Abstract:
A gear wheel construction for use in a constant mesh gear box, the gear wheel construction characterized by a single gear wheel ( 100 ) provided about a shaft ( 18 ) in a rotatable and engageable manner, the gear wheel ( 100 ) being divided longitudinally (axially) into two components, the first being a synchro-gear wheel ( 102 ) and the second gear being a partially toothed gear wheel ( 104 ), wherein the synchro-gear wheel ( 102 ) is provided in constant mesh with a gear wheel ( 106 ) forming its gear wheel pair whilst the partially toothed gear wheel ( 104 is meshed therewith intermittently during rotation, the synchro-gear wheel ( 102 ) and the partially toothed gear wheel ( 104 ) having provided therebetween at least one biasing means ( 108 ) allowing momentary asynchronous rotation therein.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a gear wheel construction. More particularly, the gear wheel construction of the present invention is intended for use in gear systems adapted to allow changing of gears under load without the need for a traditional clutch and with the substantial minimisation of any momentary reduction in power input to the system. 
     DISCUSSION OF THE PRIOR ART 
     Constant mesh gear boxes generally rely on a means to lock and unlock individual gears with respect to a drive shaft. Unlocking a gear disengages that gear ratio and allows the gear to rotate freely about the shaft. Conversely, locking a gear with respect to the shaft causes that gear ratio to be engaged. 
     This sequence allows transmission of power from the shaft in respect of which that gear has been locked to another shaft about which a complimentary gear is provided in fixed or locked relation, at that gear ratio. Such gear pairs or ratios are generally in constant mesh aligned along the length of two substantially parallel shafts. One gear pair or ratio is engaged at any one time whilst the remaining gear pairs or ratios rotate freely about the shaft. 
     The applicant&#39;s co-pending International Patent Application PCT/AU98/00181 discloses a gear system wherein gears may be changed under load by engaging the next desired gear whilst the presently engaged gear remains engaged also. The newly engaged gear assumes the load from the previous gear allowing that previous gear to unlock freely from its shaft. 
     This gear system may present a problem when a user wishes to change “down” through gears when under load as the previously engaged gears only unlock upon subsequent engagement or pre-loading of a gear wheel that causes the driven shaft to rotate more quickly. A “down” gear change from a “tall” or high gear to a “shorter” or lower gear does not allow that “tall” gear to disengage from the shaft. 
     The gear wheel construction of the present invention has as one object thereof to overcome the above problems associated with the prior art. 
     Throughout the specification, unless the context requires otherwise, the word “comprise” or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In accordance with the present invention there is provided a gear wheel construction for use in a constant mesh gear box, the gear wheel construction characterised by a single gear wheel provided about a shaft in a rotatable and engageable manner, the gear wheel being divided longitudinally (axially) into two components, the first being a synchro-gear wheel and the second gear being a partially toothed gear wheel, wherein the synchro-gear wheel is provided in constant mesh with a gear wheel forming its gear wheel pair whilst the partially toothed gear wheel is meshed therewith intermittently during rotation, the synchro-gear wheel and the partially toothed gear wheel having provided therebetween at least one biasing means allowing momentary asynchronous rotation therein. 
     Preferably, the synchro-gear wheel is provided about its shaft in a rotatable manner only, the partially toothed gear wheel alone being able to releasably engage the shaft. 
     Still preferably, the or each biasing means act to draw the partially toothed gear wheel and synchro-gear wheel into synchronous rotation after any momentary asynchronous rotation. The force required to disengage the partially toothed gear wheel from its shaft is preferably greater than the force exerted thereon by the or each biasing means. 
     In accordance with the present invention there is further provided a gear system characterised by a pair of substantially parallel shafts, each shaft having provided thereabout at least two gear wheels forming gear wheel pairs or ratios with those gear wheels on the other shaft, wherein a rotary force applied to one shaft may be transferred to the other shaft through the gear wheels associated therewith upon that gear wheel pair being engaged with the shaft, wherein at least one of the gear wheel pairs has one gear wheel of that pair divided longitudinally (axially) into two components, the first being a synchro-gear wheel and the second gear being a partially toothed gear wheel, wherein the synchro-gear wheel is provided in constant mesh with a gear wheel forming its gear wheel pair whilst the partially toothed gear wheel is meshed therewith intermittently during rotation, the synchro-gear wheel and the partially toothed gear wheel having provided therebetween at least one biasing means allowing momentary asynchronous rotation therein. 
     In accordance with the present invention there is still further provided a method of changing down from a tall or higher gear to a shorter or lower gear in a constant mesh gear system under load, the method characterised by the method steps: 
     calling for a down gear change; 
     simultaneously disengaging the taller gear from the shaft and engaging a gear wheel comprising both a synchro-gear wheel and a partially toothed gear wheel, asynchronous rotation of the partially toothed gear wheel with respect to the synchro-gear wheel allowing the taller gear to unlock; and 
     engaging the shorter gear with the shaft. 
     The method of the present invention preferably further provides for the partially toothed gear wheel to return to synchronous rotation with the synchro-gear wheel. Such may be achieved through the action of a biasing means provided between the synchro-gear wheel and the partially toothed gear wheel. 
     The method of the present invention may be achieved, in bicycles, through use of a hand controller to cause momentary engagement of the gear wheel incorporating the partially toothed gear wheel. 
     Preferably, the method of the present invention may be put into effect by way of a form of programmable logic controller, microprocessor, computer, or engine management system. The step of calling for a change in gear may be initiated automatically by the programmable logic controller, microprocessor, computer, or engine management system or may be initiated manually. 
     For bicycles, the gear system of the present invention can be incorporated into a chainless drive shaft between the crank and the rear wheel. The system may be fitted with a dual rear bevel gear and a dual direction rear wheel ratchet/roller clutch to provide power during back pedalling. This arrangement allows step pedalling and allows the rider to power forwards by alternately shifting his weight from one foot to the other whilst standing upon the pedals of the bicycle. This arrangement allows power to be maintained while the rider is negotiating rough or otherwise difficult terrain. Alternatively, the gear system may be provided with a rear foot brake. It is envisaged that a dual ratchet or full lock pawl arrangement for engagement of the gear wheels would be required for step pedalling or rear foot braking. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     The gear wheel construction of the present invention will now be described, by way of example only, with reference to one embodiment thereof and the accompanying drawings, in which: 
     FIG. 1 is a diagrammatic cross-sectional view taken longitudinally (axially) through a gear system utilising a gear wheel construction in accordance with the present invention; 
     FIG. 2 is a cross-sectional view through the shafts of the gear system of FIG. 1 showing a partially toothed gear wheel in engagement with its shaft, a synchro-gear wheel located therebehind and shown in phantom, and further showing a biasing means in phantom between the partially toothed and synchro-gear wheels; and 
     FIG. 3 is a cross-sectional view in accordance with FIG. 2, showing the partially toothed gear wheel and synchro-gear wheel moving asynchronously thereby causing the biasing means to extend or flex. 
    
    
     DESCRIPTION 
     In FIG. 1 there is shown a gear system  10  suitable for use with a bicycle. The gear system  10  comprises a casing  16 , shown in part and in section. A first shaft  18  is mounted in the casing  16  by way of bearing means, for example a single row ball bearings  20  and  22 . The ball bearings  20  and  22  are rigidly located in the end portions  24  of the casing  16 . The first shaft  18  has a first end  26  received and held within the ball bearing  22 . A free or second end  28  of the shaft  18  has rigidly located thereabout a bevel gear wheel  30 , such that upon rotation of the bevel gear  30  the first shaft  18  also rotates. 
     The first shaft  18  has provided therein a hollow bore  32 . A roving magnet  34  is located within the bore  32  in a manner such that it may travel almost the entire length thereof and the roving magnet  34  is proportioned accordingly. The roving magnet  34  has a guide cable  36  attached thereto and extends through the bore  32  therefrom and further through the second end  28  of the first shaft  18 . The guide cable  36  extends to an index member  38  to which it is rigidly but adjustably connected. An annular bush  40  is provided within the bore  32  adjacent the second end  28  and through which the guide cable  36  extends. The bush  40  acts as a seal and aids in the smooth travel of the guide cable  36 , thereby preventing wear of the guide cable  36  and the first shaft  18 . 
     A series of pawl gear wheels  42  are provided about the first shaft  18  such that these gear wheels  42  may rotate freely and independently about the shaft  18 . However, if required these pawl gear wheels  42  may be caused to engage the first shaft  18  and rotate therewith. 
     A further roving magnet  35  is additionally located within the bore  32  in a manner whereby it may travel through only a limited length thereof. The roving magnet  35  is similarly proportioned to the roving magnet  34 , allowing each to travel longitudinally or axially within the bore  32 . The roving magnets  34  and  35  are arranged such that they cannot pass or overlap one another within the bore  32 . 
     The roving magnet  35  has a guide cable  37  attached thereto and extending through the bore  32  therefrom and further through the first end  26  of the first shaft  18 . The guide cable  37  extends to an index member  39  to which it is rigidly but adjustably connected. An annular bush  41  is provided within the bore  32  adjacent the first end  26  and through which the guide cable  37  extends. The bush  41  functions similarly to the bush  40 . 
     A second shaft  60  is mounted in the casing  16  by way of bearing means, for example single row ball bearing  62  and  64 . The ball bearings  62  and  64  are rigidly located in the end portions  24  of the casing  16  and are arranged such that the shafts  18  and  60  are substantially parallel. The second shaft  60  has a first end  66  received and held within the ball bearing  64 . A free or second end  68  of the shaft  60  has rigidly located thereabout a bevel gear wheel  70 , such that upon rotation of the second shaft  60  the bevel gear  70  also rotates. 
     The second shaft  60  has provided therein a hollow bore. A roving magnet  74  is located within the bore  72  in a manner such that it may travel almost the entire length thereof and the roving magnet  74  is proportioned accordingly. The roving magnet  74  has a guide cable  76  attached thereto and extends through the bore  72  therefrom and through the first end  66  of the second shaft  60 . The guide cable  76  extends to the index member  38  to which it is rigidly but adjustably connected. An annular bush  78  is provided within the bore  72  adjacent the second end  66  and projects through a portion of the end portion  24  of the casing  16 . The bush  78  acts as a seal and aids in the smooth travel of the guide cable  76 , thereby preventing wear of the guide cable  76  and the second shaft  60 . 
     A further roving magnet  75  is additionally located within the bore  72  in a manner whereby it may travel through only a limited length thereof. The roving magnet  75  is similarly proportioned to the roving magnet  74 , allowing each to travel longitudinally or axially within the bore  72 . The roving magnets  34  and  35  are arranged such that they cannot pass or overlap one another within the bore  72 . 
     The roving magnet  75  has a guide cable  77  attached thereto and extending through the bore  72  therefrom and further through the second end  68  of the second shaft  60 . The guide cable  77  extends to the index member  39  to which it is rigidly but adjustably connected. An annular bush (not shown) is provided within the bore  72  adjacent the second end  68  and through which the guide cable  77  extends. This bush functions similarly to the bush  78 . 
     It is envisaged that the roving magnets  34 ,  35 ,  74  and  75  may be provided in the form of neodymium rare earth magnets although such should not be considered to limit the scope of the present invention. 
     A series of pawl gear wheels  80  are provided about the second shaft  60  such that these gear wheels  80  may rotate freely and independently about the shaft  60 . However, if required these pawl gear wheels  80  may be caused to engage the second shaft  60  and rotate therewith. 
     The gear wheels  42  and  80  are housed within the casing  16  in a chamber  84 . The chamber is provided with a volume of lubricant (not shown). The casing  16  is arranged on a bicycle such that the bevel gear wheel  30  of the first shaft  18  engages a gear wheel provided on a pedal-crank (not shown). Accordingly, drive imparted by a rider (not shown) through the pedal-crank is transferred to the first shaft  18  which is caused to rotate. It is to be understood that the casing  16  preferably covers or encloses the bevel gear wheels  30  and  70 . As such, the casing  16  may have appropriate apertures provided therein to allow access thereinto by the gear wheels provided on the pedal-crank and the axle. 
     The gear wheels  42  provided on the first shaft  18  engage a complimentary gear wheel  80  on the second shaft  60 . In this manner gear wheel pairs are provided and result in drive from one shaft being transferable to the other shaft. A gear wheel pair is comprised of two pawl gear wheels. The relative diameters of the fixed and pawl gear wheels in a pair determine the gear ratio provided by that gear wheel pair. It is envisaged that a number of arrangements with regard to the fixing of the gear wheels relative to their shaft may be utilised. These arrangements are discussed in more detail hereinafter. However, in each arrangement at least one of the gear wheels of each gear wheel pair or ratio is fixedly attached to its shaft whilst the other gear wheel of that pair or ratio is releasably engagable with the shaft about which it is provided. 
     The bevel gear wheel  70  provided on the second end  68  of the second shaft  60  engages a gear wheel provided on an axle of the hub of a rear wheel (not shown). In this manner, drive transferred from the first shaft  18  to the second shaft  60  is in turn transferred to the rear wheel. 
     The engagement of gear wheels  42  and  80  with their shafts  18  and  60  is achieved through positioning of the roving magnets  34  and  74  alongside those gear wheels, which in turn causes pawl members provided in either the shafts  18  and  60 , or the gear wheels  42  and  80 , to engage, This results in drive from one shaft being transferred through the gear wheels to the other shaft in the chosen gear ratio. The nature of the pawl members and the mechanism utilised to achieve engagement and disengagement of the shafts and gear wheels is fully described in the applicant&#39;s co-pending International Patent Applications PCT/AU97/00181 and PCT/AU97/00024 (WO/97/26468), the content of which is to be incorporated herein by reference. 
     The first shaft  18  has provided thereon a gear wheel  100 , the gear wheel  100  being divided into a synchro-gear wheel  102  and a partially toothed gear wheel  104 . The gear wheel  100  is provided in constant mesh with a complimentary gear wheel  106  provided about the second shaft  60 . It is to be understood that whilst only a single gear wheel  100  need be provided, more than one gear wheel  100  may improve efficiency of the gear system  10 . 
     The gear wheels  100  and  106  are generally twice the width of gear wheels  42  and  80 . The synchro-gear wheel  102  is thinner longitudinally (axially) than the load bearing partially toothed gear wheel  104 . 
     The synchro-gear wheel  102  is able to rotate freely about, and with respect to the shaft  18 . A biasing means, to be discussed hereinafter, is provided between the synchro-gear wheel  102  and the partially toothed gear wheel  104  to facilitate synchronous rotation therein. The partially toothed gear wheel is releasably engageable with the shaft  18  in known manner, as are the gear wheels  42  and  80 . 
     The roving magnets  35  and  75  are arranged within the bores  32  and  72  respectively, so as to travel longitudinally (axially) only the length of the gear wheels  100  and  106 , respectively, and a short distance into the adjacent end portion  24  of the casing  16 . 
     In FIGS. 2 and 3 there is shown the gear wheels  100  and  106 . The partially toothed gear wheel  104  is shown engaged with the shaft  18  and rotating in the direction of arrow A, thereby introducing movement in the direction of arrow B in the gear wheel  106  and shaft  60  to which it is suitably engaged. 
     The synchro-gear wheel  102  is shown behind the partially toothed gear wheel  104  and is held to synchronous rotation therewith by way of a biasing means, for example a spring  108 , shown in contracted position in FIG.  2  and in extended or flexed position in FIG.  3 . The spring  108  comprises arms  110  and  112 , arm  110  being affixed to the synchro-gear wheel  102  and arm  112  being affixed to the partially toothed gear wheel  104 . 
     Both the synchro-gear wheel  102  and gear wheel  106  are provided with regularly spaced constantly meshed teeth, whereas the partially toothed gear wheel  104  has teeth  114  provided thereon at a much greater spacing, thereby not allowing a constant mesh with the teeth of the gear wheel  106 . 
     It is envisaged that the gear system  10  of the present invention may be provided in a form such that all the gear wheels provided on the driven shaft thereof, for example shaft  60 , are fixedly attached thereto and will rotate therewith at all times. It is further envisaged that the two shafts of the gear system  10  may be provided such that half of the gear wheels provided thereabout are fixedly attached thereto and the other half are not. The arrangement would be such that each gear wheel pair has one gear wheel thereof fixedly attached to its shaft at all times. An arrangement of this nature is disclosed in the applicant&#39;s co-pending International Patent Application PCT/AU97/00024 (WO 97/26468). 
     In use, upward changes through the gears of the gear system  10  are achieved in known manner whereby the pawl members of a shorter gear are disengaged whilst the pawl members of the taller gear are engaged. The pawl members of the shorter gear do not disengage immediately and the subsequent increased rate of rotation imparted through the taller gear causes the final disengaging of the pawl members of the shorter gear, thereby “unloading” the shorter gear. This sequence has been referred to in the applicant&#39;s co-pending International Patent Applications as “pre-loading” of the gears and allows minimal interruption of power transmission. However, as noted previously this sequence is not generally successful when changing from a taller gear to a shorter gear as the taller gear is not able to “unload” in the same manner. It is necessary to introduce a system whereby the taller gear may be unloaded and thereby allow all the pawl members thereof to disengage. 
     Accordingly, when it is necessary to change from a taller gear ratio to a shorter gear ratio, alternatively referred to as a higher gear ratio to a lower gear ratio, the gear wheel pair  100  and  106  are engaged momentarily. Prior to their engagement, the gear wheels  100  and  106  will have been rotating freely with respect to their shafts  18  and  60 , respectively. At the moment of engagement the gear wheels  100  and  106  rotate with their shafts  18  and  60 , respectively. 
     As can be seen with reference to FIG. 2, the synchro-gear wheel  102  and partially toothed gear wheel  104  rotate together in the direction of arrow A through the action of the spring  108  keeping the same asynchronous rotation whilst the tooth  114  of the partially toothed gear wheel  104  is in engagement with the gear wheel  106 . Upon the gear wheel  100  rotating to the position shown in FIG. 3 in which the tooth  114  of the partially toothed gear wheel  104  is no longer in engagement with the teeth of the gear wheel  106 , the partially toothed gear wheel  104  is driven ahead or slips forward, out of sync, with respect to the synchro-gear wheel  102 . In this position the spring  108  is flexed or extended. Further, this motion allows the unloading of the taller gear and the full engagement of the shorter gear. Importantly, the force utilised to unlock pawls  116  engaging the partially toothed gear wheel must be greater than the force exerted on the partially toothed gear wheel  104  by the action of the spring  108 . 
     Upon unloading of the taller gear the pawl members  116  associated with the partially toothed gear wheel  104  may disengage thereby allowing the partially toothed gear wheel  104  to return, under the action of the spring  108 , to the position shown in FIG.  3  and synchronous movement with the synchro-gear wheel  102 . 
     If only a single gear wheel  100  is provided in a gear system it is required that it be provided at the highest gear ratio in the gear system. If it is not it cannot function to unload all other gear wheel pairs in the gear system as required. 
     It is envisaged that a separate activating system may be required for the selection and engagement of the gear wheels  100  and  106 . Such separate activating system may be mechanical, magnetic and/or electromagnetic. A programmable logic controller (PLC), computer or engine management system may be utilised to control the appropriate sequence. 
     It is further envisaged that a mechanism may be provided so as to prevent the gear wheel  104  locking and loading in a toothless region thereof. The locking of the pawl members associated with the partially toothed gear wheel  104  may be provided whereby such are only able to be deployed and engaged with the assistance or synchronisation of the teeth  114  provided thereon. In this manner, the toothless region of the partially toothed gear wheel  104  could not activate locking of the pawl members associated therewith. 
     Consequently, two actions would be required to allow engagement of the partially toothed gear wheel  104 . Firstly, the appropriate signal, whether it be mechanical, magnetic or electromagnetic must be provided and secondly a tooth  114  of the partially toothed gear wheel  104  must be in meshed engagement with the teeth of gear wheel  106 . 
     It is still further envisaged that the roving permanent magnets of the gear system  10  described herein previously may be replaced by roving electromagnets or by a series or array of electromagnets. Such electromagnets may be activated to cause engagement of a gear wheel with its shaft as required. The provision of a single electromagnet for each gear wheel, suitably positioned in the shaft or casing, is envisaged as preferable as this results in less moving components. 
     For bicycles, the gear system of the present invention can be incorporated into a chainless drive shaft between the crank and the rear wheel. The system may be fitted with a dual rear bevel gear and a dual direction rear wheel ratchet/roller clutch to provide power during back pedalling. This arrangement allows step pedalling and allows the rider to power forwards by alternately shifting his weight from one foot to the other whilst standing upon the pedals of the bicycle. This arrangement allows power to be maintained while the rider is negotiating rough or otherwise difficult terrain. Alternatively, the gear system may be provided with a rear foot brake. Alternatively, the gear system may be provided with a rear foot brake. It is envisaged that a dual ratchet or full lock pawl arrangement for engagement of the gear wheels would be required for step pedalling or rear foot braking. 
     Modifications and variations such as would be apparent to the skilled addressee are considered to fall within the scope of the present invention.