Abstract:
An automated twin-clutch multi-speed transmission is disclosed which functions to transfer power from the engine to one or more drivelines of a motor vehicle. The transmission includes a first engine clutch operable to establish a releasable drive connection between the engine and a first input shaft, a first motor/generator connected to the first input shaft, a second engine clutch operable to establish a releasable drive connection between the engine and a second input shaft, a second motor/generator connected to the second input shaft, an output shaft adapted to transfer power to the driveline, and a geartrain for selectively establishing a plurality of forward and reverse speed ratio drive connections between the input shafts and the output shaft. The transmission further includes power-operated dog clutches for selectively engaging constant-mesh gearsets associated with the geartrain, and a transmission controller for controlling coordinated actuation of the first and second engine clutches, the first and second motor/generators, and the power-operated dog clutches to permit non-power interrupted (“powershift”) sequential gear changes automatically without input from the vehicle operator. The motor/generators are used to establish speed synchronization during the gear change process.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to transmissions for use in motor vehicles and, more particularly, to a twin-clutch automated transmission applicable for use in rear-wheel drive vehicles.  
         BACKGROUND OF THE INVENTION  
         [0002]    Automobile manufacturers continuously strive to improve fuel efficiency. This effort to improve fuel efficiency, however, is typically offset by the need to provide enhanced comfort and convenience to the vehicle operator. For example, it is well known that manual transmissions are more fuel efficient than automatic transmissions, yet a majority of all passenger vehicles are equipped with automatic transmissions due to the increased convenience they provide.  
           [0003]    More recently, “automated” variants of conventional manual transmissions have been developed which shift automatically without any input from the vehicle operator. Such automated transmissions typically include a plurality of power-operated actuators that are controlled by a transmission controller to shift traditional synchronized dog clutches. However, such automated transmissions have the disadvantage that there is a power interruption in the drive connection between the input shaft and the output shaft during sequential gear shifting. Power interrupted shifting results in a harsh shift feel which is generally considered to be unacceptable when compared to smooth shift feel associated with most automatic transmissions. To overcome this problem, automated twin-clutch transmissions have been developed which can be powershifted to permit gearshifts to be made under load. Examples of such automated manual transmissions are shown in U.S. Pat. Nos. 5,966,989 and 5,890,392. While such powershift twin-clutch transmissions overcome several drawbacks associated with conventional single-clutch automated transmissions, a need exists to develop simpler and more robust transmissions which advance the automotive transmission technology.  
         SUMMARY OF THE INVENTION  
         [0004]    Accordingly, it is an object of the present invention to provide a dual-countershaft twin-clutch transmission and a control system for permitting automatic shifting of transmission.  
           [0005]    As a related object, the twin-clutch automated transmission of the present invention has a compact geartrain and is applicable for use in rear-wheel drive vehicles.  
           [0006]    These and other objects of the present invention are met by providing an automated dual-countershaft twin-clutch multi-speed transmission adapted to transfer power from the engine to a driveline of a motor vehicle. The transmission includes a first master clutch operable to establish a releasable drive connection between the input shaft and a first countershaft, a first motor/generator connected to the first countershaft, a second master clutch operable to establish a releasable drive connection between the input shaft and a second countershaft, a second motor/generator connected to the second countershaft, an output shaft adapted to transfer power to the driveline, and a geartrain for selectively establishing a plurality of forward and reverse speed ratio drive connections between the countershafts and the output shaft. The transmission further includes power-operated dog clutches for selectively engaging constant-mesh gearsets associated with the geartrain, and a transmission controller for controlling coordinated actuation of the first and second master clutches, the first and second motor/generator, and the power-operated dog clutches to permit non-power interrupted (“powershift”) sequential gear changes automatically without input from the vehicle operator. When shifting under power between gear ratios, one master clutch is released and the corresponding motor/generator is actuated to accelerate/decelerate the released countershaft into speed synchronization with the output shaft. Following completion of speed synchronization, the dog clutch for the selected gearset on the released countershaft is actuated and thereafter the released master clutch is re-engaged.  
           [0007]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the scope of this invention will become apparent to those skilled in the art.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a schematic view of a dual-countershaft twin-clutch automated transmission according to the principles of the present invention; and  
         [0009]    [0009]FIG. 2 is a diagrammatical illustration of the transmission control system adapted for use with the twin-clutch automated transmission shown in FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0010]    With reference to FIGS. 1 and 2 of the accompanying drawings, a twin-clutch automated transmission  10  will now be described. Transmission  10  is driven by the output of an engine  12  and generally includes a flywheel damper unit  14 , an input shaft  16 , a first master clutch  18 , a second master clutch  20 , a first countershaft  22 , a second countershaft  24 , a geartrain  26 , an output shaft  28 , and a shift control system  30 .  
         [0011]    First master clutch  18  is a power-operated spring-apply plate-type clutch which is normally operable in its engaged state to establish a drive connection between input shaft  16  and first countershaft  22 . Likewise, second master clutch  20  is a power-operated spring-apply plate-type clutch normally operable in its engaged state to establish a drive connection between input shaft  16  and second countershaft  24 . First master clutch  18  includes a clutch drum  32 , a hub  34  fixed to first countershaft  22 , a clutch pack  36  disposed between drum  32  and hub  34 , a spring-biased apply plate  38  acting on clutch pack  36 , and an actuator  40  for selectively releasing apply plate  38  from engagement with clutch pack  36 . Preferably, actuator  40  is an electrically-actuated device, such as an electromagnectic solenoid, that controls the position of apply plate  38 , and thus the magnitude of engagement of first master clutch  18 , in response to electric power being provided thereto.  
         [0012]    Second master clutch  20  includes a clutch drum  42 , a hub  44  fixed to second countershaft  24 , a clutch pack  46  disposed between drum  42  and hub  44 , a spring-biased apply plate  48  acting on clutch pack  46 , and an actuator  50  for selectively releasing apply plate  48  from engagement with clutch pack  46 . Actuator  50  is an electrically-actuated device that controls the position of apply plate  48 , and thus the magnitude of engagement of second master clutch  20 , in response to the electric power provided thereto. As will be detailed, shift control system  30  is operable to control actuators  40  and  50  and, in turn, the engagement and release of master clutches  18  and  20 .  
         [0013]    Geartrain  26  includes a headset  52  for transferring drive torque from input shaft  16  to master clutches  18  and  20 . In particular, headset  52  includes a first transfer gear  54  rotatably supported on first countershaft  22 , a second transfer gear  56  rotatably supported on second countershaft  24 , and an input gear  58  fixed for rotation with input shaft  16  which is in meshed engagement with first transfer gear  54  and second transfer gear  56 . As seen, first transfer gear  54  is fixed to clutch drum  32  for delivering engine power to first engine clutch  18  while second transfer gear  56  is fixed to clutch drum  42  for delivering engine power to second engine clutch  20 . Gearset  26  also includes a first set of speed gears rotatably supported on first countershaft  22  and a second set of speed gears rotatably supported on second countershaft  24 , both of which are in constant mesh with a set of output gears fixed to output shaft  28 . The first set of speed gears include a first speed gear  60  which is meshed with a first output gear  62 , a third speed gear  64  which is meshed with a second output gear  66 , and a fifth speed gear  68  which is meshed with a third output gear  70 . Similarly, the second set of speed gears includes a second speed gear  72  which is meshed with first output gear  62 , a fourth speed gear  74  which is meshed with second output gear  66 , and a sixth speed gear  76  which is meshed with third output gear  70 . Geartrain  22  also includes a reverse gearset having a reverse input gear  78  rotatably supported on second countershaft  24 , a reverse output gear  80  fixed to output shaft  28 , and a reverse idler gear (not shown) meshed with reverse input gear  78  and reverse output gear  80 .  
         [0014]    Shift control system  30  includes a plurality of power-operated shift clutches which are operable for selectively coupling a selected speed gear to its corresponding countershaft for establishing six forward and one reverse speed ratio drive connections with output shaft  28 . Preferably, these shift clutches are electrically-actuated dog clutches. In particular, a first dog clutch  82  is operable for selectively coupling/releasing first speed gear  60  and third speed gear  64  to/from first countershaft  22 , a second dog clutch  84  is operable for selectively coupling/releasing second speed gear  72  and fourth speed gear  74  to/from second countershaft  24 , and a third dog clutch  86  operable for selectively coupling/releasing fifth speed gear  68  to first countershaft  22 . Shift control system  30  also include a fourth dog clutch  88  that is operable for selectively coupling/releasing sixth speed gear  76  to/from second countershaft  24 , and a fifth dog clutch  90  operable for selectively coupling/releasing reverse input gear  78  to/from second countershaft  24 . Each dog clutch includes a sliding sleeve (denoted by the suffix “A”) which is splined for rotation with and axial movement on a clutch hub which, in turn, is fixed to a corresponding one of countershafts  22  and  24 . As is conventional, axial movement of the sliding sleeves from the neutral uncoupled positions shown results in clutched engagement with the adjacent speed gear. Preferably, each dog clutch is of the electromagnetic type having a coil (denoted by suffix “B”) adjacent to and facing a radial armature plate segment of each sliding sleeve. Electrical power delivered to the electromagnetic coils causes controlled axial movement of the shift sleeves. Since first clutch  82  and second clutch  84  are of the double-acting variety, a pair of coils are provided therewith. It is to be understood that any other type of power-operated device capable of moving each sliding sleeve between its uncoupled and coupled positions is within the scope of this invention.  
         [0015]    Shift control system  30  further includes a first motor/generator  100  operably connected to first countershaft  22 , a second motor/generator  102  operably connected to second countershaft  24 , a battery  104 , a transmission controller  106 , and vehicle sensors  108 . First motor/generator  100  includes a fixed stator  100 A and a rotor  100 B that is fixed for rotation with first countershaft  22 . Likewise, second motor/generator  102  includes a fixed stator  102 A and a rotor  102 B that is fixed for rotation with second countershaft  24 . Controller  106  is an electronically-controlled unit capable of receiving data from vehicle sensors  108  and generating electric output signals in response to the sensor signals. Sensors  108  include engine speed  108 A, throttle position  108 B, brake status  108 C, first countershaft speed  108 D, second countershaft speed  108 E, and output shaft speed  108 F. Controller  106  functions to manage shifting of motor/generators  100  and  102  between “drive” modes and “regeneration” modes as well as charging/discharging of battery  104 . Controller  108  is also operable to coordinate and monitor actuation of all the electrically-controlled devices associated with transmission  10  to permit powershifted sequential gear changes automatically without any input from the vehicle operator.  
         [0016]    Geartrain  26  is shown in FIG. 1 to further include a parking pawl wheel  130  that is fixed to output shaft  28  and a parking pawl  131  is operable to engage wheel  130  for releasably locking output shaft  28  to a stationary member (i.e. the housing of transmission  10 ) to prevent rotation of output shaft  28 . Parking pawl  131  is operable to release output shaft  28  when the gearshift lever is moved out of its PARK position and lock output shaft  28  when the gearshift lever is returned to its PARK position.  
         [0017]    If desired, a manually-operable mode selector switch  110  can be provided to shift transmission  10  from its automatic shift mode to a manual shift mode. Mode switch  110  would, when actuated, allow the vehicle operator to shift the gearshift lever manually to effect sequential gear shifts (without use of a clutch pedal). However, controller  106  would only permit the selected gearshift to be completed if the current vehicle characteristics (i.e. engine speed, vehicle speed, etc.) permit completion of the requested shift.  
         [0018]    When it is desired to operate the vehicle, engine  12  is started with the gearshift lever in its PARK position and both master clutches  18  and  20  engaged such that both countershafts  22  and  24  are in drive connection with the output of engine  12 . However, all of the electrically-actuated dog clutches are released with each shift sleeve located in its neutral uncoupled position, whereby no drive torque is delivered through geartrain  26  to output shaft  28 . When the vehicle operator moves the gearshift lever from the PARK position to the DRIVE position, parking pawl  131  is released. Next, controller  106  activates first actuator  40  for releasing first master clutch  18 , whereby the drive connection between input shaft  14  and first countershaft  22  is released. Controller  106  also shifts first motor/generator  100  into its regeneration mode for causing rotor  100 B to retard the rotary speed of first countershaft  22  to match the rotary speed of output shaft  28 . Upon completion of speed synchronization, first dog clutch  82  is actuated by controller  106  sending an electrical signal to coil  82 B for moving sliding sleeve  82 A into clutched engagement with first speed gear  60 . As such, first speed gear  60  is coupled for rotation with first countershaft  22 , whereby the first forward speed ratio drive connection is established between first countershaft  22  and output shaft  28 . Controller  106  then functions to turn off first motor/generator  100  and progressively engage first master clutch  18  for coupling input shaft  16  to first countershaft  22  for accelerating the vehicle.  
         [0019]    Thereafter, when the vehicle operating parameters indicate a need to shift transmission  10  into the second forward gear ratio, controller  106  activates second actuator  50  for releasing second master clutch  20 , whereby the drive connection between driven input shaft  16  and second countershaft  24  is released. Thereafter, controller  106  shifts second motor/generator  102  into its regeneration mode for retarding the rotary speed of second countershaft  24  so as to synchronize its rotary speed to that of second speed gear  72  which is driven by output gear  62  on output shaft  28 . When controller  106  determines that speed synchronization is complete, coil  84 B of second dog clutch  84  is activated by controller  106  for moving sliding sleeve  84 A such that second speed gear  72  is coupled to second countershaft  24 . Thereafter, controller  106  turns off second motor/generator  102  and coordinates the release of first master clutch  18  and the re-engagement of second master clutch  20 , thereby establishing a drive connection between input shaft  16  and second countershaft  24  which, in turn, drives output shaft  28 . Once first master clutch  18  is released completely, controller  106  causes first dog clutch  82  to return sliding sleeve  82 A to its neutral position for uncoupling first speed gear  60  from first countershaft  22 .  
         [0020]    As will be appreciated, this upshift process continues through each of the other forward speed gear ratios and likewise works in reverse for downshifts so as to establish six forward gear ratios. Specifically, the appropriate motor/generator is shifted into its regeneration mode during upshifts to retard the speed of the non-driven countershaft for causing speed synchronization with the geartrain  26 . Likewise, the appropriate motor/generator is shifted into its drive mode during downshifts to increase the speed of the non-driven countershaft for causing speed synchronization. When the gearshift lever is shifted into its REVERSE position, fifth dog clutch  90  is actuated by controller  106  for causing sleeve  90 A to move into clutched engagement with reverse input gear for driving output shaft  28  in the opposite direction. With this powershift methodology, transmission  10  shifts between master clutches in a power-on shift strategy (i.e. no power interruption). Transmission  10  is also shown to include a third motor/generator  120  associated with flywheel damper unit  14  for starting engine  12  or charging battery  104 . However, if the torque capacity of motor/generators  100  and  102  is adequate to start engine  12 , then third motor/generator  120  can be eliminated.  
         [0021]    Thus, the transmission of the present invention utilize the components typically associated with a manually-shifted synchromesh transmission in combination with power-operated dog clutches and a dual-countershaft twin clutch arrangement to provide a compact powershifted automated multi-speed transmission. The use of a compact geartrain allows a desired speed gear to be pre-selected and engaged while disconnected from the engine and thereafter driven by shifting between the engine clutches. Further, the use of electrically-powered motor/generators as speed synchronizer devices to controllable retard or increase shaft speeds is novel and advances the transmission art. Moreover, the use of all electric powered actuators for the engine clutches, dog clutches and motor/generators eliminates the need for a hydraulic system and should promote a highly efficient transmission since electric power is only required for shifting.  
         [0022]    While the presently preferred embodiments of the present invention have been shown and described, it is to be understood that these disclosures are for the purpose of illustration and that various changes and modifications may be made without departing from the scope of the invention as set forth in the appended claims.