Abstract:
A vehicle transmission having an input shaft, a main shaft, a countershaft and an output shaft mounted for rotation around axes of rotation and a plurality of gear wheels mounted on the countershaft and the output shaft for the transmission of torque from the input shaft to the output shaft at a gear ratio provided by the gears. The axis of rotation of the main shaft and the axis of rotation of the output shaft do not lie along the same axis and the distance between the axes of rotation of main shaft and output shaft is determined by the reduction ratio of a constant gear wheel pair located between the countershaft and the output shaft.

Description:
The invention relates to a transmission having a main shaft and a countershaft. 
     BACKGROUND OF THE INVENTION 
     From the prior art, transmissions are already known having one input shaft, one main shaft, one countershaft and one output shaft in which in the input shaft, the main shaft and the output shaft are mounted on a common axis of rotation. Transmissions of this kind can have a one piece input and output shaft or a one piece main and output shaft. A transmission of this kind is shown, e.g. in DE 195 38 192. 
     The numbers of teeth on the gear wheels of the shafts are determined on the basis of the desired reduction ratios. This implies specific diameter ratios of the gear wheels of the parallel shafts relative to each other and thus also the spatial distance between the shafts. Thus the gear wheel pair consisting of the first gear wheel upon the input shaft and the first gear wheel upon the countershaft, seen from the input side, are configured so that a gear wheel of very small diameter upon the input shaft is associated with a gear wheel of very large diameter upon the countershaft. This pair of gear wheels makes a transmission of a great torque at a lower speed level possible, but a great spatial distance results in a large size of the transmission housing which can lead to difficulties in the installation space for the vehicle manufacturer. 
     SUMMARY OF THE INVENTION 
     The problem on which the invention is based is to reduce the installation space needed for a transmission and lead to a smaller size of the transmission. 
     It is proposed, according to the invention, to non-rotationally mount a gear wheel, upon the output shaft of the transmission, which is driven by a gear wheel non-rotationally connected with the countershaft, the gear wheel pair forming one constant. The input shaft of the transmission is non-rotationally connected with the main shaft. The axis of rotation of the input shaft and the axis of rotation of the main shaft are equal and the axis of rotation of the main shaft and the axis of rotation of the output shaft do not form the same axis. The distance between the axes of rotation of main shaft and output shaft is determined by the reduction ratio of the gear wheel pair of the constant. 
     In an advantageous development, the gear wheel pair of the constant is lodged in a separate transmission housing in order to make replacement of the gear wheel pair possible. 
     In another advantageous development for driving a hydrodynamic retarder, an auxiliary output shaft is provided which can be driven directly by the main shaft or the countershaft and serves to achieve a high rotational speed of the retarder without intercalation of a high driving step. 
     For a splitter transmission, an advantageous development shows upon the output shaft when a gear shift device subdivides the gear steps in half speed steps. 
     In an advantageous development, a range-change group transmission, in the form of a planetary transmission, is provided next to the gear wheel pair of the constant for enlarging the total spreading of the transmission. 
     By shifting the arrangement of a constant of the transmission to the output side end of the transmission and the non-coaxiality of the axes of rotation of main shaft and output shaft, the diameters of the large wheel of the transmission are reduced. With reduced diameters, the weight of the gear wheels thereby can be reduced and the axial distances of the parallel shafts shortened, which results in a smaller size for the transmission. A reduced size of the transmission means in this instance advantageously less weight and more installation space in the vehicle. At the same time, less expenditure in material and processing for smaller gear wheels and a housing results in lower cost. The smaller masses of the gear wheels to move and synchronize, when shifting, result in a level of shifting effort clearly. The synchronizing devices also are less apt to fail, since the masses to be synchronized are smaller. By virtue of the smaller gear wheels on the input-side end of the countershaft with a small axial distance between input shaft and main shaft and the countershaft, the rotational speeds of the countershaft are at a higher level. A reduced torque level, on which the structural parts of the transmission must be designed, is obtained thereby in the largest part of the transmission. A high torque only generates in the output constant when an enlarged axial distance exists between the output shaft and the countershaft. With the inventive arrangement, the transmission input torque can be designed the same size for transmission constructions having direct drive and overdrive versions. 
     As a result of a one piece design for the input shaft and the main shaft, the pivot bearing of the main shaft and the input shaft of the prior art can be eliminated. The gear wheel pair mounted on the transmission end can be configured so as to be inserted as a separate unit, after the other transmission housing, making a modular design of transmissions having different wheel pairs on the output constant possible. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described in detail with reference to drawings wherein: 
     FIG. 1 is a transmission according to the prior art; 
     FIG. 2 is a diagrammatic arrangement of a transmission according to the invention; and 
     FIG. 3 is an arrangement according to FIG. 2 with splitter transmission. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows an enlarged illustration of a transmission  6  according to the prior art having, e.g. five forward gears and one reverse gear. With a control lever  18  access is had to the three gearshift rods  20 ,  22  and  24  which, via gear shift forks, move the synchronizing devices  26 ,  28  and  30  to the desired gear shift positions. Thus the synchronizing device  30  engages the reverse gear and the first transmission ratio. The synchronizing device  26  engages the second and third gear steps while the synchronizing device  28  is used to engage the fourth and fifth gear steps. The input shaft  32  is supported in the transmission housing  34  by a support such as the bearing  36  shown here. The main shaft  38  is supported in the transmission input shaft  32  by a bearing  40  and in the housing  34  by a support such as a bearing  42  shown here. The reverse direction of rotation for the reverse gear is obtained by an intermediate gear  44  the toothing of which meshes with the toothing of the reverse gear wheel upon the main shaft  38  and the toothing of the countershaft  46 . The other toothings of the gear wheels, on the main shaft  38 , likewise engage with corresponding toothings of the countershaft  46  for the forward gear ratio. A toothing is additionally provided on the transmission input  32  for mounting a clutch body  54 . 
     In an advantageous development, the combination of transmission  60  and constant gear wheels  108 ,  110  may be supplemented by the provision of a Range Change Group Transmission 60RCG next to the gear wheel  110  of the constant, wherein the Range Change Group Transmission 60RCG may be implemented as a Planetary Transmission  136  in a conventional manner and as illustrated, thereby enlarging the total gear ratio spread of the transmission. In this regard, it is well known to those of skill in the arts that a planetary transmission may be operative and used to provide two, selectable constant gear ratios, while a multiple gear ratio transmission, such as transmission  106  shown in FIG. 2, is operative and used to provide a set of selectable gear ratios defining a range of gear ratios. It is further well known to those of skill in the relevant arts that the connection of a planetary transmission in “series” with a multiple gear ratio transmission will provide, in combination, a two stage transmission wherein one stage is comprised of the multiple gear ratio transmission and the second stage is comprised of the planetary transmission. The resulting two stage transmission will therefore have two ranges of gear ratios, wherein the gear ratios within either of the two ranges are determined and provided by the multiple gear ratio transmission and the range, that is, a selected one of either of the two ranges, is determined and selected by the planetary transmission. It will be well understood by those of skill in the relevant arts that the two gear ratio ranges may be separate or may overlap or may abut, depending upon the gear ratio range of the multiple gear ratio stage, but that the effect of the addition of the planetary transmission will be to increase the total gear ratio spread, that is, the total gear ratio range, of the combined transmission. For this reason, the planetary gear transmission is often referred to as a “range-change group transmission”, that is, as a transmission selecting and changing a set of transmission gear ratios from among two or more sets of transmission gear ratios wherein the gear ratios within a given set are common to all the sets of gear ratios and are provided by another transmission or stage of the transmission. The details of a Planetary Transmission  136  and the interconnection of a Planetary Transmission  136  with other transmissions or transmission components will not be discussed in further detail herein as such are well known to and understood by those of ordinary skill in the relevant arts. FIG. 3 shows an enlarged arrangement, in comparison with that of FIG. 2, with a splitter transmission  134  in the housing  106  to form a second constant. A synchronizing device  126  is provided upon the output shaft  112  by which the gear wheel  111  or the gear wheel  128  can be optionally non-rotationally connected with the output shaft. The gear wheel  108  is non-rotationally situated jointly with a gear wheel  130  upon a shaft  132 . 
     FIG. 2 shows a diagrammatic illustration of the transmission constructions according to the invention. A transmission  60  has a housing  62  in which an input shaft  64  projects. The input shaft  64  is designed integral with the main shaft  66  of the transmission  60 . On the main shaft  66  seven gear wheels  68 ,  70 ,  72 ,  74 ,  76 ,  78 ,  80  are mounted of which the gear wheels  68 ,  70 ,  72 ,  74  can loosely rotate upon the main shaft  66  while the gear wheels  76 ,  78 ,  80  are permanently non-rotationally connected with the main shaft  66 . A synchronizing device  82  is provided between the gear wheels  68  and  70  by which the gear wheel  68  or the gear wheel  70  can be optionally non-rotationally connected with the main shaft  66 . A synchronizing device  84  is provided between the gear wheels  72  and  74  by which the gear wheel  72  or the gear wheel  74  can be optionally non-rotationally connected with the main shaft  66 . 
     Seven gear wheels  88 ,  90 ,  92 ,  94 ,  96 ,  98 ,  100  are likewise provided upon the countershaft  86  of which the gear wheels  88 ,  90 ,  92 ,  94  are permanently non-rotationally connected with the countershaft  86 . A synchronizing device  102  is provided between the gear wheels  96  and  98  by which the gear wheel  96  or the gear wheel  98  can be optionally non-rotationally connected with the countershaft  86 . For the reverse gear, the gear wheel  100  meshes, for a reverse direction of rotation, with an intermediate gear  104  which, in turn, meshes with the gear wheel  80  upon the main shaft  66 . The gear wheel  98  meshes with a gear wheel  120  upon an auxiliary output shaft  122  by which a retarder  124  is driven. Due to the large diameter of the gear wheel  98 , the auxiliary output shaft  122  is driven at a high rotational speed. 
     In the illustration shown here, one other housing  106  is provided next to the transmission housing  62 . A gear wheel pair consisting of two gear wheels  108  and  110  is mounted in the housing  106 , the gear wheel  108  is non-rotationally connected with the countershaft  86 . The gear wheel  110  is permanently non-rotationally connected with the output shaft  112 , but the gear wheels  108  and  110  can also be situated within the adequately configured transmission housing  62 . Gear wheel  110  and output shaft  112  rotate around an imaginary axis of rotation  114 . The main shaft  66  and the gear wheels mounted thereon, the same as the input shaft  64 , rotate around an axis of rotation  116 . Both axes of rotation  114  and  116  are not coaxial with respect to each other, but are separated by an axial distance  118 . 
     As described above, and as shown in FIG. 2, in an advantageous development, a range-change group transmission  136 , in the form of a planetary transmission, is provided next to the gear wheel pair  108 ,  110  of the constant for enlarging the total spreading of the transmission. FIG. 3 shows an enlarged arrangement, in comparison with that of FIG. 2, with a splitter transmission  134  in the housing  106  to form a second constant. A synchronizing device  126  is provided upon the output shaft  112  by which the gear wheel  111  or the gear wheel  128  can be optionally non-rotationally connected with the output shaft. The gear wheel  108  is non-rotationally situated jointly with a gear wheel  130  upon a shaft  132 . 
     
       
         
               
             
               
               
               
               
             
           
               
                   
               
               
                 Reference numerals 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 6 
                 transmission 
                 84 
                 synchronizing device 
               
               
                 18 
                 control lever 
                 86 
                 countershaft 
               
               
                 20 
                 gearshift rod 
                 88 
                 gear wheel 
               
               
                 22 
                 gearshift rod 
                 90 
                 gear wheel 
               
               
                 24 
                 gearshift rod 
                 92 
                 gear wheel 
               
               
                 28 
                 synchronizing device 
                 94 
                 gear wheel 
               
               
                 30 
                 synchronizing device 
                 96 
                 gear wheel 
               
               
                 32 
                 transmission input shaft 
                 98 
                 gear wheel 
               
               
                 34 
                 transmission housing 
                 100 
                 gear wheel 
               
               
                 36 
                 bearing 
                 102 
                 synchronizing device 
               
               
                 38 
                 main shaft 
                 104 
                 intermediate gear 
               
               
                 40 
                 bearing 
                 106 
                 housing 
               
               
                 42 
                 bearing\44 intermediate gear 
                 108 
                 gear wheel 
               
               
                 46 
                 countershaft 
                 110 
                 gear wheel 
               
               
                 54 
                 clutch body 
                 111 
                 gear wheel 
               
               
                 60 
                 transmission 
                 112 
                 output shaft 
               
               
                 62 
                 transmission housing 
                 114 
                 axis of rotation 
               
               
                 64 
                 input shaft 
                 116 
                 axis of rotation 
               
               
                 66 
                 main shaft 
                 118 
                 axial distance 
               
               
                 68 
                 gear wheel 
                 120 
                 gear wheel 
               
               
                 70 
                 gear wheel 
                 122 
                 auxiliary output shaft 
               
               
                 72 
                 gear wheel 
                 124 
                 retarder 
               
               
                 74 
                 gear wheel 
                 126 
                 synchronizing device 
               
               
                 76 
                 gear wheel 
                 128 
                 gear wheel 
               
               
                 78 
                 gear wheel 
                 130 
                 gear wheel 
               
               
                 80 
                 gear wheel 
                 132 
                 shaft 
               
               
                 82 
                 synchronizing device 
                 134 
                 splitter transmission