Patent Document

TECHNICAL FIELD  
         [0001]    The present invention relates to a synchronising arrangement according to the preamble to patent claim 1.  
         STATE OF THE ART  
         [0002]    A known practice in heavy-duty vehicles such as trucks is for a supplementary gearbox to be connected to the vehicle&#39;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.  
           [0003]    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.  
           [0004]    A solution to this problem has been indicated in Swedish patent specification SE 463 477 (and its counterparts U.S. Pat. No. 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  
         [0005]    The object of the invention is to provide a simplified synchronising arrangement while maintaining good function.  
         DESCRIPTION OF THE INVENTION  
         [0006]    The object of the invention is achieved by means of an arrangement with the features indicated in patent claim 1.  
           [0007]    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.  
           [0008]    Further features and advantages of the invention are indicated by the description and patent claims set out below.  
           [0009]    The invention will now be explained in more detail with reference to an embodiment depicted in the attached drawings. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 depicts a longitudinal section through a planetary gear according to invention with low gear engaged,  
         [0011]    [0011]FIG. 2 depicts a longitudinal section corresponding to FIG. 1 but with neutral position engaged,  
         [0012]    [0012]FIG. 3 depicts a longitudinal section corresponding to FIG. 1 but with high gear engaged,  
         [0013]    [0013]FIG. 4 depicts schematically the position of cooperating coupling teeth when low gear is engaged, and  
         [0014]    [0014]FIG. 5 depicts a radial partial section through the ring gear of the planetary gear. 
     
    
     DESCRIPTION OF AN EMBODIMENT  
       [0015]    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.  
         [0016]    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 .  
         [0017]    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 .  
         [0018]    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 .  
         [0019]    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.  
         [0020]    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 .  
         [0021]    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 .  
         [0022]    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 .  
         [0023]    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.  
         [0024]    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.  
         [0025]    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.  
         [0026]    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.  
         [0027]    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.  
         [0028]    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.

Technology Category: 2