Abstract:
A hybrid electric vehicle includes an engine and a traction motor coupled to the engine by a coupling device or a clutch for providing torque to wheels of the vehicle. An inverter is electrically connected to the traction motor. A second coupling device or at least one clutch at least indirectly selectively couples the motor to the drive wheels. A controller controls the second coupling device based upon a temperature of at least one of the fraction motor and the inverter.

Description:
TECHNICAL FIELD 
     The present disclosure is directed to a hill-hold in a hybrid electric vehicle. 
     BACKGROUND 
     Hybrid electric vehicles (HEV&#39;s) include an internal combustion engine and an electric traction motor, both being capable of propelling the HEV. When the operator of the HEV desires that the vehicle remain motionless, the vehicle can be at rest with the engine either on or off. When the vehicle is at rest with the engine on, a clutch downstream of the engine can be slipped in order to keep the engine from stalling. When the vehicle is at rest with the engine off, the motor can continue to spin with the downstream clutch open, or the motor can be disabled. 
     While the HEV is on an incline, the engine and/or motor must work to provide power to the wheels if the operator of the HEV desires that the vehicle remain motionless. This is known as hill-hold. There exists a need for a hill-hold system that holds the HEV on an incline by more efficiently utilizing the engine and/or the traction motor to provide torque to the wheels. 
     SUMMARY 
     According to one embodiment of the present disclosure, a vehicle comprises an engine and a traction motor for providing torque to at least one drive wheel. A first coupling device, or a clutch, selectively couples the engine to the traction motor. An inverter is electrically connected to the traction motor. A second coupling device is provided that, at least indirectly, couples the traction motor to the wheels. One or more controllers are provided that communicate with various components in the vehicle. The one or more controllers are configured to control the second coupling device. The second coupling device is controlled based at least upon a temperature of at least one of the traction motor and the inverter. In one embodiment, the controller is configured to at least partially disengage the second coupling device based upon the temperature of at least one of the traction motor and the inverter exceeding a first threshold. The engine may be activated based upon the temperature exceeding the first threshold, the activation being generally simultaneous with the disengagement of the second coupling device. 
     According to another embodiment of the present disclosure, a hill-hold system for a vehicle is provided. The system comprises an engine and a motor for providing torque to at least one drive wheel. An inverter is electrically connected to the motor. A clutch, at least indirectly, selectively couples the motor to the wheels. A controller is also provided that activates a first drive mode and a second drive mode. In the first drive mode, the clutch is locked and the engine is disabled. In the second drive mode, the clutch is partially disengaged and the engine is activated. The controller is configured to activate the second drive mode based upon a temperature of at least one of the motor and the inverter exceeding a threshold. 
     According to yet another embodiment of the present disclosure, a method for controlling hill-hold of a vehicle is provided. A temperature of at least one of a traction motor and an inverter is determined. A clutch is unlocked based upon the determined temperature being above a threshold. The clutch is disposed between the traction motor and traction wheels. An engine is activated to power the wheels generally simultaneously with the unlocking of the clutch. The torque of the traction motor may also be reduced generally simultaneously with the activation of the engine. Once the temperature of the traction motor and the inverter increase above a second threshold, the clutch may be locked and the torque in the motor may be increased. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of a hybrid electric vehicle according one embodiment of the present disclosure; 
         FIG. 2  is a schematic illustration of a transmission and other driveline components of a hybrid electric vehicle according to one embodiment of the present disclosure; 
         FIG. 3  is a graph illustrating an example of vehicle speed and transmission input speed over time when a clutch is locked; 
         FIG. 4  is a graph illustrating an example of vehicle speed and transmission input speed over time while a clutch transitions between slipping and not slipping; 
         FIG. 5  is a graph illustrating inverter temperature and motor temperature during times in which at least one of the motor and engine are holding the vehicle on a hill according to one embodiment of the present disclosure; 
         FIG. 6  is a flowchart illustrating a method according to one embodiment of the present disclosure; and 
         FIG. 7  is a flowchart illustrating another method according to one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Detailed embodiments of the present invention are disclosed herein. It is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale, as some features may be exaggerated or minimized to show details of particular components. Specific structural and functional details disclosed herein are therefore not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
     Referring to  FIG. 1 , a schematic diagram of a vehicle  10  is illustrated according to one embodiment of the present disclosure. The vehicle  10  is an HEV. The powertrain of the HEV includes an engine  12 , an electric machine or motor/generator (M/G)  14 , and a transmission  16  disposed between the M/G  14  and wheels  18 . A torque converter  19  can optionally be provided between the M/G  14  and the transmission  16 . The torque converter  19  transfers rotating power from the M/G  14  to the transmission  16 . It should be understood that instead of a torque converter  19 , one or more clutches can be provided to selectively transfer torque from the M/G  14  to the transmission  16 . 
     The M/G  14  can operate as a generator in one fashion by receiving torque from the engine  12  and supplying AC voltage to an inverter  20 , whereby the inverter  20  converts the voltage into DC voltage to charge a traction battery, or battery  22 . The M/G  14  can operate as a generator in another fashion by utilizing regenerative braking to convert the braking energy of the vehicle  10  into electric energy to be stored in the battery  22 . Alternatively, the M/G  14  can operate as a motor, in which the M/G  14  receives power from the inverter  20  and battery  22  and provides torque as an input to the torque converter  19  (or clutch), through the transmission  16  and ultimately to the wheels  18 . A differential  24  can be provided to distribute torque from the output of the transmission  16  to the wheels  18 . 
     A first coupling device, or disconnect clutch  26  is located between the engine  12  and the M/G  14 . The disconnect clutch  26  can be fully open, partially engaged, or fully engaged (locked). In order to start the engine  12 , the M/G  14  rotates the engine  12  when the disconnect clutch  26  is at least partially engaged. Once the engine  12  is rotated by the M/G  14  to a certain speed (e.g., ˜100-200 rpm), fuel entry and ignition can commence. This enables the engine  12  to “start” and to provide torque back to the M/G  14 , whereby the M/G  14  can charge the battery  22  and/or power the wheels  18  to propel the vehicle  10 . Alternatively, a separate engine starter motor (not shown) can be provided. 
     The vehicle  10  also includes a control system, shown in the embodiment of  FIG. 1  as three separate controllers: an engine control module (ECM)  28 , a transmission control module (TCM)  30 , and a vehicle system controller (VSC)  32 . The ECM  28  is directly connected to the engine  12 , and the TCM  30  can be connected to the M/G  14  and the transmission  16 . The three controllers  28 ,  30 ,  32  are connected to each other via a controller area network (CAN)  34 . The VSC  32  commands the ECM  28  to control the engine  12  and the TCM  30  to control the M/G  14  and the transmission  16 . Although the control system of the vehicle  10  includes three separate controllers, such a control system can include more or less than three controllers, as desired. For example, a separate motor control module can be directly connected to the M/G  14  and to the other controllers in the CAN  34 . 
     As illustrated in  FIG. 1 , τ eng  and ω eng  refer to the torque and speed of the engine, respectively. Furthermore, τ mot  and ω mot  refer to the torque and speed of both sides of the motor  14 , respectively. τ in  and ω in  refer to the torque and speed of the input of the transmission  16 , downstream of the torque converter  19 , respectively, while τ out  and ω out  refer to the torque and speed of the output of the transmission  16 . The final torque and speed transmitted to the wheels  18  is represented by τ final  and ω final , downstream of the engagement with the differential  24 . 
     Referring to  FIG. 2 , the transmission  16  is shown in detail. It should be understood that  FIG. 2  merely exemplifies one configuration of a transmission  16 . In a vehicle  10  utilizing the exemplified configuration of  FIG. 2 , a torque converter may not be needed in the vehicle, due to the multiple clutches and planetary gearsets within the transmission. It should therefore be understood that a simplified transmission  16  can be utilized in combination with a torque converter, in which fewer clutches and planetary gearsets are needed within the transmission  16 . Several other embodiments are contemplated with various configurations of clutches and/or planetary gearsets, with or without the use of a torque converter, as known in the art. 
     The transmission  16  of  FIG. 2  includes an input shaft  40  that receives torque from the engine  12  and the M/G  14  either separately or in combination. The input shaft  40  is operatively connected to a second clutch  42  and a third clutch  44 . A portion of each of the second clutch  42  and third clutch  44  is connected to a first planetary gearset (PG)  46 , which is connected to a second planetary gearset (PG)  48 . A reverse clutch, or fourth clutch  49  and a low-and-reverse brake, or fifth clutch  50  can also be connected to the PG  48 . The second PG  48  drives a belt or chain  52  to transmit power to a third planetary gearset (PG)  54 . Each of the planetary gearsets  46 ,  48 ,  54  can include a sun gear, a ring gear, and a planetary carrier to provide various gear ratios in the transmission  16 . The third PG  52  provides a final gear ratio to transmit torque from the transmission  16  to the differential  24 . 
     A pump  56  provides pressure to each of the clutches to engage/disengage each clutch as dictated by the TCM  30 . It should be understood that one or more of the clutches  42 ,  44 ,  49 ,  50  can be controlled to be engaged (locked), partially engaged, or fully disengaged, similar to the operation of the disconnect clutch  26 . For example, when the second clutch  42  and/or the third clutch  44  are disengaged, the transmission  16  can be isolated from the M/G  14  such that no torque is transmitted through the transmission  16  and to the wheels  18 . It should also be understood that while clutches  42 ,  44  are illustrated as being a part of the transmission  16 , one or more clutches can be separately utilized between the M/G  14  and the transmission  16  instead of being integral with the transmission  16 . 
     Referring to  FIGS. 1-2 , the engine  12  and M/G  14  can individually or together work to provide a relatively small amount of power to the wheels  18  to maintain the vehicle  10  motionless on an incline. This is hereinafter referred to as a hill-hold. When an operator of the vehicle  10  is stopped or idled on an incline, a release of the brake pedal should not enable the vehicle  10  to begin rolling backwards. The engine  12  and/or M/G  14  can provide torque to the wheels  18  to either maintain the vehicle  10  in a motionless state, or, if the incline is relatively small, provide a small amount of forward motion or “creeping” to the vehicle  10 . 
     During hill-hold, if the M/G  14  is providing the necessary torque to the wheels  18  without the engine  12  activated, a coupling device or clutch downstream of the M/G  14  can be locked such that the torque is transferred through the transmission  16  and to the wheels  18 . At a particular moment, as will be discussed further, the clutch can be unlocked such that the engine  12  can be activated by the M/G  14  and begin to provide torque to the wheels and continue the hill-hold. The present disclosure provides a system that determines whether to use the engine  12  or M/G  14 , and when to lock or unlock the clutch in order to provide hill-hold functionality. While references in the present disclosure are made to a “clutch” or a “coupling device” that is locked or unlocked during hill-hold, it should be understood that the “clutch” or “coupling device” can refer to one or more clutches downstream of the M/G  14  that, at least indirectly, couple the M/G  14  to the wheels  18  such that torque from the M/G  14  is translated into power at the wheels  18 . For example, the clutch can be any clutch in the transmission  16 , such as clutches  42  and  44 . The clutch can also be a bypass clutch in the torque converter  19 , or a clutch disposed between the M/G  14  and transmission  16  if a torque converter  19  is not included in the vehicle  10 . Furthermore, the clutch can also refer to the combination of the torque converter  19  and the transmission  16 . In all references hereinafter in the present disclosure to a “clutch”, it should be understood that any of the above-referenced clutches or combinations of clutches are contemplated unless otherwise indicated. 
     Referring to  FIG. 3 , a graph is provided that illustrates an example of an electric mode of operation in which the M/G  14  propels the vehicle  10  and the engine  12  is disabled. As shown in  FIG. 3 , the input speed (ω in ) of the transmission  16  and the speed of the vehicle  10  resemble one another. This is due to the clutch being locked and not slipping. Before time T 1  and after time T 2 , the vehicle has a speed of 0 mph. This indicates that the vehicle is either stopped or idling, and either on a flat surface or on an incline. It is during these times that the engine  12 , M/G  14  and clutch downstream of the M/G  14  must be controlled if the torque of the engine  12  is needed to maintain the hill-hold. 
     Referring to  FIG. 4 , an alternate embodiment is provided that illustrates an example in which the clutch alternates between slipping and not slipping during vehicle travel. In this case, the M/G  14  is allowed to spin at a predetermined speed or “idle speed” when the vehicle  10  is at rest. Before T 1 , the vehicle  10  is motionless, the M/G  14  is spinning, the clutch is slipping. It should be noted that in this illustrated embodiment, since the speed of the input of the transmission  16  (ω n ) is positive, the clutch that is slipping is a clutch downstream of the torque converter  19 . The clutch can thus be clutch  42 ,  44  in the transmission, for example. 
     At point T 1 , the input speed of the transmission  16  increases as the vehicle beings to be propelled. The pressure in the clutch can increase, but the clutch is still slipping between times T 1  and T 2 . The vehicle  10  can be creeping, for example, between times T 1  and T 2 . At time T 2 , the clutch is locked and the input speed of the transmission  16  resembles the speed of the vehicle  10 . Between times T 2  and T 3 , the vehicle  10  travels with no clutch slip such that the changes in the M/G  14  correspond to changes in the input speed of the transmission  16  which, in turn, corresponds to changes in the vehicle speed. At time T 3 , the clutch unlocks and beings to slip, while the speed of the M/G  14  returns to idle speed and the input speed of the transmission  16  continues to decrease as the vehicle  10  slows to a stop. At time T 4 , the vehicle  10  is again stopped with the M/G  14  spinning and the clutch slipping. 
     As previously disclosed, the vehicle  10  must remain motionless with minimal disturbances for a satisfactory hill-hold. Therefore, during hill-hold, a control system must be provided when the engine  12  is needed to be activated or the torque at least increased, as previously described. An example of such a system will now be described with reference to  FIGS. 5-7 . 
     Referring to  FIG. 5 , the temperature of the M/G  14  (“motor temp”) as well as the temperature of the inverter  20  (“inverter temp”) are illustrated during a hill-hold cycle. For each of the inverter temp and the motor temp, a hysteresis line is also provided. The “inverter temp hysteresis” and the “motor temp hysteresis” represent time-delayed data as a function of the inverter temp and motor temp data, respectively. 
     Before time T 1 , hill-hold is accomplished with the M/G  14  and the engine  12  deactivated with the clutch locked. The temperature of the inverter  20  and the M/G  14  continues to increase as hill-hold is accomplished by the M/G  14  due to the flow of electric power from the battery  22  to the M/G  14 . 
     At time T 1 , the temperature of the inverter  20  has increased above a predetermined calibrated inverter temperature (“Inverter Temp Cal”). This calibrated temperature is preferably greater than 200° F., but can be any calibrated to any temperature in which a threat of heat damage can be present. At T 1 , the clutch is slipped to off-load the heat from the M/G  14 . In order to supplement the power demands at the wheels  18  for hill-hold purposes while the clutch is slipped, the engine  12  is activated at T 1 . The activation of the engine  12  and the slipping of the clutch occurs generally simultaneously, preferably within a fraction of a second. Once the engine  12  is activated, the clutch is opened or slipped such that the speed transmitted is no lower than the engine&#39;s  12  idle speed to prevent the engine  12  from stalling. 
     Between times T 1  and T 2 , the engine  12  continues to provide the necessary torque through the powertrain to maintain the vehicle  10  in a hill-hold. As the engine  12  remains activated, the M/G  14  and the inverter  20  cool down due to their inactivity. The engine  12  is able to provide torque to the wheels  18  for a hill-hold. The engine  12  can also provide the necessary power to charge the battery  22  if needed, in the manner as previously disclosed. 
     At time T 2 , the inverter temp hysteresis has decreased below the predetermined calibrated inverter temperature amount, and the motor temp hysteresis has decreased below the predetermined calibrated motor temperature amount. It should be understood that the calibrated inverter temperature value and the calibrated motor temperature value can be different when the engine  12  is on as opposed to the engine  12  being off. In other words, the calibrated temperature values for the inverter and motor can be lower or higher when the inverter  20  and M/G  14  are cooling than when the inverter  20  and M/G are heating. 
     When both of the inverter and motor temp hysteresis values have decreased below the calibrated values at time T 2 , the temperatures of the inverter  20  and M/G  14  are determined to be at a safe temperature such that the clutch can lock and the M/G  14  can again work to provide the necessary torque for a hill-hold. After time T 2 , the inverter temp and the motor temp rise again, due to the work provided to hold the vehicle  10  on an incline. 
     Referring to  FIG. 6 , one example of a method of a hill-hold is provided in which the clutch can be locked and the M/G  14  is at 0 mph while the vehicle  10  is at rest. The VSC  32  and other controllers implement the illustrated example. The method begins at step  100 . At step  102 , a determination is made as to whether the clutch is locked. If the clutch is locked, a determination is made as to whether the temperature of the M/G  14  is above the predetermined calibrated motor temperature at step  104 . If not, then a determination is made as to whether the temperature of the inverter  20  is above the predetermined calibrated inverter temperature at step  106 . If either temperature is above respective predetermined values, the clutch is unlocked at step  108 . At step  110 , which can be generally simultaneous with step  108 , a request is made to pull-up and activate the engine  12 , and the torque of the M/G  14  is reduced. This allows the M/G  14  and the inverter  20  to cool while not providing torque to the wheels  18 . 
     If the clutch is locked as determined at step  102 , then at step  112  a determination is made as to whether the temperature of the M/G  14  is less than the calibrated motor temperature hysteresis. If so, then a determination is made as to whether the temperature of the inverter  20  is less than the calibrated inverter temperature hysteresis at step  114 . If a positive determination is made at steps  112  and  114 , the temperature of both the M/G  14  and the inverter  20  has reached a safe limit such that the M/G  14  can be increased in torque to provide hill-hold. At step  116 , the clutch is locked. At step  118 , which can be simultaneous with step  116 , a request is made to disable the engine, and the torque of the M/G  14  is increased to provide hill-hold. The method ends at  120 , at which time the method can repeat again at step  100 . 
     Referring to  FIG. 7 , another example of an algorithm for a hill-hold is provided, in which the M/G  14  remains spinning while the vehicle  10  is at rest. The VSC  32  and other controllers implement the illustrated example. The method begins at step  200 . At step  202 , a determination is made as to whether the engine  12  is activated. If the engine  12  is not activated, then at step  204  a determination is made as to whether the temperature of the M/G  14  is above the predetermined calibrated motor temperature value. If the M/G  14  is not too hot, a determination is made at step  206  as to whether the inverter  20  is too hot (i.e., the temperature of the inverter  20  is above the predetermined calibrated inverter temperature. If a positive determination is made at either steps  204  or  206 , then at step  208  a request is made to activate the engine  12  as well as reduce the torque of the M/G  14 . The engine  12  thus accomplishes the hill-hold while the M/G  14  and inverter are cooled. 
     If the engine was determined to be activated at step  202 , then at step  210  a determination is made as to whether the temperature of the M/G  14  is less than the calibrated motor temperature hysteresis. If so, then a further determination is made as to whether the temperature of the inverter  20  is less than the calibrated inverter temperature hysteresis at step  212 . If a positive determination is made at steps  210  and  212 , the temperature of both the M/G  14  and the inverter  20  has reached a safe limit such that the M/G  14  can be increased in torque to provide hill-hold. Thus, the engine is disabled at step  214  at the torque of the M/G  14  is increased to provide the necessary torque to the wheels  18 . 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation. It is also contemplated that various embodiments of the present disclosure may be combined or rearranged to achieve a specific result. Furthermore, to the extent that particular embodiments described herein are described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics, the other embodiments and the prior art implementations are not outside the scope of the disclosure and may be desirable for particular applications.