Abstract:
The present invention relates to a hybrid vehicle powertrain ( 1 ). The powertrain ( 1 ) includes an internal combustion engine ( 3 ), an electric traction motor ( 5 ) and a transmission ( 7 ). A first flexible coupling ( 55 ) drivingly connects the internal combustion engine ( 3 ) to the transmission ( 7 ). A second flexible coupling ( 65 ) drivingly connects the electric traction motor ( 5 ) to the transmission ( 7 ). The present invention also relates to a dual coupling including first and second flexible couplings ( 55, 65 ). Furthermore, the present invention relates to a vehicle incorporating a powertrain ( 1 ).

Description:
TECHNICAL FIELD The present invention relates to a hybrid vehicle powertrain. Aspects of the invention relate to a powertrain, to a coupling and to a motor vehicle. 
     BACKGROUND OF THE INVENTION 
       [0001]    It is known to provide a hybrid vehicle with an internal combustion engine for operation in conjunction with an electric traction motor. The internal combustion engine and the electric traction motor can operate independently of each other or together to increase the maximum torque output. One approach is to develop an integrated transmission in which the electric traction motor is incorporated into the transmission. However, a particular integrated transmission may not be suitable for all applications, requiring the development of an alternate transmission. It would be desirable, at least from a commercial perspective, to retain the option of using a conventional transmission (i.e. one which does not incorporate an integrated electric traction motor) in combination with a hybrid powerpack. This approach may prove problematic as conventional electric traction motors can be susceptible to damage when exposed to axial loading. A conventional transmission may, for example, generate axial loads due to changes in the fluid pressure within a torque converter at different operating speeds; or due to the front to back movement of an engine crank. 
         [0002]    It is against this background that the present invention has been conceived. At least in certain embodiments, the present invention seeks to ameliorate or overcome at least some of the problems associated with known systems. 
       SUMMARY OF THE INVENTION 
       [0003]    Aspects of the present invention relate to a hybrid vehicle powertrain; a coupling; and a motor vehicle. 
         [0004]    According to a first aspect of the present invention there is provided a hybrid vehicle powertrain comprising:
       an internal combustion engine;   an electric traction motor; and   a transmission;   wherein a first flexible coupling drivingly connects the internal combustion engine to the transmission; and a second flexible coupling drivingly connects the electric traction motor to the transmission. The first and second flexible couplings are both connected to a common input of said transmission. The first and second flexible couplings are arranged to provide driving connections (i.e. to deliver torque) from the internal combustion engine and the electric traction motor respectively to the transmission. The first and second flexible couplings are arranged to accommodate relative axial movement to reduce or inhibit the transferral of axial loads from the transmission to the internal combustion engine and/or the electric traction motor. The first flexible coupling and/or the second flexible coupling can thereby help to protect the electric traction motor from damage resulting from axial loads. At least in certain embodiments, the first and second flexible couplings can facilitate coupling of a hybrid vehicle powertrain to a conventional transmission. The first flexible coupling and/or the second flexible coupling can be resilient. The arrangement of the first and second flexible couplings can, at least in certain embodiments, manage axial load balance between multiple input devices.       
 
         [0009]    The electric traction motor can typically withstand a lower axial loading than the internal combustion engine. The transferral of axial loads to the electric traction motor can be reduced by configuring the second flexible coupling to be more flexible than the first flexible coupling. In other words, the first flexible coupling can be stiffer than the second flexible coupling. In certain variants, this arrangement can be reversed such that the first flexible coupling is more flexible than the second flexible coupling. 
         [0010]    The first and second flexible couplings can couple the internal combustion engine and the electric traction motor to a transmission input, such as a clutch plate or a torque converter. The first and second flexible couplings can both be connected to the transmission input. The clutch plate or the torque converter can be integrated into the transmission in conventional manner. For example, the clutch pate or the torque converter can be disposed within a transmission housing (which can be referred to as a bell housing). 
         [0011]    The first flexible coupling can comprise a first flex plate. The second flexible coupling can comprise a second flex plate. The first and second flex plates can have a generally circular plan form, but this may vary for different designs. For example, the first and/or second flex plates can have a multi-lobe configuration. One or more holes can be provided in the first and/or second flex plates to reduce mass. 
         [0012]    A drive shaft can be provided for outputting torque from the internal combustion engine to the transmission. The first flexible coupling can be connected to the drive shaft of the internal combustion engine. 
         [0013]    The electric traction motor can comprise a rotor and a stator. The electric traction motor can comprise an output drive for outputting torque from the electric traction motor to the transmission. The second flexible coupling can be fixedly mounted to the output drive. The output drive can comprise an output shaft. The output shaft and the drive shaft of the internal combustion engine could, for example, be arranged concentrically. Alternatively, the rotor can form the output drive of the electric traction motor. At least in certain embodiments, the second flexible coupling can be fixedly mounted to the rotor. 
         [0014]    The drive shaft and the output drive can be arranged coaxially so as to rotate about a common axis. The first and second flexible couplings can be arranged, in use, also to rotate about said common axis. An offset can be maintained between the first and second flexible couplings along said common axis. The first and second couplings can be arranged substantially parallel to each other. The first and second flexible couplings can be connected to each other, for example at or proximal to their radially outer edge. The first and second flexible couplings can be connected to the transmission input by one or more mechanical fasteners, such as threaded bolts. The first and second flexible couplings can be joined to each other by said one or more mechanical fasteners. Alternatively, the first and/or second flexible couplings could be integral with said transmission input. 
         [0015]    The electric traction motor can have an annular configuration in transverse cross-section which defines a central aperture through which the drive shaft extends. 
         [0016]    A clutch can be provided for selectively engaging/disengaging the drive shaft. The clutch can be a push or pull type clutch. An operating mechanism can be provided for actuating the clutch. The operating mechanism can be disposed radially outwardly of the drive shaft, for example at least partially within the central aperture of said electric traction motor (between the drive shaft and the electric traction motor). The operating mechanism can comprise a hydraulic chamber for operating an actuator. The hydraulic chamber can be annular in transverse section. A longitudinal axis of the hydraulic chamber could be arranged coaxial with a longitudinal axis of the drive shaft. The hydraulic chamber can, for example, be disposed around the drive shaft. The actuator can comprise a cylindrical member extending around the drive shaft for engaging a clutch plate. 
         [0017]    The electric traction motor could be a radial flux traction motor. Alternatively, the electric traction motor can be an axial flux traction motor. The axial flux traction motor can provide a high torque density and can have a relatively small depth. This arrangement is advantageous as the reduced length of the internal combustion engine and the transmission can permit either longitudinal (North/South) or transverse (East/West) powertrain configurations. At least in certain embodiments, the axial flux traction motor can be incorporated into the casing of the internal combustion engine. 
         [0018]    In certain variants, the powertrain may comprise a third flexible coupling, such as a third flex plate. The third flexible coupling could be arranged to couple a second electric traction motor to the transmission. The second electric traction motor could, for example, be a generator operable to output a tractive force. 
         [0019]    According to a further aspect of the present invention there is provided a hybrid vehicle powertrain comprising:
       a first power generator;   a second power generator; and   a transmission;   wherein a first flexible coupling drivingly connects the first power generator to the transmission; and   a second flexible coupling drivingly connects the second power generator to the transmission,   wherein the first and second flexible couplings are both connected to a common input of said transmission.       
 
         [0026]    According to a still further aspect of the present invention there is provided a dual coupling for connecting first and second power generators to a transmission; the dual coupling comprising:
       a first flexible coupling for drivingly connecting the first power generator to the transmission; and   a second flexible coupling for drivingly connecting the second power generator to the transmission. The first and second flexible couplings are both connected to a common input of said transmission. The first power generator can be an internal combustion engine. The second power generator can be an electric traction motor. The first and second power generators can form a hybrid powertrain. The dual coupling can connect the first and second power generators to a single transmission. For example, the dual coupling can connect the first and second power generators to a clutch plate or a torque converter. The torque converter can be provided within the transmission, for example as an integrated component.       
 
         [0029]    The first flexible coupling can comprise a first flex plate. The second flexible coupling can comprise a second flex plate. The first and second flexible couplings can be arranged coaxially. The first and second flexible couplings can be axially offset from each other. 
         [0030]    In an alternate arrangement, the first and second power generators could both be electric motors. For example, an electric generator could be configured selectively to operate as a traction motor to supplement a dedicated traction motor. One of said first and second power generators could equally be a mechanical power generator, such as a flywheel. 
         [0031]    A further aspect of the present invention relates to a vehicle powertrain incorporating a dual coupling of the type described herein. 
         [0032]    The term powertrain used herein refers to the vehicle powerpack and transmission. The powerpack is made up of one or more machines operable to output torque to provide a tractive force for propelling the vehicle. The powerpack can be a hybrid arrangement, for example comprising an internal combustion engine and one or more electric traction motors. 
         [0033]    Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying Figures, in which: 
           [0035]      FIG. 1  shows a schematic cross-sectional view of a hybrid vehicle powertrain in accordance with an embodiment of the present invention; 
           [0036]      FIG. 2  shows an enlarged view of the clutch arrangement for coupling the internal combustion engine to an input shaft; and 
           [0037]      FIG. 3  shows an enlarged view of the coupling to the torque converter shown in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION  
       [0038]    A hybrid powertrain  1  for a motor vehicle (not shown) in accordance with an embodiment of the present invention will now be described with reference to  FIGS. 1 ,  2  and  3 . The powertrain  1  comprises an internal combustion engine  3  (only shown schematically) and an electric machine  5 . As shown in  FIG. 1 , the internal combustion engine  3  and the electric machine  5  are coupled to a transmission  7  having an integrated torque converter  9 . The transmission  7  in the present embodiment is an automatic transmission, but it could equally be a manual transmission. 
         [0039]    The electric machine  5  is a traction motor for providing a tractive force to propel the vehicle. The electric machine  5  comprises a first casing  10  disposed between the internal combustion engine  3  and the transmission  7 . The internal combustion engine  3  comprises a second (engine) casing  11  and, in the present embodiment, the first casing  10  is mounted to the second casing  11 . It will be appreciated that the first and second casings  10 ,  11  could be integrated into a single casing. 
         [0040]    The internal combustion engine  3  is of conventional design and comprises a crankshaft  13  for outputting torque. An input shaft  15  is coupled to the crankshaft  13  to deliver an input torque to the transmission  7 . A flywheel  17  is fixedly mounted to the crankshaft  13 . A clutch disc  19  is fixedly mounted to the input shaft  15  and a clutch  21  is provided selectively to couple the crankshaft  13  to the input shaft  15 . The input shaft  15  is rotatably mounted on first and second shaft bearings  23 ,  25 . 
         [0041]    The clutch  21  in the present embodiment is a hydraulic pull type clutch. As shown most clearly in  FIG. 2 , the clutch  21  comprises a pressure plate  27 , an annular friction pad  29 , and a pull-release mechanism  31 . The pressure plate  27  forms a flexible coupling diaphragm arranged to apply a spring pressure to engage the friction pad  29 . The pull-release mechanism  31  comprises a piston  33 , a hydraulic chamber  35  and a clutch actuator  37 . The piston  33  is operable to control the axial movement of the clutch actuator  37 , thereby controlling engagement of the pressure plate  27 . A control valve arrangement (not shown) is provided for controlling the hydraulic fluid pressure within the hydraulic chamber  35  to control operation of the piston  33 . In the present arrangement, an increase in the fluid pressure within the hydraulic chamber  35  advances the piston  33  (travelling from left to right in the illustrated arrangement). A return spring (not shown) is disposed within the hydraulic chamber  35  to bias the piston  33  towards a retracted position (travelling from right to left in the illustrated arrangement). 
         [0042]    The first shaft bearing  23  is disposed in a cylindrical cupped recess  39  (referred to as the crank palm) formed in an end of the crankshaft  13 . The second shaft bearing  25  is mounted in an input shaft support  40  in the form of a tubular extension formed integrally with the first casing  10  of the electric machine  5 . The pull-release mechanism  31  is disposed within the input shaft support  40  and arranged concentrically around the input shaft  15 . The hydraulic chamber  35  is formed between the piston  33  and an inside wall of the input shaft support  40 . First and second circular seals  41 ,  43  are provided between the piston  33  and the inside wall of the input shaft support  40  to seal the hydraulic chamber  35 . 
         [0043]    The clutch actuator  37  comprises a cylindrical member  45  disposed concentrically around the input shaft  15 . A first collar  47  is provided at a first end of the cylindrical member  45  for engaging the pressure plate  27 ; and a second collar  48  is provided at a second end of the cylindrical member  45  for engaging the piston  33 . A clutch release bearing  49  is disposed between the piston  33  and the second collar  48  to accommodate rotational movement of the clutch actuator  37  with the input shaft  15 . The cylindrical member  45  is movable axially relative to the input shaft  15  to operate the clutch  21 . 
         [0044]    The input shaft  15  is coupled to the torque converter  9  which is integrated into the transmission  7 . Specifically, the torque converter  9  is disposed within a transmission housing  50  (also referred to as a bell housing). As shown in  FIG. 3 , a first flex plate  55  forms a driving coupling between the input shaft  15  and the torque converter  9 . The first flex plate  55  is a flexible coupling member configured to transmit torque to the torque converter  9  whilst permitting relative axial movement. The first flex plate  55  can thereby inhibit the transmission of axial loads between the internal combustion engine  3  and the transmission  7 . 
         [0045]    The electric machine  5  is disposed in a chamber  51  formed in the first casing  10 . The chamber  51  comprises a cylindrical outer sidewall  53  arranged concentrically with the input shaft support  40 . Thus, the chamber  51  has a generally toroidal shape. In the present embodiment the electric machine  5  is an axial flux traction motor. This type of electric machine  5  is suited for hybrid vehicles as it can provide a high torque density. Moreover, an axial flux traction motor can be configured with a relatively small axial length which enables the electric machine  5  to be disposed within the chamber  51  formed in the first casing  10 . Thus, the electric machine  5  can be packaged between the internal combustion engine  3  and the transmission  7 . This configuration is particularly advantageous as it enables a conventional (non-hybrid) transmission (i.e. a transmission without an integrated electric traction motor) to be utilised. 
         [0046]    The electric machine  5  comprises a fixed stator  59  and a rotor  61 . The stator  59  is fixedly mounted to the sidewall  53  of the first casing  10 . A bearing  63  is mounted to the stator  59  to accommodate rotational movement of the rotor  61  relative to the stator  59 . The rotor  61  provides a drive output from the electric machine  5 . A second flex plate  65  is fixedly mounted to the rotor  61  and connects the electric machine  5  to the torque converter  9 . The second flex plate  65  is a flexible coupling member which enables the transmission of torque to the torque converter  9  whilst permitting relative axial movement between the electric machine  5  and the torque converter  9 . In the present embodiment the second flex plate  65  is less stiff than the first flex plate  55  to reduce the transmission of axial loads to the rotor  61 . This arrangement is desirable as the electric machine  5  is more susceptible to damage from axial loading that the internal combustion engine  3 . 
         [0047]    The first and second flex plates  55 ,  65  are coupled to the torque converter  9  by a series of mechanical fasteners  67  (such as threaded bolts) disposed about their respective circumferences. It will be appreciated, therefore, that the first and second flex plates  55 ,  65  remain connected to the torque converter  9 . However, by controlling the operation of the electric machine  5  and/or the clutch  21 , the internal combustion engine  3  and the electric machine  5  can operate independently of each other or in combination. The electric machine  5  can be de-energised to allow the internal combustion engine  3  to deliver all of the output torque to the transmission  7  (via the first flex plate  55 ). When the electric machine  5  is de-energised, the internal combustion engine  3  rotates the rotor  61  with the input shaft  15 . Conversely, the clutch  21  can be dis-engaged to de-couple the input shaft  15  from the crankshaft  13 , thereby allowing the electric machine  5  to deliver all of the output torque to the transmission  7  (via the second flex plate  65 ). When the clutch  21  is disengaged, the electric machine  5  rotates the input shaft  15  and the clutch disc  19  without rotating the crankshaft  13 . At least in certain applications, the internal combustion engine  3  and the electric machine  5  can operate together to deliver torque to the transmission  7  simultaneously via the first and second flex plates  55 ,  65 . 
         [0048]    The operation of the vehicle powertrain will now be described with reference to  FIGS. 1 and 2 . The crankshaft  13  is driven by the internal combustion engine  3  in conventional manner. The clutch  21  is operated by the pull-release mechanism  31  selectively to engage/disengage the crankshaft  13 . The piston  33  is spring-biased towards an engaged position in which the pressure plate  27  biases the friction pad  29  against the clutch disc  19 , thereby engaging the clutch  21  and coupling the crankshaft  13  to the input shaft  15 . The clutch  21  is engaged to transfer torque from the internal combustion engine  3  to the transmission  7  via the input shaft  15 . To disengage the clutch  21 , the hydraulic fluid pressure within the hydraulic chamber  35  is increased to advance the piston  33 . The cylindrical actuator  45  is thereby displaced and applies an axial (pulling) force to the pressure plate  27 , thereby disengaging the clutch  21  and de-coupling the crankshaft  13  to the input shaft  15 . In use, the clutch  21  can be disengaged to enable the electric machine  5  to operate independently of the internal combustion engine  3 . By de-coupling the input shaft  15  from the crankshaft  13 , the internal combustion engine  3  can be switched off to permit operation in a full electric mode whereby the electric machine  5  exclusively provides a tractive force to propel the vehicle. 
         [0049]    The input shaft  15  is coupled to the torque converter  9  by the first flex plate  55 . The first flex plate  55  transfers torque to the torque converter  9  whilst accommodating relative movement between the input shaft  15  and the torque converter  9 . The electric machine  5  is disposed concentrically around the input shaft  15 . The electric machine  5  is connected to the torque converter  9  by a second flex plate  65 . Again, the second flex plate  65  is a flexible coupling member which enables the delivery of torque from the electric machine  5  to the torque converter  9  whilst accommodating axial movement. In the present embodiment, the second flex plate  65  is a more flexible coupling than the first flex plate  55  to reduce the application of axial loading to the rotor  61  of the electric machine  5 . 
         [0050]    At least in certain embodiments, the combined length of the internal combustion engine  3 , the electric traction motor  5  and the transmission  7  is reduced, thereby increasing the range of applications in which the vehicle powertrain can be implemented. The vehicle powertrain can be configured such that the internal combustion engine  3  and the transmission  7  are arranged transversely (East-West) or longitudinally (North-South) within a vehicle. 
         [0051]    The present embodiment has been directed to an electric machine  5  in the form of an axial flux traction motor. However, at least certain aspects of the present invention can be applied more broadly, for example to radial flux traction motors. The present invention has been described with reference to a single electric traction motor, but it will be appreciated that more than one electric traction motor could be coupled to the transmission  7  via the second flex plate  65 . The electric traction motors could, for example, be disposed within the first casing  10  around the input shaft  15 . 
         [0052]    It will be appreciated that various changes and modifications can be made to the powertrain described herein. For example, the invention has been described with reference to a hybrid vehicle powertrain, but the first and second flex plates  55 ,  65  could be employed for connecting two power generators of the same type (for example two electric traction motors) to the transmission  7 . Moreover, more than two of said flex plates  55 ,  65  could be provided for certain applications. Further aspects of the present invention are outlined in the following numbered paragraphs. 
         [0053]    1. A hybrid vehicle powertrain comprising:
       an internal combustion engine;   an electric traction motor; and   a transmission;   wherein a first flexible coupling drivingly connects the internal combustion engine to the transmission; and   a second flexible coupling drivingly connects the electric traction motor to the transmission   wherein the first and second flexible couplings are both connected to a common input of said transmission.       
 
         [0060]    2. A hybrid vehicle powertrain as described in paragraph 1, wherein the first flexible coupling is less flexible than the second flexible coupling. 
         [0061]    3. A hybrid vehicle powertrain as described in paragraph 1, wherein the first flexible coupling comprises a first flex plate; and the second flexible coupling comprises a second flex plate. 
         [0062]    4. A hybrid vehicle powertrain as described in paragraph 1, wherein said common input is connected to a torque converter. 
         [0063]    5. A hybrid vehicle powertrain as described in paragraph 1, wherein the first flexible coupling is connected to a drive shaft of the internal combustion engine; and a clutch is provided for selectively engaging/disengaging the drive shaft. 
         [0064]    6. A hybrid vehicle powertrain as described in paragraph 5, wherein the clutch comprises an operating mechanism arranged coaxially with the drive shaft of the internal combustion engine. 
         [0065]    7. A hybrid vehicle powertrain as described in paragraph 6, wherein the electric traction motor is disposed radially outwardly of the operating mechanism. 
         [0066]    8. A hybrid vehicle powertrain as described in paragraph 5, wherein the clutch is a pull-release clutch. 
         [0067]    9. A hybrid vehicle powertrain as described in paragraph 1, wherein the electric traction motor comprises a rotor and the second flexible coupling is fixedly mounted to said rotor. 
         [0068]    10. A hybrid vehicle powertrain as described in paragraph 1, wherein the electric traction motor is an axial flux traction motor. 
         [0069]    11. A vehicle comprising a hybrid vehicle powertrain as described in paragraph 1. 
         [0070]    12. A dual coupling for connecting first and second power generators to a transmission; the dual coupling comprising:
       a first flexible coupling for drivingly connecting the first power generator to the transmission; and   a second flexible coupling for drivingly connecting the second power generator to the transmission   wherein the first and second flexible couplings are both connected to a common input of said transmission.       
 
         [0074]    13. A dual coupling as described in paragraph 12, wherein the first flexible coupling comprises a first flex plate and the second flexible coupling comprises a second flex plate. 
         [0075]    14. A dual coupling as described in paragraph 12, wherein the first power generator is an internal combustion engine; and the second power generator is an electric traction motor. 
         [0076]    15. A vehicle powertrain comprising a dual coupling as described in paragraph 12.