GB2509357A

GB2509357A - Gear selection mechanism with rotatable selector member mounted on a carriage

Info

Publication number: GB2509357A
Application number: GB1317938.7A
Authority: GB
Inventors: Steven Prentice
Original assignee: STEVE PRENTICE DESIGN Ltd
Current assignee: STEVE PRENTICE DESIGN Ltd
Priority date: 2011-02-24
Filing date: 2012-02-24
Publication date: 2014-07-02
Anticipated expiration: 2032-02-24
Also published as: GB2488435A; GB2509357B; GB201203234D0; GB201317938D0; GB2488435B; GB201103182D0

Abstract

A gear selection mechanism 200 includes a stellate selector member 136 rotatably mounted to a carriage 210. Carriage 210 comprises a tubular body 212 having a bore 214 and is provided with a pair of arms 216 which permit the carriage 210 to locate at predetermined axial positions on a rod of the mechanism 200. The member 136 is rotatably mounted to the carriage 210 between a flange 218 and a split ring 220 received in a groove 222. Carriage 210 is moved axially by application of a pushing force on actuating pin 238 which causes actuating members to move relative to wedge members 248 that move outwardly to engage with the bore 214, thereby coupling the carriage 210 to the wedge members 248. The force coupling the wedge members 248 and carriage 210 is greater than a force exerted by arm 216 and thus the arms are disengaged from recesses (300, fig 21) which allow the carriage 210 to move to the next recess (300) and another gear is selected.

Description

Gear Selection Mechanism The present invention relates to a gear selection mechanism and particularly, though not exclusively, a gear selection mechanism for an automotive gear box.

The gear arrangement of an automotiye gearbox typically includes an input shaft which is connectable to the engine of the vehicle and an output shaft which is connectable to the driven wheels of the vehicle. Each shaft is provided with a cluster of gears which are meshed with one another. The gearbox further includes a gear selection mechanism which permits specific gear ratios to be selected. The gear selection mechanism may include a plurality of selector forks which sit over and partially around one of the shafts, and a rotatable selector drum which is positioned over and above the shafts and gears. The forks and drum increase the complexity of the gearbox and the size of the housing within which the components are contained.

According to the present invention, there is provided a gear arrangement including a gear rotatably mounted to a shaft and a gear selection mechanism arranged to selectively couple the gear for rotation with the shaft, the gear selection mechanism being located at least partially within a longitudinally extending bore of the shaft and being movable between a first axial position where the gear is coupled for rotation with the shaft and a second axial position where the gear is decoupled from the shaft, wherein the gear selection mechanism includes a gear selection member which contacts the gear when the gear selection mechanism is in the first axial position, the gear selection mechanism further including a gear selection rod which is located at least partially within the longitudinally extending bore, wherein the gear selection member is movable axially with the gear selection rod between the First arid second axial positions wherein the gear selection member is provided with a plurality of arms which, in use, contact the gear when the gear selection mechanism is in the first axial position, and wherein the gear is provided with a formation around its inner periphery which permits the gear to be rotatable relative to the shaft when the gear selection mechanism is in the second axial position, and which contacts the arms of the gear selection member when the gear selection mechanism is in the first axial position, and wherein the formation comprises a plurality of dog teeth, provided on a dog tooth ring which is connectable to the gear, wherein the dog tooth ring is comprised of two or more dog tooth segments.

By locating the gear selection mechanism at least partially within the shaft, the overall size of the gear arrangement is reduced when compared to a conventional gear arrangement having a gear selection mechanism that is positioned fully to the exterior of the shaft.

The shaft may have an annular recess within which the dog teeth of the gear are received, wherein the arms of the gear selection member extend into the annular recess when the gear selection member is in the first axial position.

The gear selection member is preferably rotatably mounted on a carriage which is movable axially on the gear selection rod. By rotatably mounting the gear selection member on the carriage, the gear selection member is able to rotate with the shaft when coupled to a gear.

The carriage and gear selection rod are preferably provided with complementary formations which correspond to the first and second axial positions. The interengagement of the formations ensure that the carriage can be located at the correct position on the gear selector rod.

The formations may comprise projections of the carriage and recesses of the gear selection rod. The projections of the carriage may be provided on opposed resilient arms of the carriage.

The gear selection mechanism may further include a carriage movement mechanism located at least partially within the gear selector rod, the carriage movement mechanism being operable to move the carriage axially on the gear selection rod between the first and second positions. The carriage movement mechanism is preferably movable relative to the gear selector rod in order to move the carriage.

More specifically, the carriage movement mechanism is preferably movable axially relative to the gear selector rod in order to move the carriage. The carriage movement mechanism is preferably movable in a first direction axially relative to the gear selector rod in order to move the carriage from the first position to the second position, and is movable in an opposite direction axially relative to the gear selector rod in order to move the carriage from the second position to the first position.

The carriage movement mechanism is also preferably movable between a coupled position whereupon it is engaged with the carriage and a decoupled position whereupon it is disengaged from the carriage. The carriage movement mechanism is preferably biased towards the decoupled position.

The carriage movement mechanism preferably includes coupling members which are located within a slot of the gear selector rod and arc movable outwardly from the slot to couple the carriage to the carriage movement mechanism. The coupling members may be provided with formations which are received in complementarily formations of the carriage when in the coupled position.

The gear selection member is preferably provided with a plurality of arms which, in use, contact the gear when the gear selection mechanism is in the first axial position.

The gear selection mechanism preferably has a stcllatc or star shaped configuration.

The shaft is preferably provided with an annular recess within which the dog teeth are located.

The gear arrangement frirther comprises an additional shaft having an additional gear coupled for rotation therewith, the additional gear being meshed with the gear of the first shaft. Preferably the first shaft has a plurality of gears, and the second shaft has a plurality of gears meshed with the gears of the first shaft. The gear selection mechanism is moveable between a plurality of axial positions within the bore of the first shaft, each axial position corresponding to the position of a gear on the first shaft.

Movement of the gear selection mechanism between positions decouples one of the plurality of gears from rotation with the first shaft and couples another of the plurality of gears with the fir st shaft, and thereby sequentially selects gear ratios. The gear selection mechanism may further be movable to an axial position where no gear is coupled for rotation with the first shaft.

According to a further aspect of the present invention there is provided a gear selection mechanism suitable thr location within a longitudinal bore of a shaft carrying a gear, the gear selection mechanism including a gear selection member and a gear selection rod, the gear selection member having formation which, in use, is able to contact a complementarily configured formation of a gear to couple the gear for rotation with a shaft, wherein the gear selection member is movable axially on the gear selection rod between first and second axial positions, wherein the gear selection member is rotatably mounted on a carriage with is movable axially on the gear selection rod.

The carriage and gear selection rod are preferably provided with complementary formations which correspond to the first and second axial positions. The formations may comprise projections of the carriage and recesses of the gear selection rod. The projections of the carriage may be provided on opposed resilient arms of the carriage.

The gear selection mechanism may further include a carriage movement mechanism located at least partially within the gear selector rod, the carriage movement mechanism being operable to move the carriage axially on the gear selection rod between the first and second positions. The carriage movement mechanism is preferably movable between a coupled position whereupon it is engaged with the carriage and a decoupled position whereupon it is disengaged from the carriage. The carriage movement mechanism is preferably biased towards the decoupled position.

The carriage movement mechanism may include coupling members which are located within a slot of the gear selector rod and are movable outwardly from the slot to couple the carriage to the carriage movement mechanism. The coupling members are provided with formations which are received in complementarily formations of the carriage when in the coupled position.

S

The gear contacting formation of the gear selection member is preferably defined by a plurality of arms of the gear selection member which, in use, contact a eomplementarily configured formation of a gear.

Embodiments of the present invention will now be described with reference to the accompanying drawings in which: Figure 1 shows a plan view of a gear arrangement having a selector mechanism in accordance with the present invention; Figure 2 shows a side view of the gear arrangement as indicated by arrow A of figure 1; Figure 3 shows an end view of the gear arrangement as indicated by arrow B of figure 1; Figure 4 shows an exploded perspective view of the output shaft, gear selector rod and gear selector member of the gear arrangement; Figure 5 shows a side view of the output shaft; Figure 6 shows an end view of the output shaft as indicated by arrow C of figure 5; Figure 7 shows a perspective cross-sectional view of the output shaft as indicated by arrows D-D of figureS; Figure 8 shows a further perspective cross-sectional view of the output shaft as indicated by arrows E-E of figure 5; Figure 9 shows a partial side view of the output shaft and gear selector member; Figure 10 shows a perspective view of the output shaft and gear selector member shown in figure 9; Figure 11 shows an end view of an output gear; Figure 12 shows a perspective view of output gear of figure 11; Figure 13 shows an end view of a dog insert of the output gear; Figure 14 shows a perspective view of dog insert of figure 13; Figure 15 shows a plan view of an alternative gear arrangement in accordance with the present invention; Figure 16 shows a cross-sectional view of the gear arrangement of figure 15 Figure 17 shows a perspective view of the dog insert of an output gear; Figure 18 shows a perspective view of an output gear; Figure 19 shows an exploded perspective view of a gear selection mechanism; Figure 20 shows a cross sectional view of the selector carriage of the mechanism of figure 19; Figure 21 shows a perspective view of the gear selection mechanism of figure 19 in a first position; Figure 22 shows a cross -sectional view of the gear selection mechanism in the first position; Figure 23 shows a cross-sectional view of the gear selection mechanism in an intermediate position between the first position and a second position; Figure 24 shows a perspective view of the gear selection mechanism in a second position; Figure 25 shows a cross-sectional view of the gear selection mechanism in the second position; Figure 26 shows a perspective view of the gear selection mechanism in a third position; Figure 27 shows a cross-sectional view of the gear selection mechanism in the third position; Figure 28 shows a perspective view of the gear selection mechanism in a fourth position; Figure 29 shows a cross-sectional view of the gear selection mechanism in the fourth position; Figure 30 shows a perspective view of the gear selection mechanism in a fifth position; Figure 31 shows a cross-sectional view of the gear selection mechanism in the fifth position; Figure 32 shows a perspective view of the gear selection mechanism in a sixth position; Figure 33 shows a cross-sectional view of the gear selection mechanism in the sixth position; Figure 34 shows a cross-sectional view of the gear selection mechanism in an intermediate position between the sixth position and a seventh position; Figure 35 shows a perspective view of the gear selection mechanism in a seventh position; Figure 36 shows a cross-sectional view of the gear selection mechanism in the seventh position; S Figure 37 shows a perspective view of the gear selection mechanism in an eighth position; Figure 38 shows a cross-sectional view of the gear selection mechanism in the eighth position; Figure 39 shows a perspective view of the gear selection mechanism in a ninth position; Figure 40 shows a cross-sectional view of the gear selection mechanism in the ninth position; Figure 41 shows a perspective view of the gear selection mechanism in a tenth position; Figure 42 shows a cross-sectional view of the gear selection mechanism in the tenth position; Figure 43 shows a perspective view of the gear selection mechanism in an eleventh position; and Figure 44 shows a cross-sectional view of the gear selection mechanism in the eleventh position.

Referring firstly to figures 1 to 3 there is shown a gear arrangement generally designated 10. The arrangement includes a first gear cluster 12 provided upon an input shaft 14, and a second gear cluster 16 provided upon an output shaft 18. In the embodiment shown, the gear clusters 12,16 provide six sets of gear pairs indicated I,II,III,IV,V and VI. The input shaft 14 is provided at each end with a bearing 20,22.

Similarly, the output shaft 18 is provided at each end with a bearing 24,26. It will be appreciated that, in use, the bearings 20,22,24,26 arc located within an appropriately configured housing (not shown) such that shafts 14,18 are rotatable relative to the housing.

In the embodiment shown, the gear arrangement 10 further includes a differential pinion 28 mounted to the output shaft 18, and a reverse idler gear 30. It will be appreciated that, depending upon the intended installation of thc gear arrangement 10 in a vehicle, the differential pinion may be located at a different position, or be replaced with an alternative arrangement tbr connection of the output shaft 18 to the driven wheels of a vehicle.

The gear arrangement 10 is further provided with a selection mechanism generally designated 32. The selection mechanism 32 includes a gear selector rod 34, a gear selector member 36 and a detent mechanism 38. The selector rod 34 and selector member 36 extend into a stellate bore 40 of the output shaft 18. The bore 40 is aligned with the longitudinal cenireline axis of the output shaft 18. The selector rod 34 is provided with a plurality of recesses 42 which thee the detent mechanism 38. In use, the selector rod 34 is movable into and out of the bore 40 as indicated by arrow 44. The interaction of the recesses 42 with the detent mechanism 38 enables the selector rod 34 to be retained at one of a number of axial positions relative to the output shaft 18. The selector rod 34 is movable to a neutral position wherein the gear selector member 36 is located in a position of the bore 40 where it is not in axial alignment with a gear. With reference to figure!, the neutral position is located to the right of the first gear I in the output shaft gear cluster 16.

Figures 4 to 10 show the gear selector rod 34, gear selector member 36 and output shaft 18 in greater detail. The gear selector rod 34 is provided with a pin-like projection 46 which, in use fits to a complementary through bore 48 of the gear selector member 36. The projection 46 and through bore 48 are dimensioned such that the gear selector member 36 is freely rotatable relative to the gear selector rod 34 when fitted to the projection 46. The gear selector member 36 is maintained upon the projection 46 by an annular retainer 50.

In the embodiment shown, the gear selector member 36 has a stellate configuration with five arms 52. It will be appreciated that the gear selector member 36 may not be limited having five arms 52, and may be provided with a greater or lesser number of arms 52 depending upon such factors as the configuration of the gear arrangement 10, the number of gear ratios, and the anticipated torque load of the gear arrangement 10.

The bore 40 of the output shaft has a complementary stellate configuration including a radially extending portion 54 for each arm 52 of the gear selector member 36. Each arm 52 of the gear selector member 36 is tapered towards its respective tip 60. As will be described in greater detail below, this tapering of the arms 52 assists in the prevention of two gears being selected simultaneously.

S

The output shaft 18 is provided with a plurality of equidistantly spaced annular recesses 56. Each recess 56 is substantially U' shaped in cross-section and is of a sufficient depth that it intersects the stellate bore 40. Each recess 56 is thus provided with a plurality of apertures 58 which extend between the recess 56 and the bore 40.

As can be seen in figures 9 and 10, when the gear selector member 36 is axially aligned with an annular recess 56, the tip 60 of each arm 52 extends through an aperture 58 and into the annular recess 56.

Figures 11 to 14 show a gear generally designated 62 which is configured for use with a output shaft 18 and gear selection mechanism 32 of the type previously described.

The gear 62 is annular and is provided around its outer periphery with a plurality of teeth 64. The inner periphery of the gear 62 is provided with five equidistantly spaced dog teeth 66. The function of the dog teeth 66 is to interact with the gear selector member 36 to couple the gear 62 for rotation with the output shaft 18 as will be described in greater detail below.

Figures 13 and 14 show the configuration of the dog teeth 66 in greater detail, the dog teeth 66 are provided on a segmented dog ring 68. The dog ring 68 is comprised of five segments 70, each of which is provided with a dog tooth 66. The outer periphery of the dog ring 68 is splined 72 so as to facilitate connection of the body of a gear to the dog ring 68. In order to assemble a gear to the output shaft 18, the dog ring segments 70 are first fitted to a recess 56. The body of the gear can then be threaded axially onto the output shaft and located onto the splincs 72 of the dog ring 68. It will be understood that the inner periphery of the body of the gear is provided with a complementarily splined surface. In the embodiment shown, the dog ring 68 is comprised of five segments 70. It will be appreciated that the dog ring 68 may be comprised of a different number of segments. For example, the dog ring 68 may alternatively be comprised of two segments.

In an alternative embodiment, the dog teeth 66 may not be provided upon a separate dog ring, but may instead be formed integrally with a gear. In such an embodiment, it will be appreciated that the external surface of the shaft upon which the gears are to be mounted would need to be configured so as enable thc gears to be introduced onto the shaft in an axial direction. In such an embodiment it is envisaged that axially extending recess would be provided upon the external surface of the shaft which would extend between the annular recesses.

Operation of the gear arrangement 10 will now be described. The gears of the input shaft gear cluster 12 are fixed for rotation with the input shaft 14. With the gear selector member 36 in the neutral position, it will be understood that the gears of the output gear cluster 16 arc freely rotatable relative to output shaft 18. Rotation of the input shaft 14 therefore resuhs in rotation of the gear clusters 12,16, however there is no transmission oftorque to the output shaft 18. Utilising an appropriately configured actuation mechanism, the gear selection mechanism 32 can be operated to move the gear selector member 36 axially within the bore 40 of the output shaft 18. The spacing of the recesses 42 on the gear selector rod 34 matches that of the annular recesses 56 of the output shaft 18. The gear selector member 36 can thus be moved sequentially between the annular recesses 56. When thc gear selector member 36 is aligned with an annular recess 56, the dog teeth 66 of the gear associated with the annular recess engage the tips 60 of gear selector member arms 52. The gear is thus coupled for rotation with the output shaft 18 torque is transmitted to the output shaft 18. Each arm 52 of the gear selector member 36 is in double shear and thus no bending of the arms 52 takes place.

The width of the gear selector member 36 is greater than the axial spacing of the annular recesses 56. Accordingly, the possibility of there being a false neutral position between adjacent gears is eliminated. In the event that the gear selector member 36 comes to rest at an axial position between two gears and their respective annular recesses 56, the dog teeth 66 of both gears will engage the chamfered lead in surfaces provided upon either side to each arm 52. The gear with the higher torque ratio will urge the gear selector member 36 into full engagement with the gear having the lower torque ratio. The gear arrangement 10 is thus prevented from being able to fully engage two gears simultaneously and thus is prevented fromjamming.

Referring now to figures 15 to 44 there is shown an alternative gear arrangement according to the present invention generally designated 110. Features common to the embodiment described with reference to figures 1 to 14 are identified with like reference numeral prefixed with "1". The gear arrangement 110 differs in the manner in which the second gear cluster 116 is connected to the output shaft 118. The gear arrangement 110 further differs in that the gear selector member 136 is provided upon a reciprocating gear selection mechanism 200. The manner in which the second gear cluster 116 is connected to the output shaft 118 is described with reference to figures 17 and 18. The reciprocating gear selection mechanism 200 is described with reference to figures 19 to 44.

Figure 17 shows a perspective view of a segmented dog ring 168. The dog ring 168 is comprised of two dog segments 170. The dog ring 168 is provided with five dog teeth 166, with two of the dog teeth 166 provided on one ring segment 170 and the remaining three dog teeth 166 provided on the other ring segment 170. The outer periphery of the dog ring 168 is splined 172 so as to facilitate the connection of a body of a gear to the dog ring 168. The splined outer periphery 172 is provided with a circumferential slot within which there is provided a split ring 202. The split ring 202 retains the dog segments 170 in association with one another. The split ring 202 further assists with connection of a gear to the dog ring as will be described in greater detail below. The outer diameter of the split ring 202 is approximately equal to the diameter of the dog ring 168 refmed by the peaks of the splines. Figure 17 shows the dog ring 168 positioned between opposed annular spacers 204 which, in use, separate adjacent dog rings. The outer diameter of each spacer 204 is slightly greater than the outer diameter of the dog ring 168.

Figure 18 shows a gear 162 adapted to connect to the dog ring 168 of figure 17. The inner periphery of the gear is splined 206 and thus is able to mesh with the splines 172 of the dog ring 168. The splines 206 include a circumferential recess 208 which, in use, receives the split ring 202 of the dog ring 168 in a snap fit coupling arrangement.

Figure 19 shows an exploded view of the reciprocating gear selection mechanism 200.

The mechanism 200 includes a stellate selector member 136, however instead of being fixed to a rod, the selector member 136 is rotatably mounted to a carriage 210. The carriage 210 comprises a tubular body 212 having a bore 214 thcrethrough. The carriage 210 is further provided with a pair of arms 216 which, as will be described in greater detail below, permit the carriage 210 to locate at predetermined axial positions on a rod of the mechanism 200. The selector member 136 is rotatably mounted to the carriage 210 between a flange 218 of the carriage 210 and a split ring 220 received in a groove 222 of the carriage 210.

Figure 20 shows a cross-sectional view of the carriage 210. As can be readily seen, the bore 214 is not uniform but instead narrows to a waist 224 at a midway point of the tubular body 212. The narrowing of the bore 204 does not occur around the entire circumference of the bore 214, but instead is present at opposed regions of the bore 214 which are aligned in a direction substantially perpendicular to the plane of the arms 216. This "hourglass" profile of the bore 214, as will be described in greater detail below, matches opposed wedge members of the mechanism 200.

The mechanism 200 further includes a rod 226. The rod 226 has a fore end 230 and a rear end 232. The rod 226 has a longitudinally extending slot 228 which is open to opposing sides of the rod 226. The fore end 230 of the rod 226 is provided with a through bore 234 which connects with the slot 228. The rear end 232 of the rod 226 is provided with a bore 236. The through bore 234, in use, receives an actuation pin 238 thercthrough. As will be described in greater detail below, the actuation pin 238 connects to a wedge mechanism of the selection mechanism 200. The bore 236 at the rear end 232 of the rod 226 permits the rod 226 to be mechanically connected to a fixed rod mount 240 by the usc of a threaded fastener 241. The rod mount 240 includes a tubular portion 242 within which the rod 226 is received, and a flange 244 which permits the rod mount 240 to be connected to fixed surface, for example an interior surface of a gearbox casing.

The selection mechanism 200 is further provided with a wedge mechanism generally designated 246. The wedge mechanism 246 includes a pair of elongate wedge members 248,250 and a pair of elongate actuation members 252,254. In use, the wedge members 248,250 and actuation members 252,254 are accommodated within the slot 228 of the rod 226. Each wedge member 248,250 is provided with an edge 256 having a plurality of shallow teeth 258. The profile of the teeth 258 substantially matches the hourglass profile within the bore 214 of the carriage 210. The wedge members 248, 250, in use, are accommodated within the slot 228 such that their teeth 258 lie on opposing sides of the rod 226.

Each wedge member 248,250 is further provided with three through apertures 260.

Each aperture 260 is substantially triangular and is provided with a pair of inclined ramp surfaces 262. Each actuation member 252,254 is provided with three projections 264 which, in use, are received in the through apertures 260 of a respective wedge member 248,250. Each projection 264 is substantially triangular and is provided with a pair of inclined ramp surfaces 266. The shape of the projections 264 is substantially the same as that of the apertures 260, however the projections 264 are smaller than the apertures 260 such that the projections 264 are received within the apertures 260 with a clearance therearound.

The ends 268 of the actuation members 252,254 which are proximal to the fore end 230 of the rod 226 are part cylindrical and include a through bore 270. The through bores 270, in use, align with a through bore 272 of the actuation pin 238 and enable the actuation pin 238 to be connected to the actuation members 252,254. The ends 274 of the wedge members 248,250 which arc proximal to the rear end 232 of the rod 226 are each provided with a key slot 276. The key slots 276 enable a spring carriage generally designated 278 to be connected to the wedge members 248,250.

The spring carriage 278 is comprised of a first member 280 and a second member 282.

The members 280,282 are connected to one another by a threaded fastener 284. The spring carriage 278 is accommodated within the slot 228 of the rod 226. The first member 280 is provided with a key projection 286 which, in usc, is received within the key slots 276 of the wedge members 248,250. The first member 280 is further providcd with a pair of opposed projections 288 which, in use, abut a first annular spring scat 290 of the selection mechanism 200. The second member 282 is similarly provided with a pair of opposed projections 292 which, in use, abut a second annular spring seat 294 of the selection mechanism 200.

The selection mechanism 200 thrther includes a coil spring 296 which is provided between the annular spring seats 290,294. In use, the rod 226 extends through the coil spring 296 and the annular spring seats 290,294.

The rod 226 is further provided with a spring flange 298 which is proximal to the rear end 232 of the rod 226. The rod 226 is further provided with a plurality of spaced recesses 300 proximal to fore end 230 of the rod 226. The recesses 300 are provided on opposing sides of the rod 226 and, in use, receive the arms 216 of the selector member carriage 210.

Operation of the selection mechanism 200 will now be described.

Figures 21 and 22 show the selection mechanism 200 in an initial rest position. The arms 216 of the selector member carriage 210 are located within the an opposed pair of recesses 300 of the rod, and the selector member 136 is aligned with a gear (not shown) such that the arms 152 of the selector member 136 engage the dog teeth of the gear. The projections 264 of the actuation members 252,254 are centrally located within the recess 260 of the wedge members 248, 250 such that the ramp surfaces 262 of the recesses 260 are spaced from the ramp surfaces 266 of the projections 264. The coil spring 296 is at its maximum extension and is constrained between the first spring seat 290 abutting the rod spring flange 298 and the second spring seat 294 abutting the tubular portion 242 of the rod mount 240.

In order to move the selector member carriage 210 axially along the rod 226 in the direction of the rear end 232 of the rod 226, as indicated by arrow 302, a force is applied to the actuation pin 238 in the direction of the rear end 232 of the rod 226.

This pushing force, indicated by arrow 304, acts to move the actuation pin 238 into the bore 234 on the rod 226. Initially, this force 304 causes the actuation members 252,254 to move axially relative to the wedge members 248,250. This relative axial movement causes the ramp surfaces 266 of actuation member projections 264 which face the rear end 232 of the rod 226 to contact the facing ramp surfaces 262 of the wedge member apertures 260. This can be seen in figure 23. The contact of the ramp surfaces 262,266 urges the toothed edge 256 of each wedge member 248,250 outwardly with respect to the rod 226 and into engagement with the bore of the 214 of the selector member carriage 210. This engagement couples the carriage 210 to the wedge members 248,250.

Continued application of the force 304 to the actuation pin 238 causes the actuation members 252,254, wedge members 248,250 and spring carriage 278 to move axially with respect to the rod 226. The force coupling the wedge members 248,250 to the carriage 210 is greater than the force exerted by the carriage arms 216, and thus the carriage 210 is entrained by the wedge members 248,250 and the carriage arms 216 disengaged from the recesses 300 of the rod 226. Figures 24 and 25 show the carriage at a midway point on the rod 226 between two adjacent sets of recesses 300. Figures 24 and 25 further show the spring 296 being compressed between the projections 288 of the spring carriage 278 and the rod mount 240 as a result of axial movement of the spring carriage 278.

Figures 26 and 27 show that continued movement of the actuation members 252,254, wedge members 248,250 and spring carriage 278 axially with respect to the rod 226 results in sufficient movement of the carriage 210 to engage the carriage arms 216 with the next set of recesses. Figures 26 and 27 show the spring 296 in a fully compressed state.

Once the carriage 210 has been moved to the next axial position on the rod 226, the pushing force 304 applied to the actuation pin 238 is removed. The compressed spring 296 is this able to move the actuation members 252,254, wedge members 248,250 and spring carriage 278 to move axially with respect to the rod 226 in the opposite direction back to their ithtial position as shown in figures 28 to 31. It will be noted that axial movement of the toothed edges 256 of wedge members 252,254 relative to the bore 214 of the carriage 210 causes the wedge members 252,254 to move inwardly and thus decouple the wedge members 252,254 from the carriage 210.

This is best shown in figures 28 and 29.

Figures 32 to 44 show the operation of the selection mechanism 200 in the opposite direction, i.e. to move the carriage 210 in the direction of the fore end 230 of the rod 226. The operation is essentially as described above except that a pnlling force 306 is applied to the actuation pin 238, and the spring 296 is compressed against the spring flange 298 of the rod 226.

In the embodiments shown, the gear arrangements 10, 110 has six ratios, and the gear selection mechanisms are located within a bore of the output shaft 18,118. It will be understood that the gear selection mechanisms of the present invention may be used in connection with a gear arrangement having a greater or lesser number of ratios. The gear selection mechanisms of the present invention may alternatively be located in the bore of the input shaft. The gear selection mechanisms of the present invention may be used in connection with both non-synchromesh straight and helical spur gears.

Within applications such as automotive racing gearboxes, a clutch is not always used to disengage drive to the driven wheels when changing gear. instead, the engine ignition or fttelling may be briefly cut to reduce the torque being transmitted through the gearbox. The gear selection mechanism of the present invention allows gear changes to take place with a shorter ignition or fuelling cut when compared to conventional gearbox configurations. Furthermore, the gear selection arrangement of the present invention permits the input and output shafts to be more compact and typically 25% to 50% shorter than conventional designs. The shafts of the present invention are provided with two bearings, each of which is located towards an end of a respective shaft. Typically a conventional input or output shaft is longer and requires an intermediate bearing.

Claims

Claims 1. A gear selection mechanism suitable for location within a longitudinal bore of a shaft carrying a gear, the gear selection mechanism including a gear selection member and a gear selection rod, the gear selection member having formation which, in use, is able to contact a complementarily configured formation of a gear to couple the gear for rotation with a shaft, wherein the gear selection member is movable axially with the gcar sclcction rod bctwccn first and second axial positions, and wherein the gear selection member is rotatably mounted on a carriage which is movable axially on the gear selection rod.
2. A gear selection mechanism as claimed in claim I wherein the carriage and gear selection rod are provided with complementary formations which correspond to the first and second axial positions.
3. A gear selection mechanism as claimed in claim 2 whereill the formations comprisc projcctions of thc carriagc and rcccsses of thc gear sclection rod.
4. A gear selection mechanism as claimed in claim 3 wherein projections of the carriage arc providcd on opposed rcsilient arms of thc carriagc.
5. A gear selection mechanism as claimed in any of claims 1 to 4 wherein the gear selection mechanism further includes a carriage movement mechanism located at least partially within the gear selector rod, the carriage movement mechanism being arranged to move the carriage axially on the gear selection rod between the first and second positions.
6. A gear sclection mechanism as claimcd in claim 5 whcrcin the carriage movcment mcchanism is movable between a coupled position whcrcupon it is engaged with the carriage and a decoupled position whereupon it is disengaged from the carriage.
7. A gear selection mechanism as claimed in claim 6 wherein the carriage movement mechanism is biased towards the decoupled position.
8. A gear selection mechanism as claimed in claim 6 or claim 7 wherein the carriage movement mechanism includes coupling members which arc located within a slot of the gear selector rod and are movable outwardly from the slot to couple the carriage to the carriage movement mechanism.
9. A gear selection mechanism as claimed in claim 8 wherein the coupling members are provided with formations which are received in complementarily formations of the carriage when in the coupled position.
10. A gear selection mechanism as claimed in any of claims 1 to 9 wherein the gear contacting formation of the gear selection member is defined by a plurality of arms of the gear selection member which, in use, contact a complementarily configured formation of a gear.
11. A gear selection mechanism as substantially described herein with reference to the accompanying figures.