Abstract:
This invention provides a common means of coupling an alternative power source to a vehicle&#39;s drive wheels which is particularly well suited for use with a countershaft-type transmission. This invention also addresses clutch wear by eliminating the need to engage the frictional clutch to launch the vehicle. This invention also improves the acceleration of the vehicle compared to a typical dry friction clutch launch by relying on the HLA system to transfer more power to the drive wheels more quickly than would be transferred by a typical launch engagement of a dry friction clutch in a commercial vehicle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/264,987, filed Nov. 30, 2009, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Known hybrid vehicle drive systems coupling an internal combustion engine and an alternative power source such as an electric motor or a hydraulic motor require means of linking the alternative power source and the internal combustion engine to the drive wheels. Each configuration may have a preferred configuration, but such configuration can vary with vehicle use and application. 
     One known electric hybrid system, of the general type described in U.S. Pat. No. 7,463,962, has an electric motor coupled to a transmission input shaft. This configuration was well suited for use with a transmission having a countershaft powerflow configuration. However, by placing the motor in line with the engine and transmission, increasing the size of the electric motor requires making many significant changes to the associated driveline components and mounting features at great expense. It is desired to have an arrangement which permits greater flexibility in changing the size of the electric motor or electric motor/generator, and which is also well suited to a countershaft transmission. Countershaft transmissions are also known as mechanical or manual transmissions, in part because countershaft transmissions have been shifted manually by the vehicle operator. Automated countershaft transmissions are known as automated mechanical transmissions or AMTs. 
     One hydraulic hybrid system, known as a hydraulic launch assist (HLA) system, has been adapted for commercial vehicles and increases fuel economy and acceleration compared to vehicles not so equipped, particularly when used in application having frequent starting and stopping and low-speed operation, such as city buses and refuse collection trucks. However, HLA systems are typically used in combination with conventional automatic transmissions employing a torque converter to communicate driving torque from an engine to the transmission. The torque converter facilitates starting the vehicle from a stopped condition without the need to gradually engage a clutch, and the torque converter also provides torque multiplication when there is a significant speed ratio across the torque converter. At low speed operation, the torque converter losses are a much more significant portion of the power from the engine. A countershaft transmission, and more particularly an automated mechanical transmission (AMT) equipped with a plate clutch for transmitting torque, is significantly more efficient at low speed and start-stop operation than a torque converter transmission, and weighs less than a torque converter transmission. However, typical dry friction clutch plates or driven discs wear out undesirably quickly under such operating conditions. Additionally, the rate of acceleration when starting from a stop is typically less for an AMT equipped vehicle than a torque converter/automatic transmission equipped vehicle in part because of the torque multiplication benefit conferred by a torque converter. It is desired to have an arrangement which permits the coupling of an HLA system with a countershaft transmission and reduces the driven disc wear concern and improves the acceleration of the system over the acceleration provided by an AMT with a dry friction clutch. 
     SUMMARY OF THE INVENTION 
     This invention provides a common means of coupling an alternative power source to a vehicle&#39;s drive wheels which is particularly well suited for use with a countershaft-type transmission. 
     This invention also overcomes the clutch wear concern by eliminating the need to engage the frictional clutch to launch the vehicle. This invention also improves the acceleration of the vehicle compared to a typical dry friction clutch launch by relying on the HLA system to transfer more power to the drive wheels more quickly than would be transferred by a typical launch engagement of a dry friction clutch in a commercial vehicle. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a drivetrain combining an automated mechanical transmission AMT and an HLA. 
         FIG. 2  is a schematic view of the drivetrain of  FIG. 1 . 
         FIG. 3  is a schematic view of a first alternative embodiment of the invention. 
         FIG. 4  is a schematic view of a second alternative embodiment of the invention. 
         FIG. 5  is a schematic view of a third alternative embodiment of the invention. 
         FIG. 6  is a schematic view of a fourth alternative embodiment of the invention. 
         FIG. 7  is a schematic view of a fifth alternative embodiment of the invention. 
         FIG. 8  is a schematic view of a sixth alternative embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a drivetrain  10  including an automated mechanical transmission (AMT)  12  connected to a hydraulic launch assist system (HLA system)  14  by an intermediate propeller shaft  16 . Another propeller shaft, referred to hereafter as a driveshaft  18 , is connected to transmission  12  on one end for connection to an axle (not shown) on the other end. An adapter module  20  is incorporated into transmission  12  to connect HLA system  14  to drivetrain. Adapter module  20  beneficially eliminates the need for a transfer case which was disposed between the transmission and the HLA system in prior art systems. Adapter module  20  provides much of the functionality of a transfer case with much less hardware. A master clutch  22  provides a selectively engaged driving connection between a vehicle drive engine (not shown) and AMT  12 . 
       FIG. 2  shows schematically one configuration of the drivetrain of  FIG. 1 . Adapter module  20  is disposed between front box  24  and auxiliary section  26 . The invention is not intended to be limited by the configuration of the transmission shown, except to extent the transmission employs an input shaft, an output shaft and a countershaft. Front box  24  has an input shaft  28 , an output shaft  30  and a countershaft  32 . Front box  24 , by way of example only, provides four selectable forward drive gear ratios and one reverse gear drive ratio. A headset of meshed gears provides driving engagement between input shaft  28  and countershaft  32 . Gears on output shaft  30  are in mesh with gears on countershaft  32 . Slideable dog clutches are used to fix the gears to the shaft on which they are disposed to achieve the targeted gear ratio. 
     Auxiliary section  26 , in the exemplary embodiment a range box, is coupled to front box  24  by output shaft  30 , providing up to an additional four ratios for each forward gear ratio. The number of ratios available in each section is not critical to the invention. Auxiliary section  26  has a countershaft  34  and an output shaft  36 . Intermediate propeller shaft  16  passes adjacent to rather than through range box  26 . 
     Adapter module  20  has a mechanism for transmitting torque between transmission output shaft  30  and an HLA system input shaft  38 . The mechanism takes the form of an adapter gear set  40  with meshed first and second gears  42  and  44  respectively. It should be appreciated that any known fixed-ratio means for transferring speed and torque between parallel shafts can be employed in place of gear set  40 , such as more complicated gear sets, or a sprocket and chain combination, potentially in combination with other fixed ratio mechanisms. 
     First gear  42  is drivingly connected to input shaft  38  of HLA system  14 . First gear  42  is shown as mounted directly to shaft  38 , but could alternatively be on a separate shaft and drivingly connected by a gear set, drive chain and sprocket combination, or any other mechanism known in the art. Such an intermediate element could provide a speed differential of a fixed ratio between countershaft  32  and the HLA input shaft  38 . 
     Second gear  44  is shown as being rotatably disposed over output shaft  30 . 
     Adapter module  20  also has two clutches: a launch clutch  46  and a regen clutch  48 . 
     Launch clutch  46  is coaxial with first gear  42  and selectively connects first gear  42  to counter shaft  32 . First gear  42  is accordingly rotationally aligned with counter shaft  32 . Regen clutch  48  is coaxial with second gear  44  and selectively drivingly connects second gear  44  with output shaft  30 . Second gear  44  is accordingly rotationally aligned with output shaft  30 . Clutches  46  and  48  do not have to be coaxial with their respective gears, as might be the case if intermediate elements are employed. An important function of launch clutch  46  is that it provides a selective driving connection between countershaft  32  and HLA system input shaft  38 . An important function of regen clutch  48  is that it provides a selective driving connection between output shaft  30  and the HLA system input shaft  38 . 
     Launch clutch  46  is shown in the figures as being a slider or dog-tooth type clutch. Such a clutch has the benefit of being self contained, requiring little energy to operate, and permitting no slippage when engaged. Launch clutch  46  can be controlled by any mechanism suitable for axially displacing a clutch sleeve. Such mechanisms are well known in the art of transmissions, and include pneumatically, hydraulically and electrically actuated shift forks. Schemes for direct displacement through electromagnetic means are also known in the art. 
     Regen clutch  48  is shown as a plate-type clutch, typical of those found in torque converter type automatic transmissions. Such clutches have the advantage of being able to permit engagement while there is a relative speed difference between the parts being engaged by the clutch. Additionally, plate clutches more easily enable declutching or releasing than typical sliding dog tooth clutches. 
     HLA system  14  includes a pump/motor unit  50  and both a high pressure accumulator  52  and a reservoir or low pressure accumulator  54 . The HLA system functions as described in U.S. Pat. No. 7,082,757. In an HLA “charging” or “regeneration” mode, torque is applied to input shaft  38  of both HLA system  14  and pump/motor unit  50  with pump/motor unit  50  operating in a pump mode. In the pump mode, pump/motor unit  50  draws hydraulic fluid from low pressure accumulator  54  and forces it into high pressure accumulator  52  where the fluid is retained under significant pressure. In a “discharging” or “driving” mode of HLA system  14 , pump/motor unit  50  operates in a motor mode. In the motor mode, pressurized fluid from high pressure accumulator  52  acts on pump/motor unit  50  to induce a torque on input shaft  38  and causing shaft  38  to rotate. Fluid exiting pump/motor unit  50  enters low pressure accumulator  54 . Torque is transferred between HLA system  14  and adapter module  20  by intermediate propeller shaft  16 . 
     A description of the invention operation follows. In a first, or launch condition, a vehicle employing the inventive drivetrain is at a complete stop with the vehicle engine idling, master clutch  22  disengaged, range box  26  in an appropriate launch mode, and high pressure accumulator  52  fully charged. A first gear ratio clutch within transmission front box  24  is engaged. Launch clutch  46  is engaged, rotatively fixing transmission counter shaft  32  to HLA input shaft  38 . Regen clutch  48  is disengaged, allowing gear  44  to rotate freely on output shaft  30 . Pump/motor  50  is operated in its motor mode, communicating torque to counter shaft  32  and through the transmission gear set of the first gear ratio to output shaft  30 , through range box  26  and driveshaft  18  to the vehicle axle (not shown), starting the vehicle in motion. It is appreciated that transmission input shaft  28  is back-driven through a gear set between the input shaft and countershaft, or headset  56 , by the rotation of countershaft  32 . When input shaft  28  reaches approximately the rotational speed of the crankshaft of the idling engine, master clutch  22  can be engaged, and the source of driving power transitioned from HLA system  14  to the vehicle engine. Launch clutch  46  can then be disengaged. 
     It should be appreciated that this sequence can be altered. For example, instead of having the engine idling, the engine could be completely stopped. With master clutch  22  engaged, launch clutch  46  engaged and transmission front box  24  in neutral, the engine would be started by torque from HLA system  14  passing through the countershaft and transmitted to the engine through headset  56 . Master clutch  22  and launch clutch  46  would be each disengaged, a start gear selected in front box  28 , and the vehicle launched by engaging master clutch  22 . Depending on the torque capabilities of HLA system  14 , it may be possible to simultaneously launch the vehicle and start the motor. With master clutch  22  engage, launch clutch  46  engaged and transmission front box  24  in a selected launch gear, the engine would be started as the vehicle starts to roll under the power of the HLA system. Once the engine is at a self-sustaining speed, launch clutch  46  is disengaged. Yet alternatively, the vehicle could be launched using the HLA alone, and the engine started by engaging master clutch  22  when the vehicle is at a predetermined speed. Launch clutch  46  would be disengaged before engaging master clutch  22 . 
     In an alternative launch mode of operation, with the vehicle at a stop, the engine idling, and high pressure accumulator  52  fully charged, master clutch  22  is disengaged, launch clutch  46  is disengaged, and regen clutch  48  is engaged. A gear set within each of transmission front box  24  and range box  26  is selected and engaged. HLA system  14  is used to launch the vehicle. Output shaft  30 , through its selected gear set, back drives countershaft  32  which in turn back drives transmission input shaft  28 . When input shaft  28  is rotating at about engine idle speed, master clutch  22  is engaged while regen clutch  48  is disengaged, enabling a smooth shift from HLA driving torque to engine driving torque. 
     To enable operation of HLA system  14  in a regeneration mode, launch clutch  46  is disengaged, regen clutch  48  is disengaged, master clutch  22  can be either engaged or disengaged, the front box  24  and range box  26  each have an appropriate gear engaged, and the vehicle is moving at or below a predetermined speed. Pump/motor unit  50  is placed in the pump mode, and regen clutch  48  is engaged to recharge the high pressure accumulator. Rotation of output shaft  36 , resulting from rotation of the vehicle wheels, through range box  26 , drives output shaft  30  which rotates second gear  44  which, through first gear  42 , causes HLA system input shaft  38  to rotate, causing motor pump  50  to draw fluid from low pressure accumulator, and force it into high pressure accumulator  52  under high pressure. Such recharging can be executed responsive to vehicle system commands to slow the vehicle, providing regenerative braking. The kinetic energy associated with the inertia of the vehicle is transformed into the potential energy associated with the pressurized hydraulic fluid in the high pressure accumulator. 
     Placing adapter module  20  between front box  24  and auxiliary section  26  of transmission  12  beneficially enables MLA system  14  to be used to provide hydraulic assist in several different drive ratios. It is anticipated that for certain applications, auxiliary section  26  would enable the anticipated range of speed of countershaft  32  to remain within the operating speed range of the HLA pump/motor unit  50 . In such cases, power from HLA system  14  would be available over the entire operational range of the vehicle. 
       FIG. 3  shows an alternative drivetrain  110  in which a transmission  112  has the more conventional arrangement of an auxiliary section or box  126  fixed directly to an end of a front box  124 . An adapter module  120  is mounted to an end of auxiliary box  126  opposite front box  124 . The launch modes and regen or recharge modes of operation would be essentially the same as described above for the embodiment of  FIG. 2 , but an HLA system  114  would only be available at a low end of the vehicle&#39;s range of operating speeds because of the fixed ratio relationship between the rotational speed of an HLA input shaft  138  and a propeller shaft  118  connecting to the axle. 
       FIG. 4  shows an alternative drivetrain  210  for a transmission  212  not having an auxiliary section. Such arrangements are typical in light and medium duty vehicle applications. Adapter module  220  is connected to an end of transmission  212  opposite a master clutch  222 . A first gear  242  and a launch clutch  246  and HLA input shaft  238  are axially aligned with a countershaft  232 . A second gear  244  and regen clutch  248  are disposed over output shaft  230 . As with the embodiment of  FIG. 3 , HLA system  214  is only available at the low end of the vehicle&#39;s operating speed range because of the fixed ratio relationship between the rotational speed of HLA input shaft  238  and the output shaft  230  which is drivingly connected to the axle. 
       FIG. 5  shows a drivetrain  310  nearly the same as that of  FIG. 2 , with an adapter module  320  disposed between a front box  324  and an auxiliary section  326  of transmission  312 . A significant change relative to the embodiment of  FIG. 2  is that the embodiment of  FIG. 5  does not have HLA input shaft  338  axially aligned with countershaft  332 . Instead, adapter module  320  has a third gear  345  in its adapter module gear set  340 . First gear  342  is in axial alignment with countershaft  332 . Launch clutch  346  selectively engages first gear  342  with countershaft  332 . Second gear  344  is disposed over output shaft  330  of front box  324 , with regen clutch  348  selectively rotatively fixing second gear  344  to output shaft  330 . Third gear  345 , drivingly meshed with first gear  342 , is rotatively fixed to input shaft  338  of HLA system  314 . 
       FIG. 6  also shows a drivetrain  410  nearly the same as that of  FIG. 2 , with an adapter module  420  disposed between a front box  424  and an auxiliary section  426  of transmission  412 . A significant change relative to the embodiment of  FIG. 2  is that the embodiment of  FIG. 6  does not have a launch clutch in axial alignment with output shaft  430 . Instead, a two-way clutch mechanism  449  employed to alternatively provide the launch and regen functions is in axial alignment with countershaft  432 . Also, first gear  442  rotates freely relative to input shaft  438  unless mechanism  449  engages clutch  448 , instead of being fixed relative thereto as in the embodiment of  FIG. 2 . Second gear  444  is accordingly fixed relative to output shaft  430 , as distinguished from the embodiment of  FIG. 2  which has the second gear rotatably mounted on the output shaft. 
     Clutching mechanism  449  selectively engages regen clutch  448  to rotatably couple first gear  442  to HLA system input shaft  438  in a regen mode. Torque is transferred between HLA system  414  and output shaft  430  by gear set  440 . Alternatively, clutching mechanism  449  selectively engages launch clutch  446  to rotatably couple HLA system input shaft  438  with a countershaft  432  in a launch mode. Arrow  458  illustrates one possible torque path in the launch mode. No torque is transmitted through gear set  440 . 
       FIG. 7  shows a drivetrain  510  similar to that of  FIG. 4 , with an adapter module  520  adjacent to a transmission  512  having no auxiliary section. A significant change relative to the embodiment of  FIG. 4  is that an electric hybrid system  560  has been substituted for the HLA system. Hybrid system  560  serves as an alternative means of converting mechanical kinetic energy to potential energy. Another difference is that regen clutch  548  is a non-synchronized dog-tooth clutch, like launch clutch  546 . Another less significant difference is that adapter module  520  has three gears like the adapter module of  FIG. 5 . 
     Hybrid system  560  includes an electric motor/generator  562  in place of a hydraulic pump/motor, and a battery  564  in place of a high pressure accumulator. Hybrid system  560  additionally includes a power electronics module  566  which may incorporate elements, by way of example, a voltage transformer, and an inverter. Power electronics module  566  can be comprised of integrated elements, or separate, discrete elements. Motor/generator  562  is scalable depending on system design requirements. An anticipated power range for the motor/generator for the anticipated applications is 30 kW to 100 kW. Packaging design will accommodate the packaging of a range of motor/generator sizes. Motor/generator capacities can potentially be varied with the length of the motor/generator. Battery  564  can also be scaled to accommodate anticipated system demands. Larger batteries incorporating additional cells may be employed. Or, alternatively, a plurality of identical batteries may be employed to increase energy storage capacity as may be desired. 
     Each of the embodiments of  FIGS. 1-7  would require systems controls to operate the transmission and hybrid system, whether hydraulic or electronic, in a coordinated fashion.  FIG. 7  shows discrete transmission and hybrid electronic control units (“ECU” or “ECUs”)  568  and  570  respectively. It should be appreciated that transmission and hybrid ECUs  568  and  570  could be integrated into a single ECU. Transmission ECU  568  is electronically connected to transmission and adapter module controllers  572  and  574  respectively. Controllers include mechanisms for shifting the transmission and the adapter module to select desired gear modes. Such mechanisms are well known in the art and can include any of electric or hydraulic or pneumatic actuating mechanisms or any combination thereof. The connections can be by wire, or can by any known wireless means such as Bluetooth®. Such connections provide a means of transmitting control signals from ECU  568  to controllers  572  and  574 . 
     By employing an electric hybrid system  560 , driveline  510  beneficially eliminates the need for a synchronizing clutch within adapter module  520 . Electric motor/generator  562  can be speed controlled with sufficient accuracy to provide the necessary low speed differential between gear  544  and output shaft  530  to enable engagement of dog clutch  548  without any mechanical synchronization to speeding up or slowing down the supplemental power source, in this case motor/generator  562 . Driveline systems employing hydraulic pump/motors preferably employ mechanical synchronization means such as plate clutches or synchronizer type dog clutches to bring the rotating speeds of the rotating parts into synchronization because the response time of a pump/motor to speed control commands is significantly greater that that of an electric motor. 
     As with the hydraulic system, alternative embodiments of the electric hybrid system are anticipated. Examples of alternative configurations are shown in  FIGS. 8 through 10 .