Abstract:
A method according to an exemplary aspect of the present disclosure includes, among other things, controlling an electrified vehicle by adjusting a deceleration rate based on a closing rate of the electrified vehicle to an oncoming object.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to a vehicle system and method associated with an electrified vehicle. The vehicle system is configured to modify a deceleration rate of an electrified vehicle based on a closing rate of the vehicle relative to an oncoming object. 
       BACKGROUND 
       [0002]    The need to reduce fuel consumption and emissions in automobiles and other vehicles is well known. Therefore, vehicles are being developed that reduce or completely eliminate reliance on internal combustion engines. Electrified vehicles are one type of vehicle currently being developed for this purpose. In general, electrified vehicles differ from conventional motor vehicles in that they are selectively driven by one or more battery powered electric machines. Conventional motor vehicles, by contrast, rely exclusively on the internal combustion engine to drive the vehicle. 
         [0003]    It is known to use an electric machine to decelerate an electrified vehicle. This is commonly referred to as regenerative braking. Regenerative braking can be achieved during braking or lift pedal conditions by configuring the electric machine as a generator. The act of generating power with the electric machine creates a negative braking torque, or regenerative torque, on the electric machine. The negative torque is transmitted to the drive wheels to slow the electrified vehicle. 
         [0004]    An accelerator pedal can be calibrated to provide either more deceleration/regeneration or less deceleration/regeneration during lift pedal conditions. However, the ideal deceleration rate may change depending on specific driving events. For example, if a customer tips out (i.e., lifts foot off of accelerator pedal) when an oncoming object is relatively far away, the vehicle may slow too quickly requiring the driver to tip in (i.e., apply pressure to the accelerator pedal) to reach the oncoming object. Conversely, if the operator tips out when the object is relatively close, the vehicle may coast too much requiring the driver to apply the brakes to stop the vehicle. 
       SUMMARY 
       [0005]    A method according to an exemplary aspect of the present disclosure includes, among other things, controlling an electrified vehicle by adjusting a deceleration rate based on a closing rate of the electrified vehicle to an oncoming object. 
         [0006]    In a further non-limiting embodiment of the foregoing method, the closing rate is based on a distance and a closing velocity from the electrified vehicle to the oncoming object. 
         [0007]    In a further non-limiting embodiment of either of the foregoing methods, the closing velocity is based on a first velocity of the electrified vehicle and a second velocity of the oncoming object. 
         [0008]    In a further non-limiting embodiment of any of the foregoing methods, the controlling step includes detecting the oncoming object and determining the closing rate to the oncoming object. 
         [0009]    In a further non-limiting embodiment of any of the foregoing methods, the method includes calculating a desired deceleration rate from the closing rate. 
         [0010]    In a further non-limiting embodiment of any of the foregoing methods, the method includes determining a negative torque demand necessary to achieve the desired deceleration rate. 
         [0011]    In a further non-limiting embodiment of any of the foregoing methods, the method includes modifying a torque demand associated with a predefined accelerator pedal position to be equal to the negative torque demand that is necessary to achieve the desired deceleration rate. 
         [0012]    In a further non-limiting embodiment of any of the foregoing methods, the method includes applying the negative torque demand to an electric machine to decelerate the electrified vehicle at the desired deceleration rate. 
         [0013]    In a further non-limiting embodiment of any of the foregoing methods, the controlling step includes correlating a desired deceleration rate to a negative torque demand and applying the negative torque demand to an electric machine of the electrified vehicle to decelerate the electrified vehicle using regenerative braking. 
         [0014]    In a further non-limiting embodiment of any of the foregoing methods, the controlling step includes adjusting the deceleration rate without applying brakes of the electrified vehicle. 
         [0015]    A method according to another exemplary aspect of the present disclosure includes, among other things, determining a desired deceleration rate of an electrified vehicle to an oncoming object and modifying a negative torque demand associated with a predefined accelerator pedal position to achieve the desired deceleration rate to the oncoming object. 
         [0016]    In a further non-limiting embodiment of the foregoing method, the method includes applying the negative torque demand to an electric machine of the electrified vehicle to decelerate the vehicle using regenerative braking. 
         [0017]    In a further non-limiting embodiment of either of the foregoing methods, the method includes detecting the oncoming object prior to the determining step. 
         [0018]    In a further non-limiting embodiment of any of the foregoing methods, the modifying step includes changing the negative torque demand on an accelerator pedal map to less negative, or zero, for a predefined accelerator pedal position if the oncoming object is relatively far or changing the negative torque demand of the accelerator pedal map to more negative for the predefined accelerator pedal position if the oncoming object is relatively near. 
         [0019]    In a further non-limiting embodiment of any of the foregoing methods, the predefined accelerator pedal position is between a 0% pedal position and a pedal position that corresponds to zero torque demand or zero acceleration. 
         [0020]    A vehicle system according to another exemplary aspect of the present disclosure includes, among other things, an accelerator pedal and a control module in communication with the accelerator pedal and configured to modify a deceleration rate of a vehicle by adjusting a negative torque demand associated with a predefined position of the accelerator pedal. 
         [0021]    In a further non-limiting embodiment of the foregoing vehicle system, an object detection subsystem detects an oncoming object ahead of the vehicle. 
         [0022]    In a further non-limiting embodiment of either of the foregoing vehicle systems, the accelerator pedal includes a sensor that detects a position of the accelerator pedal. 
         [0023]    In a further non-limiting embodiment of any of the foregoing vehicle systems, the system includes an electric machine. The control module commands application of the negative torque demand to the electric machine to decelerate the vehicle. 
         [0024]    In a further non-limiting embodiment of any of the foregoing vehicle systems, the deceleration rate is based on a closing rate to an oncoming object. 
         [0025]    The embodiments, examples and alternatives of the preceding paragraphs, the claims, or the following description and drawings, including any of their various aspects or respective individual features, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible. 
         [0026]    The various features and advantages of this disclosure will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  schematically illustrates a powertrain of an electrified vehicle. 
           [0028]      FIG. 2  illustrates a vehicle system that can be employed to adjust a deceleration rate of an electrified vehicle. 
           [0029]      FIG. 3  schematically depicts an electric vehicle traveling toward an oncoming object. 
           [0030]      FIG. 4  schematically illustrates a vehicle control strategy for adjusting a deceleration rate of an electrified vehicle based on its closing rate to an oncoming object. 
           [0031]      FIG. 5  illustrates an accelerator pedal map. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    This disclosure relates to a vehicle system and method for adjusting a deceleration rate of an electrified vehicle during specific driving events. A closing rate of the electrified vehicle to an oncoming object may be determined based on a distance and a closing velocity to the oncoming object. A negative torque demand, or regenerative torque, required to achieve a desired deceleration rate may be determined from the desired deceleration rate, which can be calculated using the closing rate. During various driving events, the negative torque demand associated with a predefined accelerator pedal position may be increased or decreased to achieve a smooth, linear deceleration to the oncoming object without the need to apply the brakes of the vehicle. These and other features are discussed in greater detail in the paragraphs that follow. 
         [0033]      FIG. 1  schematically illustrates a powertrain  10  for an electrified vehicle  12 . Although depicted as a hybrid electric vehicle (HEV), it should be understood that the concepts described herein are not limited to HEV&#39;s and could extend to other electrified vehicles, including, but not limited to, plug-in hybrid electric vehicles (PHEV&#39;s), battery electric vehicles (BEV&#39;s), and modular hybrid transmission vehicles (MHT&#39;s). 
         [0034]    In one embodiment, the powertrain  10  is a power-split powertrain system that employs a first drive system and a second drive system. The first drive system includes a combination of an engine  14  and a generator  18  (i.e., a first electric machine). The second drive system includes at least a motor  22  (i.e., a second electric machine), the generator  18 , and a battery assembly  24 . In this example, the second drive system is considered an electric drive system of the powertrain  10 . The first and second drive systems generate torque to drive one or more sets of vehicle drive wheels  28  of the electrified vehicle  12 . Although a power-split configuration is shown, this disclosure extends to any hybrid or electric vehicle including full hybrids, parallel hybrids, series hybrids, mild hybrids or micro hybrids. 
         [0035]    The engine  14 , which could include an internal combustion engine, and the generator  18  may be connected through a power transfer unit  30 , such as a planetary gear set. Of course, other types of power transfer units, including other gear sets and transmissions, may be used to connect the engine  14  to the generator  18 . In one non-limiting embodiment, the power transfer unit  30  is a planetary gear set that includes a ring gear  32 , a sun gear  34 , and a carrier assembly  36 . 
         [0036]    The generator  18  can be driven by the engine  14  through the power transfer unit  30  to convert kinetic energy to electrical energy. The generator  18  can alternatively function as a motor to convert electrical energy into kinetic energy, thereby outputting torque to a shaft  38  connected to the power transfer unit  30 . Because the generator  18  is operatively connected to the engine  14 , the speed of the engine  14  can be controlled by the generator  18 . 
         [0037]    The ring gear  32  of the power transfer unit  30  may be connected to a shaft  40 , which is connected to vehicle drive wheels  28  through a second power transfer unit  44 . The second power transfer unit  44  may include a gear set having a plurality of gears  46 . Other power transfer units may also be suitable. The gears  46  transfer torque from the engine  14  to a differential  48  to ultimately provide traction to the vehicle drive wheels  28 . The differential  48  may include a plurality of gears that enable the transfer of torque to the vehicle drive wheels  28 . In one embodiment, the second power transfer unit  44  is mechanically coupled to an axle  50  through the differential  48  to distribute torque to the vehicle drive wheels  28 . 
         [0038]    The motor  22  can also be employed to drive the vehicle drive wheels  28  by outputting torque to a shaft  52  that is also connected to the second power transfer unit  44 . In one embodiment, the motor  22  and the generator  18  cooperate as part of a regenerative braking system in which both the motor  22  and the generator  18  can be employed as motors to output torque. For example, the motor  22  and the generator  18  can each output electrical power to the battery assembly  24 . 
         [0039]    The battery assembly  24  is an exemplary type of electrified vehicle battery assembly. The battery assembly  24  may include a high voltage battery pack that includes a plurality of battery arrays capable of outputting electrical power to operate the motor  22  and the generator  18 . Other types of energy storage devices and/or output devices can also be used to electrically power the electrified vehicle  12 . 
         [0040]    In one non-limiting embodiment, the electrified vehicle  12  has two basic operating modes. The electrified vehicle  12  may operate in an Electric Vehicle (EV) mode where the motor  22  is used (generally without assistance from the engine  14 ) for vehicle propulsion, thereby depleting the battery assembly  24  state of charge up to its maximum allowable discharging rate under certain driving patterns/cycles. The EV mode is an example of a charge depleting mode of operation for the electrified vehicle  12 . During EV mode, the state of charge of the battery assembly  24  may increase in some circumstances, for example due to a period of regenerative braking. The engine  14  is generally OFF under a default EV mode but could be operated as necessary based on a vehicle system state or as permitted by the operator. 
         [0041]    The electrified vehicle  12  may additionally operate in a Hybrid (HEV) mode in which the engine  14  and the motor  22  are both used for vehicle propulsion. The HEV mode is an example of a charge sustaining mode of operation for the electrified vehicle  12 . During the HEV mode, the electrified vehicle  12  may reduce the motor  22  propulsion usage in order to maintain the state of charge of the battery assembly  24  at a constant or approximately constant level by increasing the engine  14  propulsion usage. The electrified vehicle  12  may be operated in other operating modes in addition to the EV and HEV modes within the scope of this disclosure. 
         [0042]      FIG. 2  illustrates a vehicle system  56  that may be incorporated into a vehicle, such as the electrified vehicle  12  of  FIG. 1 . The vehicle system  56  is adapted to adjust a deceleration rate of an electrified vehicle during various driving conditions, such as lift pedal conditions, as is further discussed below. In one non-limiting embodiment, the exemplary vehicle system  56  includes an accelerator pedal  54 , an object detection subsystem  58 , an electric machine  59 , and a control module  60 . 
         [0043]    The accelerator pedal  54  may be located within a passenger compartment  62  (shown schematically) onboard an electrified vehicle. The accelerator pedal  54  may be actuated by a driver to request a torque, power or drive command for propelling or decelerating the vehicle. The accelerator pedal  54  may be positioned at a plurality of accelerator pedal positions between fully tipped out (shown as position T 1 , also called lift pedal) and tip in (shown as position T 2 ). For example, at a 0% pedal position, the accelerator pedal  54  is completely tipped out (i.e., driver&#39;s foot has been removed from the accelerator pedal  54 ), and at a 100% pedal position the accelerator pedal  54  is completely tipped in (i.e., driver&#39;s foot has depressed the accelerator pedal  54  down to a floor board  64  of the passenger compartment  62 ). 
         [0044]    The accelerator pedal  54  may an electronic device that includes a sensor  66  for indicating the accelerator pedal position during vehicle operation. In general, the sensor  66  may generate a pedal position signal S 1  that is communicated to the control module  60  as the accelerator pedal  54  is depressed and/or released. 
         [0045]    The object detection subsystem  58  may be equipped to detect an oncoming object  76  (see  FIG. 3 ). In one non-limiting embodiment, the object detection subsystem  58  utilizes GPS technology to detect the oncoming object  76 . The object detection subsystem  58  could alternatively or additionally utilize radar, ladar, cameras and/or vehicle-to-vehicle communication technologies to detect the oncoming object  76 . Stated another way, the object detection subsystem  58  may utilize any known technology, or combinations of technologies, to detect the existence of the oncoming object  76 . 
         [0046]    Referring to  FIGS. 2 and 3 , the object detection subsystem  58  may determine a closing rate to the oncoming object  76  once the oncoming object  76  has been detected. The oncoming object  76  may include another vehicle, a stop sign, a stop light or any other object ahead of the electrified vehicle  12 . In one embodiment, the closing rate is based on at least a distance D from the electrified vehicle  12  to the oncoming object  76 , and a closing velocity of the electrified vehicle  12  to the oncoming object  76 . The closing velocity may be based on a velocity V 1  of the electrified vehicle  12  and a velocity V 2 , if any, of the oncoming object  76 . A closing rate signal S 2  indicative of the closing rate may be communicated to the control module  60  from the object detection subsystem  58 . 
         [0047]    The electric machine  59  may be configured as an electric motor, a generator or a combined electric motor/generator. Based at least upon input from the accelerator pedal  54  via the pedal position signal S 1 , the control module  60  may command torque (either positive torque or negative torque) from the electric machine  59 . For example, the electric machine  59  may receive torque command signals S 3  from the control module  60  for propelling the electrified vehicle  12  or for decelerating the electrified vehicle  12  during periods of regenerative braking. 
         [0048]    While schematically illustrated as a single module in the illustrated embodiment, the control module  60  of the vehicle system  56  may be part of a larger control system and may be controlled by various other controllers throughout an electrified vehicle, such as a vehicle system controller (VSC) that includes a powertrain control unit, a transmission control unit, an engine control unit, a battery electronic control module (BECM), etc. It should therefore be understood that the control module  60  and one or more other controllers can be collectively referred to as “a control module” that controls, such as through a plurality of integrated algorithms, various actuators in response to signals from various sensors to control functions associated with the electrified vehicle  12 , and in this case, with the vehicle system  56 . The various controllers that make up the VSC can communicate with one another using a common bus protocol (e.g., CAN). 
         [0049]    In one embodiment, the control module  60  includes executable instructions for interfacing with and operating various components of the vehicle system  56 . The control module  60  may include inputs  68  and outputs  70  for interfacing with the components of the vehicle system  56 . The control module  60  may additionally include a central processing unit  72  and non-transitory memory  74  for executing the various control strategies and modes of the vehicle system  56 . 
         [0050]    In one embodiment, the control module  60  is configured to determine a deceleration rate for achieving a smooth, linear deceleration of the electrified vehicle  12  to the oncoming object  76 . A desired deceleration rate may be calculated during various driving conditions based at least on the pedal position signal S 1  and the closing rate signal S 2 . The control module  60  may communicate a torque command signal S 3  to the electric machine  59  to achieve a desired deceleration rate during specific driving events. 
         [0051]      FIG. 4 , with continued reference to  FIGS. 1-3 , schematically illustrates a vehicle control strategy  100  of an electrified vehicle  12  equipped with the vehicle system  56  described above. The exemplary vehicle control strategy  100  may be performed to adjust a deceleration rate of the electrified vehicle  12  during certain driving events. For example, the deceleration rate of the electrified vehicle  12  can be adjusted based on a closing rate of the electrified vehicle  12  to an oncoming object  76 . Of course, the vehicle system  56  is capable of implementing and executing other control strategies within the scope of this disclosure. In one embodiment, the control module  60  of the vehicle system  56  may be programmed with one or more algorithms adapted to execute the vehicle control strategy  100 , or any other control strategy. In other words, in one non-limiting embodiment, the vehicle control strategy  100  may be stored as executable instructions in the non-transitory memory  74  of the control module  60 . 
         [0052]    As shown in  FIG. 4 , the vehicle control strategy  100  begins at block  102 . At block  104 , an oncoming object  76 , such as another vehicle, a stop sign or a stop light ahead of the electrified vehicle  12 , is detected by the object detection subsystem  58  of the vehicle system  56 . Detection of the oncoming object  76  indicates that the electrified vehicle  12  must begin to decelerate. The closing rate signal S 2  may be communicated to the control module  60  if an oncoming object  76  is detected (see  FIG. 2 ). 
         [0053]    If an oncoming object  76  has been detected, the vehicle control strategy  100  determines a closing rate of the electrified vehicle  12  to the oncoming object  76  at block  106 . The control module  60  of the vehicle system  56  may determine the closing rate based on a distance D to the oncoming object  76  and a closing velocity to the oncoming object  76  (see  FIG. 3 ). The closing velocity may be calculated based on both a velocity V 1  of the electrified vehicle  12  as well as a velocity V 2  of the oncoming object  76 , if any. 
         [0054]    A desired deceleration rate of the electrified vehicle  12  can be calculated at block  108 . In one embodiment, the desired deceleration rate is based at least on the closing rate obtained at block  106 . For example, if the closing rate is calculated as 2 MPH/second, then the desired deceleration rate is approximately 2 MPH/second. 
         [0055]    Once the desired deceleration rate is known, a negative torque demand necessary to achieve the desired deceleration rate can be determined at block  110 . The negative torque demand that is required to decelerate the electrified vehicle  12  may be correlated to the desired deceleration rate. For example, in one non-limiting embodiment, the negative torque demand can be obtained from a look-up table stored on the control module  60  that lists deceleration rates and negative torque demand rates required to achieve such deceleration rates. 
         [0056]    Next, at block  112 , the deceleration rate of the electrified vehicle  12  may be adjusted to achieve a smooth, linear deceleration to the oncoming object  76 . In one embodiment, the deceleration rate of the electrified vehicle  12  is adjusted by modifying the negative torque demand that is associated with a predefined accelerator pedal position. In one embodiment, the predefined accelerator pedal position is set at a 5% pedal position. In another embodiment, the predefined accelerator pedal position is set at a 0% pedal position. In yet another embodiment, the predefined accelerator pedal position is set between a 0% pedal position and a 5% pedal position. In yet another embodiment, the predefined accelerator pedal position is between a 0% pedal position and a pedal position that corresponds to zero torque demand (i.e., the point where the accelerator pedal map  78  of  FIG. 5  crosses from negative to positive) or that corresponds to zero acceleration. The negative torque assigned to the predefined pedal position may be modified to be equal to the negative torque demand obtained at block  110  in order to achieve the desired deceleration rate to the detected oncoming object  76 . 
         [0057]    The deceleration rate adjustment that occurs at block  112  of  FIG. 4  may be illustrated and described with reference to an accelerator pedal map  78  of  FIG. 5 . The accelerator pedal map  78  plots torque demand (in N-m or lb-ft) versus accelerator pedal position (in %). In one embodiment, the deceleration rate is adjusted by increasing or decreasing a negative torque demand  80  of the accelerator pedal map  78  at a predefined accelerator pedal position  82 . The negative torque demand  80  may be raised to position  84  if lower deceleration is needed to stop the electrified vehicle  12  by the time it reaches the oncoming object  76 , or may be lowered to position  86  if higher deceleration is needed to stop the electrified vehicle  12  by the time it reaches the oncoming object  76 . 
         [0058]    By way of a non-limiting example, if the oncoming object  76  is relatively “far,” and it is determined at block  108  that a 0.2 MPH/second deceleration rate is need to achieve linear deceleration, then the negative torque demand  80  associated with the predefined accelerator pedal position  82  is adjusted so that the predefined accelerator pedal position  82  achieves the desired 0.2 MPH/second deceleration rate. Alternatively, if the oncoming object  76  is relatively “close,” and it is determined at block  108  that a 2 MPH/second deceleration rate is needed to achieve linear deceleration, then the negative torque demand  80  is adjusted so that the predefined accelerator pedal position  82  achieves the desired 2 MPH/second deceleration rate. 
         [0059]    Finally, referring again to  FIG. 4 , the control module  60  can command the necessary negative torque demand (via torque demand signal S 3 ) to the electric machine  59  to achieve the desired deceleration rate of the electrified vehicle  12  for any given driving event at block  114 . In other words, the negative torque demand may be applied to the electric machine  59 . The negative torque is transmitted to the vehicle drive wheels  28  to slow the electrified vehicle  12  using regenerative braking. The vehicle control strategy  100  may be performed to control vehicle deceleration based on a positioning of the accelerator pedal  54  and without the need to apply the brakes of the electrified vehicle  12 . 
         [0060]    Although the different non-limiting embodiments are illustrated as having specific components or steps, the embodiments of this disclosure are not limited to those particular combinations. It is possible to use some of the components or features from any of the non-limiting embodiments in combination with features or components from any of the other non-limiting embodiments. 
         [0061]    It should be understood that like reference numerals identify corresponding or similar elements throughout the several drawings. It should be understood that although a particular component arrangement is disclosed and illustrated in these exemplary embodiments, other arrangements could also benefit from the teachings of this disclosure. 
         [0062]    The foregoing description shall be interpreted as illustrative and not in any limiting sense. A worker of ordinary skill in the art would understand that certain modifications could come within the scope of this disclosure. For these reasons, the following claims should be studied to determine the true scope and content of this disclosure.