SYNCHRONIZING DEVICE FOR A PLANET GEAR

Abstract: A synchronizing arrangement in a planetary gear (1) has an axially movable ring gear (22) which for various gearchange positions can be coupled to either of two coupling rings (9, 16), situated on their respective sides of the planetary gear (1), via synchronising rings (14, 20) which belong to these coupling rings, are capable of limited rotation relative to the ring gear and have external locking teeth (30, 31) to prevent gear engagement before synchronisation is achieved. The ring gear (22) is provided with two grooves (26, 27) which run round its inside and each accommodate a ring-shaped locking device (28) for transferring axial force to the respective synchronising ring at the time of gear engagement. The respective locking device is also situated in an external groove (32, 33) in the relating synchronising ring and can be compressed in the radial direction.

Description: Synchronizing device for a planet gear Technical field The present invention relates to a synchronising arrangement according to the preamble to patent claim 1. State of the art A known practice in heavy-duty vehicles such as trucks is for a supplementary gearbox to be connected to the vehicle's main gearbox to double the number of possible gear ratios. Such a supplementary gearbox usually incorporates a planetary gear to make it possible to change between a low gear range and a high gear range. Gear changing in the planetary gear is used in the low gear range but not in the high gear range. A known practice for facilitating changing between high and low gear ranges is to provide such planetary gears with synchronising arrangements. From the power distribution point of view it has been found advantageous to use the ring gear of the planetary gear as a connecting sleeve which can be brought, by axial movement, into engagement with coupling rings on both sides of the planetary gear. However, achieving efficient manoeuvring of the synchronising rings which cooperate with the coupling rings and are necessary for achieving synchronisation has been found problematical when moving the ring gear in different directions in cases where the overall length of the planetary gear is short. A solution to this problem has been indicated in Swedish patent specification SE 463 477 (and its counterparts US 5,083,993 and EP 0 423 863). According to that solution, the ring gear is provided inside with a number of locking elements in the form of balls which are spring-loaded in the radial direction and cooperate with specially designed shoulders on the synchronising rings in order, upon axial movement of the ring gear, to cause the synchronising ring concerned to move axially towards its coupling ring. Each locking element rests in a radial recess in the ring gear, and the locking elements are held in place in pairs in the ring gear by means of a spring which extends in a circumferential direction in the ring gear and is anchored between the locking elements in the ring gear by means of an axial pin. This solution has been found to work well, but a disadvantage is that a relatively large number of locking elements are required, with consequent need for machining of the ring gear. Assembly is also difficult in that it involves many locking elements, springs and pins. Object of the invention The object of the invention is to provide a simplified synchronising arrangement while maintaining good function. Description of the invention The object of the invention is achieved by means of an arrangement with the features indicated in patent claim 1. Providing the ring gear with only two ring-shaped locking devices which hold themselves in place in internal grooves in the ring gear simplifies both machining and assembly. The locking devices themselves are also of simple design. The locking devices being fitted directly in the ring gear also means that no extra space is required in the axial or radial direction. This makes possible a compact design of planetary gear. Further features and advantages of the invention are indicated by the description and patent claims set out below. The invention will now be explained in more detail with reference to an embodiment depicted in the attached drawings. Description of the drawings Fig. 1 depicts a longitudinal section through a planetary gear according to invention with low gear engaged, Fig. 2 depicts a longitudinal section corresponding to Fig. 1 but with neutral position engaged, Fig. 3 depicts a longitudinal section corresponding to Fig. 1 but with high gear engaged, Fig. 4 depicts schematically the position of cooperating coupling teeth when low gear is engaged, and Fig. 5 depicts a radial partial section through the ring gear of the planetary gear. Description of an embodiment A planetary gear according to invention as depicted in Figs. 1-3 may with advantage constitute a supplementary gearbox intended to be connected to a main gearbox of a heavy-duty vehicle such as a truck or bus. For the sake of simplicity, the housing which accommodates the planetary gear 1 has been omitted. The planetary gear 1 is arranged between an input shaft 2 from the main gearbox and an output shaft 3 from the supplementary gearbox. A sun wheel 4 is mounted on, and for joint rotation with, the input shaft 2, e.g. by means of splines, and is provided with external teeth 5 which engage with a number of surrounding planet wheels 6. These planet wheels 6 are each supported by their respective pivot pins 7 in a planet wheel carrier 8 which is integrated with the output shaft 3. The sun wheel 4 engages, in this case via teeth, and rotates jointly with a coupling ring 9 provided with external coupling teeth 10 and held in place in the axial direction on the input shaft 2 by a support ring 11. The coupling ring 9 has a conical friction surface 12 facing outwards and intended to cooperate with a corresponding conical friction surface 13 facing inwards of a synchronising ring 14. The housing, not depicted in detail, of the planetary gear 1 includes a reaction disc 15 with a central hole in which a coupling ring 16 is fitted for joint rotation with it and is also fixed in the axial direction, e.g. by means of splines and locking devices to make it possible to remove it. On the coupling ring 16 there are external coupling teeth 17 and a conical friction surface 18, facing outwards, for cooperation with a corresponding conical friction surface 19, facing inwards, on a synchronising ring 20. The two synchronising rings 14 and 20 are of the same design but are fitted mirror-image fashion on their respective sides of the planet wheels 6. The planet wheels 6 and the two synchronising rings 14 and 20 are surrounded by and engage with a ring gear 22 which is provided with internal teeth 21 and is fitted movably in the axial direction relative to the planet wheel and the coupling rings. This movability is accomplished by means of an undepicted coupling fork intended to engage in an external recess 23 in the ring gear 22. The ring gear 22 is provided at its ends with internal coupling teeth 24 and 25 which are intended to cooperate with coupling teeth 10 and 17 respectively on the coupling rings 9 and 16. It is advantageous that the coupling teeth 24,25 and the teeth 21 on the ring gear 22 be integrated with one another, as in the embodiment here depicted. The ring gear 22 is provided with two grooves 26,27 running round its inside, one at each end, at the transition between the teeth 21 and the respective coupling teeth 24,25. An annular locking device 28 is clamped in each of these grooves 26,27. As indicated in more detail by Fig. 5, these locking devices 28 each take the form of an annular curved wire, advantageously with circular cross-section, which sits springingly in the groove and has a predetermined gap 29 between its opposite ends. This gap 29 allows a certain radial compression together of the locking devices 28, as will be described below. The two synchronising rings 14 and 20 are provided with external locking teeth 30,31 which during synchronising processes do in a conventional manner lock the gearchange movement so as to achieve synchronous rotation between the ring gear 22 and the respective coupling rings 9,16. The two synchronising rings 14,20 are each provided with grooves 32,33 respectively running round their outsides and incorporating hollows 34,35 respectively. The locking devices 28 are movable in these grooves and hollows. The axial movement of the locking devices 28 relative to the synchronising rings 14,20 is limited by a number of external stop devices distributed in the circumferential direction on each synchronising ring. The synchronising rings 14,20 have axially outer stop devices 36,37 respectively and axially inner stop devices 38,39 respectively, in the form of teeth which fit in between the teeth 21. The planetary gear 1 according to invention works as follows. During a gearchange operation, the ring gear 22 may be moved in either direction from a neutral position depicted in Fig. 2 to effect the gear change. In the neutral position, the two locking devices 28 each rest in their grooves 26,27 in the ring gear 22 and are thus situated close to the outer stop devices 36,38 on the synchronising rings 14,20. When the ring gear 22 moves to the right in Fig. 2, during engagement of low gear according to Fig. 1, the right locking device 28 will move the synchronising ring 20 to the right so that it presses against the coupling ring 16. Continuing movement of the ring gear will cause the locking device 28 to be compressed radially so that the gap 29 between its ends decreases. At the same time, the locking device 28 will be pressed down into the hollow 35, after which the coupling teeth 25 on the ring gear 22 can, when synchronisation is achieved, be inserted between the coupling teeth 17 on the coupling ring 16. At the same time, the second synchronising ring 14 is subjected only to an axial movement of the corresponding locking device 28 in the groove 32. At this stage, contact with the inner stop devices 37 will cause the left locking device 28 to keep the synchronising ring 14 out of engagement with the coupling ring 9. Engaging high gear by moving the ring gear 22 to the left to the position depicted in Fig. 3 from the neutral position in Fig. 2 results in the corresponding process whereby the left locking device 28 forces the synchronising ring 14 to the left and is compressed radially. The compression of the locking elements 28 is facilitated by the presence of ramp-shaped transitions between the grooves 26,27 and the radially inner surface of the teeth 21. The stop devices 36-39, particularly the inner stop devices 37,39, also cause the ring gear 22 and the synchronising rings 14,20 to lock mutually in the circumferential direction, with a certain play. As indicated by Fig. 4, there is a certain mutual play in the circumferential direction because the stop devices 36,39 are narrower in the circumferential direction than the gaps between the teeth 21. This facilitates synchronisation and gear engagement. The twisting moment to which the two synchronising rings 14,20 are subjected during a gearchange operation is in the same direction during a certain direction of rotation of the input shaft 2, e.g. during driving forwards when the input shaft 2 has a specified direction of rotation. During reversing, the direction of rotation of the input shaft 2 will be reversed, resulting in the twisting moment acting upon the synchronising rings 14,20 likewise changing direction. In the embodiment depicted, the direction of rotation of the input shaft 2 has been assumed to be unchanged and such that in Fig. 4 the coupling ring 9 and hence also the synchronising rings 14,20 and the ring gear 22 endeavour to move upwards in the drawing. To facilitate synchronised gearchanging during both driving forwards and reversing, it is desirable that the shape of the locking teeth 30,31 on the synchronising rings be appropriate to the purpose, i.e. their shape should be such that when synchronisation is achieved the synchronising rings can rotate to a position which allows gear engagement through completed axial movement of the ring gear 22. The shape concerned may be selected as necessary and desired. The planetary gear 1 described above is advantageous from the manufacturing and assembly point of view in that the necessary machining of component parts is simple and the number of component parts is small. The design is also such as to occupy little space in both axial and radial directions. The fact that the mutually cooperating friction surfaces can be situated at relatively great radial distances from the shafts 2,3 means that the twisting moment acting during the synchronising process as a result of friction forces may reach high values. This in turn means that the axial extent of the friction surfaces can be limited, thereby contributing to compact construction of the planetary gear. The planetary gear described may of course also be used in other contexts than that described here. It is possible, for example, to use it with hydraulic automatic gearboxes where a multiplicity of planetary gears are coupled together. The invention may also be used in the type of synchronising arrangements in which a multiplicity of synchronising rings are arranged on both sides of the planetary gear. Patent claims 1. Synchronising arrangement in a planetary gear (1), including an axially movable ring gear (22), two coupling rings (9,16) which are each situated on their respective side of the planetary gear (1) and with which the ring gear (22) may alternatively be coupled for various gear positions, and at least two synchronising rings (14,20), at least one of them being between each coupling ring and the planetary gear, which synchronising rings are not only rotatable in a limited manner relative to the ring gear (22) but also have external locking teeth (30,31) which during gearchange movement lock the ring gear's axial movement and connection to the respective coupling ring (9,16) before synchronous rotation is achieved, and the ring gear (22) has at its ends internally arranged locking devices (28) for transfer of axial force from the ring gear to the respective synchronising ring so as, during gear changing, to cause contact between friction surfaces on the respective synchronising ring and coupling ring, characterised in that the ring gear (22) has two grooves (26,27) running round its inside, one at each end of the ring gear, that a substantially annular locking device (28) capable of being compressed in the radial direction is arranged in each groove (26,27) and that a groove (32,33) which runs round the outside and is intended for such a locking device (28), and in which the locking device can move when the ring gear (22) moves, is arranged in the respective synchronising ring (14,20). 2. Synchronising arrangement according to claim 1, characterised in that each of the external grooves (32,33) in the synchronising rings (14,20) has a hollow (34,35) running round it on the side of the groove situated nearest to the respective coupling ring (9,16) and that this hollow is intended for the respective locking device (28) when the latter is compressed in the radial direction. 3. Synchronising arrangement according to claim 1 or 2, characterised in that each of the synchronising rings (14,20) has radially protruding stop devices (36,37;38,39) which are adjacent to and situated on both sides of the external groove (32,33) to limit mutual axial movement between the respective locking device (28) and synchronising

Claims: 4. Synchronising arrangement according to claim 3, characterised in that at least the stop devices (37,39) situated nearest to the planetary gear are arranged to fit in between the teeth (21) on the ring gear (22) and thereby to lock the ring gear and synchronising rings (14,20) mutually in the circumferential direction. 5. Synchronising arrangement according to any one of the foregoing claims, characterised in that each locking device (28) takes the form of an open resilient ring between whose free ends there is a gap (29) when the locking device is fitted in position in the ring gear (22) and that each locking device is arranged so that when in a position of rest in its groove (26,27) in the ring gear it is resiliently fixed in the groove. 6. Synchronising arrangement according to any one of the foregoing claims, characterised in that each locking device (28) is arranged to be able, by means of the teeth (21) on the ring gear (22), to be compressed in the radial direction to a position within the teeth when the ring gear (22) moves axially to bring the respective synchronising ring into engagement with its coupling ring. 7. Synchronising arrangement according to claims 2 and 6, characterised in that the distance between the teeth (21) and the bottom of the hollows (34,35) in the respective grooves (32,33) in the synchronising rings (14,20) is at least equal to the thickness of the locking device (28).

Inventors: NILSSON DAG, NILSSON, DAG
Applicants: NILSSON DAG, SCANIA CV ABP, NILSSON, DAG, SCANIA CV AKTIEBOLAG (PUBL)
Application year: 2001
Main classification: F16H3
IPC codes: F16D23, F16H3