Increasing motor torque capacity by time-based thermal derating

Abstract

A vehicle includes a system that performs a method of derating an electric motor of the vehicle. The system includes a timer and a processor. The processor is configured to start a timer when a temperature of a stator of the electric motor exceeds a high temperature threshold, select a mixing ratio based on a time value on the timer, an intermediate derating curve of the motor is determined by interpolating between a first derating curve associated with the first target temperature and a second derating curve associated with a second target temperature greater than the first target temperature using the mix ratio, and the motor is derated along the intermediate derating curve.

Description

Technical Field

[0001] The present disclosure relates to thermal derating of torque on an electric motor, and more particularly, to shifting the derating curve of a traction motor to allow short-term operation of the motor at high temperatures. Background Art

[0002] An electric vehicle includes an electric motor that provides power to the vehicle. When the electric motor operates, the stator windings of the electric motor get hot. The electric motor can operate for a long time at low temperatures without causing thermal damage to the stator windings. The electric motor can operate for only a short time at high temperatures before thermal damage occurs. Currently, the derating algorithms for electric motors can only be used for operation of the electric motor at low temperatures, thus not fully utilizing the full torque capacity of the electric motor. Therefore, it is desirable to provide a method for enabling the electric motor to operate for a short time with an extended capacity before operating at a lower temperature. Summary of the Invention

[0003] In one exemplary embodiment, a method for derating an electric motor of a vehicle is disclosed. When the temperature of the stator of the electric motor exceeds a high temperature threshold, a timer is started. A mixing ratio is selected based on a time value on the timer. The mixing ratio is used to determine an intermediate derating curve of the electric motor by interpolating between a first derating curve associated with a first target temperature and a second derating curve associated with a second target temperature greater than the first target temperature. The electric motor derates along the intermediate derating curve.

[0004] In addition to one or more of the features described herein, the first derating curve is associated with long-term operation of the electric motor, and the second derating curve is associated with short-term operation of the electric motor.

[0005] In addition to one or more of the features described herein, the method further includes incrementing the timer between a first time and a second time, determining a first intermediate derating curve at the first time, determining a second intermediate derating curve at the second time, and derating along a composite derating trajectory that connects a first operating point on the first intermediate derating curve at the first time to a second operating point on the second intermediate derating curve at the second time.

[0006] In addition to one or more of the features described herein, the second intermediate derating curve is closer to the first derating curve than the first intermediate derating curve.

[0007] In addition to one or more of the features described herein, the method further includes selecting the mixing ratio from a mixing curve that associates the mixing ratio with time via one of a sigmoid curve and a modified sigmoid curve.

[0008] In addition to one or more of the features described herein, the method further includes storing the mixing curve as one of an equation and a look-up table.

[0009] In addition to one or more of the features described herein, the method further includes: after the temperature of the electric motor drops below a recovery temperature threshold, increasing the torque at the electric motor to operate the electric motor in an extended capacity region between the first target temperature and the second target temperature.

[0010] In another exemplary embodiment, a system for derating an electric motor of a vehicle is disclosed. The system includes a timer and a processor. The processor is configured to start the timer when the temperature of the stator of the electric motor exceeds a high temperature threshold, select a mixing ratio based on a time value on the timer, use the mixing ratio to determine an intermediate derating curve of the electric motor by interpolating between a first derating curve associated with a first target temperature and a second derating curve associated with a second target temperature greater than the first target temperature, and derate the electric motor along the intermediate derating curve.

[0011] In addition to one or more of the features described herein, the first derating curve is associated with long-term operation of the electric motor, and the second derating curve is associated with short-term operation of the electric motor.

[0012] In addition to one or more of the features described herein, the processor is further configured to increment the timer between a first time and a second time, determine a first intermediate derating curve at the first time, determine a second intermediate derating curve at the second time, and derate along a composite derating trajectory that connects a first operating point on the first intermediate derating curve at the first time to a second operating point on the second intermediate derating curve at the second time.

[0013] In addition to one or more of the features described herein, the second intermediate derating curve is closer to the first derating curve than the first intermediate derating curve.

[0014] In addition to one or more of the features described herein, the processor is further configured to select the mixing ratio from a mixing curve that associates the mixing ratio with time via one of an S-shaped curve and a modified S-shaped curve.

[0015] In addition to one or more of the features described herein, the processor is further configured to store the mixing curve as one of an equation and a look-up table.

[0016] In addition to one or more of the features described herein, the processor is further configured to: after the temperature of the electric motor drops below a recovery temperature threshold, increase the torque at the electric motor to operate the electric motor in an extended capacity region between the first target temperature and the second target temperature.

[0017] In yet another exemplary embodiment, a vehicle is disclosed. The vehicle includes a timer and a processor. The processor is configured to start the timer when the temperature of the stator of the electric motor exceeds a high temperature threshold, select a mixing ratio based on the time value on the timer, use the mixing ratio to determine an intermediate derating curve of the electric motor by interpolating between a first derating curve associated with a first target temperature and a second derating curve associated with a second target temperature greater than the first target temperature, and derate the electric motor along the intermediate derating curve.

[0018] In addition to one or more of the features described herein, the first derating curve is associated with long-term operation of the electric motor, and the second derating curve is associated with short-term operation of the electric motor.

[0019] In addition to one or more of the features described herein, the processor is further configured to increment the timer between a first time and a second time, determine a first intermediate derating curve at the first time, determine a second intermediate derating curve at the second time, and derate along a composite derating trajectory that connects a first operating point on the first intermediate derating curve at the first time to a second operating point on the second intermediate derating curve at the second time.

[0020] In addition to one or more of the features described herein, the second intermediate derating curve is closer to the first derating curve than the first intermediate derating curve.

[0021] In addition to one or more of the features described herein, the processor is further configured to select the mixing ratio from a mixing curve that associates the mixing ratio with time via one of an S-shaped curve and a modified S-shaped curve.

[0022] In addition to one or more of the features described herein, the processor is further configured to: after the temperature of the electric motor drops below a recovery temperature threshold, increase the torque at the electric motor to operate the electric motor in an extended capacity region between the first target temperature and the second target temperature.

[0023] The above features and advantages of the present disclosure, as well as other features and advantages, are apparent from the following detailed description when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Other features, advantages, and details appear only by way of example in the following detailed description, which refers to the accompanying drawings, in which:

[0025] Figure 1 A vehicle in an illustrative embodiment is shown;

[0026] Figure 2 is a graph showing the operating temperature of an electric motor in an illustrative embodiment;

[0027] Figure 3 is a graph showing various torque-temperature derating curves;

[0028] Figure 4 is a graph depicting a blending curve for determining an intermediate torque-temperature derating curve;

[0029] Figure 5 shows the use of Figure 4 the shown blending curve to determine an intermediate derating curve;

[0030] Figure 6 shows an intermediate derating curve obtained by interpolation performed from Figure 5 therein;

[0031] Figure 6A shows a graphical representation of a two-dimensional look-up table that can be used to return a torque derating percentage in an alternative embodiment;

[0032] Figure 7 shows a flowchart of a method for derating an electric motor in an illustrative embodiment;

[0033] Figure 7A shows a flowchart of an alternative method for derating an electric motor;

[0034] Figure 8 shows a graph of various blending curves in an alternative embodiment;

[0035] Figure 9 shows a graph of a blending curve in an alternative embodiment; and

[0036] Figure 10 shows a graph illustrating the torque operation of an electric motor. DETAILED DESCRIPTION

[0037] The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application, or uses. It should be understood that throughout the drawings, corresponding reference numerals denote the same or corresponding components and features.

[0038] Figure 1 shows an embodiment of a vehicle 10 that includes a body 12 that at least partially defines an occupant compartment 14. The body 12 also supports various vehicle subsystems, including a propulsion system 16, and other subsystems for supporting the functions of the propulsion system 16 and other vehicle components, such as a braking subsystem, a suspension system, a steering subsystem, and the like.

[0039] Vehicle 10 can be an electric vehicle (EV), a hybrid vehicle, or any other vehicle. In an embodiment, vehicle 10 is an electric vehicle that includes multiple electric motors and / or drive systems. Any number of drive units can be included, such as one or more drive units for applying torque to the front wheels (not shown) and / or the rear wheels (not shown). The drive units are controllable to operate vehicle 10 in various operating modes, such as a normal mode, a high-performance mode (where additional torque is applied), all-wheel drive (“AWD”), front-wheel drive (“FWD”), rear-wheel drive (“RWD”), etc.

[0040] For example, propulsion system 16 is a multi-drive system that includes a front drive unit 20 for driving the front wheels and a rear drive unit for driving the rear wheels. Front drive unit 20 includes front electric motor 22 and front inverter 24 (e.g., a front power inverter module or FPIM), as well as other components such as a cooling system. Left rear drive unit 30L includes left rear electric motor 32L and left rear inverter 34L. Right rear drive unit 30R includes right rear electric motor 32R and right rear inverter 34R. Front inverter 24, left rear inverter 34L, and right rear inverter 34R (e.g., power inverter units or PIMs) each convert direct current (DC) power from high-voltage (HV) battery system 40 into polyphase (e.g., two-phase, three-phase, six-phase, etc.) alternating current (AC) power to drive front electric motor 22, left rear electric motor 32L, and right rear electric motor 32R.

[0041] As Figure 1 shown, the drive system is characterized by separate electric motors. However, the embodiment is not limited thereto. For example, instead of separate electric motors, multiple drives can be provided by a single machine having physically independent multiple sets of windings.

[0042] Also as Figure 1 shown, the drive system is configured such that front electric motor 22 drives the front wheels (not shown), and left rear electric motor 32L and right rear electric motor 32R drive the rear wheels (not shown). However, the embodiment is not limited thereto, as any number of drive systems and / or electric motors can be present at various locations (e.g., an electric motor driving each wheel, dual electric motors for each axle, etc.). Additionally, the embodiment is not limited to a dual-drive system, as the embodiment can be used with vehicles having any number of electric motors and / or power inverters.

[0043] In propulsion system 16, front drive unit 20, left rear drive unit 30L, and right rear drive unit 30R are electrically connected to battery system 40. Battery system 40 can also be electrically connected to other electrical components (also referred to as “electrical loads”), such as vehicle electronics (e.g., via auxiliary power module or APM 42), heaters, cooling systems, etc. Battery system 40 can be configured as a rechargeable energy storage system (RESS).

[0044] In one embodiment, the battery system 40 includes a plurality of individual battery assemblies, where each battery assembly can be charged independently and can be used to power one or more drive systems independently. For example, the battery system 40 includes a first battery assembly, such as a first battery pack 44 and a second battery pack 46 connected to the front inverter 24. The first battery pack 44 includes a plurality of battery modules 48, and the second battery pack 46 includes a plurality of battery modules 50. Each battery module 48, 50 includes a plurality of individual battery cells (not shown). In various embodiments, one or more of the battery packs may include MODACS (Multi-Output Dynamic Adjustable Capacity) batteries.

[0045] Each of the front motor 22, the left rear motor 32L, and the right rear motor 32R is a three-phase motor having three-phase motor windings. However, the embodiments described herein are not limited thereto. For example, the motor can be any polyphase machine supplied by a polyphase inverter, and the drive unit can be implemented using a single machine having independent multiple sets of windings.

[0046] The battery system 40 and / or the propulsion system 16 includes a switching system having various switching devices for controlling the operation of the first battery pack 44 and the second battery pack 46 and selectively connecting the first battery pack 44 and the second battery pack 46 to the front drive unit 20, the left rear drive unit 30L, and the right rear drive unit 30R. The switching devices can also be operated to selectively connect the first battery pack 44 and the second battery pack 46 to the charging system. The charging system can be used to charge the first battery pack 44 and the second battery pack 46 and / or supply power from the first battery pack 44 and / or the second battery pack 46 to charge another energy storage system (e.g., vehicle-to-vehicle (V2V) and / or vehicle-to-everything (V2X) charging). The charging system includes one or more charging modules. For example, a first on-board charging module (OBCM) 52 is electrically connected to the charging port 54 for charging and being charged from an AC system or device (such as a utility AC power supply). A second OBCM 53 can be included for DC charging (e.g., DC fast charging or DCFC).

[0047] In one embodiment, the switching system includes a first switching device 60 and a second switching device 62. The first switching device 60 selectively connects the first battery pack 44 to the front inverter 24, the left rear inverter 34L, and the right rear inverter 34R, and the second switching device 62 selectively connects the second battery pack 46 to the front inverter 24, the left rear inverter 34L, and the right rear inverter 34R. The switching system further includes a third switching device 64 (also referred to as a "battery switching device") for selectively connecting the first battery pack 44 in series with the second battery pack 46.

[0048] Any one of a variety of controllers can be used to control the functions of the battery system 40, the switching system, and the drive unit. The controller includes any suitable processing device or unit, and existing controllers such as a drive system controller, a RESS controller, and / or a controller in the drive system can be used. For example, a controller 65 can be included to control the switching and drive control operations as discussed herein.

[0049] The vehicle 10 further includes a computer system 55, and the computer system 55 includes one or more processing devices 56 and a user interface 58. The computer system 55 can communicate with the charging system controller, for example, to provide commands thereto in response to user input. Various processing devices, modules, and units can communicate with each other via a communication device or system such as a controller area network (CAN) or a transmission control protocol (TCP) bus.

[0050] As shown herein, the vehicle 10 is an electric vehicle. In alternative embodiments, the vehicle 10 can be an internal combustion engine vehicle, a hybrid vehicle, etc.

[0051] Figure 2 FIG. 200 is a graph showing the operating temperature of an electric motor in an illustrative embodiment. Time is shown along the abscissa in seconds, and temperature is shown along the ordinate in degrees Celsius. A long-term target temperature 202 (a first target temperature) and a short-term target temperature 204 (a second target temperature) are shown. The electric motor can operate at the long-term target temperature 202 for a long time (e.g., days, months) without thermal damage occurring at the electric motor. Before thermal damage occurs at the electric motor, the electric motor can operate at the short-term target temperature 204 for a short period of time (e.g., seconds, minutes). The long-term target temperature 202 and the short-term target temperature 204 can be preset values. The long-term target temperature 202 is less than the short-term target temperature 204. The difference between the long-term target temperature 202 and the short-term target temperature 204 defines an extended capacity operating region 206 of the electric motor.

[0052] The long-term operation line 208 shows the stable operation of the electric motor. The long-term operation line 208 rises at a first rate during the operation of the electric motor. At a set temperature (referred to herein as a high temperature threshold 210), derating is implemented at the electric motor to flatten the long-term operation line 208. Thus, the long-term operation line 208 asymptotically approaches the long-term target temperature.

[0053] The short-term operating line 212 shows unstable operation of the motor. The short-term operating line 212 rises at a first rate and enters the extended capacity operating region 206. The derating begins at a temperature higher than the high temperature threshold 210. Thus, the short-term operating line 212 asymptotically approaches the short-term target temperature 204. Operating for an extended period in the extended capacity operating region (as shown by the short-term operating line 212) reduces the life of the windings and is therefore undesirable.

[0054] The method disclosed herein allows the motor to operate along the short-term operating line 212 into the extended capacity operating region 206, but also changes the derating schedule for operation to reduce the operating temperature to the long-term target temperature 202. Changing the derating schedule results in the operating trajectory 214. Thus, the operating region of the motor is bounded by the long-term operating line 208 and the short-term operating line 212, and the temperature of the motor does not rise above the short-term operating line 212.

[0055] Once the motor temperature drops to a value equal to or less than the recovery temperature threshold, the motor can operate again within the extended capacity region. In Figure 2 , the recovery temperature threshold 216 is shown to be lower than the high temperature threshold 210. However, the recovery temperature threshold 216 can be equal to or less than the high temperature threshold 210.

[0056] Figure 3 FIG. 300 is a graph showing various torque-temperature derating curves. The motor temperature is shown in degrees Celsius along the abscissa, and the motor torque capacity is shown as a percentage along the ordinate axis. The torque-temperature derating curves define a relationship by which the torque capacity of the motor can be managed based on temperature. As the temperature increases, the torque capacity decreases. As the temperature decreases, the torque capacity increases. The long-term torque-temperature derating curve is shown by the first derating curve 302. The long-term torque-temperature derating curve causes the motor to operate along the long-term operating line 208. The short-term torque-temperature derating curve is shown by the second derating curve 304. The second derating curve 304 causes the motor to operate the motor along the short-term operating line 212.

[0057] A plurality of intermediate torque-temperature derating curves 306a, 306b, 306c, 306d are shown between the first derating curve 302 and the second derating curve 304. Although four intermediate curves are shown for illustrative purposes, any number of intermediate curves can exist. During operation, the derating can occur along a series of derating curves, typically moving sequentially from the short-term torque-temperature derating curve to the long-term torque-temperature derating curve through the intermediate torque-temperature derating curves 306a, 306b, 306c, 306d. As discussed herein, moving through the selected derating curves creates a synthetic derating trajectory 308. The synthetic derating trajectory 308 corresponds to Figure 2 the operating trajectory 214.

[0058] Figure 4 is a graph 400 depicting a hybrid curve 402 for determining an intermediate torque-temperature derating curve. Time is shown along the abscissa in seconds, and the mixing ratio is shown along the ordinate in percentage. The hybrid curve 402 correlates the mixing ratio with time and includes the values of the mixing ratio at each time point. In one embodiment, the hybrid curve 402 can be stored as an equation at the processor. Alternatively, the mixing ratios of the hybrid curve 402 can be stored in a lookup table. The mixing ratio starts at 100% at time t = 0 and ends at 0% or near 0% at time = T max when it ends at 0% or near 0%.

[0059] When the temperature of the motor exceeds the baseline temperature (e.g., the high temperature threshold 210), a clock or timer can be started. The mixing ratio is obtained periodically while the timer is running. For each mixing ratio, an intermediate derating curve can be calculated as Figure 5 shown.

[0060] Figure 5 is a graph 500 showing a method for determining an intermediate derating curve 502 using the Figure 4 shown hybrid curve 402. A first derating curve 302 and a second derating curve 304 are shown. Referring to Figure 4 , the mixing ratio is selected for a time value. For example, at time t 2 , a mixing ratio of approximately 38% is selected. Then the first derating curve 302 and the second derating curve 304 are interpolated using the mixing ratio to obtain the intermediate derating curve 502. The interpolation is performed for each torque capacity percentage value such that each point on the first derating curve 302 and the second derating curve 304 is interpolated.

[0061] If the system has an over-temperature diagnosis, the over-temperature threshold can be modified to include the effect of changing the derating curve over time. The mixing ratio and the temperature dynamic deviation between the first derating curve 302 and the second derating curve 304 can be multiplied to find the dynamic deviation that is added to the existing static over-temperature threshold. For example, if point 506 on the first derating curve 302 is selected as the long-term over-temperature threshold, then the value of the dynamic over-temperature threshold at point 508 on the second derating curve 304 is when the mixing ratio is equal to 1. Then, as the mixing ratio value decreases to zero, the threshold will tend towards point 506. The calculation of the dynamic over-temperature threshold at each sampling moment is shown mathematically in Equation (1):

[0062] Dynamic over-temperature threshold = Static over-temperature threshold + (Deviation * Mixing ratio) Equation (1)

[0063] A new derating curve can be calculated periodically. Over time, a new mixing ratio is selected from the mixing curve, and the new derating curve is determined using the new mixing ratio. Since the mixing ratio decreases over time, as Figure 4 shown, each successive derating curve moves in the direction from the second derating curve 304 to the first derating curve 302.

[0064] Specifically, a first intermediate derating curve can be determined at a first time (e.g., Figure 4 t1 at Figure 4 ), and a second intermediate derating curve can be determined at a second time (e.g., Figure 4 t2 at

[0065] Figure 6 ). The motor moves from a first operating point on the first intermediate derating curve at the first time to a second operating point on the second intermediate derating curve at the second time. During this process, the operating points of the motor plot a composite derating trajectory.

[0065] Figure 6 shows an intermediate derating curve 502 obtained by interpolation performed from Figure 5 . The intermediate derating curve 502 is applicable to a single time step and is recalculated at the next time step. The current temperature of the motor is used to select a point on the intermediate derating curve 502, which selects the available torque to be used at the motor.

[0066] Figure 6A is a graphical representation of a two-dimensional look-up table 610 that can be used to return the torque derating percentage in an alternative embodiment. The look-up table is represented by a three-dimensional surface 612. The look-up table includes two inputs (i.e., time and motor temperature) shown along the x-axis and y-axis. The input values are used to locate the torque capacity percentage or derating percentage, which is shown along the z-axis. The derating trajectory curve 614 along the three-dimensional surface 612 shows the variation of the torque capacity percentage over time. The derating trajectory curve 614 is equivalent to Figure 3 the composite derating trajectory 308.

[0067] Figure 7 shows a flowchart 700 of a method for derating a motor in an illustrative embodiment. The method starts at block 702. At block 702, the motor is operated and the temperature of the motor or the stator winding (referred to herein as "stator temperature") is measured. The time value of the timer is initialized at t = 0. At block 704, the stator temperature is compared with a high temperature threshold 210. If the temperature is greater than the high temperature threshold, the method proceeds to block 706. Otherwise, the method proceeds to block 720.

[0068] At block 706, the timer is incremented. At block 708, the time value of the timer is compared with the maximum time (t max)(Compare. If the time value is less than the maximum time, the method proceeds to block 712. Otherwise, the method proceeds to block 710. In block 710, the time value is set to the maximum time. The method proceeds to block 712. In block 712, the time value is used to select a mixing ratio. In block 714, the mixing ratio is used to determine an intermediate derating curve. In block 716, the motor is derated using the intermediate derating curve. In block 718, the method ends.

[0069] Now referring to block 720, the stator temperature is compared with the recovery temperature threshold 216. If the stator temperature is less than the recovery temperature threshold, the method proceeds to block 722. In block 722, the time value is set to zero. By setting the time value back to zero, the motor can operate again in the extended capacity region. If the stator temperature is greater than the recovery temperature threshold at block 720, the method proceeds to block 712.

[0070] Figure 7A Flowchart 730 showing an alternative method for derating a motor is shown. Flowchart 730 is the same as Figure 7 flowchart 700, except that the steps shown in blocks 712, 714, and 716 have been replaced by block 732, where a lookup table as shown in Figure 6A is used to look up a derating value for the current time value and the current motor temperature.

[0071] Figure 8 Graph 800 showing various mixing curves in an alternative embodiment is shown. The first mixing curve 802 is an S-shaped curve that decreases from 100% at time t = 0 to 0% at time = t max The second mixing curve 804 is a modified S-shaped curve that decreases from 100% at time t = 0 to 0% at time = t max The S-shaped curve and the modified S-shaped curve are mathematically represented as shown in Equation (2):

[0072] Equation (2)

[0073] where the variable t is time, and a and b are adjustable parameters that determine the slope and symmetry of the curve, respectively. A value of b less than 0.5 results in an asymmetric S-shaped curve (e.g., the second mixing curve 804), where a portion of the curve (e.g., between approximately t = 30 seconds and approximately t = 70 seconds) is approximately linear.

[0074] Figure 9FIG. 900 shows a blending curve in an alternative embodiment. The blending curve 902 includes a first portion 904 and a second portion 906. The first portion 904 remains at 100% until a selected time 908. The second portion 906 can have the shape of any blending curve (402, 802, 804) having a decreasing value over time.

[0075] Figure 10 FIG. 1000 shows a graph depicting the torque operation of an illustrated electric motor. Time is shown along the horizontal axis in seconds, and torque capacity is shown along the vertical axis as a percentage. A first torque curve 1002 shows the torque capacity available to an electric motor using conventional methods. A second torque curve 1004 shows the torque capacity available to an electric motor using the methods disclosed herein. The first torque curve 1002 begins to show a significant loss of torque capacity at time t 1 The second torque curve 1004 begins to show a significant loss of torque capacity at a time t 1 greater than t 2 . In various embodiments, t 2 ~3*t 1 .

[0076] The terms "a" and "an" do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. Unless the context clearly dictates otherwise, the term "or" means "and / or". References to "aspect" throughout the specification mean that a particular element (e.g., a feature, a structure, a step, or a property) described in connection with that aspect is included in at least one aspect described herein, and may or may not be present in other aspects. Additionally, it should be understood that the described elements can be combined in any suitable manner in the various aspects.

[0077] When an element such as a layer, a film, a region, or a substrate is referred to as being "on" another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" another element, no intervening elements are present.

[0078] Unless otherwise stated herein, all test standards are the most current standards in effect as of the filing date of this application, or, if priority is claimed, the filing date of the earliest priority application in which the test standards appear.

[0079] Unless otherwise defined, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains.

[0080] While the foregoing disclosure has been described with reference to exemplary embodiments, those skilled in the art will understand that various changes may be made and equivalents may be substituted for its elements without departing from its scope. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from its basic scope. Therefore, it is intended that the disclosure not be limited to the particular embodiments disclosed, but will include all embodiments falling within its scope.

Claims

1. A method for de-rating an electric motor of a vehicle, comprising: When the temperature of the stator of the motor exceeds a high temperature threshold, a timer is started; selecting a mixing ratio based on a time value on the timer; using the blending ratio, determining an intermediate derating curve for the motor by interpolating between a first derating curve associated with a first target temperature and a second derating curve associated with a second target temperature greater than the first target temperature; and The motor is derated along the intermediate derating curve.

2. The method according to claim 1, wherein: The first derating curve is associated with long-term operation of the motor and the second derating curve is associated with short-term operation of the motor.

3. The method of claim 1 , further comprising incrementing the timer between a first time and a second time, determining a first intermediate derating curve at the first time, determining a second intermediate derating curve at the second time, and derating along a composite derating trajectory connecting a first operating point on the first intermediate derating curve at the first time to a second operating point on the second intermediate derating curve at the second time. 4 . The method of claim 1 , further comprising selecting the mixing ratio from a mixing curve that relates the mixing ratio to time via one of: (i) an S-shaped curve; and (ii) a modified S-shaped curve.

5. The method according to claim 1, further comprising: After the temperature of the electric motor drops below a recovery temperature threshold, torque at the electric motor is increased to operate the electric motor in an extended capacity region between the first target temperature and the second target temperature.

6. A system for de-rating an electric motor of a vehicle, comprising: Timer; A processor configured to: When the temperature of the stator of the motor exceeds a high temperature threshold, starting the timer; selecting a mixing ratio based on a time value on the timer; using the blending ratio, determining an intermediate derating curve for the motor by interpolating between a first derating curve associated with a first target temperature and a second derating curve associated with a second target temperature greater than the first target temperature; and The motor is derated along the intermediate derating curve.

7. The system according to claim 6, wherein: The first derating curve is associated with long-term operation of the motor and the second derating curve is associated with short-term operation of the motor.

8. The system according to claim 6, wherein: The processor is further configured to increment the timer between a first time and a second time, determine a first intermediate derating curve at the first time, determine a second intermediate derating curve at the second time, and derating along a composite derating trajectory connecting a first operating point on the first intermediate derating curve at the first time to a second operating point on the second intermediate derating curve at the second time.

9. The system according to claim 6, wherein: The processor is further configured to select the mixing ratio from a mixing curve that relates the mixing ratio to time via one of: (i) an S-shaped curve; and (ii) a modified S-shaped curve.

10. The system according to claim 6, wherein: The processor is further configured to increase torque at the electric motor to operate the electric motor in an extended capacity region between the first target temperature and the second target temperature after the temperature of the electric motor drops below a recovery temperature threshold.

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