Patent Publication Number: US-11655863-B1

Title: Electric driveline system with power take-off and electric driveline system operating method

Description:
TECHNICAL FIELD 
     The present disclosure relates to a multi-speed electric driveline system and a method for operation of said driveline system. 
     BACKGROUND AND SUMMARY 
     Multi-speed transmissions have been deployed in certain electric vehicles (EVs) due to their increased responsiveness and gains in motor operating efficiency that the transmission affords when compared to EVs using single speed geartrains. Some of these prior multi-speed electric drive units do not have components that rotate independently from the wheels when the vehicle is at standstill. Moreover, certain electric drivelines demand that the driveline components rotate in an opposite direction (in comparison to forward drive) when operating in reverse. This presents barriers to implementing power take-off (PTO) capabilities for driving auxiliaries when operating the driveline in reverse, at standstill, or in forward drive at low speeds. 
     Some attempts have been made to provide PTO functionality into certain EVs. For instance, US 2015/0135863 A1 to Dalum discloses a hybrid vehicle drive system that uses an electric motor to power a PTO which, in turn, drives accessories. The PTO in Dalum&#39;s system is not capable of concurrently driving both the accessories and providing motive power to the transmission. 
     The inventors have recognized several drawbacks with Dalum&#39;s drive system as well as other electric drive systems. For instance, the inability to simultaneously drive both the PTO accessories and provide motive power to the transmission using the electric motor constrains the system&#39;s capabilities, thereby decreasing customer appeal. Further, other systems have employed dedicated motors and inverters to independently power PTOs. These systems are complex and may present manufacturing difficulties. 
     The inventors have recognized the aforementioned issues and developed an electric driveline system. In one example, the electric driveline system includes a first electric machine and a second electric machine mechanically coupled to a transmission. The electric driveline system further includes a PTO assembly coupled to the first electric machine. This PTO assembly includes a first clutch coupled to a PTO gearset and is designed to selectively disconnect a PTO from the first electric machine. Further, in the system, the PTO gearset is mechanically coupled to the first electric machine. In this way, the first electric machine is able to provide power to both the transmission and the PTO at overlapping times, if wanted. As a result, the system&#39;s capabilities are expanded via a PTO assembly that uses power from an electric machine which is also designed to provide motive power to the transmission. Further, the complexity and cost of the system may be reduced, if wanted, when compared to electric drive systems which use dedicated motors for powering PTOs, for instance. 
     In another example, the electric driveline system may further include a second clutch designed to selectively disconnect the first electric machine from the transmission. In such an example, the system may additionally include a controller configured to operate the second clutch to disconnect the transmission from the first electric machine, while the second electric machine is transferring mechanical power to the transmission. This disconnection may occur when the second electric machine is operated to rotate the transmission in a reverse drive direction. In this way, the window of PTO operation with regard to driveline operating conditions is expanded, thereby broadening the system&#39;s capabilities and increasing customer appeal. 
     It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG.  1    shows a portion of a vehicle with an electric driveline system. 
         FIGS.  2 A- 2 B  show the power paths through the electric driveline system of  FIG.  1    in a first and second gear configuration while a power take-off (PTO) is disconnected. 
         FIGS.  2 C- 2 D  illustrate exemplary power paths which provide power to the PTO of the electric driveline system, depicted in  FIG.  1   . 
         FIGS.  2 E- 2 G  show charts correlating the various electric driveline system operating modes to clutch and synchronizer positons. 
         FIG.  3 A- 3 C  show mechanical, hydraulic, and electrical connections, respectively, in an electric driveline system of a vehicle. 
         FIG.  4    shows a method for operation of an electric driveline system. 
     
    
    
     DETAILED DESCRIPTION 
     An electric driveline with a multi-speed transmission and power take-off (PTO) disconnect capabilities is described herein. The PTO disconnect capabilities are achieved using a PTO assembly with clutches that function to selectively connect and disconnect a PTO from an electric machine as well as selectively disconnect the electric machine from the transmission, during certain operating conditions. In this way, the PTO is able to operate over a wider range of operating conditions. 
       FIG.  1    depicts a vehicle  100  with an electric driveline system  102 . As such, the vehicle  100  may be an electric vehicle (EV), such as a battery electric vehicle (BEV). All-electric vehicles may specifically be used due to their reduced complexity and therefore reduced points of potential component degradation. However, hybrid electric vehicle (HEV) embodiments may be employed where the vehicle includes an internal combustion engine (ICE). 
     The electric driveline system  102  includes a transmission  104  that is rotationally coupled to a first electric machine  106  and a second electric machine  108 . Each of the electric machines  106 ,  108  may include conventional components such as a rotor and a stator that electromagnetically interact during operation to generate motive power. Furthermore, the electric machines may be motor-generators which also generate electrical energy during regeneration operation. Further, the electric machines may have similar designs and sizes, in one example. In this way, manufacturing efficiency may be increased. However, the electric machines may have differing sizes and/or component designs, in alternate examples. 
     Further, the electric machines  106 ,  108  may be multi-phase electric machines that are supplied with electrical energy through the use of a first inverter  110  and a second inverter  112 . These inverters and the other inverters described herein are designed to convert direct current (DC) to alternating current (AC) and vice versa. As such, the electric machines  106 ,  108  as well as the other electric machines may be AC machines. For instance, the electric machines  106 ,  108  and the inverters  110 ,  112  may be three-phase devices, in one use-case example. However, motors and inverters designed to operate using more than three phases have been envisioned. The electrical connections between the inverters  110 ,  112  and the electric machines  106 ,  108  is indicated via lines  114 ,  116  (e.g., multi-phase wires), respectively. 
     The inverters  110 ,  112  may receive DC power from at least one electrical energy source  118  (e.g., an energy storage device such a traction battery, a capacitor, combinations thereof, and the like, and/or an alternator). Arrows  120  indicate the flow of electrical energy from the energy source  118  to the electric machine  106 ,  108 . Alternatively, each inverter may draw power from at least one distinct energy source. When both the inverters are coupled to one energy source, the inverters may operate at a similar voltage. Alternatively, if both inverters are coupled to distinct electrical energy sources, they may operate at different voltages, in some examples. 
     The system  102  further includes a PTO assembly  119 . The PTO assembly  119  includes a PTO  128  (e.g., a mechanical or hydraulic PTO unit) and may also include a PTO gearset  130 . The PTO gearset  130  may include a gear  137  and a gear  131  coupled to the output shaft  121  such that the gear  131  and the output shaft  121  jointly rotate. A bearing  143  may serve as an interface between the gear  137  and an input shaft  129  of the PTO  128 . Thus, the gear  137  and the input shaft  129  may independently rotate, under some conditions, elaborated upon herein. One or more auxiliary devices  115  may be driven by the PTO  128  as denoted via line  117 . These auxiliary devices may include a steering pump, a pump for working hydraulic devices, an air conditioning pump, and the like. 
     The PTO assembly  119  may utilize clutches (e.g., friction clutches, synchronizers, dog clutches, combinations thereof, and the like) to selectively provide mechanical power to the PTO  128 , as will be expanded upon herein. As such, the PTO assembly  119  may be designed to mechanically couple and decouple the PTO  128  from the electric machine  106 . Although the PTO  128  is designed to selectively rotationally couple to the first electric machine  106 , the second electric machine  108  may, additionally or alternatively, have a PTO and an associated gear and clutch assembly coupled thereto. However, when the system includes two PTOs coupled to the different electric machines, one of the PTOs may be disconnected during reverse drive operation. 
     In some examples, the output shaft  121  of the first electric machine  106  may have a gear  131  fixedly coupled thereon. The gear  131  may be coupled to a gear  137  of the PTO gearset  130 . The gears described herein include teeth, and mechanical attachment between the gears involves meshing of the teeth. The gear  137  may be disposed about, and selectively coupled to, an input shaft  129  of the PTO  128 . For instance, a bearing  143  may be used to attach the gear  137  to the PTO input shaft  129  such that the gear  137  independently rotates in relation to the PTO input shaft  129  during certain operating conditions. Further the gears  131 ,  137  included in the PTO gearset  130  may have a gear ratio that is selected to provide rotational input to the PTO within a desired torque range. 
     The PTO assembly  119  includes a first clutch  141 . The first clutch  141  is specifically illustrated as a synchronizer, although other types of clutches, such as friction clutches, may be additionally or alternatively used for selectively coupling the PTO gearset  130  to the shaft  129 , in other examples. Further, the clutch  141  may be designed to selectively couple the gear  137  for rotation with the PTO input shaft  129 , by coupling the gear  137  with a shaft interface  139  of the input shaft  129 . In this way, when the clutch  141  is engaged, mechanical power from the electric machine  106  may be transferred to the input shaft  129  of the PTO  128  via gears  131  and  137 . Conversely, when the clutch  141  is not engaged, mechanical power from the electric machine  106  may not travel through the PTO gearset  130 , whereby the gear  137  of the PTO gearset is not able to transfer mechanical power to the input shaft  129  of the PTO. In other words, the clutch  141  allows the PTO  128  to be selectively connected and disconnected from the first electric machine  106  in different operating modes. Further, a shift fork or other suitable actuator, as schematically illustrated at  113 , may be used to engage and disengage the clutch  141 . 
     The output shafts  121 ,  122  of the electric machines  106 ,  108  may have gears  124 ,  126  which reside thereon, respectively. In some examples, the gear  124  may be rotatably coupled to the output shaft  121 . To rotatably attach the gear  124  to the shaft  121 , a bearing  123  (e.g., a roller bearing such as needle roller bearing, a ball bearing, and the like) may be used. A bearing as described herein may include inner races, outer races, and roller elements (e.g., balls, cylindrical rollers, tapered cylindrical rollers, and the like). This rotatable attachment between the gear  124  and the output shaft  121  allows the first electric machine  106  to be selectively rotationally decoupled from the transmission  104 . 
     To accomplish the selective decoupling of the first electric machine  106  from the transmission  104 , a second clutch  135  may be included in the PTO assembly  119 , in some examples. Further, the second clutch  135  may be included in a clutch assembly  127 . The clutch assembly  127  may be positioned coaxial to the output shaft  121  and is designed to selectively couple the gear  124  for rotation with the output shaft  121 . The clutch assembly  127  may further include a synchronizer  133  positioned in series with a friction clutch  135 . More specifically, the synchronizer  133  and the friction clutch  135  may be coaxially arranged. A friction clutch, as described herein, may include two sets of plates designed to frictionally engage and disengage one another while the clutch is opened and closed. As such, the amount of torque transferred through the clutch may be modulated depending on the degree of friction plate engagement. Thus, the friction clutches described herein may be operated with varying amounts of engagement (e.g., continuously adjusted through the clutch&#39;s range of engagement). Further, the friction clutches described herein may be wet friction clutches through which lubricant is routed to increase clutch longevity. However, dry friction clutches may be used in alternate examples. The friction clutch  135  and other friction clutches described herein may be adjusted via hydraulic, pneumatic, and/or electro-mechanical actuators. For instance, hydraulically operated pistons may be used to induce clutch engagement of the friction clutches. However, solenoids may be used for electro-mechanical clutch actuation, in other examples. 
     The friction clutch  135  may include a drum  145  coupled to the output shaft  121  and carrying a set of the friction plates, and a clutch component  125  (e.g., clutch hub) that carries a set of separator plates. Further, the synchronizer  133  may be designed to selectively couple the gear  124  for rotation with the clutch component  125  of the friction clutch  135 . Thus, when the friction clutch  135  is engaged (e.g., in a closed position), the synchronizer  133  may engage an interface of the gear  124  so that the gear  124  is coupled for rotation with the output shaft  121  of the electric machine  106 . 
     The synchronizer  133  is designed to synchronize the speed of the clutch component  125  of the friction clutch  135  (e.g., as effected by the output shaft  121  and the degree of engagement of the friction plates in the clutch  135 ) and the gear  124 . For instance, the synchronizer  160  may include a sleeve with splines, ramped teeth, and the like designed to engage an interface of the gear  124  in order to achieve the aforementioned functionality. Further, a shift fork or other suitable actuator, as schematically illustrated at  166 , may be used to engage and disengage the synchronizer  133 . In this way, when the friction clutch  135  and the synchronizer  133  of the clutch assembly  127  engage the gear  124 , mechanical power output from the electric machine  106  (via the output shaft  121 ) may be transferred into the transmission  104 , as will be described herein. Conversely, the electric machine  106  may be decoupled from the transmission  104  when the clutch assembly  127  is disengaged from the gear  124 . 
     It will be understood that, in different examples, the PTO gearset  130  and the output shaft  121  of the electric machine  106  may utilize different configurations of clutches and/or synchronizer mechanisms for achieving the aforementioned functionalities. For instance, in some cases, the clutch assembly  127  may include a single wet friction clutch without the synchronizer  133  and/or the clutch  141  may be a wet friction clutch arranged for coupling the gear  137  of the PTO gearset  130  to the input shaft  129  of the PTO  128 . However, other clutch arrangements (e.g., dry friction clutches, dog clutches, etc.) have been contemplated, in different examples. Further, in different embodiments, the clutch  141  or the clutch assembly  127  may be omitted from the transmission  104 . In these embodiments, the transmission&#39;s packaging efficiency may be increased at the expense of reduced functionality. 
     The gears  124 ,  126  are each coupled to (e.g., in meshing engagement with) a gear  134  of a planetary gearset  136  in the transmission  104 . The planetary gearset  136  may include a shaft  140  which connects the gear  134  to a sun gear  142 . The gears  124 ,  126  may specifically be positioned on different sides  144 ,  146  of the transmission  104  to enhance packaging and provide a more balanced weight distribution in the electric driveline system  102 , if wanted. More generally, the rotational axes of the gears  124  and  126  as well as the electric machines  106  and  108  may be parallel to one another. 
     A friction clutch  148  is coupled to the shaft  140  and designed to selectively rotationally couple the shaft to an output shaft  150 . In some examples, the friction clutch  148  may be substantially similar to the friction clutch  135  as described above, and may therefore be a wet friction clutch. The sun gear  142  in the planetary gearset  136  may be coupled to the shaft  140 . Further, planet gears  152 , in the planetary gearset  136 , may be coupled to the sun gear  142 . Further, the planet gears  152  may be mechanically coupled to a ring gear  154  in the planetary gearset  136 . 
     A shaft  156  may extend from the ring gear  154  and have a second friction clutch assembly  158  residing thereon. The second friction clutch assembly  158  may include a synchronizer  160  arranged in series with a friction clutch  162 . Placing the synchronizer  160  in series with the friction clutch  162  enables the transmission&#39;s efficiency to be increased when operating in the second gear. Again, the synchronizer  160 , as well as the other synchronizers described herein, may be similar to the synchronizer  133  and actuated accordingly. To elaborate, the synchronizer  160  permits a portion of the shaft  164  to be disconnected from the clutch  162  and freely rotate while the system operates in the second gear. As such, the plates in the clutch  162  may not rotate when the synchronizer is disengaged. Conversely, when the synchronizer  160  is engaged, the shaft  164  and the shaft  156  of the ring gear  154  rotate in unison. The synchronizer  160  is designed to synchronize the speed of the shaft  156  and a shaft  164  coupled to the friction clutch  162 , and mechanically lock rotation of the shafts  156 ,  164 , when engaged. To increase system compactness, the friction clutches  148 ,  162  as well as the output shaft  150  may be coaxially arranged. To permit this coaxial arrangement, the sun gear  142  may include an opening  168  through which the output shaft extends. 
     The friction clutch  162  is designed to ground the ring gear  154 . To accomplish the ring gear grounding, the friction clutch  162  may include a housing with a portion of the friction plates coupled thereto and fixedly attached to a stationary component, such as the transmission&#39;s housing. A bearing  170  may be positioned between the shaft  156  and the output shaft  150  to enable these shafts to independently rotate, during certain conditions. 
     The output shaft  150  includes output interfaces  172 ,  174  (e.g., yokes, splines, combinations thereof, or other suitable mechanical interfaces) designed to attach to axles (e.g., front or rear axles) via shafts, joints (e.g., U-joints), chains, combinations thereof, and the like. 
     Disconnect clutches  176 ,  178  may be provided for each of the output interfaces  172 ,  174 . As such, the disconnect clutches  176 ,  178  may be designed to mechanically couple and decouple the output shaft  150  from the output interfaces  172 ,  174 . In this way, the transmission&#39;s capabilities may be further expanded to enable single and multi-axle operation. For instance, four-wheel drive may be engaged when additional traction is desired and two-wheel drive may be engaged when the additional traction is not desired to reduce driveline losses and tire wear. In this way, the handling performance of the vehicle is enhanced. The disconnect clutches  176 ,  178  may be dog clutches, synchronizers, friction clutches, combinations thereof, or other suitable clutches. Dog clutches and/or synchronizers may be specifically used as axle disconnect devices, in some examples, to reduce losses when the clutches are disengaged, when compared to friction clutches. 
     The planet gears  152  rotate on a carrier  179  of the planetary gearset  136 . The carrier  179  is rotationally coupled to the output shaft  150 . The planetary gearset  136  may be a simple planetary gearset that solely includes the sun gear  142 , ring gear  154 , planet gears  152 , and carrier  179 . By using a simple planetary assembly, transmission compactness may be increased when compared to more complex planetary assemblies such as multi-stage planetary assemblies, Ravigneaux planetary assemblies, and the like. Consequently, the driveline system may pose less space constraints on other vehicle components, thereby permitting the system&#39;s applicability to be expanded. Further, losses in the transmission may be decreased when a simple planetary gearset is used as opposed to more complex gear arrangements. 
     Depending on the gear ratio of the transmission, mechanical power may travel through the carrier  179  to the output shaft  150  or from the sun gear  142  to the output shaft. Mechanical power paths through the transmission in the different gears and shifting operation (e.g., powershifting operation) between the operating gears are discussed in greater detail herein with regard to  FIGS.  2 A- 2 D . 
     A third electric machine  180  and inverter  182  may be provided in the system  102 . The third electric machine  180  is designed to drive a transmission pump  184  which generates the flow of a fluid (e.g., a lubricant such as oil) through the transmission  104 . It will be understood that lubricant as described herein is a fluid such as oil that may be used for lubricating components as well as for component actuation and/or cooling. Furthermore, a valve  186  is coupled to an output of the pump  184  and regulates the flowrate of lubricant through the transmission  104 . The valve  186  may be in fluidic communication with components  185  (schematically depicted in  FIG.  1   ) in the transmission  104  that receive lubricant. The lubricant may be routed to the desired components via lubricant conduits, jets, additional valves, manifolds, combinations thereof, and the like. Further, the components  185  may include gears, clutches, hydraulic pistons for clutch actuation, and the like. 
     Once the lubricant is routed from the valve  186  to the lubricated components, the lubricant returns to a sump  187 . Additionally, the sump  187  may be located in a transmission housing and profiled to gather lubricant from the lubricated components in the transmission. The pump  184  may receive lubricant from the sump  187  via pick-up conduits  188 . Conversely, the pump outlets  189  deliver lubricant to the valve  186 . It will be understood that the pump  184 , the valve  186 , and the sump  187  are included in a lubrication system  190 . The lubrication system  190  may further include conduits for routing the lubricant to targeted components in the transmission such as the planetary gearset, clutches, and the like. The pump is illustrated in  FIG.  1    as a double pump with two pump modules  191 , but other pump designs have been contemplated. 
     Further, by using a separate electric machine to drive the transmission pump  184 , the electric machine&#39;s speed and therefore pump speed may be adjusted to track with the lubricant demands in the transmission. For instance, the pump speed may be increased during shifting transients and then decreased while the transmission is sustained in one of the two discrete operating gears. This reduces hydraulic losses and allows the hydraulic system to be downsized, if desired. 
     The third electric machine  180  and the inverter  182  may be operated with a lower voltage current than the first and second electric machines  106 ,  108  and corresponding inverters. For instance, the lower voltage may be in the following range: 12 Volts (V)-144V and the higher voltage may be in the following range: 350V-800V, in one use-case example. However, other higher and lower voltage values may be used, in other examples. In this way, the transmission&#39;s efficiency may be increased. However, in other examples the first electric machine  106 , the second electric machine  108 , and the third electric machine  180  may be operated at a similar voltage (e.g., a higher voltage within the range of 350V-800V or a lower voltage within the range of 12V-144V, in one use-case example). 
     The vehicle  100  further includes a control system  192  with a controller  193  as shown in  FIG.  1   . The controller  193  may include a microcomputer with components such as a processor  194  (e.g., a microprocessor unit), input/output ports, an electronic storage medium  195  for executable programs and calibration values (e.g., a read-only memory chip, random access memory, keep alive memory, a data bus, and the like). The storage medium may be programmed with computer readable data representing instructions executable by a processor for performing the methods and control techniques described herein as well as other variants that are anticipated but not specifically listed. 
     The controller  193  may receive various signals from sensors  196  coupled to various regions of the vehicle  100  and specifically the transmission  104 . For example, the sensors  196  may include a pedal position sensor designed to detect a depression of an operator-actuated pedal such as an accelerator pedal and/or a brake pedal, a speed sensor at the transmission output shaft, energy storage device state of charge (SOC) sensor, clutch position sensors, etc. Motor speed may be ascertained from the amount of power sent from the inverter to the electric machine. An input device  197  (e.g., accelerator pedal, brake pedal, drive mode selector, PTO mode selector, two wheel and four-wheel drive selector, combinations thereof, and the like) may further provide input signals indicative of an operator&#39;s intent for vehicle control. For instance, buttons, switches, or a touch interface may be included in the vehicle to enable the operator to toggle between a two-wheel drive mode and a four-wheel drive mode and/or engage and disengage the PTO from the first electric machine. However, in other examples, automated control strategies may be used to connect and disconnect the PTO. 
     Upon receiving the signals from the various sensors  196  of  FIG.  1   , the controller  193  processes the received signals, and employs various actuators  198  of vehicle components to adjust the components based on the received signals and instructions stored on the memory of controller  193 . For example, the controller  193  may receive an accelerator pedal signal indicative of an operator&#39;s request for increased vehicle acceleration. In response, the controller  193  may command operation of the inverters to adjust electric machine power output and increase the power delivered from the machines to the transmission  104 . The controller  193  may, during certain operating conditions, be designed to send commands to the clutches  141 ,  135 ,  148 ,  162 , and/or synchronizer  133  to engage and disengage the clutches or synchronizer. For instance, a control command may be sent to a clutch assembly and in response to receiving the command, an actuator in the clutch assembly may adjust the clutch based on the command for clutch engagement or disengagement. The other controllable components in the vehicle may function in a similar manner with regard to sensor signals, control commands, and actuator adjustment, for example. 
     The controller  193  may be designed to control the clutches  148 ,  162  to synchronously shift between two of the transmission&#39;s operating gears. Further, the controller  193  may be designed to operate the clutches  135 ,  141 , and/or the synchronizer  133  to selectively connect the PTO  128  and/or the transmission  104  from the first electric machine  106 . 
     An axis system  199  is provided in  FIG.  1   , as well as  FIGS.  2 A- 2 D , for reference. The z-axis may be a vertical axis (e.g., parallel to a gravitational axis), the x-axis may be a lateral axis (e.g., horizontal axis), and/or the y-axis may be a longitudinal axis. However, alternate orientations of the axes may be used, in other examples. 
     The transmission  104  has two clutches that enable it to function as a two-speed transmission. However, in other embodiments, additional clutches may be added to the transmission to enable it to be operated in a greater number of gears. As such, the transmission may have three or more speeds, in other embodiments. 
       FIGS.  2 A- 2 D  depict power paths through the transmission  104  in four different operating modes. In the operating modes, depicted in  FIGS.  2 A and  2 B , power bypasses the PTO  128 . However, in the operating modes, depicted in  FIGS.  2 C and  2 D , power is provided to the PTO  128 . The components in the electric drivelines system  102 , the transmission  104 , etc. shown in  FIGS.  2 A- 2 D  and previously described with regard to  FIG.  1    are similarly numbered and redundant description is omitted for brevity. 
       FIGS.  2 A and  2 B  show the power paths through the transmission  104  in the electric driveline system  102  in a first gear mode and a second gear mode, respectively, where the PTO  128  is disconnected from the first electric machine  106 . It will be understood that these power paths may correspond to both forward and reverse drive modes. Further, the electric machines may generate rotational output in opposite directions in the forward and reverse drive modes. In other words, in a forward drive mode, the first electric machine may rotate the output shaft  121  in a first direction and in a reverse drive mode, it may rotate the output shaft in the opposite direction. Thus, the power paths shown in  FIGS.  2 A and  2 B  generally correspond to drive mode operation. 
     The transmission&#39;s gear ratio in the first gear mode is higher than the gear ratio in the second gear mode. Thus, the first gear may be used during launch and subsequent acceleration while the second gear may be used for cruising operation, for instance. Further, as shown in  FIGS.  2 A and  2 B , the disconnect clutches  176 ,  178  are engaged and therefore permit power to be transferred from the output shaft  150  both output interfaces  172 ,  174  and drive axles, correspondingly. However, one of disconnect clutches may be disengaged while the transmission is operating in the first gear and the second gear, when additional traction is not desired. For example, one of the disconnect clutches may be disengaged and vehicle correspondingly operates in a two-wheel drive mode when a vehicle operator requests said mode or when it is determined that the vehicle is not operating under low traction conditions. 
     Turning specifically to  FIG.  2 A , while the transmission  104  is operating in the first gear mode, the ring gear  154  is held stationary by the friction clutch  162  and the clutch  148  is disengaged. Further, the clutch  141  is disengaged so that the PTO gearset  130  is disconnected from the electric machine  106 , and the clutch assembly  127  that includes the friction clutch  135  and the synchronizer  133  is engaged to couple the gear  124  for rotation with the output shaft  121  of the electric machine  106 . The mechanical power path in the first gear mode (denoted via arrows  250 ) unfolds as follows: mechanical power moves from the first and second electric machines  106 ,  108  to the gear  124 ,  126 , respectively, from the gears  124 ,  126  to the gear  134 , from the gear  134  to the sun gear  142 , from the sun gear to the planet gears  152 , from the planet gears to the carrier  179 , and from the carrier to the output shaft  150 . 
     While the transmission  104  is operating in the second gear mode, as shown in  FIG.  2 B , the clutch  148  is engaged to permit mechanical power transfer between the gear  134  and the output shaft  150  and the clutch  162  is disengaged. Again, the clutch  141  is disengaged so that the PTO gearset  130  is disconnected from the electric machine  106 , and the clutch assembly  127  is engaged to couple the gear  124  for rotation with the output shaft  121  of the electric machine  106 . In the second gear mode, the mechanical power path (denoted via arrows  260 ) unfolds as follows: mechanical power moves from the first and second electric machines  106 ,  108  to the gears  124 ,  126 , respectively, from the gears  124 ,  126  to the gear  134 , from the gear  134  to the clutch  148 , and from the clutch  148  to the output shaft  150 . 
       FIG.  2 C  shows the transmission  104  operating in a first gear mode in which the first electric machine  106  transfers power to both the transmission  104  and the PTO  128 . Thus, in the first gear mode illustrated in  FIG.  2 C , the ring gear  154  is held stationary by the friction clutch  162  and the clutch  148  is disengaged. Further, the clutch assembly  127  is engaged (e.g., the clutch  135  and the synchronizer  133  are engaged) to enable mechanical power to be transferred from the output shaft  121  to the gear  124 , and the clutch  141  is engaged enable power to be transferred from the gear  137  of the PTO gearset to the PTO input shaft  129 . In this way, the first electric machine  106  is able to provide power to both the transmission  104  and the PTO  128 . 
     In  FIG.  2 C  the mechanical power path (denoted via arrows  270  and  272 ) unfolds as follows: mechanical power moves from the first and second electric machines  106 ,  108  to the gear  124 ,  126 , respectively, from the gears  124 ,  126  to the gear  134 , from the gear  134  to the sun gear  142 , from the sun gear to the planet gears  152 , from the planet gears to the carrier  179 , and from the carrier to the output shaft  150 . Additionally, a branch of the mechanical power path (denoted by arrows  272 ) flows from the electric machine  106  to the gear  131 , from the gear  131  to the gear  137  of the PTO gearset  130 , and from the gear  137  through the PTO input shaft  129  to the PTO  128 . From the PTO  128  mechanical power may flow to the auxiliary device(s)  115 . Thus, the operating mode, depicted in  FIG.  2 C , may be implemented to jointly power the PTO while executing forward drive operation. However, it will be understood that the first electric machine  106  is capable of transferring mechanical power to the PTO  128  across a wide speed range (e.g., the entire speed range) of the electric machine, as a result of the to the configuration of the clutch  141  and the clutch assembly  127  with the PTO gearset  130 . 
     While the transmission  104  is operating in the mode illustrated  FIG.  2 D , the transmission  104  is again in the first gear ratio and operated to provide power to the PTO. However, unlike in the mode depicted in  FIG.  2 C , the first electric machine  106  is disconnected from the transmission in the mode depicted in  FIG.  2 D  and the second electric machine  108  may be spun in a reverse such that the transmission  104  propels the vehicle backwards. Thus, in this mode, the clutch assembly  127  is disengaged, and the clutch  141  is engaged. Further, the ring gear  154  is held stationary by the friction clutch  162  and the clutch  148  is disengaged. The mechanical power path in the operating mode of  FIG.  2 D  includes two power paths: a traction power path (denoted by arrows  280 ) and a PTO power path (denoted by arrows  282 ). The traction power path  280  unfolds as follows: mechanical power (e.g., produced via torque from the second electric machine  108  that has a reverse rotational direction) moves from the second electric machine  108  to the gear  126 , from the gear  126  to the gear  134 , from the gear  134  to the sun gear  142 , from the sun gear to the planet gears  152 , from the planet gears to the carrier  179 , and from the carrier to the output shaft  150 . The PTO power path  282  unfolds as follows: mechanical power moves from the electric machine  106  through the output shaft  121  to the gear  131 , from the gear  131  to the gear  137 , from the gear  137  through the PTO input shaft  129  to the PTO  128 . From the PTO  128  mechanical power may flow to the auxiliary device(s)  115 . In this way, the second electric machine  108  may be operated to provide reverse drive traction while the first electric machine  106  provides power to the PTO  128 , in some examples, or while the vehicle is at a standstill (e.g., when electric machine  108  is not providing power to the transmission), in other examples. 
       FIG.  2 E  shows a chart  290  that correlates the configurations of the friction clutches  135 ,  148 ,  162  and the synchronizers  133 ,  141 ,  160  to the first and second gears while the system is operated in a forward drive mode with the PTO disconnected. In  FIG.  2 E  as well as  FIGS.  2 F and  2 G , an “X” denotes clutch engagement and a blank field conversely denotes clutch disengagement. Specifically, in the first gear mode, the friction clutch  148  is disengaged and the friction clutch  162  as well as the synchronizer  160  are engaged. Conversely, in the second gear mode, the friction clutch  148  is engaged and the friction clutch  162  as well as the synchronizer  160  are disengaged. In both the first and second gear modes, the synchronizer  141  is disengaged and the clutch  135  and synchronizer  133  are engaged, thereby disconnecting the first electric machine from the PTO and connecting the first electric machine and the transmission. To powershift between the first gear and the second gear, the clutch  148  may be engaged while the clutch  162  is disengaged. Subsequently to disengagement of the clutch  162 , the synchronizer  160  may be disengaged. Conversely, to shift from the second gear back to the first gear, the synchronizer  160  may first be engaged and subsequently the clutch  162  may be engaged while the clutch  148  is disengaged. It will be understood that the synchronizer may be omitted from the system, in some examples. When powershifting is implemented in the transmission, power interruptions during shifting may be substantially avoided, thereby enhancing shifting performance. 
       FIG.  2 F  shows a chart  292  that correlates the configurations of the friction clutches  135 ,  148 ,  162  and the synchronizers  133 ,  141 ,  160  to the first and second gears while the system is operated in a forward drive mode with the PTO connected to the first electric machine. The configuration of the clutches  148 ,  162  and synchronizer  160  are identical to  FIG.  2 E  and repeated description is therefore omitted for brevity. However, each of the synchronizers  133 ,  141  and the clutch  135  are engaged such that power is transferred from the first electric machine to both the transmission and the PTO in both the first and second gears. In this way, power may be transferred to the PTO across a wide vehicle speed range. As a result, the vehicle PTO capabilities are expanded, thereby increasing customer appeal. 
       FIG.  2 G  shows a chart  294  that correlates the configurations of the friction clutches  135 ,  148 ,  162  and the synchronizers  133 ,  141 ,  160  to the first and second gears while the system is operated in a reverse drive mode with the PTO connected to the first electric machine. It will be appreciated, that in the reverse drive mode the second electric machine is spun in a reverse rotational direction to propel the vehicle in reverse. The configuration of the clutches  148 ,  162  and synchronizer  160  are identical to  FIG.  2 F  and repeated description is therefore omitted for concision. However, the synchronizer  141  is engaged and the synchronizer  133  and the clutch  135  are disengaged such that power is transferred from the first electric machine to the PTO in both the first and second gears while power transfer from the first electric machine to the transmission is inhibited. In this way, the second electric machine is able to provide reverse drive rotational input to the transmission without interfering with PTO operation. Consequently, the system&#39;s PTO capabilities are even further expanded. 
       FIG.  3 A- 3 C  show another example of a vehicle  300  with an electric driveline system. The boundary of the electric driveline system is denoted via dashed lines  302 . However, it will be appreciated that the system may include a different grouping of components, in other examples. The electric driveline system  302  includes a transmission  304 . The electric driveline system  302  with the transmission  304  shown in  FIGS.  3 A- 3 C  may share common features with the electric driveline system  102  and the transmission  104  shown in  FIGS.  1 - 2 D . Redundant description is therefore omitted.  FIGS.  3 A- 3 C  specifically illustrate the mechanical, coolant, and electrical connections, respectively, between components in the electric driveline system  302  as well as other vehicle components. Although the mechanical, coolant, and electrical connections are illustrated in separate figures for clarity, it will be understood that these connections may all be present in the electric driveline system. 
     The driveline system  302 , shown in  FIGS.  3 A- 3 C , include a first electric machine  306 , a second electric machine  308 , and a third electric machine  310 . The electric driveline system  302  further includes a first inverter  312 , a second inverter  314 , and a third inverter  316  that are associated with the first electric machine  306 , the second electric machine  308 , and the third electric machine  310 , respectively. The vehicle  300  further includes a pump  319  that is designed to circulate lubricant (e.g., oil) in the transmission  304 . A valve  321  coupled to the transmission  304  may be used to regulate lubricant flow from the pump  319  to the transmission. 
     The vehicle  300  further includes a first axle  320  (e.g., a front axle) and a second axle  322  (e.g., rear axle). The vehicle  300  may further include auxiliary devices  324 , such as a steering pump, an air conditioning pump, a hydraulic pump for working functions, and the like. Still further, the vehicle may include a coolant circuit  326 , a lower voltage power source  328  (e.g., a battery, a capacitor, combinations thereof, and the like), and a higher voltage power source  330  (e.g., a battery, a capacitor, combinations thereof, and the like). The driveline system  302  may include a DCU  332  and the vehicle  300  may include a VCU  334 . However, other control unit arrangements have been contemplated, such as a common control unit which is used to adjust operation of both the driveline system  302  and components in the vehicle  300 . Each of the control units may include any know data storage mediums (e.g., random access memory (RAM), read only memory (ROM), keep alive memory, combinations thereof, and the like) and a processor (e.g., micro-processor unit) designed to execute instructions stored in the data storage mediums. As such, the DCU  332  and/or the VCU  334  may perform the control methods, techniques, schemes, etc. described herein such as the method shown in  FIG.  4   . Further the DCU may be designed to coordinate operation of the inverters  312 ,  314 , and  316  to increase the system&#39;s efficiency. For instance, the DCU may be operated to balance power between the inverter  312  and  314  to increase the driveline system&#39;s efficiency. Specifically, in one example, the DCU may operate the inverter  312  and  314  to reduce torque generated by one of the electric machines and increase torque generated by the other electric machine such that they operate in a target efficiency point or range. Additionally, the DCU may be operated to control the inverter  316  to enable a desired lubricant flow to be achieved. The DCU may further be designed to implement fault reactions and diagnostics. For example, the DCU may implement a limp home mode when minor component degradation is detected, such as a degradation of a speed sensor. Further, the DCU may shutdown if the controller area network (CAN) is degraded, in some scenarios. 
     A heat exchanger  336  may further be coupled to (e.g., directly coupled to or incorporated into) the transmission  304 . In other examples, the heat exchanger  336  may be coupled to a vehicle frame  337 . The heat exchanger  336  may include components for transferring thermal energy between a coolant circuit and an oil circuit, such as adjacent coolant and oil passages, a housing, and the like. In this way, heat may be efficiently removed from the transmission&#39;s lubrication circuit. In one example, the heat exchanger  336 , such as a liquid-liquid cooler, may be bolted or otherwise mechanically attached to the transmission housing. In another example, the heat exchanger  336  may be formed by integrating coolant passages into the sump housing. 
     Electric PTOs  338 ,  340  may further be included in the vehicle  300 . The electric PTO  338  may include a higher voltage motor and an inverter  341  coupled to auxiliary devices  342  (e.g., a steering pump, a pump for working hydraulic devices, an air conditioning pump, and the like). The electric PTO  340  may include a lower voltage motor and an inverter  343  coupled to auxiliary devices  344 . Providing electric PTOs in the vehicle expands the vehicle&#39;s capabilities and adaptability. Consequently, the driveline system may be used in a wider variety of vehicle platforms. Furthermore, by using electric PTOs that operate with different voltages, the motors in the PTOs may be granularly tuned to meet the demands of the specific auxiliary devices to which they are attached, if wanted. However, in other examples, the electric PTO may be operated using a similar voltage. 
     The driveline system  302  may further include a first axle disconnect clutch  345  and a second axle disconnect clutch  346 . Each of the disconnect clutches may be friction clutches, dog clutches, or other suitable clutches that are designed to rotationally couple and decouple the transmission output interfaces from the corresponding axle. A PTO  347  may further be coupled to the transmission  304  and the auxiliary devices  324 . 
       FIG.  3 A  maps the mechanical connections between the components in the driveline system  302  as well as the vehicle  300 . These mechanical connections are denoted via lines  350 . The mechanical connections may be formed via shafts, joints, belts, chains, combinations thereof, and the like. As shown, the first electric machine  306  and the second electric machine  308  are rotationally coupled to the transmission  304 . Providing two electric machines mechanically coupled to the transmission may permit driveline efficiency to be increased. Further, the likelihood of the driveline system becoming inoperable due to motor degradation is reduced when there is electric machine redundancy in the driveline system. 
     The transmission  304  is also rotationally coupled to the first axle  320  and the second axle  322 , and the disconnect clutches  345 ,  346  may permit the axles to be connected and disconnected from the transmission  304  according to operator input and/or vehicle operating conditions, for instance. 
     The third electric machine  310  may be rotationally coupled to the pump  319  and the pump may be in fluidic communication with the transmission  304  via the valve  321 . The third electric machine  310  may be operated independently from the first and second electric machines  306 ,  308 . To elaborate, the third electric machine  310  may be adjusted to more aptly track with the lubricant demands of the transmission. In this way, the system&#39;s efficiency can be increased without impacting transmission lubrication operation, if wanted. 
     The PTO  347  is mechanically coupled to the auxiliary devices  324 . Further, the electric PTOs  338 ,  340  are mechanically coupled to the auxiliary devices  342 ,  344 , respectively. In this way, the system&#39;s PTO capabilities may be expanded to meet a variety of auxiliary device demands across a wide breadth of vehicle platforms. The system&#39;s customer appeal is consequently increased. 
       FIG.  3 B  shows the coolant connections, denoted via lines  352 , in a cooling assembly  354  of the electric driveline system  302 . The coolant connections may be established via conduits, ducts, and the like which are routed (e.g., internally and/or externally routed) through various system components. The coolant may include water and/or glycol. The cooling assembly  354  may include the coolant circuit  326  which may have a coolant pump and a heat exchanger. As shown, coolant may be routed to the heat exchanger  336 , the first electric machine  306 , the second electric machine  308 , the first inverter  312 , and the second electric machine  308  in parallel. Additionally or alternatively, the coolant may be routed to one or more of the following components in series: the heat exchanger  336 , the first electric machine  306 , the second electric machine  308 , the first inverter  312 , and the second electric machine  308 . In this way, the electric machines, inverters, and transmission lubricant may be efficiently cooled. The heat exchanger  336  is designed to transfer heat from lubricant (e.g., oil) routed through the transmission to coolant in the cooling assembly  354 . Providing the heat exchanger with an oil to coolant heat transfer functionality permits a liquid to air heat exchanger, such as a radiator, to be omitted from the system, if wanted. The system&#39;s size, complexity, and/or manufacturing costs may be reduced, as a result. 
     Alternatively, the first and/or second electric machines  306 ,  308  as well as the first and/or second inverters  312 ,  314  may be oil cooled. In such an example, the heat exchanger  336  may be omitted from the system. 
       FIG.  3 C  shows electrical and data connections in the vehicle  300  and the electric driveline system  302 . The electrical connections are specifically divided into higher voltage connections (denoted by thicker lines  356 ) and lower voltage connections (denoted by thinner lines  358 ). Data connections are denoted via dashed lines  360 . The higher voltage connections emanate from the higher voltage power source  330  and the lower voltage connections emanate from the lower voltage power source  328 . In one use-case example, the lower voltage may in the range between 12V and 144V and the higher voltage may be in the range between 350V and 800V. 
     The higher voltage power source  330  may be electrically coupled to the first inverter  312  and the second inverter  314 . Likewise, higher voltage electrical connections may be established between the first and second electric machines  306 ,  308  and the first and second inverters  312 ,  314 . A higher voltage connection may additionally be established between the electric PTO  338  and the driveline system  302 . 
     The lower voltage power source  328  may be electrically coupled to the first inverter  312 , the second inverter  314 , the third inverter  316 , and/or the DCU  332 . A lower voltage connection may additionally be established between the third inverter  316  and the third electric machine  310  as well as the electric PTO  340  and the driveline system  302 . Further, a lower voltage connection may be established between the DCU  332  and the valve  321 . 
     Data connections may be established between the VCU  334  and the DCU  332 . For instance, operating condition data such as vehicle speed, pedal position (e.g., brake pedal position and/or accelerator pedal position), drive mode selector positon, and the like may be transferred from the VCU to the DCU. Conversely, operating condition data such as electric machine speed, electric machine temperature, power source SOC, clutch position, transmission temperature, and the like may be transferred from the DCU to the VCU. In this way, data may be shared between the DCU and the VCU to enhance control routines at each control unit. A data connection may also be established between the DCU  332  and the first inverter  312 , the second inverter  314 , and/or the third inverter  316 . Further, data may be transferred from the electric PTOs  338  and  340  to the driveline system  302 . 
       FIG.  4    shows a method  400  for operation of an electric driveline system. The method  400  may be carried out via the electric driveline systems  102  and/or  302 , discussed above with regard to  FIGS.  1 - 3 C , in one example. However, in other examples, the method  400  may be implemented by other suitable electric driveline systems. Instructions for carrying out method  400  may be executed by a controller, such as the controller  193  in  FIG.  1    or the DCU  332  and/or the VCU  334  in  FIGS.  3 A- 3 C , by executing instructions stored in a memory of the controller and in conjunction with signals received from sensors at the controller. The controller may employ actuators in different system components to implement the method steps described below. 
     At  402 , the method includes determining operating conditions. The operating conditions may include speeds of the electric machines, transmission output shaft speed, vehicle speed, clutch positon, pedal position, transmission load, current PTO power demand, and the like. These conditions may be determined using sensors and/or modeling algorithms. 
     At  404 , the method judges if the PTO (e.g., PTO  128 , shown in  FIG.  1   ) should be connected to the transmission to receive power therefrom. The PTO connection judgment may be carried out based on an operator demand, and may in some cases involve determining the amount of torque demanded at the PTO. For instance, if an auxiliary device has been connected to the PTO and/or the operator requests PTO connection, it may be judged that a PTO connection is desired. However, additional or alternative factors may be taken into account when judging whether or not to connect the PTO to the transmission. 
     If it is judged that the PTO should not be connected to the transmission (NO at  404 ), such as when there is no power request for the PTO, the method moves to  406 . At  406 , the method includes sustaining the current transmission operating strategy. For instance, the transmission may be held in its current operating gear by sustaining engagement of one of the friction clutches and disengagement of the other friction clutch. Further, one of the clutches in the PTO assembly (e.g., the synchronizer  141  shown in  FIG.  1   ) may be sustained in a disengaged configuration. 
     Conversely, if it is judged that the PTO should be connected to receive power from the transmission (YES at  404 ), the method moves to  408 . At  408 , the method includes determining if the transmission is operating under a low speed condition or if the transmission output speed is substantially zero. This low speed condition may be a condition where the operating speed of the electric machines precludes the PTO from being driven to achieve current PTO power demands. 
     If it is determined that the transmission is not operating under a low speed condition (NO at  408 ) the method moves to  410 . At  410 , the method judges if the transmission is operating under a reverse operating condition. The reverse condition may be ascertained using the rotational direction of one or more of the electric machines. For instance, as previously described, the electric machines have a reverse drive rotational direction and an opposite forward drive rotational direction. When the gears  124 ,  126  on the electric machine output shafts directly mesh with the gear  134 , shown in  FIG.  1   , the rotational direction of each machine in both the forward and reverse drive modes may be opposite one another. For instance, in the forward drive mode, the first electric machine may rotate clockwise and the second electric machine may rotate counter-clockwise or vice versa. However, in other transmission configurations, the electric machines may each rotate in the same direction in the forward drive mode and may each rotate in the opposite direction in the reverse drive mode. 
     If it is determined that the transmission is operating under a low speed condition (YES at  408 ) or if it is determined that the transmission is operating in reverse (YES at  410 ), the method moves to  412 . At  412 , the method includes disengaging (or sustaining disengagement of) the clutch assembly (e.g., the clutch assembly  127 , shown in  FIG.  1   ) to disconnect (or sustain disconnection of) the first electric machine (e.g., the first electric machine  106 , shown in  FIG.  1   ) from the transmission (e.g., the transmission  104 , shown in  FIG.  1   ). In this way, one of the electric machines may be decoupled from the transmission while the other machine drives the transmission in reverse. 
     Next at  414 , the method includes engaging the clutch (e.g., the clutch  141 , shown in  FIG.  1   ) to couple the PTO (e.g., the PTO  128 , shown in  FIG.  1   ) and the first electric machine (e.g., the first electric machine  106 , shown in  FIG.  1   ). In this way, the first electric machine is used to drive the PTO while the second electric machine and transmission are operated in the reverse drive mode or while the transmission is operated at low speeds or at standstill. Consequently, the range of operating conditions over which the PTO may be used is expanded. 
     If it is determined that the transmission is not operating in reverse (NO at  410 ) the method moves to  416 . At  416 , the method includes engaging (or sustain engagement of) the clutch assembly (e.g., the clutch assembly  127  shown in  FIG.  1   ) to connect (or sustain connection of) the first electric machine (e.g., the first electric machine  106 , shown in  FIG.  1   ) to the transmission (e.g., the transmission  104 , shown in  FIG.  1   ). In this way, both the first and second electric machines may be used to drive the transmission when it is not operating under a low speed condition or in reverse. After  416  the method moves to  414 . Method  400  enables the PTO to be operated across an expansive range of operating conditions and permits the system&#39;s capabilities with regard to powering auxiliary devices using the PTO to be significantly expanded. 
     The technical effect of the electric driveline system operating method described herein is to expand the drive system&#39;s PTO capabilities and specifically allow joint PTO operation and reverse drive operation, without constraining the capabilities of the transmission or PTO, if wanted. 
       FIGS.  1 - 2 D and  3 A- 3 C  show example configurations with relative positioning of the various components. If shown directly contacting each other, or directly coupled, then such elements may be referred to as directly contacting or directly coupled, respectively, at least in one example. Similarly, elements shown contiguous or adjacent to one another may be contiguous or adjacent to each other, respectively, at least in one example. As an example, components laying in face-sharing contact with each other may be referred to as in face-sharing contact. As another example, elements positioned apart from each other with only a space there-between and no other components may be referred to as such, in at least one example. As yet another example, elements shown above/below one another, at opposite sides to one another, or to the left/right of one another may be referred to as such, relative to one another. Further, as shown in the figures, a topmost element or point of element may be referred to as a “top” of the component and a bottommost element or point of the element may be referred to as a “bottom” of the component, in at least one example. As used herein, top/bottom, upper/lower, above/below, may be relative to a vertical axis of the figures and used to describe positioning of elements of the figures relative to one another. 
     As such, elements shown above other elements are positioned vertically above the other elements, in one example. As yet another example, shapes of the elements depicted within the figures may be referred to as having those shapes (e.g., such as being circular, straight, planar, curved, rounded, chamfered, angled, or the like). Additionally, elements co-axial with one another may be referred to as such, in one example. Further, elements shown intersecting one another may be referred to as intersecting elements or intersecting one another, in at least one example. Further still, an element shown within another element or shown outside of another element may be referred as such, in one example. In other examples, elements offset from one another may be referred to as such. Even further, elements which are coaxial or parallel to one another may be referred to as such. 
     The invention will be further described in the following paragraphs. In one aspect, an electric driveline system is provided that comprises a first electric machine and a second electric machine mechanically coupled to a transmission; and a power take-off (PTO) assembly coupled to the first electric machine and comprising a first clutch coupled to a PTO gearset and designed to selectively disconnect a PTO from the first electric machine, wherein the PTO gearset is mechanically coupled to the first electric machine. 
     In another aspect, a method for operation of an electric driveline system is provided that comprises selectively mechanically coupling a power take-off (PTO) to a first electric machine while a second electric machine transfers mechanical power to a transmission through operation of a first clutch; wherein the second electric machine is mechanically coupled to a gear in a transmission gearset; and wherein the first electric machine is selectively mechanically coupled to the gear in the gear in the transmission gearset. The method may further comprise, in one example, disconnecting the first electric machine and the PTO from the transmission, while the PTO is connected to the first electric machine, through operation of a second clutch and a third clutch that are coupled to a gear on an output shaft of the first electric machine. In another example, the method may further comprise, while the first electric machine and the PTO are disconnected from the transmission, shifting the transmission between two discrete gear ratios through operation of two wet clutches in the transmission. In yet another example, the second electric machine may transfer mechanical power to the transmission to rotate the transmission in a reverse direction. Further, in another example, the first clutch may be a synchronizer or a friction clutch. 
     In yet another aspect, an electric driveline system is provided that comprises a first electric machine and a second electric machine mechanically coupled to a transmission; and a power take-off (PTO) assembly coupled to the first electric machine and comprising a first clutch designed to selectively couple an input shaft of a PTO to a PTO gearset, and a second clutch designed to selectively disconnect the first electric machine from the transmission. 
     In any of the aspects of combinations of the aspects, the electric driveline system may further comprise a second clutch designed to selectively disconnect the first electric machine from the transmission. 
     In any of the aspects of combinations of the aspects, the electric driveline system may further comprise a controller including instructions that when executed, while the second electric machine is transferring mechanical power to the transmission, cause the controller to operate the second clutch to disconnect the transmission from the first electric machine. 
     In any of the aspects of combinations of the aspects, the PTO may be disconnected when the second electric machine is operated to rotate the transmission in a reverse drive direction. 
     In any of the aspects of combinations of the aspects, the electric driveline system may further comprise a controller including instructions that when executed, while the electric driveline system is operated across its speed range, cause the controller to operate the first clutch to transfer mechanical power from the first electric machine to the PTO. 
     In any of the aspects of combinations of the aspects, the second clutch may be a friction clutch. 
     In any of the aspects of combinations of the aspects, the electric driveline system may further comprise a synchronizer arranged coaxial with the friction clutch and an output shaft of the first electric machine. 
     In any of the aspects of combinations of the aspects, the first clutch may be designed to selectively couple to a gear to an output shaft of the first electric machine; and the gear may mesh with a transmission gear. 
     In any of the aspects of combinations of the aspects, the first clutch may be a synchronizer. 
     In any of the aspects of combinations of the aspects, the first clutch may be a wet friction clutch. 
     In any of the aspects of combinations of the aspects, the transmission may be a multi-speed transmission that includes a planetary gearset and two friction clutches. 
     In any of the aspects of combinations of the aspects, the transmission may include two outputs coupled to two drive axles. 
     In any of the aspects of combinations of the aspects, the electric driveline system may further comprise a controller including instructions that when executed, while the second electric machine is transferring mechanical power to the transmission, cause the controller to: operate the second clutch to disconnect the transmission from the first electric machine; and operate the first clutch to transfer mechanical power from the first electric machine to the PTO. 
     In any of the aspects or combinations of the aspects, the second electric machine may transfer mechanical power to the transmission to rotate the transmission in a reverse direction. 
     In another representation, a method for operating an electric drive unit is provided that includes selectively engaging a first clutch to transfer power to a power take-off (PTO) from a first electric motor and selectively disengaging a second clutch to inhibit power transfer from the first electric motor to a transmission while a second electric motor is providing power to the transmission. 
     In another representation, an electric drive unit is provided that includes a first electric machine and a PTO system designed to connect and disconnect a PTO from the first electric machine based on one or more operating conditions and a second electric machine designed to transfer mechanical power to a transmission while the first electric machine is connected and disconnected from the PTO. 
     Note that the example control and estimation routines included herein can be used with various powertrain, electric drive, and/or vehicle system configurations. The control methods and routines disclosed herein may be stored as executable instructions in non-transitory memory and may be carried out by the control system including the controller in combination with the various sensors, actuators, and other transmission and/or vehicle hardware in combination with the electronic controller. As such, the described actions, operations, and/or functions may graphically represent code to be programmed into non-transitory memory of the computer readable storage medium in the vehicle and/or driveline control system. The various actions, operations, and/or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the examples described herein, but is provided for ease of illustration and description. One or more of the illustrated actions, operations and/or functions may be repeatedly performed depending on the particular strategy being used. One or more of the method steps described herein may be omitted if desired. 
     While various embodiments have been described above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant arts that the disclosed subject matter may be embodied in other specific forms without departing from the spirit of the subject matter. The embodiments described above are therefore to be considered in all respects as illustrative, not restrictive. As such, the configurations and routines disclosed herein are exemplary in nature, and that these specific examples are not to be considered in a limiting sense, because numerous variations are possible. For example, the above technology can be applied to powertrains that include different types of propulsion sources including different types of electric machines, internal combustion engines, and/or transmissions. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein. 
     As used herein, the term “substantially” is construed to mean plus or minus five percent of the range, unless otherwise specified. 
     The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.