Abstract:
A gear arrangement includes a first and a second gearwheel where the first and second gearwheels are arranged next to each other upon a first shaft such that the first and second gearwheels can rotate relative to the first shaft. At least one gearwheel of the first and second gearwheels wheels is arranged upon the first shaft such that it can be axially displaced between a distanced axial position and a contact axial position upon the first shaft, and whereby in the distanced axial position, the first and second gearwheels are distanced from each other and in the contact axial position, an axial contact between the first and second gearwheel is enabled.

Description:
BACKGROUND AND SUMMARY 
       [0001]    The present invention relates to a gear arrangement comprising a first and a second gearwheel, the invention further relates to a transmission provided with an inventive gear arrangement. 
         [0002]    In order to reduce the noise emission from two gearwheels meshing with each other, they can be provided with helical gear teeth. A disadvantage of helical gears is that during torque transfer between the gearwheels, the helical gear engagement causes axial gear mesh forces. The axial gear mesh forces will give a resulting, thrust along the axis of the gearwheel. The gearwheel must thereby be accommodated by appropriate bearings in order to take up the axial thrust 
         [0003]    Loose gearwheels arranged rotatably upon a shaft can be rotationally connected to each other and to the shaft by mechanical tooth clutches. This will be referred to as a stack of interconnectable loose gearwheels. This is common in dual clutch transmissions in order to limit the design to one countershaft. 
         [0004]    Similarly, it is not uncommon in other types of transmissions to find stacks of interconnectable loose gearwheels that are rotatably arranged on bearings on a shaft and can selectably be rotationally locked to each other. One example is transmissions with a winding power flow, where the power is transferred back and forth more than once between two rotational axes. 
         [0005]    In a stack of interconnectable loose gearwheels, at least one of the gearwheels can also be connected to the shaft. Torque can be transferred in different ways by means of selectable engagement of tooth clutches:
       between the shaft and the gear mesh of one of the gearwheels in the stack   between the gear meshes of two adjacent gearwheels in the stack   between the gear meshes of two non-adjacent gearwheels via intermediate gearwheels in the stack (the intermediate gearwheels would then function as power-transferring sleeves)       
 
         [0009]    In the first case the shaft and the gearwheel in question will be rotationally locked. There will be no relative rotation between them, and the bearings that carry the gearwheel will not be subjected to any nominal life consumption. 
         [0010]    In the second and third cases the two gearwheels with power-transferring gear meshes will be rotationally locked. In a general case they will rotate with a different speed than the shaft. So, the bearings that carry these gearwheels will be simultaneously subjected to loads from the gear mesh forces and relative rotation. This implies a consumption bearing life. 
         [0011]    The bearing life of a stack of interconnectable loose gearwheels may be limiting for the overall durability of a transmission. In many cases it would not be possible to use stronger and larger bearings due to space limitations. 
         [0012]    There is thus a need for an improved gear arrangement, which increases the lifecycle of the bearings within the gear arrangement. 
         [0013]    It is desirable to provide an inventive gear arrangement with a longer lifecycle than previous known solutions. 
         [0014]    The inventive gear arrangement comprises a first and a second gearwheel. The first and second gearwheels are arranged next to each other upon a first shaft such that said first and second gearwheels can rotate relative said first shaft. The gearwheels are thereby preferably arranged upon sonic kind of bearing arrangement, either as separate bearings or semi integrated bearings in which the outer ring is formed by a part of the inner surface of the gearwheels and/or the inner ring is formed by a part of the outer surface of the shaft. 
         [0015]    The gear arrangement is characterised in, that at least one gearwheel of said first and second gearwheels is arranged upon said first shaft such, that it can be axially displaced between a distanced axial position and a contact axial position upon said first shaft. Further, in said distanced axial position, said first and second gearwheels are distanced from each other and in said contact axial position, an axial contact between said first and second gearwheel is enabled. 
         [0016]    The inventive gear arrangement enables that, when the one gearwheel is positioned in the contact axial position, axial forces upon the one gearwheel directed towards the other gearwheel will be transferred to the other gearwheel. The axial loads upon the first and second gearwheels thereby cancel each other out. The axial load upon the bearings will be completely reduced or at least essentially reduced. 
         [0017]    By using the inventive gear arrangement such, that the axial gear meshes forces from the first and the second gearwheel cancel each other out, when the first and/or the second gear wheel rotates relative the first shaft, the bearings do not have to be subjected to large axial load when they are subjected to rotation, whereby the lifecycle of the bearings upon which the gearwheels are mounted increases. 
         [0018]    In a situation where there is no relative rotation between the gearwheels and the first shaft, i.e. no rotation in the bearings, the bearings can be subjected to axial load without any additional wear upon the bearings. 
         [0019]    There are bearings that allow an axial displacement; the one gearwheel can be arranged upon such a bearing in order to facilitate the axial displacement of the one gearwheel. A bearing facilitating the axial displacement is preferably a needle, a cylindrical roller bearing or a toroidal roller bearing. 
         [0020]    It is preferred that the at least one gearwheel is displaced into said contact axial position when it transfers a torque load. Gearwheels are subjected to axial forces when they are provided with helical gear teeth and transfer torque to another gearwheel meshing therewith. It is thereby provided that said at least one gearwheel is provided with helical gear teeth. The helical gear teeth is preferably directed such, that by transferring torque from or to the at least one gearwheel from a gearwheel meshing therewith, the at least one gearwheel is displaced in direction towards the other of the first and the second gearwheel, the direction is preferably chosen such, that the torque transfer direction that is most commonly used, is the one that causing the axial contact between the first and the second gearwheel. 
         [0021]    In a preferred embodiment, both the first and the second gearwheels are arranged such upon said first shaft, that they both can be axially displaced between a distanced axial position and a contact axial position upon the first shaft. 
         [0022]    It is further preferred that both said first and said second gearwheels are provided with helical gear teeth, whereby the helical gear teeth of said first gearwheel are cut in the same direction, i.e., have the same hand of helix, as the helical gear teeth of said second gearwheel. When the first and second gearwheels are locked to each other (and thereby rotate in the same direction and with the same speed) they will be pressed against each other due to the axial forces that arises when transferring, a torque to/from the gearwheels they are meshing with, when power is transferred in one direction between the first and second gearwheels and pressed away from each other when power is transferred in opposite direction. 
         [0023]    It is preferred that the at least one gearwheel is mounted upon a first and a second bearing and that the at least one gearwheel can slide upon the first and second bearing. In order to provide a defined sliding distance, the at least one gearwheel is provided with an inwardly directed protrusion, whereby the at least one gearwheel is arranged such upon said first and second bearing, that the inwardly directed protrusion is placed between the first and the second bearing and thereby allows a defined axial displacement. Said protrusion may also be composed of a separate part, e.g., a retaining ring or a shoulder of a bearing outer ring, as would be known to a person skilled in the art. 
         [0024]    In an alternative arrangement the defined sliding distance is provided by an outwardly directed protrusion, which is axially fixed to the first shaft, whereby the at least one gear wheel is axially fixed upon its bearings and the bearings are able to slide upon the first shaft. The axial relative motion is thereby limited by the outwardly directed protrusions upon the first shaft. 
         [0025]    It is preferred that the gear arrangement is provided with a first synchronisation mechanism or a dog clutch enabling a rotational connection between said first and said second gearwheel. The first synchronisation mechanism ensures that the first and second gearwheel rotate in the same speed and direction, whereby the axial contact can does not interfere with the individual rotation of the first and second gearwheel. 
         [0026]    It is further preferred that the gear arrangement is provided with a second synchronisation mechanism or a dog clutch, which enabling a synchronisation between one of said first and second gearwheel and said first shaft. 
         [0027]    The inventive gear arrangement can be applied in a diversity of fields, and is especially useful in fields where a bearing failure or an exchange of bearings is critical and/or expensive. One such arrangement is a transmission and especially a dual-clutch transmission. The use of the inventive gear arrangement in a transmission increases the life cycle of a transmission and lowers its maintenance costs. 
         [0028]    The gear transmission is preferably used in a transmission having a centre shaft and a countershaft, wherein said gear arrangement is provided upon said countershaft. 
         [0029]    Preferably meshes at least said first gearwheel with a first primary gear teeth of said transmission and said second gearwheel with a gearwheel upon the centre shaft. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]    The present invention will now be described in detail with reference to the figures, wherein: 
           [0031]      FIGS. 1   a  and  b  shows an inventive gear arrangement with one axial displaceable gearwheel; 
           [0032]      FIG. 2   a  to  2   d  shows an inventive gear arrangement with two axial displaceable gearwheels 
           [0033]      FIGS. 3   a  and  b  shows a transmission provided with a gear arrangement according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]    In the following only one embodiment of the invention is shown and described, simply by way of illustration of one mode of carrying out the invention. 
         [0035]    The term bearing is considered to encompass all different kinds of bearings which could be suitable to use in the gear arrangement, wherein the most common are roller bearing, however plain bearings or other form of bearings also would be possible. In the figures, the gearwheels  333 ,  535 ,  335  in the gear arrangement are provided with helical gear teeth, which are directed such that the first and the second gearwheel  333 ,  535  are pressed against each other during a transfer of the torque load T in one of the directions. Obviously gearwheels  130 ,  132  meshing with any of these gearwheels  333 ,  335 ,  535  are also provided with helical gear teeth. 
         [0036]      FIGS. 1   a  and  b  discloses a first preferred embodiment of the invention. The gear arrangement comprises a first shaft  223  upon which said first and second gearwheel  333 ,  535  is arranged. Both gearwheels are arranged upon a pair of bearings comprising a first and second beating  33   b ,  33   c ;  35   b ,  35   c  respectively. The first gearwheel  335  however, is mounted such upon its pair of bearings  33   b,    33   c  that it can be axially displaced thereupon. The axial displacement is defined by an inwardly directed protrusion (a shoulder)  333   s  upon the first gearwheel  333  and which protrusion  333   s  is arranged between the first and the second bearing  33   b,    33   c.  The axial displacement of the first gearwheel  333  is thereby limited by the position and width of the inwardly directed protrusions  333   s  between the first and the second bearing  33   b,    33   c.  Also the second gearwheel  535  is provided with an inwardly directed protrusion  535   s.  The inwardly directed protrusion  535   s  is however arranged such between the first and second bearing  35   b,    35   c  of the second gearwheel  535 , that it does not allow any significant axial displacement of the second gearwheel  535 . 
         [0037]    In the figures, the bearings are shown as being axially fixed to the shaft  223 , and the first gearwheel  333  may have a relative axial motion that is limited by the inwardly directed Protrusion  333   s.  In an alternative arrangement the first bearing  331  is axially fixed on the gearwheels  33   b,    33   c  and the axial relative motion being limited by shoulders on or axially fixed to the shaft  223 . 
         [0038]    The first gearwheel  333  is provided with a contact surface  33  in axial direction towards the second bearing  535 . Second bearing  535  is provided with corresponding contact surface  35  in direction towards the first gearwheel  333 . 
         [0039]    In  FIG. 1   a , the synchronisation mechanism  148  has locked the first and second gearwheel  333 ,  535  to each other, which thereby rotate in the same direction and with the same speed. The first and the second gearwheel  333 ,  535  are disconnected from the first shaft  223 , whereby there is a relative rotation between the two gearwheels  333 ,  535  and the first shaft  223 . A torque load T is transferred from a gearwheel  130 , which meshes with the first gearwheel  333 , and further from the first to the second gearwheel  333 ,  535  over the synchronisation mechanism  148  and there from to a gearwheel  132 , which meshes with the second gearwheel  535 . The gearwheels  130 ,  132 ,  333 ,  535  are provided with helical gear teeth, which are directed such that the first and the second gearwheel  333 ,  535  are pressed against each other during a transfer of the torque load T in the direction shown. 
         [0040]    Due to the helical gear teeth of the gearwheels  130 ,  132 ,  333 ,  535  the transfer of the torque load T thereby causes oppositely directed axial gear mesh forces F1, F2 upon the first and the second gearwheel  333 ,  535  respectively. The axial gear mesh force F1 upon the first gearwheel  333  causes the first gearwheel  333  to be axially displaced such that the axial contact surface  33  of the first gearwheel  333  comes in contact with the axial contact surface  35  of the second gearwheel  535 . 
         [0041]    Due to the axial displacement of the first gearwheel  333  during the torque transfer, the axial gear mesh forces F1, F2 are cancelled out and only the net axial force Fn needs to be transferred to the bearings, i.e. to the first bearing  235   b  of the second gearwheel  535 . Because the bearings  33   b,    33   c,    35   b,    35   c  not are subjected to any or essentially any axial load during the rotation, the wear of the bearings  33   b,    33   c,    35   b,    35   c  is decreased, whereby the lifecycles of the bearings  33   b,    33   c,    35   b,    35   c  are increased. 
         [0042]    In  FIG. 1   b  torque T is transferred from the first gearwheel  333  to the first shaft  223  over the first and second synchronisation mechanism  148 ,  149  and the second gearwheel  535 . The axial gear mesh force F1 upon the first gearwheel  333  causes the first gearwheel  333  to be displaced such that the axial contact surface  33  of the first gearwheel  333  comes in contact with the axial contact surface  35  of the second gearwheel  535 . The axial gear mesh force F1 on the first gearwheel  333  is thereby reacted via direct contact to the second gearwheel  535  and further to the first shaft  223  over the second bearing  35   c  of the bearing pair  35   b,    35   c  of the second gearwheels  535 . The bearings  33   b,    33   c  and  35   b  are thereby relieved from axial forces. Because there are no relative motion between the two gearwheels  333 ,  535  and the first shaft  223 , the axial load Fr upon the second bearing  35   c  of the second gearwheel  535 , does not cause any additional wear upon the second bearing  35 , because there are no relative rotation between the second gearwheel  535  and the first shaft  223 . 
         [0043]    in the embodiment shown in  FIGS. 1   a  and  1   b , the bearings  35   b,    35   c  of the second gearwheel  535  is preferably tapered roller bearings. Tapered roller bearings have a comparably high axial load capacity, whereby they are able to handle the additional axial load from the first gearwheel in the state shown in  FIG. 1   b . Other types of bearing would also be possible, e.g., cylindrical roller bearings, as known by a person skilled in the art. 
         [0044]    Further, for the embodiments disclosed in  FIGS. 1   a and  1   b , it can be noted that it is required that the first gearwheel  333  transfers power, thereby being subjected to gear mesh forces, only when it is rotationally locked to the second gearwheel  535 . Otherwise, there would be a sliding contact between the first and the second gearwheels  333 ,  535 . 
         [0045]    The  FIGS. 2   a  to  2   d  disclose an alternative embodiment of the invention, in which both the first and second gearwheel  333  and  335  are arranged such that they can be axially displaced. First gearwheel  333  is arranged in the same manner as for the embodiment disclosed in  FIG. 1 . The second gearwheel  335  is arranged in a correspondently manner, i.e. is provided with an inwardly directed protrusion (a shoulder)  335   s  upon the first gearwheel  333  and which protrusion  333   s  is arranged between the first and the second bearing  235   b,    235   c.    
         [0046]    In the figures, the bearings  33   b,    33   s,    235   b,    235   c  are shown as being axially fixed to the shaft  223 , and each of the gearwheels  333 ,  335  may have a relative axial motion that is limited by the protrusions  333   s,    335   s.  An alternative arrangement is that the bearings  33   b,    33   s,    235   b ,  235   c  are axially fixed on the gearwheels  333   s ,  335   s  and the axial relative motion being limited by shoulders on or axially fixed to the shaft  223 . 
         [0047]    Now the function of the inventive gear arrangement will be explained when torque T is transferred in different directions and to/from different gearwheels. 
         [0048]    In  FIG. 2   a  the same torque transfer as in  FIG. 1   a  is disclosed, i.e. the torque T is transferred from a gearwheel  130 , which meshes with the first gearwheel  333  and further from the first to the second gearwheel  333 ,  335  over the synchronisation mechanism  148  and there from to a gearwheel  132 , which meshes with the second gearwheel  335 . 
         [0049]    The gearwheels  130 ,  132 ,  333 ,  335  are provided with helical gear teeth, which are directed such that the first and the second gearwheel  333 ,  335  are pressed against each other during a transfer of the torque load T in the direction shown. 
         [0050]    Due to the helical gear teeth of the gearwheels  130 ,  132 ,  333 ,  335  the transfer of the torque load T thereby causes oppositely directed axial gear mesh forces F1, F2 upon the first and the second gearwheel  333 ,  335  respectively. The axial gear mesh forces F1, F2 upon the first and second gearwheel  333 ,  335  correspondently causes the first and the second gearwheel  333 ,  335  to be axially displaced such that the axial contact surface  33  of the first gearwheel  333  comes in contact with the axial contact surface  35  of the second gearwheel  335 . 
         [0051]    Due to the axial displacement of the first and second gearwheel  333 ,  335  during the torque transfer, the axial gear mesh forces F1, F2 cancel each other out and only the net axial force Fn needs to be taken up by the bearings. Dependent on which of the axial gear mesh forces F1, F2 that is the largest, the net axial force Fn will be taken up by either one of the second bearing  33   c  of the first gearwheel  333  or the first bearing  235   b  of the second gearwheel  335 . In the situation shown in  FIG. 2   a , the axial gear mesh force upon the second gearwheel  335  is larger than the axial gear mesh force F1 upon the first gearwheel  333 , whereby the first bearing  235   b  of the second gearwheel  335  must take up the net resulting force Fn. 
         [0052]    The situation shown in  FIG. 2   a  is preferably a situation in which the gear arrangement is commonly used, whereby the benefit of the axial force cancellation is as large as possible over time. A typical example is in a forward speed of a vehicle transmission. 
         [0053]    In  FIG. 2   b  the torque load T is transferred in the opposite direction compared to  FIG. 2   a . Whereby the axial gear mesh forces F1, F2 also is directed away from each other. Hence, the first and the second gearwheel  333 ,  335  is axially displaced away from each other. Obviously, in this situation there will be no cancellation of the gear mesh forces F1, F2. The size of the axial net forces Fn1, Fn2 will thereby correspond to the corresponding axial gear mesh force F1, F2 and will be taken up by the outer bearings  33   b,    235   c.    
         [0054]    The situation shown in  FIG. 2   b  leads to that the full axial gear mesh loads F1, F2 must be taken up by the first bearing  33   b  of the first gearwheel  333  and the second bearing  235   c  of the second gearwheel  335  correspondently. Further, because the two gearwheels  333 ,  335  are not locked to the first shaft  223 , the is a relative motion between the two gearwheels  333 ,  335  and the first shaft  223 , whereby the wear of the bearings  33   b,    235   c  will be higher in this situation. It is therefore preferred that the inventive gear arrangement is installed such that the situation in  FIG. 2   b  occurs as little as possible, e.g. during engine braking of a vehicle. 
         [0055]      FIG. 2   c  shows a condition in which torque load T is transferred from the first shaft  223  to a gear wheel  132  that meshes with the second gearwheel  335 , whereby the synchronisation clutch  149  locks the second gearwheel to the first shaft  223 . No torque transfer occurs in the first gearwheel  333  in the situation shown. The first gearwheel  333  is idling and rotating with a different speed than the first shaft  223 . In this situation there is no relative rotation between the second gearwheel  335  and the first shaft  223 , however between the first gearwheel  333  and the first shaft  223 , and the first gearwheel  333  and the second gearwheel  335  there is as relative rotation 
         [0056]    Due to the axial gear mesh force F2 between the second gearwheel  335  and the therewith meshing gearwheel  132 , the second gearwheel  335  is axially pressed against its first bearing  235   b.  The first bearing  235   b  must thereby take up the axial net force Fn2, which is essentially equal to the axial gear mesh force F2 upon the second gearwheel  335 . However, because there is no relative rotation between the first shaft  223  and the second gearwheel  335  there is no additional wear of the bearing  235   c  that is subjected to the axial load Fn2. 
         [0057]    The inwardly directed protrusion  333   s  of the first gearwheel  333  is adapted to allow an axial displacement of the first gearwheel  333  such that the axial contact surfaces  33 ,  35  of the first and the second gearwheel  333 ,  335  are not in contact with each other. If the first gearwheel  333  is in a position that its axial contact surface  33  comes in contact with the second gearwheels  335  axial contact surface  35 , when the second gearwheel is axially displaced by the gear mesh force F2, the first gearwheel  333  will be pushed away from the second gearwheel  335 . Interference between the first and the second gearwheel  333 ,  335  is thereby avoided. 
         [0058]      FIG. 2   d  shows a condition in which a torque load T is transferred from a gearwheel  130  meshing with the first gearwheel  333  to the first shaft  223  over the first gearwheel  333 , the first synchronisation mechanism  148 , the second gearwheel  335  and the second synchronisation mechanism  149 . No torque is transferred from the second gearwheel  335  to the gearwheel  132  meshing therewith, whereby the second gearwheel  335  is not subjected to any axial gear mesh forces. There is no relative rotation between the two gearwheels  333 ,  335  and the first shaft  223 , whereby an axial load Fn1 upon the bearings does not influence the lifecycle of the bearings. 
         [0059]    The first gearwheel  333  is however subjected to an axial gear mesh force F1, which presses the first gearwheel  333  towards the second gearwheel  335 . The first gearwheel  333  is thereby axially pressed against its second bearing  333   c.  The second bearing  333   c  of the first gearwheel  333  must. thereby take up the axial net force Fn1, which is essentially equal to the axial gear mesh force F1 upon the first gearwheel  335 . The inwardly directed protrusion  335   s  of the second gearwheel  335  is adapted correspondently to the inwardly directed protrusion  333   s  such that a contact between the contact surfaces  33 ,  35  can be avoided, and thereby jamming of the gearwheels with each other will not occur. 
         [0060]    There are some relevant distances between the different parts of the inventive gear arrangement. The following distances are defined in the  FIGS. 1   a, b  and  2   a - d:    
         [0061]    Distances upon the first gearwheel  333 ;
         333   d   1 : from the contact surface  33  to beginning of the downwardly directed protrusion  333   s  of the first gearwheel  333 ,     333   d   2 : from the contact surface  33  to the end of the downwardly directed protrusion  333   s  of the first gearwheel  333 .       
 
         [0064]    Distances upon the second gearwheel  335 ,  535 ;
         335   d   1 : from the contact surface  35  to beginning of the downwardly directed protrusion  335   s  of the second gearwheel  335 ,  535 ,     335   d   2 : from the contact surface  35  to the end of the downwardly directed protrusion  335   s  of the second gearwheel  335 ,  535 .       
 
         [0067]    Distances between the bearings  33   b,    33   c;    35   b,    35   c;    235   b,    233   c;  
         233   bd : Between the first and second bearing  33   b,    33   c  of the first gearwheel  333       235   bd : Between the first and second bearing  35   b,    35   c;    235   b,    235   c  of the second gearwheel  335       2335   bd : Between the inner surface of the second bearing  33   c  of the first gearwheel  333  and the inner surface of the first bearing  35   b;    235   b  of the second gearwheel  335 ,  535 .       
 
         [0071]    For the situation disclosed in  FIG. 2   a , the following must be fulfilled in order to enable the axial gear mesh forces to cancel each other out: 
         [0000]      333 d 1+335 d 1&gt;2335 bd.   (a)
 
         [0072]    To make sure that the net axial force is transferred by bearings  235   b,  the following applies: 
         [0000]      233 bd+ 2335 bd&gt; 333 d 2+335 d 1  b)
 
         [0073]    If b) not is fulfilled, the net axial force Fn would be transferred by the first bearing  33   b  of the first gearwheel  333 . More importantly, in the situation shown in  FIG. 2   c , the first gearwheel  333  would not be able to be axial displaced far enough to avoid that the contact surfaces  33 ,  35  are in contact with each other. 
         [0074]    A general conclusion is found for situations as in  FIG. 2   a , where axial forces are cancelled out between the gearwheels  333 ,  335  that are locked rotationally to each other: The net axial force Fn shall not be transferred by the bearings of a gearwheel  333  that transfers power only when it is rotationally connected to other gearwheels  335  in the in the gear arrangement. 
         [0075]    In order to avoid jamming of the second gearwheel  335  in  FIG. 2   d,  the following inequality is valid: 
         [0000]      2335 bd+ 235 bd&gt; 333 d 1+335 d 2  c)
 
         [0076]    In order to allow just one gearwheel  333  to be axially displaceable the following inequality must be valid: 
         [0000]      2335 bd+ 235 bd&lt; 333 d 1+335 d 2  d)
 
         [0077]      FIG. 3  discloses a dual-clutch transmission  300  provided with a gear arrangement according to the invention. The gear arrangement is provided upon the countershaft  223  and has two gearwheels  333 ,  335 , which both are axially displaceable according to the invention. 
         [0078]    The first gearwheel  333  is meshing with the first primary gear teeth  130  of the transmission  300 . The second gearwheel  335  is meshing with a secondary loose gearwheel  134  upon a central shaft  171  of the transmission  300 . 
         [0079]    In the transmission in  FIG. 3 , the torque is transmitted from an engine in the third gear, and the second gear is preselected. The situation in  FIG. 3  corresponds to the situation shown in  FIG. 2   a , i.e. the gear mesh force F2 upon the second gearwheel  335  is larger than the axial gear mesh force F1 upon the first gearwheel  333 . The resulting net force Fn is taken up by the first bearing  235   b  of the second gearwheel  335 . The resulting net force Fn is reduced and ideally close to zero, due to that the axial gear mesh forces F1 and F2 cancel each other out. 
         [0080]    The axial loads upon the bearings  33   b,    33   c;    35   b,    35   c;    235   b,    235   c  are thereby reduced and the lifecycle of the bearings  33   b ,  33   c ;  35   b ,  35   c ;  235   b ,  235   c  are increased because the bearings are not subjected to axial loads during rotation. The robustness of the transmission  300  is thereby increased. 
         [0081]    The situation shown in  FIG. 2   b  in the transmission shown in  FIG. 3  corresponds to an engine braking in the third gear when second gear is preselected. 
         [0082]    The situation shown in  FIG. 2   c  in the transmission shown in  FIG. 3  corresponds to that torque is transmitted from an engine in a fourth forward gear when the fifth gear is preselected. 
         [0083]    The situation shown in  FIG. 2   d  in the transmission shown in  FIG. 3  corresponds to that torque is transmitted in the first gear and the second gear is preselected. 
         [0084]    As will be realised, the invention is capable of modification in various obvious respects, all without departing from the scope of the appended claims. 
         [0085]    Accordingly, the drawings and the description thereto are to be regarded as illustrative in nature, and not restrictive.