FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION (See section 10 and rule 13)
TITLE OF THE INVENTION A differential lock mechanism
APPLICANT
Mahindra & Mahindra Ltd., Gateway Building, Apollo Bunder, Mumbai 400 001, Maharashtra,
India, an Indian company
INVENTORS
Vasan Vijay, B-302, Sneham Apartments, II Main Road, Annanagar, Peelamedu, Coimbatore-641004, Tamil Nadu, Sargar Bhupesh Dashrath, B/l0-003, Shantidoot Co. Op. Hsg. Soc. Shanti Vidyanagri, Mira Road (E), Thane 401107, Maharashtra, Gupta Girish Bhagwandas, C/510, Garden Tower, Lokhandwala Complex, all Indian nationals
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to be performed:

FIELD OF THE INVENTION
[0001] The present invention relates generally to differentials of automotive vehicles
and more particularly, to a locking mechanism for such differentials.
DESCRIPTION OF THE BACKGROUND ART
[0002] In automotive applications, differential is an essential mechanism provided to
distribute the engine power to the driving wheels by the virtue of their position during turning. While turning, in the case of dead front axle type of vehicles, the rear wheels are subjected to different radius of gyration. The inner wheel, in particular is subjected to a lesser turning radius as compared to the outer wheel, hence requiring less speed to cover lesser ground. This is done by providing a differential mechanism consisting of bevel gears and pinion gears encased in a structural member. When the vehicle moves in a straight line, the entire enclosure consisting of the gears rotates as one member. While taking turn, the bevel gears and pinion gears differentiate the torque to the rear wheels depending on their location during turning.
[0003] In off-road vehicles, especially tractors, a mechanism to nullify the effect of
differential locking is provided. While in the presence of a differential, as discussed earlier, the torque through the drive train is distributed among the two axles in normal straight line motion of vehicle. In conditions of emergency particularly in off-road working, for example the vehicle getting struck in dirt track, mud, bund, etc, it is required by the operator to provide entire power delivered by the engine to a single axle which is not slipping, thus forcing the power to equally pass on to both the wheels on such axle, thereby avoid idling of either of the wheels. This is achieved with the help of differential locking.

[0004] Differential locking mechanism provided by some of the leading tractor
manufacturers is achieved by locking an individual bevel gear against the differential case, by using a push pin or similar means as described in US patents, 4043224, 3142203, etc. When the bevel gear is locked with respect to the differential case, the other pinion gears are subjected to no relative motion with respect to each other, hence resulting in no distributing the drive train torque. In the actuated condition, the differential section in turn dissipates the drive line torque to both the axles uniformly. However, the disadvantage with this type of differential mechanism is that separate chamber for differential locking has to be provided outside the end reduction system, resulting in consumption/blocking of larger space thereby making the transmission voluminous and heavier.
[0005] Further, the differentia] locking achieved in some bull gear end reduction
transmission types is usually achieved by a coupling mechanism, usually a dog clutch or a similar member mounted on one of the bull pinion shafts. This coupling member slides on the external splines of one bull pinion shafts and gets in mesh with the external splines of the adjacent bull pinion shaft. Hence by arresting both the bull pinion shafts, the torque delivered from the drive train is equally distributed to the bull gears, and consequently to the rear axles on either side of the transmission box. However, a major disadvantage faced by manufacturers having this type of differential locking design, is that the push rod/plunger which is used to engage the dog clutch is assembled co-axially to the bull pinion shaft and the brake housing. In the case of oil immersed brakes, where the brake enclosure is filled with oil, a seal type arrangement has to be provided, which fails in many cases due to various factors, hence resulting in oil leakage and a shabby transmission case appearance causing inconvenience to many end-users.

[0006] In US patent 20080148885, a differential locking mechanism synchronized
with the brake pedal is discussed. The advantage as discussed by the patent describes the convenience provided to the operator for decelerating/stopping the tractor and applying differential brakes by providing a common linkage mechanism to achieve the later discussed operation. One of the disadvantages noted in this type of mechanism is that during application of differential locking, initially the operator has to decelerate the transmission drive so as to enable coupling of the separate axle shafts. But after application of differential lock, it is required by the operator to accelerate the drive train so as to deliver more power to both the axles as compared to the disengaged differential locking situation. When the differential locking mechanism is coupled with the brake lever, it is either difficult to achieve the delivery of full power to both the axles simultaneously. Further, a separate mechanism to disengage both the operations has to be provided, thus making the differential locking complicated. Also in this type of mechanism, separate provisions in the transmission casing has to be provided for differential locking and brake actuation, hence requiring more space and a heavier transmission.
[0007] Thus, there is a need to have a differential locking mechanism that addresses
at least some of the above mentioned drawbacks and yet provides a reliable locking of the bull pinion shafts.
SUMMARY OF THE INVENTION
[0008] An object of the present invention is to provide a differential locking
mechanism integral with a brake housing which prevents any scope of oil spillage, leakage and seepage of any kind from the transmission case.

[0009] Another objective of the present invention is to obtain an integrated
differential locking assembly along with the brake housing and a more compact transmission case.
[0010] Yet another objective of this invention is to provide a modular brake housing
which besides performing the intended functioning of braking, also provides the platform for performing differentia! locking, both actions being mutually exclusive.
[0011] Accordingly disclosed herein is a differential lock mechanism for an off-road
vehicle, the lock mechanism including a pair of bull pinion shafts arranged end to end along a common axis in spaced apart relationship with each other and rotatably disposed in a housing of a transmission of the off-road vehicle, each of the bull pinion shafts axially extending into a corresponding brake housing disposed adjacent to the housing of the transmission, each of the brake housing having oil therein, a plunger disposed within one of the bull pinion shafts and protruding outwardly therefrom into one of the brake housings, a rod vertically disposed within said one of the brake housings for angular displacement about a vertical axis and having a cam mounted thereon, the cam being adapted to linearly displace the plunger against said one of the bull pinion shafts, and a displacement means for connecting the rod with an operating lever and for angularly displacing the rod.
[0012] In some embodiments, the displacement means comprises a link, one end of
the link is pivoted to the operating lever and the other end of the link is eccentrically connected to the rod.
[0013] In some embodiments, the rod is disposed in a chamber formed in an outer
wall of the brake housing, the chamber having an opening formed on its top portion for tightly

fitting therein a seal and a bush that has an integrally formed collar, the collar being positioned around the opening so as to prevent outward spillage of the oil from the brake housing.
[0014] In some embodiments, the rod includes a lateral extension formed on a top
portion thereof, the lateral extension being disposed outside the chamber and connected to the other end of the link to provide angular displacement to the rod.
[0015] In another aspect of the present invention, an off-road vehicle having a
differential locking mechanism including a pair of bull pinion shafts arranged end to end along a common axis in spaced apart relationship with each other and rotatably disposed in a housing of a transmission of the off-road vehicle, each of the bull pinion shafts axially extending into a corresponding brake housing disposed adjacent to the housing of the transmission, each of the brake housing having an oil therein, a plunger disposed within one of the bull pinion shafts and protruding outwardly therefrom into one of the brake housings, a rod vertically disposed within said one of the brake housings for angular displacement about a vertical axis and having a cam mounted thereon, the cam being adapted to linearly displace the plunger against said one of the bull pinion shafts, and a displacement means for connecting the rod with an operating lever and for angularly displacing the rod.
[0016] It is to be understood that both the foregoing general description and the
following detailed description of the present embodiments of the invention are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the invention and together with the description serve to explain the principles and operation of the invention.

A BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The above-mentioned and other features and advantages of the various
embodiments of the invention, and the manner of attaining them, will become more apparent and will be better understood by reference to the accompanying drawings, wherein:
[0018] FIG. 1 is a perspective view of a transmission case assembly of a typical off-
road vehicle according to an embodiment of the present invention;
[0019] FIG, 2 is a perspective view of a differential assembly and a brake housing of
the transmission case assembly of FIG. 1 being mechanically coupled with each other;
[0020] FIG. 3 shows an outer wall of the brake housing of FIG. 2 having a chamber
formed thereon and a seal that is to be fitted within an opening of the chamber;
[0021] FIG. 4 shows an exploded view of a cam-rod assembly that is to be mounted
with the chamber of the cover of FIG. 3;
[0022] FIG. 5 shows a cross-sectional view of the mechanically coupled differential
assembly and the brake housing of FIG. 2 with a pair of bull pinion shafts in unlocked condition;
[0023] FIG. 6 shows a cross-sectional view of the pair of bull pinion shafts of FIG. 5
in locked condition;
[0024] FIG. 7 shows an exploded view of a connection between the outer wall of the
brake housing of FIG. 3 and an operating lever via a link according to an embodiment of the present invention; and
[0025] FIG. 8 shows a perspective view of the brake housing of FIG. 2 with the
operating lever, the link, and the cover of FIG. 7 assembled together with the brake housing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] FIG. I illustrates a transmission case assembly 100 of a typical off-road
vehicle (not shown) that has a clutch section 102, a speed reduction section 104, and a differential and axle section 106 disposed therein according to an embodiment of the present invention. The clutch section 102 has a clutch housing 108 that securely retains a clutch actuating member 110 of the off-road vehicle. Behind the clutch section 102, the speed reduction section is disposed. The speed reduction section 104 includes a gear box 112 that securely retains therein automotive gears (not shown) and that are operatively coupled with clutches retained within the clutch section 102 in known manner. Further behind the speed reduction section, the differential and axle section 106 is disposed in the transmission case assembly 100. The differential and axle section 106 includes a differential housing 114 (shown in FIG. 2) disposed within a differential assembly 116 (also shown in FIG. 2) and operatively connected to the gears. Behind the differential housing 114, a pair of axles carriers 118 are disposed that houses a corresponding axle therein. The differential assembly 116 has a pair of bull pinion shafts (not shown) and as commonly known, each of the bull pinion shaft arranged to be in constant mesh with a corresponding axle via a corresponding bull gear. The bull gear is disposed between the corresponding pair of axle-bull pinion shaft. Thus, arrangement of the pair of bull pinion shafts and the bull gears act as end reduction mechanism to the off-road vehicles. The clutch section 102 along with the speed reduction section 104 and the differential and axle section 106 constitutes the transmission of the off-road vehicle.
[0027] FIG. 1 also illustrates a brake housing 120 disposed adjacent to a first side 122
of the transmission case assembly 100 and mechanically coupled with the differential assembly 116 (See FIG. 2). Another brake housing (not shown) is also disposed on a second side 124 of

the transmission case assembly 100 and placed oppositely to the brake housing 120. The brake housings and the differentia] assembly 116 are linearly aligned with each other.
[0028] FIG. 2 shows an enlarged view of the brake housing 120 and the differential
assembly 116 mechanically connected with each other via a connecting portion 126. The brake housing 120 is defined by an outer wall 128 and a hollow enclosure 130 to which the outer wall 128 is removably attached. Within the enclosure 130, a brake set (not shown) that includes a plurality of actuating plates, friction plates, and actuating discs is disposed. The brake set is operatively connected with a brake actuating means (not shown) and positioned in proximity to a driver of the off-road vehicle for applying/releasing brakes. The enclosure 130 and the outer wall 128 consist of matching machined surfaces required for providing friction surfaces for the friction discs. Preferably, both the brake housings are oil-immersed brake housings having known oil filled therein up to a sufficient level.
[0029] The differential assembly 116, as shown in FIG, 2, is linearly connected to the
brake housing 120 and includes the pair of bull pinion shafts disposed therein and extending across the differential housing 114 towards the brake housings. Further, the brake housing 120 also includes a cam-rod assembly, described in detail in the following description, disposed therein and having operational relationship with the pair of bull pinion shafts. Furthermore, the cam-rod assembly is also operatively connected with an operating lever, positioned in proximity to the driver via a linkage mechanism. Upon actuating/de-actuating the operating lever, the cam-rod assembly enables locking and unlocking of the pair of bull pinion shafts within the differential assembly 116. Operational relationship between the cam-rod assembly, the linkage mechanism, and the pair of bull pinion shafts is detailed in the following description.

[0030] FIGS. 3 and 4 will now be referred to explain the constructional features of
the outer wall 128 of the brake housing 120 and the cam-rod assembly disposed within the brake housing 120. FIG. 3 illustrates the outer wall 128 of the brake housing 120. According to an embodiment of the present invention, the outer wall 128 of the brake housing 120 has a chamber 132, which is also filled with the oil, formed thereon and extending outwardly therefrom. The chamber 132 may be integrally casted with the outer wall 128 of the brake housing 120. Alternatively, in various other embodiments, the chamber 132 may also be formed to extend from the outer wall 128 by other known means and construed to be present within the scope of the present invention. Preferably, the chamber 132 also has a counter bore portion 134 formed on its inner surface (See FIGS. 5 and 6).
[0031] The chamber 132 has an opening 136 formed on its top portion 138
sufficiently enough to allow a bush 140 to be inserted therein. The bush 140 is constructed to have an elongated portion and a collar portion 142. The elongated portion is positioned within the chamber 132 through the opening 136 whereas, the collar portion 142 having a diameter larger than that of the opening 136 is rested outside on the top portion 138 of the chamber 132. Preferably, an oval shape or an O-shaped ring 144, as shown in FIG. 3, is also inserted within a groove 146 of the collar portion 142 (See FIGS. 5 and 6). However, there could be other ways as well, known in the art, by which the O-ring 144 may be inserted within the collar portion 142 of the housing.
[0032] FIG. 4 shows an exploded view of the cam-rod assembly that is to be fitted
with the chamber 132 of the brake housing 120. An inner surface 148 of the outer wall 128 is also shown that partially illustrates the enclosed area encapsulated by the chamber 132. The cam-rod assembly comprises of a rod 150 and a cam 152 assembled together within the chamber 132.

The rod 150 comprises of an elongated portion 154 extending between a proximal end 156 and a distal end 158. The distal end 158 has a solid head 160 formed thereon whereas the rod 150 is vertically inserted into the opening 136 of the chamber 132 through the proximal end 156. Further, the solid head 160 has a lateral extension 162 formed thereon that has a hole 164. The lateral extension 162 is connected to the linkage mechanism which in turn further connected to the operating lever. Upon actuating the operating lever, the linkage mechanism allows the lateral extension 162 and simultaneously the rod 150 to be angularly displaced along a vertical axis of the rod 150. Additionally, the elongated portion 154 of the rod 150 also has a threaded opening for allowing a fastener 166, which may be a bolt or a screw or the like items, to be coupled therein.
[0033] As shown in FIG. 4, the cam 152 that is preferably of an oval shape is also
engaged with the elongated portion 154 of the rod 150. The cam 152 has a hole 168 formed therein that receives the proximal end 156 of the elongated portion 154 of the rod 150. The rod is inserted through the cam in such a manner that a sufficient portion of the vertically disposed rod 150 extends beyond the cam 152 towards a bottom surface of the chamber 132. Furthermore, the cam 152 also has a threaded opening that receives the fastener 166 for tightly fastening the cam 152 against the rod 150. Further, a circlip 170 and a spacer 172 are also shown in FIG. 4. The circlip 170 and the spacer 172 are disposed to be rested on the counter bore portion 134 of the chamber 132 and assembled with the vertically disposed rod 150. The spacer 172 and the circlip 170 restrict vertical displacement of the rod 150 that rotates along a vertical axis.
[0034] Such construction of the cam-rod assembly and the manner in which it
engages the chamber 132 of the brake housing 120 provides multi-prong benefits to the off-road vehicles which would be appreciated by a person skilled in the art. First, the bush 140 provides a

guideway to the rod 150 for allowing the rod 150 to be stably positioned within the chamber 132. Stable rod 150 within the chamber 132 allows efficient locking and un-locking of the bull pinion shafts. Second, tight fitting of the O-ring 144 with the collar portion 142 of the bush 140 and the rod 150 prevents leakage/seepage of the oil from opening 136 of the chamber 132. Therefore, the O-ring 144 acts as a seal for prevention of oil from leaking. Thus, a skilled person in the art would appreciate that insertion of the O-ring 144 within the bush 140 solves the problem of oil leakage/seepage up to a very greater extent that are otherwise quite dominant in the available oil-immersed brake housings of the off-road vehicles.
[0035] Reference will now be given to FIGS. 5 and 6 that explain the constructional
features of the differential assembly 116 according to an embodiment of the present invention. FIG. 5 illustrates a cross-sectional view of the brake housing 120 and the differential assembly 116 mechanically coupled to each other via the connecting portion 126 as shown in FIG. 2. The differential assembly 116 includes a bull pinion cage 174 that acts as a protective casing member on the bull pinion shaft and also as a supporting member to the pair of bull pinion shafts therein. Further, the bull pinion cage 174 is also provided with a cast flange on both of its opposing sides, with which, the bull pinion cage 174 is mounted on the transmission case assembly 100 (shown in FIG. 1). Also on the same flange from the exterior side, the brake housings are mounted on the bull pinion cage 174. Hence, the bull pinion cage 174 act as a guiding and a protective sleeve like covering member for the pair of the bull pinion shafts. A first longitudinal bull pinion shaft 180 and a second longitudinal bull pinion shaft 182 are disposed within the differential assembly 116. Initially, both the first bull pinion shaft 180 and the second bull pinion shaft 182 are disposed in spaced apart relationship with each other and linearly arranged to have a common

rotational axis. Further, each of the bull pinion shaft extends axially into the corresponding brake housing 120 and is preferably submerged into the oil.
[0036] As shown in FIG. 5, the first bull pinion shaft 180 is constructed to be hollow
along its entire length whereas, the second bull pinion shaft 182 is substantially solid in formation/construction. Further, the first bull pinion shaft 180 extends between a first end 184 and a second end 186. The second end 186 of the bull pinion shaft is positioned within the differential assembly 116 whereas the first end 184 is disposed within the enclosure 130 of the brake housing 120, It is to be understood that the second bull pinion shaft 182 is also disposed within the differential assembly 116 and said another brake housing 120 in a similar manner. The first bull pinion shaft 180 has a plunger 188 disposed therein with a portion of the plunger 188 being exposed outside from the first end 184 into the brake housing 120. The exposed portion of the plunger 188 is positioned adjacent to the cam 152 tightly coupled with the vertically disposed rod 150 as shown in FIG. 5. The plunger 188 moves linearly within the first bull pinion shaft 180 when actuated upon by the cam 152. Moreover, splines 190 are formed on both the first end 184 and the second end 186 of the first bull pinion shaft 180. The splines 190 provided on the first end 184 of the first bull pinion shaft 180 receives brake discs (not shown) thereon whereas, the splines 190 provided on the second end 186 of the first bull pinion shaft 180 receives bevel gears.
[0037] A differential lock dog clutch 192 is also mounted on the splines 190 and
connected to the plunger 188 in a manner shown in FIG. 5. Similar splines 190 are also provided on the ends of the second bull pinion shaft 182 (See FIG. 2). As explained above, the vertically disposed rod 150 is angularly displaced when the operating lever is actuated. This angular displacement of the rod 150 also allows the cam 152, connected thereto, to be angularly

displaced. However, due to angular displacement of the cam 152, the plunger 188 that is positioned adjacent to the cam 152 acts as a follower to the cam 152. As a result of this, the plunger 188 traverses axially within the differential housing 114 and pushes the dog clutch 192, which slides on the splines of the first bull pinion shaft 180, towards the second bull pinion shaft 180. Further movement of the dog clutch 192 allows the dog clutch 192 to be meshed with the splines provided on the second bull pinion shaft 182 so as to lock the pair of the first and the second bull pinion shaft 180 & 182 within the differential assembly 116. Locked condition of the first and the second bull pinion shafts 180, 182 is shown in FIG. 6. On de-actuating the operating lever, the vertically disposed rod 150 is angularly displaced in a reverse direction enabling the cam 152 to rotate in counter-actuating direction. This allows plunger 188 to be linearly released outwardly towards the brake housing 120. As a result of this retrieving linear path followed by the plunger 188, the dog clutch 192 is unlatched from the second bull pinion shaft 180 resulting in unlocking of the first and the second bull pinion shaft 180 & 182 within the differential assembly 116. Again both the first and the second bull pinion shafts 180, 182 are positioned in spaced apart relationship in un-locked condition.
[0038] Reference will now be given to FIGS. 7 and 8 that describe the linkage
mechanism, which is operatively connected with the operating lever and the vertically disposed rod 150, for providing angular displacement to the cam-rod assembly within the brake housing 120. The linkage mechanism acts like a displacement means for angularly displacing the vertically disposed rod 150.
[0039] FIG. 7 illustrates a partial exploded view of a typical mechanical relationship
between an operating lever 193, a linkage mechanism 194, and the rod 150 disposed within the chamber 132 of the outer wall 128 of the brake housing 120. The operating lever 193, which may

be foot operated or hand operated, has an elongated portion 196 extending between an actuating end 198 and a mounting end 200. The actuating end 198 may be actuated by hand or foot and positioned in close proximity to the driver so that the operating lever 193 is easily accessible. The mounting end 200 is pivotally engaged with a pivot boss 202 formed on the outer wall 128 of the brake housing 120 for moving of the operating lever 193 about the pivot boss 202. The elongated portion 196 has a connecting member 204 for pivotally connecting the linkage mechanism 194.
[0040] The linkage mechanism 194 comprises of a link, which is preferably provided
with a ball joint assembly 206 at one end, and a clevis 208 at other end. One end of the ball joint assembly 206 is engaged the clevis 208 via internal threads whereas, the other end of the ball joint assembly 206 is connected to the hole 164 of the lateral extension 162 formed on the solid head 160 of the vertically disposed rod 150. A nut 210 is preferably used for tightly fastening the other end of the ball joint assembly 206 with the hole 164 of the lateral extension 162. This tight fitting ensures that there is no play/relative movement between the lateral extension 162 and the other end of the ball-joint assembly 206. It should be apparent to a skilled person that the joint between the ball-joint assembly 206 and the lateral extension 162 is eccentric to the axis of rotation of the rod 150. Further, as shown in FIG. 7, the clevis 208 is pivotally connected to the connecting member 204 of the operating lever 193 through the use of a hinge fastener 212 known in the art, for example a pin and cotter arrangement. FIG. 8 illustrates a perspective view of the brake housing 120 having the linkage mechanism 194, the operating lever 193, and the vertically disposed rod 150 assembled together.
[0041] When the operating lever 193 is actuated in one direction, the operating lever
193 pivots about the pivot boss 202 to describe a circular arc. This movement of the operating

lever 193 enables the connecting member 204 to pull the clevis 208 and the ball joint assembly 206 in a straight line with the pin and cotter acting as a pivot. The straight line travel of the linkage mechanism 194 pulls the rod 150 towards the operating lever 193. As the ball joint assembly 206 is eccentrically connected to the lateral extension 162, the straight line movement applies a torque on the lateral extension 162 with the line of action of the applied force acting along the hole 164 of the lateral extension 162. This applied torque angularly displaces the rod 150 about its vertical axis. As noted above, due to this angular displacement of the rod 150, the cam 152 also rotates therewith allowing linear traverse of the plunger 188 within the first bull pinion shaft 180 to lock the pair of bull pinion shafts within the differential assembly 116. It is to be understood by a skilled person in the art that when the operating lever 193 is actuated in a second direction opposite to the first direction, the cam 152 is angularly displaced to release the plunger 188 linearly towards the brake housing 120 thereby unlocking the pair of bull pinion shafts in the differential assembly 116.
[0042] The first and the second directional movement of the operating lever 193
should not be construed to be restricted only to any particular directional movement. Rather, any directional movement such as upward, bottom, forward, backward, sideways and the like are to be construed within the scope of the present invention. This, it should be apparent to a skilled person that the linkage mechanism 194 provides a means for smooth, effective and frictionless movement of the vertically disposed rod 150 when actuation/de-actuation of the operating lever 193.
[0043] According to another embodiment of the present invention, on the other side
of the vertically displaced rod 150, a return spring (not shown) is mounted which is connected to a bracket member 214 (See FIG. 7) on the outer wall 128 of the brake housing 120. Such

arrangement accounts for the return mechanism of the differential locking lever/pedal when the applied weight on the operating lever 193 is removed.
[0044] It will be appreciated that various other embodiments of the cam 152 and its
connection with the vertically disposed rod 150 may be envisaged and stilI be considered within the scope of the present invention. For example, according to one embodiment of the present invention, a flapper plate may be attached on the vertically disposed rod 150, preferably by means of a weld joint. The flapper plate will function as the perpendicular actuator similar in motion as the cam 152 as described above. Alternatively, in another embodiment, a vane type plate can be used to perform the same functioning of the cam 152. Further, it should also be appreciated by a skilled person that the purpose of the vertically displaced rod 150 is to angularly displace the cam 152 attached thereto. So, embodiments pertaining to a horizontally displaced rod 150 with a compatible linkage mechanism 194 configured with the operating lever 193 may also be envisaged within the scope of the present invention.
[0045J Furthermore, even though ail the above explained embodiments of the present
invention are discussed with respect to the off-road vehicles, implementation of the all of these embodiments may also be possible in on-road vehicles. Such an implementation by a skilled person in the art is also considered to be within the scope of the present invention.
[0046] It will be apparent to those skilled in the art that various modifications and
variations can be made to the present invention without departing from the spirit and scope of the invention. Thus it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

We Claim:
1, A differential lock mechanism for an off-road vehicle, the lock mechanism comprising:
a pair of bull pinion shafts arranged end to end along a common axis in spaced apart relationship with each other and rotatably disposed in a housing of a transmission of the off-road vehicle, each of the bull pinion shafts axially extending into a corresponding brake housing disposed adjacent to the housing of the transmission, each of the brake housing having oil therein;
a plunger disposed within one of the bull pinion shafts and protruding outwardfy therefrom into one of the brake housings;
a rod vertically disposed within said one of the brake housings for angular displacement about a vertical axis and having a cam mounted thereon, the cam being adapted to linearly displace the plunger against said one of the bull pinion shafts; and
a displacement means for connecting the rod with an operating lever and for angularly displacing the rod.
2. The differential lock mechanism according to claim 1, wherein the displacement means comprises a link, one end of the link is pivoted to the operating lever and the other end of the link is eccentrically connected to the rod.
3. The differential lock mechanism according to claim 2, wherein the link is a ball-joint assembly.

4. The differential lock mechanism according to claims 1 to 3, wherein the rod is disposed in a chamber formed in an outer wall of the brake housing, the chamber having an opening formed on its top portion for tightly fitting therein a seal and a bush that has an integrally formed collar, the collar being positioned around the opening so as to prevent outward spillage of the oil from the brake housing.
5. The differential lock mechanism according to claim 4, wherein the rod includes a lateral extension formed on a top portion thereof, the lateral extension being disposed outside the chamber and connected to the other end of the link to provide angular displacement to the rod.
6. The differential lock mechanism according to claims 1 to 5, wherein the operating lever is foot
operated.
7. The differential lock mechanism according to claims 1 to 5, wherein the operating lever is
hand operated.

8. An off-road vehicle having a differential locking mechanism comprising:
a pair of bull pinion shafts arranged end to end along a common axis in spaced apart relationship with each other and rotatably disposed in a housing of a transmission drive of the off-road vehicle, each of the bull pinion shafts axially extending into a corresponding brake housing disposed adjacent to the housing of the transmission drive, each of the brake housing having an oil therein;
a plunger disposed within one of the bull pinion shafts and protruding outwardly therefrom into one of the brake housings;
a rod vertically disposed within said one of the brake housings for angular displacement about a vertical axis and having a cam mounted thereon, the cam being adapted to linearly displace the plunger against said one of the bull pinion shafts; and
a displacement means for connecting the rod with an operating lever and for angularly displacing the rod.
9. The off-road vehicle according to claim 8, wherein the displacement means comprises a link,
one end of the link is pivoted to the operating lever and the other end of the link is eccentrically
connected to the rod.
10. The off-road vehicle according to claim 9, wherein the link is a ball-joint assembly.
11. The off-road vehicle according to claims 8 to 10, wherein the rod is disposed in a chamber formed in an outer wall of the brake housing, the chamber having an opening formed on its top portion for tightly fitting therein a seal and a bush that has an integrally formed collar, the collar

being positioned around the opening so as to prevent outward spillage of the oil from the brake housing.
12. The off-road vehicle according to claim 11, wherein the rod includes a lateral extension formed on a top portion thereof, the lateral extension being disposed outside the chamber and connected to the other end of the link to provide angular displacement to the rod.
13. The off-road vehicle according to claims 8 to 12, wherein the operating lever is foot operated.
14. The off-road vehicle according to claims 8 to 12, wherein the operating lever is hand
operated.