Automatic Transmission for an Internal Combustion Engine

Field of Invention

The present invention relates to "Automatic transmission for an internal combustion engine" and more particularly to single actuation system for both clutch and gear shift actuation for a single cylinder four stroke internal combustion engine.

Background of Invention

In any conventional motorcycle having a gearbox, 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 a chain drive. The gear shifting process involves disengagement of a multi-plate clutch, movement of shifter forks for changing gears and re-engagement of the multi-plate clutch. During the gear shifting, the rider needs to disengage the clutch using a hand operated clutch lever and then the gears are shifted by way of a gear shift lever operated by the rider using his foot. Hence in manual transmission, especially in heavy traffic and when the road condition is poor, frequent operation of clutch lever and gear shift lever is necessitated causing discomfort to the rider.

In order to overcome this, semi-automatic manual (SMT) transmission system has been used in the art. In Semiautomatic Manual Transmission (SMT), clutch actuation as well as movement of shifter forks for changing gears is achieved using a single mechanism. 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. During the initial few degrees of rotation of the gear shift lever, the multi-plate clutch is disengaged and the further rotation of the gear shift lever changes the gear. After this, clutch is engaged back due to action of multi-plate clutch springs. SMT system has a centrifugal clutch mounted on crankshaft.

Whenever, engine or crankshaft rotational speed is below a particular threshold value, centrifugal clutch separates multi plate clutch and gearbox. Hence, the engine does not stall. In this way, gear shift process is completed in a motorcycle having SMT. However, SMT again requires operation of gear shift pedal by the rider, which is burdensome while navigating through heavy traffic and when road conditions are poor. Consequently automatic transmission (AT) systems came into the art for ease of operation of gearshift and clutch actuation. In the art, dual motors have been used for clutch actuation and gear actuation. However, major alterations are required for adopting the motors into the vehicle, most notably crankcase alterations, etc. Hence, for same engine design and capacity, a totally new engine crankcase construction is required. This in effect increases variation and complicates overall design standardization of concerned components. Further, the number of parts is substantially increased and consequently costs would be higher and assembly time is increased. Therefore to obviate the defects in the prior art, there is a requirement for a clutch and gear actuation system that accommodates both manual transmission as well as automatic transmission without any major variation in engine assembly configuration in terms size and weight and also without much alteration in crankcase construction.

Summary of Invention

The principal objective of the present invention is to provide an arrangement for automatic transmission system that accommodates a single motor for actuating both clutch and gear shift with minimum engine assembly design alterations. The automatic transmission system as per the present invention includes a gear shift actuator system mounted on the crankcase. The gear shift actuator system comprises of a control unit, a gear shift motor, a worm wheel arrangement, a reduction gear arrangement, a spur gear arrangement and a shift position detector. Input to the control unit is given by the rider by way of a switch, which is either hand operated or is activated using a hand lever mounted in the proximity of the handlebar. The control unit can also be programmed to operate automatically based on inputs received from throttle operation and the shift position detector, which detects the position of the gear. The gear shift motor which actuates both clutch and gear shift gets its input from the control unit. Rotational force from the gear shift motor is transmitted to the worm wheel arrangement which drives the reduction gear arrangement which in turn increases the torque and reduces the rpm. The output of this reduction gear arrangement drives the spur gear arrangement, which actuates the main gear in the existing selector mechanism for gear change in the gear box. The gear shift is instigated during the final part of the rotation of gear shift motor shaft after clutch dis-engagement phase. Hence in the present invention, manual intervention through a gear shift lever is eliminated and is replaced by a single gear shift motor which performs both clutch and gear shift actuation.

The present invention, by using a single motor for both clutch and gear shift actuation, has a very compact design and brings about very minimal changes in crankcase construction. There is also very minimal new part count and therefore the system as per the present invention is highly cost efficient. Further, in addition to the mechanism as per the present invention, an over ride facility in case of system failure can be provided by way of a conventional gear shift lever.

These and other features, aspects, and advantages of the present invention will be better understood with reference to the following description, the appended claims and the accompanying drawings. This summary is not intended to limit the scope of the claimed subject matter.

Brief Description of Drawings

The above and other features, aspects, and advantages of the present invention are further illustrated by the accompanying drawings. The drawings are given by way of illustration only and are not limitative of the present invention. A brief description of the drawings is as follows:

Figure 1 shows the side view of a conventional motorcycle.

Figure 2 is a cross sectional view of the power unit of a conventional motorcycle having constant mesh type transmission.

Figure 3 is a side view of the single motor clutch and gear shift actuation system as per the present invention.

Figure 4 is a top view of the single motor clutch and gear shift actuation system as per the present invention.

Detailed Description of Invention

A motorcycle 10 as illustrated in Figure 1, includes an engine 41 a front wheel 25, a rear wheel 27, a body frame 19, a fuel tank 56. Body frame 19 includes a head pipe 12, a main tube 17, a down tube 22, and seat rails 18. The head pipe 12 is provided at the front end of body frame 19 to support a steering shaft 11 disposed within head pipe 12. The upper and lower ends of the steering shaft 11 are fixed to an upper bracket 13 and a lower bracket14 respectively. Upper bracket 13 and lower bracket 14 retain front suspensions 16 that supports front wheel 25. The front wheel 25 is connected at the lower end of the front fork 16, and the upper portion of the front wheel 25 is covered by a front fender 54 mounted to a lower portion of the front fork 16. A handlebar 15 is fixed to upper bracket 13 and can rotate to both sides. A head light 36 is arranged on an upper portion of the front fork 16. Down tube 22 is located in front of engine 41 and stretches slantingly downward from head pipe 12. A bracket 55 is provided at the lower end of down tube 22 for supporting the engine 41. Main tube 17 is located above engine 41 and stretches rearward from head pipe 12 and connects the rear of the engine 41. A vertical pipe 28 is joined to the rear end of main tube 17 and stretches upward from the point where it joins to main tube 17 to seat rails 18. Seat rails 18 are joined to main tube 17 and stretch rearward to support a seat 57 disposed above seat rails 18. A side stand 58 is arranged on lower portion of engine unit of motorcycle 10. Left and right rear arm bracket portions support a rear arm 26 to swing vertically, and a rear wheel 27 is connected to rear end of the rear arm 26. A rear wheel suspension 34 is arranged between rear arms 26. A tail light unit 64 is disposed on the rear cover 61. A pillion footrest 31 is connected to the vertical pipe 28. A grab rail 62 is also provided on the rear of the seat rails 18. Rear wheel 27 is arranged below seat and rotates by the driving force of engine transmitted through the transmission system.

The transmission system is a constant mesh type transmission (Figure 2). Power of the power unit is transmitted from the crankshaft through a clutch c, and then through the transmission system and further through a counter shaft g projecting from the rear portion of the crankcase. A main shaft d and a counter shaft g are rotatably supported by the crankcase and are provided with a plurality of paired constant mesh type gears e&f. The mesh type gears on the main shaft d and the counter shaft g are either relatively non-rotatably mounted or rotatably mounted. In shifting the transmission gears a shifting mechanism including a gear shift pedal, a gear shift arm i, shift pins j, a shift drum k and gear shift forks m and a shifter splined with one shaft is axially moved toward the rotatable transmission gear on that shaft so that the rotatable transmission gear is integrated to that shaft. Further the integrated transmission gear is meshed with the corresponding transmission gear on the other shaft and accordingly counter shaft g is rotated relative to the main shaft d at a speed determined by the gear ratio between the transmission gears. One end of the counter shaft g in the rear portion of the crank case projects outwardly from the crank case. A rear wheel drive sprocket h is attached to this end of the counter shaft g. The rear wheel 27 is drivingly rotated by the rear wheel drive chain wound between the rear wheel drive sprocket h and the rear wheel driven sprocket attached to the rear axle.

In the present invention, in addition to the conventional multi-plate clutch, there is a centrifugal clutch, which is mounted to the crankshaft. The centrifugal clutch will always be in engaged condition when engine speed is high. When the engine speed becomes less than a selected threshold speed, the centrifugal clutch is disengaged thereby disconnecting transmission of power from engine to the gearbox.
Referring to Figures 3 and 4, the single actuation system for clutch and gear shift actuation as per the present invention has a multi step gear shift mechanism and includes a gear shift actuator system mounted on the crankcase. The gearshift actuator system comprises of a control unit (kept below the rider's seat; Not shown in the figures), a gear shift motor 100, a power transmission mechanism and a shift position detector 104 which detects the position of the gear. The power transmission mechanism comprises of a worm wheel arrangement 101, a gear reduction box 102 and a spur gear arrangement 103. The control unit is manually operated by the rider using a switch, which is either hand operated or is activated by a hand-lever mounted in the proximity of the handlebar. The control unit can also be programmed to work automatically based on throttle operation and inputs from the shift position detector. The gear shift motor 100 receives its input from the control unit. Rotary motion provided by the gear shift motor 100 is transferred by the worm wheel arrangement 101 to the gears in the gear reduction box 102 resulting in increase of torque and decrease of rpm. The output of the gear reduction box drives a spur gear arrangement 103, which actuates the main gear in the existing selector mechanism for gear change in the gearbox.

Therefore using the above described configuration, manual intervention for actuation of clutch and gear shift is avoided and automation of the same is achieved by way of the gear shift actuator system. The gear shift motor 100 replaces the gear shift lever used in conventional motorcycles. In the present invention, gear shift is instigated after clutch disengagement phase during the final part of the rotation of gear shift motor shaft. The clutch disengagement happens during the initial rotation of the gear shift motor shaft. The worm wheel arrangement 101 has been included so that the drive provided by the gear shift motor 100 can be turned by 90° thereby resulting in better packaging since the gear shift motor 100 can be arranged perpendicular to the gear reduction box 102. The gear shift motor 100 is mounted externally to the transmission cover and is sealed against any ingress of oil. In the above configurations, the motor used could be 12V DC motor with around 1:32 gear ratio for the gear shift actuator system. Fail safe mechanism in case of actuator system failure is also provided in addition to thermal stability provisions so that the system works equally well in cold and also in high temperature environment.

We Claim:

1. A four-stroke internal combustion engine having a single actuation system for both clutch and gear shift actuation, the said single actuation system comprises a multi-step gear shift mechanism wherein a gear shift actuator system is mounted on the crankcase as viewed from the side.

2. The four-stroke internal combustion engine as claimed in claim 1, wherein the said gear shift actuator system comprises:

a shift position detector which detects the position of the gear;

a control unit which receives the input from the shift position detector;

a gear shift motor which receives input from the control unit; and

a power transmission mechanism which receives the rotational driving force from the gear shift motor.

3. The power transmission mechanism as claimed in claim 2, comprising:

a worm wheel arrangement;

a gear reduction box having a plurality of reduction gears that reduces the rotational speed provided by the gear shift motor; and

a spur gear arrangement connected to the gear reduction box.

3. A four-stroke internal combustion engine having a single actuation system for both clutch and gear shift actuation, as hereinabove described in the specification with the accompanying drawings.