Method and drive system for determining the regenerative braking capacity in a vehicle with a stepped transmission

Abstract

Method for controlling an electric machine (35) configured to generate traction torque in a drive system (20), wherein the drive system (20) comprises the electric machine (35) rotatably coupled to a crankshaft (36) of an internal combustion engine (40) coupled to a transmission (50) via a torque converter (44), and wherein an output element (62) is coupled to an axle (64) of a drive train (60), the method comprising: Determining a short-term axle torque capacity (405), a long-term axle torque capacity (505) and a maximum regenerative standstill brake torque capacity (605); Determining an operator request for brakes (106); Determining a preferred regenerative braking capacity (205) based on the short-term axle torque capacity (405), the long-term axle torque capacity (505), the maximum regenerative standstill braking torque capacity (605), and the operator request for braking (106); and Control of torque output from the electric machine (35) based on the preferred regenerative braking capacity (205).

Description

TECHNICAL AREA

[0001] The present invention relates to a method and a drive system for vehicles for controlling an electric machine. BACKGROUND

[0002] Known vehicle propulsion systems include internal combustion engines and electric motors / generators coupled to transmissions to transfer torque to a drivetrain for traction. Known electric motors / generators are powered by electrical current from high-voltage energy storage systems. Propulsion systems can use regenerative control systems to utilize electrical current to charge the high-voltage energy storage system in response to operator commands, including braking and / or idling. SUMMARY

[0003] According to the invention, a drive system is presented that is characterized by the features of claim 1. The transmission is coupled to a drive train to transmit traction torque and braking torque to it. A method for controlling the electric machine comprises determining a short-term axle torque capacity, a long-term axle torque capacity, and a maximum regenerative braking standstill torque capacity, as well as determining an operator request for braking. A preferred regenerative braking capacity is determined based on the short-term axle torque capacity, the long-term axle torque capacity, the maximum regenerative braking standstill torque capacity, and the operator request for braking. Torque output from the electric machine is controlled based on the preferred regenerative braking capacity.

[0004] Furthermore, a drive system is presented which is characterized by the features of claim 10.

[0005] The aforementioned features and advantages, as well as further features and advantages of the present teachings, will become clearly evident from the following detailed description of some of the best types and further embodiments of the present teachings with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The following describes one or more exemplary embodiments with reference to the accompanying drawings, in which: Fig. 1 schematically illustrates a vehicle comprising a drive system with an internal combustion engine having a crankshaft connected to a transmission via a torque converter and connected to an electrically driven torque machine, wherein the transmission is a stepped transmission connected to a drive train in accordance with the invention; Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6 to Fig. 7 schematic flowcharts that illustrate in more detail a regenerative brake torque capacity control routine for controlling an embodiment of the drive system in order to transfer traction torque and braking torque to the drive train in accordance with the invention; and Fig. Figure 8 graphically illustrates the operation of sections of the regenerative brake torque capacity control routine in an embodiment of the vehicle with the drive system described herein in accordance with the invention. DETAILED DESCRIPTION

[0007] With reference to the drawings, the illustrations of which serve only to demonstrate certain exemplary embodiments, it is illustrated Fig. Figure 1 schematically depicts a vehicle 100 comprising a drive system 20, which has a stepped transmission 50 coupled to a drive train 60, and is controlled by a control system 10. The same reference numerals refer to the same elements throughout the description.

[0008] The drive system 20 comprises an internal combustion engine 40, which has a crankshaft 36 mechanically coupled to the transmission 50 via a torque converter 44. The crankshaft 36 is mechanically rotatable and coupled to an electrically driven torque machine 35 via a roller mechanism 38 or another suitable mechanism. The electrically driven torque machine 35 and the internal combustion engine 40 are torque-generating devices. The electrically driven torque machine 35 comprises an output component that is mechanically rotatable and connected to the crankshaft 36 of the engine 40 via the roller mechanism 38, which provides a mechanical force path between them.The idler pulley mechanism 38 is configured to effect torque transmission between the motor 40 and the torque machine 35, including, among other things, the transmission of torque from the torque machine 35 to the motor 40 for the motor's automatic start and stop operation, traction torque assistance, and regenerative braking, as well as torque transmission from the motor 40 to the torque machine 35 for high-voltage electrical charging. In one embodiment, the idler pulley mechanism 38 comprises a serpentine belt that runs between the first idler pulley, which is mounted on the crankshaft 36 of the motor 40, and another idler pulley that runs on the rotating shaft coupled to a rotor of the lathe 35, referred to as the belt-driven alternator starter system (BRS). Alternatively, the idler pulley mechanism 38 may include a displacement gear mechanism.The transmission 50 includes an output component 62 which is connected to the drive train 60. In one embodiment, the motor 40 may include an electromagnetically actuated low-voltage electric starter 39 for starting the motor in response to the starting event initiated by a key.

[0009] The engine 40 is preferably a multi-cylinder internal combustion engine that converts fuel into mechanical power via a thermodynamic combustion process. The engine 40 is equipped with a variety of actuators and sensor devices for monitoring the operation and delivery of fuel to form a combustion charge in order to generate torque that responds to an output torque request. The sensor devices include a crankshaft position sensor 41, which can be any suitable rotary position sensor system, preferably communicating directly with the control module 12 via a wiring harness 13 and with the inverter controller 11 via a communication bus 18. Alternatively, the crankshaft position sensor 41 communicates directly with the control module 12 via the wiring harness 13 and directly with the inverter controller 11 via a wiring harness 13'.

[0010] The torque machine 35 is preferably a multiphase high-voltage electric motor / generator configured to convert stored electrical energy into mechanical power and to convert the mechanical power into electrical energy that can be stored within a high-voltage battery 25. The torque machine 35 comprises a rotor and a stator, as well as an associated position sensor 37, which in one embodiment is a coordinate converter. The position sensor 37 communicates directly with the inverter controller 11 via the wiring harness 33 and is used to monitor the rotational position of the rotor of the torque machine 35. The rotational position of the rotor of the torque machine 35 is used by the inverter controller 11 to control the operation of an inverter module 32, which controls the torque machine 35.The inverter controller 11 is preferably also arranged in the inverter module 32 (as shown), or can be arranged remotely, e.g. within the control module 12.

[0011] The high-voltage battery 25 is electrically connected to the inverter module 32 via a high-voltage DC bus 29 to transmit high-voltage direct current electrical energy to the torque machine 35 in response to control signals from the control system 10. The inverter module 32 is electrically connected to the torque machine 35 via a multi-phase motor control power bus 31. The inverter module 32 is configured with suitable control circuits, including power transistors such as IGBTs for converting high-voltage direct current electrical energy to high-voltage alternating current electrical energy and for converting high-voltage alternating current electrical energy to high-voltage direct current electrical energy.The inverter module 32 preferably employs pulse-width modulation (PWM) control to convert stored DC electrical energy from the high-voltage battery 25 into AC electrical energy to drive the electric machine 35 and generate torque. Similarly, the inverter module 32 converts mechanical power transferred to the torque machine 35 into DC electrical energy to generate electrical energy that can be stored in the high-voltage battery 25, among other uses, as part of a regenerative control strategy. It should be noted that the inverter module 32 is configured to receive motor control commands and control inverter states to provide motor drive and regenerative functionality.

[0012] In one embodiment, an electrical DC / DC current transformer 34 is electrically connected to a low-voltage bus 28 and a low-voltage battery 27, and is also electrically connected to the high-voltage bus 29. Such electrical connections are known and will not be described in detail here. In another embodiment, the low-voltage battery 27 can be electrically connected to an additional power supply system 45 to provide low-voltage electrical current to the vehicle's low-voltage systems, such as electric windows, HVAC fans, seats, and the electromagnetically actuated low-voltage electric starter 39. Alternatively, the electrical current transformer 34 can provide low-voltage electrical current to the vehicle's low-voltage systems, thereby replacing the additional power supply system 45.

[0013] The torque converter 44 is a torque coupling device arranged between the motor 40 and the transmission 50. The torque converter 44 preferably comprises a fluid torque coupling via an internal pump and vanes, and a mechanical torque coupling via a controllable, selectively activatable coupling mechanism.

[0014] The transmission 50 is preferably arranged in a stepped transmission configuration and may include one or more differential gear sets and actuable clutches configured to transmit torque through one of a plurality of stepped transmission states over a range of speed ratios between the motor 40 and the output element 62. The transmission 50 comprises any suitable configuration and is preferably configured as an automatic transmission to automatically shift between the different stepped transmission states in order to operate in a gear ratio that achieves a preferred match between an output torque request and a motor operating point.The 50 transmission automatically performs upshifts to engage a gear ratio with a lower numerical multiplication ratio (gear ratio) and downshifts to engage a gear ratio with a higher numerical multiplication ratio. Upshifting requires a decrease in engine speed so that, at a gear ratio corresponding to the desired gear condition, the engine speed matches the transmission output speed multiplied by the gear ratio. Downshifting requires an increase in engine speed so that, at a gear ratio corresponding to the desired gear condition, the engine speed matches the transmission output speed multiplied by the gear ratio.The drivetrain 60 can include a differential gear device 65, which is mechanically coupled to an axle 64, a final drive, or a half-shaft, which in turn is mechanically coupled to a wheel 66 in one embodiment. The drivetrain 60 transmits traction power between the transmission 50 and a road surface. The drive system 20 is for illustrative purposes only, and the concepts described herein are applicable to other drive systems that are similarly configured.

[0015] The control system 10 comprises a control module 12 that communicates with an operator interface 14. The control module 12 preferably communicates with individual elements of the drive system 20 either directly or via the communication bus 18. The control module 12 communicates with the sensor devices of each of the high-voltage battery 25, the inverter module 32, the torque machine 35, the motor 40, and the transmission 50 to monitor their operation and determine their parametric states. The operator interface 14 of the vehicle 100 comprises a plurality of human-machine interface devices through which the vehicle operator controls the operation of the vehicle 100, including, for example, an ignition switch to enable an operator to start and start the engine 40, an accelerator pedal 15, a brake pedal 16, a transmission range selector (PRNDL), a steering wheel, and a headlight switch.The accelerator pedal 15 provides a signal input that includes an accelerator pedal position indicating an operator request for vehicle acceleration, and the brake pedal 16 provides a signal input that indicates a brake pedal position indicating an operator request for vehicle deceleration. The transmission range selector provides a signal input that indicates a direction of movement of the vehicle intended by the operator, comprising a discrete number of operator-selectable positions that specify the preferred direction of rotation of the output component 62 in either a forward or a reverse direction.

[0016] The drive system 20 comprises a communication scheme, including the communication bus 18, to facilitate communication in the form of sensor signals and actuator command signals between the control system 10 and elements of the drive system 20. The communication scheme enables the transmission of information to and from the control system 10 using one or more communication systems and devices, including, for example, the communication bus 18, a direct connection, a LAN bus, a Serial Peripheral Interface bus, and wireless communication.

[0017] The terms controller, control module, module, controller, control unit, processor, and similar terms refer to one or more combinations of application-specific integrated circuit(s) (ASIC), electronic circuit(s), central processing unit(s), such as microprocessor(s), and associated non-transitory memory components in the form of memory and storage devices (read memory, programmable read memory, direct access, hard disk, etc.). The non-transitory memory component is capable of storing machine-readable instructions in the form of one or more software or firmware programs or routines, combinational logic circuit(s), input / output circuit(s) and devices, signal conditioning and buffer circuits, and other components that can be accessed by one or more processors to provide a described functionality.An input / output circuit (or circuits) and devices comprise analog-to-digital converters and related equipment that monitor inputs from sensors, such inputs being monitored at a predetermined sampling frequency or in response to a trigger event. Software, firmware, programs, instructions, control routines, code, algorithms, and similar terms refer to any set of instructions executable by a controller, such as calibrations and lookup tables. Each controller executes control routine(s) for the desired functions, such as monitoring inputs from sensor devices and other networked controllers, and executing control and diagnostic routines to control the actuation of actuators. Routines may be executed at regular intervals, such as every 100 microseconds or every 3.125, 6.25, 12.5, 25, and 100 milliseconds during operation.Alternatively, routines can be executed in response to a trigger event. Communication between controllers and between controllers, actuators, and / or sensors can be achieved via direct wiring, a networked communication bus connection, a wireless connection, or any other suitable communication link. Communication includes the exchange of data signals in any suitable form, including, for example, electrical signals transmitted over a conductive medium, electromagnetic signals through the air, optical signals via fiber optics, and the like. Data signals can include signals representing sensor inputs, signals representing actuator commands, and communication signals between controllers.The term "model" refers to processor-based or processor-executable code and associated calibration that simulates the physical existence of a device or physical process. As used here, the term "dynamic" describes steps or processes that are executed in real time and are characterized by monitoring or otherwise determining parameter states and regularly or periodically updating parameter states when executing a routine or between iterations of the routine.

[0018] Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6 to Fig. Figure 7 schematically depicts flowcharts that illustrate in more detail a regenerative brake torque capacity control routine (control routine) 200 for controlling an embodiment of the drive system 20 in order to transfer traction torque and brake torque to the drive train 60 in accordance with the invention, which is based on Fig. 1 is described. Overall, the control routine 200 executes in response to operator inputs, including operator inputs via the accelerator pedal 15 and the brake pedal 16, including when the operator input via the accelerator pedal 15 is less than a minimum threshold indicating idle or braking.

[0019] The control routine 200 mediates between a short-term axle torque capacity 405, a long-term axle torque capacity 505, and a maximum regenerative braking standstill torque capacity 605 to select a preferred regenerative braking capacity 205 based on an operator request for braking 106, a current transmission ratio state 104, and an anticipated or predicted future transmission ratio state 105. As used herein, the term "short-term" refers to any operation applied or implemented within a single iteration of a control routine. As used herein, the term "long-term" refers to any operation applied or implemented across multiple iterations of a control routine. As used herein, the term "capacity" refers to a maximum or minimum order of magnitude of a controlled operation, e.g.,Brakes that the relevant system can complete, taking into account mechanical, electrical and other factors.

[0020] Torque power from the electric motor / generator 35, which is transmitted to the drivetrain 60 to effect vehicle braking, is controlled to apply regenerative braking in response to the preferred regenerative braking capacity 205, taking into account factors related to the capabilities for generating and transmitting torque and power between the motor 40, the track roller mechanism 38, the electric machine 35, the battery 25, the torque converter 44, the transmission 50, and the drivetrain 60 to the vehicle wheels 66. This includes a short-term axle capacity calculation routine 400 that determines the short-term axle torque capacity 405, a long-term axle capacity calculation routine 500 that determines the long-term axle torque capacity 505, and an engine standstill prevention routine 600 that determines the maximum regenerative standstill torque capacity 605.A preferred regenerative net braking capacity mediation routine 700 determines the preferred regenerative braking capacity 205 based on the short-term axle torque capacity 405, the long-term axle torque capacity 505, and the maximum regenerative braking standstill torque capacity 605. The regenerative braking applied by the drive system 100 may differ from the preferred regenerative braking capacity 205 due to operating factors related to the battery capacity and the operation of the drive system.

[0021] The short-term axle capacity calculation routine 400 determines the short-term axle torque capacity 405 based on inputs including a short-term (ST) crankshaft torque capacity 102 and a current transmission state 104, whether the torque converter clutch of the torque converter 44 is in a locked or unlocked state, and whether the transmission 50 is shifting gears. The current transmission state 104 indicates the gear ratio in which the transmission 50 is currently operating. This process is best described with reference to Fig. 4 shown.

[0022] Routine 410 concerns determining the short-term axle torque capacity 405 when the torque converter clutch of the torque converter 44 is in the locked state. The short-term (ST) crankshaft torque capacity 102 is multiplied by the current transmission ratio in conjunction with the current transmission state 104 of the transmission in Routine 420 to determine a short-term drive system output torque limit 425, which is combined with Routine 430, e.g., divided by the axle ratio 112 of the drive train 60, to determine the short-term axle torque capacity 405 when the torque converter clutch of the torque converter 44 is in the locked state.

[0023] Routine 440 relates to determining the short-term axle torque capacity 405 when the torque converter clutch of the torque converter 44 is in the unlocked state. The short-term (ST) crankshaft torque capacity 102 and the current transmission ratio associated with the current transmission state 104 are used by a torque converter conversion routine 450 to determine a short-term drive system output torque limit 455 based on the torque conversion of the torque converter 44 in the unlocked state and a current transmission ratio associated with the current transmission state 104. The torque conversion of the torque converter 44 in the unlocked state can be determined using a K-factor specific to an embodiment of the torque converter 44, which correlates speed and torque when operating at a standstill speed.The short-term drive system output torque limit 455 is combined with routine 460, e.g. divided by the axle ratio 112 of the drive train 60 to determine the short-term axle torque capacity 405 when the torque converter clutch of the torque converter 44 is in the unlocked state.

[0024] Routine 470 concerns determining the short-term axle torque capacity 405 when the transmission 50 undergoes gear shifting. Under certain conditions related to the clutch control in the transmission 50, negative or braking torque can be transmitted through the transmission 50 during gear shifting, allowing regenerative braking operation during shifting. A certain amount of regenerative braking is controlled to maintain and provide acceptable shift quality as perceived by the vehicle operator. This includes engaging (480) a trigger 474 at the beginning of a shift operation 472 when regenerative braking is applied, thus capturing a certain amount of regenerative braking at the start of the shift operation 485.The magnitude of regenerative braking at the start of the shifting process 485 is compared with an upper regenerative braking limit for an upshift 484, and a minimum of the two values ​​is selected as a regenerative braking magnitude 487 (486). The regenerative braking magnitude 487 is applied as the short-term axle torque capacity 405 as long as it has a negative value between 0 and -9999 (490).

[0025] In Fig. Figure 8 graphically depicts the operation of sections of the control routine 200 in an embodiment of the vehicle 100 with the drive system 20, including applied regenerative braking 814 in Nm and the regenerative braking capacity 812 in Nm in relation to the vehicle speed 818 in km / h, the selected gear position 816, the operator request for braking 820 in %, and the occurrence of gear shifts 822 in True (1) and False (0), all in relation to time 840, shown on the horizontal axis. Orders of magnitude of the regenerative braking times 804 are indicated by the left vertical axis, and orders of magnitude of the vehicle speed 806 and braking 808 are indicated by the right vertical axis. Initially, the regenerative braking capacity 812 is -200 Nm until time 841, when braking is applied as indicated by the operator request for braking 820.At time 841, a shift is commanded 822(1), and the regenerative braking capacity 812 is currently regulated to 0 Nm until the shift is completed at time 842. At this point, the regenerative braking capacity 812 is set to -150 Nm due to the driving request initiated during the shift, and the applied regenerative braking 814 is gradually increased.

[0026] During the subsequent upshift at time 843, regenerative braking is regulated to -150 Nm below the regenerative braking threshold. During the subsequent upshift, which occurs between times 843 and 844, regenerative braking 814 and the regenerative braking capacity 812 are kept constant. After the shift is completed, the applied regenerative braking 814 is allowed to increase again. When the vehicle decelerates, as indicated by the vehicle speed 818 after time 843, downshifting occurs, as indicated at times 846 and 847. The applied regenerative braking 814 and the regenerative braking capacity 812 follow the normal control path, i.e., a normal gradual reduction of the regenerative braking, which follows the long-term axle torque capacity 205, as specified in the [reference to] Fig. The tax routine 200 described in 2-7 can be determined.

[0027] The long-term axle capacity calculation routine 500 determines the long-term axle torque capacity 505 based on inputs including the predicted transmission state 105 and a predicted crankshaft torque capacity or limit 305, whether the torque converter clutch of the torque converter 44 is in a locked or unlocked state, and whether the transmission 50 is shifting gears. This process is best described with reference to Fig. Figure 5 is shown. The predicted crankshaft torque capacity or limit of 305 is best understood by reference to Fig. Figure 3 shows the predicted gear state 105. This is a gear state that the control routine 200 anticipates the transmission 50 will shift into in response to changes in operator inputs to the accelerator pedal 15 and the brake pedal 16, including those that might result in regenerative braking. For example, the transmission 50 can be calibrated to downshift to the next lower gear in response to an operator input to the accelerator pedal 15 indicating neutral.

[0028] In Fig. Figure 3 schematically illustrates a routine 300 for determining the predicted crankshaft torque capacity 305. Inputs include a maximum belt slip torque 125 and associated belt slip times 127, which are combined (315) to define a maximum belt torque 318 that can be transmitted between the crankshaft 36 of the internal combustion engine 40 and a rotating shaft of the engine / generator 35 via the idler pulley mechanism 38. The maximum belt torque 318 is converted into an engine torque 325 (320), and the engine torque 325 is compared to an engine torque limit determined based on battery current 123.A maximum motor torque 335 and a motor torque limit based on the battery current 123 are selected (330), and the maximum motor torque 335 is compared with a motor torque limit 121 (340), where the motor torque limit 121 is based on the mechanical and electrical capacities of the motor / generator 32. A second maximum motor torque 345 is converted into a crankshaft torque (350) and combined with crankshaft torque limits 129 (360) to determine the predicted crankshaft torque capacity 305.

[0029] With renewed reference to Fig. Procedure 510 concerns determining the long-term axle torque capacity 505 when the torque converter clutch of the torque converter 44 is in the locked state. The predicted crankshaft torque capacity 305 is multiplied by the predicted transmission ratio 105 to determine a long-term drive system output torque limit 525 (520), which is combined with (530), e.g., divided by the axle ratio 112 of the drive train 60 to determine the long-term axle torque capacity 505 when the torque converter clutch of the torque converter 44 is in the locked state.

[0030] Routine 540 concerns the determination of the long-term axle torque capacity 505 when the torque converter clutch of torque converter 44 is in the unlocked state. The predicted crankshaft torque capacity 305 and the current transmission ratio associated with the current transmission state 104 are used by the torque converter conversion routine 450 to determine a long-term drive system output torque limit 555 based on the torque conversion of torque converter 44 in the unlocked state and the current transmission ratio associated with the current transmission state 104. The torque conversion of torque converter 44 in the unlocked state can be determined using the K-factor, which is specific to torque converter 44. The long-term drive system output torque limit 555 is combined with (560), e.g.,divided by the axle ratio 112 of the drive train 60 to determine the long-term axle torque capacity 505 when the torque converter clutch of the torque converter 44 is in the unlocked state.

[0031] Routine 570 concerns determining the long-term axle torque capacity 505 when the transmission 50 is shifting gears. When the transmission 50 is shifting gears, as indicated by a signal input 575 from the transmission 50, the long-term axle torque capacity 505 is set to zero to allow all shifts (580).

[0032] In Fig. Figure 6 schematically illustrates an embodiment of the engine standstill prevention routine 600 for determining the maximum regenerative braking standstill torque capacity 605, which is intended to prevent engine standstill that may be caused by regenerative braking at low engine speeds. The engine standstill prevention routine 600 monitors the current transmission ratio in relation to the current transmission state 104, which is subjected to range state mediation (610) to select either the current transmission ratio in relation to the current transmission state 104 or the predicted transmission state as the mediated transmission state 615, which is coupled with the transmission temperature 114 and vehicle speed 110 (620) to determine a minimum axle torque for engine standstill 625, wherein engine standstill occurs when the engine speed falls below a minimum engine speed, such as...400 rpm. The minimum axle torque for engine standstill 625 is compared with the long-term axle torque capacity 505, and a maximum value 635 is selected (630). The selected maximum value 635 of the minimum axle torque for engine standstill 625 and the long-term axle torque capacity 505 are used to calculate an effective regenerative net braking time (640), which is the maximum regenerative braking standstill torque capacity 605. Thus, in the event of a fault related to a command to release the torque converter clutch, the transmission 50 can release the torque converter clutch to protect hardware, which may cause regenerative braking to be applied at low speeds and thus affect ride quality.Instead, the engine stall prevention routine 600 gradually reduces regenerative braking using transmission temperature, transmission condition, and vehicle speed to improve ride quality. This process mediates the transmission range condition to prevent the torque converter clutch condition from limiting axle torque per gear, and thus limits the regenerative braking capacity depending on vehicle speed (and indirectly engine speed) to avoid excessive regenerative braking during a sudden torque converter clutch release, and limits the maximum regenerative braking capacity based on the transmission temperature.

[0033] In Fig.Figure 7 schematically illustrates an embodiment of the regenerative net braking capacity mediation routine 700 for determining the preferred regenerative braking capacity 205 based on the short-term axle torque capacity 405, the long-term axle torque capacity 505, and the maximum regenerative standstill braking torque capacity 605. The long-term axle torque capacity 505 is compared with a regenerative net braking capacity 206 from an immediately preceding iteration of the control routine 200 (702) for determining a differential regenerative braking capacity 705, which is used to determine a regenerative time-rate braking ramp rate 715 (710).The regenerative time rate braking ramp rate 715 is combined with the long-term axle torque capacity 505 and the previous regenerative net braking capacity 206 using a gradient limiter routine (720) that generates an updated long-term axle torque capacity 725, which includes control routines for ramping towards less long-term torque capacity and immediately transitions to a larger amount of long-term torque capacity.

[0034] A creep idle torque 726 can be determined based on the vehicle speed and reduced by the operator's request for braking 106 (722) to determine an operator-requested braking torque 723, which is compared to the updated long-term axle torque capacity 725. The operator-requested braking torque 723 and the updated long-term axle torque capacity 725, which provides less regenerative braking torque, are selected as input 735 (730), which is compared to the long-term axle torque capacity 505 (740), from which a minimum (more regenerative braking torque) is selected as a resulting long-term torque 745. The resulting long-term torque 745 is compared to the short-term axle torque capacity 405 and the maximum regenerative standstill braking torque capacity 605 (750).One of the resulting long-term torque 745, the short-term axle torque capacity 405 and the maximum regenerative brake standstill torque capacity 605, which achieves a minimum order of magnitude of regenerative brake torque, is selected as the preferred regenerative brake capacity 205.

[0035] As such, the control routine 200 gradually reduces regenerative braking before upshifting the transmission to improve shift quality, or maintains regenerative braking throughout the shift to ensure proper axle torque is present when control is fed back at the end of the shift. This includes allowing regenerative braking during some upshifts based on the transmission's ability to carry regenerative torque, including using the transmission clutch control to predict torque carrying capacity, and manipulating the short-term capacity to exit regenerative braking during shifting when necessary. This involves using hybrid engine limits, current and predicted transmission range conditions, transmission operating parameters, and torque converter clutch release points to apply additional regenerative braking.

[0036] The control routine 200 described herein facilitates the determination of long-term crankshaft capacity using the predicted transmission state, and the use of transmission parameters to convert short-term and long-term crankshaft capacities into regenerative axle domain braking capacities. This includes using the current transmission state in a regenerative short-term axle domain capacity calculation and using the predicted transmission state in a long-term axle domain capacity calculation. The mediation enables the combination of the regenerative braking capacity into a single effective axle torque capacity.

Claims

[1] Method for controlling an electric machine (35) configured to generate traction torque in a drive system (20), wherein the drive system (20) comprises the electric machine (35) rotatably coupled to a crankshaft (36) of an internal combustion engine (40) which is coupled to a transmission (50) via a torque converter (44), and wherein an output element (62) is coupled to an axle (64) of a drive train (60), the method comprising: Determining a short-term axle torque capacity (405), a long-term axle torque capacity (505) and a maximum regenerative standstill brake torque capacity (605); Determining an operator request for brakes (106); Determining a preferred regenerative braking capacity (205) based on the short-term axle torque capacity (405), the long-term axle torque capacity (505), the maximum regenerative standstill braking torque capacity (605), and the operator request for braking (106); and Control of torque output from the electric machine (35) based on the preferred regenerative braking capacity (205). [2] The method of claim 1, further comprising: Determining an actual gear ratio state (104) and an anticipated gear ratio state (105); and Determining the preferred regenerative braking capacity (205) based additionally on the current transmission ratio state (104) and the anticipated transmission ratio state (105). [3] Method according to claim 1, comprising determining the short-term axle torque capacity (405) based on a short-term crankshaft torque capacity and a current transmission ratio state (104) when a torque converter clutch is locked. [4] Method according to claim 1, comprising determining the short-term axle torque capacity (405) based on a short-term crankshaft torque capacity, a current gear ratio state (104) and a torque conversion in the unlocked state when a torque converter clutch is unlocked. [5] Method according to claim 1, comprising determining the short-term axle torque capacity (405) based on an order of magnitude of regenerative braking at the beginning of a shifting event when the transmission (50) performs a shifting event. [6] The method of claim 1, further comprising: Determining the predicted crankshaft torque capacity (305); and Determining the long-term axle torque capacity (505) based on the predicted crankshaft torque capacity (305). [7] Method according to claim 6, wherein the drive system (20) further comprises a DC power supply (25) which is electrically connected to the electric machine (35); and wherein determining the predicted crankshaft torque capacity (305) comprises: Determining a maximum belt torque (318) that can be transmitted between the internal combustion engine (40) and the electric machine (35); Determining a maximum motor torque limit (121) based on battery power in conjunction with the DC power source; and Determining the predicted crankshaft torque capacity (305) based on the maximum belt torque (318) and the maximum engine torque limit (121). [8] Method according to claim 1, wherein determining the maximum regenerative braking standstill torque capacity (605) comprises determining a regenerative braking capacity in connection with engine standstill. [9] Method according to claim 1, wherein determining the preferred regenerative braking capacity (205) based on the short-term axle torque capacity (405), the long-term axle torque capacity (505), the maximum regenerative standstill braking torque capacity (605) and the operator request to brake (106) further comprises mediating between the short-term axle torque capacity (405), the long-term axle torque capacity (505) and the maximum regenerative standstill braking torque capacity (605). [10] Drive system (20), comprising: an electric machine (35), an internal combustion engine (40) and a stepped transmission (50); wherein the electric machine (35) is rotatably coupled to a crankshaft (36) of the internal combustion engine (40) and electrically connected to a DC power source; wherein the internal combustion engine (40) is coupled to the stepped transmission (50) via a torque converter (44) which includes a torque converter clutch; wherein the stepped transmission (50) comprises an output element (62) coupled to an axle (64) of a drive train (60); and a control unit which is operationally coupled to the internal combustion engine (40), the electric machine (35), the transmission (50) and the torque converter clutch, wherein the control unit has a set of instructions which can be executed as follows: Determining a short-term axle torque capacity (405), a long-term axle torque capacity (505) and a maximum regenerative standstill brake torque capacity (605); Determining an operator request after braking (106): Determining a preferred regenerative braking capacity (205) based on the short-term axle torque capacity (405), the long-term axle torque capacity (505), the maximum regenerative standstill braking torque capacity (605), and the operator request for braking (106); and Control of the electric machine (35) to generate torque based on the preferred regenerative braking capacity (205).

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