A gear coupler

Abstract: A gear coupler for coupling a gear (24) to a shaft (14) comprising a first coupling member (12) which is connected for rotation with the shaft (14) and a second coupling member (18a) connected for rotation with the gear (24) and engageable by the first coupling member (12). The second coupling member is capable of limited circumferential movement relative to the gear (24) to allow the first and second coupling members to engage each other without the need to rotate the gear.

Description: The present invention relates to a gear coupler for coupling a gear to a shaft and more particularly to such a coupler which is comparatively easy to engage when the gear to be engaged is not freely rotatable when engagement is to be achieved. For example, a number of different types of synchromesh coupler are known in which friction surfaces which rotate with the gear and shaft respectively are brought into contact with each other to synchronise the rotational speeds of the gear and shaft and baulking means are provided to prevent engagement between a coupling member associated with the shaft and a coupling member associated with the gear until synchronization has occurred. For instance, one form of synchromesh coupler, described in EP-A-O 184 077 and US-A-4,817,773, is designed to reduce the phenomenon of "cold scratch". In common with other prior art synchromesh couplers it incorporates a gearshift, or coupling sleeve, connected for rotation with the shaft via a central guide sleeve, or hub, and a synchronising, or baulking ring. It also incorporates a countercone, or synchronising cone, splined to the gear and a coupling member, in this case in the form of external teeth formed integrally with the countercone. The splines are such that the cone and coupling member rotate with the gear without any relative circumferential movement. The design includes spring loaded poppets incorporated in the synchroniser ring and acting against the central hub to bias the synchroniser ring towards a particular position. Whilst the various prior art types of synchromesh couplers operate adequately in most circumstances, problems can arise when they are used in applications where large gear ratios are employed, for example, in the output stages of a transmission where range changing stages are employed. In such applications, in order to complete the coupling of the gear to the shaft after synchronisation it may be necessary for the synchromesh coupler to generate sufficient rotational force to rotate the coupling member associated with the gear together with the gear itself and any associated meshing gears against a large torque reaction. Since the force required to rotate the coupling member associated with the gear and any associated meshing gears must be provided by the vehicle operator via a gear lever which controls the synchromesh coupler, this may lead to unacceptably high (even impossible) gear lever forces being required. Some forms of coupler do not provide for synchronisation of the parts to be coupled. One such coupler is described in DE-B-1 040 385. It is designed to couple first and second parts together by interposition of respective sets of teeth as the second part approaches the first. In order to aid meshing of the two sets of teeth one or more of the teeth on the first part are arranged such that they protrude further than the remaining teeth on that part and are able to slide along a diagonal groove angled backwards and to one side. A spring is provided which resists such movement. This arrangement provides that, when the teeth of the second part begin to engage on the protruding teeth of the first part, pushing the protruding teeth backward, the diagonal movement forces the second part to rotate sufficiently to bring the two sets of teeth into alignment for full meshing. Thus the above design overcomes problems of pre-engagement alignment of sets of teeth by having individual teeth which are capable of a limited degree of circumferential movement. In many situations, however, it is not possible to implement such a solution. It is an object of the present invention to obviate or mitigate the problem discussed above of completing the coupling of a gear to a shaft. According to the present invention, there is provided a coupler for coupling a gear to a shaft comprising: a first coupling member bearing engaging teeth which is connected for rotation with the shaft, and a second coupling member bearing engaging teeth which is connected for rotation with the gear by means of connecting teeth, wherein the first and second coupling members are engageable, by means of their respective engaging teeth, to couple the gear to the shaft, the coupler being characterised in that the connecting teeth of the second coupling member are interposed between and engageable with connecting teeth provided on the gear and in which the thickness of each of the teeth on the second coupling member is less than the distance between each of the teeth on the gear such that the second coupling member is capable of limited circumferential movement relative to the gear to allow the first and second coupling members to engage each other without the need to rotate the gear. Preferably, there is provided a synchronising means for substantially synchronising the speed of rotation of the shaft and gear, and a baulking means interposed between the first and the second coupling members to inhibit engagement of the first coupling member by the second coupling member until their respective rotational speeds are substantially synchronised. The coupler may be provided with a means for resisting the limited circumferential movement of the second coupling member relative to the gear and to centralise the second coupling member relative to the gear. This may comprise a plurality of spring-loaded poppets which operate in angled grooves provided in the second coupling member. The engaging teeth borne by the first coupling member are positioned around an inner circumference and the engaging teeth borne by the second coupling member are positioned around an outer circumference. The connecting teeth provided on the gear and second coupling member may be in the form of splines which are respectively interposed and engageable. The thickness of each of the splines on the second coupling member is less than the distance between each of the splines on the gear thereby allowing the second coupling member to move circumferentially relative to the gear in either direction from a centralised position by an amount not greater than the thickness of one of the teeth on the second coupler. Preferably, the second coupling member is allowed to move circumferentially relative to the gear in either direction from its centralised position by an amount sufficient to index the teeth positioned thereon a distance equal to half the thickness of one of the teeth positioned thereon. The present invention will now be more particularly described by way of example only, with reference to the accompanying drawings in which: Figure 1 is a cross-section view of a coupling arranged in accordance with the present invention; Figure 2 is a view of the teeth arrangement taken in the direction of arrow A in Figure 1, and Figure 3 is a view of the spring-loaded poppet arrangement taken in the direction of arrow B in Figure 1. Referring to Figure 1, a coupler 10 comprises a first coupling member in the form of a coupling sleeve 12 connected for rotation with a shaft 14 via a central hub member 16, a second coupling member formed in two parts 18a, 18b, a baulking ring 20 having teeth 22 provided on an outer surface thereof, a gear 24 having splines 26 provided on an extension 28 thereof, and three spring-loaded struts 30 at equally spaced circumferential locations. The coupling sleeve 12 is moved axially by a selector fork and other linkage (not shown) which connects the coupling sleeve to a gear selector lever (not shown) which is operated by a vehicle operator. The first part of the second coupling member 18a is provided with a plurality of teeth 32 on an outer surface and a plurality of splines 36 on an inner surface. The teeth 32 engage with teeth 34 provided around an inner circumference of the coupling sleeve whilst the splines 36 engage with the splines 26 provided on the extension 28 of the gear 24. A dog (not shown) is provided to allow limited circumferential movement of the baulking ring 20 relative to the coupling sleeve 12. The thickness of each of the splines 36 on the first part 18a is less than the distance between each of the splines 26 on the gear, thereby permitting the part 18a to move circumferentially relative to the gear 24 in either direction from a centralised position by an amount not greater than the thickness of one of the teeth 39 on the second coupling member before the splines 36, 26 engage and torque is transmitted there-through. Preferably, the first part of the second coupling member 18a is allowed to move circumferentially relative to the gear 24 in either direction from its centralised position by an amount sufficient to index the teeth 32 positioned thereon a distance equal to half the thickness of one of the teeth 32 positioned thereon. The second part 18b of the second coupling member is provided with splines 39 on an inner surface for direct engagement and movement with the splines 26 on the gear 24. An external friction cone surface 38 provided on the second part 18b is positioned to co-operate with a corresponding internal friction cone surface 40 provided on the baulking ring 20. Referring to Fig 2, each of the teeth 22, 32, 34 provided on the baulking ring 20, the first part 18a and she coupling sleeve 12 respectively are provided with a lead-in portion 22a, 32a, 34a formed by chamfering each side of the leading edge of said teeth. The chamfered portions 34a on the coupling sleeve teeth slide over the chamfered portions 22a of the teeth provided on the baulking ring 20 or chamfered portion 32a of the teeth on the first part 18a to rotate the baulking ring 20 or first part 18a upon axial displacement of the coupling sleeve 12. A means is provided for resisting the limited circumferential rotation of the first part 18a relative to the gear 24 such as, for example, a plurality of poppets 42 circumferentially spaced around the gear 24 and housed in holes 44 provided therein. Each poppet 42 is spring-loaded by means of a coil spring 46 or the like provided around the poppet 42. Each poppet 42 is retained in its hole 44 by a ring 48 which abuts against a flange 50 provided on the poppet. The outer end 52 of each poppet engages an angled recess 54 provided in the rear face 56 of the first part of the coupling member 18a (best seen in Figure 3). The recess 54 is positioned such that circumferential displacement in either direction of the first part 18a relative to the gear 20 causes the spring-loaded poppets 42 to be displaced into their respective holes 44. The force stored in the compressed springs 46 acts as a restoring force and effectively biases the first part 18a towards a neutral position in which the splines 36, on the first part 18a are centralised circumferentially within the splines 26 on the gear 24. The spring-loaded struts 30 each comprise a detent poppet 30a which is spring-loaded radially outwardly in a bore 30b in a block 30c by a coil spring 30d. The head of each poppet 30a engages a circumferential extending groove 12a cut in the teeth 34 to act as a detent against movement of the coupling sleeve relative to the blocks 30c. In operation, to initiate engagement of gear 24, the gear selector lever is moved to displace the coupling sleeve 12 towards the gear 24 such that the spring-loaded struts 30 tilt and move axially and force the friction cone surface 40 on the baulking ring 20 into contact with the friction cone surface 38 on the second part 18b of the second coupling member. A drag effect known as cone torque is created between the two friction surfaces which acts to rotate the baulking ring 20 relative to the coupling sleeve until the chamfered portions 34a and 22a of the teeth on the sleeve and baulking ring come into contact. Further axial movement of the coupling sleeve generates an axial thrust on the baulking ring 20, via teeth portions 34a, 22a, to increase the drag effect at surfaces 38, 40 to synchronise the speed of rotation of sleeve 12 and the gear 24. During synchronisation rotation of the baulking ring 20 by the cone torque prevents the teeth 34 of the coupling sleeve 12 passing between the teeth 22 of the baulking ring 20 to engage the teeth 32 which rotate with the gear 24. The detent capability of poppets 30a is arranged to be such that the force which must be applied to sleeve 12 to disengage the heads of poppets 30a from the groove 12a is sufficient to generate the necessary drag effect at surface 38, 40 to initiate rotation of the second part 18b. During synchronisation the cone torque generated at surfaces 38, 40 is arranged to be greater than or equal to the index torque generated by teeth 34, 22 so that the interengaging teeth portions 34a, 22a are then prevented from rotating the baulking ring 20 to allow full gear engagement. After synchronisation has occurred the cone torque is less than the indexing torque and the interengaging teeth portions 34a, 22a, are then able to rotate the baulking ring 20 backwards sufficiently to allow teeth 34 to pass between teeth 22 and engage teeth 32 associated with the gear to couple the gear. Because of the capability of the first part 18a of the second coupling member to rotate through a limited circumferential distance relative to gear 24, should the teeth 34 not be in alignment with the gaps between teeth 32, it is only necessary for the co-operating chamfered portions 34a and 32a of these teeth to generate sufficient rotational force to rotate the part 18a relative to gear 24 against the action of spring-loaded poppets 42 to allow coupling of the sleeve 12 with the teeth 32 associated with gear 24. This avoids the necessity for the coupler to generate sufficient force to rotate gear 24 itself and any associated meshing gears in the transmission against possibly high torque loads thus significantly lowering the forces which the operator must apply to the gear lever to achieve complete synchronisation and coupling of the gear 24 with shaft 14. As will be appreciated, when sleeve 12 is coupled to teeth 32, the first part 18a rotates relative to gear 24 through a small distance. When transmitting torque the splines 36 abut the splines 26 on gear 24. Whenever the gear 24 is disengaged the spring-loaded poppets 42 act to re-centralise the first part 18a relative to the gear in preparation for gear re-engagement. It will be appreciated from the above that engagement of a gear in a gearbox incorporating a coupler arranged in accordance with the present invention will not be limited by the operator's ability to exert sufficient force to rotate the coupling member associated with the gear together with the gear itself and any associated meshing gear against a large torque reaction. Although the present invention has been described above with reference to a baulking ring type synchromesh coupler it will be appreciated that it is applicable to all other types of synchromesh coupler such as, for example, the blocking pin type as described and claimed in EP-B-0098841. Also the invention is applicable to a crash type of coupler which includes no synchronisation function such as would be obtained if baulking ring 20 and second part 18b were omitted from the arrangement described above.

Claims: A coupler for coupling a gear (24) to a shaft (14) comprising:- a first coupling member (12) bearing engaging teeth (34) which is connected for rotation with the shaft (14), and a second coupling member (18a) bearing engaging teeth (32) connected by means of connecting teeth (36) for rotation with the gear (24) and being engageable by the first coupling member (12) to couple the gear (24) to the shaft (14), wherein the first and second coupling members (12,18a) are engageable, by means of their respective engaging teeth (34,32), to couple the gear (24) to the shaft (14), the coupler being characterised in that the connecting teeth (36) of the second coupling member (18a) are interposed between and engageable with connecting teeth (26) provided on the gear (24) and in which the thickness of each of the teeth (36) on the second coupling member (18a) is less than the distance between each of the teeth (26) on the gear (24) such that the second coupling member (18a) is capable of limited circumferential movement relative to the gear (24) to allow the first and second coupling members (12, 18a) to engage each other without the need to rotate the gear (24). A coupler as claimed in Claim 1 in which there is provided a synchronising means (38, 40) for substantially synchronising the speed of rotation of the shaft (14) and gear (24) and a balking means (20) interposed between the first and the second coupling members (12, 18a) to inhibit engagement of the first coupling member (12) by the second coupling member (18a) until their respective rotational speeds are substantially synchronised. A coupler as claimed in Claim 1 in which there is provided a means (42) for resisting the limited circumferential movement of the second coupling member (18a) relative to the gear (24). A coupler as claimed in Claim 3 in which the means for resisting the limited circumferential movement comprises a plurality of spring-loaded poppets (42) which operate in angled grooves (54) provided in the second coupling member (18a). A coupler as claimed in Claim 3 in which the means (42) for resisting the limited circumferential movement of the second coupling member (18a) also act to centralise the second coupling member (18b) relative to the gear (24). A coupler as claimed in Claim 1 in which the engaging teeth (34) borne by the first coupling member (12) are positioned around an inner circumference and the engaging teeth (32) borne by the second coupling member (18a) are positioned around an outer circumference. A coupler as claimed in Claim 6 in which the connecting teeth (26,36) borne by the gear (24) and the second coupling member (18a) are splines which are respectively interposed between and engageable and in which the thickness of each of the splines (36) on the second coupling member is less than the distance between each of the splines (26) on the gear (24) thereby allowing the second coupling member (18a) to move circumferentially relative to the gear (24). A coupler as claimed in Claim 6 in which the second coupling member (18a) is provided with splines (36) which are interposed between and engageable with splines (26) provided on the gear (24) and in which the thickness of each of the splines (36) on the second coupling member is less than the distance between each of the splines (26) on the gear (24) thereby allowing the second coupling member (18a) to move circumferentially relative to the gear (24) in either direction from a centralised position by an amount not greater than the thickness of one of the teeth (32) on the second coupling member (18a). A coupler as claimed in Claim 6 in which the second coupling member (18a) is provided with splines (36) which are interposed between and engageable with splines (26) provided on the gear (24) and in which the thickness of each of the splines (36) on the second coupling member is less than the distance between each of the splines (26) on the gear (24) thereby allowing the second coupling member (18a) to move circumferentially relative to the gear (24) in either direction from a centralised position by an amount equal to half the thickness of one of the teeth (32) on the second coupling member (18a).

Inventors: BARTON JOHN ROBERT, WEYMAN ROGER MICHAEL, BARTON, JOHN ROBERT, WEYMAN, ROGER MICHAEL
Applicants: MASSEY FERGUSON MFG, MASSEY FERGUSON MANUFACTURING LIMITED
Application year: 1991
Main classification: F16D23
IPC codes: F16D23, F16H3