Multi-speed transmission and method for transmission operation

Systems and methods for an electric drive unit are provided. A transmission system, in one example, includes a higher-lower range clutch assembly positioned downstream of a multi-speed clutch assembly and designed to shift the transmission system between a higher range operating mode and a lower range operating mode. The higher-lower range clutch assembly includes a lower range clutch and a higher range clutch each positioned on one of a first layshaft and an output shaft.

TECHNICAL FIELD

The present disclosure relates to a multi-speed transmission system and a transmission shifting method.

BACKGROUND AND SUMMARY

Transmissions are used in vehicles to control propulsive power delivered to drive wheels from a power source such as internal combustion engines or electric motors. Electric vehicles make use of electric drive units to generate motive power and provide an attractive alternative in terms of hydrocarbon emissions in relation to vehicles that solely rely on internal combustion engines for propulsion. However, electric motors may have different gear reduction demands than internal combustion engines. Therefore, gearboxes used in internal combustion engine vehicles may have compatibility issues in certain electric vehicle platforms.

US 2007/0113693 A1 to Chen teaches a multi-speed transmission for a conventional internal combustion engine (ICE). Chen's transmission includes two countershafts that are positioned on opposing sides of an input shaft as well as a Hi-Low shifting device that includes a high torque transmitting mechanism and a low torque transmitting mechanism. These torque transmitting mechanisms are positioned coaxial to one another. Chen's transmission further includes synchronizers coupled to the countershafts.

The inventors have recognized several drawbacks with Chen's transmission as well as other previous transmissions. For instance, positioning the high and low torque transmitting mechanisms coaxial to one another increases the transmission's length which may not align with packaging demands in certain vehicle platforms. Additionally, Chen's transmission transfers power directly from the engine to synchronizer gear reductions via the input shaft. Due this direct power transmission Chen's transmission may not be able to meet gear reduction demands in certain electric drives. Chen's transmission therefore may not be applicable in at least some electric powertrains.

The inventors have recognized the aforementioned issues and developed a transmission system to at least partially overcome the issues. The transmission system includes, in one example, a higher-lower range clutch assembly positioned downstream of a multi-speed clutch assembly and designed to shift the transmission system between a higher range operating mode and a lower range operating mode. In the system, the higher-lower range clutch assembly includes a lower range clutch and a higher range clutch each positioned on one of a first layshaft and an output shaft. Further in the system, the output shaft is designed to rotationally couple to at least one drive axle. In this way, a high-low range clutch arrangement is positioned near the output of the transmission to effectively expand the number of available gear ratios in the transmission. Further, placing the higher and lower range clutches near the transmission output allows the gear range in the upstream multi-speed clutches to be reduced, if so desired. This gear range reduction in the multi-speed clutch zone may result in more equal gear sizes and lower speeds of the gears and shafts. Consequently, transmission longevity is increased. Still further, when the lower range clutch is activated, the load levels circulating through the input section of the transmission are reduced, allowing for a reduction in components size for a similar high power level, if desired.

Further in one example, the multi-speed clutch assembly may include a first set of clutches arranged coaxial to a second layshaft and a second set of clutches arranged coaxial to a third layshaft. In this way, the transmission achieves a wider variety of gear ratios that may achieve a more equal gear spacing due to the downstream positioning of the high-low clutch assembly. Consequently, the transmission achieves enhanced controllability, enhanced driver comfort, and less ratio step variability, if desired when compared to previous transmissions.

Still further in another example, the transmission system additionally includes an input assembly that includes an input gear on an input shaft that is designed to mesh with a gear on an electric machine interface shaft. In this example, the input assembly may further include an output gear that meshes with one or more gears in the multi-speed clutch assembly. Using an input assembly with the aforementioned features allows the comparatively high speed output of an electric motor, when compared to an engine, to be strategically reduced prior to entering the clutch zones in the gearbox.

DETAILED DESCRIPTION

A transmission system that achieves increased longevity, enhanced controllability, and increased driver comfort is described herein. To achieve these characteristics, the transmission system includes a higher-lower range clutch assembly positioned in a location of the transmission which is downstream of a multi-speed clutch assembly. To elaborate, one of the clutches in the higher-lower range clutch assembly is positioned coaxial to an output shaft of the transmission. In this way, a wide spread, in relation to gear ratio, is created in an output zone, enabling the gear spread in the multi-speed clutch assembly to be reduced, and in turn more equal gear sizes and lower gear and shaft speeds can be achieved, if desired. The decreased shaft and gear speed allows smaller bearings to be used in the system. Further, smaller gear sizes may be used which reduces the transmission's installation envelope. The use of the higher-lower clutch assembly also enables the presence of shaft and clutch overspeed conditions to be avoided. Further, the use of a considerable reduction at the transmission's output, when the low range is activated, reduces the load levels circulating through the gearbox. Lower load on transmission components permits the components have a smaller size for a similar high power level, further decreasing the transmission's space efficiency.

FIG.1depicts a transmission system100. The transmission system100in the illustrated example, is included in an electric drive unit102of an electric vehicle (EV)104(e.g., a battery electric vehicle (BEV)).

The electric drive unit102generates motive power for vehicle propulsion. The EV104may be an off-highway vehicle such as a material handling, mining, or railway vehicle. More generally, the EV104may be a light, medium, or heavy duty vehicle, for instance.

The electric drive unit102includes an electric machine106. The electric machine106may include components such as a rotor and a stator that electromagnetically interact during operation to generate motive power. Further in one example, the electric machine may be a motor-generator which is designed to generate electrical energy during regeneration operation.

The electric machine106may be electrically coupled to one or more energy storage device(s)108(e.g., one or more traction batteries, capacitor(s), fuel cell, combinations thereof, and the like) by way of an inverter110when the machine is designed as alternating current (AC) machine. However, a direct current (DC) electric machine may be used in alternate examples.

Arrows114denote the electrical connection between the electric machine106, the inverter110, and the energy storage device(s)108. The inverter110is designed to convert direct current (DC) to AC and vice versa. In one use-case example, the electric machine106and the inverter110may be three-phase devices which can achieve greater efficiency when compared to other types of motors. However, motors and inverters designed to operate using more than three phases have been envisioned.

The electric machine106is rotationally coupled to the transmission system100. Further, the transmission system100includes a multi-speed transmission116(e.g., a multi-speed gearbox) with multiple assemblies. When the multi-speed transmission is used in an EV it may be referred to as an electric multi-speed transmission.

The multi-speed transmission116includes a higher-lower range clutch assembly118and a multi-speed clutch assembly120. The higher-lower range clutch assembly118is positioned downstream of the multi-speed clutch assembly120. Positioning these assemblies in this manner creates a wider range of available gear ratios, enabling for a reduction in the gear spread in the multi-speed clutch assembly120. The reduced gear spread multi-speed clutch assembly results in smaller gear sizes and lower gear and shaft speeds. This also allows clutch and shaft overspeed conditions to be avoided, if desired. The use of a considerable gear reduction at the transmission's output through the use of the higher-lower range clutch assembly118allows for a reduction in the load levels circulating through the gearbox, if desired. Lower loads on transmission components enables the components to be downsized for a similar high power level, further increasing the transmission's space efficiency.

The higher-lower range clutch assembly118includes a higher range clutch122positioned coaxial to an output shaft124and a lower range clutch126positioned coaxial to a first layshaft128. However, in another example, the higher range clutch may be positioned coaxial to the first layshaft and the lower range clutch may be positioned coaxial to the output shaft.

The higher range clutch122as well as the other clutches described herein may be friction clutches (e.g., wet friction clutches). The friction clutches described herein may be operated with varying amounts of engagement (e.g., continuously adjusted through the clutch's range of engagement) of friction plates and spacers. Further, the friction clutches described herein may be wet friction clutches through which lubricant is routed to increase clutch longevity. The higher range clutch122and the other 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. Using friction clutches allows power interruptions during shifting transients to be reduced.

In the friction clutch example, the higher range clutch122includes an inner carrier130and an outer carrier132. The inner carrier130has a first set of plates mounted thereto and the outer carrier132has a second set of plates mounted thereto. These plates frictionally engage when the clutch is closed to permit torque transfer from the inner carrier130to the outer carrier132. Conversely, when the clutch is open the plates are frictionally disengaged. As such, the clutch is in an engaged state when it is closed and a disengaged state when it is open. The outer carrier132is fixedly coupled to a gear134that is fixedly coupled to the output shaft124. A bearing136serves as the rotational connection between the inner carrier130and the output shaft124. The inner clutch carriers depicted inFIG.1are shown coupled to a single bearing. However, it will be understood that the clutch carriers may be coupled to multiple bearings, in other examples. Further, the inner carrier130is fixedly coupled to a gear138which meshes with a gear140coupled to the first layshaft128.

The lower range clutch126again includes an inner carrier142and an outer carrier144which each have different sets of plates mounted thereto and functions in the similar manner to the higher range clutch122with regard to plate engagement and disengagement. The other friction clutches described herein also includes plates the function in a similar manner and repeated description of the plates is omitted for brevity. The inner carrier142is fixedly coupled to a gear146that meshes with the gear134. Conversely, the outer carrier144is fixedly coupled to the gear140that meshes with the gear138and a gear148.

In the illustrated example, the higher and lower range clutches122and126are axially offset along their rotational axes150and151. In this way, the transmission's space efficiency is increased when compared to clutches that have the same position along their respective rotational axes. However, in other examples, the higher and lower range clutches may have alternate axial positions.

As illustrated, the output shaft124includes two mechanical interfaces152which are designed to mechanically attach to downstream driveline components such as shafts, joints, and the like that transfer mechanical power to drive axles154. This mechanical power transfer is denoted via arrows155. In other examples, the output shaft124may include one mechanical interface or more than two mechanical interfaces.

The multi-speed clutch assembly120includes multiple clutches arranged on a second layshaft156and a third layshaft158. To elaborate, in the illustrated example, a first pair of clutches which includes a first gear clutch160and a third gear clutch162are positioned coaxial to the third layshaft158and a second pair of clutches which includes a second gear clutch164and a fourth gear clutch165are positioned coaxial to the second layshaft156.

The second gear clutch164includes an inner carrier166and an outer carrier167. The inner carrier166is fixedly coupled to the gear148that meshes with the gear140. The outer carrier167if fixedly coupled to the second layshaft156.

The fourth gear clutch165includes an inner carrier168and an outer carrier169. The inner carrier168is fixedly coupled to a gear170that meshes with a gear171on the first layshaft128. The outer carrier169is again fixedly coupled to the second layshaft156.

The first gear clutch160includes an inner carrier172and an outer carrier173. The inner carrier172is fixedly coupled to a gear174that is rotationally coupled to the gear140as denoted via curved line178. In other words, the gear174may mesh with the gear140. However, in other examples, the gear174may be coupled to the gear140via a mechanical coupling such as one or more gears, shafts, joints, and the like. The inner carrier172is fixedly coupled to the third layshaft158.

The third gear clutch162includes an inner carrier175and an outer carrier176. The inner carrier175is fixedly coupled to a gear177that is rotationally coupled to a gear179on the first layshaft128as denoted via curved line180. In other words, the gear177may mesh with the gear179. However, in other examples, the gear177may be coupled to the gear179via a mechanical coupling such as one or more gears, shafts, joints, and the like. The inner carrier175is fixedly coupled to the third layshaft158.

The multi-speed transmission116further includes, in the illustrated example, an input assembly181that includes an input shaft182with a gear183and a gear184fixedly coupled thereto. The gear183meshes with a gear185fixedly coupled to the third layshaft158. The gear185is rotationally coupled to a gear186that is fixedly coupled to the second layshaft156as denoted via curved line187. In other words, the gear185may mesh with the gear186. However, in other examples, the gear185may be coupled to the gear186via a mechanical coupling such as one or more gears, shafts, joints, and the like. Further, the gear184meshes with a gear188on an electric machine interface shaft189. In turn, the electric machine interface shaft189is coupled to a rotor shaft in the electric machine106.

A second electric machine198may additionally be coupled to the multi-speed transmission116, in one example, via a gear199that meshes with the gear184. However, in other examples, the second electric machine198may be omitted from the electric drive unit102.

The output shaft124is arranged below the layshafts128,156,158as well as an input shaft182. In this way, the transmission achieves a desired drop that has applicability in a wide range of vehicles.

The transmission116further includes bearings147that are coupled to inner carriers of the clutches and the corresponding shafts that are coaxial to the inner carriers. In this way, the inner carriers can independently rotate with regard to the shafts when the clutches are disengaged.

The EV104further includes a control system190with a controller192as shown inFIG.1. The controller192may include a microcomputer with components such as a processor193(e.g., a microprocessor unit), input/output ports, an electronic storage medium194for 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 controller192may receive various signals from sensors195coupled to various regions of the EV104and the multi-speed transmission116. For example, the sensors195may 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, and the like. Motor speed may be ascertained from the amount of power sent from the inverter to the electric machine. An input device145(e.g., accelerator pedal, brake pedal, drive mode selector, combinations thereof, and the like) may further provide input signals indicative of an operator's intent for vehicle control.

Upon receiving the signals from the various sensors195ofFIG.1, the controller192processes the received signals, and employs various actuators196of vehicle and/or transmission components to adjust the components based on the received signals and instructions stored on the memory of controller192. For example, the controller192may receive an accelerator pedal signal indicative of an operator's request for increased vehicle acceleration. In response, the controller192may command operation of the inverter110to adjust electric machine power output and increase the power delivered from the electric machine106to the multi-speed transmission116. The controller192may, during certain operating conditions, be designed to send commands to the clutches122,126,160,162,164,165, to engage and disengage the clutches. For instance, a control command may be sent to the higher range clutch122and in response to receiving the command, an actuator in the clutch 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.

An axis system is provided inFIG.1as well asFIGS.2A-2D and3, 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, in one example. However, the axes may have other orientations, in other examples.

The multi-speed transmission116may be designed to operate with an equal number of forward and reverse driving gear modes. For instance, in the illustrated example, the transmission has eight forward and reverse gear modes. However, it will be appreciated that the transmission may be designed with a fewer number of symmetric gear modes. For instance, the transmission may have four or sixteen forward and reverse gear modes.

To operate the multi-speed transmission116in a reverse drive mode the electric machine106may spin the rotor shaft in an opposite direction as the forward drive mode. Designing the electric machine106in this manner allows the compactness of the transmission to be reduced when compared to transmissions with mechanical reverse assemblies. However, in other examples, the transmission may include a mechanical reverse that decreases the system's space efficiency.

FIGS.2A and2Bshow the power paths200and202through the multi-speed transmission116in a higher-range mode and a lower-range mode respectively. It will be understood that these power paths may correspond to both forward and reverse drive modes. Further, the electric machine may generate rotational output in opposite directions in the forward and reverse drive modes. In other words, in a forward drive mode, the electric machine may rotate the electric machine interface shaft189in a first direction and in a reverse drive mode, it may rotate the output shaft in the opposite direction. Thus, the power paths shown inFIGS.2A and2Bgenerally correspond to drive mode operation.

As illustrated inFIG.2A, while the transmission116is operating in the higher-range mode, the higher range clutch122and the first gear clutch160are engaged while the remainder of the clutches are disengaged. However, it will be understood that the transmission may be operated in the higher-range mode in the second, third, and fourth gears where the respective second, third, or fourth clutch is engaged while the remainder of the multi-speed clutches are disengaged.

The mechanical power path200unfolds as follows: mechanical power moves from the electric machine106to the gear188; from the gear188to the gear184; from the gear184to the input shaft182; from the input shaft to the gear183; from the gear183to the gear185; from the gear185to the third layshaft158; from the third layshaft to the first gear clutch160; from the first gear clutch to the gear174; from the gear174to the gear140; from the gear140to the gear138; and from the gear138to the output shaft124via the clutch122; and from the output shaft to downstream components. As such, the power path200bypasses the second layshaft156.

While the transmission116is operating in the lower range mode, as shown inFIG.2B, the lower range clutch126and the first gear clutch160are engaged while the remainder of the clutches in the transmission are disengaged.

The mechanical power path202unfolds as follows: mechanical power moves from the electric machine106to the gear188; from the gear188to the gear184; from the gear184to the input shaft182; from the input shaft to the gear183; from the gear183to the gear185; from the gear185to the third layshaft158; from the third layshaft to the first gear clutch160; from the first gear clutch to the gear174; from the gear174to the lower range clutch126via the gear140; from the lower range clutch to the gear146; from the gear146to the gear134; from the gear134to the output shaft124; and from the output shaft to downstream components. As such, the power path202bypasses the second layshaft156.

FIGS.2C and2Dshow the power paths204and206through the multi-speed transmission116in a higher-range mode and a lower-range mode respectively, with different gears in the multi-speed clutch zone thanFIGS.2A and2B.

As illustrated inFIG.2C, while the transmission116is operating in the higher-range mode, the higher range clutch122and the fourth gear clutch165are engaged while the remainder of the clutches are disengaged.

The mechanical power path204unfolds as follows: mechanical power moves from the electric machine106to the gear188; from the gear188to the gear184; from the gear184to the input shaft182; from the input shaft to the gear183; from the gear183to the gear186; from the gear186to the second layshaft156; from the second layshaft to the fourth gear clutch165; from the fourth gear clutch to the gear170; from the gear170to the first layshaft128via the gear171; from the first layshaft to the gear140; from the gear140to the gear138; from the gear138to the higher range clutch122; from the higher range clutch122to the output shaft124; and from the output shaft to downstream components. As such, in the higher range mode of operation, the power path204bypasses the second layshaft156and the first layshaft128. As such, in the higher range mode of operation, the power path204bypasses the third layshaft158.

As illustrated inFIG.2D, while the transmission116is operating in the lower-range mode, the lower range clutch126and the fourth gear clutch165are engaged while the remainder of the clutches are disengaged.

The mechanical power path206unfolds as follows: mechanical power moves from the electric machine106to the gear188; from the gear188to the gear184; from the gear184to the input shaft182; from the input shaft to the gear183; from the gear183to the gear186; from the gear186to the second layshaft156; from the second layshaft to the fourth gear clutch165; from the fourth gear clutch to the gear170; from the gear170to the first layshaft128via the gear171; from the first layshaft to the lower range clutch126; from the lower range clutch126to the gear146; from the gear146to the gear134; from the gear134to the output shaft124; and from the output shaft124to downstream components. As such, the power path206bypasses the third layshaft158.

FIG.2Eshows a table250that indicates the configurations of lower range clutch126, the higher range clutch122, the first gear clutch160, the second gear clutch164, the third gear clutch162, and the fourth gear clutch165. As shown, the transmission can be operated in eight forward and reverse gears.

FIG.3shows an example of a multi-speed transmission300. The multi-speed transmission300shares similarities with the multi-speed transmission116, shown inFIG.1. For instance, the multi-speed transmission300includes a higher-lower range clutch assembly positioned downstream of a multi-speed clutch assembly. Redundant description of the overlapping features is omitted for brevity.

The multi-speed transmission116includes a housing302with an electric machine interface shaft304with an interface306that is profiled to attach to a rotor shaft of an electric machine.

The housing302includes two main sections308and310that are attached to one another via fasteners312and/or other suitable attachment devices. However, other housing contours may be used in other examples. The housing302at least partially encloses an input assembly, a range clutch assembly, and a multi-speed clutch assembly.

A mechanical output interface314is further included in the transmission300. The interface314is positioned below the electric machine interface306. In this way, the transmission may achieve a desired amount of drop. A charging pump316may further be included in the transmission300. The charging pump316may be driven via an electric motor318that is distinct from the traction motor. Further, the charging pump may be designed to provide pressurized fluid (e.g., oil) to the clutches for actuation and/or lubrication, in one example. In this way, a space efficient transmission unit with charging pump functionality can be achieved, if desired.

FIG.4shows a method400for operation of a transmission system. The method400may be carried out by any of the transmission systems or combinations of the transmission system described herein with regard toFIGS.1-3B. However, the method400may be carried via other suitable transmissions, in other examples. Furthermore, the method400may be implemented by a controller that includes a processor and memory, as previously discussed. Method400specifically shows a downshift sequence. However, it will be appreciated that an upshift sequence may be similarly implemented where the higher range clutch is engaged while the lower range clutch is disengaged.

At402, the method includes determining operating conditions. The operating conditions may include input device position (e.g., gearshift lever position), clutch configuration, transmission speed, motor speed, vehicle speed, vehicle load, ambient temperature, and the like. The operating conditions may be ascertained via sensor inputs, modeling, look-up tables, and/or other suitable techniques.

Next at404, the method includes judging if a high-low range powershift in the transmission should be implemented. Such as determination may be carried out responsive to vehicle speed surpassing a threshold value, in one example. In other examples, operator interaction with gear selector may initiate powershift operation.

If it is determined that a high-low range powershift should not occur (NO at404) the method moves to406where the method includes sustaining the current transmission operating strategy. For instance, the transmission may be maintained in its current operating gear.

Conversely, if it is determined that a high-low range powershift should occur (YES at404) the method moves to408where the method includes engaging a lower range clutch and disengaging a higher range clutch while power delivery from the electric machine to the transmission is sustained to transition from higher range operating mode to the lower range operating mode. In this way, the shift may occur with little or no power interruption, if wanted.

Next at410, the method includes judging if a multi-speed clutch powershift in the transmission should be implemented. Such as determination may be carried out responsive to vehicle speed surpassing a threshold value, in one example. In other examples, operator interaction with gear selector may initiate powershift operation.

If it is determined that a multi-speed clutch powershift should not occur (NO at410) the method moves to406. Conversely, if it is determined that a high-low range powershift should occur (YES at410) the method moves to412where the method includes engaging one of the gear clutches while disengaging another gear clutch. In this way, the shift may again occur with little or no power interruption, if wanted.

FIG.5illustrates a timing diagram500of a use-case control strategy for a transmission system, such as any of the previously described transmissions or combinations of the transmissions. In each graph, time is indicated on the abscissa and increases from left to right. The ordinate for plot501indicates vehicle speed. The ordinates for plots502and504indicate the operational states (“Engaged” and “Disengaged”) of the lower and higher range clutches. Other parameters that may trigger an up-shift or a down-shift include load, throttle pedal position, and the like.

From t0to t1the vehicle speed increases and at t1the speed surpasses a threshold value506. Responsive to the vehicle speed surpassing the threshold value a powershifting event occurs where the lower range clutch transitions into a disengaged state and the higher range clutch transitions into an engaged state. It will be understood that the specific clutch control strategy may be more nuanced, in practice. For instance, clutch pressure in the clutches may be less abruptly ramped up and down to allow a smoother transition into the higher range mode to occur and reduce the likelihood of unwanted noise, vibration, and harshness (NVH).

The technical effect of the transmission systems and operating methods described herein is to efficiently transition between the transmission's discrete gears with a decreased amount of power interruption and/or provide a technique which allows the transmission to achieve a targeted range of gear ratios in a space efficient package.

FIG.3is drawn approximately to scale. Although other relative component dimensions may be used, in other embodiments.

The invention will be further described in the following paragraphs. In one aspect, a transmission system is provided that comprises a higher-lower range clutch assembly positioned downstream of a multi-speed clutch assembly and designed to shift the transmission system between a higher range operating mode and a lower range operating mode; wherein the higher-lower range clutch assembly includes a lower range clutch and a higher range clutch each positioned on one of a first layshaft and an output shaft; and wherein the output shaft is designed to rotationally couple to at least one drive axle.

In another aspect, a method for operation of a transmission system is provided that comprises during a first operating condition, operating a higher-lower range clutch assembly positioned downstream of a multi-speed clutch assembly to shift the transmission system between a higher range operating mode and a lower range operating mode; wherein the higher-lower range clutch assembly is positioned downstream of the multi-speed clutch assembly; wherein the higher-lower range clutch assembly includes a lower range clutch and a higher range clutch each positioned on one of a first layshaft and an output shaft; and wherein the output shaft is designed to rotationally couple to a drive axle. In one example, the method may further include during a second operating condition, operating the multi-speed clutch assembly to powershift the transmission system between two gear speed modes. In yet another example the method may further include operating an electric motor to drive a charging pump, wherein the electric motor and the charging pump are coupled to a housing of the transmission system.

In yet another aspect, an electric transmission system is provided that comprises a higher-lower range clutch assembly positioned downstream of a multi-speed clutch assembly and designed to shift the electric transmission system between a higher range operating mode and a lower range operating mode; wherein the higher-lower range clutch assembly includes a lower range friction clutch and a higher range friction clutch each positioned on one of a first layshaft and an output shaft; and wherein the output shaft is designed to rotationally couple to a drive axle.

In any of the aspects or combinations of the aspects, the multi-speed clutch assembly may include a first set of clutches arranged coaxial to a second layshaft and a second set of clutches arranged coaxial to a third layshaft.

In any of the aspects or combinations of the aspects, the first and second sets of clutches may each include two or more friction clutches.

In any of the aspects or combinations of the aspects, the higher range clutch and the lower range clutch may be friction clutches.

In any of the aspects or combinations of the aspects, the transmission system may be designed with an equal number of forward and reverse driving gear modes.

In any of the aspects or combinations of the aspects, the transmission system may further comprise an input assembly that includes an input gear on an input shaft that is designed to mesh with a gear on an electric machine interface shaft.

In any of the aspects or combinations of the aspects, the input assembly may further include an output gear that meshes with one or more gears in the multi-speed clutch assembly.

In any of the aspects or combinations of the aspects, the input shaft may be positioned above an electric machine interface shaft.

In any of the aspects or combinations of the aspects, the transmission system may further include a charging pump driven by an electric motor coupled to a housing of the transmission system.

In any of the aspects or combinations of the aspects, the input shaft may be positioned above the output shaft.

In any of the aspects or combinations of the aspects, the output shaft may be rotationally coupled to multiple drive axles.

In any of the aspects or combinations of the aspects, operating the higher-lower range clutch assembly to shift the transmission system between the higher range operating mode and the lower range operating mode may be implemented during a reverse driving operating condition.

In any of the aspects or combinations of the aspects, the system may further comprise an input assembly that includes an input gear on an input shaft that is designed to mesh with a gear on a first electric machine interface shaft.

In any of the aspects or combinations of the aspects, the input gear may be designed to mesh with a gear on the output shaft of a second electric machine.

In any of the aspects or combinations of the aspects, the input shaft may be positioned above the output shaft and the first electric machine interface shaft.

In any of the aspects or combinations of the aspects, the first layshaft and the output shaft may be positioned below the first electric machine interface shaft.

In another representation, a symmetric powershift transmission in an electric vehicle is provided that includes a high-low range clutch section positioned downstream of a multi-speed clutch section, coupled to an output shaft, and including a high range clutch positioned on the output shaft and a low range clutch positioned on a layshaft that is above the output shaft.

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 electric drive unit and/or vehicle 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. 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.