This invention relates to an automated manual transmission system, for example for automotive vehicles, for example motorcycle or other vehicle. The automated manual transmission system may be used in combination with a prime mover which may, for example, be in form of an internal combustion engine or an electric motor.

Two wheelers, three wheelers and four wheeler vehicles, of small engine capacity, are commonly used for commuting in cities and urban areas. Such vehicles are an affordable mode of transportation due to the advantage of fuel efficiency.

Reducing the size and weight of such a vehicle, and its prime mover (whether internal combustion engine or electric motor), has real advantages from the perspectives of reducing capital cost and improving fuel economy. Size/weight reduction can also be relevant to emission performance. The challenge is to reduce size and weight of the vehicle, and particularly its, power train as far as possible. An essential but typically bulky component of a power train (i.e. combination of prime mover and drive train) for a vehicle is the transmission system which is subject to rigorous operation during commuting in dense traffic conditions.

The transmission system transmits motive force, in a controlled manner, through a pathway from rotating crankshaft to driving wheel(s) of the vehicle at a gearing ratio selected, through a gear shifting mechanism, for the motorcycle operating conditions. Transmissions may be automatic (which use fluid type torque converters instead of a clutch), semiautomatic, automated manual or manual. Automatic or automated manual transmissions (AMT transmissions) have advantages for vehicle control because the rider does not need to frequently operate the gear shifting mechanism, a potentially fatigue inducing task. Such automatic or automated transmissions allow the vehicle to be operated by an electronic control unit with a particular .operating strategy, ideally optimized over the operating strategy a competent operator would use. In this regard, automatic transmissions suffer from efficiency losses due to the use of the fluid coupling. Known automated manual transmissions, whilst retaining the efficiency of manual transmissions, require complex componentry and control systems to control clutch engagement/disengagement and gear shifting. It would be desirable to reduce the cost and complexity of an automated manual transmission.

Furthermore, automated manual transmissions (and other transmission systems for that matter) typically include synchromesh gear shifting which smoothes gear shifting and increases probability of gear shifting up to 100% but at the added cost of complex and costly synchromesh components requiring more space than a clash mesh type transmission system. Comparative design calculations show that employing a synchromesh system would require increase in center distance (between input and out shaft) at least by 20 % and approximately doubled length of the shafts between the bearing supports. For example, calculations done for a 150cc engine having 5 speed gear ratios show that length of shaft between the bearing support required in clash mesh type gear box is 82 mm while the equivalent synchromesh gear system with 5 speed gear ratios requires shaft length of 180 mm. Thus use of synchromesh type system consumes more weight and space.

Also typically included in automated manual transmission systems are components such as a separate electronically controlled manual clutch or similar controlling mechanism. Such devices consume space and add cost and challenge efficient control over operation because synchronization of the operation of manual clutch device with automated gear shifting is a complex phenomenon. Complexity in synchronization also leads to problems with jerkiness on gear shift and addressing such jerkiness remains an ongoing concern.

Where an AMT clutch actuation system uses a conventional plate type clutch, a bulky clutch mechanism, a complex control strategy is required to enable satisfactory completion of gear shifting, especially during initial take off and during down shifting. During initial take off, it is important to correctly and simultaneously maneuver clutch, accelerator control and gear shift mechanism depending on the inertial load so that there is no stalling or over revving of the engine. Only in this way can smooth takeoff be achieved. This requirement necessitates a very complex feedback and control system to achieve smooth take off. Such control challenge is further compounded by individual rider habits when using the accelerator control.

Similarly, during down shifting, after completing gear shifting, the requirement for re-engagement of the clutch differs depending on specific gear ratios and vehicle speed. This requires a complex and precise clutch actuation control strategy.

The above requirements put a heavy demand on the clutch actuation system and make this a very complex and hence expensive system.

It is an object of the present invention to provide an automated manual transmission system for a vehicle that is less bulky, less complex and more compact than currently available transmission systems.

It is a further object of the present invention to provide a less expensive automated manual transmission system.

It is a still further object of the present invention to provide an automated manual transmission system significantly less prone to jerks and gear shifting problems.

With this object in view, the present invention provides an automated manual transmission system for a vehicle comprising a prime mover engageable with, and disengageable from, a clash mesh type transmission system comprising a plurality of gears; a transmission control unit; and a gear shifting mechanism controlled by the transmission control unit to shift transmission gear during a gear shift phase wherein said transmission system and prime mover are engageable and disengageable by a self-actuating clutch system during said gear shift phase.

The present automated manual transmission system avoids requirement for a clutch actuating mechanism, operable by operator or by any controlling mechanism of the transmission system. This saves space and makes the transmission system more compact. Engine weight and cost may thereby be reduced.

The self-actuating clutch system must comprise one or more self-actuating clutches. The specific types of self actuation clutch and their use at specific locations in the drive or power train, or the motive force pathway from prime mover to vehicle wheels, provides transmission system simplification consistent with the object of the present invention. Advantageously, in a present transmission system having prime mover as an IC engine, one of the self actuating clutches is centrifugal clutch mounted on, connected to or optionally formed integral with, the engine crankshaft. The centrifugal clutch located on prime mover shaft and engagable to transmission system after achieving a threshold speed (RPM) of prime mover shaft .Yet another self-actuating clutch used in the motive force pathway, advantageously is a one way clutch located to automatically engage a prime mover drive shaft with input and output shafts of a transmission system, when drive is required, by meshing selected correspondent gears on each of the input and output shafts. The employment of above explained self actuating clutch system does not require use of conventional plate clutch/s and its actuation means & complex strategies associated with it which are being used in known AMTs. Further, this self clutch actuating clutch system facilitates smooth gear shifting operations as explained in specification below. The one way clutch is always in automatically engaged condition during torque transmission from prime mover drive shaft to input shaft but automatically disengaged at other times. Use of a one-way clutch assists in making the transmission system more compact. In general, an input shaft of a transmission system is mounted with many components. A conventional plate clutch and its actuating elements have-significant width (and weight) and set a constraint on input shaft length which must be sufficient to bear the clutch. For example, for a 150 cc engine with a 5 speed AMT transmission system, additional packaging space of 33 mm along the axis of the input shaft would be required for accommodating a conventional plate clutch and its actuating mechanism and controls. These factors would increase the size of the transmission system as well as its weight by approximately 250 grams. Use of a one way clutch reduces the constraint on input shaft length reducing it in comparison with conventional automated manual transmission systems.

The centrifugal clutch is operable by centrifugal force to engage the input shaft as engine speed increases, above a threshold speed, after cranking through rider actuation of accelerator/throttle. The centrifugal clutch therefore provides takeoff torque and allows an engine idle speed to be maintained irrespective of whether input and output shafts are linked. The centrifugal clutch therefore acts as an anti-engine stalling device. To that end, the centrifugal clutch should remain engaged at all times whilst engine rpm is equal or above threshold value and the vehicle is in motion in a selected gear ratio. This precludes requirement for a clutch actuation mechanism and complex control strategy during initial take off.

During subsequent gear shift, while the centrifugal clutch remains in engaged condition as long as engine speed remains above a threshold speed value and when the torque flow is reversed from output shaft to input shaft (achieved by reduction in prime mover drive shaft torque by the transmission control unit), the one way clutch gets disengaged, thereby facilitating smooth gear shift by the gear shift mechanism with respect to predefined operating strategy. During down shift, as there is no connection between input shaft and prime mover drive shaft (due to disengagement of the one way clutch), there is no impact on engine speed and down shift can be smooth without need for complex control apparatus and strategy. This also helps in reducing the gear shift noise of synchronization of respective gear as there no clutch drag , the basic inertia of a one way clutch being significantly less than for a comparable conventional plate clutch.

Use of a centrifugal clutch as one of the self-actuating clutch also assists in making the transmission system more compact. Centrifugal clutches normally have less width or dimension in axial direction than manual clutch mechanisms or systems. Torque capacity is selected to minimize the size of the centrifugal clutch and reduce slip times. Vehicle gross vehicle weight is also in the range where a low capacity centrifugal clutch can be usefully adopted. Further placement of the centrifugal clutch in the overall vehicle layout is done in a manner requiring a minimum of the drive-train torque to be transmitted through it. As the minimum torque axis also has the highest rotational speed (rpm) giving the required centrifugal force with minimum weight, both factors greatly assisting reduction of torque, keeping the size and inertia of the centrifugal clutch low and allowing quick engagement/take-off characteristics.

A low torque requirement also allows a wet centrifugal clutch to be used. While wet clutches have considerably lower capacity than a comparable dry clutch (due to lower coefficient of friction), usable life is superior due to better heat dissipation. Clutch life may be further improved by providing a continuous oil flow through the clutch by providing oil jets, such oil jets preferably being of optimized size and being provided at optimized locations.

The centrifugal clutch shoes may be provided with grooves, ideally arranged in the direction of rotation of the clutch and perpendicular to the direction of clutch rotation. This improves oil flow rate through the shoes of the centrifugal clutch. These features improve heat dissipation, reducing the wear of the frictional material, thereby improving clutch life. Such wear would be a particular concern on rider take off at higher gears (for example, 3rd, 4th and 5th gears in a 5 speed transmission system). This situation could occur in a limp home or comparable problematic situation.

Use of a clash mesh type transmission system also reduces engine weight and cost. In a clash mesh shifting gearbox, dog clutches are typically used for engaging and disengaging gears. One of the fixed or freewheeling gears has male lugs/projections while a corresponding gear carries female kidneys/slots. Lugs and slots are intended to engage on gear engagement. When gear shifting, the male lugs must enter the female slots in order to lock the fixed and freewheeling gears together and thus complete the gear shift phase. However, there is always non-trivial probability that the male lug would collide/clash with the kidney wall. In such a scenario, the gear shift phase would not occur and the operator would have to overcome the clash by force modulation (for example holding foot on clutch for a period of time) or reattempting the gear shift phase in case of manually operated transmission system.

Such an approach is, intentionally, not possible with the presently described automated manual transmission system being the gear shifting decided by a predefined operating strategy and gear shifting operation achieved by gear shift actuating means such as an shifter motor. A human operator cannot address issues with clashing of gears in any meaningful way. Further, the automated nature of the transmission system means that gear shift occurs on average four times faster than in a manual transmission system. Human operator intervention, even if made possible, could not be effective. In event of a clash of gears, the shifting motor reacts to a mechanical lock condition and applies higher torque (up to stall torque of the shifting motor) which may lead to the speed synchronization of the fixed and freewheeling gears in the clash state ( i.e. dog clutch is not engaged with its correspondent slot). As the speed differential between the two gears falls, the possibility of overcoming the clash zone reduces significantly. This leads to problems such as increased gear shift times and, less commonly, full speed synchronization and inability to shift gear.

The Applicant has found that such problems can be overcome by use of a, clash relieving device, located between the shifting motor and the gear shifting drum. This clash relieving device controls torque magnitudes resulting from clashing of gears and avoids clashing gear speed synchronization which otherwise will result in a failed attempt to shift gear. Relative speed of the fixed and freewheeling gears is prevented such that probability of gear shifting is maximized, as closely to 100% as possible.

The clash relieving device forms a further aspect of the invention. In this aspect of the invention, there is provided a gear shifting mechanism for an automated manual transmission system having a clash mesh shifting gearbox comprising an input shaft; an output shaft; a gear shift mechanism for engaging corresponding gears respectively located on said input shaft and said output shaft ; and a shifting motor having a drive shaft for driving the gear shift wherein said drive shaft further transmits torque to the gear shift through an intermediate shaft bearing a clash relieving device operative when torque delivered by said shifting motor exceeds a predetermined value to control relative speed of engaging elements of said correspondent gears during clash conditions. The clash relieving device acts in such a way that it allows relative rotational motion (or lost motion) between shifting motor drive shaft and the intermediate shaft when the torque output of shifting motor is above a preset threshold. The clash relieving device provides sufficient time to shift the gear in clash condition.

A preferred clash relieving device comprises an intermediate shaft located for transmitting torque between said gear drum shifter drive shaft and said gear drum shifter wherein said intermediate shaft is provided with a drive cam mounted freely on said shaft and a cam driven operatively and slidably connected to said intermediate shaft and biased into engagement with said drive cam by a spring, said spring having a preload determining a torque value at which said clash relieving device is actuated and above which said cam drive and cam driven disengage.

The problem of clash is overcome by the clash relieving device as follows:

1. The clash relieving device holds the lugs to ensure that the specific kidney angle
required for engagement is achieved.

2. If desired engagement does not happen, then the clash relieving device
momentarily but completely disconnects the torque transmission of the shifting motor from
the shifting drum due to disengagement of cam drive and cam driven against spring force.

3. The spring force pushes the cam driven to engage with the cam drive, causing a
reverse rotation of the gear shift drum. This results in momentary disconnection of lug and
kidney facilitating a relative speed difference between lug and kidney, relieving the no go
clash condition and engaging a lug with correspondent kidney slots.

Conveniently, the engaging elements of gear shift mechanism comprise two complementary components. One component comprises lugs as engaging elements. Complementary slots or kidneys (being kidney shaped slots) are provided on the other component. Engagement of these lugs and kidneys enables torque to be transferred for a selected gear ratio or till the time the engine speed drops below the threshold value of clutch engagement speed.

Where clash occurs, during gear shifting, position of the lug and kidney slot do not perfectly match and the selected gear is not engaged. Such probability is higher for engagement of lower gear ratio (for example 4th and 5th gears) than for engagement of lower gear ratio (for example 1st and 2nd gears) since the relative speed between the lower gears is less. To improve upon the probability of engagement of lug and kidney a 2x2 lug (i.e. two numbers of lugs and corresponding two numbers of kidneys) and kidney arrangement is conveniently provided. Use of this lug and kidney arrangement may improve probability of gear shifting above 70%. However, the 2x2 arrangement may not be required for all gears rather being selected for particular gear ratios, that is lower gear ratios, where clashing is more likely.

Circumferential clearances between lugs and corresponding slots (kidneys) may be increased to more than about 40 degrees (refer clearance angles A and B in figure 5) in contrast to conventional clash mesh type transmissions where circumferential clearance is restricted to reduce lug/kidney impact noise during sudden power transfer direction changes and/or during engagement phases. This is not an issue where a one way clutch is used as in advantageous embodiments of the invention. The increased circumferential clearance significantly improves probability of lug and kidney engagement.

Engagement and disengagement of the self-actuating clutch, for example the above described one way clutch, is automatic or self-regulating. Actuation of a one-way clutch would be dependent on relation between prime mover speed (RPM) and vehicle wheel speed, vehicle driving wheel(s) being provided with motive force, when the vehicle is "in gear", by the output shaft. When the speed on the prime mover side of the one way clutch is greater than the speed on wheel side of the clutch, the one way clutch automatically links or engages the prime mover drive shaft to input shaft which in turn transmits input shaft torque to the output shaft through the selected gear train. However, the converse is not true. When prime mover side speed is less than vehicle wheel side speed, such as in an "over-run condition" but here not limited to this, the input shaft is automatically de-linked or disengaged from the drive shaft. Thus a reverse torque from wheel rotation is not transmitted to the drive shaft or prime mover.

Disengagement or de-linking of input and drive shafts allows an opportunity for a gear shift to occur. When the transmission control unit determines requirement for a gear shift, the prime mover - whether internal combustion engine or electric motor - is controlled by the prime mover control unit to reduce or stop its drive shaft speed by air fuel control and/or prevention or retardation of spark plug firing (internal combustion engine) or shut off of electric current (electric motor). In the case of an internal combustion engine, the engine control unit reduces torque output.

The transmission control unit may, for example reduce, or, more preferably stop, air fuel supply to the engine during a gear shift phase (for example through use of the fuel shut off device described in the Applicant's co-pending 3740/CHE/2011 filed 1st November 2011, the contents of which are hereby incorporated herein by reference. This is desirable to perform smooth gear shifting and promote fuel economy and avoid hydrocarbon emissions caused by unnecessary combustion events during a gear shift phase. An alternative strategy would be to prevent spark plug firing during a gear shift phase. Such prevention of spark plug firing may be controlled by the engine control unit. Further adaptation combining both air/fuel mixture cut off and prevention of spark firing may also be used.

By way of further background information, the fundamental operating principle of one-way clutches is well known to those skilled in the art and this specification is not intended to be a primer on such. However, in one common form, relative rotation of inner and outer elements or races is prevented in one direction, enabling the transmission of torque across the clutch, while inner and outer elements or races can overrun or freewheel in the opposite direction. The most common one-way clutch types are:

(1) Ratchet one-way clutch
(2) Roller one-way clutch
(3) Cam or sprag one-way clutch

One-way clutches of type (2) or (3) are actuated in radial direction, not axial direction. When the inner or outer race begins to rotate in a determined direction relative to one another, the rolling elements are wedged between an outer periphery of the inner race and an inner surface of the outer race such that both races are engaged together to rotate together and are able to transmit a torque. Conversely, when the inner or outer race rotates in the opposite direction to the determined direction relative to one another, the rolling elements disengage from the wedged position such that the inner and outer races do not transmit a torque there between. It is to be understood that the above information is by way of background information only and that the invention herein is not to be limited to any particular type of one-way clutch or a one-way clutch at all though such a clutch is most conveniently to be adopted.

During linking and de-linking of prime mover and transmission system through the one way clutch, the clutch is subject to shock and wear as operation is frequent. This would tend to reduce one way clutch service life if not compensated for. Frequent 'on' and 'off of the one way clutch, being used in the drive train to directly drive (and engage/disengage) the wheel through the engine, leads to high torque fluctuations on the clutch. These fluctuations are highly detrimental to clutch life and require significant increase in the size and cost of the clutch. Advantageously, the one way clutch comprises a dampening mechanism to reduce shock on engagement and disengagement of said one way clutch, said dampening mechanism preferably including a biased damping means with a plurality of damping rates achieved by using springs and an elastic dampening material. Conveniently, a plurality of pre-compressed springs provides initial dampening and a dampening material (such as rubber or like polymer) provides further damping of shock during one way clutch engagement.

The dampening mechanism comprises an input shaft comprising a primary driven gear provided with a plurality of slots, said driven gear being connected to a housing provided with a plurality of lugs engageable with said slots of the primary driven gear. The housing is freely rotatable on the input shaft, being rotatably connected to a flange of the one way clutch through a plurality of one way clutch sprags (or like means). The flange is rigidly fixed (optionally through splines) to the input shaft. The sprags are shaped and positioned to be placed between said one way clutch flange and said housing to allow rotation of said housing in one direction.

The lugs are fitted with a dampening material which acts to reduce shock when the lugs engage with slots of the primary driven gear on engagement of the one way clutch. The primary driven gear is covered by a cover plate from the opposite side of the housing. The lugs and correspondent dampening material are positioned in a biased location substantially in the direction of power transfer from prime mover to wheel in said slots of said primary driven gear, being fixed in position with suitable fixing means (such as rivets) which connect cover plate, dampening material and housing. By substantially in biased direction is meant, for example, 90% towards power transfer direction from prime mover to wheel.

Advantageously, remaining slots of the primary driven gear are provided with pre-compressed springs and the cover plate is provided with a plurality of pairs of arms which are positioned in said slots at both ends of each pre-compressed spring.

The torque transmitted by the primary driven gear is transmitted to the housing and then to the one way clutch flange through the sprags. Subsequently, the flange transmits the torque to the input shaft.

The dampening mechanism, as above described, provides dampening when torque from the primary driven gear is transmitted to said cover plate and housing, the torque or thrust being firstly absorbed or dampened by the plurality of pre-compressed springs and then by the dampening material. For example, dampening may be greater than about 12 degrees of rotation (or deflection angle) of the primary driven gear. The dampening through dampening material and springs acting in combination provides sufficient time to lock all sprags for transmission of torque, causing less wear and tear and improving the life of the one way clutch. The Applicant has tested the one way clutch for accelerated durability cycles, reflecting likely operating conditions, without damage or abnormal wear being observed.

The automated manual transmission system may be used with vehicles using either electric motor or internal combustion engine as prime mover. One of the self-actuating clutch i.e. centrifugal clutch is not required where the prime mover is an electric motor with zero speed torque capability, notably at idle. Where an electric motor is the prime mover, the transmission system, and typically an input shaft thereof, may be directly linked to the electric motor drive shaft.

Advantageously, the prime mover drive shaft, drive gear, driven gear, input shaft and output shaft are arranged with axes parallel. In case where the prime mover is IC engine, the engine and transmission elements are accommodated in a single engine casing. This increases in the size of the transmission system in comparison with the transmission system described here.

The gear shifting mechanism is conveniently a drum shifter mechanism of type often used for motorcycles. However, a drum shifter transmission could be used for three and four wheeler vehicles as well as two wheeler vehicles. The drum shifter has cam grooves formed in an outer peripheral surface and shift forks mounted on a shift for sliding movement in the groove, to this end the ends of the shift forks being received in the cam grooves.

When operating the automated manual transmission, operation of the gear shift is controlled by the transmission control unit, not the vehicle operator, to rotate or index the drum shifter to shift gear. The transmission control unit actuates an actuation device, conveniently in the form of an electric shifting motor, to rotate the drum shift. In such manner, the rotation of a prime mover drive shaft is transmitted to the output shaft at a selected gear or transmission ratio. As many gears or transmission ratios may be provided, as desired, without compromising the objective of providing a compact transmission system.

Therefore, three, four or five or more gears (including reverse gear if desired) may be employed. The drum shifter may be operated by the shifting motor under control of the transmission control unit in such a way that the gears are selected in a rising or descending sequence with respect to a predefined control strategy.

Advantageously, the gear shift mechanism also has its components including drum shift, electric motor to drive the drum shifter and corresponding gears arranged with axes parallel. In case where the prime mover is IC engine, the engine and transmission elements are accommodated in a single engine casing . This avoids increases in the size of the transmission system in comparison with the transmission system described here.

In addition, the electric motor to drive the drum shifter is conveniently located, and can be accommodated, on the engine crankcase proximate to the starter motor. An alternative mounting location on the crankcase would likely require an increased crankcase size, making the overall engine and transmission system less compact.

The automated manual transmission system may be used in combination with any vehicle prime mover such as an internal combustion engine or electric motor. The engine may be fuel injected or carbureted. In a preferred embodiment, the engine may be a gas fuelled engine using a fuel such as CNG or LPG. In such case, the fuel metering device is a mixer which operates on similar principle to a carburetor. Other above described constructional details of the invention would be the same. It will be understood that the engine could also be dual fuelled.

The cylinder head of a spark ignited internal combustion engine includes ignition means, preferably a plurality of ignition means, in the form of spark plugs. Use of dual spark plugs, in accordance with the applicant's DTSi technology, provides particular benefits of fuel economy and lowered hydrocarbon and CO emissions during engine operation, particularly for an engine operated in a lean burn combustion mode. Ignition timing may also be controlled by an engine control unit to reduce jerkiness during a gear shift.

The transmission system is advantageously used with vehicle prime movers for two, three or four wheeler vehicles or powered vehicles of any description, preferably having engine capacity up to 500 cc. The gross vehicle weight (GVW) of such vehicles would be relatively low, allowing vehicle braking with vehicle wheel brakes and without requirement for engine braking.

Although the terms "transmission control unit" and "prime mover control unit" or "engine control unit" are used in this specification, the control units need not be separate. The transmission control unit could form part of the prime mover control unit or engine control unit.

A preferred embodiment of the automated manual transmission system of the present invention will now be described with reference to the drawings with description of numerals as detailed below:

3 Drive Shaft of Shifting Motor
10 Automated Manual Transmission System
11 Primary Driving Gear 13 Primary Driven Gear
14a Engine Crankshaft (Prime mover shaft)
15 Self-Actuating One Way Clutch
15a Housing
15c Coil Spring Dampers
15d Rubber Damping Elements
16 Input Shaft 16a,b,c,d,e Driving Gears
17 Starter Motor
18 Output Shaft 18a, b Driven Gears

20 Drum Shifter 20a Drum Shifter Axis
21 Electric Motors
22 Primary Drive Gear
23 Starwheel Gear
24 Drive Shaft of Electric Motor 21 (Prime mover shaft)

30 Electric Servo Shifting Motor
32 Cam Drive Gear (in Shifting Motor's Intermediate Shaft 35)
35 Intermediate Shaft of Shifting Motor 30
37 Gear of Shifting Motor's Drive Shaft 3
41 Cam Drive Teeth on Cam Drive Gear 32
43 Cam Driven Teeth
44 Cup or spring Cap
45 Clash Relieving Device
46 Spring
51 Crankcase
52 Inside Cover
110 Engine
140 Centrifugal Clutch
153 Spragof one way clutch
159,160 Dog Clutch or Lugs of Gear 18
166,167 Complementary Lug/Kidney Slots for All Gears
161 Open Kidney Slot of Gear 18
162 Blind Kidney Slot of Gear 18
170 Input Shaft Axis

180 Output Shaft Axis
210 Damping Mechanism
216 Jet
217 Shoes
218 Grooves
220a,b,c,d,e,f Slots in Primary Driven Gear 13
222a,b,c Lugs in Housing 15a
223 One Way Clutch Flange
225 Cover Plate
225a Arms of Cover Plate
226 Riveting

Fig. 1 is an end schematic view of the automated manual transmission system of the preferred embodiment in which an internal combustion engine is prime mover;

Fig. la is an end schematic view of the automated manual transmission of another preferred embodiment in which an electric motor is prime mover;

Fig. 2 is a side section view of the automated manual transmission system of the preferred embodiment and taken along section line A-A of Fig. 1;

Fig. 2a is a side section view of the automated manual transmission system of Fig. la and taken along section line A-A of Fig. la;

Fig. 3 is an end view of the one way clutch as shown in detail in Fig. 4;

Fig. 4 is a side section view of the one way clutch as shown in detail in Fig. 3;

Fig. 5 is a set of schematic illustrations showing how the gears of the automated manual transmission system as shown in Figs. 1, la, 2 and 2a engage;

Fig. 6a and 6b are detail views showing how gears on input and output shafts of the automated manual transmission system are brought into engagement;

Fig. 7 is a schematic view of a gear shift mechanism for the automated manual transmission system as shown in Figs. 1 and 2 and taken along section line B-B of Fig. 1;

Fig. 8 is an end view of the one way clutch and primary driven gear showing location and design of the damping arrangement for the one way clutch;

Fig 9c is a sectional view of the one way clutch in a direction perpendicular to Fig. 8;

Figs. 9a and 9b are three dimensional representations of Fig. 9c

Fig. 10 is a graphical representation of the torsional damping characteristics of a one way clutch used in preferred embodiments of the automated manual transmission system of the invention;

Fig. 11a is a detailed front view of a shoe of the centrifugal clutch used in the automated transmission system of Figs. 1 and 2 to 5;

Fig. lib is a 3 dimensional representation of the centrifugal clutch shoe of Fig. 11a

Fig. 12a is a side section view of the centrifugal clutch used in the automated transmission system of Figs. 1 and 2 to 5;

Fig. 12b is a 3 dimensional representation of the centrifugal clutch of Fig. 12a;

Fig. 13 is a graphical representation of torque characteristics of the centrifugal clutch of the preferred embodiment of automated transmission system of the invention.

Figs. 14a to 14d show views of the various key operating phases of the clash relieving (torque limiting) device in a preferred embodiment of the automated transmission system of the present invention;

Fig. 15 is a graphical representation of gear shifting drum vs time showing the operation of the clash relieving device when used in an automated transmission system of a preferred embodiment of the invention;

Fig. 16a provides section views of an engine having a conventional 5 speed manual transmission with 5 speed gear ratios;

Fig. 16b is an engine having the same capacity as that of Fig. 16a and using a 5 speed gear ratio automated transmission system of a preferred embodiment of the invention;

Referring to Figs. 1 and 2, there is shown an automated manual transmission system 10 to be used as part of a power train including a prime mover in the form of an internal combustion engine for a motorcycle (not shown). The engine 110 is a single cylinder four stroke engine and is of small capacity. The engine 110 may be operated in lean burn combustion mode, for fuel economy and effective emission performance. It is to be understood that the invention is not limited to prime movers in form of internal combustion engines. Electric motors, for example, may also be used as prime movers in accordance with the invention and as shown in Figs, la and 2a.

The automated manual transmission system 10, as apparent from Figs. 1 and 2, has a number of components working in combination. The transmission system 10 is linked to the engine crankshaft 14a, enclosed within crankcase 51, which has left and right hand side sections. Here engine crankshaft 14a is the prime mover drive shaft, the rotation of which provides motive force to driving wheel (here the rear wheel) of a motorcycle when "in gear". On the right hand section of crankshaft 14a is connected a primary driving gear 11 and a centrifugal clutch 140 forming part of a self-actuating clutch system for the motorcycle.

The primary driving gear 11 is intended to mesh with a primary driven gear 13 mounted on input shaft 16 of the transmission when the engine 110 reaches a cranking speed. Centrifugal clutch 140 operates to transmit torque from crankshaft 14a to the primary driving and driven gears 11 and 13 when the threshold engagement speed of the centrifugal clutch 140 is reached. In this state, centrifugal clutch 140 is engaged assisting initial take off of the vehicle from at least idle speed. Centrifugal clutch 140 also allows idling without engagement of input and output shafts 16 and 18 of transmission system 10. After initial engagement, centrifugal clutch 140 is thereafter intended to remain engaged at all times whilst the engine is operating.

Use of centrifugal clutch 140 assists in making automated manual transmission system 10 more compact. Centrifugal clutches normally have less width or dimension in axial direction than other clutch mechanisms as the engaging element acts in radial direction. Centrifugal clutch 140 is of wet type in which oil is supplied continuously to the clutch shoes. An oil jet 216 is positioned to direct oil to the clutch 140 and clutch shoes (as shown in Figs, 12a and 12b). The jet 216 size is optimized to direct the correct quantity of lubricating oil to the clutch 140 and clutch shoes 217. Further clutch shoes 217 are provided with grooves 218 facilitating oil spreading over the entire width/surface that is the frictional area, of the clutch shoes 217 as illustrated in Fig. lib. The lubrication grooves 218 extend in the direction of rotation of the clutch 140 as well as perpendicular to the direction of rotation of shoes 217. These features improve heat dissipation, reducing the wear of the frictional material, thereby improving the life of clutch 140 as shown in Figs. 11 and 12. Fig. 13 provides a graphical representation of improvement achieved in torque transmission characteristics for centrifugal clutch 140 during an accelerated durability test (clutch burnt test). It can be observed that improvement could be achieved from 1.8x to 1.3x; meaning that a clutch without oil jet 216 and lubrication grooves 218 provided on the clutch shoes 217 would suffer 80% deterioration of engagement (due to wear), this being controlled to 30% deterioration when oil jet 216 and lubrication grooves 218 were provided.

Input shaft 16 bears five gears 16a-16e in addition to primary driven gear 13. Output shaft 18, of transmission system 10, also bears five gears 18a-18e each of which is meshable in constant or clash mesh, when engaged, with, a correspondent gear 16a-16e of the input shaft 16. The transmission system 10 does not incorporate synchromesh devices in order to maintain transmission system 10 simplicity and to reduce bulk and cost. The transmission system 10 therefore allows for five transmission ratios or gears for the motorcycle engine 110. Five transmission ratios is not a limiting number of transmission ratios. Three or four transmission ratios could also readily be accommodated. Gear shift is achieved using a drum shifter as is common in motorcycle transmissions.

A reverse gear arrangement may readily be employed if required, that is, in the case of three and four wheeler low GVW vehicles.

Drive is not provided to a driving wheel of the motorcycle unless torque is provided from the engine crankshaft 14a to input and output shafts 16 and 18, that is all shafts are linked. Such linking involves self-actuating one way clutch 15 forming a further clutch of the self-actuating clutch system. One way clutch 15 is so-called because it only transmits power in one direction, from the engine crankshaft 14a to the input shaft 16. That is, one way clutch 15 engages the driven gear 13 of input shaft 16 with the driving gear 11 on the engine crankshaft 14a when engine speed (speed of engine crankshaft 14a) is greater than vehicle speed, i.e. wheel speed without human or automatic control being required to control engagement. When torque is transmitted in such manner to input shaft 16, torque is also transmitted, at a selected transmission ratio, to output shaft 18 and the drive wheel. When wheel speed exceeds engine speed, one way clutch 15 simply de-links or disengages the driven gear 13 of input shaft 16 from the engine without human or automatic control being required to control disengagement. Linking and de-linking, engagement and disengagement, occurs automatically dependent on relation between vehicle and engine speeds.

Use of a one-way clutch 15 which is of radial engagement cam or sprag 153 type also assists achievement of a more compact transmission system 10. In prior systems, an input shaft of a transmission system is typically mounted with many components such as a plate clutch.

A conventional plate clutch has significant width and sets a constraint on input shaft length which must be sufficient to bear the clutch. For example, for a 150 cc engine with a 5 speed AMT transmission system, additional packaging space of 33 mm along the axis of the input shaft would be required for accommodating a conventional plate clutch and its actuating mechanism and controls. These factors would increase the size of the transmission system as well as its weight by approximately 250 grams.

Use of one way clutch 15 reduces the constraint on input shaft 16 length reducing it in comparison with conventional automated manual transmission systems. Selection of a one way clutch of axial engagement type is possible but it would not achieve reduction in input shaft length.

The engagement and disengagement of one way clutch 15 tends to cause shocks and vibration at high frequency as one way clutch 15 is used in the drive-train to directly drive (& connect/disconnect) the wheel through engine, lead to high torque fluctuations . Such shocks and vibration, if not compensated for, can cause rapid wear of the one way clutch 15 thus reducing the life of one way clutch 15. To reduce this problem substantially, assembly of the one way clutch 15 and primary driven gear 13, is provided with a dampening mechanism 210 with plural damping rates as shown in Figs. 3, 4, 8, 9a and 9b. The dampening mechanism 210 is of biased type being comprised of three pre-compressed coil spring dampers 15c and three rubber damping elements 15d of damping material, such as rubber. While transferring the torque, initial partial dampening is provided by the coil springs 15c and subsequently after a fixed deflection angle, further partial damping is provided by rubber damping elements 15d .The number of coils and number of dampers is not limited to three , it could be more or less.

The detailed construction of the one way clutch dampening mechanism is now described.

The primary driven gear 13 is provided with a plurality, 6, of slots 220a, 220b, 220c, 220d, 220e, 220f. The primary driven gear is connected to a housing 15a provided with 3 lugs 222a, 222b and 222c. The housing 15a is freely rotatable on the input shaft 16. The said housing is rotatably connected to a one way clutch flange 223 (itself rigidly fixed, optionally through splines, to the input shaft) through the plurality of one way clutch sprags 153. The housing 15a forms the inner race of the one way clutches sprags 153 and is free to rotate on the flange 223 of the one way clutch 15. The clutch sprags 153 are shaped specially and precisely placed between the said flange 223 and housing 15a in manner to allow motion/torque transfer from housing 15a to flange 223 but not to transfer torque from flange 223 to housing 15a. This is achieved by locking or slipping of the one way clutch sprags 153.

Each of lugs 222a, 222b and 222c of housing 15a are fitted with rubber dampening elements 15d which along with the lugs 222a-c are engageable with three of the slots 220a, 220b and 220c of primary driven gear 13. The primary driven gear 13 is covered by cover plate 225 from the opposite side of housing 15a. The lugs and dampening material are positioned in a biased location towards direction of rotation ( or drive side biased)in the said slots of primary driven gear and are fixed with use of suitable hardware arrangements such as riveting 226. The biasing is substantially towards the direction of rotation (say for example 90% towards direction of rotation). The riveting arrangement rivets the cover plate 225 and the dampening elements 15d with housing 15a.

Further, remaining slots 220d, 220e, and 220f of primary driven gear 13 are provided with coil spring dampers 15c. The cover plate 225 is provided with three arms 225a arranged in pairs. The arms 225a are positioned in the said slots 220d, 220e, 220f at both the ends of spring dampersl5c.

Torque is transmitted by primary driven gear 13 to housing 15a and then on to one way clutch flange 223 through the clutch sprags 153. Subsequently, the flange 223 transmits the torque to input shaft 16.

The above described dampening mechanism 210 provides dampening i.e. when torque from primary driven gear is transmitted to said cover plate 225 and housing 15a. Torque or thrust is firstly partially absorbed or dampened by the plurality of spring elements (15c) and then also by the rubber dampening material elements (15d). This in totality provides dampening for more than 12 degrees of rotation (or deflection angle)of primary driven gear. The combination of dampening by pre-compressed coil springs 15c and rubber damping elements 15d provides sufficient time to lock the sprags 153 for transmission of torque causing less wear and tear thereby improving the life of the one way clutch 15.

The dampening mechanism 210 provides high deflection angles (or rotation of degrees), during a durability test, as illustrated in the graph represented in Fig. 10. The graph shows comparison of rotation of degrees of one way clutch 15 for the above described dampening mechanism 210 and with other dampening arrangements. The graph confirms that use of such dampening arrangement allows one way clutch sufficient time to lock all the sprags 153, thus causing significantly less wear and tear thereby improving life of one way clutch 15. No damage or abnormal wear to the one way clutch 15 was observed during the test.

As an additional benefit, the dampening mechanism also ensures smooth reinstatement of power after gear shifting.

Transmission system 10 includes further design features to achieve compactness. In particular, engine crankshaft 14a, primary drive gear 11, primary driven gear 13, input shaft 16 and output shaft 18 are arranged, in a single engine casing, with axes parallel as shown in Fig. 1: see crankshaft axis 14a (which is axis for primary drive gear 11), input shaft axis 170 (which is also axis for driven gear 13) and output shaft axis 180. This avoids need for worm gears and rack and pinion arrangements which would lead to increases in the size of the transmission system in comparison with the transmission system 10 described here. The axes of the transmission system components are also parallel to the axes of components in the gear shifting mechanism described below.

Using the automated manual transmission system 10, as here described, involves a gear shifting process that does not require direct motorcycle rider involvement, for example through the rider's operation of a gear shifting mechanism. That is, operation of transmission system 10 is under control of a transmission control unit (TCU) which has inputs such as engine speed, vehicle speed and throttle position. Based on these signals, the TCU decides gear upshift or downshift in accordance with an optimized vehicle operating strategy. During gear shifting the TCU sends a signal to the engine control unit (ECU) requesting that the speed of the engine be retarded during the gear shift.

The gear shifting mechanism of transmission system 10 includes a drum shifter 20 which comprises a rotatable drum having curved cam grooves formed in an outer peripheral surface and shift forks mounted on a shift for sliding movement in the cam grooves. When the drum shifter 20 is rotated, the forks move to select correspondent gears on the input and output shafts 16 and 18 for engagement. In a manual transmission system, the motorcycle rider would cause rotation of the drum shifter 20, through manual operation of a gear shift device and a clutch. With transmission system 10, apart from there being no facility for the rider to operate a clutch (the clutches are self-actuating), no such gear shift device is provided, rather the drum shifter 20 is rotated by operation of an electric servo shifting motor 30 driving a shaft to rotate, or indexing, through a gear 32 mounted on an intermediate shaft 35, a starwheel gear 23 integral with drum shifter 20 to select particular gears for engagement when required by the transmission control unit (TCU). As described above, transmission system 10 requires clash meshing of gears on input shaft 16 and output shaft 18 to engage selected gear ratio. The engagement process of selected gears requires that the lug provided for the purpose on the wall of an input gear should engage with a corresponding kidney (slot) provided on the wall of the corresponding output gear. For this reason, the clash mesh type gear transmission has comparatively less probability of gear engagement, normally creating the risk of mechanical locking where two corresponding components(i.e. lug and kidney) of the selected gears (one fixed, and one freewheeling) clash with each other and fail to engage due to insufficient relative speed between them. The transmission system 10 includes a feature to compensate for this risk, namely a clash relieving device 45 located between the shifting motor 30 and the drum shifter 20 as illustrated in figure 7. The clash relieving device (which may be called a torque limiting device) 45 does not form part of the drive train of the transmission system 10, however, being positioned within transmission casing or crank case (51. That is, it is not located in a pathway for motive force between crankshaft 14a and output shaft 18 which is used for driving the motorcycle.

Shifting motor 30 has a drive shaft 3 which may have portion formed as a gear 37.

Gear 37 could be arranged to mesh directly with starwheel gear 23 but this is not preferred since if gears clash and torque exceeds the stall torque of shifting motor 30, the transmission system 10 would fail in that an attempt to shift gear would be unsuccessful.

Therefore, the gear shift mechanism includes a clash relieving device 45 comprising an intermediate shaft 35, cam drive gear 32 provided with drive cams; said drive cams has a number of cam teeth which mesh with similar cam teeth on the cam driven 43 which is slidably fixed or coupled to the intermediate shaft 35.

A spring 46 is provided at the rear end of cam driven 43 to force teeth of cam driven 43 and teeth of cam drive 41 into engagement. Spring 46 is fixed to the cup 44 at the other end. Thus drive from shifting motor 30 must be transmitted to drum shifter 20 through the intermediate shaft 35 and a cam drive 41 and cam driven 43. Cam drive gear 32 meshes (continuously) with shifting motor drive shaft gear portion 37 but is free to rotate on intermediate shaft 35. The preload of spring 46, which may be adjusted by means included within spring cap 44, determines a torque value at which clash relieving device 45 is actuated. The spring load at maximum deflection also determines the torque value at which teeth of cam drive 41 and cam driven 43 respectively slip from one tooth to another.

Whenever clash of corresponding gears on input shaft 16 and output shaft 18 occurs, the load on shifting motor 30 increases and the clash relieving device 45 is actuated once a predetermined torque value (as set by spring 46 preload) is exceeded.

To overcome this clash, the clash relieving device 45 is used in 2 ways: 1 . it holds the lugs in position to get the specific kidney angle for engagement. 2 . If desired engagement does not happen, then clash relieving device 45 momentarily and completely disconnects the torque transmission of shifter motor 30 to drum shifter 20 due to disengagement of cam drive and cam driven 32 and 43 against spring force. This spring force pushes the cam driven 43 to engage with cam drive 32. This phenomenon generates a reverse rotation of drum shifter 20. This results into momentary but complete disconnection of lug and kidney surfaces. This disconnection facilitates the relative difference of RPM between lug and kidney helping to overcome the no-go clash condition, thereby engaging a lug into a correspondent kidney slots.

For example, this predetermined torque value could be 1 Nm drum torque). Actuation of clash relieving device 45 actively controls the force being applied at the clashed lug and kidney surface (for example, the gears 18a, 18b and 16c, 16d of Figs. 6a and 6b could be considered from this perspective), thus preventing synchronization of speed and failure of gears to engage (and stalling of shifting motor 30).

Figure 14 illustrates the function of clash relieving device 45 in detail .The function of device 45 is shown through four operating phases i.e. A, B, C, D.

Phase A: This is the normal condition i.e. shifting without clash, during this time the shifting torque is below the predetermined limit.

Phase B: When Clash happens, the shifting motor 30 gets overloaded and the torque exceeds the predetermined value, the cam drive and driven teeth 32 and 43 starts to slip and limits the shift torque, thus preventing the synchronization of lug & kidney RPM while protecting the motor as well.

If the clash is cleared within the available travel of slippage, the damper is restored back to its original condition (A).

Phase C: If clash isn't cleared in the available travel of slippage as stated in Phase B, the cam drive and driven teeth 32 and 43 slip further and slip out of engagement completely. During this condition, the shifting torque on the drum (subsequently the lugs) drops to zero, this allows the lug and kidney to freely rotate relative to each other and get out of the no-go/clash condition.

Phase D: Subsequent to phase C, due to the force of spring 46, the cam drive and driven teeth 32 and 43 then moves into the next teeth. During this phase, the drum shifter 20 rotates backwards by certain number of degrees due to spring and damper angle, after which it is again rotated forward by the shifting motor 30, this action being similar to a human rider taking his foot off and trying to shift again in clash condition.

Figure 15 shows a graphical presentation of real time image/record of torque dampening system in action. In this particular case, spring 46 is limited to a maximum travel of 3.33mm and a maximum drum torque value of 1.3 Nm (which may be set by trial and error in the design/engineering phase for a particular transmission system and motorcycle). Above this drum torque value, cam drive gear 32 and cam driven 43 would slip from one tooth to another. However, this is sufficient to avoid the problem of failed gear engagement. Either the clash is cleared within the available 3.33 mm travel of the spring 46 or slip occurs and the torque limiting device starts to act once again. Torque on the drum shifter 20 is not allowed to exceed the predetermined torque value. At the same time, relative speed between corresponding gears (for example 18a, 18b; 16a, 16c of Figs. 6a and 6b maximises the probability that lugs 159 and 160 engage kidney slots 161 and 162 respectively with the consequence of successful gear engagement.

The application of said clutch relieving device employed advantageously in present invention and has resulted in significant improvement in gear shifting, however this device can be employed in any gear shifting mechanisms having electric motor drive to actuate a drum shifter.

Shifting motor 30 is accommodated on crankcase 51 and inside cover 52 proximate to the starter motor 17. An alternative mounting location for shifting motor 30 would likely increase crankcase 51 bulk and this is contrary to objects of the invention.

A further effort to increase the probability of engagement of lug and kidney during gear shifting in the clash mesh gearbox of transmission system 10 is illustrated in Figs. 5 and 6 This embodiment shows use of complementary lug/kidney slot 166, 167 mechanisms for all gears and, in particular, 2x2 lug/kidney slot 166, 167 mechanisms to improve probability of gear engagement for 3rd, 4th and 5th gears. In this regard, it will be understood that in a clash mesh transmission system, such as transmission system 10, gears must be engaged through dog clutch or lug of one gear engaging with a corresponding slot on a correspondent gear (see gears 18a and 18b of Fig. 6a where dog clutch 159 is to engage with slot (or open kidney 161), so called because the slot has a kidney shape; and gears 16c and 16d of Fig. 6b where dog clutch 160 is to engage with slot (or blind kidney) 162.

However, transmission system 10 maintains a 3x3 lug/kidney mechanism 166, 167 for 1st and 2nd gear. For 1st and 2nd gear engagement, the kidney slots are of open or through type (see Fig. 6a) and so making these slots in a 2x2 arrangement would result in a weak section which would be critical to strength. However, for the other gears, the kidneys are of blind type (see Fig 6b showing 5th gear) which allows a 2x2 arrangement. The gear design allows optimization of benefit to be gained by use of a 2x2 arrangement while avoiding cost of a gearbox redesign which would be necessary if all gears were to be provided with a 2x2 lug/kidney mechanism design for increasing probability of gear engagement.

Fig. 5 shows probability of successful engagement of gears using the lug/kidney mechanisms 166, 167 and so on as described above. These probabilities, at above 60%, are higher than for conventional clash mesh gearboxes.

Further the usual circumferential clearances between lug and slots could be increased more than 40 degrees. In a conventional transmission system, this clearance value is restricted to avoid impact noise of lug and kidney during sudden motion changes and / or during engagement phases. In the presently described automated manual transmission system 10, the reverse motion through a lug is not transmitted to a corresponding kidney due to employment of one way clutch 15. This improvement in circumferential clearance assists in substantial increase in the probability of lug and slot engagement.

The gear shifting mechanism has a compact layout. Importantly, drum shifter 20, shifting motor 30 and star wheel gear 23 are arranged with axes parallel (see drum shifter axis 20a (which is also axis for star wheel gear 23) and axis of shifting motor 30). This avoids any use of worm gears or rack and pinion arrangements which would lead to a bulky gear shifting mechanism. It will be observed that the described axes of the gear shifting mechanism components are also parallel to the axes of components in the transmission system as described above, i.e. crankshaft axis 14a (which is axis for primary drive gear 11), input shaft axis 170 (which is also axis for driven gear 13) and output shaft axis 180.

When a gear shift phase is initiated, in accordance with a predefined engine operating strategy, the engine 110 needs to be de-linked or disengaged from the transmission system 10. Transmission system 10 facilitates such de-linking through use of one way clutch 15 as described below. When a gear shift phase is initiated, the TCU implements a strategy to retard engine speed, strategy for such engine speed retardation being under control of the engine control unit (ECU). A preferred strategy is for the ECU to reduce or stop air/fuel mixture delivery to the engine, and/or interrupt spark plug firing, for the duration of the gear shift phase. Air/fuel mixture delivery to the engine is preferably stopped altogether to promote fuel economy and reduced hydrocarbon emissions.

Conveniently, air/fuel mixture delivery to the engine 110 may be reduced or stopped using a restriction element located in the intake system. The apparatus for such air/fuel mixture control is described in the Applicant's co-pending Indian Application No. 3740/CHE/2011 dated 1st November 2011.

In the case of a fuel injected engine, the ECU controls the fuel supply to the engine during the gear shift phase. If a carburetor is employed for fuel delivery, the ECU controls the supply of air/fuel mixture to the engine.

When the air/fuel mixture delivery is stopped by the ECU but with the motorcycle running, engine speed falls rapidly. When the engine speed falls below vehicle or wheel speed, one way clutch 15 disengages the input shaft 16 from the engine crankshaft 14a. This occurs automatically, no actuating mechanism is required. At the same time, the TCU actuates the shifting motor 30 for drum shifter 20 to rotate or index the drum shifter 20 so that the selected gears on input and output shafts 16 and 18 are ready for engagement. When this operation is complete, the ECU recommences air/fuel mixture delivery to the engine 110, likely at a different fuelling level than for the preceding gear. A variety of fuelling strategies could be implemented by the ECU dependent on engine and vehicle operating conditions. At this point, engine speed increases to a level greater than vehicle or wheel speed and one way clutch 15 engages the engine crankshaft 14a with the input shaft 16. Input shaft 16 in turn transmits torque to output shaft 18.

In another embodiment, where the prime mover is an electric motor (see layouts of Figs, la and 2a), the torque is transmitted from electric motor 21, through electric motor drive shaft 24 and primary drive gear 22 to primary driven gear 13. This does not necessitate need for a centrifugal clutch. Otherwise, further elements of the automated manual transmission system are as described above for the internal combustion engine.

Referring to Figs. 16 and 16b, there is shown a comparison - with respect to dimensions and weight - between an engine using a conventional manual transmission having 5 speed gear ratios and an equivalent engine employing an automated transmission system (AMT) having 5 speed gear ratios according to the preferred embodiment of the invention. The Applicant's AMT system restricts increase in weight over the manual transmission system to about 10%. There is a very marginal increase in length (i.e. by 11 mm which is compensated by a reduction in height of 11 mm. There is also a marginal increase in width by 38 mm. Details of dimensions are indicated in Figs. 16a and 16b.

The above data is for a vehicle employing a kick start mechanism. For vehicles not employing a kick start mechanism, the weight increase could be restricted to about 5% with increase in width of 10 mm. No increase in length is required. Accordingly, the automated manual transmission (AMT) system described herein is less expensive and less complex, not requiring any clutch actuating means or complex clutch actuation control strategies. The AMT system is also very compact and less bulky in comparison with alternative AMT systems.

Modifications and variations to the automated manual transmission system disclosed in the present specification may be apparent to the skilled reader of this specification. Such modifications and variations are deemed within the scope of the present invention.

WE CLAIM:

1. An automated manual transmission system for a vehicle comprising a prime mover engageable with, and disengageable from, a clash mesh type transmission system comprising a plurality of gears; a transmission control unit; and a gear shifting mechanism controlled by the transmission control unit to shift transmission gear during a gear shift phase wherein said transmission system and prime mover are engageable and disengageable by a self-actuating clutch system during said gear shift phase.

2. A transmission system as claimed in claim 1 comprising input and output shafts wherein said prime mover is an internal combustion engine and said self-actuating clutch system comprises a centrifugal clutch and a one way clutch wherein said centrifugal clutch is mounted on prime mover shaft and said one way clutch is mounted on an input shaft of said transmission system to automatically engage and disengage said prime mover shaft from said input and output shafts.

3. A transmission system as claimed in claim 2 wherein prime mover said and said transmission system is accommodated in a single casing.

4. A transmission system as claimed in claim 1 comprising input and output shafts wherein said prime mover is an electric motor and said self-actuating clutch system consists of a one way clutch, said one way clutch being mounted on an input shaft of said transmission system to automatically engage and disengage said prime mover drive shaft from said input and output shafts

5. A transmission system as claimed in claim 2 or 4 wherein actuation of said one-way clutch is dependent on relation between prime mover speed and vehicle wheel speed.

6. A transmission system as claimed in any one of the preceding claims wherein, when the transmission control unit determines requirement for a gear shift, the prime mover is controlled by the prime mover control unit to reduce speed and torque of its drive shaft during said gear shift phase.

7. A transmission system as claimed in claim 6 wherein said prime mover is an internal combustion engine and said transmission control unit controls fuel or air fuel mixture delivery to the engine during said gear shift phase.

8. A transmission system as claimed in claim 7 wherein said engine is gas fuelled.

9. A transmission system as claimed in claim 7 or 8 wherein said engine is fuel injected or carbureted.

10. A transmission system as claimed in any one of claims 2 or 5 to 9 wherein said prime mover is an internal combustion engine comprising a cylinder head including a plurality of ignition means.

11. A transmission system as claimed in any one of the preceding claims wherein said one way clutch includes a dampening mechanism to damp shock, said dampening mechanism comprising a biased damping means with a plurality of damping rates.

12. A transmission system as claimed in claim 2 to 11 wherein said dampening mechanism comprises an input shaft comprising a primary driven gear provided with a plurality of slots and freely rotatable on said input shaft, said primary driven gear being connected to a housing provided with plurality of lugs each engageable with said slots of said primary driven gear; said housing being rotatably connected to a flange of said one way clutch through plurality of one way clutch sprags; being placed between said flange and said housing in manner to allow rotation of said housing in one direction; wherein said lugs are fitted with a dampening material; said lugs and dampening material being positioned in a biased location substantially towards a direction of power transmission in said slots of primary driven gear and wherein remaining slots of said plurality of slots of said primary driven gear are provided with a pre compressed springs; the said dampening material and pre-compressed coil springs acting in combination to cause less wear on said one way clutch.

13. A transmission system as claimed in claim 12 capable of providing combined dampening for more than 12 degrees of rotation of a primary gear.

14. A transmission system as claimed in any one of the preceding claims wherein said gear shift mechanism for engaging corresponding input and output gears comprises a gear drum shifter; and a drive shaft for driving the gear drum shifter wherein said drive shaft transmits torque to the gear drum shifter through a clash relieving device operative to prevent reduction in relative speed between engaging elements of corresponding input and output gears during clash conditions in a gear shift phase.

15. A transmission system as claimed in claim 14 wherein said prime mover is an internal combustion engine having a crankcase and said clash relieving device, positioned within said crankcase, comprises an intermediate shaft located for transmitting torque between said gear drum shifter drive shaft and said gear drum shifter wherein said intermediate shaft is provided with a drive cam mounted freely on said shaft and a cam driven operatively connected to said intermediate shaft and biased into engagement with said drive cam by a spring, said spring having a preload determining a torque value at which said clash relieving device is actuated and above which said cam drive and cam driven disengage.

16. A transmission system as claimed in claim 14 or 15 wherein said gear drum shifter drive shaft is driven by an electric motor.

17. A transmission system as claimed in claim 15 and 16 wherein said clash relieving device is located between the electric shifting motor and the gear drum shifter.

18. A transmission system as claimed in any one of claims 14 to 17 wherein said drum shifter, electric shifting motor and corresponding gears are arranged with axes parallel.

19. A transmission system as claimed in any one of claims 14 to 18 wherein said electric motor to drive the drum shifter is located on said engine crankcase proximate to the starter motor.

20. A transmission system as claimed in any one of the preceding claims wherein said prime mover includes a drive shaft and driven gear and said transmission system includes an input shaft and an output shaft and wherein said prime mover drive shaft and said input shaft are arranged with axes parallel.

21. A transmission system as claimed in any one of claims 14 to 20 wherein said engaging elements of said gear shift mechanism comprise two complementary components, a first component comprising lugs as engaging elements; and a second component comprising slots complementary to said lugs such that engagement of said lugs and slots enables torque to be transferred for a selected gear ratio or till the time the engine speed drops below the threshold value of clutch engagement speed wherein circumferential clearance between lug and corresponding slot is more than 40 degrees to improve probability of engagement without compromising shift noise.

22. A prime mover comprising a transmission system as claimed in any one of the preceding claims.

23. A prime mover as claimed in claim 22 being an internal combustion engine having cubic capacity less than or equal to 500 CC.

24. A prime mover as claimed in claim 22 being an electric motor.

25. A vehicle comprising a prime mover as claimed in any one of claims 22 to 24.

26. A gear shifting mechanism for an automated manual transmission system having a clash mesh shifting gearbox comprising an input shaft; an output shaft; wherein said gear shift mechanism engages corresponding gears respectively located on said input shaft and said output shaft; and a shifting motor having a drive shaft for driving the gear shift and wherein said drive shaft further transmits torque to the gear shift through an intermediate shaft bearing a clash relieving device operative when torque delivered by said shifting motor exceeds a predetermined value to prevent reduction in relative speed of engaging elements of said correspondent gears during clash conditions.