Elongated Synchroniser Hub And Synchroniser Ring Functioning within An Extended Synchroniser Hub & Catcher Teeth Arrangement

The present invention relates to automotive transmission systems and more particularly to synchroniser clutches for controlling gear changes in transmission gearing.

Synchroniser clutch assemblies are used to facilitate the smooth engagement of meshing teeth during changes of gear in a transmission. A typical assembly includes a hub positioned between two gears of different pitch diameter, the hub having a central opening in which are formed a plurality of teeth for drivingly mounting the hub on a drive shaft. A clutch sleeve with internal clutch teeth is mounted for axial sliding movement on the hub, and each gear also carries corresponding external sleeve teeth which are engageable by the inner teeth of the sleeve in order to create a drive path from the shaft, through the hub and sleeve to the gear. Each gear also carries an external cone clutch surface which is engageable by a complementary internal cone clutch surface formed on a synchroniser ring component disposed between the hub and each gear. Upon movement of the sleeve towards a gear, the associated synchroniser rings is first engaged and caused to move axially towards the gear so as to bring its internal cone surface into engagement with the external surface formed on the gear. The resulting frictional engagement ensures that the speeds of the hub and gear are synchronised before the sleeve is slide further into engagement with the sleeve teeth of the gear, thereby ensuring smooth engagement. Examples of such synchronisers are shown in European Patent no. 0756098, US-A-2221900 and US-A-3366208.

An important consideration in the design of such synchroniser clutch assemblies is the desire to minimise size of the assembly, particularly in the axial direction, although this consideration must be offset against the need to

ensure that the components are sufficiently strong to carry the high loads which will be transmitted therethrough during operation as well as to ensure that an acceptable shift feel is maintained for the user.

FR 2845140 discloses a synchroniser system in which the hub of the synchroniser assembly has a plurality of circumferentially extending recesses formed in each of its axially faces and the synchroniser ring disposed between each side of the hub and its associated gear is formed with a corresponding plurality of complementary circumferentially extending radial lugs, each lug having a plurality of teeth formed thereon which match with the splines formed on the outer surface of the hub. When assembled, each lugs locates in one of the recesses in the hub such that the synchroniser ring is recessed into the hub - the outer face of the synchroniser ring being flush with the axial face of the hub when the hub is disengaged from the associated gear. The circumferential length of each lug is furthermore shorter than that of each recess in the hub so that the ring is rotatable relative to the hub to a limited degree, thereby enabling indexing of the ring to take place relative to the hub.

Catcher teeth type synchronisers are also known in the art, in which the sleeve of the synchroniser is formed with a plurality of axially longer teeth interspaced between a plurality of axially shorter teeth. The sleeve is oriented within the synchroniser assembly so that the shorter or synchroniser teeth of the sleeve align with the outer teeth of the synchroniser ring whilst the longer or catcher teeth align with circumferential gaps between banks of outer teeth of the synchroniser ring. As the sleeve is moved towards the gear during synchronisation, the catcher teeth engage through the circumferential gaps in the banks of teeth of the synchroniser ring before the shorter synchroniser ring reach and engage the teeth of the synchroniser ring. Since the catcher tooth do not make contact to the synchro - their function is only to make contact with the dog plate, the taper angles of the leading edges can be designed to be much

steeper to optimise engagement with the dog teeth which have matching steeper angles, therefore helping the two components to engage. On the other hand, the synchroniser teeth are designed with tooth angles which are calculated to identify the correct positivity ratio for the particular application.

The teeth of the synchroniser ring are conventionally formed into three banks circumferentially distributed around the outer edge of the synchroniser ring, the circumferential extent of each bank being at least equal to the radial extend of the circumferential gaps between each bank such that the number of synchroniser teeth on the sleeve is equal to or greater than the number of engagement teeth. Typically, the ratio has been 50:50 in prior art systems because of loading requirements for the synchroniser ring. The arrangement has the drawback however that the area which makes contact to the hub whilst indexing was very small.

According to present invention there is provided a synchroniser ring having a plurality of synchroniser teeth extending radially outwardly from an outer surface thereof, said synchroniser teeth being arranged into at least four circumferentially extending banks distributed around the outer periphery of the ring, the circumferential extent of each bank being less than the circumferential extent of the space between neighbouring banks.

A synchroniser ring in accordance with the invention has the advantage that it avoids the potential impact wear on the three indexing faces of a typical synchroniser by increasing the number of banks of teeth as compared with the prior art. The system also distributes load more evenly so there is less load carried on each bank, and also increasing the number of catcher teeth and hence the torque transfer capability between the sleeve and the gear.

Preferably the banks of teeth are equi-angularly distributed around the outer periphery of the ring.

Preferably, the ring has six banks of teeth with two teeth in each bank equi- spaced around the ring. This allows the even spread of load applied by the sleeve and doubles the contact surface area between the sleeve and the ring whilst redistributing the impact force more evenly through the synchroniser ring. However, other number of banks, for example 5, is also possible. By having six sections of teeth the load is spread which is generated when the sleeve teeth make contact with synchroniser, more evenly around the circumference of the synchro tooth rail to minimise any local deflection whilst under load (Rail = flange that the teeth are placed upon). Furthermore, by increasing the sections from three large sections to more smaller sections the ratio of catcher teeth to synchroniser teeth increases (increasing the number of catcher teeth increases the contact between the sleeve and the dog to minimise tooth tip wear). Six sections enables a ratio of 2:1 to be achieved. The provision of six small sections increases the strength of the hub by increasing the area of the extended sections.

The present invention further provides a shift sleeve for a synchroniser having a first plurality of axially extending teeth or splines formed on its inner circumferential surface having a first axial length and a second plurality of axially extending teeth or splines formed on its inner circumferential surface having a second axial length which is shorter than said first axial length, said second plurality of splines being formed into a plurality of groups each having the same number of teeth, said groups being distributed around the hub, a plurality of said teeth having said axial length being disposed in the regions between said groups.

The present invention furthermore provides a synchroniser clutch assembly according to the invention including a synchroniser ring according to the invention.

Preferably, the groups of teeth are equi-angularly distributed around the hub

In a particularly advantageous arrangement, this system furthermore includes a shift sleeve according to the invention so as to provide a catcher tooth arrangement in a particularly simple manner.

According to another aspect of the present invention there is provided a synchroniser clutch assembly comprising a clutch hub assembly which, in use, is non-rotatably but axially movably mounted on a torque delivery shaft, the hub assembly having a web portion extending radially between a central support and an outer flange portion, said flange portion being formed with a plurality of axially wider portions interspaced between axially narrower portions so as to formed axial recesses around each axial face of the hub, at least one gear assembly which is axially spaced from the hub assembly and which, in use, is journal mounted on the shaft so as to be rotatable independent thereof, a shift sleeve which engages the outer surface of the flange portion of the hub so as to be constrained to rotate therewith whilst being axially moveable relative to said hub; and at least one synchroniser ring positioned between the hub assembly and the at least one gear assembly, the or each synchroniser ring having a conical friction surface formed thereon which is engageable with a complementary shaped conical friction surface associated with the at least one gear assembly in order create a drive coupling therebetween, and having a plurality of radially lugs extending radially outwardly from the outer surface of the ring, the circumferential extent of each of which lugs is shorter than the circumferential extent of each of the axial recesses in the hub such that the ring is engageable in the face of the hub with

said lugs engaged in said recesses in order to allow only a limited degree of rotational movement of the ring relative to the hub, characterised in that depth each of said axial recesses is greater than the axial thickness of each of the lugs such that the wider regions of the hub project beyond the outer face of the synchroniser ring when the ring is fully engaged into the face of the hub (1; 101).

A synchroniser clutch assembly according to this further aspect of the invention has the advantage that due to the fact that flange of the hub extends beyond the outer face of the synchroniser ring, a greater portion of the width of the shift sleeve is supported on the hub during its axial movement toward engagement with the drive gear. In this way, the ability of the sleeve to twist or tilt during engagement due to the differential torques exerted from the hub and the gear is significantly reduced.

Preferably, the hub has a plurality of axially extending teeth or splines formed on its outer surface and the shift sleeve has a complementary set of splines or teeth formed in its inner circumferential surface which mesh with those of the hub in order to effect a rotational drive coupling therebetween. The synchroniser ring is then also provided with matching teeth or splines on each of its lugs, and the gear is also provided with matching teeth of splines, in each case engageable with the teeth or splines of the shift sleeve in order to effect a positive drive coupling with the hub.

Preferably, the assembly further includes radially resiliently deformable or moveable means which are engageable by the shift sleeve in order to apply an axial load thereto as the sleeve is moved towards the gear, and which, in turn, transmit that axial load to the radial lugs of the ring in order to press the ring towards the gear and hence bring the conical friction surface surfaces of the ring and the gear into engagement in order to initiate synchronisation of the

gear and the hub. The resiliently deformable or moveable means then deform or retract radially inwardly upon the load applied through the shift sleeve reaching a pre-defined level so as to allow the shift sleeve to pass over said means and into engagement with ring and then the gear.

In one embodiment, a plurality, in particular three struts are positioned in pockets formed in the outer radial surface of the narrower regions of the flange of the hub, each pocket extending across the whole width of its associated narrow region and the associated strut being located therein so as to be axially slidable relative to whilst rotating with the hub. The resiliently deformable or moveable means are then located on the outer surface of each strut and extend into the sleeve, engaging for example, in a recess such as an circumferential groove formed in the inner surface of the sleeve, so as to constrain the struts to move axially with the sleeve, the means retracting into the struts out of the sleeve when sufficient load to applied through the sleeve. More particularly, each strut may be formed with a radial hole extending from its outer surface in which is located a spring and a ball, the spring biasing the ball out of the hole into a position in which it protrudes from the outer surface of the strut. An opening, in particular a circumferentially extending groove is then formed centrally in the inner annular surface of the sleeve, each ball engaging in the groove so as to constrain the struts to move with the sleeve in either axial direction, the ends of the groove being ramped so to develop a camming action which will press the balls into the holes against the biasing load of the springs which sufficient force is applied.

Due to the hub being extended, even when the sleeve has been moved to either of its extreme axial positions, i.e. in which it is positively engaged with a gear, more than half of the shift sleeve is still engaged with the hub and hence the presence of a groove extending centrally around the entire inner periphery of the sleeve does not give rise to issues with tilting of the sleeve which occurred

with prior art systems, necessitating provision of individual recesses at discrete points on the inner surface of the sleeve.

Alternatively, the resiliently deformable or moveable means may be attached to each of the lugs of the ring, extending radially outwardly from the ring into the path of the shift sleeve so as to be engaged by the sleeve as it moves towards the gear, and retracting or deforming radially when the shift force exceeds a predefined level. More particularly, a leaf spring is preferably attached to the face of each lug which is proximate to the hub, which leaf spring extends radially outwardly as it extends across the lug so as to be engaged by the sleeve as it is pressed towards the gear. The leading edge of the inner periphery of the sleeve is then chamfered inwards away from the ring so as to form a ramp surface which imparts both an axial and a radial load to the springs, such that the springs will be pressed radially inwards out of the path of the sleeve upon sufficient force being applied. Preferably, the inner surface of the sleeve, which is preferably toothed or splines, increases in diameter again after the ramped region so as to form an area in which the springs can expand once the sleeve has moved passed them in order to relieve the stress therein. The springs are then re-engaged during movement of the sleeve away from the gear during disengagement of the gear, pulling the ring away from the gear in order to ensure that the friction surfaces are disengaged.

Other forms of deformable member are also possible such as a c-spring member disposed between the hub and the ring.

Preferably, the synchroniser ring forms the outer ring of a synchroniser ring assembly, having an inner conical surface which tapers outwardly towards the gear and which is engageable with a complementary shaped outer conical surface formed on an intermediate ring. The intermediate ring also, then, has an inner conical surface which similarly tapers outwardly towards the gear and

which is engageable with a complementary shaped outer conical surface formed on an inner ring. The intermediate ring is then engaged with the gear so as to be constrained to rotate therewith, whilst the inner ring is engaged with the outer ring, again so as to be constrained to rotate therewith and hence to rotate with the hub. The engagement, in each case, is preferably achieved by means of axially extending tabs on each of the intermediate and inner rings which engage in openings formed in the gear and outer ring respectively. The outer ring advantageously has a plurality of radially inwardly extending lugs, the opening for receiving a tab of the inner ring being formed in each of said inwardly extending lugs. The inner ring may alternatively be actually secured to the gear to form a connected system .

Preferably, the teeth or splines on the inner surface of the sleeve have no back taper on them. Back taper has typically be provided on prior art systems in order to provide an engagement taper lock that prevents unintentional disengagement of the sleeve from the gear for example upon excessive tilting of the sleeve. The elimination, or at least substantial reduction of tilting in the extended hub of the present invention eliminates the possibility of such disengagement without requiring expensive machining operations to form back taper on the teeth.

Preferably, the pressure angle, that is the angle of inclination of the sides or flanks of the teeth or splines such as on the sleeve, is reduced as compared to prior art systems in order to change the angle of contact between the mating components. In particular, the teeth or splines of the various components preferably have a pressure angle of greater than 40 degrees, in particular 45 degrees.

Advantageously, the synchroniser ring or ring components of the synchroniser ring assembly are formed of steel and preferably have friction material attached

to the conical friction surfaces thereof, manufacture from steel suiting 3 bank designs as well as designs having 4 or more banks in accordance with the present invention.

Advantageously, the synchroniser ring and shift sleeve are formed in accordance with the first aspects of the invention defined above and described below in connection with Figures 17 to 19.

It will, of course, be understood that it is within the scope of the teaching of the present invention that features of the different aspects of the inventions as defined above may be combined with each other.

In order that the invention may be well understood, there will now be described some embodiments thereof, given by way of example, reference being made to the accompanying drawings, in which:

Figure 1 is an exploded view of a synchroniser assembly according to a first embodiment of the present invention;

Figure 2 is a sectional side view of the synchroniser assembly of Figure 1;

Figure 3 is an enlarged view of a part of the synchroniser assembly of Figure 1;

Figure 4 is a detail view of the teeth of the toothed synchroniser ring and sleeve of the assembly of Figure 1;

Figure 5 is a side view of the hub of the assembly of Figure 1 ;

Figure 6 is a perspective view of the shift sleeve of the assembly of Figure 1;

Figure 7 is a perspective view of the toothed synchroniser ring of the assembly of Figure 1;

Figure 8 is a perspective view of the intermediate ring of the assembly of

Figure 1;

Figure 9 is a perspective view of the inner ring of the assembly of Figure 1;

Figure 10 is a sectional side view of part of the assembly of Figure 1;

Figure 11 is a sectional side view of a synchroniser assembly according to a second embodiment of the invention;

Figure 12 is an exploded view of the assembly of Figure 11;

Figure 13 is a perspective view of a hub which forms part of the assembly of

Figure 11 ;

Figure 14 is a perspective view of a shift sleeve which forms part of the assembly of Figure 11;

Figure 15 is a perspective view of a toothed synchroniser ring which forms part of the assembly of Figure 11;

Figure 15a is an enlarged view of part of the toothed ring of Figure 15;

Figure 15b is a side, partially exploded view of the toothed ring of Figure 15;

Figure 15c is a front view of the toothed ring of Figure 15;

Figure 16 is an enlarged view of part of the assembly of Figure 11;

Figure 17 is a perspective view of a hub assembly according to a third embodiment of the present invention;

Figure 18 is a perspective view of a synchroniser ring which forms part of the assembly of Figure 17;

Figure 19 is an enlarged view of part of the assembly of Figure 17; and

Figure 20 is a sectional side view of the assembly of Figure 17 illustrating the synchronisation and location diameters of the system.

Referring first to Figure 1, there is shown a synchroniser assembly composed of a hub 1, an annular shift sleeve 2, a synchroniser ring assembly 3 and a drive gear 4. The hub 1 has a central opening 10 on the inner circumferential surface of which is formed a plurality of teeth or splines 11 as shown more clearly in Figure 1. A shaft member 5(not shown) extends through said opening 10 in the hub 1 and has a plurality of external splines or teeth which engage with the teeth 11 of said opening 10 so that the hub is secured to and rotates with the shaft. A radial web portion extends outwards from the central opening 10, terminating in an outer circumferential flange 12 which forms the outer

circumferential surface of the hub 1 and which extends axially on either side of the hub beyond the web portion.

The outer circumferential surface of the flange 12 has a plurality of axially extending teeth or splines 13 formed thereon which engage with a corresponding plurality of teeth or splines 23 formed on an inner surface 24 of the annular shift sleeve so as drivingly to couple the shift sleeve 2 to the hub whilst permitting axial movement of the shift sleeve along the hub 1 for gear shift operations as described below. Such axial movement of the shift sleeve 2 is effected by means of a linkage arm (not shown) which engages in a circumferential groove 21 formed in the outer surface of the shift sleeve 2, and may be achieved manually, hydraulically, electronically, electro-magnetically or any other well known means.

The teeth or splines 23 of the shift sleeve 2 are separated into a plurality of circumferentially extending groups, each group being separated from its neighbours by a channel 25, and a circumferential groove 26 extends centrally around the entire inner periphery of the sleeve 2, extending across the centre of each of the teeth or splines 23 as shown in Figure 1.

The flange 12 of the hub is composed of axially narrower regions 15a interspaced between axially wider regions 15b equi-angularly around the periphery of the hub 1 such that each narrower region 15a forms an axial recess 14a, 14b, 14c in either side of the hub 1 into which is engageable a set of indexing teeth of the synchroniser ring assembly 3 as described below. A radial recess 16, which forms a gap in the teeth or splines 13 of the hub, is also formed in each of the narrower regions 15 a, and an engagement strut 17 is seated in each of said recesses 16, each strut 17 having an outer surface 18 which has the same curvature as the outer surface 12 of the hub. In this way, the shift sleeve 2 meshes with the external surface of the hub 1 as well as with

the teeth 18 of the struts 17, the sleeve 2 trapping the struts 17 in the hub against radially outward movement. Each strut 18 also has a radially inwardly extending post 19 which engages in an axial through slot 16b formed in the base of the recess 16 so as to constrain the struts against circumferential movement relative to the hub 1. The struts may alternatively be formed with a flat outer surface.

A hole 20a is formed in the centre of the outer surface 18 of each strut 17, in which is mounted a spring 20b and a ball 20c, the spring 20b urging the ball 20c radially outwardly from the hole 20a so that it protrudes into said central trough. When assembled, the shift sleeve 2 overlies the ball 20c in each strut 17 so as to prevent it from falling out of the hole 20a, and when the sleeve 2 is positioned centrally on the hub 1, the groove 26 in the sleeve aligns with the balls 20c such that each ball is urged by its associated spring 20b into the recess in the tooth of the sleeve 2 with which it is aligned formed by the groove 26. As a result, the struts 17 are constrained to move axially with the shift sleeve 3, relative to the hub, until a restraining force is imposed on the strut as described below of sufficient magnitude to develop a camming action between the groove 26 and ball 20c which overcomes the biasing force of the spring 20b and presses the ball into the hole 20a, allowing the shift sleeve 2 to pass thereover.

The hub 1 is positioned on the shaft between a pair of gears having different gear ratios, only one of which gears 4 is shown in the drawings. It will, however, be understood that the construction and operation of the outer gear and its associated synchroniser ring assembly will be identical to that of the gear 4 as described below, the only difference being the outer pitch diameter of the gears. Gear 4 is journal mounted on the shaft so as to be rotatable about the longitudinal axis of the shaft independent thereof, and it meshes with an associated second gear (not shown) which is, in turn, drivingly mounted on a

second shaft (not shown) for transmitting drive between said gear 4 and said second shaft.

Gear 4 furthermore has an annular recess 41 formed in is face which is proximate to the hub 1, in which recess 41 is formed a disc member 42 having an outer circumferential surface with teeth or splines 43 formed thereon which match and align with the teeth or splines 13 on the hub. Movement of the shift sleeve 2 towards the gear 4 accordingly brings the teeth or splines 23 of the sleeve 2 into engagement with the teeth or splines 43 of the disc member, the shift sleeve 2 creating a bridge between the hub and the gear which effects a drive coupling therebetween.

In order to ensure synchronisation of the teeth of the hub and those of the gear prior to engagement of the shift sleeve 2 so as to avoid crunching of the teeth of the sleeve with those of the gear 4, the gear 4 is further formed with a circumferentially extending conical friction surface 44 on its side facing the hub 1, which surface tapers inwardly towards the hub 1 as shown in Figure 1. A number of openings 45 are also formed in the face of the gear proximate to the hub 1, equi-angularly distributed around the friction surface 44.

Synchroniser ring assembly 3 is disposed between the conical friction surface 44 of the gear 4 and the hub 1 and is composed of an outer toothed ring 31, an intermediate friction ring 32, and an inner friction ring 33. Inner friction ring 33, shown in Figure 9, has an inner conical friction surface 33a which faces and tapers outwardly towards the gear 4 so as to complement the conical friction surface 44 of the gear 4 such that when the inner ring 33 is pressed towards the gear 4, the surfaces frictionally engage in order to create a drive coupling between the inner ring 33 and the gear. The inner friction ring 33 also has an outer conical friction surface 33b which tapers inwardly towards the hub 1 and has drive lugs 33c extending axially from its edge which faces the hub 1

towards the hub 1, said lugs 33c engaging in complementary shaped channels 35 formed in the toothed ring 31 so as to drivingly couple the inner ring 33 to the toothed outer ring 31 as described below.

The intermediate friction ring 32, illustrated in Figure 8, has an inner conical friction surface 32a which faces and tapers outwardly towards the gear 4 and is shaped to complement the outer conical friction surface 33b of the inner friction ring 33, the intermediate ring 32 being of larger diameter than the inner ring 33 such that it engages over the inner ring 32. In this way, when the intermediate ring 32 is pressed towards the gear 4, the inner friction surface 32a of the intermediate ring 32 frictionally engages the outer friction surface 33b of the inner ring 33 so as to create a drive coupling between the intermediate and inner rings 32, 33. The intermediate friction ring 32 also has an outer conical friction surface 32b which tapers inwardly towards the hub 1 and has drive lugs 32c extending axially from its edge which faces the gear 4 towards the hub 4, said lugs 32c engaging in the openings 45 formed in the face of the gear 4 so as to drivingly couple the intermediate ring 32 to the gear 4.

The outer toothed synchroniser ring 31, shown in more detail in Figure 7, has an inner conical surface 31a which tapers outwardly towards the gear 4 and is sized and shaped to complement the outer friction surface 32b of the intermediate ring 32, such that when the toothed ring 31 is pressed towards the gear 4, the inner friction surface 31a of the toothed ring 31 frictional engages the outer friction surface 32b of the intermediate ring 32 in order to transmit drive therebetween. The toothed ring 31 furthermore has three lugs 34a, 34b, 34b projecting radially inwardly from its edge remote from the gear 4, the lugs 34a, 34b, 34c being equi-angularly distributed around the toothed ring 31 and each lug having a channel 35 formed therein of complementary shape to the lugs 33c of the inner ring 33, said lugs 33c engaging in said channels 35 so as to constrain the inner ring 33 to rotate with the toothed ring 31.

The toothed ring 31 furthermore has three circumferentially extending lugs 36a, 36b, 36c projecting radially outwardly from its outer surface adjacent to the end of the ring 31 which faces the gear 4. The outwardly projecting lugs 36a, 36b, 36c are equi-angularly distributed around the toothed ring 31 and each has teeth or splines 37 formed in its radially outer edge which match and are radially aligned with the teeth or splines of both the hub 1 and disc member 42 (also referred to as a dog ring or dog cone) of the gear 4, so that the teeth or splines 23 of the shift sleeve 2 are engageable with the teeth or splines 37 of the toothed 31 as the sleeve 2 is moved towards the gear 4, thereby creating a drive path from the hub 1, through the sleeve 2 to the toothed ring 31.

The circumferential length of each of the outwardly projecting lugs 36a, 36b, 36c of the toothed ring 31 is shorter than the circumferential length of each of the axial recesses 14a, 14b, 14c formed in each face of the hub, and the lugs 36a, 36b, 36c are distributed around the toothed ring 31 in alignment with the axial recesses such that the lugs are engageable into the axial recesses 14a, 14b, 14c with a small degree of circumferential play, preferably 1 tooth pitch, so as to allow indexing of the toothed ring 31 relative to the hub 1. Furthermore, the axial length of each of the axial recesses 14a, 14b, 14c is greater than the axial thickness of each of the lugs 36a, 36b, 36c such that the assembled synchroniser ring assembly 3 can be seated in the end of the hub 1 with the lugs 36a, 36b, 36c engaged in the axial recesses 14a, 14b, 14c and the ends of the teeth or splines 13 of the axially wider regions 15b of the flange 12 of the hub 1 extending axially beyond the end of the toothed ring 31 which faces the gear 4. In this way, the space between the ends of the teeth or splines 13 of the hub 1 and the teeth or splines 43 of the disc member 42 mounted on the gear 4 is reduce compared with the prior art, increase the tooth spline contact and hence support of the shift sleeve 2 during the shift operation and thereby reducing sleeve tilt or twist.

The system operates as follow:

The shift sleeve 2 starts in the neutral position centralised on the hub 1 as shown in Figure 2 with the struts 17 similarly centralised on the hub 1 and the balls 20c engaged in the grove 26 where is traverses one of the teeth or splines 23 of the sleeve 2 which are aligned therewith. In the absence, then, of any axial load on the synchroniser ring assembly 3 pressing the toothed ring 31 towards the gear 4, the conical friction surfaces of the inner, intermediate and outer toothed rings 33, 32, 31 are disengaged and the hub and sleeve rotate independently of the gear 4.

In order to engage drive through the gear 4, the shift sleeve 2 is movement axially across the hub 1 towards the gear 4. The engagement of the balls 20c of the struts 17 in the circumferential groove 26 in the shift sleeve 2 causes the struts 17 to move axially with the sleeve, bring them into engagement with the inner edge of the toothed ring 31 and pressing the toothed ring 31 towards the gear 4 so as to generate a relative torque between the hub and gear. This initial torque generated from the relatively light load from the struts is enough to index the synchroniser, i.e. to rotate the synchroniser so as to moving radially the synchroniser teeth into a position in which they are offset from the channels between the sleeve teeth by less than half a tooth width, thereby blocking the path of the sleeve teeth.

As the shift load in increased, the camming action developed by engagement of the sloping flanks of the central groove 26 with the balls 20c presses the balls 20c into their holes 20a against the biasing action of the springs 20b, releasing the sleeve to move axially further across the hub 1. However, the offset of the synchroniser teeth with the channels between the sleeve teeth block the path of the sleeve and tapering leading edges of the teeth or splines 23 of the sleeve 2

abut against the facing tapering edges of the teeth or splines 37 of the outwardly projecting lugs 36a, 36b, 36c of the toothed ring 31, further pressing the toothed ring 31 against towards the gear 4 so as to increase the synchronisation torque. Although the engagement of the inclined flanks of the tapering edges of the two sets of teeth 23, 27 will produce a camming action which will try to rotate the toothed ring 31 into a position in which the sleeve can pass over the teeth 37, the torque through the toothed ring resulting from the differential rotational speed of the toothed ring and the gear is much greater than the shift force applied through the sleeve and hence prevents such movement - the torque being generated between the friction faces must always be greater than the indexing torque being generated by the sleeve tooth trying to push the synchroniser tooth out of the way - so called positive ratio.

However, as the differential rotation decreases, the torque generated between the friction faces will reduce until it is less than the indexing torque, at which time the indexing toque will cause the toothed ring to rotate into a position in which its teeth align with the channels of the shift sleeve, allowing the sleeve to continue to move forward and engage the gear dog teeth.

As shown in Figure 4, the facing edges of the teeth 13 of the sleeve 2 and the teeth 37 of the toothed ring 31 are tapered such that the engagement of the inclined flanks of the leading edges of the teeth develops a camming action, producing the indexing torue which rotates the toothed ring 31 into a position in which its teeth 37 are aligned with the troughs between the teeth 23 of the sleeve 2, allow the sleeve to positively engage the toothed ring 31.

Continued movement of the shift sleeve 2 towards the gear 4 brings the leading edges of the teeth 23 of the sleeve into engagement with the facing edges of the teeth 43 of the disc member 42 of the gear 4, which are tapered in a similar fashion to the leading edges of the teeth 37 of the toothed ring so that as the

sleeve 2 engages the teeth 43, a camming action is developed which rotates the gear 4 relative to the sleeve until the teeth are aligned and the sleeve 2 can then move onwards to bring its teeth 23 into meshing engagement with the teeth 43 of the gear. Drive is then transmitted from the hub through the sleeve 2 directly to the gear 4 through the teeth 23 of the sleeve as opposed to through the synchroniser ring assembly 3.

The proximity of the end of the wider regions 16b of the hub to the gear mean that the teeth of the sleeve remain in engagement with the hub right up to the point of engagement with the gear 4, which thereby reduces twisting of the sleeve on the hub as it engages the gear and hence improves the feel and effectiveness of the shift operation.

Furthermore, due to the extended width of the hub, even when the shift sleeve 2 is fully meshed with the gear 4, and hence is at the limit of its axial movement relative to the hub 1, the groove 26 on the inner periphery of the shift sleeve 2 is still set back from the edge of the hub 1 and hence does not provide an opening into which the edge of the hub could engage to enable twisting or tilting of the sleeve on the hub. This is in contract with prior art systems in which the shift sleeve would move to a position in which at least half of the sleeve was overhanging the edge of the hub, and if a circumferential groove 26 were present, the tilting of the sleeve would be increased as the groove provided a recess into which the edge of the hub could be received as the sleeve tilted. As a result, in the prior art, it was not possible to include a circumferential groove which can easily be machined in a single operation. Instead, pockets have to be machined individually in individual teeth of the sleeve and then the sleeve correctly oriented on the hub - increasing the time and cost of manufacture.

Referring now to Figures 11 to 16, there is shown a second embodiment of the assembly of the invention. The assembly is very similar to the embodiment of Figures 1 to 10, with corresponding features being identified by the same reference numeral increased by 100. In this embodiment, instead of struts being mounted in the hub which engage and move with the shift sleeve in order to apply a synchronising load through the synchroniser ring assembly, the outer surface of the hub 101 is continuous, i.e. without recesses 16 in the narrower regions 115a, although it still has three narrower regions 115a interspaced between three wider regions 115b as in the first embodiment. Similarly, because the struts 17 are not present and hence neither are the balls 20c, the shift sleeve 102 of the embodiment does not have a central circumferential groove 26. Instead, the central portion of the inner periphery of the sleeve 102 is recessed as shown in Figure 16, with inwardly ramping surfaces 126a, 126b at each end of the recess 126 and outwardly tapering ramp surface 127a, 127b tapering radially outwardly from the outer end of each inwardly ramping surface 126a, 126b to the associated edge of the sleeve 102.

Each lug 136, 136b, 136c of toothed outer ring 131 then has a leaf spring 138a, 138b, 138c attached to its face which is proximate to the hub 101, each leaf spring 138a, 138b, 138c extending across the face of its associated lug, circumferentially partially around the toothed ring 131 and furthermore having a radially outwardly projecting portion 139 which extends in front of at least the central teeth or splines 137 formed on the outer radially edge of the lug, thereby lying in the path of the inner most protrusion formed on each end of the teeth of splines 123 of the sleeve 102 by the ramp surfaces when the sleeve is moved axially towards the toothed ring 131.

Upon initiation of a shift operation, then, the sleeve is pressed towards the gear in the same way as in the first embodiment. As the sleeve approaches the toothed ring 131, the leading ramp 127a of the teeth 123 engage the outwardly

projecting protrusions 139 of the springs 138a, 138b, 138c, imparting an axial load to the toothed ring 131 which presses it towards the gear and brings the conical friction surfaces of the outer toothed ring 131, the intermediate ring 132 and the inner ring 133 into engagement, thereby initiating synchronisation of the gear and the hub. As the shift force exerted through the sleeve 102 increases, the protrusions 139 of the leaf springs 138a, 138b, 138c eventually retract radially inwards under the camming action developed with the leading ramps 127a of the teeth 123, allowing the sleeve to move across the toothed ring 131, so as to effect indexing and then synchronous engagement in the same manner as described in relation to the first embodiment above.

In all other respects the construction and operation of the assembly of Figures 11 to 16 is identical with that of the first embodiment.

Referring now to Figures 17 to 20, there is shown a further embodiment of the present invention which uses a modified sleeve 202 and outer toothed ring 231. The sleeve 202 differs from the previous embodiments in that its includes teeth or splines 223 which are of two different axial lengths. The axially shorter teeth 223a being formed into groups which are equi-angularly circumferentially distributed around the sleeve and axially longer teeth 223b filing the spaces between the groups of shorter teeth 223 a. In the illustrated embodiment, six groups of shorter teeth 223a are provided with three teeth in each group. The shorter or synchroniser teeth 223 a are provided for engaging with teeth 237 of the synchroniser ring 231 as described hereinafter, whilst the longer or catcher teeth 223b, in operation, align with the spaces between the groups of teeth 237 of the synchroniser ring 231 and engage directly with the dog teeth of the gear. The extended length of these catcher teeth 223b means that they overlap the synchroniser ring before the synchroniser teeth 223a engage the teeth 237 of te synchroniser ring 231 and hence a shorter shift is required to bring the catcher

teeth 223b into engagement with the dog teeth once synchronisation as occurred.

Figure 19 shows an enlarged view of the outer synchroniser ring 231, which, like those of the previously described embodiments, has an inner conical friction surface 231a which tapers outwardly towards a gear with which, in use, it engages, has a circumferential flange 234 extending radially inwardly from its edge which, in use, is remote from the gear, and has six circumferentially extending lugs 236 projecting radially outwardly from its edge which, in use, is proximate to the gear. The circumferential flange 234 includes a plurality, in the illustrated example six, channels 235 formed in it, equi-angularly distributed around the flange, which channels 235 are of complementary shape to lugs of an inner ring (not shown) which forms part of a synchroniser ring assembly with the ring 231 as described above in connection with the previous embodiments.

Each of the six circumferentially extending lugs 236 has a pair of teeth of splines 237 formed in its radially outer edges which are shaped and positioned to meshingly engage with the synchroniser teeth 223a of the sleeve 202 in order to drivingly couple the sleeve to the synchroniser ring assembly - the three teeth in each group of synchroniser teeth 223a on the sleeve defining two channels for meshing of a pair of teeth 237 of the ring. The illustrated embodiment has six groups of teeth with two teeth in each group, however other combinations are possible - the important thing being that the circumferential extent of each group is shorter than the circumferential length of the gap between neighbouring teeth so that there are more catcher teeth than synchroniser teeth on the sleeve.

In all other respects, the system of the third embodiment is identical with those of the previously described embodiments.

It should be noted that the synchroniser ring of the third embodiment, although advantageously used with a catcher tooth sleeve ring as described above, can also be used with a standard shift sleeve, affording the advantages of decreasing impact wear as described below. However, the modified synchroniser ring enables particularly simple implementation of the catcher tooth system.

By increasing the number of groups of teeth on the outer ring, the number of indexing faces in the system is correspondingly increased (one end of each group forming an indexing face), so that the potential impact wear within the system is reduced. At the same time, using catcher and synchroniser teeth on the hub maintains the torque carrying capability of the arrangement. As a result, the modification of this third embodiment allows the even spread of load applied by the sleeve. The centralisation of the synchroniser ring is improved because, as illustrated in Figure 20, the synchronisation diameter Dl, that is the diameter at which the shift sleeve teeth engage the teeth of the synchroniser ring, is very close to the location diameter, that is the diameter of the toothless portion of the synchroniser ring which locates in the recess within the hub. As a result, the synchroniser if centralised at a larger diameter as compared with the prior art system in which centralisation occurred towards the centre of the hub. The wear on the indexing faces is somewhat negated by the introduction of an extra three faces, thereby doubling the contact surface are and redistributing the impact force more evenly through the synchroniser ring.