Patent ID: 12209658

DETAILED DESCRIPTION

In a power shift transmission it is desirable to decrease torque changes, and consequently speed changes, at the output during shifting. However prior transmissions are not capable of maintaining a constant output torque during shifting transients. This is referred to as a torque dip. The factor by which the torque is decreased during a shift may be inversely proportional to the gear ratio spread. The gear ratio spread is defined as the ratio between the higher gear ratio and the lower gear ratio of the shift. For instance, in case of a shift from first to second gear, the ratio spread is defined by the ratio of a first gear ratio to a second gear ratio. In one prior example of an electric transmission, the spread may be larger (e.g., 2.75 in one specific use-case example) than the spread in some combustion engine driven transmissions (e.g., 1.3-1.8 in a specific use-case example). Therefore, many previous power shift electric transmission have a higher torque dip than prior engine powered transmissions, leading to a decreased shift quality. The power shift transmission systems and operating methods described herein aim to increase shift quality by transiently peaking a traction motor to diminish torque interruptions and maintain a substantially constant transmission output torque during power shifting events, in some cases. Consequently, transmission performance is increased.

FIG.1Ashows a first example of an electric powertrain100in a system101. The electric powertrain100may be included in a vehicle102. The vehicle102may for example be an off-highway vehicle such as a wheel loader, an excavator, a dumper, a material handling vehicle, a tractor, a harvester, a mining vehicle, or the like. An off-highway vehicle is vehicle whose size, weight, and/or top speed precludes it from being driven on highways and other roadways, in some cases. The powertrain100includes a traction motor104and a transmission106. In the illustrated example, the traction motor104is electrically coupled to an inverter108via an electrical connection109(e.g., multi-phase wires, bus bars, combinations thereof, and the like). As such, the traction motor104is an alternating current (AC) type motor in the illustrated example. To elaborate, the traction motor may be a multi-phase (e.g., three, six, or nine phase) AC motor. In one specific use case example, the traction motor may be a three phase AC motor that is less costly and more efficient than single phase type motors. However, in alternate examples, a direct current (DC) traction motor may be used in the electric powertrain100.

The inverter108may be electrically connected to an energy storage device110(e.g., one or more traction batteries, capacitor(s), fuel cell(s), combinations thereof, and the like). As such, electrical energy may flow between the inverter and the energy storage device during drive operation and regeneration operation, when the motor is designed as a motor-generator.

The electric powertrain100may further include one or more drive axle assemblies112that are mechanically coupled to output interface(s)114which may be included in the transmission106. The drive axle assemblies may specifically be a front drive axle assembly and a rear drive axle assembly, in one example. The drive axle assemblies may include differentials, axle shafts (e.g., half shafts) coupled to the associated differential, drive wheels coupled to the axle shafts), and the like. The drive wheels may be mounted on wheel hubs and may contact a driving surface while the vehicle is in operation.

The traction motor104may include components such as a rotor and a stator that electromagnetically interact during operation to generate motive power. Further in one example, the motor may be a motor-generator which is designed to generate electrical energy during regeneration operation.

The transmission106may include an input shaft116that is mechanically coupled (e.g., directly mechanically coupled) to a rotor shaft in the traction motor104. Splines, bolts and flanges, combinations thereof, and/or the like may be used to form the mechanical connection between the rotor shaft and the input shaft116. Inputs and outputs of the transmission generally denote the power flow occurring while the vehicle is operating under a drive condition where mechanical power is transferred from the traction motor to the drive wheels to propel the vehicle in a desired direction (e.g., forward drive direction or reverse drive direction). However, it will be appreciated that during regeneration operation, the mechanical power flow occurs in the reverse direction (i.e., from the drive wheels to the traction motor).

In the illustrated example, the input shaft116has a gear118fixedly coupled thereto. Fixedly coupling the components allows both components to co-rotate. Further, as illustrated, the gear118meshes with a gear120on a shaft122(e.g., idler shaft). The gear120is fixedly coupled to the shaft122. However, other gear layouts and/or other mechanical connections may be established between the input shaft and the idler shaft, in other example.

The transmission106further includes an output shaft124in the illustrated embodiment. A first friction clutch128may be mounted to the shaft122. A second friction clutch126may be mounted to the output shaft124. The second friction clutch126may be associated with a second operating gear ratio formed between a gear130and a gear132. The gear132may be idly mounted to the output shaft124via a bearing133. As such, when the second friction clutch126is disengaged, the gear132and the output shaft124can independently rotate. Likewise, the first friction clutch128may be associated with a first operating gear ratio formed between a gear134and a gear136. The second operating gear ratio may be greater than the first operating gear ratio. As such, the first operating gear ratio may be used at vehicle launch and during lower speed maneuvers. Conversely, the second operating gear ratio may be used during higher speed maneuvers. However, in other examples, the first operating gear ratio may be greater than the second operating gear ratio.

The first friction clutch128may include an inner plate carrier138(e.g., a hub) that is fixedly coupled to the shaft122and an outer plate carrier140(e.g., a drum) that is fixedly coupled to the gear134. The plate carriers each may include sets of plates141that are designed to frictionally engage and disengage during clutch closing and opening, respectively. To elaborate, the plates (e.g., friction and spacer discs) may be interleaved to allow selective torque transfer therethrough. For instance, the plates may be splined to the carriers, in some examples. However, other attachment techniques for the plates and carriers have been contemplated. The gear134may be idly mounted on the shaft122. For instance, a bearing142may be used to idly mount the gear134to the shaft122. The bearings described herein may include outer races, inner races, roller elements (e.g., balls, cylinders, tapered cylinders, and the like). Idly mounting refers to the attachment of a gear to a shaft such that the gear and shaft are able to independently rotate. The gear134meshes with the gear136that is fixedly coupled to the output shaft124, in the illustrated example.

The second friction clutch126may include an outer plate carrier144that is fixedly coupled to the gear132, an inner plate carrier146that is fixedly coupled to the output shaft124, and plates148in both of the carriers. As such, the second friction clutch126may have a similar construction to the first friction clutch128.

The friction clutches126,128may be wet friction clutches to reduce the temperature of the clutches during shifting events, to reduce the chance of the clutches experiencing over temperature conditions. The friction clutches126,128may therefore, in such an example, receive lubricant (e.g., natural and/or synthetic oil) from a lubrication system150. The lubrication system150may include a sump that collects the lubricant, a pump, lines, conduits, valves, and the like that route lubricant to the clutches and other components with lubrication needs such as bearings, gears, and the like, for instance. Still further, the lubrication system150may in one example be designed with hydraulic actuation circuits that enable the friction clutches to be hydraulically actuated. For instance, the friction clutches may include hydraulically actuated pistons that are in fluidic communication with the actuation circuit. However, in other examples, the hydraulic actuation circuits may be formed in a separate system that is distinct from the lubrication system or the friction clutches may be electro-mechanically and/or pneumatically actuated.

The friction clutches126,128are positioned on different shafts in the transmission which may enable the transmission to achieve greater space efficiency and load distribution. However, in other examples, the clutches may be coaxially positioned on the same shaft.

The output interfaces114(e.g., splines, flanges, yokes, and the like) may be used to attach the output shaft124to downstream components. To elaborate, as indicated via arrows152, a mechanical connection may be established between the output interfaces and the drive axle assemblies112. Shafts, joints, gears, chains, combinations thereof, and the like may be used to establish the mechanical connection between the output interfaces and the drive axle assemblies.

It will be appreciated that the transmission106may include additional shafts, gears, and/or clutches which may have different layouts, in other examples. For instance, the transmission106may include a second idler shaft with another clutch mounted thereto and/or an additional shaft that functions as an output shaft. As such, the transmission106may have three or more speeds, in other examples. However, increasing the number of available operating gears in the transmission increases the transmission's size and complexity. Therefore, the transmission may specifically be a two-speed transmission to reduce the transmission size, complexity, and likelihood of component degradation. Using a two-speed transmission may be particularly suited for a traction motor due to motor having a wider power band than internal combustion engines, for instance.

The powertrain100may further include a control system190with a controller192as shown inFIG.1A. 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 that are 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. As such, control techniques, methods, and the like expanded upon herein may be stored as instructions in non-transitory memory.

The controller192may receive various signals from sensors195coupled to various regions of the powertrain100. 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 traction motor104. An input device198(e.g., accelerator pedal, brake pedal, drive mode selector, gear selector199, combinations thereof, and the like) may further provide input signals indicative of an operator's intent for vehicle control. The gear selector199may include discrete positions such as drive and reverse as well as first gear and second gear that allow an operator to place the transmission in a forward drive mode, a reverse drive mode, a first gear mode, and a second gear mode. It will be appreciated, that when an operator places the transmission in a forward drive mode, the transmission may then automatically trigger power shifts based on transmission speed and load.

Upon receiving the signals from the various sensors195ofFIG.1A, the controller192processes the received signals, and employs various actuators196of powertrain 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 inverter108to adjust the motor's mechanical power output and increase the power delivered from the traction motor104to the multi-speed transmission106. The controller192may, during certain operating conditions, be designed to send commands to the friction clutches126,128, to carry out a power shift where the clutches are simultaneously engaged and disengaged. For instance, a control command may be sent to the first friction clutch and 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.1Aas well asFIGS.2A,1C, and1D, 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 traction motor104may be designed to spin the rotor shaft in opposing directions which correspond to forward and reverse drive. Therefore, in such an example, the transmission106may be designed to operate with an equal number of forward and reverse driving gear modes, in one example. However, in alternate examples, the transmission may have an asymmetric number of forward and reverse gear ratios.

FIG.1Bshows a table160that indicates the configurations of the second friction clutch126and the first friction clutch128in the first gear mode and the second gear mode. As previously indicated, in the first gear mode, the first friction clutch is engaged and the second friction clutch is disengaged and conversely, in the second gear mode the first friction clutch is disengaged and the second friction clutch is engaged.

FIGS.1C and1Dshow mechanical power paths170and180that occur in the transmission106of the electric powertrain100in the first operating gear and the second operating gear, respectively. In bothFIGS.1C and1D, the inverter108transfers electrical energy to the traction motor104and the traction motor generates mechanical power and inputs this power into the transmission106. However, as previously discussed the inverter may be omitted from the powertrain, in other embodiments.

In both of the mechanical power paths170and180, power travels from the traction motor104to the input shaft116, from the input shaft to the gear118, from the gear118to the gear120, and from the gear120to the shaft122.

In the power path170, shown inFIG.1C, power then travels from the shaft122to the gear134by way of the first friction clutch128, from the gear134to the gear136, from the gear136to the output shaft124, and from the output shaft124to the drive axle assemblies112.

On the other hand, in the power path180, shown inFIG.1D, first friction clutch128power then travels from the shaft122to the gear130, from the gear130to the gear132, from the gear132to the output shaft124by way of the second friction clutch126, and from the output shaft124to the drive axle assemblies112.

FIG.2Ashows another example of a transmission200in an electric powertrain202. The transmission200within the electric powertrain202shown inFIG.2shares some component which are similar in function and/or structure to the transmission106and the electric powertrain100depicted inFIG.1A. For instance, the electric powertrain202again includes a traction motor204and an inverter206and the transmission includes an input shaft208, a shaft210, an output shaft212, a gear214, a gear216, a gear218, a gear220, a gear222, a gear224, and output interfaces226. Repeated description of the overlapping components is omitted for concision.

The transmission200shown inFIG.2Aincludes a first synchronizer230and a second synchronizer228. The second synchronizer228is positioned adjacent to and directly coupled to a second friction clutch232and the first synchronizer230is likewise positioned adjacent to and directly coupled to a first friction clutch234. To elaborate, a first hollow shaft236may be used to attach the second synchronizer228to an inner plate carrier238and a second hollow shaft240may be used to attach the first synchronizer230to the inner plate carrier242. Further, hollow shafts244and246may be used to attach mating splines or toothed faces in the synchronizers228,230, respectively to the gear220and the gear222, respectively. The synchronizers228,230may each include a sleeve248as well as other components such as one or more synchronizer rings and the like. The synchronizers228,230are configured to bring the shaft speeds together to enable alignment and meshing of the splines or teeth in the clutch. Further, the synchronizers may be electromechanically, hydraulically, and/or pneumatically actuated. For instance, the sleeves248may be adjusted via shift forks or other suitable actuator. The use of synchronizers in the transmission200allows the slip speed of the clutch to be very low and in some cases equal or approach zero when the clutch is open, thereby reducing the drag power loss.

FIG.2Bshows a table260that indicates the configurations of the second friction clutch232, the second synchronizer228, the first friction clutch234, and the first synchronizer230in the first gear mode and the second gear mode. In the first gear mode, the second friction clutch232is engaged, the second synchronizer228is engaged, the first friction clutch234is disengaged, and the first synchronizer230is disengaged. Conversely, in the second gear mode, the second friction clutch232is disengaged, the second synchronizer228is disengaged, the first friction clutch234is engaged, and the first synchronizer230is engaged.

FIGS.3A and3Bshow prophetic torque vs speed graphs corresponding to an exemplary upshift event and a downshift event, respectively. Although specific numerical values are not provided on the ordinates and the abscissas, the torque and speed increase in the direction of the arrows.

FIG.3Aspecifically depicts load points on an example electromotor curve during an upshift (e.g., full throttle upshift) from a first gear (e.g., first friction clutch closed and second friction clutch open, at point300) to second gear (e.g., first friction clutch open and second friction clutch closed at point302). As described herein an open clutch configuration denotes that the torque transfer through the clutch is inhibited and a closed clutch configuration denotes that torque transfer through the clutch is occurring. Further, as described herein, a full throttle upshift is a shift event when an accelerator pedal has been depressed to an extent that generates an acceleration requests that is equal to or greater than the available acceleration in the powertrain given the current operating conditions.

A maximum continuous power curve304for the traction motor in the powertrain is illustrated inFIG.3A. The maximum continuous power curve304indicates the upper threshold of power at which the traction can be operated continuously. Therefore, operation of the motor above the continuous power threshold increases the temperature of the motor and specifically the end windings, thereby increasing the chance of motor degradation. However, the motor may be peaked above the continuous power curve for a comparatively short duration while avoiding heating the motor beyond a desired value (e.g., a temperature threshold indicative of an over-temperature condition). This operation is referred to as motor peaking. Motor peaking may not be deployed to significantly accelerate the vehicle due to the short duration it can be used due to heat generated during peaking. However, the inventors have unexpectedly recognized that motor peaking can be deployed during shifting transient due to their comparative short duration (e.g., less than three seconds (s)). As such peaking, which is elaborate upon below is deployed during shifting transients in various powertrain control strategies set forth herein. Further, it will be appreciated that to peak the motor the inverter may transfer an amount of electrical energy to the motor that is greater than the amount needed to maintain the motor at maximum continuous torque output.

The upshift, depicted inFIG.3A, begins with a torque overlap phase during which the torque path is transferred from the first friction clutch to the second friction clutch. During the torque overlap phase the clutch pressure in the first friction clutch is reduced while the clutch pressure in the second friction clutch is increased. As such, the torque through the first friction clutch is reduced while the torque through the second friction clutch is increased.

To diminish or completely avoid a torque dip, the traction motor is peaked during the overlap phase of the upshift. In particular, the traction motor torque is increased (via peaking) from point300to point301, during the overlap phase. To elaborate, the traction motor torque from point300to point301is greater than the motor's continuous torque threshold.

The torque dip that occurs in previous transmissions at the end of the overlap phase due to the transmission torque ratio already equaling the ratio of the second gear, but the speeds still equaling the ratio of the first gear. To elaborate, in previous transmissions, the second gear ratio is a factor equal to the spread lower than the first gear ratio, as such the torque dip is a factor equal to the spread that appears at the output. To avoid a decrease in the transmission's output torque, the peak traction motor torque is higher than the continuous torque by a factor that is greater than or equal to a spread between the first operating gear ratio and the second operating gear ratio. For instance, in one use-case example, a spread between the first and second operating gear ratios may be 2.75 and therefore to avoid a torque drop, the peak traction motor torque is 2.75 times higher than the maximum continuous motor torque. However, numerous gear ratio spreads have been contemplated and the gear ratio spread may be selected based on factors such as the target performance characteristics of the transmission, vehicle weight, traction motor configuration, and the like. However, when the peak motor torque is higher than the maximum continuous motor torque but not by a factor that is greater than or equal to the gear ratio spread, the motor may still be peaked to diminish the drop in transmission output torque and enhance shifting performance.

FIG.3Bspecifically depicts load points on an example electromotor curve during a downshift (e.g., full throttle downshift) from the second gear (e.g., first friction clutch open and second friction clutch closed, at point350) to the first gear (e.g., first friction clutch closed and second friction clutch open at point352).

The maximum continuous power curve354for the traction motor in the powertrain is again illustrated inFIG.3B. The downshift begins with a synchronization phase which occurs from point350to point351. During the synchronization phase, the second friction clutch is slipped to allow the speed of the transmission input to be increased. Further, during the synchronization phase, the traction motor is peaked to maintain the traction motor torque constant. As previously discussed peaking the motor involves operating the motor above its continuous power threshold by delivering additional electrical power to the motor. In other examples, the motor may be peaked but the torque may slightly decrease, due to a large spread between the gear ratios. In either case, the shifting smoothness is increased by decreasing or avoiding torque interruptions during shifting transients.

Next, during the downshift, a torque overlap phase occurs (from point351to point352), in which during which the torque is transferred from the second friction clutch to the first friction clutch. Further, during the overlap phase, the traction motor torque is gradually reduced as the gear ratio is increased, keeping the transmission's output torque constant. As the gear ratio is increasing during the torque overlap phase, the torque dip is reduced (e.g., avoided) and at the end of the overlap phase the output torque will be equal to the initial output torque again.

The transmission shafts, gears, bearings, and friction clutches are designed to allow for traction motor peaking during shifting transients. For instance, the number of friction and separator plates, the separator plate thickness and/or the plate surface area (e.g., diameters) may be increased to allow for higher thermal loading. Therefore, the clutch assemblies (e.g., drum, hub, discs, and the like) may be larger.

FIGS.4A and4Bshow methods402and450, respectively, for operation of an electric powertrain. Specifically,FIG.4Ashows an upshift method andFIG.4Bconversely shows a downshift technique. The methods400and450may be carried out by the electric powertrain100shown inFIG.1A, in one example. In other examples, the methods may be implemented via the electric powertrain202shown inFIG.2A, by other suitable powertrains, or combinations of the powertrains described herein. Furthermore, the methods400and450may be implemented by a controller that includes memory holding instructions for the method steps that are executable by a processor, as previously indicated.

The method400illustrated inFIG.4Aincludes at402, determining operating conditions. The operating conditions may include input device position (e.g., gearshift lever position), clutch configuration, accelerator pedal position, transmission input/output 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 power up-shift in the transmission should be implemented. Such a determination may be automatically carried out responsive to vehicle speed exceeding a threshold value and/or vehicle load dropping below a threshold value, in one example. In other examples, operator interaction with gear selector may initiate the power upshift.

If it is determined that a power upshift 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 ratio (e.g., the first gear ratio).

Conversely, if it is determined that a power upshift should occur (YES at404) the method moves to408where the method includes executing a power upshift from a first operating gear to a second operating gear.

Executing the power upshift includes steps410-414. Steps410-412occur during an overlap phase of the upshift and step414occurs during a synchronization phase of the upshift.

At410, the method includes engaging a second friction clutch while a first friction clutch is disengaged. In other words, torque transfer through the second clutch is increased while torque transfer through the first friction clutch is reduced. This clutch engagement may be initiated via hydraulic actuators with pistons that receive pressurized fluid (e.g., oil) from a hydraulic system. However, in other examples, the friction clutches may be electromechanically actuated via solenoids, for instance.

At412, the method includes peaking a traction motor. It will be appreciated that steps410and412occur at overlapping (e.g., concurrent) times. Peaking the traction motor may specifically include peaking the traction motor to maintain the torque at the output of the transmission at a substantially constant value. In this way, torque dips during shifting is avoided. However, in other examples, the traction motor may be peaked and the output torque may slightly drop due to the constraints of the motor and/or the spread between the first and second gear ratios. As indicated above, peaking the motor includes operating the motor above a threshold continuous power curve. Further, it will be appreciated that the motor may be operated on a threshold continuous power curve prior and subsequent to peaking of the motor.

At414, the method includes operating the traction motor to maintain the motor at a constant torque while the motor speed is reduced to return the motor to the threshold continuous power curve. In this way, the motor is peaked for a relatively short duration to avoid thermal degradation of the motor. For example, the motor may be peaked for less than three seconds, in one specific example. In particular, the traction motor may be peaked for one second or less. In this way, the chance of motor thermal degradation is significantly decreased (e.g., avoided). Method400allows the smoothness of upshifting to be increased while avoiding motor thermal degradation, if desired. After414, the method ends.

When the transmission includes synchronizers such as in the transmission200depicted inFIG.2A. Executing the power upshift between the first operating gear and the second operating gear may include, prior to step410, engaging the second synchronizer while the first synchronizer remains engaged, and subsequent to step414disengaging the first synchronizer while the second synchronizer remains engaged.

The method450, shown inFIG.4B, illustrates a downshifting strategy. At452, the method includes determining operating conditions. The operating conditions may be determined in a similar manner to step402, shown inFIG.4A.

Next, method450includes step454where the method includes determining if a power downshift should be implemented. Such a determination may be automatically carried out responsive to vehicle speed decreasing below a threshold value and/or vehicle load increasing above a threshold value, in one example. In other examples, operator interaction with gear selector may initiate the power downshift.

If it is determined that a power downshift should not occur (NO at454) the method moves to456where the method includes sustaining the current transmission operating strategy. For instance, the transmission may be maintained in its current operating gear ratio (e.g., the second gear ratio).

Conversely, if it is determined that a power upshift should occur (YES at454) the method moves to458where the method includes executing a power downshift from the second operating gear to the first operating gear. Executing the power downshift includes steps460-466. Steps460-462are specifically implemented during a synchronization phase and steps464-466are implemented during an overlap phase.

At460, the method includes slipping the second friction clutch while all of the torque in the transmission is traveling through the second friction clutch. Next at462, the method includes peaking the traction motor. It will be appreciated that steps460and462occur at overlapping (e.g., concurrent) times. Specifically, in one example, the traction motor may be peaked to maintain the transmission's output torque at a substantially constant value. However, in other examples, the motor may be peaked to reduce a torque dip in the transmission's output. In this way, the downshift smoothly occurs, thereby increasing shifting performance.

Next at464, the method includes engaging the first friction clutch while the second friction clutch disengages. To elaborate, torque is handed off from the second friction clutch to the first friction clutch.

Next at466, the method includes decreasing traction motor torque until the motor returns to the continuous power curve. It will be appreciated that steps464and466occur at overlapping (e.g., concurrent) times. In this way, the motor is peaked for a relatively short time during a downshifting transient to enhance shifting performance. After466, the method ends.

FIGS.5A and5Bshow prophetic graphs500and550that depict the torque and speed of various transmission components vs time. Although specific values are not provided inFIGS.5A and5B, time increases from left to right and speed and torque increase in the direction of the arrows on the ordinates, respectively.

Graph500specifically indicates a transmission input speed502, a transmission output torque504, a first friction clutch torque506, and a second friction clutch torque508. The upshift begins at t1. Further, the overlap phase occurs between t1and t2and the synchronization phase occurs between t2and t3.

As shown, the torque of the second clutch increases as the torque of the first clutch decreases during the overlap phase while the input speed and the output torque remain constant. Next during the synchronization phase, the input speed is decreased while the output torque remains constant.

Graph550again indicates a transmission input speed552, a transmission output torque554, a first friction clutch torque556, and a second friction clutch torque558.

The downshift begins at t1. Further, the synchronization phase occurs between t1and t2and the overlap phase occurs between t2and t3. During the synchronization phase, the speed of the input increases while the output torque and the second clutch torque are held at a constant speed and the torque of the first clutch is zero.

In both graphs500and550the input speed and the output torque of the transmission are held constant during overlap phases to enable the power shifting to smoothly unfold. Transmission efficiency is increased as a result.

The technical effect of the electric powertrain operating methods described herein is to increase shifting performance by decreasing or avoiding, in some cases, drops in torque during shifting transients (e.g., upshifts and downshifts) by temporarily operating the traction motor under a peak condition which is greater than a continuous power curve of the traction motor.

FIGS.1A,1C,1D, and2Ashow 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.

The invention will be further described in the following paragraphs. In one aspect, a method is provided that comprises receiving a first shift command to initiate a first shift event in a transmission; in response to receiving the first shift command, engaging a second friction clutch while disengaging a first friction clutch to transition from a first operating gear ratio to a second operating gear ratio; and during the gear ratio transition, operating a traction motor under a peak condition; wherein the peak condition includes a condition where a torque of the traction motor exceeds a maximum continuous torque threshold. In one example the method may further comprise receiving a second shift command to initiate a second shift event; in response to receiving the second shift command, engaging the first friction clutch while disengaging the second friction clutch to transition from the second operating gear ratio to the first operating gear ratio; and operating the traction motor under the peak condition. The method may further comprise, in one example, during the first shift event, decreasing a torque of the traction motor to operate the traction motor at or below the maximum continuous torque threshold. Further, in one example, the transmission may include a first synchronizer directly coupled to the first friction clutch and a second synchronizer directly coupled to the second friction clutch; and the method may further comprise in one example, the method further comprises: prior to engaging the first friction clutch while disengaging the second friction clutch, engaging the first synchronizer while sustaining engagement of the first synchronizer; and subsequent to engaging the second friction clutch while disengaging the first friction clutch, disengaging the first synchronizer while sustaining engagement of the second synchronizer.

In another aspect, an electric powertrain system is provided that comprises a first friction clutch configured to selectively engage a first operating gear ratio in a transmission; a second friction clutch configured to selectively engage a second operating gear ratio; and a controller including instructions that when executed, in response to receiving a shift command, cause the controller to: engage the second friction clutch and disengage the first friction clutch at an overlapping interval to implement a first power shift event; and during the overlapping interval, operating a traction motor under a peak condition; wherein the peak condition includes a condition where a torque of the traction motor exceeds a maximum continuous torque threshold; and wherein the second operating gear ratio is greater than the first operating gear ratio.

In yet another aspect, a method for operation of an electric powertrain system, is provided that comprises operating a traction motor above a maximum continuous torque threshold, during a torque hand-off between a second wet friction clutch and a first wet friction clutch in a power shift event; and operating the traction motor at or below the maximum continuous torque threshold prior and subsequent to the power shift event.

In any of the aspects or combinations of the aspects, a torque of an output of the transmission that includes the first and second friction clutches may be maintained at a substantially constant value during the engagement of the first friction clutch and the disengagement of the second friction clutch.

In any of the aspects or combinations of the aspects, the second operating gear ratio may be greater than the first operating gear ratio.

In any of the aspects or combinations of the aspects, the first shift command that triggers initiation of the first shift event may be automatically generated based on a change in vehicle speed and/or load.

In any of the aspects or combinations of the aspects, the transmission may include an output shaft configured to couple to a front axle assembly and a rear axle assembly.

In any of the aspects or combinations of the aspects, operating the traction motor under the peak condition may occur during an overlap phase of the first power shift event where torque handoff between the first friction clutch and the second friction clutch occurs.

In any of the aspects or combinations of the aspects, the electric powertrain system may further comprise a first synchronizer directly coupled to the first friction clutch; and a second synchronizer directly coupled to the second friction clutch.

In any of the aspects or combinations of the aspects, the controller may further include instructions that when executed, prior to the engagement of the second friction clutch and disengagement of the first friction clutch, cause the controller to: engage the second synchronizer while engagement of the first synchronizer is maintained; and the controller further includes instructions that when executed, subsequent to the engagement of the second friction clutch and disengagement of the first friction clutch, cause the controller to: disengage the first synchronizer while engagement of the second synchronizer is maintained.

In any of the aspects or combinations of the aspects, the transmission may be a two-speed transmission.

In any of the aspects or combinations of the aspects, the electric powertrain system may be included in an all-electric vehicle.

In any of the aspects or combinations of the aspects, the electric powertrain system may be included in an off-highway vehicle.

In any of the aspects or combinations of the aspects, operating the traction motor above a maximum continuous torque threshold may include operating the traction motor above the maximum continuous torque threshold to maintain an output torque of a transmission at a substantially constant value, wherein the first and second wet friction clutches are included in the transmission.

In any of the aspects or combinations of the aspects, the first wet friction clutch may be associated with first gear ratio and the second wet friction clutch is associated with a second gear ratio and wherein the first gear ratio is not equivalent to the second gear ratio.

In any of the aspects or combinations of the aspects, a duration of the power shift event may be less than three seconds (s).

In another representation, an electric drive system is provided that includes a pair of friction clutches, a traction motor, and a controller that including instructions that when executed during a power shift between the pair of friction clutches, cause the controller to transiently increase a torque produced by the traction motor above a continuous torque threshold.

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 and/or internal combustion engines. 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.

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.

As used herein, the term “approximately” 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.