DESC:FIELD OF INVENTION:
This invention generally relates to a system and method for controlling a gear shift drum and more specifically though not exclusively to a system and method for controlling the engagement and disengagement of gears through enablement of precise control over the velocity and position of the gear shift drum in an Automated Manual Transmission (AMT) system for a prime mover such as an internal combustion engine or electric motor.
BACKGROUND OF THE INVENTION
In a non-synchromesh type transmission, for example a clash mesh type transmission, a lug and kidney arrangement is typically used for engaging and disengaging gears. Gear shift operation entails the selection and engagement of a desired gear as per the vehicles torque demand. This may call for disengagement from existing gear and engagement to a desired gear which is given effect by rotating a gear shift drum that has a guiding pathway, also called a cam or actuator groove, set into its external profile. A gear selector forks movement is guided by said groove upon the rotation of the drum which enables the desired movement of a gear selector fork. The gear selector fork is in turn operably fixed to one of the fixed or freewheeling gears which have male lugs/projections while a corresponding gear carries female kidneys/slots. Lugs and slots are designed such as to interlock and engage with each other. During gear shift operation, the lugs enter the slots in order to lock the fixed and freewheeling gears together and thus complete the gear shift operation. When the gear shift drum rotates to enter a gear engagement zone, there is a non-trivial probability that the lug could clash with the kidney wall while the drum is traversing that zone. The gear engagement zone therefore is a clash prone zone.

Such a condition restricts the gear from being engaged and must be avoided if possible. A swift gear engagement operation increases the chances of encountering a clash condition. In event of a clash condition, the gear shift drum rotation 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. lug 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. A mechanism to such effect is disclosed in a patent application numbered 3470/CHE/2011 and the same is incorporated herein by reference.

Thus to minimise its occurrence during shift operation, the engagement must be precisely timed and positioned. But doing so has shortcomings of its own. The overall time taken to shift gears is increased as a consequence of increased precision and control over the gear shift operation.

In vehicles where the prime mover is mated to an AMT, the gear shift operation and all its concomitant operations including clutch disengagement, gear drum rotation and clutch engagement are automated using electromechanical actuators, motors and sophisticated control systems, all of which are governed by a controller. AMT systems are chosen over Continuously Variable Transmission (CVT) systems because of their higher torque transmission capacity and higher transmission efficiency. CVTs offer better ease of operation and given their continuous nature of transmission, they operate without undesirable phenomenon such as shift shock, commonly observed in Manual Transmission (MT) and AMT systems where the vehicle experiences jerks, for example, when it moves from 1st gear to 2nd gear, due to torque variations.

It is pertinent that in such AMT based vehicles, the gear shift operation concludes in the shortest time period with no noticeable drop in torque. This is a challenge when the AMT uses a non-synchromesh type transmission system, for example a clash mesh type transmission as aforementioned, where the occurrence of clash condition during gear engagement is sought to be avoided. Therefore for gear shift operation to be successful without undesirable delay, the position of the gear shift drum as well as the speed at which it is made to rotate by a shifter motor must be controlled with precision and speed.

Conventional control systems which employ a control loop feedback mechanism based approach to set the position of the gear shift drum have several shortcomings, the most prominent of which is that of shifter motor overshoot, whereby the gear shift operation’s precise control is lost giving rise to situation wherein the gear shift operation may leak through to a consecutive gear range. Such overshoot may represent a substantial angle of rotation, for example more than 70º or more than 80º, depending on the number of gear ratios provided by the transmission system.

The aforementioned actuator grooves formed into the shift drums external profile are designed such that every degree of its rotation translates into a specific motion of the selector forks. Fig. 1 shows a conventional gear shift drum 710 used in an AMT system with three actuator grooves 720 and associated shift forks (not shown). One complete rotation of the drum 710 corresponds to a gear shift from 1st gear to the 5th gear with each gear in between being engaged after a rotation of 72 degrees.

Any overshoot by the shifter motor may cause a shift fork to enter into the clash zone prematurely or reach beyond the gear engagement zone respectively. It is noticed that conventional techniques based on a control loop feedback mechanism are problematic because of an overshoot in the range of 15 to 20 degrees which further aggravates the aforementioned issues. This hinders gear engagement and may give rise to the above described undesirable clash condition. Clash itself is most likely to occur in certain angle ranges.

Furthermore, when a gear shift operation entails the rotation of the gear shift drum towards either ends of the actuator groove set into the external profile of the shift drum, there is a non-trivial probability that the gear shift drum rotation is overshot and the drum, instead of coming to rest at the designated gear position, traverses further towards the actuator grooves end point. This causes the portion of the gear selector fork which follows the actuator groove to collide with the actuator groove’s end point and produce an undesirable noise.

Therefore for an AMT to be efficient in its operation, it must strike the right balance in optimising gear engagement, minimising occurrence of clash and minimising the time it takes to conclude a gear shift.
OBJECTS OF THE INVENTION:
It is the primary object of this invention to provide a system and method for more precise control of the gear shift drum in an AMT.

It is a further object of this invention to provide a system and method for optimising the time taken for the gear shift operation to conclude whilst minimising the odds of occurrence of clash condition during gear engagement in an AMT.

It is also an object of this invention to provide a system for controlling gear shift drum with minimal computational load on the controller thereby providing a cost effective, efficient and responsive control system.

It is yet another object of this invention to provide a simple, robust and cost effective solution to the above stated technical problem in an AMT.

SUMMARY OF THE INVENTION:
With such objects in view, the present invention provides A gear shift drum control system for a prime mover mated to an automated manual transmission comprising:
a. a gear shift drum;
b. a gear shift drum position determining means;
c. a gear shift drum rotating means; and
d. a control means configured to accept at least one input from a gear shift drum position sensor; to process the received input using at least one processor and to generate an output command to control the gear shift drum rotating means wherein the control means receives input from at least one vehicle or engine parameter sensing means and sets a target velocity for the rotating means corresponding to each of a plurality of predefined drum positions based on the inputs received from vehicle or engine parameter sensing means within shifting of a gear ratio.

In another aspect of the invention, the control means accepts input from at least the gear shift drum position determining means and outputs a command to control the gear shift drum rotating means wherein the rotation of the gear shift drum for a gear shift is controlled at least in one velocity control phase and at least one position control phase. Such gear shift may occur between two gears corresponding with differing transmission ratios or between a gear having a transmission ratio and a neutral gear.

In the event of a clash condition occurring during gear engagement, the control means may halt the rotation of the rotating means until the clash condition is resolved and then proceeds towards gear engagement by setting a target velocity for the rotating means corresponding to each of the plurality of predefined drum positions within the shift operation.
Further, the control means may also switch from the velocity control phase to the position control phase by directing the gear shift drum rotating means to reach, for example, a previous position and maintain the position until the clash condition is resolved and then proceed towards gear engagement by switching to a velocity control phase.

The gear shift drum rotating means is conveniently an electric drum shifter motor, a duty cycle for whose operation can readily be controlled by an electronic control means or transmission control unit.

Conveniently, in the velocity control phase, the control means sets a desired velocity control strategy for the gear shift drum and its associated motor during a gear shift, this strategy being programmed into a processor of the control means advantageously configured to operate with a minimal number of sensors which would reduce cost and failure risk. The processor is conveniently pre-programmed with a look up table programmed with target velocities for a plurality of predefined drum positions corresponding with the different gear ratios of the transmission system. Based on the current position of the gear shift drum, the processor looks up the target velocity for the demanded gear shift and commands the motor to reach target velocity following the feed forward control strategy. Based on determined drum position, the target velocity is updated, as required, based on instructions in the look up table. This process continues until the gear shift drum reaches its final resting position with gear engagement concluded – the conclusion phase described above.
The above control strategy includes feedback or PID control to reduce error between actual velocity and target velocity for the gear shift drum by controlled operation of the drum shift motor.

A further control algorithm is also included in the processor to control velocity of the drum shift motor having regard to a reference model including target velocities for the drum shift motor for the plurality of predefined drum positions taking a number of manufacturing and operational parameters for a representative reference or control AMT system as programmed into the control means under factory conditions. Such parameters may include a plurality of drum shape and size; degree of drum position at which lug and kidney – gear mating portions – just meet (as probability of gear clash is governed by drum speed at this drum position; gear ratio between gear shift drum and rotating means where, as desirable, this is governed by speed of an electric motor with its own transmission; rotating means characteristics; shift fork inertia; clutch bite point and clutch stroke; and relative speed control between the input and output shafts of the transmission system. This selection of parameters is not limiting.

The processor will also allow for correction of error between the actual drum velocity and the reference model drum velocity through a feedback control strategy such as a PID control strategy.

Based desirably on a combination of these strategies, the processor outputs a final duty cycle for the shift drum motor allowing avoidance of any substantial overshoot problem while minimising sensor expense and expense for the transmission control system. It is to be noted that other vehicle and engine operating parameters may be taken into account in the velocity control strategy, for example engine speed, wheel speed and clutch bite point location. By way of still further example, target gear shift drum rotation velocity can be modified depending on the rate of rise or fall of engine speed. If the rate of rise of engine speed is higher than a threshold value, the target drum velocity may be increased. Target drum velocity may be decreased if the rate of fall of engine speed is higher than a threshold value. The processor may include values for a range of gear shift drum motor speeds corresponding with each of the plurality of drum positions and gear ratios which may include neutral position or neutral position(s) placed intermediate selected or all gear ratios to accelerate gear shifts. The processor may also be configured to select an optimum speed profile from within the range of values depending on vehicle operational requirements.

As described above, the gear shift drum is desirably provided with neutral positions between the gear positions to avoid a complete down shift or up shift as the case may be, to move from an engaged gear to a neutral position. This becomes particularly undesirable when the engaged gear is a higher gear, and shifting to a neutral position from said gear is time consuming. Further, if the vehicle were to malfunction due to issues including sensor failure, hardware malfunction or an abrupt vehicle turn off due to any reason, the vehicle must not remain stuck in a gear. It is desirable that the vehicle be brought to a neutral position so as to enable the user to at least manually transport the vehicle. Since gear shift drum moving into neutral position is not subject to the occurrence of a clash condition, a different rotation speed profile at substantially lower speed can be used when moving into neutral position thereby minimising the chances of an overshoot. An overshoot is undesirable in a situation when the gear shift drum is rotated such as to enter a neutral position as that would lead to the successive gear being engaged.

Further, when the gear shift is initiated from a neutral position towards the engagement of a gear, there is a non-trivial possibility of the occurrence of a clash condition. In such a situation a new profile may be provided or the same velocity profile configured for a gear shift operation from an engaged gear to a neutral position may be employed.

The control means switches from a velocity control phase to a position control phase gear engagement zone after completion of gear engagement as determined by gear shift drum position or gear shift drum position being in a predefined acceptable position range where feedback control over the rotating means is quite sufficient. Such control may depend solely on control over the operation of the gear shift drum rotating means, this being rotated when required because of determined error in gear shift drum position following a feedback or PID control strategy. One strategy may simply involve pulsing a motor as required where a motor, as would be typical, is used as the gear shift drum rotating means. Through implementation of the position control strategy, in particular, there is no requirement for the mechanical detents of prior AMT systems.

In a particularly desirable gear shift drum velocity profile, which may assist in avoiding clash, the control means operates the gear shift drum motor so that the velocity, i.e. angular velocity, of the shift drum peaks upon initiation of rotation and reduces subsequently as the gear drum approaches a predefined gear engagement zone. On conclusion of engagement, gear shift drum velocity should be zero.

The control velocity profile may vary depending on the demanded gear shift. That is, clash is a more common phenomenon for particular gear shifts, for example from first to second speed in a conventional AMT system. The control means may deploy the drum velocity profile strategy taking such considerations into account.

This system and its corresponding method of operation enable control of the gear shift drum such that the time required for gear shifting operations is minimised whilst also minimising the chances of occurrence of a clash condition during gear engagement in a non-synchromesh type AMT system. The system comprises a control means in the form of at least one programmable processor which accepts inputs from a desirably minimal number of sensors including vehicle or engine parameter sensors and controls at least one electromechanical actuator for rotation of the gear shift drum based on pre-programmed control strategies by utilizing the sensed parameters.

Vehicle or engine parameter sensors may be selected from those commonly used in AMT systems but with a view to controlling cost as mentioned above. Such sensors may be selected from the group comprising at least of engine speed (RPM) sensors, throttle position sensors, clutch position sensors, gear shifter drum position sensors and vehicle or wheel speed sensors. Gear shift drum position sensors is particularly useful and is the most convenient and inexpensive way to determine gear shifter drum position.

Conveniently, the control means such as the programmable processor described above accepts inputs from a gear shifter drum position sensor and processes the inputs to control the drum rotation means, for example the shifter motor which rotates the gear shift drum in accordance with the above described strategy. Within the entire range of rotation of the gear shift drum are defined a gear engagement zone for each sequential shift (B to C), being the zones in which the likelihood of occurrence of clash condition during gear engagement for each gear is maximum and gear engagement zone where the gear shift operation concludes.

The system enables clash detection. When, for example, gear shifter drum position is mapped against time, a reverse in slope of a gear shifter drum position versus time characteristic evidences clash.

Further, the reference model described earlier includes optimised gear shift drum velocity information for the various gear shifts with a view to minimised probability of clash during gear engagement and the control means may control velocity accordingly as described above. Such velocity information includes information optimised for avoidance of clash in clash prone zones, such as the approximate 44 to 64 degree clash prone zone noted above.
A clash mechanism may advantageously be included, this mechanism being activated when clash is detected to reverse the direction of rotation of the gear shifter drum without requiring reversal of direction of the drum rotation means such as the above mentioned shifter motor. A mechanism to such effect is disclosed in a patent application numbered 3470/CHE/2011 and the same is incorporated herein by reference.

The control means will advantageously not switch between shifter drum velocity control and shifter drum position control if clash is detected.

The control means, for example the above mentioned processor, senses clutch actuation and advantageously controls the gear shifter drum rotation means to overlap gear shifter drum rotation with clutch disengagement to reduce overall time for a demanded gear shift.

On conclusion of the gear engagement, the control means switches from velocity control as above described to position control. Position control may depend on feedback or PID control over gear shifter drum position so that any error between sensed position and demand position is corrected by operation of the rotation means. This involves finer control over gear shifter drum rotation than during a velocity control phase, minimised overshoot and makes the need for detent mechanisms redundant.

This system advantageously reduces the changes of occurrence of clash condition by precisely controlling the position of the gear shift drum and also reduces the jerks perceived by the user under clash condition. Therefore the proposed system and method reduces the lag in gear shift operation in a non-synchromesh type AMT system without noticeable drop in torque.

The term ‘prime mover’ as used in this specification includes any device for providing motive force for a vehicle, for example an internal combustion engine or electric motor. Application is not limited to vehicles; other devices using an AMT system are also included.

BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 shows the calibration of the rotation of the gear shift drum for each shift event and the corresponding pathway on the drums external profile.
Fig. 2 is a sectional view of a sequential transmission system according to one embodiment of the present invention
Fig. 3 is a cross sectional developed view of the sequential transmission system of Fig. 2 showing the gear shift actuator system.
Fig. 4 is a front view of the gear train of the sequential transmission system as shown in Fig. 3.
Fig. 5 is a detail side cross-sectional view of the drum shift and drum shift actuator of the sequential transmission system as shown in Figs. 2 to 4.
Fig. 6 is a rear side view showing the sequential transmission system and its relationship to the rear wheel of a motorcycle employing the sequential transmission system.
Fig. 7 is an orthogonal view of the shift drum of the sequential transmission system as shown in Figs. 2 to 6.
Fig. 8 is a top view of the shift drum of Fig. 7 showing its mounting in the transmission system and
Fig. 9A is a developed view of the shift drum for a five speed transmission shown in Figs. 7 and 8.
Fig. 9B is a developed view of the shift drum for a five speed transmission shown in Figs. 7 and 8 showing index and ramp angles for the shift drum.
Fig. 10 is a block diagram representing the gear shift drum control strategy.
Fig. 11 is a flowchart explaining the operation and decision making involved in the control of the gear shift drum subject to the various parameters.
Fig. 12 is a block diagram explaining the processing of the input signals to gain outputs which can be used as parameters in the decision making in the control logic for the gear shifter drum.
Fig. 13 shows a velocity profile used in a reference model for the control strategy illustrated through the block diagram of Fig. 10.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION:
Now, the present invention will be described by referring to the above drawings that illustrate preferred but non-limiting embodiments of the invention. The gear shift drum size, shape, index angles, gear positions, drum angular positions and corresponding drum velocities and the values of other associated parameters are disclosed as per one of the embodiment of the present invention and may change based on the requirement, vehicle type etc. Therefore the examples should not be construed as limiting the scope of the present invention described herein.

Referring now to Figs. 2 to 8, there is shown an automated manual transmission system 10 mounted in a scooter type motorcycle for transmitting power from the crankshaft 200 of a prime mover in the form of single cylinder internal combustion engine 150 to the rear wheel 300 (as conveniently shown in Fig. 6) through a drive chain 90 and, through operation of the transmission system 10, at a desired gear ratio. The prime mover need not be an internal combustion engine; it could be an electric motor for example.

Cylinder 400 is shown together with its associated connecting rod 410 connecting its piston 412 to the linkage 415 for providing drive to the crankshaft 200 as a gaseous or liquid fuel is combusted in cylinder 400. Magneto 270 is also shown mounted to crankshaft 200. The crankshaft 200 and linkage 215 are mounted within crankcase 210.
Rotation of the crankshaft 200 causes rotation of drive sprocket 205 and chain 90. A substantial portion of the chain drive 90 is enclosed within chain case 220. Chain drive 90 is lubricated using a lubrication system (not shown). To facilitate operation of transmission system 10, the direction of rotation of the chain drive 90 is made common with the engine (through crankshaft 200) and the rear wheel 300 by including intermediate shaft 23.

Automated manual transmission system 10 includes a powertrain housing 20 which is separated and made distal from, though integral with, engine crankcase 210 by chain case 220. Rotatably mounted within powertrain housing 20 is the rotating output sprocket 95 of drive chain 90. The output sprocket 95 rotates essentially at engine speed so speed reduction, through the transmission system 10 is required for driving rear wheel 300. To that end, the output sprocket 95 is engageable with the primary gear 94 of an input shaft 22 rotatably mounted to the housing 20, through operation of clutch 60 by automatically controlled clutch motor 620, required speed being achieved through establishment of a gear ratio.

Transmission system 10 is a sequential drum shift clash mesh transmission system having five gear ratios in the illustrated embodiment and includes input, intermediate and output gear trains comprising three gears for each of the input shaft 22 (gears 22a-22c), intermediate shaft 23 (gears 23a-23c) and output shaft 24 (gears 24a-24c).
Movement between the gear ratios, in sequential manner, involves a gear shift drive system 35 including a gear shift drum 40 and a shifter drum drive 45 as rotating means for turning the shift drum 40, on demand, through a selected angular movement to a position corresponding to a selected gear ratio under control of a transmission control unit such as a micro-processor 1000.

Arrangement of the components of gear shift drive system 35, including gear shift detector 410 and its protective cover 412, is conveniently shown in Fig. 3. The absence of detent mechanisms, in particular made possible through the gear shift drum position control strategy described below may especially be noted.

Shift drum 40 is provided on its outer peripheral surface with three actuator or cam grooves 40A, each corresponding with the respective input shaft 22, intermediate shaft 23 and output shaft 24, which extend around substantially the whole circumference, approximately 330º, of the shift drum 40. Such features have the advantages described in the Applicant’s co-pending Indian Provisional Patent Application No. 4942/MUM/2015, the contents of which are hereby incorporated herein by reference.

The configuration of actuator grooves 40A, which accommodate and enable sliding movement of shift forks 47a-47c (respectively operating the respective gear trains Gi, Gin and Go to establish the required gear ratio) within them through an index angle of rotation of shift drum 40 enabling change in gear ratio under control of the transmission control microprocessor 1000 following a strategy which will be described further below.

Shift drum drive 45 comprises a single phase DC electric drum shift motor 120, or a stepper motor, operated on demand by the microprocessor 1000, mounted using suitable bearings 20B to portion 20A of the housing 20. Shift motor 120 has an output shaft 121 projecting into a reduction gearbox 90 comprising a reduction gear train including a drive gear 122 forming a splined portion of output shaft 121, sector gear 123, driving gear 124 and driven gear 41 connected to an axle 42 of shift drum 40. Axle 42 has an axis also in parallel with input shaft 22, intermediate shaft 23 and output shaft 24. Sector gear 123 is rotatably mounted on shaft 127 and driving gear 124 is formed integral with rotatable shaft 127. The reduction gear train allows shifter motor 120 to be operated in a gear ratio appropriate to the gear shift demanded by the transmission control microprocessor 1000.
Connected to shaft 127 is a clash mesh mechanism 300 to reduce jerk when the drive gear 122 rotates, during operation of shift motor 120, rotating sector gear 123 and shaft 127 and its fixed driving gear. Spring 310 of clash mesh mechanism 300 urges the sector gear 123 into engagement with driving gear 124.

Angular movement of shift drum 40, by controlled movement on operation of drum shift motor 120 by the transmission control microprocessor 1000, causes its associated shifters or forks 47a-47c to controllably slide along cam grooves 40a to move freewheeling gears included in each of the gear trains described above into position to establish the required gear ratio.

Gear shift position is sensed by a position sensor 420 in the form of a relatively inexpensive Hall Effect sensor which provides a signal processable by microprocessor 1000 to determine the gear shift drum speed.

Shift forks 47a-47c are slidably mounted on guide shafts 471, 472 and 473 and move into position, as they move along actuator grooves 40A to bring required gears in gear trains Gi, Gin and Go into engagement to establish a gear – when commanded by the transmission control microprocessor - by positioning shift forks 47a-47c in particular portions corresponding with each gear within each actuator groove 40A.

The portions corresponding with each gear are shown, in Figs. 9A and 9B marked “1”, “2”, “3”, “4” and “5” for each of actuator grooves 40A. These positions are separated by an index angle of about 81º as shown in Figs. 9A and 9B. In between each gear ratio position at 40.5º is an intermediate neutral position, N. The magnitude of the index angle achievable for transmission system 10 reduces gear shift actuator complexity, cost and ease of operation compared with such prior transmission systems, especially when factors as further described below are accounted for.
For effective gear shifting, including avoidance of clash, it is important to control the gear shift to minimise or avoid any substantial overshoot beyond the 81º index angle, and hence can result in engagement of an incorrect gear, Such incorrect gear selection could at least result in vehicle operability issues and could also result in engine damage. These challenges are addressed by the gear shift control strategy in the following manner.

In short, the transmission control micro-processor 1000 accepts inputs from the gear shift drum 40 position sensor (giving position information) and outputs commands to control operation of the drum shift motor 120 wherein the rotation of the gear shift drum during a gear shift is controlled in a velocity control phase and a subsequent position control phase. The block diagram of Fig. 10 illustrates the strategy showing a feed forward control strategy driving the velocity control phase to minimise probability of clash and overshoot, though allowing for feedback or PID control where gear shift drum 40 speed departs from a target velocity profile including comparison with reference model velocity ; and a feedback or PID control strategy for the position control phase where gear shifter drum 40 is at or acceptably close to the required position for the selected gear. The gear shift control strategy enables the drum shift motor 120 to perform the required final duty cycle to achieve these objectives.

In the velocity control phase, the transmission control micro-processor 1000 sets a target velocity for the gear shift drum 40 corresponding to a demanded one of a plurality of predefined drum positions within the velocity control phase of the gear shift operation and transits into the position control phase where a predefined final target position of the gear shift drum 40 is set. In particular, the transmission control micro-processor 1000 sets a desired velocity profile for the drum shift motor 120, for example as shown in Fig. 13

A sample from a look up table for a gear shift in which the gear shift drum 40 is rotated through the 81 degree index angle between gear ratio positions is as follows:
Angular Position of Drum Velocity profile for
Neutral to Gear Velocity profile for
Gear to Neutral Velocity profile for
Gear to Gear shift
0 225±50 100±50 200±50
12.5±5 225±50 100±50 831±50
22.5±5 225±50 100±50 980±50
33±5 95±20 100±50 1040±50
41±3 95±20 100±50 1081±50
47±3 - - 1209±50
55±3 - - 728±50
62±3 - - 450±50
70±4 - - 100±50
81 - - -
A table provided above illustrates the different velocity profiles based on the angular positions of drum and required gear shift as per one of the embodiment of the present invention. The values provided in the table may change based on the drum size, shape, gear ratios and changes in the other associated parameters of said gear drum control system.

The gear shift column provides the gear shift drum 40 speed in degrees per second. The speed accelerates until the sensed gear shift drum 40 position shows that the gear engagement zone is being reached, around 55±3 degrees when speed is rapidly dropped through to zero at the 81 degree concluded gear position. Gear shift drum 40 is provided with neutral positions between the gear positions to avoid a complete down shift or up shift as the case may be, to move from an engaged gear to a neutral position. This becomes particularly undesirable when the engaged gear is a higher gear, and shifting to a neutral position from said gear is time consuming. Further, if the vehicle were to malfunction due to issues including sensor failure or hardware malfunction or an abrupt vehicle turn off due to any reason, the vehicle must not remain stuck in a gear. It is desirable that the vehicle be brought to a neutral position so as to enable the user to at least manually transport the vehicle. Since gear shift drum 40 moving into neutral position is not subject to a clash event, a different rotation speed profile at substantially lower speed can be used when moving into neutral position thereby minimising the chances of an overshoot. An overshoot is undesirable in a situation when the gear shift drum is rotated such as to enter a neutral position as that would lead to a successive gear being engaged.

To this end the microprocessor 1000 is pre-programmed with a look up table programmed with target velocities for a plurality of predefined drum positions corresponding with the different gear ratios of the transmission system 10 including the demanded gear ratio. Based on the current position of the gear shift drum 40, the processor looks up the target velocity for the demanded gear shift and commands the drum shift motor 120 to rotate at target velocity following a feed forward control strategy. Based on determined drum 40 position, the target velocity is updated, as required, based on instructions in the look up table. This process continues until the gear shift drum 40 reaches its final resting position with gear engagement concluded – the conclusion phase described above.

The above control strategy also includes simultaneous feedback or PID control to reduce error between actual velocity and target velocity for the gear shift drum 40 by controlled operation of the drum shift motor 120.

A further control algorithm is also included in the processor to control velocity of the drum shift motor 120 having regard to a reference model including target velocities for the drum shift motor 120 for the plurality of predefined drum 40 positions (including the demand drum position for a selected gear ratio) taking a number of manufacturing and operational parameters for a representative reference or control AMT system as programmed into the microprocessor 1000 under factory conditions into account. Such parameters may include a plurality of drum 40 shape and size; degree of drum position at which lug and kidney – gear mating portions – just meet (as probability of gear clash is governed by drum speed at this drum position; gear ratio between gear shift drum 40 and rotating means where, as desirable, this is electric drum shift motor 120 with its own transmission; motor characteristics; shift fork inertia; clutch bite point and clutch stroke; and relative speed control between the input and output shafts of the transmission system 10. This selection of parameters is not limiting.

The microprocessor 1000 also allows for correction of error between the actual drum velocity and the reference model drum velocity through a feedback or PID control strategy over the operation of drum shift motor 120.

Based on these strategies, the microprocessor 1000 outputs a final duty cycle for the drum shift motor 120 allowing substantial avoidance of the overshoot problem while minimising sensor expense and expense for the transmission control system.

In order to avoid the clash condition in B-C and overshoot beyond C-D, the entire operation is divided into three phases: disengagement phase A-B, (0-22 degrees of gear shift drum 40 rotation) engagement phase B-C (44-64 degrees of gear shift drum 40 rotation) and a conclusion phase C-D (64-81 degrees of gear shift drum 40 rotation) . The gear shift is initiated in this phase where the gear shifter drum 40 is initially rotated by shifter motor 120 to rapidly accelerate to reach the point X which marks the onset of the gear engagement zone (B) whilst ensuring that the angular overshoot is minimised, certainly to a value significantly less than the index angle to the next gear. Subsequently, in phase B-C, the gear shift drum 40 is rotated in a manner in which the speed of rotation of the gear shift drum 40 at any instance within said zone is controlled to ensure that the velocity remains optimally suited for the gear engagement operation and avoid clash condition. The velocity may be different for different gear ratio, for example 1st to 2nd and 2nd to 3rd etc. and vice versa. Once the drum 40 reaches the end point of the gear engagement zone (C), whereby the dog teeth have engaged with the lugs successfully, the drum shift motor 120 enters phase C-D to conclude the gear shift operation rapidly by moving to the end position (D) without any overshoot. Overshoot beyond the end point (D) undesirably initiates the subsequent gear engagement process. Therefore, during the entire operation, the duty cycle of drum shift motor 120 is controlled so as to minimise the time taken for concluding a gear shift operation whilst minimising overshoot. It may be noted here that gear shift drum 40 is rotated during clutch disengagement with a further objective of reducing gear shift time.

In the instance when the system detects a clash condition, the control means temporarily discontinues the velocity control phase and switches over to a position control phase. In position control phase, an additional fluctuating PWM is applied across the drum rotating means, preferably the shifter motor. This PWM fluctuation leads to a fluctuation in the torque applied on the gear shift drum. Further the duty cycle of the gear shifter motor is modulated such that the time spent in the clash condition is reduced to a minimum. Also the modulation takes place in a way so as to effectively counteract any variations in system properties including stiction, etc. Eventually the clash condition is overcome and thereupon, the control means switched to velocity control phase and resumed the gear engagement process.

Other aspects involved in overcoming a clash condition include clutch control, engine RPM control, ignition control etc. The system is capable of operating independently but a combination of the aforesaid control operations in addition to the gear shift control strategy administered by the system is desirable.

The control strategy may be further understood from the flowchart of Fig. 11.

In step S1, the transmission control microprocessor 1000 determines whether gear shift is required, for example detecting any demand for a gear upshift or downshift. If so, the strategy proceeds to step S2. If not, the control strategy requires no update.

In step S2, the transmission control microprocessor 1000 further checks whether clutch position has passed a threshold, as measured by the clutch position sensor or clutch biting point. This step ensures that the gear shift control strategy is only updated if clutch movement confirms a gear shift demand. Again, if the clutch threshold is not passed, the control strategy requires no update.

In step S3, the transmission control microprocessor 1000 executes the control strategy to operate the drum shift motor 120 to implement the gear shift drum 40 velocity profile as shown in Fig. 13 and described above. Target velocity is mapped and controlled taking into account the current gear, the current gear shift drum 40 position, rate of change of engine speed, rate of change of wheel speed and rider demand (in case of an upshift) and vehicle deceleration (in case of a downshift). Clutch bite location may also be taken into account, this being compared with the reference clutch bite point and rate of engagement of clutch stroke.

In step S4, the transmission control microprocessor 1000 checks whether the gear shift drum position has reached its target position for the gear shift by checking the input from the gear shift drum position sensor 420. If the target gear shift drum 40 position has been reached – which could include the gear shift drum being within acceptable range of the target position – then the transmission control microprocessor will switch control strategy from the velocity control phase to the position control phase as described for step S8. If not, the control strategy moves to step S5.

In step S5, the transmission control microprocessor 1000 checks for clash. The transmission control microprocessor includes a timer and so gear shifter drum position is mapped against time. Where the microprocessor 1000 detects a reverse in slope of a gear shifter drum position versus time characteristic, this evidences clash. In this situation, the drum shift motor 120 is operated in step S7 to modulate torque output to overcome clash (“clash PWM”) for the particular gear shift. Such torque output modulation takes into account the optimised gear shift drum 40 velocity information developed in the reference model with a view to minimising probability of clash in the reference AMT system. If clash is detected, drum shift motor 120 may be stopped until the clash condition is resolved and transmission control unit 1000 then controls movement towards gear engagement by setting a target velocity for the drum shift motor 120 corresponding to each of the plurality of predefined drum positions within the shift operation, for example as tabulated above.

If no clash is detected, and gear shift drum 40 target position is still not reached, the transmission control strategy remains in the velocity control phase in step S6.

When target gear shift drum 40 position is reached in the absence of clash, the control strategy implements position control strategy in step S8. Here feedback or PID control over the gear shift drum 40 position is quite sufficient. Such control may depend solely on control over the operation of the drum shift motor 120 which may be operated when required because of determined error in gear shift drum position. Through implementation of the position control strategy, there is no requirement for the mechanical detents of prior AMT systems.
Following the above strategy, serious overshoot in either velocity or position control phases can be avoided

Fig. 12 provides a summary schematic showing the mapping of various inputs to the transmission control microprocessor 1000 against various outputs from corresponding lookup maps as described above.

This gear shift drum control system advantageously reduces the changes of occurrence of clash condition by precisely controlling the velocity of the gear shift drum 40 during a gear shift and also reduces the jerks perceived by the user under clash condition. Therefore the proposed system and method reduces the lag in gear shift operation in a non-synchromesh type AMT system without noticeable drop in torque.

This system and its corresponding method of operation enable control of the gear shift drum 40 such that the time required for gear shifting operations is minimised whilst also minimising the chances of occurrence of a clash condition during gear engagement in a non-synchromesh type AMT system.

Modifications and variations to the gear shift drum control system described above may be apparent to the skilled reader of this disclosure. Such modifications and variations are deemed within the scope of the present invention. The applicant also intends to rely on provisional specification and drawings filed previously.
,CLAIMS:1. A gear shift drum control system for a prime mover mated to an automated manual transmission comprising:
a. a gear shift drum;
b. a gear shift drum position determining means;
c. a gear shift drum rotating means; and
d. a control means configured to accept at least one input from a gear shift drum position sensor; to process the received input using at least one processor and to generate an output command to control the gear shift drum rotating means wherein the control means sets a target velocity for the rotating means corresponding to each of a plurality of predefined drum positions based on the inputs received from at least one vehicle or engine parameter sensing means within shifting of a gear ratio.

2. A gear shift drum control system as claimed in claim 1; wherein the vehicle and engine parameter sensing means comprises engine speed (RPM) sensors, throttle position sensors, clutch position sensors, clutch bite location sensor, vehicle acceleration sensor, gear position sensors, wheel speed sensor.

3. A gear shift drum control system as claimed in claim 1; wherein a control means is configured to operate at least one electromechanical actuator of gear shift drum rotating means for rotation of gear shift drum; wherein the rotation of the gear shift drum is controlled at least in one velocity control phase and at least one position control phase.

4. A gear shift drum control system as claimed in claim 1; wherein the control means is configured to select target speed for rotation of the gear shift drum from a list of pre-defined ranges of velocities corresponding to each of a plurality of predefined drum positions within a gear shift operation.

5. A gear shift drum control system as claimed in claim 1; wherein the control means is configured to change the speed for rotation of the gear shift drum based on the required gear shift.

6. A gear shift drum control system as claimed in claim 1; wherein the speed of rotation changes continuously and dynamically based on the corresponding change in gear drum position within a gear shift operation till the desired gear engagement or desired drum position is achieved.

7. A gear shift drum control system as claimed in claim 1; wherein the one velocity control phase comprise at least two phases wherein in the speed of rotation of gear drum shift is different in different phases.

8. A gear shift drum control system as claimed in claim 1; wherein the control means capable to switch from a velocity control phase to a position control phase once the position of gear shift drum reaches the predefined zone of gear engagement and further controls the operation of the gear shift drum rotating means till the desired target position is achieved.

9. A gear shift drum control system as claimed in claim 1; wherein the control means is configured to detect clash condition of gear by mapping of sensed gear shifter drum position against time and the clash condition is identified if a reverse in slope of the gear shifter drum position versus time is detected.

10. A gear shift drum control system as claimed in claim 1; wherein the control means is configured to detect a clash prone zone which is a predefined angles of rotation of gear shift drum.

11. A gear shift drum control system as claimed in claim 1; wherein the control means is further configured to rotate the gear shift drum at optimized pre-defined velocities during rotation through the clash prone zone.

12. A gear shift drum control system as claimed in claim 1; wherein the control means is configured to take at least one of the following action upon detection of clash condition including:
a. stopping the rotation of rotating means until the clash condition is resolved and then proceeds towards gear engagement by setting a target velocity for the rotating means corresponding to each of the plurality of predefined drum positions within the shift operation;
b. preventing the gear shift drum to switch between velocity control phase to position control until the clash condition is resolved;
c. switching from the velocity control phase to the position control phase by directing the gear shift drum rotating means to reach a predefined position and maintain the position until the clash condition is resolved and then proceed towards gear engagement by switching to a velocity control phase.

13. A system as claimed in claim 1; wherein the gear shift drum control system comprises a clash mechanism which is configured to reverse the direction of rotation of the gear shifter drum without requiring reversal of direction of the drum rotation means when a clash condition is detected.

14. A gear shift drum control system as claimed in claim 1; wherein the gear shift drum is provided with at least one neutral position between any gear ratios to avoid a complete down shift or up shift of gears.

15. A gear shift drum control system as claimed in claim 1; wherein the control means is configured to rotate the gear shift drum at a different rotation speed which is at substantially lower speed when the gear is shifted into neutral position as compare to the speed when the gear is not shifted into the neutral position.

16. A gear shift drum control system as claimed in claim 1; wherein the control means is capable to identify at least one or both of following errors:
a. between the sensed position and desired position of gear shift drum;
b. between the actual drum velocity and the predetermined drum velocity of gear shift drum; and
to correct the identified error by controlling the operation of the rotation means.
17. A gear shift drum control system as claimed in claim 1; wherein the gear shift drum rotating means is an electric drum shifter motor, a duty cycle for whose operation can readily be controlled by control means.

18. The control system of claim 1 wherein said gear shift is between two gears corresponding with differing transmission ratios or between a gear having a transmission ratio and a neutral gear.

19. A gear shift control method comprising steps of:
receiving at least input from at least a gear shift drum position sensor;
processing the received input using at least one processor according to pre-defined control strategy for generating a control signal for gear shift drum rotating means; and
receiving at least one input from vehicle or engine parameter sensor; and
controlling the gear shift drum rotating means for rotating gear shift drum by setting a target velocity corresponding to the plurality of predefined drum positions based on at least one vehicle or engine parameter within a gear ratio using control means.
20. A gear shift drum control method as claimed in claim 19; wherein the method of controlling the gear shift drum rotating means comprising steps of:
a. detecting the requirement of gear shift using control means;
b. determining clutch position using a clutch position sensor; comparing it with the predetermined threshold value and confirming the requirement of gear shift if the clutch position has passed the threshold value;
c. setting a target velocity for gear drum rotating means by taking inputs from gear drum position sensor and at least one sensor vehicle or engine parameter sensor;
d. determining whether the gear shift has reached within set acceptable range of target position by comparing the current and desired position of gear shift drum and repeating the steps from a to d till the gear shift drum reaches the acceptable position;
e. switching from velocity control phase to position control phase once the gear shift drum reaches in the acceptable position range;
f. identifying error in the drum position by comparing the desired target position and current position of the gear shift drum; and
g. controlling the gear shift rotating means based on the identified error till the final desired position is achieved.

21. A gear shift control method as claimed in claim 19; wherein the method of controlling the gear shift drum rotating means comprises method for identifying a clash condition comprising steps of:
mapping the gear shifter drum position time;
detecting if a reverse in slope of a gear shifter drum position versus time from the mapped data using control means is observed; and
confirming the clash condition.

22. A method of controlling the gear shift drum rotating means as claimed in claim 21; wherein method for detecting the clash condition comprises method for resolving the clash condition comprising at least one of the steps of:
a. stopping the drum shift rotating means until the clash condition is resolved and then controlling the movement of drum rotating means towards gear engagement by setting a target velocity corresponding to each of the plurality of predefined drum positions within the shift operation; or
b. preventing the switching of drum rotating means from the velocity control phase to position control phase; or
c. switching from the velocity control phase to the position control phase by directing the gear shift drum rotating means to reach a predefined position and maintain the position until the clash condition is resolved and then proceeding towards gear engagement by switching to a velocity control phase.

23. A gear shift control method as claimed in claim 19; wherein the method of controlling the gear shift drum rotating means comprises steps of identifying at least one or both errors by:
a. comparing the achieved position and target position of the gear drum using control means;
b. comparing the desired velocity and achieved velocity of the gear drum using control means; and
and controlling the drum rotating means till the error is resolved.