Abstract:
A vehicle and a method of controlling the vehicle are provided. The vehicle controller is configured to (i) in response to the user interface receiving input selecting an electric-only operating (EV) mode, disable the engine such that the vehicle is propelled by the electric machine, (ii) in response to the user interface receiving input overriding EV mode, re-enabling the engine for a predetermined time period. A vehicle is provided with a controller. In response to input selecting an electric-only operating (EV) mode, an engine is disabled such that the vehicle is propelled by an electric machine. In response to user power demand being greater than power available during the EV mode, a prompt is generated inquiring whether to override the EV mode. In response to user confirmation to override the EV mode, the engine is re-enabled to satisfy the user power demand.

Description:
TECHNICAL FIELD 
     Various embodiments relate to electric operation of a hybrid vehicle and methods of controlling the vehicle. 
     BACKGROUND 
     A hybrid electric vehicle (HEV) or a plug-in hybrid electric vehicle (PHEV) has more than one source of power. An electric machine may be configured to propel the vehicle and uses a battery as a source of energy. For a PHEV, the battery may be recharged using an external power source, such as a charging station. An engine may also be configured to propel the vehicle and use fuel as a source of energy. The PHEV can be controlled to use the electric machine and/or the engine to operate the vehicle and meet user demand. 
     SUMMARY 
     In an embodiment, a vehicle is provided with an electric machine, an engine, and a controller. The controller is configured to (i) in response to input selecting an electric-only operating mode, disable an engine such that the vehicle is propelled by an electric machine, (ii) in response to user power demand being greater than power available during the electric-only operating mode, generate a prompt to inquire whether to override the electric-only operating mode, and (iii) in response to user confirmation to override the electric-only operating mode, re-enable the engine to satisfy the user power demand. 
     In another embodiment, a vehicle is provided with an engine, an electric machine, a user interface, and at least one controller. The at least one controller is configured to (i) in response to the user interface receiving input selecting an electric-only operating (EV) mode, disable the engine such that the vehicle is propelled by the electric machine, (ii) in response to the user interface receiving input overriding EV mode, re-enabling the engine for a predetermined time period. 
     In yet another embodiment, a method for controlling a vehicle is provided. In response to user input selecting an electric-only operating (EV) mode, an engine is disabled such that the vehicle is propelled by an electric machine. In response to receiving a user input to override the EV mode, the engine is re-enabled for a predetermined time period. 
     Various embodiments of the present disclosure have associated non-limiting advantages. For example, the vehicle is configured to provide a user selected, electric-only (EV) mode of operation, allowing user control and input regarding vehicle operation. The user may override the user selected EV mode of operation using a user interface. The override may be used when a user input or request to the vehicle indicates a need for the engine to be enabled, and the vehicle to operate in a hybrid mode. The controller is configured to change the operating state of the vehicle to a hybrid mode of operation after receiving the user override. The controller sends a message to the user to select and/or confirm the override. The controller may also provide a message that the vehicle is operating in a hybrid mode via a user interface such that the user&#39;s expectations regarding vehicle operation are met and the user is informed of potential engine operation after having selected an EV mode of operation for the vehicle. The controller is configured to return the vehicle to the user selected EV mode after the user input or request to the vehicle that caused the EV mode override and the engine to be enabled ends. The vehicle is returned to the user selected EV mode by the controller. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a chart illustrating two modes of operation for a plug-in electric vehicle according to an embodiment; 
         FIG. 2  is a schematic of a hybrid vehicle capable of implementing various embodiments of the present disclosure; 
         FIG. 3  is a flow chart illustrating an algorithm for use with the vehicle of  FIG. 2  for a user override of a user selected EV mode of operation according to an embodiment; and 
         FIG. 4  is a flow chart illustrating a user interface implementing the algorithm of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     As required, detailed embodiments of the present disclosure are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary and may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the claimed subject matter. 
     Plug-in hybrid electric vehicles (PHEV) utilize a larger capacity battery pack than a standard hybrid electric vehicle (HEV). PHEVs have the capability to recharge the battery from a standard electrical outlet or charging station connected to the external electric grid to reduce fuel consumption and to improve the vehicle&#39;s fuel economy. The PHEV structure is used in the figures and to describe the various embodiments below; however, it is contemplated that the various embodiments may be used with vehicles having other vehicle architectures as are known in the art. The PHEV engine may be a compression or spark ignition internal combustion engine, or an external combustion engine, and the use of various fuels is contemplated. In one example, the vehicle has the ability to connect to an external electric grid, such as in a plug-in electric hybrid vehicle (PHEV). 
     Besides the gasoline fuel energy, a PHEV also has an additional energy source of electrical energy stored in the battery, which may be electric energy from the electric grid deposited in the vehicle&#39;s battery during charging. The power management of the PHEV allocates the drive power demand of the vehicle to one or both of the two energy sources in order to achieve an improved fuel economy and meet the other comparable HEV/PHEV control objectives. While conventional HEVs may be operated in order to maintain the battery State of Charge (SOC) around a constant level, it may be desirable for PHEVs to use as much pre-saved battery electric (grid) energy as possible before the next charge event (when the vehicle is “plugged-in”). To increase fuel economy, the relatively inexpensive, grid-supplied electric energy may be preferentially used to save as much gasoline fuel as possible. 
     Generally, a PHEV has two basic operating modes as seen in  FIG. 1 . In a Charge Depleting (CD) mode  20  the battery electric energy  21  may be primarily used to propel the vehicle. The engine assists the vehicle drive power supply only in certain driving conditions or at excessive drive power requests during the basic charge depleting mode. One characteristic in the CD mode  20  is that the electric motor consumes more energy from the battery  21  than can be regenerated. In a Charge Sustaining (CS) mode  22  (or HEV mode), the vehicle reduces the electric motor propulsion usage to be able to keep the battery&#39;s State of Charge (SOC)  21  at a constant or approximately constant level by increasing the engine propulsion usage such that the SOC level is generally maintained. 
     The PHEV may operate in an Electric Vehicle (EV) mode where the electric motor is used (without help from the gasoline engine depending on PHEV strategy) for vehicle propulsion, depleting the battery up to its maximal allowable discharging rate under certain driving patterns/cycles. The EV mode is an example of a CD mode of operation for a PHEV. During an EV mode, the battery charge may increase in some circumstances, for example due to a period of regenerative braking. The engine is generally not permitted to operate under a default EV mode, but may need to be operated based on a vehicle system state or as permitted by the operator through an override or hybrid operation selection as described further below. 
     For the vehicle operation as shown in  FIG. 1 , once the battery SOC  21  decreases to a predefined charge sustaining level  28 , the vehicle switches to CS mode  22 , where the battery SOC  21  is kept within a vicinity of the charge sustaining SOC level, and the vehicle is primarily powered by the engine (fuel energy). The vehicle may also operate with the CD and CS modes in any order, or with CD and CS modes occurring multiple times during a key cycle. Also, the CD mode may have various battery discharging rates, or slopes. For example, the vehicle may be operated in CS mode at a battery SOC above level  28 , either based on a user selection, vehicle management, or the like, and then be operated in a CD mode to use additional battery power. 
     In order to extend PHEV operational flexibility, the user may have the ability to select a preferred PHEV operation mode actively between electric and hybrid operation (EV/HEV) to override the automatic mode where the vehicle controller selects an operational mode for the vehicle. This permits a user to control the vehicle emissions, noise, and the like along the trip, and control the source of the power used by the vehicle, i.e. gasoline vs electricity. For example, the user may start by requesting an HEV driving mode  28  (battery charge sustaining at a high SOC off-charge) in the initial section of the trip. This saves the battery electric energy  21  such that the user can later switch to an EV driving mode  24  at another location where EV operation of the vehicle is desirable. 
     When the user selects a preferred PHEV operation mode using an interface in the vehicle, such as EV/HEV buttons, the user&#39;s inputs may disrupt the normal vehicle energy management strategy. The user has the freedom to actively manage the energy usage for his/her vehicle. The more a user uses the vehicle, the better he/she can understand the vehicle energy usage property, which will lead to familiarity and better optimization that the user can exercise with the battery energy usage tool. The manual energy planning feature will not only enable the user to simply select EV/HEV driving mode, but allows the user to actively plan the battery electric energy usage and fuel usage for the trip. Although the present disclosure describes the various embodiments in terms of a PHEV, any hybrid electric vehicle having an interface permitting the user to select or control the operating mode of the vehicle may be used. 
     One example of a power split PHEV  50  capable of implementing the present disclosure is shown in  FIG. 2 . Of course, the PHEV  50  may be any hybrid vehicle as is known in the art that has an interface permitting the user to select or control the operating mode.  FIG. 2  illustrates a power split hybrid electric vehicle  50  powertrain configuration and control system, which is a parallel hybrid electric vehicle. In this powertrain configuration, there are two power sources  52 ,  54  that are connected to the driveline. The first power source  52  is a combination of engine and generator subsystems using a planetary gear set to connect to each other. The second power source  54  is an electric drive system (motor, generator, and battery subsystems). The battery subsystem is an energy storage system for the generator and the motor and includes a traction battery. 
     During operation of the vehicle  50  using the second power source  54 , the electric motor  60  draws power from the battery  66  and provides propulsion independently from the engine  56  to the vehicle  50  for forward and reverse motions. An inverter  65  may be positioned between the battery  66  and the electric machine  60  and generator  58 . The inverter  65  may include a variable voltage converter as well. This operating mode is called “electric drive”. In addition, the generator  58  can draw power from the battery  66  and drive against a one-way clutch coupling on the engine output shaft to propel the vehicle forward. The generator  58  can propel the vehicle forward alone when necessary. 
     The operation of this power split powertrain system, unlike conventional powertrain systems integrates the two power sources  52 ,  54  to work together seamlessly to meet the user&#39;s demand without exceeding the system&#39;s limits (such as battery limits) while optimizing the total powertrain system efficiency and performance. Coordination control between the two power sources is needed. 
     As shown in  FIG. 2 , there is a hierarchical vehicle system controller (VSC)  68  that performs the coordination control in this power split powertrain system. Under normal powertrain conditions (no subsystems/components faulted), the VSC  68  interprets the user&#39;s demands (e.g. PRND and acceleration or deceleration demand), and then determines the wheel torque command based on the user demand and powertrain limits. In addition, the VSC  68  determines when and how much torque each power source needs to provide in order to meet the user&#39;s torque demand and achieve the operating point (torque and speed) of the engine. 
     The VSC  68 , which includes an electronic control unit (ECU), is connected to or integrated with a human-machine interface (HMI)  70 , or user interface. The user interface  70  may include a user input and a display. The user input may be touch screen and/or a series of tactile buttons. The display may be a screen and/or gauges for displaying information to the user. 
     The control system for the vehicle  50  may include any number of controllers, and may be integrated into a single controller, or have various modules. Some or all of the controllers may be connected by a controller area network (CAN) or other system. 
     The engine  56  is fueled by gasoline or another fuel contained in a fuel tank in fluid communication with the fuel injectors or another fuel delivery system for the engine  56 . The fuel tank may be refueled by a user. 
     The battery  66  may be recharged or partially recharged using a charging adapter  67  connected to a charging station powered by an external power source, such as the electrical grid, a solar panel, and the like. In one embodiment, the charging adapter  67  contains an inverter and/or a transformer on-board the vehicle. 
     The VSC  68  may receive signals or inputs from various sources to control the vehicle. These inputs include a user selected vehicle mode and a vehicle state such as battery state, fuel level, engine temperature, oil temperature, tire pressure, and the like. Route and map information may also be provided to the VSC  68  from a navigation system, which may be incorporated into the user interface  70 . 
     An EV button  72 , or other user input of the user interface  70 , provides for user selection of PHEV operation using electrical energy from the battery in an EV mode, resulting in a user selected EV mode. In the user selected EV mode, the PHEV operates in a charge depletion (CD) mode and the engine  56  may be disabled. The engine may be pulled up by the VSC  68  beyond predetermined vehicle power, speed, or other thresholds in an override of the user selected EV mode. The EV button  72  may be incorporated into the VSC  68  and the human machine interface  70  to allow the user to manually select between EV, HEV, and automatic operational modes for the vehicle. The button  72  allows the user to pre-determine and control the vehicle operation mode among EV, HEV, and automatic (VSC  68  selected) modes for a charge cycle or a key cycle. 
     The VSC  68  may also be in communication with a heating, ventilation, and air-conditioning system (HVAC)  74  for the vehicle. The HVAC system  74  may be in thermal communication with the engine  56 , the engine coolant, the engine exhaust, an electric heater powered by the battery  66 , and the like to provide heat to the passenger cabin, or to provide a defrost function for the vehicle as is known in the art. 
       FIG. 3  illustrates an embodiment of an algorithm  100  for implementing a user override of a user selected EV mode of operation for the vehicle. The algorithm  100  provides for a user override based on a user input or request to the vehicle that makes EV operation undesirable or requires the engine to be enabled to meet the user demand or request. The algorithm  100  causes the engine  56  to be enabled such that the vehicle can operate in a temporary hybrid mode of operation. The algorithm returns to the user selected EV mode of operation after a specified time period or when the user input or request requiring engine  56  enablement ceases to exist. The algorithm  100  then re-disables the engine  56  and returns to operate the vehicle in the user selected EV mode. 
     The algorithm  100  begins at  102 , and proceeds to  104  to determine if the vehicle is operating in a user selected EV mode. For a user selected EV mode in one embodiment, the user has requested EV mode using the EV input  72  through the user interface  70 . The controller  68  may determine if the vehicle is operating in EV mode based on the switch input from  72 , as well as other vehicle states such as the engine  56  being disabled and the electric machine  60  being enabled or operating. If the vehicle is not in a user selected EV mode at  104 , the algorithm  100  returns to the start at  102 . 
     If the vehicle is operating in a user selected EV mode at  104 , the controller  68  proceeds to determine if the user has selected an override of the EV mode at  105 . The user override of EV mode places the vehicle in a hybrid mode of operation, such as a charge sustaining mode, and effectively delays operation of the vehicle in the EV mode that was originally selected. The user override of EV mode may be selected at any time the vehicle is operating in the user selected EV mode of operation using the user interface  70  and/or the switch input  72 . For example, the user may select a user override of the user selected EV mode via user interface  70  and/or the switch  72  in anticipation of a passing maneuver, entering an expressway entrance ramp, driving up a steep grade, or the like. The engine  56  is now enabled, but will only be operated as necessary, i.e. when power demand exceeds what the battery and electric machine are capable of delivering. The engine  56  may be enabled for a predetermined time period, such that it is disabled and the vehicle returns to the user selected EV mode after the time period. If the power demand exceeds the capability of the electric driveline and the user override was selected, the engine  56  will be pulled up and used to help propel the vehicle. If the power demand on the vehicle does not require the engine to be used, the engine is not pulled up and at the end of the time period, the engine is disabled. If the user has not selected an override of the user selected EV mode, the algorithm  100  proceeds to  106 . 
     At block  106 , the controller  68  proceeds to determine if a user input or user request for the vehicle is beyond a threshold such that the engine  56  needs to be enabled to meet the request. In one embodiment, the controller  68  determines if a wheel torque demand is above a threshold, or above what the vehicle is capable of delivering electrically. In another embodiment, the controller  68  determines if an accelerator pedal position is beyond a threshold at  106 , or within a predetermined range of positions. The accelerator pedal position threshold may be a specified value or may be obtained from a look up or calibration table in the VSC  68  that includes various factors including accelerator pedal position, torque demand, and torque available from the electric machine  60  and the engine  56  at the vehicle operating conditions and states. Ambient temperature, altitude, battery  66  SOC, battery  66  temperature, and other factors may also affect the threshold and be included in a calibration table. 
     The accelerator pedal position may be obtained from a pedal position sensor APPS, as shown in  FIG. 2 . The accelerator pedal relates to the torque demand or torque request for the vehicle  50 . If the accelerator pedal position is beyond a threshold, the vehicle may not be able to meet torque demand using the electric machine  60  alone, and the engine  56  would need to be enabled to meet the user request. Pulling up the engine  56  at this point conflicts with the user placing the vehicle into a user selected EV mode of operation, and so the algorithm  100  proceeds to determine if the user wants to override the user selected EV mode at  108 . The algorithm  100  prompts the user to select an override via the user interface  70 , for example, using a message or popup. The user can select a user override using the user interface  70 . The message or popup may remain on a display screen of the user interface  70  until the user request ends. For an accelerator pedal position, the pedal may need to be released past another threshold level to prevent hysteresis. 
     At  110 , the algorithm  100  determines if an override was selected at  108 . If the override was not selected, the algorithm  100  returns to the start at  102 . The vehicle may not meet the torque demand or other user request, as the engine  56  was not enabled, and the electric machine  60  does not have the capacity to meet the request alone. The controller  68  may provide a message to the user interface  70  stating that the user selected EV operation is limiting vehicle performance in light of the user request. Alternatively, the controller  68  may enter an override mode if the user request, such as the accelerator pedal past a threshold value, exists for a predetermined time period. 
     If the override was selected at  108 , the algorithm  100  proceeds from  110  to block  112 . The algorithm  100  also proceeds to  112  from block  105  if the user has selected an override of the EV mode. At  112 , the controller enables engine  56  operation, and in some embodiments starts a timer. The engine  56  is enabled such that the vehicle operates in an HEV mode with both the electric machine  60  and the engine  56  available for use. In one embodiment, the vehicle is operated in a charge depletion mode where the engine  56  and/or the electric machine  60  is used to propel the vehicle and the state of charge of the battery is generally decreased. In other embodiments, the vehicle may be operated in a charge sustaining mode, or other hybrid mode of operation. The controller has enabled the engine  56  for operation; however, the engine  56  may not operate continually during the user override based on the operating conditions for the vehicle. For example, the engine  56  may be enabled and not operating at  112  for some time period, such as when torque demand for the vehicle is met by the electric machine, and the like. 
     The controller  68  commands the display in the user interface  70  to provide a message to the user at  114 . The user is informed of the user override of the user selected EV mode. The message provides information to the user to confirm the user selection of the override, to meet user expectations regarding vehicle operation, prevent confusion regarding engine operation after selecting an EV mode, to provide vehicle information to the user, and the like. 
     The algorithm  100  then determines if the entry condition or user request causing the override still exists at  116 . The accelerator pedal position or overall vehicle wheel torque demand may need to be below its threshold for some predetermined time period to prevent hysteresis or cycling of the user override requests. If the user request still exists, such as the accelerator pedal remaining above its threshold value, the algorithm returns to  112  to continue enabling the engine  56 . 
     If the user request ceases to exist after entering a user override, such as the accelerator pedal or wheel torque demand going below its threshold, or the specified time period expiring, the algorithm proceeds to  118  and re-disables operation of the engine  56  and returns vehicle operation to the original user selected EV mode automatically. The vehicle now operates using electric energy only and is propelled by the electric machine  60 , as the engine  56  is disabled and not operating. 
     The algorithm  100  clears any messages displayed by the user interface  70  regarding the override at  120 . These messages or popups were provided by block  114 , as the vehicle state causing the system override of the EV selected mode has ceased to exist. The algorithm  100  either ends at  122  or cycles back to the start at  102 . 
       FIG. 4  illustrates an embodiment of a user interface  70  for use with the algorithm  100  and vehicle  50 . The user interface  70  has a display screen  150 . The screen  150  may be on the dashboard, the center console, incorporated into the vehicle gauge system, or the like. Of course, the screens as shown in  FIG. 4 , including any icons and messages, are according to an embodiment. Other embodiments may include other screen layouts, designs, and messages regarding the disclosure. The user interface has a general screen as shown at  152 . The general screen  152  may be displayed during typical vehicle operation, and may include such information as the power available from the traction battery  154 , mileage available in EV mode  156 , the instantaneous or short term fuel economy  158 , the average or long term fuel economy  160 , and a fuel tank level gauge  162 . When the EV mode is selected, an EV indicator light  164  may appear on the screen  150  to inform the user that the vehicle is operating in the EV mode. The indicator light  164  may change colors to inform the user of the status of the electric operation status of the vehicle, or there may be multiple indicators present to provide information regarding the mode of operation of the vehicle, i.e. EV, HEV, automatic, and the like. 
     When a user input or user request for the vehicle is beyond a threshold such that the engine  56  needs to be enabled to meet the request, the algorithm  100  sends a message to the display  150  requesting an override from the user to enable the engine  56 , as shown by  166  on screen  168 . In one embodiment, the controller  68  determines if the accelerator pedal position is beyond a threshold. Message  166  may be a popup, another display screen, or the like. In one embodiment, message  166  appears regardless of the background screen when the user input or request is above the threshold and the vehicle is in a user selected EV mode. 
     When the user acknowledges the message  166  by confirming the override through a user input, or after expiration of a suitable time period, the algorithm  100  changes the screen  150  to a general override screen at  170  or an EV override screen at  178 , as described further below. The user input may be through a switch on the steering wheel, though the user interface  70  directly, via voice command, or the like. Override screen  170  may have an indicator light or message  172  that continues to inform the user of the override of the EV mode and that that engine  56  is enabled and may be operating. In one embodiment, the message  172  may be the indicator light  164  illuminated in a different color. 
     When the user input or request for the vehicle that causing the user override of EV mode ends such that the engine  56  no longer needs to be enabled, the screen  150  may be changed back to a general operating screen  152  with the EV indicator light  164  present. The controller  68  re-disables the engine  56  and returns the vehicle to operating in the user selected EV mode. 
     Alternatively, the user interface  70  display  150  may begin by showing an electric (EV) screen  174  before the user input or user request for the vehicle is beyond a threshold such that the engine  56  needs to be enabled to meet the request. The screen  174  may display various electric energy uses, such as electrical energy use by the HVAC system. The screen  174  may be displayed whenever the user has entered a user selected EV mode, and provides an interface for the user to select a user override of the EV mode whenever the user desires during the user selected EV mode. The user may navigate within the user interface  70  as well, for example by switch from screen  174  to screen  150  and vice versa. When a user input or user request for the vehicle is beyond a threshold such that the engine  56  needs to be enabled to meet the request, the algorithm  100  sends a message to the display  150  requesting an override from the user to enable the engine, as shown by the message or popup  176  on screen  174 . 
     When the user acknowledges the message  176  by confirming the override through a user input, the algorithm  100  changes the screen  174  to the EV override screen at  178 . The user input may be through a switch on the steering wheel, or though the user interface  70  directly. Override screen  178  may have an indicator light or message  180  that continues to inform the user of the override of EV mode and that that engine  56  is enabled and may be operating. In one embodiment, the message  180  may be the indicator light  164  in a different color. 
     When the user input or request for the vehicle that caused the user override of EV mode ends such that the engine  56  no longer needs to be enabled, the screen  178  may be changed back to a general EV screen  174  with the EV indicator light  164  present. The controller  68  re-disables the engine  56  and returns the vehicle to operating in the user selected EV mode. 
     Alternatively, from EV screen  174 , the user may select another mode of operation for the vehicle using the EV input  72 . In the embodiment shown, the user may select from automatic VSC operation of the vehicle, a user selected EV mode, and a user selected delayed EV mode where the vehicle may be operated in an HEV mode as shown by the popup or message  182  in screen  184 . In some embodiments, the message  164  may clear from the screen  150  after a specified time period, and revert to a general screen display  152  with the addition of the EV indicator  185 , which is shown as a delayed EV mode or EV later icon. If the user selects an automatic mode, the VSC  68  controls the mode of operation of the vehicle and exits the user selected EV mode, such that the vehicle continues to operate in the automatic mode even when the user input or request above its threshold ends. If the user selects HEV mode, the vehicle operates in a hybrid mode of operation where operation in an electric only mode is delayed. The HEV mode may be a generally charge sustaining mode. 
     After the user makes a selection using EV input  72 , the user interface  70  may change the display  150 . For example, if the user selects a delayed EV mode, or HEV mode, at screen  184 , the display  150  will show screen  186 . Screen  186  is a delayed EV mode screen, or HEV screen, as can be seen by the delayed EV mode or EV later icon  185 . 
     As such, various embodiments according to the present disclosure provide associated non-limiting advantages. For example, the vehicle is configured for a user selected electric only (EV) mode of operation, allowing user control and input for vehicle operation. The user may override the user selected mode of operation using the user interface when a user input or request to the vehicle indicates a need for the engine to be enabled, and the vehicle to operate in a hybrid mode. The controller is configured to change the operating state of the vehicle to a hybrid mode of operation based on the user override. The controller sends a message to the user to confirm the override and that the vehicle is operating in a hybrid mode via a user interface such that the user&#39;s expectations regarding vehicle operation are met and the user is informed of potential engine operation after having selected an EV mode of operation for the vehicle. The controller is configured to return the vehicle to the user selected EV mode after the user input or request to the vehicle that caused the EV mode override and the engine to be enabled ends. The vehicle is returned to the user selected EV mode by the controller. 
     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, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments that are not explicitly illustrated or described. Where one or more embodiments have been described as providing advantages or being preferred over other embodiments and/or over prior art with respect to one or more desired characteristics, one of ordinary skill in the art will recognize that compromises may be made among various features to achieve desired system attributes, which may depend on the specific application or implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, any embodiments described as being less desirable relative to other embodiments with respect to one or more characteristics are not outside the scope of the claimed subject matter.