Motor and torque converter clutch control strategies for electric drive units with motor-driven torque converter

Abstract

This application relates to motor and torque converter clutch control strategies for electric drive units with motor driven torque converters. A method for controlling an electric drive unit (EDU) with a motor driven torque converter includes receiving a request signal indicative of a requested output torque of the EDU, and operating a motor using the requested output torque at a target motor speed. The target motor speed minimizes system losses while achieving the requested output torque. When the requested output torque remains below a calibrated threshold and a turbine speed is less than a rotational speed of the motor, a torque converter clutch (TCC) transitions to or remains in a locked state. A controller commands the TCC to transition to an unlocked state to achieve the target motor speed, thereby selectively achieving torque multiplication. A powertrain system includes a driven load and the EDU. A computer readable storage medium can include executable instructions for performing the method.

Description

[0001] INTRODUCTION

[0002] Powertrain systems are equipped with one or more torque actuators. When the powertrain system is configured for use on a mobile system, the output torque provided by the various torque actuators is used for locomotion, for example. In this case, the individual torque actuators act as a set of propulsion actuators in aggregate. Electric vehicles, robots, and other mobile platforms can include electric drive units (EDUs) in which motor output torque from one or more electric traction motors is directed to a set of weight-bearing wheels. Stationary systems can use similar EDUs for other beneficial purposes, such as rotating drive belts while powering a driven load or while generating electricity.

[0003] Electric traction motors, generators, and other rotating electric machines are capable of producing a relatively high level of output torque at low rotational speeds, for example, relative to the low-speed torque production capability of internal combustion engines. However, the relative speed-torque performance advantage of electric machines diminishes substantially at higher rotational speeds. The output power capability of an electric traction motor is equal to the product of its output torque and speed. Accordingly, electric traction motors have traditionally been designed in size to provide sufficient output power capability for a particular application. As an alternative solution, electrically powered hydrodynamic torque converters can be used to boost the torque and power output of an electric traction motor, thereby avoiding the need for an oversized motor design. SUMMARY

[0004] The present disclosure relates to real-time control of a powertrain system of a motor vehicle. The powertrain system includes an electric traction motor (“motor”) and a hydrodynamic torque converter assembly (“torque converter”). The torque converter includes an input member in the form of an impeller (also referred to hereinafter as a pump) that, in the present embodiment, is connected to a rotor shaft or other output member of the motor, such that the torque converter is “motor-driven” within the scope of the present disclosure. The torque converter further includes a stator, an output member in the form of a turbine that is connected to a transmission, and a torque converter clutch (TCC). The TCC is operable for selectively locking the pump to the turbine to allow the pump and turbine to rotate in unison, i.e., at the same speed / without slipping. The torque converter includes an output member, such as a turbine shaft, that is drivingly connected to a rotatable input member of the transmission, thereby transferring torque from the motor to the transmission.

[0005] As appreciated by those skilled in the art, torque converter assemblies are often equipped with a TCC that serves as an internal lock-up clutch mechanism. The TCC is selectively applied to rigidly connect one rotating member to another when the respective rotational speeds are nearly equal. The methods described below are used to regulate the rotational speed of an electric traction motor ("motor speed") and the lock-up / unlock apply state of the TCC, where a powertrain control module or other system controller executes the methods in a manner that coordinates the motor / pump acceleration profile in a manner that minimizes overall system losses. In the disclosed controller-implemented strategy detailed below, the electric traction motor follows a predetermined speed profile to achieve a particular output torque request and associated vehicle acceleration.

[0006] Aspects of the present disclosure include a method for controlling an electric drive unit (EDU) of a motor vehicle. The EDU includes a torque converter connected to an electric traction motor such that a pump of the torque converter is driven by an output member of the electric traction motor. The method according to embodiments includes receiving, via a controller, a request signal indicative of a requested output torque of the EDU. The method further includes accelerating the motor to a target motor speed with a calibrated speed profile, where the calibrated speed profile corresponds to a predetermined vehicle acceleration rate. The calibrated speed profile and the target motor speed are structured to minimize overall system losses of the EDU while achieving the requested output torque.

[0007] When the predetermined vehicle acceleration rate remains below a calibrated acceleration threshold and a turbine speed of a turbine of the torque converter is less than a corner speed of the electric traction motor, the method includes commanding the TCC to transition to or remain in a locked state. The method further includes commanding the TCC to transition to an unlocked state to reach the target motor speed, whereby a multiplication of input torque from the electric traction motor is selectively achieved when operating at the target motor speed. As appreciated in the art, the term "corner speed" as used herein is a particular rotational speed at which the motor reaches its maximum power.

[0008] The target motor speed as used herein can correspond to an actual output torque that can be achieved by the torque converter when the TCC is in an unlocked state, which is equal to an actual output torque that can be achieved by the torque converter when the TCC is in a locked state.

[0009] In some embodiments, the disclosed motor vehicle includes an accelerator pedal having a measurable pedal position, in which case receiving the request signal includes receiving a pedal position signal indicative of a percentage of applied force or travel of the accelerator pedal. The method can include extracting the target motor speed from a lookup table indexed according to pedal position or applied force.

[0010] When the TCC is in the locked state, the method can further include applying a hysteresis band that operates below a predetermined rotational speed of the electric traction motor. This action is performed to prevent the TCC from transitioning from the locked state to the unlocked state when the motor is operating to produce a vehicle acceleration level within the hysteresis band. The hysteresis band contemplated herein can be defined by a corresponding output torque threshold.

[0011] In some embodiments, the EDU can be used to power a vehicle propulsion function. In this representative use case, the method can further include determining whether the motor vehicle is stationary or moving, and then ramping up a rotational speed of a pump of the torque converter to a target motor speed at a first rate or a second rate, respectively, depending on whether the motor vehicle is stationary or moving.

[0012] When the motor vehicle is stationary, the method can include ramping up the rotational speed of the pump to the target motor speed at a first rate, wherein the first rate is a calibrated maximum acceleration rate of the electric traction motor. When the motor vehicle is moving, the method can include ramping up the rotational speed of the pump to the target motor speed at a second rate. The second rate, which is less than the first rate, is limited by an available battery power level of a propulsion battery connected to the electric traction motor.

[0013] In another aspect of the disclosure, the method can include maintaining the TCC in the locked state when the electric traction motor is operating below a peak motor torque, and unlocking the TCC when the requested output torque exceeds the peak motor torque.

[0014] A powertrain system having an EDU and a driven load is also disclosed herein. The EDU includes an electric traction motor operatively connected to the driven load, and a torque converter having a pump and a turbine, wherein the pump is connected to and driven by the motor. A controller is in communication with the motor and the torque converter. The controller is configured to perform the method outlined above.

[0015] Additionally, a computer-readable storage medium having instructions recorded thereon for controlling an EDU is disclosed. Execution of the instructions by a processor causes the processor to receive a request signal indicative of a requested output torque of the EDU, and accelerate the motor to a target motor speed for a predetermined vehicle acceleration rate. Execution of the instructions also causes the processor to command the TCC to transition to or remain in a locked state when the predetermined vehicle acceleration rate remains below a calibrated acceleration threshold and a turbine speed of the torque converter is less than a rotational angular speed of the electric traction motor. The processor also commands the TCC to transition to an unlocked state upon reaching the target motor speed, thereby selectively enabling multiplication of an input torque from the electric traction motor when operating above the target motor speed.

[0016] Scheme 1. A method for controlling an electric drive unit (EDU) of a motor vehicle, the EDU having a torque converter connected to an electric traction motor such that a pump of the torque converter is driven by an output member of the electric traction motor, the method comprising:

[0017] receiving, via a controller, a request signal indicative of a requested output torque of the EDU;

[0018] accelerating the electric traction motor to a target motor speed with a calibrated speed profile, the calibrated speed profile corresponding to a predetermined vehicle acceleration rate, wherein the calibrated speed profile and the target motor speed are structured to minimize total system losses of the EDU while achieving the requested output torque;

[0019] commanding a torque converter clutch (TCC) of the torque converter to transition to or remain in a locked state when the predetermined vehicle acceleration rate remains below a calibrated acceleration threshold and a turbine speed of a turbine of the torque converter is less than a rotational angular speed of the electric traction motor; and

[0020] commanding the TCC to transition to an unlocked state to reach the target motor speed, whereby a multiplication of input torque from the electric traction motor is selectively achieved when operating at the target motor speed.

[0021] Scheme 2. The method of scheme 1, wherein the target motor speed corresponds to an actual output torque that can be achieved by the torque converter when the TCC is in the unlocked state, the actual output torque being equal to an actual output torque that can be achieved by the torque converter when the TCC is in a locked state.

[0022] Scheme 3. The method of scheme 1, wherein receiving the request signal comprises receiving a pedal position signal indicative of an applied force or a percentage of travel of an accelerator pedal of the motor vehicle.

[0023] Scheme 4. The method of scheme 3, further comprising: extracting, via the controller, the target motor speed from a lookup table indexed according to the pedal position.

[0024] Scheme 5. The method of scheme 1, further comprising:

[0025] applying a hysteresis band below a predetermined speed of the electric traction motor when the TCC is in the locked state to prevent the TCC from transitioning from the locked state to the unlocked state when the motor vehicle is operating within the hysteresis band.

[0026] Scheme 6. The method according to Scheme 1, further comprising:

[0027] determining whether the motor vehicle is stationary or moving; and

[0028] ramping a speed of the pump of the torque converter to the target motor speed at a first rate or a second rate, respectively, depending on whether the motor vehicle is stationary or moving.

[0029] Scheme 7. The method according to Scheme 6, further comprising:

[0030] ramping the speed of the pump of the torque converter to the target motor speed at the first rate when the motor vehicle is stationary, wherein the first rate is a calibrated maximum acceleration rate of the electric traction motor.

[0031] Scheme 8. The method according to Scheme 6, further comprising:

[0032] ramping the speed of the pump of the torque converter to the target motor speed at the second rate when the motor vehicle is moving, wherein the second rate is less than the first rate and is limited by an available battery power level of a propulsion battery connected to the electric traction motor.

[0033] Scheme 9. The method according to Scheme 1, further comprising:

[0034] maintaining the TCC in the locked state when the electric traction motor is operating below a peak motor torque; and

[0035] unlocking the TCC when the requested output torque exceeds the peak motor torque.

[0036] Scheme 10. A powertrain system for a motor vehicle, the powertrain system comprising:

[0037] a driven load; and

[0038] an electric drive unit (EDU) coupled to the driven load, the EDU comprising:

[0039] an electric traction motor operatively connected to the driven load;

[0040] a torque converter having a pump and a turbine, wherein the pump is connected to and driven by the electric traction motor; and

[0041] a controller in communication with the electric traction motor and the torque converter, wherein the controller is configured to:

[0042] receiving a request signal indicative of a requested output torque of the EDU;

[0043] accelerating the electric traction motor to a target motor speed with a calibrated speed profile, the calibrated speed profile corresponding to a predetermined vehicle acceleration rate, wherein the target motor speed and the calibrated speed profile are structured to minimize total system losses of the EDU while achieving the requested output torque;

[0044] commanding a torque converter clutch (TCC) of the torque converter to transition to or remain in a locked state when the predetermined vehicle acceleration rate remains below a calibrated acceleration threshold and a turbine speed of the turbine of the torque converter is less than an angular speed of the electric traction motor; and

[0045] commanding the TCC to transition to an unlocked state to achieve the target motor speed, whereby a multiplication of input torque from the electric traction motor is selectively achieved when operating at the target motor speed.

[0046] Scheme 11. The powertrain system of Scheme 10, wherein the calibrated acceleration threshold is a predetermined vehicle acceleration rate at which an output torque that can be achieved by the torque converter when the TCC is in the unlocked state is equal to an output torque that can be achieved by the torque converter when the TCC is in a locked state.

[0047] Scheme 12. The powertrain system of Scheme 10, further comprising an accelerator pedal, wherein the request signal comprises a pedal position signal indicative of a percentage of applied force or travel of the accelerator pedal.

[0048] Scheme 13. The powertrain system of Scheme 12, wherein the controller is structured to extract the target motor speed from a lookup table indexed according to a pedal position of the accelerator pedal.

[0049] Scheme 14. The powertrain system of Scheme 10, wherein the controller is structured to prevent the TCC from transitioning from the locked state to the unlocked state when the motor vehicle is operating in a hysteresis band.

[0050] Scheme 15. The powertrain system of Scheme 10, wherein the driven load comprises one or more road wheels of the motor vehicle and the EDU is used on the motor vehicle to power a vehicle propulsion function of the motor vehicle.

[0051] Scheme 16. The powertrain system of Scheme 15, wherein the controller is structured to determine whether the motor vehicle is stationary or moving, and thereafter ramp the rotational speed of the pump of the torque converter to the target motor speed at a first rate or a second rate, respectively, depending on whether the motor vehicle is stationary or moving.

[0052] Scheme 17. The powertrain system of Scheme 16, wherein, when the motor vehicle is stationary, the controller is structured to ramp the rotational speed of the pump of the torque converter to the target motor speed at the first rate, and wherein the first rate is a calibrated maximum acceleration rate of the electric traction motor.

[0053] Scheme 18. The powertrain system of Scheme 16, wherein, when the motor vehicle is moving, the controller is structured to ramp the rotational speed of the pump of the torque converter to the target motor speed at the second rate, wherein the second rate is less than the first rate and is limited by an available battery power level of a propulsion battery connected to the electric traction motor.

[0054] Scheme 19. A computer-readable storage medium having instructions recorded thereon for controlling an electric drive unit (EDU) having a torque converter connected to an electric traction motor such that a pump of the torque converter is driven by an output member of the electric traction motor, wherein execution of the instructions by a processor causes the processor to:

[0055] receive a request signal indicative of a requested output torque of the EDU;

[0056] accelerate the electric traction motor to a predetermined target motor speed at a predetermined speed profile, the calibrated speed profile corresponding to a predetermined vehicle acceleration rate, wherein the predetermined target speed and the calibrated speed profile are structured to minimize total system losses of the EDU while achieving the requested output torque;

[0057] command a torque converter clutch (TCC) of the torque converter to transition to or remain in a locked state when the predetermined vehicle acceleration rate remains below a calibrated acceleration threshold and a turbine speed of the torque converter is less than a rotational angular speed of the electric traction motor; and

[0058] command the TCC to transition to an unlocked state to reach the target motor speed, thereby selectively achieving multiplication of input torque from the electric traction motor when operating at the target motor speed.

[0059] Scheme 20. The computer-readable storage medium of Scheme 19, wherein the execution of the instructions causes the processor to maintain the TCC in the locked state when the electric traction motor is operating below a peak motor torque, and to unlock the TCC only if the requested output torque exceeds the peak motor torque.

[0060] The foregoing features and advantages of the present disclosure, as well as other features and attendant advantages of particular embodiments thereof, will be readily appreciated as the same becomes better understood by reference to the following detailed description. The disclosure should be illustrated in accordance with the accompanying drawings and the appended claims. Additionally, the disclosure expressly encompasses all possible combinations between various elements and features presented. BRIEF DESCRIPTION OF DRAWINGS

[0061] Figure 1 is a schematic illustration of a representative electrified powertrain system having a motor-driven torque converter and an electronic controller configured to regulate the rotational speed of the motor and the ON / OFF application state of a torque converter clutch of the torque converter.

[0062] Figure 1A is a partial cutaway view of a representative electric drive unit (EDU) that can be used as part of the powertrain system shown in Figure 1

[0063] Figure 2 Figure 1 is a time plot of a representative motor ramp-up speed for controlling the traction motor depicted in

[0064] Figure 3 is a time plot of representative motor and turbine speeds, where time in seconds is plotted on the horizontal axis and motor speed in revolutions per minute (RPM) is plotted on the vertical axis.

[0065] Figure 4 is a flowchart depicting an embodiment of the method.

[0066] Figure 5 is a time plot of representative motor and turbine torques and battery power for controlling the powertrain system depicted in Figure 1

[0067] Figure 6 is a comparative plot of representative motor speeds, where time in seconds is plotted on the horizontal axis and motor speed in RPM is plotted on the vertical axis.​​​ DETAILED DESCRIPTION

[0068] The present disclosure allows for many different embodiments. Representative examples of the present disclosure are shown in the drawings and described in detail herein as non-limiting examples of the disclosed principles. To that end, elements described in the Abstract, Introduction, Summary, and DETAILED DESCRIPTION sections but not expressly set forth in the claims should not be incorporated by implication or otherwise into the claims.

[0069] For the purposes of this description, unless otherwise specified, the use of the singular includes the plural and vice versa, the use of the terms “and” and “or” means both conjunctive and disjunctive, the use of the terms “any” and “all” means both “any and all”, and the use of the word “including” means “including but not limited to”. In addition, words of approximation such as “about”, “nearly”, “substantially”, “generally”, “approximately”, and the like, can be used herein in the sense of “at, near, or nearly at”, or “within 0-5% of”, or “within acceptable manufacturing tolerances”, or logical combinations thereof.

[0070] Referring to the drawings, wherein like reference numerals designate like features throughout the several views, and initially Figure 1 The motor vehicle 10 includes a powertrain system 12. The powertrain system 12, in the representative configuration depicted and similar configurations, can be used in other types of systems, including but not limited to mobile platforms, robots, or stationary power devices, and thus Figure 1 Embodiments of the present disclosure are intended to illustrate only one possible beneficial application. In the exemplary embodiment depicted, the motor vehicle 10 includes one or more road wheels 11 that are in rolling contact with a road surface (not shown). The actual number of road wheels 11 used on a given configuration of motor vehicle 10 can vary, with as few as one road wheel 11 possible in the context of, for example, a motorcycle, scooter, tricycle, or electric bicycle (“e-bike”), and with more than the number illustrated possible in other configurations, such as but not limited to four-wheel drive or all-wheel drive vehicles, trucks, and the like.

[0071] As described in detail herein, the powertrain system 12 includes an electronic controller (C) 50, for example a powertrain control system. The controller 50 automatically regulates operation of the powertrain system 12, and in particular the operation of its electric drive unit (EDU) 13. The EDU 13 (in the representative configuration depicted) includes an electric motor 14, for example a three-phase AC induction motor, and a power inverter 15, for example a three-phase AC inverter, that is electrically coupled to the motor 14. The motor 14 is mechanically coupled to the road wheels 11, for example via a transmission 16, for example a reduction gear, that is in turn mechanically coupled to the road wheels 11. The power inverter 15 is electrically coupled to a power source 17, for example a battery, that is in turn electrically coupled to an electrical power supply 18, for example a power grid. Figure 1AThe EDU 13 (depicted in its example embodiment) in turn includes a hydraulic torque converter 14 whose pump 14P is in turn driven as the input of the torque converter 14 via an electric traction motor (M A ) 16A, where the electric traction motor is operable by converting stored electrical power into rotational mechanical torque as is understood in the art. That is, an output member 160 (such as a rotor shaft) of the motor 16A is drivingly connected with the torque converter 14, where rotation produced by a rotor 16R of the motor 16A ultimately causes rotation of the pump 14P. The pump 14P is fluidically coupled with an oppositely disposed turbine 14T of the torque converter 14 through an intervening stator 14S (see Figure 1A ) ultimately produces a variable input torque (arrow T I ) to a transmission (PGS) 18, where “PGS” in this case refers to a planetary gear set or another suitable torque transfer mechanism. Output torque (arrow T O ) from the transmission 18 is then transmitted to one or more of the road wheels 11 via an output shaft 200 of the transmission 18, for example via an electronic or mechanical differential 22.

[0072] Briefly referring to Figure 1A , a representative configuration of the EDU 13 includes the electric traction motor 16A coupled to the torque converter 14. The motor 16A includes a rotor 16R that is fixed for rotation about an output member 160. Thus, the motor 16A can selectively drive or generate electricity from rotation of the output member 160, for example during coasting of the motor vehicle 10. Figure 1A The output member 160 at an end opposite the motor 16A is fixed to the torque converter 14 such that rotation of the output member 160 turns the pump 14P, which drives the turbine 14T via fluidic coupling effects as is understood in the art. A disconnect clutch (not shown) is disposed within the torque converter 14 between the pump 14P and a housing of the torque converter 14, where the disconnect clutch selectively locks the pump 14P, the housing, and the output member 160 together for co-rotation as is understood in the art. Although omitted for clarity and simplicity of illustration, the EDU 13 typically includes a hydraulic pump or other actuation means for pressurizing such a disconnect clutch, as well as a torque converter clutch (TCC) 14C described below.

[0073] The torque converter 14 is structured to facilitate fluid flow therethrough while governing the extent of fluidic coupling between the pump 14P and the turbine 14T. To this end, the torque converter 14 includes a stator 14S formed within the torque converter 14 for selectively coupling the pump 14P and the turbine 14T for co-rotation. The stator 14S alters fluid flow between the pump 14P and the turbine 14T such that returning fluid assists rotation of the pump 14P, thereby enabling the stator 14S to multiply torque from the motor 16A. Additionally, the torque converter 14 includes a TCC 14C (also shown schematically in Figure 1 ) operable for selectively locking the pump 14P and the turbine 14T together for co-rotation without slip. This occurs at times and under conditions described below in Figures 2-6 . Various internal components of the torque converter 14 are housed within and protected by a fluid-tight annular "pancake" housing, as is understood in the art, with a pump cover fixedly attached to a turbine cover (not shown) such that a hydraulic fluid chamber within the torque converter 14 is formed therebetween.

[0074] As is understood in the art, Figure 1 and Figure 1A the torque converter 14 selectively multiplies torque from the electric traction motor 16A via fluidic coupling of the pump 14P and the turbine 14T. As such, selective torque multiplication allows for use of a relatively small motor 16A when compared to competing powertrain systems lacking the torque converter 14. The EDU 13 can provide a rotational output, e.g., via an output shaft 140 driven by the turbine 14T. For example, the output shaft 140 can be directly connected to the turbine 14T, or the output shaft 140 can be used to drive Figure 1 a transmission 18, a vehicle driveline, a final drive unit, etc., e.g., through at least one gear 21 disposed at an end of the output shaft 140.

[0075] Referring again to Figure 1 , as part of the present control strategy, the controller 50 is operable for selectively locking the pump 14P to the turbine 14T via the TCC 14C. As part of this work, the rotational speed of the electric traction motor 16A ("motor speed") and the lock / unlock application state of the TCC 14C are regulated by the controller 50 using the method 100 (see Figure 4 ) described below and associated hardware solutions.

[0076] To this end, as part of its ongoing monitoring and control work, the controller 50 is structured to receive a request signal (arrow CC R ), which itself indicates a requested output torque and corresponding speed of the powertrain system 12 (including the EDU 13). In response, the controller 50 is operable to adjust the motor speed and the lock / unlock application state of the TCC 14C in accordance with the method 100 described below.Figure 1 In embodiments of the system 10 (where the powertrain system 12 is used on a motor vehicle 10), the request signal (arrow CC R ) can be provided by or measured on an accelerator pedal 19. Thus, the act of receiving the request signal (arrow CC R ) can include receiving an electronic pedal position signal, such as a proportional voltage signal, that is indicative of a percentage of applied force or travel of the accelerator pedal 19, as described below. The controller 50 responds to the request signal (arrow CC O ) via a set of output signals (arrow CC R ), where the set of output signals (arrow CC O ) includes a motor control signal (arrow CC 16 ) and a torque converter control signal (arrow CC 14 ).

[0077] Figure 4 The constituent process blocks of the method 100 can be programmed as computer-readable instructions in the form of an algorithm that can be executed by the processor 52 of the controller 50 from its memory 54 during ongoing operation of the motor vehicle 10 (i.e., in real-time while the motor vehicle 10 is operating in the drive mode). In this manner, the controller 50 is able to optimize the efficiency of the EDU 13 by minimizing losses therein during a wide range of possible acceleration events, some of which correspond to sufficient power reserves of the motor 16A and others of which require selective augmentation from the torque converter 14, as detailed below. In Figure 2 , Figure 3 and Figures 5-6 exemplary parameters for controlling the motor 16A and the TCC 14C of the Figure 1 and Figure 1A are shown and described below.

[0078] In the illustrated representative construction of the Figure 1 , the electric traction motor 16A includes a stator 16S that is spaced a short distance from a rotor 16R. The particular construction of the rotor 16R can vary based on the construction of the motor 16A, with permanent magnet or induction rotors being two possible embodiments. In the exemplary embodiment of the Figure 1 , the motor 16A is a multiphase / alternating current (AC) traction or propulsion motor for producing a motor output torque (arrow T MA ). As noted above, the motor output torque (arrow T MA ) is ultimately transmitted to the torque converter 14 via an output member 160, whereafter an input torque (arrow T I ) is provided to the transmission 18 and / or another coupled load via the torque converter 14.

[0079] On the motor vehicle 10, the coupled loads can include one or more of the road wheels 11, and / or one or more drive axles 24A and / or 24B connected thereto. The output member 160 can variously be embodied as a rotatable gear set, shaft, or another suitable mechanical coupling mechanism. In different embodiments, the road wheels 11 in the illustrated use case can be configured as front and / or rear road wheels 11. In the case of a single traction motor 16A, a differential 22 can be connected to the output shaft 200 of the transmission 18 and used to direct or vector torque as needed to the road wheels 11 arranged on the drive axles 24A and 24B.

[0080] Still referring to Figure 1 , in some implementations, the electric traction motor 16A can operate as the sole electric propulsion source on the motor vehicle 10. Alternatively, the drive axles 24A and 24B can be powered individually by corresponding motors (M B and M C ) 16B and 16C, which can be smaller or have lower voltage capability than the motor 16A. In this configuration, motor output torques (arrows T MB or T MC ) can be generated and delivered to the corresponding drive axles 24A and 24B, respectively. In some embodiments, the motors 16B and 16C can have corresponding torque converters 14B and 14C, which can be controlled in the same or similar manner as the torque converter 14 described in detail herein. Although omitted for clarity of illustration, in other embodiments, individual wheel motors can be operatively connected to or integrated with the road wheels 11 to enable wheel-based propulsion, e.g., in place of the illustrated axle-based propulsion. Thus, within the scope of the present disclosure, Figure 1 various propulsion actuators of FIG. 1 can be used together, individually, or in different locations of the electrified powertrain system 12.

[0081] For a multi-phase / alternating current (AC) embodiment of the electric traction motor 16A, the powertrain system 12 includes a power inverter module (PIM A ) 25A connected to the motor 16A via an AC voltage bus 28. The AC voltage bus 28 provides an AC voltage (VAC) to the stator 16S. A direct current (DC) voltage bus 26 supplies power to a DC side of the same PIM 25A. The DC voltage bus 26 carries a DC voltage (VDC) and is thus connected to an on-board voltage source 35, which in this case is an exemplary rechargeable high-voltage battery pack (B HVSince the voltage capability of voltage source 35 is typically much higher than the auxiliary 12-15 V auxiliary voltage level, such as 60 V-300 V or higher, powertrain system 12 may also be equipped with a DC-DC converter (not shown), which is then connected to a 12-15 V auxiliary battery, typically a lead-acid battery. Because DC-DC converters and auxiliary batteries are well known in the art, they are omitted for simplicity of illustration. Figure 1 These components are omitted. For electric axle drive or wheel drive implementations, motors 16B and 16C can be connected via a similarly constructed power inverter module (PIM). B and PIM C 25B and 25C are connected to voltage source 35.

[0082] Figure 1 The controller 50 is equipped with an application-specific amount of volatile and non-volatile memory (M) 54 (embodied in a computer-readable storage medium) and one or more processors 52 (e.g., a microprocessor or central processing unit), as well as other associated hardware and software, such as digital clocks or timers, input / output circuitry, buffer circuitry, application-specific integrated circuits (ASICs), system-on-a-chip (SoCs), electronic circuitry, and other necessary hardware required to provide the programmed functionality. In the context of this disclosure, the controller 50 executes instructions via the processor(s) 52 to cause the controller 50 to perform this control strategy.

[0083] refer to Figure 2 As part of its programmed functionality, controller 50 is configured to execute a "spin-up" strategy, in which the electric traction motor 16A is accelerated according to a predetermined speed curve or acceleration trajectory, which in turn accelerates the pump 14P and turbine 14T of torque converter 14. The degree of acceleration of turbine 14T depends on the locked / unlocked state of TCC 14C and the level of fluid connection across torque converter 14. Figure 1 If the motor vehicle 10 is stationary, for example, the controller 50 can use the torque converter control signal (arrow CC). 14 This is the initial command that commands TCC 14C to transition to a locked state. This occurs when... Figure 2 At t=0 in the diagram. When TCC 14C is locked, pump 14P and turbine 14T are locked together and therefore rotate at a common speed (i.e., motor speed) without slippage, as is known in the art.

[0084] For illustrative purposes, in Figure 2 Two exemplary motor speed traces, 60 and 61, are depicted in the figure. Figure 1 and Figure 1AWith TCC 14C locked, controller 50 will send a motor control signal (arrow CC). 16 The control signal is transmitted to the electric traction motor 16A, for example, to its residing motor controller processor or other associated control logic. This control action causes the pump 14P to start rotating to the target motor speed (N) as quickly as possible. TGT ), where the target motor speed (N) TGT The starting speed used in this early stage of speed control coincides with the first target point P1. Figure 1 Request signal (arrow CC) R The request signal includes output torque requested by the operator or requested autonomously.

[0085] However, when the vehicle 10 is moving and the TCC 14C is currently locked (L), the controller 50 may employ different methods during the speed control mode of the electric traction motor 16A and / or during the transition timing between the locked and unlocked states of the TCC 14C. For example, the operator of the vehicle 10 may use slight pedal pressure to slowly accelerate from a standstill until the time it takes to coincide with the second target point P2, whereby the operator may then perform a tip-in event, for example, by applying greater pedal force. This event is indicated by the trace 61 between the second target point P2 and the third target point P3. In this case, the controller 50 controls the torque converter via a control signal (arrow CC). 14 To unlock Figure 1 The TCC14C, where the unlock status is determined by Figure 2 The UL indication in the document.

[0086] After that, Figure 1 and Figure 1A The controller 50 shown accelerates the electric traction motor 16A to the target motor speed (N). TGT Target motor speed (N) TGT This corresponds to a predetermined vehicle acceleration rate at which the output torque achievable by the torque converter 14 when the TCC 14C is unlocked exceeds the output torque achievable by the torque converter 14 when the TCC 14C is locked. Acceleration continues at this rate until a target speed (N) corresponding to the third target point P3 is reached. TGT Up to this point, controller 50 receives the motor control signal (arrow CC). 16 This is achieved as described above. The acceleration of motor 16A can continue until a fourth target speed point P4 is reached at a later time, where the fourth target speed point P4 corresponds to the speed point from the request signal (arrow CC). RThe desired torque request. Subsequently, if the TCC 14C is not already in the locked state, the controller 50 commands the TCC 14C to be fully applied / locked, where the transition between the unlocked and locked states is completed before reaching the fifth target point P5.

[0087] In fact by Figure 1 The acceleration rate or speed curve of the electric traction motor 16A, powered by the voltage source 35 (e.g., a propulsion / traction battery pack), is limited by the available battery power. The motor 16A can then remain in a torque control mode, which is the opposite of the speed control mode; that is, the controller 50 adjusts the output torque to match the commanded torque rather than following the target speed (N). TGT The calculations can be used to determine the additional torque required to achieve the desired vehicle speed. Alternatively, if it is advantageous from a performance, system loss, and / or efficiency standpoint to do so, the controller 50 can switch the motor 16A to speed control mode and switch the corresponding control to the target speed (N). TGT Therefore, during the start-up of the motor vehicle 10, or at other times when the torque request exceeds the torque capacity of the motor 16A, and when notified of battery power limitations, the controller 50 operates at the target speed (N). TGT The above advantages can be achieved by selectively unlocking the TCC 14C and using the available torque multiplication capability of the torque converter 14.

[0088] Brief reference Figure 3 ,when Figure 1 When the TCC 14C is locked, that is, when the turbine speed (N) T ) equals motor speed (N) M When the electric traction motor 16A provides the baseline motor speed trajectory 70, the speed trajectory 70 is originally present without... Figure 1 The torque converter 14 represents the baseline in the assumed powertrain system. The motor speed trajectory 72 represents several different exemplary speed curves for a predetermined vehicle acceleration rate. Figure 3 The corresponding turbine speed trajectory 172 is also shown. Starting from t=0 (e.g., at startup), there exists a speed range for which... Figure 1 The locked and unlocked states of the TCC 14C produce similar results, i.e., from an optimization point of view. This so-called "chatter zone" 75 in Figure 3 The region is indicated by a zigzag pattern. In other words, controller 50 is neutral regarding whether the TCC14C is locked or unlocked. Therefore, using the exemplary hysteresis band method described below, multiple steps are taken in the logic of controller 50 to avoid alternating between the two possible application states.

[0089] As part of this solution, controller 50 can use one or more system models to determine the qualitatively “optimal” motor speed trajectory 72 or curve of the electric traction motor 16A. This is based on the requested vehicle acceleration rate occurring. For example, controller 50 can... Figure 1 The entire travel range of the accelerator pedal 19 is considered to correspond to a vehicle acceleration rate from 0% to 100% of the requested acceleration rate. Each corresponding pedal position can then be assigned a corresponding vehicle acceleration rate; for example, a 10% pedal position or travel could correspond to 1 m / s. 2 20% corresponds to 3 m / s 2 And so on. For a given pedal position and optimal trajectory, controller 50 can employ various optimization strategies, such as a cost function that minimizes total system losses while achieving the desired output torque. The speed curve specific to the pedal position or stroke, and the corresponding target speed, can be programmed in the memory 54 of controller 50, for example, programmed into one or more lookup tables, and executed during operation. Figure 1 The method 100 is used by the controller 50 during the process.

[0090] At or below a given speed trajectory of 72, the controller 50 can command Figure 1 The TCC 14C remains locked. The corresponding target speed (at which the TCC 14C is unlocked) is based on a specific motor speed curve at which the same output torque can be achieved by locking or unlocking the TCC 14C (i.e., operation in the flutter region 75). Therefore, the controller 50 maintains the TCC 14C locked at low vehicle speeds and during periods of rapid acceleration, during which the motor 16A is able to provide the requested output torque and also has the battery power necessary to do so.

[0091] refer to Figure 4 Used to control the above-mentioned application states and motor speed (N) of the electric traction motor 16A. M Method 100 assumes that the torque demand will either fall within or equal to the peak torque envelope of motor 16A. If the latter is the case, the use of torque converter 14 will be ineffective because motor 16A will be power-limited in this situation. Therefore, controller 50 preserves the torque multiplication capability of torque converter 14 when executing method 100, as the benefits of unlocking TCC 14C outweigh the accompanying losses and other inefficiencies.

[0092] In a typical implementation, method 100 includes: receiving, via controller 50, a request signal (arrow CC) indicating a request for output torque from EDU 13 (e.g., belonging to a motor vehicle having EDU 13).R ), and accelerate the electric traction motor 16A to the target motor speed (N). TGT The target motor speed corresponds to a predetermined vehicle acceleration rate, for example, Figure 3 As shown in the figure. Target motor speed (N) TGT The system parameters and their corresponding vehicle acceleration rates are configured to minimize the total system losses of EDU 13 while still achieving the requested output torque (T). O When the vehicle acceleration rate remains below the calibrated acceleration threshold and the turbo speed of torque converter 14 (N) T The angular velocity (N) is less than that of motor 16A. C When the torque converter 14 reaches the target speed (N), the controller 50 commands the torque converter 14's TCC 14C to either switch to the locked state or remain in the locked state. Additionally, the controller 50 commands the TCC 14C to switch to the unlocked state to allow the motor 16A to reach the target speed (N). TGT Therefore, the target speed (N) should be used. TGT During operation, the input torque from motor 16A is selectively achieved (arrow T). I The target speed is a multiple of the vehicle's acceleration, which is part of the optimal speed trajectory 72 used for the requested vehicle acceleration.

[0093] The exemplary embodiment begins at box B102 (“REC CC”). R ) at, among which Figure 1 Controller 50 receives request signals (arrow CC) R For the purposes of method 100, a request signal (arrow CC) is requested. R This includes output power request (hereinafter abbreviated as P). O ) and the current speed (N) of motor vehicle 10 10 As part of its usual programmed functions, controller 50 measures and monitors such values, and can obtain such values ​​via controller area network or other vehicle communication systems, as will be known to those skilled in the art. Method 100 then proceeds to block B105.

[0094] In box B104 ("CALC N") T At point B102, controller 50 then uses the value determined in box B102 to calculate the equivalent turbine speed (N). T Then proceed to box B106. That is, controller 50 calculates... Figure 1 The turbine 14T of the torque converter 14 shown is designed to meet a request signal (arrow CC) from box B102. R The speed achieved by conveying a specific torque request.

[0095] In box B104 ("CALC N")TP At point B102, controller 50 uses the value determined in block B102 to calculate the predicted turbine speed (N). TP Then proceed to box B126. That is, controller 50 calculates... Figure 1 The turbine 14T of the torque converter 14 shown is designed to output torque T. O The torque disturbance is minimized when TCC 14 is off, and the speed will be reached. Box B104 transmits control to box 126.

[0096] In box B105 ("N") T ≥ N C At point "), the measured turbine speed (N) T ) and the motor angular velocity (N) of the 16A electric traction motor C In comparison, the angular velocity is a function of the system battery voltage. As is known in the art, for a given torque-speed curve of an electric machine (e.g., motor 16A), there exists a speed-angular velocity N. C --At this speed, the output torque reaches its peak or decreases regardless of the speed of motor 16A. Therefore, when block B105 is executed, controller 50 can refer to one or more lookup tables or otherwise access information describing the torque-speed relationship of a specific configuration of motor 16A. When the turbine speed (N T Exceeding the angular velocity (N) C When ), method 100 continues to box B107, and instead, when the angular velocity (N) C Exceeding turbine speed (N) T When ), method 100 continues to box B108.

[0097] Figure 4 Box B106 (“TCC = L”) needs to lock TCC 14C. To achieve this, controller 50 will... Figure 1 The corresponding torque converter control signal (arrow CC) 14 The torque is transmitted to torque converter 14, or more precisely, to the residing hydraulic piston or its electrical clutch actuator mechanism (not shown). Method 100 then returns to box B102.

[0098] Box B107 ("TCC U") The current locked / unlocked state of TCC 14 is determined. If TCC 14 is locked, control is passed to box B106. However, if box B107 detects that TCC 14 is unlocked, control is passed to box B104.

[0099] In box B108 ("N") M ≥ NC ) place, Figure 1 The controller 50 determines the motor speed (N). M Does it exceed the motor's angular velocity (N)? C This situation occurs when TCC 14C is open and the electric traction motor 16A is following the desired speed curve specified by method 100. If the motor speed (N) M ) equal to or greater than angular velocity (N) C If so, controller 50 responds by passing control to box B107 to initiate the process of locking TCC 14C.

[0100] In box B109 ("P") O < MIN(P M , P B At the location ) Figure 1 The controller 50 will then receive the requested output power (P) from the electric traction motor 16A. O (i) Current maximum motor power (P) M (ii) Current maximum battery power (P) B The minimum of (i) and (ii) is compared. When the requested output power is less than the minimum of the two related comparison values, method 100 continues to box B110, and alternatively, when the output power exceeds the minimum of (i) and (ii), method 100 continues to box B107.

[0101] In box B110 ("T") O < T UL ) place, Figure 1 The controller 50 shown will request the output torque (T) O ) and the calibrated torque threshold (T) used to unlock TCC 14C UL ) for comparison. When the output torque (T) O Exceeding the calibrated torque threshold (T) UL When ), method 100 continues to box B112, and alternatively, when the output torque (T) O ) does not exceed the calibrated torque threshold (T) UL When ), method 100 continues to box B107.

[0102] If TCC 14C is not already in the unlocked state, then block B112 (“TCC = UL”) of method 100 requires unlocking TCC 14C. As described above, controller 50 unlocks TCC 14C via a control signal (arrow CC). 14 This command controls the lock / unlock state of TCC 14C. Afterward, method 100 continues to box B114.

[0103] Box B114 ("DET N") TGT It is necessary to determine the target motor speed (N) for the current vehicle acceleration rate. TGT (See above for reference) Figure 3 The example motor speed trajectory 72 described herein, for example, allows the controller 50 to determine the target motor speed (N) by referring to a lookup table or other calibration information. TGT Then, method 100 continues to box B116.

[0104] In box B116 ("SC; N") 10 = 0 At the point where the controller 50 is not already operating in the speed control mode of the motor 16A, the controller 50 then switches to that mode. As is understood in the art, when the load on the machine is constant, the speed of a rotating electric machine is proportional to the voltage. Therefore, speed control involves controlling the voltage supply to the motor 16A to achieve a target motor speed (N) according to a defined speed curve. TGT Then, controller 50 determines... Figure 1 Is motor vehicle 10 stationary (i.e., is it N)? 10 = 0), such as by processing speed signals from one or more wheel speed or transmission output speed sensors (not shown). If the motor vehicle 10 is stationary, method 100 continues to box B118, and otherwise continues to box B120.

[0105] Box B118 (“RMP=MAX”) includes linearly increasing the motor speed or ramping the motor speed (N) at the maximum ramp rate. M The maximum ramp rate is the predetermined maximum rate at which the electric traction motor 16A can accelerate based on the specific construction of the motor 16A, battery power limitations, etc. Box B118 continues in the cycle with box B129A, where the target motor speed (N) has been reached. TGT When ), method 100 continues to box B124.

[0106] Box B120 ("N" M ≠N TGT This includes: determining the motor speed (N) via controller 50. M ) and target motor speed (N) TGT Are they not equal? ​​When the two values ​​are equal, method 100 continues to box B122, and when the motor speed (N) M ) is not equal to the target motor speed (N) TGT When ), method 100 continues to box B124.

[0107] Box B122 ("RMP = f(X) includes ramping the motor speed (N M ) at a calibrated ramp rate for purposes of block B122, which can be a function of the difference between the current motor speed and the target motor speed (N TGT ) and / or the difference between the maximum required battery power and the current battery power, i.e. f (X). Method 100 then continues to block B124.

[0108] Block B124 (“N M = N TGT ”) includes setting the motor speed (N M ) to the target motor speed (N TGT ) while operating in the speed control mode before continuing to block B106. The torque demand either falls within the peak torque envelope of the electric traction motor 16A or is equal to the peak torque envelope of the electric traction motor 16A or is equal to the peak torque. If the latter, then the use of the torque converter 14 would not be effective because the traction motor 16A is power limited.

[0109] At block B126 (“Set N TGT = NTP”), the controller 50 sets the new target motor speed N TGT to the predicted turbine speed N TP from block B104 and proceeds to block B127.

[0110] At block B127 (“RMP = f (dTo / dt”), the controller 50 next estimates the required motor speed change in making the ramp to reach the target motor speed (N TGT ) and provides a limit on the ramp rate in order to minimize torque disturbance in the output torque (T O ). Blocks B127 and B129B loop until the motor speed reaches the target motor speed, i.e. N M =N TGT . Control is then passed to block B106.

[0111] Blocks B129A and B129B verify whether the respective blocks B118 and B122 have met their speed targets, e.g. using comparator circuits.

[0112] Reference is now made to Figure 5Graph 80 shows the equivalent motor torque and turbine torque selected for various motor speed trajectories when the electric traction motor 16A is operating in speed control mode, along with the corresponding battery power limits. Trajectories 81 and 82 represent the turbine torque levels for representative cases. Trajectories 181 and 182 represent the corresponding motor torque levels for the same cases, with trace 183 showing the motor torque of motor 16A (i.e., without torque converter 14). The corresponding traces 281 and 282 represent the battery power (P... BAT ), where trace 282 is again a reference trace, which corresponds to the maximum torque when TCC 14C is locked.

[0113] The optimal lock-up point for TCC 14C is defined as the point at which peak battery power or peak motor power (if lower) is reached. This occurs when the available battery power exceeds the requested output power (i.e., P). BAT > P O When ), it is possible to pass Figure 1 The torque converter 14 achieves torque multiplication. Therefore, the battery power exceeding the requested output power is used as a power reserve, which can then be used by the controller 50 to offset some of the power loss in the torque converter 14.

[0114] To avoid motor speed (N) during the lock-up period M If a sharp, perceptible drop occurs, controller 50 can automatically adjust the lock-up point initially determined based on pure optimization. That is, using cost optimization analysis, controller 50 can initially determine the optimal lock-up point for a given acceleration rate. Optimal lock-up points, such as points PL1 and PL2, occur when the battery has reached peak power and the turbine output torque drops below the maximum achievable motor torque. Controller 50 can adjust the lock-up point slightly later to avoid noise, vibration, and acoustic roughness. One way to do this is to establish a hysteresis control band that applies TCC 14C at the most energy-efficient point along a given speed curve before TCC 14C lock-up occurs. For example, when TCC 14C is locked, applying a hysteresis band based on vehicle acceleration or output torque below a predetermined speed of electric traction motor 16A will help prevent TCC 14C from transitioning from locked to unlocked when motor 16A operates within the hysteresis band. This, in turn, helps the controller 50 avoid frequently turning the TCC 14C on and off, as well as the associated noise, losses, and inefficiencies.

[0115] refer to Figure 6 And also about the Figure 1The aforementioned lock-up control of TCC 14C, as shown, when TCC 14C is unlocked (i.e., in torque converter mode when doubling the torque from traction motor 16A), allows controller 50 to use the same optimization strategy to determine the motor speed trajectory and target motor speed (N) that minimizes total system losses. TGT ).exist Figure 6 (A representative embodiment of the motor vehicle 10 is illustrated on the vertical axis with motor speed (N) in RPM.) M ) and wheel and axle power in kW (P AXL (And the time in seconds (s) is illustrated on the horizontal axis. Trajectory 90 corresponds to the early locking wheel axle power, while trajectory 92 corresponds to the wheel axle power without TCC 14C locking.) Figure 6 The diagram also shows the corresponding velocity trajectories 190 and 192 for the early locked and unlocked examples.

[0116] As shown in region 95, early lock-up can cause perceptible powertrain torque disturbances. A corresponding decrease in motor speed is seen in trajectory 190. Therefore, controller 50 avoids this disturbance by setting the lock-up point slightly later in time, causing controller 50 to follow one of the alternative trajectories 96, which in turn allows trajectory 98 to be used to ensure a smoother increase in lock-up axle power. The motor speed trajectory closest to the optimal lock-up point (e.g., derived using optimization calculations such as those based on peak battery power, as described above) can be interpolated based on the current turbine speed. Thus, controller 50 can, as needed, weigh the torque disturbances caused by lock-up-induced motor deceleration against the different available axle power transitions in trajectory 98.

[0117] In view of the foregoing disclosure, those skilled in the art will understand that method 100 may alternatively be in the form of a computer-readable storage medium (e.g., Figure 1 The processor 52 implements a memory 54, on which instructions for controlling EDU 13 are recorded. In such an embodiment, the execution of the instructions by the processor 52 causes the processor 52 to: receive the output torque (arrow T) requested by the EDU 13. O The request signal (arrow CC) R The execution of the command also causes the controller 50 to accelerate the electric traction motor 16A to the target motor speed (N) according to a given speed curve. TGT ), where the predetermined target motor speed (N) TGT It is configured to minimize the total system loss of EDU 13 while achieving the requested output torque.

[0118] Furthermore, the command is executed while the optimal vehicle acceleration rate remains below the calibrated acceleration threshold and the turbine speed (N) of the torque converter 14 is maintained. T The angular velocity (N) is less than that of the 16A electric traction motor. C When the target speed (N) is reached, the controller 50 or its processor 52 commands TCC 14C to either transition to a locked state or remain in a locked state. TGT This also causes controller 50 to command TCC 14C to switch to the unlocked state, thus enabling the system to operate at the target speed (N). TGT During operation, the input torque from motor 16A is selectively achieved (arrow T). I () multiplied.

[0119] In some embodiments of the computer-readable storage medium or memory 54, execution of the instructions causes the processor 52 to: keep the TCC 14C locked when the motor 16A operates below the peak motor torque, and unlock the TCC 14C when the requested output torque exceeds the peak motor torque.

[0120] Using the method 100 described above, when operating in speed control mode, the controller 50 is able to select the optimal motor speed trajectory or curve. The controller 50 can do this for different vehicle acceleration rates in a manner that minimizes overall system losses and improves drive quality while simultaneously achieving the desired output torque. Therefore, this teaching enhances the performance benefits of adding a motor-driven torque converter 14 to the powertrain system 12 by controlling the electric traction motor 16A or a variant thereof and the TCC 14C in a well-coordinated manner. These and other benefits will be appreciated by those skilled in the art in light of the foregoing disclosure.

[0121] The detailed description and accompanying drawings are intended to support and describe this teaching, but the scope of this teaching is defined solely by the claims. While some of the best modes and other embodiments for carrying out this teaching have been described in detail, various alternative designs and embodiments exist for practicing the teaching as defined in the appended claims. Furthermore, this disclosure explicitly includes combinations and sub-combinations of the elements and features presented above and below.

Claims

1. A method for controlling an electric drive unit of a motor vehicle, the electric drive unit having a torque converter connected to an electric traction motor, such that a pump of the torque converter is driven by an output member of the electric traction motor, the method comprising: The controller receives a request signal indicating the requested output torque of the electric drive unit. The electric traction motor is accelerated to a target motor speed using a calibrated speed profile, the calibrated speed profile corresponding to a predetermined vehicle acceleration rate, wherein the calibrated speed profile and the target motor speed are configured to minimize the total system loss of the electric drive unit while achieving the requested output torque. When the predetermined vehicle acceleration rate remains below a calibrated acceleration threshold and the turbine speed of the torque converter is less than the angular velocity of the electric traction motor, the torque converter clutch of the torque converter is commanded to either shift to a locked state or remain locked; and The torque converter clutch is commanded to disengage to the unlocked state to achieve the target motor speed, thereby selectively multiplying the input torque from the electric traction motor when operating at the target motor speed. The target motor speed corresponds to the actual output torque that the torque converter can achieve when the torque converter clutch is in the unlocked state, and the actual output torque is equal to the actual output torque that the torque converter can achieve when the torque converter clutch is in the locked state.

2. The method according to claim 1, wherein, Receiving the request signal includes receiving a pedal position signal indicating the percentage of applied force or travel of the accelerator pedal of the motor vehicle.

3. The method according to claim 2, further comprising: The target motor speed is retrieved from a lookup table indexed according to the pedal position via the controller.

4. The method according to claim 1, further comprising: When the torque converter clutch is in the locked state, a lag band is applied below a predetermined speed of the electric traction motor to prevent the torque converter clutch from transitioning from the locked state to the unlocked state when the motor vehicle is operating within the lag band.

5. The method according to claim 1, further comprising: Determine whether the motor vehicle is stationary or moving; as well as Depending on whether the motor vehicle is stationary or moving, the rotational speed of the pump in the torque converter is ramped up to the target motor speed at a first rate or a second rate, respectively.

6. The method of claim 5, further comprising: When the motor vehicle is stationary, the rotational speed of the pump of the torque converter is ramped up to the target motor speed at the first rate, wherein the first rate is the calibrated maximum acceleration rate of the electric traction motor.

7. The method according to claim 5, further comprising: When the motor vehicle is moving, the rotational speed of the pump of the torque converter is ramped up to the target motor speed at the second rate, wherein the second rate is less than the first rate and is limited by the available battery power level of the propulsion battery connected to the electric traction motor.

8. The method according to claim 1, further comprising: When the electric traction motor operates below its peak motor torque, the torque converter clutch is kept in the locked state; as well as When the requested output torque exceeds the peak motor torque, the torque converter clutch is unlocked.

9. A powertrain system for a motor vehicle, the powertrain system comprising: Driven load; as well as An electric drive unit connected to the driven load, the electric drive unit comprising: An electric traction motor, operatively connected to the driven load; A torque converter having a pump and a turbine, wherein the pump is connected to and driven by the electric traction motor; and A controller that communicates with the electric traction motor and the torque converter, wherein the controller is configured to: Receive a request signal indicating the requested output torque of the electric drive unit; The electric traction motor is accelerated to a target motor speed using a calibrated speed profile, the calibrated speed profile corresponding to a predetermined vehicle acceleration rate, wherein the target motor speed and the calibrated speed profile are configured to minimize the total system loss of the electric drive unit while achieving the requested output torque. When the predetermined vehicle acceleration rate remains below a calibrated acceleration threshold and the turbine speed of the torque converter's turbine is less than the angular velocity of the electric traction motor, the torque converter clutch of the torque converter is commanded to either shift to a locked state or remain locked; and The torque converter clutch is commanded to disengage to the unlocked state to achieve the target motor speed, thereby selectively multiplying the input torque from the electric traction motor when operating at the target motor speed. Wherein, the calibrated acceleration threshold is a predetermined vehicle acceleration rate, at which the output torque that can be achieved by the torque converter when the torque converter clutch is in the unlocked state is equal to the output torque that can be achieved by the torque converter when the torque converter clutch is in the locked state.

10. The powertrain system of claim 9, further comprising an accelerator pedal, wherein, The request signal includes a pedal position signal, which indicates the percentage of applied force or travel of the accelerator pedal.

11. The powertrain system according to claim 10, wherein, The controller is configured to extract the target motor speed from a lookup table indexed according to the pedal position of the accelerator pedal.

12. The powertrain system according to claim 9, wherein, The controller is configured to prevent the torque converter clutch from transitioning from the locked state to the unlocked state when the vehicle is operating within a lag zone.

13. The powertrain system according to claim 9, wherein, The driven load includes one or more road wheels of the motor vehicle, and the electric drive unit is used on the motor vehicle to provide power for the vehicle propulsion function.

14. The powertrain system according to claim 13, wherein, The controller is configured to determine whether the motor vehicle is stationary or moving, and then, depending on whether the motor vehicle is stationary or moving, to ramp up the rotational speed of the pump of the torque converter to the target motor speed at a first rate or a second rate, respectively.

15. The powertrain system according to claim 14, wherein, When the motor vehicle is stationary, the controller is configured to ramp up the rotational speed of the pump of the torque converter to the target motor speed at the first rate, wherein the first rate is the calibrated maximum acceleration rate of the electric traction motor.

16. The powertrain system according to claim 14, wherein, When the motor vehicle is moving, the controller is configured to ramp up the rotational speed of the pump of the torque converter to the target motor speed at a second rate, wherein the second rate is less than the first rate and is limited by the available battery power level of the propulsion battery connected to the electric traction motor.

17. A computer-readable storage medium having instructions recorded thereon for controlling an electric drive unit, the electric drive unit having a torque converter connected to an electric traction motor, such that a pump of the torque converter is driven by an output member of the electric traction motor, wherein... The processor's execution of the instruction causes the processor to: Receive a request signal indicating the requested output torque of the electric drive unit; The electric traction motor is accelerated to a predetermined target motor speed using a calibrated speed profile, the calibrated speed profile corresponding to a predetermined vehicle acceleration rate, wherein the predetermined target speed and the calibrated speed profile are configured to minimize the total system loss of the electric drive unit while achieving the requested output torque. When the predetermined vehicle acceleration rate remains below a calibrated acceleration threshold and the turbine speed of the torque converter is less than the angular velocity of the electric traction motor, the torque converter clutch of the torque converter is commanded to either shift to a locked state or remain locked; and The torque converter clutch is commanded to disengage to the unlocked state to achieve the target motor speed, thereby selectively multiplying the input torque from the electric traction motor when operating at the target motor speed. The target motor speed corresponds to the actual output torque that the torque converter can achieve when the torque converter clutch is in the unlocked state, and the actual output torque is equal to the actual output torque that the torque converter can achieve when the torque converter clutch is in the locked state.

18. The computer-readable storage medium according to claim 17, wherein, The execution of the instruction causes the processor to maintain the torque converter clutch in the locked state when the electric traction motor is operating below the peak motor torque, and to unlock the torque converter clutch only when the requested output torque exceeds the peak motor torque.

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