Patent Publication Number: US-2010108414-A1

Title: Drive line

Description:
This application claims priority from German patent application serial no. 10 2008 043 341.1 filed Oct. 31, 2008. 
     FIELD OF THE INVENTION 
     The invention concerns a drivetrain of a motor vehicle, comprising at least a transmission and a hybrid drive, according to the preamble of claim  1 . 
     BACKGROUND OF THE INVENTION 
     The main components of a drivetrain of a motor vehicle are a prime mover and a transmission. The transmission transforms torques and rotational speeds, and thereby converts the traction force supplied by the prime mover. The present invention relates to a drivetrain which comprises at least an automatic conventional transmission as the transmission and, as the prime mover, a hybrid drive system with an internal combustion engine and an electric motor. 
     An automatic conventional transmission should in particular be understood to mean a transmission in which gearshifts are carried out automatically, with interruption of the traction force. However, an automatic conventional transmission can also be one in which gearshifts are carried out automatically, without traction force interruption. 
       FIG. 1  shows a drivetrain diagram known from the prior art, with a hybrid drive system comprising an internal combustion engine  1  and an electric motor  2 . A transmission  3  converts the traction force supplied by the hybrid drive and delivers it to a drive output  4 . In  FIG. 1  a clutch  5  is located between the combustion engine  1  and the electric motor  2 . In addition, in  FIG. 1  a transmission-external starting element  6  is located between the electric motor  2  and the transmission  3 . Instead of a transmission-external starting element  6 , a transmission-internal starting element can also be present. The structure of a drivetrain with a hybrid drive shown in  FIG. 1  is also called a parallel-hybrid drivetrain. 
     In the parallel-hybrid drivetrain known from the prior art and shown in  FIG. 1 , the starting element  6  is subjected to high loads. This can lead to premature wear of the starting element. Furthermore, when a transmission is used in which gearshifts are carried out automatically with traction force interruption, gearshifts cannot be carried out while maintaining the traction force at the drive output. There is therefore need for a drivetrain with which these disadvantages can be avoided. 
     SUMMARY OF THE INVENTION 
     Starting from there, the present invention addresses the problem of providing a new type of drivetrain. According to the invention the internal combustion engine is coupled to a transmission input of the automatic change-speed transmission, and the electric motor is coupled to a planetary gear set which creates a second power path parallel to the first power path through the automatic conventional transmission. 
     In the concept according to the invention for a drivetrain with a hybrid drive system two power paths are provided, namely one power path through the automatic conventional transmission and another power path through the planetary gear set, with the electric motor of the hybrid drive coupled to the planetary gear set, namely to a sun gear thereof. This makes it possible, when starting off, to reduce the load on a starting element that may be present. It may even be possible to do without a starting element completely. Moreover, even when an automatic conventional transmission is used with which gearshifts are carried out with traction force interruption, gearshifts can be carried out while maintaining torque and accordingly while maintaining the traction force at the drive output. If the electric motor of the hybrid drive and/or an energy accumulator thereof should fail, the drivetrain can be operated conventionally, exclusively by the combustion engine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Example embodiments of the invention, to which it is not limited, are explained in more detail with reference to the drawings, which show: 
         FIG. 1 : Diagram of a motor vehicle drivetrain known from the prior art; 
         FIGS. 2 and 2A : Diagrams of a first motor vehicle drivetrain according to the invention; and 
         FIG. 3 : Diagram of a second motor vehicle drivetrain according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 2 and 2A  show a first example embodiment of a motor vehicle drivetrain according to the invention such that, as shown in  FIGS. 2 and 2A , the drivetrain comprises an internal combustion engine  10 , a transmission  11  and a drive output  12 . In  FIGS. 2 and 2A  the combustion engine  10  is coupled to the transmission input of the transmission  11  with an interposed starting element  13 , the transmission  11  in question being an automatic conventional transmission. With an automatic conventional transmission, shifting operations and thus gearshifts are carried out automatically, in particular with traction force interruption in the transmission  11 . The transmission output of the transmission  11  is coupled to the drive output  12 . 
     In addition, the drivetrain of  FIGS. 2 and 2A  has an electric motor  14  coupled to a planetary gear set  15 , so that the planetary gear set  15  forms a power path that extends parallel to the power path formed by the automatic conventional transmission  11 . The power path of the planetary gear set  15  extends parallel to the automatic conventional transmission and to the starting element  13 . 
     The electric motor  14  engages a sun gear of the planetary gear set  15 . In a first variant, shown in  FIG. 2 , the internal combustion engine  10  engages a ring gear  24  of the planetary gear set  15  and the drive output  12  with a carrier  22  of the planetary gear set  15 . In a second alternative, shown in  FIG. 2A , the combustion engine  10  is coupled to the carrier  22  of the planetary gear set  15  and the drive output  12  to the ring gear  24  of the planetary gear set  15 . 
     In the case of the drivetrain shown in  FIGS. 2 and 2A , the drivetrain starts up and/or maneuvers and/or crawls when a driver&#39;s-wish-dependent drive output torque is delivered to the drive output  12 , with the electric motor  14  coupled to the planetary set  15  supporting the torque supplied by the internal combustion engine  10  as much as possible and transmitting it, via the planetary gear set  15 , to the drive output  12 , whereas in contrast the starting element  13  converts as little as possible of the torque supplied by the combustion engine  10  and delivers it, via the automatic conventional transmission  11 , to the drive output  12 , so that in total the driver&#39;s-wish-dependent output torque is delivered to the drive output  12 . 
     Accordingly, to start off and/or maneuver and/or crawl, torque desired by the driver for the drive output  12  is determined and so far as possible this desired output torque, which is supplied by the internal combustion engine  10 , is delivered to the drive output  12  via the power path of the automatic conventional transmission  11 . The torque that can be supported by the electric motor  14  at the planetary gear set  15  and thus the torque that can be delivered to the drive output  12  via the power path of the planetary gear set  15  depends on the size of the electric motor  14  and on the size of an electrical energy accumulator of the drivetrain. 
     In the event that the driver&#39;s-wish-dependent drive output torque for starting off, maneuvering or crawling can be supplied to the drive output  12  completely via the power path with the planetary gear set  15 , the starting element  13  can also be or remain fully open and this enables wear-free starting, maneuvering or crawling. 
     In the drivetrain shown in  FIGS. 2 and 2A , if a shift or gear-change operation is to take place in the automatic conventional transmission  11 , then this can be done with the starting element  13  either open or closed. In either case, to carry out a shift operation in the automatic conventional transmission  11 , torque supplied by the internal combustion engine is supported with the help of the electric motor  14  at the planetary gear set  15 , to enable a shift without interruption of the traction force, since via the power path of the transmission  12  a drive output torque is delivered to the drive output  12  even when carrying out a shift in the automatic conventional transmission  11 . 
     In the drivetrain shown in  FIGS. 2 and 2A , if a shift operation is to take place in the automatic conventional transmission  11  with the starting element  13  at least partially open, then the internal combustion engine  10  reduces the torque it delivers at the same time as the torque at the planetary gear set  15  is being supported, to an extent that enables the starting element  13  to be opened while free from torque. Using transmission-internal synchronizers, the automatic conventional transmission  11  then carries out a gearshift from a current gear to a target gear, the starting element  13  then closes and the combustion engine  10  builds up its load and therefore the torque that it supplies. Transmission-internal synchronization is also referred to as passive synchronization, which operates by means of transmission-internal synchronizing devices. 
     As already mentioned, in the drivetrain shown in  FIGS. 2 and 2A  gearshifts in the automatic conventional transmission  11  can even be carried out with the starting element  13  closed, and to do this the combustion engine  10  reduces the torque it is supplying at the same time as the torque at the planetary gear set  15  is being supported, to an extent such that the transmission input of the automatic change-speed transmission  11  is or becomes free from load. After the current gear has been disengaged, to carry out the gearshift a transmission-external synchronization takes place, the target gear is engaged in the automatic conventional transmission  11 , and the combustion engine  10  then increases the torque it is supplying and builds up a load again. Transmission-external synchronization is also referred to as active synchronization and takes place when the combustion engine  10  and/or the electric motor  14  adapts the torque at the transmission input of the automatic conventional  11  to the change of rotation speed, after the current gear has been disengaged and before the target gear has been engaged. 
     In the drivetrain shown in  FIGS. 2 and 2A , if the combustion engine  10  is to be actively stopped or actively started, then for example a vehicle brake of the drivetrain supports the torque delivered by the combustion engine  10  and at the same time the automatic conventional transmission  11  adopts a neutral position and/or the starting element  13  is opened. Alternatively, for active starting of the combustion engine  10  or for active stopping thereof, it is possible for the automatic conventional transmission  11  to be locked and the starting element opened. 
     In the drivetrain shown in  FIGS. 2 and 2A  a so-termed boost can be produced when the starting element  13  is closed and a gear is engaged in the automatic conventional transmission  11  by operating the electric motor  14  as a motor. If the starting element  13  is closed and a gear is engaged in the automatic conventional transmission  11 , then if the electric motor  14  is operated as a generator, so-termed recuperation takes place. 
     According to a further development of the present invention, the starting element  13  in  FIGS. 2 and 2A  can even be omitted and the power path of the planetary gear set  15  is then again parallel to the power path of the automatic conventional transmission  11 . Even when there is no starting element  13  and the combustion engine  10  is therefore coupled directly to the transmission input of the automatic conventional transmission  11 , the above functions of starting off, maneuvering, crawling, shifting, starting and stopping the combustion engine  10 , boosting and recuperation can all be carried out. 
     When the combustion engine  10  is directly coupled to the transmission input of the automatic conventional transmission without a starting element  13  interposed between them, starting off and/or maneuvering and/or crawling of the drivetrain takes place by the supply of a driver&#39;s-wish-dependent output torque to the drive output  12  exclusively by the electric motor  14  and the planetary gear set  15 , and to do this the automatic conventional transmission  11  adopts a neutral position and the size of the electric motor  14 , as well as that of an electrical accumulator associated with the electric motor  14 , are chosen having regard to the maximum driver&#39;s-wish-dependent output torque possible. 
     A shift operation and hence gear-change in the automatic conventional transmission  11  in a drivetrain with no starting element  13 , takes place analogously to the shift with a closed starting element  13  described with reference to  FIGS. 2 and 2A . 
     Active starting and active stopping of the combustion engine  10  also take place as described in connection with  FIGS. 2 and 2A , with the automatic conventional transmission  11  in a neutral position and the torque supplied by the combustion engine  10  supported by a vehicle brake. 
     In a drivetrain with no starting element  13 , boosting and recuperation take place as described above, analogously to a drivetrain having a starting element  13 . 
       FIG. 3  shows another advantageous design of the drivetrain according to the invention, such that in  FIG. 3  a clutch  16  is interposed between the electric motor  14  and the planetary gear set  15 . With the help of this separating clutch  16  the electric motor  14  can be decoupled from the planetary gear set  15 , for example in order to avoid zero-load losses. If the clutch  16  is not present, the electric motor  14  always has to rotate together with the planetary gear set  15  and, depending on the fixed transmission ratio of the latter and its connection thereto, can reach considerably higher speeds than the combustion engine  10 . 
     According to another advantageous development of the invention, a brake  17  engages in the second power path between the combustion engine  10  and the planetary gear set  15 , the brake  17  acting on a crankshaft of the combustion engine  10 . Actuation of this brake  17  enables purely electric-powered driving and recuperation with the combustion engine  10  stopped. For this, the starting element  13  is open and the automatic conventional transmission  11  is in its neutral position. 
     Likewise, a brake  18  can act in the second power path between the planetary gear set  15  and the drive output  12 , so that actuation of the brake  18  enables active starting and active stopping of the combustion engine  10  by the electric motor  14  when at rest. 
     INDEXES 
     
         
           1 . Internal combustion engine 
           2 . Electric motor 
           3 . Transmission 
           4 . Drive output 
           5 . Clutch 
           6 . Starting element 
           10 . Internal combustion engine 
           11 . Transmission 
           12 . Drive output 
           13 . Starting element 
           14 . Electric motor 
           15 . Planetary gear set 
           16 . Clutch 
           17 . Brake 
           18 . Brake 
           20 . Sun gear 
           22 . Carrier 
           24 . Ring gear