DESC:FIELD OF INVENTION
The invention relates to a non-synchromesh transmission system and, in particular, to a controlled drag inducing mechanism for inclusion in the transmission system to address the problem of clash.
BACKGROUND OF INVENTION AND PRIOR ART
In a geared transmission system, power from the engine is transferred to the transmission system, in particular the gearbox, through a clutch assembly.

In the non-synchromesh type or dog clutch type transmission system, for example as used in a motorcycle though also in 3 and 4 wheeler vehicles, selective gear pairs are engaged, by a gear shift actuator, to establish a desired gear ratio. The gears are mounted on various transmission shafts, e.g. input shaft, intermediate shaft, output shaft within the transmission system. Such transmission systems are typical for use in smaller light weight vehicles. Torque is transferred from the input shaft through specific or required gear pairs to the intermediate shaft and/or output shaft. Torque from the output shaft then drives wheel(s) of the vehicle, for example the rear wheel of a motorcycle.

When selecting a gear ratio, a clutch is disengaged and, in the specific selected gear pair, either a drive or driven gear is freewheeling, this freewheeling gear being mounted on either input or output shaft of a shaft transmission system. This freewheeling gear gets connected to another spline gear/shifter which is rotatably fixed on the same shaft to ensure engagement of freewheeling gear with the shaft. Typical clash mesh type transmissions utilise dog clutches for engaging and disengaging gears on the same shaft. For engaging/disengaging gears, one or both of the fixed or freewheeling gears have male lugs/projections. Alternatively, one of the gears may carry female kidneys/slots. While gear shifting, the complementary male lugs of the corresponding gear must mate with the corresponding female slots or gaps of the male lugs of the other gear in order to lock or mesh the fixed and freewheeling gears together and thus complete the gear shift.

The above mentioned transmission system is subject to a phenomenon known as ‘clash’, which occurs when engaging gears do not mesh with each other while selecting/changing gear ratio. That is because fixed and freewheeling gears rotate at different speeds. The fixed gear rotates at higher or lower speed relative to the freewheeling gear. In such case, there are incidences when the lug/s provided on a fixed or freewheeling gear does/do not engage or lock with corresponding kidneys/slots provided on the pairing fixed or freewheeling gear. This means that the lug/s of one gear miss the target kidney slot/s (or lugs) and clash with a solid part of the other gear and power is not transferred from selected gear pair as required. It is essential to relieve the clash at the earliest possible time as long duration clash is detrimental and may cause heavy damage to transmission components. Further, during the clash situation, power flow is interrupted until the clash situation resolves and may lead to undesirable engine and vehicle operating conditions and driveability.

In addition, if such a transmission system is adopted in a two/three/four wheeled vehicle, the clash condition may cause false neutral gear position. To avoid this situation, in a manual transmission system, the rider could operate the engine at a half-clutch state thereby introducing drag in the clutch mechanism from the input-shaft end. Such a solution depends on the rider’s skill of controlling clutch operation, and consumes fuel until the clash is removed. In the case of a manually operated two wheeled vehicle, the rider may stop the vehicle and move the two-wheeler back-and-forth. However, such a privilege is not available with three wheeled, four wheeled or two wheeled vehicles with Automated Manual Transmission (AMT) where a gear change is not controlled by a rider but rather by a control unit.
To address this issue, a wet multi-plate clutch could be used, as described in EP1669270B. In this situation, dog collision can be resolved easily since the clutch plates normally move with the friction discs owing to the viscosity and distribution of the oil in the clutch, even when the clutch is in a disengaged position. As viscosity is temperature dependent, operability varies with temperature. However, drag is dependent on the oil quantity and viscosity between clutch plate interfaces. Hence, drag is not consistent. In case of no oil between interface of clutch plate for e.g. during initial start condition, no drag is produced and tendency of clash conditions is increased unless the engine is warmed and some clutch drag is induced due to oil circulation. Hence, a considerable quantity of fuel, besides time, may be consumed in this process.

Alternatively, a common response to avoid the clash problem is the use of synchromesh mechanisms but these involve additional cost and space as synchromesh systems are complex and bulky for equivalent capacity.
OBJECT OF INVENTION
It is an object of the present invention to provide a transmission system with a controlled drag inducing mechanism to address the problem of clash in a non-synchromesh type transmission system.

SUMMARY OF INVENTION

With this object in view, the present invention provides, in one aspect, a transmission system for a vehicle comprising:
a drive means for supplying power from a prime mover to said transmission system;
a shaft co-operable with said drive means to accept power from said drive means; and
a clutch assembly for controlling supply of power from said prime mover to said shaft dependent on whether said clutch assembly is disengaged to interrupt power supply or engaged to provide power supply;
wherein said shaft includes a drag inducing mechanism operative for accepting a controlled amount of drive from said drive means independently of whether said clutch assembly is engaged or disengaged.

The drag inducing mechanism is well adapted to operate under transmission system operating conditions including, in particular, gear clash conditions where the delivery of a controlled amount of drag assists to reduce or minimise clash duration. However, the drag inducing mechanism may operate under other conditions as well.

In another aspect, the present invention provides a transmission system for a vehicle, said transmission system being a non-synchromesh type transmission system and having a plurality of gear ratios comprising:
at least one rotatable shaft receiving drive from a prime mover comprising at least one fixed gear or gear shifter mounted to said shaft and at least one freewheeling gear mounted on said shaft or constantly meshed with said rotatable shaft, said fixed gear and said freewheeling gear being provided with complementary engagement means for engaging the gears as a pair when selected for a gear shift; and
a clutch assembly for controlling supply of power from a prime mover to the transmission system and operable during a gear shift;
wherein a drag inducing mechanism is co-operable with at least one of said rotatable shaft to induce or increase relative motion between said fixed and freewheeling gears to establish a selected gear ratio independently of whether said clutch assembly is engaged or disengaged. The drag inducing mechanism may introduce relative motion either between the gears, as intended to mesh, or between a gear and a shifter for the gear.
The drag inducing mechanism may be used for eliminating the clash between the engaging dog clutches on a single shaft, for example the input shaft. However, the drag inducing mechanism also assists in avoiding clash during mating of complementary gears, whether fixed or freewheeling, mounted on at least two different rotatable shafts while gear shifting. This becomes especially useful in case of reverse gear shifting. However, the functionality of the drag inducing mechanism to provide relative motion and torque may be useful in other engine operating situations as well.

As to location of the clutch assembly, the clutch assembly may conveniently be mounted on a crankshaft, i.e the engine crankshaft. The clutch assembly could, alternatively, be mounted on the shaft co-operable with said drive means to accept power from said drive means, that is, the input shaft.

The drag inducing mechanism is, functionally, located distal from the clutch assembly. That is, the drag inducing mechanism does not form part of the clutch assembly and so a path of drag torque transfer using the transmission system bypasses the clutch assembly. This has various advantages including that while using the transmission system configuration according to the invention, clutch design is not required to be compromised for providing minimum amount of clutch drag. Further, this configuration allows the drag inducing mechanism to be retrofitted in conventional non-synchromesh transmission systems. Finally, and importantly, the drag inducing mechanism as described herein requires no re-design of the clutch assembly. A conventional clutch assembly can be used.

The drag inducing mechanism is advantageously arranged to induce positive drag and controlled rotation of the rotatable shaft, for example an input shaft, which is preferably arranged to receive drive from the prime mover independently of whether the clutch assembly is engaged or disengaged. This amount of drive is substantially small in quantum compared to that required to properly operate the vehicle with the transmission system. The drive induced by the drag inducing mechanism should be just enough to induce relative motion between a fixed and freewheeling gear pair to clear the clash. The amount of drag is also small enough such that increase in shifting noise and shifting force is prevented. Advantageously, the drag inducing mechanism is connected to the input shaft such that drive from the prime mover is converted into positive drag acting to rotate said input shaft rather than acting against rotation of the input shaft.

As alluded to above, the transmission system takes power from a prime mover, such as an internal combustion engine, and more particularly a rotating crankshaft or drive shaft forming part of the prime mover. The crankshaft torque is transmitted to the first shaft through a drive means comprising a primary driving gear engageable with a primary driven gear mounted on said input shaft. The drive means may include means such as a chain drive, or more likely a driving and a driven sprocket forming part of the chain drive and which causes rotation of the primary driven sprocket to transmit power to the rest of the transmission system. Alternatively, the primary driving gear and primary driven gear are meshed directly with each other. The drag inducing mechanism is placed such that a portion of torque from said primary driven gear acts on the input shaft enabling a positive drag and rotation of the input shaft sufficient to reduce duration of clash. Further, the drag inducing mechanism facilitates quick torque transmission from the primary driven gear to the input shaft in amount sufficient to induce or increase relative motion to desired level. This quick torque transfer helps in reducing gear shift time. This also enables quick gear shifting from very high gear to lower gears for e.g. Fifth gear to first gear.

Conveniently, the drag inducing mechanism is in frictional engagement with said primary driven gear, for example through use of a spring element so that torque is transmitted from the primary driven gear to the rotatable shaft in amount sufficient to induce or increase relative motion to desired level.
The drag inducing mechanism may comprise a sleeve element mounted fixedly on the input shaft; an abutting element which is in friction/pressure-based contact with the primary driven gear and which rotates relative to the input shaft when the clutch is disengaged; and a spring element mounted to rotate with the sleeve element and act against the abutting element to increase friction/pressure between the abutting element and the primary driven gear to induce positive drag and rotation of said input shaft.

In this case, while the clutch is in a disengaged state, the power from the engine is transferred along the path defined by the primary driven gear, the abutting element, the spring and the sleeve element, in that order, to the input shaft.

The transmission system as above described may operate in the following manner to address clash where fixed and freewheeling gears, intended to mesh, are mounted on the same shaft, for example the input shaft. When the clutch assembly is in a disengaged state, the input shaft still receives a small amount of torque due to rotation of a primary driven gear by the prime mover through drag inducing mechanism. The abutting element slip-rotates due to its pressurized surface contact with the primary driven gear due to force exerted by the spring element. As a result, the spring element also rotates. Due to its inherent elasticity, the spring causes the sleeve element to rotate. As a result, the input shaft is also caused to rotate sufficiently to induce a relative motion between the above mentioned fixed and freewheeling gears selected for engagement. One of the fixed or freewheeling gear is provided with engagement means, for example in the form of lug/s, whereas its pairing gear is provided with complementary engagement means, for example in the form of kidney/s. In case the lug/s do not match with the corresponding kidney/s, the described relative motion caused by the drag inducing mechanism allows the lug/s to match with kidney/s. This leads to removal of ‘clash’ between mating engagement means of the fixed and freewheeling gears, thus successfully completing gear-shift operation.
During the clutch disengaged condition, the speed of rotation of the input shaft, which should not be confused with speed of rotation in non-clash conditions, is based on the slip present between the primary driven gear and the abutting element, which in turn depends on the axial pressure exerted by the spring on the abutting element. By changing the spring dimension and/or spring constant, the amount of positive drag torque transferred to the input shaft from the prime mover can be varied. In one aspect of the invention, for controlling the amount of drag, a helical compression spring with low spring rate may advantageously be used (e.g. approx. 1.4 N/mm). Preferably, spring rate of the spring used in in the range of 0.5 N/mm to 4 N/mm. The spring is configured such that the variation in axial load acting on the abutting element remains low even with considerable stack and part variations

The system of the invention facilitates control over drag value as follows. The system should advantageously give just enough drag to induce the required relative motion to clear the clash. The amount of drag should also be small enough to prevent any increase in the shifting noise and force required for shifting. Spring adjustment may be used to tune the system and optimise the amount of drag.

The drag inducing mechanism may be mounted to introduce relative motion between a gear mounted on the at least one rotatable shaft and a shifter mounted on the at least one shaft and movable to engage with the gear when selected. Such shifter may have lugs which move into engagement with kidneys or other lugs formed on the gear and so susceptible to clash under certain conditions. Such arrangement may be convenient for adoption in a reverse gear mechanism.

As described above, the drag inducing mechanism allows clash during reverse gear shifting to be avoided. In an advantageous arrangement, the transmission system includes a reverse gear mechanism comprising a reverse input gear mounted on an input shaft; a reverse idle gear meshed with said reverse input gear; and a reverse output gear mounted on an output shaft and meshable with the reverse idle gear. The reverse output gear freely rotates about the output shaft and is movable into engagement in response to movement of a reverse output gear shifter mounted on the output shaft. The drag inducing mechanism is operable to induce relative motion between said reverse output gear and said reverse output gear shifter to avoid clash during reverse gear engagement. The reverse output gear shifter is conveniently a sleeve slidably mounted on the output shaft, the sleeve comprising lugs engageable with complementary engaging means of the reverse output gear.

The drag inducing mechanism can be adopted in various types of non-synchromesh transmission systems subject to gear clash such as sliding mesh or clash mesh transmission systems. The drag inducing mechanism is particularly suitable for inclusion in automated manual transmission systems as it acts to automatically overcome clash without need for any manual intervention or operator skill. The drag inducing mechanism can be adopted in two/ three/four wheeled vehicles for eliminating the clash in the transmission system.

The transmission system and its drag inducing mechanism operate with particular advantage in wet and dry modes of lubrication and when operating from a standing start or standstill where clash has been observed as a particular challenge as described in EP 1669270.

The transmission system may be used with a range of prime movers, not just internal combustion engines. Indeed, electric or hybrid vehicles or combination thereof, having an electric motor, can encounter clash issues which the drag inducing mechanism described herein will address. The drag inducing mechanism may easily be installed at the OEM stage. Further, the drag mechanism may be used in various transmission layouts such as two shaft, three shaft, four shaft, etc.

The transmission system may be used in a range of vehicle applications for two, three and four wheelers with the latter being preferred. It may also be used in motorcycle vehicles including scooters.

BRIEF DESCRIPTION OF DRAWINGS
REFERENCE NUMBER TABLE
No. Feature
1 Sleeve element
2 Abutting element
2a Face of abutting element
3 Primary driven gear
3a Face of the primary driven gear
4 Spring element
5 Primary driving Gear
6 Clutch Assembly
7 Input shaft
30 Output Shaft
10 Transmission system
9 Washer
11 Body of a sleeve element
12 Sleeve collar
13 Spring retainer part
14 Sleeve
15 Bearing
61a, 62a, 63a, 64a, 65a Forward input gears
61b, 62b, 63b, 64b, 65b Forward output gears
66 Lugs
67 Kidneys
320 Reverse gear mechanism
324 Reverse input gear
326 Reverse idle gear
328 Reverse output gear
328a Kidneys on reverse output gear
330 Shifter sleeve
330a Lugs on shifter sleeve
700 Drag mechanism

The transmission system of the present invention may be more fully understood from the following description of a preferred embodiment made with reference to the accompanying drawings in which:

Figure 1 shows a sectional view of part of a transmission system including a drag inducing mechanism according to one embodiment of the invention.

Figure 2 shows a sectional view of the drag inducing mechanism of the transmission system shown in Figure 1.

Figures 3A and 3B show exploded views of the drag inducing mechanism as shown in Figures 1 and 2.

Figures 4A and 4B show assembled views of the drag inducing mechanism as shown in Figures 1 to 3B.

Figure 5 shows an orthogonal view of part of the transmission system illustrating the gear train for reverse gear shifting.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF INVENTION
Referring now to Figure 1, there is shown a 5 speed transmission system 10 for a three wheeler vehicle powered by a prime mover in the form of an internal combustion engine (not shown) which transmits power through engine crankshaft (not shown), driven gear 3 and transmission system 10 at a selected gear ratio. It will be understood that other prime movers such as electric motors could be used and the transmission system 10 could also be used for hybrid vehicles. Further, other power transmission mechanisms, such as chain drives, could be used. Transmission system 10 could be used in vehicles such as motorcycles, scooters, light 3 and 4 wheeled vehicles but not limited to these applications.

The transmission system 10 is a non-synchromesh type automated manual transmission system, operation of which is controlled by a control unit. The control unit selects the appropriate gear ratio in accordance with a pre-determined strategy programmed into it. Clutch assembly 6 is included to control power transmission from the engine to the rest of transmission system 10.

The transmission system 10 has a housing to which are rotatably mounted an input shaft 7 and an output shaft 30 to rotate in co-operation during engine operation to transmit power to wheel via a suitable arrangement of meshing gears.

The input shaft 7 and output shaft 30 of the transmission system 10 are rotatably disposed in parallel relation and have five forward input gears 61a, 62a, 63a, 64a, 65a and five forward output gears 61b, 62b, 63b, 64b, 65b respectively mounted on them. Forward input gears 61a, 62a, 63a are fixed to input shaft 7. Forward input gear 64a and 65b are freewheeling gears not fixed to the input shaft 7. To establish selected gear ratios, specific fixed input gear is moved into engagement with adjacent input freewheeling gear by a shift fork of a gear shift actuator (not shown). For one such selected gear ratio, fixed input gear 62a is moved into engagement with adjacent input gears 64a by a shift fork of a gear shift actuator. For this purpose the input gears are provided with complementary engagement means in the form of lugs 66 and kidneys/slots 67 arranged in a circular array on each of the input gears 62a, 64a respectively. Establishment of a gear ratio requires mating of the lugs 66 and kidneys/slots 67.

In the absence of the drag inducing mechanism 700 which is to be described, the lugs 66 provided on fixed input gear 62a may not mesh or lock with corresponding kidneys/slots 67 provided on the pairing freewheeling input gear 64a, particularly the fixed input gear 62a to the left of freewheeling gear 64a, for example when fourth gear is engaged. Rather, the lugs 66 may miss the target kidney slots 67 and impact, or clash, with a solid part of the input gears 64a preventing power transfer at the intended gear ratio.

A primary driving gear 5 is mounted on the crankshaft (not shown) and a primary driven gear 3 is mounted to rotate about input shaft 7. The primary driving gear 5 and primary driven gear 3 may be directly meshed with each other for continuous power transmission. Alternatively, the primary driving sprocket 5 and primary driven sprocket 3 may be connected by chain drive to transmit power. When the clutch assembly 6 is engaged, the primary driven gear 3 and the input shaft 7 are engaged, so that power from the engine causes input shaft 7 to rotate at a first operational speed suitable for operation of the vehicle. Conversely, the power transmitted between engine crankshaft and the transmission system 10 is interrupted, for example to change gear, through disengagement of clutch assembly 6. Engagement and disengagement of the clutch assembly 6 is done through a clutch actuator in the form of an electric stepper motor (not shown) controlled by the control unit. Alternatively, clutch assembly 6 engagement and disengagement can be done manually as well.

The forward input and output gears 61a to 65a and 61b to 65b of non-synchromesh transmission system 10 are in constant mesh. While changing the speed of the vehicle, the input and output gears are shifted using a gear shift actuator to establish different gear ratios according to the pre-determined transmission control strategy.

During vehicle running, the control unit implements a predetermined gear selection strategy and so a clutch engagement/disengagement strategy. When, a gear change is required, the transmission control unit operates the clutch actuation motor to engage clutch assembly 6. At the same time, the transmission control unit operates a gear shift actuator (through an electric gear shift actuator stepper motor) to select the required gear ratio.

To address the potential clash problem, transmission system 10 includes a drag inducing mechanism 700 mounted to act on primary driven gear 3 and provide a drag force that can induce and increase a relative motion between the freewheeling gear 64a and fixed gear 62a. To this end, the drag inducing mechanism 700 is positioned in contact with primary driven gear 3 and mounted on the input shaft 7.

Figure 2 shows a sectional view of the drag inducing mechanism 700 which comprises a sleeve element 1, an abutting element 2 and a spring element 4. Drag mechanism 700 is fixedly mounted, through sleeve element 1, to input shaft 7 and rotates with it. Order of mounting of elements of the drag inducing mechanism 700 from clutch assembly 6 side of the transmission assembly 10 is the abutting element 2, the spring element 4 and the sleeve element 1.

As shown in Figures 3A to 4B, the abutting element 2 is of annular cross-section and mounted such that the sleeve 14 extending inwards from the inner periphery of the abutting element 2 fits over the cylindrical body 11 of the sleeve element 1. A spring retainer part 13 of the abutting element 2 faces towards an outwardly projecting sleeve collar 12 and holds the spring element 4 within its inner periphery. Sleeve 14 extending separates a face 2a of abutting element 2 (this face 2a acting on primary driven gear 3 and the spring retainer part 13. The drag inducing mechanism 700 is further provided with a washer 9 which fits within the cavity formed by the abutting part of the abutting element 2. The washer 9 helps to achieve uniform surface contact and force transmission of spring force through the abutting element 2 to primary driven gear 3. In the assembled mode of the drag mechanism 700, the spring element 4 is compressed between the sleeve element 1 and the abutting element 2. Indeed, the spring element 4 is a helical compression spring here with a low spring rate (for e.g. approx. 1.4 N/mm). Preferably, spring rate of the spring used in in the range of 0.5 N/mm to 4 N/mm. The spring element 4 is configured such that the variation in axial load acting on the abutting element remains low even with considerable stack and part variations

From this description, it is apparent that this is a low cost and easy to manufacture drag inducing mechanism 700 readily installed at the vehicle OEM manufacturer.

Abutting element 2 abuts and acts under spring force of spring element 4, through its face 2a, against a face 3a of the primary driven gear 3. The spring constant of spring element 4 is selected, through factory testing, to bias drag inducing mechanism 700, through its face 2a and washer 9 into sufficient frictional engagement with primary driven gear 3 such that a small amount of torque or positive drag will be transmitted from primary driven gear 3 to the input shaft 7. The quantum of torque transmitted is much less than the above mentioned first operational speed required for operation of the vehicle under non-clash conditions. However, the torque is sufficient to create relative motion of input gears 62a and 64a to enable successful engagement of lugs 66 and kidneys 67, meshing of gears 62a and 64a (left hand to gear 62a in Fig. 1) and avoidance of a clash problem. The transmitted torque, through turning of the spring force of spring element 4, is also selected to minimise noise and shifting force required during the gear shift.

The above described approach differs from conventional practice in the prior art where drag is applied by increasing the clutch drag. However, it is very difficult to control the drag value by this method and clutch applied drag is usually higher than required with potential to adversely affect the clutch life.

To expand, when the clutch assembly 6 is disengaged by the control unit, power transmission from the primary driven gear 3 to the input shaft 7 stops. In this case, the primary driven gear 3 freely rotates (or “freewheels”) over the input shaft 7. However, the drag inducing mechanism 700 remains frictionally engaged with the primary driven gear 3 through the abutting element 2. The abutting element 2 slip-rotates due to its pressurized surface contact with the primary driving gear 5 due to force exerted by the spring element 4. As a result, the spring element 4 also rotates. Due to its inherent elasticity, the spring element 4 makes the sleeve element 1 rotate and creates a drag force.

It can clearly be seen that the drag inducing mechanism 700 is distal from clutch assembly 6. Torque transmitted to input shaft 7 through primary driven gear 3 bypasses the clutch assembly 6. This torque is transmitted to input shaft 7 independently of whether the clutch assembly 6 is engaged or disengaged. This means that clash can be addressed without need for complex clutch actuation strategies though these could be adopted as a further corrective action in certain circumstances.
In contrast, when the clutch assembly 6 is engaged by the transmission control unit, engine power is transmitted through the primary driving gear 5 and primary driven gear 3 to the input shaft 7 in the normal way. In this case, the drag inducing mechanism 700 rotates with the input shaft 7 without any functional role.

Clash situations similar to dog and kidney engagement of gears on a single shaft may occur while meshing the gear teeth of gears on different shafts. The described drag inducing mechanism 700 also assists in avoiding clash during mating of complementary gears, whether fixed or freewheeling, mounted on at least two different rotatable shafts while gear shifting. The drag mechanism helps to induce and increase the relative speed between the shaft on which clashing gears are mounted and thus remove the clash. This becomes especially useful in case of reverse gear shifting. However, the functionality of the drag inducing mechanism to provide relative motion and torque may be useful in other situations as well.

Referring now to Fig. 5, the drag inducing mechanism 700 allows clash during reverse gear shifting to be avoided. As shown, the reverse gear mechanism 320 comprises a reverse input gear 324 fixedly mounted by spline joint on the input shaft 7 and meshed with a reverse idle gear 326, the reverse idle gear 326 being meshable with reverse output gear 328 mounted to freely rotate on output shaft . Reverse output gear 328 is moved into engagement with reverse idle gear 326 in response to movement of a reverse output gear shifter in the form of shifter sleeve 330. Shifter sleeve 330, which is slidably mounted on the output shaft 30 and movable in response to movement of a reverse shift fork (not shown), has lugs 330a for engaging with complementary kidneys 328a on the reverse output gear 328 when reverse gear shift is completed.

If, while engaging reverse idle and reverse output gears 326 and 328, a clash condition occurs, the drag inducing mechanism 700, as described above, causes relative motion between the reverse output gear 328 and the shifter sleeve 330 to eliminate clash.

The drag mechanism described above may be used in various shaft transmission layouts such as two shafts, three shafts, four shafts, etc.

In two wheeled vehicles with manual transmission such as dog clutch type non-synchromesh transmission system, when clash condition occurs and in case the vehicle gets stalled due to clash condition, the vehicle is moved forward and backward by disengaging clutch to remove the clash. However, in three and four wheeled vehicles with dog clutch type non-synchromesh manual transmission system, when clash situation occur and vehicle gets stalled, it is not feasible to move vehicle forward and backward by pressing clutch to eliminate clash. The drag mechanism according to the invention can be used conveniently in such transmission systems to avoid such situations.

All variations and modifications of the transmission system or drag inducing mechanism described above that are obvious to skilled persons are deemed within the scope of the present invention. The applicant intends to rely on the provisional specification and drawings submitted with provisional specification.
,CLAIMS:1. A transmission system for a vehicle comprising:
a drive means for supplying power from a prime mover to said transmission system;
a shaft co-operable with said drive means to accept power from said drive means; and
a clutch assembly for controlling supply of power from said prime mover to said shaft dependent on whether said clutch assembly is disengaged to interrupt power supply or engaged to provide power supply;
wherein said shaft includes a drag inducing mechanism operable for accepting a controlled amount of drive from said drive means independently of whether said clutch assembly is engaged or disengaged.

2. A transmission system for a vehicle, said transmission system being a non-synchromesh type transmission system and having a plurality of gear ratios comprising:
at least one rotatable shaft receiving drive from a prime mover comprising at least one fixed gear or gear shifter and at least one freewheeling gear mounted on said shaft or constantly meshed with said rotatable shaft, said fixed gear and said freewheeling gear being provided with complementary engagement means for engaging the gears as a pair when selected for a gear shift; and
a clutch assembly for controlling supply of power from a prime mover to the transmission system and operable during a gear shift;
wherein a drag inducing mechanism is co-operable with at least one of said rotatable shafts to induce or increase relative motion between said fixed and freewheeling gears to establish a selected gear ratio independently of whether said clutch assembly is engaged or disengaged.
3. The transmission system of claim 1 wherein said operating conditions include, gear clash conditions where the delivery of a controlled amount of drive assists producing drag to reduce clash duration.
4. The transmission system of claim 3 wherein said operating conditions include gear clash conditions during reverse gear shifting.

5. The transmission system of any one of claims 1 to 4 wherein said clutch assembly is mounted on the input shaft.

6. The transmission system of any one of the preceding claims wherein said clutch assembly is mounted on a crankshaft.

7. The transmission system of any one of the preceding claims wherein the drag inducing mechanism is arranged to induce positive and controlled drag by connection of the drag inducing mechanism to the input shaft as at least one rotatable shaft, said input shaft being arranged to receive drive from the prime mover independently of whether the clutch assembly is engaged or disengaged, said drive being substantially small in quantum compared to that required to properly operate a vehicle with the transmission system.

8. The transmission system of claim 7 wherein drive induced by the drag mechanism is just enough to induce relative motion between gears of a gear pair to clear the clash.

9. The transmission system of any one of the preceding claims wherein said drive means comprises a primary driving gear engageable with a primary driven gear mounted on said input shaft and said drag inducing mechanism is placed such that a portion of torque from said primary driven gear acts on the input shaft enabling a positive drag and rotation of the input shaft sufficient to reduce duration of clash.
10. The transmission system of any one of claims 2 or 5 to 9 as dependent from claim 2 wherein said at least one gear and said corresponding gear are mounted on different shafts of the transmission system.

11. The transmission system of any one of claims 2 or 5 to 9 as dependent from claim 2 wherein said at least one gear and said corresponding gear are mounted on the same shaft of the transmission system.

12. The transmission system of claim 11 wherein said at least one gear is fixed on said shaft and said corresponding gear is mounted to freewheel on said shaft.

13. The transmission system of claim 9 wherein said drag inducing mechanism is in frictional engagement with said primary driven gear so that torque is transmitted from the primary driven gear to the input shaft in amount sufficient to induce or increase relative motion to desired level while reducing gear shift time.

14. The transmission system of any one of the preceding claims wherein said drag inducing mechanism comprises a sleeve element mounted fixedly on the input shaft; an abutting element which is in friction/pressure-based contact with the primary driven gear and which rotates relative to the input shaft when the clutch is disengaged; and a spring element mounted to rotate with the sleeve element and act against the abutting element to increase friction/pressure between the abutting element and the primary driven gear to induce positive drag and rotation of said input shaft.

15. The transmission system of claim 14 wherein, during the clutch disengaged condition, the speed of rotation of the input shaft is based on slip present between the primary driven gear and the abutting element, which in turn depends on the axial pressure exerted by the spring on the abutting element.
16. The transmission system of claim 14 or 15 wherein the amount of positive drag torque transferred to the input shaft from the prime mover is varied by changing the spring dimension and/or spring constant.

17. The transmission system of any one of claims 14 to 16 wherein said spring element is a helical compression spring.

18. The transmission system of claim 16 or 17 wherein said spring constant is a low spring constant in the range of 0.5N/mm to 4N/mm.

19. The transmission system of claim 2 or any one of claims 5 to 18 as dependent from claim 2 wherein said at least one gear shifter and at least one freewheeling gear mounted on said shaft or constantly meshed with said rotatable shaft, said shifter being movable to engage with said at least one freewheeling gear when selected and wherein said drag inducing mechanism is mounted to introduce relative motion between said at least one freewheeling gear and gear shifter.

20. The transmission system of claim 19 including a wherein said freewheeling gear is a reverse output gear mounted on an output shaft of said transmission system.

21. The transmission system of claim 20 including a reverse gear mechanism comprising a reverse input gear mounted on an input shaft; a reverse idle gear meshed with said reverse input gear; and a reverse output gear mounted on an output shaft and meshable with said reverse idle gear wherein said reverse output gear is movable into engagement with said reverse idle gear in response to movement of a reverse output gear shifter mounted on said output shaft and wherein said drag inducing mechanism is operable to induce relative motion between said reverse output gear and said reverse output gear shifter.
22. The transmission system of claim 21 wherein said reverse output gear shifter is a sleeve slidably mounted on said output shaft, said sleeve comprising lugs engageable with complementary engaging means of said reverse output gear.

23. The transmission system of any one of the preceding claims being selected from sliding mesh or clash mesh transmission systems, which could be manual or automated or a combination thereof.

24. The transmission system of any one of the preceding claims wherein said prime mover is selected from internal combustion engines, electric motors or combination thereof.

25. A drag inducing mechanism for a transmission system having input and output shafts, said input shaft having a primary driven gear mounted thereon and said drag inducing mechanism comprising a sleeve element mounted fixedly on the input shaft; an abutting element which is in friction/pressure-based contact with the primary driven gear and which rotates relative to the input shaft when the clutch is disengaged; and a spring element mounted to rotate with the sleeve element and act against the abutting element to increase friction/pressure between the abutting element and the primary driven gear to induce positive drag and rotation of said input shaft.

26. A vehicle comprising the transmission system of any one of claims 1 to 24.