FORM 2
THE PATENTS ACT, 1970
( 39 of 1970 )
COMPLETE
SPECIFICATION SECTION 10
TITLE
A GEAR SHIFTING DEVICE FOR A TWO WHEELED VEHICLE
APPLICANT
BAJAJ AUTO LIMITED, an Indian Company, of Akurdi, Pune 411 035, Maharashtra, India.


The following specification particularly describes the nature of the


This invention relates to a gear shifting device for a 2 wheeled vehicle with a manually operated gear shift control. The present invention particularly relates to a gear shifting device for a 2 wheeled vehicle having an engine and transmission unit located substantially on one side of the centerline of the vehicle having a monocoque chassis.
Although invention particularly relates to a gear shifting device for a 2 wheeled vehicle having monocoque chassis such device can also be adopted for vehicles having tubular chassis. One may even adopt such system where engine is located on the centreline of a vehicle which may be having a monocoque or tubular chassis.
Gear shift device of the known vehicles essentially consists of following component parts.
1. Left hand operated twist grip type gear shift control unit provied on the handle bar which transmits gear shifting force to the shifting device through gear control cables.

2. Gear control cable means which operate the gear control disc mounted in the housing which in turn operates gear shift lever. The gear control disc is held in position by a roller, lever and a spring arrangement in the desired gear position by retaining the roller in respective notch provided in the gear control disc.
3. Gear shifting lever pulls or pushes the gear control pin and on the other side of the pin an element called cross is fixed.
4. The cross transmits rotational movement of the desired speed gear to main shaft and subsequently to the rear wheel which moves the vehicle forward.
The arrangement as stated above in the conventional gear shifting device has the following disadvantages:
1. The arrangement of roller, lever and spring for retaining the gear control disc in position has inherent drawback for due to constant shifting of gears, the roller becomes loose in the lever.
2. When cross engages with gears, the entry edges of cross get damaged and this reduces life of the cross.

3. The gear shifting in the existing design is not smooth and therefore after some use, it creates noise.
4. Manufacturing of parts like cross is expensive.
In order to avoid the above problems, the applicants have invented an improved gear shifting device.
An object of the invention is to avoid the use of roller, lever and spring, still retaining the control location ie. twist grip means arrangement of gear control disc substantially same.
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Another object of the invention is to avoid use of cross but still retaining the location of speed gears and the main shaft substantially same.
Yet another object of the invention is to provide smooth gear shifting in the vehicle.
Further objects and disadvantages of this invention will be more apparent from the ensuing description when read in conjunction with the accompanying drawings.

The present invention provides a gear shifting device for a two wheeled vehicle conprising a left hand operated twist grip, a gear control disc operated by said twist grip through control cable means, said gear control disc having spherical grooves on lower surface in which a steel ball and a spring are provided to hold the said gear control disc in position corresponding to desired driving gear position, said gear control disc through lever means being capable of moving forward and backward gear selector pin provided in the main shaft, said main shaft being provided with multiple radial holes and steel balls held in position by a expandable circular ring such that at the desired position of gear shift the gear selector pin lifts said balls radially outward through radial holes into the slots provided in the inner periphery of the speed gears thus transmitting rotary motion of speed gears to the said main shaft and further to wheel to achieve forward motion.
1fre present invention further provides, a gear shifting device for a two wheeled vehicle comprising a left hand operated twist grip, a gear control disc operated by said twist grip through control cable means, said gear control disc having plurality of notches on its outer periphery, a spring loaded lever which keeps said control disc in positioin with the help of roller in one of said notches, said control disc through lever means being capable of moving forward and backward gear selector pin provided in the main shaft, said main shaft being provided with multiple radial holes and steel balls held in position by a expandable circular ring such that at the desired position of gear shift the gear selector pin lifts said balls radially outward through radial holes into the slots provided in the inner periphery of the gears thus transmitting rotary motion of speed gears on to the said main shaft and further to wheel to achieve forward motion.
In the drawings -
Pig.l shows view of vehicle from rear where engine transmission are located substantially on one side of the centreline of the vehicle.
Fig$2&2A show complete and cross sectional view of gear shifting device of the prior art.

Fig.3 shows the assembly of speed gears of the main shaft in the prior art.
Pig. 4 shows assembly of gear shifting disc of the present invention.
Fig.4A shows assembly of gear shifting cjisc in the present invention in another view.
Fig.5 shows the assembly of speed gears on the main shaft of the present invention.
Fig.6 shows the position of steel balls inside the slots in the speed gears of the present invention.
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Fig. 7 shows a cross sectional view of main shaft portion where steel balls are located in the present invention.
Pig.8 shows location of one of the steel balls inside, the main shaft hole in the present invention.
Figure 1 illustrates a two wheeled vehicle where both the engine and transmission unit are positioned substantially on the right hand side of the centreline of the vehicle.

Figures 2 & 2A show two views of the gear shifting device assembled in housing (H). When a gear shifting is desired by driver, he twists the left hand operated twist grip type gear shift control located on the handlebar which creates tension force in one of the control cables (Cl or C2). Either of these cables rotate* a gear control disc (1). A lever (2) is fixed at predetermined position with respect to said gear control disc (1) and in turn moves slider block (3) which is riveted (4) to the lever (2). The slider block (3) thus moves alongwith the lever (2) with reference to axis (Al) of the gear control disc (1).
The gear control disc (1) has five notches on its outer periphery. A spring (5) loaded lever (6) keeps the gear control disc (1) in position with the help of a roller (7) in one of the notches. The notches Nl, K2, N3, N4, NS are the positions of gear control disc (1) corresponding to First, Neutral, Second, Third and Fourth gear engagement position respectively.
Figure 3 shows the assembly of mainshaft (14) and speed gears (10,11,12,13). The slider block (3 of Fig.2) is engaged in the cavity (8) formed in gear shifter Pin (9), which moves

forward and backward alongwith retainer pin (9B) at the time of gear shift as the gear control disc (1) rotates about the axis (Al). A cross (9A) fixed at the end of said pin (9) acts as a key and ' transmits the rotary motion of one of the gears (10), (11), (12) or (13) depending upon position of gear control disc (1), to the main shaft (14) which moves the vehicle with the help of wheel mounted on the main shaft (14). The positions Nl, N3, N4 and N5 of gear control disc (1) correspond to engagement of gears 13, 12, 11 and 10 respectively. The cross (9A) is maintained at its position with the help of spring (15) and ball (16) which remain in the respective circular grooves
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provided on the retainer pin (9B).
In order to avoid the problems experienced in prior art, we have designed a new gear shifting device for retention of gear control disc in position and transmission of rotational motion from gears to mainshaft through steel balls.
The operation of the improved gear shifting device will now be explained with reference to the drawings.
Figures 4 and 4A explain new arrangement of gear control disc retaining system. According to this new system, the notches

on the gear control disc are dispensed with and replaced by spherical grooves (Gl,G2,G3,G4 and G5) on lower face (Lf) of gear control disc (27). The transmission of gear shifting force from left hand operated twist grip on handle bar to gear control disc is same as in prior art. The steel ball (17) and spring (18) are assembled at fixed location. The gear control disc (27) rotates about its axis (A2) when gearshift is desired. When the steel ball is say, at spherical groove G5, due to rotation of the gear control disc (27), the steel ball (17) compresses the spring (18) and acquires new position in groove G4. Similar process takes place when the shifting from groove G4 to G3 and so on and vice versa.
Figure 5 shows speed gears (22,23,24,25) assembled on the mainshaft (26) in the improved device. The gears are rotatably mounted on the mainshaft and are always in rotating condition when the engine runs and clutch is in engaged condition. Circlip (29) and washer (30) are assembled on both sides to restrict axial movement of speed gears. A gear selector pin (19) moves backward and forward in the inner hole (34) on the main shaft (26). This pin has partial flat portions (31) equal to the number of balls in each gear and a pin (32) which is assembled to main shaft protrudes within one of the slots to prevent gear control pin (19) from rotational movement.

Figure 6 illustrates the position of steel balls (21) inside the slots (36) provided on inner periphery of speed gears at predetermined locations.
Figure 7 illustrates a cross sectional view of main shaft portion where steel balls are located. The main shaft (26) is provided with radial holes (33) in which steel balls (21) are assembled. The radial movement of steel balls (21) is controlled with the help of a expandable circular ring (28) provided in a circular groove (35) perpendicular to hole (33) at predetermined location.
Figure 8 illustrates location of one of the steel balls (21) inside the main shaft hole (33). In this figure the position of steel balls is shown in a cross sectional view when the pin (19) is not in contact with the steel ball (21). In order to achieve proper function of assembly, radial distance d1 and radial distance d2 have predetermined values and necessarily d1 should be greater than d2 by an amount such that when pin (19) pushes the ball radially outward, the ball (21) protrudes sufficiently into the slot (36) on speed gears to transmit the rotational movement of the speed gear to the main shaft (26).

For the working of new gear shifting device when the pin (19) is shifted to a desired gear position, it moves the steel balls (21) radially outward against the radial force of expandable circular ring (28) and projects out from outer surface (37) of the main shaft (26) into the slots (36) provided oh the inner periphery of speed gears, thus transmitting the rotary motion of the desired speed gear to the main shaft (26) and further to the driving wheel mounted on the main shaft so that vehicle moves forward. In this connection other steel balls protrude either in the inner hole (34) or on flat portions (31) of the gear selector pin (19).
Illustrations given above are for gear shifting device with 3 steel balls at each gear location. It is however possible to design such a system with one or more number of steel balls depending upon requirement of torque to be transmitted, availability of space and other design aspects.
The description given hereinabove describes number of slots on inner periphery of speed gears as 6. However, it is possible to provide above system with number of slots equal to number of steel balls or multiples thereof with equal spacing.

Also the description given above is meant for 2 wheeled vehicle having left hand operated twist grip for gear shifting. However, it is possible to adopt the above system with foot operated gear shift control.
As seen from the above, in new invented system we have been able to eliminate problematic parts like roller and cross etc and improve the gear shifting mechanism.
Although it is not described herein above the obvious alterations and/or modifications of the gear shifting device of the kind described herein are within the scope of the present invention.

WE CLAIM:
1. A gear shifting device for a two wheeled vehicle comprising a left hand operated twist grip, a gear control disc (1) operated by said twist grip through control cable means, said gear control disc having plurality of notches on its outer periphery, a spring (5) loaded lever (6) which keeps said control disc <1) in position with the help of roller (7) in one of said notches, said control disc through lever means being capable of moving forward and backward gear selected pin (19) provided in the main shaft (26), said main shaft being provided with multiple radial holes (33) and steel balls (21) held in position by a expandable circular ring (28) such that at the desired position of gear shift the gear selector pin (19) lifts said balls (21) raidally outward through radial holes (33) into the slots provided in the inner periphery of the gears thus transmitting rotary motion of speed gears on to the said main shaft and further to wheel to achieve forward motion.
2. A gear shifting device as claimed in claim 1 wherein said two wheeled vehicle is provided with a monocoque chassis.
3. A gear shifting device as claimed in claim 1 or 2 wherein engine and transmission unit are located substantially on
ne side of the vehicle.

4. A gear shifting device as claimed in any one of claims
1 to 3 wherein said vehicle is provided with a monoc'oque chassis
where engine and transmission unit are located substantially on
right hand side of the vehicle,
5. A gear shifting device as claimed in claim 1 wherein said two wheeled vehicle is provided with a tubular chassis.
6. A gear shifting device as claimed in claim 1 wherein the number of steel balls for each gear is at least one.
7. A gear shifting device as claimed in claim 1 wherein the slots in the inner periphery of the speed gears are equal to number of steel balls provided or in multiples thereof.
8. A gear shifting device as claimed in any one of the proceeding claims wherein the gear shifting device is provided to be used with foot operated gear shift mechanism.
9. A gear shifting device substantially as herein
described and as illustrated in the accompanying drawings.