Claims:WE CLAIM:
1. A gearshift mechanism (100) for a saddle-type motor vehicle (10), comprising:
a gearshift shaft (100) protruding outwardly in a vehicle-width direction from a crankcase (24); and
a gearshift lever (120) mounted pivotally on the crankcase (24) rearwardly from the gearshift shaft (110) in a vehicle side view, the gearshift lever (110) connected to the gearshift shaft (120) by a gearshift linkage member.

2. The gearshift mechanism (100) as claimed in claim 1, wherein the gearshift linkage member comprises a first linkage member (130) having a first end connected to the gearshift shaft (110) and a second end; and a second linkage member (140) having a first end connected to the gearshift lever (120) and a second end coupled with the second end of the first linkage member (130).

3. The gearshift mechanism (100) as claimed in claim 1, wherein the gearshift lever (120) comprises a central mounting portion (126) pivoted to the crankcase (24); a forward extending portion (122) extending forwardly from the central mounting portion (126); and a rearward extending portion (124) extending rearwardly from the central mounting portion (126).

4. The gearshift mechanism (100) as claimed in claim 4, wherein length of the forward extending portion (122) is substantially equal to length of the rearward extending portion (124).

5. The gearshift mechanism as claimed in claim 4, wherein the first end of the second linkage member (140) is connected to said rearward extending portion (124) of the gearshift lever (120).

6. The gearshift mechanism (100) as claimed in claim 5, wherein the distance between the central mounting portion (126) of the gearshift lever (120) and the first end of the second linkage member (140) is 1.5 times greater than length of the first linkage member (140).

7. The gearshift mechanism (100) as claimed in claim 1, wherein the vehicle (10) comprises a rider footrest (160) positioned substantially below the pivotal mounting of the gearshift lever (120) in a vehicle side view.
, Description:FIELD OF THE INVENTION
[001] The present invention relates to a gearshift mechanism for a saddle-type motor vehicle.

BACKGROUND OF THE INVENTION
[002] In conventional saddle-type vehicles, gear shifting is performed by means of a gear shifting lever operated by one foot of a rider with toe of the rider resting on one end of the gear shifting lever and heel of the rider resting on other end of the gear shifting lever. Generally, for an upshift operation, the rider pushes the heel down and for a downshift operation, the rider pushes the toe down.
[003] The problem associated with such a conventional gear shifting in saddle-type vehicles is that for each gear shifting operation, the angular travel of the gear shifting lever is low, i.e. approximately 8.5o. Such a small angular travel of the gear shifting lever provides poor gear shifting feel to the rider. This means that it would be difficult for the rider to ascertain whether the gear shifting operation has been completed or not, which confuses the rider during running of the vehicle.
[004] Another problem associated with conventional gear shifting in saddle-type vehicles is that owing to the uneven length of the gear shifting lever with respect to the pivot point where the gear shifting lever is mounted. More particularly, length of the gear shifting lever extending forward from the pivot point is substantially shorter than length of the gear shifting lever extending rearward from the pivot point. As a result, gear shifting operation is made further difficult by uneven angular travel of the gear shifting lever for upshift and downshift operations.
[005] Such uneven length of the gear shifting lever with respect to the pivot point also leads to difficulty in downshifting for the rider that is performed with the help of shorter forward portion of the lever as compared to the upshifting that is performed with the help of longer rearward portion of the lever. This means that there is a difference in force needed to be exerted by the rider on the gear shifting lever between upshift and downshift operations. The difference of force may be of the order of 1.5 KG. Such a difference in the force needed to be exerted makes a downshift operation more difficult than an upshift operation.
[006] Attempts have been made to solve the aforementioned problems, but such configurations require modification of the frame structure for placing the gear shifting lever in an ergonomically optimal position for increasing the rider comfort. Adapting a similar configuration to the existing layout of a saddle-type vehicle would require an additional modification of the frame structure which would increase both the weight and cost of the vehicle.
[007] Thus, there is a need in the art for a gearshift mechanism which addresses at least the aforementioned problems.

SUMMARY OF THE INVENTION
[008] In one aspect, the present invention is directed towards a gearshift mechanism for a saddle-type motor vehicle. The gearshift mechanism has a gearshift shaft that protrudes outwardly in a vehicle-width direction from a crankcase, and a gearshift lever mounted pivotally on the crankcase rearwardly from the gearshift shaft in a vehicle side view. The gearshift lever connected to the gearshift shaft by a gearshift linkage member.
[009] In an embodiment of the invention, the gearshift linkage member has a first linkage member having a first end connected to the gearshift shaft and a second end, and a second linkage member having a first end connected to the gearshift lever and a second end coupled with the second end of the first linkage member.
[010] In another embodiment of the invention, the gearshift lever has a central mounting portion pivoted to the crankcase, a forward extending portion extending forwardly from the central mounting portion, and a rearward extending portion extending rearwardly from the central mounting portion.
[011] In yet another embodiment of the invention, length of the forward extending portion is substantially equal to length of the rearward extending portion.
[012] In a further embodiment of the invention, the first end of the second linkage member is connected to said rearward extending portion of the gearshift lever.
[013] In a further embodiment of the invention, the distance between the central mounting portion of the gearshift lever and the first end of the second linkage member is 1.5 times greater than length of the first linkage member.
[014] In a further embodiment of the invention, the vehicle has a rider footrest positioned substantially below the pivotal mounting of the gearshift lever in a vehicle side view.

BRIEF DESCRIPTION OF THE DRAWINGS
[015] Reference will be made to embodiments of the invention, examples of which may be illustrated in accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.
Figure 1 shows an exemplary saddle type motor vehicle in accordance with an embodiment of the invention.
Figure 2 shows an exploded view of a gearshift mechanism in accordance with an embodiment of the invention.
Figure 3 shows a perspective view of the gearshift mechanism in accordance with an embodiment of the invention.
Figure 4A shows a side view of a gearshift lever connected to a gearshift linkage member in accordance with an embodiment of the invention.
Figure 4B shows a top view of the gearshift lever connected to the gearshift linkage member in accordance with an embodiment of the invention.
Figure 4C shows a front view of the gearshift lever connected to the gearshift linkage member in accordance with an embodiment of the invention.
Figure 5 shows the gearshift mechanism with a rider footrest in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION
[016] The present invention relates to a gearshift mechanism for a motor vehicle. More particularly, the present invention relates to a gearshift mechanism for a saddle-type motor vehicle.
[017] Figure 1 illustrates an exemplary saddle-type motor vehicle, in accordance with an embodiment of the invention. The saddle type vehicle 10 comprises an IC engine 12 that is vertically disposed. Preferably, the IC engine 12 is a single-cylinder type IC engine. The saddle type vehicle 10 further comprises a front wheel 14, a rear wheel 16, a frame member (not shown), a seat 18 and a fuel tank 20. The frame member includes a head pipe 22, a main frame, rear down tubes, and seat rails. The head pipe 22 supports a steering shaft (not shown) and two telescopic front suspensions 26 (only one shown) attached to the steering shaft through a lower bracket (not shown). The two telescopic front suspensions 26 support the front wheel 14. The upper portion of the front wheel 14 is covered by a front fender 28 mounted to the lower portion of the telescopic front suspension 26 at the end of the steering shaft. A handlebar 30 is fixed to upper bracket not shown and can rotate to both sides. A head light 32, a visor guard (not shown) and instrument cluster (not shown) is arranged on an upper portion of the head pipe 22. The frame member comprises a down tube that may be located in front of the IC engine 12 and extends slantingly downward from head pipe 22. The main frame of the frame member is located above the IC engine 12 and extends rearward from head pipe 22. The IC engine 12 is mounted at the front to the down tubes and a rear of the IC engine 12 is mounted at the rear portion of the main frame. In an embodiment, the IC engine 12 is mounted vertically, with a cylinder block extending vertically above a crankcase. In an alternative embodiment, the IC engine 12 is mounted horizontally (not shown) with the cylinder block extending horizontally forwardly from the crankcase. In an embodiment, the cylinder block is disposed rearwardly of the downtube.
[018] The fuel tank 20 is mounted on the horizontal portion of the main frame. Seat rails are joined to main frame and extend rearward to support a seat assembly 18. A rear swing arm 34 is connected to the frame member to swing vertically, and a rear wheel 16 is connected to rear end of the rear swing arm 34. Generally, the rear swing arm 34 is supported by a mono rear suspension 36 or through two suspensions on either side of the saddle type vehicle 10 (as illustrated in the present embodiment). A taillight unit (not shown) is disposed at the end of the saddle type vehicle 10 and at the rear of the seat assembly 18. A grab rail (not shown) is also provided on the rear of the seat rails. The rear wheel 16 arranged below seat 18 rotates by the driving force of the IC engine 12 transmitted through a chain drive (not shown) from the IC engine 12. A rear fender 38 is disposed above the rear wheel 16.
[019] Further, an exhaust pipe (not shown) of the vehicle extends vertically downward from the IC engine 12 up to a point and then extends below the IC engine 12, longitudinally along the vehicle length before terminating in a muffler (not shown). The muffler (not shown) is typically disposed adjoining the rear wheel 16.
[020] Figure 2 illustrates an exploded view of a gearshift mechanism 100 in accordance with an embodiment of the present invention. As illustrated in the Figure, the gearshift mechanism 100 has a gearshift shaft 110. The gearshift shaft 110 protrudes outwards from a crankcase 24 in vehicle-width direction. The gearshift shaft 110 is generally further connected to a shift drum (not shown) which converts the motion of the gearshift lever 110 to a horizontal motion for a shift fork (not shown). The shift fork moves the gear pairs (not shown) horizontally to engage and disengage the gear pairs with output shaft (not shown) of the engine.
[021] As illustrated in the Figure, the gearshift mechanism 100 further has a gearshift lever 120. The gearshift lever 120 is pivotally mounted on the crankcase 24 such that the mounting of the gearshift lever 120 is rearwardly from the gearshift shaft 110 in the front-rear direction of the vehicle, as opposed to the conventional configuration wherein the gearshift lever 120 is directly mounted upon the gearshift shaft 110. The rider operates the gearshift lever 120 by pushing a front end 120A of the gearshift lever 120 by toe for a downshift operation and pushing a rear end 120B of the gearshift lever 120 by heel for an upshift operation. The gearshift lever 120 is connected to the gearshift shaft 110 by the means of a gearshift linkage member. As further illustrated in the Figure, the pivotal mounting of the gearshift lever 120 on the crankshaft 24 is done with a spacer 150. The spacer 150 allows for the mounting of the gearshift lever 120 in such a manner that the gearshift lever 120 is at a distance from the crankcase 24.
[022] Figure 3 illustrates the gearshift mechanism 100 mounted on the crankcase 24 in accordance with an embodiment of the invention. As illustrated in Figures 2 and 3, the gearshift lever 120 is connected to the gearshift shaft 110 by the means of a gearshift linkage member. The gearshift linkage member has a first linkage member 130 and a second linkage member 140. A first end of the first linkage member 130 is connected to the gearshift shaft 110 and, as shown in Figure 4a, a second end of the first linkage member 130 is connected to a second end of the second linkage member 140. A first end of the second linkage member 140 is then connected to the gearshift lever 120, thus completing the connection of the gearshift lever 120 to the gearshift shaft 110. Resultantly, in the present invention, the pivot point of the gearshift lever 120 is shifted backwards from the location of the gearshift shaft 110 to the location of pivotal mounting of the gearshift lever 120.
[023] In operation, when the rider pushes the front end 120A or the rear end 120B of the gearshift lever 120 for a downshift or an upshift, the gearshift lever 120 moves up or down along its pivotal mounting. The said movement of the gearshift lever 120 causes the gearshift shaft 110 to move via the gearshift linkage member, i.e. through the first linkage member 130 and the second linkage member 140. The resulting movement of the gearshift shaft 110 then causes the gear to change via the shift drum and the shift fork.
[024] Figure 4A, Figure 4B and Figure 4C illustrate the gearshift lever 120 in connection with the gearshift linkage member in a side view, top view and front view respectively, in accordance with an embodiment of the invention. As illustrated in the Figures, the gearshift lever 120 has a central mounting portion 126. The gearshift lever 120 is pivotally mounted on the crankcase 24 at the central mounting portion 126 of the gearshift lever 120. The gearshift lever 120 further has a forward extending portion 122 extending forwardly from the central mounting portion 126 to the front end 120A of the gearshift lever 120 and a rearward extending portion 124 extending rearwardly from the central mounting portion 126 to the rear end 120B of the gearshift lever 120. In this embodiment, the length of the forward extending portion 122 is substantially equal to the length of the rearward extending portion 124.
[025] As further illustrated in the Figures, the second end of the second linkage member 140 is connected to the rearward extending portion 124 of the gear shifting lever 120.
[026] It is known that for a successful upshift or downshift operation, the gearshift shaft 110 must rotate by a certain angle. In conventional configuration, when the gearshift lever 120 is directly mounted on the gearshift shaft 110, the extent of the angular movement of the gearshift lever 120 will be the same as that of the gearshift shaft 110. However, in the configuration defined by the present invention, the extent of the angular movement of the gearshift lever 120 will be greater than that of the gearshift shaft 110 as the movement of the gearshift lever 120 is transmitted to the gearshift shaft through the gearshift linkage member. It is discernible that the extent angular movement of the gearshift lever 120 on its pivotal mounting on the crankcase 24 for an upshift or a downshift operation is directly proportional to the ratio of distance between the central mounting portion 126 of the gearshift lever 120 and the first end of the second linkage member 140 (R1) to the length of the first linkage member 130 (R2). Thus, it is obvious that greater is the ratio of distance between the central mounting portion 126 of the gearshift lever 120 and the first end of the second linkage member 140 (R1) to the length of the first linkage member 130 (R2), greater will be the angular movement of the gearshift lever 120 required for an upshift or a downshift operation. In the present invention, the angular movement of the gearshift lever 120 to cause an angular movement of the gearshift shaft 110 is given by the required angular movement of the gearshift shaft 110 multiplied by the ratio R1/R2. In this embodiment, the ratio R1/R2 is always kept greater than one, and hence increasing the gearshift lever 120 angular movement required to cause the requisite angular movement in the gearshift shaft 110.
[027] In an exemplary embodiment of the present invention, the angular movement of the gearshift shaft 110 required for an upshift or a downshift operation is 8.5o. While in the conventional configuration, the angular movement of the gearshift lever 120 to cause an 8.5o movement of the gearshift shaft 110 would also be 8.5o, in the embodiment of the present invention the ratio R1/R2 is kept at 1.5, and hence the angular movement of the gearshift lever 120 to cause an 8.5o angular movement of the gearshift shaft 110 is calculated as 8.5o multiplied by 1.5. Hence in the present invention, the angular movement of the gearshift lever 120 required to cause an angular movement of 8.5o in the gearshift shaft 110 is increased from 8.5o to about 13.5o. The increased extent of angular movement of the gearshift lever 120 gives a better gear shifting feel to the rider, leaving no room for uncertainty as to whether the upshift or downshift operation has been completed or not.
[028] Figure 5 illustrates the gearshift mechanism 100 with a rider footrest 160 in accordance with an embodiment of the invention. As illustrated in the Figure, in a vehicle side view, a rider footrest 160 positioned substantially vertically below the pivotal mounting of the gearshift lever 120. Such a mounting of the gearshift lever 120 is substantially vertically above the rider footrest 160 and ensures that the distance of the front end 120A of the gearshift lever 120 from the rider footrest 160 is substantially the same as the distance of the rear end 120B of the gearshift lever 120 from the rider footrest 160, as the length of the forward extending portion 122 and the rear extending portion 124 of the gearshift lever 120 are of substantially equal length. Such equal distance of the front end 120A and the rear end 120B of the gearshift lever 120 from the rider footrest 160 warrants that the force required to be exerted by the rider to push the front end 120A of the gearshift lever 120B for a downshift operation is the same as the force required to be exerted by the rider to push the rear end 120B of the gearshift lever 120 for an upshift operation.
[029] Further as illustrated in the Figure, the first end of the second linkage member 140 which is connected to the rearward extending portion 124 of the gearshift lever 120 is located rearward of the rider footrest 160 in the vehicle front-rear direction, ensuring that the first end of the second linkage member 140 does not interfere with the foot of the rider while operating the gearshift lever 120 while also ensuring that the banking angle of the vehicle is not affected.
[030] Advantageously, the present invention provides a gearshift mechanism in which the extent of angular movement of the gearshift lever for an upshift or a downshift operation is increased, thereby providing better gear shifting feel to the rider as a gear shift operation becomes more perceivable to the rider and enhances the overall comfort of gear shifting for the rider.
[031] Further, in the present invention the force required to be exerted by the rider for a downshift operation is reduced and is substantially the same as the force required to be exerted by the rider for an upshift operation, providing over all comfort of gear shifting for the rider.
[032] Furthermore, the gearshift mechanism as disclosed by the present invention requires no modification of the frame structure and the gearshift lever can be mounted on the existing crankcase without making any changes to the gear shifting assembly inside the engine or any other components of the engine. The minimal modifications of the vehicle required for the gearshift mechanism also make the gearshift mechanism suitable for retrofitting on existing saddle-type motor vehicles.
[033] While the present invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims.