Abstract:
A synchronising device is provided for synchronising a first rotatable part with a second rotatable part adjacent to the first rotatable part. The synchronising device includes a first part provided with an engaging sleeve and a second part provided with a synchroniser ring. The synchronising device has at least one positioning resilient member which is arranged to act upon the synchroniser ring and the second part, in order to allow a design with few parts and also to presynchronise the synchronising ring with the second part. A transmission including such a synchronising device is also provided.

Description:
BACKGROUND AND SUMMARY 
       [0001]    This invention relates to transmissions and especially to synchronising devices for a transmission and a transmission provided with a synchronising device. The invention is particularly advantageous in the field of transmission in heavy vehicles, such as trucks and buses. 
         [0002]    Most modern vehicles are fitted with a synchronized gear box. In such a gear box, the teeth of the gearwheels are permanently meshed. The action of the gear selector is thus not to engage or disengage the teeth of the actual gear, but instead to lock its rotation to the shaft that runs through its hub. When a gear is disengaged, it is unlocked from the shaft and rotates freely. 
         [0003]    Locking the shaft with a gearwheel is achieved by means of a so called dog collar. It is splined to, and thus rotates with, the shaft and has gear-like teeth which may engage with corresponding teeth on the gearwheel. The engagement of the two set of teeth lock the rotation of the gearwheel to the dog collar, and thus also to the shaft. 
         [0004]    However, if the dog collar and the gearwheel are spinning at different speeds, the teeth will fail to engage and a loud grinding sound will be heard as they clatter together. For this reason, modern dog collars have a synchroniser mechanism that prevents the teeth from making contact before the rotating speeds of the two parts are synchronized. These synchronisers usually comprise a cone clutch and a blocking ring. The cone clutch brings the gearwheel and the dog collar to the same rotational speed using friction, and the blocking ring prevents the teeth from making contact by means of oblique blocking surfaces interacting with corresponding blocking surfaces on the gearwheel. As the speeds are synchronized, the friction force on the blocking ring is revealed and it twists slightly, allowing, engagement of the teeth. 
         [0005]    However, the dog collar has to be brought towards gearwheel quite slowly in order to give the blocking surfaces of the dog collar a fair chance to find the corresponding blocking surfaces. If the blocking surfaces fail to find each other, they will not interact and thus cannot prevent the teeth of the dog collar from making contact with the teeth of the gearwheel before their rotational speeds are synchronized. 
         [0006]    There is thus a need for an improved synchronising device at least partly removing the above mentioned disadvantage. 
         [0007]    It is desirable to provide a product for synchronization of two rotating parts where the previously mentioned problem is at least partly avoided. 
         [0008]    The disclosure concerns a synchronising device for synchronising a first rotatable part with a second rotatable part adjacent to said first rotatable part. The synchronising device comprises a first part provided with an engaging sleeve and a second part provided with a synchroniser ring. The first part may typically be a shaft, and the second part may typically be a gearwheel arranged upon an adjacent shaft. 
         [0009]    The engaging sleeve is provided with a first set of internal teeth enabling a rotationally fix and axially displaceable arrangement upon said first part, and a first conical friction surface. The engaging sleeve is adapted to be positioned in a first and in a second axial position. In the first axial position, the first set of internal teeth engages only with said first part. Thus, in the first axial position, the first and second parts are not interconnected and the two shafts may rotate independently of each other. In the second axial position, the first set of internal teeth engages with both said first and said second part. Hence the two parts are rigidly interconnected and the two shafts are bound to rotate at the same speed. 
         [0010]    The synchroniser ring is provided with a mating conical friction surface adapted to interact with the first conical friction surface in order to synchronise the engaging sleeve and the synchroniser ring, i.e. the first and second parts. Preferably and most commonly, the first conical friction surface is constituted by an internal cone and the mating conical friction surface is constituted by an external cone. The synchroniser ring is further provided with a second set of internal teeth that enables arrangement upon said second part. The second set of internal teeth is provided with a first blocking surface adapted interact with a corresponding second blocking surface upon the second part. The interaction of the blocking surfaces blocks a rotational movement of the synchroniser ring relative to the second part during synchronisation of the rotational speeds of the first and second parts. 
         [0011]    The synchroniser ring is adapted to be positioned in a first and a second rotational position relative to the second part. The first rotational position enables said blocking surfaces to interact with each other and the second rotational position enables an axial displacement of the synchroniser ring. The synchroniser ring is further adapted to be positioned in a first and a second axial position. In the first axial position of the synchroniser ring, said blocking surfaces can interact with each other, and in the second axial position the blocking surfaces of the synchronising ring are positioned such that they not face the blocking surfaces of the second part, enabling an axial displacement of the engaging sleeve. 
         [0012]    The synchroniser device is characterised in that it has at least one axial positioning resilient member which is arranged to act upon the synchroniser ring and the second part. The axial positioning resilient member is arranged such relative said synchroniser ring and said second part that it exercises a force upon said synchroniser ring in direction towards its first axial position, i.e. towards the first part, when the synchroniser ring is in any position between its first and second axial positions. The force exercised by the at least one axial positioning resilient member is enough to press the synchroniser ring towards its first axial position as long as the engaging sleeve is in, or on its way to, its first axial position. However, the force exercised by the at least one axial positioning resilient member on the synchroniser ring is substantially smaller than the force exercised on the synchroniser ring by the engaging sleeve moving towards its second axial position, i.e. towards the second part. Hence, the axial positioning of the synchroniser ring carried out by the at least one axial positioning resilient member is easily overcome by moving the engaging sleeve in direction of the second part. 
         [0013]    The axial positioning resilient member keeps the synchroniser ring in its first position, unless the engaging sleeve acts upon the synchroniser ring in the opposite direction, i.e. towards the second part With the axial positioning, the synchroniser ring is arranged in the correct axial position for its blocking surfaces to interact with the blocking surfaces on the second part. The synchronising device can be provided with blocking surfaces such that it is able to synchronise rotations in both rotational directions. The axial positioning, also results in less drag losses between the friction surfaces of the engaging sleeve and the synchroniser ring since by preventing the friction surface of the synchronising ring from unintentionally rattling against the conical friction surface of the engagement sleeve. The disclosed arrangement also enables a synchroniser device with fewer parts than in traditional synchronising devices due to the fact that the synchroniser ring acts directly upon the second part, thus providing a simpler and less expensive solution. Further, larger conical friction surfaces can be provided on the engaging sleeve and the synchroniser ring, because the friction surfaces can be provided with a large radius and still be inside the engaging sleeve outer radius, due to that fewer parts are arranged between the engaging sleeve and the second part. 
         [0014]    Further advantages are achieved by implementing one or several of the features of the dependent claims. 
         [0015]    The at least one axial positioning resilient member may be provided in the synchroniser ring and acts upon an axial reaction surface of said second part, wherein said axial positioning resilient member and said axial reaction surface are arranged such relative each other, that said axial positioning resilient member exercises a force upon said synchroniser ring in direction towards its first axial position. However, it would also be possible to arrange the at least one axial positioning resilient member in the second part, and the corresponding axial reaction surface on the synchroniser ring. 
         [0016]    The axial reaction surface may have a radial inwardly directed inclination in an axial direction of said first part. When the axial positioning resilient member acts upon the inclined surface, a reactive force will be executed on the synchroniser ring, in direction towards its first axial position. As a result, synchroniser ring moves axially towards its first axial position, the resilient member sliding upon the inclined surface. 
         [0017]    The radial inwardly directed inclination may have a transition to a radial outwardly directed inclination directed in an axial direction of said first part at an end of said axial reaction surface arranged close to said first part. The transition between the inwardly and outwardly directed inclinations forms a groove that functions as a stop for the axial positioning resilient member. The groove prevents the axial positioning resilient member from forcing the synchroniser ring further towards the first part, since its sliding motion is stopped by the groove. The synchroniser ring is in its first axial position when the axial positioning resilient member is positioned in said transition between the inwardly and outwardly inclined axial reaction surfaces. Alternatively, another form of groove or stop can be arranged upon the rotational reaction surface, such as a protrusion or groove or shoulder, instead of the transition between the inwardly and outwardly directed inclinations. 
         [0018]    The axial reaction surface may be provided upon a first external tooth of the second part. Such an arrangement provides an advantageous manufacturing process, since the axial reaction surface may be created by an after-treatment process, such as grinding or milling off a portion of a tooth of the second part. 
         [0019]    The synchroniser ring may be provided with a plurality of axial positioning resilient embers substantially equally spread about said synchroniser ring. Preferably, the synchroniser is provided with at least three essentially evenly spread out axial positioning resilient members. With axial positioning resilient members acting on the synchroniser ring in evenly spread out points, a balanced positioning of the synchroniser ring can be achieved, avoiding unwanted tilt of the synchroniser ring. Here, evenly spread means that small deviations from absolute evenness are allowed as long as they are small enough in order to be easily compensated for by the internal friction of the device, i.e. between the different parts of the device. 
         [0020]    In a preferred embodiment the synchroniser ring is further provided with at least a rotational positioning resilient member, which acts upon a rotational reaction surface of said second part, wherein said rotational positioning: resilient member and said rotational reaction surface are arranged such relative each other, that said rotational positioning resilient member exercises a force upon said synchroniser ring in direction towards its first rotational position. The purpose of the rotational positioning resilient member is thus to bring the synchroniser ring towards its first rotational position. Having the synchroniser ring already provided in its first rotational and axial positions when the synchronisation is to start, i.e. at contact between the conical friction surfaces, results in faster and more reliable synchronisation since the blocking surfaces are already in contact and consequently in the correct position to interact with each other. With both axial and rotational positioning of the synchroniser ring, the synchronisation can be performed faster, because no time has to be spent on letting the corresponding blocking surfaces find each other—they are already in contact when the synchronisation starts. It would also be possible to arrange the rotational positioning resilient member in the second part, and the corresponding rotational reaction surface on the synchroniser ring. However, due to the rotational positioning, the synchroniser device can only synch the rotations between the first and the second parts for that direction the blocking surfaces are adapted for. The inventive synchronising device is therefore especially suitable to be arranged as a range and/or splitter synchronisation. 
         [0021]    The axial and rotational positioning members may preferably be constituted by spring loaded plungers. 
         [0022]    The rotational reaction surface may be provided with an inclination directed radially inwardly in a circumference direction of said second part. When the rotational positioning resilient member acts this inclination, a reactive force will push the synchroniser ring in the direction towards it first rotational position. 
         [0023]    The inclination directed radially inwardly in a first circumference direction of said second part may have a transition to a radial outwardly directed inclination in said first circumference direction of said second part. The transition between the inwardly and outwardly directed inclinations forms a groove that functions as a rotational stop for the synchroniser ring—here is the first rotational position. The groove prevents the rotational positioning resilient member from forcing the synchroniser ring further in rotational direction. Thus, when the rotational positioning resilient member is positioned in the transition between the inwardly and outwardly inclined rotational reaction surfaces, then the synchroniser ring is positioned in its first rotational position. Alternatively, another form of groove or stop can be arranged upon the rotational reaction surface, such as a protrusion or groove or shoulder, instead of the transition between the inwardly and outwardly directed inclinations. 
         [0024]    The rotational reaction surface may be provided upon a second external tooth of the second part. Such an arrangement provides an advantageous manufacturing process, since the rotational reaction surface may be created by an after-treatment process, such as grinding or milling off a portion of a tooth of the second part. 
         [0025]    As an alternative to or in combination with inclined rotational reaction surfaces, the rotational positioning resilient member may be arranged with direction of action having an angle to a radial direction of the synchronising ring. The rotational positioning resilient member can thereby become a larger lever for the spring force. 
         [0026]    An alternative position of the rotational reaction surface is constituted by a flank of an external tooth of the second part. Such an arrangement utilizes the original geometry of the external tooth of the second part, and thus no after-treatment such as grinding or milling is needed. 
         [0027]    The synchroniser ring may be provided with a plurality of rotational positioning resilient members substantially equally spread about said synchroniser ring. Preferably, the synchroniser is provided with at least three evenly spread out rotational positioning resilient members. With axial positioning resilient members acting on the synchroniser ring in evenly spread out points, a balanced positioning of the synchroniser ring can be achieved, avoiding unwanted tilt of the synchroniser ring. Here, evenly spread means that small deviations from absolute evenness are allowed as long as they are small enough in order to be easily compensated for by the internal friction of the device, i.e. the friction between the different parts of the device. 
         [0028]    The engaging sleeve may be provided with a groove provided in an axial central position among said first set of inner teeth. The groove is adapted to interact with a detent resilient member arranged in the first part. The detent resilient member acts radially outwards such that it holds the engaging sleeve in its first position, in which it only engages with the first part. 
         [0029]    Said detent resilient member may be able to hold said engaging sleeve in its second position, by protruding outside the first set of inner teeth. The detent resilient member thus keeps the engaging sleeve in an engaged position, preventing it from unintentionally unlocking the rotational motions of the first and second parts. 
         [0030]    Said detent resilient member is preferably a spring loaded plunger. 
         [0031]    The axial resilient positioning member and the rotational axial positioning member can be provided as individual resilient members or as a combination member, performing both the axial and the rotational positioning. If the rotational and axial positioning members are integrated in the same resilient positioning member, the reaction surfaces are correspondently adapted. 
         [0032]    The invention further concerns a transmission provided with a synchronising device as described above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    In the detailed description of the disclosure given below reference is made to the following schematic figures, in which: 
           [0034]      FIG. 1   a  shows a cross-sectional layout of the synchronising device in its neutral position, 
           [0035]      FIG. 1   b  shows a cut in the plane of the engaging teeth, the synchronising device being in its neutral position, 
           [0036]      FIG. 2   a  shows a cross-sectional layout of the synchronising device when the speeds of the two rotating parts have just been synchronised, 
           [0037]      FIG. 2   b  shows a cut in the plane of the engaging teeth when the speeds of the two rotating parts have just been synchronised, 
           [0038]      FIG. 3   a  shows a cross-sectional layout of the synchronising device with the engaging sleeve being engaged with the second part, 
           [0039]      FIG. 3   b  shows a cut in the plane of the engaging teeth with the engaging sleeve being engaged with the second part, 
           [0040]      FIG. 4   a  shows an engaging sleeve of the synchronising device, 
           [0041]      FIG. 4   b  shows a shaft of the synchronising device, 
           [0042]      FIG. 5   a  shows a synchroniser ring of the synchronising device, 
           [0043]      FIG. 5   b  shows a gearwheel of synchronising device, 
           [0044]      FIG. 5   c  shows a detailed view of an axial reaction surface, 
           [0045]      FIG. 5   d  shows a detailed view of a rotational reaction surface, 
           [0046]      FIG. 6  shows a cross-sectional layout of a double-sided synchronising device. 
       
    
    
     DETAILED DESCRIPTION 
       [0047]    Various aspects of the invention will hereinafter be described in conjunction with the appended drawings to illustrate but not to limit the invention. In the drawings, like designations denote like elements. Variations of the different aspects are not restricted to the specifically shown embodiment, but are applicable on other variations of the disclosure. 
         [0048]      FIG. 1   a  shows a cross-sectional layout of the synchronising device  1  in its neutral position, which is also the position at the start of the synchronising process. The synchronising device  1  comprises of a input shaft (first part)  100 , a gearwheel (second part)  200 , an engaging sleeve  110  and a synchroniser ring  210 .  FIG. 1   b  shows a cut in a plane through a first set of external teeth  101  of the input shaft  100  and a first set of internal teeth  111  of the engaging sleeve  110 . The input shaft  100  is provided with an engaging sleeve  110 . The engaging sleeve  110  is provided with a first set of internal teeth  111 , as shown in  FIG. 1   b , that engages with a corresponding set of external teeth  101  on the input shaft  100 . This enables a rotationally fixed but axially displaceable arrangement of the engaging sleeve  110  upon the input shaft  100 , i.e. the engaging sleeve  110  can move axially between a first axial position where its first set of internal teeth  111  engages only with the teeth  101  of the input shaft  100  (as shown in  FIGS. 1   a  and  1   b ) and a second axial position where its internal teeth engages with both the first set of external teeth  101  of the input shaft  100  and the second set of external teeth  111  of the gearwheel  200  (as shown in  FIGS. 3   a  and  3   b ), thus locking their rotational motions. The engaging sleeve  110  further comprises a first conical friction surface  112 . 
         [0049]    The input shaft  100  may further comprise at least one detent resilient member  102 , for example a spring-loaded detent plunger, which is adapted to interact with a groove  113  in the engaging sleeve  110  in order to keep the engaging sleeve in its neutral, disengaged position, as long as no actuating force is acting on it Preferably, the input shaft  100  comprises at least three and even more preferably six detent resilient members  102 . 
         [0050]    In order for the engaging sleeve  110  to be able to smoothly enter its second position and engage with the second part, the rotational speeds of the first and second parts  100 ,  200  have to be synchronised. 
         [0051]    For this purpose, the gearwheel  200  is provided with a synchroniser ring  210 . The arrangement of the synchroniser ring  210  upon the second part  200  is enabled by a second set of internal teeth  211  that engages with a second set of external teeth  201  on the gearwheel  200 . A second set of internal teeth  211  of the synchroniser ring engages with a second set of external teeth  201  on the gearwheel  200 . This arrangement fixes the synchroniser ring  210  rotationally to the gearwheel  200 , but allows axial displacement. However, the teeth in the second set of internal teeth  211  are slightly narrower than the gaps in the second set of external teeth  201 , which permits a slight rotation of the synchroniser ring  210  in relation to the gearwheel  200 . The second set of internal teeth  211  of the synchroniser ring  210  is provided with at least one first blocking surface  212  which is adapted to interact with a corresponding second blocking surface  202  upon the second set of external teeth  201  of the second part in order to prevent an axial motion of the synchroniser ring  210 , and thus preventing the engaging sleeve from engaging with the gearwheel  200 , during the process of synchronising the rotational speeds of the first and second parts. In  FIG. 1   b , the synchroniser ring  210  is shown in its first axial and rotational positions where its first blocking surface  212  can interact with the second blocking surface  202  of the gearwheel  200 . The synchroniser ring  210  further comprises a mating conical friction surface  213  which is adapted to interact with the conical friction surface  112  of the engaging sleeve  110  in order to synchronise the speeds of the input shaft  100  and the gearwheel  200  by means of friction. During synchronisation, the frictional force on the synchroniser ring  210  act as to press the first blocking surface  212  against the second blocking surface  202 , the shapes of the blocking surfaces preventing the synchroniser ring  210  from moving axially in the direction of the gearwheel  200 . The function of the blocking surfaces is well known to the person skilled in the art. 
         [0052]    Furthermore, an axial positioning resilient member  220  is arranged to act upon the synchroniser ring  210  and the gearwheel  200  such that it exercises a force upon the synchroniser ring towards a first axial position in which the blocking surfaces  212 ,  202  of the synchroniser ring  210  and the second part  200  can interact. In the example of  FIG. 1   a , the axial positioning resilient member  220  is constituted by a spring loaded plunger. 
         [0053]      FIG. 2   a  shows a cross-sectional layout and  FIG. 2   b  shows a cut in the plane of the engaging teeth of the synchronising device  1 , when the speeds of the input shaft  100  and the gearwheel  200  have just been synchronized by means of friction between the conical friction surface  112  and the mating conical friction surface  213 . When the speeds of the input shaft  100  and the gearwheel  200  have become synchronised, there will no longer be any frictional forces between the conical friction surfaces  112 ,  213  since the engaging sleeve  110  and the synchroniser ring  210  now rotate at the same speed. As the frictional force on the synchroniser ring  210  ceases, the blocking surfaces  212 ,  202  cease to be pressed together and the synchronization ring  210  will rotate slightly as to reach a rotational position where the synchroniser ring  210  can move axially in the direction towards the second part. 
         [0054]      FIG. 3   a  shows a cross-sectional layout and  FIG. 3   b  shows a cut in the plane of the engaging teeth of the synchronising device with the engaging sleeve being engaged with the second part. Here, the synchroniser ring  210  has moved to its second axial position, where its internal teeth  211  are fully inserted between the external teeth  201  of the gearwheel  200 . The engaging sleeve  110  has followed the synchroniser ring  210  in its axial movement. Here, in its second axial position, the internal teeth  111  of the engaging sleeve  110  are engaged with both the external teeth  101  of the input shaft  100  and the external teeth  201  of the gearwheel  200 , thus interconnecting and locking the rotations of the input shaft  100  and the gearwheel  200  to each other. 
         [0055]    When the engaging sleeve  110  reaches its second axial position, the at least one detent resilient member  102  protrudes outside the first set of internal teeth in order to keep the engaging sleeve  110  in said second axial position. 
         [0056]      FIG. 4   a  shows a perspective view of an engaging sleeve  110  of the disclosed synchronising device. A first set of internal teeth  111  fixes the engaging sleeve  110  rotationally on a rotatable input shaft  100 , but allows axial displacement. Consequently, the engaging sleeve  110  does always rotate at the same speed as the input shaft  100 . A conical friction surface  112  is adapted to interact with a mating conical friction surface  213  during synchronisation, and grooves  113  are provided for interacting with detent resilient members  102  arranged in the input shaft  100 . 
         [0057]      FIG. 4   b  shows a perspective view of an input shaft  100 , a part that typically constitute the rotatable first part in the disclosed synchronising device. This example of an input shaft  100  has a first set of external teeth  101 , so called splines, with which the first set of internal teeth  111  of the engaging sleeve  110  are engaged. This arrangement prevents rotational displacement but allows axial displacement of the engaging sleeve  110  in relation to the shaft. Furthermore, the input shaft is provided with a first set of holes  103 , wherein each hole is adapted for housing a detent resilient member  102 . Preferably, the first set of holes  103  comprises at least three holes and even more preferably six holes as shown in the example of  FIG. 4   b,  but there may be more or fewer holes or no holes at all, dependent on the desired amount of detent resilient members  102 . 
         [0058]      FIG. 5   a  shows a perspective view of an example of a synchroniser ring  210  of the disclosed synchronising device. The second set of internal teeth  211 , which comprises six internal teeth  211 , is situated on the inside of the synchroniser ring. The number of internal teeth  211  can however be varied, whereby at least three internal teeth  211  is preferred, in order to achieve a balanced arrangement. The teeth ends are provided with a first blocking surface  212 . The mating conical friction surface  213  is situated on the exterior of the synchronising ring  210 . The synchronising ring  210  further comprises a second set of holes  214 , wherein each hole is adapted for housing an axial positioning resilient member  220 . The second set of holes  214  comprises at least one hole, and preferably it comprises three holes. The synchronising ring  210  also comprises a third set of holes  215 , wherein each hole is adapted for housing a rotational positioning resilient member  221 . The third set of holes  215  comprises at least one hole, and preferably it comprises three holes. The holes of the second and third set of holes  214 ,  215  may extend radially, i.e. perpendicularly to the surface, into the synchronising ring  210 , as shown in  FIG. 5   a,  or they may be arranged at an angle to a radial direction of the synchronising ring  210 . 
         [0059]      FIG. 5   b  shows a perspective view of the second part, typically constituted by a gearwheel  200 . The second part  200  is provided with a second set of external teeth  201 , with which the second set of internal teeth  211  of the synchroniser ring  210  engages. Some of the teeth in the second set of external teeth  201  are provided with a second blocking surface  202 . The number of teeth in the second set external teeth  201  provided with a second blocking surface  202  should equal the number of first blocking suffices  212  on the synchroniser ring  210 , since the first and second blocking surfaces  202 ,  212  are adapted to interact with each other. Some of the teeth in the second set of external teeth  201  are provided with an axial reaction surface  203  or a rotational reaction surface  204  respectively, as shown and in greater detail in  FIG. 5   c  and  5   d.    
         [0060]    In an alternative not shown embodiment, the axial positioning resilient member and the rotational positioning resilient member is the same resilient member, and which thereby acts upon a combined reaction surface, having both the inclinations of the axial and rotational reaction surfaces  203 ,  204 . 
         [0061]      FIG. 5   c  shows an enlargement of an axial reaction surface  203  on a first external tooth  230  in the second external set of teeth  201  of the second part  200 . The axial reaction surface  203  comprises a first inclination  231  which is radially inwardly directed in axial direction of the first part  100  and a second inclination  232  which is radially outwardly directed in axial direction of the first part  100 . This inclined axial reaction surface  203  is adapted to interact with an axial positioning resilient member  220  which is arranged in a perpendicular hole of the second set of holes  214  of the synchronising ring  210 . When the axial positioning resilient member  220  presses against the first inclination  231 , a reaction force acts on the axial positioning resilient member  220  in the axial direction of the first part  100 . The axial positioning resilient member  220  will consequently slide down the inclination in direction of the first part  100 , bringing along the synchroniser ring  210  in which it is housed. The movement in direction of the first part  100  ends when the axial resilient positioning member  220  reaches the transition between the first and second inclinations  231 ,  232 . As long as no external force acts on the synchroniser ring  210 , it will remain in this position, referred to as the first axial position of the synchroniser ring  210 . Thus, in summary, the purpose of the axial reaction surfaces  203  and the axial resilient positioning members  220  is to bring the synchroniser ring  210  to its first axial position and to keep it there unless no other forces act on it. 
         [0062]      FIG. 5   d  shows an enlargement of a rotational reaction surface  204  on a second external tooth  240  in the second external set of teeth  201  of the gearwheel  200 . The rotational reaction surface  204  comprises a third inclination  241  which is radially inwardly directed in a first circumference direction of the second part  200  and a fourth inclination  242  which is radially outwardly directed in said first circumference direction of the gearwheel  200 . This inclined rotational reaction surface  204  is adapted to interact with a rotational positioning resilient member  221  which is arranged in a hole of the second set of holes  214  of the synchronising ring  210 . When the rotational positioning resilient member  221  presses against the third inclination  241 , a reaction force acts on the rotational positioning resilient member  221  in said first circumference direction. The rotational positioning resilient member  221  will consequently slide down the inclination in said first circumference direction, and thereby rotate the synchroniser ring  210  in which it is housed. The movement of the synchroniser ring  210  in said first circumference direction ends when the rotational resilient positioning member  221  reaches the transition between the third and fourth inclinations  241 ,  242 . This position, in which the rotational resilient positioning member  221  rests in the groove that is formed by the transition between the third and fourth inclinations  241 ,  242  corresponds to the first rotational position of the synchroniser ring  210 . A prerequisite for the synchroniser ring to be able appear in its first rotational position is that the synchroniser ring  210  simultaneously is in its first axial position. In the said first rotational position, the first blocking surfaces  212  of the synchroniser ring  210  are enabled to interact with the second blocking surfaces  202  of the second part  200 . Thus, in summary, the purpose of the rotational reaction surfaces  204  and the rotational resilient positioning members  221  is to bring the synchroniser ring  210  to its first rotational position and to keep it there unless the engaging sleeve  110  exercises a force on the synchronisation ring  210  in order to initiate a synchronisation. When the synchroniser ring is arranged in its first axial position and first rotational position, the blocking surfaces  202 ,  212  of the synchroniser ring and the gearwheel  200  is mating and a synchronisation can start immediately at initiation by the engaging sleeve. 
         [0063]    However, within the scope of this invention, it is possible to have a gearwheel with only axial positioning resilient members  220 , whereby a synchronisation between the first and second part  100 ,  200  can be made in both rotational directions. 
         [0064]      FIG. 6  shows a cross-sectional layout of a double-sided synchronising device  1 . This device comprises a second gearwheel  300 , i.e. third part. The third part is arrange correspondently as the second part  200 , however arranged on the other axial side of the engaging sleeve  110 . The third part  300  can be provided with the same features as already described for the second part  200 . 
         [0065]    The second and third part  200 ,  300  may be adapted for only axial positioning or for both axial and rotational positioning independently of each other. Any combination of these variants of second and third parts  200 ,  300  fall within the scope of this invention. 
         [0066]    The invention is capable of modification in various obvious respects, all without departing from the scope of the appended claims. Accordingly, the drawings and the description thereto are to be regarded as illustrative in nature, and not restrictive. 
         [0067]    Reference signs mentioned in the claims should not be seen as limiting, the extent of the matter protected by the claims, and their sole function is to make the claims easier to understand.