Patent Publication Number: US-2023132811-A1

Title: Switchable powertrain

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/013,670, filed Sep. 7, 2020, which in turn claims priority to Indian Patent Application No. 201911036122, filed Sep. 7, 2019, the disclosures of which are incorporated by reference in their entireties. 
    
    
     FIELD 
     This application provides a switchable powertrain. A hybrid powertrain can comprise a switchable configuration with four points of freedom. 
     BACKGROUND 
     Vocational and line-haul classes of vehicles can be preconfigured differently. For example, the vehicle can be configured to transfer torque from an electric motor to a driveline. The same vehicle can be configured to transfer torque from an engine to a driveline. Such a vehicle can be characterized as a hybrid vehicle (“HEV” or “HV”). The preconfigurations can be related to the average operation speed or the average operation output torque. Typically, there is a single set-point for the preconfiguration with the electric motor and engine handing off along one of two torque transfer pathways. With a set-point for the average operation speed or average operation torque, it is difficult to switch to other operation modes and to then operate the vehicle efficiently. The efficiency and utility of the vehicle is preconfigured rigidly and dissimilar from other classes of vehicle. 
     SUMMARY 
     In one embodiment, a switchable powertrain includes a first torque source for providing a first torque, a second torque source for providing a second torque, and a main gear set configured for gear ratio selection. The main gear set includes an input shaft, first gears coupled to a main shaft, and second gears coupled to a second shaft. The second gears are meshed with the first gears. A clutch is configured for selectively coupling the first torque source to the input shaft of the main gear set. The switchable powertrain further includes an adapter having a first selective coupling configured to selectively couple the second torque source to the main shaft, and a second selective coupling configured to selectively the second torque source to the second shaft. The switchable powertrain further includes an output. The adapter is configured to operate in a first configuration where the second torque source outputs the second torque to the first selective coupling and to the output without passing the second torque through the main gear set. The adapter is also configured to operate in a second configuration where the second torque source outputs the second torque to the second selective coupling and to the output while passing the second torque through the main gear set. 
     In another embodiment, a switchable powertrain includes a main gear set configured for gear ratio selection. The main gear set includes an input shaft, first gears coupled to a main shaft, and second gears coupled to a second shaft. The second gears are meshed with the first gears. The switchable powertrain further includes a first torque source, a second torque source, a clutch configured for selectively coupling the first torque source to the input shaft of the main gear set, and an adapter. The adapter includes a first selective coupling for forming a first adapter torque transfer pathway from the second torque source directly to the main shaft, and a second selective coupling for forming a second adapter torque transfer pathway from the second torque source, through the main gear set, and to the main shaft. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       In the accompanying drawings, structures are illustrated that, together with the detailed description provided below, describe exemplary embodiments of the claimed invention. Like elements are identified with the same reference numerals. It should be understood that elements shown as a single component may be replaced with multiple components, and elements shown as multiple components may be replaced with a single component. The drawings are not to scale and the proportion of certain elements may be exaggerated for the purpose of illustration. 
         FIGS.  1 A- 1 F  are views of a first switchable powertrain; 
         FIG.  2    is a view of an alternative switchable powertrain; 
         FIG.  3    is a view of another alternative switchable powertrain; 
         FIGS.  4 A- 4 E  are views of another alternative switchable powertrain; 
         FIG.  5    is a schematic incorporating an electronic control unit; and 
         FIG.  6    diagrams a method of operation of the switchable powertrain. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the examples which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. Directional references such as “left” and “right” are for ease of reference to the figures. 
     A switchable powertrain  101 ,  102 ,  103 ,  104  comprises at least four points of freedom. At least three torque transfer pathways can be implemented using the switchable powertrain. The switchable powertrain comprises a main gear set  201 ,  203 ,  204  configured for gear ratio selection. Main gear set can also be called a gear box or transmission. Gear shift controller  220  can be mounted to the main gear set  201 ,  203 ,  204 . Gear shift controller  220  can be configured to communicate with an electronic control unit (ECU) or lever, pedal, button, or other actuator for automated or manual shifting among the various gear ratios offered for selection. Based on the configuration of the main gear set, for example, 5, 6, 10, 12 or 20 gear ratios can be selected, among other numbers of gear ratios, including gear ratios for forward motion and reverse (REV) motion of a main shaft  251 ,  253 ,  256 . Gear shift controller  220  can connect to various actuators  231 - 234 ,  235 - 237 ,  238 - 240  configured to couple gears of the main gear set to the main shaft  251 ,  253 ,  256 , second shaft  252 ,  254 ,  257 , or alternative third shaft  255 ,  258 . Main gear set  201  can constitute a transmission with a single countershaft in the example of  FIGS.  1 A &amp;  2    or main gear set  203 ,  204  can constitute a transmission with dual countershafts in the example of  FIGS.  3  &amp;  4   . Various aspects of connecting the gear shift controller  220  to the actuators  231 - 240 , can be included, such as rods, forks, levers, pneumatics, hydraulics, electronics, among others. The switchable powertrain  101 - 104  can comprise an automated transmission (AMT) or ENDURANT transmission for land vehicles, and parts therefor manufactured by Eaton Cummins Automated Transmission Tec Limited Liability Company, among other types of transmissions compatible with the teachings herein. Actuators  231 - 241  can comprise numerous alternatives for selective coupling to main shaft  251 ,  253 ,  256 , such as splined teeth, dog couplings, clutched discs, pistons, among others. Keyway combinations, other slots, or guides can be fashioned for two or three-way positioning of the actuators such as for on/off positioning or neutral/first position/second position actuation. 
     The main gear set  201 ,  203 ,  204  comprises main gears coupled to a main shaft  251 ,  253 ,  256  and second gears coupled to a second shaft  252 ,  254 ,  257 . A main gear set  203 ,  204  comprising third gears coupled to a third shaft  255 ,  258  can be seen in  FIGS.  3  &amp;  4   . In  FIGS.  1 A- 3   , there are 6 main gears of various size shown in schematic on the main shaft  251 ,  253 . On the second shaft  252 ,  254 , there are 6 second gears of various size configured to mesh with the main gears. In  FIG.  4 A , there are pairings among 5 gears so that there are 5 main gears on main shaft  256 , 5 second gears on second shaft  257 , and  5  third gears on third shaft  258 . In each main gear set  201 ,  203 ,  204 , reverse gears REV for reversing the rotation direction of the main shaft  251 ,  253 ,  256  have been included. By controlling various actuators  231 - 234 ,  235 - 237 ,  238 - 240 , the main shaft  251 ,  253 ,  256  can be coupled to a selected main gear of a selected size. Gear tooth mating, or meshing, between the main gear and the corresponding second or third gear transfers torque across the mesh of the gears. The selection of the gear pairings via the actuators controls the step up or step down of shaft rotation implemented by the torque applied. Torque can transfer from main shaft  251 ,  253 ,  256  to second shaft  252 ,  254  or from second shaft to main shaft, for example. Torque can transfer from third shaft  255 ,  258  to main shaft  251 ,  253 ,  256  or from main shaft to third shaft, as another example. The torque so transferred can be regenerative torque T 3 , as when the driveline of a vehicle of a larger device  700  transfers rotational energy back to the electric motor to charge its corresponding battery (i.e. the output  701  becomes an input of torque). Or, the torque can be first torque T 1  from the first torque source  501 ,  502 ,  503 . Or, the torque can be second torque T 2  from the second torque source  401 ,  403 . 
     An adapter  301  can comprise first adapter gears  320  and second adapter gears  310 . A first selective coupling A is configured to selectively couple the first adapter gears  320  to the main shaft  251 . Adapter  303  comprises a first selective coupling C that can comprise, for example, a three-way shifter  384  configured to selectively couple an adapter coupling  385  to a shaft coupling  386 . Now, main shaft  253 ,  256  is coupled to first selective coupling C. The adapter  303  comprising a three-way shifter  384  can couple to the second torque source  403  to selectively couple to the first selective coupling C, the second selective coupling D, or a neutral position N. 
     The switchable powertrain  101 ,  102  can comprise the first selective coupling A comprising a first adapter gear  314 . The second selective coupling B can comprise second adapter gears  311 ,  312 ,  313 . The first adapter gears can be meshed with the second adapter gears. 
     A second selective coupling B, D is configured to selectively couple the second adapter gears  310 ,  380  to the second shaft  252 ,  254 ,  257 . Coupling to main shaft  251 ,  253 ,  256  can occur within main gear set  201 ,  203 ,  204  via gear mesh and an actuator  231 - 240  being actuated. For the dual countershaft embodiment, second selective coupling D is further configured to selectively couple third adapter gears  390  to the third shaft  258  via third shaft portion  355 . Coupling to the main shaft  253 ,  256  can occur within main gear set  203 ,  204  via gear mesh and an actuator  231 - 240  being actuated. Coupling can also be accomplished via gear mesh in the adapter  303 . A third adapter gear  392  at third shaft portion  355  can couple with a first or shared adapter gear  391 . Second adapter gears  382  at second shaft portion  354  can also couple with shared adapter gear  391 . Shared adapter gear  391  can be coupled and decoupled from three-way shifter  384  as part of second selective coupling D. Adapter coupling  385 , able to move to three positions, can couple second torque T 2  from second torque source  403  via hub  344  to a corresponding feature on shared adapter gear  391  such as mating splines or dogs features or pistons with clutch plates. 
     Main shaft  251 ,  253  can extend from clutch  550  to output  701 . In the case of  FIGS.  2  &amp;  3   , a range gear set  602  is coupled around main shaft portion  651 . Range gear set  602  can be coupled to selectively apply a second gear ratio to the main shaft  251 ,  253 . From a location standpoint, the first selective coupling A can be coupled between the range gear set  602  and the main gear set  201  along the main shaft  251 ,  253 . 
     Range gear set  602  adds additional degrees of freedom by permitting additional gear ratio selection. The range box that can comprise range gear set  602  can comprise additional actuators  631 ,  632  to couple one of three gears in the alternative to main shaft portion  651 , which can also be called a first range shaft. These three gears can be meshed with three additional gears on a second range shaft  652 . A HI or LO range gear ratio selection can be selected and applied. 
     In  FIG.  4 A , main shaft  256  can extend from clutch  550  to planetary gear system  630  of range gear set  603  (range box). A second main shaft  259  can extend to output  701 . The planetary gear system  630  can comprise a sun gear  681 , a ring  682 , planetary gears  683 ,  684 , and actuators  634 ,  635 . This alternative range gear set  603  enables a HI or LO range gear ratio selection. 
     Main shaft, second shaft, and third shaft can be unitary or can comprise shaft sections coupled together. So, main shaft portion  351 ,  353  extending in adapter  301 ,  303  can be unitary with or a shaft section of main shaft  251 ,  253 ,  256 . Likewise, second shaft portion  352 ,  354  can be unitary with or a shaft section of second shaft  252 ,  254 ,  257 . And so forth for third shaft portion  355  and third shaft  255 ,  258 . A range gear portion  651 ,  656  of main shaft can be unitary with or a shaft section of main shaft  251 ,  253 ,  256  extending in or through range gear set  602 ,  603 . 
     Output  701  can couple to power a larger device  700  such as a vehicle or other motive device. Larger device  700  can comprise a line-haul or vocational vehicle such as a construction vehicle, off-road vehicle, lifting vehicle, transporter, tractor trailer, bus, delivery truck, hauling among many others. Accessories such as lifts, compressors, mining tools, mixing equipment, among others can be affiliated with the vehicle. Vehicles that need power/torque when stopped can benefit from the switchable powertrain, as the power/torque needs during transport, maneuvering, and stationary work can each be fulfilled. The switchable powertrain can also be used in linehaul vehicles for smooth operation. 
     A first torque source  501 ,  502 ,  503  and a clutch  550  are configured for selectively coupling or decoupling first torque T 1  to the main shaft  251 ,  253 ,  256 . First torque source  501 ,  502 ,  503  can comprise an electric motor or a combustion engine. First torque source  501  can comprise a combustion engine such as a diesel engine or gasoline engine. Alternative energy sources can be used. Electric motor can be such as are used in hybrid electric vehicles or other powered devices. First torque source  501 ,  502 ,  503  can be tailored for the application of the switchable powertrain. Torque output, rotations per minute of the shaft connected to the clutch  550 , among other parameters can be designed for. 
     A second torque source  401 ,  403  can be configured for selectively outputting second torque T 2  to either the first selective coupling A, C or the second selective coupling B, D. Second torque source  401 ,  403  can output torque to the first adapter gears  320 , the second adapter gears  310 ,  380 , and the third adapter gears  390 . Second torque source  401 ,  403  can be an electric motor. It can be one-way powered from a battery  450 . Or, it can be bidirectional and can be configured for charging an associated battery. As  FIG.  5    shows, the battery  450  can supply a charge level signal to an electronic control unit (ECU)  1000 . It can be determined if sufficient battery power is available to power the second torque source  401 ,  403  by analyzing the charge level signal. Or, a regeneration command can be sent from the ECU  1000 . Regeneration can be from other sources in the vehicle such as a regenerative braking system coupled to the battery  450 . 
     An advantage of the adapter  301 ,  303  is that it can be configured to return torque to the second torque source  401 ,  403 . An electric motor can be coupled to a battery  450 . The adapter  301 ,  303  can be switchable to provide torque to the electric motor to charge the battery  450 . A bidirectional electric motor can be configured as a generator. As an example, the electric motor can comprise a casing  440  seating the electric motor inside the adapter  303  or external from the adapter  301 . A stator assembly  430  can be braced against the casing  440 . A rotor assembly  420  can be positioned to rotate on spindles  410 . Spindles  410  can be secured to an axle  341  or hub  344  for rotation of the rotor assembly  420 . Numerous alternatives exist for forming the bidirectional device including number of windings, number of electrical phases supported, top rotations per minute, among many others. 
     ECU  1000  can be partitioned to provide many control aspects to larger device  700 . In the case of a vehicle, operation inputs can be received such as accelerator position, forward or reverse command, gear shift request, braking commands, accessory usage, and sensed conditions such as slip, coast, wheel or traction speed among many others. Such operation inputs can be stored in a storage device such as memory  1001  comprising input storage  1012  and operation inputs can be forwarded to a processor such as degree of freedom processor  1021 . Algorithms and other programming  1011  can be stored in memory  1001 . An output tracking  1013  can be included in memory  1001  for comparative analysis, among other uses. First torque source  501 ,  502 ,  503  can output data to input storage  1012  for use in degree of freedom processor  1021 . Example output data can include engine rotations per minute, torque capacity, combustion efficiency, crankshaft speed, among others. In the case of another electric motor or motor-generator, output data can comprise rotations per minute of an output shaft, torque capacity, battery life, among others. 
     Degree of freedom processor  1021  can process stored programming  1011  to determine how to use the degrees of freedom available given the operation inputs from larger device  700 . A range selection command can be sent to range gear set (also called a range box)  602 ,  603  to increase the range of the torque output. An input command can be given to the first torque source  501 ,  502 ,  503  to increase or decrease rotations per minute or to turn the first torque source on or off. In synchrony, and in the case of a combustion engine, the clutch  550  can be opened or closed via a command to the clutch  550  or affiliated electronic clutch actuator (ECA)  551 . As another degree of freedom, the use of the main gear set  201 ,  203 ,  204  can be determined. A gear selection ratio command can be sent to gear shift controller  220  which can in turn actuate the actuators  231 - 240  to select the corresponding gear ratio. With the adapter  301 ,  303  as another degree of freedom, a selection command can be sent to activate the first selective coupling A or C, the second selective coupling B or D, or the neutral position N. In the case of adapter  301 , adapter actuator  362  can slide from a neutral position N to a position engaged with gear coupling  332  to activate the first selective coupling A. The adapter actuator  361  can slide from a neutral position N to a position engaged with gear coupling  331  to activate second selective coupling B. In the case of adapter  303 , a three-way shifter  384  can slide among a neutral position N, a position engaging first selective coupling C, and a position engaging second selective coupling D. Alternatives can comprise clutch, piston, disc, spline, or other mechanisms for shifting among the three positions. Being close to the rotor  420  and stator  430 , it is possible to arrange electromagnetic forces to move the three-way shifter  384  so that it moves automatically based on signal strength. 
     Main gear set  203 ,  204  can be a twin countershaft design transmission such as an ENDURANT transmission for land vehicles, and parts therefor manufactured by Eaton Cummins Automated Transmission Tec Limited Liability Company. Three-way shifter  384  can engage shared adapter gear  391  in such a way that adapter gear  392  meshes and can transfer second transfer second torque T 2  to third shaft portion  355  affixed to adapter gear  392 . 
     Turning to  FIGS.  1 B- 1 E , the torque transfer pathways can be seen for the switchable powertrain in thick arrows. In  FIG.  1 B , a first torque pathway for first torque T 1  from the first torque source  501 , through the clutch  550 , through the main gear set  201 , and out the main shaft  251  to the output  701  can be seen. The first torque T 1  can be acted on to vary its quantity by increasing or decreasing engine speed, changing gear ratio in the main gear set  201  or drawing on it in the larger device  700  as part of output  701 . In  FIG.  1 B , the first torque pathway passes through the adapter  301  but is not acted on by the adapter  301 . The adapter  301  is a pass-through device in this operation state. This operation state can be a key-on operation state, a drive operation state, or a second operation state implemented after a first spin-up operation state. The gear ratio selections shown are for purposes of example, only. For example, the first torque pathway of  FIG.  1 B  can be for a low speed drive condition, such as a 3 to 4 mile per hour (MPH) maneuver. The low speed can make the first torque pathway a Low Torque Pathway TPL. But,  FIG.  1 C  can be for a higher speed drive condition, such as a 401 MPH cruise condition. This can make the first torque pathway a High Torque Pathway TPH. 
     Turning to  FIG.  1 D , a first adapter torque transfer pathway ATP 1  from the second torque source  401 , through a mesh of adapter gears  311 ,  312 ,  313 , and gear shaft  314 , through the adapter actuator  362  of first selective coupling A, and out the main shaft portion  351  can be seen. Such a pathway can be used during drive conditions for purposes such as torque filling during powershifts and for continuous regenerative braking. It can be possible to use this pathway at the same time that the clutch  550  is coupled to the first torque source  501  thus permitting addition of first torque T 1  and second torque T 2 . By way of example, this first adapter torque transfer pathway ATP 1  can be used when a vehicle is operating from 4 to 40 MPH. This limitation can be due to the maximum speed of the second torque source  401 . For example, if the maximum speed is 10,000 rotations per minute, then the second torque source cannot rotate the main shaft enough for output  701 . A different gear ratio could be needed to rotate the main shaft enough for output  701 . 
     To enable different gear ratios than the first adapter torque transfer pathway ATP 1 , alternative second and third adapter torque transfer pathways ATP 2 , ATP 3  are shown in  FIGS.  1 E &amp;  1 F . Second torque T 2  from the second torque source  401  passes through a second mesh of second adapter gears  311 ,  312 , through the second selective coupling B, through the main gear set  201 , and out the main shaft  251 . First selective coupling A is switched off or neutral. This second adapter torque transfer pathway ATP 2  can be used for purposes such as launching from rest. A slow moving vehicle can begin its initial motions. The second torque source  401  can be applied to spin up the main gear set  201  in preparation for more work. With the main gear set  201  spun up, the first torque path TP 1  can be initiated after a key-on event, meaning the first torque source  501 , including the engine, can be powered off when second adapter torque transfer pathway ATP 2  is used. 
     The alternative third adapter torque transfer pathway ATP 3  is shown in  FIG.  1 F . This pathway uses a different gear ratio in main gear set  201 . This pathway can be used for purposes of cruising at higher vehicle speeds such as 40-60 MPH. The second torque source  401  can output 2500-3600 RPMs, yet the main gear set  201  can translate that to high enough torque to power output  701 . 
     It can be seen from the torque pathways that a vehicle can switch from a stopped or off condition of zero MPH to full highway speed by selecting aspects of the degrees of freedom in the system.  FIG.  6    outlines various operational states discussed above for  FIGS.  1 B- 1 F . Implementing the first state S 61  can launch the vehicle. Implementing the second state S 62  can creep the vehicle and start an engine as a first torque source. Implementing the third state S 63  can bring the vehicle near cruise and can be alternated with the second state S 62 . Cruise speeds and above can be accomplished by alternating between all three states, but a ZEV vehicle can comprise switching between the first state S 61  and third state S 63 . 
     In  FIGS.  4 B- 4 E  various operation states are outlined. A first torque pathway TP 1  from the first torque source  503 , through the clutch  500 , through the main gear set  204 , and out the main shaft  256  can be seen in  FIG.  4 B . The gear ratio selection is an example, only, and other gear ratios can be selected in the main gear set  204 . First torque path TP 1  can be used for purposes such as drive or basic vehicle operations. 
       FIGS.  4 D &amp;  4 E  show alternative first adapter torque transfer pathways ATP 1 A, ATP 1 B from the second torque source  403 , through the three-way shifter  384  of the first selective adapter coupling C, and through the main shaft portion  353  of main shaft  256 . Having the range gear set  603  coupled via sun gear  681  and planet gear  684 , a range gear ratio is applied. Such a pathway can be used during upshifts as for torque-filling. Acceleration and regeneration can also be accomplished in LO range gears  1 - 6 . In the alternative of  FIG.  4 E , the range gear ratio is not applied. This alternative first adapter torque transfer pathway ATP 1 B can also be used during upshifts for torque-filling. But, acceleration and regeneration can be accomplished in HI range gears  7 - 12 . As with  FIG.  4 D , the effects of the second torque source  403  can be additive such that clutch  550  is closed and first torque source  503  is adding torque to the switchable powertrain  104 . And, torque-filling, where the second torque source is used to fill torque gaps when the clutch  550  is open, can be used in both low and high speed operation modes. 
     A second adapter torque transfer pathway ATP 2  can be seen in  FIG.  4 C . Second adapter torque transfer pathway ATP 2  can be from the second torque source  403 , through three-way shifter  384  of the second selective coupling D, through a first mesh of adapter gears  391 ,  382 , and out the main shaft  256 , including main shaft portion  353 . Because range gear set  603  is also coupled, a pathway through the sun and planet gears to output  701  can also be seen. Such a pathway can be used alone or along with first torque pathway TP 1  for purposes such as electric launch. The second torque source  403  can spin up the main gear set  204  and range gear set  603  and can begin launching the vehicle. Then, the engine can be started or coupled for additional torque output. First adapter torque transfer pathway ATP 1  can also be used with the clutch  550  decoupled (open) for purposes such as electric launch, creep mode, or engine-off driving (zero emission vehicle “ZEV”). 
     Instead of additive torque, the second torque source  401 ,  403  can be configured to output the second torque T 2  to the main shaft  251 ,  253 ,  256  when the first torque source  501  is decoupled from the main shaft. That is, the clutch can be commanded open before outputting second torque T 2 . Or, the second torque source  401 ,  403  can be used at start-up before there is sufficient power to couple or close the clutch  550 . As another example, the second selective coupling B or D is configured to couple to the second shaft  252 ,  254 ,  257  when the first torque source  501 ,  502 ,  503  is decoupled from the main shaft. In yet another implementation, the second torque source  401 ,  403  is configured to output the second torque T 2  to the second selective coupling B or D when the first torque source  501 ,  502 ,  503  is decoupled from the main shaft  251 ,  253 ,  256 . In yet another alternative, the switchable powertrain is configured so that the first selective coupling A, C is decoupled from the main shaft  251 ,  253 ,  256  and the second selective coupling B, D is decoupled from the second shaft  252 ,  254 ,  257  when the first torque source  501 ,  502 ,  503  is coupled to the main shaft. 
     In one aspect, the location of the second torque source  401 ,  403  achieves an advantage in torque coupling efficiency. While it is possible to attach an external motor to a transmission housing to implement the switchable powertrain  101 ,  102 , it is also possible to integrate an electric motor inside the compartment of transmission, as in  FIGS.  3  &amp;  4 A . In either implementation, the location of the second torque source  401 ,  403  yields a benefit. So, the switchable powertrain can be configured so that the second gears of the main gear set  201 ,  203 ,  204  comprise a range of sizes from a smallest second gear of a smallest second gear size to a largest second gear of a largest second gear size. The second torque source  401 ,  403  can be coupled in a location nearer to the smallest second gear than the location of the first torque source  501 ,  502 ,  503 . As yet another implementation, the switchable powertrain can be configured so that the main gears comprise a range of sizes from a smallest main gear of a smallest main gear size to a largest main gear of a largest main gear size. The first torque source can be in a location that is nearer to the smallest main gear than the location of the second torque source  401 ,  403 . Now, each torque source is nearest to the smallest gears to which it will couple. The low speed operations can be especially efficient. And, the main gear set is available to apply a large range of gear ratios to both torque sources. 
     Said another way, the main shaft  251 ,  253 ,  256  and the second shaft  252 ,  254 ,  257  are parallel. The first torque source  501 ,  502 ,  503  can be configured to selectively couple to or decouple from the main shaft via the clutch  550  on a first end of the main gear set  201 ,  203 ,  204 . The second torque source  401 ,  403  can be configured to selectively output second torque to the second shaft via the second selective coupling B, D at a second end of the main gear set  201 ,  203 ,  204 . 
     Several methods of switching the switchable powertrains  101 - 104  have been described. It is additionally possible, commensurate with  FIG.  6   , to implement additional methods. A first state S 61  can be implemented where the clutch  550  is decoupled from the main shaft  251 ,  253 ,  256 . This can comprise coupling second torque T 2  to the second selective coupling B, D and coupling the second torque T 2  from the second selective coupling to the main shaft  251 ,  253 ,  256  through the main gear set  201 ,  203 ,  204 . Switching from the first state S 61  to a second state S 62  can comprise terminating outputting second torque T 2  from the second torque source  401 ,  403 . Then, coupling the clutch  550  to the main shaft  251 ,  253 ,  256 . Lastly, outputting first torque T 1  from the first torque source  501 ,  502 ,  503  to the main shaft  251 ,  253 ,  256 . It is also possible to switch between the first state S 61 , the second state S 62 , and a third state S 63 , the third state comprising decoupling the first torque source  501 ,  502 ,  503  from the main shaft  251 ,  253 ,  256  and coupling the second torque source  401 ,  403  to the first selective coupling A or C. Then, it is possible to output second torque T 2  from the second torque source  401 ,  403  to the main shaft  251 ,  253 ,  256 . 
     The methods herein can further comprise implementing the first state S 61  to further comprise spinning up the main gear set  201 ,  203 ,  204  by applying the second torque T 2  to the main gear set. Implementing the second state S 62  can further comprise turning on the first torque source  501 ,  502 ,  503 . 
     The methods herein can comprise implementing the first state S 61  by terminating outputting first torque T 1  from the first torque source  501 ,  502 ,  503 . Or, switching between the first state S 61  and the third state S 63  can be accomplished by actuating a three-way shifter  384 . 
     A desired outcome of the methods herein can be accomplished by timing the switching among first state S 61 , second state S 62 , and third state S 63  so that the main shaft, and therefor the output  701 , experiences a constant supply of torque, the constant supply of torque being one or the other of the first torque T 1  or the second torque T 2 . 
     The switchable powertrain and methods herein enable significant fuel savings through powertrain hybridization, while improving the vehicle drivability, low-speed maneuverability, power gear shifting, electric launch and full electric driving. 
     A summary of operation modes can be made for the first state S 61 : vehicle e-launch, ZEV(zero emission vehicle) mode when a vehicle is operated in pure electric vehicle mode within city limits, coast mode, and engine cranking with main clutch engaged &amp; transmission in neutral. 
     In summary, the third state S 63  can be used for power shifting as while changing gear, the motor (second torque source) can be used in peak power to fill the torque hole between shifts. Third state S 63  can also be used for coast mode and low speed maneuverability mode when the vehicle needs to move at very slow speed to do certain operations. 
     More detailed examples and explanations follow to provide working modes for implementing the switchable powertrain  101 - 104 . 
     A launch assist or electronic launch mode can comprise, when launching the vehicle, the first torque source such as the engine is not cranked and the main clutch is dis-engaged. Then, the vehicle will launch with the second torque source, such as an e-motor, configured to give a smooth start. As a degree of freedom, the second torque source operating parameters can be chosen so that the e-motor has very high torque at low speed. This can be used to launch the vehicle. With the vehicle launched in an electric mode with an e-motor, the clutch life is increased significantly. Once the vehicle attains a certain speed, the engine is cranked and the main clutch is closed to propel the vehicle with an internal combustion engine 
     In certain operations, the vehicle needs to run at very slow speed (0.5 to 2.5 mph) and the driver also needs to have control over speed and torque. These can be in situations such as docking, grading, or maneuvering in tight spaces. In such conditions, the first torque source (engine) is switched off, the clutch  550  is disengaged and the vehicle is propelled with second torque source (electric motor). Creep, ultra creep, and low speed operation modes can be accomplished. 
     In another mode, it is possible to crank an engine for start-up. The main gear set  201 ,  203 ,  204  (transmission) can be put in neutral. The main clutch  550  is engaged &amp; the second torque source (motor) is used to crank the engine by connection through the second selective adapter coupling B or D. 
     In another mode, a synchronization is made for the engine start. The vehicle is launched with the second torque source (electric motor). The main clutch  550  can be engaged when the vehicle speed is synchronized with first torque source (engine). 
     In another mode, torque assist and blending can be accomplished. The second torque source (motor)  401 ,  403  can be used to add torque to wheels coupled to output  701 . First torque source  501 ,  502   503 , can be coupled and used when needed. This can be done with first selective coupling A, C engaged. Then, there will not be a transmission-related torque handling limit. With this feature, the first torque source as an engine can be operated at its peak efficiency point. Additional power can be supplied by the second torque source in the form of a motor. Any battery can be charged with regenerating techniques. 
     An electronic powershift mode can be implemented. When the main gear set  201 ,  203 ,  204  as a transmission is shifting gears, the clutch  550  can be dis-engaged. This creates a torque supply hole &amp; reduces the acceleration. In this case, the second torque supply  401 ,  403  as an electric motor or traction motor can be used at peak power to propel the vehicle while the transmission is shifting gears. This will reduce jerks as well as improve acceleration. This can also be referred to as torque-filling for smoother upshifting. 
     In an e-generation drive mode, the vehicle will be propelled by first torque source comprising an engine as per a baseline vehicle. If the state of charge (SoC) in the battery goes below a certain level, a charge level signal will trigger the electric machine to be engaged to charge the battery up to a certain percentage. 
     In coasting modes, such as when a vehicle is going down hill, the first torque source  501 ,  502 ,  503  as an engine will be switched off, the main clutch  550  will be dis-engaged, and the vehicle will coast down in top gear. Second torque source  401 ,  403  as an electric machine will be engaged in an appropriate first or third state S 61 , S 62  to operate the electric machine at an optimum speed. The electric machine can be configured to be regenerative and charge battery  450 . 
     It is possible to implement an electronic-creep (e-creep) mode while using the power take off (PTO). There can be a situation in vocational application, when the vehicle needs to be moved very slowly while the engine PTO needs to run fast. In such a situation, the vehicle can be propelled in an appropriate first or third state S 61 , S 62  with the second torque source  401 ,  403  as an e-motor. The main clutch can be dis-engaged. And, the first torque source  501 ,  502 ,  503  as an engine can be revved up to meet the PTO requirement. 
     In another mode, braking, retarding, and regeneration can be combined. While a vehicle is going down hill (coasting, braking, etc.), the second torque source as an electronic machine (e-machine) can be used in a generator mode to regenerate energy at the same time that it can act as a retarder to slow down the vehicle. If the vehicle speed increases beyond a certain limit while going down-hill, clutch  550  is engaged and the first torque source as an engine is started to give engine braking. The e-machine can also be used to assist the engine to brake along with the regeneration. 
     Selection of first state S 61  or third state S 63  can also be used along with main gear set  201 ,  203 ,  204  optimization to maximize regeneration energy. Also, during Engine Off Coasting mode (master clutch  550  open) selection of first state S 61  or third state S 63  can enable motor gear ratio changes of the second torque source. Then, the master clutch actuator ECA  551  can be controlled to provide negative torque fill to minimize vehicle jerk and to smooth downshifts. 
     There can be engine-off driving modes. In certain conditions when a vehicle is not allowed to use an internal combustion engine within city limits, the vehicle can be run with the second torque source as an electric motor in pure electric vehicle (EV) mode. In this case, the first torque source as an engine is switched off. The clutch  550  is dis-engaged. The vehicle is propelled in either first or third state S 61 , S 62  based on a torque speed requirement. 
     Electric vehicle launch mode can be done with first torque source as an engine “off” To (re)start the engine using blended electric power and vehicle inertia, it is possible to coordinate the control of second torque source  401 ,  403  in the form of a traction motor, master clutch actuator (ECA)  551 , and gear shift controller  220  for the selected launch gear of the main gear set  201 ,  203 ,  204  as a transmission box. This eliminates the stock starter/alternator from the engine. The peak power capability of the second torque source in the form of an e-machine is used to crank the engine while driving the vehicle. 
     Low-speed maneuvering modes can also be implemented. It is possible to drive a vehicle fully electric until a certain state-of-charge (SOC) threshold. At that threshold, it is possible to switch to driving with constant engine power from first torque source and keeping the master clutch  550  locked. The second torque source is controlled as speed control device to recharge the battery. 
     A mode selection for drive can be implemented with a power blend. It is possible to perform an optimization of the 4 degrees of freedom (DOFs) available in the system, namely: first torque source output torque (engine torque), second torque source output torque (motor torque), main gear set ratio (main box ratio), and adapter coupling ratio (motor gear box ratio). This can be done instantaneously using programming  1011  in the ECU  1000  based on operation inputs such as current driver demand. In a more advanced version, the programming  1011  can comprise using a forecast of vehicle duty cycle to optimize the variables over a short horizon and control the degrees of freedom accordingly. 
     The switchable powertrain can be used to provide a fault-tolerant shift strategy. The shift strategy can adapt to aging and bearing or gear faults. The second torque source as a traction motor can be used to enable skip-shifts during both drive and regeneration. The adapter  301 ,  303  can be used so as to distribute wear across the main gear set  201 ,  203 ,  204 . For example, if gear  2  is wearing more than the other gears, the adapter  301 ,  303  can be controlled to provide electric power from second torque source  401 ,  403  in lieu of torque transfer from first torque source  501 ,  502 ,  503  through the worn gear  2 . 
     The disclosure enables a vehicle to switch between the first state S 61  or third state S 63  configurations. This deviates from most powertrains that are either configured as first state S 61  or third state S 63  and are not switchable. Instead of two degrees of freedom (one at the gearbox of the transmission and one at the torque output of the engine), the disclosure provides four degrees of freedom: engine torque, motor torque, main box ratio, motor gear box ratio (P 2 /P 3  mode of hybrid adapter). 
     In the first state S 61 , it is possible to combine torque from first torque source (diesel power from engine) with electric power of the second torque source. 
     In the third state S 63 , a high torque output can be achieved with the electric power “in front” of the transmission (at the end with the smallest gear). The placement of the electric power enables sufficient torque. 
     It is possible to switch between first and third states S 61  &amp; S 63  and to provide torque filling modes seamlessly such that the driver does not feel the switching. This is unlike shudder than can be felt when clutch open or clutch close switching is made without torque filling. 
     The disclosed switchable powertrain  101 - 104  is more efficient than powertrains with viscous torque converters because there is no torque loss &amp; there is better fuel economy. But, the performance of constant torque transfer is achieved. 
     Other implementations will be apparent to those skilled in the art from consideration of the specification and practice of the examples disclosed herein.