Abstract:
A method of managing available operating states in an electrified powertrain includes: identifying a plurality of operating states; determining an allowable hardware operating speed range for each of the plurality of operating states; determining a real operating speed range for each of the plurality of operating states; determining an ideal operating speed range for each of the plurality of operating states, the ideal operating speed range being a subset of the allowable real operating speed range; indicating an operating state of the plurality of operating states as ideal-allowed if an actual output speed of the electrified powertrain is within the ideal operating speed range for that operating state; and commanding the electrified powertrain to operate within one of the operating states that is indicated as ideal-allowed.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a method of managing operating states in an electrified vehicle powertrain. 
       BACKGROUND 
       [0002]    Motorized vehicles include a powertrain operable to propel the vehicle and power the onboard vehicle electronics. The powertrain, or drivetrain, generally includes an engine that powers a final drive system through a multi-speed transmission. In some vehicles, the engine is a reciprocating-piston type internal combustion engine. The transmission may be supplied with transmission fluid or transmission oil to lubricate the components therein. 
         [0003]    Hybrid vehicles utilize multiple, alternative power sources to propel the vehicle, minimizing reliance on the engine for power. A hybrid electric vehicle (HEV), for example, incorporates both electrical energy and chemical energy, and converts the same into mechanical power to propel the vehicle and power any of the vehicle&#39;s systems. The HEV generally employs one or more electric machines (motor/generators) that operate individually or in concert with the internal combustion engine to propel the vehicle. An electric vehicle (EV) also includes one or more electric machines and energy storage devices used to propel the vehicle. 
         [0004]    The electric machines convert kinetic energy into electrical energy, which may be stored in an energy storage device. The electrical energy from the energy storage device may then be converted back into kinetic energy for propulsion of the vehicle, or may be used to power electronics, auxiliary devices, or other components. 
       SUMMARY 
       [0005]    A method of managing available operating states in an electrified powertrain begins by first identifying a plurality of operating states of the electrified powertrain, where each operating state represents a distinct physical configuration of the electrified powertrain. The electrified powertrain is configured to operate in a manner that rotatably drives a vehicle wheel at a rotational output speed. Following this, the method includes determining an allowable hardware operating speed range for each of the plurality of operating states, with the allowable hardware operating speed range being defined by a first hardware limit and a second hardware limit. Additionally, a controller may determine a real operating speed range for each of the plurality of operating states, with the real operating speed range being a subset of the allowable hardware operating speed range, and being defined by a first real limit that is greater than the first hardware limit, and by a second real limit that is less than the second hardware limit. An ideal operating speed range may then be determined for each of the plurality of operating states, where the ideal operating speed range is a subset of the allowable real operating speed range, and is defined by a first ideal limit that is greater than the first real limit, and by a second ideal limit that is less than the second real limit. 
         [0006]    Once the ranges are determined, the method may include indicating an operating state of the plurality of operating states as “ideal-allowed” if an actual output speed of the electrified powertrain is within the ideal operating speed range for that operating state; and commanding the electrified powertrain to operate within one of the operating states that is indicated as ideal-allowed. 
         [0007]    The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic diagram of a hybrid electric vehicle powertrain. 
           [0009]      FIG. 2  is a schematic flow diagram of a method of determining available operating states within an electric powertrain. 
           [0010]      FIG. 3  is a schematic plot of a plurality of operating state speed ranges. 
           [0011]      FIG. 4  is a schematic plot of a plurality of operating state speed ranges with a fault detected on one operating state. 
           [0012]      FIG. 5  is a schematic plot of a plurality of operating state speed ranges. 
           [0013]      FIG. 6  is a schematic plot of a plurality of operating state speed ranges with an intermediate state unavailable. 
           [0014]      FIG. 7  is a schematic flow diagram of a method of determining available operating states within an electric powertrain. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Referring to the drawings, wherein like reference numerals are used to identify like or identical components in the various views,  FIG. 1  schematically illustrates an electric vehicle powertrain  10 . In one configuration, the vehicle powertrain  10  may include a first traction motor  12 , a second traction motor  14 , and an energy storage system  16  (e.g., a battery  16 ). As such, the vehicle powertrain  10  may be configured as a hybrid electric vehicle powertrain (HEV), a battery electric vehicle powertrain (BEV), or an extended-range electric vehicle powertrain (EREV). Such vehicles can generate torque using one or both of the traction motors  12 ,  14  at levels suitable for propelling the vehicle in an electric-only (EV) mode. 
         [0016]    In one configuration, the first and second traction motors  12 ,  14  may be in mechanical communication through a transmission  18 . The transmission  18  may include a plurality of rotating gears, clutches, and or other components (i.e., torque transmitting devices  20 ) that may selectively couple, either alone or in combination, a transmission input shaft  22  with a transmission output shaft  24 . 
         [0017]    In one configuration, the transmission input shaft  22  may be selectively coupled with the first traction motor  12 , and the transmission output shaft  24  may be selectively coupled with the second traction motor  14 . In one configuration, the selective coupling may be accomplished through one or more friction clutches, torque converters, or other coupling devices that may be integral with the shafts  22 ,  24 , to allow each motor  12 ,  14  to transmit/receive torque at the command of a transmission control module. 
         [0018]    The transmission  18  may be, for example, an electrically-variable transmission (EVT), such that the input characteristics of the input shaft  22  and the output characteristics of the output shaft  24  need not have fixed ratios of the input shaft  22  via continuously variable speed ratios. For example, in some embodiments, the output speed at the output shaft  24  may be positive even though the input speed at the input shaft  22  may be zero. 
         [0019]    The torque transmitting devices (collectively shown at  20 ) may be selectively engageable within the transmission  18  to establish different forward and reverse speed ratios or operating modes between the input shaft  22  and output shaft  24 . Shifting from one speed ratio or mode to another may occur in response to vehicle conditions and operator (driver) demands. The speed ratio is generally defined as the input speed divided by the output speed of the transmission  18 . Thus, a low gear range has a high speed ratio, and a high gear range has a relatively lower speed ratio. 
         [0020]    Electrically-variable transmissions, including the transmission  18 , may be designed to operate in both fixed-gear (FG) modes and EVT modes. Because electrically-variable transmissions are not limited to single-speed gear ratios, the different operating states may be referred to as ranges or modes instead of gears. When operating in a fixed-gear mode, the rotational speed of the output shaft  24  of the transmission  18  is a fixed ratio of the rotational speed of the input shaft  22 . Electrically-variable transmissions are also configured for operation that is mechanically independent from the final drive, thereby enabling high-torque continuously-variable speed ratios, electrically dominated launches, regenerative braking, and engine-off idling and launches. 
         [0021]    In some designs, an internal combustion engine  30 , shown in phantom in  FIG. 1 , may be used to generate torque via an engine output shaft  32 . Torque from the engine output shaft  32  can be used to either directly propel the vehicle powertrain  10 , i.e., in an HEV design, or to power a generator  34 , i.e., in an EREV design. The generator  34  can deliver electricity (arrow  36 ) to the battery  16  in a manner that may recharge the battery  16 . A clutch and damping assembly  38  may be used to selectively connect/disconnect the engine  30  from a transmission  18 . Torque may be ultimately transmitted from the first and/or second traction motors  12 ,  14 , and/or the engine  30  to a set of drive wheels  40  via an output  42  of the second traction motor  14  (and/or the transmission  18  if the second motor  14  is omitted). 
         [0022]    Each traction motor  12 ,  14  may be embodied as a multi-phase permanent magnet/AC induction machine rated for approximately 60 volts to approximately 300 volts or more depending on the vehicle design. Each fraction motor  12 ,  14  may be electrically connected to the battery  16  via a power inverter module (PIM)  44  and a high-voltage bus bar  46  (it should be noted that the schematic depiction of the high voltage bus bar extending to the second traction motor  14  has been omitted from  FIG. 1  for clarity). The PIM  44  may generally be configured for converting DC power to AC power and vice versa as needed. The battery  16  may be selectively recharged using torque from the first traction motor  12  when that traction motor  12  is actively operating as generator, e.g., by capturing energy during a regenerative braking event or when being driven by the internal combustion engine  30 . In some embodiments, such as plug-in HEV (PHEV), the battery  16  can be recharged via an off-board power supply (not shown) when the vehicle powertrain  10  is idle. 
         [0023]    Both traction motors  12 ,  14 , the transmission  18 , and the engine  30  may be in electronic communication with a controller  50 . In one configuration, the controller  50  may include, for example, an engine control module  52  (ECM  52 ) for controlling the operation of the engine  30 , a hybrid control module  54  (HCM  54 ) for controlling the operation of the traction motors  12 ,  14 , and/or a transmission control module  56  (TCM  56 ) for controlling the operation of the transmission  18 . The controller  50  may be embodied as one or multiple digital computers or data processing devices, having one or more microcontrollers or central processing units (CPU), read only memory (ROM), random access memory (RAM), electrically-erasable programmable read only memory (EEPROM), a high-speed clock, analog-to-digital (A/D) circuitry, digital-to-analog (D/A) circuitry, input/output (I/O) circuitry, and/or signal conditioning and buffering electronics. 
         [0024]    The ECM  52 , HCM  54 , and TCM  56  may be embodied as software or hardware and may or may not be physically separated from each other. In one configuration, the modules  52 ,  54 ,  56  may be compartmentalized functions executed by the same physical structures of the controller  50 . In another configuration, each module  52 ,  54 ,  56  may be relegated to its own hardware computing device. Regardless, every module  52 ,  54 ,  56  may be in digital communication with the other modules  52 ,  54 ,  56  to coordinate the overall behavior of the vehicle powertrain  10  Each module  52 ,  54 ,  56  may be configured to automatically perform one or more control/processing routines that may be embodied as software or firmware associated with the module  52 ,  54 ,  56 . It should be noted that this specific configuration of the “modules” is described as such for clarity. In practice, however, any specific function described as within one of the modules may be executed by another module, or alternatively, all of the functions may simply be executed by the controller  50  without separate identification of the modules. 
         [0025]    In general the various hardware components described above may be selectively engageable with adjacent components to form a torque transmitting path from one or more torque sources (i.e., traction motors  12 ,  14 , and engine  30 ) to the vehicle drive wheels  40 . Each combination of engaged/disengaged components, operational/non-operational torque sources, and torque generating/torque consuming modes (i.e., for motors  12 ,  14 ) may be characterized generally as an “operating state.” 
         [0026]    In one configuration, the controller  50  may further include a state management module  58  (SMM  58 ), which may be resident within any of the ECM  52 , HCM  54 , and TCM  56 , or may be a separate as generally shown. The SMM  58  may receive a torque request from a user (such as from an accelerator pedal  60 ), and determine the best operating state to achieve the desired torque request. The SMM  58  may choose the operating state in a predictive manner that forecasts an acceleration/deceleration trend, while also preventing operation of the electric vehicle powertrain  10  in a manner that may compromise the integrity or longevity of the various motor or transmission components described above. 
         [0027]    Each operating state may have a corresponding hardware limit for various parameters such as speed, torque, and temperature. If the powertrain, in a particular state, is operated beyond of the hardware limit, one or more components within the system may be at a drastically increased likelihood of failing (i.e., losing its ability to transmit torque from a torque source to the vehicle wheels). In general, the hardware limit may be a function of physical factors, such as individual component design, construction, lubrication, and/or arrangement. 
         [0028]    To guard against a hardware limit being inadvertently crossed, the controller  50  may include a speed request limiter  62  that may alter the behavior of the powertrain  10  and/or the amount of torque generated/consumed within the powertrain  10  if a hardware limit is being approached. The speed request limiter  62  may generally operate in software by saturating a requested amount of torque prior to transmitting the request to the ECM/HCM. In this manner, the performance and/or responsiveness of the vehicle will be noticeably affected if a hardware limit is being approached and the speed request limiter  62  must intervene. 
         [0029]    The SMM  58  may include an optimization routine  64  and an available state identifier  66 . The optimization routine  64  may receive the torque request from the user and select the optimal operating state from the available operating states that may achieve the desired response. The list of available operating states may be generated by the available state identifier  66 , and may be made available to the optimization routine  64 . 
         [0030]      FIG. 2  illustrates a method  70  of determining available operating states within an electric powertrain. The method  70  may be performed, for example, by the SMM  58  via the available state identifier  66 . The method  70  may be embodied as a software routine that may ultimately be executed by the controller  50 . The method may begin at  72  by identifying all of the operating states that may exist within the electric powertrain.  FIG. 3  schematically illustrates a plot  90  of a plurality of such operating states  92 , with the horizontal axis  94  representing a state parameter (e.g., speed, torque, or temperature), and the vertical axis  96  merely being used to spread the states out for clarity. For clarity,  FIG. 3  only illustrates a 1-parameter range for each state, however, in practice, the present method may be expanded to an unlimited parameter (n-parameter) situation. 
         [0031]    In the interest of clearly describing the present method  70 , the states  92  in  FIG. 3  will be analogized to sequential gears, however, in practice, and as described above, the states may, in fact, represent discrete states of a significantly more complex system. Using the gear analogy,  FIG. 3  then illustrates six discrete gears (i.e., states  98   a - 98   f ), that may be ordered along the vertical axis  96  of the plot  90 , with the gear having the highest gear ratio (e.g., gear 1) shown as  98   a , and the gear having the lowest gear ratio (e.g., gear 6) shown as  98   f . Additionally, in this analogy, the horizontal axis  94  may represent a final output speed. As may be understood, gears in a typical transmission are generally sequential, meaning that they are used in an ordered manner. Said another way, to transition from gear/state  98   a  to  98   c , it is common to use/transition through an intermediate gear/state  98   b . Such an ordered arrangement may occur, for example, if gears  98   a  and  98   c  share common hardware that must be reconfigured prior to engaging the new state. 
         [0032]    For each of the plurality of operating states  90 , an actual hardware limit  100  is indicated in phantom, and the hardware limits  102  imposed by the speed request limiter  62  are indicated inside of the actual hardware limits  100 . Additionally, “real” limits  104  may be imposed by the system inside of the limiter limits  102 . These “real” limits  104  may be used to force state transitions prior to the system being limited in a fail-safe manner. Said another way, the speed request limiter  62  is a limiter of last-resort. The real limits  104  may represent a desired extreme operating condition within a state, and are inside of the hardware limiter limits  102  by a given safety factor. 
         [0033]    Referring again to  FIG. 2 , once all of the operating states are identified in step  72 , the controller  50  may then poll the various states in step  74  to determine if a fault exists in any state that may physically render that state unavailable. In one embodiment, the controller  50  may perform the fault detection in step  74  through direct communication with diagnostic sensors associated with each respective state. In another embodiment, the controller  50  may perform the fault detection in step  74  in an inferential manner by comparing certain known or expected behavior with actual current or past behavior of the system.  FIG. 4  generally illustrates the gear system of  FIG. 3 , where a fault  110  has been detected on gear 5 (state  98   e ) that may render gear 6 (state  98   f ) inoperable or physically unavailable. 
         [0034]    Referring again to  FIG. 2 , one fault detection has occurred in step  74 , the controller  50  may then determine if the fault prevents other states from physically being available in step  76 . For example, as shown in  FIG. 4 , where the vertical line  112  represents the current vehicle speed  94 , the fault  110  may prevent a future shift into gear 6 (state  98   f ). Said another way, because the gears are ordered, it may be impossible or impractical to shift directly from gear 4 (state  98   d ) into gear 6 (state  98   f ) without the use of gear 5 (state  98   e ). This ordered nature, together with the fault on gear 5 (state  98   e ), may render it impossible to eventually up-shift into gear 6 (state  98   f ), given the current speed  112  below gear 5 (state  98   e ). 
         [0035]    Referring again to  FIG. 2 , once the list of all states (determined in step  72 ) has been reduced to eliminate both the faulty states (in step  74 ) and fault-prevented states (in step  76 ), the controller may then determine (in step  78 ) which of the remaining states are “real allowed,” given the current operating conditions of the vehicle and/or systems of interest. As used herein, a state is “real allowed” if the current operating parameters are within the established real limits  104  of that state. For example,  FIG. 5  generally illustrates the plot of  FIG. 4 , with actual hardware limits  100  and hardware limiter limits  102  removed for clarity (leaving only the real limits  104 ). In this plot, given the current operating speed  112 , gears 1, 2, and 3 (states  98   a ,  98   b , and  98   c ) are “real allowed,” while gear 4 (state  98   d ) is not. 
         [0036]    Once it has been determined which states are “real allowed” in step  78 , any real limits for adjacent states may be mapped onto a current active state in step  80  (see  FIG. 2 ).  FIG. 5  illustrates a “mapped” real shift limit  114  on gear 1 (state  98   a ) that corresponds to the upper limit of gear 2 (state  98   b ). Note that  FIG. 5  is a zoomed in view of gears 1-3 from  FIG. 4 . The mapping of real limits in step  80  may be necessary when an intermediate operating state is required, though may have a real operating range that does not extend to the real limit of the current operating state. 
         [0037]    For example, as generally illustrated in  FIG. 5 , the vehicle may be operating in gear 1 (state  98   a ) at point  116 . During an acceleration, the controller  50  may wish to upshift from gear 1 to gear 3 (state  98   c ), though may be required to transition through gear 2 (state  98   b ) or risk shifting to neutral. This situation may exist, for example, if gears/states 1 and 3 require the same hardware, with gear 2 being separated to allow the hardware of gears 1/3 to time to transition (e.g. as with a dual clutch transmission). If the system remains in gear 1 past the mapped, real shift limit  114  (i.e., into range  118 ), then gear 2 (state  98   b ) will no longer be “real allowed,” and the shift may be restricted. Therefore, the real shift limit  114  may become the new upper real limit of gear 1 (state  98   a ). 
         [0038]    While the preceding description provides a method of determining which operating states are actually allowed in an electric powertrain, as described, it does not account for any lag that may be inherent transitioning from one state to another, nor does it account for other desired performance characteristics that may be considered during the shift optimization. In this manner, in step  82  ( FIG. 2 ) the controller  50  may impose various “ideal” shift limits  120  that may be separated from the real limits  104  or the real shift limits  114  by a margin  122 , as generally illustrated in  FIG. 5 . 
         [0039]    The margin  122  that separates an ideal shift limit  120  from a real limit  104  or real shift limit  114  may be either be a fixed value or may be a function of one or more operating parameters (e.g. speed, torque, acceleration, etc). In either case, the ideal shift limit  120  may be set such that given the rate of change of the parameter, along with the time required to effectuate a state transition, a real limit  104  may not be violated during the transition. For example, as shown in  FIG. 5 , if the speed  112  is accelerating and the controller  50  causes a shift right at the real shift limit  114 ,then the time required to shift, the acceleration, and the proximity to the real limit  104  of gear 2 (state  98   b ) may likely cause the real limit to be exceeded. 
         [0040]    In one embodiment, the ideal shift limit  120  may solely be an anticipatory/predictive limit, which may be used to account for shift times and acceleration/deceleration of the monitored parameters. In another embodiment, other factors may be accounted for, such as, but not limited to, shift synchronization, powertrain jerk, power-handling capacity, powertrain efficiency, battery charging/discharging capacity, battery state-of-charge, and/or temperature. 
         [0041]    If no subsequent operating state exists (e.g., a fault  110  occurs on gear 2 (state  98   b ), such as shown in  FIG. 6 ), then, in step  84 , the controller  50  may override the ideal shift limit  120 , the real shift limit  114 , and/or the real limit  104  within the current operating state, to provide a marginal increase in operating range before the speed request limiter  62  intervenes to limit the speed/torque at  102 . 
         [0042]      FIG. 7  illustrates a method  130  that is similar to that provided in  FIG. 2 . The method  130  begins at step  132  by identifying all operating states. The method  130  proceeds to step  134  where the controller  50  may calculate (or look up from a stored lookup table) the individual hardware limiter limits  102  for each state, as well as the state&#39;s real limits  104  in step  136 . This process may loop until the values have been found for each of the states. 
         [0043]    In step  138 , the controller  50  may determine if a particular state is real allowed. If not, the method  130  may draw the conclusion at  140  that that state is also not ideal allowed. If, however, the controller  50  determines that the state is real allowed at  138 , it may then inquire at  142  whether there is a state that can be shifted into that is also real allowed. If so, adjacent real shift limits may be mapped into the current state in step  144 , and ideal limits may be applied on top of the real shift limits in step  146 . If no state can be shifted into that is real allowed at  142 , then the controller  50  may override any applied ideal or real limits on that particular operating state at  148 . In step  150 , the controller may then determine wither the current operating parameters are within the ideal limits that may be required for a successful or ideal shift into the adjacent state. If the limits are satisfied, the adjacent state may be considered ideal allowed at  152 . Otherwise, the controller  50  may draw the conclusion that the state is not ideal allowed at  140 . This process may loop for all adjacent states and/or combinations of states. Finally, any states that are considered “ideal allowed” may then be passed to the optimization routine  64 , where the best state may be selected, commanded to occur via the ECM  52 , HCM  54 , and TCM  56 , where it may be used to implement the torque request from the user. 
         [0044]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not as limiting.