GEAR SHIFT MECHANISM FOR A MOTORCYCLE
FIELD OF THE INVENTION
[0001] The present subject matter relates generally to a transmission system, and more particularly to an improved powered gear shift mechanism for an internal combustion engine.
BACKGROUND OF THE INVENTION
[0002] A conventional two wheeled vehicle is powered by an internal combustion engine generally disposed at a lower half of the vehicle. This engine converts converts chemical energy into mechanical energy by combustion of air-fuel mixture within a combustion chamber of the engine. The said engine, among other components, has a cylinder comprising a cylinder head atop the cylinder and receiving a reciprocating piston from the bottom. On combustion of the air-fuel mixture, the piston transfers the energy generated during combustion to a crankshaft through a connecting rod thereby driving the crankshaft. In this way, the reciprocatory motion of the piston is converted to rotatory motion of the crankshaft. The crankshaft is housed inside a crankcase beneath the cylinder block. In order to set the vehicle into motion, the power supplied to the crankshaft of the internal combustion engine is carried to a wheel of the vehicle, in a controllable way, through a transmission system. The transmission system employs a clutch and a gearbox with plurality of gears, wherein gear shift is achieved either manually or electronically which enables gears to be selected only in a rising or descending sequence.

[0003] FIGs. 1 and 2 illustrate a powered gear shift actuation system as described in the Applicant's co-pending Indian Patent Application No. 4589/CHE/2011, the contents of which are hereby incorporated herein by reference. Here, the power transmission to the shift drum is carried through the use of gearing system comprising a set of gears internal to a clutch cover and supported on the crankcase. The gear shift motor 201 and reduction gear box 202 are positioned into a housing 211 external to the clutch cover 25 and laterally on the right side of the engine, thus being on the same side as that of starter lever 209. The drive gear 203 of the gear shift motor 201 drives an idler gear big 401 in contact with idler gear small 402 on the crank facing side. Idler gear big 401 is driven by the gear shift motor 201. The idler gear big and idler gear small are fabricated into one component, albeit on the opposite sides. The idler gear small 402 further drives a driven gear 403 which is meshed with the idler gear small 402. A star index (indexing guide of star shape) 207 is located anterior to the driven gear 403 and is connected to the rotatably movable shift drum 210 through pins. Thus the driven gear 403 is sandwiched between the shift drum 210 and star index 207. A shift control unit (ECU) to control and run the motor in both directions and a gear position sensor 407 are included. The gear position sensor 407 determines the gear position based on the position of shift drum 210 and provides its output in voltage. The output voltage determines the current gear ratio in which the transmission system is being operated and provides input to the shift control unit. The gear shift motor 201 receives its input from the shift control unit based on vehicle speed, engine rpm and throttle position.

[0004] On receiving suitable input, the gear shift motor 201 drives the drive gear 203 which further drives the idler gear big 401. The idler gear big 401 rotates idler gear small 402. The idler gear small 402 rotates the driven gear 403 which further turns the shift drum 210 through the star index 207. The extent of rotation of the star index 207 determines the extent of the gear shift. A stopper 404 is provided below the star index 207 to keep the star index in the chosen position i.e. in the selected gear ratio. The stopper 404 is held interior to the clutch cover 25 through a loaded spring 405.
[0005] Further to the gear shift actuation, the shift drum rotates and in response the sliding shift forks carry out the gear shift. A conventional gear box has two parallel shafts, a main shaft (input) and a countershaft (output). The main shaft is rotated by the engine while the countershaft rotates the rear wheel. Several selectively operable pair of gears are installed on main shaft and the countershaft and they are generally in constant mesh with each other. For a particular transmission ratio, one gear is mounted on the main shaft whereas the corresponding gear is mounted on the countershaft. One of these gears is engaged to its respective shaft and spinning with it, while the other freewheels on its shaft thus not transmitting drive. In order to transmit drive, the gear next to it (which is locked to its shaft and therefore turning) is slid along splines on the shaft through the shift forks until it touches the freewheeling gear. Dogs (or projecting lugs) from the locked gear engage with equivalent cavities in the freewheeling gear, locking it into engagement and transmitting drive thus completing the gear shift. Thus, the shift forks drivingly connect the main shaft and countershaft together

through the meshed gears, thereby transmitting the rotation of the crankshaft of the engine to the countershaft at the selected gear ratio.
[0006] The rotation of shift drum controls the transmission ratio, i.e., the shift drum rotates according to the required transmission ratio. During gear shifting, the freewheeling gear having cavities should properly accomodate the projecting lugs of corresponding locked gear in the gear box. If this does not happen properly, it may cause improper gear engagement or partial gear engagement during which the stopper may get trapped into incorrect position as shown in FIG. 3. The aforementioned powered gear shift actuation system is a rigid system and there is no freedom in the system to address improper/partial engagement-of" gears. Because of this, the transmission system may get jammed and the user of the vehicle would be stuck without any gear shift or improper gear shift for a significant time.
[0007] Therefore, there is a need to develop an improved powered gear shift actuation system/mechanism devoid of any aforementioned problems which would improve gear shift feeling, increase operational efficiency and lead to better customer satisfaction. During a dog to dog situation, the proposed system self recovers to complete the gear shift event within less time and with increased probability. The present invention intends to solve all or any of the above problems.
SUMMARY OF THE INVENTION
[0008] The present subject matter discloses an improved powered gear shift actuation system for an internal combustion engine for actuating the operation of

change of gear comprising: a power source, a reduction gear box connected to said power source, a set of gears supported interior to a clutch cover for transmitting rotational driving force of the said power source to a shift drum, the set of gears including an idler gear big, an idler gear small and a driven gear; characterised in that the idler gear big and idler gear small are separate, individual and mechanically connectable elements, the said idler gear big comprises a recess for achieving free play in the said system during gear shift, the said idler gear big and said idler gear small are connected by a pin whose end is mounted on idler gear small and the other end penetrates the recess in the idler gear big, and wherein, on transmission ratio selection, the said shift drum turnably supported by a crankcase is driven by the said powered gear shift actuation system.
[0009] According to an aspect of the present invention, during dog to dog condition, required rotation of the shift drum to effect change in transmission ratio is carried out partially by torque provided by the power source and remaining by radial force of a stopper.
[00010] The foregoing objectives and summary provide only a brief introduction to the present subject matter. To fully appreciate these and other objects of the present subject matter as well as the subject matter itself, all of which will become apparent to those skilled in the art, the ensuing detailed description of the subject matter and the claims should be read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS
[00011] The above and other features, aspects, and advantages of the present invention will be better understood with regard to the following description, appended claims and accompanying drawings where:
FIG. 1 is an assembly view of a powered gear shift mechanism according to the prior art.
FIG. 2 is a front view of the shift drum gear arrangement in the powered gear shift mechanism of Figure 1.
FIG. 3 shows powered gear shift mechanism according to FIG. 1 in improper engagement condition.
FIG. 4(a) shows a perspective view of a first embodiment of an improved powered gear shift mechanism.
FIG. 4(b) shows a sectional view of the first embodiment of the improved powered gear shift mechanism of FIG. 4 (a).
FIG. 5(a) shows a perspective view of a second embodiment of the improved powered gear shift mechanism as well as the top view of the driven gear.
FIG. 5(b) shows a sectional view of the second embodiment of the improved powered gear shift mechanism of FIG. 5 (a).
FIG. 6 shows position of a stopper after powered gear shifting devoid of improper engagement condition.

DETAILED DESCRIPTION OF THE INVENTION
[00012] The subject matter described herein relates to an improved gear shift actuation system which has self-recovering ability in less time with increased probability in case of a failed or incomplete gear shift event. Various other features of the present subject matter here will be discernible from the following further description thereof, set out hereunder. The detailed explanation of the constitution of parts other than the subject matter which constitutes an essential part has been omitted at suitable places.
recess 501 system and
[00013] The improved powered gear shift actuation mechanism provides for a timely and accurate gear shift with reduced instances of improper gear engagement. FIGs. 4(a) and 4(b) show a first embodiment of the said system wherein the idler gear is split into two individual and separate components namely idler gear big 401' and idler gear small 402'. A recess 501 is provided in the idler gear big 401' near its center. The idler gear big 401' is electrically driven through the drive gear 203 of the gear shift motor whereas idler gear small 402' is driven by idler gear big 401' through a pin 502 whose one end is mounted on the idler gear small 402' and the other end penetrates the recess 501 in the idler gear big 401'. Unlike the prior art, the idler gear small 402' does not rotate simultaneously with idler gear big 401' because firstly they are separate, individual and mechanically connectable elements connected by the pin 502, and secondly the
in the idler gear big provides free play for flexible coupling in the supports some degrees of free rotation of idler gear big 401'.

[00014] According to an aspect of the present invention, the proposed powered gear shift actuation system is usable with a four speed, or a five speed or a six speed gearbox. In case of a four speed transmission gearbox with four upshifts from neutral, or four downshifts from neutral, or one downshift and four upshifts from neutral, the shift drum 210 needs to be rotated by 72 degrees for a gearshift event to take place. The gear position sensor determines the current gear ratio and based on the ECU inputs, drive is received by the driven gear through the power source. If no dog to dog (or improper engagement) condition is encountered during the gear shift event, the required rotation of the shift drum (72°) to effect change in transmission ratio is carried out entirely by the torque provided by the power source after overcoming the introduced free play and the spring loaded stopper will secure this position through its roller provided therein. When the shift drum completes certain degrees of rotation, the spring loaded stopper enters the next gear region and keeps the shift drum in that position after the gear shift event. However, in no dog to dog condition, the radial force of the stopper is not put to fruitful use.
[00015] When dog to dog condition is encountered in the stated four speed transmission gearbox with four upshifts from neutral or four downshifts from neutral, or one downshift and four upshifts from neutral (with a possibility of incomplete/failed gear shift event), required rotation of the shift drum to effect change in transmission ratio is carried out partially by torque provided by the power source and remaining by radial force of the stopper. In an embodiment of the present invention, the recess 501 is so adjusted that 40° of shift drum is driven

by the power source after which the stopper slides into the next gear region and the remaining rotation of 32° leading to a gear shift is complete by the radial force of the stopper on the star index 207. The radial force is provided by the spring preload. The spring preload is adjustable depending on the radial force required. During the incomplete gearshift event, the power source switches off in such a way that the idler gear big can rotate back and forth to adjust itself by using the free play provided and self-recover from the incomplete/failed gearshift event. Thus there is no load on the system due to the power source and the remaining gear shift is completed naturally. After the gear shift, the roller of the stopper holds its position before the next gear shift is powered by the power source. The direction of rotation of the power source during an upshift is opposite to its direction of rotation during a downshift.
[00016] The recess is provided near to the centre of idler gear big and its angular dimensions depend on the required transmission ratio. Due to the recess, the idler gear big may rotate within the range of 30 degrees to 150 degrees relative to idler gear small.
[00017] Likewise, in case of a five speed transmission gearbox with five upshifts from neutral or five downshifts from neutral, the shift drum needs to be rotated by 60 degrees for a gearshift event to take place. During dog to dog condition, 40° of shift drum is driven by the power source after which the stopper slides into the next gear region and the remaining rotation of 20° leading to a gear shift is complete by the radial force of the stopper. The above illustrations are based on the assumption that all upshifts or downshifts are in one direction.

[00018] A second embodiment for achieving the objective of hassle free gear shifting is also provided in this description as depicted in FIGs. 5(a) and 5(b). In the second embodiment, the idler gear big and idler gear small are unified into a single element so as to rotate together without any free play whereas the driven gear 403' connected to the shift drum comprises a recess 503. The driven gear 403' is beneath the star index. The unified idler gear drives the driven gear 403' which in turn drives the shift drum through pin 504 mounted on the shift drum. Here, the free play is provided in the driven gear rather than in the idler gear with the same effect as that of the first embodiment. During a partial or incomplete gearshift event (no dog to dog condition), the required rotation of the shift drum to effect change in transmission ratio is carried out entirely by the torque provided by the power source. However, during dog to dog condition, required rotation of the shift drum to effect change in transmission ratio is carried out partially by torque provided by the power source and remaining by radial force of the stopper. For a stated five speed gearbox, the recess 503 is so adjusted that first 40° of driven gear 403' is driven by the power source after which the stopper slides into the next gear region and completes the gear shift through its radial force on the star index. FIG. 6 shows good gear shifting without any improper engagement. It may be noted that all the gearshifts are carried out only when the clutch is disengaged from the engine.
[00019] From the foregoing description, it will be appreciated that the present invention offers many advantages including those described above. The proposed powered gear shift actuation system removes rigidity in the transmission system

by introducing a free play which makes the system flexible. The free play has been provided in the form of recess in the first and second embodiment and it reduces the probability of occurrence of a failed or incomplete gearshift event (dog to dog condition) while providing self-recovering capability to the system. In the prior art, improper engagement condition arose because there was no free play whereas in the present invention. Therefore the instances of improper engagement condition in the present invention are significantly reduced leading to better gear shift feel, operational efficiency and consequently customer satisfaction. During improper gear shift the system recovers within milliseconds and retries the gear shift. The present gear shift actuation system may be included within a vehicle such a motorcycle, scooter or a small vehicle.
[00020] The present subject matter is thus described. The description is not intended to be exhaustive nor is it intended to limit the invention to the precise form disclosed. It will be apparent to those skilled in the art that the disclosed embodiments may be modified in light of the above description. The embodiments described are chosen to provide an illustration of principles of the invention and its practical application to enable thereby one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore the forgoing description is to be considered exemplary, rather than limiting, and the true scope of the invention is that described in the appended claims.

We: claim:
11. A powered gear shift actuation system for an internal combustion engine for actuating the operation of change of gear comprising: a power source,
a reduction gear box connected to said power source, a set of gears supported interior to a clutch cover for transmitting rotational driving force of the said power source to a shift drum, the set of gears including an idler gear big, an idler gear small and a driven gear, characterised in that,
the idler gear big and idler gear small are separate, individual and mechanically connectable elements,
the said idler gear big comprises a recess for achieving free play in the said system during gear shift,
the said idler gear big and said idler gear small are connected by a pin whose end is mounted on idler gear small and the other end penetrates the recess in the idler gear big,
and wherein, on transmission ratio selection, the said shift drum turnably supported by a crankcase is driven by the said powered gear shift actuation system. 2. The powered gear shift actuation system as claimed in claim 1, wherein during dog to dog condition, required rotation of the shift drum to effect change in transmission ratio is carried out partially by torque provided by the power source and remaining by radial force of a stopper.

3. The powered gear shift actuation system as claimed in claim 1, wherein during no dog to dog condition, the required rotation of the shift drum to effect change in transmission ratio is carried out entirely by the torque provided by the power source.
4. The powered gear shift actuation system as claimed in claim 1, wherein the idler gear big may rotate 30 degrees to 150 degrees relative to idler gear small.
5. The powered gear shift actuation system as claimed in claim 1, wherein the recess is adjusted for free rotation of the idler gear small.
6. A powered gear shift actuation system for an internal combustion engine for actuating the operation of change of gear comprising:
a power source,
a reduction gear box connected to said power source,
a set of gears supported interior to a clutch cover for transmitting
rotational driving force of the said power source to a shift drum, the set of
gears including an idler gear big, an idler gear small and a driven gear,
characterised in that,
the said idler gear big and idler gear small are unified into a single
element,
the said driven gear comprises a recess for achieving free play in the said
system during gear shift,

the said driven gear and the said shift drum are connected by a pin whose
end is mounted on shift drum and the other end penetrates the recess in the
driven gear,
and wherein, on transmission ratio selection, the said shift drum turnably
supported by a crankcase is driven by the said powered gear shift actuation
system.
7. The powered gear shift actuation system as claimed in claim 6, wherein during dog to dog condition, required rotation of the shift drum to effect change in transmission ratio is carried out partially by torque provided by the power source and remaining by radial force of a stopper.
8. The powered gear shift actuation system as claimed in claim 6, wherein during no dog to dog condition, the required rotation of the shift drum to effect change in transmission ratio is carried out entirely by the torque provided by the power source.
9. The powered gear shift actuation system as claimed in any of the preceding claims, wherein the angular dimensions of the said recess depend on the total transmission ratio.
10. The powered gear shift actuation system as claimed in any of the preceding claims usable with a four speed, or a five speed or a six speed gearbox.