Patent Publication Number: US-2015080169-A1

Title: Powershift transmission

Description:
This application claims priority from German patent application serial no. 10 2013 218 615.0 filed Sep. 17, 2013. 
     FIELD OF THE INVENTION 
     The invention concerns a powershift transmission. 
     BACKGROUND OF THE INVENTION 
     Automatic variable-speed transmissions, particularly for commercial vehicles, as a rule comprise a starting element in the form of a torque converter which, in particular, brings about an increase of the torque delivered by the internal combustion engine. The disadvantages of such a torque converter are, on the one hand, the hydraulic losses caused by the slip between the pump and turbine wheel, and, on the other hand, the relatively large weight of the converter. 
     In DE 10 2008 041 887 A1 by the present applicant, in the case of hybrid drives for motor vehicles it has been proposed to replace the hydrodynamic torque converter with a transmission input stage having a high transmission ratio, wherein the transmission input stage is in the form of a planetary gearset with a sun gear, a planetary carrier and a ring gear. In this case the ring gear can be coupled to the internal combustion engine and/or the electric machine, the planetary carrier is connected to the transmission input shaft and the sun gear is fixed permanently relative to the transmission housing. This produces a fixed transmission ratio for the planetary transmission. By virtue of the transmission input stage, the torque of the electric machine is increased by around 70%. 
     SUMMARY OF THE INVENTION 
     The purpose of the present invention is, in an automatic powershift transmission of the type mentioned to begin with, to reduce the losses occurring in the starting element. 
     This objective is achieved by the characteristics of the automatic powershift transmission described below. Advantageous design features emerge from the subordinate claims. 
     According to the invention, the torque converter previously usually present in an automatic powershift transmission is replaced by a planetary gearset wherein the ring gear and the planetary carrier of the planetary gearset can be coupled to one another and the sun gear can be fixed. During starting, this results in a transmission ratio between the drive input shaft and the transmission input shaft in the slow range, i.e. the torque delivered by the internal combustion engine is increased—similarly to the way it is by the hydrodynamic converter. This enables quick and easy starting. In particular, however, losses are low since there are no hydraulic losses and only geartooth frictional losses occur. Furthermore, the weight of an automatic transmission with a starting element according to the invention is lower compared with one having a conventional converter. 
     In a preferred embodiment at least one shifting element of the variable-speed transmission serves as the starting element, i.e. the shifting elements in any case present in the transmission additionally adopt a starting function, namely the bridging of the rotational speed difference between the driveshaft or transmission input shaft and the transmission output shaft when starting. 
     In another preferred embodiment, the planetary carrier can be coupled by means of a shifting clutch to the driveshaft, i.e. the two transmission elements, the ring gear and the planetary carrier, can be “locked” to one another so that they run synchronously. The clutch is engaged as soon as the starting process has ended; this eliminates the need for the starting transmission ratio. 
     In a further preferred embodiment, during the starting process the sun gear or the sun gear shaft is supported, i.e. held fixed relative to the housing, by means of a freewheel. Thus, during the starting process the planetary gearset operates with a fixed transmission ratio between the ring gear and the planetary carrier. As already mentioned, a transmission ratio is obtained in the slow range and the torque on the transmission input shaft is thereby increased. 
     According to another preferred embodiment, the ring gear is connected directly to the drive input shaft, i.e. the internal combustion engine drives the ring gear of the planetary gearset directly. 
     In a further preferred embodiment, the ring gear can be coupled to an electric machine, so that the electric machine preferably adopts the function of a starter-generator. Thus the internal combustion engine can be started by means of the electric machine (starter function), or the electric machine is driven by the internal combustion engine (generator function). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
       Example embodiments of the invention are illustrated in the drawing and are described in more detail below, so that further characteristics and/or advantages can emerge from the description and/or the drawings, which show: 
         FIG. 1 : A schematic representation of an automatic powershift transmission with a starting element according to the invention, and 
         FIG. 2 : A design of the starting element, with an integrated electric machine. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       FIG. 1  shows an automatic powershift transmission  1 , called automatic transmission for short in what follows, which comprises a drive input side AN, a drive output side AB, a variable-speed transmission  2  and a starting element  3 . The variable-speed transmission  2  comprises a transmission input shaft  4  and a transmission output shaft  5 , three planetary gearsets RS 1 , RS 2 , RS 3  and five shifting elements A, B, D, E, F. With this variable-speed transmission  2 , seven forward gears and one reversing gear can be engaged. Between the drive input side AN and the transmission input shaft  4  is arranged the starting element  3 , which comprises a planetary gearset  6 , a shifting clutch  7  and a freewheel  8 . The planetary gearset  6  comprises a ring gear  9  with its ring gear carrier, a planetary carrier  10  with planetary gearwheels  11  and a sun gear  12  with its sun gear shaft  12   a.  The starting element  3  is driven by a driveshaft  13  of an internal combustion engine (not shown), which is connected, on the one hand, by way of the ring gear carrier  9   a  to the ring gear  9  and, on the other hand, to the input side (inner disk carrier) of the clutch  7 . The planetary carrier  10 , also referred to as the spider shaft  10 , is connected on the one hand to the output side (outer disk carrier) of the clutch  7  and on the other hand to the transmission input shaft  4 . The sun gear  12  is connected by way of its sun gear shaft  12   a  to a freewheel  8  supported on the housing. The ring gear  9 , planetaries  11  and sun gear  12  mesh permanently with one another. 
     The automatic transmission  1  with the starting element  3  according to the invention works as follows: 
     When starting, the clutch  7  is opened and the sun gear  12  is held fast by the freewheel  8 . This produces for the planetary transmission  6  a fixed transmission ratio from the ring gear  9  to the spider shaft  10 , i.e. a step-down transmission ratio (as viewed from the drive input side AN to the drive output side AB). The torque from the internal combustion engine transmitted by the driveshaft  13  is thus increased. The starting process takes place by way of a starting clutch, whose function is performed by the shifting element A (clutch) and by the shifting element F (brake) of the variable-speed transmission  2 . At the beginning of the starting process the clutch A is closed, so that the torque is transmitted via the sun gear to the gearset RS 3 . By closing the brake F in a controlled manner the ring gear of the gearset RS 3  is braked, so that the drive output can take place via the spider shaft of the gearset RS 3  to the transmission output shaft  5 . 
     As soon as the starting process has ended, the clutch  7  is closed so that the spider shaft  10  and the ring gear  9  are connected with one another in a fixed manner, i.e. “locked”. The ring gear  9  and the spider shaft  10  then rotate synchronously. The freewheel  8  is unlocked, so that the sun gear  12  can rotate freely. The torque delivered by the internal combustion engine is now transmitted one-to-one to the transmission input shaft  4 . The starting transmission ratio stage is omitted. 
       FIG. 2  shows a starting element  20  which constitutes a constructive design of the starting element  3  represented schematically in  FIG. 1 . The starting element  20  comprises a planetary gear system consisting of a ring gear  21 , a planetary carrier  22  with planetary gearwheel  23  and a sun gear  24 . The ring  21  gear is connected to a ring gear carrier  21  a which is mounted in a housing  25 . Between the planetary carrier  22  and the ring gear carrier  21  a is arranged a shifting clutch in the form of a disk clutch  26 , which has an inner disk carrier  26   a  connected to the ring gear carrier  21  a and an outer disk carrier  26   b  connected to the planetary carrier  22 . Thus, the planetary carrier  22  or spider shaft  22  and the ring gear  21  can rotate separately from one another or be locked to one another. In a manner not explained in more detail, the sun gear  24  is connected to a freewheel (not indexed). The spider shaft  22  is connected to a transmission input shaft (not shown). To that extent the starting element  20  corresponds to the representation in  FIG. 1 . 
     In addition, in  FIG. 2  an electric machine  27  is integrated in the starting element  20 . The electric machine  27  has a stator  27   a  connected to the housing  25  and a rotor  27   b  connected to the ring gear carrier  21   a.  The electric machine  27  performs the function of a starter-generator and can therefore either start the internal combustion engine or be driven by the internal combustion engine as a generator. Recovery of braking energy (recuperation) is also possible. 
     INDEXES 
     
         
           1  Automatic powershift transmission (automatic transmission) 
           2  Variable-speed transmission 
           3  Starting element 
           4  Transmission input shaft 
           5  Transmission output shaft 
           6  Planetary gearset 
           7  Clutch 
           8  Freewheel 
           9  Ring gear 
           9   a  Ring gear carrier 
           10  Planetary carrier 
           11  Planetary gearwheel 
           12  Sun gear 
           12   a  Sun gear shaft 
           13  Drive input shaft 
           20  Starting element 
           21  Ring gear 
           21   a  Ring gear carrier 
           22  Planetary carrier 
           23  Planetary gearwheel 
           24  Sun gear 
           25  Housing 
           26  Disk clutch 
           26   a  Inner disk carrier 
           26   b  Outer disk carrier 
           27  Electric machine 
           27   a  Stator 
           27   b  Rotor 
         AN Drive input side 
         AB Drive output side 
         RS 1 , RS 2 , RS 3  Gearsets 
         A, B, D, E, F Shifting elements