188宝金博页面版

[0001] The present invention relates toa synchro-nised coupling forthe gearbox ofa vehicle.[0002] In gearboxes for vehicles it is known touseasynchronised coupling to connect angularly an idlegearwheel toa respective shaft. Typically,a coupling isinterposed beMeentwo gearwheels and is ableto con-nectthe gearwheels themselves selectivelytothe shaft.[0003] Synchronised couplings are known whichcomprisea hub keyed on tothe shaft,a pair of driveelements disposed on axially opposite sides with re-spect totheh ub, which are angularly secured toa re-spective gearwheel and are provided with respectiveouter toothings, anda motion-transmitting device inter-posed betweenthehub andthe drive elements so astoactuate selectively the drive elements themselves.[0004] Normally, the motion-transmitting device com-prisesa pair of synchronising rings each interposed ax-ially between thehub and the respective drive element.The synchronising rings have respective conical frictionsurfaces adapted to co-operate, in operation, with cor-responding conjugate friction surfaces ofthe respectivedrive elements, and they are provided with respectiveouter toothings.[0005] Finally, the transmission device comprisesaselection sleeve which is angularly secured totheh ubby meansof innertoothing thereof and which can moveaxially on opposite sides ofsaid hub so as to carry outrespective coupling travel. During each coupling travelsaid innertoothing ofthe sleeve firstly engagesthe outertoothing of the synchronising ring and then the outertoothing of the drive element, when the relative speedofthe latter with respecttothe synchronising ring is re-duced to zero asa result of the frictional contact be-tween the respective conjugate friction surfaces.[0006] Although they are widely used, known syn-chronised couplings ofthe above-mentioned type havethedrawbackof requiringa relatively long coupling timeand axial forces which are variable and, in some cases,relatively high especially during the final phases ofthecoupling travel.[0007] In particular, this can be attributed to the pos-sible sticking of the sleeve with respect tothe relevantdrive element during the phase of angular alignment ofthe respective toothings. In fact, the teeth of these tooth-ings are normally provided with tapered axial ends hav-ing inclined flanks so as to facilitate mating and, there-fore, alignment. The powerful forces acting tangentiallyon the drive element in the direction opposite to itsspeedof rotation, depending on the flankofthe teeth onwhich contact occurs during mating, may be favourableor opposed thereto, thereby occasionally creating vari-able operating forces. In an unfavourable case, thesepowerful forces result in an increase in the axial operat-ing force. Moreover, in known synchronised couplingsthe phenomenon known as "double release" occurs, orduring each coupling travel there isa reduction in the10203040502ring, and then an increase in the load itself as a resultof the successive alignment beMeenthe toothing ofthesleeve itself and the toothing ofthe drive element.[0008] US 2,916,939 describesa syncronised cou-pling havinga sleeve anda gear, the first having innerteeth of four different lengths, the second outer teethhaving two different tenghts.[0009] The object ofthe present invention is to devisea synchronised coupling forthe gearbox ofa vehicle,which makes it possibletoresolvethe above-mentionedproblems ina simple and economic manner.[0010] Accordingtothe present invention there is pro-f5videda synchronised coupling forthe gearbox ofa ve-hicle, comprisinga shaft and at least one gearwheelwhich is coaxial with respect tothe shaft itself and idlewith respect thereto, the coupling comprisinga hub se-curely keyed on to said shaft, drive means interposedbeMeen said gearwheeland said hub, said drive meansbeing secured to said gearwheel and comprisinga con-ical friction surface and an external spur gear, at leastone synchronising ring interposed beMeen said huband said drive means and comprisinga conical friction25surface conjugate withthe conical friction surfaceof saiddrive meansandan external spur gear, anda selectionsleeve which is angularly secured and axially free withrespect to said hub and having an internal spur gearadapted to engage the toothings of said synchronisingring and of said drive means, the toothings of said se-lection sleeve and of said drive means each havingafirst and second plurality of teeth, the teeth of said firstplurality of teeth being axially projecting with respecttothe teeth of said second plurality of teet, characterised35in that each said first tooth has at least one end portionboundedbya pairof flanks and bya front cut-off surfacesaid flanks being mutually convergent from said frontcut-off surface.[0011] The invention will now be described with refer-ence tothe accompanying drawings which illustrateanon-restrictive example of embodiment thereof, inwhich:Figure1 illustratesa section ofa preferred form of45embodiment ofa synchronised coupling for thegearboxof a vehicle, in accordance withthe presentinvention, connected witha shaftanda pairof gear-wheels ofa gearbox.Figure2 is view in radial direction, on an enlargedscale and with parts omitted for greater clarity, ofone sector ofthe synchronised coupling during anintermediate phase ofthe coupling operation, andFigure3 is analogous to Figure 2, which illustratesthe synchronised coupling atthe end ofthe coupling55operation.[0012] In Figure1 the reference numeral1 denotesasynchronised coupling forming partofa gearbox2 (part-