Patent ID: 12252039

DETAILED DESCRIPTION

Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale and may be simplified; some features could be exaggerated, minimized, or omitted 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. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described, but within the scope of the claimed subject matter. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations.

The present inventors have recognized that electrified vehicles, particularly Battery Electric Vehicles (BEVs), are not designed to be flat towed (i.e. all wheels in contact with the road surface) with the ignition off because the transaxle bearings require active lubrication from an electric oil pump. As such, flat towing speed and distance of a BEV may be limited to 35 MPH/50 miles range, for example, to reduce potential bearing wear. While the BEV could be placed in Driving mode while being towed behind a towing vehicle, this could result in the BEV shifting to Park when the vehicle door is closed, and may require the key to be left in the vehicle for the vehicle to actively perform regenerative braking to maintain or increase the HV battery state of charge and support the low-voltage loads. If the vehicle shuts down due to a fault or timeout, the control system may enter Park or Neutral, which can cause tire wear, parking pawl wear, or transaxle bearing wear if the vehicle is subsequently moved. Finally, towing in Drive mode may set diagnostic codes and generate alerts or issues with driver assistance features such as lane centering/departure steering and alerts or emergency braking assist, for example, as the towing vehicle may be identified as a threat requiring active braking or steering intervention. Similarly, certain diagnostic codes may disable or shut down the assistance systems, such as a blocked sensor code, for example. There are also cases where a customer may want to tow the vehicle to recharge a completely depleted HV battery, which may not be possible with current designs. As such, various embodiments according to the disclosure solve one or more of these issues and related issues that may otherwise arise from towing an electrified vehicle while providing one or more advantages with respect to vehicle operation and performance as well as operator convenience.

FIG.1Aillustrates a representative embodiment of a system20having a towing vehicle30coupled to a towed electrified vehicle112by a tow bar50. While illustrated as a recreational vehicle, towing vehicle30may be any type of vehicle and may include a conventional powertrain or be implemented by an electrified vehicle. Similarly, while illustrated as a passenger car, towed electrified vehicle112may be any type of vehicle with a partially or fully electrified propulsion system including but not limited to a battery electric vehicle (BEV) or plug-in hybrid electric vehicle (PHEV). In some embodiments, tow bar50may include a force or strain sensor52that detects the relative push/pull force between the towing vehicle30and the towed electrified vehicle112for use by towed electrified vehicle112in controlling automatic braking, detecting disconnection from the towing vehicle, etc. Tow bar50may include an associated electrical connection54to supply electric power and/or control signals from towing vehicle30to one or more components or systems62of towed electrified vehicle112. As described in greater detail herein, depending on the particular implementation of a towed vehicle operating mode according to this disclosure, a wired or wireless connection between the towing vehicle30and towed electrified vehicle112may be optional, or may be required for utilization of some, but not all towed vehicle operations. For example, if both the traction battery and auxiliary battery of electrified vehicle112are fully depleted, an electrical connection52may provide temporary low-voltage power to electrified vehicle112sufficient to operate a vehicle HMI to activate the towed vehicle control with temporary limited functionality of electric components until subsequent power provided by regenerative braking or other generator operation of the towed electrified vehicle112is sufficient to power the system and charge the auxiliary battery and/or traction battery.

WhileFIG.1Aillustrates electrified vehicle112being flat towed by towing vehicle30with all wheels of electrified vehicle112in contact with the road surface, the present disclosure is not limited to flat towing with some or all features described herein available for use by electrified vehicles towed by a dolly or similar arrangement with only some of the towed electrified vehicle wheels in contact with the road surface. Those of ordinary skill in the art will recognize various features described herein that may be unavailable or inoperable depending on whether one or more wheels of the electrified vehicle in contact with the road surface are coupled to the electrified vehicle propulsion system including at least one electric machine and energy store. As a non-limiting example, battery charging and regenerative braking may be unavailable or inoperable when none of the wheels of the electrified vehicle contacting the road surface are coupled to the propulsion system.

FIG.1Billustrates a representative towed electrified vehicle112implemented by a plug-in hybrid-electric vehicle (PHEV) for purposes of illustration and description. As previously described, those of ordinary skill in the art will recognize that towed vehicle operation as described herein may be used in other types of towed electrified vehicles, such as a battery electric vehicle (BEV), which do not include an engine118. Similarly, towed vehicle operation is not limited to passenger vehicles and may include commercial and transportation vehicles as well as other non-vehicle applications.

A plug-in hybrid-electric vehicle112may include one or more electric machines114mechanically coupled to a gearbox or hybrid transmission116. The electric machines114may be capable of operating as a motor and a generator. In addition, the hybrid transmission116is mechanically coupled to an engine118. The hybrid transmission116is also mechanically coupled to a drive shaft120that is mechanically coupled to one or more of the wheels122. While representative electrified towed vehicle112is illustrated with a front-wheel drive propulsion system, the claimed subject matter is generally independent of the particular type of propulsion system and may include rear-wheel drive, all-wheel drive, four-wheel drive, e-drive systems, for example. The electric machines114can provide propulsion and regenerative braking capability when the engine118is turned on or off. The electric machines114may also act as generators and can provide fuel economy benefits by recovering energy that would normally be lost as heat in a friction braking system. The electric machines114may also reduce vehicle emissions by allowing the engine118to operate at more efficient speeds and allowing the hybrid-electric vehicle112to be operated in electric mode with the engine118off under certain conditions. An electrified vehicle112may also be a battery electric vehicle (BEV) without an engine118may not be present.

A battery pack or traction battery124stores energy that can be used by the electric machines114. The traction battery124may provide a high voltage (HV) direct current (DC) output. As generally understood by those of ordinary skill in the art, high voltage generally refers to voltages above 60 VDC and representative traction battery packs may connect multiple low-voltage cells to operate at a pack voltage in the hundreds of volts, such as 300-800 VDC, for example. Low voltage (LV) systems and components for passenger vehicles may operate at a nominal 12 VDC, while commercial vehicles or transportation vehicles may have LV systems that operate at 24 VDC or 48 VDC, for example.

Towed electrified vehicle112may include a contactor module142having one or more contactors configured to isolate the traction battery124from a high-voltage bus152when opened and connect the traction battery124to the high-voltage bus152when closed. The contactor module142may disconnect the HV bus152at key-off or when the vehicle is in an accessory (ACC) or other non-propulsion mode. As described herein, activation of a towed vehicle mode may control contactor module142to couple the traction battery124to the HV bus152to provide LV system support, auxiliary battery charging, traction battery charging, and/or regenerative braking.

Contactor module142may include one or more contactors to connect or isolate power conversion module or charger132from the high-voltage bus152. The high-voltage bus152may include power and return conductors for carrying current over the high-voltage bus152. The contactor module142may be located in the traction battery124. One or more power electronics modules126(also known as an inverter) may be electrically coupled to the high-voltage bus152. The power electronics modules126are also electrically coupled to the electric machines114and provide the ability to bi-directionally transfer energy between the traction battery124and the electric machines114. For example, a traction battery124may provide a DC voltage while the electric machines114may operate with a three-phase alternating current (AC) to function. The power electronics module126may convert the DC voltage to a three-phase AC current to operate the electric machines114. In a regenerative mode, the power electronics module126may convert the three-phase AC current from the electric machines114acting as generators to the DC voltage compatible with the traction battery124.

In addition to providing energy for propulsion, the traction battery124may provide energy for other vehicle electrical systems. The towed electrified vehicle112may include a DC/DC converter module128that converts the high voltage DC output from the high-voltage bus152to a low-voltage DC level of a low-voltage bus154that is compatible with low-voltage loads156. As illustrated and described in greater detail with respect toFIG.1C, LV loads may include one or more fluid pumps that pump a lubricating and/or cooling fluid to the vehicle drivetrain or propulsion system, which may include electric machines114, transmission116, engine118, traction battery124, DC/DC converter module128, and power conversion module132, for example. Other LV loads include various system controllers or control modules that power and/or control vehicle accessories, lights, displays, interfaces, driver inputs, etc.

An output of the DC/DC converter module128may be electrically coupled to a low-voltage auxiliary battery130(i.e., 12V, 24V, or 48V battery) for charging the auxiliary battery130. The low-voltage loads156may be electrically coupled to the auxiliary battery130via the low-voltage bus154. One or more controllers, such as system controller148may be powered by the low-voltage bus154. Similarly, various vehicle actuators, including contactor module142may have low-voltage control signals powered by the low-voltage bus, or by drivers of an associated controller or I/O interface that provide low-voltage control signals. One or more high-voltage electrical loads146may be coupled to the high-voltage bus152. The high-voltage electrical loads146may have an associated controller that operates and controls the high-voltage electrical loads146when appropriate. Examples of high-voltage electrical loads146may be a fan, an electric heating element, and/or an air-conditioning compressor.

As generally understood by those of ordinary skill in the art, low-voltage components may have different voltage levels for operation, and different applications or implementations may utilize different voltage levels for similar components. Low-voltage generally refers to voltages less than 60 VDC (or 30 VAC) with some vehicles having a nominal 12V system, while others have 24V or 48V systems for powering convenience features and controllers. High-voltage generally refers to voltages greater than 60V and may range up to 1500V DC (or 1000 VAC), for example. Typical high-voltage traction batteries for passenger vehicles are in the range of 200-450 VDC while some commercial vehicles include traction batteries operating at 400-800 VDC.

The electrified vehicle112may be configured to recharge the traction battery124from an external power source136. The external power source136may be a connection to an electrical outlet. The external power source136may be electrically coupled to a charge station or electric vehicle supply equipment (EVSE)138. The external power source136may be an electrical power distribution network or grid as provided by an electric utility company. The EVSE138may provide circuitry and controls to manage the transfer of energy between the power source136and the vehicle112. The external power source136may provide DC or AC electric power to the EVSE138. The EVSE138may have a charge connector140for coupling to a charge port134of the vehicle112. The charge port134may be any type of port configured to transfer power from the EVSE138to the vehicle112. The charge port134may be electrically coupled to an on-board power conversion module or charger132. The charger132may condition the power supplied from the EVSE138to provide the proper voltage and current levels to the traction battery124and the high-voltage bus152. The charger132may be electrically coupled to the contactor module142as previously described to connect charger132to high voltage bus152. The charger132may interface with the EVSE138to coordinate the delivery of power to the vehicle112. The EVSE connector140may have pins that mate with corresponding recesses of the charge port134. Alternatively, various components described as being electrically coupled or connected may transfer power using a wireless inductive coupling.

Wheel brakes144may be provided for slowing the vehicle112and preventing motion of the vehicle112. The wheel brakes144may be hydraulically actuated, electrically actuated, or some combination thereof to actuate friction pads to contact a disc or drum of the wheel. The wheel brakes144may be a part of a brake system150. The brake system150may include other components to operate the wheel brakes144. For simplicity, the figure depicts a single connection between the brake system150and one of the wheel brakes144. A connection between the brake system150and the other wheel brakes144is implied. The brake system150may include a controller to monitor and coordinate the brake system150. The brake system150may monitor the brake components and control the wheel brakes144. The brake system150may respond to driver commands and may also operate autonomously to implement features such as automatic emergency braking, anti-lock braking, and stability control. The controller of the brake system150may implement a method of applying a requested brake force when requested by another controller or sub-function, such as system controller148. When regenerative braking is enabled and available, system controller148may coordinate braking force generated by regenerative braking with the braking force of brake system150provided by the friction brakes144. Friction brakes144may be applied to all wheels when a parking brake is activated. Some electric vehicles may automatically apply or activate the parking brake after a predetermined time under specified conditions, such as while the vehicle gear selector is in Drive, the vehicle is on an incline, the brake pedal is depressed, driver's door is open with the gear selector in Drive, etc.

As described in greater detail herein, activation of towed vehicle operation may control brake system150including regenerative braking and/or friction braking to slow or stop the towed electrified vehicle112under various operating conditions, such as if the towed electric vehicle112becomes disconnected from the towing vehicle30, in response to braking of the towing vehicle30, or to charge the traction battery124and/or auxiliary battery130. Activation of towed vehicle operation may also suspend or modify operation of selected automatic braking functions or features to facilitate towed vehicle operation, such as suspending automatic parking brake apply, automatic emergency braking based on detection of an object, etc.

The electrified vehicle112may further include a human-machine interface (HMI) or user interface (UI)160. The user interface160may provide a variety of display elements for communicating information to the operator. The user interface160may provide a variety of input elements for receiving information from the operator. The user interface160may include one or more displays. The displays may be touch-screen displays that both display information and receive input. The user interface160may include discrete lamps/lights. For example, the lamps may include light-emitting diodes (LED). The user interface160may include switches, rotary knobs, sliders, and buttons for allowing the operator to change various settings. The user interface160may include a control module that communicates via the vehicle network. In various embodiments, the HMI160may be used to select or activate towed vehicle operation and may be used to select various options within the towed vehicle operation mode, such as whether to enable regenerative braking, whether to charge traction battery124, a desired state of charge (SOC) or distance to empty (DTE) for traction battery124, a charging rate for traction battery124(i.e. whether to charge as soon as possible, or spread charging events over anticipated trip time/distance/route), and various other selections and settings that may vary by the particular application and implementation.

Electronic modules in the vehicle112may communicate via one or more vehicle networks. The vehicle network may include a plurality of channels for communication. One channel of the vehicle network may be a serial bus such as a Controller Area Network (CAN). One of the channels of the vehicle network may include an Ethernet network. Additional channels of the vehicle network may include wired or wireless discrete connections between modules and may include power signals from the auxiliary battery130. Different signals may be transferred over different channels of the vehicle network. For example, video signals may be transferred over a high-speed channel (e.g., Ethernet) while control signals may be transferred over CAN or discrete signals. The vehicle network may include any hardware and software components that aid in transferring signals and data between modules. The vehicle network is not explicitly shown inFIGS.1A-1C, but it may be implied that the vehicle network may connect to any electronic modules that are present in the vehicle112. A vehicle system controller (VSC)148may be present to coordinate the operation of the various components.

While illustrated as a single controller, controller148generally represents multiple vehicle controllers that receive signals from associated sensors and control corresponding actuators. Controllers or control modules may be dedicated to a particular vehicle system, subsystem, or component and may include programmable microprocessor-based controllers and microcontrollers that perform various functions and algorithms based on stored program instructions. Various controllers may communicate over one or more channels of the vehicle network(s).

FIG.1Cillustrates representative electrified vehicle sensors, components, driver assistance features and related features and systems that may be enabled, disabled, modified, or otherwise controlled while a towed vehicle mode is active. Towed vehicle system controller(s)148may directly or indirectly control various vehicle systems, sensors, actuators, etc. when operating in a towed vehicle mode as previously described. Controller(s)148may enable, disable, modify, or otherwise control driver assistance and automatic convenience and similar features as represented at170, system diagnostics, fault detection, and alerts as represented at190, driver controls and inputs as represented at200, braking system control as represented at220, LV system support as represented at230, and HV traction battery charging or depletion as represented at240, for example.

Driver assistance and automatic features170may include automatic emergency braking172that is otherwise applied in response to detecting an excessive closure rate with respect to a forward object based on vehicle sensors, that may include distance sensors using one or more camera(s), radar, lidar, and similar sensors or detectors. This feature may be disabled or control thresholds modified when operating in the towed vehicle mode to reduce or eliminate inadvertent triggering based on detecting the towing vehicle or any objects that may fall from or be deflected by the towing vehicle.

Automatic shifting of the propulsion system to Park as represented at174is a feature that some electrified vehicles include to limit vehicle motion and stop the vehicle if an operator exits the vehicle while the propulsion system is in Neutral, Reverse, or Drive, for example. The feature may normally be triggered based on detecting the driver door being opened with the propulsion system in Drive. Automatic parking brake apply as represented at176is a feature that some electrified vehicles include to automatically apply the parking brake under some operating conditions. For example, if the vehicle is stopped on an incline with the gear selector is in Drive for a predetermined time period, such as several minutes, the parking brake may be automatically applied. Accelerator pedal position based torque control as represented at178is a feature that some electrified vehicles include to provide automatic regenerative braking when the accelerator pedal is released (lift-pedal braking). Similarly, the vehicle may generate accelerator pedal position-based creep torque when the vehicle gear selector is in Drive, the accelerator pedal is released, and the vehicle speed is below a predetermined threshold. Lane departure steering and/or alerts as represented at180is a feature that may provide active steering to center the electrified vehicle within a lane, or to keep the vehicle from crossing a recognized lane marker without the turn signal/indicator active. Parking assist as represented at182is a feature that may provide visual or audio alerts and/or active steering based on detecting objects near the vehicle when operating at low speed with the gear selector in Drive or Reverse.

As also illustrated inFIG.1C, various system faults, diagnostic codes, and/or alerts190may be enabled, disabled, or modified when operating in a towed vehicle mode. For example, external object detection192, sensor blocked194, and/or following distance196alerts or faults may be disabled. Other system faults, alerts, or diagnostic codes specific to towed vehicle operation may be enabled, such as faults and alerts related to electric pump operation, regenerative braking operation, traction battery or auxiliary battery status, etc.

Towed vehicle operation mode may also control or modify control of various driver controls and inputs as represented at200. Inputs may be disabled as a theft deterrent feature that requires the presence of the vehicle key and key off/on cycle to deactivate the towed vehicle operation mode and reset the vehicle systems. Driver controls and inputs that may have an altered response, may be disabled, or may be otherwise modified include inputs from a steering wheel202, headlights and daytime running lights (DRL)204, turn signal indicator206, cruise control208, gear selector210, accelerator212, and windshield wipers214, etc. As an example, turn signal/indicator206may be disabled so that inadvertent operation when enabling the towed vehicle mode does not continue while the vehicle is being towed. The turn signals, tail lights, brake lights, and other vehicle exterior lighting may be controlled based on an electrical signal from the towing vehicle. Alternatively, or in combination, turn indicators may be controlled in response to automatic detection of an active turn indicator of the towing vehicle using one or more vehicle cameras or sensors such that a wired or wireless connection to the towing vehicle is not required. Similarly, brake lights may be controlled in response to detecting active brake lights of the towing vehicle, or in response to applying friction brakes of the towed vehicle. Operation of headlights/DRL204based on ambient lighting or gear selector position may be disabled regardless of the particular setting of the headlight control knob. Accelerator pedal212input may be disabled to prevent vehicle drive-away theft. Various other systems or features that may otherwise unnecessarily use power from the towed vehicle may be disabled, such as windshield wipers214, vehicle ambient lighting, infotainment system/speakers, climate control, etc. Depending on the particular application and implementation, the towed vehicle operation mode may provide various configuration settings or options for the user to select particular features to enable/disable and/or select a modified response for a particular feature. For example, the system may allow operation of the vehicle climate control based to heat/cool the vehicle cabin while being towed and/or specify a minimum battery SOC or DTE for operation of climate control. Those of ordinary skill in the art may recognize numerous other settings or configuration options that may be used to control individual vehicle features or inputs based on the representative examples of this disclosure.

The towed vehicle system controller(s)148may also enable, disable, or modify control of various braking system features/functions as represented at220. This may include providing regenerative braking assist222, friction braking assist224, and breakaway braking226. Regenerative braking assistance as represented at222may be provided to slow the electrified vehicle in response to a braking signal from the towing vehicle, or may be automatically actuated by detecting deceleration of the towed vehicle using towed vehicle speed sensors or accelerometer, for example, as described in greater detail herein. Regenerative braking assist may be activated independently from regenerative braking used to charge the traction battery. Similarly, friction braking assist224may be provided in response to a braking signal from the towing vehicle, or may be automatically actuated. Breakaway braking226detects disconnection of the electrified vehicle from the towing vehicle and may be used to bring the towed electrified vehicle to a controlled stop and apply the parking brake as described in greater detail with respect toFIGS.2-8. Other braking system control functions may be modified when the vehicle is operating in a towed vehicle mode, such as traction control or stability control, for example.

Low voltage system support230may include control of the HV traction battery system232to close associated contactors to couple the traction battery to the HV bus to operate a coolant pump234and/or oil pump236or to charge the LV auxiliary battery238. As previously described, the traction battery may supply power to the LV bus via a DC/DC converter. Depending on the particular system configuration and settings, the traction battery may be coupled to the HV bus to operate HV or LV loads as previously described. Similarly, coolant pump234and/or oil pump236may be powered by LV auxiliary battery238via the LV bus under various operating conditions with LV system support230provided by the HV traction battery232to charge the LV auxiliary battery238based on associated operating thresholds or settings for the HV traction battery232and LV auxiliary battery238.

Towed vehicle operation mode may also enable, disable, or modify control of the HV battery charging as represented at240. As described in greater detail with respect toFIGS.2-8, HV traction battery charging may be enabled while the electrified vehicle is being towed using regenerative braking to achieve or maintain a desired SOC or DTE242for the traction battery. Alternatively, or in combination, the system may use regenerative braking to charge the traction battery to a minimum SOC to provide LV system support and various other functionality while the vehicle is being towed regardless of whether the user has activated traction battery charging or selected a desired target SOC/DTE242.

FIGS.2-8illustrate operation of a system or method for controlling an electrified vehicle having a towed vehicle operating mode. Control logic or functions performed by one or more controllers, modules, processors, etc. is generally represented in the diagrams ofFIGS.2-8. This illustration provides a representative control strategy, algorithm, and/or logic that may be implemented using one or more processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various steps or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Although not always explicitly illustrated, one of ordinary skill in the art will recognize that one or more of the illustrated steps or functions may be repeatedly performed. Similarly, the order of processing is not necessarily required to achieve the features and advantages of the claimed subject matter as described herein, but is provided for ease of illustration and description. The control logic may be implemented primarily in software executed by a microprocessor-based vehicle, engine, electric machine, and/or powertrain controllers, generally represented by system controller148ofFIG.1B. Of course, the control logic may be implemented in software, hardware, or a combination of software and hardware in one or more controllers depending upon the particular application. When implemented in software, the control logic may be provided in one or more non-transitory computer-readable storage devices or media having stored data representing code or instructions executed by a computer to control the vehicle or its subsystems. The computer-readable storage devices or media may include one or more of a number of known physical devices which utilize solid state, electric, magnetic, and/or optical storage to keep executable instructions and associated calibration information, operating variables, and the like.

FIGS.2-3are block diagrams illustrating operation of a system or method for controlling a towed electrified vehicle including activation of a towed vehicle mode via a vehicle human-machine interface (HMI).

As illustrated inFIG.2, representative control logic or algorithm250begins at block260with starting the vehicle in Accessory mode with the gear selector in Park. As generally understood by those of ordinary skill in the art, the Accessory mode powers various vehicle convenience features using the LV auxiliary battery but does not enable propulsion of the vehicle. In contrast, a Run mode powers the system using the HV traction battery and enables vehicle propulsion. Activation of a Run/Drive mode often requires depressing the brake pedal while pressing a Start/Ignition button. In one or more embodiments according to the present disclosure, the HV traction battery contactor may be closed while operating in towed vehicle mode with the ignition in Accessory mode to provide LV system support, regenerative braking, HV traction battery charging, and various other system features and functions as described herein. While in Accessory mode, the towed electrified vehicle HMI may display a menu on an associated touchscreen an generate a towed vehicle operation signal in response to an operator selecting the recreational tow mode as represented at262. As an anti-theft deterrent, once entered, the towed vehicle operation mode cannot be exited without an ignition/key power off cycle, which requires presence of the vehicle key to restart the vehicle and enter propulsion (Drive) mode.

The operator may input a desired target SOC (or DTE) for the traction battery as well as a travel distance or duration as represented at264. Alternatively, travel distance, trip duration and/or route may be entered via the vehicle navigation system, or transferred from a mobile device, such as a smartphone, by a wired or wireless connection to the electrified vehicle. The system then calculates a non-braking regenerative power estimate to achieve the desired target SOC based on the travel distance, route, or time as represented at266and described in greater detail with reference toFIGS.5-6. The non-braking regenerative power is used to control the electric machine(s) to operate as generator(s) to charge the traction battery, which may in turn be operated to charge the LV auxiliary battery in various embodiments.

Block268determines whether active charging of the traction battery has been requested via the HMI menu. If Yes, block270sets the HV traction battery desired target SOC (or DTE as illustrated and described with reference toFIG.7) to an active charge level as selected by the user. If No, block272sets the HV traction battery SOC target to the higher of the current SOC or preset minimum SOC. Block272will charge the HV traction battery to the minimum SOC or maintain the current SOC while being towed. Block274displays a towed vehicle mode message on the vehicle HMI with a reminder to verify that the towed vehicle is properly coupled to the towing vehicle and that the vehicle must be placed in Drive gear after starting the vehicle as represented at276. Block290provides a non-braking regenerative energy capture for HV traction battery charging as illustrated and described with reference toFIG.4.

Block278determines whether the gear selector is in Drive. If No, control continues to block380ofFIG.3. If Yes, block280disables one or more driver assistance or convenience features that are undesirable in towed vehicle operation mode. In the representative example ofFIG.2, block280disables automatic return to Park, which may otherwise shift the vehicle into Park upon detecting that the driver door is open with the vehicle at low speed and in Drive. Block282disables one or more driver inputs/controls as previously described, which may include the accelerator pedal, cruise control, headlight mode selector, etc. Brake pedal control remains active to allow use of a commercially available third-party brake pedal pusher in the towed vehicle if desired. Block284displays via the HMI that the towed vehicle mode is fully active and control continues with block310ofFIG.3.

Block310ofFIG.3determines whether the HV traction battery is depleted to below a minimum SOC where the vehicle would not be drivable without being towed, but has sufficient power to close the HV traction battery contactors so that the traction battery is coupled to the HV bus. Block310also determines whether the vehicle speed is below a speed threshold, such as 10 kph. If Yes, the towed electrified vehicle will attempt to conserve power by keeping the electric pumps off as represented at312until the traction battery reaches the minimum SOC or the vehicle speed exceeds the speed threshold where regenerative power capture is sufficient to charge the traction battery and/or operate the electric pumps as previously described. If No at block310, then the electric pumps are enabled for operation as represented at314. After being enabled, the pumps may be controlled to operate continuously or intermittently in response to corresponding operating criteria, such as cooling system temperature, vehicle speed, elapsed time, etc. to maximize system efficiency.

Block316monitors operation of the lubrication system including the lubrication pump, which may include monitoring pressure, flow, temperature, or other feedback signals, for example. If no lubrication fault is detected, block318monitors the propulsion system for proper operation. Propulsion system monitoring may detect the HV battery contactor opening, a DC/DC converter fault, electric machine fault, electric isolation fault, or HV battery depleted below a shutdown threshold, for example. If a lubrication fault is detected at316or a propulsion system fault is detected at318, then block320generates a corresponding alert and may store one or more corresponding diagnostic codes. The corresponding alert(s) may be transmitted to a mobile device via a wired or wireless connection between the towed electric vehicle and the towing vehicle to alert the driver of the towing vehicle. As a non-limiting illustrative example, alerts may be communicated via cellular, Bluetooth, Wi-Fi, or similar wireless technologies to a smartphone app with a push notification to alert the driver. Alternatively, a wired connection between the towed vehicle and the towing vehicle may generate a prompt on the towing vehicle HMI, or illuminate a dedicated LED, for example. In one or more embodiments, alerts may include an intermittent horn beep with a predetermined pattern, lights flashing, and/or headlights flashing, for example.

In response to the lubrication and/or propulsion system fault, block322may automatically shift the propulsion system from Drive to Neutral while inhibiting any other fault responses that may otherwise shift the towed vehicle to Park or apply the parking brake to reduce or eliminate undesirable wear to various propulsion system components. The propulsion system is then shut down, the HV traction battery contactor is opened to disconnect the traction battery from the HV bus, and the electric oil and water pumps are turned Off as indicated at324. After a predetermined time, such as five minutes for example, the ignition system is automatically commanded Off with the vehicle remaining in Neutral as represented at326to preserve the LV auxiliary battery charge and the towed vehicle operating mode is exited as indicated at330.

If neither block316nor block318detect a fault, then block340monitors vehicle speed of the towed electrified vehicle to determine whether the vehicle is stationary based on vehicle speed being below an associated threshold for a predetermined period of time, such as being below 1 kph for 2 hours, for example. If Yes, block350may alert the user via a wired or wireless alert and/or using one or more vehicle audible or visual notifications similar to those previously described with respect to block320. This alert reminds the user that the towed vehicle has been stationary while the towed vehicle operation mode is active to reduce the possibility for unintended depletion of the LV auxiliary battery and/or the HV traction battery. If No, or after sending notification to the user, block360determines whether the vehicle remains in Drive. If the vehicle is no longer in Drive mode, then block370may override the gear selection and shift to Neutral, unless Park is selected, in which case the vehicle will remain in Park.

Block380determines whether the ignition has been switched to Off and if Yes, exits the towed vehicle operation mode as represented at330. Otherwise, control continues with block410ofFIG.4as represented at390.

FIG.4is a block diagram illustrating operation of a system or method that controls the braking system for active braking or regenerative energy capture for traction battery charging in an electrified vehicle while towed vehicle operation is enabled. System or method400determines whether an active braking signal or condition has been detected as represented at410. The active braking signal may be detected in response to depressing of the vehicle brake pedal by a commercially available brake pedal pusher installed in the vehicle. Alternatively, or in combination, the towed vehicle may receive a braking signal from a wired connection to the towing vehicle, or may automatically engage active braking in response to vehicle deceleration exceeding a threshold. Towed vehicle deceleration may be determined by monitoring towed vehicle speed and/or from one or more accelerometers, for example. If yes, block420may engage regenerative braking and/or friction braking to meet the active braking demand, with regenerative braking subject to traction battery SOC and charge rate/current limits. The towed vehicle brake lights may also be activated based on a signal from the towing vehicle, an active braking request exceeding a corresponding threshold, or a towed vehicle deceleration exceeding a corresponding threshold, for example. Control then continues to block290ofFIG.2as represented at480.

If an active braking request is not detected at410, then the system continues to determine whether operating conditions are favorable for regenerative energy capture to charge the traction battery as generally represented by blocks430-480. In the representative embodiment illustrated, block430determines whether the towed vehicle is above a minimum regenerative energy recapture threshold. If Yes, block440determines whether the towed vehicle acceleration is below a corresponding threshold, and block450determines whether the detected road grade is below a corresponding threshold so that regenerative energy capture does not adversely affect the ability of the towing vehicle to accelerate or maintain speed while ascending a grade. If the conditions of blocks430,440, and450are satisfied, then regenerative energy capture is engaged as indicated at460with the rate of capture determined as illustrated and described in greater detail with respect toFIG.5. If any of the conditions of blocks430,440, or450is not satisfied, then the regenerative energy capture is suspended or disengaged as represented at432. Control then continues to block290ofFIG.2as represented at480.

FIGS.5-6are block diagrams illustrating operation of a system or method that controls non-braking regenerative energy capture to achieve or maintain a battery target state of charge (SOC) in an electrified vehicle while being towed. As shown inFIG.5, system or method500determines whether the HV traction battery SOC is below an associated minimum low threshold for vehicle operation. If Yes, then blocks512,514, and516set associated respective thresholds for minimum vehicle speed, maximum vehicle acceleration, and maximum grade to enable HV traction battery charging to different, lower thresholds relative to the respective thresholds of blocks520,522, and524, which are set when the HV traction battery SOC is above the minimum low threshold as determined at block510. In the representative embodiment illustrated, block512sets the vehicle minimum speed to 1 kph, block514sets the vehicle maximum acceleration to zero, and block516sets the maximum grade to zero so that regenerative energy capture may occur under more operating conditions than the thresholds of blocks520,522, and524to charge the HV traction battery to the minimum low threshold for vehicle operation. In the representative embodiment illustrated, block520sets the vehicle minimum speed to 10 kph, block522sets the vehicle maximum acceleration to 0.5 m/s2, and block524sets the maximum grade to 2%. Of course, thresholds may vary depending on the particular electrified vehicle configuration and desired performance specifications for various vehicle applications and implementations.

Block530determines whether the HV traction battery SOC is below the target threshold, which may be specified by the user via the HMI or may be a default target or a target otherwise determined by the vehicle controller(s). If No, block540determines whether the HV traction battery SOC is above the target threshold. If Yes, block542sets the non-braking regenerative energy capture maximum power limit to a negative value to discharge the HV traction battery to a calibratable level, such as −2 kW in this example. Otherwise, the non-braking regenerative energy capture maximum limit is set to zero (to provide zero net current to the traction battery) as represented at544. It should be noted that regenerative capability may also be expressed as a torque limit as a function of vehicle speed as power is equivalent to torque multiplied by speed. The corresponding regenerative power limit from blocks542or544is then provided to block266ofFIG.2as represented at560.

If block530determines that the HV traction battery SOC is below the target SOC, then block550determines whether active charging has been selected via the HMI when entering the towed vehicle operation mode. If Yes, then block554sets the non-braking regenerative charging power to the minimum or lesser of the regenerative charging power and the lift pedal regenerative power limit as described with respect toFIG.6. Otherwise, block552sets the regenerative power maximum limit to the lift pedal maximum as described with respect toFIG.6. The corresponding regenerative power limit from blocks552or554is then provided to block266ofFIG.2as represented at560.

As illustrated by diagram600ofFIG.6, the non-braking regenerative energy capture calculates an average speed for the trip as represented at610. The average speed may have a default minimum value, such as 30 mph, for example. The odometer reading at the start of a trip as represented at620is used in combination with the current odometer reading at622and the total trip distance at624to calculate the trip distance remaining at630. As previously described, the trip distance may be manually entered via the HMI, entered via a connected mobile device, or obtained from the vehicle navigation system if a destination has been entered. The remaining trip distance from block630and the average speed from block610is used to calculate the trip time remaining at640. The energy needed to achieve the desired target HV traction battery SOC by the end of the trip is determined at660based on the target HV traction battery SOC at662, the current HV traction battery SOC at664, and a lookup table or calculation that provides a relationship between SOC and energy as represented at666. The remaining trip time from block640and the energy needed to charge the traction battery as determined at660is used to calculate the non-braking regenerative energy capture power as represented at650, which is then used to determine the regenerative charge power into the HV traction battery as previously described with respect to block554ofFIG.5.

FIG.7is a block diagram illustrating operation of a system or method that uses a desired range or distance to empty (DTE) to control battery charging in an electrified vehicle while being towed. Algorithm700may be used to determine a target traction battery SOC for the electrified vehicle based on a desired range or DTE entered via the HMI as represented at710. Block720calculates the Watt-hours (WH) needed based on the DTE consumption (WH/mi) as indicated at722and the current DTE as indicated at724. Block730calculates the target HV traction battery SOC using a corresponding lookup table to convert SOC to energy based on the current HV traction battery WH available at732and accessing the SOC to energy lookup table at734. The calculated SOC based on the entered DTE is then used by the non-braking regenerative capture strategy as previously described.

FIG.8is a block diagram illustrating operation of a system or method that controls active braking based on vehicle acceleration/deceleration in an electrified vehicle while being towed. Towed electrified vehicles using automatic deceleration detection to provide breakaway braking should come to a complete stop if they become disconnected form the towing vehicle. System or method800monitors the electrified vehicle deceleration to detect a potential breakaway situation and will apply more aggressive braking force using regenerative braking and friction braking to bring the towed electrified vehicle to a controlled stop. Because a hard stop by the towing vehicle may be difficult to distinguish from a breakaway condition, any subsequent acceleration will allow the towed electrified vehicle to release the brakes and resume normal towed vehicle functions.

Block810determines whether the brake pedal is depressed by a brake pusher installed in the vehicle. If Yes, block820applies active braking torque based on the brake pedal demand. This may include regenerative braking and friction braking as previously described. Control then returns to block410ofFIG.4as indicated at830. Otherwise, block840calculates a vehicle acceleration/deceleration rate at840based on vehicle speed842and/or input from one or more accelerometers844. If deceleration exceeds an associated threshold at850, then block852calculates an active braking torque using a lookup table854that provides a relationship between braking torque and deceleration. Control then returns to block410ofFIG.4as indicated at830.

If deceleration is below the associated threshold at850, then block860determines whether vehicle speed is below a threshold, prior deceleration as represented at862was above a threshold, and acceleration is below a threshold. If yes, then block880sets the active braking request to a preset vehicle hold torque and control continues with block410ofFIG.4as indicated at830. Otherwise, block870sets the active braking torque to a value based on the estimated road grade from block864when the vehicle stops and control continues with block410ofFIG.4as indicated at830.

As generally represented in at least blocks860,862,864,870, and880ofFIG.8, if the towed electrified vehicle is disconnected from the towing vehicle, the towed vehicle will begin to decelerate. This will generate a braking signal that will add to the deceleration, generating more deceleration, and therefore pass the deceleration rate threshold. As the disconnected towed vehicle slows under this hard deceleration, the system commands the friction brakes to a preset vehicle hold torque, achieving the slowing of a vehicle that is disconnected and also keeping the vehicle at a stop when it comes to a rest. If the disconnection is a false detection, then the vehicle will begin to accelerate as the towing vehicle accelerates and the braking torque is released. Depending on the particular application, block870may set the predetermined active braking torque to zero. In other applications, block870may provide a predetermined active braking torque less than the predetermined vehicle hold torque of block880, but greater than zero. The predetermined braking torque of block870may be selected based on road grade estimated at block864when the vehicle comes to a stop to so that the weight of the towed vehicle does not result in movement of the towing/towed vehicles on higher grades. The predetermined braking torque of block870may be less than the preset vehicle hold torque of block880so the vehicle combination can more easily accelerate after stopping.

As generally illustrated and described above, a system or method according to the disclosure may provide a strategy or algorithm for automatic braking of a towed electrified vehicle without any connection (hydraulic, mechanical, or electrical) to the towed vehicle braking system. As such, automatic braking of the towed electrified vehicle is provided without any added hardware, such as a brake pedal pusher, to the towed vehicle to perform this function. However, the towed electrified vehicle may automatically detect and work with a brake pedal pusher system, if desired. Embodiments may also provide the ability for the towed electrified vehicle to come to a complete controlled stop and maintain a stop with the friction brakes if the vehicle has become disconnected from the towing vehicle. Detection of acceleration of the towed vehicle after a breakaway condition has been triggered provides the ability for this condition to be reversed if the friction brakes were applied due to a fast or hard stop of the towing vehicle. Towed vehicle brake lights may also be activated, eliminating the need for a connection to be made to the towing vehicle braking system. Those of ordinary skill in the art may recognize additional advantages based on the teachings and representative embodiments described above.

The representative embodiments described are not intended to encompass all possible forms within the scope of the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made consistent with the teachings of the disclosure within the scope of the claimed subject matter. As previously described, one or more features of various embodiments can be combined to form further embodiments that may not be explicitly described or illustrated. Although embodiments that have been described as providing advantages over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes can include, but are not limited to strength, durability, life cycle, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.