Abstract:
A method according to an exemplary aspect of the present disclosure includes, among other things, controlling an electrified vehicle by engaging a parking brake if a battery state of charge is depleted below a predefined threshold.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to an electrified vehicle, and more particularly, but not exclusively, to a vehicle system and method for permitting neutral engine starting of an electrified vehicle. 
       BACKGROUND 
       [0002]    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 an internal combustion engine to drive the vehicle. Electrified vehicles may use electric machines instead of, or in addition to, internal combustion engines. The electric machines are typically powered by high voltage batteries. 
         [0003]    In some operating conditions, an electrified vehicle may be powered on and in neutral gear for an extended amount of time. When this occurs, the high voltage battery may be depleted to the point that it becomes necessary to shut down the vehicle. 
       SUMMARY 
       [0004]    A method according to an exemplary aspect of the present disclosure includes, among other things, controlling an electrified vehicle by engaging a parking brake if a battery state of charge is depleted below a predefined threshold. 
         [0005]    In a further non-limiting embodiment of the foregoing method, the method includes starting an engine of the electrified vehicle after the step of engaging the parking brake. 
         [0006]    In a further non-limiting embodiment of either of the foregoing methods, the method includes disengaging the parking brake after the engine is started. 
         [0007]    In a further non-limiting embodiment of any of the foregoing methods, the controlling step is performed if the electrified vehicle is keyed-on and in neutral. 
         [0008]    In a further non-limiting embodiment of any of the foregoing methods, the controlling step is performed if an engine of the electrified vehicle is off. 
         [0009]    In a further non-limiting embodiment of any of the foregoing methods, the controlling step is performed if the electrified vehicle is being operated at zero speed. 
         [0010]    In a further non-limiting embodiment of any of the foregoing methods, the method includes confirming that the parking brake is engaged prior to requesting an engine crank. 
         [0011]    In a further non-limiting embodiment of any of the foregoing methods, the method includes monitoring a torque being applied at the wheels of the electrified vehicle. 
         [0012]    In a further non-limiting embodiment of any of the foregoing methods, the monitoring step includes assuming the electrified vehicle is in park and determining whether the torque being applied at the wheels is below a predefined threshold. 
         [0013]    In a further non-limiting embodiment of any of the foregoing methods, the method includes performing a neutral engine start of the electrified vehicle if the torque being applied at the wheels is below the predefined threshold or preventing the neutral engine start if the torque being applied at the wheels is above the predefined threshold. 
         [0014]    A method according to another exemplary aspect of the present disclosure includes, among other things, engaging a parking brake of an electrified vehicle and starting an engine of the electrified vehicle subsequent to the engaging step. 
         [0015]    In a further non-limiting embodiment of the foregoing method, the engaging step is performed if the electrified vehicle is keyed-on, in neutral and the engine is off. 
         [0016]    In a further non-limiting embodiment of either of the foregoing methods, the engaging step is performed if a state of charge of a battery of the electrified vehicle is depleted below a predefined threshold. 
         [0017]    In a further non-limiting embodiment of any of the foregoing methods, the method includes communicating a neutral engine start message to an instrument panel of the electrified vehicle. 
         [0018]    In a further non-limiting embodiment of any of the foregoing methods, the method includes monitoring a torque being applied at the wheels of the electrified vehicle between the engaging step and the starting step. 
         [0019]    A vehicle system according to another exemplary aspect of the present disclosure includes, among other things, a parking brake, a battery and a controller configured to command engagement of the parking brake in response to a state of charge of the battery being depleted below a predefined threshold. 
         [0020]    In a further non-limiting embodiment of the foregoing vehicle system, the parking brake is an electronic parking brake that includes an electronic control unit and an actuator. 
         [0021]    In a further non-limiting embodiment of either of the foregoing vehicle systems, the controller or a second controller monitors the state of charge of the battery. 
         [0022]    In a further non-limiting embodiment of any of the foregoing methods, the systems includes an engine, the controller is configured to command a neutral engine start after engaging the parking brake. 
         [0023]    In a further non-limiting embodiment of any of the foregoing methods, the system includes an instrument panel configured to display a neutral engine start message. 
         [0024]    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. 
         [0025]    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 
         [0026]      FIG. 1  schematically illustrates a powertrain of an electrified vehicle. 
           [0027]      FIG. 2  illustrates a vehicle system of an electrified vehicle. 
           [0028]      FIG. 3  illustrates an instrument panel of a vehicle system. 
           [0029]      FIG. 4  schematically illustrates a vehicle control strategy for controlling an electrified vehicle. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    This disclosure relates to a vehicle system that provides neutral engine starting in electrified vehicles. The vehicle system engages a parking brake if a state of charge of a battery of the electrified vehicle is depleted below a predefined threshold. Momentary engagement of the parking brake permits the electrified vehicle to be started in neutral without a risk of unintended vehicle movement. These and other features are discussed in greater detail herein. 
         [0031]      FIG. 1  schematically illustrates a powertrain  10  of 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. 
         [0032]    In one embodiment, the powertrain  10  is a power split system that employs a first drive system that includes a combination of an engine  14  and a generator  16  (i.e., a first electric machine) and a second drive system that includes at least a motor  36  (i.e., a second electric machine), the generator  16  and a battery  50 . For example, the motor  36 , the generator  16  and the battery  50  may make up an electric drive system  25  of the powertrain  10 . The first and second drive systems generate torque to drive one or more sets of vehicle drive wheels  30  of the electrified vehicle  12 . 
         [0033]    The engine  14 , such as an internal combustion engine, and the generator  16  may be connected through a power transfer unit  18 . In one non-limiting embodiment, the power transfer unit  18  is 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  16 . The power transfer unit  18  may include a ring gear  20 , a sun gear  22  and a carrier assembly  24 . The generator  16  is driven by the power transfer unit  18  when acting as a generator to convert kinetic energy to electrical energy. The generator  16  can alternatively function as a motor to convert electrical energy into kinetic energy, thereby outputting torque to a shaft  26  connected to the carrier assembly  24  of the power transfer unit  18 . Because the generator  16  is operatively connected to the engine  14 , the speed of the engine  14  can be controlled by the generator  16 . 
         [0034]    The ring gear  20  of the power transfer unit  18  may be connected to a shaft  28  that is connected to vehicle drive wheels  30  through a second power transfer unit  32 . The second power transfer unit  32  may include a gear set having a plurality of gears  34 A,  34 B,  34 C,  34 D,  34 E, and  34 F. Other power transfer units may also be suitable. The gears  34 A- 34 F transfer torque from the engine  14  to a differential  38  to provide traction to the vehicle drive wheels  30 . The differential  38  may include a plurality of gears that enable the transfer of torque to the vehicle drive wheels  30 . The second power transfer unit  32  is mechanically coupled to an axle  40  through the differential  38  to distribute torque to the vehicle drive wheels  30 . 
         [0035]    The motor  36  can also be employed to drive the vehicle drive wheels  30  by outputting torque to a shaft  46  that is also connected to the second power transfer unit  32 . In one embodiment, the motor  36  and the generator  16  are part of a regenerative braking system in which both the motor  36  and the generator  16  can be employed as motors to output torque. For example, the motor  36  and the generator  16  can each output electrical power to a high voltage bus  48  and the battery  50 . 
         [0036]    The battery  50  may be a high voltage battery that is capable of outputting electrical power to operate the motor  36  and the generator  16 . Other types of energy storage devices and/or output devices can also be incorporated for use by the electrified vehicle  12 . In a non-limiting PHEV embodiment of the electrified vehicle  12 , the battery  50  may be recharged or partially recharged using a charging adapter  45  that is connected to a charging station powered by an external power source, such as an electrical grid, a solar panel, or the like. 
         [0037]    The motor  36 , the generator  16 , the power transfer unit  18 , and the power transfer unit  32  may generally be referred to as a transaxle  42 , or transmission, of the electrified vehicle  12 . Thus, when a driver selects a particular shift position, the transaxle  42  is appropriately controlled to provide the corresponding gear for advancing the electrified vehicle  12  by providing traction to the vehicle drive wheels  30 . 
         [0038]    The powertrain  10  may additionally include a control system  44  for monitoring and/or controlling various aspects of the electrified vehicle  12 . For example, the control system  44  may communicate with the electric drive system  25 , the power transfer units  18 ,  32  or other components to monitor and/or control the electrified vehicle  12 . The control system  44  includes electronics and/or software to perform the necessary control functions for operating the electrified vehicle  12 . In one embodiment, the control system  44  is a combination vehicle system controller and powertrain control module (VSC/PCM). Although it is shown as a single hardware device, the control system  44  may include multiple controllers in the form of multiple hardware devices, or multiple software controllers within one or more hardware devices. 
         [0039]    A controller area network (CAN)  52  allows the control system  44  to communicate with the transaxle  42 . For example, the control system  44  may receive signals from the transaxle  42  to indicate whether a transition between shift positions is occurring. The control system  44  could also communicate with a battery control module of the battery  50 , or other control devices. 
         [0040]    Additionally, the electric drive system  25  may include one or more controllers  54 , such as an inverter system controller (ISC). The controller  54  is configured to control specific components within the transaxle  42 , such as the generator  16  and/or the motor  36 , such as for supporting bidirectional power flow. In one embodiment, the controller  54  is an inverter system controller combined with a variable voltage converter (ISC/VVC). 
         [0041]    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  36  is used (generally without assistance from the engine  14 ) for vehicle propulsion, thereby depleting the battery  50  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  50  may increase in some circumstances, for example due to a period of regenerative braking. The engine  14  is generally not permitted to operate under a default EV mode but could be operated as necessary based on a vehicle system state or as permitted by the operator. 
         [0042]    The electrified vehicle  12  may additionally be operated in a Hybrid (HEV) mode in which the engine  14  and the motor  36  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  36  propulsion usage in order to maintain the state of charge of the battery  50  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. 
         [0043]    It may be desirable during some situations to start the engine  14  when the electrified vehicle  12  is in neutral and operating in EV mode. Exemplary vehicle systems and control strategies for achieving such a neutral engine start are described in greater detail below. 
         [0044]      FIG. 2  schematically illustrates a vehicle system  60  that may be incorporated into an electrified vehicle, such as the electrified vehicle  12  of  FIG. 1 . The vehicle system  60  may be employed to control operation of an electrified vehicle, such as to provide neutral engine starting of an engine  14  of the vehicle. Just prior to a neutral engine start, the engine  14  is off, the vehicle is in neutral gear, and the vehicle is being powered solely by an electric machine  15  (e.g., a motor, a generator, or a combined motor/generator). 
         [0045]    The exemplary vehicle system  60  includes a parking brake  62  that can be engaged to avoid unintended vehicle movement during a neutral engine start. In one non-limiting embodiment, the parking brake  62  is an electronic parking brake that includes an electronic control unit (ECU)  64  and an actuator  66 . During certain operating conditions, such as when the vehicle is in neutral, the ECU  64  may command the actuator  66  to engage the parking brake  62  and thereby prevent the vehicle from rolling. 
         [0046]    The vehicle system  60  may additionally include a battery controller  68  (i.e., a first controller) and a powertrain controller  70  (i.e., a second controller). Although shown as separate, stand-alone components, the battery controller  68  and the powertrain controller  70  could be part of a single control system. For example, the battery controller  68  and the powertrain controller  70  may be part of the control system  44  (see  FIG. 1 ). In this embodiment, the battery controller  68 , the powertrain controller  70 , and the ECU  64  communicate with one another and/or with other controllers, modules and/or components over the CAN  52  (see  FIG. 1 ). 
         [0047]    The battery controller  68  and the powertrain controller  70  may communicate with one another to control operation of the vehicle system  60 . In one embodiment, the battery controller  68  monitors the status of the battery  50 . For example, among other operating parameters, the battery controller  68  may monitor the state of charge (SOC) of the battery  50 . 
         [0048]    The powertrain controller  70  may monitor and control multiple other aspects of the vehicle system  60 . For example, the powertrain controller  70  can communicate with the ECU  64  to selectively command engagement of the parking brake  62 , can command starting and operation of the engine  14 , and can control operation of the electric machine  15 . The battery controller  68  and the powertrain controller  70  may include the necessary hardware and/or software for executing a plurality of interrelated algorithms for controlling the vehicle system  60 . 
         [0049]    In one non-limiting neutral engine start embodiment (i.e., the engine  14  is off and the vehicle is operating in EV mode and is in neutral), the battery controller  68  may communicate a signal S 1  to the powertrain controller  70  indicating that the SOC of the battery  50  is below a predefined threshold. The predefined threshold could be programmed at any threshold percentage amount. In response to receiving the signal S 1 , the powertrain controller  70  may communicate a signal S 2  to the ECU  64  to command engagement of the parking brake  62  via the actuator  66 . Engaging the parking brake  62  prevents unintended vehicle movement during a neutral engine start. Once the parking brake  62  has been engaged, the powertrain controller  70  may communicate another signal S 3  to the engine  14  to command the engine on (i.e., to command engine crank) and begin HEV operation of the vehicle. 
         [0050]    The vehicle system  60  may additionally include an instrument panel  72 . Although shown schematically in  FIG. 2 , the instrument panel  72  is typically located within the vehicle passenger cabin for displaying vehicle information to a vehicle operator or driver. In one embodiment, the instrument panel  72  may display a neutral engine start message to the vehicle operator. 
         [0051]      FIG. 3  illustrates one non-limiting embodiment of an exemplary instrument panel  72  of a vehicle system such as the vehicle system  60  of  FIG. 2 . The instrument panel  72  may include a display  74  that presents vehicle information to the vehicle operator. In one embodiment, the display  74  includes a multitude of indicators  76 , such as a mileage indicator, a fuel indicator and a RPM indicator. Of course, various other indicators may additionally or alternatively be provided within the scope of this disclosure. 
         [0052]    The display  74  may additionally include a message center  78 . Various messages  80  can be presented to the vehicle operator on the message center  78 . In this embodiment, a neutral engine start message is presented to the vehicle operator on the message center  78  to indicate that a neutral engine start is being performed. 
         [0053]      FIG. 4 , with continued reference to  FIGS. 1-3 , schematically illustrates a vehicle control strategy  100  for performing a neutral engine start by employing the vehicle system  60  described above. Of course, the vehicle system  60  is capable of implementing and executing other control strategies within the scope of this disclosure. In one embodiment, the battery controller  68  and the powertrain controller  70  of the vehicle system  60  may be programmed to employ one or more algorithms for executing the exemplary vehicle control strategy  100 , or any other control strategy. 
         [0054]    In one embodiment, the vehicle control strategy  100  includes a control channel  101  and a torque monitor channel  201 . Both of these channels, including their various control sequences, are discussed in detail below. 
         [0055]    The exemplary vehicle control strategy  100  begins at block  102  of the control channel  101 . At block  102 , the vehicle system  60  determines whether the vehicle is keyed-on, in neutral, and that the engine  14  is turned off. In other words, the vehicle system  60  determines whether the vehicle is being operated in EV mode and is in neutral gear. In one embodiment, a neutral engine start is performed only if these conditions exist and are confirmed by the powertrain controller  70  or some other controller(s). 
         [0056]    If the vehicle is in neutral, keyed-on, and the engine  14  is off, the control strategy  100  may proceed to block  104  by determining whether the vehicle is operating at zero speed. If so, the parking brake  62  is engaged at block  106 . In one embodiment, the parking brake  62  is engaged only if the battery controller  68  determines that the SOC of the battery  50  has been depleted below a predefined threshold. If the vehicle is not operating at zero speed or the battery SOC is not below a certain threshold, the vehicle control strategy  100  returns to block  102 . 
         [0057]    Next, at block  108 , the vehicle system  60  confirms whether or not the parking brake  62  has been engaged. If no, the vehicle control strategy  100  returns to block  102 . If engagement of the parking brake  62  is confirmed at block  108 , the vehicle control strategy  100  may proceed to the torque monitor channel  201 . 
         [0058]    The torque monitor channel  201  sequence begins execution at block  202 . Here, various vehicle system checks may be performed. For example, by way of non-limiting examples, the vehicle system  60  may confirm that the shifter of the vehicle is in neutral, that the vehicle is stationary, that the parking brake  62  is active, and/or that no vehicle health faults have been detected. If any vehicle system check returns a failure, the vehicle control strategy  100  proceeds to block  206  and prevents the engine  14  from being cranked. In other words, the neutral engine start sequence is cancelled. 
         [0059]    If each vehicle system check passes at block  202 , the vehicle control strategy  100  may proceed to block  204  of the torque monitor channel  201 . Here, a torque check may be performed on the vehicle. In one embodiment, as part of the torque check, the vehicle system  60  assumes that the vehicle is in park and monitors the torque being applied by various actuators at the wheels of the vehicle. If the torque check of block  204  confirms that the various torques are within a predefined threshold, the vehicle control strategy  100  returns to the control channel  101 . 
         [0060]    At block  110  of the control channel  101 , the vehicle system  60  confirms whether or not the torque monitor channel  201  has determined that an engine crank is permissible. If confirmation is made at block  110 , the engine  14  is cranked to start the engine with the vehicle in neutral at block  112 . 
         [0061]    In one embodiment, the parking brake  62  is only momentarily engaged at block  106 . For example, subsequent to starting the engine  14  at block  112 , the parking brake  62  may be automatically disengaged at block  114 . Block  114  may be commanded after a predefined threshold amount of time has passed since the engine  14  was started at block  112 . 
         [0062]    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. 
         [0063]    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. 
         [0064]    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.