FIELD OF INVENTION

The present disclosure relates to "Automated manual transmission system for a motorcycle" and in particular relates to use of an automated manual transmission for carrying out gear-shift in a motorcycle having a vertically mounted engine.

BACKGROUND

In any conventional motorcycle having a gear box, power transmission from the crankshaft to a drive shaft and finally to the wheel is achieved through a clutch and a series of reduction gears and chain drive. The gear shifting process involves disengagonent of wet, multi-plate clutch, movement of shifter forks for changing gears and engagement of wet, multi-plate clutch. During the gear shifting, the rider needs to disengage the clutch by hand operated clutch lever. Hence in the manual transmission frequent operation of clutch lever and gear shift is necessitated by the rider causing discomfort especially under city traffic condition. In order to overcome this, semi¬automatic manual (SMT) transmission system is used. In Semiautomatic Manual Transmission (SMT), wet clutch actuation as well as movement of shifter forks for changing gears is achieved using single mechanism. Additionally, SMT also includes a centrifugal clutch. In a SMT system, foot lever is used by the rider to shift gear. Once the rider has pressed the gear shift lever the multi plate clutch is disengaged. Same gear-shift mechanism subsequently rotates the gear shift drum provided with radial helical grooves to which the shifting forks top end is engaged. When the drum rotates the groove position changes the position of gear shifting fork engaged with gears and hence, shifts the gear. After this, clutch is engaged back due to wet multi-plate clutch springs. SMT system also has centrifugal clutch mounted on crankshaft. Whenever, engine or crankshaft rotational speed is below a particular threshold value, centrifugal clutch separates wet multi plate clutch and gear-box. Hence, engine does not stall. Thus, gear shift process is complete in SMT of a motor cycle. Hence use of SMT system eliminates the need for frequent operation of clutch lever (since the lever is redundant) under urban driving conditions. This gives an advantage over the manually operated clutch / gear shifting system. But however, such SMT system is predominately used in step through motorcycles incorporating horizontally mounted engines. Such steps through vehicles are defined by having a step through space between the handle bar and the seat. (Refer Fig 1).

Use of SMT system in motorcycles with nearly vertically mounted system in unheard of This is due to instability especially during acceleration from the first gear in SMT motorcycle having vertically mounted engine. Motorcycles having vertically mounted engines are preferred by majority of Indian customers owing to their rugged appeal and aesthetics. Customers prefer these motorcycles for the following reasons inter alia. Comfortable seating and riding posture having the legs hugged on the side of fuel tank thus reducing the overall fatigue; Better maneuverability over high speeds owing to longer wheel base and wider tires.

However the customers using these of vehicles are denied of the convenience of SMT system due the above said problem of instability during acceleration from the first gear. Hence there is a need to address this problem so that user of such motorcycle gets the benefit of the SMT system.

SUMMARY OF THE INVENTION

The present disclosure relates to a semi automatic clutch transmission system for a motorcycle particularly for engines having cubic capacity from 90 to 125, having its fuel tank mounted between the handle bar and the seat incorporating a nearly vertically mounted single/multiple cylinder engine with reference to ground. The cylinder block axis of the said engine with respect to the ground plane is inclined in an angle of 55 deg to 90 deg. A starter motor is mounted ahead of crankshaft of the said engine with its axis located substantially below the axis of crankshaft so as to move the CG of the motorcycle a little forward. The overall transmission ratio of first gear to rear wheel outer diameter of the said engine of the said motor cycle is modified such that it is in the range of 50 to 60 times the overall wheel diameter including tire (in meters) so as to ensure minimal slip
and smooth synchronisation of the first gear and centrifugal clutch of the said semi automatic clutch transmission system of the said engine during gear shift.

BRIEF DESCRIPTION OF DRAWING ACCOMPANYING THE PROVISIONAL SPECIFICATION

Fig.1 illustrates a conventional view of Two-wheeled vehicle;

Fig. 2 illustrates a perspective side view of a SMT step-through two-wheeled vehicle;

Fig. 3 illustrates the working of a gear shifting mechanism in a conventional SMT step- through vehicle;

Fig. 4 illustrates a centrifugal clutch is mounted on a crankshaft;

Fig. 5 illustrates the sectional view of Engine with manually activated secondary clutch; and

Fig. 6 illustrates the sectional view of Engine with automatic clutch on crankshaft.

DETAILED DESCRIPTION OF THE INVENTION

Any known motorcycle (straddle type) can be divided into three major portions, the front portion F, the middle portion M and the rear/tail portion R. The front portion F comprises of the steering, front wheel 1 with necessary brakes, front suspension and fender, the middle portion M comprises of the handle bar 7, fuel tank 8, rider seat 9, foot rest for both the rider and the pillion member, starter motor 3, engine 4, chain wheel drive 5, gear shift lever, stand etc and the rear/tail portion R comprises of back wheel 2, chain wheel driven 6 with necessary suspension and rear fender. In such a motorcycle, the use of Semi automatic transmission is used only with horizontally placed engines and the use of the same in motorcycles having nearly vertically mounted engines is not known.

Fig. 2 shows a perspective side view of a SMT step-through two-wheeled vehicle 10, interchangeably referred to as SMT vehicle 10 hereinafter. Among other components, the SMT vehicle 10 as shown includes a body mounted on two tires 1 and 2, a gear-shift lever 11, and a handlebar 7, which is usually located just above the fuel tank 8. The left foot movement of a rider riding the vehicle 10 in order to shift gear ratio operates the gearshift lever 11 in absence of any hand operated lever. In order to change gears, the rider releases a throttle grip (not shown in the figure), which is usually present on a right- hand side of the handlebar 7, as seen from the rider's perspective, and pushes an end of the gear-shift lever (see Fig. 3) fix)m his or her left foot in downwards direction. The end of the gear-shift lever to be pushed to get the desired gear ratio or a transmission equivalent to the gear ratio depends on the make of the vehicle 10 and may vary from one vehicle to another.

Fig. 3 shows the working of a gear shifting lever 11 in a conventional SMT step-through vehicle 10 shown in Fig.2. The release of the throttle grip and a subsequent push at either ends of the gear-shift lever arm 12 mounted on the gear shift shaft 13 in a downward direction actuates a gear shift mechanism 15. The gear shift mechanism 15 first disengages a multi-plate clutch 14 and moves gear shifting forks (not shown in the figure), which are housed inside a crankcase housing of an internal combustion (IC) engine of the vehicle 10, to shift a gear. The multi-plate clutch is engaged back to its normal position once a gear is shifted due to the multi-plate clutch springs 16. In this way, a gear or gear ratio is shifted or changed, thus providing a transmission ratio required for the vehicle at an instance.

This type of transmission system also includes a centrifugal clutch. The centrifugal clutch uses centrifugal force to connect two concentric shafts, the drive shaft nested inside a driven shaft. As shown in Fig. 4, which indicates the cross sectional view of the gear box 17. The gear box 18 has a centrifugal clutch 19, which is mounted on a crankshaft 20. When the centrifugal clutch 19 mounted on the crankshaft 20 reaches a certain RPM (revolutions per minute), the centrifugal clutch 19 engages to centrifugal clutch drum 21 which is connected to the gear primary drive 22 and gets connected to the gear primary driven 23. In addition, whenever the rotational speed of the crankshaft 20 is below a particular threshold value, the centrifugal clutch 19 separates the wet multi-plate clutch 14 and the gear-box 18 so that the engine does not stall.

In conventional motorcycles with vertical engines a centrifugal oil filter 27 is mounted on the crankshaft 20 beyond primary driven gear 22 to supply clean oil to big end bearing of connecting rod (not indicated). Where as in the SMT type of transmission, a centrifugal clutch that is mounted on the crankshaft 20 houses a centrifugal oil filter 27 which supplies clean oil to the connecting rod big end bearing (not indicated).

The gear primary driven 22 is directly connected to crankshaft 20 in conventional gear box, where as it is connected to clutch drum 21 directly in SMT transmission. When ever the engine is started the gear primary drive 23 fitted on crankshaft 20 starts rotating the gear primary driven 23 connected to manually actuated clutch 14 being disengaged by forward movement of clutch actuator 25 connected to clutch actuating lever (not shown) mounted on clutch cover 24 fitted on drive shaft 26. In conventional gear shifting the rider has to depress the clutch operating lever fitted on handle bar to disengage the manually actuated clutch 14. The rider then needs to operate the gear shift lever 11 which in turn rotates the shifter drum (not shown) connected to shifter forks engaged with a set of gears fitted on drive shaft 26 engages with another set of gears fitted on driven shaft (not indicated) to effect different gear ratios based on gear shift fork position (not indicated). The first gear set 28 and 29 are shown as an illustration for having different member of teeth engaged to each other. The drive sprocket 30 fitted on driven shaft 26 is connected to chain wheel fitted on rear wheel.

This arrangement of SMT on the said motorcycle therefore alienates the use of hand operated clutch lever while riding and therefore reduces the fatigue experienced by the rider considerably. Further it reduces the material cost owing to absence separate clutch lever & cables

We Claim:

1. An automated manual transmission system for a straddle type motor cycle having vertically mounted engine/s with fuel tank between the handle bar and the seat base comprising a gear shift mechanism connected to the gear shift lever, said lever capable of actuating a centrifugal clutch which houses a centrifugal oil filter, a gear primary driven being connected to clutch drum, a starter motor located substantially below the axis of the crankshaft, the transmission ratio of first gear to rear wheel outer diameter of the said motorcycle being set in the range of 50-60 times the overall wheel diameter of the wheel (including tire).

2. An automated manual transmission system as claimed in claim 1, wherein primary gear drive fitted on the said crankshaft includes the gear primary driven connected to a manually actuated clutch.

3. An automated manual transmission system as claimed in claim 1, wherein the clutch drum comprises of a clutch cover which is fitted on the drive shaft, said clutch cover houses a clutch actuating lever and a clutch actuator.

4. An automated manual transmission system as claimed in claim 3, wherein the clutch actuation is performed by either forward or backward motion of the gearshift lever.

5. A straddle type motor cycle having vertically mounted engine/s with fuel tank between the handle bar and the seat base including an automated manual transmission system comprising a gear shift mechanism connected to the gear shift lever, said lever capable of actuating a centrifugal clutch which houses a centrifugal oil filter, a gear primary driven being connected to clutch drum, a starter motor located substantially below the axis of the crankshaft, the transmission ratio of first gear to rear wheel outer diameter of the said motorcycle being set in the range of 50-60 times the overall wheel diameter of the wheel (including tire).

6. A straddle type motorcycle as claimed in claim 5, wherein a primary gear drive fitted on the said crankshaft includes the gear primary driven connected to a manually actuated clutch.

7. A straddle type motorcycle as claimed in claim 5, wherein the clutch drum comprises of a clutch cover which is fitted on the drive shaft, said clutch cover houses a clutch actuating lever and a clutch actuator.

8. A straddle type motorcycle as claimed in claim 7, wherein the clutch actuation is performed by either forward or backward motion of the gearshift lever.