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
Speed retarding mechanism for the inertia driven clutch shaft of an off-road vehicle
APPLICANTS
Mahindra & Mahindra Ltd, Gateway Building, Apollo Bunder, Mumbai 400 001, Maharashtra, India, an Indian company
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
This invention relates to a speed retarding mechanism for the inertia driven clutch shaft of an off-road vehicle.
BACKGROUND OF THE INVENTION
Off-road vehicles or work vehicles such as tractors, earth movers or mowers are used to carry out heavy work in adverse terrains and working conditions. An off-road vehicle includes a drive system comprising an engine with a crank shaft housed in a crank case and having a flywheel mounted on the crank shaft. The drive system also comprises a clutch system comprising a clutch shaft or drive shaft rotatably disposed in a clutch house coaxially with the crank shaft. One end of the clutch shaft is releasably coupled to the fly wheel on the crank shaft generally through a pressure plate and clutch plate assembly and a spline and groove coupling. A clutch release mechanism is mounted on the said one end of the clutch shaft adapted to couple and decouple the said one end of the clutch shaft to the flywheel on the crank shaft.
The clutch system also comprises an actuator assembly for the clutch release mechanism having a U-shaped member (fork) disposed in the clutch house with the tips thereof pivoted to the clutch house and with the clutch shaft extending therethrough. The U-shaped member is so disposed as to describe a to and fro angular displacement in the axial direction of the clutch shaft. A clutch rail extends across the U-shaped member in rigid contact therewith and in spaced apart relationship with the clutch shaft. The clutch rail is connected at one end thereof to a clutch linkage assembly disposed for operation by a clutch pedal.

The clutch shaft is releasably connected at the other end thereof to the input shaft of a gear box generally through a spline and groove coupling. The output shaft of the gear box is operatively coupled to the rear wheel axle assembly of the vehicle which drives the rear wheels of the vehicle and hence the vehicle. The gear box houses a gear mechanism which is generally constant mesh or sliding mesh type and comprises a gear shifting lever.
During the running condition of the vehicle, the said one end of the clutch shaft is releasably coupled to the flywheel on the crank shaft and the other end of the clutch shaft is releasably coupled to the input shaft of the gear box. As a result, the engine drive gets transmitted to the rear wheels of the vehicle and the vehicle runs at the speed selected by the gear shifting lever of the gear box. In order to change the speed of the vehicle during running condition of the vehicle, the operator (driver) of the vehicle depresses the clutch pedal and declutchs the clutch shaft. On depressing the clutch pedal, the clutch linkage assembly rotates the clutch rail in the clockwise direction by certain angle away from the clutch release mechanism. Consequently the U-shaped member rotates with the clutch rail in the clockwise direction by the same angle and pulls the clutch release mechanism to disengage the said one end of the clutch shaft from the flywheel thereby disconnecting the drive from the engine to the clutch shaft temporarily.
The operator then operates the gear shifting lever of the gear box to change the gear ratio and select the required speed. On releasing the clutch pedal by the operator, the clutch linkage assembly swings the clutch rail and the U-shaped member in the anticlockwise direction towards the clutch release mechanism and the clutch release mechanism moves' back to the original position thereof thereby allowing the said one end of the clutch shaft to engage against the

flywheel. Engine drive gets transmitted to the rear wheels of the vehicle and the vehicle starts running at the selected speed.
During the short period the clutch pedal is depressed and the said one end of the clutch shaft is disengaged from the flywheel and the gear change takes place, the clutch shaft continues to rotate under inertia, the speed of rotation of the clutch shaft under inertia will be obviously higher for higher vehicle speeds. The rotation of the clutch shaft under inertia generates noise which increases with speed. Furthermore, the inertia driven clutch shaft continues to drive the input shaft of the gear box thereby aggravating the noise problem. The gears of the gear mechanism also continue to rotate under inertia thereby further aggravating the noise level. Noise is very unpleasant and harmful and does not give a good driving experience. Due to the inertia driven rotation, wear and tear to the clutch shaft and gear box also increases thereby reducing the life thereof.
In order to address the above problems, gear box comprising synchronised gear arrangement and gear mechanisms comprising combination of synchronised gears and constant mesh or sliding mesh type gears are used. Gear boxes comprising only synchronised gears are very expensive and gear boxes comprising hybrids of synchronised gears and constant mesh or sliding mesh gears suffer from problems of noise and wear and tear associated with constant mesh or sliding mesh gears, besides being expensive. There is thus need for off-road vehicles in which the above problems are obviated and which are cost effective.

DESCRIPTION OF THE INVENTION
According to the invention there is provided a speed retarding mechanism for the inertia driven clutch shaft of an off-road vehicle, wherein the off-road vehicle includes a drive system comprising an engine with a crank shaft having a fly wheel mounted on the crank shaft and a clutch system having a clutch shaft rotatably disposed in a clutch house coaxially with the crank shaft and releasably coupled at one end to the flywheel and at the other end to a gear box of constant mesh or sliding mesh gears, a clutch release mechanism mounted at said one end of the clutch shaft and an actuator assembly for the clutch release mechanism having a U-shaped member disposed in the clutch house with the tips thereof pivoted to the clutch house to describe to and fro angular displacement in the axial direction of the clutch shaft and with the clutch shaft extending therethrough, a clutch rail extending across the U-shaped member in rigid contact therewith and in spaced apart relationship with the clutch shaft, the clutch rail being connected at one end thereof to a clutch linkage assembly disposed for operation by a clutch pedal and wherein the speed retarding mechanism comprises a disc mounted on the clutch shaft, an actuator depending down from the U-shaped member and a fluid pressure operated reciprocating mechanism operatively connected to the disc and the actuator to retard the speed of rotation of the inertia driven clutch shaft during declutching.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig 1 of the accompanying drawings is a schematic isometric view of a clutch house including the speed retarding mechanism according to an embodiment of the invention;

Fig 2 is a schematic isometric view of the clutch shaft and the speed retarding mechanism of Fig l;
Fig 3 is a schematic isometric view of the hydraulic cylinder and hydraulic fluid containing reservoir and calliper of the speed retarding mechanism of Fig 2;
Figs 4 and 5 are schematic sectional views of the calliper of Fig 3 showing the piston thereof in the deactuated and actuated positions, respectively; and
Figs 6 and 7 are schematic sectional views of the hydraulic cylinder and hydraulic fluid containing reservoir of Fig 3 with the plunger of the fluid cylinder in the deactuated and actuated positions respectively.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION As explained in the background description in this specification, the off-road vehicle (not shown) includes a drive system (not shown) comprising a clutch system (not shown) having clutch shaft 108 rotatably disposed in a clutch house 100 coaxially with the crank shaft (not shown) of the engine (not shown) driving the vehicle and releasably coupled at one end 110 to the engine and at the other end 112 to the input shaft (not shown) of a gear box of constant mesh or sliding mesh gears (not shown) through splins 114. The clutch system also includes a clutch release mechanism (not shown) mounted at the said one end of the clutch shaft and an actuator assembly (not shown) for the clutch release mechanism having a U-shaped member 118 disposed in the clutch house with the tips thereof pivoted to the clutch house (pivoting not

shown) to describe a to and fro angular displacement in the axial direction of the clutch shaft and with clutch shaft extending therethrough. A clutch rail 122 extends across the U-shaped member in rigid contact therewith and in spaced apart relationship with the clutch shaft. The clutch rail is connected at one end thereof to a clutch linkage assembly (not shown) disposed for operation by a clutch pedal (not shown).
The drive system including the clutch system of an off-road vehicle as described above is known to a person skilled in the art. Therefore, features or details like engine, crank shaft, gear box, clutch release mechanism, clutch linkage assembly or clutch pedal have not been illustrated and described in detail as such are not necessary for understanding the invention. As illustrated in Figs 1 to 7 of the accompanying drawings, the speed retarding mechanism 102 for the inertia driven clutch shaft of the off-road vehicle comprises a disc 138 mounted on the clutch shaft 108 with the help of a bracket 144. 158 is a fluid pressure operated reciprocating mechanism comprising a calliper 146 disposed in the clutch house 100 below the disc and comprising a stationary friction pad 1 and a movable friction pad 2 disposed in an enclosed chamber 3 defining a space or gap 148 therebetween with the disc extending into the space. A piston 4 is reciprocally disposed in the enclosed chamber with the piston defining a fluid chamber 5 within the enclosed chamber. The movable friction pad is fixed to the piston
160 is a fluid cylinder disposed in the clutch house in fluid communication with the fluid chamber through a fluid pipe 162. The cylinder is mounted to an angular pipe 166 which in turn is supported on base 168 fixed to the clutch house. A plunger 164 is reciprocally disposed in the fluid cylinder. The plunger comprises a plunger rod 6 protruding out of the fluid cylinder. The fluid cylinder further comprises a fluid containing reservoir 7 mounted on the fluid cylinder and

communicating with the fluid cylinder through a pair of spaced apart fluid flow control ports 8 and 9, one located ahead of the front face of the plunger and the other located behind the rear face of the plunger. The fluid cylinder is preferably a hydraulic cylinder and the fluid reservoir contains a hydraulic fluid.
The plunger 164 is biased axially in the reverse direction with a tension spring 12 one end of which is fixed to the front face of the plunger and the other end of which is fixed to the confronting front wall of the cylinder. The plunger is preferably tapered (Figs 6 and 7) in order to ensure smooth movement of the plunger in the cylinder. The protruding outer end of the plunger rod 6 is fixed to a pair of links 13, 14 disposed one above the other in spaced apart relationship. A further pair of links 15, 16 are disposed one above another in spaced apart relationship and fixed to the hydraulic cylinder 160. 17 is a connector link located in the space between links 13 and 14 and links 15 and 16 and pivoted thereto (pivots marked 18 and 19). As the plunger reciprocates in the cylinder, the plunger rod also reciprocates with the plunger. Because of the pivoting of the connector link to links 13 and 14 and links 15 and 16, the plunger rod is flexible to allow the plunger to reciprocate in the fluid cylinder about the pivots 18 and 19 of the. connector link. 170 is an actuator depending down from the bottom of the U-shaped member and abutting the protruding outer end of the plunger rod 6 through links 13 and 14.
During running of the off-road vehicle, in order to change the speed of the vehicle the operator (driver of the vehicle) depresses the clutch pedal and declutchs the clutch shaft. On depressing the clutch pedal, the clutch linkage assembly rotates the clutch rail 122 in the clockwise direction by certain angle away from the clutch release mechanism. As a result, the U-shaped member

118 rotates with the clutch rail in the clockwise direction by the same angle and pulls the clutch release mechanism to disengage the said one end of the clutch shaft from the crank shaft of the engine thereby disconnecting the drive from the engine to the clutch shaft temporarily. Simultaneously the actuator 170 also rotates in the clockwise direction with the U-shaped member thereby pushing the plunger rod 6 and the plunger in the fluid cylinder 160 forward. The tension spring 12 gets compressed allowing the plunger to displace and move forward in the cylinder.
As the plunger moves forward in the fluid cylinder, fluid in the fluid cylinder is forced out into the fluid chamber 5 in the calliper 146. Simultaneously fluid in the fluid cylinder at the plunger side 10 also escapes into the reservoir 7 via the port 8 and the fluid in the reservoir flows into the plunger rod side 11 of the cylinder through port 9 to control the fluid flow and counter balance the fluid pressure in the cylinder. Due to the fluid pressure developed in the fluid chamber, the piston 4 with the movable friction pad 2 moves forward and presses against the disc 138 continuing to rotate with the inertia driven clutch shaft 108 during the declutching operation. As a result, the rotation of the clutch shaft is retarded or decelerated during declutching. The fluid being forced out of the fluid cylinder 160 into the fluid chamber 5 is controlled as required by controlling the clockwise rotation of the U-shaped member and the actuator 170 thereby controlling the rate of retardation or deceleration of the disc and the clutch shaft.
The operator then operates the gear shifting lever of the gear box to change the gear ratio and select the required speed. On releasing the clutch pedal by the operator, the clutch linkage assembly swings the clutch rail 122 and the U-shaped member 118 in the anticlockwise direction

towards the clutch release mechanism and the clutch release mechanism moves back to the original position thereby allowing the said one end of the clutch shaft to get engaged to the crank shaft. During the anti-clockwise rotation of the U-shaped member, the actuator moves back or swings back to its original position thereby releasing the force on the plunger rod and the plunger in the forward direction.
As a result, the spring 12 expands and allows the plunger to move back to its original position in the fluid cylinder. The fluid in the fluid cylinder at the plunger rod side 11 starts flowing into the reservoir 7 via port 9 and the fluid in the reservoir starts flowing into the plunger side 10 in the cylinder via port 8 thereby controlling the fluid flow and counter balancing the fluid pressure in the cylinder. As the plunger moves back in the cylinder, fluid in the fluid chamber 5 of the calliper 146 also flows back into the fluid cylinder thereby releasing the fluid pressure on the piston 4 and allowing the piston with the movable friction pad 2 to move back to the original position because of the roll back seal 20 in the calliper 146. The disc 138 is now free to rotate with the clutch shaft and the clutch shaft rotates at the selected speed to transmit drive from the engine to the rear wheel of the vehicle and to run the vehicle at the selected speed.
During the declutching operation of the off-road vehicle, the speed retarding mechanism of the invention retards the speed of rotation of the clutch shaft under inertia in a controlled manner. Therefore, noise generation during declutching of the clutch shaft is substantially reduced. As the speed of rotation of the inertia driven clutch shaft is retarded in controlled manner, the noise level generation at the coupling between the said other end of the clutch shaft and input shaft of the gear box also reduces. Speed of rotation of the gears of the gear box under inertia also reduces. Because of the substantial reduction in the noise level the driving experience becomes

very pleasant and enjoyable. Wear and tear to the clutch shaft and gear box also reduces thereby increasing the life thereof. Besides, the invention employs constant mesh or sliding mesh gears and is, therefore, cost effective.
The fluid pressure counter balancing mechanism for retarding the rotation of the disc 138 and clutch shaft and releasing the disc and clutch shaft during declutching may be of a different configuration or construction. The fluid containing reservoir need not be mounted on the fluid cylinder. There can be more number of fluid flow control ports 8 and 9. Such variations in the construction or configuration of the speed retarding mechanism of the invention are obvious to a person skilled in the art and should be construed and understood to be within the scope of the invention.

We claim :
1. Speed retarding mechanism for the inertia driven clutch shaft of an off-road vehicle, wherein the off-road vehicle includes a drive system comprising an engine with a crank shaft having a fly wheel mounted on the crank shaft and a clutch system having a clutch shaft rotatably disposed in a clutch house coaxially with the crank shaft and releasably coupled at one end to the flywheel and at the other end to a gear box of constant mesh or sliding mesh gears, a clutch release mechanism mounted at said one end of the clutch shaft and an actuator assembly for the clutch release mechanism having a U-shaped member disposed in the clutch house with the tips thereof pivoted to the clutch house to describe to and fro angular displacement in the axial direction of the clutch shaft and with the clutch shaft extending therethrough, a clutch rail extending across the U-shaped member in rigid contact therewith and in spaced apart relationship with the clutch shaft, the clutch rail being connected at one end thereof to a clutch linkage assembly disposed for operation by a clutch pedal and wherein the speed retarding mechanism comprises a disc mounted on the clutch shaft, an actuator depending down from the U-shaped member and a fluid pressure operated reciprocating mechanism operatively connected to the disc and the actuator to retard the speed of rotation of the inertia driven clutch shaft during declutching.
2. The speed retarding mechanism as claimed in claim 1, wherein the fluid pressure operated reciprocating mechanism comprises a calliper disposed below the disc in the clutch house and comprising a stationary friction pad and a movable friction pad disposed

in an enclosed chamber defining a space therebetween with the disc extending into the space and a piston reciprocally disposed in the enclosed chamber defining a fluid chamber within the enclosed chamber and with the movable friction pad fixed thereto, a fluid cylinder disposed in the clutch house in fluid communication with the fluid chamber and having a plunger reciprocally disposed in the fluid cylinder, the plunger being spring biased axially in the reverse direction and having a plunger rod protruding out of the fluid cylinder with the protruding outer end of the plunger rod abutting the actuator, the fluid cylinder further having a fluid pressure counter balancing means.
3. The speed retarding mechanism as claimed in claim 2, wherein the plunger is tapered.
4. The speed retarding mechanism as claimed in claim 2, wherein the plunger is tension spring biased.
5. The speed retarding mechanism as claimed in claim 2, wherein the fluid pressure counter balancing means comprises a fluid containing reservoir communicating with the fluid cylinder through at least one pair of spaced apart fluid flow control ports, one located ahead of the front face of the plunger and the other located behind the rear face of the plunger.
6. The speed retarding mechanism as claimed in claim 5, wherein the fluid containing reservoir is mounted on the fluid cylinder.

7. The speed retarding mechanism as claimed in claim 6, wherein the fluid cylinder is a hydraulic cylinder and the fluid reservoir contains a hydraulic fluid.