Patent Publication Number: US-2017356534-A1

Title: Compact planetary gearbox

Description:
This application claims priority from German patent application serial no. 10 2016 210 078.5 filed Jun. 8, 2016. 
     FIELD OF THE INVENTION 
     The invention concerns a transmission having a driven planetary stage and a downstream spur gear stage. 
     BACKGROUND OF THE INVENTION 
     In transmissions of this type known from the prior art a planetary carrier of the planetary stage, mounted to rotate in a transmission housing, is supported on both sides, i.e. by means of at least two bearings arranged on the two sides of the planetary carrier. A first spur gear of a spur gear stage is driven by a sun gear shaft. The sun gear shaft projects into a recess of the spur gear and is there connected to the spur gear in a rotationally fixed manner by means of entrainment teeth. Like the planetary carrier, the spur gear is mounted to rotate in the transmission housing supported on both sides, i.e. by means of at least two bearings arranged on the two sides of the spur gear. This is problematic since the twofold bearing support of both the planetary carrier and the spur gear takes up axial structural space. 
     SUMMARY OF THE INVENTION 
     The purpose of the present invention is to provide a transmission with improved characteristics. In particular the weight of the transmission should be reduced and the axial space it occupies should be smaller. 
     This objective is achieved by a transmission according to the claims. 
     The transmission comprises at least one planetary stage, at least one spur gear stage and a transmission housing. A planetary stage is understood to be an arrangement having a planetary carrier, which is in this case mounted to rotate, one or more planetary gearwheels mounted to rotate on the planetary carrier, a sun gear, in this case mounted to rotate, and a ring gear which in this case is rotationally fixed. Each planetary gearwheel meshes with the sun gear and/or the ring gear. 
     Analogously, a spur gear stage is understood to be an arrangement having at least one spur gear. 
     In the present case the spur gear and the sun gear are connected to one another in a rotationally fixed manner. In particular, the sun gear and the spur gear thus have a common rotational axis. Preferably, that axis coincides with a rotational axis of the planetary carrier. 
     According to the invention, the transmission housing has at least one spindle. A spindle is understood to be a projecting means that serves to hold some other component. The function of the spindle is to support and provide a bearing for the other component. 
     The spindle of the transmission housing of the transmission according to the invention can be made integrally with the rest of the transmission housing, or fixed detachably in the rest of the transmission housing. Preferably the spindle is screwed into the rest of the transmission housing. In particular, the spindle and the rest of the transmission housing are fixed in such manner that no relative movement is possible between them. 
     The spur gear is mounted and can rotate on the spindle. Preferably, the spur gear is mounted on the spindle alone, which implies that any forces that act upon the spur gear are transmitted by way of the spindle to the rest of the transmission housing. 
     Relative to comparable transmissions, the transmission according to the present invention can be made particularly compact in the axial direction. This results in a substantial weigh reduction. 
     In a preferred further development, the spur gear constitutes a hub. A hub is defined as a means that is pushed onto a shaft, an axle or a spindle. Correspondingly, the spur gear is pushed onto the spindle of the transmission housing in such a manner that the spindle projects at least partially into the hub. Thus, part of the spindle is inside the hub. Between this part of the spindle and the hub there is a radial overlap. Since the spindle projects into the hub of the spur gear, the bearing required for mounting the spur gear can be accommodated inside the hub. Correspondingly, in a preferred further development an inner ring of at least one bearing by which the spur gear is mounted on the spindle is fixed on the spindle. Preferably, the inner ring is shrink-fitted onto the spindle. In particular, the inner ring is fixed so that it cannot move relative to the spindle. Correspondingly, an outer ring of the bearing is preferably fixed into the hub by expansion. In particular, the outer ring of the bearing is fixed so that it cannot move relative to the hub. In relation to reducing the axial fitting space of the transmission, the arrangement of the bearing inside the hub in accordance with this further development is advantageous. 
     Furthermore, the mounting of the planetary carrier offers further potential for reducing the axial fitting space of the transmission. Thus, in a preferred further development, no bearing is located axially between at least part of the planetary carrier and at least part of the spur gear. For an arrangement of the bearing in this area, fitting space would be needed, which may be dispensed with according to this further development. 
     As for the arrangement of the bearing, by means of which the planetary carrier is mounted, axially between at least part of the planetary carrier and at least part of the spur gear, according to a preferred further development at least part of the planetary carrier is arranged axially between each of the bearings with which the planetary carrier is mounted, and the spur gear. Thus, for each bearing with which the planetary carrier is mounted, at least part of the planetary carrier is arranged axially between that bearing and the spur gear. This means that the planetary carrier has a bearing on one side only. In that way the fitting space for a bearing on the second side of the planetary carrier is saved. 
     The sun gear has teeth that mesh with at least one planetary gearwheel of the planetary stage. In a preferred further development, some of those teeth form splines that mesh with teeth of the hub, by virtue of which the spur gear and the sun gear are connected rotationally fixed with one another. Since there is no separate spline array, the axial space occupied by the transmission is reduced further. Moreover production is simplified since the sun gear only has to be made with one set of teeth. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred example embodiment of the invention is illustrated in the sole FIGURE, in which matching indexes denote similar or functionally equivalent features. In detail, the sole FIGURE shows a transmission with a planetary and a spur gear stage. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The transmission shown in  FIG. 1  comprises a planetary stage  101  on the input side and a spur gear stage  103  on the output side. The planetary stage  101  comprises a planetary carrier  107 , planetary gearwheels  109  mounted to rotate on the planetary carrier  107 , a fixed ring gear  111  and a rotatable sun gear  113 . The planetary gearwheels  109  mesh with the ring gear  111  and the sun gear  113 . 
     By means of just one bearing  115 , the planetary carrier  107  is mounted to rotate in a transmission housing  117 . The ring gear  111  forms part of the transmission housing  117  and is bolted to other parts of the transmission housing  117 . Relative to a flank of the planetary carrier  107 , the bearing  115  is offset on the drive input side, i.e. in the direction of a drive input shaft  119 . 
     By means of the drive input shaft  119 , drive torque is exerted on the planetary carrier  107 . For this purpose, the drive input shaft  119  is connected in a rotationally fixed manner to the planetary carrier  107  by splines  121 . 
     The spur gear stage  103  comprises a first spur gear  123  and a second spur gear  125 . The two spur gears  123 ,  125  are mounted to rotate and mesh with one another. 
     To mount the first spur gear  123  a spindle  127  is provided. This is screwed into the transmission housing  117 . The first spur gear  123  forms a hub  129  into which a cylindrical part of the spindle  127  projects. By means of a bearing  131  the first spur gear  123  is mounted and can rotate on the spindle  127 . Forces acting on the first spur gear  123  are in this way transmitted by way of the bearing  131  to the cylindrical part of the spindle  127 . 
     By way of spline teeth  133  inside the hub  129 , the first spur gear  123  is connected in a rotationally fixed manner to the sun gear  113 . 
     The second spur gear  125  drives an output shaft  135 . Correspondingly, there is a rotationally fixed connection between the second spur gear  125  and the output shaft  135 . 
     In the transmission shown in  FIG. 1  the planetary carrier  107 , the planetary gearwheels  109 , the ring gear  111 , the sun gear  113  and the first spur gear  123  are each at least partially located in an axial intermediate space between the bearings  115 ,  131 . This enables a reduction in the axial installation space. 
     INDEXES 
     
         
           101  Planetary stage 
           103  Spur gear stage 
           107  Planetary carrier 
           109  Planetary gearwheel 
           111  Ring gear 
           113  Sun gear 
           115  Bearing 
           117  Transmission housing 
           119  Drive input shaft 
           121  Spline teeth 
           123  First spur gear 
           125  Second spur gear 
           127  Spindle 
           129  Hub 
           131  Bearing 
           133  Spline teeth 
           135  Output shaft