Abstract:
A transmission includes an input shaft, a main shaft, a countershaft, and an oil pump. The input shaft, the main shaft and the countershaft are provided with gearwheels in order to enable torque transfer in a plurality of forward and backward gear speeds. The oil pump is provided with a freewheel mechanism, which includes an oil pump driveshaft, a first pump drive gearwheel and a first and a second freewheel arranged upon the oil pump driveshaft. Both the first and the second freewheel can transfer torque to the oil pump drive shaft in one and the same direction. The first freewheel is in drive connection with the countershaft and the second freewheel is connected to the first pump drive gearwheel, which meshes with a first gearwheel coaxial with the main shaft and which first gearwheel transfers torque in at least one of the forward or backward gear speeds.

Description:
BACKGROUND AND SUMMARY 
       [0001]    The present invention relates to field of transmissions and especially to the arrangement of an oil pump in a transmission with a plurality of forward and backward gear speeds. 
         [0002]    Especially for heavy road vehicles a large number of forward and backward gear speeds are required. In the reverse gear speeds the direction of rotation of some shafts of the transmission will be opposite to the direction of rotation in the forward gear speeds. 
         [0003]    Lubrication of the gears and bearings of the transmission can be facilitated in different ways, by splashing through gearwheels partly submerged in oil or by an oil pump providing a lubrication and cooling flow to bearings and gearwheels distanced from the oil level and not reached by the splashing oil. This flow is normally directed to bearings located high above the oil level and/or not subjected to the splashing flow. 
         [0004]    The oil pump is usually located at a low position in the transmission. Thereby, it will be close to the oil level. That reduces the suction height, which implies a lower risk for cavitation and a more reliable oil flow. Then, it is convenient to drive the pump by the countershaft or by the intermediate gearwheel in a reversing secondary gear set. 
         [0005]    However, in combination with a reversing primary gear set, this will not function properly. When the reversing primary gear set is engaged, the countershaft will have opposite sense of rotation compared to forward driving, when an ordinary primary gear set is active. The oil pump would not provide any flow at reverse driving. This would be acceptable only for very short distances in reverse gears. A relocation of the pump would require a lot of redesign, and would often not be feasible due to space constraints. 
         [0006]    US 2011/0252906A1 shows a solution to the problem with opposite sense of rotation in reverse gears; the pump is driven by either of two counter-rotating elements via one-way clutches. This will be rather costly, though, requiring four additional gearwheels and additional axes of rotation. 
         [0007]    There is thus a need for an improved oil pump arrangement solving the aforementioned problems. 
         [0008]    It is desirable to provide a transmission with an oil pump, connected in a space and cost effective way and that can be driven in all forward and backward speeds of the transmission. 
         [0009]    The inventive transmission according to an aspect of the invention comprises an input shaft, a main shaft, a countershaft and an oil pump. Said input shaft, said main shaft and said countershaft are provided with gearwheels in order to enable torque transfer in a plurality of forward and backward speeds. Said oil pump is provided with a freewheel mechanism, which comprises an oil pump driveshaft, a first pump drive gearwheel and to first and a second freewheel arranged upon said oil pump driveshaft. The oil pump drive shaft is the input shaft for the pump and is constantly connected to the oil pump. The first and the second freewheel are of any suitable freewheel mechanism, which allows to transfer a torque in a first direction and freewheels in the second. Both said first and said second freewheel can transfer torque to said oil pump drive shaft in one and the same direction. 
         [0010]    It is important that the first and the second freewheels transfer torque in one and the same direction, such that the oil pump can work one direction. 
         [0011]    Normally a freewheel comprises an input and an output part, wherein the input part is rotational fix to a driving part and the output part is rotational fix to the driven part. 
         [0012]    According to an aspect of the invention, said first freewheel is in drive connection between said countershaft and said oil pump drive shaft and said second freewheel is in drive connection between said first pump drive gearwheel and said oil pump drive shaft. Said first pump drive gearwheel meshes with a first gearwheel coaxial with said main shaft and which first gearwheel is used in at least one of said forward or backward speeds. 
         [0013]    The countershaft rotates in opposite direction when the transmission is in a forward gear speed relative when the transmission is in a backward gear speed. Due to the torque transfer to the oil pump drive shaft over said gearwheel mechanism, the oil pump drive shaft can be driven in one and the same direction independent of the direction of rotation of the countershaft. Further, because said first gearwheel is used in at least one of the forward and backward gear speeds, the oil pump can be driven in all forward and backward speed. By arranging the oil pump in this inventive manner, a minimum of addition gearwheels is needed in order to drive the oil pump in both forward and backward gear speeds. Due to the use of existing gearwheels to drive the oil pump a cost effective arrangement of the oil pump is achieved, whereby the oil pump still can be driven when the transmission is in a reverse gear speed. 
         [0014]    It is preferred that said oil pump driveshaft is arranged coaxial with the countershaft and thereby the first freewheel is connected to said countershaft, i.e. the input part of the first freewheel is rotationally fixed with the countershaft and the output part of the second freewheel is rotationally fixed with the oil pump drive shaft. No additional gearwheels are thereby needed to drive the oil pump drive shaft over the countershaft. 
         [0015]    It is further preferred that said first oil pump drive gearwheel is arranged upon the countershaft, such that it can rotate thereupon. The first oil pump drive gearwheel is further connected to the second freewheel, i.e. the input part of the second freewheel is rotationally fixed to the first oil pump drive gearwheel, and the output part of the second freewheel is rotationally fixed to the oil pump drive shaft. The oil pump drive gearwheel is thereby suitably arranged upon a bearing. The arrangement of the oil pump drive gearwheel upon the countershaft, gives the gearwheel a robust arrangement. 
         [0016]    Said first gearwheel is preferably a loose gearwheel arranged upon an input shaft of said transmission, wherein said loose gearwheel is a reverse gearwheel upon the input shaft, and which meshes with a reverse idler gearwheel which transfers torque to said countershaft in a reverse gear speed. Said first pump drive gearwheel thereby transfers torque to the pump drive input shaft over the second freewheel when the transmission is in a reverse gear speed. 
         [0017]    In some transmissions the oil pump is arranged on the main housing of the transmission on the output side of the transmission. To allow such an arrangement it is suggested that the countershaft is a hollow shaft and wherein the oil pump driveshaft extends within the countershaft such that said oil pump is arranged at one end of the countershaft and said freewheel mechanism is arranged at the other end of said hollow shaft. The oil pump can thereby still be driven with the inventive freewheel mechanism, and especially can the first pump drive gearwheel be driven by the reverse gearwheel upon an input shaft. The first freewheel can however be arranged on either end of countershaft. 
         [0018]    In an alternative embodiment of the invention, the first freewheel is connected to a second pump drive gearwheel, i.e. the input part of the first freewheel is connected to the second pump drive gearwheel. The second pump drive gearwheel meshes with a second gearwheel which is provided upon said countershaft and which is used in at least one of said forward or backward gear speeds. By providing the first freewheel with the second pump drive gearwheel a higher flexibility of the arrangement of the oil pump within the transmission is achieved. The first pump drive gearwheel can thereby be driven by the first gearwheel coaxial with the main shaft and the second pump drive gearwheel can be driven by a second gearwheel which is provided upon the countershaft. 
         [0019]    It is preferred that said first gearwheel which is coaxial with the main shaft and meshes with said first pump drive gearwheel of said second freewheel also meshes with said second gearwheel which is provided upon said countershaft and meshes with said second pump drive gearwheel. The freewheel mechanism can thereby be arranged in a compact manner. The pump can be driven according to the invention both in forward gear speeds and backward gear speeds. 
         [0020]    Further advantages and advantageous embodiments of the invention are disclosed and illustrated in the figures with reference to the detailed description thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The present invention will now be described in detail with reference to the schematic figures, wherein: 
           [0022]      FIG. 1  shows a transmission according to the invention; 
           [0023]      FIG. 2  shows a first arrangement of the oil pump according to the invention; 
           [0024]      FIG. 3  shows a second arrangement of the oil pump according to the invention; and 
           [0025]      FIG. 4  shows a third arrangement of the oil pump according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    In the following only a limited numbers of embodiments of the invention are shown and described, simply by way of illustration of some ways of carrying out the invention. 
         [0027]      FIG. 1  shows a transmission  300  according to the invention, having a freewheel mechanism  385  that enables the oil pump  101  to provide oil flow independent of the direction of rotation of the countershaft  223 . 
         [0028]    A transmission  300  is arranged inside a housing  102 . There are three shafts in the transmission  300 ; an input shaft  121 , a countershaft  223  and a main shaft  124 . The input shaft  121  and the main shaft  124  are coaxial, and the countershaft  223  is arranged parallel to them. On the input shaft  121  and the main shaft  124  a number of rotatable, loose gearwheels ( 381 ,  130 ,  132 ,  134 ,  136 ,  138 ) are arranged. Each of these loose gearwheels ( 381 ,  130 ,  132 ,  134 ,  136 ,  138 ) are in mesh with a gearwheel ( 282 ,  131 ,  133 ,  135 ,  137 ,  139 ) that are either fixed on or integral with the countershaft  223 . 
         [0029]    The transmission  300  is provided multiple reverse gears, which are achieved by a reversing primary gear unit  380 . This reversing primary gear unit  380  comprises a reversing primary loose gearwheel  381 , a reversing idler gearwheel  383 , a reversing primary gearwheel  282 , and a reversing primary tooth clutch  284 . Here, the reversing primary loose gearwheel  381  is rotatably arranged on the input shaft  121 . It can selectably be rotationally locked to the input shaft  121  by the reversing primary tooth clutch  284 . Furthermore, the reversing primary gearwheel  282  is rotationally fixed to the countershaft  223  and it is in mesh with the reversing idler gearwheel  383 , which is also in mesh with the reversing primary loose gearwheel  381 . 
         [0030]    When the reversing primary tooth clutch  284  is engaged, reversing idler gearwheel  383  will have the opposite sense of rotation as the input shaft  221 . Analogously, the reversing primary gearwheel  282  and countershaft  223  will then rotate in the same direction as the input shaft  121 . A number of reverse gears can now be obtained, ranging from fast vehicle speed, intermediate vehicle speed to low vehicle speed, in which all a lubricating oil flow is needed. The general function of a transmission  300  is known and will therefore not be explained in detail. 
         [0031]    The oil pump  101  and the freewheel mechanism  385  is shown in more detail in  FIG. 2 . An oil pump drive shaft  386  is constantly connected to the oil pump  101  and coaxial with the countershaft  223 . A countershaft one-way clutch  387  is arranged between the countershaft  223  and oil pump drive shaft  386 . The first one-way clutch  387  allows the oil pump  101  to be driven when the countershaft  223  rotates in the direction that corresponds to forward driving of the vehicle. When the countershaft  223  rotates in the opposite direction, which corresponds to driving in reverse, the first one-way clutch  387  will freewheel with no influence on the oil pump chive shall  386 . In order to make the oil pump  101  produce an oil flow, a second one-way clutch  388  is arranged between the oil pump drive shaft  386  and a first pump drive gearwheel  389 . This first pump drive gearwheel  389  is in mesh with the reversing primary loose gearwheel  381 . The reversing primary loose gearwheel  381  is thereby slightly widened, in order to facilitate the gear mesh with the first pump drive gearwheel  389 . The reverse pump drive gearwheel  389  is thereby in drive connection with the reversing primary gearwheel  282 . The reversing primary gear wheel  282  is arranged as a loose gearwheel upon the input shaft  121  and is coaxial with the main shaft  124 . 
         [0032]    Being rotationally connected via three external gear meshes, the reverse pump drive gearwheel  389  will always rotate in the opposite direction as the countershaft  223 . The oil pump  101  provides a lubricating and cooling oil flow independent of the direction of rotation of the countershaft, i.e. independent of the direction of driving. 
         [0033]    The freewheel mechanism  385  enables a low position of the oil pump  101  along with the ability to provide a lubricating and cooling oil flow at forwards as well as reverse driving. A transmission  300  provided therewith requires just a few additional parts; the oil pump drive shaft  386 , the first one-way clutch  387 , the second one-way clutch  388 , and the first pump drive gearwheel  389 , whereby the costs for the oil pump arrangement is low. Further, the impact on overall size of the transmission is minimal, just a length increase corresponding to the width of the first pump drive gearwheel  389  is needed. This width can be made very small, since the power required to drive the oil pump  101  is very low. 
         [0034]    Of the gearwheels used for driving the oil pump  101 , only the first pump drive gearwheel  389  is not used to transfer propulsive power in at least one gear. 
         [0035]    In some transmissions the oil pump is arranged on the transmission end that is opposite to the engine, input shaft and primary gear sets.  FIG. 3  shows an embodiment of the invention for such transmissions. Such a transmission could be similar to the transmission  300  with exception of the arrangement of the oil pump  101 ; therefore transmission  300  will be used as starting point. In a transmission  300  an oil pump  101  is located on main housing  102  on the output side of the transmission  300 . A freewheel mechanism  385  drives the oil pump  101  via an oil pump drive shaft  386  that is arranged inside a hollow countershaft  323 . The freewheel mechanism is arranged at the input side of the transmission, whereby the oil pump  101  is arranged on the output side of the transmission, wherein the oil pump drive shaft  386 , is driven in the same way as in transmission  300  in  FIGS. 1 and 2 . The countershaft  323  drives the oil pump drive shaft  386  via the first freewheel  387  at forward driving, and the first pump drive gearwheel  389  drives the oil pump drive shaft  386  via the second freewheel  388  in reverse gears. 
         [0036]    A version (not shown) of the embodiment shown in  FIG. 3 , the first freewheel  387  is arranged at the output of the transmission  300  end together with the oil pump  101 , wherein the second freewheel  388  is arranged as disclosed in  FIGS. 1 ,  2  and  3 . Thereby the space needed for the freewheel mechanism  385  can be spread between the input and output side. 
         [0037]    In the embodiments disclosed in  FIG. 1-3 , there is only one additional gearwheel (the first pump drive gearwheel  389 ) in order to facilitate that the oil pump  101  will provide an oil flow at forwards as well as reverse driving. This will limit the additional cost for embodying a proper lubricating and cooling oil flow that is independent of the driving direction. Moreover, first pump drive gearwheel  389  is coaxial with the oil pump drive shaft  386  and the countershaft  223 ,  323 . Thus, no additional axes of rotation are necessary. That will limit the costs further, since no additional machining is required in main housing  102 . 
         [0038]    In some transmissions the oil pump is arranged at the side of a transmission and thereby normally, driven by the reverse idler  383  (disclosed in transmission  300  in  FIG. 1  and also shown in  FIGS. 2 and 3 ). An embodiment of the invention facilities the arrangement of the oil pump  101  at the side of the transmission, this embodiment is disclosed in  FIG. 4 . The oil pump  101  is driven by a freewheel mechanism  485 . The oil pump  101  is constantly connected to, and driven by the oil pump drive shaft  386 . A first freewheel  487  is arranged between a second pump drive gearwheel  490  and the oil pump drive shaft  386 . The second pump drive gearwheel  490  is in mesh with a secondary gearwheel  139  on countershaft  223 . The first pump drive gearwheel  389  is coaxial with the oil pump drive shaft  386 , and is in mesh with the secondary loose gearwheel  138 , which is arranged upon the main shaft  124 . The second freewheel  388  is arranged between the oil pump drive shaft  386  and first pump drive gearwheel  389 . 
         [0039]    The direction of rotation of the second pump drive gearwheel  490  is opposite to that of the countershaft  223 , because the second pump drive gearwheel  490  meshes with the secondary gearwheel  139  on the countershaft  223 . The first pump drive gearwheel  389  has the same direction of rotation as the countershaft  223 , since it meshes with the secondary gearwheel  238  upon the main shaft  124 , which also meshes with the secondary gearwheel  139  upon the countershaft  223 . Hence, independent of the direction of rotation of the countershaft  223 , the oil pump drive shaft  386  will be driven in the correct direction of rotation by either of the first or the second freewheel  487 ,  388 . The oil pump  101  will provide an oil flow at forwards as well as reverse driving. 
         [0040]    Depending on how the oil pump  101  and thereby the pump drive shaft  386  is arranged relative the secondary gearwheels  138 ,  139 , one of the secondary gearwheels  138 ,  139  must be slightly widened in order to facilitate the gear mesh with the first respectively the second pump drive gearwheel  389 ,  490 . In  FIG. 4  the second pump drive gearwheel  490  meshes with the second secondary gearwheel  139  adjacent to the first secondary gearwheel  138 , whereby the secondary gearwheel  139  upon the countershaft  223  is widened in order to facilitate the gear mesh between the second pump drive gearwheel  490  and the second secondary gearwheel  139 . 
         [0041]    In the embodiment disclosed in  FIG. 4 , there are only two additional gearwheels (the first and the second pump drive gearwheel  389 ,  490 ) in order to facilitate that the oil pump  101  will provide an oil flow at forwards as well as reverse driving. This will limit the additional cost for embodying a proper lubricating and cooling oil flow that is independent of the driving direction. Moreover, first pump drive gearwheel  389  and the second pump drive gearwheel  490  are coaxial with the oil pump drive shaft  386 . Thus, no additional axes of rotation are necessary. That will limit the costs further, since no additional machining is required in the transmission housing. 
         [0042]    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 claims easier to understand. 
         [0043]    As will be realised, 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.