Abstract:
The invention relates to a drive train ( 10 ) for a hybrid vehicle comprising an internal combustion engine ( 12 ) having a motor shaft ( 18 ) for providing a torque for driving the hybrid vehicle, and comprising an electric machine ( 30 ) for providing a torque for driving the hybrid vehicle, wherein the electric machine ( 30 ), in particular for starting of the internal combustion engine ( 12 ), can be coupled to the motor shaft ( 18 ) by means of a selectively engageable planetary gear unit ( 38 ) for providing at least two different transmission ratios, wherein the electric machine ( 30 ) can be coupled by means of a transmission gearing ( 48 ), in particular a sun gear system having a transmission ratio different from 1.0, having an intermediate shaft ( 46 ) for introducing the torque into the planetary gear unit ( 38 ).

Description:
BACKGROUND 
     1. Field of the Invention 
     The invention relates to a drive train for a hybrid motor vehicle, with the aid of which a torque produced by an internal combustion engine and/or by an electric machine can be transmitted. 
     2. Description of the Related Art 
     US 2010/0216584 A1 discloses a drive train for a hybrid motor vehicle, in which an electric machine has a rotor, which is designed as an annulus of a planetary gearset. The annulus is coupled via planet wheels supported by a planet carrier to a sun wheel, which is connected for conjoint rotation to a transmission output shaft of a motor vehicle transmission to enable the hybrid motor vehicle to be driven electrically. The planet carrier is connected to a shaft connected via gearing to an engine shaft of an internal combustion engine in order to be able to start the internal combustion engine with the aid of the electric machine. 
     There is a constant need to reduce the space required to install a drive train. 
     It is the object of the invention to indicate measures which allow a drive train with a small installation space requirement. 
     SUMMARY 
     According to the invention, a drive train for a hybrid motor vehicle is provided, said drive train having an internal combustion engine, which has an engine shaft, for supplying a torque to drive the hybrid motor vehicle, and an electric machine for supplying a torque to drive the hybrid motor vehicle, wherein the electric machine can be coupled to the engine shaft, in particular in order to start the internal combustion engine, via a shiftable planetary gearset for supplying at least two different transmission ratios, wherein the electric machine can be coupled, via a speed-transforming gear, in particular a spur wheel gear, having a transmission ratio differing from 1.0, to an intermediate shaft in order to introduce the torque into the planetary gearset. 
     The speed-transforming gear can be positioned so as to be spaced apart from the planetary gearset by a defined distance in an axial direction, i.e. substantially parallel to an axis of rotation of the engine shaft of the internal combustion engine, depending on the design of the intermediate shaft. As a result, the electric machine can be arranged adjacent to the planetary gearset in an axial direction, ensuring that the electric machine does not have to fit radially around the planetary gearset. It is thereby possible to reduce the extent of the electric machine in a radial direction, thus allowing the installation space requirement for the drive train to be reduced. The planetary gearset and a link to the engine shaft which follows the planetary gearset, e.g. via a toothed chain or a roller chain, provide a transmission ratio which leads, in particular, to a reduction in the speed of the electric machine, allowing a correspondingly high torque to be introduced in order to start the internal combustion engine. To cold-start the internal combustion engine, a transmission ratio of 1:3, for example, can be provided for this purpose by the planetary gearset. Since the electric machine does not act directly on the planetary gearset but is first coupled to the intermediate shaft via the speed-transforming gear, an additional transmission ratio can be achieved with the aid of the speed-transforming gear, leading, in particular, to an additional reduction in the speed of the electric machine. A correspondingly high torque can thereby be introduced at a lower speed into the planetary gearset. As a result, the planetary gearset can be designed for lower speeds and hence for lower loads due to centrifugal forces, thereby enabling the design requirements on the planetary gearset to be reduced and production costs to be lowered. Through the arrangement of the electric machine at a distance from the planetary gearset, as made possible by the intermediate shaft, and through the additional reduction in the speed of the electric machine that can be achieved with the speed-transforming gear, the dimensions of the electric machine can be reduced, thereby allowing a drive train with a small installation space requirement. 
     The engine shaft of the internal combustion engine can be a crankshaft or a cardan shaft, for example, which can be driven directly or indirectly by the combustion of a fuel mixture in the internal combustion engine. As functional elements, the planetary gearset has, in particular, a sun wheel, an annulus, at least one planet wheel meshing with the sun wheel and with the annulus, and a planet carrier THAT supports the at least one planet wheel in a rotatable manner. The transmission ratio of the planetary gearset can be modified, in particular, by braking and/or rotationally coupling one of the functional elements of the planetary gearset with respect to another functional element and/or with respect to a fixed component, e.g. a housing, or canceling said braking and/or coupling. By way of example, the speed-transforming gear has a first wheel, in particular gearwheel or belt pulley, connected for conjoint rotation to an electric motor shaft of the electric machine, and a second wheel, in particular gearwheel or belt pulley, which is connected for conjoint rotation to the intermediate shaft, wherein the first wheel and the second wheel have different effective diameters in order to provide a desired transmission ratio. By using a spur wheel gear as a speed-transforming gear, a fixed transmission ratio can be specified with a small installation space requirement. However, it is also possible to provide a variable transmission ratio for the speed-transforming gear, e.g. with the aid of a continuously variable flexible transmission (CVT). The electric machine can be in permanent mesh and connected to the intermediate shaft via the speed-transforming gear. 
     The electric machine can be coupled to at least one auxiliary unit via an auxiliary shaft, which is spaced apart radially from the engine shaft and can be coupled to the intermediate shaft, wherein, in particular, the auxiliary shaft is spaced apart radially from the internal combustion engine. This makes it possible to drive auxiliary units, e.g. an oil pump, water pump, air conditioning compressor of an air conditioning system or the like, mechanically, in particular via a belt drive, with the aid of the electric machine even when the internal combustion engine is switched off. In addition, the internal combustion engine can have a torque output, e.g. a belt pulley or chain wheel connected to the engine shaft, in order to drive the auxiliary units mechanically via the same mechanical link as that also used by the auxiliary shaft. In particular, the auxiliary units that can be driven via the auxiliary shaft can be positioned on a side of the internal combustion engine remote from the motor vehicle transmission, while coupling of the electric machine to the engine shaft via the planetary gearset can be provided on the same side as the motor vehicle transmission. The axial spacing between the link to the engine shaft and a link to the auxiliary units made, in particular, via the belt drive can easily be bridged by the auxiliary shaft and the intermediate shaft, preferably to the outside of the internal combustion engine. 
     The electric machine may be positioned at an axial level of the internal combustion engine and spaced apart radially from the internal combustion engine, wherein, in particular, the intermediate shaft and/or the auxiliary shaft is/are positioned between the internal combustion engine and the electric machine in a radial direction. As a result, the electric machine can be positioned adjacent to the internal combustion engine in a radial direction, making it unnecessary to provide axial installation space for the electric machine between the internal combustion engine and the motor vehicle transmission. It is thereby possible to keep the axial installation space requirement for the drive train small, ideally with a neutral effect on length. 
     The planetary gearset may have at least one clutch for changing a transmission ratio, wherein, in particular, a first clutch can brake an annulus of the planetary gearset so that it is fixed against relative rotation, and/or a second clutch can couple the annulus of the planetary gearset for conjoint rotation to the intermediate shaft, wherein the planetary gearset preferably has a sun wheel connected for conjoint rotation to the intermediate shaft. The first clutch and/or the second clutch are, in particular, capable of being power-shifted and/or electronically controlled, thus allowing the transmission ratio to be changed, preferably at least in part continuously, with a slipping clutch in continuous operation. With the first clutch open and the second clutch closed, this enables the planetary gearset to revolve as a block, giving a transmission ratio of 1.0. If the first clutch is closed and the second clutch is opened, a transmission ratio that differs from 1.0 is obtained. If both the first clutch and the second clutch are open, torque transfer between the electric machine and the engine shaft can be interrupted. 
     The engine shaft can be coupled to a motor vehicle transmission via a transmission clutch in order to shift transmission gears, wherein the motor vehicle transmission has at least one transmission input shaft for introducing a torque, one transmission output shaft for outputting a transformed torque, and at least one selector shaft for transmitting the torque from the transmission input shaft to the transmission output shaft, wherein the electric machine can be coupled to the selector shaft, bypassing the transmission input shaft, in order to introduce a torque into the selector shaft, or to the transmission output shaft in order to introduce a torque into the transmission output shaft. In particular, the motor vehicle transmission can be designed as a dual clutch transmission for shifting transmission gears substantially without an interruption in tractive effort. In particular, the transmission clutch is designed as a dual clutch. During purely electric operation of the hybrid motor vehicle, the torque provided by the electric machine can be introduced directly into the motor vehicle transmission without the power first having to flow via the transmission clutch and the transmission input shaft before the torque reaches the motor vehicle transmission. This optimizes the efficiency chain and supplies the conditions for high efficiency. In particular, a transmission clutch for coupling the engine shaft to the at least one transmission input shaft is opened to interrupt a torque input into the transmission input shaft from outside the motor vehicle transmission. The internal combustion engine may be decoupled from the motor vehicle transmission for purely electric operation of the hybrid motor vehicle, and a torque produced by the electric machine is then introduced into the motor vehicle transmission via the selector shaft of the motor vehicle transmission, bypassing the at least one transmission input shaft and the transmission clutch. This makes it possible, in particular, to avoid a drag torque caused by the engine shaft and the transmission clutch in the electric driving mode. 
     In particular, the electric machine can be coupled to the selector shaft or to the transmission output shaft via a spur wheel gear pair, which acts directly on the selector shaft or on the transmission output shaft, and/or via a flexible transmission, which acts directly on the selector shaft or on the transmission output shaft. Intermediate components can thereby be avoided. Particularly if the torque of the electric machine is introduced into the selector shaft, the torque is transmitted only indirectly to the transmission output shaft, optionally via the transmission input shaft, thus making it possible to achieve an additional transmission ratio between the electric machine and the transmission output shaft, depending on the transmission gears selected. 
     The motor vehicle transmission has a first selector shaft, which can be coupled to the electric machine, and a second selector shaft, which is coupled to the output shaft, wherein the torque that can be introduced into the motor vehicle transmission by the electric machine flows to the output shaft both via the first selector shaft and via the second selector shaft. This makes it possible to arrange the transmission output shaft and the intermediate shaft on different sides of the motor vehicle transmission. A radial spacing between the intermediate shaft and the output shaft can be bridged by the selector shafts. 
     The invention is explained by way of example below by means of a preferred embodiment with reference to the attached drawings, wherein the features described below may represent one aspect of the invention either individually or in combination. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic diagram of a drive train for a hybrid motor vehicle. 
     
    
    
     DETAILED DESCRIPTION 
     The drive train  10  shown in  FIG. 1  for a hybrid motor vehicle has an internal combustion engine  12 , which can be coupled to a motor vehicle transmission  16  by means of a transmission clutch  14  designed as a dual clutch. The transmission clutch  14  has a first component clutch C 1  for coupling an engine shaft  18  of the internal combustion engine  12  to a first transmission input shaft  20  designed as a solid shaft, and a second component clutch C 2  for coupling the engine shaft  18  to a second transmission input shaft designed as a hollow shaft. Within the motor vehicle transmission  16 , the transmission input shafts  20 ,  22  mesh with a first selector shaft  24  for transmission gears  3 ,  4 ,  7  and  8  and with a second selector shaft  26  for transmission gears  1 ,  2 ,  5  and  6  via shiftable transmission stages. The second selector shaft  26  meshes via an output gearwheel Ko 1  with an input gearwheel K of a transmission output shaft  28 , which is coupled by a differential  29  to driven wheels (not shown) of the hybrid motor vehicle, in order to move the hybrid motor vehicle. 
     With the aid of an electric machine  30 , the internal combustion engine  12  can be started. For this purpose, the engine shaft  18  of the internal combustion engine  12  has a belt pulley or a chain wheel  32 , which is coupled to a planet carrier  36  of a planetary gearset  38  by a first belt drive or chain drive  34 . The planet carrier  36  supports planet wheels  40 , which mesh with a sun wheel  42  and an annulus  44 . The sun wheel  42  is connected to an intermediate shaft  46 , with the aid of which the electric machine is connected via a transmission gear  48  at an axial distance from the planetary gearset  38 . The planetary gearset  38  has a first clutch K 1 , with the aid of which the annulus  44  can be held in a manner fixed relative to the housing, giving a transmission ratio that differs from 1.0 for cold-starting the internal combustion engine, for example, making it possible to modify the speed of the intermediate shaft  46  and to increase the corresponding torque on the engine shaft  18 . With the aid of a second clutch K 2 , the annulus  44  can be connected for conjoint rotation to the intermediate shaft, resulting in a transmission ratio via the planetary gearset of 1.0 for warm-starting the internal combustion engine  12 , for example, when the first clutch K 1  is open. 
     Connected to the intermediate shaft  46  for conjoint rotation, in particular integrally, is a coaxial auxiliary shaft  50 . With the aid of the auxiliary shaft  50 , auxiliary units, in particular an air-conditioning compressor  54  of a motor vehicle air-conditioning system or a water pump  56 , can be driven via a second belt drive  52  by means of the electric machine  30  when the internal combustion engine  12  is switched off. Also provided is an oil pump  58 , which is connected to the engine shaft  18  in the embodiment shown and, alternatively, can be driven via the second belt drive  52 . 
     For purely electric operation of the hybrid motor vehicle, a drive shaft  60  coaxial with the intermediate shaft  46  can be coupled for conjoint rotation to the intermediate shaft  46  with the aid of a third clutch K 3 . Via the drive shaft  60 , the torque of the electric machine  30  can be introduced directly into the motor vehicle transmission  16 , bypassing the transmission clutch  14  and the transmission input shafts  20 ,  22  and, in the case where both the first clutch K 1  and the second clutch K 2  are open, also bypassing the planetary gearset  38  and the engine shaft  18 . For this purpose, the drive shaft  60  extending outside the motor vehicle transmission  16  can mesh with a driving gearwheel Ko 2  of the first selector shaft  24 . The torque introduced into the first selector shaft  24  is passed via a connection  62  to the transmission output shaft  28 , which can be provided on the opposite side of the motor vehicle transmission  16  from the drive shaft  60  if the transmission output shaft  28  is arranged between the two selector shafts  24 ,  26 . 
     For cold-starting the internal combustion engine  12 , the first clutch K 1  can be closed, while the second clutch K 2  and the third clutch K 3  are open, allowing a cold start with a high torque requirement to be performed by virtue of the additional transmission ratio of the planetary gearset  38  and, at the same time, allowing the auxiliary units  54 ,  56  to be driven. After the internal combustion engine  12  has been started, the electric machine  30  can be operated as a motor in this position of the clutches K 1 , K 2 , K 3  in order to perform a boost and/or assist function by means of the additional power input, it being possible for an additional transmission ratio to be provided by the planetary gearset  38 . The electric machine  30  can also be operated as a generator, allowing some of the power of the internal combustion engine  12  to be fed into the electric machine  30 , e.g. to charge a motor vehicle battery, wherein an additional transmission ratio is provided by the planetary gearset  38 . In this case, the auxiliary units  54 ,  56  are driven by the internal combustion engine  12  via the intermediate shaft  46  and the auxiliary shaft  50 . 
     When the first clutch K 1  and the third clutch K 3  are open, while the second clutch K 2  is closed, a transmission ratio of 1.0 is obtained in the planetary gearset  38 , allowing the internal combustion engine  12  to be started while warm, in particular. After the internal combustion engine  12  has been started, the electric machine  30  can be operated as a motor in this position of the clutches K 1 , K 2 , K 3  in order to perform a boost and/or assist function by means of the additional power input, with no additional transmission ratio being provided by the planetary gearset  38  in this case. The electric machine  30  can also be operated as a generator, allowing some of the power of the internal combustion engine  12  to be fed into the electric machine  30 , with no additional transmission ratio being provided by the planetary gearset  38  in this case. In this case, the auxiliary units  54 ,  56  are driven by the internal combustion engine  12  via the intermediate shaft  46  and the auxiliary shaft  50 . 
     For purely electric operation, the first clutch K 1  and the second clutch K 2  are open, while the third clutch K 3  is closed. In purely electric operation, the internal combustion engine  12  is switched off and can be started in a simple manner during electric operation by closing the first clutch K 1  or the second clutch K 2 . During this process, the third clutch K 3  can remain closed until the internal combustion engine  12  has been started and/or the transmission clutch  14  is to be closed. When the first clutch K 1 , the second clutch K 2  and the third clutch K 3  are open, power flow from the electric machine  30  to the engine shaft  18  and to the motor vehicle transmission  16  is interrupted, allowing the auxiliary units  54 ,  56  to be driven by the electric machine  30 , even when the internal combustion engine  12  is switched off. 
     Thus, the auxiliary units  54 ,  56  can be operated independently of the speed of the engine. At low speeds, the auxiliary units can thus turn more quickly and, at high speeds, more slowly than the engine. This can have positive ramifications for the design of the auxiliary units and/or the efficiency thereof. Moreover, a recovery mode is possible by passing the power flow from a wheel of the hybrid motor vehicle to the electric machine  30  via the transmission output shaft  28 , bypassing the transmission  16 .