to increased inventory, time and cost.

[004] Thus there exists a need to reduce stresses acting on a component/assembly by inducing a pretension in the assembly.

SUMMARY
[005] According to embodiments of the present invention, there is provided a method for reducing the stress by inducing a predetermined load to a coupling assembly is disclosed. The method includes providing a first coupling member and a second coupling member having an aligned opening to receive a fastening member. Further, the method includes fastening said fastening member to said first coupling member and said second coupling member through the openings to prevent relative movement between the coupling assembly.

OBJECT OF INVENTION
[006] The principal object of this invention is to provide a method for reducing tensile failure of a coupling assembly/member by preloading said coupling assembly/member.
[007] Another object of the invention is to provide a method to induce a compressive stress in the assembly/member to reduce tensile failure of the coupling assembly/member.
[008] These and other objects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.
BRIEF DESCRIPTION OF FIGURES
[009] This invention is illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:
[0010] Fig. 1 illustrates a top view of rear axle shaft of a conventional tractor having a shorter bolt;
[0011] Fig. 2 illustrates a top view of rear axle of the tractor having a longer bolt according to an embodiment of the present invention;
[0012] FIG. 3 depicts a perspective view of the rear axle shaft of the tractor consisting of spline which is subjected to torsional load and bending load according to an embodiment of the present invention;
[0013] FIG. 4 depicts an enlarged view of the spline of the rear axle shaft showing cone angle and vertex distance of the stress concentrated area according to an embodiment of the present invention;
[0014] FIG. 5 is a graph depicting the percentage of improvement in the stress concentration according to an embodiment of the present invention; and
[0015] FIG. 6 is a flow chart depicting a method for preloading a coupling assembly according to an embodiment of the present invention.

DETAILED DESCRIPTION OF INVENTION
[0016] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. For example, it should be noted that while some embodiments are explained with respect to a coupling first coupling member (101) having a pre induced compressive stress, it should be noted that the first coupling member (101) having a pre induced compressive stress as disclosed in the present invention could be used in any coupling by incorporating the subject matter of the invention with little or no modifications. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

[0017] The embodiments herein achieve a method for inducing a predetermined load to a coupling assembly (100). Furthermore, the embodiments herein provide a method wherein a compressive stress is induced in the first coupling member (101) to reduce tensile failure of the first coupling member (101). Referring now to the drawings, and more particularly to FIGS. 1 to 5, where similar reference characters denote corresponding features consistently throughout the figures that are shown in the embodiments.
[0018] Conventionally rear axle shaft of a tractor is coupled to a coupling member using a shorter bolt (106). Fig. 1 illustrates a top view of the rear axle of the tractor having the shorter bolt (106). The purpose of this shorter bolt (106) is to provide coupling between the shaft of the rear axle and the second coupling member. The rear axle of the tractor consists of a spline which is subjected to very high torsional and bending load which leads to high stress concentration (108) in the spline area of the axle shaft. In order to reduce this stress in the spline either the geometry of the coupling parts are to be altered or the strength of the material used in the coupling has to be increased.

[0019] A method (200) for reducing the stress by inducing a predetermined load is explained herein below. The method includes providing a first coupling member (101) and a second coupling member (102) having an aligned opening (103) (Not shown in Figure) to receive a fastening member (104) (step (202)) as shown in Fig. 6. Further, the method includes fastening said fastening member (104) to said first coupling member (101) and said second coupling member (102) through the openings (103) to prevent relative movement between the coupling assembly (100) (step (204)).

[0020] In one embodiment the first coupling member (101) of the coupling assembly (100) is a shaft of rear axle of a tractor. The shaft of the rear axle of the tractor includes a spline which is subjected to very high torsional and bending load. In one embodiment the spline includes plurality of teeths as shown in fig. 3.

[0021] In another embodiment the second coupling member (102) of the coupling assembly (100) is a member coupled to the first coupling member (101) of the tractor. In an embodiment, both the first coupling member (101) and the second coupling member (102) are provided with an opening (103) to receive the fastening member (104). The fastening member (104) is selected from a group consisting of bolt, stud and similar members. In one embodiment the fastening member (104) includes a head portion and a longer shank portion. In one embodiment the shank portion of the fastening member (104) is longer than conventional fastener. In an embodiment the fastening member is a longer bolt (107). In one embodiment the shank portion of said fastening member (104) is provided with an external thread referred as first threaded portion.

[0022] In one embodiment the opening (103) is provided with an internal threaded portion referred as second threaded portion. In an embodiment the first threaded portion of the fastening member engages with the second threaded portion of the opening (103) to provide a rigid coupling between the first coupling member (101) and the second coupling member (102). In another embodiment a standard torque is applied to the fastening member depending upon the diameter of the fastening member. This prevents relative movement between the coupling assembly (100) and induces compressive stresses in the splines of rear axle shaft. In an embodiment a washer (105) is provided between the first coupling member (101) and the second coupling member (102).

[0023] In another embodiment the fastening member (104) is fastened to the first coupling member (101) and the second coupling member (102) by an actuating means. In one embodiment the fastening member (104) is actuated to induce a predetermined compressive force on the coupling members (101 and 102). In another embodiment the fastening member (104) induces a predetermined loading on the first coupling member (101) which counters a tensile force created in the coupling first coupling member (101) due to the bending and torsional load acting on the coupling members (101 and 102).

[0024] In one embodiment, the stress acting on the spline of the rear axle shaft is determined by performing finite element analysis on the spline. The torsional load, bending load and stress concentration (108) at the spline are determined by finite element analysis as shown in fig. 3. This analysis is performed on the spline to determine a cone angle ‘?’ and vertex distance D to reduce the stress. In one embodiment the cone angle ‘?’ of the spline is defined by connecting three points i.e. a stress point A on the spline, a vertex point B and any point C on the axis of the shaft towards the start of the opening. Further the vertex distance D of the spine is defined as the distance between the stress point A on the spline and the vertex point B as shown in fig. 4. The governing equation for cone angle is tan-1(R/V) Where R= is the root radius of the spline and V=Vertex Distance.

[0025] In one embodiment the finite element analysis is performed by varying the length of the shank of the fastening member (104) to determine the optimum cone angle ‘?’ and vertex distance D. In one embodiment FIG. 5 depicts a graph indicating the percentage of improvement in the stress concentration (108) in the spline according to an embodiment of the present invention. Following table indicates the effect of using longer fastener for reducing stress in spline at optimum cone angle ‘?’.


[0026] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.
Referral numerals:
100 Coupling assembly
101 First coupling member
102 Second coupling member
103 Opening (Not shown in Figure)
104 Fastening member
105 Washer
106 Shorter Bolt
107 Longer bolt
108 Stress concentration
? Cone angle
A Stress point
B Vertex point
C Point on the axis of the shaft
D Vertex distance

CLAIMS
We claim:
1. A method for loading a coupling assembly (100) to a predetermined load, said method comprising:
providing a first coupling member (101) and a second coupling member (102) having an aligned opening (103) to receive a fastening member (104); and
fastening said fastening member (104) to said first coupling member (101) and said second coupling member (102) through the openings (103) to prevent relative movement between the coupling assembly (100),
wherein
said fastening member (104) imparts a predetermined amount of force to said first coupling member (101).
2. The method as claimed in claim 1, wherein said fastening member (104) includes a head and a shank having a first threaded portion on its outer surface.
3. The method as claimed in claim 1, wherein said opening (103) includes a second threaded portion formed on internal surface of the first coupling member (101).
4. The method as claimed in claim 1, wherein said first coupling member (101) and said second coupling member (102) are mechanical components designed for transmitting motion.
5. The method as claimed in claim 1, wherein said fastening member (104) is fastened to the first coupling member (101) by an actuating means.
6. The method as claimed in claim 6, wherein a standard torque is applied to the fastening member depending upon the diameter of the fastening member.

Date: 28th March 2013 Signature:
Vikram Pratap Singh Thakur

ABSTRACT
A method (200) for reducing the stress by inducing a predetermined load is disclosed. The method includes providing a first coupling member (101) and a second coupling member (102) having an aligned opening (103) to receive a fastening member (104) (step (202)). Further, the method includes fastening said fastening member (104) to said first coupling member (101) and said second coupling member (102) through the openings (103) to prevent relative movement between the coupling assembly (100) (step (204)).
Fig. 2